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《Acta Materialia》2007,55(19):6541-6552
In this work, stationary crack tip fields in amorphous materials such as metallic glasses under mode I loading are studied to understand the factors that control crack tip plasticity and in turn impart toughness to those materials. For this purpose, finite element simulations under plane strain, small scale yielding conditions are performed. A continuum elastic–viscoplastic constitutive theory, which accounts for pressure sensitivity of plastic flow as well as the localization of plastic strain into discrete shear bands, is employed to represent the material behavior. The influence of internal friction and strain softening on the plastic zone, stress and deformation fields and notch opening profile is examined. It is found that higher internal friction leads to a larger plastic zone. Also, it enhances the plastic strain ahead of the notch tip but leads to a substantial decrease in the opening stress. Thus, it appears that a higher friction parameter promotes toughening of amorphous solids. The shear band patterns within the plastic zone and brittle crack trajectories around the notch root generated from the simulations match qualitatively with those observed in experiments. 相似文献
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WEI Xuejun ZHOU Xiangyang LI Jin LIU Guanglei KE Wei Corrosion Science Laboratory Academia Sinica Institute of Corrosion Protection of Metals Academia Sinica Shenyang China Institute of Corrosion Protection of Metals Academia Sinica Shenyang China 《金属学报(英文版)》1993,6(12):453-458
A computerized digital speckle-interferometry(SPI)system has been set up to determinethe in-plane distribution of displacement and strain at crack tip of CF specimens.Theprinciple and the experimental method of this technique are described in detail.Theeffect of corrosion factors on plastic deformation at crack tip in CF process has beenexamined by comparing the near-tip strain fields of steel A537 before and after hydrogencharging,and of pure copper before and after applying an anodic current in 3.5% NaCl.The results shows that the clasic finite element mathematical models are not suitable todescribe the near-tip deformation under the experimental conditions.Hydrogen chargingmade the crack tip plasticity decreased for steel A537 and the anodic dissolution enhancethe near tip deformation of pure copper specimen. 相似文献
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钛制承压设备在制造和服役过程中会产生塑性变形,影响其抗疲劳性能。为了研究预应变对工业纯钛TA2疲劳裂纹扩展行为的影响,本文对原始材料、预应变量为10%、20%和30%的材料进行疲劳裂纹扩展试验,结合数字图像相关(Digital image correlation, DIC)技术获取裂纹尖端应变场,研究预应变对裂纹尖端应变场的影响。结果表明:随着预应变量的增加,稳态疲劳裂纹扩展阶段的扩展速率减小,裂纹张开位移减小,裂纹张开载荷增大,裂纹尖端塑性区、塑性变形量以及循环塑性应变累积量均减小。因此预应变抑制了裂纹尖端的塑性变形及循环塑性累积,致使裂纹闭合效应愈加明显,从而抑制了裂纹的扩展。研究结果对钛制承压设备的安全评定具有参考意义。 相似文献
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Jette Oddershede Bettina Camin Søren Schmidt Lars P. Mikkelsen Henning Osholm Sørensen Ulrich Lienert Henning Friis Poulsen Walter Reimers 《Acta Materialia》2012,60(8):3570-3580
