J-INTEGRAL COMPUTATIONS IN THE INCREMENTAL AND DEFORMATION PLASTICITYANALYSIS OF SMALL-SCALE YIELDING

Detailed numerical studies of small-scale yielding in elastic power-la w plastic materials under Mode I loading reveal a path dependence of t he J-integral in small-strain incremental-theory plasticity calculatio ns, while corresponding studies employing deformation-theory plasticit y show no such behavior. The path dependence of the incremental-theory calculations is sensitive to the presence of T-stresses and deviates substantially from the remote elastic J-value at radial distances, r, on the order r less-than-or-equal-to CTOD (crack-tip opening displacem ent). A comparison of the fields predicted by the two different plasti city implementations reveals that deep within the plastic zones, stres ses are in reasonable agreement over the angular interval 10-degrees < theta < 160-degrees with moderate disagreement in the regions near th e crack faces. However, the predicted strains differ markedly in regio ns directly ahead of the tip, at approximately 60-degrees, and borderi ng the crack faces. The differences in J-integral behavior lie primari ly in the traction-displacement-gradient term and are conjectured to a rise from the integrated effects of the slight differences in stress a nd strain fields.