Ductile resins

Fig. 8.4. Schematic illustrations of the formation of a fracture process zone in front of the crack tip for composites containing (a) a brittle resin matrix and (b) a ductile resin matrix. After Bradley and Cohen (1987). Reproduced by permission of ASTM.

Figure 4.18. Optimum elastomeric drop diameter vs. entanglement density of the matrix resin for brittle resins (polystyrene, styrene-acrylonitrile and polymethylmethacrylate), and for semi-ductile resins (polyvinylchloride and polycarbonate).

Ductile with flow. These materials show still greater deformability than the typical ductile materials. Initially, the stress-strain dependence resembles that described for ductile resin, but before the rupture there is a zone of deformation where the stress remains about constant. Within this zone there is flow of material that usually leads to molecular alignment and/or to changes to the crystalline structure (viz. deformation of polyolefins). 

Formation of co-continuous stmctures in blends of either a brittle or pseudo-ductile resin with an elastomer may result in a quantum jump of toughness, without greatly affecting the key engineering properties of the high-performance resin. Conunercial blends of this type, e.g., POM, PA, PC, or PET with an elastomer, are available (viz., Triax series). 

Fibrous minerals NA Ductility resins. As with tensile strength, fibrous minerals increase HDT only slightly. Fillers do not increase HDT. 

Modified ETEE is less dense, tougher, and stiffer and exhibits a higher tensile strength and creep resistance than PTEE, PEA, or EEP resins. It is ductile, and displays in various compositions the characteristic of a nonlinear stress—strain relationship. Typical physical properties of Tef2el products are shown in Table 1 (24,25). Properties such as elongation and flex life depend on crystallinity, which is affected by the rate of crysta11i2ation values depend on fabrication conditions and melt cooling rates. 

One approach for ameliorating the highly brittle nature of these cements has involved the use of tougher, more ductile fillers (62,63). Another approach for improving the overall properties of traditional glass—ionomer cements involves the development of hybrid cement-composites and resin-modified cements (64—68). 

Ultem PEI resins are amber and amorphous, with heat-distortion temperatures similar to polyethersulfone resins. Ultem resins exhibit high modulus and ate stiff yet ductile. Light transmission is low. In spite of the high use temperature, they are processible by injection mol ding, stmctural foam mol ding, or extmsion techniques at moderate pressures between 340 and 425°C. They are inherently flame retardant and generate Httie smoke dimensional stabiUties are excellent. Large flat parts such as circuit boards or hard disks for computers can be injection-molded to maintain critical dimensions. 

Of these properties the most interesting is the figure given for impact strength. Such high impact strength figures are in part due to the ductility of the resin. 

The single filament pull out test, sometimes called the microdebond test, has received attention for some years as a way to assess the adhesion between fibers and matrices in fiber composite [90,91]. It provides a direct measure of interfacial adhesion and can be used with both brittle and ductile matrix resins. 

Strength Fibrous minerals Ductility gaining tensile strength. Carbon fibers are more expensive fibrous minerals are least expensive but only slightly reinforcing. Reinforcement makes brittle resins tougher and embrittles tough resins. Fibrous minerals are not commonly used in amorphous resins. 

Flexural Carbon fibers Ductility, cost Ductility, cost than the base resin... 

Other important parameters for the correlation between GJJ and GJ include the ductility or the failure strain, particularly the non-linear strain (Jordan and Bradley, 1988 Jordan et al., 1989) of the matrix resin, the bond strength of the fiber-matrix interface (Jordan and Bradley, 1987 Bradley 1989a, b), and the fiber V and their distributions in the composites (Hunston et al., 1987). A high failure strain promotes the intrinsic capacity of the resin to permit shear deformation, and is shown to increase the G and G. values almost linearly, the rate of increase being steeper for G j than for Gf. ... 

Thermoplastic structural foams with bulk densities not less than 50% of the solid resin densities are considered. Cellular morphology, uniform-density cell behaviour, the I-beam concept in designing, core-density profile and the role of the skin, mechanical properties, and ductile-brittle transitions are discussed. 63 refs. 

---