图像处理技术在板料激光弯曲中的应用

为了提高激光弯曲过程数值模拟结果的验证精度,用图像处理技术对铝合金板料AA6056进行了激光弯曲变形过程的实时测量.自行设计了硬件测量系统和软件的测试系统,使用MV21300UM CCD拍摄板料上测量点在激光照射过程中的动态变化过程,通过软件测试系统中实时采集软件记录动态变化过程、图像处理软件进行图像处理,得到了测量点动态变化的实测曲线.实测曲线表明,板料厚度对激光弯曲过程的位移变化影响较大,板料越薄,边界效应越明显,使得位移的变化曲线越易出现突变.实验结果证明该实测方案是可靠有效的.     

Four-point bending fatigue behaviour of an iron-based laser sintered material

New material processing methods such as laser sintering of metal powder necessitates new knowledge and characterization of the material to support its implementation in technical applications. Fatigue behaviour of a laser sintered FeNiCu-alloy was studied with emphasis on crack path, initiation and propagation. Fatigue crack growth was investigated by surface replication in four-point bending fatigue tests. The fatigue behaviour was controlled by the complex layered structure. Pores on or under the surface were preferable places for crack initiation. Crack linkage and deflection occurred due to crack tip interaction with microstructure and sinter layers where microcracks initiated at pores adjacent to the advancing crack tip. Crack growth rate and stress intensity factor were calculated from surface replicas and showed an oscillating behaviour.     

Selection of process parameters in a single-pass laser bending process

In this article, a strategy for the optimum selection of laser process parameters, namely, scan speed, power and beam diameter, is presented that considers not only the accuracy of laser bending, but also the residual stresses, the maximum temperature along with temperature-affected zone, radius of bend, energy consumption and production rate. Performance is predicted by means of a three-dimensional thermoelastic–plastic finite element model, incorporating certain features to make it computationally efficient. In addition, an empirical model is used for the quick prediction of the maximum temperature, which helps in reducing the number of time-consuming runs of the finite element model. As the optimization of the process is multi-objective in nature, a fuzzy-set based strategy is suggested for a higher level decision. The efficacy of the procedure is demonstrated through examples and in-house experiments.     

Experimental analysis of behavior and damage of sandwich composite materials in three-point bending. Part 2. Fatigue test results and damage mechanisms

The analysis of stiffness degradation and the identification of damage mechanisms during and after fatigue tests of sandwich panels with PVC foam cores have been performed. The sandwich panels with cross-ply laminates skins made of glass fiber and epoxy resin were manufactured by vacuum moulding and subjected to three-point bending tests. Two PVC cores of similar type but with differing densities were investigated. The effect of core density and thickness on the damage behavior was highlighted. Using the cyclic life criterion, fatigue curves were plotted according to two models and compared with those of the literature. It has been demonstrated that the sandwich SD 2, with the higher core density, withstands a higher load and possesses greater rigidity in static tests, combined with an enhanced fatigue resistance, when compared to sandwich SD 1 which has a lower core density. Translated from Problemy Prochnosti, No. 3, pp. 32–44, May–June, 2009.     

Formation mechanism and three-point bending behaviour of directly fabricated aluminium foam plates

New-style smooth-faced aluminium foam plates (AFPs) covered by dense skins have been fabricated directly. AFPs with porosity ranging from 79.3 to 85.2% and with an average diameter of 2.3 to 2.7?mm are obtained via the melt foaming method. The formation mechanism of external dense skins is studied. The dense skin is composed of a cell wall of non-ruptured bubbles, a coarse region formed from ruptured bubbles and plateau borders. The fracture mechanism of AFPs is studied based on static three-point bending tests. They show that the cracked region is only observed at the centre of the experimental samples and that brittle fracture is the main fracture mechanism of these AFPs.     

Device for determining the ultimate strength in bending for refractories at elevated temperature

A device is developed and prepared for determining the ultimate strength in bending of refractories at elevated temperature according to GOST R 50523-93 and ISO 5013-85, that in functional possibilities, metrological characteristics, accuracy of determining physicomechanical and thermomechanical properties of test objects and other parameters surpasses existing Russian analogs. Translated from Izmeritel’naya Tekhnika, No. 2, pp. 34–37, February, 2009.     

Numerical correction of Weibull function’s nomogram for three-point bending test

In this technical note the stress field in the three-point bending test is calculated by means of the finite element method. The emphasis is placed in the distortion, with regard to the elementary theory of beams, of the tensile stress in the vicinity of the application point of load. With the numerical values of the stress field calculated, the Evans function is corrected and new Weibull function’s nomograms are obtained to evaluate the Weibull parameters. The new nomograms predict lower values of σ_L and σ₀, while the value of m is not modified.     

Laser bending of friction stir processed and cement-coated sheets

In this work, laser bending of friction stir processed and cement-coated sheets of aluminum alloy and mild steel was carried out using CO₂ laser. For comparison, the laser bending of uncoated raw sheets was also carried out. It was noted that friction stir processing roughened the surface and helped in getting larger bend angle due to increased absorptivity in laser bending. However, the cement-coated sheets provided much larger bend angles. The micro-hardness of friction stir processed sheets was larger compared with unprocessed sheets and it further increased after laser bending. After laser bending, the micro-hardness increased from bottom surface to irradiated top surface. It was always more than the micro-hardness of the raw sheet. A study of microstructures revealed that the grain size reduced after laser bending and increased from top irradiated surface to bottom surface.     

棉织物弯曲性能与折皱回复角的关系研究

本文概述了目前主要抗皱评价方法存在的问题,着重介绍了折皱回复角测量方法,以棉织物为例,分析了不同织物的弯曲性能及其与抗皱性的关系。通过SAS回归分析得到织物弯曲刚度、弯曲滞后矩与折皱回复角的线性回归方程。回归方程显示:随着弯曲刚度的增加,折皱回复角线性增大;而随着弯曲滞后矩增加,折皱回复角线性减小,并用其他样本回代检验了回归方程的适用性。     

The influence of temperature on integrated circuit failure mechanisms

Temperature is generally considered to be a key parameter in the design of electronic equipment, and cautions concerning temperature and its relationship to reliability are widely documented. While some studies suggest that temperature is the most critical stress influence on microelectronic device failures, the actual failure mechanisms have generally not been quantified in terms of whether a steady state temperature, temperature change, rate of temperature change, or spatial temperature gradient induced failure. In this paper, the influence of temperature on major integrated circuit failure mechanisms is discussed, with emphasis placed on those failure mechanisms which occur in the temperature range of -55°C to 125°C. This paper shows that no simple expression can adequately describe temperature as a failure accelerator for all integrated circuit failure mechanisms. In fact, a generic statement that can be attributed to temperature is lacking. This suggests that a much deeper level of insight into temperature dependencies is necessary to achieve reliable equipment and avoid unnecessary thermal design complexities. Thermal management in electronic equipment can involve additional costs and system complexities that can be of consequential importance, and temperature control should not be routinely employed without close study and justification.