Sheet metal formability analysis for anisotropic materials under non-proportional loading

Sheet metal formability is conventionally assessed in a two-dimensional plot of principal strains or stresses in comparison to a forming limit curve. This method of assessment implicitly assumes that the forming limit is isotropic in the plane of the sheet. While the assumption of isotropy in the forming limit is perhaps a good engineering approximation, it is intrinsically inconsistent with the use of material models that are anisotropic. Since the trend today is to utilize models with full anisotropy in order to more accurately capture the physics of material behavior, the issue of anisotropy of forming limits must also be addressed. The challenge is that the forming limit is no longer defined by a curve but requires the definition of a surface in strain or stress space, and therefore it is no longer appropriate to view these limits with the convenience of two-dimensional diagrams. Furthermore, recent developments in the characterization of sheet forming limits under non-proportional loading suggest that is advantageous to view forming limit behavior in terms of stresses rather than strains, a view that is adopted in this paper. A solution to the challenge of assessing formability for an anisotropic material is proposed that rescales the stresses by a factor so that the scaled stresses have the same relationship to a single forming limit curve in a 2D plot in stress-space, as the actual stresses have to the true anisotropic forming limit in 3D space. The rescaling enables engineers to accurately view the formability of all the elements at the same time for a given finite element analysis of an application. This paper also discusses other challenges of using stresses in the assessment of formability, focusing on an analysis of the 2-Stage Forming Benchmark highlighted in the Numisheet ’99 Conference. Stresses are found in this application to unload to non-critical values after reaching critical levels earlier in a forming process, which suggests that a full integration of the stress-based forming limit criterion with FE simulation is required to detect critical states that may temporarily occur during the forming process.     

One hypothesis concerning metal microfailure under polyharmonic loading

A mathematical model describing the process of metal microfailure taking into account the processes of nucleation and the development of submicroscopic-, microscopic-, short-, and macrocracks has been developed. The concept of crack length reduction is introduced. The fatigue curves (stress-cycle diagram), including typical values of reduced crack length, are obtained.     

Plate bending wave propagation behavior under metal sphere impact loading

A loose part can cause component damages and material wear on nuclear power plants; thus, a mass estimation of the loose part is crucial to safety management. A bending wave propagation of a structure under the loose part impact loading is precisely simulated to accurately estimate the mass of a loose part. Lamb’s general solution for an arbitrary impact force function and Hertz impact theory have been used to identify the characteristics of the bending wave that is impacted by a metallic loose part in reactor pressure boundary components. However, these approaches cannot provide accurate information on the acceleration response that is required to identify the impact source. In this study, the bending wave propagation behavior of plate structures under a simulated loose part (Metal sphere) impact loading was modeled using a Finite element analysis (FEA) technique. The characteristics (e.g., Maximum acceleration amplitude, primary frequency, and bending wave velocity) of the impact response signal from a metal sphere were analyzed with the FEA results and were verified with experimental results. In addition, the correlation between plate thickness and characteristic length was presented. Results from this study can be utilized to estimate the location and mass of a loose part for condition monitoring and diagnostics in nuclear power plants.     

晶振芯片在高g值冲击下的失效机理分析

芯片是弹载存储测试系统的最基本的单元,它的抗强冲击能力直接影响测试系统的可靠性.为了研究芯片抗高过载能力,本实验利用Hopkinson杆对最典型的晶振芯片进行高g值冲击,以一维应力波理论估计芯片受到的加速度.对实验现象进行理论分析后得出与应力波传播方向平行放置的芯片抗冲击性能要高于与应力波传播方向垂直的芯片.     

Acoustic-emission testing of the strength of metal structures under complex loading

Russian Journal of Nondestructive Testing - The interpretation of the results of acoustic-emission (AE) testing of the states of objects under complex loading, which possess a branched structure...     

Wake instability mechanism for wave formation in explosive welding

Two recent theories of interface wave formation in explosive welding are compared and shown to be similar. The relationship between the two is discussed. The extension of the theory to cover a welding arrangement of practical importance is discussed and a major difficulty is identified.     

排爆机器人越障机理及对爆炸物的动态响应分析

排爆机器人发现爆炸物后,需要将爆炸物运到排爆罐里进行引爆.这个过程机器人要夹着爆炸物跨越各种复杂的路面环境,比如跨台阶,壕沟,甚至上下楼梯等障碍,因而容易造成对机器人本体较大的冲击和振动,尤其是对爆炸物产生冲击和振动,严重时使爆炸物从手爪中脱落,掉到地上.对华南理工大学自主研制的履带式排爆机器人越障过程的机理进行分析,研究机器人越障时产生的冲击载荷及其爆炸物的动力学响应,以及其对手爪夹持力影响分析.这对于研究排爆机器人在复杂路面运动时其爆炸物的动力学特性具有重要指导意义.     

