Grain sliding

One scenario in which thin shear layers and large shear strains can occur in plastic-bonded explosives is at the interface between grains sliding past one another or along closed cracks within a grain. These processes have been postulated by Dienes [48] as the dominant dissipative mechanism for generating hot spots in plastic-bonded explosives, and have been incorporated into the Statistical Crack Mechanics (SCRAM) model for high-explosive response. 

The wear situation is likely to be aggravated should hard additives of a coarser grain fraction be embedded in a softer matrix, such as clay, as the result of an upstream kneading process. This may lead to grain sliding wear (besides a two-body and even a proper three-body abrasive wear), which could, in the absence of an intermediate lubricating medium, have drastic consequences. Similarly, lack of an intermediate medium will favour any likely adhesive wear. 

Microscope appearance. Place a small amount of dry starch on a microscope slide, add a drop of water, cover with a slip and examine under the microscope. Characteristic oval grains are seen which have concentric rings round a hilum which is towards one end of the grain. Run a drop of very dilute iodine solution under the slip from a fine dropping-tube the grains become blue. 

A series of events can take place in response to the thermal stresses (/) plastic deformation of the ductile metal matrix (sHp, twinning, cavitation, grain boundary sliding, and/or migration) (2) cracking and failure of the brittle fiber (5) an adverse reaction at the interface and (4) failure of the fiber—matrix interface (17—20). 

Sereen-plate. separators. These include a metal slide at ground potential that is extended with a conducting screen of suitable screenopening size to allow easy passage of the largest grains being treated, A stationary electrode is placed above the slide and screen sections as... 

More distinct regularities observed in the Al-phase allow us to distinguish dislocation slips expressed by the movement of orientation peaks along the fibres from the grain boundary sliding responsible for the smoothing effects and thus for the superplasticity of the alloy... 

There apparently exists a critical amount of liquid phase for the optimization of grain/interface boundary sliding during superplastic deformation. The optimum amount of liquid phase may depend upon the precise material composition and the precise nature of a grain boundary or interface, such as local chemistry (which determines the chemical interactions between atoms in the liquid phase and atoms in its neighboring grains) and misorientation. The existence of an equilibrium thickness of intergranular liquid phase in ceramics has been discussed [14]. This area of detailed study in metal alloys has not been addressed. 

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