Mechanical properties and fracture mechanism of glass fiber/epoxy composites

Glass fiber/epoxy composites exhibit varied behaviors in the Z direction (the direction perpendicular to the layers) and X direction (the direction parallel to the layers). The mechanical properties of these materials, subject to quasi-static compressive and tensile loadings, are investigated using a tensile testing machine and by means of the pasting strain gauge method. The results of the tests show that the compressive strength in the Z direction is higher than that in the X direction, whereas tensile strength exhibits the opposite. A split Hopkinson pressure bar was used to investigate the dynamic behavior of the composite. The strain rate-reinforcement effect of the material can clearly be found. In the Z direction and X direction, compressive strength attains its maximum at a strain rate of 2030 s^-1 and 2100 s^-1 respectively. The maximum compressive strength in the Z direction is 90 MPa higher than that in the X direction. At the same strain rate, the elastic modulus in the Z direction is higher than that in the X direction, which means that stiffness in the Z direction is higher than that in the X direction. The focus then turns to failure modes and fracture mechanisms of the composite. A scanning electron microscope shows that a macroscopic brittle fracture is mainly caused by fiber breakage and matrix cracking. However, shear failure of the matrix and delamination and buckling of the glass fiber laminates also lead to macroscopic shear failure.