Creep damage model considering unilateral effect based on bimodulus theory

Based on the continuous damage mechanics (CDM) theory, Ambartsumyan bimodulus theory and creep damage theory, a bimodulus creep damage constitutive model is proposed in this paper. The model is able to describe the damage-induced unilateral behaviour related to the microdefect closure effect. The unilateral behaviour is considered a special bimodulus property. By judging the tension or compression state in bimodulus theory, different elasticity properties matrixes are selected according to signs of principal stresses. Then, an elasticity properties matrix is linearly converted to a general stress space. The model effectively solves the difficulty of determining tension or compression in complex stress states when the unilateral effect of damage is considered in the analysis of actual structures. The tangent elasticity matrix is used to improve the convergence of the proposed algorithm. In this study, a numerical simulation of the proposed model is achieved by writing subroutines in the FORTRAN language. A numerical example of a hole-in-plate structure under uniaxial stress is analysed. By comparing the results with those obtained by the traditional model, which does not consider the unilateral effect of damage, it is demonstrated that the proposed model is capable of describing the damage-induced unilateral behaviour related to microcracked closure effects. The numerical example validates the effectiveness and realizability of the proposed model.