Corner forming of AZ61A magnesium alloy tube within warm hydroforming

The corners with small radii on cross sections are crucial for forming hydroformed components with polygonal sections.In this paper,warm hydroforming experiments of AZ61A magnesium alloy tubes were carried out to study the forming regularity of round corners by using a demonstration part with square sections.Effects of temperature on radius forming,thinning ratio distribution and microstructure were revealed and a component with relative outer corner radius of 3.0 was obtained by warm hydroforming at 240℃.The minimum thickness of the formed square section was located in the transition position between the corner and the straight wall.The thinning ratio of the round corner increased with the increase of forming temperature.Formability of the magnesium tube was improved by raising temperature under the effect of dynamic recrystallization at 240℃.     

A sink moving scheme based on local residual energy of nodes in wireless sensor networks

In the application of periodic data-gathering in sensor networks, sensor nodes located near the sink have to forward the data received from all other nodes to the sink, which depletes their energy very quickly. A moving scheme for the sink based on local residual energy was proposed. In the scheme, the sink periodically moves to a new location with the highest stay-value defined by the average residual energy and the number of neighbors. The scheme can balance energy consumption and prevent nodes around sink from draining their energy very quickly in the networks. The simulation results show that the scheme can prolong the network lifetime by 26%–65% compared with the earlier schemes where the sink is static or moves randomly. Foundation item: Project(60673164) supported by the National Natural Science Foundation of China; Project(20060533057) supported by the Specialized Research Foundation for the Doctoral Program of Higher Education of China     

考虑冷变形加工硬化的翻边力理论计算

在分析现有计算公式存在不足的基础上,根据翻边变形区材料的应力应变特点,考虑了冷变形加工硬化(取幂函数硬化规律)和变形区材料厚度变化(翻边为变薄)两个因素的影响,利用金属塑性成形问题求解理论中的主应力法,推导和提出了圆孔翻边力计算的一个新公式.通过用钢板(SPCC)和铜板(T1)进行了翻边工艺试验的验证,并与经验公式和现有理论公式的计算结果进行了比较,表明新公式计算结果能接近于实际,且原理上更为科学合理.     

Characteristics of shell thickness in a slab continuous casting mold

The key to reduce shell breakout in the continuous casting process is to control shell thickness in the mold.A numerical simulation on the turbulent flow and heat transfer coupled with solidification in the slab mold using the volume of fluid (VOF) model and the enthalpy-porosity scheme was conducted and the emphasis was put upon the flow effect on the shell thickness profiles in longitudinal and transverse directions.The results show that the jet acts a stronger impingement on the shell of narrow face,which causes a zero-increase of shell thickness in a certain range near the impingement point.The thinnest shell on the slab cross-section locates primarily in the center of the narrow face,and secondly near the comer of the wide face.Nozzle optimization can obviously increase the shell thickness and make it more uniform.     

基于灰色残差GM（1，1）模型的建筑物沉降预测的研究

针对现代高层建筑进行沉降观测,对其未来的变形趋势进行准确地预测具有重要的意义。针对传统灰色GM（1,1）模型存在的模型精度不高的问题,提出了灰色残差GM（1,1）模型,并将其应用于对建筑物的沉降变形进行定量分析。通过与原始模型的对比分析可以发现,灰色残差模型在精度上有了显著的提高,更加适用于基础沉降的预测,具有很好的工程应用价值。     

激光冲击LY2铝合金的薄膜性能

脉冲激光冲击LY2铝合金,在试样表面形成约1.7mm的薄膜,研究了薄膜与基体接合处横截面的微观形貌以及激光冲击搭接率和激光冲击次数对薄膜层残余应力的影响。研究结果表明:激光冲击的光斑搭接率对试样横截面的残余应力影响显著;在薄膜层最大残余应力存在于试样的表层或者近表层,深度方向的残余应力值和残余压应力值变化率均与表层深度成反比;多次冲击能够获得较大的残余应力值,但对于激光冲击LY2铝合金薄膜深度影响较小。     

考虑腐蚀的埋地灰口铸铁管失效预测及可靠度分析

针对早期埋设的灰口铸铁管存在的破损频繁、漏失严重等影响输配水安全问题,通过管土相互作用模型得到管道应力,应用腐蚀模型预测管道腐蚀深度,进而评估管道的剩余强度,结合失效准则得到管道失效预测模型,并运用蒙特卡罗方法对管道可靠度进行分析.计算模型充分考虑了管道腐蚀、各种外部荷载以及参数的不确定性对管道失效的影响.计算结果表明,在通常荷载作用下仅考虑管道受力,管道不会失效,腐蚀是导致管道失效的重要因素;管道安全因子的概率密度分布曲线呈对数正态分布;当使用时间为20～50 a时管道失效风险较大,在使用时间超过80 a之后,管道失效风险变小且呈现出略有下降的趋势;由于渗漏或不均匀沉降引起的管道基础局部流失在腐蚀深度超过一定值时对管道失效概率的影响较大.     

倾斜疲劳裂纹在混合型应力下张开及滑移特性

对于存在裂纹的机械零件或者构件,它很有可能会受到来自不同方向的作用力, 因此有必要研究裂纹在混合型应力条件下的传播特性. 该文使用具有不同倾斜角度的裂纹--这些裂纹是在应力比R=0的Ⅰ型循环应力下制作的,通过测量裂纹的开口方向和滑移方向的位移量,计算了裂纹端部Ⅰ型应力强度因子(KⅠ)mes和Ⅱ型应力强度因子(KⅡ)mes.裂纹的倾斜角度是指载荷方向与裂纹间的夹角.结果表明,对于存在压缩残余应力的疲劳裂纹,当倾斜角度较大,即β=60°时,应力强度因子的实验值(KⅠ)mes小于理论计算值(KⅠ),但此时实验值(KⅡ)mes与理论值(KⅡ)基本一致.另一方面,对于倾斜角度较小β=45°的疲劳裂纹,其(KⅠ)mes减少的同时,由于裂纹上下表面相互接触,从而导致(KⅡ)mes同时下降.     

关于基体曲率的热障涂层残余应力分析

采用空心和实心四相同心圆模型,导出了轴对称温度应力状态下的位移公式,分析了基体曲率对热障涂层残余应力的影响。结果表明:热障涂层结构中各层内既有环向应力,又有径向应力,应力大小与温降成线性关系;当陶瓷层在外层时,在氧化层/陶瓷层和粘结层/氧化层界面上产生垂直界面的拉应力,且实心模型的拉应力远大于空心模型的拉应力;当陶瓷层在里层时,空心模型中相应界面上的应力为压应力。     

高压蒸汽管道保温研究

计算了不同管径和保温厚度下蒸汽管道输送高压蒸汽的热损失和温度降。结果表明:保温厚度越大,蒸汽的热损失越小、温度降越小;保温材料导热系数与蒸汽的热损失呈正比;环境温度越高,蒸汽的热损失越小;环境风速对热损失的影响不大。同时研究了保温材料选择和保温结构对节能的影响。