CFRTPの曲げ特性に及ぼすひずみ速度依存性の粘弾性および結晶構造的考察

抄録

The effects of strain rate on the bending properties of carbon-fiber-reinforced thermoplastics (CFRTP) with polyamide6 (PA6) as a matrix were investigated using three-point bending tests. The results of the tests, in conjunction with acoustic emission (AE) measurements, confirmed the increase in the bending strength, Young’s modulus, and failure strain with an increase in the strain rate. The scale of damage, determined from the AE measurements, also increased with an increase in the strain rate. Dynamic mechanical analysis was performed to elucidate the reason for the strain-rate dependence of the results of the bending tests. The results indicated an increase and decrease in the storage modulus and loss tangent, respectively, with an increase in the strain rate. The frequency dependence of the storage modulus was consistent with the strain-rate dependence of the Young’s modulus. The loss tangent corresponded to the scale of damage, owing to the change in the energy-absorption properties. The crystal structure of the CFRTP before and after the bending tests was evaluated using X-ray diffraction. The results revealed the destruction of α-form crystals and the formation of γ-form crystals during the bending tests. The presence of γ-form crystals results in ductility. Therefore, the formation of γ-form crystals during bending deformation rendered the CFRTP ductile. This resulted in an increase in the failure strain.