The stress field around a notch in a coarse grained Mg AZ31 sample has been measured under tensile load using the individual grains as probes in an in situ high energy synchrotron diffraction experiment. The experimental set-up, a variant of three-dimensional X-ray diffraction microscopy, allows the position, orientation and full stress tensor of each illuminated grain to be determined and, hence, enables the study of evolving stress fields in coarse grained materials with a spatial resolution equal to the grain size. Grain resolved information like this is vital for understanding what happens when the traditional continuum mechanics approach breaks down and fracture is governed by local heterogeneities (e.g. phase or stress differences) between grains. As a first approximation the results obtained were averaged through the thickness of the sample and compared with an elastic–plastic continuum finite element simulation. It was found that a full three-dimensional simulation was required to account for the measured transition from the overall plane stress case away from the notch to the essentially plane strain case observed near the notch tip. The measured and simulated stress contours were shown to be in good agreement except at the highest applied load, at which stress relaxation at the notch tip was observed in the experimental data. This stress relaxation is attributed to the initiation and propagation of a crack. Finally, it was demonstrated that the measured lattice rotations could be used as a qualitative measure of the shape and extent of the plastic deformation zone. 相似文献
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为了实现工业纯钛TA2疲劳裂纹尖端循环应变场的表征,采用数字图像相关(digital image correlation, DIC)方法并结合Irwin模型,研究了TA2紧凑拉伸试样在多级疲劳载荷下的裂纹扩展规律、循环应变场的实验划分方法以及循环应变环的演化规律。首先通过多级载荷试验获得了TA2紧凑拉伸试样的疲劳裂纹扩展规律,在此基础上结合DIC和Irwin模型,建立了疲劳裂纹尖端循环应变场的实验划分方法,实现了循环塑性区、单调塑性区和弹性区的划分。另一方面,采用DIC获得不同区域的滞回应变环,讨论了不同区域应变环的差异,从而论证了划分方法的有效性,并且揭示了裂纹扩展过程中裂纹尖端应变场从弹性区、单调塑性区到循环塑性区的演化规律。研究工作实现了TA2疲劳裂纹扩展过程中裂纹尖端循环应变场的表征,能够满足疲劳裂纹扩展研究的需要。 相似文献
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考察了爆炸复合层状双金属板LY12 /Cu界面两侧材料弹塑性失配对面裂纹疲劳扩展行为的影响。结果表明 ,界面两侧材料的弹塑性失配对复合板面裂纹的扩展驱动力具有重要影响。当裂纹由弹性模量、屈服强度高的一侧向低的一侧扩展时 ,实际驱动力大于外加名义值 ;当裂纹由弹性模量、屈服强度低的一侧向高的一侧扩展时实际驱动力小于外加名义值 ,从而造成裂纹扩展的加速或止裂 ,其影响离界面越近效果越显著。但弹性失配在裂纹开始扩展直至界面的整个过程都起作用 ,而强度失配只在裂尖距界面一定距离内 (Rp)才起作用 相似文献
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1.~onItiswellknownthatthefatigUefailureisoneofthecornmonfailuresinmetalstructuresincludingweldedstmctures.VariousformulaehavebeensuggestedtopredictfatigUecrackgrowthrates,andthosewidelyusedinpracticeareasfollows:da/dN=cI(AK)acda/dN=c2(ACOD)?/dN=c3(AJ)%FortnulaeaboverelatedfatigUecrackgrowthrate(da/dN)eitherwiththerangeofstressintensityfactor(isK),orwiththerangeofcrackopeningdisplacement(ACOD),orwiththerangeofJ--intendvalue(6J)ofafatigUeloadcycle.However,sincethediscoverybyW.Elb..['… 相似文献
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含有第二相的高强铝合金疲劳模型 总被引:3,自引:0,他引:3
基于疲劳裂纹尖端的应力和应变以及高强铝合金中不同尺度第二相性态对其延性的影响,建立了高强铝合金中粗大第二相、中间尺度第二相以及细小时效强化相性态与其疲劳裂纹扩展速率之间的多元非线性关系模型。结果表明:对于2024铝合金的疲劳扩展速率,该模型的预测趋势与他人的实验研究结果吻合良好。同时借助于对该模型的理论分析,提出了在确保高强铝合金强度不降低的前提下降低其疲劳裂纹扩展速率的优化方案。 相似文献
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通过对2A12铝合金搭接搅拌摩擦焊接头的强度试验,研究了搭接搅拌摩擦焊接头的断裂行为,应用有限元方法对2A12铝合金板材搭接搅拌摩擦焊接头的拉伸力学响应进行了模拟计算,获得了搭接搅拌摩擦焊接头在外载作用下的局部应力应变分布与变形规律.结果表明,在搭接接头的搭接面上存在两个类裂纹的未焊接区域,塑性变形首先在搭接界面裂纹尖端区域发生,上板受拉侧裂纹尖端周围区域的塑性变形最大,是导致搭接搅拌摩擦焊接头上板的前进侧热影响区断裂的主要原因. 相似文献
