Effects of mechanical properties, residual stress and indenter tip geometry on instrumented indentation data in thin films

In this work, an axisymmetric two-dimensional finite element model was developed to simulate instrumented indentation testing of thin ceramic films deposited onto hard steel substrates. The level of film residual stress (σ_r), the film elastic modulus (E) and the film work hardening exponent (n) were varied to analyze their effects on indentation data. These numerical results were used to analyze experimental data that were obtained with titanium nitride coated specimens, in which the substrate bias applied during deposition was modified to obtain films with different levels of σ_r. Good qualitative correlation was obtained when numerical and experimental results were compared, as long as all film properties are considered in the analyses, and not only σ_r. The numerical analyses were also used to further understand the effect of σ_r on the mechanical properties calculated based on instrumented indentation data. In this case, the hardness values obtained based on real or calculated contact areas are similar only when sink-in occurs, i.e. with high n or high ratio Y/E, where Y is the yield strength of the film. In an additional analysis, four ratios (R/h_max) between indenter tip radius and maximum penetration depth were simulated to analyze the combined effects of R and σ_r on the indentation load-displacement curves. In this case, σ_r did not significantly affect the load curve exponent, which was affected only by the indenter tip radius. On the other hand, the proportional curvature coefficient was significantly affected by σ_r and n.     

基于仪器化Vickers压入比功与马氏硬度识别材料维氏硬度的方法

针对传统维氏硬度测试中因Vickers压痕形貌不清晰导致的维氏硬度无法识别问题,应用量纲定理和有限元数值分析方法对仪器化Vickers压入响应进行了系统分析,同时,结合维氏硬度有限元数值计算结果,揭示仪器化Vickers压入比功、马氏硬度与维氏硬度的近似函数关系。基于上述关系,提出由Vickers压入比功We/Wt和马氏硬度HM识别材料维氏硬度HV的新方法,对该方法进行测试精度分析,验证结果表明该方法较ISO14577中所提维氏硬度仪器化Vickers压入方法具有更高的测试精度。     

折弯机机械补偿机构接触应力的有限元分析

机械补偿机构是金属板材折弯机中普遍使用的挠度补偿机构,它可以减小折弯工件时滑块与工作台挠曲变形带来的不利影响,提高折弯机的制件精度。工作时机械补偿机构受到反复的挤压与拉伸,容易产生强度和疲劳破坏,因此,设计中对其进行强度校核是必不可少的一个环节。本文采用三维弹性接触有限单元法对折弯过程中某型机械补偿机构的接触应力和变形进行了数值模拟。分析结果表明:该机械补偿机构的接触应力满足强度要求,凹槽台面的变形曲线能较好吻合理想加凸曲线。该方法对类似机械补偿机构的强度校核与设计,具有指导意义。     

平面应变鼓包实验测量薄膜力学性能的精度分析

采用有限元法系统地研究了平面应变鼓包实验中鼓包尺寸、薄膜初始条件以及材料参数对薄膜变形行为的影响。然后,根据有限元结果,分析平面应变鼓包实验测量薄膜力学性能的精度。结果表明：尽管原有的平面应变鼓包理论模型测量平面应变模量的精度很高,但是依其测量残余应力的精度并不高,尤其是在低残余应力阶段。最后,根据上述情况,提出一种新的分析鼓包实验数据的方法以提高平面应变鼓包技术的精度和可靠性。     

Structure and mechanical properties of arc evaporated Ti-Al-O-N thin films

The structure, mechanical properties, and machining performance of arc evaporated Ti-Al-O-N coatings have been investigated for an Al_0.66Ti_0.34 target composition and O₂/(O₂+N₂) gas flow-ratio varied between 0 to 24%. The coating structure was analysed using SEM, EDX, XRD, XPS, TEM, and STEM. Mechanical properties were analysed using nanoindentation and the deformation behaviour was analysed by probing the nanoindentation craters. The coatings performances in cutting tests were evaluated in a turning application in low carbon steel (DIN Ck45). It is shown that the addition of oxygen into the arc deposition process leads to the formation of a dual layer structure. It consists of an initial cubic NaCl-structure solid solution phase formed closest to the substrate, containing up to 35 at.% oxygen (O/O+N), followed by steady-state growth of a nanocomposite compound layer comprised of Al₂O₃, AlN, TiN, and Ti(O,N). The addition of oxygen increases the ductility of the coatings, which improves the performances in cutting tests. At high levels of oxygen, (> 13 at.%), however, the performance is dramatically reduced as a result of increased crater wear.     

