Research On Low-velocity Impact Damage Of Laminates And Residual Strength And Fatigue Life Of Impacted Laminates Under Temperature Environment

With the development of the aviation industry,the use of advanced composite materials in aviation structures is increasing.The overall performance of the composite materials is superior,but the impact resistance is poor,and in the process of manufacturing,use and maintenance,the composite laminates are inevitably subjected to the impact of foreign objects.When the impact energy is low,in addition to the visible damage on the surface of the laminate,various forms of damage will be generated inside.These damages cannot be directly observed,but the strength of the laminate will be seriously reduced.When subjected to alternating loads,these damage will also expand rapidly,reducing the fatigue life of the laminate.In addition,aerospace components often work in a hot environment.At elevated temperatures,the mechanical properties of the composite materials are generally reduced and its impact resistance is also affected.Therefore,it is very necessary to carry out the impact damage and residual strength and residual life of composite laminates under temperature environment.The research works in this paper can be summarized as follows:1.The gradual damage analysis model and the whole-process analysis method for impact damage and residual strength and residual fatigue life of composite laminates considering temperature effects were developed.In this paper,the low-velocity impact damage analysis method of laminates considering the influence of temperature was firstly developed and established.Then,based on the damage equivalent theory,the final damage state of the low-velocity impact process was taken as the initial damage state of the residual strength analysis and the residual fatigue life analysis.The method for the residual strength and residual fatigue life analysis of impacted laminates was established.2.The high-temperature plywood integrated impact scheme and test technology were proposed.The cold junction compensation error of temperature is within ±2 °C.The method is suitable for the drop-hammer impact test of composite materials considering temperature effects.3.The low-velocity impact test of composite laminates under temperature environment and the residual strength and residual fatigue life test of impacted laminates were carried out.In this paper,the low-velocity impact tests of T300QY8911-IV composite laminates were carried out at 20 °C,130 °C and 180 °C,and the tensile tests and the fatigue tests at different stress levels of the impacted laminates were carried out at the corresponding temperature.The low-velocity impact damage area of the laminate,the residual strength after impact and the residual fatigue life at different stress levels after impact were obtained.4.The validity of the model was proved and the damage propagation law of the laminate was analyzed.By comparing the simulation prediction results with the experimental results,the effectiveness of the developed analysis method for impact damage and residual strength and residual fatigue life of composite laminates considering temperature effects was verified.Combined with the test and simulation analysis,The effects of temperature and impact energy on the low-velocity impact damage area,the residual strength and the residual fatigue life of the laminates were analyzed.The damage propagation law of the laminate during different loading processes was further analyzed by numerical simulation.