TC21钛合金缺口疲劳试样的应力分布计算

采用有限元程序计算TC21钛合金圆形缺口试样不同载荷下缺口根部的应力分布，以及循环载荷下缺口根部的循环应力比的变化。结果表明，缺口根部的轴向应力集中因子Kσ和应变集中因子Kε与载荷大小有关，但变化趋势不同。缺口根部区处于三向应力状态，尽管三向应力的最大值的位置随载荷变化而变化，但等效应力最大值在表面。根部位置切向应力与轴向应力的比值随着载荷的变化而变化。由于缺口根部的塑性变形，随载荷升高，缺口根部的应力比降低，当名义应力超过1100MPa时，应力比反而增加。在疲劳过程中，高循环应力时，缺口根部的应力比也有一定变化。     

残余应力与外加载荷共同作用对裂尖前端应力场的影响

用机械预压缩法在裂纹前端引入残余应力,模拟了残余应力与外加载荷共同作用下CT试样裂尖前端的应力场,对比分析了外加载荷、刚体压缩位置和缺口半径对裂尖前端残余应力重新分布的影响。结果表明,随着外加载荷的增大,残余应力拉压应力峰值均有远离缺口前端的趋势,外加载荷和刚体压缩位置的改变对裂纹尖端周向张开应力几乎没有影响。小的缺口半径会产生更大的张开应力,更容易导致裂纹的起裂和扩展。     

缺口对TC21合金高周和低周疲劳的影响

研究了缺口对TC21合金在不同温度高周和低周疲劳强度的影响。疲劳试样为光滑和V型缺口（Kt=3）2种试样，疲劳载荷为应力控制，循环应力比为0．1，高周疲劳实验温度为315℃，低周疲劳实验温度为室温及400℃。结果表明，在循环应力较低，缺口根部未塑性变形时，缺口使疲劳强度明显降低。循环应力升高使缺口根部产生塑性变形时，缺口对疲劳强度影响降低，当循环应力升高使光滑试样失稳时，缺口试样的疲劳强度高于光滑试样的疲劳强度。断口的SEM分析表明，缺口试样的疲劳裂纹在缺口根部萌生，即使高周疲劳裂纹源也是多个。     

45钢V缺口轴向和扭转疲劳行为

研究了带环形V缺口45钢轴类的疲劳行为,使用了两种不同缺口尺寸的样品,分别施加轴向和扭转载荷,测试其轴向缺口应力强度因子和扭转应力强度因子以及相应的疲劳寿命,得到了缺口对工件疲劳寿命不同的影响:在轴向载荷下比在扭转载荷下更大,同时得到了缺口应力强度因子与疲劳寿命很好的相关性—缺口应力强度因子越大,工件疲劳寿命越低。     

DOUBLE PEAK OF HYDROGEN ACCUMULATION NEAR NOTCH TIP UNDER Ⅰ＋Ⅱ LOADING MODE

利用ＫＹＫＹ离子探针微分析仪和有限元定量计算发现，２１Ｃｒ７Ｎｉ９ＭｎＮ奥氏体钢在复合型（Ⅰ＋Ⅱ）载荷下，缺口顶端无论在开裂方向还是塑性区尺寸最大方向上，皆有两个氢浓度的富集峰，且随着Ⅱ型分量的增加，远离缺口的氢富集峰有下降且移向缺口顶端的趋势．钢中原始氢浓度的改变、并不严重影响缺口顶端双氢峰的形成。缺口前端塑性应变和静水应力的梯度分布是导致其氢浓度再分布的主要因素．据此提出了复合型载荷缺口顶端双氢峰富集模型．     

Ⅰ＋Ⅱ复合型载荷缺口前端双氢峰规律的研究

利用ＫＹＫＹ离子探针微分析仪和有限无定量计算发现，２１Ｃｒ７Ｎｉ９ＭｎＮ奥氏体钢在复合型载荷下，缺口顶端无论在开裂方向是塑性区尺寸最大方向上，皆有两个氢浓度的富集峰，且随着Ⅱ型分量的增加，远离缺口的氢富集峰有下降且移向缺口顶端的趋势。钢中原始氢浓度的改变，并不严重影响缺口顶端双氢峰的形成。     

