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1.
Ti-46Al-2Cr-2Nb和Ti6Al4V合金的干摩擦学性能对比研究   总被引:1,自引:1,他引:0  
本文以商业Ti-6Al-4V合金为参照,考察了Ti-46Al-2Cr-2Nb(原子比)金属间化合物在不同载荷和速率下的干摩擦学行为,结果表明:Ti-46Al-2Cr-2Nb和Ti6Al4V合金的摩擦系数几乎相同,而Ti-46Al-2Cr-2Nb金属间化合物比Ti-6Al-4V具有更好的抗磨性;Ti-46Al-2Cr-2Nb和Ti6Al4V合金的磨损率均随载荷的增加而增加,Ti-46Al-2Cr-2Nb合金磨损率随滑动速率增加而增加,Ti-6Al-4V合金磨损率却随滑动速率增加呈下降直至稳定的趋势;Ti-46Al-2Cr-2Nb合金的磨损机制主要为疲劳磨损,Ti-6Al-4V合金的磨损机制为塑性变形,犁沟和剥落.  相似文献   

2.
通过对航空发动机空心风扇叶片用Ti-6Al-4V 随炉试样的高周和超高周疲劳试验研究,揭示了Ti-6Al-4V 材料在107 循环周次以上同样会发生疲劳破坏. 采用三参数幂函数寿命曲线拟合了高周和超高周的疲劳性能数据,发现可以较好地将两种试验下的数据衔接起来,结果显示在此试验条件下基于超声的超高周疲劳试验的频率效应可以忽略. 通过断口分析表明,超高周试样在试样表面没有缺陷的情况下,裂纹大多数是从材料内部或次表面萌生,而高周疲劳试样的裂纹是从材料表面开始萌生.  相似文献   

3.
通过对航空发动机空心风扇叶片用Ti-6Al-4V随炉试样的高周和超高周疲劳试验研究,揭示了Ti-6Al-4V材料在10~7循环周次以上同样会发生疲劳破坏.采用三参数幂函数寿命曲线拟合了高周和超高周的疲劳性能数据,发现可以较好地将两种试验下的数据衔接起来,结果显示在此试验条件下基于超声的超高周疲劳试验的频率效应可以忽略.通过断口分析表明,超高周试样在试样表面没有缺陷的情况下,裂纹大多数是从材料内部或次表面萌生,而高周疲劳试样的裂纹是从材料表面开始萌生.  相似文献   

4.
网纹型表面微结构对Ti-6Al-4V水润滑摩擦学特性的影响   总被引:1,自引:1,他引:0  
研究了Ti-6Al-4V合金表面网纹型微结构与Si3N4小球对摩时的水润滑摩擦学性能.利用电火花加工技术在Ti-6Al-4V合金表面加工出不同尺寸的网纹结构,运用正交试验设计方法分析了网纹宽度、深度、间宽比和网纹角度对Ti-6Al-4V合金水润滑摩擦学性能的影响.结果表明:具有合适几何参数的网纹结构能够降低摩擦副在水润滑条件下的摩擦系数和磨损量.当网纹角度在45°时,摩擦副的摩擦系数和磨损量能同时降低.网纹宽度对稳态摩擦系数的影响最大,而网纹深度和夹角对摩擦副材料的磨损影响最大.  相似文献   

5.
摩擦系数对钛合金等通道转角挤压影响的有限元分析   总被引:2,自引:0,他引:2  
以Ti-6Al-4V钛合金高温变形行为研究为基础,建立了等通道转角挤压(ECAE)的三维模型,运用DEFORM-3D有限元分析软件模拟了600 ℃等温条件下不同摩擦系数对Ti-6Al-4V合金ECAE过程中的温度场,等效应力,等效应变以及等效应变率的影响。结果表明:核心高温区以及核心应力区主要集中于转角处;随着摩擦系数增大,核心高温区面积增大,转角入口区的应力也有所增加;点迹跟踪结果表明各点应变均在经过转角处达到最大值,内角点及外角点处的变形较不稳定。  相似文献   

