Design, manufacturing and testing of hoop wound tubular in-plane shear specimens.

Abstract

High performance fibre reinforced polymer composite materials have become popular replacements for many traditional materials. Unfortunately, some of the methods used to determine composite material properties have not developed as quickly. In particular, there are presently more than ten different test methods used to determine in-plane shear properties. Many of these methods are criticized for their inability to produce a pure shear state in the test region. Tubular in-plane shear specimens, however, are generally accepted as the only specimens which do (at least theoretically) produce a pure shear state. In this study, design, manufacturing and testing procedures were developed for tubular in-plane shear specimens. A specimen was designed which included a thin-walled composite tube and an internal tapered bonded end fitting. In the manufacturing study, techniques were developed to fabricate a tube of excellent quality with high geometrical tolerances. Tubular in-plane shear specimens were then tested and the results compared to test results for three of the most popular tests in use today, namely, the $90\sp\circ$ Iosipescu, $10\sp\circ$ off-axis and $\pm$45$\sp\circ$ tensile in-plane shear test methods. The four tests were compared on the basis of their respective shear states and on their ability to produce shear modulus values which could be used to predict the tensile modulus of shear-sensitive laminates. Results indicate that, though the tubular shear specimens produce the most consistent state of pure shear, they do not accurately predict the tensile moduli of actual laminates. Of the five laminates tested, the $\pm$45$\sp\circ$ tensile shear test best predicted the tensile modulus of four laminates and was next best for the remaining laminate. It was found that as laminate shear sensitivity decreased, the suitability of different test methods changed.