记忆光塑性法

文章介绍了一种新的网格实验法—记忆光塑性法。该方法利用光塑性材料在塑性变形后,经高温退火可以恢复到原坯形状尺寸的一次性记忆性质,研究变形体内的塑性应变分布和材料在塑变过程中的流变特征等。综合分析光塑性测试分析结果和记忆光塑性法试验结果,可为金属塑性成形工艺的研究(如毛坯设计、模具设计等工艺参数的选择)提供实验依据。文章列举了记忆光塑性法在模锻工艺、旋压工艺中的具体应用结果。     

光塑性在连续挤压成形研究中的若干关键技术

分析了光塑性和连续挤压技术的特点,总结了光塑性在连续挤压成形研究中的若干关键技术,重点研究了连续挤压过程的光塑性实验建模、光塑性材料的选取、试样制取过程中存在的问题,为今后本领域工作的开展指出可能涉及到的问题.     

对“金属塑性成形原理”一书中用主应力法求反挤压时单位流动压力公式的商榷

“金属塑性成形原理”中用主应力法求得的反挤压时的单位流动压力 p=s[_(d~2)~(D~2)ln(D~2)/(D~2+d~2)+(1+ln(D~2)/(D~2-d~2)(1+M/3-d/h)],由于在推导假设中,应用边界条件时已包含了金属被挤入凸模与凹模之间的环状间隙所需的变形力,该式又另加上这部分变形力,显然是不适当的。采用该书正挤压实心件时的解析法来推导,反挤压时的单位流动压力应为:p=s(1+ln(D~2)/(D~2-d~2)(1+(Md/3h))。     

流函数法在确定上限流动模式中的应用

1967年E.R.Lambert和S.Kobayashi等人对稳定状态成形过程引用了流函数法来确定上限流动模式。这种方法可用之于平面应变问题,也可处理轴对称流动问题。Lambert首先对平面应变状态的挤压过程进行了动可容速度场的研究。以后C.T.Chen与F.F.Ling用流函数法研究了金属经过曲线轮廓凹模的棒料挤压问题,V.Nagpal对通过任何轮廓凹模的平面应变挤压过程进行过分析。他们对不可压缩材料用估计的流线形状来选择动可容速度场族,要求动可容场要满足流线的预定形状以求得与真实变形模型接近一致。本文以通过余弦曲线轮廓凹模的平面应变挤压为例,阐述流函数法在上限流动模式中的应用。     

挤压应力场的图解分析

挤压成形过程中一种常见的缺陷就是挤压件中心部位发生爆裂(Central brust).如果坯料长度足够长,则这种中心爆裂会沿坯料长度重复出现(图1)。当挤压变形程度较小,凹模锥度又较大,模璧摩擦力也较大,材质塑性又较差时,这种中心爆裂现象更容易发生。为了预计发生这种缺陷的可能性,B.Avitzur曾用上限法进行了研究,     

光塑性方法在三维大塑性变形问题中的应用与探讨

文章简单介绍了光塑性方法的发展过程与实验原理,应用这种方法研究了菱形型槽辊锻方坯料金属三维流动的规律,得到了比较满意的结果。光塑性法是研究三维大塑性变形的有效手段。     

挤压金属的流动理论(2)

五复合挤压金属流动的规律复合挤压的变形规律比较复杂,研究的资料也很少。即使在一些有影响的著专中,也只是几句话一带而过,避而不谈。根据挤压金属的流动理论,下面对复合挤压的变形规律进行研究。在进行这种整体的流动规律研究时,假设挤压金属流体为理想流体,即不考虑流体的粘性。并且设备为靠上凸模运动挤压毛坯的单动立式压力机。     

超塑性恒压充模胀形过程中材料的流动和充填规律

采用刚粘塑性有限元法模拟超塑性恒压充模胀形过程,给出了材料质点的流动轨迹和不同时刻的胀形件剖面形状,分析了模具几何形状参数对单元贴模次序、贴模部位的影响。     

矩形截面毛坯挤压矩形工件的上限研究

应用上限法建立了由矩形毛坯正挤压矩形截面工件的等挤压比流动模型 ,推导出了三次多项式表示的流线方程 ,给出了变形区的动可容速度场、应变速率场及上限功率的表达式 ,获得了挤压力的上限数值解 ;分析了变形程度、工件截面形状等参数对挤压力的影响 ,并获得了相对挤压应力与截面形状系数之间的近似关系式。研究证明采用流线速度场进行上限分析比其他方法更符合实际情况 ,根据流线设计的凹模优于常规凹模 ,如平底模。     

