Technical Publications

A selection of publications about our work and software are available for reference. Abstracts, full papers or online links are included.

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Thoughts on the Importance of Similitude and Multi-Axial Loads When Assessing the Durability and Damage Tolerance of Adhesively-Bonded Doublers and Repairs

Rhys Jones [1][2], Ramesh Chandwani [3], Chris Timbrell [3], Anthony J. Kinloch [4], Darren Peng [1][2]
[1] Centre of Expertise for Structural Mechanics, Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3800, Australia
[2] ARC Industrial Transformation Training Centre on Surface Engineering for Advanced Materials, Faculty of Science, Engineering and Technology, Swinburne University of Technology, John Street, Hawthorn, VIC 3122, Australia
[3] Zentech International Limited, 590B Finchley Road, London NW11 7RX, UK
[4] Department of Mechanical Engineering, Imperial College London, Exhibition Road, London SW7 2AZ, UK

Aerospace 2023, 10(11), 946.

Adhesively bonded doublers and adhesively bonded repairs are extensively used to extend the operational life of metallic aircraft structures. Consequently, this paper focuses on the tools needed to address sustainment issues associated with both adhesively bonded doublers and adhesively bonded repairs to (metallic) aircraft structures, in a fashion that is consistent with the building-block approach mandated in the United States Air Force (USAF) airworthiness certification standard MIL-STD-1530D and also in the United States (US) Joint Services Structural Guidelines JSSG-2006. In this context, it is shown that the effect of biaxial loads on cohesive crack growth in a bonded doubler under both constant amplitude fatigue loads and operational flight loads can be significant. It is also suggested that as a result, for uniaxial tests to replicate the cohesive crack growth seen in adhesively bonded doublers and adhesively bonded repairs under operational flight loads, the magnitude of the applied load spectrum may need to be continuously modified so as to ensure that the crack tip similitude parameter in the laboratory tests reflects that seen in the full-scale aircraft.

Simulation of fatigue crack growth behavior in welded plates considering different material properties of weld and base metals

JIAO Guangchen [1], ZHAN Yong [1], WEN Jianfeng [2]
[1] Shanghai Huice Information Technology Co., Ltd., Shanghai 201108, China
[2] Key Laboratory of Pressure Systems and Safety (MOE), School of Mechanical and Power Engineering, East China University of Science & Technology, Shanghai 200237, China

Transactions Of The China Welding Institution, Vol.44(11):52-58, November 2023

Study on application range of SIF calculation method for nozzle corner crack in pressure vessel for ASME XI code

Chao Liu [1], Guang-chen Jiao [2], Ramesh Chandwani [3], Chris Timbrell [3]
[1] School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai, PR China
[2] Shanghai Hui Ce Information Technology Co., Ltd, Shanghai, PR China
[3] Zentech International Limited, London, UK

International Journal of Pressure Vessels and Piping, Volume 193, October 2021

Crack Growth Prediction on Critical Component for Structure Life Extension of Royal Malaysian Air Force (RMAF) Sukhoi Su-30MKM

Arvinthan Venugopal 1,2, Roslina Mohammad 2, Md Fuad Shah Koslan 1, Ashaari Shafie 3, Alizarin bin Ali 4 and Owi Eugene5
1 RMAF Centre of Aerospace Engineering Services Establishment, Subang Airbase, Shah Alam 40000, Malaysia
2 Razak Faculty of Technology and Informatics, Universiti Technology Malaysia, Jalan Sultan Yahya Petra, Kuala Lumpur 54100, Malaysia
3 Aerospace Technology Systems Corporation Sdn Bhd, ATSC Corporate Centre, PT 192, Jalan Lapangan Terbang, Subang 47200, Malaysia
4 CAIDMARK Sdn Bhd, Damansara Utama, Petaling Jaya 47400, Malaysia
5 RMAF Combat Training School, TUDM Bukit Ibam, Muadzam Shah 26700, Malaysia

Metals 2021, 11(9), 1453 (Special Issue : Fatigue Crack Propagation Micromechanisms of Metallic Materials)

Stress corrosion cracking behaviors of FV520B stainless steel used in a failed compressor impeller

Defu Nie, Xuedong Chen, Qiaoguo Wu, Yan Liu
National Safety Engineering Technology Research Center for Pressure Vessels and Pipelines, Anhui Province Safety Technology Laboratory for Pressure Vessels and Pipelines, Hefei General Machinery Research Institute, Hefei, Anhui 230031, China

Engineering Failure Analysis, Volume 116, October 2020, 104701

Numerical simulation of dynamic fracture toughness tests: using RKR criterion

Jianhua Pan [1,2], Mingjie Guo [1]
[1] State Key Laboratory of Nuclear Power Safety Monitoring Technology and Equipment, China Nuclear Power Engineering Co., Shenzhen, 518172, China
[2] School of Mechanical Engineering, Hefei University of Technology, Hefei, 230009, China

SN Applied Sciences (2019) 1:1085

Tunnel boring machine cutterhead crack propagation life prediction with time integration method

Jianbin Li1 [1], Zhange Zhang [2], Zhichao Meng [2], Junzhou Huo [2], Zhaohui Xu [2], Jing Chen [3]
[1] China Railway Hi-Tech Industry Co., Ltd, Beijing, People’s Republic of China
[2] School of Mechanical Engineering, Dalian University of Technology, Dalian, People’s Republic of China
[3] School of Navigation and Naval Architecture, Dalian Ocean University, Dalian, People’s Republic of China

Advances in Mechanical Engineering, 2019;11(6)

Non-linear models for assessing the fatigue crack behaviour under cyclic biaxial loading in a cruciform specimen

M. Lepore [1], F.Berto [2], D.Kujawski [3]
[1] Department of Industrial Engineering, University of Salerno, Salerno, Italy
[2] Department of Mechanical and Industrial Engineering, NTNU, Trondheim, Norway
[3] Department of Mechanical and Aerospace Engineering, WMU, Kalamazoo MI, USA

Theoretical and Applied Fracture Mechanics, Volume 100, April 2019, Pages 14-26

Dual boundary element method and finite element method for mixed-mode crack propagation simulations in a cracked hollow shaft

R. Citarella [1], V. Giannella [1], M. Lepore [1], G. Dhondt [2]
[1] Department of Industrial Engineering, University of Salerno, Salerno, Italy
[2] MTU Aero Engines AG, Dachauer Strasse 665, 80995 Munich, Germany

Fatigue Fract Engng Mater Struct, 2018; 41:84-98

Demonstrating Structural Integrity Under Challenging Load And Material Conditions

Chris Timbrell [1], Ramesh Chandwani [1], Ma Chunlei [2]
[1] Zentech International Limited
[2] Consys Group Limited

ISSI 2018 - Nanjing, China, 2-5 November 2018

Since the industrial revolution when a German mining engineer August Wohler first studied the frequent breaking of chains causing several casualties and developed the concept of what we now know as the S-N curve, many experimental, theoretical and software-aided simulation techniques have been developed to study ageing material behaviour and to design new materials. Over time the demands placed on new materials have required operation under more severe temperatures and loads in order to conserve natural resources and minimise emissions.
Fracture mechanics based finite element algorithms to simulate 3D cracks in components / structures have proved very useful in assessing the residual life and developing repair and maintenance strategies as mandatorily required by various licensing authorities for the continuous operation of infrastructure projects in Aerospace, Power, Transportation, Oil and Chemical industries under the ever more demanding operating conditions. Here one such software tool for crack simulation of industrial applications is presented with examples including combined fatigue and time dependent crack growth under thermo-mechanical loading including hold-time and weld defect assessment with inclusion of dis-similar materials.

Multiple cracks failure rule for TBM cutterhead based on three-dimensional crack propagation calculation

Wei Sun, Jun-Zhou Huo, Xiao-Hong Chen
Dalian University of Technology, Dalian, China

Engineering Failure Analysis, Volume 93, November 2018, Pages 224-240

A 3D Crack Evolution In Weld Metal, Base Metal And The Transitional Fusion Line Under A Mixed Fatigue Loading

Mahyar Asadi[1], Majid Tanbakuei Kashani[1], Mathew Smith[1], Chris Timbrell[2], Ramesh Chandwani[2], Arasch Rodbari[2]
[1] SKC Engineering (A division of Applus)
[2] Zentech International Limited

ESIA 14 – ISSI 2017 (Engineering Structural Integrity Assessment 14 in conjunction with the International Symposium on Structural Integrity 2017), Manchester, UK, 16-17 May 2017.

