Fracture brittle/ductile

Maintaining Integrity of Machirtery, Plant and Structures Identification of causes and consequences of failure of components or structures main modes of causes and consequences of failure of materials metals and concrete main modes of failure fractures (brittle, ductile and fatigue) buckling corrosion wear main causes sources of stress stress concentrations environmental conditions material composition ... 

Hydraulic piston-type compactors for collection vehicles, on-site compactors, and transfer-station compactors roll crushers used to fracture brittle materials and to crush tin and aluminum cans and other ductile materials... 

Carpick, R.W., Enachescu, M., Ogletree, D.F. and Salmeron, M., Making, breaking, and sliding of nanometer-scale contacts. In Beltz, G.E., Selinger, R.L.B., Kim, K.-S. and Marder, M.P., (Eds.), Fracture and Ductile vs. Brittle Behavior-Theory, Modeling and Experiment. Materials Research Society, Warrendale, PA, 1999, pp. 93-103. 

Materials with a high yield stress tend to go through the ductile to brittle transition at higher temperatures. This property has led to the assumption that true brittle fracture, unlike ductile fracture, is not accompanied by the motion of dislocations. The validity of this assumption is sometimes confirmed by the appearance of brittle fractures, which show essentially no ductility. 

In addition to plastic deformation, materials may fail by either brittle fracture or ductile fracture fracture being the separation of a body into two or more parts. 

Impact modifiers for PET are generally elastomeric compounds that increase impact strength and elongation while usually decreasing modulus. An effective way to enhance the impact strength and to induce a brittle/ductile transition of the fracture mode, is by the dispersion of a rubber phase within the PET matrix. The... 

To complete the analysis of the fracture toughness the values of and Ic calculated from the maximum load and the energy for crack initiation are summarized in Fig. 52. It becomes obvious that the brittle-ductile transition, which... 

Besides deformation, fracture is the other response of materials to a stress. Fracture is the stress-induced breakup of a material. Two types of fracture are commonly defined. A brittle fracture is breakup which occurs abruptly without localized reduction in area. A ductile fracture is the failure of the material which is preceded by appreciable plastic deformation and localized reduction in area (necked region). The brittle fracture and ductile fracture are schematically illustrated in Fig. 1.10. 

Primary deformation Ductile Ductile Brittle fracture Brittle fracture... 

FIG. 13.60 Generalised tensile stress-strain curves for brittle and ductile plastics efib, y and W = strain at brittle fracture, at yield and at ductile fracture, respectively b, and fffd = ultimate strength at brittle fracture and ductile fracture, respectively yield strength ( ) fracture points ( ) yield point. 

By increase of the temperature the mode of failure is changed from brittle fracture to ductile fracture, characterised by the appearance of a yield point prior to fracture, and sometimes by indications of necking. 

Malleability and ductility These terms refer respectively to how readily a solid can be shaped by pressure (forging, hammering, rolling into a sheet) and by being drawn out into a wire. Metallic solids are known and valued for these qualities, which derive from the non-directional nature of the attractions between the kernel atoms and the electron fluid. The bonding within ionic or covalent solids may be stronger, but it is also directional, making these solids subject to fracture (brittle) when struck with a hammer, for example. A metal, by contrast, is more likely to be simply deformed or dented. 

Tihe brittle-ductile transition of metals as reported by Orowan (I) is explained on the basis that brittle fracture occurs when the yield stress exceeds a critical value. This is based on the Ludwik-Davidenkov-Orowan hypothesis that brittle fracture and plastic flow are independent processes yielding separate curves as a function of temperature and strain rate. Therefore, the operative deformation process is the one occurring at the lower stress. The intersection of the brittle stress and yield stress curves therefore defines the brittle-ductile transition. 

The fracture test on three-point-bend samples revealed that the fracture behavior of ABS remains ductile for temperatures above -80 °C at a crosshead speed of 5mm/min. The maximum fracture energy at crack initiation is also observed around -80 °C. Figure 27.20 shows that above this temperature, G, decreases continuously with increasing temperature. When the test speed is increased to lOOmm/min, the temperature at brittle ductile transition is shifted to about -40 °C as shown in Figure 27.21. At an impact velocity of 2.5 m/s, the brittle-ductile transition occurs at around -20 °C as shown in Figure 27.22. The results also confirm that the fracture energy at crack initiation is maximum at the brittle-ductile transition. 

With these limited experimental data, it can be nevertheless seen that the activation energy of the brittle-ductile transition is significantly lower than that of the glass transition of PBD and SAN. It is important to point out that the fundamental difference between DMTA and fracture tests is that DMTA only... 

The fact that the fracture is ductile, and not brittle, may give rise to... 

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