较高应变速率下结构钢屈服强度的估计

本文给出了一种考虑应变速率效应时材料屈服强度近似求法，它依据两组低应变速率的拉伸试验数据，对其它应变速率下的屈服强度进行估计，并具有良好的精度。     

氢对10#钢高应变速率下力学性能的影响

利用Hopkinson试验，研究了氢对高应变速率下10#钢力学性能的影响，导出了应力、应变和应变速率的本构方程．     

金属基复合材料的高应变速率超塑性

综述并评论了金属基复合材料的高应变速率超塑变形机制，描述了金属基复合材料在高应变速率超塑变形中的一些理化现象，说明了变形过程中的各种影响因素，总结了具有高应变速率超塑性能的金属基复合材料及其性能，并指出了在金属基复合材料的高应变速率超塑性研究方面的不足。     

热变形参数对Ti-6554合金流动软化行为的影响

目的 研究不同热变形参数下Ti-6554合金对应变速率敏感指数m、应变硬化指数n的影响。方法 采用Gleeble-3500热模拟实验机，在变形温度为810~930 ℃、应变速率为0.001~10 s⁻¹条件下，对Ti-6554合金进行等温恒应变速率热压缩实验。结果 应变速率敏感指数m随应变速率的升高和变形温度的降低而减小，当真应变为0.9时，m在变形温度为930 ℃、应变速率为0.001 s⁻¹的条件下达到峰值，为0.43。应变硬化指数n随应变速率的升高呈先升高后降低的趋势，在高温区间(870~930 ℃)的软化程度较大。结论 Ti-6554合金对变形温度、应变速率等热变形参数十分敏感，该合金的流动应力随着应变速率的升高和变形温度的降低而增大。分析微观组织可知，从应变速率敏感指数m角度考虑，该合金发生软化行为的最佳区域是变形温度为870~930 ℃、应变速率为0.001 s⁻¹。从应变硬化指数n的角度考虑，在变形温度为870~930 ℃条件下，Ti-6554合金在低应变速率区间(0.001~0.01 s⁻¹)的软化行为以动态再结晶(DRX)为主，在高应变速率区间(0.1~10 s⁻¹)的软化行为以动态回复(DRV)为主。     

SiC颗粒增强6061Al基复合材料的动态拉伸性能Ⅱ应变速率效应

用拉伸split Hopkinson bar实验装置进行了SiCp/6061Al得合材料及基体合金的动态拉伸实验，研究了材料的应变速率敏感性。结果表明，SiCp/6061Al复合材料及其基体合金均具有明显的应变速率效应，且复合材料的应变速率敏感性高于基体合金的应变速率敏感性，根据位错机制对此进行了解释。     

Ti2AlNb合金应变速率敏感指数和应变硬化指数与变形参数和晶粒尺寸关系研究

以Ti₂AlNb合金板材为研究对象，基于变形温度为1 273～1 423 K、应变速率为0.001～10 s^-1范围内的等温恒应变速率热压缩实验，深入分析了变形参数和微观组织对应变速率敏感指数m和应变硬化指数n的影响。结果表明：Ti₂AlNb合金的流动应力随变形温度的升高和应变速率的降低而减小；Ti₂AlNb合金等温压缩过程中的峰值m为0.61，出现在1 323 K/0.001 s^-1；当变形温度为1 273～1 323 K时，m随应变速率的增大而减小，当变形温度为1 373～1 423 K时，m随应变速率的增大而增大；当应变速率为0.001 s^-1时，n随应变的增大呈现先减小后增大的趋势，而当应变速率为0.01～10 s^-1时，n却呈现先增大后减小的变化趋势；Ti₂AlNb合金应变硬化指数n值和应变速率敏感指数m值均随着晶粒尺寸的增大而减小；Ti₂AlNb合金板材较优的加工区间为1 273...     

速率相关混凝土模型中一个值得商榷的问题

本文对一种广泛应用于钢筋混凝土结构动力分析的速率相关的混凝土模型进行讨论，该模型的基本特征是粘性参数与应变速率有关。为了比较和验证该模型的正确性，本文严格按照弹粘塑性理论并结合过应力概念，提出了一种应变速率相关模型。文中给出了在常应变速率、应力松弛和蠕变等加载情况下二种模型的分析解。理论和数值计算结果都表明，先前提出的应变速率相关模型不仅理论上有缺陷，而且在稳态响应阶段段值计算存在较大误差。     

