共查询到18条相似文献,搜索用时 140 毫秒
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冲击加载下,相界面的传播是一热力耦合过程。相变波阵面不仅是力学和物质间断面,也是温度界面。为考虑温度对相变波传播的影响,本文首先建立了相界面上的热传导方程和热力耦合的相变本构方程,然后采用一维特征线理论和有限差分数值计算相结合的方法,分析了温度界面和相变波的基本相互作用规律,进而给出了连续温度梯度下和绝热冲击下相变波传播规律。结果表明,温度对相变波传播的作用主要体现在两个方面,一方面是作为温度界面将与各类间断面相互作用,另一方面冲击相变波阵面后区域热力学状态变化影响卸载波结构。其原因在于相变方式(可逆、不可逆)和相变阈值应力具有强烈的温度相关性。 相似文献
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采用激光速度干涉仪(VISAR),应用逆向加载实验装置FeMnNi飞片/蓝宝石窗口和FeMnNi飞片/LiF缓冲层/LiF窗口,分别对低相变阈值金属FeMnNi合金含相变的低压和高压冲击加卸载历程进行实验研究。参阅文献[3,4]分析了实验结果。在低压加载下,FeMnNi合金样品存在α→ε相变,卸载时存在逆相变ε→α及逆相变引发的卸载稀疏冲击波;在高压加载下,FeMnNi合金样品存在α→ε相变,卸载时可能存在逆相变ε→γ和γ→ε行为及逆相变引发的卸载稀疏冲击波。 相似文献
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获取不同热力学路径下锡的动态响应实验数据,是深入研究其相变和损伤物理过程的基础.利用小型磁驱装置CQ-4完成了金属锡的斜波加载实验,获取了锡含有相变和层裂损伤物理信息的实验数据.实验结果显示,在加载段锡依次经历了弹塑性转变和β-γ相变两种物理过程,屈服强度约0.194 GPa,相变压力随着锡厚度的增加从7.54 GPa减小到7.14 GPa.在卸载段出现了明显的层裂损伤,层裂强度约1.1 GPa,与相同加载压力下冲击实验结果有巨大差异,层裂片厚度约0.38 mm.结合由锡的多相Helmholtz自由能计算的多相状态方程、Hayes相变动力学方程和损伤度理论,对斜波压缩实验过程进行一维流体动力学数值模拟,计算结果可以很好描述锡的弹塑性转变、相变和层裂三个物理过程. 相似文献
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横向冲击载荷下伪弹性TiNi合金矩形悬臂梁结构响应的实验研究 总被引:1,自引:0,他引:1
利用改装的霍普金森压杆装置对伪弹性TiNi合金矩形截面悬臂梁进行了横向冲击实验研究.结果表明:冲击自由端时,只在根部附近产生一个相变铰,冲击梁中间某位置时,则可能在多处形成相变铰;相变铰形成时拉伸和压缩两侧应变存在一定的不对称性,但是差别并不明显;相变铰的形成与发展过程中,应变并不是单调增加的,而是带有波动性;卸载后相变铰消失,TiNi悬臂梁形状完全回复;自由振动前期,应变的平衡位置与挠度的平衡位置有一定偏离,并且这种偏离随着梁的振动逐渐减小直至消失.TiNi悬臂梁的冲击特性受热弹性马氏体相变和逆相变的支配,不同于传统的弹塑性机制. 相似文献
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采用材料试验机和SHPB实验技术,对在不同初始温度(298~873K)和应变率(5×10-4、~2.3×103s-1)下的NiTi形状记忆合金的压缩力学行为进行了实验研究。结果表明:马氏体状态下的NiTi合金的力学行为对应变率的变化敏感,位错屈服段的硬化模量、相屈服段的硬化模量及马氏体重取向前的弹性模量对应变率的变化不敏感,而位错塑性变形前的弹性模量随应变率的提高迅速增大;奥氏体状态下的NiTi合金随着实验温度升高,无论是应力诱发马氏体相变应力还是奥氏体相屈服应力都逐渐下降,材料表现出温度软化效应。从超弹性温度范围内的卸载曲线中观察到了应力诱发马氏体到奥氏体的逆转变。 相似文献
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采用改进的SHPB (split Hopkinson pressure bar)装置和高速CCD (charge-coupled device)相机对TiNi合金圆柱壳进行了径向冲击实验研究,得到了动态载荷-位移曲线,并采用数字边界提取技术和纯弯曲假定对结构的动态全场变形过程进行了定量分析。结果表明,相变柱壳经受动态冲击后可以恢复,其加、卸载非线性行为与相变状态和相变铰的演化相关。同时,该结构具有良好的横向抗冲效应,对冲击加速度和冲击载荷的衰减量达到95%以上,耗能率为42.4%,可望在可重复使用的抗冲装置中得到应用。 相似文献
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圆柱薄壳的动相变屈曲行为 总被引:1,自引:0,他引:1
利用MTS809材料试验机对TiNi圆柱薄壳进行了轴向动渐进相变屈曲实验,对轴向冲击下处于伪弹性状态的TiNi合金柱壳的动相变屈曲行为进行了数值模拟研究。结果表明,不同的加载强度将会激发出柱壳不同的动屈曲响应模态。当冲击速度较高时,柱壳两端首先形成轴对称环形相变屈曲波纹,并产生应力平台;随着马氏体含量不断增加,环形相变屈曲波纹逐渐贯穿整个壳体,名义应力缓慢抬升;当名义应变超过一定阈值时,对称环形屈曲模态突变为非轴对称块状屈曲模态,名义应力大幅下降。撞击速度为40 m/s的算例(含10%随机缺陷)与S.Nemat-Nasser等的实验结果很好吻合,说明本文中计算模型、方法和结果的有效性经过了实验的考核。结果还表明,相变耗能是TiNi柱壳吸收冲击能量的主要机制,适合制作可重复使用的高效吸能元件,并给出了相应的理想厚径比。 相似文献
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对马氏体相变支配的伪弹性TiNi合金圆柱薄壳进行了准静态屈曲实验研究和分析,结果表明,TiNi柱壳的屈曲模态以非轴对称钻石型为主,卸载时可恢复,与马氏体相变和相变铰的行为相关,明显不同于传统弹塑性柱壳。还讨论了长径比和边界条件对屈曲模态、比能、临界失稳阈值等的影响。研究发现:随着长径比和边界条件的变化,TiNi圆柱薄壳呈现出多样化的屈曲模态发展。相同长径比下,两端简支的TiNi圆柱薄壳比能Se较大;随着长径比增大,边界条件的影响有逐步弱化趋势。相同边界条件下,长径比较小的TiNi圆柱薄壳比能较大。 相似文献
