Development of the combined loading shear test method and shear strain measurement in the v-notched rail shear test

Unique constraints are present when shear properties of orthotropic materials are desired, as they typically cannot be derived from tensile material properties like isotropic materials. Specific test specimen geometry, and in some instances specimen layup, are required in order to obtain valid shear property data. The V-Notched Rail Shear Test Method is one such test method developed to provide reliable shear test data for compo-site laminates. However, specimens made from suitably high strength materials will slip prior to failure providing invalid results. Previous work has been performed which im-proves on this test method by altering the specimen dimensions and fixture design in or-der to prevent slipping. Changes made to the fixture introduced another load path into the specimen, which can influence the stress state within the specimen. The current work looks at several aspects of the new Combined Loading Shear test fixture and how they affect the stress and strain state, as well as the measured shear strength. Photoelastic test-ing is performed to validate numerical models and to investigate the strain state in several different specimen layups as a result of the fixture changes. Accurate shear strain measurement is required when determining the shear modu-lus of a material. Bonded strain gauges are often used when strain measurements are re-quired; however, extensometers can provide the same functionality as strain gauges and have the advantage of being reusable. Extensometers are typically application specific and require careful consideration with regards to attachment and the region where exten-sion is measured. The current study proposes a shear extensometer for a V-Notched Rail Shear or Combined Loading Shear test specimen. A mechanics of materials model is used to calculate the shear strain in the specimen based on the relative displacement of a discrete set of points on the specimen face. Numerical simulations were performed to determine the points on the specimen face which would yield the most accurate measure of the in-plane shear modulus. A prototype device is tested using carbon/epoxy, glass/epoxy, and Kevlar/epoxy cross-ply laminates and the data from the extensometer are compared to data from bonded strain gauges to validate the extensometer.