Zn-5Al超塑合金的恒载荷拉伸实验研究

研究表明，Zn-5Al超塑性合金的应变速率敏感指数m和超塑性变形激活能Q值和超塑性流动粘滞系数η可采用恒载荷蠕变法进行测定，在恒载荷变形条件下，应变速率敏感指数m随应变速率的增加而增大，超塑性流动的粘滞系数η随应变速率的增加而减小，超塑拉伸前对轧态试样进行保温处理时，由于通过回复和再结晶释放了合金中的储能，降低了超塑变形的动力，导致变形抗力增加而延伸率下降。     

Ti－17合金的热压缩变形行为研究

通过热模拟压缩试验，测试了Ｔｉ－１７合金在温度Ｔ＝８０５～９４５℃，应变速率ε＝１０（－３）～８０ｓ（－１）、变形程度ε＝５０％范围内的真应力－应变曲线，研究了不同温度、不同应变速率下的流动应力及组织变化规律。发现，在（α＋β）两相区降低温度或提高应变速率，流动应力σ变化较大，动态再结晶易于进行；在β区通常只发生动态回复，流动应力σ随温度和应变速率变化较小，高温、低应变时发生连续再结晶。试验还用Ｚｅｎｅｒ－Ｈｏｌｌｏｍｏｎ因子确定了该台金发生连续再结晶的临界因子Ｚｃ的数值，ｌｏｇＺＣ＝４１．２。     

Ti─17合金高温变形机理研究EI

用热模拟压缩试验研究了Ｔｉ－１７合金高温变形特点，通过金相组织和ＴＥＭ观察发现，β区变形是以扩散回复型变形机制占主导地位；高应变速率下只发生动态回复；低应变速率下发生连续再结晶。（α＋β）区变形是界面滑移，高应变速率下易发生动态再结晶。试验还确定了变形激活能Ｑ和应变速率敏感因子ｍ值，β和（α＋β）区中分别为１６１ｋＪ／ｍｏｌ、４３７ｋＪ／ｍｏｌ和０．３２、０．２５。     

Hydrogen transport and large strain elastoplasticity near a notch in alloy X-750

The finite element method is used to solve the coupled large strain elastoplasticity boundary value problem and transient hydrogen diffusion initial boundary value problem. As an example, solutions are obtained in the neighborhood of a rounded notch in a 4-point bend specimen of alloy X-750 at two temperatures under plane strain deformation conditions. The model accounts for the dilatational strain caused by the presence of hydrogen in the lattice and the hydrostatic stress induced drift of hydrogen. The hydrogen population profiles in both normal interstitial lattice sites (NILS) and trapping sites are calculated and conditions for the predominance of the total amount of hydrogen by either of the populations are studied. The competition between hydrostatic stress and plastic strain in the enhancement of local hydrogen concentrations is investigated. The effect of different types of traps on the relative level of trapped hydrogen as a portion of the total hydrogen is examined. The numerical analysis in conjunction with current experimental evidence suggests a specifically designed line of experiments that will isolate the parameters crucial to hydrogen induced material degradation in X-750.     

Studies on hydrogen embrittlement of nitrogen containing austenitic alloys

Abstract

The influence of hydrogen on the mechanical properties of four austenitic CrNiMo and CrMn alloys with nitrogen contents up to 0.57 wt-% were investigated concerning their resistance against hydrogen embrittlement in correlation to nitrogen content, chemical composition, and hydrogen diffusivity and solubility. Tensile tests were carried out at room temperature and at strain rates between 10^-4 and 10^-6 s^-1 with simultaneous hydrogen charging and after precharging to different hydrogen contents. The mechanical properties have been found to be dependent on both strain rate and hydrogen content in the material. Simultaneous hydrogen charging and mechanical testing have accelerated the failure process owing to a faster hydrogen uptake especially at low strain rates. Hydrogen has shown a softening effect in the elastic range of the stress strain curve, which becomes more pronounced with decreasing strain rate. The favoured mechanism of hydrogen damage of alloys with high nitrogen contents seems to be the hydrogen enhanced localised plasticity mechanism. A correlation between hydrogen embrittlement and stress corrosion cracking has been discussed. It has been established that both the damaging processes in nitrogen containing steels are influenced by the same mechanism.     

