Reinforcement plies

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. 

During the press operation, which is actually a form of compression mol ding, the resin-treated laminate pHes 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 pHes together. The appHed 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 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. 

Steel bead wires are used at the extremes of the reinforcing plies to ensure a complete seal to the rim. Many turns of small diameter wire are wrapped in a rubber-impregnated tape to form a flexible hoop of high strength. 

However, a severe and persistent problem in laminated composites made of anisotropic fiber-reinforced plies is delamination. High interlaminar peel and shear stresses near edges start delamination cracks that grow along the non-reinforced interlaminar planes with little resistance. Delamination substantially reduces the load-bearing capacity and durability of advanced composites and has led to disastrous structural failures. Since the discovery and explanation of the mechanisms of delamination in advanced composites in the early 70s, many researchers have tried to... 

Hose with any damage extending through the outer reintcrcement ply. (Rubber Impregnated fabric cover is not a reinforcement ply), (Thermoplastic nylon may have braid relntorcement or color difference between cover and Inner tube. Exoosure ot second color Is cause tor rejection.)... 

The basic elements of composite materials are the uni-directionally reinforced ply or strand. Plies are thin plates (or shells), with a typical thickness h = 0.125 nun, containing randomly arrayed fibers miming parallel to each other, all embedded in a polymeric resin. Typical values of the fiber volume fraction Vf range between 40 and 60%. Strands are essentially uni-directional elements, with varying values of thickness and width, both of which are much shorter than the strand s length, and a similar range of Vf. 

Uni-directionally reinforced strands are the essential components in the manufacture of woven composites. In similar maimer, the uni-directional reinforced plies are the basic building blocks of laminates. The latter contain a lay-up of several, multi-oriented plies and are formed by the appUcation of a prescribed regime of pressure and temperature within an autoclave or a vacuum press. 

A state of plane stress is considered to hold for the in-plane response of thin plates. Consequently, the stress-strain relations for a uni-directionaUy reinforced ply, with fibers parallel to the Xi direction, employing truncated notation, read... 

Closed RTM molds, as illustrated in Figure 1.238, have to fulfill other important tasks besides contour forming of the component. In this mold from upper and lower mold, the force f has to be applied from the outside over the mold to the reinforcing structure, to compact the reinforcement plies. 

NOTE Rubber impregnated fabric cover is not a reinforcement ply. 

Hydraulic or vacuum lines, hoses, or connections are restricted, crimped, broken or damaged through the outer reinforcement ply. (Restricted/Crimped/Broken - 393.45(a) or Damaged - (393.45(b)(2))... 

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