A limited number of automated algorithms and software are available that predict the 3D evolution of crack fronts in a mixed loading condition in welds in particular in the interface of weld and base metal i.e. fusion line. In this paper, the authors present a study of common low carbon steel pipe weld joints containing a crack detected in radiography films and embedded into a 3D FE pipe model that is constructed with different weld and base metal properties including different crack growth laws and fracture properties. Evolution of the detected crack front is predicted in 3D under mixed fatigue loading. This paper shows that a 3D model of crack growth captures the transient change of stress intensity factor along the crack front and therefore the immediate change in the direction of crack growth and the dynamic shape of crack can be predicted. A solution is also presented for handling the stress intensity factor on the boundary of weld metal and base metal when the crack front reaches the weld fusion line. From the structural integrity management viewpoint, the number of fatigue cycles, time for the crack to start growing, time to break to surface and leak-before-break, and the total time to final fracture are calculated. This paper shows that a fracture critical region such as welds with a high likelihood of service cracking or welding flaw can precisely be analyzed and life can be estimated to avoid early life failure in welded structures.

Retardation effects due to overloads in aluminium-alloy aeronautical components

A. R. Maligno [1], R. Citarella [2], V. V. Silberschmidt [3]
[1] Institute for Innovation in Sustainable Engineering, University of Derby, Derby, UK
[2] Department of Industrial Engineering, University of Salerno, Fisciano, SA, Italy
[3] Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough, UK

Fatigue Fract Engng Mater Struct, 2017; 40:1484-1500

A combination rule for multiple surface cracks based on fatigue crack growth life

Jian-Feng Wen [1,2], Yong Zhan [1], Shan-Tung Tu [1], Fu-Zhen Xuan [1]
[1] Key Laboratory of Pressure Systems and Safety (Ministry of Education), School of Mechanical and Power Engineering, East China University of Science and Technology, Shanghai 200237, China
[2] Department of Materials Science and Engineering, Texas A&M University, College Station, TX 77843, USA

AIMS Materials Science, 2016, Volume 3, Issue 4: 1649-1664

Design methodology to ensure the structural integrity of the through wall cracked sodium piping system in-service

R. Suresh Kumar [1], K. Velusamy [2], P. Puthiyavinayagam [3], P. Selvara [4]
[1] Head Structrual Mechanics Laboratory, Indira Gandhi Centre for Atomic Research, Kalpakkam
[2] Head Mechanics & Hydraulics Division, Indira Gandhi Centre for Atomic Research, Kalpakkam
[3] Director, Reactor Design Group, Indira Gandhi Centre for Atomic Research, Kalpakkam
[4] Director, Fast Reactor Technology Group, Indira Gandhi Centre for Atomic Research, Kalpakkam

Proceedings of First Structural Integrity Conference and Exhibition (SICE-2016), Bangalore July 4-6, 2016

One of the most desirable safety features of a sodium piping system to be ensured during service condition is the structural integrity during in-service condition. Leak-Before-Break (LBB) is one of the necessary criteria to be respected towards achieving the required level of structural integrity for the pressure retaining the piping system and vessels. It is necessary to ensure the inherent safety capability of providing a clear warning before breakage. The term refers to a demonstration of the system to leak before catastrophic failure. The breakage of the system pressure boundary can cause large sodium leakage. It can lead to rapid disruption and the shutdown of the plant function.
The LBB approach requires application of fracture mechanics methodology to demonstrate that the sodium piping system will ensure detectable leakage and demonstrates that the crack will be stable under the maximum credible loading conditions. The size of this crack should be large enough so that leakage is assured of detection with a margin using the installed leak detection equipment under in-service conditions. This paper discusses the design methodology adapted to Fast Breeder Reactor (FBR) piping system to ensure the structural integrity of a through wall cracked sodium piping system under service conditions. RCCMR A16 & CEGB R6 design methodology is adopted in this paper towards demonstrating the structural integrity of a typical secondary sodium piping system. Failure Assessment Diagram is used for computing the critical crack length. Using the fracture mechanics concepts the crack growth has been computed against fatigue loading. It is demonstrated that the typical 500 NB FBR pipe bend critical crack length is much greater than that the minimum crack length responsible for the detectable leak rate.

Stress Intensity Factor of Nozzle Corner in Pressure Vessel Under Condition of Thermal and Mechanical Loads

Guang-chen Jiao[1], Ming Cao[2], Rui Shen[2], Zhi-jie Li[1], Chun-lei Ma[1], Chris Timbrell[3]
[1] Consys Group Limited
[2] Shanghai Nuclear Engineering Research & Design Institute
[3] Zentech International Limited

18th National Conference on Fatigue and Fracture (NCFF2016), Zhengzhou, China, April 2016

Stress intensity factor (SIF) of nozzle corner in pressure vessel was calculated by using FEA and method of ASME appendix G (2013 section XI) under condition of thermal and mechanical loads. Because the computational formula in ASME appendix G can only be explained in analysis of nozzle structure with specific crack position, but engineering application is limited by using this formula. So the Stress intensity factors of nozzle corner with different crack positions were calculated, the application condition of this method and safety assessment of vessel nozzle were investigated in this paper.

Fatigue Crack Growth Analysis of Internal Surface Crack on Pressure Vessels

Zhi-jie Li [1], Geng-yu Zhou [2], Guang-chen Jiao [1], Chun-lei Ma [1]
[1] Consys Group Limited
[2] Suzhou Nuclear Power Research Institute

18th National Conference on Fatigue and Fracture (NCFF2016), Zhengzhou, China, April 2016

The reactor pressure vessels are important parts in nuclear power plants, the integrity of which is a barrier for the reactor safety. Small cracks would generate with the reactor running and the complex conditions in the reactor would cause fatigue crack growth. The pressure vessel cannot be replaced during its service life, so the fatigue crack growth should be considered in an accurate or conservative way to ensure the size of the crack are under limit. In addition, the calculation of fatigue crack growth is necessary in life extension program for old nuclear power plants. Meanwhile, simulating the whole process from a surface crack to a through-wall crack is helpful and useful in LBB evaluation. In a word, crack growth analysis is very important.
In this paper, the whole growth process of internal surface crack in the circumferential direction on the pressure vessel under fatigue loads is simulated on the basis of Zencrack and parameters in the whole process are monitored such as stress intensity factor, J integral. The specific value of the parameters in the whole growth process are achieved. This analysis provides a practicable method for the design and safety evaluation when taking cracks of the pressure vessel into consideration, the life extension evaluation of old power plant and LBB evaluation.

Research on fatigue crack propagation in CT specimens subjected to loading modes I, II or III

Paulo Chambel [1], Rui F. Martins [1], Luís Reis [2]
[1] UNIDEMI, Department of Mechanical and Industrial Engineering, Faculty of Science and Technology, Universidade NOVA de Lisboa, Campus de Caparica, 2829-516 Monte de Caparica, Portugal
[2] IDMEC, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, Portugal

Procedia Structural Integrity, Volume 1, 2016, Pages 134-141
XV Portuguese Conference on Fracture, PCF 2016, 10-12 February 2016, Paco de Arcos, Portugal

Numerical Simulation of Stress Intensity Factor for Socket Weld Toe Cracks in Small Branch Pipes

J.H.Jia, Z.Q.Zhang, C.Zhang
Key Laboratory of Pressure Systems and Safety, Ministry of Education, East China University of Science and Technology, Shanghai, 200237, China

Procedia Engineering, Volume 130, 2015, Pages 150-157

Engineering fracture assessment of FV520B steel impeller subjected to dynamic loading

Qiaoguo Wua [1,2], Xuedong Chena [1], Zhichao Fana [1], Defu Niea [1,2], Jianhua Pana [1]
[1] National Safety Engineering Technology Research Center for Pressure Vessels and Pipelines, Anhui Province Safety Technology Laboratory for Pressure Vessels and Pipelines, Hefei General Machinery Research Institute, Hefei 230031, China
[2] National Key Laboratory of Compressor Technology, Hefei General Machinery Research Institute, Hefei 230031, China

Engineering Fracture Mechanics, Volume 146, September 2015, Pages 210–223

Fatigue crack growth study of CFRP patch repaired Al 2014-T6 panel having an inclined center crack using FEA and DIC

R. Srilakshmia [1], M. Ramjia [1], Viswanath Chinthapentab [2]
[1] Engineering Optics Lab, Department of Mechanical and Aerospace Engineering, IIT Hyderabad, India
[2] Micro-Mechanics Lab, Department of Mechanical and Aerospace Engineering, IIT Hyderabad, India

Engineering Fracture Mechanics, Volume 134, January 2015, Pages 182–201

FEM simulation of a crack propagation in a round bar under combined tension and torsion fatigue loading

R.Citarella [1], M.Lepore [1], A.Maligno [2], V.Shlyannikov [3]
[1] Dept. of Industrial Engineering, University of Salerno, Fisciano (SA), Italy
[2] Institute for innovation in Sustainable Engineering, University of Derby, Quaker Way, DE1 3HD, Derby, UK
[3] Researches Center for Power Engineering Problems of Russian Academy of Sciences, Lobachevsky Street, 2/31, 420111, Kazan, Russia

Frattura ed Integrità Strutturale, 31 (2015) 138-147

The Use of Fracture Mechanics for Fatigue Life Assessment

Ramesh Chandwani, Zentech International Ltd.

