The use of X-ray diffraction measurements to determine the effect of bending loads on internal stresses in aluminum inclusions embedded in a unidirectional graphite-fibre/PMR-15 composite

A testing methodology for the determination of residual thermal stresses in the polymer-matrix of unidirectional polymer-matrix composites has been pr oposed in Ref. [1] [Benedikt B, Kumosa M, Predecki PK, Kumosa L, Castelli M G, Sutter JK. An analysis of residual thermal stresses in a unidirectional graphite/PMR-15 composite based on the X-ray diffraction measurements. Comp osites Science and Technology (in press)]. The methodology is based X-ray d iffraction (XRD) measurements of residual strains in embedded metallic part icles. The residual stresses in the polymer matrix can be extracted from th e X-ray strains in the particles using the visco-elastic Eshelby method for multiple inclusions. The purpose of this work has been to show that the ne wly developed experimental/analytical methodology can also be applied to co mposites subjected to external loads, in this case: spherical aluminum part icles embedded in a unidirectional graphite/PMR-15 composite subjected to f our-point bending loads. The total stresses and strains in the aluminum par ticles caused by residual thermal stresses in the composite and the applied stresses generated by four-point bending have been determined by XRD measu rements under low bending displacements. Subsequently, the total strains an d stresses in the aluminum particles have been numerically predicted by app lying, elastic and visco-elastic laminate theories and the Eshelby method. It has been shown in this research that not only the residual thermal strai ns and stresses in the aluminum particles and the matrix can be determined by using the proposed technique but also the effect of external loads on th e stresses and strains in the particles can be monitored. This research has provided another verification of the newly proposed methodology presented in Ref. [1]. (C) 2001 Elsevier Science Ltd. All rights reserved.