The 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 fibers.

A package of procedures have been developed to collect and analyze the response of dynamic variables such as pressure, temperature, and mold separation during the compression molding of Sheet Molding Compound (SMC). From the dynamic responses, the molding process was found to consist of two regions: the flow and the subsequent curing reaction region. With an R‐25 formulation and a mold closing rate of 30 mm/s, these two regions are well separated and the average flow time is not significantly affected by the maturation time for the material up to 30 days. Several mechanical parameters were estimated based on relatively simple flow models. The relationship between the press force, mold separation, and mold closing rate is found to be sensitive to the restrictions of the flow.

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The dynamic curing behavior of sheet molding compound (SMC) has been investigated by using a cylindrical cure reactor. Both thermal and mechanical responses were determined for R-25 SMC paste. The responses from this material were analyzed to determine the chemical and physical transformations that occur during the SMC molding process. The thermal response was obtained from a thermocouple placed along the centerline of the paste sample in the cure reactor.The thermal history at this location shows distinctive stages associated with heat transfer and crosslinking reactions during the cure cycle. The R-25 paste has a precure time of 160 seconds, a reaction time of 25 seconds, and a temperature rise of 134°C. The mechanical response describes the volume change and the pressure of the paste. The displacement curve shows volume changes due to thermal expansion, cure shrinkage, and thermal contraction during the course of a cure cycle. We found a less than 1 % shrinkage during the reaction of the R-25 paste. The pressure response of the paste was found to parallel the volume transformation, although it also is strongly influenced by mechanical interactions between the press and the paste. Paste PreparationThe R-25 paste was mixed in a laboratory Ross mixer (7.5 L) following established steps to prepare the acidic and alkaline mixtures separately before

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