Axial elongation of cast iron thin-walled tubes occurs beyond the elastic limit at pure torsion and it is accompanied by a residual increase of its volume. Tension-torsion (tension-compression) is known to produce dilatancy. A model of inelastic deformation for such semi-brittle material is formulated. According to this model, plane-plastic strain is occurred in certain cases of the stress state, which (in accordance with the hypothesis of V.V. Novozhilov) causes overall loosening (or seal) of the material.
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