Finite element modeling of ultrasonic surface rolling process

Ultrasonic surface rolling (USRP) is a newly developed process in which ultrasonic vibration and static force are applied on work-piece surface through the USRP operator to generate a nanostructured surface layer with mechanical behaviors highly improved. Compared with other surface severe plastic deformation (S²PD) methods, it can realize mechanized machining and be directly used for preparing final product. Notwithstanding the excellent performance of USRP, elaborate relation between process parameters and surface layer characteristics is still inadequacy due to inconvenient and costly experimental evaluation. Therefore, in this paper a three-dimensional finite element model (FEM) has been developed to predict the treatment conditions that lead to surface nanocrystallization. Simulated results of surface deformation, stress and strain are investigated to assess the formation of nanostructured layer. The numerical results from the FEM corresponds well with the values measured experimentally, indicating that this dynamic explicit FEM is a useful tool to predict the processing effects and to relate the treating parameters with the surface layer in terms of the size of nanostructured layer, residual stress and work hardening.     

T型管接头挤压胀形过程的有限元分析

根据T形管挤压胀形双重非线性的变形特点，建立了动力分析有限元方程。开发了在HP715／50工作站上运行的程序软件SFMP。对T形管挤压胀形过程及主要因素的影响进行模拟分析，总结归纳了分析结果。     

Finite element modeling of erosive wear

Material damage caused by the attack of particles entrained in a fluid system impacting a surface at high speed is called ‘Erosion’. Erosion is a phenomenon that takes place in several engineering applications. It also can be used in several manufacturing process such as abrasive waterjet machining. Erosion is a complex process dependent on particle speed, size, angle of attack as well as the behavior of the eroded material. Extensive experimental results have been reported in the literature on the erosion of different materials. Simulating the erosion process through finite element enables the prediction of erosion behavior of materials under different conditions, which will substitute the need of experimentation, and will enable the identification of constants required for existing analytical models.In this paper, an elasto-plastic finite element (FE) model is presented to simulate the erosion process in 3D configuration. The FE model takes into account numerical and material damping, thermal elastic–plastic material behavior and the effect of multiple particle impacts as well as material removal. The workpiece material modeled was Ti–6Al–4V. The effects of strain hardening, strain rate and temperature were considered in the non-linear material model. Comparison against results reported in literature and erosion models by Finnie, Bitter and Hashish are made. It is shown that the predicted results are in agreement with published results obtained experimentally and from analytical erosion models.     

矫直计算中钢轨截面简化的有限元分析

平直度是衡量钢轨质量的重要指标之一,铁路发展对钢轨平直度提出更高要求,因而钢轨矫直技术越来越受到重视.在钢轨矫直工艺的参数理论计算中,钢轨截面的简化是重要环节.本文以60kg/m钢轨为例,进行了截面简化原则的探讨,并通过建立适当的有限元模型,运用ANSYS有限元软件对简化前后的钢轨弯曲变形进行了模拟计算,验证了简化结果的准确性,为钢轨矫直的理论研究奠定了基础.     

微纳米覆盖层材料的力学性能表征探讨

使用Agilent公司G200微/纳米压痕仪对多种微纳米覆盖层材料的力学性能进行了测量。结果表明,通过连续刚度法测量微纳米涂层材料,可以获得涂层硬度和弹性模量,并能得到涂层硬度或弹性模量随厚度的变化规律;通过试验也可以看到,纳米压痕法测量膜材的力学性能存在明显的表面效应;基材对膜材的力学性能没有影响;膜材厚度越大,同一深度测得的膜材的弹性模量越高。     

碾压强化有限元建模及分析研究

碾压是强化金属表层的一种重要且很有发展潜力的强化方法,工件表层经碾压变形强化后会表层留有应力,能提高表层硬度和强度,同时还能改善工件表面粗糙度.对装备构件进行碾压模拟,模拟结果显示工件表层经碾压后产生较高应力且内部状态无明显变化,强化效果明显.接着改变下压量进行模拟,发现在一定范围内,随下压量增大,碾压强化效果愈好.     

