Wave Propagation in a Composite with Wavy Reinforcing Fibers

Abstract

In the manufacture of composite structures the alignment of the reinforcing fibers can be distorted into wavy patterns due to uneven curing and shrinkage of the resin. Such wavy distortions will reduce both the strength and the stiffness of the composite structure. Yet if the fibers are intentionally formed into wavy patterns in an elastomer matrix a composite material with a stiffness that responds to changing loads and strains is produced. Such materials can be applied to uses were great flexibility is required within a limited range but high stiffness is required outside the range. This is the requirement for athletic knee braces and aircraft arrestor nets to name only two applications. Wave propagation techniques can be used to study the effects of fiber waviness on the stiffnesses of composite materials. The specific case under study at this time is an elastomeric matrix composite material. This case proved the most interesting for the following reasons. The use of an elastomeric or low Young's modulus matrix material allows the amplitude and wavelength of the waves in the reinforcing fibers to change as the composite is stretched. This change in wave shape with strain causes the properties of the composite to change as well. The elastomeric matrix introduces greater nonlinearity to the problem under study, thus allowing greater application of the results.