共查询到20条相似文献,搜索用时 109 毫秒
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采用有限元法数值模拟了TiNi形状记忆合金(SMA)的低速冲击性能。考察马氏体相变过程中不同伪弹性模量和弹性应变极限对TiNi合金低速冲击性能的影响。结果表明,随着冲击速度的增加,4种材料的最大接触载荷和位移量都呈线性增加趋势;冲击速度相同时,3种不同伪弹性模量TiNi合金试样的最大接触载荷和位移量近似相等且都低于45#钢,TiNi合金试样产生的最大Von Mises应力和最大塑性应变都低于45#钢;超弹性模量为2.9GPa的TiNi合金产生的最大Von Mises应力和最大塑性应变均最低。TiNi形状记忆合金较低的超弹性模量和较大的弹性应变极限能够减小冲击过程中的最大Von Mises应力,抑制高塑性应变的产生并使塑性变形区域减小,从而提高TiNi合金的抗冲击性能。 相似文献
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离散磁道式磁盘在与磁头瞬态接触过程中极易损坏.为改善离散磁道式磁盘的瞬态接触状况,采用有限元仿真方法,建立了平整化前后离散磁道式磁盘与磁头的瞬态接触模型,分析了平整化前后离散磁道式磁盘接触应力分布特点,研究了磁头冲击速度、径向速度、磁盘表面摩擦系数等接触条件及平整化对离散磁道式磁盘最大等效塑性应变、塑性应变总体积的影响.结果表明:磁头冲击速度、寻道速度增大均可导致磁盘最大等效塑性应变、塑性应变总体积增大;摩擦系数增大可增大磁道最大等效塑性应变、减小塑性应变总体积;在接触初期,平整化离散磁道式磁盘可以减小磁道最大接触应力,缓解应力集中现象;在接触全过程中,平整化离散磁道式磁盘可以减小磁道最大等效塑性应变及塑性应变总体积;平整化所用2种弹性模量等力学特性不同的填充材料,即磁道材料与类金刚石碳,对于磁道接触状况的改善作用区别较小.以上结论可为降低离散磁道式磁盘的破坏程度提供理论指导. 相似文献
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本文的研究首次表明,可以通过分析恒定拉伸速度得到的拉伸试验数据来建立超塑性变形的应力、应变速率及应变的三维力学行为图。在此基础上,对Pb—So共晶合金的三维力学行为进行分析,可以获得应变速率敏感性指数m值作为应变和应变速率的二元函数的变化(应变速率和应变的对数坐标系上的等m值曲线)。由此可以给出超塑性变形时应变和应变速率区的限度,有益于指导实际的超塑性成型。 相似文献
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Adi Arieli 《Journal of Materials Science》1981,16(10):2760-2766
This paper considers to what extent the second-phase volume fraction in superplastic binary alloys affect the matrix grain
size stability during deformation and, through it, the flow stress at constant temperature and strain rate. It is shown for
five different superplastic binary alloy systems, that at constant temperature and strain rate the flow stress will increase
with the deviation of the second-phase volume fraction in the alloys from that required for maximum matrix grain size stability.
A new parameter (Z) which quantifies these deviations has been introduced in this paper. The possible errors in determining
the pertinent parameters in the rate equation for superplastic flow by testing alloys withZ is discussed. 相似文献
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针对7B04铝合金开展了变形温度为470~530℃,应变速率为0.0003~0.01s~(-1)的高温超塑性拉伸实验,研究了材料的超塑性变形行为和变形机制。结果表明,7B04铝合金的流动应力随着变形温度的升高和应变速率的降低而逐渐减小,伸长率随之增加;在变形温度为530℃,应变速率为0.0003s~(-1)时,7B04铝合金的伸长率达到最大1105%,超塑性能最佳;应变速率敏感性指数m值均大于0.3,且随变形温度的升高而增加;在500~530℃的变形温度范围内,m值大于0.5,表明7B04铝合金超塑性变形以晶界滑动为主要变形机制;变形激活能Q为190kJ/mol,表明7B04铝合金的超塑性变形主要受晶内扩散控制;7B04铝合金超塑性变形中在晶界附近有液相产生,且适量的液相有利于提高材料的超塑性能。 相似文献
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The effect of phases having a range of hardnesses on the superplastic tensile behaviour of microduplex Pb-Sn eutectic has been studied. The presence of relatively hard particles induced cavitation at particle/matrix interfaces during deformation in an otherwise noncavitating system, and the growth and interlinkage of cavities led to brittle superplastic fractures. Density measurements showed that cavitation increased as the volume fraction, hardness and size of intermetallic particles was increased. Increasing strain rate and decreasing deformation temperature also led to an increased level of cavitation. Cavity nucleation was attributed to the limited ability of the relatively hard phases to contribute to the accommodation processes occurring during superplastic flow. 相似文献
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《Materials Science & Technology》2013,29(9):761-768
AbstractMicrostructural changes occurring during superplastic deformation of Ti-6Al-6V-2Sn alloy with an initial microstructure consisting of mixed fine lamellar and equiaxed α grains were investigated. Uniaxial tensile tests with constant strain rate were conducted at temperatures ranging from 775 to 925°C and at strain rates rangingfrom 7 × 10-5 to 1 × 10-3 S-l. To investigate the microstructural changes occurring during deformation, some of the tests were terminated at preprogrammed true strains of 0.5, 0.9, and 1.5 for subsequent metallographic investigation. The effects of high temperature exposure on the microstructural changes and on the superplastic deformation behaviour were also evaluated. It was found that both static and dynamic recrystallisation were initiated under certain test conditions and could be related to the flow stress behaviour during the superplastic deformation tests. For tests at low temperature and high strain rate, the flow stress increased quickly at the very beginning of the deformation without significant microstructural change. After the flow stress reached its maximum value, dynamic recrystallisation occurred at a lamellae accompanied by a decrease of the flow stress, known as strain softening. Raising the test temperature or decreasing the deformation strain rate provided the opportunity for thermal energy to initiate static or semidynamic recrystallisation. Thereafter, the flow stress behaviour at the beginning of the test changed to a slow strain hardening type. There also existed a transition temperature; soaking before tensile testing above this temperature would result in static recrystallisation, and the superplastic deformation characteristics would be affected. 相似文献
