题目：Microstructure-based models for simulation of short fatigue crack initiation and growth in 3-D，用于模拟疲劳短裂纹在三维空间萌生与生长的微观组织模型
The talk will begin with a brief review on our recent research activities including: 1) anomalous strain rate effect on ductility in Mo-Re alloys; 2) formation mechanism of an unusual texture in Al alloys; 3) formation mechanism of the high-temperature precipitation in 6000 Al alloys; and 4) 3-D effects of microstructure on fatigue crack initiation in engineering alloys, etc. The talk will then be focused on a microstructure-based model that has recently been developed to quantify short fatigue crack growth in 3 dimensions in planar slip alloys, such as high strength Al alloys and Ni-base superalloys, etc. The model takes into account both the local driving force and resistance in calculating short crack growth. The resistance of a gran boundary to short fatigue crack growth was characterized to be as a Weibull-type function of the twist angle of the crack plane deflection at the boundary, using an experimental technique newly developed in the author’s lab. The total resistance at a grain boundary is also contributed by all its neighboring grain boundaries as a normal distribution function of distance. The driving force for crack growth is the ΔK at the furthest point along the crack. The effective driving force is then this driving force minus the total resistance at each grain boundary along the crack front, and used in the modified Parisequation to quantify the growth behavior of the crack in 3 dimensions. This model has been verified by the surface growth rate of a short crack, measured experimentally, in an Al-Li alloy. The model could incorporate the effects of grain structure and texture in simulating the short fatigue crack growth. It shows that texture could significantly affect the life of a short fatigue crack. This model presents the potentials for more accurate prediction of the life of an engineering alloy and advancement of alloy design technology.
Tongguang Zhai:Currently tenured Associate professor in the Department of Chemical and Materials Engineering at University of Kentucky. He has been working in the research fields of alloy fabrication, characterization, mechanical properties, simulation, and failure analysis for well over 20 years.
Professor Zhai obtained his bachelor degree in metal physics from University of Science and Technology Beijing in 1983. He was a recipient of Sir Run Run Shaw Scholarship for his PhD study in Materials Science at University of Oxford. During his PhD study, he published 7 technical papers including four in Acta Materialia, one in Phil. Mag. A, one in J. of Physics B, and one in Materials Characterization (selected for the Best Technical Paper Award in 1993/4). He worked as a postdoctoral research fellow at Universityof Oxford and Universityof Kentucky, respectively, before he joined University of Kentucky as an Assistant Professor in 2001. He was a recipient of US-National Science Foundation CAREER Award, and promoted to a tenured Associate Professor in 2007. He has been the principal investigator of 14 research projects supported by US-NSF, DOD and materials industry, etc.
His main research interests include microstructure-based simulation of fatigue crack initiation and early growth; design and development of Al alloys, and relationships of microstructure and properties in engineering alloys, etc.
Significant scientific contributions and findings: identification of net irreversible slip accumulation in surface being the mechanism for fatigue crack initiation in pure metals; development of experimental methods 1) to characterize fatigue weak-link density and strength distribution in engineering alloys; and 2) to measure resistance of grain boundaries to fatigue crack growth; establishment of microstructure-based models for quantification of fatigue crack initiation and early growth; and identification of formation mechanisms for P texture in Al-Mn alloys and for αphase in 6000 series Al alloys, etc.