6.
采用基于霍普金森压杆的新型加载技术对Ti-6Al-4V材料的动态剪切特性及失效机理进行了测试研究。获得了Ti-6Al-4V材料在超过104 s-1应变率下的剪应力-剪应变曲线及失效参数。研究发现,材料的流动应力存在明显的应变率强化效应;随着应变率的增加,材料的失效应力逐渐增大,而失效应变逐渐减小。采用ABAQUS/Explicit对加载过程进行了数值模拟。结果显示,剪切区材料基本处于平面剪切状态,应力应变场分布较为均匀,计算得到的剪应力-剪应变曲线与实验结果吻合较好。经断口分析可知,随着应变率的升高,Ti-6Al-4V的失效机理存在由韧窝、拉伸韧窝至台阶及河流花样的演化过程,材料的失效模式主要表现为韧性断裂。  相似文献   

7.
本文研究疲劳载荷作用下双相钛合金Ti-6Al-4V中片层结构对微观几何缺陷区域演化的影响.基于晶体塑 性有限元(Crystal Plasticity Finite Element, CPFE)理论,建立含微观椭圆缺陷的双相片层代表性体积单元 (Representative Volume Element, RVE)模型,通过调控缺陷附近的微观组织形貌,使缺陷两端分别出现单相结构和 片层结构,以突出双态合金中片层结构分布对微观缺陷演化的影响.模拟结果表明,位于微观缺陷两侧的晶粒, 片层结构的应变敏感性更大,应变沿缺口环向和沿晶内均呈不连贯波动.片层结构通过调节晶内应变,扩大承载 范围,可提高双相钛合金的抗疲劳特性.这一研究结果可为双相钛合金的疲劳裂纹萌生提供一个新的解释途径  相似文献   

8.
采用超声疲劳方法,开展了医用Ti-6Al-4V在实验室大气和模拟体液两种环境条件下105~109周次范围内的疲劳实验,研究了Ti-6Al-4V的疲劳裂纹萌生与初始扩展行为。实验结果表明:与实验室大气相比,在模拟体液环境下,Ti-6Al-4V的疲劳强度降低了约200MPa。主要原因是疲劳裂纹扩展门槛值减小,促进了疲劳裂纹的萌生和扩展。在两种环境下都发现:高应力短寿命条件下,疲劳裂纹萌生源于微区破碎;而在低应力长寿命条件下,疲劳裂纹萌生源于微区开裂。理论分析表明,粒状亮面(Granular Bright Face,GBF)区的形成与裂纹尖端塑性区和Ti-6Al-4V晶粒尺寸大小有关。  相似文献   

9.
为分析不同材料和尺寸的薄板试样在室温下拉伸破坏后均形成与横截面夹角在20°~25°之间斜断口的原因,首先用统计方法对试样内随机分布微缺陷进行讨论,提出一种在宏观尺度上材料内微缺陷分布局部非均匀简化模型的假设.应用含孔材料损伤本构模型对含有不同方向微缺陷分布局部非均匀薄带区域的16MnNb薄板试样变形至破坏全过程进行数值模拟.结果表明,斜断口形成主要是由于试样内在与横截面夹角小于45°的带形区域内微缺陷分布局部非均匀造成,且与该带形区域在试样中位置无关;由于考虑微缺陷分布局部非均匀,得到试样的斜断口形成过程与试验现象完全一致;同时结合试验断口形貌,对变形过程中颈缩截面内损伤演化和破坏过程进行研究,进一步解释薄板试样的损伤破坏机制.  相似文献   

10.
三轴应力场中不同形状孔洞的长大及其新模型   总被引:2,自引:0,他引:2  
对不同形状孔洞在从光滑试样到裂纹试样这样广泛三轴应力场中的长大规律,本文通过控制体胞宏观应力三维度的方法进行了精确的有限元分析,计算结果表明:(1)孔洞的体积改变和形状变化是孔洞演化的两种基本机制,在不同的三轴应力场中,这两种机制的作用不同;(2)现有模型对孔洞长大规律的描述是不准确的,由它们得到的临界孔洞扩张比参数HGC与临界孔洞体积分数fc不具备一一对应关系,因此不以很好地反映也洞的实际扩张。在此基础上,提出了一个描述孔洞长大的新模型,与四种常用的现有模型相比,该模型不仅能更好地描述不同三轴应力场中孔洞的长大,而且能反映不同应力三维度水平下材料破坏模式的变化。  相似文献   

