Brittle/ductile transition pressure

The CDM has two additional features that allow it to represent fracture in rocks. First, there is a brittle/ductile transition pressure. Above this pressure, the rock behaves as an elastic/plastic ductile solid, the failure surface is independent of the level of damage, and the damage is not allowed to increase, even if the failure surface is exceeded. Second, the CDM allows for non-vanishing plastic volume strain to approximate the dilatancy observed in certain laboratory experiments on oil shale. 

The Nil-Ductility Transition (NDT) temperature, which is the temperature at which a given metal changes from ductile to brittle fracture, is often markedly increased by neutron irradiation. The increase in the NDT temperature is one of the most important effects of irradiation from the standpoint of nuclear power system design. For economic reasons, the large core pressure vessels of large power reactors have been constructed of low carbon steels. 

When pressure tests are conducted at metal temperatures near the ductile-to-brittle transition temperature of the material, the possibility of brittle fracture shall be considered. 

Dual nickel, 9 820—821 Dual-pressure processes, in nitric acid production, 17 175, 177, 179 Dual-solvent fractional extraction, 10 760 Dual Ziegler catalysts, for LLDPE production, 20 191 Dubinin-Radushkevich adsorption isotherm, 1 626, 627 Dubnium (Db), l 492t Ductile (nodular) iron, 14 522 Ductile brittle transition temperature (DBTT), 13 487 Ductile cast iron, 22 518—519 Ductile fracture, as failure mechanism, 26 983 Ductile iron... 

To avoid brittle fracture during operation, maintenance, transportation, erection, and testing, good design practice shall be followed in the selection of fabrication methods, welding procedures, and materials for vendor furnished steel pressure retaining parts that may be subjected to temperature below the ductile-brittle transition point. 

The degree of fragmentation was found to diminish with smaller sieve fractions at the same compression load when several sieve fractions of unmilled crystalline a-lactose monohydrate was used. The authors concluded that particle fragmentation would reduce as porosity approached zero and elastic behavior would start to dominate the consolidation process (43). With a decrease in particle size, yield pressure decreased and the strain rate sensitivity index increased (44) which suggested a reduction in the extent of fragmentation. The transition from brittle to ductile material was thought to occur for a median particle size of around 20 pm (45). 

Based on the observations and discussions presented here, a relationship between burial diagenesis, rock properties and faulting in sandstones has been generated. This is displayed in Fig. 11. As shown in this figure, the depth at which sandstones behave ductile or brittle when deformed will depend on the cementation processes during the burial diagenesis. It should be noted, however, that other factors such as strain rate and pore pressure will have impact on the indicated transition between ductile and brittle properties of sandstones as presented in Fig. 11. 

Materials such as austenitic stainless steels, nickel-based alloys, and titanium alloys can be used as materials for pressure vessel components in cryogenic applications at temperatures as low as 200°C. Alloy steels have brittle transition points making their impact properties at low temperatures unsuitable for pressure applications. Closures and bolts must also be made of materials that remain ductile at low temperatures. 

D R Harries, R W Nichols and C Judge,The effect of neutron irradiation on the ductile-brittle transition temperature of steels and its relevance to reactor pressure vessels. Symposium on Steels for Reactor Pressure Circuits, Iron and Steel Institute Special Report, No 69,1961,297-327. 

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