Abstract
Nonlinear properties of metal matrix composites (MMCs) are studied. The research combines results of loading–unloading tensile tests, microstructural observations and numerical predictions by means of micromechanical mean-field models. AA2124/SiC metal matrix composites with SiC particles, produced by the Aerospace Metal Composites Ltd. (AMC) are investigated. The aluminum matrix is reinforced with 17% and 25% of SiC particles. The best conditions to evaluate the current elastic stiffness modulus have been assessed. Tensile tests were carried out with consecutive unloading loops to obtain actual tensile modulus and study degradation of elastic properties of the composites. The microstructure examination by scanning electron microscopy (SEM) showed a variety of phenomena occurring during composite deformation and possible sources of elastic stiffness reduction and damage evolution have been indicated. Two micromechanical approaches, the incremental Mori–Tanaka (MT) and self-consistent (SC) schemes, are applied to estimate effective properties of the composites. The standard formulations are extended to take into account elasto-plasticity and damage development in the metal phase. The method of direct linearization performed for the tangent or secant stiffness moduli is formulated. Predictions of both approaches are compared with experimental results of tensile tests in the elastic–plastic regime. The question is addressed how to perform the micromechanical modelling if the actual stress–strain curve of metal matrix is unknown.
Highlights
Materials such as metal matrix composites (MMCs) during exploitation sustain nucleation and accumulation of defects called damage
Researchers observed that damage accumulation during tension depends on microstructure of the MMC and can be initiated and propagated by three damage mechanisms: fracture of reinforcement particles, matrix voiding as well as the particle/matrix debonding at the interface between two composite phases, what was discussed e.g. in [3]
Reduction of micorplasticity effects explains why the range 90–70% taken for both unloading loops gives the closest values of damage parameter: in this initial part of unloading, almost all grains in the polycrystalline matrix remain in the elastic regime
Summary
Materials such as metal matrix composites (MMCs) during exploitation sustain nucleation and accumulation of defects called damage. Researchers observed that damage accumulation during tension depends on microstructure of the MMC and can be initiated and propagated by three damage mechanisms: fracture of reinforcement particles, matrix voiding as well as the particle/matrix debonding at the interface between two composite phases, what was discussed e.g. in [3]. Authors of [6] studied tensile properties of AA7075 aluminum alloy MMC with SiC particles as reinforcement They reported that during composites, loading stress is transferred to reinforcement particles. Fine microcracks initiated at low stresses at or near particle–matrix interfaces caused by non-uniform distribution of SiC particles were reported The latter shows another reason that can lead to MMC damage i.e. formation of reinforcement particle clusters during MMC production observed e.g. for Al/SiC composites and reported in [8] and [9]. The paper is organized as follows: the second section contains description of the composites; in the third section, experimental procedure and results of tensile tests are presented; the fourth one comprises microstructure observations; the fifth numerical modelling and the last one (the sixth) summary and conclusions
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