Design sandwich construction

As reviewed throughout this book and particularly in Chapter 3, Design Concept, there are many design features that keep expanding the use of plastics in different products. These features include shapes, sandwich constructions, shrinkages, tolerances, and processes. 

As will be shown, the chosen glass-silicon-glass sandwich construction with the electrical conductors on glass, the areas exposed to the analyte made of silicon or glass, and the use of functional elements simultaneously for different tasks fulfills all the cited demands and, due to their special design, all the necessary subsystems can be generated in one patterning process. 

A similar specimen design uses a sandwich construction with a dissimilar material bonded between the two cylindrical halves of the button specimen. This design is commonly used to measure the tensile strength of adhesives between dissimilar materials or if the adherend does not have the strength or characteristics to be machined into the shape of the button specimen. With some modifications in the dimensions, the button tensile test has also been adapted for testing adherence of honeycomb-cover sheets to the core (ASTM C 297). 

Uniaxial compressive properties are important to the design engineer who can utilize the foams inherent high compressive strength in reinforcing other structural members. Sandwich construction is a typical example of such a use, as in submarine-hull construction. Syntactic-foam prepregs have been developed for this application (7). 

A. Starlinger, U. Purtschert, Hybrid design in mass transport vehicles - stmc-tural concept and analysis, in Proceedings of Fifth International Conference on Sandwich Construction, Zurich, EMAS, 2000. 

One application is honeycomb sandwich construction that consists of thin high strength prepreg skins bonded to a thicker honeycomb, foam, or balsa core. The advantages are very low weight, high stiffness, durable, design freedom, and reduced production costs. 

A sandwich structure is composed of two skins and a core material. The same or different materials are combined in the form of sandwich construction (Figure 7.46). They can be used in products with an irregular distribution of the different materials, and in the form of large structures or sub-structures. Overall load-carrying capabilities depend on average local sandwich properties, but materials failure criteria depend on local detailed stress and strain distributions. Design analysis procedures for sandwich materials composed of linear elastic constituents are well developed. In principle, sandwich materials can be analyzed as RP structures, but incorporation of viscoelastic properties will be subject to the limitations discussed throughout this book. 

For RP-faced sandvdch structures the design approaches includes both the unique characteristics introduced by sandwich construction and the special behavior introduced by RP materials. The overall stiffness provided by the interaction of the faces, the core, and their interfaces must be sufficient to meet deflection and deformation limits set for the structures. Overall stiffness of the sandwich component is also a key consideration in design for general instability of elements in compression (Figure 7.47). 

With most typical sandwich constructions, the faces provide primary stififhess under in-plane shear stress resultants (Nxy), direct stress resultants (N, Ny), and bending stress resultants (Mx, My) (Figure 7.48). Also as important, the adhesive and the core provide primary stiffness under normal direct stress resultants ( z), and transverse shear stress resultants (Q, Qy). Resistance to twisting moments (T, TyJ that is important in certain plate configurations, is improved by the faces. Capacity of faces is designed not to be limited by either material strength or resistance to local buckling. 

Dakers, J.J. The Design and Construction of Wester Duntanlich Bridge Deck using the Open Sandwich Slab Technique, MSc Thesis. University of Dundee, 1985. 

The term structural foams designates components possessing full density skins and cellular cores, similar to structural sandwich constructions, or to bones, whose surfaces are solid but whose cores are cellular. For structural purposes, they have favourable strength and stlffness-to-welgh ratios, because of their sandwich type configuration. Frequently, they can provide the necessary structural performance at a reduced cost of materials. 

A modified epoxy, foaming adhesive in sheet form which during the 120 C curing expands to fill gaps and adhere strongly to all parts of the typically honeycomb sandwich construction. Designed for use in conjunction with Araldite 312, 312/5 or 609, where the operating temperature can be between -55 C and +100 C. 

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