共查询到18条相似文献,搜索用时 140 毫秒
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采用纳米压痕技术和数值模拟研究灵芝孢子孢壁的弹性模量和硬度.利用原位纳米力学测试与分析系统,测试灵芝孢子孢壁的弹性模量和硬度.得到了载荷--位移曲线图和硬度、弹性模量随压痕深度变化的值.并用有限元方法模拟压痕过程,利用ANSYS软件,按照灵芝孢子孢壁和Berkovich压头的结构,建立了二维计算模型,得到纳米压痕的等效应力分布以及压痕过程中加载和卸载时的载荷--位移曲线.考察了摩擦、压头尖端半径对模拟结果的影响.结果显示:灵芝孢子孢壁的平均弹性模量为2.0GPa,硬度为0.13GPa.模拟结果在趋势上与实验结果有较好的吻合,与理论分析的载荷--位移关系基本一致.摩擦、压头尖端半径小于100nm时对模拟结果不会造成明显影响.研究结果为分析孢子的破壁机理提供必要参数. 相似文献
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结合近来发表的对金属材料采用球形压头的微压痕实验结果及Johnson对应原理,讨论了在传统弹塑性理论下锥形压头在计及压头顶端曲率半径影响时硬度的解答形式.进而得出结论:压头尖端曲率半径不是引起尺度效应的根源,相反,它会使尺度效应减弱. 相似文献
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针对水化硅酸钙纳米压痕模型忽视了压头与基底之间相互作用的问题,由尺寸差异引起的金刚石压头难以计算的问题,以及Wittmann模型无法得到实际接触面积的问题,提出了新的模型与计算方法.结合分子动力学方法,采用金刚石压头-Wittmann模型基底的组合方式构建无定形态水化硅酸钙纳米压痕试验模型.在建模阶段,考虑到压头模型与基底模型粒子间尺寸差异,提出了等比例替换模型,通过公式推导并就不同尺寸模拟结果验证了等比例替换模型的可行性.在计算阶段,提出了局部前处理的弛豫方法进行模拟.确定最大荷载位置处的接触面积为546 nm2,进而求出水化硅酸钙模型硬度H为0.84 GPa、折合模量Er为30.52 GPa.并通过纳米压痕试验,验证了模拟结果的准确性,证明了模型的科学性,对今后水化硅酸钙(C-S-H)纳米层面的模拟具有重要借鉴意义. 相似文献
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本文通过纳米压痕实验技术得到混凝土材料细观各相参数,基于渐进均匀化理论,采用蒙特卡洛方法和双向游走方法建立了含孔隙混凝土的胞元模型.分析了孔隙在冻融循环次数增加情况下对混凝土有效弹性模量的影响,同时与有限元模拟分析进行了比较.结果表明:随着冻融循环次数增加,孔隙体积分数增大,界面与砂浆压痕模量相对降低,但对骨料影响较小,导致混凝土宏观弹性模量随之降低;理论分析预测的混凝土有效弹性模量与有限元模拟结果吻合良好.应用含孔隙混凝土胞元模型能有效地预测混凝土宏观弹性模量,进而也为其在冻融作用下老化演变机理的研究评估提供了基础. 相似文献
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为了研究压头晶体各向异性对纳米压痕的影响,采用多尺度准连续介质(QC)法模拟了不同晶向Ni压头与Ag薄膜的纳米压痕过程。通过对比不同晶向下压头在薄膜上触发的原子滑移,发现压头的晶向引起的界面失配位错在很大程度上决定薄膜开启初始原子滑移系的难易。然后对比了压头在不同晶向下测得的薄膜纳米硬度,发现其计算值是一样的。最后研究压头表面和压痕表面的正应力和切应力的分布,分析了应力分布与原子滑移系的关系。 相似文献
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采用准连续介质法模拟了单晶铝纳米压痕试验过程,分析了不同宽度的刚性矩形压头所引起的初始塑性变形特点,获得了载荷-压深、应变能-位移和硬度-压深曲线.从位错理论的角度分析了压头尺寸对纳米压痕测试结果的影响.研究发现:随着压头宽度的不断增大,压头下方位错形核所需要的载荷和压深程度增大,需要的应变能增加,应变能的变化速率递增,纳米硬度值减小,呈现出明显的尺寸效应.同时表明在一定的压入深度下,硬度与压头尺寸之间存在着一定的比例关系,不同尺寸压头获得的硬度值可以相互换算,但当矩形刚性压头宽度大于或等于120时这种尺寸效应消失.研究结果为纳米压痕实验过程中压头尺寸的选择提供了参考依据. 相似文献
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E. Harsono S. Swaddiwudhipong Z.S. Liu L. Shen 《International Journal of Solids and Structures》2011,48(6):972-978
A series of nanoindentation experiments with maximum depths varying from 1200 to 2500 nm were conducted to study indentation size effects on copper, aluminium alloy and nickel. As expected, results from classical plasticity simulation deviate significantly from experimental data for indentation at micron and submicron levels. C0 continuity finite element analysis incorporating the conventional theory of mechanism-based strain-gradient (CMSG) plasticity has been carried out to simulate spherical and Berkovich indentation tests at micron level where size effect is observed. The results from both numerical and actual spherical and Berkovich indentation tests demonstrate that materials are significantly strengthened for deformation at this level and the proposed approach is able to provide reasonably accurate results. 相似文献
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B. Poon D. Rittel G. Ravichandran 《International Journal of Solids and Structures》2008,45(24):6018-6033
The conventional method to extract elastic properties in the nanoindentation of linearly elastic solids relies primarily on Sneddon’s solution (1948). The underlying assumptions behind Sneddon’s derivation, namely, (1) an infinitely large incompressible specimen; (2) an infinitely sharp indenter tip, are generally violated in nanoindentation. As such, correction factors are commonly introduced to achieve accurate measurements. However, little is known regarding the relationship between the correction factors and how they affect the overall accuracy. This paper first proposes a criterion for the specimen’s geometry to comply with the first assumption, and modifies Sneddon’s elastic relation to account for the finite tip radius effect. The relationship between the finite tip radius and compressibility of the specimen is then examined and a composite correction factor that involves both factors, derived. The correction factor is found to be a function of indentation depth and a critical depth is derived beyond which, the arbitrary finite tip radius effect is insignificant. Techniques to identify the radius of curvature of the indenter and to decouple the elastic constants (E and ν) for linear elastic materials are proposed. Finally, experimental results on nanoindentation of natural latex are reported and discussed in light of the proposed modified relation and techniques. 相似文献
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Numerical Modeling of Elastic Spherical Contact for Mohr-Coulomb Type Failures in Micro-Geomaterials 总被引:1,自引:0,他引:1
