Mechanical characterization of anisotropy on a carbon fiber sheet molding compound composite under quasi-static and fatigue loading

The paper presents an experimental analysis of the anisotropic effects of the structural advanced carbon fiber sheet molding compound composites (AC-SMCs) subjected to quasi-static and fatigue loading. Two configurations of AC-SMC composites (randomly oriented and highly oriented) considering three different orientations (0°, 45°, 90°) with respect to the material thermo-compression flow direction are investigated under quasi-static and fatigue tensile loading. The effects of fibers orientation induced by the thermo-compression process are analyzed in terms of ultimate strength, elastic modulus, and macroscopic damage corresponding to the stiffness reduction, and related to the quasi-static and fatigue behavior. For both loading conditions, the macroscopic damage of AC-SMC randomly oriented exhibits a two-stage evolution without any damage saturation prior to the samples' failure. In addition, the difference between the highly oriented and randomly oriented configurations is pronounced especially for the 45° and 90° orientations. Post-mortem X-ray radiography and SEM observations show that damage mechanisms such as microcracks appear between and inside bundles, and their occurrence depends on the sample orientation. Experimental findings are compared with those of an equivalent advanced glass fiber reinforced sheet molding compounds composite. The degree of anisotropy is more pronounced for AC-SMC. Indeed, the dependency of the behavior during the manufacturing process induces orientation. Furthermore, the damage evolutions of the two types of SMCs have displayed different kinetics, especially for the saturation stage which is not observed for the AC-SMC composite.