Effects of Specimen Size and Tensile-Torsional Combined Stress Ratio on Fracture Strength for Short-Glass-Fiber-Reinforced Plastics

Abstract

To study the effects of specimen size and tensile-torsional combined stress ratio on fracture strength in compression molded short-glass-fiber-reinforced phenolic resin composites (SGP), tensile-torsional combined tests were carried out using round-bar specimens. Moreover, the finite element method analysis was employed to calculate the effective volume of the specimen. Finite element models were validated by the digital image correlation techniques. The fracture strength followed the Tsai-Hill failure criterion in the tensile-torsional stress plane. The angle of fracture surfaces was approximately perpendicular to the maximum principal stress directions. The greatest value of maximum principal stress was therefore assumed as fracture strength of SGP. The fracture strength was decreased with increasing the effective volume of the specimen regardless of fiber volume fraction and loading mode. Those relationships were well described by the equation of the effective volume theory as the double logarithmic chart based on Weibull statistical theory.