2019年IntroductiontoCompositeMaterials复合材料概论

Introduction to Composite Materials References

•AERO 304 notes and Introduction to Aerospace Structural Analysis, Allen and Haisler

•Principles of Composite Material Mechanics, . Gibson,

McGraw-Hill, 1994

•Mechanics of Composite Materials, Robert M. Jones, McGraw-Hill, 1975

•Introduction to Composite Materials, . Tsai and . Hahn,

Technomic Publishing Co., 1980

Introduction and Terminology

Structural materials can be divided into 4 basic categories: •Metals

•Polymers

•Ceramics

•Composites

Composites, which consist of two or more separate materials combined in a macroscopic structural unit, are made from various combinations of the other three materials.

The relative importance of the four basic materials in a historical context has been presented by Ashby (Technology of the 1990s: Advanced Materials and Predictive Design, . Ashby, Philosophical Transactions of the Royal Society of London, A322, 393-407, 1987) and is shown schematically below (figure taken from Gibson):

Mankind has used composites since early time; for example, straw-reinforced clay bricks used by Israelites (the book of Exodus in the Old Testament), plant fiber-reinforced pottery, etc. They knew from daily use that fiber reinforcement of a material is very effective because many materials (but not all) are much stronger and stiffer in fiber form than they are in bulk form.

For example, Griffith found that as glass rods and fibers got thinner, they got stronger. He found that that for very small diameters the fiber strength approached the theoretical cohesive strength between adjacent layers of atoms, whereas for large diameters the fiber strength dropped to near the strength of bulk glass.

Fibers allow one to obtain the maximum tensile strength and stiffness of a material, but there are disadvantages. Fibers alone cannot support longitudinal compressive loads and their transverse mechanical properties are generally not as good as the

corresponding longitudinal (fiber direction) properties. Thus, there is often the need to place fibers in different directions depending upon the particular loading application.

Types of Fiber-Reinforced Composites

One generally finds four types of fiber-reinforced composites as shown below (from Gibson). They differ in how the fibers are utilized to make the composite (orientation and length of fibers).

Continuous fiber composites are generally "laid-up" in plies (or laminae) with each ply having fibers oriented in the same direction.

A layer of fibers all oriented in the same direction is imbedded in a homogeneous material (called the matrix) to make a single ply or laminae. For example, glass-epoxy has a layer of glass fibers running more-or-less parallel within an epoxy resin matrix material. Individual plies can be stacked or layered and bonded together with individual ply fiber directions being selected so as to tailor

the lay-up (or laminate) to have desired overall structural characteristics of the laminate. Under loading, the potential for delamination (or separation of the laminae) is a major problem because the interlaminar strength is matrix dominated ., if the matrix is weak, ply delamination can occur).

Woven fiber composites are similar to ordinary cloth used in the textile industry. The woven fiber may be 2-D (fibers interwoven in 2 directions) or 3-D (fibers interwoven in 3 directions). Woven