Fabrication of micro-sized specimen for axial compressive strength evaluation of single fiber using UV lithography and its testing method

Abstract

In this paper, a newly developed process to fabricate micro-sized specimen for axial compressive strength evaluation of single fiber using ultraviolet (UV) lithography was proposed. Technique of UV lithography, which was used in semiconductor production, was adopted to fabricate a test specimen that fiber was partially embedded in a photo-polymer. The photo-polymer SU-8 was used as a resist for high aspect ratio test specimen. A PBO fiber, which has excellent characteristics in tensile strength, tensile modulus and chemical resistance, was used as a test fiber material. Direct axial compression test was performed using the micro-compression testing machine with a flat indenter of 50 μm in diameter and two camera units. Finite element analysis was carried out to compute the internal stress distribution in the fiber under compression and to determine the optimum fiber length. The results showed that the proposed specimen fabrication method using UV lithography was demonstrated to be effective for direct measurement of the compressive strengths of PBO fibers. Finite element analysis revealed that the PBO fiber length in the compression test should be at least 20 μm to avoid the influence of fiber rooting in the resin. The experimental values obtained for the compressive strengths of PBO fibers exhibited Weibull distribution with a mean of 217 MPa, which is lower than the values generally obtained by other test methods such as the loop test or resin embedment test. © 2012 The Japan Society of Mechanical Engineers.