内容提要：
Magnesium is the fourth most common element on the
Earth and is a green material due to its lightweight, nontoxicity, and
recyclability. With two-thirds the density of aluminum, magnesium alloys are
the lightest metals that can be used for load-bearing structures. A wrought
magnesium alloy, either rolled or extruded, differs from a conventional metal
in two major aspects: deformation twins and material anisotropy. The current
presentation will cover characteristic cyclic deformation and fatigue behavior
observed on several typical wrought magnesium alloys (AZ31B, AZ61A, AZ90, ZK60)
under strain- and stress-controlled uniaxial, torsional, and combined
axial-torsion loading. For a given loading path under the fully reversed
strain-controlled condition, a distinguishable kink point in the strain-life
fatigue curve demarcates the involvement of twinning-detwinning deformation.
The influence of twinning is significant on fatigue behavior of a magnesium
alloy when the loading amplitude exceeds the kink point. Twinning-detwinning in
a magnesium alloy is often reflected in an asymmetric sigmoidal-shaped
stress-strain hysteresis loop during cyclic loading. As a result, there is a tensile or
compressive mean stress, dependent on the material orientation, under fully reserved
strain-controlled tension-compression loading. Cyclic twinning-detwinning
deformation leads to significant cyclic hardening particularly under
stress-controlled loading. Under pure shear loading, the stress-strain
hysteresis loops are symmetric although twinning-detwinning occurs at high
shear strain amplitudes. When a magnesium alloy is subjected to combined
axial-torsion loading, asymmetric shear stress-shear strain hysteresis loops
are observed due to alternative occurrence of twinning and detwinning with
reversed axial stress. No nonproportional hardening is observed on the
magnesium alloys but the fatigue life is reduced significantly under
nonproportional loading as compared to that under proportional loading with the
same equivalent strain magnitude. Material orientation- and amplitude-dependent
cyclic deformation and fatigue behavior of magnesium alloys will be presented
together with an assessment of the existing multiaxial fatigue criteria for the
application to the magnesium alloys. The crack growth characteristics of
magnesium alloys with the influence of twinning deformation and material
anisotropy will be briefly discussed.
报告人简介：
Yanyao Jiang is Professor in the Mechanical
Engineering Department at the University of Nevada, Reno (UNR). He received his B.S. degree in Mechanical
Engineering at the Northeast University in China in 1983, M.S. degree in Solid
Mechanics from the Zhejiang University in 1996, and Ph.D. degree in the
Department of Mechanical Engineering at the University of Illinois at
Urbana-Champaign in 1993. Professor
Jiang has made significant contributions in cyclic plasticity, fatigue and
fracture, rolling contact, and durability of bolted joints. His research work has led to an understanding
of the relationship between cyclic plasticity and fatigue failure. Professor
Jiang has done pioneering research on the inhomogeneous cyclic plastic
deformation and ratcheting deformation.
His approach for crack growth predictions bridges the crack initiation
stage and the crack growth stage in fatigue research.
Professor Jiang is an ASME Fellow. He was the recipient of the US NSF CAREER
award, the Ford University Research Program, the Alexander von Humboldt
Foundation Fraunhofer Bessel Research Award, and the Joint Research Fund for Overseas
Chinese Young Scholars from the National Natural Science Foundation of
China. He served as an Associate Editor
of the ASME Journal of Engineering
Materials and Technology and is a member of the Editorial Board for the International Journal of Plasticity and
the International Journal of Fatigue.
欢迎广大师生积极参听！
主办：研究生院
承办：牵引动力国家重点实验室
力学与工程学院
