Finite element analysis of the Arcan specimen for fiber reinforced composites under pure shear and biaxial loading

Linearly elastic finite element analyses were used to examine the effects o f fiber orientation, notch angle and notch root radius on the stress distri bution in Arcan specimens in order to optimize the specimen geometry for th e unidirectional, fiber reinforced composite AS4/PEEK under shear and biaxi al 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 th e specimen from grip to grip (1-2 orientation), a 134 degrees notch angle w as found to be the best choice due to superior stress uniformity along the gage section and minimum transverse normal stress along the notch flank. Ho wever, specimens with fibers running from notch to notch (2-1 orientation), required a 90 degrees 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 c oncentration 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 wa s also found that the butterfly-shaped specimen bonded to steel grips provi ded much more uniform normal stresses than the original circular S-shaped s pecimen did. As a result, a butterfly-shaped Arcan specimen with a 2-1 fibe r orientation, a 90 degrees notch angle, a 2.38 mm root radius and bonded t o steel grips was found to be very suitable for examining the longitudinal deformation behavior of this particular fiber reinforced composite under bo th shear and biaxial loading. Strain distributions from the finite element analyses were also compared to those obtained from moire measurements. At l ow load levels, there was excellent agreement between the two. Nonlinear ef fects mitigated stress concentrations at higher load levels.