13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- PREDICTION OF CREEP CRACK INITIATION UNDER THE INTERACTION BETWEEN LONG RANGE RESIDUAL STRESS AND APPLIED LOAD Yiqiang Wang1,*, David J Smith1, Christopher E Truman1, A. M. Shirahatti1 1 Department of Mechanical Engineering, University of Bristol, BS8 1TR, UK * Corresponding author: yw9146@bristol.ac.uk Abstract In this paper, a three bar structure is examined to simulate the behaviour of a component subjected to combined applied and residual stresses. This structure (or system) permits long-range residual stress to be created in a compact tension (CT) specimen through the introduction of a misfit. The magnitudes of the residual and applied stresses in the CT specimen are a function of the initial misfit displacements, applied load and the relative stiffness of the components of the system. The prediction of cracking initiation under combinations of residual and apply loads are investigated when the compact tension specimen creep according to a power law. We find that the creep crack initiation time is sensitive to the assumed creep constants and is significantly different under different loading conditions. The effect of residual stress on the crack initiation time is dependent on the ratio of the residual stress to the total stress. Overall, this study provides important insights into the assumptions adopted in structural analysis for creep crack initiation. Keywords Crack initiation, Residual stress , elastic follow-up, 316H stainless steel 1. Introduction Many components operating at high temperature are subjected to combinations of applied and residual stresses, especially welded steel sections. Evidence from industry is that the presence of residual stress is a contributing factor for initiation and growth of creep cracks, which has important consequences for the lifetime of components at high temperature. A typical practical example is reheat crack initiation observed in stainless steel welded components where the presence of residual stress is seen as a major factor [1]. In this paper, the purpose is to better understand whether the existence of residual stress plays an important role in contributing the crack initiation in components driven by a combination of applied and residual stress at elevated temperature. Previous work involved generating residual stresses directly into specimens using a variety of methods. A recent review of this work [2] concluded that in order to improve our understanding of the effects of residual stress on fracture new methods should be sought that do not introduce microstructural changes during the generation of residual stress. Therefore, in this paper we develop a simple method of introducing long range residual stress through strain incompatibility in a classical three bar model. An additional force can applied to the three bar structure system to simulate the behaviour of a component subjected to combined applied and residual stresses. The subsequent creep behaviour is governed by the materials properties and elastic follow-up provided by the system. Elastic follow-up is a consequence of the presence of a region of differing stiffness relative to the remainder of the structure. [3].
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