Experimental and numerical multi-scale approach for Sheet-Molding-Compound composites fatigue prediction based on fiber-matrix interface cyclic damage

In this paper, a multi-scale approach is proposed to predict the stiffness reduction of a Sheet-Molding-Compound (SMC) composite submitted to low cycle fatigue (until 2.10(5) cycles). Strain-controlled tensile fatigue tests (R = 0.1) are carried out at various strain ranges. Damage is investigated at both macroscopic and microscopic scales through the evolutions of Young's modulus and SEM observations, after interrupted fatigue tests at different lifetime periods. The results show that the fatigue degradation of the composite is mainly controlled by fiber-matrix interface debonding. A quantitative analysis allows determining the threshold and kinetics of the fiber-matrix interface damage during cyclic loading as a function of the orientation of fibers. Moreover, a fiber-matrix interface damage criterion, taking into account the local cyclic normal and shear stresses at the interface, is introduced in the Mori and Tanaka approach in order to predict the loss of stiffness. The parameters of this local criterion are identified by reverse engineering on the basis of the experimental results described above. Finally, the predicted loss of stiffness is very consistent with the experimental results.