Bending Strength of a Thick-Walled Composite in a Thermoplastic Matrix

Abstract

The research was carried on specimens made of composite laminate with thermoplastic matrix PA6 reinforced with continuous glass fiber. Specimens were subjected to a static three- and four – point bending tests at different spacings of the supports, resulting in different values of the ratio between normal and shear stresses. Both distribution of normal stress that comes from bending and distribution of shear stress, according to transverse shear stress in beams, coming from shear were considered. In the case of analyzing composite materials, shear stress is significant and considered cases have to be treated as stressed in complex stress condition. The results of the analysis were as follows: variation in cross-section of shear stresses according to the transverse shear stress in beams equation and distribution of bending stresses on the triangle. It was proposed to calculate the equivalent stress according to an equation obtained basing on the Azzi-Tsai-Hill criterion at a coefficient being a ratio of tensile strength to transverse shear strength determined experimentally. Depending on the combination of shear and normal stresses, cracking is initiated either by shear or normal stress.