Crushing of composite structures: experiment and simulation

A systematic experimental investigation is conducted to evaluate the effect of geometric features on crush behavior. From a carbon/epoxy square tube, individual test segments are machined in order to isolate corner radii and flat sections of varying sizes, for a total of five different test geometries. Laminate thickness, material system, manufacturing process, and test methodology are kept constant throughout the study. For the material system and lay-up considered in this study, fiber tensile fracture and tearing at the corners is responsible for the vast percentage of the energy absorbed, while frond formation and splaying of the flat segments is responsible for a much lower percentage. An analytical expression is derived that accounts for the combined behavior of corner elements and flat segments in the crush behavior of more complex test articles, such as tubes. Explicit dynamic Finite Element Analyses using LSDYNA’s progressive failure MAT54 material model are performed for each of the specimens tested. It is found that the SOFT crash front parameter, a key numerical parameter used to facilitate controlled collapse failure over unstable crushing, is not a constant for the material but it needs to change with each shape tested in order to yield successful simulations. Furthermore, a striking relationship is found between the SOFT parameter and the degree of stability of the section.