AbstractThe impact behavior of sheet molding compound (SMC) plaques was determined by using an instrumented Instron puncture test machine and the failure mechanism was qualitatively assessed by examining the damage. The impact response of SMC in terms of the load‐deflection curve is fairly consistent and shows the characteristics of a composite, intermediate between a brittle and a ductile material. At the speed of 2 m/s (about 5 miles per hour) the fracture energy, i.e., energy to break, was determined to be about 10 J for a regular 3 mm thick R‐25 SMC panel. This value decreases exponentially with a decrease in the thickness of the panel (power of 2.7). The failure process could also be affected by the material factors (resin and fibers used in the composite). For instance, an examination of the length distribution of the fibers in the damage region indicates that a combination of fiber pull‐out and severe fiber breakage have contributed to the impact resistance. Also, the fiber length in the composite could alter the failure modes. With the 25 mm fibers, the damage consists of an even mixture of fiber breakage and fiber pull‐out, but with a mixture of equal numbers of longer (38 mm) and shorter (13 mm) fibers in the composite, the damage is shifted to predominantly breakage of the longer
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