11.
This study presents a microlithography-based approach to increase the spatial resolution of strain mapping by micrographic digital image correlation. A micro-mesh with a lattice size of 500 nm was added on the surface of a Ti-6Al-4V alloy specimen with a coarse lath size of 1.1 μm. Although the micro-mesh pattern was not random, a combination of the laminated microstructure and the micro-mesh enabled sub-micrometer strain mapping through digital image correlation even for coarse lath larger than 1 μm. Specifically, the strain mapping technique used in this study was applied to characterize the strain component and distribution near an artificial sharp micro-stress concentration site introduced by a focused ion beam. The strain characterization under tensile deformation clarified that cracking occurred via shear strain localization at the micro-stress concentration site, indicating that accumulation of damage (such as vacancy or dislocation) plays an important role in the cracking mechanism of the Ti-6Al-4V alloy.  相似文献   

12.
The two-dimensional functionally graded materials, (2D-FGMs) have been recently introduced in order to significantly reduce the thermal stresses in machine elements that subjected to sever thermal loading. To the author’s knowledge no work was found that investigates the elastic–plastic stress analysis for 2D-FGMs. In the current work, a 3D finite element model of 2D-FGM plates made of ZrO2, 6061-T6 and Ti-6Al-4V with temperature dependent material properties has been proposed to perform such analysis. An elastic plastic stress–strain relation based on the rule of mixture of the 2D-FGM has been introduced in the model. Also, a 3D finite element model of conventional FGM plates, of ZrO2/Ti-6Al-4V and ZrO2/6061-T6, with temperature dependent material properties has been proposed for the investigation of these plates too. Then, elastic–plastic stress analysis of the considered four plates (two conventional FGMs and two 2D-FGMs) under the same transient cyclic heating and cooling was carried out. It was found that heat conductivity of the metallic constituents of FGM has great effect on the temperature distributions that resulting from the thermal loads. Minimum temperatures variation and minimum stresses can be obtained using ZrO2/6061-T6/Ti-6Al-4V 2D-FGM. Also, the results indicate that only ZrO2/6061-T6/Ti-6Al-4V 2D-FGM can stand with the adopted sever thermal loading without fracture or plastic deformations.  相似文献   

13.
This paper summarizes our recent studies on modeling ductile fracture in structural materials using the mechanism-based concepts. We describe two numerical approaches to model the material failure process by void growth and coalescence. In the first approach, voids are considered explicitly and modeled using refined finite elements. In order to predict crack initiation and propagation, a void coalescence criterion is established by conducting a series of systematic finite element analyses of the void-containing, representative material volume (RMV) subjected to different macroscopic stress states and expressed as a function of the stress triaxiality ratio and the Lode angle. The discrete void approach provides a straightforward way for studying the effects of microstructure on fracture toughness. In the second approach, the void-containing material is considered as a homogenized continuum governed by porous plasticity models. This makes it possible to simulate large amount of crack extension because only one element is needed for a representative material volume. As an example, a numerical approach is proposed to predict ductile crack growth in thin panels of a 2024-T3 aluminum alloy, where a modified Gologanu–Leblond–Devaux model [Gologanu, M., Leblond, J.B., Devaux, J., 1993. Approximate models for ductile metals containing nonspherical voids – Case of axisymmetric prolate ellipsoidal cavities. J. Mech. Phys. Solids 41, 1723–1754; Gologanu, M., Leblond, J.B., Devaux, J., 1994. Approximate models for ductile metals containing nonspherical voids – Case of axisymmetric oblate ellipsoidal cavities. J. Eng. Mater. Tech. 116, 290–297; Gologanu, M., Leblond, J.B., Perrin, G., Devaux, J., 1995. Recent extensions of Gurson’s model for porous ductile metals. In: Suquet, P. (Ed.) Continuum Micromechanics. Springer-Verlag, pp. 61–130] is used to describe the evolution of void shape and void volume fraction and the associated material softening, and the material failure criterion is calibrated using experimental data. The calibrated computational model successfully predicts crack extension in various fracture specimens, including the compact tension specimen, middle crack tension specimens, multi-site damage specimens and the pressurized cylindrical shell specimen.  相似文献   

