In this study, the nonlinear flexural behavior of discontinuous and randomly oriented chopped strand thermoplastic CFRP was found to be related to the damage depth of the surface layer of the specimen, which were observed using an in-situ three-dimensional X-ray CT bending test system. The nonlinear behavior of the developed CFRP showed correlation between the occurrence of damage at the outer edge of the compression side and the process of development, and the stress of starting point of the nonlinear behavior was similar to the in-plane compressive strength obtained by the in-plane compression test. A simple theoretical model using the damage depth at the outer edge of the compression side of the developed CFRP under three-point bending load and in-plane compressive strength that was confirmed the nonlinear bending behavior of the developed CFRP agreed with the experimental value.

Owing to their high cycle moldability and recyclability, carbon fiber reinforced thermoplastics (CFRTP) are applicable in aerospace, automobiles, and sports industries. The elucidation of the tensile and compressive properties of CFRTP is significant for their reliable structural design. Generally, the compressive properties of fiber reinforced plastics depend heavily on their matrix properties. Moreover, CFRTP exhibit greater plastic elongation capacity than carbon fiber reinforced thermosettings (CFRTS). From this perspective, the prediction of compressive properties is required to successfully predict the plastic deformation of CFRTP. In this study, the theoretical model of the compressive strength of discontinuous and dispersed CFRTP was constructed, based on the compressive model proposed by Sun (1994). The model was verified using discontinuous carbon fiber mat reinforced thermoplastics (CMT) with in-plane isotropic. These results indicate that the model can predict the strength of the compressive failure of polypropylene (PP) or polyamide (PA)-CMT initiated by shear fracture at various temperatures using the tensile properties of the matrix resins as input value only.

We fabricated a modeled automotive structure using mixed discontinuous carbon fiber and thermoplastic resin (LFT-D) stiffened using prepreg with the same matrix. This structure was shaped in the form of a hat closed by an LFT-D flat plate. Subsequently, we performed axial compression tests on these specimens. We also conducted non-linear finite element analysis to predict the axial compression behavior. Thereafter, the numerical and experimental results were compared and discussed. Ultimately, we discovered that fusion bonding is superior to adhesion bonding because it offers a higher maximum load capability owing to the higher fracture toughness.

In this study, we proposed an optimization method for carbon fiber allocation and orientation to reduce the cost of CFRTP. CFRTP is effective in reducing the weight of transportation equipment. However, the high material cost of CFRTP possesses a problem for the practical application of CFRTP. Therefore, we focused on the allocation and orientation of carbon fibers that affect the material properties of CFRTP to develop low cost and high stiffness CFRTP using minimal carbon fibers. The allocation of carbon fiber is determined by topology optimization employed in the proposed optimization method. Similarly, the orientation of carbon fiber is determined by the principal stress. Thus, high stiffness CFRTP with fewer fibers can be obtained using the proposed optimization method.