Browsing by Subject "Residual stresses"
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Item Experimental measurement of residual stresses in cold-drawn aluminum tubes(Texas Tech University, 1990-08) Farahaninia, KamalOne of the most common sources of residual stresses is the non-uniform plastic deformation encountered in metal-forming operations. Determination of residual stresses is of major importance in many processes as well as precision equipment components. All destructive techniques, such as hole-drilling and boring-out techniques, are based on the principle of removing part of the stressed material and measuring the resulting strains as the material adjusts its shape to maintain equilibrium. The purpose of this study was to measure the residual stress distributions in cold-drawn aluminum tubes via a modified Sachs boring-out technique utilizing electrochemical machining (ECM) as the means of material removal. Electrochemical machining (electropolishing) was performed on the inner surface of the tubes while measuring the developed strains at the outer surface. Material removal by electropolishing technique was found suitable enough to produce a homogeneous and damage-free surface for measurement of required strains.Item Prediction of the dimensional instability resulting from machining of residually stressed components(Texas Tech University, 1995-08) Shin, Shang HyonResidual stresses, built into most manufactured components, are revealed most dramatically during subsequent machining operations. Depending on the magnitude and distribution of the original residual stress state, the remaining part of a machined component distorts in order lo maintain the equilibrium of internal forces, resultng in a new state of residual stress distribution in the remaining material. Given a known residual stress state in a material, the purpose of this research was to develop a methodology for the prediction of machining-induced distortions and the determination of the new state of residual stresses in the remaining material. In the first phase of this work, closed-form equations for the distortions of a residually stressed block, subjected to surface layer removal, were developed. Experimental and finite element simulations of the surface layer removal were also conducted and compared to the closed-form solutions. In the second phase of this study, analytical solutions for the distortions and residual stress re-distribution in a cylinder subjected to machining of the inner surface were developed. The original residual stress state was determined by the elasto-plastic solution of a cylinder subjected to the autofrettage process as well as the finite element simulations of the autofrettage process. The effect of isotropic as well as cylindrically orthotropic material properties on the ensuing machining distortions and the redistributions of residual stress state were studied. Closed-form solutions and finite element results of this study demonstrated excellent agreement in the determination of distortions and the new state of residual stresses due to material removal operations.