Rhys Jones [1][2], Andrew Ang [1], Nam Phan [3], Michael R. Brindza [4], Michael B. Nicholas [5], Chris Timbrell [6], Daren Peng [1][2], and Ramesh Chandwani [6]

[1] ARC Industrial Transformation Training Centre on Surface Engineering for Advanced Materials, School of Engineering, Swinburne University of Technology, John Street, Hawthorn, VIC 3122, Australia
[2] Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3800, Australia
[3] Structures Division, Naval Air Systems Command, Patuxent River, MD 20670, USA
[4] Air Warfare & Weapons Department, Air Platforms Division, Office of Naval Research, Arlington, VA 22203-1995, USA
[5] US Army Research Laboratory, U.S. Army Combat Capabilities Development Command Weapons and Materials Research Directorate, Aberdeen Proving Ground, Aberdeen, MD 20852, USA
[6] Zentech International Limited, 590B Finchley Road, London NW11 7RX, UK

Materials 2026, 19(2), 372.

Abstract:

This paper reviews the fracture mechanics parameters associated with the variability in the crack growth curves associated with forty-two different tests that range from additively manufactured (AM) steels to cold spray additively manufactured (CSAM) 316L steel. As a result of this review, it is found that, to a first approximation, the effects of different building processes and R-ratios on the relationship between ΔK and the crack growth rate (da/dN) can be captured by allowing for changes in the fatigue threshold and the apparent cyclic toughness in the Schwalbe crack driving force (Δκ). Whilst this observation, when taken in conjunction with similar findings for AM Ti-6Al-4V, Inconel 718, Inconel 625, and Boeing Space Intelligence and Weapon Systems (BSI&WS) laser powder bed (LPBF)-built Scalmalloy^®, as well as for a range of CSAM pure metals, go a long way in making a point; it is NOT a mathematical proof. It is merely empirical evidence. As a result, this review highlights that for AM and CSAM materials, it is advisable to plot the crack growth rate (da/dN) against both ΔK and Δκ. The observation that, for the AM and CSAM steels examined in this study, the da/dN versus Δκ curves are similar, when coupled with similar observation for a range of other AM materials, supports a prior study that suggested using fracture toughness measurements in conjunction with the flight load spectrum and the operational life requirement to guide the choice of the building process for AM Ti-6Al-4V parts. The observations outlined in this study, when taken together with related findings given in the open literature for AM Ti-6Al-4V, AM Inconel 718, AM Inconel 625, and BSI&WS LPFB-built Scalmalloy^®, as well as for a range of CSAM-built pure metals, have implications for the implementation and certification of limited-life AM parts.

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.

Abstract:
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.

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