Study On Impact Response And Damage Characteristic Of Two-dimensional Woven Carbon Fiber Composites

The composite materials have been widely used in aviation,aerospace and automobile industries because of their excellent comprehensive mechanical performance and weight reduction ability.However,during the service of composite structures,it is inevitable to encounter the threat of impact load such as bird strike,gravel impact and car accident,which puts forward requirements for the safety and reliability of the composite structures.The 2D woven fabric composites exhibit better in-plane mechanical properties and impact resistance as compared with the traditional unidirectional composite laminates.However,the complex architecture of woven fabrics with the fiber bundles interlacing each other further increases the complexity in mechanical properties and damage mechanism.In this study,systematic investigation on the dynamic mechanical behavior,constitutive model,impact response and damage characteristic of satin weave carbon/epoxy composites were conducted by means of experimental test,numerical simulation and theoretical analysis.The main research contents and conclusions of this thesis are shown as follow,（1）The in-plane compressive mechanical properties of satin weave composites in a wide strain rate range（0.001/s-1100/s）and a wide temperature range（298K-448K）were tested using the electronic universal testing machine and enhanced split Hopkinson pressure bar（SHPB）system coupled with single loading technique.The variations of strength,modulus and stress-strain behavior with temperature and strain rate were obtained.The strain distribution and damage growth process under high strain rate loading were obtained by digital image correlation（DIC）technology.The microscopic damage analysis of the fractured samples was carried out by using the scanning electron microscope（SEM）.The results indicate that the mechanical behavior and damage characteristic of 2D woven carbon composites are significantly affected by the temperature and strain rate.The elastic modulus and strength show decreasing trend with the increase of temperature,which further deteriorate dramatically as the testing temperature exceeds the glass transition temperature of epoxy resin.With the increase of strain rate,the elastic modulus and strength of satin weave composites increase linearly.At normal temperature,the main failure mode under dynamic compression is delamination,while the main quasi-static compression failure mode is shear fracture.At high temperatures above glass transition temperature,the main failure modes of dynamic compression are delamination and matrix cracking,while the main quasi-static compression failure is matrix cracking and fiber kinking.（2）Based on viscoelastic-plastic mechanics and damage mechanics,two in-plane compressive constitutive models of 2D woven composites are established.The viscoelastic-plastic constitutive model assumes that the non-linear mechanical behavior of 2D woven carbon fiber composites at large strain state is mainly caused by the viscoelastic characteristics of epoxy resin materials.The strain rate and temperature sensitivity of the material stress-strain relationship are taken into account in the model.The constitutive model based on damage mechanics describes the non-linear part of the stress-strain curve by damage coefficient,which not only takes into account the strain rate and temperature sensitivity of the elastic modulus of component materials,but also considers the strain rate and temperature effect of damage propagation.The results show that the constitutive models established in this paper can accurately describe the in-plane compressive stress-strain behavior of 2D woven carbon fiber composites at different strain rates and temperatures.（3）The damage-based constitutive model was applied to a rate dependent 3D progressive damage model in the numerical simulation.Based on the low-speed impact tests and numerical simulation analysis method,the low-speed impact response characteristics of 2D woven carbon fiber composite under different stacking sequence,impact energy and impact velocity were analyzed.The delamination initial load,maximum contact load,delamination aera and damage evolution law of were revealed.It is found that for composite laminates with the same thickness,the maximum contact load decreases with the increase of±45°ply content,but the critical delamination load remains basically unchanged.At the same impact velocity,with the increase of impact energy,the delamination damage area and dent depth increase.At the same impact energy,with the increase of impact velocity,F_cri increases significantly while the impact time is obviously shortened.These phenomena indicate that the strain rate effect of 2D woven carbon fiber composites under low-speed impact can not be neglected.In addition,the main damage mode of composite laminates under low speed impact load is fiber tensile fracture and delamination,while fiber compression damage is mainly located at the impact surface and the damage degree is relatively low.（4）The dynamic response characteristics of satin weave composite laminates under high-speed impact loading were investigated through systematic experimental tests.The stress wave propagation in the composite laminates during the whole impact process was revealed.The impact response and damage characteristics at different impact locations were analyzed.In addition,a theoretical analytical model for high-velocity-impact response analysis of 2D woven composite laminates was proposed.This model takes into account the independent deformation of warp and weft fibre bundles within the deformation zone of secondary fibre bundles.The different energy absorption and transformation modes（deformation zone kinetic energy and secondary fiber deformation energy,fiber bundle fracture energy,energy absorption caused by delamination and matrix cracking）were revealed.Further,the effect of impact location on the high-speed impact response of 2D woven carbon fiber composite laminates was studied.The results show that with the increase of the distance between impact point and boundary,the ballistic limit exhibits increasing trend,and the residual velocity of the projectile decreases under the same impact velocity.In addition,the energy absorption characteristics of composite laminates are dependent on the impact velocity.For impact velocity above the ballistic limit of 2D woven composite laminates,the dominated energy absorption modes are cone kinetic energy and delamination energy,while for impact velocity below the ballistic limit,the main energy absorption modes are cone kinetic energy,secondary fiber deformation energy and delamination energy.