接触疲劳试验机伺服电动缸加载系统设计

通过对比接触疲劳试验机杠杆砝码加载和液压加载的优缺点,发现这两种方法都已经不适合对轴承越来越高的试验要求。为了优化加载性能,采用伺服电动缸加载技术,对接触疲劳试验机加载系统机械结构和电气测控系统进行了重新设计。试验结果表明,伺服电动缸加载响应速度快、精度高、稳定性好,并且具有低噪音和节能环保等优点,为保证轴承质量打下了坚实的基础。     

Modeling of a locking mechanism between two rough surfaces under cyclic loading

The work is motivated by experimental studies on energy dissipation due to micro-slip in mechanical joints. It has been observed that the loss of energy undergoes certain evolution under cyclic shear loading. It manifests itself in the form of the gradual decrease approaching a steady state as cycling progresses. This behavior has a repeatable character if contact is re-established and subjected to cycling again. In the present work, a simple multiple-asperity model is developed that suggests a physical hypothesis that when two rough surfaces are brought in contact and subjected to shear loads a certain locking mechanism comes into play at the interface. Such locking occurs due to the tendency of the interface to adapt its contact microstructure to the loading conditions. The adaptation mechanism is described in the present work through the contact inclination angles. The developed model is simple in application and it relates micro-characteristics of the contact to macro-behavior of the system exhibiting itself in energy dissipation.     

基于压电式压力传感器的冲击波载荷测试系统设计

为了满足对爆炸冲击波载荷精确测量的技术要求,设计了以压电式压力传感器为测试元件的爆炸冲击波载荷测试系统,并对所选压电式压力传感器的固有频率ωn与采样频率ω的关系进行了研究。试验表明,所选压电式压力传感器及设计的测试系统性能稳定、可靠,测试结果符合设计要求。     

受载复合材料曲板结构的失效特征研究

为研究飞机复合材料曲板的失效过程与失效模式,对一组复合材料弯角试验件进行了准静态拉伸试验.同时基于ABAQUS软件及其USDFLD子程序,考虑复合材料的渐进损伤特征,建立了受载曲板的有限元模型,分析弯角区的应力分布特征.研究发现：数值仿真能够较准确的模拟弯角结构的受载过程,模拟结果与试验结果吻合较好;结构受载过程中,在弯角区域发生分层破坏,随着载荷的增大,分层沿着周向和径向都有扩展;随着外加载荷的增大,弯角区域的最大法向应力的位置逐渐移向加载端.     

Novel method to determine blast resistant glazing system response to explosive loading

The goal of the measurement system presented herein is to provide a rich set of data detailing the forces and displacements within a Blast Resistant Glazing System (BRGS) subjected to an explosive load. Designers often rely on post test examination and develop inferences based upon forensic remains when failure occurs. A comprehensive measurement system would alleviate guesswork allowing cost effective solutions to be implemented more quickly and with more confidence.     

用于缸体缸盖清洗的机器人机构分析与仿真

针对汽车发动机缸体缸盖清洗行业的特殊需要,研发了可应用于该领域的六自由度发动机清洗机器人。运用D-H方法,建立了六自由度发动机清洗机器人的连杆坐标系,给出了结构参数表,确定了六自由度清洗机器人的运动学方程。利用牛顿-欧拉递推算法,完成了六自由度清洗机器人的动力学分析。在Matlab环境下,利用Robotics Toolbox建立了机器人的三维仿真模型,并对发动机清洗机器人进行了动力学仿真,得到了各关节驱动力矩的变化曲线。     

Comparison of the potentials of ultrasmall-angle tomography and integral small-angle tomography for recording spall and shear fractures in iron and steel shells under explosive loading

The fundamental possibility of the adequate reproduction of the peculiarities of spall and shear fractures in studied shells with the required spatial resolution using methods of ultrasmall-angle and integral small-angle gamma tomography is demonstrated. The efficiency of such approaches and the comparison of the results of image reconstruction based on algorithms with data obtained using the method of small-angle gamma tomography performed by applying multiplicative algebraic algo-rithms and with photographs of meridian cross sections of recovered shells subjected to explosive loading are evaluated.     

波义耳定律在液压缸加载系统中的应用

针对某液压缸需施加恒定压载荷的试验要求,该文以密闭容器的气体作为试验介质,利用波义耳定律设计了加载系统,不需要加载泵就能准确实现加载功能,节能节支效果好.     

Analysis of variations of the dynamic characteristics of acoustic-emission sources under static loading of metal specimens

Changes in the energy of acoustic-emission (AE) signals and their cross-correlation coefficient for sources of different types have been experimentally studied for statically loaded specimens. The results allow separation of AE signals appearing during irreversible changes in the region of stress concentrators and signals of other types.     

爆炸性气体环境用工程车辆电气控制箱设计

针对爆炸性气体环境下作业的工程车辆,通用防爆器件无法满足车辆的紧凑性要求,以某工程车辆的主令电气控制箱隔爆设计为例,对工程车辆专用隔爆器件的设计要点及关键技术进行了阐述.     

起重机液压缸变幅机构的计算程序化

针对起重机液压缸变幅机构的设计计算,运用多目标优化设计方法进行理论分析并建立数学模型,采用黄金分割一维搜索优化计算方法,在DELPHI平台上构架参数计算软件,程序根据输入已知参数按照优化流程进行液压缸参数优化计算,以图形示意的方式显示计算结果,并保存结果和数据输出。采用DLEPHI平台构建的起重机液压缸变幅机构计算软件具有专用性强、运算效率高等优点,可大幅减少设计人员的工作量,提高设计效率和准确性,对起重机变幅机构及其部件设计具有现实指导意义。