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Mechanically Based Nonlocal Euler-Bernoulli Beam Model 基于机械的非局部欧拉-伯努利梁模型
Pub Date : 2014-03-01 DOI: 10.1061/(ASCE)NM.2153-5477.0000077
M. Paola, G. Failla, M. Zingales
AbstractThis paper presents a nonlocal Euler-Bernoulli beam model. It is assumed that the equilibrium of a beam segment is attained because of the classical local stress resultants, along with long-range volume forces and moments exchanged by the beam segment with all the nonadjacent beam segments. Elastic long-range volume forces/moments are considered, built as linearly depending on the product of the volumes of the interacting beam segments and on generalized measures of their relative motion, based on the pure deformation modes of the beam. Attenuation functions governing the space decay of the nonlocal effects are introduced. The motion equations are derived in an integro-differential form by applying Hamilton’s principle. Numerical results are presented for a variety of nonlocal parameters. A comparison with experimental data is also provided.
摘要本文提出了一种非局部欧拉-伯努利梁模型。假设由于经典的局部应力结果,以及梁段与所有非相邻梁段交换的远程体积力和弯矩,梁段达到平衡。考虑弹性长程体积力/力矩,建立线性依赖于相互作用的梁段的体积积和它们的相对运动的广义度量,基于梁的纯变形模式。介绍了控制非局部效应空间衰减的衰减函数。应用哈密顿原理,导出了运动方程的积分微分形式。给出了各种非局部参数的数值结果。并与实验数据进行了比较。
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引用次数: 8
Cyclic Indentation Behavior of Layered Nanocomposites: Viscoplastic Numerical Study 层状纳米复合材料的循环压痕行为:粘塑性数值研究
Pub Date : 2014-03-01 DOI: 10.1061/(ASCE)NM.2153-5477.0000076
C. Blada, Y. Shen
AbstractThe indentation behavior of layered metal/ceramic nanocomposites was studied. The primary objective was to examine the evolving plastic deformation in the ductile metal constrained by the hard ceramic layers, during indentation cycling with respect to fixed maximum and minimum indentation loads. The model consists of alternating aluminum and silicon carbide thin films on a silicon substrate, with the Al/SiC layered structure being indented by a diamond indenter. The rate-dependent viscoplastic response of Al was specifically taken into account in the numerical model. Plastic deformation in the ductile Al layers continued to occur during the unloading phase of the first cycle, in addition to during subsequent reload/unload processes. Cyclic plasticity resulted in an open load-displacement loop and the indenter continued to move deeper in accordance with each cycle. For the control model of a thick homogeneous Al layer, there was no hysteresis loop and the transient behavior approached stabilization...
摘要研究了层状金属/陶瓷纳米复合材料的压痕行为。主要目的是研究受硬陶瓷层约束的韧性金属在压痕循环过程中,相对于固定的最大和最小压痕载荷,塑性变形的演变。该模型由硅衬底上交替的铝和碳化硅薄膜组成,Al/SiC层状结构由金刚石压头压痕。在数值模型中特别考虑了铝的速率相关粘塑性响应。在第一个循环的卸载阶段,以及随后的加载/卸载过程中,韧性Al层的塑性变形继续发生。循环塑性导致了一个开放的载荷-位移回路,压头在每个循环中继续向纵深移动。对于厚均匀铝层的控制模型,不存在滞回环,暂态行为趋于稳定。
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引用次数: 1
Transmission X-Ray Microscope Nanoscale Characterization and 3D Micromechanical Modeling of Internal Frost Damage in Cement Paste 水泥浆体内部冻损的透射x射线显微镜纳米尺度表征及三维微力学建模
Pub Date : 2014-03-01 DOI: 10.1061/(ASCE)NM.2153-5477.0000080
Qingli Dai, Kenny Ng
AbstractThis study employed the transmission X-ray microscope (TXM) characterization and three-dimensional (3D) cohesive zone modeling (CZM) techniques to investigate the internal-frost damage in cement paste samples. The microscale cement samples were tested under controlled freeze-thaw cycles. The TXM technique was applied to perform fast-image acquisition of capillary pores and micro-damage evolution at 30 nm resolutions. The constructed 3D nanostructures of tested specimens were used in two ways: digital sample generation for model simulation and model prediction on crack propagation. The thermodynamics principles were applied to calculate the ice crystallization pressure within saturated pores under subcooling temperatures. The 3D bilinear CZM techniques were applied to predict the internal-frost damage evolution under the calculated crystallization pressure exerted on pore walls. The CZM predicted crack propagation was favorably compared with the TXM captured micro-damage. The micromechanical modeli...
