Filled epoxy

In Figure 5.24 the predicted direct stress distributions for a glass-filled epoxy resin under unconstrained conditions for both pha.ses are shown. The material parameters used in this calculation are elasticity modulus and Poisson s ratio of (3.01 GPa, 0.35) for the epoxy matrix and (76.0 GPa, 0.21) for glass spheres, respectively. According to this result the position of maximum stress concentration is almost directly above the pole of the spherical particle. Therefore for a... 

Casting resin Thermoplastic elastomer Cast resin, flexible Mineral- and/or glass-filled Epoxy molding and encapsulating compound Polystyrene... 

In addition to electrical uses, epoxy casting resins are utilized in the manufacture of tools, ie, contact and match molds, stretch blocks, vacuum-forrning tools, and foundry patterns, as weU as bench tops and kitchen sinks. Systems consist of a gel-coat formulation designed to form a thin coating over the pattern which provides a perfect reproduction of the pattern detail. This is backed by a heavily filled epoxy system which also incorporates fiber reinforcements to give the tool its strength. For moderate temperature service, a Hquid bisphenol A epoxy resin with an aHphatic amine is used. For higher temperature service, a modified system based on an epoxy phenol novolak and an aromatic diamine hardener may be used. 

First-generation polymer composites (e.g., fiberglass) used thermosetting epoxy polymers reinforced with randomly oriented short glass fibers. The filled epoxy resin could be cured into a permanent shape in a mold to give lightweight, moderately strong shapes. 

A part, consisting of a carbon fiber composite tube, was initially adhered to the inside of a short titanium coupling by a silica-filled epoxy. The bond failed and a fluorinated mold release was believed to be the cause of the failure and was the purpose for this investigation. A sample of the epoxy (Sample A) and the part (Sample B) were submitted for X-ray photoelectron spectroscopy (XPS) to analyze for the presence of both fluorine and silicon. 

Fracto-emission (FE) is the emission of particles (electrons, positive ions, and neutral species) and photons, when a material is stressed to failure. In this paper, we examine various FE signals accompanying the deformation and fracture of fiber-reinforced and alumina-filled epoxy, and relate them to the locus and mode of fracture. The intensities are orders of magnitude greater than those observed from the fracture of neat fibers and resins. This difference is attributed to the intense charge separation that accompanies the separation of dissimilar materials (interfacial failure) when a composite fractures. 

Fig. 13. Optical micrograph of fra-ture surface of glass-filled epoxy polymers showing the crack front pinned between glass particles 22) (Arrow indicates direction of crack growth)...

Epon 828 resins, which are based on diglycidyl ether of bisphenol A filled with 40wt.% Si02, were irradiated at 4.9 K and tested at 77 K after being warmed up to room temperature. The flexural and compressive strengths of the filled epoxy resins were found to be little affected by a y-ray dose of 2 x 107 Gy, but to deteriorate significantly after exposure to 1 x 108 Gy [49],... 

TABLE 3.7 Effect of Curing Agents on the Shrinkage of Highly Filled Epoxy-Amine Systems during Cure16... 

It should be pointed out that diluents are not the only way to lower the viscosity of filled epoxy resins systems. Surface active agents can also be added to the system. They provide better wetting of the filler by the epoxy resin matrix. This can lead to substantial viscosity reduction for systems having equivalent filler concentration. The surface active agent, in turn, could also be used to produce formulations with higher filler loading at equivalent viscosity. These surface active agents are discussed in Chap. 10. 

Some inorganic particulate fillers have also been considered as toughening agents for epoxy materials. Glass beads, fly ash, alumina trihydrate, and silica were used early on to improve the toughness of filled epoxy resins. Various studies, however, have demonstrated that the fracture energy of filled epoxies reaches a maximum at a specific filler concentration. 

FIGURE 9.1 Effect of reactive diluent concentration on the viscosity of a filled epoxy resin.4... 

FIGURE 9.5 The coefficients of thermal expansion of filled epoxy resins compared with those of common metals.15... 

Fillers with a density lower than that of epoxy can be used to provide reduced specific gravity in cured products. These are usually gas-filled microballoons. Although they generally bring about a significant increase in viscosity, the microballoon filled epoxies (sometimes called syntactic foam adhesives) are often used in marine applications where low density and buoyancy are important criteria. 

Epoxy-nylon Epoxy-phenolic Epoxy-polyamide Filled epoxy... 

Since the in-mold pressures in RIM are generally relatively low [50 to 150 psi (0.4 to 1.1 MPa)] a variety of tooling constructions have been used. These include machined steel or aluminum, cast aluminum or kirksite, sprayed metal or electroplated shells, and reinforced or aluminum filled epoxy (Chapter 17). With mold pressures usually below 100 psi (0.7 MPa), mold-clamp-pressure requirements can accordingly be low when compared to injection and compression molding. 

Fig. 25. Effective Young s modulus for silica filled epoxy 46]. Circles are experimental data [45]...

Fig. 26. Comparison of the predicted (solid lines [46]) and measured (points [45]) strain rate dependence of the compressive yield stress of silica filled epoxy at different filler concentrations...

Fig. 28. Dependence of the compressive stress-strain curves on strain rate of silica filled epoxy [46]...

---