Prof. Zhuo Zhuang [from Tsinghua University]

Title: Investigation on Dislocation Mechanism inCrystal Plasticity at Submicron Pillars

Time: 14:00 - 15:00, November 17

Place: Conference Room 201, Building 6, HPSTAR (Shanghai)

Host: Bin Chen

Abstract:

Recently, some interest results are obtainedfor uniaxial compression experiments conducted on FCC single crystal metallicmicro-pillars, e.g. size effect and strain burst, etc. In these experiments,the surfaces are transmissible and loading gradients are absent. The mobiledislocations may escape from the free surface leading to the state ofdislocation starved whereby an increase in the applied stress is necessary tonucleate or activate new dislocation sources. This dislocation-escape inducedstrengthening is called dislocation starvation hardening. With the developmentof in-situ experiments, the viability and efficiency of dislocation starvation mechanismare verified. However, the size effect and temporal-spatial intermittency ofsingle-crystal plasticity observed by experiments remains mysterious. Our groupdevelops a unified computational model which directly combines 3D DDD andFinite Element (FEM) continuum mechanics. This coupling model is built on thatDDD methodology serves as a material constitutive law and based on the finitedeformation theory of crystal plasticity.
As an application, the deformation of micro-pillar under uniaxial compressionis predicted. The results show that mobile dislocation exhaustion hardening isthe main mechanism for flow intermittency and stress heterogeneity inside thecrystal plays a key role in the observed strain hardening. The compressionstress-strain curve of Cu single-crystal micro-pillar can be divided into threedistinct stages: a linear elastic stage, a normal strain hardening stage, and adislocation starvation induced hardening stage accompanying a rather highstress level. At last, a perfect dislocation-free pillar is obtained. Inaddition, the single arm source (SAS) controlled plastic flow is alsoextensively investigated by a statistically-based theoretical model and 3D DDDmethod.

Biography of the Speaker:

ZHUANG, Zhuo, Professor, Tsinghua University. Ph.D at Dept. of CivilEngineering, University College Dublin, Ireland (1995). Published more than 240papers (90 SCI and 50 EI cited) at International and National Journals.Published 16 books in Chinese and 1 book in English: Extended Finite ElementMethod (Elsevier/Tsinghua Press). IACM General Council member; APCOM GeneralCouncil member. Vice-director of Supervise Committee on Mechanics Discipline,Ministry of Education, China. President of Computation Mechanics Committee ofChinese Mechanics Society.