Fatigue crack propagation characteristics of a diesel engine crankshaft are studied by measuring the fatigue crack growth rate using a frequency sweep method on a resonant fatigue test rig. Based on the phenomenon tha...Fatigue crack propagation characteristics of a diesel engine crankshaft are studied by measuring the fatigue crack growth rate using a frequency sweep method on a resonant fatigue test rig. Based on the phenomenon that the system frequency will change when the crack becomes large, this method can be directly applied to a complex component or structure. Finite element analyses （FEAs） are performed to calibrate the relation between the frequency change and the crack size, and to obtain the natural frequency of the test rig and the stress intensity factor （SIF） of growing cracks. The crack growth rate i.e. da/dN-AK of each crack size is obtained by combining the testing-time monitored data and FEA results. The results show that the crack growth rate of engine crankshaft, which is a component with complex geometry and special surface treatment, is quite different from that of a pure material. There is an apparent turning point in the Paris＇s crack partition. The cause of the fatigue crack growth is also discussed.展开更多
The influence of the magnetic field sweep rate on the hysteresis loops of exchange bias Ni0.8Fe0.2/Fe0.5Mn0.5 bilayers has been investigated with a vibrating sample magnetometer. It was found that the sweep rate of 13...The influence of the magnetic field sweep rate on the hysteresis loops of exchange bias Ni0.8Fe0.2/Fe0.5Mn0.5 bilayers has been investigated with a vibrating sample magnetometer. It was found that the sweep rate of 13.6 kA/4πms is high enough to bring about obvious changes in the hysteresis loops of the exchange bias bilayer. High sweep rate in the magnetization reversal stage enlarges the coercivity of the sample, while high sweep rate in the saturation state reduces the coercivity. The above phenomena were attributed to magnetic viscosity in the ferromagnetic layer enhanced by the interface exchange interaction and domain magnetization reversals assisted by thermal fluctuation in the antiferromagnetic layer respectively.展开更多
We study the effect of Landau-Zener （LZ） tunneling caused by the varying sweeping rate of the external field, and solve the problem about the LZ tunneling rate among many levels. The LZ tunneling rate is essentially...We study the effect of Landau-Zener （LZ） tunneling caused by the varying sweeping rate of the external field, and solve the problem about the LZ tunneling rate among many levels. The LZ tunneling rate is essentially changed by the unsteady variation of the time-dependent sweeping field and is different from the steadily varying sweeping field, which makes the particles in lower states transit periodically to upper states within a finite time.展开更多
基于均质油藏水驱油物理模拟实验,研究不同黏度均质油藏在不同采油速度下的水驱特征。低黏度油藏（黏度小于5 m Pa·s）水驱波及均匀,流线粗。随采油速度的提高,注水沿油层底部突进减弱,纵向波及更均匀,油层顶、底面波及系数差异减...基于均质油藏水驱油物理模拟实验,研究不同黏度均质油藏在不同采油速度下的水驱特征。低黏度油藏（黏度小于5 m Pa·s）水驱波及均匀,流线粗。随采油速度的提高,注水沿油层底部突进减弱,纵向波及更均匀,油层顶、底面波及系数差异减小。低黏度油藏高速开发无水期采出程度明显高于低速开发,含水上升速度低于低速开发,适宜高速开发模式。中高黏度油藏（黏度5~50 m Pa·s）水驱过程中注入水表现出明显的指进现象,水驱流线细,水驱波及不完全,流线间波及程度弱,油层顶、底面波及系数差异大。随采油速度的提高,中高黏度油藏水驱流线更细,波及更不完全,油层顶、底面波及系数明显降低。中高黏度油藏高速开发见水时间短,无水期采出程度明显低于低速开发,含水上升速度高于低速开发,不适合高速开发。展开更多
文摘Fatigue crack propagation characteristics of a diesel engine crankshaft are studied by measuring the fatigue crack growth rate using a frequency sweep method on a resonant fatigue test rig. Based on the phenomenon that the system frequency will change when the crack becomes large, this method can be directly applied to a complex component or structure. Finite element analyses （FEAs） are performed to calibrate the relation between the frequency change and the crack size, and to obtain the natural frequency of the test rig and the stress intensity factor （SIF） of growing cracks. The crack growth rate i.e. da/dN-AK of each crack size is obtained by combining the testing-time monitored data and FEA results. The results show that the crack growth rate of engine crankshaft, which is a component with complex geometry and special surface treatment, is quite different from that of a pure material. There is an apparent turning point in the Paris＇s crack partition. The cause of the fatigue crack growth is also discussed.
文摘The influence of the magnetic field sweep rate on the hysteresis loops of exchange bias Ni0.8Fe0.2/Fe0.5Mn0.5 bilayers has been investigated with a vibrating sample magnetometer. It was found that the sweep rate of 13.6 kA/4πms is high enough to bring about obvious changes in the hysteresis loops of the exchange bias bilayer. High sweep rate in the magnetization reversal stage enlarges the coercivity of the sample, while high sweep rate in the saturation state reduces the coercivity. The above phenomena were attributed to magnetic viscosity in the ferromagnetic layer enhanced by the interface exchange interaction and domain magnetization reversals assisted by thermal fluctuation in the antiferromagnetic layer respectively.
基金Project supported by the National Natural Science Foundation of China (Grant No. 20804039)the Natural Science Foundation of Zhejiang Province of China (Grant No. Y4080300)
文摘We study the effect of Landau-Zener （LZ） tunneling caused by the varying sweeping rate of the external field, and solve the problem about the LZ tunneling rate among many levels. The LZ tunneling rate is essentially changed by the unsteady variation of the time-dependent sweeping field and is different from the steadily varying sweeping field, which makes the particles in lower states transit periodically to upper states within a finite time.
文摘基于均质油藏水驱油物理模拟实验,研究不同黏度均质油藏在不同采油速度下的水驱特征。低黏度油藏（黏度小于5 m Pa·s）水驱波及均匀,流线粗。随采油速度的提高,注水沿油层底部突进减弱,纵向波及更均匀,油层顶、底面波及系数差异减小。低黏度油藏高速开发无水期采出程度明显高于低速开发,含水上升速度低于低速开发,适宜高速开发模式。中高黏度油藏（黏度5~50 m Pa·s）水驱过程中注入水表现出明显的指进现象,水驱流线细,水驱波及不完全,流线间波及程度弱,油层顶、底面波及系数差异大。随采油速度的提高,中高黏度油藏水驱流线更细,波及更不完全,油层顶、底面波及系数明显降低。中高黏度油藏高速开发见水时间短,无水期采出程度明显低于低速开发,含水上升速度高于低速开发,不适合高速开发。
