Journal of Composite Materials

The elastic behaviour of a bimaterial interface with interfacial cracks, misfit dislocations and interfacial thermal stresses can be described in a simple manner by using the com posite parameters α and β, and the effective modulus of elasticity E*, assuming a plane deformation of ideally bonded isotropic materials. A coefficient K_T for the thermally in duced stress intensity at the interface serves as a measure of the mechanical compatibility of two bonded materials. An examination of these parameters for many composite materials shows that the values of the composite parameters α and β are limited to a nar row range and that the material transition can be classified into six groups with regard to their mechanical compatibility.

In this paper, the use of contour plotting to display the mode shapes of free vibration and buckling of laminate plates is reported. Contour plotting is shown to be superior to three- dimensional hidden-line plots. In addition to easy distinction of the nodal and peak-valley lines and isometric contours of equal elevations of the deformed mid-plane of the plate, contour plotting exhibits the fiber direction in the dominating layers of the laminate plate. Although only square laminate plates symmetric about their respective mid-planes and fully clamped are discussed, application of the contour plotting method can be extended for other types of laminate plates and boundary conditions.

Aramid/epoxy laminates often exhibit substantial material nonlinearity when subjected to bending. This is a consequence of the yield-like behavior of a Kevlar 49/epoxy lamina in fiber-directed compression. In this paper, analyses that utilize a simple idealization of compressive yielding are described and calculated results for Kevlar 49 reinforced beams and rings are compared with available data. Fabric reinforced beams are considered first. An existing analysis for unidirectionally reinforced beams is extended to accommodate the bilinear compressive behavior exhibited by a Kevlar 49 fabric reinforced lamina. Next, results of a finite element analysis of a thin, unidirectionally reinforced ring subjected to diametral compression are presented. This analysis uses beam elements that incorporate linear tensile and elastic-perfectly plastic compressive behavior. Finally, a method used to analyze quasi-isotropic beams tested in four-point bending and rings tested in diametral compression is discussed. This finite element analysis uses a layered shell element with a lamina constitutive model that permits elastic-perfectly plastic response to fiber-directed compression, but otherwise assumes linear elastic behavior. Comparison of calculated and experimental results corroborate the ability of analyses using a simple compressive yield model to account for much of the observed flexural nonlinearity in Kevlar 49/epoxy beams and rings.

Studies were conducted to examine the influence of the thermo-oxidative resistance characteristics of the fiber and matrix resin on the thermal stability of composites made from these materials. Celion 6000 graphite fiber, PMR-15 matrix resin, and Celion 6000/PMR-15 unidirectional composites were isothermally aged in air-circulating ovens at 288, 316, 329, and 343 °C. Microscopy (SEM) studies indicate extreme oxidative erosion of the graphite fiber occurs at elevated temperatures in the presence of the polyimide matrix. Activation energies were calculated for the thermal degradation of the three materials. The activation energy of oxidation of the composite was found to be greater than those of the fiber and the matrix resin.

The effect of the geometric arrangement of spherical aggregates in a highly filled polymer composite (such as polymer concrete) on the setting stresses, due to resin shrink age during cure was investigated using three-dimensional finite element analysis. Simple cubic and face-centered cubic arrangements of perfect spherical aggregate were con sidered as well as a hexagonal-close-packed arrangement of hexagonal, prism-shaped aggregate. The shape of the aggregate has a very significant effect on the setting stresses. The effects of packing factor of aggregate particles were investigated. The higher the pack ing factor of spherical particles the lower the magnitude of setting stresses throughout the polymer composite system.