Design of Laminates

The analytical tools to accomplish laminate design are at least twofold. First, the invariant laminate stiffness concepts developed by Tsai and Pagano [7-16 and 7-17] used to vary laminate stiffnesses. Second, structural optimization techniques as described by Schmit [7-12] can be used to provide a decision-making process for variation of iami-nate design parameters. This duo of techniques is particularly well suited to composite structures design because the simultaneous possibility and necessity to tailor the material to meet structural requirements exists to a degree not seen in isotropic materials. 

The key to the design of efficient laminates is to resist both the magnitude and the directional nature of the loads without overdesign in either respect. That is, the laminate is taiiored to just meet specific requirements. Structures made of isotropic materials are usually inefficient, i.e., overdesigned because excess strength and stiffness are inevitabiy available in some direction. By appropriate consideration of the loads and their directions, a laminate can be constructed of individual laminae 

FIND A LAMINATE THAT WILL MEET THE DESIGN PERFORMANCE GOALS EXPRESSED IN TERMS OF, E.G., 

CHANGE THE STACKING SEQUENCE AND/OR THE THICKNESS TO CHANGE THE BEHAVIOR UNTIL THE DESIRED RESPONSE IS OBTAINED 

TOO LOW OR TOO HIGH, CHANGE STACKING SEQUENCE AND/OR NUMBER OF LAMINAE 

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The influence of the orientation of the laminae on the stiffness of the composite is illustrated in Figure 15.15b, where generic stress-strain curves for unidirectional cross-ply random laminates are shown. In the design of laminates it is necessary to define not only the orientation of the plies but also the stacking sequence, i.e., the order in which the plies are placed through the thickness. Figure 15.16 shows examples of symmetrical and non-symmetrical laminates. The most standard ply orientations are 0°,... 

Computer codes for the analysis and design of laminates and laminated structural elements are discussed in 4.10.6.2-4.10.6.5. General purpose finite element (FE)... 

With the extensive use of laminated composite materials in almost all engineering fields, the optimal design of laminated composites has been an extensive subject of research in recent years. The dimensions of the composite leaf spring are taken as that of the conventional steel leaf spring. Each leaf of the composite leaf spaing consists of 20 plies of thickness 0.275 mm each. The number of leaves is also the same for composite leaf spring. The design parameters selected are listed in Table 4... 

An understanding of the structure, property relationship in the PET-PEI-Surlyn interface is necessary in order to facilitate the design of laminate structure with desirable performance properties. Therefore, we wish to characterize the chemical nature of the poly(ethylene imine), and polyvinylamine in the tie coat layer between poly(ethylene terepthalate) and Surlyn . 

Interactive Optimum Parametric Design of Laminated Composite Flange... 

Pig. 2. (a) The cell mount design of the integrated PV array of Pigure 1, which uses laminated conductive and insulating layers on top of an aluminium substrate in a printed circuit board-type panel (7). The array produces 20 kW at 20°C ambient and 850 W/m direct sunlight, and measures 155 m. The lens is a molded acryUc Presnel lens parquet mounted on the front of the array stmcture. The PV panel is mounted on the back of the array stmcture and is... 

Poly(phenylene sulfide) (PPS) is another semicrystalline polymer used in the composites industry. PPS-based composites are generally processed at 330°C and subsequently cooled rapidly in order to avoid excessive crystallisation and reduced toughness. The superior fire-retardant characteristics of PPS-based composites result in appHcations where fire resistance is an important design consideration. Laminated composites based on this material have shown poor resistance to transverse impact as a result of the poor adhesion of the fibers to the semicrystalline matrix. A PPS material more recently developed by Phillips Petroleum, AVTEL, has improved fiber—matrix interfacial properties, and promises, therefore, an enhanced resistance to transverse impact (see PoLYAffiRS containing sulfur). 

The steel of laminations plays a very significant role in determining the heating and the power factor of a motor. See Section 1.6.2A(iv). A better design with a judicious choice of flux density, steel of laminations and its thickness are essential design parameters for a motor to limit the core losses to a low level. 

A separate study was the improvement of magnetic permeability in soft alloys such as are used in transformers and motors by lining up the orientations of individual crystal grains, also known as a preferred orientation this became an important subspeciality in the design of transformer laminations made of dilute Fe-Si alloys, introduced more than 100 years ago and still widely used. 

The Mosquito was a laminated wood monocoque design that although unusual, was not new. More uniquely, the monocoque shell was fabricated by gluing plywood skins to balsa wood core. This construction foreshadowed the popular honeycomb core/facesheet aluminum and composite designs of later years. Fuselage halves of the Mosquito were formed in closed wooden female tools (tools... 

The stiffness ratios (i.e. stiffness of the foam sandwich beam relative to the original solid beam) are also given in Fig. 2.21. In both cases the values given are independent of the original solid material or its dimensions, so this provides a good design chart. The design of solid/foam sandwich structures is also considered in Chapter 3 in the laminate analysis. 

Mechanical stress analysis, treated earlier in this chapter, does not suffice for analysis of laminates that have been cured at temperatures different from the design operating temperature. In such cases, thermal stresses arise and must be accounted for. The concepts of mechanical stress analysis will be reiterated in this section along with the necessary modifications for thermal stress analysis. 

R. L. Foye and D. J. Baker, Design of Orthotropic Laminates, AIAA/ASME 11th Structures, Structural Dynamics, and Materials Conference, Denver, Colorado, 22-24 April 1970 (presentation only — no paper). 

Figure 7-1 Basic Questions of Laminated Piate Design...

The purpose of this subsection is to familiarize the reader with some of the basic characteristics and problems of composite laminate joints. The specific design of a joint is much too complex for an introductory textbook such as this. The published state-of-the-art of laminate joint design is summarized in the Structural Design Guide for Advanced Composite Applications [7-5] and Military Handbook 17A, Plastics for Aerospace Vehicles, Part 1, Reinforced Plastics [7-6]. Further developments can be found in the technical literature and revisions of the two preceding references. 

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