Experimental and numerical study of in-plane compressive properties and failure of 3D six-directional braided composites with large braiding angle

Abstract

Three-dimensional (3D) six-directional braided carbon/epoxy composites are widely used in aerospace field and this is successfully fabricated in this study. The composite is thoroughly analyzed with regard to both mechanical properties and failure mechanism in connection with the affecting factors, i.e., loading direction and temperature. At room and elevated temperatures, the in-plane compressive properties of such composites are obtained, and their failure mechanism is evaluated. A progressive damage model is established to predict the mechanical properties and to quantitatively interpret the failure behavior. At room temperature, longitudinal curve increases linearly and then drops suddenly, indicating brittle characteristics; the transverse curve is linear up to the failure point and drops gradually after the peak point. At elevated temperatures, the curves become non-linear up and the mechanical properties of composites decrease. At room temperature, the longitudinal compression presents shear fracture and shear plane exfoliation. Meanwhile, failure is observed in fiber rupture in various directions and matrix cracks. The transverse failure is observed in shear cracks and braiding fibers shedding. At elevated temperatures, 45° shear cracks are developed, the fibers are pulled out, the texture of matrix softens and exfoliates, and a noticeable debonding of the interface occurs.