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利用扫描电镜(SEM)和超塑性拉伸实验对一次热挤压加工成型的AZ61镁合金薄板(晶粒尺寸~12μm)超塑性变形特征进行了研究.结果显示,在最佳的变形温度(623K)和应变速率(1×10-4s-1)条件下,可获得的最大的超塑性形变量为920%.在523~673 K实验温度和1×10-2~1×10-5s-1应变速率范围内,材料的应变速率敏感指数(m值)随实验温度升高和应变速率的降低而增加.较高的m值(0.42~0.46)对应于晶界滑动机制(GBS),而较低的m值(0.22~0.25)则对应于位错滑移机制.变形温度和应变速率是影响超塑性变形量和变量机制的主要因素. 相似文献
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High strain rate superplastic deformation potential of an Al–4.5%Mg matrix composite reinforced with 10% SiC particles of 3 μm nominal size was investigated. The material was manufactured using powder metallurgical route and mechanical alloying which was then processed by equal channel angular extrusion (ECAE). The composite showed a high resistance to static recrystallization. The manufacturing operations atomized SiC particles to nanoscale particles and the severe plastic deformation process resulted in a dynamically recrystallized microstructure with oxide dispersoids distributed homogeneously throughout the matrix. These particles stabilized the ultra-fine grained microstructure during superplastic (SP) deformation. Testing under optimum conditions at constant strain rates led to tensile elongations >360%, but it could be further increased by control of the strain rate path. Transmission electron microscope (TEM) studies showed that the low angle boundary sub-grain structure obtained on heating to the SP deformation temperature developed on straining into a microstructure containing high angle boundaries capable of sustaining grain boundary sliding. 相似文献
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A rapidly solidified Al-17Si alloy was pre-pared by the ultrasonic gas atomization andextrusion method.Its superplasticity was studiedunder constant cross-head speed tensile test condi-tion over the temperature range of 450℃ to 550℃and strain rate range of 1.67×10~(-4) to 6.17×10~(-2) s~(-1).The superplastic behaviour of theas-extruded and the thermomechanically treatedsamples was compared.It was found that thethermomechanical treatment was essential toachieving superplastic deformation.A maximumelongation of 445% was obtained at test tempera-ture of 550℃ and strain rate of 6.17×10~(-4) s~(-1).The microstructures before and after deformationwere studied using OM,SEM and TEM.Void for-mation on the primary Si phase interfaces wasfound to have detrimental effect on superplasticity.It was also noted that the primary Si phasecoarsened rapidly during superplastic deformation.The micromechanisms of superplasticity,phasecoarsening and void formation were discussed. 相似文献
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The stress-strain rate behaviour of a superplastic Zn-22% Al alloys was investigated by the differential strain rate and constant load cycling tests on an Instron machine. A region with a rate sensitivity approaching unity was observed at low strain rates. On increasing the strain rate, a transition to the superplastic region occurred through an intermediate region of lower m (0.35). These observations are interpreted in terms of a transition from diffusional creep to superplastic flow with a threshold stress for superplastic deformation. 相似文献
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Bolu XIAO Zongyi MA Jing BI) Institute of Metai Research Chinese Academy of Sciences Shenyang China) Department of Metallurgical Engineering University of Missouri Rolla Rolla MO USA 《材料科学技术学报》2003,19(4):382-384
High strain rate superplastic deformation behavior of powder metallurgy (PM) processed 17 vol. pct SiCp/2024 Al composite sheet after heat treatment was investigated over a range of temperature from 753 to 833 K. At 813 K,a maximum elongation of 259% was discovered at a strain rate of 10^-1 s^-1. The activation energy was closed to that for lattice diffusion of Al and increased at temperature upon incipient melting temperature. The mechanism of superplastic deformation for present composites was attributed to lattice diffusion controlled grain boundary sliding. 相似文献
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It is important for practical applications that some commercial alloys with stabilized finegrained structure should exhibit superplastic behaviour at high temperatures. In this paper the results of impression creep tests conducted on AlMgZn alloys are reported and the strain rate sensitivity and activation enthalpy were determined. The mechanical behaviour of the alloys as a function of the strain rate sensitivity can be divided into three regions. At low and high stresses the strain rate sensitivity parameter is low and the deformation process is not superplastic. Superplastic deformation takes place only at intermediate stresses. The microstructural interpretation of these processes involves, in general, the change of the micromechanisms controlling the different deformation processes. It was determined that by the supposition of a threshold stress depending strongly on temperature, the two regions due to low and intermediate stresses of the deformation can be described by the same constitutive equation. 相似文献