14.
考虑三轴约束时孔洞的聚合机理及有效能量准则   总被引:10,自引:0,他引:10  
李振环  匡震邦 《力学学报》2000,32(4):428-438
通过体胞分析方法,对不同状孔洞在从光滑试样到裂纹试样的三轴应力场中的聚合机理进行了较精解的有限元分析,计算结果表明:(1)孔洞的相互靠近和横向扩展是导致相邻孔洞发生内颈缩聚合的两种基本机制,在应力三维度Rσ等于1.25附近,这两种机制发生较明显的变化。(2)单纯以孔洞体积分数fC概念为基础的材料破坏参数一般敏感于应力三维度,不能很好地预报不同三轴应力场中材料的破坏,在此基础上,提出了描述孔洞聚合的  相似文献   

15.
Molecular dynamics simulations using Modified Embedded Atom Method (MEAM) potentials were performed to analyze material length scale influences on damage progression of single crystal nickel. Damage evolution by void growth and coalescence was simulated at very high strain rates (108–1010/s) involving four specimen sizes ranging from ≈5000 to 170,000 atoms with the same initial void volume fraction. 3D rectangular specimens with uniform thickness were provided with one and two embedded cylindrical voids and were subjected to remote uniaxial tension at a constant strain rate. Void volume fraction evolution and the corresponding stress–strain responses were monitored as the voids grew under the increasing applied tractions.The results showed that the specimen length scale changes the dislocation pattern, the evolving void aspect ratio, and the stress–strain response. At small strain levels (0–20%), a damage evolution size scale effect can be observed from the damage-strain and stress–strain curves, which is consistent with dislocation nucleation argument of Horstemeyer et al. [Horstemeyer, M.F., Baskes, M.I., Plimpton, S.J., 2001a. Length scale and time scale effects on the plastic flow of FCC metals. Acta Mater. 49, pp. 4363–4374] playing a dominant role. However, when the void volume fraction evolution is plotted versus the applied true strain at large plastic strains (>20%), minimal size scale differences were observed, even with very different dislocation patterns occurring in the specimen. At this larger strain level, the size scale differences cease to be relevant, because the effects of dislocation nucleation were overcome by dislocation interaction.This study provides fodder for bridging material length scales from the nanoscale to the larger scales by examining plasticity and damage quantities from a continuum perspective that were generated from atomistic results.  相似文献   

16.
爆炸金属管的绝热剪切断裂宏观研究   总被引:3,自引:2,他引:1  
本文介绍了45号钢、TC4钛合金及WTG05钨合金三种金属管在内部爆炸载荷下的宏观剪切断裂行为,并对此作了一些初浅的分析,提到了实验中发现的钛合金的一种反常单向性剪切起裂现象,同时发现该钨合金在爆炸应变率下表现为脆性断裂。  相似文献   

17.
Hydrostatic stress can affect the non-elastic deformation and flow stress of polymeric materials and certain metallic alloys. This sensitivity to hydrostatic stress can also influence the fracture toughness of ductile materials, which fail by void growth and coalescence. These materials typically contain a non-uniform distribution of voids of varying size-scales and void shapes. In this work, the effects of void shape and microvoid interaction in pressure-sensitive materials are examined via a two-prong approach: (i) an axisymmetric unit-cell containing a single ellipsoidal void and (ii) a plane-strain unit-cell consisting of a single large void and a population of discrete microvoids. The representative material volume in both cases is subjected to physical stress states similar to highly stressed regions ahead of a crack. Results show that oblate voids and microvoid cavitation can severely reduce the critical stress of the material. These effects can be compounded under high levels of pressure-sensitivity. In some cases, the critical stress responsible for rapid void growth is reduced to levels comparable to the yield strength of the material. The contribution of void shape and pressure-sensitivity to the thermal- and moisture-induced voiding phenomenon in IC packages is also discussed.  相似文献   

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