Residual Stresses And Three Dimensional Stress Intensity Factors Analyses For Shot Peened Single-edge-notch-tension Specimen

Shot Peening is always used to increase fatigue strength of materials and structures, and it is also one of the most effective ways of increasing fatigue life in industry. Quantitative study of the effect of shot peening on three dimensional small crack's stress intensity factor, crack propagation rate and fatigue life in the surface layer is a very active and important subject. Therefore, study of shot peening will promote the reliability and safety of aircraft structures, which has important theoretical and practical significance.Firstly, the shot peening process of TA15 titanium alloy single-edge-notch-tension specimen by ceramic shot and steel shot was simulated by FEM using ABAQUS/Explicit codes. The residual stress induced by shot peening using FEM agreed with that gained by X-ray diffraction method. Then the relationship between shot peening parameters and residual stress field was studied in the paper. In addition, four characteristic parameters were used to analyze different residual stress fields induced by different shot peeing parameters.To study the effect of shot peening on where small fatigue crack initiates and the shape of small crack, SEM was used to study the fatigue fracture surface. The results demonstrate that: 1) Small crack initiates from surface in both shot peened and un-shot peened specimen; 2) Corner crack happens in shot peened specimen and surface crack happens in un-shot peened specimen; 3) All crack length in thickness direction a, is similar to the crack length in width direction c , and a/c=1.0 in both shot and un-shot peened specimen.On the basis of residual stress fields induced by different shot peening parameters, three dimensional weight function method was used to calculate compressive stress intensity factors Kres under different residual stress fields. The influence of shot peening parameters on Kres was studied and the results show that: 1) When the crack is relatively small, Kres is mainly influenced by the maximum compressive residual stress; 2) With the increase of crack size, the deeper the compressive residual stress field is, the deeper where the maximum -Kres takes place; 3) When the crack gets a certain dimension, Kres changes mainly with the depth of compressive residual stress, the deeper the compressive residual stress field is, the larger the -Kres.