高强度钢拉伸试验液压夹具改进

针对高强度钢在进行拉伸试验时,液压夹具报废率高,试样时常发生打滑、滑脱,导致试验结果出现异常甚至作废的情况,提出了改变试样夹紧方式、增加台阶加力面的改进方案。结果表明:液压夹具经改进后,不仅有效避免了试验过程中试样打滑、滑脱现象的发生,还使拉伸试验机液压夹具有了更多的新用途。     

试样夹具对钛合金板材室温拉伸试验曲线的影响

从大量钛合金板材室温拉伸试验中发现,如果板材试样夹具使用不当,会造成拉伸曲线异常,直接影响试验结果.为此,按照GB/T228-2002室温拉伸试验方法,分别选用规格为3.0 mm和1.2 mm厚的TA15以及2.5mm厚的TC4钛合金板材试样,采用打孔夹具和楔形夹具夹持试样进行室温拉伸试验,对拉伸曲线出现的异常现象进行了分析.结果表明,用打孔夹具夹持强度高达1 000 MPa的TA15,TC4板材试样进行拉伸试验时,将会发生连接销和试样孔接触打火、震动,孔变形而造成拉伸曲线出现异常驼峰现象,因此无法根据拉伸曲线计算出正确的屈服强度(σ0.2).如果换用楔形夹具夹持试样进行试验,则可得到正常的拉伸曲线而不影响真实屈服强度的计算.故合理选取夹具进行试验,是获得正常拉伸曲线及真实强度值的关键因素.     

试验参数对不锈钢包壳管环向拉伸的影响

包壳管是反应堆内重要的安全屏障,其在服役环境下承受一定裂变气体内压,同时面临芯块和包壳间机械相互作用的考验.开展包壳管环向拉伸性能研究,对反应堆燃料组件设计和安全分析具有重要意义.奥氏体不锈钢是快中子反应堆包壳管重要候选材料,具有良好的高温力学性能.本文针对奥氏体不锈钢包壳管高温环向拉伸试验,研究了夹具、标距段宽度和润滑条件等试验参数对包壳管环向拉伸试验的影响.结果表明:三嵌块夹具可以避免试样标距段向内展平,且夹具和试样间摩擦力较小;标距段的宽度对包壳管环向拉伸强度影响不大,但是标距段宽度过大或者过小都会造成试样延伸率下降;夹具与试样间隙的摩擦会增加拉伸载荷,降低延伸率,使用石墨润滑可以有效减小摩擦力的影响.     

介绍一种在试样上打钢字模的夹具

金属材料的拉伸、冲击等试验中,在试样端头打钢字模时,由于试样端面小,不易夹持,会出现将拉伸试样打弯,冲击试样打飞的情况。若试样较多,会使这一问题更棘手。在实践中,我们自制了一个试样打钢字模用夹具,很好地解决了这一难题。     

20SiMn2MoVA钢氢脆断口的分析及消除

针对20SiMn2MoVA高强钢拉伸试验中断面收缩率低的情况，利用扫描电镜和能谱仪等手段对拉伸试样断口进行了分析。试验结果表明，出现在20SiMn2MoVA高强钢拉伸试样断口表面上的圆形白亮斑点是一种氢致缺陷。它是在氢和拉伸应力共同作用下，在应变过程中形成的一种独特断裂面，也是引起钢材断面收缩率低的主要原因。通过采用低温去氢处理后，钢材的断面收缩率得到明显恢复，消除了氢脆断口。     

钢绞线拉伸试验的夹具及引伸计的改造应用

钢绞线强度高,缺口敏感性大,拉伸试样长,对它进行拉伸试验,必须具备特制的夹具和大标距引伸计,本文介绍了改造后夹具与引伸计在钢绞线上试验中应用的成功经验.     

金属圆棒试样室温下高应变速率拉伸试验浅析

在不同应变速率下对铸铁和铸铝圆棒试样进行了单轴高速拉伸试验,研究了它们的动态力学性能及断裂情况,分析了相关因素对试验的影响。结果表明:测试应变、应力的方法,试样标距长度及夹持端长度等对试验准确性和曲线振荡程度有较大影响;使用比刚度和比强度高的夹具、短标距试样、应变片测试应力、两台相机测试应变、适当增加夹持端长度可以提高试验结果的准确性。     

基于尺寸效应的镁合金箔材本构关系的研究

目的探究AZ31镁合金微拉伸过程中存在的尺寸效应,提出适用于镁合金微拉伸的本构模型。方法以AZ31镁合金箔材为试验材料,分别针对不同厚度和不同晶粒大小的试样进行微拉伸试验。结果试样在单向拉伸时存在明显的尺寸效应,在实验数据的基础上对Swift模型进行修正,得到了适用于镁合金微拉伸过程的本构方程。结论用表面层模型解释了不同厚度的试样,在微拉伸试验时出现的尺寸效应现象,用细晶强化理论解释了不同晶粒尺寸的试样,在微拉伸试验时出现的尺寸效应现象;修正后的本构模型与试验数据吻合较好。     

