Fiber-reinforced composite material

A.K Jain M P Debuisson. Segmentation of X-ray and C-scan Images of Fiber Reinforced Composite Materials. Pattern Recognition, vol 25, N°.3, pp 257-270, 1992... 

Also, laminated fiber-reinforced composite materials are obviously both laminated and fibrous composite materials. Thus, any classification system is arbitrary and imperfect. Nevertheless, the system should serve to acquaint the reader with the broad possibilities of composite materials. 

Fiber-reinforced composite materials such as boron-epoxy and graphite-epoxy are usually treated as linear elastic materials because the essentially linear elastic fibers provide the majority of the strength and stiffness. Refinement of that approximation requires consideration of some form of plasticity, viscoelasticity, or both (viscoplasticity). Very little work has been done to implement those models or idealizations of composite material behavior in structural applications. 

Unlike most conventional materials, there is a very close relation between the manufacture of a composite material and its end use. The manufacture of the material is often actually part of the fabrication process for the structural element or even the complete structure. Thus, a complete description of the manufacturing process is not possible nor is it even desirable. The discussion of manufacturing of laminated fiber-reinforced composite materials is restricted in this section to how the fibers and matrix materials are assembled to make a lamina and how, subsequently, laminae are assembled and cured to make a laminate. 

Three principal layup processes for laminated fiber-reinforced composite materials are winding, laying, and molding. The choice of a layup process (as well as a curing process) depends on many factors part size and shape, cost, schedule, familiarity with particular techniques, etc. 

The advent of advanced fiber-reinforced composite materials has been called the biggest technical revolution since the jet engine [1-4], This claim is very striking because the tremendous impact of the jet engine on military aircraft performance is readily apparent. The impact on commercial aviation is even more striking because the airlines stwitched from propeller-driven planes to all-jet fleets within the span of just a few years because of superior performance and lower maintenance costs. 

Not all of the strength and stiffness advantages of fiber-reinforced composite materials can be transformed directly into structural advantages. Prominent among the reasons for this statement is the fact that the joints for members made of composite materials are typically more bulky than those for metal parts. These relative inefficiencies are being studied because they obviously affect the cost trade-offs for application of composite materials. Other limitations will be discussed subsequently. 

Robert M. Jones ar Harold S. Morgan, Analysis of Nonlinear Stress-Strain Behavior of Fiber-Reinforced Composite Materials, AIAA Journal, December 1977, pp. 1669-1676. 

The mechanics of materials approach to the micromechanics of material stiffnesses is discussed in Section 3.2. There, simple approximations to the engineering constants E., E2, arid orthotropic material are introduced. In Section 3.3, the elasticity approach to the micromechanics of material stiffnesses is addressed. Bounding techniques, exact solutions, the concept of contiguity, and the Halpin-Tsai approximate equations are all examined. Next, the various approaches to prediction of stiffness are compared in Section 3.4 with experimental data for both particulate composite materials and fiber-reinforced composite materials. Parallel to the study of the micromechanics of material stiffnesses is the micromechanics of material strengths which is introduced in Section 3.5. There, mechanics of materials predictions of tensile and compressive strengths are described. 

The nonlinear shear stress-shear strain behavior typical of fiber-reinforced composite materials is ignored, i.e., the behavior is regarded as linear. 

For fiber-reinforced composite materials, Tsai gives expressions for E, E2, v 2> 12 9 ° agreement with experimental data... 

Prediction of the strength of fiber-reinforced composite materials has not achieved the near-esoteric levels of the stiffness predictions studied in the preceding sections. Nevertheless, there are many interesting physical models for the strength characteristics of a matrix reinforced by fibers. Most of the models represent a very high degree of integration of physical observation with the mechanical description of a phenomenon. 

A unidirectional fiber-reinforced composite material deforms as the load increases in the following four stages, more or less, depending on the relative brittleness or ductility of the fibers and the matrix ... 

Figure 3-46 Deformation Stages of a Fiber-Reinforced Composite Material...

The difference between Equations (3.119) and (3.124) is slight for high ratios of E, to E , as in practical fiber-reinforced composite materials. 

Figure 3-62 Compressive Strain at Microbuckling for Fiber-Reinforced Composite Materials (After Dow and Rosen [3-28])...

The micromechanics approaches presented in this book are an attempt to predict the mechanical properties of a composite material based on the mechanical properties of its constituent materials. In nearly all fiber-reinforced composite materials, there is considerable difference between expectation and reality. Thus, we must ask what is the usefulness of micromechanical analysis beyond gaining a feeling for why composite materials behave as they do Basically, there are two answers one related to designing a material and one related to designing a structure. 

The strength of special classes of laminated fiber-reinforced composite materials has been analyzed on the basis of several hypotheses ... 

Note that no assumptions involve fiber-reinforced composite materials explicitly. Instead, only the restriction to orthotropic materials at various orientations is significant because we treat the macroscopic behavior of an individual orthotropic (easily extended to anisotropic) lamina. Therefore, what follows is essentially a classical plate theory for laminated materials. Actually, interlaminar stresses cannot be entirely disregarded in laminated plates, but this refinement will not be treated in this book other than what was studied in Section 4.6. Transverse shear effects away from the edges will be addressed briefly in Section 6.6. 

Wave propagation in an inhomogeneous anisotropic material such as a fiber-reinforced composite material is a very complex subject. However, its study is motivated by many important applications such as the use of fiber-reinforced composites in reentry vehicle nosetips, heatshields, and other protective systems. Chou [6-56] gives an introduction to analysis of wave propagation in composite materials. Others have applied wave propagation theory to shell stress problems. 

Harold S. Morgan and Robert M. Jones, Analysis of Nonlinear Stress-Strain Behavior of Laminated Fiber-Reinforced Composite Materials, Proceedings of the 1978 International Conference on Composite Materials, Bryan R. Noton, Robert A. Signorelli, Kenneth N. Street, and Leslie N. Phillips (Editors), Toronto, Canada, 16-20 April 1978, American Institute of Mining, Metallurgical a Petroleum Engineers, New York, 1978, pp. 337-352. 

Fibers are often regarded as the dominant constituents in a fiber-reinforced composite material. However, simple micromechanics analysis described in Section 7.3.5, Importance of Constituents, leads to the conclusion that fibers dominate only the fiber-direction modulus of a unidirectionally reinforced lamina. Of course, lamina properties in that direction have the potential to contribute the most to the strength and stiffness of a laminate. Thus, the fibers do play the dominant role in a properly designed laminate. Such a laminate must have fibers oriented in the various directions necessary to resist all possible loads. 

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