Picture Frame Test of Woven Composite Reinforcements with a Full-Field Strain Registration

Results of picture frame shear tests with optical registration of the strain fields are presented for glass (plain and twill, three types) and glass/PP woven (plain and twill) fabric reinforcements for composite materials. Four problems were investigated. (1) How does the shear diagram vary with differences in test conditions? The major factor is the sample pretension, which is influenced by its gripping, removing/preserving yarns near the grips and “conditioning” in the shear cycles. (2) Does the shear of the fabric differ from the pure shear prescribed by the frame? The differences are normally negligible. (3) How large are the variations of the local fabric shear? The scatter of the local fabric shear does not exceed 2°. (4) How is shear of the fabric translated into deformations of the yarns on the micro-scale? Different stages of the fabric deformation are identified: rotation of the yarns followed by their lateral compression.