THE EFFECT OF VOLUME FRACTION OF REINFORCEMENT ON THE ELASTIC-VISCOPLASTIC RESPONSE OF METAL-MATRIX COMPOSITES

Analysis of the elastic-viscoplastic response of a particulate-reinfor ced Aluminium-Silicon Carbide Metal-Matrix Composite material has been carried out, using the finite element ''unit-cell'' approach. The ana lysis has revealed that the various material dependent parameters in t he elastic-viscoplastic constitutive equations are strongly affected b y the volume fraction of reinforcement. Relationships are proposed to determine the values of the various material parameters for the compos ite material at low and medium volume fractions of reinforcement (up t o about 20%), when the corresponding parameters for the unreinforced m atrix material are known. Investigation of the kinematic hardening cha racteristics of the composite material showed that the strengthening o ffered by the particulate reinforcement only occurs over a small range of plastic strain from the onset of composite yielding. For higher vo lume fractions of reinforcement ( > 30%), the hardening rate eventuall y drops below that of the unreinforced matrix material at higher level s of plastic strain. Detailed investigation of the hardening and the d ynamic recovery components of the kinematic hardening has revealed tha t the drop in the composite's kinematic hardening relative to that of the unreinforced matrix material is due to the rapidly increasing reco very component, the rate of which surpasses that of the hardening comp onent 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 vo lume fraction of reinforcement for the range of volume fraction consid ered.