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 proposed in Ref. [1] [Benedikt B, Kumosa M, Predecki PK, Kumosa L, Castelli MG, Sutter JK. An analysis of residual thermal stresses in a unidirectional graphite/PMR-15 composite based on the X-ray diffraction measurements. Composites Science and Technology (in press)]. The methodology is based X-ray diffraction (XRD) measurements of residual strains in embedded metallic particles. The residual stresses in the polymer matrix can be extracted from the 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 newly developed experimental/analytical methodology can also be applied to composites subjected to external loads, in this case: spherical aluminum particles embedded in a unidirectional graphite/PMR-15 composite subjected to four-point bending loads. The total stresses and strains in the aluminum particles caused by residual thermal stresses in the composite and the applied stresses generated by four-point bending have been determined by XRD measurements under low bending displacements. Subsequently, the total strains and stresses in the aluminum particles have been numerically predicted by applying elastic and visco-elastic laminate theories and the Eshelby method. It has been shown in this research that not only the residual thermal strains 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 the stresses and strains in the particles can be monitored. This research has provided another verification of the newly proposed methodology presented in Ref. [1].