Effects of coating on dynamic stress concentration in fiber reinforced composites

Fiber reinforced materials consisting of aligned fibers within a matrix are effective for applications in nature and engineering in which strength and stiffness are required in a dominant direction. The fibers are typically coated. Optimization of these materials is typically based upon choosing elastic properties of phases to reduce static stresses. However, materials with well-matched moduli can have mismatched acoustic impedance, and thus a fiber reinforced material that is strong in quasistatic loading may be weak in dynamic loading. To explore this trade-off, we modeled perfectly bonded, isotropic, linear elastic coated fibers in an infinite, isotropic, linear elastic matrix and calculated dynamic stresses and interfacial stress concentrations induced by continuous and transient waves using the wave function expansion method. Results revealed ways that the physical properties and geometrical dimensions of a coating around a fiber can be tailored to reduce dynamic stress concentration, and point to a pathway for improving the shock resistance of fiber reinforced materials.