Ductile Fracture Simulation of Full-scale Circumferential Cracked Pipes: (I) Carbon Steel

Abstract

This paper reports ductile fracture simulation and comparison with carbon steel test data of full-scale cracked pipes via 3-D finite element damage analysis based on stress-modified fracture strain model. Although there are few test results and discussion of full-scale cracked pipes, it is not an easy task to properly evaluate fracture behaviour of large-scale components for various pipe sizes with different shape of a crack-like defect. In such a situation, finite element (FE) damage analysis can be a competitive alternative to characterize the fracture behaviour of cracked components such as crack initiation and maximum loads. In recent years, a simple FE method [1] to simulate ductile fracture has been developed based on the stress-modified fracture strain model [2,3]. The technique appropriately simulated ductile failure for miscellaneous cracked components [4,5]. However, for some cases, large-scale components using small element size, FE analysis couldn’t give reliable values because of numerical instability. Element-size-dependent critical damage model enhanced by taking the effect of element-size on the ductile fracture damage analysis is introduced to overcome this problem and to be applicable to the large-scale structures. In order to validate proposed method, two types of carbon steel (A106 Gr. B and SA333 Gr. 6) pipes with a circumferential crack taken from [6] are considered, subjected to four-point bending only and combined loading. It is shown that predicted crack initiation and maximum loads are compared with experimentally measured values, showing overall good agreements.