Deformation and Fracture of Zirconium Alloy at Low Temperatures

This paper describes the results of an experimental study on deformation and fracture of a Zr–1% Nb zirconium alloy in the case of multiple loads at low temperatures (?80°C). Samples cut out of pipes and applied as shells of nuclear fuel elements of fuel assemblies of nuclear reactors are used to conduct a series of experiments on low-cycle stretching and compression at low temperatures and study the effect of low temperature on stress relaxation in the material under different numbers of preliminary loads.     

A Numerical Study of the Applicability of the Shear Compression Specimen to Parabolic Hardening Materials

This paper addresses quasi-static loading of the shear compression specimen (SCS), that has been especially developed to investigate the shear response of materials at various strain rates. Previous work [4, 5] addressed bi-linear hardening materials, whereas the present work concerns parabolic hardening materials. The investigation is done numerically using three-dimensional elastoplastic finite element simulations. The analyses show that the averaged von Mises stress ( ) and strain ( ) on a mid-section of the gauge reflect accurately the prescribed parabolic hardening model. A method for finding the parabolic hardening coefficients and reducing the measured load, P, and displacement, d, into equivalent stress and strain is introduced and tested. A very good agreement is observed, thus confirming the potential of the technique for large strain testing of parabolic hardening materials.     

Influence of Portevin-Le Chatelier Effect on Shear Strain Path Reversal in an Al-Mg Alloy at Room and High Temperatures

The main objective of this study is to characterize the mechanical behaviour of an Al-Mg alloy in conditions close to those encountered during sheet forming processes, i.e. with strain path changes and at strain rates and temperatures in the range 1.2×10^?3–1.2×10^?1 s^?1 and 25–200°C, respectively. The onset of jerky flow and the interaction of dynamic strain ageing with the work-hardening are investigated during reversed-loading in specific simple shear tests, which consist of loading up to various shear strain values followed by reloading in the opposite direction, combined with direct observations of the sample surface using a digital image correlation technique. Both strain path changes and temperature are clearly shown to influence the occurrence and onset of the Portevin-Le Chatelier (PLC) effect. Moreover, the Bauschinger effect observed in the material response shows that the PLC effect has a major influence on the kinematic contribution to work-hardening as well as its stagnation during the reloading stage, which could open up interesting lines of research to improve theoretical plasticity models for this family of aluminium alloys.     

冰在低温下的单轴压缩力学行为和破坏机制

利用带有低温装置的Instron5848材料实验机和分离式Hopkinson压杆装置(SHPB),在-10℃、-20℃和-30℃温度下,对多晶冰进行了应变率为10-4~102 s-1范围内的单轴压缩力学性能实验,分析了实验结果的可靠性和有效性.研究发现:冰的压缩强度具有明显的温度和应变率敏感性,随应变率的增大、温度的降低而提高;压缩强度与应变率对数呈线性关系,应变率的升高会增强降温对压缩强度的强化效应.在研究的应变率和温度范围内,冰主要有径向膨胀、纵向劈裂和整体破碎三种破坏模式,内应力释放速率和氢键强度的变化是导致多晶冰破坏模式改变的主要原因.     

A Modified Iosipescu Method to Study In-Plane Shear Strength of C/SiC Composites at Elevated Temperatures in Air

Experimental Mechanics - Accurate evaluation of life-limiting failure behavior is a prerequisite to ensure the successful design and application of ceramic matrix composites (CMCs). To investigate...     

新型铝锡硅合金高温塑性变形流变应力的研究

采用高温等温压缩变形方法,在温度为373-673K范围和应变速率为0.001-1.0s^-1范围内,测定了新型Al-10Sn-4Si合金的流变应力曲线,结果表明,该合金为正应变速率敏感材料并且具有稳态流变特征;稳态流变应力随变形速率的增加而增大,随变形温度的升高而降低,通过回归分析,建立了该合金高温塑性变形时稳态流变应力的半经验方程,这种稳态流变特征与动态回复、动态再结晶及局部晶界粘滞性流动行为有关,受热激活过程控制。     

多晶纯钛在高应变率不同温度下的拉伸力学行为实验研究

利用MTS809和自行研制的旋转盘冲击拉伸试验机,对多晶纯钛进行了应变率为0.001s-1和300s-1、温度为298K至973K的拉伸试验和应变率为300 s-1不同温度下的冲击拉伸复元试验,得到了多晶纯钛的拉伸应力应变曲线和高应变率等温应力应变曲线。试验结果表明,多晶纯钛的拉伸力学行为具有应变率和温度相关性。采用修正的Johnson-Cook模型进行数值拟合,结果表明,该本构模型能较好地表征多晶纯钛在试验应变率和温度范围内的拉伸力学行为。     

