This study developed a material model with a damage function that supports finite element analyses in crash strength analyses of beams manufactured using randomly-oriented long fiber thermoplastics composites. These materials are composites with randomly-oriented carbon tow having a fiber length of approximately one inch, and are isotropic in-plane from a macro perspective, but exhibit different damage properties for tension and compression. In the out-of-plane direction, the influence of the resin matrix properties increases, and the materials properties are similar to those of laminate materials. This means they are anisotropic materials with physical properties that differ from those in the in-plane direction. In order to verify the influence of these characteristics, the damage process was observed by three-point bending of a flat plate, which is a mixed mode that includes tension, compression, and out-of-plane shear. Digital image correlation was used to analyze the strain distribution in the edgewise direction, and the results showed that damage progresses from the surface toward the inside of the plate. A damage model was created that takes this phenomenon into account. This damage model uses a format that organizes the difference between the in-plane tension and compression damage properties in terms of the triaxial stress level, and accumulates damage according to each stress level. This model also separately accumulates the out-of-plane shear damage, and associates it with the in-plane compression damage. The accuracy of the developed material model was verified by comparison with three-point bending tests of closed-hat-section beams. The verification results showed a close approximation in terms of the load- stroke profiles and fracture format. This indicates that a material model that takes into account in-plane and out-of-plane damage can accurately express macro bending behavior.
