Prediction Of Compressive Strength Of Carbon Fiber Composites And Study On Its Influencing Factors

The low compression/tension ratio of carbon fiber composites limited its application in main bearing structure.Three elements of composites:carbon fiber,resin matrix and fiber/matrix interface,have great influences on compressive strength of composites.Based on the theoretical calculation of prediction model of compressive strength,the weight ratio of the influencing factors of compressive strength of composites was analyzed,and the effects of properties of carbon fiber and resin matrix on compressive strength of composites were discussed.The compressive failure mechanism of composites was proposed on dependence of macro/micro compression failure modes and a association between experimental data and theoretical predictions of compressive strength of composites was established.1.Based on Berbinau-Modified Budiansky prediction model of compressive strength of composites,the weight ratio of the influencing factors including carbon fiber and resin matrix on compressive strength of composites was analyzed,using material parameters of four classical carbon fiber composites.The factors were arranged in descending order:elastic modulus of fiber,volume fraction of fiber,elastic modulus of resin matrix,micro-buckling half-wavelength of fiber,initial misalignment angle of fiber.2.Resin matrix stiffened by organic rigid segment were designed and prepared,and the effects of fiber volume fraction(55%,60%,65%and 70%)and elastic modulus of T700,T800 and M40J carbon fibers on compressive strength and failure mechanism of composite were studied.When the fiber volume fraction was 55%,the predictions and experimental data of compressive strength of composite were 1192 MPa and 1113 MPa,respectively,with a deviation of 7.1%.The compressive failure modes were mainly exhibited by one-side shear plane,wedge splitting and brooming.When the volume fraction of fiber was increased to 70%,the predictions and experimental data of compressive strength of composites were 1516 MPa and 1537 MPa,respectively,and the deviation was 1.37%.The compressive failure modes were gradually transformed to fiber crushing,longitudinal splitting and fiber kink-band.When the fiber elastic modulus was 231 GPa,the predicted and experimental composite compressive strength were 1338 MPa and 1298 MPa,respectively,the deviation was 3.08%.The compressive failure modes were mainly shown by fiber kink-band and delamination buckling.When the fiber elastic modulus was increased to 399 GPa,the predictions and experimental data of compressive strength of composites were 1689 MPa and 1527 MPa,respectively,and the deviation was 10.61%.The compressive failure modes were gradually transformed to fiber crushing and fiber kink-band.4.Three kinds of epoxy matrix,unstiffened,stiffened by organic rigid segment and synergistically stiffened by organic rigid segment/inorganic rigid nanoparticles,were designed and prepared,the effects of different elastic modulus(3.8 GPa,4.2 GPa,4.7 GPa)of resin matrix on compressive strength and failure mechanism of composite were studied.When the elastic modulus of resin matrix was 3.8GPa,the predictions and experimental data of compressive strength of composites were 1210 MPa and 1123 MPa,respectively,with a deviation of 7.19%.The compressive failure modes were mainly exhibited by brooming and delamination buckling.When the elastic modulus of resin matrix was raised to 4.2 GPa,the predictions and experimental data of compressive strength of composites were 1338 MPa and 1298 MPa,respectively,with a deviation of 3.08%.The number of fiber kink-band significantly increased.When the elastic modulus of resin matrix was increased to 4.7 GPa,the predictions and experimental data of compressive strength of composites were 1520 MPa and 1587 MPa,respectively,with a deviation of 4.41%.The compressive failure modes were gradually transformed to fiber kink-band and fiber crushing.