Material Model Development for Impact Strength Validation of a Composite Truck Bed Design

A recently developed pick-up truck has a unique bed structure which includes an under bed storage system. This truck bed and storage system design is made of sheet molded composite (SMC) material. SMC is a composite material where chopped glass fiber is laid on a poly(vinyl)ester sheet and run through a compaction process. SMC sheets are then loaded into a press to mold the desired part. During the molding process, certain design features such as molded-in ribs can cause the random orientation of the glass fibers to become directional, causing non- homogeneous material properties in the final product. A finite element material model of the SMC material was developed using material tests performed on flat SMC specimens and SMC specimens with molded-in ribs. This paper presents the details of the SMC material model development and application of the model to static and impact strength simulations on the truck bed design. The truck bed design did not include molded-in ribs, as simulations showed these ribs would crack during impact requirement tests. Furthermore, simulation was able to validate the final design prior to test without having to re- work the tooling.