Lamination critical factors

Critical factors. The sole critical factor is the presence of a lamination of sufficient size to prevent the forming of a satisfactory weld. 

Many applications of conducting textiles involve the formation of laminates or composites with various thermoset resins such as epoxy, imide, and rubber. The adhesion between the various layers of the composite is a critical factor in the utility of these structures. Only a few papers have addressed the adhesion of polypyrrole-coated fabrics with epoxy resins [44,451. The adhesion at the polypyrrole/textile interface is reasonably strong because of the intermolecular forces between the adsorbed polymer layer and the substrate. The adhesion at the polypyrrole/epoxy interface benefits from the po-... 

Another aspect to be considered is the difficulty in producing curved structures with the same fibre content as flat laboratory panels. This effect is shown in Figure 16, at the comer the laminate thickness is larger than at the flat section and fibre content is rather lower. This will affect the bending stiffness of the arm and the predicted failure load. This figure also shows the fillet, which is critical to initiation in the specimens without implanted defects. It is well known that fillets can significantly alter the load path in lap shear joints and increase the failure loads (see [1] and Figure 3 for example). If a fracture mechanics approach is to be applied this effect must be considered. Some recent studies on stress intensity factors for such cases may allow this to be addressed [22]. 

Tensile stresses are critical in tank design. The designer assumes the pressure in this application will not exceed 100 psi (700 Pa) and selects a safety factor of 5. The stress must be known so that the thickness can be determined. The stress or the strength of the final laminate is derived from the makeup and proportions of the resin, mat, and continuous fibers in the RP material. 

Laminate failure analysis predicts the criticality of a loading condition by comparing actual ply stresses and strains with ply stresses and strains corresponding to the failure of the laminate. Failure criterion functions are used to take into account the combined effect of stress or strain components. The criticality of the loading condition is indicated with a reserve factor which defines how much the load can be increased before failure occurs. The importance of the analysis is evident. The need for a computer code is also obvious since the failure analysis is even more complicated than the load response analysis. 

Thermal residual stresses in the transverse direction contribute to about 80 to 98% of the total stresses in both laminates, which means the thermal residual stress is the dominant factor that should be critically considered for cryogenic composite fuel tank design. 

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