In‐plane shearing stress–strain response of glass‐fiber‐reinforced composites as determined from four‐point bending tests

In this article an experimental study to determine the longitudinal (or in‐plane) shearing stress–strain response of a unidirectional fiber‐reinforced composite material is presented. The test method used is the four‐point blending of a ±45° off‐axis glass‐fiber‐reinforced laminate. Although a laminate is used for the investigation of the shearing stress–strain response, it is shown that unidirectional shear properties can be found from the laminate test data following a procedure analogous to that used in previously. Also, the 45° off‐axis test of unidirectional composite in bending was carried out to obtain the in‐plane shear modulus and compare it with that obtained by the ±45° off‐axis method. Finally both values were compared with the theoretical value of the in‐plane shear modulus obtained from a theoretical formula where the concept of boundary interphase between fiber and matrix was introduced. © 1995 John Wiley & Sons, Inc.