Electrical-mechanical Coupling Behaviours Of Three-dimensional Angel-interlock Woven Composites Under Three-point Bending Loading

Three-dimensional angle interlocking woven composite materials have been widely used in aerospace,transportation,sports equipment and construction industry due to the advantages of high interlayer shear strength and low production cost.Taking into account the damage caused by external load to composite materials,the structure health monitoring technology based on resistance has attracted great attention.Carbon fiber has good electrical conductivity,Using the change of carbon fiber resistance with stress / strain to monitor the damage of composite materials is one of the important contents of structural health monitoring.In this paper,the relationship between electrical properties and woven structure of threedimensional angle interlocking woven composites has been studied,and the laws of potential distribution,resistance change and damage evolution under three-point bending quasi-static and cyclic loading have been revealed,which provides a theoretical reference for structural health monitoring of carbon fiber composites.The research contents are as follows:（1）The relationship between electrical properties and woven structure of carbon fiber/ epoxy three-dimensional angle interlocking woven composites has been revealed;the law of potential distribution and resistance change under quasi-static three-point bending load has been explored,and the influence of woven structure on resistance change and potential distribution has been analyzed.（2）The relationship between quasi-static damage and resistance change rate has been analyzed,the damage stress and damage rate have been defined,and the influence law of damage on resistance change rate has been revealed.（3）The resistance change of three-dimensional angle interlocking woven composites under three-point bending cyclic load has been studied.The relationship between the resistance change rate of the specimen and the woven structure during cyclic loading under different stress levels has been analyzed.The research findings are as follows:（1）In the range of 0.0～0.1A constant current,the voltage of three-dimensional angle interlocking woven composites increases linearly with the increase of current.Under quasistatic conditions,the load displacement curve of three-dimensional angle interlocking woven composites under three-point bending can be divided into three stages: elastic stage,progressive failure stage and sharp failure stage.The corresponding resistance change can also be divided into three stages: constant,slow increase and rapid increase.The surface potential of the sample changes linearly along the axial direction and has an equipotential distribution perpendicular to the axial direction.The change of quasi-static surface potential is similar to the change of resistance.When yarn breakage damage occurs,the potential increases.When crack or delamination damage leads to poor contact,the potential suddenly changes to negative value.The damage location and damage type can be detected according to the potential diagram.（2）The damage stress and damage rate have been used as independent variables to fit the change of resistance,and the effect is good.The damage state of the sample can be judged according to the change of resistance.The two fitting methods have their own advantages and disadvantages.Taking the damage stress as the independent variable,the overall effect is good and the consistency is high;Taking the damage rate as the independent variable fitting,the effect is better in the first two stages,but the effect is poor in the final failure.（3）At the same stress level,the fatigue life of the warp sample is lower than that of the weft sample.The change of hysteresis loop area has experienced three stages: stable,slow increase and rapid increase,and the change trend is similar to that of resistance.The progressive fatigue damage of three-dimensional angle interlocking woven composites leads to the gradual degradation of its mechanical properties,which is manifested in the decrease of bending modulus and the increase of damage index.In a single cycle,the sample shows negative pressure resistance effect,but the peak resistance increases with the increase of deflection due to the accumulation of specimen damage.When the deflection increases sharply,there is a positive piezoresistive effect.