Gradient thermoplasticity

International audienceStrain gradient plasticity effects arise from the interplay between the typical wavelength of applied mechanical loading conditions and microstructural length scales. Grain and particle size effects are well known in mechanical metallurgy. They can be represented in the continuum thermomechanics of materials by means of additional contributions of the plastic strain or hardening variable gradients to the free energy density or viscoplastic dissipation potentials of nonlinear materials. A general micromorphic framework is presented here that is based on the introduction of additional degrees of freedom and their gradient into constitutive functionals. The theory is specialized so as to recover the well-known Aifantis strain gradient plasticity model which includes an extra hardening term associated with the Laplacian of cumulative plastic strain. The effect of the gradient of the plastic strain tensor leads to a similar Laplacian term in the expression of kinematical ha