应力/应变场对插销试验焊接接头氢扩散的影响

采用ABAQUS有限元分析软件及有关焊接接头中氢扩散与集聚的计算模拟技术计算分析了不同外加载荷条件下插销试件的能力、应变场及其对氢扩散与聚集过程的影响。计算结果表明，静载拉伸条件下插销缺口前沿有明显的应力应变集中，随着外加载荷的增加，缺口尖端应力逐渐增大，但应力集中系数逐渐减小；在相同初始氢条件下，随着外加载荷的增加，缺口前沿应力应变集中部位氢的峰值浓度逐渐提高，氢浓度达到峰值的时间也逐渐增长。分析认为，插销缺口附近产生的应力应变集中是导致氢在该区域产生聚集的重要原因。     

小幅载荷在A537钢疲劳裂纹扩展过程中作用的研究

采用Ａ５３７钢单边缺口试样，研究了以不同方式叠加在主载荷△Ｐ上的小幅载荷在疲劳裂纹扩展过程中的作用，并采用激光散斑技术测量了循环加载过程中的裂纹闭合效应。结果表明：３０％△Ｐ以下的小幅载荷叠加在主载荷底部时，对由主载荷引起的裂纹扩展速率ｄａ／ｄＮ几乎没有影响，３０％△Ｐ以上的小幅载荷可使裂纹扩展速率增加。叠加在主载荷顶部的各小幅载荷均可使裂纹扩展速率加大。通过对加载条件下裂纹闭合效应的测量，并结合裂尖的应力应变状态的变化进行分析认为：小幅载荷对裂纹扩展速率的影响受裂纹闭合程度的制约，其损伤作用只体现在裂尖材料产生不可逆塑性形变的外加载荷范围内。     

半固态铜合金压缩变形力学行为及显微组织

采用Gleeble-1500热/力模拟试验机对铜合金半固态坯料进行压缩试验,研究了压缩条件对铜合金变形行为和组织的影响。结果表明,枝晶试样由于发达的枝晶而使得在相同条件下进行压缩变形时所需载荷高于半固态试样;压缩过程中载荷位移曲线受压缩速率和温度影响较大:温度越高,试样中的液相率越高,在受到相同的变形作用时,载荷降低;速率越大,在相同位移下载荷越大。压缩过程中组织不断发生变化,在一定范围内,较高的压缩速率和温度有利于固液两相的协同变形。     

基于连续损伤力学的高低周复合疲劳损伤

基于连续损伤力学(CDM)的经典损伤理论和不可逆热力学原理，分别对高周和低周疲劳载荷下的损伤演化模型进行了研究，进而推导出一个新的高低周复合疲劳损伤模型；将该模型编写为UMAT耦合到ABAQUS有限元分析软件中，实现了对缺口材料高低周复合疲劳损伤的模拟及裂纹萌生位置和萌生寿命的预测；同时研究了不同的高低周循环比对裂纹萌生寿命的影响.结果表明,裂纹容易在缺口根部应力集中处萌生；该模型考虑了高低周循环的交互作用，模拟计算结果更符合实际情况；同时通过研究发现高的循环比会使裂纹的萌生加速.     

