Characterization of the interlaminar fracture toughness of unidirectional thermoplastic composites

In this study, the critical energy release rate in mode I (G1c) for thermoplastic composites made of carbon fiber (CF) and glass fiber (GF) with a polyamide 6 (PA6) matrix is investigated. Double cantilever beam (DCB) was used as the specimen for the mode I test, and the ASTM D 5528-13 was chosen as standard. Moreover, different methodological approaches were applied by comparing different data reduction schemes from the ASTM D 5528-13 and further analytic approaches from the literature. In addition to the conducted experiments, a numerical model of the DCB test is developed and the virtual crack closure technique (VCCT) is performed on the numerical model to determine G1c for PA6-CF and PA6-GF. For the interlaminar fracture toughness G1c a value of 2.87 mJ/mm2 was determined for PA6-GF and a value of 2.16 mJ/mm2 for PA6-CF, which indicate that the use of PA6 as matrix in a composite structure leads to good resistance to damage. A comparison of the different methodological approaches showed a good agreement between the analytical approaches from the literature and the ASTM D 5528-13. In contrast, the values generated for G1c by the VCCT method were significantly higher than those of the other methods.