细密沟槽铝合金挤压件模具的改进

对细密沟槽铝合金挤压件的结构进行了分析,研究和探讨了该类冷挤压件的成形过程。通过对挤压过程中金属的流动,以及模具的受力分析和模具结构的改进,解决了该类零件在挤压过程中上模的断齿问题。     

Cr12MoV模具钢堆焊工艺及组织研究

研究了Cr12MoV模具钢堆焊工艺,对堆焊接头组织形貌分析和显微硬度测定表明,堆焊层具有高硬度,热影响区中的白亮带为残余奥氏体,它有利于缓解热应力。     

Numerical study of the lateral crushing and re-inflation of stainless steel and aluminum tubes

The purpose of this numerical study is to investigate the possibility of re-inflating laterally crushed tubes back to their original circular-cylindrical shape, without using a die. This can find applications in a non-conventional tube bending process as well as in the repair of damaged offshore pipelines. Two materials were investigated, aluminum Al-6061-T6 and 304 stainless steel, which have very different ductility and work hardening characteristics. Three models, of increasing complexity were created and used to investigate the nature of the plastic deformation during the crushing and re-inflation, the punch load–displacement and pressure–volume responses and the geometric accuracy of the final tubes. The models demonstrated that for both materials, it is challenging to return the tubes to their original circular-cylindrical shape without using a suitable die for the crushing and re-inflation.     

LDR and hydroforming limit for deep drawing of AA5754 aluminum sheet

The goal of the research was to determine the limits and conditions in which the sheet hydroforming process provides a significant advantage over stamping in deep drawing of AA5754 aluminum sheets. Specifically, the maximum draw depth achievable by stamping, warm stamping (WF), sheet hydroforming (SHF), and sheet thermo-hydroforming (THF) of AA5754 aluminum alloy were quantified through experimental and computational modeling. A limited number of forming experiments were conducted with AA5754 aluminum sheets using a cylindrical punch and counteracting fluid at different temperatures and pressures. Several parameters, such as force–displacement, hydroforming pressure and temperature, and the maximum draw depth prior to wrinkling or tearing were measured during the forming process to make comparisons with simulations. The computational study included the simulation of stamping, WF, SHF and THF of AA5754 aluminum sheet with the LS-Dyna code, and the Barlat 2000-2d yield function with temperature-dependent coefficients. To predict the onset of wrinkling and tearing, the numerically generated, temperature-dependent forming limit diagrams (FLDs) based on the Barlat 2000-2d yield function were used. It was found that compared with stamping, SHF and THF can achieve more than 100% deeper draw depths with AA5754 aluminum sheet. The stamping simulations were used also to calculate the optimum blank size and die corner radii for the limiting draw ratio (LDR). The LDR was found to be very sensitive to the punch and die corner radii used in the experiments, which represent the curvature of character lines in an actual part. The LDR for AA5754 aluminum sheet was found to be 1.33 and 2.21 for sharp and round die corner radii, respectively. Overall, it was concluded that SHF is most ideal for deep drawing of aluminum sheets with sharp radii features. With the additional drawability provided by SHF, the automotive industry would be able to make difficult-to-form aluminum parts that cannot be stamped without product concessions such as increasing the die radii.     

铝合金大气腐蚀行为及其防腐措施研究进展

综述了铝合金的大气腐蚀机理和大气主要环境因素对铝合金的大气腐蚀的影响。重点介绍了近年来所采用的对环境无害的铝合金无铬防腐蚀处理方法（激光熔覆法、溶胶-凝胶法、聚合物防腐蚀膜等）及其发展前景。     

铝合金大气腐蚀行为及其防腐措施研究进展

综述了铝合金的大气腐蚀机理和大气主要环境因素对铝合金的大气腐蚀的影响。重点介绍了近年此捎玫亩曰肪澄藓Φ穆梁辖鹞薷醴栏创矸椒ǎす馊鄹卜ā⑷芙?凝胶法、聚合物防腐蚀膜等）及其发展前景。     

