Design Guidelines
Design of a composite structure requires a good knowledge of how composites differ from traditional engineering materials, and what effect those differences have on analysis and manufacturing. Like metal alloys, composites are formed from two or more materials. Unlike metals, the composite constituents remain
Design of a composite structure requires a good knowledge of how composites differ from traditional engineering materials, and what effect those differences have on analysis and manufacturing. Like metal alloys, composites are formed from two or more materials. Unlike metals, the composite constituents remain visibly distinct. This sets composites apart from metals in two ways:
• Heterogeneity: As compared to metals and plastics, which are relatively homogeneous in all directions, composite properties vary from ply to ply. The fibers remain distinct from matrix, although individual plies are assumed to be homogeneous.
• Directionality: Composite properties depend on the direction of the fibers. Most composites display some degree of material symmetry and thus are not generally anisotropic. Unidirectional plies are transversely isotropic (an orthotropic material with one isotropic plane); the most common laminates are specially orthotropic (with three mutually perpendicular planes of symmetry).
It is these properties, and not just their lower density, higher strength and stiffness, that give composites an advantage over isotropic materials. By exploiting nonuniformity and directionality, it is possible to tailor the material — not just the structure — for the load conditions.
