Out-of-plane shear properties of im7/8552 carbon/epoxy by v-notched shear testing

IM7/8552 is a carbon fiber reinforced polymer composite of interest for composite structures in aircraft. Some computational models for predicting the mechanical response of structures consisting of layered composites such as IM7/8552 require tabulated stress-strain relationships, including those for out-of-plane shear stress—i.e., τ13 parallel to the fibers and τ23 perpendicular to the fibers. Because the out-of-plane shear stress-strain curves were not available in the open literature, an investigation was devised to measure these constitutive behaviors via V-notched shear testing under quasi-static loading to failure. Four methods of measuring strain were used during the testing: three using digital image correlation (DIC) and one using a bonded resistance-based shear-pattern strain gauge. The four methods of measuring strain produced varied results for the τ13 specimens and less varied results for the τ23 specimens. The variation in measured strains suggests that a test standard for measuring shear stress-strain behavior of composites using DIC is necessary to produce repeatable results.