STUDY ON FRACTOGRAPHY OF TRANSGRANULAR SCC OF 70Cu-3OZn IN AN AMMONIACAL SOLUTION

1.IntroductionThemechanismsofstresscorrosioncracking(SCC)havenotyetbeenresolved,andthisproblemremainsasignificalltengineeringconcernandisofacademicillterest.Ofparticularinterestisthecaseoftransgranularstresscorrosioncracking(TSCC)oftheductileface-centeredcubic(FCC)metalsandalloyssincethesematerialshavemultipleslipsystemsandarecharacterizedbyhighdislocationvelocities.SinceSCCisacrackingphenomenon,thepropagationmechanismsmustbeabletofullyexplainthedetailsonthefracturesurfacesproducedbyanddu…     

Role of Crystallographic Textures on Failure Behavior in HSLA Grade-420 Steel During Cold Rolling

The microstructural and textural evolution was analyzed during rolling at room temperature to obtain detailed information about the failure behavior in HSLA grade-420 steel. Electron backscatter diffraction measurements were carried out in both non-cracked and cracked areas after cold rolling to find a correlation between microstructural parameters (i.e., grain orientation, grain boundary characteristics and Taylor factor) and crack propagation. The results showed that the crack tended to propagate along grains oriented with {001} planes parallel to the normal direction with high Taylor factor value. The special boundaries associated with the {111}, {110} and {221} planes were indicated as crack resistance, while ∑ 5, 13a and 17a, which related to the {001} planes, were crack-susceptible. Transgranular cracking was subjected within grains with high Taylor factor, while mismatch in Taylor factor between neighboring grains could provide an easy path for intergranular crack propagation.     

单晶Ni_3Al裂纹扩展的TEM原位观察

利用透射电镜（ＴＥＭ）原位拉伸在室温下对（１１０）［１１０］取向 Ｎｉ３ＡＩ合金单晶中裂纹的萌生与扩展进行了研究结果表明：裂纹沿之字形路径扩展且裂纹的总体扩展路径与拉伸轴平行迹线分析表明,首先激活的是（１１１）和（１１１）两个主滑移面上的滑移系;其后在 Ｓｃｈｍｉｄ因子为零的两个滑移面上的滑移系激活．为了解释所观察到的现象而建立了一个位错塞积模型位错应力场的计算表明,塞积位错列所产生的应力场导致了第二滑移系的启动,并使得裂纹扩展路径平行于拉伸轴的方向     

The crystallography of stress corrosion cracking in face centered cubic single crystals

The crystallography of transgranular stress corrosion cracking was studied for single crystals of α-brass (tested in 14 N NH₃), copper (tested in 1 M NaNO₂), and 304L austenitic stainless steel (tested in boiling 45 wt% MgCl₂). All fracture surfaces had characteristic flat parallel facets separated by crystallographic and/or fan-shaped steps. In α-brass and copper the facets consisted of {110} planes with the crystallographic steps following {111} planes. In 304L austenitic stainless steel cracking occurred primarily on the {100}, but secondary cracking on {110} was also found. Very smooth crystallographic-like steps were observed, generally following {100} planes. It is concluded that stress corrosion cracking in all systems tested occurred by cleavage. It is suggested that the stress corrosion cracks propagate on the lowest surface energy planes.     

单晶Nb拉伸,压缩及恒应变疲劳后的滑移系和滑移特征

研究了单滑移位向和多滑移位向Ｎｂ单晶在拉伸，压缩及循环变形时的滑移系，根据试样表面滑移线的方向，在极图上确定滑移面，单滑移位向（［３２１］）的单晶，在拉伸时的滑移系为（１０１）［１１１］，在压缩时是（１０１）［１１１］和（２１３）［１１１］．根据ｂｃｃ晶体变形特点，分析了拉伸，压缩和循环变形的滑移系之间的关系，用光学显微镜和透射电镜复型观察了试样的表面形貌，确定了多滑移位向（［１１０］位向）单晶滑     

一种5083铝合金中晶界面热轧织构的研究

通过电子背散射衍射技术,测定了一种5083铝合金中的热轧织构。结果表明：在结构中的不同位置,织构组分呈现非均匀发展的特点,特别地,晶界面亦呈现取向织构。在样品的中心位置,晶界面趋向于{111}取向,且其数量高出随机晶界50%;同时,在样品的边缘位置,晶界面趋向于{110}与{112} 取向,且其数量高出随机晶界28%。更具体地,小角和大角晶界中均呈现这种晶界面的各向异性分布。     

