Analytical and numerical modeling of the mechanical behavior of metal matrix composites.

摘要

Metal matrix composites (MMCs) subjected to both external and thermal cycling loading can experience enhanced creep deformation, leading to dimensional instability in some cases. Three-dimensional finite element models have been constructed to predict the behavior of composites under such loading conditions. The different possible types of composite behavior are discussed in detail. The language and ideas developed in the continuum mechanics area of ratcheting and shakedown was shown to correlate quite closely to the thermal cycling behavior of composites and to apply to their analysis and design. Three composite configurations were analyzed analytically and their models were used to construct Composite Behavior Maps (CBMs). CBMs are diagrams which delineate regions of dimensionally stable and unstable composite behavior, and were shown to have a characteristic shape. Experimental and analytical methods are outlined for constructing conservative CBMs for complex composite configurations for which analytical solutions are not possible. The utility of such diagrams as both an analysis and design tool for MMCs on the microstructural scale is discussed in detail.; The fundamental elastic and plastic properties of a new non-traditional alumina/aluminum composite where both phases are continuous, known as C{dollar}sp4{dollar}, were investigated analytically using finite element simulations and compared to experimental results. The composite behaves in a nearly bilinear manner defined by an elastic modulus and an elastic-plastic modulus. The apparent plasticity in the composite was shown to occur by true plastic deformation of aluminum and elastic accommodation of alumina. Effects of residual stresses and matrix strength on the tensile and compressive behavior of the composite were also investigated. The concept of selective reinforcement is discussed, along with its special considerations and limitations. The applicability and effectiveness of selective reinforcement as a design approach for composites on a macro-structural scale was best demonstrated using a real life example. The C{dollar}sp4{dollar} material, characterized by its high strength and modulus ratios to its density, was considered an ideal model material to selectively reinforce aluminum products. Using a detailed step-by-step iterative procedure, a cast iron brake caliper was replaced by a comparable C{dollar}sp4{dollar}-reinforced aluminum one with 59% mass reduction using selective reinforcement.