Weldability of polyetheretherketone(PEEK) with polyetherimide(PEI) is tested. And carbon fiber reinforced PEEK laminates are resistance welded using stainless steel mesh heating element. The effects of the welding tim...Weldability of polyetheretherketone(PEEK) with polyetherimide(PEI) is tested. And carbon fiber reinforced PEEK laminates are resistance welded using stainless steel mesh heating element. The effects of the welding time and welding pressure on the lap shear strength of joints are investigated. Results show that PEEK can heal with PEI well in welding condition and the lap shear strength of PEEK/CF(carbon fibre) joint increases linearly with welding time, but reaches a maximum value when welding pressure ranging from 0.3 MPa to 0.5 MPa with constant welding time. The fracture characteristics of surface are analyzed by SEM techniques, and four types of fracture modes of lap shear joints are suggested.展开更多
A combination of experimental measurements and numerical analysis was utilized to study the low-velocity impact damage of domestic carbon fiber-reinforced composites(CFRCs).The results indicated that the low-velocity ...A combination of experimental measurements and numerical analysis was utilized to study the low-velocity impact damage of domestic carbon fiber-reinforced composites(CFRCs).The results indicated that the low-velocity impact damage induced pits and longitudinal cracks on the front side,oblique cracks and delaminationin on the back side.The pit depth increased with the increasing impact energy.It was demonstrated that the numerical analysis strain history curve was similar to the experimentally measured strain history curve,which verified the accuracy of numerical analysis in which the Hashin failure criterion was used.The work provides basic data and theoretical basis for the promotion and application of the domestic carbon fiber,and demonstrates the feasibility of replacing imported carbon fibers with domestic carbon fibers.展开更多
Sizing treatment has shown great potential in improving the interfacial properties of poly(p-phenylene benzodioxazole)(PBO)fiber-reinforced composites,but is severely limited due to the use of flammable and explosive ...Sizing treatment has shown great potential in improving the interfacial properties of poly(p-phenylene benzodioxazole)(PBO)fiber-reinforced composites,but is severely limited due to the use of flammable and explosive organic solvents.Herein,a new high-efficiency waterborne sizing agent has been developed by using functionalized carbon nanospheres(CNSs)as a nano-reinforcement.Due to abundant oxygen-containing groups,the CNSs greatly improves the surface activity,wettability,and roughness of the PBO fibers.As a result,the interfacial shear strength of the CNSs sized fiber-reinforced composite increases by 79.6%compared with that of the pristine fiber-reinforced composite.Moreover,the excellent mechanical and thermal properties of the PBO fibers remain almost unchanged after sizing treatment.Thus,this work provides an environmentally friendly and scalable method for constructing a strong interface between the PBO fibers and the matrix resins,which makes sense in promoting the application of PBO fiber-reinforced composites in aerospace and military industries.展开更多
Solid-phase-sintered Si C-based composites with short carbon fibers（Csf/SSi C） in concentrations ranging from 0 to 10wt% were prepared by pressureless sintering at 2100°C. The phase composition, microstructure,...Solid-phase-sintered Si C-based composites with short carbon fibers（Csf/SSi C） in concentrations ranging from 0 to 10wt% were prepared by pressureless sintering at 2100°C. The phase composition, microstructure, density, and flexural strength of the composites with different Csf contents were investigated. SEM micrographs showed that the Csf distributed in the SSi C matrix homogeneously with some gaps at the fiber/matrix interfaces. The densities of the composites decreased with increasing Csf content. However, the bending strength first increased and then decreased with increasing Csf content, reaching a maximum value of 390 MPa at a Csf content of 5wt%, which was 60 MPa higher than that of SSi C because of the pull-out strengthening mechanism. Notably, Csf was graphitized and damaged during the sintering process because of the high temperature and reaction with boron derived from the sintering additive B4C; this graphitization degraded the fiber strengthening effect.展开更多
