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

Abstract

Prediction of crack propagation or postulated flaw of structures is important in the assessment of their life, performance and reliability. Aerospace structures, gas turbine engines, pressure vessels and pipelines are some examples where crack propagation prediction plays an important role in estimating the system reliability, life and safety. Life of any component can be evaluated by means of experiments which are very time consuming and difficult to carry out on complex structures. In order to eradicate the difficulties associated with experiments one can use finite element modeling of the given system to estimate its life under different loading conditions. Cracks propagate in structures as a result of dynamic or cyclic loading. In the proposed work, a 3D finite element based life assessment study is carried out for an interacting parallel crack specimen under constant load amplitude cyclic loading and it is compared with experiments for assessing the accuracy of finite element modeling technique in case of complex structures. The commercially available finite element analysis (FEA) package ANSYS is used for the finite element modeling and is coupled with Zencrack package for crack propagation studies. Virtual Crack Extension (VCE) method is used for crack growth prediction. In VCE technique, strain energy release rate (ERR) is calculated for a series of virtual crack extensions along the normal plane at the crack tip and the direction of crack propagation is estimated along the direction in which maximum energy release rate is obtained. Stress intensity factor (SIF) at each crack extension is obtained using FEA and number of cycles is estimated using Paris law. Fatigue experiments are also conducted for estimating the life of the same interacting crack system along with digital image correlation (DIC) technique for obtaining strain fields surrounding crack tip. SIF obtained from FEA are compared with the analytical solution. Plot relating number of cycles and crack length is obtained from both FEA and experiment.

Keywords

Interacting crack, Finite element method, Fatigue life, Stress intensity factor.