Using Carrier Fringes to Study the High Temperature Deformation Behavior of a BGA Package Under Extended Dwell Times

There is a compelling need to experimentally understand solder joint deformation behavior at high temperatures over an extended period of time. Accordingly, the deformation behavior of solder joints in a Ceramic Ball Grid Array (CBGA) package mounted on an organic FR4 board under extended dwell time at a high temperature has been studied using laser moiré interferometry. The warpage and the in-plane horizontal deformation of the ceramic substrate and the organic board as a function of time were determined. The variation of the normal strains and shear strains in the solder joints with time were also investigated. It was found that increased sensitivity was necessary to accurately determine the strains in the small sized solder joints. A new method utilizing carrier fringes to increase the sensitivity of the moiré interferometry system is proposed and has been used to determine the strains in the small sized solder joints. Increased sensitivity can be obtained merely by changing the incident angle of the laser light on the surface of the specimen, thereby making it unnecessary to use expensive phase shifting apparatus with the traditional laser moiré system.     

一种高比压润滑涂层的研制及其摩擦学性能研究

利用粘结剂共混改性和填料复合等技术研制了一种润滑涂层,该涂层适用于高比压、低速度下的滑动和滚动摩擦部件,具有良好的摩擦磨损性能,与同类产品相比,该润滑涂层能够随1500-2000MPa的高比压,并具有低摩擦、长寿命及良好的储存稳定性和耐温性等特点,已成功应用于国家某重点工程的零部件上。     

铝合金2A70高应变率力学性能及其本构关系实验研究

在室温下,利用分离式Hopkinson拉杆系统进行了平行和垂直流线方向切割的铝合金2A70圆棒试样的高应变率(1300~2300/s)拉伸实验;利用分离式Hopkinson压杆系统进行了圆柱试样的高应变率(1100~11000/s)压缩实验,分析了应变率与试样切割方向对试样力学性能的影响,并对比研究了不同应变率下试样断口的形貌。实验结果表明,铝合金2A70的屈服强度在应变率达到11000/s时会得到一定提高;垂直流线切割的试样强度略高于平行流线切割的试样;随应变率升高,拉伸试样的断口更为平滑,颗粒细密,但压缩试样会形成环状的粗晶区。最后基于实验数据拟合了J-C(Johnson-Cook)本构模型参数。     

云纹干涉反转倍增法及其在微电子组件变形场测量中应用

本文提出并介绍了云纹干涉反转倍增法，该方法将光学载波、反转剪切、富立叶变换倍增技术巧妙地结合于云纹干涉光路中。利用载波频率，把带载波的云纹干涉变形图在富立叶变换系统中进行条纹倍增，而试样变形信息也倍增了相同倍数，将云纹干涉的测量灵敏度又提高了一个数量级。在实验中实现了１６倍倍增，即位移测量灵敏度由０．４μｍ提高到０．０２５μｍ（虚栅频率１／２４００）。将这一方法用于测量热载下金属Ｎｉ膜／ＺｒＯ２陶瓷基界面裂纹尖端面内位移场，分析裂尖位移奇异性。实验表明：热载作用下，膜／基组件界面裂纹尖端的位移奇异性具有指数奇异特性，其奇异性指数与膜／基材料，界面层特性等有关     

Modal Analysis of a Servo-Hydraulic High Speed Machine and its Application to Dynamic Tensile Testing at an Intermediate Strain Rate

This paper describes the experimental procedure to identify the predominant frequencies of the high speed testing machine by conducting modal analysis. The effects due to the predominant frequencies of the system and loading rate on the magnitude of system ringing and the flow stress were analyzed by using a single degree-of-freedom (SDOF) spring-mass-damper model. The system was then used to study the dynamic tensile behavior of two engineering materials, i.e., polyethylene (PE) fabric-cement composite and Alkaline Resistant (AR) glass fabrics at an intermediate strain rate. The stress oscillations in the response of these materials due to system ringing were addressed. The failure behavior of each material was studied by examining high speed digital camera images of specimens during the test. The validity of the dynamic tensile tests was investigated by examining the condition of dynamic stress equilibrium—a criterion used in split Hopkinson pressure bar (SHPB) tests. The results show that the quantitative criterion for a valid SHPB test is also applicable to dynamic tensile tests of these materials at the intermediate strain rate.