摘要采用透射x射线显微镜(TXM)表征和三维黏结区建模(CZM)技术研究水泥浆体样品的内部冻损。对微尺度水泥试样进行了控制冻融循环试验。采用TXM技术在30 nm分辨率下进行毛细管孔隙和微损伤演化的快速图像采集。将所构建的三维纳米结构用于两种方式:数字样品生成模型模拟和裂纹扩展模型预测。应用热力学原理计算了过冷温度下饱和孔隙内的冰结晶压力。应用三维双线性CZM技术预测了在计算的结晶压力作用下孔壁内霜损伤的演化过程。与TXM捕获的微损伤相比,CZM对裂纹扩展的预测效果更好。微观力学模型…
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引用次数: 7
Fractional-Order Thermal Energy Transport for Small-Scale Engineering Devices 小型工程装置的分数阶热能输运
Pub Date : 2014-03-01 DOI: 10.1061/(ASCE)NM.2153-5477.0000074
M. Zingales, G. Failla, Umberto Rizzo
AbstractFractional-order thermodynamics has proved to be an efficient tool to describe several small-scale and/or high-frequency thermodynamic processes, as shown in many engineering and physics applications. The main idea beyond fractional-order physics and engineering relies on replacing the integer-order operators of classical differential calculus with their real-order counterparts. In this study, the authors aim to extend a recently proposed physical picture of fractional-order thermodynamics to a generic 3D rigid heat conductor where the thermal energy transfer is due to two phenomena: a short-range heat flux ruled by stationary and nonstationary transport equations, and a long-range thermal energy transport representing a ballistic effects among thermal energy propagators. Thermodynamic consistency of the model is investigated introducing the state function of the temperature field, namely the entropy, and obtaining the thermodynamic restrictions on the signs of the coefficients involved in the pro...
摘要分数阶热力学已被证明是描述一些小尺度和/或高频热力学过程的有效工具,在许多工程和物理应用中得到了证明。分数阶物理和工程以外的主要思想依赖于用实阶算子取代经典微分中的整数阶算子。在这项研究中,作者的目标是将最近提出的分数阶热力学的物理图像扩展到一般的3D刚性导热体,其中热能传递是由于两种现象:由固定和非固定传输方程控制的短程热通量,以及代表热能传播体之间弹道效应的远程热能传输。引入温度场的状态函数即熵,对模型的热力学一致性进行了研究,并得到了模型中各系数符号的热力学限制。
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引用次数: 1
Piezoelectric Effect on the Buckling of Piezoelectric Thin Film with Viscoelastic Substrate 压电效应对粘弹性压电薄膜屈曲的影响
Pub Date : 2014-03-01 DOI: 10.1061/(ASCE)NM.2153-5477.0000081
Zhidong Zhou, Dong-dong Wang, Q. Jiang
AbstractThis work aims to study the buckling kinetic process of a piezoelectric thin film (nanoribbon) bonded to a viscoelastic compliant layer with rigid support. The piezoelectric thin film is assumed to be poled in the thickness direction and is governed by the nonlinear coupled electromechanical equations. Subsequently, on the basis of the classical elastic-viscoelastic correspondence principle, the kinetic process of the thin film buckling under the intermediate stress state is analyzed in a systematic manner. In particular the piezoelectric effect is examined with respect to the critical wavelength, the wavelength of the fastest growing mode, the critical stress, and the fastest growth rate in detail. The results evince that the piezoelectricity has an evident stiffening effect on the kinetic buckling process of the thin film with viscoelastic substrate.
摘要本工作旨在研究压电薄膜(纳米带)与刚性支撑粘弹性柔顺层结合的屈曲动力学过程。假设压电薄膜沿厚度方向极化,并由非线性耦合机电方程控制。随后,根据经典弹粘弹性对应原理,系统分析了薄膜在中应力状态下屈曲的动力学过程。特别从临界波长、最快增长模态波长、临界应力和最快增长速率等方面详细考察了压电效应。结果表明,压电对粘弹性衬底薄膜的动力学屈曲过程有明显的加劲作用。
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引用次数: 0
Nanoindentation Characterization of Asphalt Concrete Aging 沥青混凝土老化的纳米压痕表征
Pub Date : 2014-03-01 DOI: 10.1061/(ASCE)NM.2153-5477.0000061
R. Tarefder, H. Faisal
AbstractAsphalt concrete (AC) consists of coarse aggregate, asphalt binder, and fines. The asphalt binder creates an asphalt film around the coarse aggregate and fines. Fines are trapped inside the binder film, which is also known as mastic. Mastic and aggregate govern most of the mechanical properties of AC. Therefore, researchers have performed various tests on mastic to understand macroscale behavior of AC. Nanomechanical characterization is more appropriate for mastic, as the thinness of mastic is approximately 15–20 μm around an aggregate particle. For this paper, the authors conducted nanoindentation tests on mastic and aggregate as integral parts of AC. In particular, they compared the modulus and hardness of oven-aged mastic and aggregate with those of unaged mastic and aggregate. To deal with the heterogeneity of the mastic part, they made hundreds of indents on the mastic part of each AC sample. On the aggregate part, they made 60 indents to determine the mechanical properties of the aggregate o...
