Using digital image correlation for in situ strain and damage monitoring in hybrid fiber laminates under in-plane shear loading

Official URL: https://dx.doi.org/10.1002/pc.26114

Utilizing resistive strain gauges for V-notch shear tests in fiber reinforced laminates is usually limited to low strain values due to technical uncertainties imposed by the measurement technique and also the progressive damage development in the notched region of the composite. Therefore, this study investigates an alternative approach by using digital image correlation system and further comparison with resistive strain gauge to identify the effect of heterogenous nature of damage development on measurement results. Moreover, glass/carbon fiber hybrid and non-hybrid laminates are tested in two major directions through the same approach to determine the effect of stacking sequence in spatial microdamage accumulation. It is shown that tailoring appropriate region of interest for full field strain measurement at various stages of loading enables proper monitoring of microdamage accumulation and thereby delivers a precise stress–strain behavior for hybrid and non-hybrid laminates. Comparison of the strain maps for hybrid laminates tested in 0° direction, shows that the presence of carbon plies at the surface results in uniform strain distribution between the notches of the test sample. In contrast, a non-homogeneous strain map with separate regions of high strain gradient are observed for hybrid specimens with glass plies at surface, which can cause underestimation of average shear strain by resistive strain gauges. On the other hand, it is shown that strain maps for hybrid samples tested at 90° configuration is analogous regardless of the stacking sequence, and damage accumulation in these samples is most likely related to relative volume fraction of various fibers in hybrid laminate.