应变速率对单晶高温合金中温拉伸性能的影响

研究了应变速率对一种单晶高温合金760和850 ℃拉伸性能的影响,分析了试样的断口形貌和断裂组织特征。结果表明,随着应变速率的增加,合金的中温拉伸强度稍有增加,伸长率稍有减小。合金中温拉伸性能对应变速率的敏感性非常小。合金中温拉伸断裂机制为类解理断裂,随着应变速率的增加,解理面的总面积减小,滑移带间距变窄。     

Tensile properties and fracture behavior of Ti2AlNb based alloys at room temperature

1　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｃｌａｓｓｏｆｏｒｔｈｏｒｈｏｍｂｉｃｔｉｔａｎｉｕｍａｌｕｍｉｎｉｄｅａｌｌｏｙｓｃｕｒｒｅｎｔｌｙａｐｐｅａｒｓｔｏｏｆｆｅｒｅｘｃｅｌｌｅｎｔｐｏｔｅｎｔｉａｌａｓａｅｒｏｓｐａｃｅａｎｄｅｌｅｖａｔｅｄｔｅｍｐｅｒａｔｕｒｅｓｔｒｕｃｔｕｒａｌｍａｔｅｒｉａｌｓｂｅｃａｕｓｅｏｆｔｈｅｉｒｌｏｗｄｅｎｓｉｔｙａｎｄｈｉｇｈｓｔｒｅｎｇｔｈ[1,2].ＴｈｅｃｏｎｖｅｎｔｉｏｎａｌＴｉ3ＡｌｂａｓｅｄａｌｌｏｙＴｉ24Ａｌ11Ｎｂｐｏｓｓｅｓｓｅｓｈｉｇｈｅｒｔｏｕｇ…     

超细镍纳米线拉伸性能的温度和应变率相关性的分子动力学研究

基于EAM势,采用分子动力学方法对超细镍纳米线（直径分别为3．94、4．95和5．99nm）在（100）晶向的拉伸性能进行研究,并对其温度相关性和拉伸应变率相关性进行探讨。结果表明：弹性模量和屈服强度随着温度的升高而逐渐降低,并且随着拉伸应变率的增大,应力一应变曲线波动程度变大,超细镍纳米线发生断裂时的应变越来越小。在0．01K温度下,超细镍纳米线屈服强度随拉伸应变率的升高迅速降低;但在其它温度条件下,拉伸应变率对弹性模量和屈服强度的影响较小。简要分析尺寸大小对镍纳米线拉伸性能的影响。     

Effects of some material and experimental variables on the slurry wear characteristics of zinc-aluminum alloys

In this study, the slurry wear behavior of a zinc-based alloy has been examined by the sample rotation method over a range of traversal speeds and distances. The influence of adding silicon to the alloy system on its wear characteristics has also been examined. The wear rate of the samples increased with increasing traversal distance initially, attained a peak, and then tended to decrease at longer distances. The initial increase in wear rate with distance was attributed to the indenting effect of the slurry constituents (i.e., liquid droplets and the erodant particles) associated with the corrosive action of the liquid in slurry. On the contrary, factors such as entrapment of the erodant mass as well as the corrosion products in the cavities formed on the specimen surfaces could lead to the decrease in wear rate at longer traversal distances. The existence of silicon particles in the alloy microstructure led to improved wear resistance of the alloy system. This was due to the resistance offered by the hard silicon particles against the impinging action of the slurry constituents. Attainment of the wear rate peak at longer traversal distances in the case of the silicon-containing alloy over the one without the element further substantiated the superior wear resistance offered by the silicon particles. Traversal speed led to higher wear rates irrespective of the test conditions and material composition due to the more severe attack of the medium on the specimen surface. However, the presence of silicon particles in the alloy microstructure offered improved wear resistance (inverse of wear rate).     

