Experimental Characterization and Finite Element Simulation of Laser Shock Peening Induced Surface Residual Stresses using Nanoindentation
As a non-destructive technique, nanoindentation has been extensively used in the determination of material properties such as hardness and Young’s modulus at both the macro and micro scale. This thesis explores the use of nanoindentation for measuring the surface residual stress induced by laser shock peening. While the technique has been studied by a number of groups, accurate measurement using nanoindentation is hindered by a good method of estimating the contact area, which is the basis of all the calculations in the literature. Due to the sink-in and pile-up effects, the contact area can be underestimated leading to erroneous values of the residual stresses. The overall objective of the thesis is to improve the existing methodology by incorporating the pile-up effects for the contact area calculation. The accuracy of the residual stresses is further validated with the experimental measurements conducted using X-ray diffraction technique. Along with this experimental development, the thesis also aims at developing a finite element model for simulating the nanoindentation process. A simulation model for nanoindentation in region with and without residual stresses is developed and the results reported are in agreement with the experimental results. A parametric study is performed to understand the effect of stress and strain hardening on the indentation curves for the Nickel based alloy IN718.
Engineering, Nanoindentation, Residual Stress measurement, Finite Element Analysis, X-ray diffraction, Different methods
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