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用抛光的恒载荷试样对40CrNiMoA和AISI4330M两种高强度钢在水介质中应力腐蚀裂纹的产生和扩展进行了金相跟踪观察,研究了裂纹亚临界扩展的形貌。结果表明:表面裂纹前端产生阴影区(塑性变形区),它的形貌随钢种不同而不同。对于40CrNiMoA,阴影区是扩展、闭合,再扩展、再闭合。而对于4330M,阴影区不闭合,近乎平行扩展。只有在刚开始加载、阴影区呈耳朵状时,它才反映了裂纹尖端的塑性区。在以后绝大部分的扩展过程中,阴影区并不代表裂纹尖端的塑性,而只反映产生剪切唇所引起的变形,且与裂纹的“突进”(Pop-in)密切有关,必须和小范围屈服断裂力学中裂纹尖端的塑性区相区别。 相似文献
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在高温水环境中,应力会提高镍基合金裂纹尖端的阳极溶解速率并加速裂纹扩展。采用弹塑性有限元方法,对高温水环境中镍基合金裂纹尖端应力和电化学腐蚀的关系进行研究。分析了应力强度因子对模拟高温水环境中600合金1T-CT试样裂纹尖端表面电化学腐蚀电位的影响,并讨论了弹性变形和塑性变形对裂纹尖端电化学腐蚀电位变化的影响。 相似文献
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《Acta Materialia》2007,55(11):3929-3942
In situ synchrotron X-ray diffraction measurements are used to create two-dimensional maps of elastic strain and texture, averaged over a compact-tension specimen thickness, near a crack tip in a martensitic NiTi alloy. After fatigue crack propagation, the material ahead of the crack and in its wake exhibits a strong texture, which is eliminated by subsequent shape-memory heat treatment, indicating that this texture is due to detwinning, the main deformation mechanism of NiTi. Upon subsequent application of a static tensile stresses, the highly textured zone reappears and grows around the crack tip as the applied stress is increased. At the highest applied stress intensity of 35 MPa m1/2, large tensile strains are measured ahead of the crack tip and considerable elastic anisotropy is observed. This detwinning zone is similar to the plastic zone produced by dislocation slip present around cracks in other metals. The texture in this zone is not significantly altered after mechanical unloading, despite the development of substantial triaxial compressive residual strains in this zone. 相似文献
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通过考察碳素工具钢的表面滑移、疲劳破坏及表面裂纹的扩展条件,以统一的局部应力讨论了光滑试样和裂纹试样的疲劳特征。分析和实验结果表明,在裂纹试样的名义应力小于光滑试样表面滑移门槛应力的范围内,线弹性断裂力学是有效的,对应裂纹扩展门槛值的裂尖性区为一常数。 相似文献
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裂纹长度是影响裂纹尖端力学特性及裂纹扩展速率的重要因素,但现有环境致裂研究中的裂纹类型主要为长裂纹而忽略了小裂纹。本文采用有限元数值计算的方法,研究高温水环境下具有单边裂纹的镍基合金试样环境致裂过程中小裂纹裂尖力学特征。结果表明小裂纹裂尖具有比长裂纹更高的应力和应变,并使小裂纹具有更高的裂纹扩展趋势。文中给出了计算小裂纹裂尖塑性区尺寸的修正方法,J 积分计算的Irwin修正方法适用于长裂纹,但计算小裂纹条件下的J积分时会产生误差。提出在缺乏成熟理论指导下应采用弹塑性有限元数值计算的方法获取准确的小裂纹裂尖J积分。基于小裂纹与长裂纹裂尖力学特征的明显不同,建议在分析核电结构材料环境致裂时,将裂纹扩展分为小裂纹扩展及长裂纹扩展阶段分别研究。 相似文献
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CHEN Huangpu DENG Zengjie Xi''''an Jiaotong University Xi''''an China CHEN Huangpu Lectuer Research Institute for Strength of Metals Xi''''an Jiaotong University Xi''''an China 《金属学报(英文版)》1990,3(3):194-198
The resistance to crack propagation at earlier stage for a high strength structural steel withcertain ductility and its correlation to microstructures,stress states,deformation history andstrain characteristics have been investigated.The resistance to crack propagation is mainly de-termined by the plastic constrain ahead of the crack tip,the elastic energy and plastic workabsorbed in the stress-strain field.These are connected with the state function of triaxialstress.The deformation history and strain characteristic during deformation of material aredescribed by the flow line in which the deformation history and strain characteristic restrainthe crack initiation at stage Ⅱ and the crack propagation at stage Ⅲ.The strain hardeningrate may sensitively reflect the stress distribution and micro-fracture mechanism in the interi-or of material. 相似文献