Va. Lubarda et al., SOME COMMENTS ON PLASTICITY POSTULATES AND NONASSOCIATIVE FLOW RULES, International journal of mechanical sciences, 38(3), 1996, pp. 247-258
The plasticity postulates of Drucker and Ilyushin do not in general ap
ply to materials whose mechanical behavior is described by non-associa
tive flow rules, although for many stress and strain cycles and under
many loading conditions the corresponding work inequalities defining t
he postulates are not violated. This is illustrated in this paper by c
onsidering pressure-dependent dilatant materials subjected to combined
shear-pressure, add triaxial compression loadings. Both, hardening an
d softening ranges of material response are analyzed. It is shown that
, depending on the relationship between the dilatancy factor and the i
nternal friction coefficient, the net work of added stresses in some t
ypical closed stress cycles can be either positive or negative, while
the net work in the corresponding closed strain cycles is in each case
positive. Constitutive implications and the relationship between plas
ticity postulates and actual material stability are also discussed.