摘要沥青混凝土由粗集料、沥青粘结剂和细粉组成。沥青粘合剂在粗骨料和细粒周围形成沥青膜。细粒被困在粘合剂薄膜中,也被称为胶乳。胶粘剂和骨料决定了AC的大部分力学性能。因此,研究人员对胶粘剂进行了各种测试,以了解AC的宏观行为。纳米力学表征更适合于胶粘剂,因为胶粘剂的厚度约为15-20 μm。在本文中,作者对作为AC的组成部分的胶泥和骨料进行了纳米压痕试验,特别是比较了烘干后的胶泥和骨料与未烘干后的胶泥和骨料的模量和硬度。为了处理乳脂部分的不均匀性,他们在每个AC样品的乳脂部分做了数百个凹痕。在骨料部分,他们做了60个压痕来测定骨料的力学性能。
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引用次数: 42
Atomic-Level Shear Stress-Strain Behavior of β-Sn β-Sn的原子水平剪应力-应变行为
Pub Date : 2013-12-01 DOI: 10.1061/(ASCE)NM.2153-5477.0000066
Yongchang Lee, C. Basaran
AbstractShear deformation of β-Sn along five different lattice orientations is studied at the atomic level. Simulated models are perfect β-Sn lattice without defects. To study the atomic behavior and constitutive relationship of β-Sn in shear, the β-Sn models are simulated by a molecular dynamics simulation package, LAMMPS, and the shear stress is computed by using virial stress. A modified embedded-atom method is employed for the β-Sn potential. The constant shear strain rate, 17.5 (%/ns), is applied. Simulation is conducted by using a canonical ensemble. To investigate thermal effects, the models are simulated at three different temperatures, 27, 127, and 227°C, and the results were compared with experimental data.
摘要在原子水平上研究了β-Sn沿5种不同晶格取向的剪切变形。模拟模型是完美的无缺陷β-Sn晶格。为了研究β-Sn在剪切过程中的原子行为和本构关系,利用分子动力学模拟软件LAMMPS对β-Sn模型进行了模拟,并利用维里应力计算了剪切应力。采用改进的嵌入原子法测定β-Sn电位。采用恒定剪切应变速率17.5 (%/ns)。通过使用规范集成进行仿真。为了研究热效应,在27、127和227℃三种不同温度下对模型进行了模拟,并将结果与实验数据进行了比较。
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引用次数: 2
Efficient Numerical Evaluation of Semianalytical Models for Squeeze Film Damping for Torsion Mirrors 扭力镜挤压膜阻尼半解析模型的有效数值评价
Pub Date : 2013-09-12 DOI: 10.1061/(ASCE)NM.2153-5477.0000075
M. Gugat
Abstract In the semianalytical models for squeeze film damping, the coefficient of damping torque is expressed as an infinite double series. To work with these models, methods for the efficient numerical evaluation of these double series are important, because, as has been pointed out, the results are given by complicated equations; the application of the results is difficult. This paper presents a transformation of the equations that allows a fast and reliable numerical evaluation of the coefficient of damping torque for torsion mirrors. We give precise error bounds and present examples that illustrate that approximations with one or two terms are often sufficient in practice.