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TiNi相变悬臂梁的横向冲击特性实验研究 总被引:10,自引:0,他引:10
利用改装的霍普金森压杆装置对TiNi形状记忆合金圆截面悬臂梁进行了横向冲击实验研究,并与45#钢悬臂梁的实验结果进行了对比,目的是探索相变对结构动态响应的影响。结果表明:在同样冲击条件下,TiNi悬臂梁的吸能效率优于钢悬臂梁;发现冲击过程中,TiNi试件根部内侧可能形成局部相变铰,使阻力曲线的斜率发生变化;卸载后相变铰消失,TiNi悬臂梁试件基本回复原状,钢试件则留下显著的残余变形。TiNi悬臂梁的冲击特性受热弹性马氏体相变和逆相变的支配,不同于传统的弹塑性机制。 相似文献
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Experimental characterization and micromechanical modeling of superelastic response of a porous NiTi shape-memory alloy 总被引:1,自引:0,他引:1
Sia Nemat-Nasser Yu Su Jon Isaacs 《Journal of the mechanics and physics of solids》2005,53(10):2320-2346
Porous shape-memory alloys are usually brittle due to the presence of various nickel-titanium intermetallic compounds that are produced in the course of most commonly used synthesizing techniques. We consider here a porous NiTi shape-memory alloy (SMA), synthesized by spark-plasma sintering, that is ductile and displays full shape-memory effects over the entire appropriate range of strains. The porosity however is only 12% but the basic synthesizing technique has potential for producing shape-memory alloys with greater porosity that still are expected to display superelasticity and shape-memory effects. The current material has been characterized experimentally using quasi-static and dynamic tests at various initial temperatures, mostly within the superelastic strain range, but also into the plastic deformation regime of the stress-induced martensite phase. To obtain a relatively constant strain rate in the high strain-rate tests, a novel pulse-shaping technique is introduced. The results of the quasi-static experiments are compared with the predictions by a model that can be used to calculate the stress-strain response of porous NiTi shape-memory alloys during the austenite-to-martensite and reverse phase transformations in uniaxial quasi-static loading and unloading at constant temperatures. In the austenite-to-martensite transformation, the porous shape-memory alloy is modeled as a three-phase composite with the parent phase (austenite) as the matrix and the product phase (martensite) and the voids as the embedded inclusions, reversing the roles of austenite and martensite during the reverse transformation from fully martensite to fully austenite phase. The criterion of the stress-induced martensitic transformation and its reversal is based on equilibrium thermodynamics, balancing the thermodynamic driving force for the phase transformation, associated with the reduction of Gibbs’ free energy, with the resistive force corresponding to the required energy to create new interface surfaces and to overcome the energy barriers posed by various microstructural obstacles. The change in Gibbs’ free energy that produces