NAFEMS UK Seminar: Current Best Practices in Fatigue Analysis using FEA, London, UK, 16 September 2014

Fatigue failure is a complex physical process, encompassing both crack initiation and crack propagation phases. Using fracture mechanics, fatigue crack growth can be characterised and residual fatigue life evaluated. In the case of a failure, the cause of fracture can be determined forensically. Indeed, fracture mechanics, In conjunction with finite element analysis techniques, has become a very powerful tool for the assessment of the safety and durability of new and legacy based infrastructure projects, the failure of which could have enormous economical and loss of human life consequences. This paper highlights some of the techniques available and demonstrates their application to a range of fatigue life assessments.

Prediction of fatigue crack propagation lives of turbine discs with forging-induced initial cracks

Jianfu Hou, Ron Wescott, Marco Attia
Aerospace Division, Defence Science and Technology Organisation (DSTO), 506 Lorimer Street, Fishermans Bend 3207, Australia

Engineering Failure Analysis, Volume 131, November 2014, Pages 406–418

Comparing Crack Growth Testing and Simulation Results Under Thermo-Mechanical Fatigue Conditions

Chris Timbrell, Ramesh Chandwani, Zentech International Ltd., Steve Jacques, Lee Waterhouse, Andrew Wisbey, Amec Technical Services (was Serco), Steve Williams, Rolls-Royce plc

13th International Conference on Fracture, Beijing, China, 16-21 June 2013

As the need for improved prediction of component life and development of new materials for use at high temperatures becomes more demanding, there is increasing requirement for a detailed understanding of thermo-mechanical fatigue (TMF) behaviour including the combined effects of fatigue and dwell on the overall crack growth rates under such conditions. To generate experimental TMF crack growth test data, a conventional servo-electric load frame, used in combination with a radiant lamp furnace, has been employed. The method for the measurement of crack growth under the TMF load cycle is also described. The performance of the experimental method is demonstrated with trials on an advanced nickel-based superalloy, RR1000. To reduce future testing requirements, simulation via the finite element method provides a means for crack growth prediction. This clearly requires validation with real test data at the outset. A method is described whereby separate fatigue and time dependent growth data can be combined and applied to TMF load cycles ranging from simple test cycles to full flight cycles. Results of this method used in conjunction with finite element based crack growth simulation are compared with experimental data, using the test method described above, from several TMF load cycles for RR1000 specimens.

Simulation of Complex 3D Non-planar Crack Propagation Using Robust Adaptive Re-meshing and Radial Basis Functions

Chris Timbrell, Angelo Maligno, Zentech International Ltd.
David Stevens, BLOS International

NAFEMS World Congress 2013, Austria, 9-12 June 2013

An improved numerical technique for complex shaped non-planar three-dimensional crack growth simulations is proposed. This technique couples the adaptive re-meshing method used during crack growth simulation in the FE- based fracture mechanics code Zencrack with mesh relaxation using radial basis functions. This allows the uninterrupted simulation of crack propagation in engineering structures where the component geometries and local loading conditions may develop complex 3D crack configurations. Collocation with radial basis functions (RBFs) is an effective methodology for the interpolation of arbitrary scalar and vector fields defined over scattered datasets. By defining a mesh displacement field over a volumetric domain, the RBF collocation approach may be used to smoothly map a user-defined displacement of elements onto the entire domain, thereby "relaxing" the mesh around the imposed displacements. This mesh deformation leads, in most cases, to significantly improved element quality in comparison to traditional mesh-relaxation approaches such as Laplacian relaxation. In particular, elements that lie close to the source of a large displacement can be expected to exhibit significantly improved characteristics (such as aspect ratio and skew) in comparison to traditional approaches. The application of RBF deformation to fracture-tracking problems introduces many additional complexities that require novel and creative solutions. The most significant of these is the large difference in length scales between the imposed deformations - which are of element scale, and the constraints at the domain boundaries - which are of problem-scale. These differences in length scales make the problem unsuitable for use with compactly supported collocation methods. To retain a computationally efficient interpolation which is scalable to large problem sizes, a new method for RBF collocation has been developed which is based on large numbers of overlapping local collocation systems, using the underlying elemental structure as a framework. By linking together these overlapping local collocation systems a sparse global matrix may be formed, which can be solved to obtain the displacement at each node within the relaxation domain. For crack propagation simulation it is desirable to allow the mesh to move freely within the domain, as defined by the imposed displacements around the crack-tip, and to constrain the motion of surface and edge nodes such that they remain within their pre-existing geometric surfaces. In this work we describe surface-constraint methods which are suitable for use with complex 3D geometries where the mesh relaxation is performed using globally or locally supported RBF collocation systems.

Modelling the manufacturing history, through life creep-fatigue damage and limiting defect sizes of a pipework joint using finite element based methods

M.J. Stevens [1], R.J. Dennis [1], I.J.M. Bottomley [2], R.A.W. Bradford [3]
[1] Frazer–Nash Consultancy Limited, 1 Trinity Street, College Green, Bristol BS1 5TE, UK
[2] Frazer–Nash Consultancy Limited, Stonebridge House, Dorking RH4 1HJ, UK
[3] EDF Energy Nuclear Generation Limited, Barnett Way, Barnwood, Gloucester GL4 3RS, UK

International Journal of Pressure Vessels and Piping, Volumes 108–109, August–September 2013, Pages 13–27

Comparison of Handbook and 3-D Finite Element Analysis LEFM Solutions for a Threaded Fastener

D.Sommerville, Structural Integrity Associates, Inc., Seattle, WA, USA
M.Qin, M.Walter, Structural Integrity Associates, Inc., Centennial, CO, USA.

Proceedings of the ASME 2013 Pressure Vessels & Piping Division Conference PVP2013 July 14-18, 2013, Paris, France; PVP2013-97727

Congratulations to Structural Integrity Associates for their award for Outstanding Technical Paper under the Computer Technology & Bolted Joints Technical Committee at the 2013 PVP Conference.

Fatigue crack growth modeling of an interacting crack system using Finite Element Analysis

Saranath K.M, M.Ramji
Indian Institute of Technology Hyderabad, Andhra Pradesh, India, 502205

International Conference on Computer Aided Engineering (CAE-2013), Department of Mechanical Engineering, IIT Madras, India

An advanced numerical tool to study fatigue crack propagation in aluminium plates repaired with a composite patch

A.R. Maligno [a,b], C. Soutis [c], V.V. Silberschmidt [d]
[a] Zentech International Ltd., London NW11 7RX, UK
[b] Unmanned Vehicle University, Lake Havasu City, AZ 86403, USA
[c] Aerospace Research Institute, University of Manchester, Manchester M1 3NL, UK
[d] Wolfson School of Mechanical Engineering, Loughborough University, Loughborough LE11 3TU, UK

Engineering Fracture Mechanics, Volume 99, February 2013, Pages 62-78

A Time Dependent Crack Growth Law For High Temperature Conditions

Chris Timbrell, Ramesh Chandwani, Zentech International Ltd.
Duncan MacLachlan, Steve Williams, Rolls-Royce plc, Derby

NAFEMS European Conference: Multiphysics Simulation, Frankfurt, Germany, Oct 16-17 2012

Alloys, especially nickel based ones used in the aerospace industry, are continuously being improved to provide greater strength against component failure and also to increase resistance against crack propagation. This involves altering their composition and, under controlled conditions, modification of precipitate and grain sizes. At high temperatures under both sustained and cyclic loading conditions, these microstructural changes interact synergistically with time dependent mechanisms such as creep, oxidation and corrosion and affect the crack growth rate (CGR). The individual effects of environmental conditions such as oxidation and corrosion and microstructural evolution of grain size at high temperatures, are generally difficult to evaluate. In addition, thermo-mechanical testing of large numbers of specimens under a variety of conditions can be prohibitively costly. Attempts have been made over the last few decades by a number of investigators to conduct standardised tests under controlled environmental conditions and compare them with the results obtained in neutral environments such as vacuum or inert gas [1-4]. It has been found that these environmental effects interact and their combined effect is generally greater than if they were considered separately. In this paper a time dependent crack growth law, COMET (Creep Oxidation Microstructure Environment Temperature), is described which considers the effect of these combined processes using a temperature dependent parameter based on an Arrhenius equation. Using this time dependent law in conjunction with a fatigue crack growth law, a finite element based implementation has been developed to carry out detailed 3D crack propagation analysis and simulation of a cracked component under the effect of thermo-mechanical loading at high temperatures.

A numerical fracture mechanics tool to help assess the structural integrity of nuclear power plant components

Chris Timbrell, Ramesh Chandwani, Angelo Maligno, Zentech International Ltd.
Charly Ma, Consys Company Limited

ISSI 2011 - Structural Integrity in Nuclear Engineering, Heifei, China, Oct 27-30 2011

Many nuclear power plant facilities have been operating for longer than twenty years. Along with ageing of structural materials come other issues, such as creep and corrosion, which can impact upon plant safety and the integrity of the primary circuit. Plant lifetime extension and continued safe and economic operation depends on ageing and lifetime management. To be effective, this requires an understanding of how safety may be maintained as components degrade over extended time periods under operational conditions. Potential structural integrity issues for future generation IV reactors are also paramount to further develop the nuclear industry. This paper describes some aspects of the numerical analysis tool, Zencrack, which can assist in crack growth prediction and fitness for service investigations for a range of nuclear power plant applications.

