塑性論に基づいたEnd Cap型の降伏関数について

抄録

The determination of yield functions is the first step for the derivation of the constitutive law of geo-materials. In thi: paper, a new yield function is proposed by incorporating a parameter k, which is related to the creation of new fracture surfaced uring failure of materials, into the modified Cam-Clay model based on the classical plasticity theory and the critical state concept in soil mechanics. The critical state is the stress state where materials plastically deform without plastic volumetric strain increments. The proposed model characteristically shows that plastic strain increment vectors are normal to the yiek surfaceswhich have more general shape on the Rendulic stress plane than an ellipse of the modified Cam-Clay model and that the yield surfaces intersect perpendicularly the hydrostatic axis aside from the origin of stress space.
The application of the proposed model to the experimental data of cement mortar (uniaxial compressive strength Dc=205kgf/cm₂) givesM=0.77 andk=0.66, where M is the ratio of octahedral shear stressτ_octto mean principal stressσ_mat the critical state. These values of M and k are considered to be appropriate in comparison with those of rocks in published papers. The assumption that M does not depend on Lode's parameter but is constant, in the proposed model, represents that the shape ofyield surfaces is a circle of Von Mises on the octahedral stressplanes. Furthermore, the initial yield stress, experimentally obtained, of am=250kgf/cm²on the hydrostatic axis causes the onset of dilatancy at about 80% stress level ofσ_cwhich may be a little higher. Since the experimental data used in this paper cover the region of contractancy only, it is necessary to confirm the validity of the proposed model for all stress states including that of dilatancy.