在挤压膜阻尼半解析模型中,将阻尼力矩系数表示为无限双级数。为了处理这些模型,对这些二重级数进行有效数值计算的方法是重要的,因为,正如已经指出的,结果是由复杂的方程给出的;结果的应用是困难的。本文提出了一种可以快速可靠地计算扭力镜阻尼力矩系数的方程变换方法。我们给出了精确的误差范围,并举例说明,在实践中,一项或两项的近似通常是足够的。
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引用次数: 2
New and Improved Analytical Solutions for the Self-Folding Problem of Carbon Nanotubes 碳纳米管自折叠问题的新改进解析解
Pub Date : 2013-09-04 DOI: 10.1061/(ASCE)NM.2153-5477.0000078
Y. Mikata
AbstractIt has been observed experimentally and computationally that a carbon nanotube with a large aspect ratio can self-fold because of the van der Waals force between parts of the same carbon nanotube. The primary issue in the self-folding problem is to determine the minimum threshold length of a carbon nanotube at which it becomes possible for a carbon nanotube to self-fold because of the van der Waals force. In this paper, approximate mathematical models based on both energy and force methods are constructed for the self-folding problem of carbon nanotubes and they are solved exactly as an elastica problem using elliptic functions. This paper is a sequel to previous papers by the writer and a more realistic and accurate deformation of a self-folded CNT (carbon nanotube) is used in the models. The primary result of this paper is determination of the critical threshold (minimum) length of a carbon nanotube as a function of geometry, material parameters, and force field parameters for particular atomic ...
摘要通过实验和计算发现,由于同一碳纳米管各部分之间存在范德华力,大纵横比碳纳米管可以自折叠。自折叠问题的主要问题是确定碳纳米管的最小阈值长度,使碳纳米管由于范德华力而可能自折叠。本文建立了基于能量法和力法的碳纳米管自折叠近似数学模型,并将其作为弹性问题用椭圆函数精确求解。这篇论文是作者之前论文的续集,在模型中使用了更真实和准确的自折叠碳纳米管变形。本文的主要结果是确定了碳纳米管的临界阈值(最小)长度作为几何形状、材料参数和特定原子结构的力场参数的函数。
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引用次数: 4
Special Section on Mechanics of Nanocomposites and Nanostructures 纳米复合材料和纳米结构力学专题
Pub Date : 2013-09-01 DOI: 10.1061/(ASCE)NM.2153-5477.0000073
N. Rahbar, Caglar Oskay, H. Yin
This special section includes a selection of original research papers focused on the mechanics of nanocomposites and nanostructures. The September issue includes the first set of papers on the subject. Most of the papers were also presented at the Nanomechanics and Nanocomposites Symposium at the 2012 Conference of the Engineering Mechanics Institute of the American Society of Civil Engineers held at Notre Dame University in South Bend, Indiana. The Nanomechanics and Nanocomposites Symposium provided a unique venue for researchers exploring the intersections of applied and computational mechanics within the field of materials science at the nanoscale. In this area, there are both tremendous challenges and opportunities. It is humbling to consider the limitations of our current knowledge about the structures and properties of materials at the smaller scales. On the other hand, it is bewildering to consider all of the possibilities for breakthroughs in the engineering disciplines that might be achieved by understanding our world and employing that knowledge to make advances in the materials we use. Although this symposium featured papers on a wide variety of topics, mechanics of materials at the nanoscale was a dominant theme discussed. Indeed, four of the five papers in this first series were devoted entirely to nanomechanical behavior of materials, and a majority of the remaining papers also focused, at least in part, on aspects of nanomechanics. Accordingly, we are pleased to publish this collection of papers in the similarly themed Journal of Nanomechanics and Micromechanics. We believe these papers represent some of the wide scope seen in the field.
这个特别的部分包括一些原创的研究论文,这些论文集中在纳米复合材料和纳米结构的力学上。9月的这期包括了第一批关于这个主题的论文。大多数论文也在2012年美国土木工程师学会工程力学学会在印第安纳州南本德圣母大学举行的纳米力学和纳米复合材料研讨会上发表。纳米力学和纳米复合材料研讨会为研究人员在纳米尺度上探索材料科学领域中应用力学和计算力学的交叉点提供了一个独特的场所。在这个领域,既有巨大的挑战,也有巨大的机遇。考虑到我们目前对小尺度材料的结构和性质的知识的局限性,这是令人谦卑的。另一方面,考虑到通过理解我们的世界并利用这些知识在我们使用的材料上取得进步,在工程学科中取得突破的所有可能性是令人困惑的。虽然本次研讨会的论文主题广泛,但纳米尺度下的材料力学是讨论的主要主题。事实上,在第一个系列的五篇论文中,有四篇完全致力于材料的纳米力学行为,其余的大多数论文也集中在纳米力学方面,至少部分集中在纳米力学方面。因此,我们很高兴在类似主题的纳米力学和微力学杂志上发表这篇论文。我们相信这些论文代表了该领域的一些广泛范围。
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引用次数: 0
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Journal of nanomechanics & micromechanics
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