Journal of the Japan Society for Composite Materials

The unidirectional compressive failure of fiber reinforced plastics is dominantly influenced by plastic kinking process which starts from any initial local fiber misalignment. Compressive strength in the fiber direction is much less than tensile strength and plays a significant role for designing a robust structural member. In case of the unidirectional composite laminate, particularly compressive molded and using versatile thermoplastic resin, its compressive strength depends a great deal on initial fiber misalignment in the out-of-plane direction and the elastic-plastic behavior of the matrix. By using a compressive test specimen with a shape of hourglass, the dependence of kinking and shear property caused by initial fiber misalignment in the out-of-plane direction has been verified theoretically.

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In this study, compression-after-impact (CAI) test, compression test after repairing impact damage by thermal fusion bonding (CAR_TFB), compression tests with specimen removed the residual stress (CAR_A) and out-of-plane deformation (CAR_D) caused by the dent below melting point, were carried out in order to evaluate the efficiency of repair of carbon fiber reinforced thermoplastic (CFRTP) laminates with barely visible impact damage (BVID) and to experimentally confirm the existence of a threshold of the damage length. Cross-ply laminates used for specimens was made of carbon fiber/polyamide 6 unidirectional semi-prepreg which have 0.043 mm in thickness and 54% in fiber volume fraction. Not only strength of CAR_TFB, but also that of CAR_A and CAR_D were recovered to the same level of compressive strength of intact specimen, although internal impact damages in CAR_A and CAR_D specimens were not bonded by thermal fusion. The results show that residual stress and/or out-of-plane deformation were govern the residual compressive strength of the laminates with BVID. Thus, not only thermal fusion bonding but also repairing only dent below melting point are expected as one of the promising repair method to recover the compressive strength of the CFRTP laminates with BVID.

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