As an important component,the bond behavior of carbon fiber-reinforced polymer(CFRP)-concrete interface for a reinforced concrete(RC)beam is very significant.In this study,a theoretical model was established to analyz...As an important component,the bond behavior of carbon fiber-reinforced polymer(CFRP)-concrete interface for a reinforced concrete(RC)beam is very significant.In this study,a theoretical model was established to analyze the flexural behavior of CFRP-strengthened RC beams,and the CFRP-concrete interfacial bond-slip relationship under hygrothermal environment was unified into one model.Two failure criteria corresponding to two types of failure modes,i.e.,concrete crushing and intermediate crack(IC)-induced debonding,were developed.Through the theoretical model,the flexural behavior of deflection,interfacial shear stress distribution and ultimate load of a CFRP-strengthened RC beam under hygrothermal environment were obtained and predicted.Moreover,the theoretical model was verified by test results.The results showed that the hygrothermal environment had a significant impact on the CFRP-concrete interface behavior.Compared with the control beam without hygrothermal environment pretreatment,the deflection and ultimate load of the strengthened RC beam decreased by 51.9%and 20%,respectively.展开更多
A method for strengthening damaged tubular steel T-joints under axial compression by wrapping them with carbon fiber-reinforced polymer(CFRP)sheets was proposed and evaluated.The influence of the CFRP strengthening on...A method for strengthening damaged tubular steel T-joints under axial compression by wrapping them with carbon fiber-reinforced polymer(CFRP)sheets was proposed and evaluated.The influence of the CFRP strengthening on the failure mode and load capacity of T-joints with different degrees of damage was investigated using experiments and finite element analyses.Five T-joints were physically tested:one bare joint to obtain the peak load and corresponding displacement(D1m),two reinforced joints to provide a reference,and two pre-damaged then retrofitted joints to serve as the primary research objects.The ratio of the pre-loaded specimen chord displacement to the value of D1m was considered to be the degree of damage of the two retrofitted joints,and was set to 0.80 and 1.20.The results demonstrate that the maximum capacity of the retrofitted specimen was increased by 0.83%–15.06%over the corresponding unreinforced specimens.However,the capacity of the retrofitted specimen was 2.51%–22.77%lesser compared with that of the directly reinforced specimens.Next,111 numerical analysis models(0.63≤b≤0.76,9.70≤g≤16.92)were established to parametrically evaluate the effects of different geometric and strengthening parameters on the load capacity of strengthened tubular T-joints under different degrees of damage.The numerical analysis results revealed that the development of equivalent plastic strain at the selected measuring points was moderated by strengthening with CFRP wrapping,and indicated the optimal CFRP strengthening thickness and wrapping orientation according to tubular T-joint parameters.Finally,reasonable equations for calculating the load capacity of CFRP-strengthened joints were proposed and demonstrated to provide accurate results.The findings of this study can be used to inform improved CFRP strengthening of damaged tubular steel structures.展开更多
文摘Weldability of polyetheretherketone(PEEK) with polyetherimide(PEI) is tested. And carbon fiber reinforced PEEK laminates are resistance welded using stainless steel mesh heating element. The effects of the welding time and welding pressure on the lap shear strength of joints are investigated. Results show that PEEK can heal with PEI well in welding condition and the lap shear strength of PEEK/CF(carbon fibre) joint increases linearly with welding time, but reaches a maximum value when welding pressure ranging from 0.3 MPa to 0.5 MPa with constant welding time. The fracture characteristics of surface are analyzed by SEM techniques, and four types of fracture modes of lap shear joints are suggested.
基金Funded by the Fundamental Research Funds for the Central Universities(No.2018IB001)and the National High-tech Research and Development Program of China(863 Program)(No.2013AA031306)。
文摘A combination of experimental measurements and numerical analysis was utilized to study the low-velocity impact damage of domestic carbon fiber-reinforced composites(CFRCs).The results indicated that the low-velocity impact damage induced pits and longitudinal cracks on the front side,oblique cracks and delaminationin on the back side.The pit depth increased with the increasing impact energy.It was demonstrated that the numerical analysis strain history curve was similar to the experimentally measured strain history curve,which verified the accuracy of numerical analysis in which the Hashin failure criterion was used.The work provides basic data and theoretical basis for the promotion and application of the domestic carbon fiber,and demonstrates the feasibility of replacing imported carbon fibers with domestic carbon fibers.
