Time-temperature dependence of tensile strength of unidirectional CFRP

摘要

We have observed in our previous work that the tensile strength along the longitudinal direction of unidirectional CFRP under constant strain-rate loading is highly timetemperature dependent. The trend of the inherently scattered strength data seemed to obey the time-temperature superposition principle with the shift factor for the matrix resin. In this paper, we propose a prediction scheme of the master curve for the tensile strength of CFRP; we extend Rosen's analysis for tensile failure of unidirectional fibrous composites with elastic matrix to CFRP with viscoelastic matrix by making two modifications. First, we replace the ineffective length with the recovery length over which the interfacial shear stress is uniform. Second, we substitute the value of shear relaxation modulus of polymer matrix at the time of failure for shear modulus in Rosen's formula after the first modification. The tensile test for CFRP strand was carried out at various loading rates and temperatures; a smooth curve was drawn to represent inherently scattered strength data for each temperature. The master curve of the tensile strength together with the shift factor was obtained based on the curves for various temperatures. The master curve for CFRP strength predicted by the proposed method captured the test results adequately over the entire range tested.