Study On Compressive Strength And Thermal Conductivity Of Interlay Reinforced And Stiffened CFRP Composites With CNT Film

At present,the structure-function integration has become the inevitable development trend of advanced CFRP composites.However,the poor interlaminar properties of CFRP composites laminates resulted in weak transverse support of rich-resin region to carbon fiber and delamination,which further led to decreased longitudinal compressive strength.Furthermore,the low thermal conductivity of resin and poor interfacial compatibility of interlay region resulted in the poor in-plane thermal conductivity of CFRP composites.So,in this paper,the method of interlay reinforcing and stiffening based on CNT film as interlay carrier was proposed.The structure-function integrated CFRP composites was prepared by optimizing physicochemical structure with wet stretching and epoxidation.The effect of CNT film on longitudinal compressive strength of CFRP composites and the correlative mechanism between CNT film and compression failure was studied,and the mechanism of enhancing the in-plane thermal conductivity of composites was explored,achieving synchronous enhancement of longitudinal compression strength and in-plane thermal conductivity.(1)The oriented CNT film(S-CNTF),epoxidized CNT film(ECNTF)and stretch-epoxidation CNT film(S-E-CNTF)were prepared by wet stretching and epoxidation to optimizing the physicochemical structure of CNT film(P-CNTF).The P-CNT/epoxy film,S-CNT/epoxy film,E-CNT/epoxy film and S-E-CNT/epoxy film based on hot-melting pre-impregnation method.Compared with P-CNTF,on the one hand,the degree of alignment of S-CNTF and S-E-CNTF was obviously increased,and the CNTs were rearranged and presented directional arrangement with large bundling state,on the other hand,the surface of E-CNTF and S-E-CNTF was confirmatively grafted with epoxy group,and the surface chemical activity was improved.The optimized physicochemical structure resulted in enhancement of tensile strength and modulus of SCNTF,E-CNTF and S-E-CNTF,and the tensile strength of S-CNTF,ECNTF and S-E-CNTF was increased from 26.8 ± 2.1 MPa to 81.2 ± 3.2MPa,64.3 ± 1.3 MPa and 116.2 ± 2.7 MPa,respectively,and the tensile modulus of S-CNTF,E-CNTF and S-E-CNTF was increased from 0.33 ±0.04 GPa to 3.13 ± 0.42 GPa,1.13 ± 0.31 GPa and 6.32 ± 0.75 GPa,respectively.Furthermore,the tensile modulus of S-CNT/epoxy film,ECNT/epoxy film and S-E-CNT/epoxy film was increased by 1.9 times,1.2 times and 3.3 times,respectively,in comparison to P-CNT/epoxy film,among which,the S-E-CNT/epoxy film presented the highest stiffness.(2)The interlay reinforced and stiffened CFRP composites(CFRP/P-CNTF,CFRP/S-CNTF,CFRP/E-CNTF and CFRP/S-E-CNTF)were prepared by using P-CNTF,S-CNTF,E-CNTF and S-E-CNTF as interlay carrier,respectively.Compared with CFRP composites,the inplane shear modulus of CFRP/P-CNTF,CFRP/S-CNTF,CFRP/E-CNTF and CFRP/S-E-CNTF was enhanced by 8.6%,21.2%,13.8% and 28.3%,respectively,and the interlaminar shear strength of CFRP/P-CNTF,CFRP/S-CNTF,CFRP/E-CNTF and CFRP/S-E-CNTF was enhanced by5.3%,7.4%,22.1% and 34.2%,respectively,revealing that the ability of resisting to shear deformation and interlay crack growth was improved.The model prediction also showed that the theoretically elastic compressive stress of CFRP/P-CNTF,CFRP/S-CNTF,CFRP/E-CNTF and CFRP/S-E-CNTF was increased from 857.5 ± 59.6 MPa to 907.1 ±53.1 MPa,1012.6 ± 36.5 MPa,978.3 ± 46.9 MPa and 1120.8 ± 42.3 MPa,respectively,and plastic of the longitudinal compressive strength was increased from 207.3 ± 21.1 MPa to 237.5 ± 29.1 MPa,241.0 ± 19.5 MPa,256.7 ± 26.2 MPa and 274.2 ± 37.4 MPa,respectively,compared to CFRP composites,which was in accord with experimental values.The longitudinal compressive strength of CFRP/P-CNTF,CFRP/S-CNTF,CFRP/E-CNTF and CFRP/S-E-CNTF by experimental test was enhanced by 5.5%,16.4%,21.7% and 35.2%,respectively,indicating that the increased interlaminar stiffness and interlaminar shear strength restrained the kink-band failure and delamination during compression process.Moreover,the in-plane thermal conductivity of CFRP/P-CNTF,CFRP/SCNTF,CFRP/E-CNTF and CFRP/S-E-CNTF was improved from 4.32 ±0.08 W/(m·K)to 5.70 ± 0.04 W/(m·K),6.43 ± 0.24 W/(m·K),6.11 ± 0.07W/(m·K)and 7.8 ± 0.11 W/(m·K),respectively,in comparison to CFRP composites,manifesting that the three-dimensional thermally-conductive network through interlay region of composites was established to improve the heat transfer efficiency.