The contact behavior for geological materials, such as reservoir shale rock, is simulated using the finite element method by considering a nano-indenter tip indenting into a geomaterial obeying the Mohr-Coulomb failure criterion. The deformation and slip at the micro-scale along the shear direction in grain-to-grain contact follows the Coulomb frictional/sliding failure criterion, while the linear elastic force-displacement law is enforced in the direction normal to the contact surface. A series of simulations are performed to study the effect of cohesion, friction angle, and tensile strength on the contact response. For a material with very high cohesion and frictionless contact, the indented geomaterial behaves almost purely as an elastic medium. In this case, the indentation process converges to the classic Hertz grain-to-grain spherical contact model. For a material with extremely low cohesion, the geomaterial behaves like cohesionless granular material at the micro-scale. For materials with finite cohesion values, such as shales, the force-displacement responses are analyzed and reported. This simulation is compared to micro-indentation tests using a spherical indenter tip conducted on preserved samples of Woodford shale. 相似文献
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Nix and Gao established an important relation between the microindentation hardness and indentation depth. Such a relation
has been verified by many microindentation experiments (indentation depths in the micrometer range), but it does not always
hold in nanoindentation experiments (indentation depths approaching the nanometer range). Indenter tip radius effect has been
proposed by Qu et al. and others as possibly the main factor that causes the deviation from Nix and Gao's relationship. We
have developed an indentation model for micro- and nanoindentation, which accounts for two indenter shapes, a sharp, conical
indenter and a conical indenter with a spherical tip. The analysis is based on the conventional theory of mechanism-based
strain gradient plasticity established from the Taylor dislocation model to account for the effect of geometrically necessary
dislocations. The comparison between numerical result and Feng and Nix's experimental data shows that the indenter tip radius
effect indeed causes the deviation from Nix-Gao relation, but it seems not be the main factor.
The project supported by the National Natural Science Foundation of China (10121202) and the Ministry of Education of China
(20020003023) 相似文献
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Determination of the mechanical properties of individual sand grains by conventional material testing methods at the macroscale
is somewhat difficult due to the sizes of the individual sand particles (a few μm to mm). In this paper, we used the nanoindentation
technique with a Berkovich tip to measure the Young’s modulus, hardness, and fracture toughness. An inverse problem solving
approach was adopted to determine the stress-strain relationship of sand at the granular level using the finite element method.
A cube-corner indenter tip was used to generate radial cracks, the lengths of which were used to determine the fracture toughness.
Scatter in the data was observed, as is common with most brittle materials. In order to consider the overall mechanical behavior
of the sand grains, statistical analysis of the mechanical properties data (including the variability in the properties) was
conducted using the Weibull distribution function. This data can be used in the mesoscale simulations. 相似文献
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The relationships between indentation responses and Young’s modulus of an indented material were investigated by employing
dimensional analysis and finite element method. Three representative tip bluntness geometries were introduced to describe
the shape of a real Berkovich indenter. It was demonstrated that for each of these bluntness geometries, a set of approximate
indentation relationships correlating the ratio of nominal hardness/reduced Young’s modulus H
n
/E
r and the ratio of elastic work/total work W
e/W can be derived. Consequently, a method for Young’s modulus measurement combined with its accuracy estimation was established
on basis of these relationships. The effectiveness of this approach was verified by performing nanoindentation tests on S45C
carbon steel and 6061 aluminum alloy and microindentation tests on aluminum single crystal, GCr15 bearing steel and fused
silica. 相似文献
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基于对室温压头和热试样接触后传热过程的分析, 重点研究热接触引起的压头基托热膨胀对高温仪器化压入测试中位移测量漂移的影响. 首先, 通过热传导理论分析, 获得热接触后基托内温度场分布的解析解, 进而研究基托热膨胀引起的位移测量漂移量; 然后, 建立有限元分析模型, 数值模拟高温仪器化压入过程, 验证理论模型的准确性. 研究发现, 压头与热试样接触面间的热传导性质显著影响基托内的温度场分布; 对于不同材料的试样, 接触面间传热性能不同, 基托的热膨胀量差异可以达到几个数量级. 研究结果有助于优化高温压入测试程序, 提高测试的可靠性. 相似文献