Personal decisions and their impacts on energy use and the environment

With increasing frequency, individuals deliberately choose specific actions that they hope will lessen environmental impact. Given the complexity of modern society, it is not always easy to know how to minimize environmental harm without undue sacrifice. Government policies can have a role in helping individuals make decisions and encouraging them to act in certain ways. Recycling of solid waste materials is a personal choice made by many people in the USA guided by the belief that recycling is not only good for the environment but that it constitutes a major contribution to improving environmental quality. By using energy usage as a proxy for overall environmental impact, we show that the impact reduction achieved through recycling varies for different materials. It is small but significant for some materials, such as aluminum, and minimal for other materials, such as plastic, especially when compared to other choices that individuals have direct control over, such as the type of vehicle they drive or the amount they drive. While the recycling of certain materials, such as aluminum, does result in measurable energy savings, the net benefit of recycling is orders of magnitude smaller than the gains that can be achieved from switching to more fuel-efficient vehicles. Despite this, perception and policy in the USA have focused on recycling rather than personal vehicle choice and increased reliance on public transportation.     

Experimental analysis of friction stir forming for dissimilar material joining application

Mass reduction of automotive body structures is a critical part of achieving reduced CO₂ emissions in the automotive industry. There has been significant work on the application of ultra high strength steels and aluminum alloys. However, the next paradigm is the integrated use of both materials, which poses a challenge of how to join the dissimilar materials. Friction stir forming is a new manufacturing process for joining dissimilar materials. The concept of this process is stir heating one material and forming it into a mechanical interlocking joint with the second material. In this research the process was experimentally analyzed in a position controlled robotic friction stir welding machine between aluminum and steel workpieces. New tool geometries were evaluated toward the goal of optimizing joint strength. The significant process parameters were identified and their optimized settings for the current experimental conditions defined using a design of experiments methodology. A scanning electron microscope was used to characterize the bonding and joint structure for single and multi-pin configurations. Two failure modes, aluminum sheet peeling and bonding delamination, i.e. braze fracture, were identified. It was found that the presence of zinc coating on the steel and overall joint geometry greatly affected the joint strength. The aluminum–zinc braze joint appears to be the largest contributor to joint strength for the single-pin joint configuration. The multi-pin geometry enabled a distribution of load to the four pins following fracture of the braze for increased joint toughness and ductility. Thus, the FSF method has been shown to exhibit potential for joining of aluminum to steel.     

含汞原料中汞挥发速率的测试方法研究

以PVC行业废汞触媒、糊式锌锰电池浆液、含汞锌膏为原料,采用动力通量箱法测试其挥发速率,研究了最佳试验操作条件。结果表明:通量箱气体流速在0.5 L/min以下,采用两级大型气泡吸收管吸收挥发汞时效率可达99%以上,增加1次空白测量可测得通量箱壁汞吸附量。     

铝合金杯形件反挤压力计算方法的评比

通过对铝合金杯形件反挤压力计算方法的评比 ,得到了其在不同变形程度下较接近于实测值的计算方法用以估算挤压力。经验证 ,所得结论是较可靠的 ,可用于指导生产实践。对于其它挤压条件 (不同挤压方式 ,挤压材料等 )下的同种问题 ,可以参照这种研究方法得出相应结论     

Environmental chamber for study of the deposition flux of gaseous pollutants to material surfaces

A specially designed recirculating environmental chamber was constructed to study the environmental factors affecting the deposition of pollutant gases to the surface of stone and other building materials. The chamber and sample holder are designed to place samples in an aerodynamically well-defined air flow. The system is designed to permit use of radioactive ³⁵SO₂ as a tracer if necessary. A wide range of typical environmental conditions can be continuously maintained in the chamber. Wind speeds in the test section can range up to about 5 ms⁻¹, exposing replicate samples to air flow that is uniform to within approximately 3%. Relative humidity in the chamber can be maintained to within 3%, and SO₂, NO₂ and O₃ concentrations in the chamber air can be maintained to within 4%. Test results indicate SO₂ deposition and wind speed in the chamber are closely correlated, allowing for a direct determination of the surface resistance (r_c) component of the SO₂ deposition velocity to various test materials. Initial studies of SO₂ deposition to limestone and marble indicate the r_c values are approximately 1.3 s cm⁻¹ for fresh limestone and 34 s cm⁻¹ for fresh marble at 75% relative humidity, 26°C and 50 ppb SO₂.