the driving thermodynamic force for phase transformation is assumed to be due to the reduction of mechanical potential energy corresponding to the applied stress, and the reduction of the chemical energy corresponding to the imposed temperature. The energy required to overcome the resistance imposed by various nano- and subnano-scale defects and like barriers, is modeled empirically, involving three constitutive constants that are then fixed based on the experimental data. Reasonably good correlation is obtained between the experimental and model predictions. 相似文献
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Nucleation and development of phase transformation fronts in TiNi shape memory alloy subjected to the stress- and strain-controlled
tension tests were investigated. A thermovision camera was applied to register the distribution of infrared radiation emitted
by the specimen and to find its temperature variations. During the loading, narrow bands of considerably higher temperature
corresponding to the martensitic phase, starting from the central part of the specimen and developing towards the specimen
grips, under both approaches, were registered. The inclined bands of heterogeneous temperature distribution were observed
also during the unloading process of the SMA, while the reverse transformation accompanied by temperature decrease took place.
Thermomechanical aspects of martensitic and reverse transformations for various strain rates were analyzed under both stress-
and strain-controlled tests. 相似文献
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J. Niemczura 《Journal of the mechanics and physics of solids》2006,54(10):2136-2161
Propagating boundaries of phase transformation have been generated in polycrystalline NiTi specimens under a tensile impact loading condition. Multiple strain gages were used to monitor the time evolution of the strain at different spatial locations in the specimen. Nucleation and propagation of multiple phase fronts were detected in these experiments; the phase front speed was found to be in the range between 37 and 370 m/s. The strain measurements were interpreted through the one-dimensional analysis of Abeyaratne and Knowles [1997. On the kinetics of an austenite→martensite phase transformation induced by impact in Cu-Al-Ni shape-memory alloy. Acta Mater. 45, 1671-1683] and a model of partial phase transformation in the polycrystalline specimen. The driving force for the motion of the phase front was evaluated from the measurements in order to establish the kinetic relation. 相似文献
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采用改装的霍普金森压杆装置结合数值模拟对伪弹性TiNi合金固支梁的结构动态响应特性进行了研究。结果表明,在子弹冲击下,撞击点和固定端附近首先发生相变,并随着载荷增加,进一步产生相变铰,梁演变为二杆铰接机构。由于轴力作用,此处相变铰为拉伸侧的单边铰。与传统塑性铰不同,卸载后相变铰完全消失,梁回复原状没有残余变形。此外,对固支边界条件的实现及其对实验结果的影响进行了专门研究。 相似文献