Case studies of computational simulations of fatigue crack propagation using finite elements analysis tools

V. Infantea [1], J.M. Silva [2]
[1] Departamento de Engenharia Mecânica, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal [2] Departamento de Ciências Aeroespaciais, Universidade da Beira Interior Edifício II das Engenharias, 6200-358 Covilhã, Portugal

Engineering Failure Analysis, Volume 18, Issue 2, March 2011, Pages 616–624

Creep-fatigue behavior of a new generation Ni-base superalloy for aeroengine usage

J.M. Silva [1], R.A. Cláudio [2], Moura Branco [3], Martins Ferreira [4]
[1] Depart. of Aerospace Sciences, University of Beira Interior, 6201-001 Covilhã, Portugal
[2] Depart. of Mech. Engineering, ESTS/IPS, 2910-761 Setúbal, Portugal
[3] Depart. of Mech. Engineering; IST/UTL, 1049-001 Lisboa, Portugal
[4] Depart. of Mech. Engineering, FCTUC, 3030-788 Coimbra, Portugal

Procedia Engineering, Volume 2, Issue 1, April 2010, Pages 1865-1875, Fatigue 2010

Using a standard specimen geometry for crack propagation under plain strain conditions

J.M. Silva [1], V. Infante [2], F. Antunes [3], F. Ferreira [1]
[1] Departamento de Ciências Aeroespaciais, Universidade da Beira Interior; 6201-001 Covilhã - Portugal
[2] Departamento de Engenharia Mecânica Instituto Superior Técnico; 1049-001 Lisboa - Portugal
[3] Departamento de Engenharia Mecânica FCTUC; 3030-788 Coimbra - Portugal

International Journal of Structural Integrity, Vol. 1 (4):12, 2010

Prediction Of Crack Growth In Bridge Roller Bearings

Nawal K. Prinja, Joseph M. Bushell, AMEC Nuclear UK Ltd.
R. Chandwani, C. Timbrell, Zentech International Ltd.

NAFEMS World Congress 2009, Crete, Greece, Jun 16-19 2009

This paper explains how the general purpose FE code Abaqus was combined with Zencrack to predict 3D crack growth as part of an investigation conducted to explain failure of single cylinder bridge roller bearings. Finite Element analyses were conducted to gain an understanding of the stresses caused during operation and explain the possible cause of crack growth resulting in failure. It was important to predict sub-surface crack growth in the rollers induced by repeated rolling as the bridge expands due to daily and seasonal temperature cycles. Models of the bearings were required to represent the contact between the roller and plates, daily movement of the load and the non-linear behaviour of the material. A band of pressure due to contact with the plates traverses back and forth over the roller as it rotates. The ambient temperature changes were such that the roller would experience at least one stress cycle per day of operation. A number of initial crack scenarios are studied, based on crack initiation sites identified during inspections of the failed rollers. Stress intensity factors (SIFs) for all three modes of cracking (KI, KII and KIII) are plotted against angle of roll bearing is misaligned, the roller is subjected to additional twist. The Abaqus and Zencrack analyses showed that in the absence of any twist, the load cycling caused by the rotation of the roller propagates initial end cracks along the roller axis which can lead to the roller splitting in half. Twisting of the roller due to bearing misalignment causes out of plane growth of the crack indicating that a part of the roller can break away.

Numerical Investigations Of Fatigue Crack Growth In Shafts

Angelo R Maligno, University of Nottingham
R. Chandwani, C. Timbrell, Zentech International Ltd.

NAFEMS World Congress 2009, Crete, Greece, Jun 16-19 2009

Numerical modelling of three dimensional (3D) non-planar fatigue crack growth under mixed mode conditions represent a crucial factor in fracture mechanics in order to assess the residual life of components. This paper focuses on developing a damage tolerance approach that can be used for the design of aeroengine shaft components under the general mixed-mode loading conditions in the presence of stress-raising features. The initial work has validated numerical results against crack growth measurements on uniaxial tensile specimens under Mode-I loading. Then, more realistic loading scenarios have been applied on shafts to investigate the influence of different parameters (e.g. crack orientation) on fatigue crack growth. All of the present work is based on linear elastic fracture mechanics approaches, including the Paris and Walker theories.

A three-dimensional (3D) numerical study of fatigue crack growth using remeshing techniques

A.R. Maligno [a], S. Rajaratnam [b], S.B. Leen [b], E.J. Williams [b]
[a] Loughborough University, Wolson School of Mechanical and Manufacturing Engineering, Loughborough, UK
[b] The University of Nottingham, School of M3, Nottingham, UK

Engineering Fracture Mechanics, September 2009

Fatigue Crack Growth Rate Evaluation in a Turbine Disc after Spin Rig Testing

W. Beres, D. Dudzinski, A. Murzionak
National Research Council Canada, Institute for Aerospace Research Ottawa, Ontario, Canada

12th International Conference on Fracture 2009 (ICF-12), Ottawa, Ontario, Canada, July 12-17, 2009, Volume 4, pp.3265-3273, 2009, Paper 00587

Modelling Composite Repairs To Cracked Metal Structures

M. Roy [1], C. Lang [2], I.M. May [2]
[1] QinetiQ Limited, Dunfermline, UK
[2] Heriot-Watt University, Edinburgh, UK

Proceedings of the Institution of Civil Engineers, Structures & Buildings 162, April 2009, Issue SB2, Pages 107-113

Analysis on Fatigue Crack Propagation of Pipe Components of Container Cranes Based on Zencrack

Zhang Weiguo, Mi Weijian, Liu Haiyang
College of Logistics Engineering, Shanghai Maritime University, Shanghai 200135, China

Computer Aided Engineering, Vol. 17 No. 1, March 2008

Simulation Of 3D Non-Planar Crack Propagation

R. Chandwani, C. Timbrell

NAFEMS World Congress 2007, Vancouver, Canada, May 22-25 2007

Numerical modelling of three dimensional (3D) non-planar fatigue crack growth under mixed mode conditions represent a crucial factor in fracture mechanics in order to assess the residual life of components. This paper focuses on developing a damage tolerance approach that can be used for the design of aeroengine shaft components under the general mixed-mode loading conditions in the presence of stress-raising features. The initial work has validated numerical results against crack growth measurements on uniaxial tensile specimens under Mode-I loading. Then, more realistic loading scenarios have been applied on shafts to investigate the influence of different parameters (e.g. crack orientation) on fatigue crack growth. All of the present work is based on linear elastic fracture mechanics approaches, including the Paris and Walker theories.

Crack Modelling In Power Plant Components

R. Chandwani, C. Timbrell, M. Wiehahn

International Conference On Pressure Vessels And Piping, Chennai, India, Feb 7-9 2006

Much of the process plant designed in the early 1970s, in response to increased demand for power, is now 'ageing' and necessitates an on-going 'fitness for service' assessment. This is necessary to satisfy licensing authorities requirements for continuous operations. Fitness for service assessment involves many issues including evaluation of structural flaws, material degradation, damage due to creep, fatigue and plasticity and the overall effect on the residual life of components. Codes of practice such as API 579, BS 7910 and R6 give detailed assessment procedures and may involve very detailed and time consuming finite element analyses. The authors have developed an FEA tool, Zencrack, to accurately evaluate single or multiple cracks in any structure (e.g. pressure vessels, piping, etc.). Further, 3D non-planar crack growth under general fatigue or time dependent loading is possible. The software can help to increase efficiency in performing sensitivity studies, thus allowing more accurate assessment of the residual life of the plant than would otherwise be possible in a given timeframe.

Corner Crack Propagation in the Presence of Residual Stresses

A.L. Hutson [1], M. Huelsman [1], D. Buchanan [1], R. John [2], S. Haering [2]
[1] University of Dayton Research Institute, Ohio, USA.
[2] AFRL/MLLMN, Wright Patterson Air Force Base, Ohio, USA.

