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层裂微裂纹的形态及层裂程度的表征参量 总被引:3,自引:0,他引:3
层裂是冲击载荷造成材料破坏的一种典型方式。文中运用超声C扫描检测系统对层裂试件的微损伤形态进行检测,确是出在一维应变加载条件下的微裂纹形态呈钱币型;另一方面,根据钱币型微纹形态,通过对层裂损伤演化过程的分析,提出了一个描述层裂程度的无量纲参量,与层裂实验数据的对比说明了这个参量能够很好地描述层裂损伤程度。 相似文献
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对爆轰加载下低熔点金属锡的层裂破碎问题开展了数值模拟。在利用实验数据对所采用数值方法和材料模型开展对比验证的基础上,通过对样品内部物理量时间及空间分布演化对比分析,剖析了冲击加-卸载中样品内部应力波与材料相互作用过程。此外,通过对比分析不同厚度锡样品在爆轰加载下的动态行为特征,进一步认识了自由面反射稀疏波、边侧稀疏波和入射稀疏波共同作用下层裂破碎演化机制。结果表明,当样品较薄时,层裂破碎行为由反射稀疏波主导;随着样品厚度的增大,反射稀疏波主导区缩小,入射稀疏波和边侧稀疏波主导区逐渐增大。 相似文献
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初始应力状态对材料层裂破坏特性影响研究 总被引:3,自引:0,他引:3
通过对球面飞片加载条件下的应力/应变状态分析表明采用施加径向应变方法可以近似模拟球面加载的受力过程. 采用过盈配合的热装配方法对平面样品施加了径向预应变,一维平面应变气炮实验结果显示初始预应力(变)明显降低了LY12铝层裂强度. 从空洞长大基本原理出发分析了各向异性受力条件下空洞长大的路径和所消耗能量不同于各向同性应力加载.通过数值模拟对含损伤的材料本构模型进行分析,得到了材料层裂强度与其外部宏观应力场密切相关,也间接的与构型相关的结论. 相似文献
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利用任意反射面位移干涉系统(DISAR)激光测速技术,成功地获得了滑移内爆加载和柱壳结构条件下无氧铜的内表面(自由面)速度剖面,并对其层裂特性进行了初步分析。结果表明:(1)在固定炸药和改变无氧铜圆管壁厚条件下,层裂片厚度随着圆管壁厚h的减小而增加;以圆管壁厚h为参照进行归一化,则相对层裂片厚度(/h)随相对装药厚度(he/h)的增大而增加,这种规律与以往对20钢的研究结果一致,但圆管发生层裂的临界条件,却显示出明显的材料相关性。(2)初步来看,无氧铜的层裂强度对结构的依赖性不明显,而与加载脉冲的幅值和宽度相关。(3)受无氧铜粘性和Taylor波衰减的影响,无氧铜的层裂强度随管壁厚度的增加而略有降低;同时,材料分散性也对此有一定影响。 相似文献
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一维应变条件下金属层裂的实验研究 总被引:1,自引:0,他引:1
材料的层裂是由两个相向的拉伸应力作用引起材料断裂的一种现象,是一个被普遍关注的力学问题。本文中主要对层裂研究的意义、历史和现状,一维应变条件下层裂的原因、表征、加载方式及测试技术等问题进行了综述,并讨论了影响层裂强度的几种主要因素。 相似文献
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三角形波致LY12铝层裂的平板冲击实验研究 总被引:1,自引:1,他引:1
采用基于冲击波衰减动力学的实验技术,使平板碰撞层裂实验的LY12铝样品中,产生三角形冲击脉冲.采用VISAR技术记录样品自由表面历史,获得样品中发生层裂的信号.在经过高应力三角形波实验的软回收样品上,发现了两个层裂面.就样品中呈现三角形脉冲的平板冲击实验而言,样品中可以存在一些高拉伸应力区域并发生多次层裂.将该文提出的基于空穴聚集的层裂模型用于数值模拟这些特定条件的平板冲击试验,并将计算的样品自由面速度历史及样品中的损伤分布与实测的VISAR数据及软回收的样品层裂面等作了比较.研究表明,人为粘性、状态方程、本构方程以及层裂模型对于数值模拟三角形冲击脉冲引起的层裂有严重影响. 相似文献
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为研究激光冲击Ti17合金中厚样品的层裂特性和层裂阈值,对样品(厚5 mm)表面进行单点连续1~8次激光冲击,激光工艺参数为:频率1 Hz,脉宽15 ns,激光能量30 J,方形光斑4 mm×4 mm。采用白光干涉仪、超声波无损检测技术和扫描电镜,分析和检测中厚样品冲击区域的表面形貌、内部损伤以及层裂形貌。实验结果表明,连续从4次到5次激光冲击中厚样品的表面凹坑深度增加值最大为64.5%。连续5次激光冲击为中厚样品层裂阈值,层裂面积随冲击次数增加而增加。连续5~8次激光冲击中厚样品层裂厚度的实验值为280~310 μm。层裂机理为韧性微孔洞的形核、增长和汇合,形成晶界失效和晶内失效。研究结果可为激光冲击强化整体叶盘改性提供工艺参考。 相似文献
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基于如下假设,给出了层裂过程中的应力松弛方程,并建立了一种基于空穴聚集的延性层裂模型:在层裂早期,微空穴的主要效应是减小应力作用面积;在层裂后期,应力按空穴聚集时的应力-空隙度依赖关系减小。把P.F.Thomason、D.L.Tonks等及S.Cochran等给出的依赖于应力(压力)的层裂空隙度方程分别耦合于守恒方程、计及损伤的状态方程及本构方程,建立了求解所有变量包括损伤的封闭方程组。这种基于空穴聚集的层裂模型已被应用于一维层裂试验的数值模拟。模型中的层裂强度及临界损伤度初始可以估计,最终的确定将使数值模拟结果与实测的速度(或应力)剖面以及观测的层裂面上的损伤基本一致。分别基于D.L.Tonk等及S.Cochran等给出的依赖于压力的层裂空隙度方程所作的一维层裂试验数值模拟结果基本一致,而与基于P.F.Thomason给出的依赖于应力的层裂空隙度方程所作的相应数值模拟结果有明显差异。 相似文献
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Measurement results for the shock wave compression profiles of 12Cr19Ni10Ti steel and its dynamic strength in the strain rate range 105–106 s?1 are presented. The protracted viscous character of the spall fracture is revealed. With the previously obtained data taken into account, the measurement results are described by a polynomial relation, which can be used to construct the fracture kinetics. On the lower boundary of the range, the resistance to spall fracture is close to the value of the true strength of the material under standard low-rate strain conditions; on the upper boundary, the spall strength is more than twice greater than this quantity. An increase in the temperature results in a decrease in both the dynamic limit of elasticity and the spall fracture strength of steel. The most interesting result is the anomaly in the dependence of the spall fracture strength on the duration of the shock wave compression pulse, which is related to the formation of deformation martensite near the growing discontinuities. 相似文献
