Colloquia

Summary

In the aerospace industry, the use of composite materials has steadily increased. Their high strength-to-weight ratio, high fatigue life, and corrosion resistance make them an attractive material choice. Manufacturing techniques such as injection overmolding enable the injection molding of complex geometries using short-fiber-reinforced thermoplastics onto a continuous fiber-reinforced thermoplastic laminate. This manufacturing method has many applications, such as rib stiffener geometries or brackets for laminates. Characterization of the interface between the overmold and the laminate is necessary to assess the performance of components. However, there are currently no standard methods to characterize the strength at the interface of the laminate and overmold.

This research focuses on characterizing the shear strength at the interface between the overmold and laminate. The Short Beam Shear test(a setup based on the 3-point bending test with a shorter span between supports) is chosen for its simple specimen geometry and setup. Following Short Beam Shear tests, a modified setup of the short beam shear test was developed to reduce indentation occurring under the loading nose. Different overmold geometries, such as a chamfer or fillet, and ply orientation of the laminate at the interface are tested to observe their effects. Finite element simulations of the tests were performed with the plasticity of the overmold taken into consideration.

The tests showed low deviations, indicating good repeatability. Although specimens with a fillet failed close to the interface, interface failure was not the first failure observed when the overmold had a chamfer at the base. The modified setup failed to initiate failure at the interface as well for specimens with the chamfer, indicating the bond strength at the interface is higher than the strength of the rib. Simulations capture trends observed in the experiments, which is beneficial as the simulation model captures the underlying physics, which can reduce the need for physical tests. The observations and analysis performed in this research have shown that while the Short Beam Shear test is consistent, it is not suitable for all overmolded cross-sections. Future work should focus on loading the laminate instead of the overmold.