Fracture and Failure

A bolt fails when it can no longer provide the support it is designed for. Fracture is the separation of a solid body into two or more parts under the action of stress. It consists of crack initiation and propagation. 

Brittle fracture in metals is characterized by a rapid rate of crack propagation, with no gross deformation and very little microdeformation. This is demonstrated by cleavage. Brittle fracture can occur without warning. Cleavage fracture exhibits little or no plastic deformation and occurs along well-defined crystallographic planes. 

A dimple is a concave depression on the fracture surface resulting from microvoid growth in coalescence. As a result of the state of stress during fracture, the dimple may be elongated, oval or equiaxed. 

The average composition of Swellex bolts is given in Table 7.5. 

Metallographic analysis allows the determination of the surface reduction along the fracture and defines the fragile or ductile nature of the fracture. By employing a longitudinal section, it was possible to evaluate the magnitude of corrosion close to the surface of the fracture. 

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Bucknall, C. B. Fracture and Failure of Multiphase Polymers and Polymer Composites. Vol. 27, pp. 121-148. 

In general, the use of FE signals accompanying the deformation and fracture of composites offer elucidation of failure mechanisms and details of the sequence of events leading upto catastrophic failure. The extent of interfacial failure and fiber pull-out are also potential parameters that can be determined. FE can assist in the interpretation of AE and also provide an independent probe of the micro-events occurring prior to failure. FE has been shown to be sensitive to the locus of fracture and efforts are underway to relate emission intensity to fracture mechanics parameters such as fracture toughness (Gjp). Considerable work still remains to fully utilize FE to study the early stages or fracture and failure modes in composites. 

Very recently, attempts have been made to develop PP/EOC TP Vs. In order to make TPVs based on PP/EOC blend systems, phenolic resin is ineffective because the latter needs the presence of a double bond to form a crosslinked network structure. Peroxides can crosslink both saturated and unsaturated polymers without any reversion characteristics. The formation of strong C-C bonds provides substantial heat resistance and good compression set properties without any discoloration. However, the activity of peroxide depends on the type of polymer and the presence of other ingredients in the system. It has been well established that PP exhibits a (3-chain scission reaction (degradation) with the addition of peroxide. Hence, the use of peroxide only is limited to the preparation of PP-based TPVs. Lai et al. [45] and Li et al. [46] studied the fracture and failure mechanism of a PP-metallocene based EOC based TPV prepared by a peroxide crosslinking system. Rajesh et al. 

Most studies identify three critical properties in the quality of meat and its products. These dimensions are toughness/tendemess, juiciness/dryness, and of course flavour. The first two of these are obviously materials properties related to the architecture of the product, and its subsequent fracture and failure modes. Attempts to match these attributes to simple physical tests proves successful provided that the range of specimens have similar architecture. 

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