Abstract—The evaluation of energy release rate and centre Crack Opening Displacement (COD) for circumferential Through-Wall Cracked (TWC) pipes is an important issue in the assessment of critical crack length for unstable fracture. The ability to predict crack growth continues to be an important component of research for several structural materials. Crack growth predictions can aid the understanding of the useful life of a structural component and the determination of inspection intervals and criteria. In this context, studies were carried out at CSIR-SERC on Nuclear Power Plant (NPP) piping components subjected to monotonic as well as cyclic loading to assess the damage for crack growth due to low-cycle fatigue in circumferentially TWC pipes. Keywords—304LN stainless steel, cyclic J-integral, Elastic- Plastic Fracture Mechanics, J-integral, Through-wall crack I. INTRODUCTION HE use of fracture mechanics in fatigue propagation life prediction has become widespread since it was first applied. The basic assumption made in fracture mechanics is that crack growth starts from a very small size defect, which can even be an inherent flaw in the material. Hence, by this approach towards fatigue life evaluation, major portion of fatigue life is expended in crack propagation. The parameter that describes the stress field around the advancing crack tip is an important component in the fracture mechanics approach (LEFM). The stress intensity factor, K, is used in Linear Elastic Fracture Mechanics. When plasticity effects are considered, various parameters such as Crack Tip Opening Displacement (CTOD) and J-integral are most commonly used in Elastic Plastic Fracture Mechanics (EPFM). For small-scale plasticity conditions, the K approach, corrected for the effect of small plastic zone effect, is advantageous. However, in highly ductile materials and where the crack tip plastic zone is large, EPFM is more appropriate. The J-integral has enjoyed great success as a fracture characterizing parameter for nonlinear materials. Rice [1] identified a parameter used to characterize dissipative material behaviour ahead of a crack that is far from any edges. By idealizing elastic-plastic deformation as non- linear elastic, Rice provided the basis for extending fracture mechanics methodology well beyond the validity limits of LEFM. Rohit is with CSIR-Structural Engineering Research Center, Tamil Nadu, Chennai 600113 (e-mail: rohit@serc.res.in). S. Vishnuvardhan is with CSIR-Structural Engineering Research Center, Tamil Nadu, Chennai 600113 (e-mail: svvardhan@serc.res.in). Tami P. Gandhi is with CSIR-Structural Engineering Research Center, Tamil Nadu, Chennai 600113 (e-mail: pgandhi@serc.res.in). Nagesh R. Iyer is with CSIR-Structural Engineering Research Center, Tamil Nadu, Chennai 600113 (e-mail: nriyer@serc.res.in). He showed that a non-linear energy release rate could be quantified by using a line integral, which he called the J- integral, evaluated along an arbitrary contour surrounding the crack tip. Rice proved the path independence of J-integral for linear as well as non-linear elastic materials using the deformation theory of plasticity which excludes consideration of unloading. The analyses showed that the J-integral can be viewed as a non-linear stress intensity parameter as well as an energy release rate. Path independence permitted the calculation of the J-integral from a path that is away from the crack tip for which stresses and strains may not be known. Dowling and Begley [2] made an attempt to apply the J- integral concept as an elastic-plastic criterion for fatigue crack growth. The tests employed Compact Tension [C(T)] specimens made of material A533B pressure vessel steel. The cyclic J values were determined by the following expression: (1) Hutchinson and Paris [3] carried out analysis and showed that outside of a core of non-proportional loading the deformation is nearly proportional. Provided the region of non-proportional loading is well contained within the region dominated by the J-singularity, there will exist an annular region where the Hutchinson-Rice-Rosengren (HRR) field holds. If a specimen’s uncracked ligament is sufficiently large compared with the inner core of non-proportional loading and the J-stress field dominates the crack extension, the crack growth will be controlled by the J-integral. Zahoor and Kanninen [4] proposed a method of evaluating the J-integral for a circumferentially cracked pipe in bending which made possible the evaluation of a J-R curve directly from the load- displacement record obtained in a pipe fracture experiment. It also permitted an analysis for fracture instability in a circumferential crack growth using a J-R curve and the tearing modulus parameter. However, in order to make reasonable predictions of stable crack growth and instability, the proper J- R curve satisfying the constraint at the crack tip had to be used. Works were also carried by Rahman and Brust [5] in which a methodology was proposed to predict the J-integral and COD of TWC ductile pipe weldments subjected to remote bending loads. Closed form solutions were obtained in terms of elementary functions for approximate evaluation of energy release rate and center COD. Cho et al. [6] described enhanced J-integral estimation schemes for pipes with circumferential semi-elliptical cracks subjected to tensile loading, global bending and internal pressure. The schemes which were given in two different forms to cover the wide ranges of geometries and material parameters; the modified GE/EPRI method and the modified reference stress method were validated against corresponding detailed elastic-plastic FE analyses by using actual material data of typical stainless steels. Rohit, S. Vishnuvardhan, P. Gandhi and Nagesh R. Iyer Monotonic and Cyclic J-integral Estimation for Through-Wall Cracked Straight Pipes T World Academy of Science, Engineering and Technology International Journal of Civil and Environmental Engineering Vol:6, No:8, 2012 686 International Scholarly and Scientific Research & Innovation 6(8) 2012 scholar.waset.org/1307-6892/13620 International Science Index, Civil and Environmental Engineering Vol:6, No:8, 2012 waset.org/Publication/13620