碳纤维增强环氧树脂基复合材料湿热残余应力的微Raman光谱测试表征

Testing and characterization of hygrothermal stresses in carbon-fibers reinforced epoxy composites using Raman spectroscopy

采用微Raman光谱仪对碳纤维增强环氧树脂复合材料CF/EP(纤维体积分数为30%)的湿热残余应力进行了研究。实验结果表明:湿热残余应力能够使碳纤维Raman光谱发生频移,根据频移可对纤维所受湿热残余应力进行表征;选择合适的试验点是复合材料湿热残余应力Raman测试成功的关键;在湿热环境下长期吸湿,纤维所受轴向残余应力由吸湿前的热残余压应力转变成吸湿后的湿热残余拉应力;由吸湿后碳纤维所受湿热残余拉应力减去吸湿前热残余压应力获得的吸湿拉应力非常大,平均为2272 MPa,接近所用碳纤维的拉伸强度(2800 MPa);适当的加工热残余压应力有利于降低吸湿导致的应力。

The hygrothermal stresses in the composite with fiber volume fraction of 30% were investigated by using micro Raman spectroscopy. The results show that the Raman wavenumber shift for carbon fibers can be caused by the hygrothermal stresses, which can be used to characterize the hygrothermal stress in the fibers. The appropriate selections of the tested points are the key to success in the hygrothermal stress test with Raman spectroscopy for the composites. The results also show that during the long-term moisture absorption process, the axial residual stresses within the fibers transform from thermal residual compressive stresses before absorption into hygrothermal tensile stresses after absorption. The axial stresses within the fibers induced purely by the absorption can be obtained by using the tensile stresses after absorption minus the compressive stresses before absorption, which is rather high （2272 MPa on average） and close to the tensile strength of 2800 MPa of the carbon fibers used in this paper. The suitable thermal residual stresses can reduce the moisture induced stresses to some extent.