Micromechanics based discrete damage model with multiple non-smooth yield surfaces: theoretical formulation, numerical implementation and engineering applications
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The discrete damage model presented in this paper accounts for 42 non-interacting crack microplanes directions. At the scale of the Representative Volume Element (RVE), the free enthalpy is the sum of the elastic energy stored in the non-damaged bulk material and in the displacement jumps at crack faces. Closed cracks propagate in pure mode II, whereas open cracks propagate in mixed mode (I/II). The elastic domain is at the intersection of the yield surfaces of the activated crack families, and thus describes a non-smooth surface. In order to solve for the 42 crack densities, a Closest Point Projection algorithm is adopted locally. The RVE inelastic strain is calculated iteratively, by using Newton-Raphson method. The proposed damage model was rigorously calibrated for both compressive and tensile stress paths. FEM simulations of triaxial compression tests showed that the transition between brittle and ductile behavior at increasing confining pressure can be captured. The cracks’ density, orientation and location predicted in the simulations are in agreement with experimental observations made during compression and tension tests, and accurately show the difference between tensile and compressive strength. Plane stress tension tests simulated for a fiber-reinforced brittle material also demonstrated that the model can be used to interpret crack patterns, design composite structures and recommend reparation techniques for structural elements subjected to multiple damage mechanisms.