# Numerical Evaluation of Residual Stress Influence on SIF in CT Specimen
###### Abstract
[PERSON] [16] evaluated the residual stresses effect on a surface crack with a brittle fracture behavior. He recommended a post-heat treatment to relax the residual stress in the weld joints. In trying to understand what influence makes residual stresses on austenitic stainless steels and how they interact with the initial level of pre-straining, research work was carried out in the CEA Saclay, France [17]. The SCC resistance of the initially pre-strained plate (from 30% to 60%) was analyzed in these experiments. To carry out such an experiment, the CT specimen was machined from the pre-strained plate. Before the SCC test, a fatigue pre-cracking is performed on each specimen. At the end of the SCC tests, the CT specimen was completely broken by using the testing machine. The fracture surface revealed a particular fatigue crack with a smaller propagation at the center of the specimen and no SCC crack growth at this location, whereas significant SCC propagation has been obtained near the edges. The numerical simulation of the stress intensity factors along the crack front of the CT specimen was carried out. Usually research is made for a not pre-strained material on a specimen with an initial straight crack front or machined notch, and the higher values of the stress intensity factor are observed in the middle of the specimen and lower values are observed at the sides of the specimen: a larger crack growth in the middle of the specimen is then expected, which was not the case here. However, in the case when the plate was initially pre-strained (plate with residual stresses), it seems that an opposite distribution of stress intensity factor along the crack front is observed: the higher values were at the sides of the specimen and the lower ones were in the middle. It was also justified by the obtained crack shape after pre-cracking. The main goal of this paper is to numerically evaluate how the residual stress affects the SIF profile at the crack front. To achieve the main goal of the research, the following tasks should be conducted:  
1. create the residual stress profile in the numerical model by adding a temperature profile;
2. apply the created residual stress profile to the standard CT specimen model;
3. compare the numerically determined SIF profile in cases with and without residual stress. To accomplish the previously described tasks, the computer program Cast3M was chosen [16]. This program is based on the FEM which is validated for the calculation of fracture parameters such as SIF and J-integral. To make this research close to a real-life scenario, the experimentally determined material properties and the measured residual stress profile of highly pre-strained stainless-steel plates were used. The experimental tests and FE simulation were conducted at an elevated 325 \({}^{\circ}\)C temperature. The analysis results of this research show how residual stresses affect the SIF profile along the crack front and that these stresses have a bigger influence on the surface rather than the central part of the specimen. As the secondary goal of the paper, the method for residual stress application to the FE model was demonstrated.