Finite element analysis of a center crack specimen warm pre-stressed under different modes of loading

Load bearing capacity of cracked specimens can be improved following pre-loading procedures like warm pre-stressing (WPS). In this paper, the effects of modes I and II pre-loading on fracture load of a central angled crack specimen are studied by finite element analysis. The specimen is reloaded either in mode I or in mode II. To predict the fracture load of cracked specimen after pre-loading, the maximum tensile stress (MTS) and maximum shear stress (MSS) criteria are used. It is shown that mode II fracture load is independent of pre-loading but the mode I fracture load is highly improved after warm pre-stressing. The mode mixity of the specimen is also changed when the pre-loading and reloading modes are not identical. An increase in the fracture load of the specimen following pre-loading may be due to change of failure mode as predicted by finite element analysis in this work.     

5182铝合金板温成形工艺及摩擦学特性的研究

通过对5182铝合金板的室温及高温力学性能的实验研究与分析，提出了5182铝板的温成形工艺。实验研究了工艺参数对5182可成形性能的影响，并分析了成形过程中材料表面化学性能、表面几何形貌和润滑状态等因素对摩擦学特性的影响，最后进行了仿车门零件的成形实验和有限元模拟。     

Experimental and numerical study of warm deep drawing of AZ31 magnesium alloy sheet

Warm forming of magnesium alloy sheet has attracted more and more attention in recent years. The formability of magnesium alloy sheet at elevated temperature depends on appropriate processes, and the fabrication of high-performance sheet. In this research, an AZ31 magnesium alloy sheet with excellent performances is fabricated by the cross-rolling and the uniform annealing treatments. The uniaxial tensile tests are conducted using a Gleeble 3500 thermal–mechanical simulator, and the mechanical properties of AZ31 magnesium alloy sheet are analyzed. Finally, some limiting drawing ratio (LDR) experiments are performed. The experiments show that the LDR can reach 2.0 at the forming temperature of 150 °C and the drawing velocity of 15 mm/s. A warm deep drawing process is also simulated by the finite element method. The influences of drawing temperature and blank holder force on the formability are numerically investigated. The simulation demonstrated that variable blank holder force technology can improve the LDR from 3.0 to 3.5, and decrease the wall thinning ratio from 15.21% to 12.35%.     

Warm deep drawing of wrought magnesium alloy sheets produced by semi-solid roll strip-casting process

This paper is concerned with the development of a continuous strip-casting technology to facilitate the manufacture of magnesium sheet alloys economically whilst maintaining high quality. Established in the paper is warm formability of cast magnesium alloy sheets after being hot rolled by semi-solid roll strip-casting process. It has been found that magnesium sheet with 2.0–4.0 mm thickness could be produced at a speed of 25 m/min. Hot rolling and annealing temperatures during hot rolling were also changed to examine which condition would be appropriate for producing wrought magnesium alloys with good formability. Microstructures of the crystals of the manufactured wrought magnesium alloys were observed. It has been found that a limiting drawing ratio of 2.7 was possible in a warm deep-drawing test of the cast magnesium alloy sheets after being hot rolled.     

Mechanism of Springback-Free Bending of High-Strength Steel Sheets under Warm Forming Conditions

Tensile loading-unloading tests of high-strength steel sheets in an elevated temperature range are conducted using a 100 kN servo-controlled hydraulic dynamic fatigue testing machine, aiming at clarifying the mechanism of the springback-free phenomenon occurring in warm sheet forming. From stress-strain curves obtained by the tests, it is found that the abrupt decrease in the springback of formed steel sheets at approximately 750 K in isothermal v-bending tests is mainly caused by high-temperature transient creep deformation. Also, from the results obtained by the isothermal v-bending test, bending-unbending deformation observed at temperatures higher than 750 K, as a result of high-temperature creep, was found to have a secondary effect in the springback-free phenomenon.     

钻柄温挤成形及模具设计

介绍了钻柄温挤成形工艺及其模具设计。     

金属粉末温压成形的数值模拟研究

本文借助MSC公司的Marc有限元分析软件对铁粉温压成形过程进行了数值模拟。通过采用基于总体拉格朗日方法的热 机耦合分析,得到了铁粉温压成形过程中材料的几何形变、应力场、密度分布等数据,为金属粉末温压工艺参数的优化设计提供了理论依据。     

Architecture Takes Time

Though condensed between the stages of design and completion, the conventional process of designing a building is time consuming, involving various stakeholders, planning processes and a wide team of consultants and contractors. What happens, though, if the time period of an architect's involvement is expanded? How might a more process-orientated approach shift the role of the architect? Tobias Armborst, Daniel D'Oca and Georgeen Theodore , principals of Interboro Partners in New York, describe how they have developed projects that have sought opportunities in expanding the timescale and remit of traditional practice.     

滚挤压加工对颗粒增强金属基复合材料表面粗糙度的影响

将滚挤压加工工艺引入到颗粒增强铁基复合材料的精加工领域,得出了各工艺参数、增强相含量等因素对表面粗糙度的影响规律,分析了这种复合材料的滚挤压加工机理,并优化了工艺条件.     

户式中央空调系统不同设计方案比较

本文以某公寓A型为分析对象。通过VRV系统和冷／热水系统进行户式中央空调设计，对两种系统的能耗比、性价比、控制系统等方面进行比较，并分析了在两种系统的优缺点，总结出在户式中央空调设计、选型时应注意的问题。