A Study On Residual Stress Distribution Of Shot-peened TC4 ELI Titanium Alloy By Depth-sensing Indentation Technique And Numerical Simulation

TC4 titanium alloy is widely used in aerospace industry due to its advantages such as low density and high yield ratio. And in practical industrial fields, a large number of engineering equipments in service are often subjected to complicated cyclic loading and it is occasionally difficult to satisfy its engineering requirements of long life and high reliability just relying on the fatigue resistance of material itself. Shot peening, an effective surface treatment method, has been largely applied to improve the fatigue strength of metallic components and structures under cycle loading. Therefore, it is very significant to systematically study the residual stress field and mechanical properties in deformed layer of shot-peened titanium alloy, then explore the relationship of shot peening process parameters and residual stress distribution and establish the quantitative evaluation method of its residual stress field in order to promote the better application of titanium alloys in aerospace industry.In this paper, the depth-sensing indentation tests and metallographic examinations, combined with the finite element numerical simulation, were carried out to sufficiently investigate the residual stress field and mechanical properties in deformed layer of shot-peened TC4 ELI titanium alloy smooth specimens and notched specimens.Firstly, the depth-sensing indentation technique, combined with the reverse algorithm put forward by M.Dao et al, was used to obtain mechanical properties in shot-peened layer. The results show that the inhomogeneous deformation hardening and ductility dissipation caused by shot impact enhance the stiffness and plastic deformation resistance but lower the plasticity and toughness in shot-peened layer. The aforementioned mechanical properties distribution characteristics of material is relevant to shot peening intensity.The study based on metallographic microscopy indicates that obvious slip bands are found in the shot-peened layer; the shot impact increases its dislocation density and further leads to cyclic hardening in the deformed layer. Its microstructure tends to transform to be equiaxed and the impact induces the transition from β to a.The depth-sensing indentation testing,combined with the Suresh et al’s modified model, was carried to evaluate residual stress distribution of the shot-peened layer. The results show that the residual stress field induced by shot impact is composed of the compressive residual stress in the surface layer and the tensile residual stress inside the internal layer; the improvement of shot peening intensity increases the compressive residual stress zone, but has little impact on the maximum compressive residual stress; this residual stress distribution is relevant to shot peening intensity. The residual stresses based on the quantitative evaluation method presented in this paper basically approach to the indentation testing results.The residual stress fields of smooth specimens obtained by finite element numerical simulation were analyzed in comparison with the indentation testing results. It shows that the results nearly accord with the residual stress distribution obtained by the indentation testing.