Partial-composite behavior of sandwich beams composed of fiberglass facesheets and woven fabric core

In this study, thin-walled sandwich composites made of glass fiber-reinforced polymer (GFRP) facesheets and a three-dimensional (3D) woven fabric core were studied. A total of 30 small-scale sandwich beam specimens were manufactured across six unique beam varieties with dimensions of 50 mm in width, and 200 or 350 mm in length to be tested under four-point bending up to failure. The load-deflection behavior, load-strain behavior, moment-curvature behavior, and neutral axis location were analyzed. Based on the test results, the flexural stiffness, shear stiffness, core shear modulus of the sandwich beams were calculated. Also, an analytical model is presented to consider the effect of core shear modulus on deformation and composite action of the test specimens. The model is capable to quantify the degree of composite action based on the geometry and material properties of sandwich beams. Overall, the sandwich beams displayed a partial-composite behavior raging from 15% to 91% of full-composite behavior, which was a function of the relative stiffness of the facesheets and the core plus the length of the shear span. It was shown that compatibility between the mechanical properties of the facesheet and core is a key factor in optimizing sandwich panels made of the core. The results will be used for the design of thin-walled sandwich liners for the rehabilitation of underground infrastructure including existing highway culverts and large diameter drainage systems.