应变速率对TC18钛合金厚板电子束焊接接头组织和力学性能的影响

研究了在优化后的焊接工艺参数下,TC18钛合金厚板电子束焊接接头沿板厚方向(上层、中层、下层)应变速率对显微组织、拉伸性能和应变硬化行为的影响。结果表明:焊接后焊缝微观结构发生了明显变化,熔合区显微组织由粗大的β相和次生α相组成。与母材相比,沿厚度方向的焊接接头表现出较低的强度和塑性,但其硬化能力增强。焊缝下层的强度和延伸率高于中层和上层。当应变速率为1×10~(-2)s~(-1)时,焊缝的最大屈服强度和极限抗拉强度达到母材的83%。随着应变速率的增加,焊缝的硬化能力下降。拉伸断裂发生在焊缝区,上层的断裂过程为解理断裂,中下层为准解理断裂。     

Minimum creep rate from primary creep using strain relaxation and recovery test

Minimum creep rate and ‘irreversible’ viscous strain rate, evaluated by strain relaxation and recovery test, during primary creep in a nickel-based Waspaloy at 732 °C (0.62T_m) are shown to obey the same power-law with a stress exponent of 11 from 450 to 650 MPa. Viscous strain rate exhibits a continuous stress dependency from 315 to 725 MPa.     

高伸长率QP钢在高应变速率下的力学特性

为研究高伸长率QP钢的动态力学特性,以两种强度级别的QP钢为研究对象,进行准静态和高应变速率下的单向拉伸试验,得到了不同应变速率下的应力-应变曲线。通过对试验数据的分析,研究了应力与应变速率的关系,并提出动态本构模型来描述QP钢的动态力学特性。基于QP980制作的帽型梁零件,使用HyperWorks进行建模,使用LS-DYNA进行模拟轴向压溃过程的计算,并与实际碰撞试验结果进行对比和验证。通过分析发现:QP钢具有明显的应变速率效应,而且应变速率硬化与相对应变速率不呈线性关系。QP钢帽形梁碰撞试验与仿真对比表明,使用修正的Johnson-Cook模型能较好地描述QP钢在不同应变速率下的动态力学特性。     

Slurry wear characteristics of zinc-based alloys： Effects of sand content of slurry, silicon addition to alloy system and traversal distance

This investigation deals with the observations pertaining to the effects of specimen and slurry compositions as well as traversal distance on the slurry wear response of a zinc-based alloy. The composition of the alloy was altered by adding 4% silicon to it. The slurry composition was varied through changing the concentration of the sand particles in the range of 0-60% that were suspended in the (liquid) electrolyte. The electrolyte contained 4 g sodium chloride and 5 mL concentrated sulphuric acid dissolved in 10 L of water. The slurry wear tests were conducted at a speed of 7.02 m/s over the traversal distance range of 15-500 km. The wear rate increased initially with traversal distance, attained a maximum and decreased thereafter irrespective of the specimen and test environment. However, the wear rate peaks were less prominent in the liquid plus sand environments than the liquid-only medium. Further, the wear rate peak in the liquid-only medium appeared at a shorter traversal distance than the one in the sand containing slurries. Addition of sand particles to the electrolyte reduced the wear rate of the samples to 5%-15% depending on the sand concentration of the slurry. Moreover, intermediate (40%) sand content led to a maximum wear rate when compared with in the liquid plus sand media. However, this maximum was still less than in the liquid-only medium. The silicon containing alloy suffered from higher wear rates than the silicon free alloy samples when tested in the liquid-only medium. On the contrary, the trend reversed in liquid plus 20% and 40% sand environments whereas a mixed response was noted in the slurry containing 60% sand. In the latter case, the presence of silicon proved deleterious initially while an opposite trend was observed at longer traversal distances. The wear response of the samples was discussed in terms of specific features of their microconstituents like silicon and the predominant material removal mechanism in a given set of experimental conditions. The observed behaviour of the alloys was also substantiated further through the characteristics of their affected surface and subsurface regions.     

Influence of low temperature working on microstructure and mechanical properties of AI-7Si-(Fe) alloys

Changes in the microstructure and mechanical properties of Al-7Si-(Fe) alloys by low temperature working have been investigated. The size and shape of eutectic Si and intermetallic AlSiFe compound were controlled by the low temperature working process. This process consisted of repeated cold working at 77 K and recovery treatment at 793 K. By applying this process to the Al-7Si-1Fe alloy, the eutectic Si and acicular Fe compound(β-AlSiFe) phases were broken down to the size of 2-3 μm, with spherical shape. The refined particles were uniformly distributed, and a fine microstructure was obtained. The strength and elongation of Al-7Si-1Fe alloy increased as the temperature was lowered due to the microstructural refinement. This elongation was well reflected in the fracture surface.     

