Multiscale mechanics for the study of high strength and high ductility nanomaterials
J.Lu1, L.L.Zhu2,H.L.Chan1, A.Y.Chen2, H.N.Kou1
1. Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Kowloon, Hong Kong, China
2. Department of Mechanical Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China
The ability to create structural materials of high yield strength and yet high ductility has been a dream for materials scientists for a long time. This talk will summarize the recent work related to the study of the mechanical behavior of the surface nanostructured materials using SMAT (Surface Mechanical Attrition Treatment). Significant enhancements in mechanical properties of the nanostructured surface layer in different materials will be analyzed. The effect of surface nanostructures on the mechanical behavior and on the failure mechanism of metallic material shows the possibility to develop a new strength gradient composite. The nanoindentation method is developed for the investigation of the gradient structures.The role of the residual stress is studied. The results shown that the compressive residual stress is one of the key mechanisms for the enhancement and the extraordinary properties of layered nanostructured metallic stainless steel sheet.Finally, some new results of the simulations will be presented and discussed. The simulation of SMAT process using the finite element methods will be compared with the experimental investigation using high speed camera. The computational models successfully simulate the enhanced ductility and strength and provide valuable information about the mechanical behavior of nanostructured layered composite material.
(1) Y.P.Cao, J.Lu, A new method to extract the plastic properties of metal materials from an instrumented spherical indentation loading curve,ActaMaterialia, 52 (13): 4023-4032 AUG 2 2004
(2) Y.P.Cao, J.Lu, Size-dependent sharp indentation-I: A closed-form expression of the indentation loading curve,Journal of the Mechanics and Physics of Solids, Jan. 2005, vol. 53, pp33-48
(3) J.C.Ye, J.Lu, C.T.Liu, Q.Wang, Y.Yang, Atomistic Free-Volume Zones and Inelastic Deformation of Metallic-Glasses Characterized by High-Frequency Dynamic Micropillar Tests,Nature Materials, Volume 9, Issue 8, August 2010, Pages 619-623
(4) A.Y.Chen, H.H.Ruan, J.Wang, H.L.Chan, Q.Wang, Q. Li, J.Lu, The influence of strain rate on the microstructure transition of 304 stainless steel,ActaMaterialia, Volume 59, Issue 9, May 2011,\ pages 3697-3709
(5) L.L.Zhu, H.H.Ruan, X.Y.Li, M.Dao, H.J.Gao,J.Lu, Modeling grain size dependent optimal twin spacing for achieving ultimate high strength and related high ductility in nanotwinned metals,ActaMaterialia, Volume 59, Issue 14, August 2011, Pages 5544-5557
(6) L.L.Zhu,J.Lu,Modelling the plastic deformation of nanostructured metals with bimodal grain size distribution,International Journal of Plasticity,March 2012,Volumes 30–31, Pages166-184
Prof. J.LU isChair Professorand Dean ofCollegeofScienceand Engineeringat City University of Hong Kong.Hecommenced his undergraduate education in 1978 atPekingUniversitywhere he was selected for a national scholarship for overseas study in 1979. He obtained the Dip. Ing., Master degree(DEA)and Doctoral degree(Ph.D)fromUTC(Compiegne)Francein 1984 and 1986 respectively. He obtained the Habilitation from theUniversityParis6 (UPMC)in 1993. In 1994, he was appointed as Professor,Head of Department of Mechanical Systems Engineering and Director of Mechanical Systems and Concurrent Engineering Laboratory jointly supported by the French Ministry of Education and CNRS at theUniversityofTechnologyofTroyes,France.From December 2005 to August 2010, he was appointed as Chair Professor and Head of Department of Mechanical Engineering at The Hong Kong Polytechnic University.His research interests are:mechanicsof advancedstructuralmaterials,experimental mechanics and residual stress.He has published more than 220 SCI journal papersincludingScience, Nature Materials,PRL,JMPS, ActaMaterialia, IJNME.He was elected as aFellowofthe Society for Experimental Mechanics (USA)andnominatedby the French Government in2006 intheOrder of National Merit (Knight).