Lower fracture transitions

The mechanical properties of the blend of silane/size and bulk epoxy matrix (at concentrations representing likely compositions found at the fiber-matrix interface region) also suggest that the interaction of size with epoxy produces an interphase which is completely different to the bulk matrix material (Al-Moussawi et al., 1993). The interphase material tends to have a lower glass transition temperature, Tg, higher modulus and tensile strength and lower fracture toughness than the bulk matrix. Fig. 5.4 (Drown et al., 1991) presents a plot of Tg versus the amount of... 

Later tool materials included additions of up to 25% Re to tungsten, which lowered the transition temperature to below room temperature. Tungsten-rhenium tools show increased fracture resistance and improved wear resistance compared to pure tungsten and appear to have become the most widely used refractory metal. Development of production processes continues to improve the tool life of tungsten-rhenium tools. Molybdenum has been used on at least one occasion as a tool material for FSW of steel (Ref 4). 

Figure 1337 Schematic comparison of the brittle-ductile temperature transition in four different tests ( ) Hertzian indentation (lower transition), (2) plastic-elastic indentation (upper transition), (3) Double cantilever beam (lower transition) and (4) notched bar (upper transition). (Reproduced from Puttick, K.E. (1980) The correlation of fracture transitions. ). Phys. D, 13, 2249. Copyright (1980) Institute of Physics.)...

EPDM-ZnO-stearic acid systems could not be extruded even at 190°C. This is not unexpected since the material, in the absence of zinc stearate, shows no transition from the rubbery state to the viscous flow state (Fig. 1). In the presence of 10 phr of zinc stearate, the m-EPDM-ZnO-stearic acid system could be extruded but melt fracture occurred at a lower temperature (150°C) at all shear rates. At 160°C and 170°C, however, the extrudates showed melt fracture only at high shear conditions. At 20 phr loading of zinc stearate, melt fracture of the extrudate occurred at high shear conditions at 150°C, but at higher temperatures no melt fracture occurred and the extrusion was smooth under all shear conditions. At 30 and 40 phr loadings of zinc stearate, the extrudates were smooth under all shear conditions at all temperatures. 

Below their glass transition temperatures Tg, noncrystalline polymers (without fillers) usually exhibit high tensile strengths, although lower than those of typical crystalline polymers if the strength is referred to the cross section at rupture in both cases. A brittle type of fracture occurs, which probably is initiated by a different mechanism... 

The transition metal carbides do have a notable drawback relative to engineering applications low ductility at room temperature. Below 1070 K, these materials fail in a brittle manner, while above this temperature they become ductile and deform plastically on multiple slip systems much like fee (face-centered-cubic) metals. This transition from brittle to ductile behavior is analogous to that of bee (body-centered-cubic) metals such as iron, and arises from the combination of the bee metals strongly temperature-dependent yield stress (oy) and relatively temperature-insensitive fracture stress.1 Brittle fracture is promoted below the ductile-to-brittle transition temperature because the stress required to fracture is lower than that required to move dislocations, oy. The opposite is true, however, above the transition temperature. 

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