Lateral crack

By considering wear to occur by the intersection of subsurface lateral cracks which depend on the load and material properties, Evans and Wilshaw (1976) determined the volumetric wear rate, Vwean to be... 

The theory of Evans includes lateral crack formation and leads to an expression for the volume lost from the surface material per volume of the impacting particle, S, as follows ... 

Fig. 6.2.10. (a) A schematic diagram of the composite block illustrating the grain orientation and the indentations Q and R respectively, along and away from the bulk interface, a—a. (b) A schematic diagram of flow lines in the porous zone, pz, and radial, median and lateral cracks, rc, me and 1c respectively within the deformed zone. (After van der Zwaag et al., 1980)... 

The bulk densities of all the materials were determined using Archimedes method (AS 1774.5, 1979). The Vickers indentation technique was used to measure the hardness in each case. The applied load in the Vickers hardness tests was 10 kg for silicon nitrides and sialons. However, using the same load produced severe lateral cracking in silicon carbides around indents, which prevented the accurate measurement of the diagonals of indents. Therefore the load was reduced to 0.3 kg for silicon carbide samples. 

The best possible repair for a leak within a glass system is for the leak to be removed (see Fig. 7.66), the whole area to be heated and blown smooth, and, finally, the worked area to be flame-annealed to prevent later cracking. 

The three attrition mechanisms are in turn governed by different failure modes brittle, semibrittle, and ductile (Ghadiri, 1997). Brittle failure occurs when internal or surface cracks already exist and is dominant at low elastic deformation at the powder contact surface (Shipway and Hutchings, 1993). Semibrittle failure, at limited plastic deformation, is responsible for flaw initiation and occurs when the impact forces surpass the yield point. In fact, median and radial cracks cause particle fragmentation, and lateral cracks cause chipping. Soft materials are usually ductile and the mechanisms for particulate solids under ductile mode have not yet been elucidated (Ghadiri, 1997). 

Ghadiri et al. (1991) used SEM to study the impact damage on NaCl particles developed from different processing routes. Local plastic deformation phenomena leading to cracks, including lateral cracks, and flaw paths are illustrated in Ghadiri et al. (1991). Yan and Barbosa-Canovas (1997)... 

Submarine landslide (=s=98 million yd ) extending inland up to 500 ft along 6500 ft of coastline with an estimated depth of 200 ft, and distance traveled of several thousand feet. Lateral cracking reported up to 3600 ft behind coastline. Settlements up to 9 ft observed in dock area. Pumping observed in many basements... 

Figure 8.86 Schematic illustration of radial and lateral crack formation a) and b) no median crack nucleated c) radial cracks (R) form during unloading and d) lateral cracks (L) form close to complete unload.

Figure 8.87 Optical micrograph showing cracking at Vickers indentation in glass A is the radial crack surface trace B shows an interference pattern from the lateral crack below the surface and C is a spall produced by a lateral crack intersecting the surface. (Courtesy of Matt Chou.)...

Four microcrack morphologies may develop in a brittle solid after formation of the plastic zone beneath the indent median cracks, Fig. 9a, radial cracks (a halfpenny shaped elliptical crack Fig. 9b, much larger than the median crack), lateral cracks (in a plane normal to the median and radial cracks). Fig. 9c, and Palmqvist... 

Figure 9. Cracks formed during an indentation toughness test (a) median cracks (b) radial cracks (c) lateral cracks and (d) Palmqvist cracks. Reproduced with permission of.(3).

Upon unloading, the compressive stress normal to the surface reverses sign to become tensile, due to the previous irreversible plastic deformation beneath the indentor. If a suitable flaw is present, a lateral vent crack may be generated. This shallow crack can pop-in parallel to the surface and terminate subsequently at the surface to remove a flake of material. The lateral crack is larger the plastic zone, and may be larger that the radial cracks. 

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