Experimental evidence of the high-gradient behaviour of fiber reinforced materials

• Experimental evidence of the high-gradient behaviour of fiber reinforced materials.
• The shear (matrix) and bending (fibers) yields a generalised continuum at the leading order.
• Experiments on a physical model (foam and steel bars) validate the homogenized description.

This paper deals with the theoretical and experimental dynamics of materials behaving as generalised continua. We focus on composites consisting in a soft matrix with stiff embedded linear parallel fibers. Such composites depart from usual elastic composites because (i) the properties of the constituents are highly contrasted, and (ii) the axial geometry of each fiber is continuous over a distance much larger than the Representative Elementary Volume size. Consequently, both the shear in the soft matrix and the bending in the fibers participate in the macroscopic behaviour. This corresponds to a generalised continuum with a second gradient effect at the leading order.The homogenised modelling of the dynamic of highly contrasted fiber reinforced composite is recalled (Soubestre and Boutin, 2012). The design of a physical model consisting of a polyurethane foam block permeated by steel bars is presented and the principle of the dynamic tests conducted using a shaking table is explained. Experimental results on the different tested configurations are described. From the analysis of the recorded responses the role of the bending effect is identified. The correlation between theory and experiments is exposed through the analysis of the fundamental and two higher modes response. The high level of agreement demonstrated for the several configurations prove the applicability of the generalised continuum model.