Teoretická pevnost fcc krystalů v tahu předpovězená z výpočtů smykové pevnosti

The theoretical tensile strength of fcc crystals predicted from shear strength calculations

journal article in Web of Science

en

This work presents a simple way how to estimate the uniaxial tensile strength on the basis of the theoretical shear strength calculations taking its dependence on a superimposed normal stress into account. The presented procedure enables us to avoid complicated and time-consuming analyses of elastic stability of crystals under tensile loading. The atomistic simulations of coupled shear and tensile deformations in cubic crystals are performed using first principles computational code based on pseudo-potentials and plane wave basis set. Six fcc crystals are subjected to shear deformations in convenient slip systems and a special relaxation procedure controls the stress tensor. Obtained dependence of the ideal shear strength on the normal tensile stress seems to be almost linearly decreasing for all investigated crystals. Taking these results into account, the uniaxial tensile strength values in three crystallographic directions were evaluated by assuming a collapse of the weakest shear system. Calculated strengths for <100> and <111> loading were found to be mostly lower than previously calculated tearing stresses related to tensile instability but rather close to those obtained by means of the shear instability analysis. On the other hand, the strengths for <110> almost match the tearing stresses.

Tato práce prezenuje prostý způsob jak odhadnout pevnost v tahu na základě smykové pevnosti při uvážení vlivu normálového napětí na smykovou pevnost. Tato procedura nám umožňuje vyhnout se náročné analýze elastické stability krystalů při tahu. Atomistické simulace párované smykové a tahové deformace v kubických krystalech jsou provedeny s užitím prvoprincipiálních kodů založených na pseudo-potencialech rovinném bázovém souboru. Šest fcc crystals are subjected to shear deformations in convenient slip systems and a special relaxation procedure controls the stress tensor. Získaná závislost idealní smykové pevnosti na normalovém napětí v tahu se zdá být linearně klesající pro všechny zkoumané krystaly. Při zohlednění těchto výsledků byly spočteny hodnoty tahové pevnosti na základě předpokladu kolapsu krystalu v nejslabším smykovém systému. Pevnosti pro <100> a <111> zatížení jsou nižší než dříve spočtená apětí odpovídající smykové nestabilitě. Na druhou stranu, pevnosti v tahu <110> se s tahovými nestabilitami téměř shodují.

This work presents a simple way how to estimate the uniaxial tensile strength on the basis of the theoretical shear strength calculations taking its dependence on a superimposed normal stress into account. The presented procedure enables us to avoid complicated and time-consuming analyses of elastic stability of crystals under tensile loading. The atomistic simulations of coupled shear and tensile deformations in cubic crystals are performed using first principles computational code based on pseudo-potentials and plane wave basis set. Six fcc crystals are subjected to shear deformations in convenient slip systems and a special relaxation procedure controls the stress tensor. Obtained dependence of the ideal shear strength on the normal tensile stress seems to be almost linearly decreasing for all investigated crystals. Taking these results into account, the uniaxial tensile strength values in three crystallographic directions were evaluated by assuming a collapse of the weakest shear system. Calculated strengths for <100> and <111> loading were found to be mostly lower than previously calculated tearing stresses related to tensile instability but rather close to those obtained by means of the shear instability analysis. On the other hand, the strengths for <110> almost match the tearing stresses.

Teoretická pevnost, ab initio výpočty, smyková pevnost, fcc krystaly

Theoretical strength, ab initio calculations, shear strength, fcc crystals

2009

13.03.2009

0953-8984

Journal of Physics: Condensed Matter

21

14

145406–145406

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