Numerical investigation of spherical indentation on elastic-power-law strain-hardening solids with non-equibiaxial resid
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Research Letter
Numerical investigation of spherical indentation on elastic-power-law strain-hardening solids with non-equibiaxial residual stresses Taihua Zhang, Wenqiang Cheng, Guangjian Peng , Yi Ma, Weifeng Jiang, Jiangjiang Hu, and Heng Chen, College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou 310014, China Address all correspondence to Guangjian Peng at [email protected] (Received 16 September 2018; accepted 17 December 2018)
Abstract The finite element simulations show that non-equibiaxial residual stresses (RS) can shift the load–depth curve from the unstressed curve and cause elliptical remnant indentation in spherical indentation. Thus the relative load change between stressed and unstressed samples and the asymmetry of elliptical remnant indentation were employed as characteristic parameters to evaluate the magnitude and directionality of RS. Through theoretical and numerical analysis, the effects of RS on indentation load and remnant impression as well as the affect mechanism were systematically discussed. Finally, two equations which could provide foundations for establishing spherical indentation method to evaluate non-equibiaxial RS were obtained.
Introduction Residual stresses (RS), which commonly exist in engineering structures and parts due to thermal mismatch or mechanical/ thermal processing, have significant effects on the mechanical behavior of materials, such as fatigue, fracture, corrosion, wear, and friction.[1] The measurement of RS in engineering structures is of great value for understanding and predicting their mechanical performance. Recently, a number of methods[2–20] have been proposed to estimate RS using instrumented indentation technique due to the advantages of simplicity, nondestruction, and convenience at various scales. These indentation methods can be divided into equibiaxial RS methods[2–14] and non-equibiaxial RS methods according to the type of residual stress.[15–20] For equibiaxial residual stress evaluation, it is not necessary to determine the directionality. Thus, the equibiaxial RS methods can only evaluate the magnitude of residual stress. As shown in Fig. S1, the basic principle is that the load–depth (F − h) curve is shifted upward by compressive residual stress and downward by tensile residual stress compared to the unstressed state, and the magnitude of residual stress can be related to easy-to-measure parameters, such as the load difference,[2,13] or the loading curvature difference,[8] or the mean contact pressure difference[3,5] between stressed and unstressed samples. Most of the current indentation methods are equibiaxial RS methods, which are easy to carry out but have limitations in engineering due to the premise of equibiaxial RS. For non-equibiaxial residual stress evaluation, both the magnitude and directionality of principal stresses should be determined. Generally, the calculation of magnitude is coupled
with the determination of stress directionality. To determine stress directionality, it must be related to sensitive in
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