FATIGUE 2006, 9th International Fatigue Congress, May 14-19 2006, Atlanta, Georgia, USA

A Study On The Thermo-Mechanical Fatigue Loading For Attaining Minimum Cycles In Fabricating An Artificial Cracked Specimen

Jooho Choi, Gyubeom Lee, Boyoung Lee
School of Aerospace & Mechanical Engineering, Hankuk Aviation University, Korea

The Fourth China-Japan-Korea Joint Symposium on Optimisation of Structural and Mechanical Systems, Kunming, China, Nov 6-9, 2006

In the nuclear facilities, fatigue cracks are often observed in pipes during the operation of the Reactor Coolant System (RCS), which originate from the cyclic loading caused by thermal stratification. Though the NDT methods are employed to detect the crack, sufficient number of repeated exercise should be preceded using artificial cracked specimen of a same kind for the reliable on-site detection. The crack of this kind, which has less than 150 m width, can not be made by the conventional machining methods such as EDM, but should be made under thermal cyclic load that is close to that of the RCS. The time for obtaining the wanted crack, however, is prohibitively long, which makes it difficult to be supplied in sufficient number for NDT evaluation. In this work, single edge crack of a rectangular plate is considered as a preliminary study, in which constant tensile as well as repeated thermal loads are applied to let the crack grow. Optimum loading condition is sought that minimizes the time for fabricating the wanted crack size. The crack growth phenomenon is evaluated through the coupling of crack growth simulation software Zencrack with the general purpose analysis code ANSYS.

A Numerical Fracture Analysis of a Stationary Semi-circular Interface Crack During Interfacial Indentation Test

G. Liu [1], A. Mouftiez [1], J. Lesage [2] and S. Panier [1]
[1] Département Technologie des polymères et composites and Ingénierie mécanique, Ecole des Mines de DOUAI, BP 10838, 59508 Douai, France
[2] Laboratoire de Mécanique de Lille, URA CNRS 1441, U.S.T Lille, IUT A GMP, Villeneuve d'Ascq, France

Surface and Coatings Technology, Volume 201, Issue 5, 25 October 2006, Pages 2086-2091, The 2nd International Meeting on Thermal Spraying - 2nd RIPT

3D Crack Growth Modelling In Gas Turbine Engines

Dr J. Hou
Air Vehicles Division, DSTO, Australia

MSC.Software VPD Conference 2006, Sydney, Australia, July 25-26, 2006

Presentation Title: 3D Crack Growth Modelling in Gas Turbine Engines
DSTO has been continuously enhancing its capability to provide through-life support to the ADF in aircraft engine component life management. One of the major requirements is an enhancement in computational 3D crack growth modelling and analysis. During service, gas turbine engine components experience both cyclic and sustained thermal and mechanical loadings which may result in fatigue and creep damage. As the damage sustained is highly dependent on the variations in both operating stresses and temperatures, finite element analyses (FEA) of the components can be very useful. This presentation outlines the critical issues involved in 3D crack growth and evaluates the results of a 3D crack growth capability in the ZENCRACK software with an emphasis on its validity and applicability to engine components. The primary issues to be dealt with in practice for 3D crack modelling are outlined, and the methodology and techniques implemented in ZENCRACK are described and discussed. Practical applications of ZENCRACK and individual evaluations for particular problems are presented. The various limitations and uncertainties encountered in the practical applications are identified. In particular, it is found that ZENCRACK is a useful tool for the calculation of stress intensity factors. Conclusions and recommendations are made for more accurate 3D crack growth modelling.

An FE Simulation Tool For Fracture Mechanics

R. Chandwani, C. Timbrell, M. Wiehahn

International Seminar on "Fatigue, Reliability & Performance Considerations In Design", Indian Institute of Science, Bangalore, India, Jul 14-15 2005

The use of fracture mechanics techniques in the assessment of performance and reliability of structures is on the increase and the prediction of crack propagation of an existing or postulated flaw in a structure plays an important part. A software simulation tool, which uses FEA, has been developed to quantitatively predict the propagation of 3D non-planar cracks through structures. This tool allows calculation of stress intensity factors and energy release rates and can be applied in a variety of commercially important applications. These include design of laboratory experiments, testing and developing advanced materials, assessing the effects of surface treatments and the study of component repairs.

Simplified Modeling And Detailed Crack Propagation Analysis For Cracked Pipes

Hitachi Ltd., Japan

2005 ASME Pressure Vessels and Piping Division Conference, Denver, Colorado, USA, July 17-21, 2005, paper PVP2005-71259

Computers In Engineering - Crack Prediction Down Under

Two page article

Aerospace Engineering, July 2005

Determination Of Interfacial Toughness Curves Using Experiments And Simulations

F.Leblanc [1], J.Roger [1], A.Zimmermann [1], D.Coutellier [2]
[1] Robert Bosch GmbH, Corporate Research and Development, Stuttgart, Germany
[2] Université de Valenciennes et du Hainaut Cambrésis, France

Journées Nationales sur les Composites #14, UTC, Compiègne, France, March 22-24, 2005

Within the fracture mechanics frameworks, adhesion can be considered in terms of an interfacial toughness. The interfacial fracture energy Gc depends on the mixed mode angle (the relative proportion of tensile and shear forces at a given distance ahead of the crack tip). Such an approach has been shown to efficiently predict the behaviour of multi-layered structures or components containing different materials and to provide a usefull simulation technique for the development of industrial products. In order to determine the interfacial toughness, lots of sample geometries exist (i.e. the Asymmetric Double Cantilever Beam Single Leg Bending, End Notched Flexure, Symmetrical Center Cracked Beam, Brazil Nut Sandwich). Besides, some authors quote the influence of surface pre-treatment on the delamination (chemical as well as physical interactions) or manufacturing processes and underline the influence on the interfacial toughness. The numerous test methods enable the choice of different loading conditions and at the same time allow to reach a wide range of mixed mode angles. In this paper, we present a method to determine the interfacial toughness curves, based on the correlation between experimental techniques and numerical simulations. Experiments were conducted for typical polymer/polymer interfaces, similar to those encountered in electronic packaging applications, and a commercial finite element code was used in combination with a meshing tool to compute the mixed mode angle and the related energy release rate.

Modelling of Stable Tearing in Aircraft Structures

Q. Liu, P. Hamel, W. Hu, P.K. Sharp, A. Lahousse and G. Clark
Air Vehicles Division, DSTO Platforms Sciences Laboratory, Australia

Internal document approved for public release in March 2005

Stress Intensity Factors For Cracked Plates Under Out-of-plane Bending

M.R. Roy, J.D.G. Sumpter, QinetiQ, Rosyth Business Park, Dunfermline
C. Timbrell, M. Wiehahn, Zentech International Ltd.

Abaqus Users' Conference, Stockholm, Sweden, May 18-20 2005

Stiffened plate structures such as ships and bridges often develop local stress concentrations which are a mixture of membrane tension and out of plane bending. Any cracks which initiate due to fatigue soon grow through the plating thickness. Modern steels are resistant to brittle fracture, but if cracks are left un-repaired, they may spread rapidly by fatigue. The rate of increase in fatigue crack length can be quantified using the elastic stress intensity factor, K.
Routines for the determination of K are available in ABAQUS, but they have limitations for performing extensive parametric studies on fatigue crack growth. Multiple fatigue crack tip positions must be analysed, requiring frequent re-meshing; and the crack direction and through thickness profile must be anticipated in advance. Zentech have developed the ABAQUS compatible software Zencrack specifically to deal with these problems.
This paper describes the problems of applying existing ABAQUS J integral methods to model cracks in structures under out-of-plane bending. Shell elements are shown to give path dependent and unreliable J values. Solid elements can be used, but the crack shape under fatigue cannot be easily predicted. Zencrack provides re-meshing techniques which allows the crack shape and speed of fatigue crack propagation to be efficiently predicted.
It is shown that Zencrack analysis overcomes ambiguities over how to take account of variations in K along the crack front in fatigue crack growth predictions. A set of results are presented which suggest that an out-of-plane bending stress is very much less detrimental for the fatigue life of a through thickness crack than a membrane stress of the same magnitude.

3D Fracture Mechanics In Ansys

R. Chandwani, M. Wiehahn, C. Timbrell

UK Ansys Conference, Stratford-upon-Avon, England, Nov 15-16 2004

This paper will address methods of performing truly three-dimensional fracture mechanics analyses in ANSYS.
Generally available fracture mechanics techniques and their implementation and use with ANSYS for 3D analysis will be briefly discussed. Techniques include the crack opening displacement (COD) method for LEFM, crack tip opening displacement (CTOD) method for EPFM, and the J-Integral method.
A software implementation using the COD method in conjunction with ANSYS will be presented. This implementation addresses generation of cracked 3D meshes and crack growth prediction. Examples will demonstrate large-scale crack growth under generalised mixed-mode loading and the development of complex 3D crack surfaces.

