The Fracture Characteristics of a Near Eutectic Al-Si Based Alloy Under Compression

The fracture of eutectic Si particles dictates the fracture characteristics of Al-Si based cast alloys. The morphology of these particles is found to play an important role in fracture initiation. In the current study, the effects of strain rate, temperature, strain, and heat treatment on Si particle fracture under compression were investigated. Strain rates ranging from 3 x 10(-4)/s to 10(2)/s and three temperatures RT, 373 K, and 473 K (100 A degrees C and 200 A degrees C) are considered in this study. It is found that the Si particle fracture shows a small increase with increase in strain rate and decreases with increase in temperature at 10 pct strain. The flow stress at 10 pct strain exhibits the trend similar to particle fracture with strain rate and temperature. Particle fracture also increases with increase in strain. Large and elongated particles show a greater tendency for cracking. Most fracture occurs on particles oriented nearly perpendicular to the loading axis, and the cracks are found to occur almost parallel to the loading axis. At any strain rate, temperature, and strain, the Si particle fracture is greater for the heat-treated condition than for the non-heat-treated condition because of higher flow stress in the heat-treated condition. In addition to Si particle fracture, elongated Fe-rich intermetallic particles are also seen to fracture. These particles have specific crystallographic orientations and fracture along their major axis with the cleavage planes for their fracture being (100). Fracture of these particles might also play a role in the overall fracture behavior of this alloy since these particles cleave along their major axis leading to cracks longer than 200 mu m.

Flow Characteristics and Its Friction Coefficient of Laminar Near-Wall Boundary Layer in Dusty Atmosphere

采用双向耦合的双流体模型,研究了大气悬浮沙尘的存在对大气边界层中层流底层流动特性及摩阻系数的影响,计算并讨论了不同沙尘含量下含尘大气相对于无尘大气摩阻系数的变化。结果表明：摩阻系数的变化取决于悬浮沙尘的初始运动状态和质量载荷率。

Thickness of the near-interface regions and central bulk ohmic resistivity in lead lanthanum zirconate titanate ferroelectric thin films

Thickness of the near-interface regions (NIR) and central bulk ohmic resistivity in lead lanthanum zirconate titanate ferroelectric thin films were investigated. A method to separate the low-resistive near-interface regions (NIRs) from the high-resistive central bulk region (CBR) in ferroelectric thin films was presented. Results showed that the thickness of the NIRs depended on the electrode materials in use and the CBR resistivity depended on the impurity doping levels.

Flow-Induced Vibrations Of A Cylinder With Two Degrees Of Freedom Near Rigid Plane Boundary

Based on similarity analyses, the flow-induced vibrations of a near-wall cylinder with 2 degrees of freedom are investigated experimentally by employing a hydroelastic apparatus in conjunction with a flume. The cylinder's vibration amplitude, vibration frequency and vortex shedding frequency were measured and analyzed. The effects of gap-to-diameter ratio (e,ID) upon the vibration responses are further investigated. The experimental results indicate that, when the reduced velocity (Vr) is small (e.g. Vr = 1.2 similar to 2.6), only streamwise vibration occurs, and its frequency is quite close to its natural frequency in still water. When increasing Vr (e.g. Vr > 3.4), both streamwise and transverse vibrations of the near-wall cylinder may occur. In the examined range of gap-to-diameter ratio (0.42 < e(0)/D < 2.68), 2 vibration stages (in terms of Vr) of streamwise vibrations usually exist: First Streamwise Vibration (FSV) and Second Streamwise Vibration (SSV). In the SSV stage, the vortex shedding frequency may either undergo a jump to that of the streamwise vibration, or stay consistent with that of the transverse vibration. The amplitudes of transverse vibration are usually much larger than those of streamwise vibration for the same value of e(0)/D. The maximum amplitudes of both streamwise and transverse vibration get larger with the increase of e(0)/D (0.42 < e(0)/D < 2.68).

Experimental Study on Flow Induced Vibration of a Cylinder with Two Degrees of Freedom Near a Rigid Wall

The flow-induced vibration of a cylinder with two degrees of freedom near a rigid wall under the action of steady flow is investigated experimentally. The vibration amplitude and frequency of the cylinder and the vortex shedding frequency at the wake flow region of the cylinder are measured. The influence of gap-to-diameter ratio upon the amplitude response is analyzed. The experimental results indicate that when the reduced velocity (Vr) is in the range of 1.2 < Vr < 2.6, only streamwise vibration with small amplitude occurs, whose frequency is quite close to its natural frequency in the still water. When the reduced velocity Vr > 3.4, both the streamwise and transverse vibrations of the cylinder occur. In this range, the amplitudes of transverse vibration are much larger than those of streamwise vibrations, and the amplitudes of the streamwise vibration also get larger than those at the range of 1.2 < Vr < 2.6. At the range of Vr > 3.4, the frequency of streamwise vibration undergoes a jump at certain values of Vr, at which the streamwise vibrating frequency is twice as much as the transverse one. However, when the streamwise vibration does not experience a jump, its frequency is the same as that of the transverse vibration. The maximum values of second streamwise and transverse vibration amplitudes increase with increasing gap-to-diameter ratios.