The effect of volume fraction of reinforcement on the elastic-viscoplastic response of metal-matrix composites

Abstract

Analysis of the elastic—viscoplastic response of a particulate-reinforced Aluminium Silicon Carbide Metal—Matrix Composite material has been carried out, using the finite element “unit-cell” approach. The analysis has revealed that the various material dependent parameters in the elastic—viscoplastic constitutive equations are strongly affected by the volume fraction of reinforcement. Relationships are proposed to determine the values of the various material parameters for the composite material at low and medium volume fractions of reinforcement (up to about 20%), when the corresponding parameters for the unreinforced matrix material are known. Investigation of the kinematic hardening characteristics of the composite material showed that the strengthening offered by the particulate reinforcement only occurs over a small range of plastic strain from the onset of composite yielding. For higher volume fractions of reinforcement (> 30%), the hardening rate eventually drops below that of the unreinforced matrix material at higher levels of plastic strain. Detailed investigation of the hardening and the dynamic recovery components of the kinematic hardening has revealed that the drop in the composite's kinematic hardening relative to that of the unreinforced matrix material, is due to the rapidly increasing recovery component, the rate of which surpasses that of the hardening component at plastic strain levels coinciding with the commencement of the drop in the kinematic hardening observed. Both the hardening and the dynamic recovery components show a non-linear relationship with the volume fraction of reinforcement for the range of volume fraction considered.