טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentShahak Nativ
SubjectStrengthening of Light Metals with Particles for Large
Deformation
DepartmentDepartment of Mechanical Engineering
Supervisors Professor Emeritus Jehuda Tirosh
Dr. Amnon Shirizly
Full Thesis textFull thesis text - English Version


Abstract

The strength performance of Metal Matrix Composite (MMC), reinforced with small particles (deformable or rigid), is crucially depended on the thermal history by which it was manufactured. Beside the inherent properties of the composite constituents, few engineering-like variables (as volume fraction of the particles, blending temperature with particles, etc.) show some counter-intuitive effects in strengthening or weakening the composite. The goal of this study is to get a wider view on these effects. In particular, it is intended to focus on the composite strength via particle/matrix stress interaction with residual back-stress environment. We herewith offer a rigorous solution to the thermo-elastic residual stresses near deformable hard particles. After applying certain loads on the bulk composite (by remote tension and/or compression) anisotropy in plastic yielding is generated by increasing volume fraction of particles. It is characterized by a moderate enhancement of the yield strength when subjected to tensile load (with maxima at a certain volume fraction) and a severe weakening of the yield strength under compression. The solution includes a tacit reliance on Eshelby’s result (stating that an imbedded inclusion in a loaded elastic matrix is 'unyieldable'). We restrict our analysis to relatively dilute, equal-sized spherical particles. The theoretical results are backed by experiments, using MMC of silicon-carbide particles (SiC) in aluminum matrix (blended at about 300). Beside some mechanical gain in tensile strength, the agreement with compression experiments indicates the potential benefit of energy-saving by using MMC for compression-dominated metal forming processes (like extrusion, rolling, forging, etc.).

Keywords: Metal Matrix Composite (MMC), blending temperature, hard particles (inclusions), thermal residual stresses.