Elastic moduli and mechanical properties of bulk metallic glasses after quasi-static compression

The effect of quasi-static compressive stress on the elastic moduli and mechanical properties of a Cu₄₆Zr₄₆Al₈ bulk metallic glass (BMG) was investigated. When the applied quasi-static stress is below 2 GPa (equivalent to 1.4 times the yield strength of the BMG), the elastic moduli of the deformed BMGs are found to decrease with the applied stress, revealing the softening or dilatation of the bulk metallic glass. The Poisson ratio is relatively stable when the stress is below 1000 MPa, but it decreases significantly afterwards. Both the plasticity and strength of the BMG are found to increase at low applied stress, and achieve a maximum value before decreasing at higher applied stress. The applied stress is shown to enhance the mechanical properties of the BMG and the properties can be controlled by quasi-static compressive stress. The results demonstrate that an applied stress far below the macroscopic yield strength can still result in microscopic yielding and microstructure change in metallic glass systems.     

Microstructure and mechanical properties of pulsed DC magnetron sputtered nanocomposite Cr-Cu-N thin films

The nanocomposite Cr-Cu-N thin films have been deposited at a substrate temperature of 250 °C by a bipolar asymmetric pulsed DC reactive magnetron sputtering process. Different Cu contents ranging from 0.4 to 14.9 at.% were achieved. The structures of Cr-Cu-N thin films were analyzed by XRD. The surface and cross sectional morphologies of thin films were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The nanoindentation and scratch tests were adopted to evaluate the mechanical and tribological properties of Cr-Cu-N coatings. The influences of Cu content on the structure, mechanical and tribological properties of Cr-Cu-N coatings were explored. It is observed that the columnar structure no longer exists when the Cu content exceeds 10.9 at.%. The stability of CrN phase in the coating is influenced by the Cu content. The scratching coefficient of thin films decreases with increasing Cu content. Sufficient adhesion and tribological properties of Cr-Cu-N coatings are achieved. The maximum average hardness around 20 GPa and scratching coefficient around 0.1 are found in the coatings with around 2.1 to 2.6 at.% Cu in this work.     

2000kN压力机曲轴有限元分析

曲轴作为机械压力机的关键零部件,承受周期性的冲击载荷,其受力分析是压力机设计中的一个重要环节。本文对某公称力为2000kN压力机的曲轴进行了三维实体有限元建模,分析曲轴在公称力冲击下的应力分布,并将分析结果与许用应力进行比较,为压力机曲轴的优化设计提供了有价值的理论依据。     

折弯机侧板有限元分析与优化

折弯机侧板是承受工作载荷最主要的部件之一,其刚度和强度直接影响折弯机的使用性能。本文采用有限元分析软件对折弯机整体建模并仿真计算,描述了侧板不同厚度、不同宽度及不同喉口半径对整体最大变形与喉口最大应力的影响。优化后的机身不但有效降低了喉口处的应力,而且还节约了材料,降低了制造成本。     

滚切式剪板机剪切过程有限元分析

滚切剪是一种先进的中厚钢板剪切机,在板材剪切质量和剪切效率方面存在诸多优点.本文以某厂4300滚切剪为研究对象,对滚切剪的剪切模型进行简化,在三维有限元软件DEFORM-3D软件中建立了滚切剪的有限元模型;对该模型进行剪切过程模拟,分析了剪切过程中剪切力的变化趋势.     

液压管道受迫振动的有限元分析

本文讨论了液压系统管道受迫振动的有限元分析法。通过对管壁的三角形网格划分,建立了管道质点受迫振动的动态模型。     

SP-160开式压力机机身的有限元分析及优化

通过对SP-160型开式压力机机身的受力进行有限元分析及计算,研究在公称压力下机身各部位的变形和应力分布,依此对机身结构进行优化设计。使用SolidWorks进行机身的有限元三维模型的创建,利用ANSYS和SolidWorks的接口直接导入ANSYS Workbench,对机身进行强度和刚度分析,根据分析结果在SolidWorks中完成机身三维模型结构的改进,从而达到减轻自重、降低成本的目的。     

插件板和电机壳冲压成形有限元模拟分析

结合插件板和电机壳两个多工序冲压成形模拟实例，介绍DYNAFORM—PC软件在钣金成形有限元分析中的应用和技巧。     

Evaluation of mechanical properties of structural materials by a spherical indentation based on the representative strain-an improved algorithm at great depth ratio

At great depth ratio,two methodologies based on the representative strain were improved to extract mechanical properties of metallic engineering structural materials from P-h curve of an indentation response. The improved aspects include:the combination of great ratio h 1 /R=0.1 and h 2 /R=0.4 replaced h 1 /R=0.01 and h 2 /R=0.06(Cao s method) and h 1 /R=0.1 and h 2 /R=0.3(Ogasawara s method) ;three types of metallic engineering structural materials with obviously different elastic modulus were dealt with t...