An improved understanding of fatigue behavior of a cast aluminum alloy（2-AS5U3G-Y35）in very high cycle regime is developed through the ultrasonic fatigue test in axial and torsion loading.The new developed torsion f...An improved understanding of fatigue behavior of a cast aluminum alloy（2-AS5U3G-Y35）in very high cycle regime is developed through the ultrasonic fatigue test in axial and torsion loading.The new developed torsion fatigue system is presented.The effects of loading condition and frequency on the very high cycle fatigue（VHCF）are investigated.The cyclic loading in axial and torsion at 35 Hz and 20 kHz with stress ratio R=-1 is used respectively to demonstrate the effect of loading condition.S-N curves show that the fatigue failure occurs in the range of 105—1010 cycles in axial or torsion loading and the asymptote of S-N curve is inclined,but no fatigue limit exists under the torsion and axial loading condition.The fatigue fracture surface shows that the fatigue crack initiates from the specimen surface subjected to the cyclic torsion loading.It is different from the fatigue fracture characteristic in axial loading in which fatigue crack initiates from subsurface defect in very high cycle regime.The fatigue initiation is on the maximum shear plane,the overall crack orientation is on a typical spiral 45° to the fracture plane and it is the maximum principle stress plane.The clear shear strip in the torsion fatigue fracture surface shows that the torsion fracture is the shear fracture.展开更多
Across-wind loads and effects have become increasingly important factors in the structural design of super-tall buildings and structures with increasing height. Across-wind loads and effects of tall buildings and stru...Across-wind loads and effects have become increasingly important factors in the structural design of super-tall buildings and structures with increasing height. Across-wind loads and effects of tall buildings and structures are believed to be excited by inflow turbulence, wake, and inflow-structure interaction, which are very complicated. Although researchers have been focusing on the problem for over 30 years, the database of across-wind loads and effects and the computation methods of equivalent static wind loads have not yet been developed, most countries having no related rules in the load codes. Research results on the across-wind effects of tall buildings and structures mainly involve the determination of across-wind aerodynamic forces and across-wind aerodynamic damping, development of their databases, theoretical methods of equivalent static wind loads, and so on. In this paper we first review the current research on across-wind loads and effects of super-tall buildings and structures both at home and abroad. Then we present the results of our study. Finally, we illustrate a case study in which our research results are applied to a typical super-tall structure.展开更多
基金Supported by the National Natural Science Foundation of China(50775182)the Scientific Research Foundation for the Returned Scholars of the Ministry of Education of China~~
文摘An improved understanding of fatigue behavior of a cast aluminum alloy（2-AS5U3G-Y35）in very high cycle regime is developed through the ultrasonic fatigue test in axial and torsion loading.The new developed torsion fatigue system is presented.The effects of loading condition and frequency on the very high cycle fatigue（VHCF）are investigated.The cyclic loading in axial and torsion at 35 Hz and 20 kHz with stress ratio R=-1 is used respectively to demonstrate the effect of loading condition.S-N curves show that the fatigue failure occurs in the range of 105—1010 cycles in axial or torsion loading and the asymptote of S-N curve is inclined,but no fatigue limit exists under the torsion and axial loading condition.The fatigue fracture surface shows that the fatigue crack initiates from the specimen surface subjected to the cyclic torsion loading.It is different from the fatigue fracture characteristic in axial loading in which fatigue crack initiates from subsurface defect in very high cycle regime.The fatigue initiation is on the maximum shear plane,the overall crack orientation is on a typical spiral 45° to the fracture plane and it is the maximum principle stress plane.The clear shear strip in the torsion fatigue fracture surface shows that the torsion fracture is the shear fracture.
基金supported by the National Natural Science Foundation of China (Grant Nos. 90715040, 50878159)
文摘Across-wind loads and effects have become increasingly important factors in the structural design of super-tall buildings and structures with increasing height. Across-wind loads and effects of tall buildings and structures are believed to be excited by inflow turbulence, wake, and inflow-structure interaction, which are very complicated. Although researchers have been focusing on the problem for over 30 years, the database of across-wind loads and effects and the computation methods of equivalent static wind loads have not yet been developed, most countries having no related rules in the load codes. Research results on the across-wind effects of tall buildings and structures mainly involve the determination of across-wind aerodynamic forces and across-wind aerodynamic damping, development of their databases, theoretical methods of equivalent static wind loads, and so on. In this paper we first review the current research on across-wind loads and effects of super-tall buildings and structures both at home and abroad. Then we present the results of our study. Finally, we illustrate a case study in which our research results are applied to a typical super-tall structure.