State Of The Art In Crack Propagation

C. Timbrell, R. Chandwani, G. Cook

Journée Scientifique 2004: Les méthodes de dimensionnement en fatigue, Centre de Compétences Matériaux & Conception (CCM&C), Fribourg, Switzerland, Oct 27 2004

This paper discusses the issues involved in numerical crack growth prediction for general 3D cracks and describes the state of the art methods that are available to practising engineers. This is a wide ranging subject in which no single theoretical method is appropriate for all cases. Different approaches are adopted, for example, for crack propagation under static load, sustained load, fatigue load and impact load. The historical pedigree of the various approaches dictates the extent to which commercial software can provide practical solutions on a day-to-day basis. A brief overview is given of the relevant fracture mechanics parameters and their use in crack growth prediction under various load conditions.
The difficulties imposed by real-life problems are further compounded by the complex 3D geometries that are involved. These complexities may arise from general component shape such as turbine disk-to-blade connections or from individual geometric discontinuities such as chamfers or stiffeners. Further complications may be introduced from a variety of sources including residual stress effects, propagation along dissimilar material interfaces and propagation in non-metallic materials or metals which are non-homogenous, large grained or anisotropic.
A number of numerical approaches are discussed and the advantages and disadvantages of each are noted. Difficulties associated with growth of a general 3D crack front are considered in general and with respect to each method.
Of the various load types that may cause crack propagation, fatigue is the most advanced in terms of useable prediction capabilities. The current state of the art for fatigue crack propagation allows for growth of multiple non-planar defects through a 3D structure under general mixed mode loading. Stress ratio and load interaction effects may be included within the analysis. The most general integration schemes allow for proprietary crack growth models, including stress ratio and temperature dependency. In addition, the effect of a static load component such as residual stress may be included within the analysis. Sustained load damage (e.g. Creep) may be combined with instantaneous damage due to rainflow counted fatigue cycles.

Residual Stress in a 3D Finite Element Fracture Mechanics Analysis

C. Timbrell, R. Chandwani

FENET Technology Workshops - Durability and Life Extension, Palma, Majorca, Mar 25-26 2004

Failure Assessment Diagrams from 3D Finite Element Analysis

M. Wiehahn, C. Timbrell, R. Chandwani

FENET Technology Workshops - Durability and Life Extension, Palma, Majorca, Mar 25-26 2004

Crack Growth In Pin-Loaded Tubes

S. Berdouk, R.J. Grant, P. Meynier, J. Smart
North East Wales Institute, Wrexham, Wales

The First International Conference On Computational Mechanics (CM'04), Belgrade, Serbia and Montenegro, November 15-17, 2004

Previously, Grant & Smart [1,2] have reported on both experimental and numerical results for pin-loaded tubes. In the experimental work, tubes were loaded by means of a central shank and transferred to the tube by means of a transverse pin. (It should be noted that this work originated because this resembles a part of an aircraft structure.) The crack growth rate and trajectory were noted and some experiments were finished early to obtain the crack profile which was found not to lie in a radial direction. In the finite element modelling, at various 'radial lengths', the crack was given a twist and a tilt and the crack profile was estimated. It was found that the numerical and experimental results correlated with each other. The same experimental set up is now been replicated using a boundary element programme, Beasy, and the finite element programme, Zencrack. In both programs, an initial crack is given and the program automatically calculates the crack growth. The objective of the research is to compare the crack growth trajectory and the profile of the crack with the previous results and to compare critically the different methods. This work is currently in progress and the results from the different procedures will be compared and contrasted.

[1] Grant RJ & Smart J (1999) Crack growth in pin-loaded tubes. Part 1: numerical analysis, J Strain Analysis, 34, 253-269
[2] Grant RJ & Smart J (1999) Crack growth in pin-loaded tubes. Part 2: comparison of experimental data with numerical results, J Strain Analysis, 34, 271-284

Propagação de Trincas em Defeitos de Soldas Circunferenciais de 'Risers' Rígidos

B.C. Pinheiro, I.P. Pasqualino
Programa de Engenharia Oceânica, COPPE/UFRJ, Rio de Janeiro, Brazil

20º Congresso Nacional de Transportes Marítimos, Construção Naval e Offshore, Rio de Janeiro, Brazil, November 8-12, 2004

Simulation Of Deformation Modes For Damage Detection In Turbine Engine Disks

R. Brockman [1], R. John [2]
[1] University of Dayton Research Institute, Dayton, OH, USA
[2] Air Force Research Laboratory, Metals, Ceramics, and NDE, Wright Patterson AFB, OH, USA

Materials Science & Technology 2004 Conference & Exhibition, New Orleans, Louisiana, USA, September 26-29, 2004

Recent studies have shown that analytical predictions of crack growth in rotating components can be used in conjunction with displacement measurement techniques to identify critical levels of fatigue damage. However, investigations of this type traditionally have focused on the detection of damage at known flaw locations. This presentation will address the related problem of assessing damage associated with flaws at unknown locations, through the combined use of analytical models and measured vibration signatures. Because the measured data are insufficient to identify a unique solution for the location and severity of fatigue cracks, the analytical procedure must be able to bound the extent of damage occurring at life-limiting locations. The issue of analyzing successive measurements to improve estimates of worst-case damage and crack locations will also be discussed.

Recent Developments In 3D Fatigue Crack Growth Prediction Using The Finite Element Method

C. Timbrell, R. Chandwani, M. Wiehahn, G. Cook

FENET Technology Workshops - Durability and Life Extension, Noordwijk, The Netherlands, Oct 9-10 2003

Simulation Of Crack Propagation In Rubber

C. Timbrell, M. Wiehahn & G. Cook, Zentech International Ltd., Camberley, Surrey, UK
A.H. Muhr, TARRC/Rubber Consultants, Hertford, UK

Proceedings of the Third European Conference On Constitutive Models For Rubber, London, England, Sep 15-17 2003

Software for simulating crack propagation ("Zencrack") has been developed which handles adaptation of the finite element mesh in the region of the crack tip as the crack propagates, and calls up a finite element solver as a subroutine to calculate the strain energy release rate at each increment in crack length. The objective of this paper is to demonstrate its applicability to rubber components.
First, the reliability of Zencrack, with ABAQUS as the solver, for calculations of strain energy release rate for an edge crack in a strip of rubber in simple extension is investigated. The results are in reasonable agreement with previous analyses and experimental work from the literature. 3D analyses show that the crack front would be ex-pected to develop curvature during propagation. The application of Zencrack to failure of "O" rings by internal cracking is also presented to show how the approach could be applied to a rubber component.

Using Abaqus To Analyse Fatigue Crack Growth Under The Combined Influence Of Residual Stress And Cyclic External Load

G. Cook, C. Timbrell, M. Wiehahn

Abaqus UK Users Group Conference, Warrington, England, Nov 12-13 2002

Many analysts are keen to investigate cracks in components under static or cyclic external loading. In the latter case fatigue crack growth prediction is also of importance. It is known that surface treatment effects such as shot peening have a beneficial effect on component life due to the compressive residual stresses introduced in the vicinity of the surface. Such treatments are used in maintenance programmes to extend the life of components in service. The effect on crack growth rate can be dramatic with significant changes in the crack growth profiles and increase in fatigue life to failure. The approach discussed in this paper applies fracture mechanics techniques to establish crack growth rates based on detectable defect sizes above the crack initiation stage established by non-destructive inspection. Thereby, extended fatigue life can be predicted, extended inspection periods calculated and the retirement of some components may be avoided.
This paper demonstrates how the Abaqus DLOAD user subroutine can be used to include the effect of residual stresses from shot peening in the analysis of crack growth in 3D finite element models. The inclusion of these effects may be so beneficial that a crack will change from a "growing" state without residual stress to a "non-growing" i.e. below threshold state, if residual stress is included.
Initially the effect of residual stresses are presented using a linear fracture mechanics approach for a single edge notched specimen and a corner crack specimen. Subsequently, the non-linear effects of contact at the crack surfaces are modelled and the effects on the cyclic energy release rates are presented.

Finite Element Based Fatigue Crack Growth Simulations in Featured Plate Specimens

A.M. Gilmartin, M.B. Henderson*, T.J.W. Ward, B. Vermeulen
QinetiQ, Cody Technology Park, Farnborough, Hampshire GU14 0LX, United Kingdom
*ALSTOM Power Tech. Centre, Whetstone, Leicester LE8 6LH, United Kingdom

The 2002 Abaqus User Conference, Newport, Rhode Island, USA, May 28-31, 2002

Gas turbine engine combustor manufacturers face the challenge of achieving improved efficiency against the increasingly stringent regulations concerning NOx emissions. Revolutionary changes in design styles will be required with the increased use of high stress concentration features such as effusion cooling holes. Lifetime prediction for new combustor designs will require an estimation of life to first crack and an estimation of the crack propagation life. This paper studies crack propagation in featured low cycle fatigue specimens intended to simulate cooling holes within a combustor liner wall. Based on extensive fatigue crack growth testing of corner notch specimens, linear elastic fracture mechanics crack growth laws have been postulated for the g¢ strengthened, nickel-based superalloy C263 at 300 and 800°C. These laws have been used to predict the growth rates for cracks growing within featured specimens and the results compared with data obtained from experimental testing of specimens with 90° holes. Direct comparison with growth rates obtained from load-controlled fatigue testing of the specimens at 300 and 800°C has shown the growth laws to provide good predictions for the behaviour of the material in the vicinity of the feature. The meshing of the test specimens with elliptical and straight through cracks was performed with the aid of ZENCRACK software, which provides singular elements to a conventional mesh. The 3-D analysis was performed using ABAQUS Standard.

