| Carbon Fiber Reinforced Plastic/Polymer(CFRP)and titanium alloy,as important structure materials during the manufacture of advanced aircraft,provided the light density,high specific intensity,excellent mechanical properties,good resistance to corrosion,and CFRP/Ti alloy mechanical structure.The upgrading of the aeronautics and astronautics products and the rising of the performance requirements are calling for structural materials with better synthetical performance.The results show that interference fit can improve the strength and fatigue life of joint structure,so the CFRP/Ti alloy interference fit joint increases gradually in aeronautics and astronautics field.However,the vibration condition of joint during service process is inevitable,and fretting damage occurs in the contact surface which leads to fretting wear and fretting fatigue.The fretting damage affects the health service of CFRP/Ti ally joint significantly.The literature about fretting behavior and damage mechanism of CFRP/Ti alloy interference fit mechanical joint are few,which limits the application.In this paper,the fretting behavior and damage mechanism of CFRP/Ti alloy interference fit bolted joint have been investigated.At first,the surface damage behavior during the installation process of interference bolt joint was presented,and the relationship of interference fit size and damage type were revealed.And then,the fretting behavior of CFRP/Ti alloy bolted joint were analyzed under dynamic load,and the evolution of fretting amplitude and fretting damage mechanism were shown in interference area.The local surface fretting wear behavior(including CFRP/Ti alloy contact,Ti/Ti contact)were presented,and the fretting wear mechanism of CFRP/Ti alloy in fray surface were displayed.The main works of this study are as follows:Firstly,the damage types of CFRP/Ti alloy bolted joint have been explained with various interference fit size based on micro level analysis and the damage mechanism has been revealed.The installation test of CFPR/Ti alloy interference fit bolted joint were carried out,and the installation model were established and analyzed by ABAQUS.The damage mechanism has been defined by user subroutine.The loading-displacement curve with various interference fit size were obtained.The damage type were analyzed,and matrix compression,fiber-matrix shear fracture were suggested to be the most important damage types.In addition,the microstructure were characterized,and it verified the accuracy of FEM and showed the micro flaws with various interference fitsize.Surface wear,fiber buckling,formation of mid-layer,and the CFRP debris are the important foundation for fatigue improvement,and it is an initiation of fretting.Secondly,the fretting test of CFRP/Ti alloy interference fit bolted joint were designed and carried out,and the fretting behavior were analyzed and the fretting damage mechanism were performed in interference area.The strain-stress and S-N curve were obtained under various interference fit.It shows that appropriated interference fit can improve the performance of bearing strength and fretting fatigue life significantly.The fretting behavior were analyzed,and the evolution of fretting amplitude under various interference fit sizes and loading were presented.In addition,the model of circumferential stress-strain calculation is presented by consideration of the stiffness degradation.Thirdly,the fretting wear behavior of Ti/Ti contact has been investigated,and the wear mechanism with various fretting amplitude has been shown.The test were designed to stimulate the Ti/Ti contact in interference area.The effect of fretting amplitude on fretting wear behavior has been investigated.The relationships between fretting amplitude and fretting friction coefficient,fretting type have been performed.The microstructure and element were tested by SEM.The fretting wear mechanism were revealed.Based on the above,two prediction models of fatigue life for CFRP/Ti alloy interference fit bolted joint were established,and relationship between the interference fit sizes,load levels and fretting life is studied,and the optimal interval of interference fit size is obtained.Fourthly,the fretting wear behaviors of CFRP/Ti alloy have been analyzed and the fretting wear mechanism has been presented.In this paper,the fretting contact between CFRP and Ti alloy were designed and tested with various fretting condition.The influence of factors(fretting amplitude,frequency,applied load,temperature and fiber direction orientation)on fretting wear were display,and these factors influence the friction coefficient in fretting condition as follows: fretting amplitude > applied load > fiber orientation > frequency.The wear morphology and surface roughness were measured,and microstructure were characterized.The fretting wear mechanism of CFRP/Ti contact are also been given with a low fretting amplitude,and the main mechanisms are fiber polishing,fiber shear fracture and fatigue cracking of matrix. |
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