Laminate ply

Particleboard (waste wood chips or dust plus a resin) panelling, subflooring, general plywood and lumber replacement Paper-base laminates (plies of wood plus a phenolic, urea, or melamine resin) structural and machine parts... 

Collation. Collation is the process by which the individual laminate plies are assembled prior to curing in the press. The buildup of the laminate determines the final properties of the product. The topmost sheet in the buildup may be a texturing or embossing paper as well as being a release sheet to allow for separation of the laminate from the caul plate used to mold it. 

During the press operation, which is actually a form of compression molding, the resin-treated laminate plies are heated under pressure and the resins cured. The initial heating phases cause the resin to melt and flow into voids in the reinforcing ply and bond the individual plies together. The applied heat simultaneously causes the resin to polymerize and eventually to cross-link or gel. Therefore, resin viscosity reaches a minimum during the press cycle. This is the point at which the curing process becomes dominant over the melt flow process. Dynamic mechanical and dielectric analyses (11) are excellent tools for study of this behavior. 

The Tg requirement has increased from about 115-120°C. to a level of 120-130°C. for the cured laminate. The pressure cooker test is run by subjecting the test laminate to 15 psi steam in a conventional pressure cooker for 20-40 minutes. The test laminate is removed from the pressure cooker, conditioned one hour at room temperature and immediately placed in a hot solder bath (about 500°F.). The laminate is then tested for water blistering between the laminate plies. Any visible blistering is considered a failure. 

LDPE is frequently used as a lamination ply to bond two materials together... 

Warship builder Vosper Thornycroft, initially a SCRIMP licensee, subsequently developed its own method for single-shot infusion of up to 30 laminate plies, including heavy shipbuilding fabrics, and complex structures with inserts, cores, stiffeners and festeners. Since vacuum bags are used for consolidation rather than precision matched tooling, set-up costs are modest and labor is said to be halved compared with hand lay-up. 

For the case of an orthotropic laminate under conditions of plane stress, which can be assumed when the thickness of a laminate ply is small compared to its length and width, the stress in each constituent ply of a laminate can be determined with the aid of classical laminate plate theory [5-7]. The elastic stress-strain relationship for an orthotropic unidirectional plate then becomes... 

Subsequent laminate plies should be maintained as free of air inclusions as possible and should provide a good bond to foregoing plies. If laminating is interrupted overnight or over the weekend, the recommendations of the resin supplier should be sought with regard to any surface preparation which may be necessary before lamination recommences. 

Laminate Plies Material Thickness mm Tensile strength MNm Flexural strength MNm" Modulus GNm" Relative cost Per squ. m... 

Stitching. The benefit of through-the-laminate-thickness stitching has already been demonstrated to lock the laminate plies together and to reduce the propensity for transverse tensile failure... 

PVDC Neoprene Sodium silicate Acrylic PVAC Laminating plies of facing... 

Laminated board laminate plys of paperboard for beverage packaging... 

Lafarie-Frenot, M.C. and Henaff-Gardin, C., Formation and Growth of 90° Ply Fatigue Cracks in Carbon/Epoxy Laminates , Composites Science and Technology Vol. 40, p. 307-324, 1991... 

Telega J.J., Lewinski T. (1994) Mathematical aspects of modelling the macroscopic behaviour of cross-ply laminates with intralaminar cracks. Control and Cybernetics 23 (3), 773-792. 

Laminates aie materials made up of plies or laminae stacked up like a deck of cards and bonded together. Plywood is a common example of a laminate. It is made up of thin pHes of wood veneer bonded together with various glues. Laminates ate a form of composite material, ie, they ate constmcted from a continuous matrix and a reinforcing material (1) (see also Reinforced plastics). 

Laminates ate a special form of composite material or reinforced plastic because the continuous reinforcing ply of fibrous material imparts significant strength in the x—j plane. The strength along the axis results from interlaminar bonding of resins. Very few fibers ate oriented in the direction, so it tends to be the weak link in this type of composite. 

The reinforcing ply of laminates may be a woven fabric scrim, a nonwoven web of polymer monofilaments, or a mat of fibers. One of the most common reinforcements in use is also one of the oldest, ordinary cellulose fiber paper. 

The reinforcing ply acts as the carrier for the plastic resin during intermediate processing steps known as saturation and B-staging. It is this ply that together with the resin makes a laminate a composite material, and the layering of these pHes that makes the final product a laminate. 

The quantity of resin appHed to the reinforcing ply to achieve a state of full densification varies inversely with the laminating pressure. Therefore, high pressure laminates pressed at about 7 MPa (1000 psi) need only about 25—30% phenoHc resin in kraft paper, whereas low pressure (1 MPa = 145 psi) laminates need 50—60% resin in the reinforcing ply if all voids are to be filled in the final product. 

In the case of the fibrous laminate not much work has been done, but it has been observed that a significant loss of stiffness in boron—aluminum laminate occurs when cycled in tension—tension (43,44). Also, in a manner similar to that in the laminated PMCs, the ply stacking sequence affects the fatigue behavior. For example, 90° surface pHes in a 90°/0° sequence develop damage more rapidly than 0° pHes. In the case of laminates made out of metallic sheets, eg, stainless steel and aluminum, further enhanced resistance against fatigue crack propagation than either one of the components in isolation has been observed (45). 

The characteristic features of a cord—mbber composite have produced the netting theory (67—70), the cord—iaextensible theory (71—80), the classical lamination theory, and the three-dimensional theory (67,81—83). From stmctural considerations, the fundamental element of cord—mbber composite is unidirectionaHy reinforced cord—mbber lamina as shown in Figure 5. From the principles of micromechanics and orthotropic elasticity laws, engineering constants of tire T cord composites in terms of constitutive material properties have been expressed (72—79,84). The most commonly used Halpin-Tsai equations (75,76) for cord—mbber single-ply lamina L, are expressed in equation 5 ... 

Inter-ply shear is prominently featured in cord—mbber composite laminates, and may relate to delamination-induced failures. Studies utilizing experimental, analytical, and finite element tools, with specific apphcation to tires, are significant in compliant cord—mbber composites (90—95). 

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