On certain aspects of strain rate sensitivity of sheet metals

The formability of a material depends upon the strain hardening and strain rate hardening of the material. In this study, constitutive parameters using the power law constitutive equation are determined for six different strength steels and two aluminum alloys over different strain ranges, including approximations of the postuniform elongation range. Constitutive parameters are found to be different at different strain ranges. The strain hardening of steels increases with strain at low strain levels (less than 5%) and decreases at high strain levels (greater than 10%). Strain rate hardening decreases with strain for all steels and aluminum alloys. Uniform elongation depends only on strain hardening, and postuniform elongation depends only on strain rate hardening. However, the total elongation depends on both strain hardening and strain rate hardening.     

不锈钢管力学性能的拉伸试验

通过单向拉伸试验获得7种规格的21-6-9不锈钢管及3种规格的321不锈钢管的基本力学性能参数,21-6-9不锈钢管强度高、塑性差,其力学性能特征不利于拉深、弯曲等塑性成形;与21-6-9不锈钢管相比,321不锈钢管强度低、塑性好。分别通过弧形试样拉伸试验和管段试样拉伸试验,获取了Φ1.25mm×0.02mm厚的规格21-6-9不锈钢管的力学性能参数,发现由管段试样获得的延伸率大于弧形试样获得的延伸率,其屈服强度及抗拉强度略小于弧形试样获得的屈服强度及抗拉强度。由于弧形试样拉伸过程中,试样受到的并不是单向应力状态,因此管段试样获得的结果更准确。     

典型汽车用钢板应变速率敏感性实验

为研究应变速率对汽车钢板冲压成形性能的影响,采用单向拉伸实验,对3种不同强度级别的典型汽车用钢板进行应变速率敏感性研究。结果显示,电镀锌BSUFD+Z钢板的屈强比对应变速率的敏感性最大,其次是烘烤硬化BH220钢板,敏感性最小的是双相DP600钢板;双相DP600钢板的硬化指数具有较大的应变速率敏感性,而电镀锌BSUFD+Z钢板和烘烤硬化BH220钢板的硬化指数对应变速率的敏感性较低;3种钢板的应变速率敏感指数,电镀锌BSUFD+Z钢板最大,烘烤硬化BH220钢板次之,双相DP600钢板最小。研究结果为汽车钢板快速冲压生产工艺设计提供了参考。     

不同拉伸速率对SUS304不锈钢室温拉伸力学性能的影响

研究拉伸速率对SUS304不锈钢室温拉伸性能的影响,分析了材料在拉伸过程中微观组织、马氏体转变量和温度的变化。实验结果表明,当拉伸速率为0.005s-1时,材料表面温度升高明显;速率小于0.005s-1时,随着速率的减小,马氏体转变量明显增多;当速率大于0.005s-1时,马氏体转变量少,但变化不大。随着拉伸速率的提高,材料的屈服强度略有增加,抗拉强度和延伸率明显降低。基于拉伸实验结果,提出了考虑应变速率的SUS304不锈钢本构模型,该模型能较好的反映拉伸速率对真应力-应变曲线的影响规律。     

高温电阻应变合金的研究及应用进展

电阻应变计是将被测构件的应变量转换为电阻变化的测试单元,是发动机涡轮叶片应力/应变分析监测的有效手段,而电阻应变敏感栅材料是电阻应变计的关键材料。随着发动机推重比不断增大,涡轮前温度越来越高,要求敏感栅材料的工作温度也越来越高。本文阐述了高温电阻应变材料的发展现状,重点介绍贵金属钯基合金、铂基合金电阻应变材料的成分设计、组织与性能、使用温度等特性。其中PtWReNiCr(Y)合金已经成功应用到1000 ℃动态应变测试;PtRhWZr(Y)可以用于1138 ℃的动态应变测试;PtRhMoWZr(Y)可望用于1150 ℃的动态应变测试,工作温度比传统的电阻应变合金Pt-8W提高了近350 ℃。最后介绍了使用温度更高的金属氧化物应变计的研究现状。     

Tensile and creep properties of Mg-9Al based alloys containing bismuth

1　ＩＮＴＲＯＤＵＣＴＩＯＮＭａｇｎｅｓｉｕｍａｌｌｏｙｓａｒｅｂｅｉｎｇｉｎｃｒｅａｓｉｎｇｌｙｕｓｅｄｉｎａｕｔｏｍｏｂｉｌｅｉｎｄｕｓｔｒｙｉｎｏｒｄｅｒｔｏｄｅｃｒｅａｓｅｍａｓｓｔｈｅｒｅｂｙｒｅｄｕｃｉｎｇｆｕｅｌｃｏｎｓｕｍｐｔｉｏｎａｎｄｐｏｌｌｕｔｉｏｎ[1～ 4 ] .Ｈｏｗ ｅｖｅｒ,ｔｈｅｒｅｄｕｃｔｉｏｎｏｆｙｉｅｌｄｓｔｒｅｎｇｔｈａｎｄｃｒｅｅｐｒｅｓｉｓ ｔａｎｃｅｏｆＭｇ Ａｌａｌｌｏｙａｂｏｖｅ 12 0℃ｌｉｍｉｔｓｔｈｅｉｒａｐｐｌｉｃａ ｔｉｏｎｓｉｎａｕｔｏｍｏｂｉｌｅ…     