介质及应变速率对10钢的氢脆敏感性的影响

本文研究了 10钢在 H2 SO4溶液和 Na Cl溶液中渗氢后 ,在不同应变速率下其氢脆敏感性 .结果表明 :在 H2 SO4溶液中渗氢后 ,10钢具有明显的氢脆特征 ,应变速率从 3.33× 10 -1.sec-1～ 3.33×10 -6 .sec-1范围内 ,截面收缩率Ψ从 35 .36%降至 18.35 % ;延伸率δ从 2 9.34 %降至 14 .95 % ,10钢显示出最大的氢脆敏感性     

Effects of hydrogen on the mechanical response of X80 pipeline steel subject to high strain rate tensile tests

Hydrogen‐induced degradation of X80 pipeline steel was investigated through a high strain rate tensile test (2 × 10^?4/s) with interposed unloading, reloading, aging at 30°C, or annealing at 200°C with or without hydrogen charging. The results indicated that plasticity degradation does not occur in the hydrogen‐precharged specimens; however, hydrogen embrittlement occurs in the reloading stage when the specimens are charged with hydrogen in the unloading stage after applying a prestrain. Interposed aging at 30°C or annealing at 200°C can also increase the degradation. It indicates that the hydrogen traps caused by the strain along with hydrogen charging are the major source of dislocations. The formation of a hydrogen atmosphere around mobile dislocations, which is related to the rates of hydrogen diffusion and dislocation movement, plays an important role in the degradation process. Both pinning and depinning of dislocations affect plasticity degradation.     

Hydrogen-induced Modification in the Deformation and Fracture of a Precipitation-hardened Fe-Ni Based Austenitic Alloy

Hydrogen-induced modification in the deformation and fracture of a precipitation-hardened Fe-Ni based austenitic alloy has been investigated in the present study by means of thermal hydrogen charging experiment, tensile tests, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. It is found that the γ＇ particles are subjected to the multiple shearing by dislocations during plastic deformation, which promotes the occurrence of the dislocation planar slip. Moreover, the alloy will be enhanced by hydrogen resulting in the formation of strain localization at macroscale. So, the mechanisms of deformation and fracture in the alloy have been proposed in terms of serious hydrogen-induced planar slip at microscale which can lead to macroscopic strain localization.     

Effect of grain size on the hydrogen-assisted cracking in duplex stainless steels

The embrittlement behavior of 2205 duplex stainless steels with two different grain sizes in 26 wt% NaCl (pH 2) under cathodic potential were investigated by slow strain rate testing. The electrochemical permeation technique was used to characterize the permeation rate and effective diffusivity of hydrogen. The results indicated that both the effective diffusivity and the susceptibility of hydrogen embrittlement were lower for the finer grain size specimen. Ultimate tensile strength (UTS) and uniform elongation (UEL) decrease linearly with decreasing logarithm of strain rate. The dependence of UTS and UEL on the logarithm of strain rate was higher for the finer grain specimen. The microstructural examination revealed that internal cracks resulted from hydrogen embrittlement of the ferrite phase under cathodic charging conditions were arrested by austenite in duplex stainless steels.     

Hydrogen embrittlement behavior of Inconel 718 alloy at room temperature

Hydrogen embrittlement of Inconel 718 alloy was investigated. Multi-scale observation technique were employed, comprising slow strain rate tensile tests, scanning electron microscopy and transmission electron microscopy analysis. The results demonstrate that hydrogen charging deteriorates mechanical properties of the alloy. Inconel 718 alloy shows partial Portevin-Le Chatelier(PLC) effect at room temperature when hydrogen charging current density is 220 mA cm~(-2) and 590 mA cm~(-2). Moreover, plastic deformation features with dislocation cells are detected in hydrogen-induced brittle zone. Thus, it is concluded that dragging effect of hydrogen atoms on dislocations contributes to PLC effect.     

氢对TC21合金高温变形行为的影响

采用连续升温金相法研究了氢对TC21合金相变温度的影响,通过热模拟压缩实验,研究了氢对TC21合金高温变形行为的影响.结果表明:置氢可以显著降低TC21合金的相变温度,置氢0.7%(质量分数,下同)的TC21合金相变温度为810℃,与未置氢合金相比,降幅达145℃;同时,置氢还可以有效降低TC21合金的流变应力,并且温...     

Strain-amplitude dependent fatigue resistance of low-alloy pressure vessel steels in high-temperature water

Low cycle fatigue resistance of low-alloy pressure vessel steels was investigated in 561 K air and water over a wide strain amplitude range. It was found that fatigue resistance of the steels was enhanced in high-temperature water relative to high-temperature air under the low strain amplitude conditions (<0.3%) or in the high cycle regime (>2 × 10⁴ cycles), while it was remarkably degraded in high-temperature water under the higher strain amplitude conditions. Fatigue cracking and fractographic features suggested that effects of hydrogen be involved in the present corrosion fatigue process in high-temperature water. Possible environmentally assisted cracking mechanisms are discussed.