避免拉伸试样严重打滑的几种方法

指出要重视拉伸试样的“严重打滑”。对楔型夹具夹紧力公式作了推导。对试样的夹紧过程及夹紧操作的通病作了讨论。最后,给出了6种避免拉伸试样严重打滑的方法。     

SS400热扎钢板拉伸试验分层断口的显微分析

对SS400热轧钢板拉伸试验出现的断口分层进行了分析。用扫描电镜分别对断口、断口磨面以及平行于拉伸方向、垂直于钢板表面的剖面进行了显微观察，发现分层现象与试样中超长的带状组织密切相关。用能谱仪对断口分层处和超长铁素体带上的夹杂物进行了成分分析，证实均为硫化物。试样拉伸时在铁素体带上密集分布的硫化物处产生大量微裂纹，同时超长铁素体带的变形又受到阻碍，导致该处在试样拉断之前裂纹已经贯通，最终在断口上形成分层。因此，拉伸试验断口出现分层的原因是试样中存在密集分布的硫化物和超长的带状组织。     

整体中空夹层复合材料的弹性性能分析

基于织物真实形态选取了整体中空夹层复合材料的最小结构单元,确定了几何参数和纤维体积含量的计算方法,建立了力学模型,并在此基础上预测了整体中空夹层复合材料的弹性常数。分析了当绒经和地经纱的织造密度保持一定的比例不变时,不同织造参数下面板弹性性能的变化。制作了侧拉、平压试件并进行了性能测试,通过实验值和理论预测值的对比,表明了力学模型的正确性。     

Study of microcellular injection-molded polypropylene/waste ground rubber tire powder blend

Microcellular polypropylene/waste ground rubber tire powder blend processing was performed on an injection-molding machine with a chemical foaming agent. The molded samples produced based on the design of experiments (DOE) matrices were subjected to tensile testing and scanning electron microscope (SEM) analyses. Molding conditions and waste ground rubber tire (WGRT) powder have been found to have profound effects on the cell structures and mechanical properties of polypropylene (PP) and waste ground rubber tire powder composite samples. The result shows that microcellular PP/WGRT blend samples exhibit smaller cell size and higher cell density compare with polypropylene resin. Among the molding parameters studied, chemical foaming agent weight percentage has the most significant effect on cell size, cell density, and tensile strength. The results also suggest that tensile strength of microcellular PP/WGRT composites is sensitive to weight reduction, and skin thickness.     

基于响应面法橡皮成形侧压块参数优化及验证

橡皮成形是飞机钣金零件制造的一种重要的成形工艺,为提高典型零件橡皮成形的效率,针对橡皮成形过程中产生的起皱问题,基于响应面法对侧压块参数进行优化.首先对新淬火状态下的铝合金板料进行材料试验,分析了其成形性能指标参数,为有限元模拟提供材料本构关系与模型;然后以起皱量化为优化目标,将凸弯边的最大增厚率作为侧压块优化的目标函数,为得到典型零件橡皮成形侧压块精确的几何参数,采用Abaqus有限元软件对带侧压块成形过程进行正交模拟试验,得出侧压块几何参数对起皱指标影响程度的主次关系,并得到最优的参数水平组合.基于响应面建模方法建立了侧压块最优几何参数和起皱指标之间的多项式关系,并用遗传算法进行参数优化,利用优化后的工艺参数进行有限元模拟,阐述了侧压块防皱原理;最后通过实际成形试验,验证了有限元模拟的可行性和优化方法的可靠性.     

Tensile Properties of Electrodeposited Nanocrystalline FCC Metals

Bulk nanocrystalline Ni and Ni-15wt%Fe alloy were fabricated via electrodeposition techniques. The nominal grain size of nickel samples was varied from 15 to 200 nm by employing different deposition parameters. The grain size was further reduced to 9 nm by alloying nickel with iron. The tensile properties were evaluated at room temperature using dog-bone shaped samples. The results of this study confirm that strength and strain hardening rate increase with decreasing grain size. The fracture behavior was found to depend on the grain size, presence of large and small defects, and the stress state. The tensile elongation and reduction in area varied significantly among the samples and did not correlate with the fracture behavior. Three categories of behavior were identified. In Type I the samples showed completely ductile fracture but very low tensile elongation. In Type II the samples showed a relatively brittle behavior but impressive tensile elongation. In Type III the samples showed ductile behavior with reasonable tensile elongation. In this article, the tensile elongation and the fracture mode of nanocrystalline face centered cubic (FCC) metals are discussed in terms of deformation behavior and presence of defects.     