Crack Growth Prediction in Girth Welds of Steel Catenary Risers

I.P. Pasqualino [1], I.A. Valeriano [1], T.M.J. Alves [2]
[1] Ocean Engineering Department, COPPE, UFRJ, Rio de Janeiro, Brazil
[2] PETROBRAS/CENPES, Rio de Janeiro, Brazil

The Twelfth International Offshore and Polar Engineering Conference, Kitakyushu, Japan, May 26-31, 2002

The Application of 3D Finite Element Analysis to Engine Life Prediction

G. Cook, C. Timbrell, B. Browning

Symposium on "Turbine Engine and Airframe Sustainment", AeroMat 2001 - 12th Advanced Aerospace Materials & Processes Conference & Exhibition, Long Beach, CA, U.S.A., June 11-14 2001

No formal papers were required or proceedings issued for the Aeromat 2001 conference.

Predicting Large Scale Crack Growth In 3D Finite Element Models

B. Browning, G. Cook, C. Timbrell

Abaqus Users' Conference, Maastricht, The Netherlands, May 30 - June 1 2001

Crack growth prediction techniques have been available for 3D models under mixed mode loading for a number of years. Previous techniques were limited to crack growth within a small region of a model. A new method is presented for automatically predicting large scale crack growth in a 3D finite element model by allowing the crack front to move through the model. Some simple examples are presented in addition to comparison of analysis results against published experimental spin test data for a cracked turbine engine compressor disc. This spin test analysis includes high levels of plasticity and crack closure effects.

The Inadequacy of Safe-Life Prediction: Aero-Engine Fan and Compressor Disk Cracking

B.J. Wicks, R.A. Antoniou, S.L. Slater and J. Hou
Aeronautical and Maritime Research Laboratory, Defence Science and Technology Organisation, Department of Defence, Box 4331 GPO, Melbourne 3001, Australia

Presented at RTO AVT Symposium on "Ageing Mechanisms and Control: Part B - Monitoring and Management of Gas Turbine Fleets for Extended Life and Reduced Costs", Manchester, UK, 8-11 October 2001, and published in RTO-MP-079(I)

An Evaluation of 3D Crack Growth Using Zencrack

J. Hou, M. Goldstraw, S. Maan, M. Knop

Airframes and Engines Division, DSTO Aeronautical and Maritime Research Laboratory, Victoria, Australia: Internal document approved for public release in May 2001

3D Crack Analysis Using MSC.Marc

C.Timbrell, G.Cook, R.Chandwani

1st Northern European Technology Conference, Manchester, England, June 7-8 2000

This paper describes software which is interfaced to MSC.Marc for analysis of arbitrary 3D cracks. The software, Zencrack, can be used in three ways:

1. For generating 3D finite element meshes containing multiple crack fronts from a finite element model of an uncracked component.
2. For determining the distribution of the maximum energy release rates and stress intensity factors along crack fronts.
3. For automatically calculating fatigue or sustained load crack growth in a general 3D body under arbitrary loading.

Items 2 and 3 use the results from the LORENZI option of a MSC.Marc analysis. The raw data from this option is processed to calculate energy release rates along the crack front. There are many complex issues to be addressed in 3D crack growth prediction. This paper presents the key concepts of the software implementation and the interface to MSC.Marc.

Design of Flexible Risers

R.Chandwani, I.Larsen

Proceedings of the "Workshop on Subsea Pipelines", COPPE/UFRJ-Federal University of Brasil, Rio de Janeiro, Brasil, December 8-9 1997

Flexible pipes, composed of bonded, unbonded or high strength steel or other alloy materials, used as high pressure dynamic risers have increased multifold in the past 20 years or so. Since 1978, when flexible risers were first specified and installed in the Enchova field, offshore Brazil, as part of a floating production system, developments in the design of particularly unbonded and steel risers have made the exploitation of oil/gas resources in deep waters with hostile environments economically viable. Also, in deep waters a compliant topside structure is more economical than a fixed platform. Various designs of compliant topside structural systems such as converted tankers, semi-submersibles with single or multi-point mooring systems with different types of turret and DP systems, tension leg platforms, deep draft platforms, spar platforms, etc., with varying specifications are currently available which comply with the wave motions rather than resist them. Flexible risers are critical components of such floating production systems because they provide the means of transferring the condensate from the seabed to the topside structure and also to exporting the processed fluids from the structure.
In this workshop lecture, some aspects of the design of dynamic flexible risers, unbonded, steel or titanium, are discussed.

3D FE Fracture Mechanics Analysis for Industrial Applications

C.Timbrell, G.Cook

Seminar on "Inelastic Finite Element Analysis", Institute of Mechanical Engineers, London, October 14 1997

This paper gives an overview of techniques that have been used by Zentech for analysis of cracks in 3D geometries in a number of commercial applications. These techniques are incorporated into the Zentech program (Ref. 1) which is interfaced to Abaqus (Ref. 2) and Marc (Ref. 3). Simple demonstrative examples and some consultancy applications are included. Some of the difficulties encountered in this type of analysis are noted and future areas of interest are outlined.

Analysing the Effects of Integrating Riser / Mooring Line Design

P.Chakrabarti, Zentech Inc.; R.Chandwani, I.Larsen, Zentech International

OMAE'96 Conference, Florence, Italy, June 16-20 1996

The design of riser and mooring systems for a floating production system usually assume uncoupled behaviour of the two systems, and each system is analysed for the effects of the vessel response given as input. In certain situations the presence of the risers can affect natural periods, damping, and slow drift response of the vessel thereby influencing the system design. This paper discusses a method for analysing the coupled riser/mooring system using Zentech's suite of programs with emphasis on the effect of the risers on the total system behaviour.

Rapid Application Development in PowerHouse : The Use of Iterative Development Techniques on a Large Project


Cognos North American User Conference, Ottowa, Canada, June 28-30 1995

This paper is about the iterative development methods used by Zentech during a two year system development project for Statoil, a major Norwegian oil company. I called the paper Rapid application Development in PowerHouse after reading an article in a UK computer paper which seemed to have just discovered the techniques which we, and I suspect a good many other PowerHouse developers, have been using for a number of years.
I shall be discussing an extension of the prototyping techniques which I am sure your Cognos salesman cited as one of the benefits of PowerHouse. Strictly prototyping suggests the building of a working model from which design and construction decisions can be made. This model is then discarded and the real business of development undertaken. In practise it is a waste to throw away perfectly good code, so people started to use something called iterative development. That is a cycle of design, construction, user review, change implementation and further reviews. At Zentech we applied those techniques in a larger than usual project, allowing us to meet tight deadlines, while overcoming problems caused by a loose original user specification.
Firstly I will tell you something about the people and companies involved. Then I will give you some project background, explain how the project developed, what changes we had to make to our working practises to meet the challenges presented, and what our final solutions were. I will touch briefly on some of the technical issues raised and how they were resolved. Finally I will try to draw some conclusions from our experiences.

Fracture Mechanics Studies at TWI Using Abaqus

R.M. Andrews, A.P. Dyer
Structural Integrity Department, TWI, Abington Hall, Abington, Cambridge, U.K.

Presented at the 10th U.K. Abaqus User Group Conference, Abington, U.K., September 21, 1995

TWI's Structural Integrity Department uses ABAQUS to support work in fast fracture and fatigue. Two widely differing examples are presented in this paper. A study of ductile tearing in thin sheet aluminium alloys has required the reproduction of extensive crack advance to evaluate candidate fracture parameters. Welded tubular joints in three dimensions have been modelled with solid elements including the weld. Weld toe cracks have been included in these models and both linear elastic analyses (to generate stress intensity factors) and full non-linear analyses have been carried out. Results from ABAQUS analyses are presented and compared with experimental results. Some remarks on the future development of fracture mechanics facilities in ABAQUS conclude the paper.

Application of Abaqus to Analysis of 3D Cracks and Fatigue Crack Growth Prediction

C.Timbrell, P.W.Claydon, G.Cook

Abaqus Users' Conference, Rhode Island, U.S.A., June 1-3 1994

A practical and well proven method is presented for generation of 3D meshes for modelling cracks, including fully automatic techniques for 3D (non-planar) fatigue crack growth prediction. The techniques, used successfully in various industries for a number of years, have recently been applied for the first time with ABAQUS. Results are presented for a number of cases, including comparisons against theoretical and experimental data.

