Residual strength prediction of multiple cracked stiffened panels

Prediction of the coalescence of adjacent cracks is critical for residual strength estimation of structures under multiple site damage conditions. A methodology successfully developed for the case of crack link‐up prediction of un‐stiffened plates, is extended for the case of typical cracked stiffened aircraft panels. The proposed link‐up criterion is based on the change in the magnitudes of elastic and plastic strain energies of the stiffened panel, before and after the cracks coalesce. The strain energy magnitudes of interest are calculated using non‐linear elastic–plastic finite‐element analysis. For the application and verification of the method, experimental results from the open literature are used. Residual strength values calculated by the proposed methodology are in good agreement with the experimental results. The present criterion provides superior results when compared to the existing and commonly applied link‐up criteria.     

Stresses in bent copper tubing: Application to fatigue and stress-corrosion cracking failure mechanisms

The residual and applied stresses in u-bent copper tubing are addressed in the context of both cyclic fatigue and stress-corrosion cracking. Failures as a result of fatigue and stress corrosion cracking in u-bent copper tubing have been observed to initiate at nonintuitive locations when only the applied stresses on the component are considered. This paper presents both qualitative classical and quantitative finite-element stress analysis results for the forming of u-bends. The resulting residual stress distributions are compared to fracture patterns generated by both fatigue and stress-corrosion cracking mechanisms.     

采空区对地面建筑物的影响及工程措施

介绍了采空区上覆岩层“三带”的形成和采空区对建筑物的影响以及场地稳定性的评价 ,用工程实例来说明了在建筑设计中应注意的问题 ,并给出了一些处理措施     

基于矢量合成的平衡机最小可达剩余不平衡度测试方法的研究

通过对国标规定的平衡机最小可达剩余不平衡度评定方法的分析和研究，指出了该方法在原理和方法上所存在的问题，并且提出了一种全新的评定方法。这种基于矢量分析的新的评定方法能够快速、准确地计算出转子的最小可达剩余不平衡度，提高平衡机测试的准确性和现场测试效率，为更加客观地评价被测平衡机的综合性能提供了依据。     

余热处理高强度钢筋中冷却模型的研究

本文通过研究余热处理高强度钢筋的控制冷却原理和低碳钢相变规律,建立控制冷却的数学模型。研究表明,建立的数学模型实用可靠,冷却强度可以随化学成分、终轧速度、终轧温度、自回火温度等生产条件的变化而进行逻辑分析,进而确定控冷工艺参数,生产性能合格稳定的钢筋。此外,根据生产条件的不同,冷却程序具有可移植性。     

Characterization of residual stresses from cold expansion using spatial statistics

Residual stress fields from cold expansion have been widely used to extend the fatigue life of aircraft structures. However, the spatial statistical character of these residual stress fields has not been established and has not been incorporated in current analysis methods. The objective of this study was to establish a spatial statistical method to quantify the residual stress field around a cold expanded hole. A framework called the Spatial Analysis of Residual Stress (SpARS) was developed utilizing spatial correlation, response surface modelling techniques and statistical resampling methods to characterize the residual stress field. Our results showed that tolerance bounds on residual stress can be quantified using this method. We also demonstrated the SpARS method using recently published round robin case studies. The newly developed model will be useful for aircraft structural fatigue crack growth analyses to incorporate residual stress fields for extending inspection intervals for fatigue and fracture critical structures.     

Characteristics of Ions Emitted from Laser-Induced Silver Plasma

In this work, study of laser-induced ions is presented. The plasma was produced by focusing a Nd：YAG laser, with a wavelength of 1064 nm, a pulsed width of 9-14 ns, a power of 1.1 MW and energy of 10 mJ, on silver target in vacuum （10-3 Torr= 1.3332 Pa）. The characteristics of ion streams were investigated by CR-39 detectors located at angles of 0°, 30°, 60° and 90° with respect to normal of the target. The distance between the silver target and each detector was 11 cm. The energy of silver ions was found ranging from 1.5 eV to 1.06E4 eV. There was a high concentration of ions with low energy as compared to those with high energy, showing the energy distribution amongst the ions. The flux of ions was maximum in the axial direction which was decreasing with the angle increase with respect to normal of the target, and finally became minimum in the radial direction. Hence the silver ions have shown anisotropic behaviour.     

无线传感器网络LEACH路由协议研究与改进

针对LEACH算法随机选取簇头,未考虑节点剩余能量及单跳与sink节点通信造成能量损耗过快的问题。引入以剩余能量及邻居节点数作为权重因子的时间等候簇头竞争模式选取簇头,并提出LEACH与蚁群算法相结合建立簇间路由机制,采用局部信息素更新,综合簇头节点的剩余能量及节点距离,为簇首与sink节点通信建立多跳路由,达到降低簇头节点能耗过快的目的。仿真实验结果表明,改进算法在降低能耗、延长网络生命周期等方面较LEACH算法有较大提高。     

全数字控制无变压器式单相光伏并网逆变器

研究了一种两级式非隔离式光伏并网方案,前级采用交错并联双Boost电路,后级使用半桥逆变器。分析了无变压器式逆变器的剩余电流问题及半桥逆变器抑制剩余电流的机制。给出了Boost电感和逆变电感关键参数的设计方法。给出了数字方法实现的两级电路复合控制策略及实现方法。重点分析并提出了单定时器交错并联驱动生成策略。试验验证了控制方法的有效性和可行性。     

阀控铅酸蓄电池内阻研究

用ＨＩＯＫＩ３５５１ 电池内阻测试仪对大容量（＞ １００Ａｈ）阀控式密封铅酸蓄电池的内阻及其影响因素进行了研究。研究表明,在１０ ｈ 率放电过程中,剩余容量高于５０％ 时,电池内阻变化不大（仅增大５％ ）;并且内阻和放电时间可拟合为指数函数Ｒｔ＝ Ｒ０ ＋ Ｃ１ ×ｅｘｐ（ｔ／Ｃ２）。极板只有与汇流排完全断开,内阻才会明显增大。蓄电池温度在－ ４０～０℃和０～５０℃时,随温度上升,蓄电池电导线性增加。在０～５０ ｋＰａ时,电池内部压力每增大１０ｋＰａ,内阻增大３ μΩ。另外,接触电阻对测试值有一定影响。