Fiberglass reinforced composites have seen increased use in the automotive industry for exterior body panel applications. Car makers find these plastic components to offer design freedom, increased durability, and weight savings compared to steel parts. The assembly of plastic components is accomplished using structural adhesives since most types of welding and mechanical fastening, which were commonly used to join steel, are not feasible. Structural adhesives have been used in the automotive industry for several years to bond fiberglass reinforced composite inner reinforcements to outer body panels. Bonded assemblies are strong, corrosion resistant, and sound-dampened.Before any component reaches the production stage, extensive laboratory testing is performed. Test methods which simulate stresses imposed on an assembly are used to evaluate joint strength. Also, field simulation testing of prototype vehicles is conducted.