10° Off-Axis Tensile Testing of Carbon Fiber Reinforced Polymers Using Digital Image Correlation
The current work describes the use of DIC (digital image correlation) for full-field strain and deformation response while performing 10° off-axis tensile tests on rigidly clamped unidirectionally carbon fiber reinforced (CFRP-UD) coupon specimens with a nominal reinforcing fraction of 50 volume percent. Off-axis testing of anisotropic materials produces a nonuniform state of stress and strain when the ends are rigidly clamped and bending moments cannot be eliminated by free rotation. Under this configuration, the application of constant end displacements induces shearing forces and bending couples, which result in the nonuniform deformation. The extension-shear coupling compliance causes the coupon to deform into an S-shape, which is qualitatively visualized using DIC. Quantitative photomechanical investigations of vertical and horizontal displacements of the coupon are compared to approximate analytical solutions originally derived in the 1960s. Additionally, a description of deformation and fracture mechanisms using the DIC calculated strains is provided. In addition to the shear strain in the specimen coordinate axis, the maximum shear strain (used to quantify the shear modulus and the strain to fracture) and normal strain (transverse to fiber orientation) are calculated via strain transformation equations and visualized.
KeywordsIntralaminar shear DIC CFRP Unidirectional Extension-shear coupling
Edward Pompa for waterjet cutting, Alex Jennion for fractography. Louise Ahure Powell for uniaxial tensile testing results.
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