Effects of porosity on in-plane and interlaminar shear strengths of two-dimensional carbon fiber reinforced silicon carbide composites

Porosity effects on shear properties of 2D C/SiC were investigated based on the corresponding shear damage mechanisms. The results show that as the total porosity increases from 12.2% to 26.1%, the interlaminar shear strength decreases from 44.58 MPa to 17.80 MPa according to a power law, while the in-plane shear strength decreases linearly from 143.25 MPa to 74.38 MPa. Under interlaminar shear stress, delamination is resulted from matrix cracking and interface debonding/sliding mechanisms. Effects of porosity on interlaminar shear strength is controlled by the volume fraction of the delaminated matrix. Under in-plane shear stress, echelon matrix shear cracking and large scale fiber bridging mechanisms occur. The decreasing of in-plane shear strength depends on the spacing between the echelon cracks. Since the interface debonding/sliding mechanism occurs under both in-plane and interlaminar shear stresses, a relationship is obtained that the in-plane shear strength equals the sum of the interlaminar shear strength and the fiber bridging term under the minimum total porosity about 30.5%.