Finite Element Analysis of the Arcan Specimen for Fiber Reinforced Composites under Pure Shear and Biaxial Loading

Abstract

Linearly elastic finite element analyses were used to examine the effects of fiber orientation, notch angle and notch root radius on the stress distribution in Arcan specimens in order to optimize the specimen geometry for the unidirectional, fiber reinforced composite AS4/PEEK under shear and biaxial loadings. Two fiber orientations, three notch angles and five notch root radii were examined. A comparison between butterfly-shaped and circular S-shaped specimens was also made. For specimens with fibers running across the specimen from grip to grip (1-2 orientation), a 1340 notch angle was found to be the best choice due to superior stress uniformity along the gage section and minimum transverse normal stress along the notch flank. However, specimens with fibers running from notch to notch (2-1 orientation), required a 900 notch angle for optimum stress uniformity along the gage section and minimum transverse normal stress along the specimen notch. It was also found that, along the gage section, the largest shear stress concentration occurred near the notch roots of the 1-2 specimen, yet it was not seen in the 2-1 specimen. This made the 2-1 specimen a better candidate for determining the shear properties of fiber reinforced composites. It was also found that the butterfly-shaped specimen bonded to steel grips provided much more uniform normal stresses than the original circular S-shaped specimen did. As a result, a butterfly-shaped Arcan specimen with a 2-1 fiber orientation, a 900 notch angle, a 2.38 mm root radius and bonded to steel grips was found to be very suitable for examining the longitudinal deformation behavior of this particular fiber reinforced composite under both shear and biaxial loading. Strain distributions from the finite element analyses were also compared to those obtained from moire measurements. At low load levels, there was excellent agreement between the two. Nonlinear effects mitigated stress concentrations at higher load levels.