Brittle materials, transitions

The materials for solid solutions of transition elements in j3-rh boron are prepared by arc melting the component elements or by solid-state diffusion of the metal into /3-rhombohedral (/3-rh) boron. Compositions as determined by erystal structure and electron microprobe analyses together with the unit cell dimensions are given in Table 1. The volume of the unit cell (V ) increases when the solid solution is formed. As illustrated in Fig. 1, V increases nearly linearly with metal content for the solid solution of Cu in /3-rh boron. In addition to the elements listed in Table 1, the expansion of the unit cell exceeds 7.0 X 10 pm for saturated solid solutions " of Ti, V, (2o, Ni, As, Se and Hf in /3-rh boron, whereas the increase is smaller for the remaining elements. The solubility of these elements does not exceed a few tenths at %. The microhardness of the solid solution increases with V . Boron is a brittle material, indicating the accommodation of transition-element atoms in the -rh boron structure is associated with an increase in the cohesion energy of the solid. 

Solvent-modified thermosets display enhanced toughness due to the incorporation of a second phase material. A brittle-tough transition has been observed which cannot be attributed to changes in the interparticle distance. The chemically induced phase separation technique offers new routes and strategies to prepare such materials and enter new areas of applications. Hence, engineered porosity is demonstrated as a research concept developed into a toolbox for material scientists. 

Plastic properties of TNT. In 1945 Jefremov and Khaibashev [60] found that at a temperature of 50°C and above, TNT exhibits the properties of a plastic material, as under pressure (e.g. 31.6 kg/mm2) at 50°C it flows off through the holes in the vessel. At a temperature ranging from 0°C to 35°C TNT behaves as typical brittle material. At a temperature of 35-40°C (or at 45-47°C with TNT of high purity) a transition from the brittle to the plastic state can be observed. 

There is a basic difference between rupture above the glass transition temperature (where the polymer backbones have an opportunity to change their configurations before the material fails) and well below Tg (where the backbone configurations are essentially immobilised within the period of observation brittle materials). 

For brittle materials the stress-strain curves are almost linear up to the fracture point and the fracture strain is small, of the order of a few percentages. Figs. 13.74 and 13.75 show the tensile strain and flexural strength as functions of temperature for PMMA. At 10 °C the fracture strain increases, which points to a transition to ductile behaviour. The brittle... 

All experiments in this section were performed with a constant sample geometry of aAV = 0.5. As obvious from the section typical force-displacement curves", it was difficult to define unambiguously a single brittle-ductile transition four elementary materials behaviours involve three distinct ductile-brittle transitions ... 

Another feature that emerges here is the difference to be expected between brittle and extensible solids. For brittle materials, like glass, the transition from... 

Low-temperature embrittlement occurs in carbon and low-alloy steels at temperatures below their brittle-ductile transition temperature range. The effect is reversible when the alloy is heated above the transition range, ductility is restored. This embrittlement is avoided by following the Charpy impact test requirements of the relevant engineering codes. The need to test depends primarily on the material, its thickness and the minimum design temperature. 

Adding small amounts of reactive flexibilizers to an epoxy resin can reduce the modulus of elasticity, glass-transition temperature (Tg), and CTE of an otherwise hard and brittle material. Rubber-like materials such as a carboxyl-terminated... 

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