In-Plane Shear Response of GFRP Laminates by ± 45° and 10° Off-axis Tensile Testing using Digital Image Correlation
Matthias J. Merzkirch, Qi An, Aaron M. Forster
For the determination of the shear strength, strain and modulus of reinforced composites, nearly a dozen measurement techniques exist, several of which are supported by ASTM or ISO standards. One reason for so many options is the difficulty in obtaining a reasonably pure and uniform shear stress state in the test specimen. Typically, linear strain gauges and rosette strain gauges have been used to measure deformations for the determination of the elastic modulus and the strain to failure in many of these methods. The advent of optical strain measurement techniques such as digital image correlation (DIC), provide new opportunities to generate high resolution maps of the shear strain field as a function of the globally applied strain. DIC allows for the easy full-field mapping of the deformations (in-plane and out-of-plane for stereo DIC) and strains (normal and shear), revealing the pattern of deformation and damage throughout the specimen. In this work, it is shown that non-contact measurements of the strain field are an important enhancement to measuring the shear properties of FRP composites. This contribution describes the use of DIC for the shear strain response while performing standardized bias extension tests on ± 45° layups and non-standardized 10° off-axis tensile tests on glass fiber reinforced (GFRP) coupon specimens. Shear moduli and shear strengths obtained will be compared to V-notched specimens investigated in an earlier contribution.