Abstract
Powdered polystyrene which was prepared by grinding at a temperature of liquid nitrogen was compacted into a cylindrical shape for a triaxial compression test. These specimens having various void fractions n0 were compressed at various confining pressures σ3.The mode of fracture of the specimens changed with an increase in σ3 or n0 from axial cleavage fracture to typical shear fracture, and then to shear fracture accompanied by consolidation. Yield loci were obtained from Mohr's stress circles using σ3 and the axial stress σ1 corrected by Taylor-Bishop's method. The yield criterion was expressed by τ2=μt2σ2+4σt(1+μt2)(σ+σt), where τ is shear stress, σ is the normal stress, μt is a constant, which is related to the sliding friction between particles and is close to the coefficient of effective internal friction, and σt is a constant corresponding to the tensile strength of the powder compact. The criterion can be related to the mechanisms of fracture of powder compacts. The second term of the criterion is larger than the first one under the condition where n0 and σ3 are small; in this case the specimens showed axial cleavage fracture which is characteristic of brittle materials. For larger values of n0 and σ3, on the other hand, the first term is larger than the second, and the specimens showed shear fracture.
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