Deformation Mechanisms of Alpha-Uranium Single Crystals

The operative deformation elements in α-uranium single crystals under compression at room temperature have been determined as a function of the compression directions. The deformation mechanisms noted may be arranged with respect to their frequency of occurrence and ease of operation in the following order: 1—(010)-[100] slip, 2—{130} twinning, 3—{~172} twinning, and 4—under special conditions of stress application, kinking, cross-slip, {~176} twinning, and {011} slip. The composition planes of the {172} and {176} systems were found to be irrational. Cross-slip was shown to be associated with the major (010) slip system, coupled with localized interaction of slip on the (001) planes. The mechanism of kinking was found to be similar to that observed in other metals in that it occurred chiefly when the compression direction was nearly parallel to the principal slip direction [100] and was associated with a lattice rotation about an axis contained in the slip plane and normal to the slip direction: the [001] in the uranium lattice. The resolved critical shear stress for slip on the (010)-[100] system was found to be 0.34 kg per mm². In a single test it was shown that under compression in suitable directions twinning on the {130} also occurs at 600°C     

Crystallographic Texture Evolution of ■-Fe_4N and Its Influences on Tribological Property of Nitrided Steel

The crystallographic texture of ■-Fe4 N in compound layer and its influences on the tribological properties of nitrided steel 38 Cr Mo Al are investigated in the study. The preferred orientation of(200)■ is produced by low-temperature nitriding in atmosphere with low nitrogen–hydrogen ratio and increases with the nitriding time. The preferred orientation of(220)■ appears after 72 h cyclic nitriding. The orientation relationships(0001)_ε//(101)_■ and [110]_ε//[111]_■,(111)_■//(0001)_ε and 011_■//[1■10]_g,(200)■//(110)_■ and [011]_■//[111]_■, as well as (1■03)_ε //(220)_■ and [0100]_ε//[1■0]_■ are established by first-principles method. The misfit of interatomic distance(δ), determining the phase transition resistance, is calculated. Accordingly, two reaction pathways during nitriding, ■→■ and ■→ε→■, are assumed, which determines the preferred orientations of ■-Fe_4 N. Results of wear tests demonstrate that the specimen with preferred orientation of(200)■ exhibits lower frictional coefficient and lower wear rate in comparison with the specimen with(220)■ preferred orientation.(111)■ texture usually relates to the lower frictional coefficient but higher wear rate due to the main slip system parallel to the sliding plane. Therefore, the(200)■ preferred orientation has a positive significance in improving the wear properties of steels.     

Discontinuous surface cracks during stress corrosion cracking of stainless steel single crystal

Single crystal 321 stainless steel stress corrosion cracking was studied in a 42 wt.% MgCl₂ solution. Cracks propagated macroscopically in the maximum tensile stress plane regardless of the notch orientation with respect to the applied tensile load direction. Some stress corrosion cracks nucleated discontinuously at the intersection of the two slip bands. Most cracks, however, were not related to the slip bands. Cleavage-like fracture was observed, and the river-markings exhibited microshear facets along the {1 1 1} plane. Interaction between the main crack and the discontinuous microcracks increased the calculated stress intensity factor by 17 times and promoted crack coalescence, resulting in mechanical fracture of the ligaments between the cracks.     

化学气相沉积钨单晶管材表面电解蚀刻形成的{110}晶面形貌

报导了具有<111>晶向(轴向)的管状钼单晶基体化学气相沉积(CVD)钨单晶涂层的电解蚀刻工艺及形成的{110}晶面形貌。实验发现,通过电解蚀刻,表面的{110}晶面可以完全被蚀刻出来。蚀刻出来的{110}晶面呈台阶结构,并同<111>晶轴相平行。蚀刻出来的{110}晶面在圆管的表面分成均等六个区。每个区内{110}晶面的台阶面的宽度呈现周期性的变化,开始台阶面较宽,逐渐变窄,然后通过一过渡区后,进入下一周期,{110}晶面的台阶面的宽度又逐渐变宽。