Ten-deg off-axis test for shear properties in fiber composites

In-plane and interlaminar shear strength of a unidirectional Hi-Nicalon fiber-reinforced celsian matrix composite

“…However, results in figure 8 showed that the interlaminar strength was lower than in-plane strength at all temperatures, i.e., "-13 (interlaminar) <"-12 (i n-plane) (6) This discrepancy between the prediction and the experiments indicates that the stress concentration could no t be responsible for the difference observed in strength values. Moreover, even if the calculated elastic constants in table III had underestimated the "actual" anisotropy, 8 this conclusion would have still been valid since the anisotropy, which is higher in the interlaminar orientation, is expected to reduce the stress concentration and thus increase the strength of interlaminar specimens.…”

“…Buckling of specimens was checked by two strain gages which were mounted on the opposite lateral faces. 6 The difference in strain values from these two strain-gages was <3 percent, indicating that the buckling effect on strength values would be small. Force in both specimens was applied along the longitudinal axis by an MTS 7 machine in displacement control with a cross-head speed of 2 /-lm/s.…”

“…So, the failure is expected to initiate at a critical crack whenever the combination of shear stress 't and tensile stress Cl satisfy the above condition. Note that regardless of mode-mixity, equation (6) shows that stress to failure (strength) is inversely proportional to crack length, which means that the material with the largest initial crack would likely have lower strength. Therefore, the difference between shear strength of in-plane and interlarninar specimens could be attributed to the difference in the defect density on the corresponding shear planes in these two specimens, i.e., lower interlarninar shear strength is due to favorable orientation of the defective fiber-rich region with the shear plane.…”

“…In-plane shear strength could be measured by an off-axis tension test (ref. 6 In the material development stage it is common to use test methods which are simple and require small specimens, although they may not provide the desired uniform stress-state. The double-notched shear (DNS) test, where notches make the shear stress distribution in the specimen highly nonuniform (refs.…”

A phantom node formulation with mixed mode cohesive law for splitting in laminates

“…All other results presented in this paper, were obtained using T = 10 5 N/mm 3 . (Chamis and Sinclair 1977;Van Paepegem et al 2006). Experiments show brittle matrix failure.…”