基金financially supported by the National Natural Science Foundation of China (No. 51903237)Beijing Natural Science Foundation (No. 2222091)
文摘Sizing treatment has shown great potential in improving the interfacial properties of poly(p-phenylene benzodioxazole)(PBO)fiber-reinforced composites,but is severely limited due to the use of flammable and explosive organic solvents.Herein,a new high-efficiency waterborne sizing agent has been developed by using functionalized carbon nanospheres(CNSs)as a nano-reinforcement.Due to abundant oxygen-containing groups,the CNSs greatly improves the surface activity,wettability,and roughness of the PBO fibers.As a result,the interfacial shear strength of the CNSs sized fiber-reinforced composite increases by 79.6%compared with that of the pristine fiber-reinforced composite.Moreover,the excellent mechanical and thermal properties of the PBO fibers remain almost unchanged after sizing treatment.Thus,this work provides an environmentally friendly and scalable method for constructing a strong interface between the PBO fibers and the matrix resins,which makes sense in promoting the application of PBO fiber-reinforced composites in aerospace and military industries.
基金financially supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China(No.20110006110025)the National Natural Science Foundation of China(No.U1134102)
文摘Solid-phase-sintered Si C-based composites with short carbon fibers（Csf/SSi C） in concentrations ranging from 0 to 10wt% were prepared by pressureless sintering at 2100°C. The phase composition, microstructure, density, and flexural strength of the composites with different Csf contents were investigated. SEM micrographs showed that the Csf distributed in the SSi C matrix homogeneously with some gaps at the fiber/matrix interfaces. The densities of the composites decreased with increasing Csf content. However, the bending strength first increased and then decreased with increasing Csf content, reaching a maximum value of 390 MPa at a Csf content of 5wt%, which was 60 MPa higher than that of SSi C because of the pull-out strengthening mechanism. Notably, Csf was graphitized and damaged during the sintering process because of the high temperature and reaction with boron derived from the sintering additive B4C; this graphitization degraded the fiber strengthening effect.
基金The authors would like to acknowledge the financial support from the National Natural Science Foundation of China(Nos.11872185,11627802,51678249,11132004)the Natural Science Foundation of Guangdong Province(No.2019A1515012222).
文摘As an important component,the bond behavior of carbon fiber-reinforced polymer(CFRP)-concrete interface for a reinforced concrete(RC)beam is very significant.In this study,a theoretical model was established to analyze the flexural behavior of CFRP-strengthened RC beams,and the CFRP-concrete interfacial bond-slip relationship under hygrothermal environment was unified into one model.Two failure criteria corresponding to two types of failure modes,i.e.,concrete crushing and intermediate crack(IC)-induced debonding,were developed.Through the theoretical model,the flexural behavior of deflection,interfacial shear stress distribution and ultimate load of a CFRP-strengthened RC beam under hygrothermal environment were obtained and predicted.Moreover,the theoretical model was verified by test results.The results showed that the hygrothermal environment had a significant impact on the CFRP-concrete interface behavior.Compared with the control beam without hygrothermal environment pretreatment,the deflection and ultimate load of the strengthened RC beam decreased by 51.9%and 20%,respectively.
基金This research work was supported and funded by Shandong Provincial Science and Technology Plan Project(No.J13LG05).
文摘A method for strengthening damaged tubular steel T-joints under axial compression by wrapping them with carbon fiber-reinforced polymer(CFRP)sheets was proposed and evaluated.The influence of the CFRP strengthening on the failure mode and load capacity of T-joints with different degrees of damage was investigated using experiments and finite element analyses.Five T-joints were physically tested:one bare joint to obtain the peak load and corresponding displacement(D1m),two reinforced joints to provide a reference,and two pre-damaged then retrofitted joints to serve as the primary research objects.The ratio of the pre-loaded specimen chord displacement to the value of D1m was considered to be the degree of damage of the two retrofitted joints,and was set to 0.80 and 1.20.The results demonstrate that the maximum capacity of the retrofitted specimen was increased by 0.83%–15.06%over the corresponding unreinforced specimens.However,the capacity of the retrofitted specimen was 2.51%–22.77%lesser compared with that of the directly reinforced specimens.Next,111 numerical analysis models(0.63≤b≤0.76,9.70≤g≤16.92)were established to parametrically evaluate the effects of different geometric and strengthening parameters on the load capacity of strengthened tubular T-joints under different degrees of damage.The numerical analysis results revealed that the development of equivalent plastic strain at the selected measuring points was moderated by strengthening with CFRP wrapping,and indicated the optimal CFRP strengthening thickness and wrapping orientation according to tubular T-joint parameters.Finally,reasonable equations for calculating the load capacity of CFRP-strengthened joints were proposed and demonstrated to provide accurate results.The findings of this study can be used to inform improved CFRP strengthening of damaged tubular steel structures.
