Direct Measurement of the Transverse Modulus of Carbon Fibres

Abstract

Abstract Background The transverse compressive properties are integral to fully utilizing the high performing mechanical properties of carbon fibres (CF). Direct measurements of transverse properties of CFs are difficult. Objective A system that directly measures transverse compressive modulus (ET) by utilizing interference speckle patterns to measure sub-pixel resolutions is presented. Methods The compression data from an isotropic glass fibre was fitted using an elastic contact mechanics model. An initial section was observed, which was not readily fitted using the model and was systematically removed, resulting in an ET of 82 GPa, comparable to the reported longitudinal tensile modulus (EL) of 86 GPa. Results The response of Ag wire to cyclic compression was measured, with the behaviour consistent with a material undergoing typical cyclic stress–strain into a stable hysteretic loop. Several CFs were compressed and an inversely proportional relationship between ET and EL was observed. Transverse compressive moduli of 8.2 (0.8), 6.5 (0.7), 4.3 (0.3), and 2.1 (0.4) were obtained for Toray T300 and Mitsubishi Pyrofil HS40, Pyrofil TR50S, and Dialead K13312, respectively (numbers in parenthesis are standard deviations). Conclusion Hysteresis was observed for some of the polyacrylonitrile (PAN)-based CFs and a method for ensuring an accurate fitting of CFs, including hysteretic load/unload curves, was proposed.