The non-uniaxial creep under complex loading

Based on the model of incomplete reversibility of creep deformation, constitutive equations for the non-uniaxial stress state of metals under complex loading paths are proposed. The tensors of the viscoelastic, viscoplastic, and viscous components of the creep deformation are assumed to develop independently. The deformation kinetics is associated with the initial and deformation anisotropy. The measure of creep intensity for initially orthotropic materials is the equivalent stress introduced by Hill. In this case, the similarity of the stress and strain deviators is not required. The nature of the anisotropy of the deformation is associated with the value of the viscoplastic component of the deformation in the direction of the principal axes of the stress tensor. A superposition of the initial and deformation anisotropy is assumed. Samples made of 3KhV4SF tool steel and EI437B heat resistant alloy were tested, which are initially isotropic materials. The rheological coefficients of 3KhV4SF steel and EI437B alloy were calculated from the results of the uniaxial tension test samples at various levels of initial stresses. A comparative analysis of the forecast under complex loading according to the proposed equations with the test results was carried out.