Laminated Composites


Preface

The term analysis in engineering typically means the application of an acceptable analytical procedure to a design problem based on established engineering principles. One performs analysis to verify the structural or thermal integrity of a design. Sometimes this can be done using handbook formulas or analytical procedures for simple designs. More often, however, this analysis is being performed using numerical analysis and computers to predict structural or product performance. The predominate type of engineering software used in these analyses is based on the finite element method, and this type of analysis is termed finite element analysis (FEA).

What Are Composites?

The term composite, used here, refers to fiber-reinforced plastic (FRP), manufactured from fibers and resins. Composites consist of a reinforcing material (fibers, whiskers) supported in a binder or matrix material. Fibers are the reinforcing material that provides strength in a composite material. Typical fibers include glass, graphite, and boron. Matrices are the filler (resins or glues) that bind fibers together. Typical matrix materials are epoxy, metal, ceramic, and carbon. Composites are a series of lamina or plies of varying thickness and/or materials The lamina are stacked with various orientations of the fiber direction between lamina, to obtain a laminate which has the desired directional stiffness and strength properties required for an acceptable design. The reinforcing material is normally the load carrying medium of the material, and the matrix serves as a carrier, protector, and load splicing medium around the reinforcement.

Why Use Composites?

Composite fibers are deliberately oriented in a matrix in such a way as to increase the directional structural stiffness and strength of the material. Fibers typically have high static and fatigue strength. The plies are stacked with various orientations of the fiber direction between plies to obtain a laminate which as the desired stiffness and strength properties to handle the directional flow of forces through the structure or product. Because of the variety of combinations and arrangements of the fibers and matrices, combined with the concept of lamination, designers today have greatly increased opportunities of tailoring structures and/or materials to meet systems of forces and changing environments. The most efficient configuration for a unidirectional force system is a unidirectional composite oriented in the load path direction. If loads are such that unidirectional composites are inadequate and/or inefficient, than multi-directional laminates will be required. Basic purpose of using composites is to use the directional dependent properties of the laminate effectively to transfer forces. Composites are also typically lighter than traditional structural materials and offer versatility in the fabrication process.

Complexity Of Analysis/Design

Both micro-mechanics and macro-mechanics of composite materials are required in design of composite structures and products. Micro-mechanics establishes the relation between the properties of the constituents and those of the unit composite ply. Macro-mechanics (laminate plate theory) relies on measured ply data to establish optimum laminates for a struc