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Elastoviscoplasticity

The elasto viskoplastic rheological model consisits of a slider and a dashpot in parallel and this combination is in series whit a Hookean spring. Fort he uniaxial model the behaviour is purely elastic until the stress exceeds the yield stress . Onece in the plastic region the viscous component becomes active and for raidly applied loads the stress can exceed the pşastic limit. If unloading takes place form the yielded state the strain path followed is different form that of loading and permanent deformation takes place. Elastoviskoplastic behaviour is also loading path dependent since it has been demonstrated by experiments that if two loading paths reach the same point on the yield surface by different routes .

(The Finite element method in heat transfer analysis ; Roland Wynne Lewis ; pg.198 , 1996)

Grain boundary strengthening

In fcc lattices the dislocat,ons glide in (111) planes which do end at grain boundaries . If there are large orientation differences between neighbouring grains a group of moving dislocations in grain 1 will be stopped at the boundary and the deformation in the neighbouring grain 2 can continue only after another dislocation has been nucleated in that grain . This stress concentration is proportional to the external stress multipled by the number of dislocations in the pile-up . the latter depends on the external stress and the grain size .

(Structure and structure development of Al-Zn alloys ; Hans Löffler, D. Bergner ; pg 163 , 1995)

Grain boundary sliding

Grain boundary sliding a the deformation mechanism that effectively oprates and competes with both the conventional lattice dislocation slip and diffusunonal deformation odes in nanocrystalline materials with the dislocation slip and diffusional deformation modes in nanocrystalline materials with the the fines grains. Grain boundary sliding means a relative shear of neighboring grains that is localized in boundaries between the grains. Comonly grain-boundary sliding occurs in high angle grain boundaries in coarse-grained and nanocrystalline solids .In particular ,the sliding along grain boundaries whit translationally ordered structures can be effectively conducted by movement of sliding grain boundary dislocations.

(Structural nanocrystalline materials: fundamentals and applications ; C. C. Koch; pg 232; First Edition)

Policrystaline Cubic Boron Nitride

PCBN is next to diamond on the hardness scale it is used in the manufacturing industry as a super hard abrasive tool and as a cutting tool. As a cutting tool PCBN is most commonly used for the manhining of hardned of steels , tool steels , hard cast irons , and hardfaceing alloys.

Solid PCBN cutting tool materials exhibit an exectionally high value of thermak conductivity which is about the same as c-8 or k-10 tungsten carbides have , and about 4-5 times higher than for ceramic cutting tool material.

(Cutting Data for Turning of Steel ; Edmund Isakov ; pg 119 ;2007)