孔隙对碳纤维增强环氧树脂复合材料超声衰减系数及压缩性能的影响

Effects of voids on ultrasonic attenuation coefficient and compressive properties of carbon fiber/epoxy resin composite

孔隙对碳纤维增强环氧树脂(CF/EP)复合材料的力学性能和破坏模式有显著的影响,因此需要建立准确的孔隙率无损检测评估方法,并基于所评估的孔隙率提高CF/EP复合材料压缩性能预测的可靠性。本文主要研究了孔隙对CF/EP复合材料的超声衰减系数和压缩性能的影响,通过降低固化压力至0.7~0.2 MPa和延长预浸料室温贮存时间至30~180天的方法,制备了不同孔隙率的CF/EP复合材料层压板,通过金相验证其孔隙率在0%~3.0%之间,孔隙类型主要为层中孔隙和层间孔隙。通过理论和试验的方法,基于超声反射法建立了孔隙率与超声衰减系数的关系曲线,由孔隙引起超声衰减系数为αv=1.08Pv^2(Pv为孔隙率),与前人基于超声穿透法所得的超声衰减系数αv=0.61Pv^2较好地符合2倍声程的关系。对不同孔隙率的CF/EP复合材料层压板进行压缩测试实验,特别考虑了贴片和加载方向对测试结果的影响。从细观角度研究了含孔隙的CF/EP复合材料层压板的压缩破坏模式。结果表明:CF/EP复合材料层压板的压缩强度随孔隙率增加而下降,孔隙率增加至2.5%时,压缩强度下降13.7%,孔隙细观特征影响压缩破坏的形式,主要原因是孔隙诱发微裂纹的萌生和扩展,削弱了纤维与树脂间的结合力并引发纤维微屈曲。

Voids produced in the manufacturing process have significant influence on the mechanical properties and failure modes of carbon fiber reinforced epoxy resin(CF/EP)composite,which highly desire an accurate nondestructive evaluation of the void content and a reliable prediction of compressive properties based on the measured void content.In this paper,the effects of voids on ultrasonic attenuation coefficient and compressive properties were investigated extensively.CF/EP composite laminates were fabricated of quasi-isotropic layups and produced by applying various autoclave pressures of 0.7-0.2 MPa and increasing prepreg out storage time of 30-180 days to acquire controlled levels of void content.The void content,ranged from 0%to 3.0%,as well as the microstructure of intra-and inter-laminate voids could be verified and characterized using light microscopy.Ultrasonic reflection test was performed on laminates containing voids and the correlation between ultrasonic attenuation and void content,namelyαv=1.08Pv2(Pv is void content),was established theoretically and experimentally,which gave good duple-path agreement with published experimental results of ultrasonic through-transmission test,namelyαv=0.61Pv2.Then,the dependency of the reduced compressive strength on laminates containing voids was investigated experimentally by counter-posing the compressive performances of four types of CF/EP composite laminate specimens,namely 0°un-tabbed,90°un-tabbed,0°tabbed and 90°tabbed.The result shows that the compressive strength of CF/EP composite laminates significantly decreases with the increasing of void content,saying a drop of 13.7%with void content up to 2.5%.The microscopic examination of the compressive failure modes shows that the microstructure of voids of CF/EP composite laminates also has a significant effect on the compressive failure mode,which can be attributed to the initiation and propagation of micro cracks,the reduced fiber-matrix bonding as well as the micro-buckling of fibers.