The Effect Of Low Temperatures On The Impact Compressive Properties Of3-D Braided Composite Materials

Complex engineering components can be manufactured wholly without machining from3-Dbraided composite materials which have good structural integrity and resistant to delaminationunder impact loading. Due to these advantages, the3-D braided composite materials have becomeincreasingly used as structural materials in aviation and aerospace fields. During its applications,the3-D braided composite materials are often subjected to impact loading at low temperatureenvironments. For this reason, it is important to study the dynamic impact behavior of the3-Dbraided composite materials under low temperature conditions to aid component design and safetyuse.In this paper, a split Hopkinson pressure bar and cryogenic device were built successfullyaccording to the test requirements. The composite preform was fabricated by four-step braidingtechnique. Vacuum assisted resin transfer molding technique (VARTM) was used to manufacture3-D carbon fiber/epoxy braided composites. The tests on the impact compression properties of3-D carbon fiber/epoxy resin braided composites and epoxy resin at different temperature（-100℃、-50℃、23℃）and different strain-rate were carried out by a split Hopkinson pressure bar (SHPB)apparatus combined with cryogenic device. In order to have a better understand the impactcompression behaviors of3-D braided composites, the thermal properties of epoxy resin was alsotested. The effects of low temperature and strain rate on the impact compression behaviors of3-Dcarbon fiber/epoxy resin braided composites were analyzed.The experimental method and conclusions of this research are as follows:(1) The thermodynamic properties of epoxy resin were tested with DMA-Q800tester with atemperature scan between-100℃to25℃. The experimental results showed that the storagemodulus, loss modulus, and loss tangent of epoxy resin decreased with the increasing temperature.(2) The impact compression properties of3-D carbon fiber/epoxy resin braided composites andcured epoxy resin were tested by low-temperature impact compression testing system. Theexperimental stress vs. strain curves under different temperatures with varies strain rates wereobtained. The results showed that the impact compression properties of3-D carbon fiber/epoxy braided composites and cured epoxy resin was significantly affected by temperature and strainrate.(3) The experimental stress vs. strain curves of the3-D carbon fiber/epoxy braided compositesand cured epoxy resin under different temperatures with varies strain rates were analyzedcombining with thermodynamic properties and impact compression behaviors of epoxy resinunder low temperature. The failure stress and compressive modulus of the cured epoxy resindecreased with the increasing temperature, while the compression modulus increased with theincreasing strain rate. The compressive modulus, failure stress and the specific energy absorptionof3-D carbon fiber/epoxy braided composites decreased with the increasing temperature. Thefailure strain in out-of-plane direction increased with the increasing temperature. The compressivemodulus, failure strain, failure stress and the specific energy absorption increased with theincreasing strain rate. The impact compression properties of the3-D carbon fiber/epoxy resinbraided composites under low-temperature were affected by the epoxy matrix and the preformstructure. The compressive modulus was dominated by the epoxy resin matrix, while the failurestrength was mainly affected by the3-D braided preform. The compressive failure mode of3Dbraided composites in the in-plane direction were mainly deformation of reinforcement andcracking of matrix, while for the out-of-plane direction it was mainly shear failure at various strainrates. The brittle failure feature became more obvious as the temperature decreased.