The Mechanical Behavior Of 4-step 3-D Braided Composites Under Impact Tension

Compared with laminated composites, 3-D braided composites has higher fracture toughness and inter-layer shear strength because of its structural integrity. This leads applications of 3-D braided composites to impact resistance regime. However, there are not references concerned with mechanical parameters testing of the 3-D braided composites under impulsive loading, i.e., tensile test under high strain rates.The E-glass filament tows were employed to weave 8 ×2 braided preform with 4-step l ×1 braided technique. The epoxy resin, as a matrix, was used to form 3-D braided composites with RTM (Resin Transfer Molding) technique. The tensile properties of 3-D braided composites under different strain rates were tested on MTS 810 and the split Hopkinson tension bar (SHTB). The stress-stain, stress-time curves of the composites under strain rates of 0.001s~-1, 1600s~-1, 2100s~-1, 2400s~-1, and 3200s~-1 were obtained. The Young's modulus, failure stress and strain were also gotten. It was found that the Young's modulus, failure stress increase with the increase of the strain rate while failure strain decreases. From the stress-strain curves of the composites at various strain rates, it is shown that the E-glass/epoxy 3-D braided composites is strain rate sensitive material. The fractograph of the composites depicts that the 3-D braided composites fails in more brittle mode at high strain rate. As the increasing of strain rate, the fractograph becomes more smooth compared with that in lower strain rates.