A Flexible Riser System for Multiple Use on Marginal Fields

R.Chandwani, D.Mahmood, I.Larsen, Zentech International; J.Neffgen, JMN & CEN Consultants, Scotland

Offshore and Arctic Operations - 16th Annual Energy Sources Technology Conference, Houston, February 1993

Design Life Prediction of Flexible Riser Systems

G.Cook, P.W.Claydon

MARINFLEX 92 Conference on Flexible Pipes, Umbilicals, Marine Cables, London, November 1992

Flexible risers have been traditionally used to transport fluids at high pressure under dynamic loading conditions. Typically within the offshore industry they are used in a catenary type configuration to connect say a floating production system to the sea bed, or, either a fixed structure or another floating vessel. The risers themselves are designed to have a high axial stiffness yet be flexurally compliant to withstand the static and dynamic offshore loading. This loading arises from direction induced motion of the connected vessel.
A riser configuration is designed to withstand extreme wave and current loading conditions, typically the 100 year conditions, within the allowable integrity limits of the riser. Once the system configuration has been established, an additional and equally important requirement for full qualification is the prediction of its design life under operational loading conditions. Due to dynamic loading and the different layer structures forming the riser cross-section its design life is governed by combined wear and fatigue. The evaluation of stresses, slip and wear within unbonded flexible risers under these conditions have been addressed by a number of papers [1-6]. It is the intention of this paper not to reiterate these evaluation techniques but to present an engineering approach using them for predicting the design life of flexible risers.
A basic chart showing the input into the design life prediction is given in figure 1. From the frequency of occurrence diagram defining the environmental wave data the configuration experiences, all possible damaging load cases are analysed using a 3D flexible riser package, in this case Zenriser. The corresponding time history results are stored for subsequent life prediction using a post-processor referred to as ZENLIFE. In addition to the general equivalent cross-sectional riser properties available from the riser analyses the processor must also access the pipe geometrical description, material properties and the criteria against which the design life prediction is to be made. The processor can then evaluate stresses, slip and wear during each load case from which the design life for the riser can be assessed. This is expanded in greater detail throughout the paper.
The procedure outlined in this paper has been used on a number of cases ranging from existing risers already in use to the qualification of future riser designs. However, at present confidentiality prevents the disclosure of any of these results. Instead a demonstration case is presented - the design life assessment of a lazy 'S' configuration. For simplicity all wave loading was applied in a single direction with the riser configuration in its 'far' position. In practice a spread of wave directions consistent with environmental conditions would have to be applied in addition to all vessel offsets and rotations consistent with this wave loading.

Maximum Energy Release Rate Distribution From A Generalised 3D Virtual Crack Extension Method


Engineering Fracture Mechanics, Volume 42, Issue 6, August 1992, Pages 961-969

A Theoretical Approach to Prediction of Service Life of Unbonded Flexible Pipes under Dynamic Loading Conditions

P.W.Claydon, G.Cook, P.A.Brown, R.Chandwani

Marine Structures Journal, Volume 5, Issue 5, 1992, Pages 399-429

The Design of Flexible Marine Risers in Deep and Shallow Water

D.Hoffman, HMC Offshore Corp.; N.M.Ismail, R.Nielsen, Wellstream Corp.; R.Chandwani, Zentech International Ltd.

Offshore Technology Conference, Houston, May 6-9 1991, Paper Number OTC-6724-MS

Interaction between Flexible Risers and Mooring Lines within a Floating Production System

P.A.Brown, R.Chandwani, I.Larsen, Zentech Consultants; E.Dasambiagio, Petrobras/Cenpes, Rio de Janeiro, Brazil

SPE Latin American Petroleum Engineering Conference (LAPEC), Rio de Janeiro, Oct. 1990, Paper Number SPE-21191-MS

Fatigue Crack Growth Prediction in 3D Crack Fronts

G.Cook, P.W.Claydon, C.Timbrell

STRUCENG & FEMCAD Conference, Grenoble, France, 1990

A method is presented for predicting full 3D fatigue crack growth of arbitrary 3D crack fronts under mixed I, II and III mode loading. It uses a generalized 3D virtual crack extension (VCE) method to evaluate the distribution of the local maximum energy release rate, Gmax, along the crack front. A modified Paris equation, relating the local Gmax to the local crack growth rate, is then used to evaluate the magnitude of the crack growth. The direction of local crack growth is taken as the direction of the local Gmax.Good agreement with experimental data is produced for fatigue growth against the number of cycles for an elliptical crack under mode I cyclic loading. Although no experimental results are available, the prediction of full 3D crack growth for a crack front under mixed mode loading is also demonstrated.

Automatic and Adaptive Finite Element Mesh Generation For Full 3D Fatigue Crack Growth

G.Cook, C.Timbrell, P.W.Claydon

STRUCENG & FEMCAD Conference, Grenoble, France, 1990

A method is presented for automatically generating meshes containing 3D crack fronts. Further, an adaptive meshing scheme is presented for automatically updating meshes during full 3D fatigue crack growth prediction.
Cracks are introduced into a valid mesh of the intact component by a mapping scheme which replaces standard 20 noded brick elements with 'superelements'. In the context of this paper, the term 'superelement' refers to a set of 20 noded brick elements which models a quarter circular or through crack front using collapsed 'quarter point node' brick elements. Replacement of elements in a mesh allows introduction of one or more distinct crack fronts, with more than one superelement permitted on each distinct crack front. A special mapping controls the crack size in each superelement and maintains original isoparametric surfaces thus creating a valid mesh for the cracked component. Following incremental fatigue crack growth prediction, all superelements are re-mapped to obtain a mesh with the new crack position. The mapping scheme allows non-planar crack growth in 3D geometries.
The procedure has been found to be flexible, efficient and a great time saver in 3D fatigue crack growth analyses. Good agreement with experimental fatigue crack growth data has been demonstrated using this meshing scheme.

Tools For Predicting Service Life Of Dynamic Flexible Risers

R.Nielsen, R.S.Colquhoun, A.McCone, Wellstream Corp.; J.A.Witz, Univ. College London; R.Chandwani, Zentech, London

Proceedings of The First ISOPE European Offshore Mechanics Symposium, EUROMS-90, Norway, Aug. 1990, Paper Number ISOPE-E-90-054

Investigation into Optimised Design of Flexible Riser Systems

P.A.Brown, A.Soltanahmadi, R.Chandwani, I.Larsen

The Institute of Marine Engineers, London, Oct. 1989

During the last seven years, Zentech Consultants have been involved in a number of projects that may be broadly classified within the heading 'Analysis and Design of Flexible Riser Systems'. The basis for their involvement has been the development of an advanced analytical tool for detailed design and hydrodynamic response of these systems. This paper summarises some of the experience gained by Zentech over the last seven year and presents an investigation into optimisation techniques used during design of single and multiple flexible riser systems. An introduction to this subject is given which addresses the reasons behind performing advanced analysis within the design procedure. The purpose and definition of flexible riser systems and the characteristics of flexible pipe are also presented, followed by a discussion of the methodology commonly used within design. The analytical tools required during design are identified and guidelines are given for validation of these software packages. A series of case studies showing typical system analysis are then presented with emphasis on parameters used for system optimisation.

Application of the Finite Difference Technique to the Analysis of Flexible Riser Systems

P.A.Brown, A.Soltanahmadi, R.Chandwani

CIVIL-COMP 89, Civil & Structural Engineering Conference, City University, London, Sept. 1989

Transient Analysis of Liquid Pipeline Systems During ESV Trip

M.W.Spiteri, R.Chandwani

Proceedings of Seminar on Subsea Emergency Shutdown Systems, London, 1989

Problems Encountered in Detailed Design of Flexible Riser Systems

P.A.Brown, A.Soltanahmadi, R.Chandwani

International Seminar on Flexible Risers, University College, London, January 1989

This paper was originally presented at a meeting on ‘Flexible risers’, held on 9 January 1989 at University College, London, UK and later published in:

Engineering Structures, Volume 11, Issue 4, October 1989, Pages 234-241

SIMULUS - Subsea Design Cost and Scheduling System

E.Rasten, Seanor Eng., Oslo; E.Lorentzen, Zentech Consultants; L.Bilstad, Statoil, Stavanger

Proceedings of SUBSEA '88, International Conf., London, December 1988

Dynamic Analysis of Secondary SubSystems

R.Chandwani, D.Mahmood, Zentech Consultants; J.Colloff & D.Daintith, British Nuclear Fuels, Risley

U.K. Proceedings of Conference held at University Of Bristol, March 1988

Flexible Riser Dynamics Modelled in 3-Dimensions

P.A.Brown, R.Chandwani, I.Larsen

Proceedings of International Conference on Offshore Structures, City University, London, Sept. 1987

An extensive series of 3-D numerical simulations is required in order to design a dynamic flexible riser system. This paper presents an efficient method of solving the corresponding non-linear equation system using a lumped mass finite difference scheme and gives details of the software package developed, namely FLEX-RISER. The verification of this numerical model is discussed and a set of example analyses are presented showing some applications of the package. These examples describe the key modelling points for this type of analysis and show the type of results necessary for the design of such systems. It is concluded that an efficient analytical tool is essential for the comprehensive dynamic design of a flexible riser system.

Precast Prestressed Sections Under Axial Load and Bending

R.Chandwani, N.D.Nathan

Journal Of Prestressed Concrete Institute, Vol 16 Issue 3 Pages 10-18, May-June 1971

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