Shear fractures

Aksoy, A. and Carlsson, L.A. (1992). Interlaminar shear fracture of interleaved graphite/epoxy composites. Composites Sci. Technoi. 43, 55-69. 

Under the title Shear Fracture, Cook (Ref 4, p 346) noted that under conditions in which the tensile forces cannot develop or are restricted, a type of fracturing that can be associated with trajectories of maximum shear stress may develop. Rinehart 8t Pearson (Ref 1) detonated a 1/8 inch layer of expl on the cylindrical surface of a 2)4 inch OD aluminum (24S-T) cylindrical block with a 3/4 inch cylindrical relief hole drilled thru the longitudinal axis. The shock wave moving in toward the relief hole developed at each point of the block two mutually orthogonal trajectories of maximum shear stress. The trajectories, where the shear stress was maximal, spread out in 8 to 12 curved continuous lines from points on the surface of the relief hole. The shear fraction patterns observed along trajectories of maximum shear resembled the "Luder s... 

Figure 7.64 shows a failed bolt where the failure surface is investigated by SEM at 1000 magnification. The observed dimples are relatively shallow with respect to the surface and oblique. The presence of inclusions as in (A), characteristic of this type of steel that initiate dimples. The shape and orientation of dimples can be used to indicate the direction and application of load as well as the degree of ductility of the samples. In this case, as the dimples are parallel to the direction of fracture, this was classified as a shear fracture. 

How finishing temperature affects the Figure 5.13 Long distance rupturing of pipe tested Charpy V-notch 50% shear fracture- wjth aagii... 

Dr op weight tear testing on a 20 In. (50 a mm) dimeter and larger pipe shall be carried out at 32 F (oaC) in accordance with Appendix SR-6 of API 5L however, igg percent Of the heats shall exhibit 85 percent or more shear fracture area. 

The aim was to investigate deep chert-haematite-bearing veins and fractures. The fractures below 100 m are nearly completely cemented (shallower ones are filled with deep ground water and were not investigated in this study). It is possible to distinguish two types of fractures wide shear fractures several centimetres in diameter filled with breccia of the surrounding host rock cemented by fine-grained haematite and disseminated chert, and fractures 1 mm-1 cm wide with a clear zonation of... 

In a final chapter a closely related phenomenon, the formation of shear bands in semi-crystalline polymers under compressive load will be described. It is attempted to discuss under which conditions shear bands are formed in semi-crystalline materials and how they interact with each other or with certain microstructural features, finally leading to crack initiation and shear fracture of the bulk polymer. 

Fig, 37a—d. Structure of shear fracture surface a SEM-micrograph of a shear fracture in PP 1120 (T = —80 °C) b secondary crack formation (white arrow) in one of the shear bands of type B in fine spherulitic PB-l (T = -196 °C) c traces of shear bands B containing fibrillated polymer substance on a shear fracture plane in fine spherulitic PP 1120 (T = —196 °C) d preferred shear fracture along spherulite boundaries (SB) of coarse spherulitic PP 1120 (T = —80 °C)... 

Further fracture surface features, especially distinct for the highly isotactic, coarse spherulitic PP, are polyhedron shaped regions at which the shear crack has left the shear fracture plane in order to stay in a spherulitic boundary region oriented at a flat angle to the sliding direction (Fig. 37d). These sites often constitute secondary crack nuclei in boundaries perpendicular to the shear fracture plane. 

In comparing the shear fracture surfaces of amorphous and semi-crystalline polymers, it appears that the features in both cases are quite similar (Fig. 39a -c ). This indicates that, under comparable conditions, the local stress field rather than details of the crystalline-amorphous microstructure of the polymers tested determines the operating deformation mechanism. Only secondary effects arise from the morphology of the cry stalline material. 

Fig. 14. Optical micrograph of a thinned section showing the fracture subsurface. One half of the shear band pairs can be seen along the initial fracture subsurface (top left) and the transition to shear fracture at 45° to the craze plane can be seen (rigJjt)...

Fig. 28. An optical micrograph of a thinned section showing a partially fatigued sample showing plane-strain shear fracture. Reprinted courtesy of Matsumoto ...

PC shows either craze or shear behavior, with no mixed behavior, i.e., successively regenerated localized DCG zones. There is a sharp transition between the craze and the shear branches, as seen in Fig. 35. The competition between crazing and shear is temperature and stress sensitive. The mode, once determined, persists as the barrier is high between these two modes. At 75 °C and above, no craze-crack growth is observed, although shear fracture does persist down to —25 °C, albeit only at high stresses. 

In PEI (Fig. 37), the shear fracture process never fully develops (under the tested conditions). A mixed mode develops, with some elements of shear fracture, but without the epsilon plane strain shear bands, a true 45° shear fracture process cannot develop. The lifetime enhancement is not as substantial, as seen in PC and PEC. 

Wang, Y. and J.G. Williams, Corrections for mode II fracture toughness specimens of composite materials. Composites Science and Technology, 1992. 43 p. 251-256. O Brien, T.K., Composite interlaminar shear fracture toughness, Gnc Shear measurement or sheer myth in Composite Materials Fatigue and Fracture 7. 

Fracturing by Shear in Detonation. See Shear Fracture in Vol 4, p D544-R. The method has... 

Loosveld, R.J.H. and Franssen, R.C.M.W. 1992. Extensional versus shear fractures - implications for reservoir characterisation. SPE.250I7. 

Both mode I (tensile) and mode II (shear) fractures are commonly generated in sedimentary rocks during burial and uplift, and it is well established that the horizontal stresses (o and a ) as a function of burial and loading alone are related to the vertical stress according to... 

The alluvial and fluvial strata were flooded by meteoric pore water and got cemented prior to faulting. While clay smear and intergranual shear fractures dominate in fine-grained and poorly cemented intervals (Fig. 7a), well cemented intervals cut by faults display fault gouges characterized by brecciation and granulation (Fig. 7b). Within these (brittle) fault... 

The exposed fault structures are very similar to the deformation bands as described by Antonellini and Aydin (1994) and Fowles and Burley (1994). Numerous, sub-parallel shear fractures up to ca. 10 mm thickness have developed fault zones up to 5 m wide. Displacements are in the millimetric scale for each individual band, adding up to a maximum of ca. 100 m for the fault zones. Based on isotope data of fault abundant quartz cement, the minimum depth at which faulting occurred has been estimated to ca. 3000 m (Fig. 8). 

The main micro-scale controls on dilatancy during shear failure in shales can be described by considering the processes taking place in a stressed rock element. Strain begins to localise in the sample at peak differential stress and this leads to the formation of undulating shear zones (shear fractures). Sliding on... 

Cored Upper Jurassic claystones from a well located within the Lindesnes trend display both dila-tional and shear fractures (Fig. 9). Although both shear and dilational fractures can be produced by hydraulic fracturing (Lockner and Byerlee, 1977), the location of this well within a major wrench zone suggests tectonic breaching as the most likely cause. 

SEM observations showed that fracture surface of the HPT-processed Ti tested at room temperature has the dimpled surface typical for many nanomaterials, but after annealing the dimples looked lager and their orientation in the direction of shear fracture was observed [9],... 

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