Laminated structural composites

The important point to note from this Example is that in a non-symmetrical laminate the behaviour is very complex. It can be seen that the effect of a simple uniaxial stress, or, is to produce strains and curvatures in all directions. This has relevance in a number of polymer processing situations because unbalanced cooling (for example) can result in layers which have different properties, across a moulding wall thickness. This is effectively a composite laminate structure which is likely to be non-symmetrical and complex behaviour can be expected when loading is applied. 

A surface is that part of an object which is in direct contact with its environment and hence, is most affected by it. The surface properties of solid organic polymers have a strong impact on many, if not most, of their apphcations. The properties and structure of these surfaces are, therefore, of utmost importance. The chemical stmcture and thermodynamic state of polymer surfaces are important factors that determine many of their practical characteristics. Examples of properties affected by polymer surface stmcture include adhesion, wettability, friction, coatability, permeability, dyeabil-ity, gloss, corrosion, surface electrostatic charging, cellular recognition, and biocompatibility. Interfacial characteristics of polymer systems control the domain size and the stability of polymer-polymer dispersions, adhesive strength of laminates and composites, cohesive strength of polymer blends, mechanical properties of adhesive joints, etc. 

Nylon, aluminum, PVC (OPA-aluminum-PVC) composites offer functional alternatives to traditional ther-moformed materials. With a laminate structure of 25 pm OPA, 45 pm aluminum, with 60 pm PVC (1 mL OPA 1.8 mL aluminum-2.4 mL PVC), it is possible to almost completely eliminate water-vapor permeability [25]. 

Cellulose, which is more fibrous than wood flour, is used as a filler for urea and melamine plastics. Melamine dishware is a laminated structure consisting of molded resin-impregnated paper. Starch and soybean derivatives are biodegradable, and the rate of disintegration of resin composites containing these fillers may be controlled by the amount of these fillers present in polymers. 

The process by which a thermoplastic matrix composite consolidates to form a laminated structure has been attributed to autohesive bond formation at the ply interfaces. Autohesive bond formation is controlled by two mechanisms (1) intimate contact at the ply interfaces, and (2) diffusion of the polymer chains across the interface (healing). The rate of autohesive bond formation and hence the speed of the composite consolidation process is directly related to the temperature-pressure-time processing cycle. 

Wood (qv) is aiguably the oldest building material used by humans to construct their dwellings. It is a natural product obtained from trees, used in both structural and decorative applications. The chemical composition of wood is largely cellulose (qv) and lignin (qv). Today there are a variety of composite or reconstituted wood products, such as plywood, particle board, wood fiber boards, and laminated structural beams, where small pieces of wood or wood fiber are combined with adhesives to make laiger sheets or boards (see Laminates). 

Laminated Strand Products. The most recent developments in the family of wood-based composites are a group of laminated strand products, made with strands oriented in the long direction of the product and marketed as structural composite lumber. One product is made with long, narrow strips of softwood veneer. The strips or strands are about 2.5 x 13 x 600 mm (0.1 x 0.5 x 24 in.), coated with a PRF adhesive, and pressed under heat and pressure into large blocks. After the resin is cured the blocks are resawn and planed into lumber dimension stock. 

A number of articles on the design of ceramic laminates leading to a significant increase of their mechanical properties were published in the past [15-19]. Our work is based on the control of thermal residual stresses by optimization of the layered structure [20, 21], The proposed approach targets the fracture toughness increase of laminate ceramic composites and is based on the preliminary results both from our work [22, 23] and from the work of others [24-26],... 

Using this concept, it has been shown by cone calorimetry that over a 3 min combustion period, 3 and 6 mm thick laminated structures, made with different fire-retardant skin and unfilled core combinations can give similar resistance to ignition and comparable HRR and smoke extinction area (SEA) results to fully fire-retardant compositions (Table 7.4). Mechanical properties, in particular impact strength, were also found to be greatly enhanced by this approach, since less fire-retardant filler is present in the material. Whereas this approach has been demonstrated to be effective with hydrated fillers, it is applicable to all fire-retardant types. 

Phenolic/ adhesives adhesives / sealants / gaskets abrasives and break pad binders printed circuit boards structural composites/laminates Metal/glass binders metal oxide binders retroreflective coatings glass optical coatings Hard copy printing inks toners... 

A model has been developed for the prediction of the lay-up consolidation process during the lamination of prepreg lay-ups for the manufacture of printed circuit boards. This model can be used advantageously in prepreg material screening and in the optimization of lamination schedules for high-performance structural composites. 

HDPE, composite materials such as epoxy-glass fiber and epoxy-carbon fiber, and laminate structures such as polymer films on bulk metal substrates. Thin-conductive film heaters were made of electrically conductive paints, electrically conductive polymer films, metal foils (stainless-steel, copper, titanium, and titanium alloys), and thin metal films sputtered on a ceramics or glass. The samples dimensions varied from a few centimeters to 5m. 

Figure 10.18. Three examples of structural composite lumber (top to bottom) laminated veneer lumber (LVL), parallel strand lumber (PSL), and oriented strand lumber (OSL).

Fig. 15. I-V characteristics of OLED with different laminated structure, (a) - Single MEH-PPV, SMED (b ) - with HTL layer, PPMD (c) - with HTL and EL composite layers, PMCD and (d) -with LiF, MMCD...

Laminates (multilayer structures), where each layer itself may be either a single-phase material or a multiphase material [10]. Examples of laminates include some electronic components, many structural composites, adhesive joints, and any other fabricated article where a coating layer (such as an anticorrosion coating or paint) is deposited on another material. See sections 7.C and ll.C.S.d for earlier discussions of such structures in this book. 

Fracture toughness tests for isotropic materials normally use edge-notched flexure beams and compact tension specimens. These methods are. as for the impact tests, only suitable for the injected or compression molded materials, which do not have a strongly laminated structure. Laminated composite materials have their primary failure path between the layers, and a new set of test geometries has been developed. 

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