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Mallick D. D. Zhao M. Parker J. Kannan V. Bosworth B. T. Sagapuram D. Foster M. A. Ramesh K. T. 《Experimental Mechanics》2019,59(5):611-628
Experimental Mechanics - We describe a laser-launched micro-flyer apparatus designed for spall strength measurement. The launcher uses a single pulse from a pulsed laser that is stretched in time... 相似文献
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V. K. Golubev A. P. Pogorelov 《Journal of Applied Mechanics and Technical Physics》1999,40(5):791-795
Results from examination of the spall fracture ofGTK-70 explosive compound under shock loading are reported. Specimens 20 and 30 mm thick were impacted by 1.0-mm-thick steel plates
accelerated by an explosion to velocities of 180–370 m/sec. Calculations of the loading conditions and spall fracture of the
specimens are performed in an elastoplastic formulation. An analysis of the data obtained yields a simple empirical relation
among the maximum tensile stress in the spall plane, the stress gradient in the tensile pulse, and the maximum stress in the
loading shock wave. Normalization of the specimens leads to a certain decrease in the fracture load.
Institute of Experimental Physics, Sarov 607190. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No.
5, pp. 18–22, September–October, 1999. 相似文献
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On the basis of the structural-temporal approach, we explain the rapid increase in the spall strength and its stabilization
in the nanosecond range of load duration, observed in several experiments. We give a detailed presentation of the method for
describing the time-dependence of the spall strength. We obtain a qualitative coincidence of the computational curves and
the experimental data and show that the strength significantly depends on the pulse parameters. An analysis of the obtained
results allows us to conclude that it is incorrect to introduce a limit stress as the material “dynamic” strength by analogy
with equilibrium processes; it is necessary to use the strength structural-temporal characteristics instead. 相似文献
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A new model for spall-rolling-element interaction 总被引:1,自引:0,他引:1
Evaluation of the spall size of a radially loaded rolling-element bearing is required for the assessment of the bearing damage severity and estimation of its remaining useful life. A new multi-body, nonlinear dynamic model of the interaction between the rolling-element and a spalled outer race is presented. The study focuses on the physics of rolling-element contact in a broader range of spall sizes than has been investigated to date, with intermittent contact between rolling-element and the outer race, which is a relevant defect size for diagnostics and prognosticsquery. The analysis is performed in several time intervals according to periods of rolling-element/race contact and periods when the rolling-element is not connected with the outer race. An explicit expression of the spall size as function of the time-to-impact has been developed by considering radial load, shaft speed, and gravity. The expression of the spall size was used in a sensitivity study of the effect of parameters such as geometry and radial load. The results obtained from the new model are in good agreement with a well-established general bearing model. The acceleration of the outer ring during the rolling-element/spall interaction with intermittent rolling-element race connection is a novel contribution, which allows verification of the model from direct observations using vibration sensors mounted on the structure 相似文献