应变速率和应力三轴度对316LN钢强度的影响

为了获得应变速率和应力三轴度对316LN钢强度的影响,在Gleeble-1500D热模拟实验机上进行了温度为1050℃的热拉伸实验。对于光滑试样,应变速率分别为0.005,0.05,0.5和1 s-1。对于缺口试样,应变速率设为0.5 s-1,缺口半径分别设为0.5,1,2和4 mm。结果表明,随应变速率和应力三轴度的增加,屈服强度和抗拉强度增加,屈强比减小,裂纹不易萌生。通过回归分析,分别建立了强度指标与应变速率和应力三轴度之间的数学模型,并通过敏感性分析得到:随应变速率增加和应力三轴度减小,应变速率和应力三轴度对强度的影响变小。     

Tensile properties of martensitic stainless steels at elevated temperatures

Tensile properties of quenched and tempered martensitic alloys EP-823, HT-9, and 422 were evaluated at temperatures ranging from ambient to 600 °C as a function of three different tempering times. The results indicated that the yield strength, ultimate tensile strength, and the failure strength were gradually reduced with increasing temperature. The ductility parameters were enhanced at elevated temperatures due to increased plastic flow. However, the tempering time did not significantly influence these properties. The evaluation of the fracture surfaces by scanning electron microscopy revealed reduced cracking and dimpled microstructures, indicating enhanced ductility at higher testing temperatures.     

应变振幅对过共晶Al-Si-xLa合金室温阻尼行为的影响

研究了过共晶A1—Si—xLa合金在室温下不同频率的阻尼-应变振幅行为。A1—Si合金通过常规的铸造和喷射成形工艺制备，并采用动态热机械分析仪(DMTA)对其阻尼行为进行研究。结果表明：大多数铸态以及喷射成形态过共晶A1—Si—xLa合金显示了类似的室温应变振幅-阻尼行为，即随振幅的增加，阻尼先不增大，然后明显升高出现阻尼峰，最后回落，此行为可以用G—L位错阻尼理论加以解释；铸态下添加La对A1—17Si合金的阻尼行为影响不大，过量La(6％)添加明显降低阻尼性能，而La的添加明显提高喷射成形态Al-Si合金阻尼性能；Si含量高的铸态A1—25Si合金的阻尼比铸态A1—17Sl合金的阻尼降低，所需振幅大，而喷射成形态A1—Si合金的阻尼明显比相应铸态A1—Si合金的阻尼高。     

Tensile properties and fracture surface of 07MnNiCrMoVDR steel welded joint at low temperature

The tensile properties and fracture surfuce of 07MnNiCrMoVDR steel welded joint at low temperature have been studied by universal testing machine and scanning electron microscope. The results show that the tensile properties of 07MnNiCrMoVDR steel welded joint are greatly affected by temperature. Tensile strength and yield strength of 07MnNiCrMoVDR steel welded joint increase, bat elongation and reduction of area decrease with temperature decreasing. The macro-fracture of 07 MnNiCrMoVDR steel welded joint exhibits that the shear lip is not significant and micro-fracture makes up of dimpled fracture and tear fracture, and dimple becomes tiny and uniform with temperature decreasing.     

温度和应变速率对双辊铸轧、轧制和热处理态AZ31镁合金流动应力行为的影响(英文)

在单轴拉伸条件下研究温度和应变速率对双辊铸轧、轧制和热处理AZ31镁合金流动应力行为的影响。结果表明,在高温下,动态回复、连续动态再结晶、晶界滑移和附加滑移系的活化使合金的延展得到改善。在473~523 K和10-2~10-1 s-1条件下,合金的断裂伸长率几乎与应变速率无关,而与应变速率依赖于临界剪切应的非基面滑移有关。由于经上述工艺加工的AZ31镁合金具有较低的临界剪切应力,因此在573 K和10-3 s-1条件下出现了孪晶。