Mechanical characterization of a Low Density Sheet Molding Compound (LD-SMC): Multi-scale damage analysis and strain rate effect

This paper presents the results of an overall experimental characterization of the mechanical behavior of a Low Density Sheet Molding Compound (LD-SMC). LD-SMC is a polyester matrix containing mineral charge (CaCO3) reinforced by discontinuous bundles of glass fibers and Hollow Glass Microspheres (HGM). After a description of its specific microstructure using several experimental methods (notably a new ultrasonic method), the overall mechanical response of two microstructure configurations (Randomly Oriented (RO) and Highly oriented (HO)) is analyzed at both macroscopic and microscopic scales in the case of tensile and compression tests. HGMs are homogeneously distributed into the overall volume of the material. At the microscopic scale, in-situ tensile tests inside a SEM and fracture surfaces observations allows analyzing the specific damage mechanisms occurring during tensile and compression loading performed in the mold flow direction (HO-0°) and perpendicularly to it (HO-90°). A strong coupled influence of the presence of the HGM and fibers orientation has been emphasized. The results show that for HO-0° configuration fiber-matrix debonding appears to be the predominant damage mechanism, whereas for HO-90° configuration HGM-matrix debonding appears to be the predominant damage mechanism. High speed tensile tests are achieved using servo-hydraulic test equipment in order to study the strain rate effects (until 80 s−1) on mechanical macroscopic responses of HO-0°, RO and HO-90° samples. Strain rate has an obvious influence on the inelastic properties of LD-SMCs samples for all microstructures particularly on the damage threshold.