Impact Compression Damage Of3-d Braided Composite Under High Temperature Environment

The3-D braided composite materials have the characteristics with the overall structure and forming a complex shape of the Engineering structures. It does not produce delamination under the impact loading and widely used in the structural designs of impact resistance. Under the condition of high temperatures, the mechanical properties of3-D braided composites is far different from the room temperature condition. It has important theoretical value and practical significance to study the mechanical properties of the3-D braided composite materials under high temperature conditionsIn this research, the tests on the impact compression properties of3-D carbon fiber/epoxy resin braided composites at different temperatures were carried out by the split Hopkinson pressure bar combined with high temperature apparatus. The dynamic mechanical analyses (DMA) tests of epoxy resin matrix were also conducted to study its thermodynamic properties. The effects of temperature and strain rate on the impact compression behaviors of3-D carbon fiber/epoxy resin braided composites were analyzed.The main achievements and conclusions of this research are as follows:(1) In order to avoid the influences of temperature on the split Hopkinson pressure bar and the signal acquisition, a pre-heating method was adopted during the high temperature dynamic testing. A finite element method was also used to analyze the heat transfer performance of3-D braided composites, in order to determine the heating time of the sample.(2) The glass transition temperature (Tg) was an important index of the thermodynamic performance of epoxy resin achieved from the test results of Dynamic Mechanical Analysis (DMA) of the epoxy resin matrix. When the temperatures was below the glass transition temperature of epoxy resin, the mechanical properties was maintained at a higher level, while at the temperatures above the Tg, the mechanical properties decreased drastically.(3) The impact compression test results of the3-D carbon fiber/epoxy resin braided composites at high temperatures showed that the3-D carbon fiber/epoxy resin composites had obvious temperature effects. The compression modulus of the composites decreased rapidly with the increase of test temperatures, especially around the Tg of epoxy resin matrix. The failure stress and specific energy absorption also decreased gradually while the failure strain increased with the increasing temperatures.(4) The research also indicated that the3-D carbon fiber/epoxy resin braided composites were sensitive to the strain rate. At higher strain rate, there was a larger failure stress, the failure strain and energy absorption. The compression modulus was varied with the different test temperatures. At the lower test temperatures, the compression modulus was greater for the higher strain rate, however, the trend was just the opposite at the higher test temperatures.(5) The compressive modulus of3-D carbon fiber/epoxy braided composite materials were dominated by the epoxy resin matrix at high temperatures, while the failure strength was mainly affected by the3-D braided preform enhancement.(6)Shear deformation was the main failure mode of3-D carbon fiber/epoxy resin braided composites at high strain rates and the damaged extents increased with the increase of temperatures. However, the3-D braided composites exhibited no obvious damages except for matrix cracks at lower strain rates.