基于正交试验分析的阳极键合强度研究

采用抗拉强度作为键合质量评价的指标,对硅-玻璃阳极键合的键合温度、冷却速度、退火温度和时间等四个参数的三个位级下的键合效果进行了分析。通过采用正交试验分析法,将81组试验减少为9组并进行了试验。采用自制的抗拉强度测试机对强度进行了测试,结果发现,阳极键合后的冷却速度对强度的影响最为显著,冷却速度越低,强度越高。最后对断裂面进行了SEM分析并对试验结果进行了讨论。     

The graphical interpretation of fracture load data for doubly-convex cylindrical discs

A set of graphs is developed for the determination of the material tensile strength of a brittle, doublyconvex cylindrical disc from the disc dimensions and the fracture load in in-plane diametral compression. Graphs are also presented relating the normalized geometric variables of the disc and giving the normalized volume of the disc in terms of the geometric parameters.     

Equivalent Tensile Properties Analysis of the Dimpled Sheet

A dimpled sheet is a novel cold-roll structure made from a plain sheet. The yield strength and elastic modulus of the sheet are altered significantly during the dimpling process. In this study, the equivalent tensile properties of a dimpled sheet are examined. First, tensile testing of a dimpled sheet with typical structural parameters is conducted. Then, finite element analysis based on a unit cell is used to analyze the tensile properties; the results are found to be in good agreement with the experimental findings. Finally, the effects of different structural parameters on the equivalent tensile properties of the dimpled sheet are investigated. The results show that the tensile properties can be obtained using the unit-cell finite element method. Further, the changes in the tensile properties are caused by geometric variations and work hardening occurring during the dimpling process. The yield strength of the dimpled sheet first increases and then decreases as the relative thickness increases. However, the yield strength decreases with increasing relative period distance. The equivalent elastic modulus decreases as the relative thickness increases, but increases with the relative period distance. This study and its findings provide theoretical support for optimal design of a dimpled sheet under tensile loading.     

Experimental identification of a lattice model for woven fabrics: Application to electronic textile

Lattice models employing trusses and beams are suitable to investigate the mechanical behavior of woven fabrics. The discrete features of the mesostructures of woven fabrics are naturally incorporated by the discrete elements of lattice models. In this paper, a lattice model for woven materials is adopted which consists of a network of trusses in warp and weft direction, which represent the response of the yarns. Additional diagonal trusses are included that provide a resistance against relative rotation of the yarns. The parameters of these families of discrete elements can be separately identified from tensile experiments in three in-plane directions which correspond with the orientations of the discrete elements. The lattice model and the identification approach are applied to electronic textile. This is a fabric in which conductive wires are incorporated to allow the embedment of electronic components such as light-emitting diodes. The model parameters are established based on tensile tests on samples of the electronic textile. A comparison between the experimental results of an out-of-plane punch test and the simulation results shows that the lattice model and its characterization procedure are accurate until extensive biaxial tensile deformation occurs.     

Modeling and prediction of weld shear strength in friction stir spot welding using design of experiments and neural network

Friction Stir Spot Welding (FSSW) is a kind of the friction stir welding (FSW) process, creates a spot, lap‐weld without bulk melting work materials. The tensile shear strength of the FSSW welded joints mainly depends on the pin height, tool rotation and welding time. In the present study, two of the techniques, namely factorial design and neural network (NN) were used for modeling and predicting the tensile shear strength of EN AW 5005 aluminum alloy. Tensile shear strength was taken as a response variable measured after welding pin height, tool rotation and welding speed were taken as input parameters. Relationships between tensile shear strength and welding parameters have been investigated. The level of importance of the FSSW parameters on the tensile shear strength was determined by using the analysis of variance method (ANOVA). The mathematical relation between the tensile shear strength and FSSW welding parameters were established by regression analysis method. This mathematical model may be used in estimating the tensile shear strength of FSSW joints without performing any experiments. Finally, predicted values of tensile shear strength by techniques, NN and regression analysis, were compared with the experimental results and their nearness with the experimental values assessed. Results show that, NN is a good alternative to empirical modeling based on full factorial design.     

Residual tensile strength monitoring of drilled composite materials by acoustic emission

Drilling results in damage such as delamination and matrix cracking around the hole and might ultimately causes degradation in the residual tensile strength of the drilled components. The damage induced during the drilling of composites can be detrimental to the mechanical behavior of the composite products. In this work, the effects of machining parameters (feed rate and cutting speed) and drill point angle on thrust force, the adjusted delamination factor and residual tensile strength are investigated. The Taguchi technique for the design of experiments was employed to analyze the thrust force, adjusted delamination factor and residual tensile strength of woven glass/resin epoxy. The results show that feed rate and drill point angle are the most important parameters. During tensile testing of drilled laminates, acoustic emission (AE) events were recorded. By feature extraction of AE time domain parameters, the suitable parameter for detecting the characteristics of thrust force and tensile force were determined. The AE mean power (MP) and cumulative count correlated well with thrust force and tensile force, respectively.