Laminate aerospace structures

Figure 1. Specific ultimate tensile strength vs. specific stiffness of current and developmental aerospace structural materials. Data are displayed on a log-log plot in (a), where P signifies PAN-based reinforcements Gr represents graphite fibers 0 0 and 90 0 indicate data collected parallel to and transverse to the fiber direction in uniaxial composites, respectively and Q/I represents quasi-isotropic laminates. The (f represents fiber reinforcements in MMCs. The dashed line in (b) represents the combinations of specific strength and stiffness that are double those of conventional metal alloys.

IM-AD resins A line of BMI resins designed for the manufacture of printed circuit boards, aerospace laminates, and structural composites... 

Hazardous Decomp. Prods. Heated to decomp., emits toxic vapors of NOx Uses Structural resin providing elec, transparency used for high-performance radome applies., adhesives/laminates (aerospace, aircraft, defense)... 

The increasing amount of research in waterborne systems should some day overcome technological difficulties. Howeverr the change-over from some solvent-borne to waterborne systems has presented difficulties (107), for exampler poor coating quality, excessive foam, insufficient water resistance, and even some corrosion and clean-up problems. Despite the problems, some waterborne systems have already been adopted for the manufacture of PSA s, contact adhesives, laminating adhesives, and wood adhesives. However, few applications of the waterborne systems as structural adhesives, especially as aerospace structural adhesives have been found. 

Loos and co-workers [11] have discussed the use of a carbon fibre uni-weave fabric with a tackifier coating as a potential replacement for tailored composite aerospace structures. The fibre was impregnated with epoxy resin and oven cured. Composite laminates that were fabricated using the modified process. These had higher mechanical properties than the composite laminates fabricated using a traditional process. 

Cyanate esters are used in circuit boards because of their low dielectric constant of 2.91 and a high Tg of 290°C. Prepregs and laminates are made with conventional technology, and they are tougher and more moisture resistant than FR-4 copper clad. Laminates are also used in radomes, antennas, and aerospace structures. 

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. 

The two major categories of polymer composite used in aerospace are laminates and sandwich stmctures, which require some differences in NDT inspection methods. The inspection of choice at the time of manufacture may be different from the inspection of choice for in-service assessments. The form of the stmcture determines the types of features of concern and the NDT techniques that may be apphed to detect and measure them. Table 15.1 summarizes some general thoughts and considerations on NDT of polymer composite stmctures. American Society for Testing and Materials (ASTM) also provides guidance on NDT for polymer composites [12]. The primary concerns in laminates are voids and porosity, inclusions, delamination, the fiber-to-resin ratio, and wrinkles (wavy or out-of-plane ply). Ultrasound is the predominate method for composite laminate inspection. In sandwich structures, the core material-to-facesheet bond, core condition, and fluid ingress are the usual concerns. 

Structural composites can range widely in performance from high-performance materials used in the aerospace industry down to wood-based composites, which have lower performance requirements. Within the wood-based composites, performance varies from multilayered plywood and laminated lumber to low-cost particleboard. Structural wood-based composites intended for indoor use are usually made with a low-cost adhesive, which is not stable to moisture, while exterior-grade composites use a thermosetting resin that is higher in cost but stable to moisture. Performance can be improved in wood-based as well as jute and kenaf composites by using chemical modification techniques, fire retardant, and decay control chemicals, etc. 

M Baruch, J Arbocz and G Q Zhang, Laminated conical shells - considerations for the variation of the stiffness coefficients, Technical Report LR-671, Faculty of Aerospace Engineering, Delft University of Technology, April 1992 also. Proceedings of the 35th AAIA/ASME/ASCE/ASC Structures, Structural Dynamics and Materials Conference, Hilton Head, SC, USA, pp 2505-2516. 

Requirements for space suits are more complex and frequently involve garments that can circulate water and/or air through the fibrous assembly. Laminated and/or coated garments with specific requirements to pressure, radiation, temperature, and humidity are more structurally complex as a textile product relative to the types of fibers used in this aerospace fabrication. 

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