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Deposition Temperature Induced Texture and Strengthening of Ti/Ni Multilayer Thin Films Ti/Ni多层薄膜沉积温度诱导织构及强化
IF 2.6 4区 工程技术 Q2 Engineering Pub Date : 2023-06-21 DOI: 10.1115/1.4062775
Zhou Yang, Junlan Wang
Strong thermal effect on microstructure and mechanical properties of Ti/Ni multilayer thin films was observed from in-situ heating during deposition and subsequent annealing. Films deposited at low-temperature show preferred crystallographic texture for both Ti and Ni layers, with columnar structure extending through the layers. The columnar structure become more distinct and complete with the increase of temperature up to 300°C, and meanwhile more atomic diffusion and intermixing occur along the Ti/Ni interfaces, promoting the formation of Ti-Ni intermetallic precipitates. High-temperature deposition causes disintegration of the layered structure. Columnar Ti-Ni alloys and further recrystallized alloys were detected with preferred crystallographic texture. For material strength, an increased hardness trend is observed with increasing deposition temperature even with much larger grain size compared to room temperature case. Furthermore, for multilayer system deposited under low temperature, post annealing results in higher hardness with minimal microstructure modification, with more strengthening observed in lower deposition temperature case.
在沉积和随后的退火过程中,原位加热对Ti/Ni多层薄膜的微观结构和力学性能产生了强烈的热影响。在低温下沉积的薄膜显示出Ti和Ni层的优选结晶结构,柱状结构延伸穿过层。随着温度升高至300°C,柱状结构变得更加明显和完整,同时沿Ti/Ni界面发生更多的原子扩散和混合,促进了Ti-Ni金属间沉淀物的形成。高温沉积导致层状结构的分解。柱状Ti-Ni合金和进一步的再结晶合金被检测到具有优选的结晶织构。对于材料强度,即使与室温情况相比晶粒尺寸大得多,随着沉积温度的升高,也观察到硬度增加的趋势。此外,对于在低温下沉积的多层系统,后退火导致硬度更高,微观结构变化最小,在较低沉积温度的情况下观察到更多的强化。
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引用次数: 0
Perspective: Large Language Models in Applied Mechanics 透视:应用力学中的大语言模型
IF 2.6 4区 工程技术 Q2 Engineering Pub Date : 2023-06-21 DOI: 10.1115/1.4062773
Neal R. Brodnik, Samuel Carton, Caelin Muir, Satanu Ghosh, Doug Downey, M. Echlin, T. Pollock, S. Daly
Large language models (LLMs), such as ChatGPT and PaLM, are able to perform sophisticated text comprehension and generation tasks with little or no training. Alongside their broader societal impacts, these capabilities carry great promise for the physical sciences, including applied mechanics. We present a summary of recent developments in these models, their application to mechanics and adjacent fields, and a perspective on their future use in applied mechanics, taking into account their limitations and the unique challenges of the field.
大型语言模型(LLM),如ChatGPT和PaLM,能够在很少或没有训练的情况下执行复杂的文本理解和生成任务。除了更广泛的社会影响外,这些能力对包括应用力学在内的物理科学也有很大的前景。我们总结了这些模型的最新发展,它们在力学和邻近领域的应用,并展望了它们在应用力学中的未来应用,同时考虑到它们的局限性和该领域的独特挑战。
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引用次数: 2
Correlation of Microstructure and Nanomechanical Properties of Additively Manufactured Inconel 718 添加铬镍铁合金718微观结构与纳米力学性能的相关性
IF 2.6 4区 工程技术 Q2 Engineering Pub Date : 2023-06-21 DOI: 10.1115/1.4062776
Allen Kim, Lily Vu, Tony Chung, David Song, Junlan Wang
Additive manufacturing (AM) has emerged as a crucial technology in recent decades, particularly within aerospace industry. However, the thermally cyclic nature of these processes introduce significant variations and defects in microstructure, which can adversely affect final part performance and hinder the widespread adoption of the technology. Traditionally, characterization of AM parts has relied on conventional bulk testing methods, which involve analyzing many samples to gather sufficient data for statistical analysis. Unfortunately, these methods are unable to account for local nanoscale variations in material properties caused by the microstructure, as they measure a single averaged property for each tested sample. In this work, we use AM Inconel 718 as a model system in developing a novel approach to correlate nanomechanical properties obtained through nanoindentation with microstructure obtained through electron backscatter diffraction (EBSD). By associating mechanical properties obtained from each indent with the corresponding crystallographic direction measured with EBSD, we calculate the weighted average hardness and modulus for each orientation. This enables us to generate inverse property figure maps depicting the relationship between mechanical properties and crystallographic direction. Our method yields results in good agreement with literature when calculating the part modulus and hardness. Furthermore, it effectively captures nanoscale variations in properties across the microstructure. The key advantage of this methodology is its capability to rapidly test a single AM part and generate a large dataset for statistical analysis. Complementing existing macroscale characterization techniques, this method can help improve AM part performance prediction and contribute to the wider adoption of AM technologies.
近几十年来,增材制造(AM)已成为一项关键技术,尤其是在航空航天行业。然而,这些工艺的热循环性质在微观结构中引入了显著的变化和缺陷,这可能会对最终零件的性能产生不利影响,并阻碍该技术的广泛采用。传统上,AM零件的表征依赖于传统的批量测试方法,该方法涉及分析许多样本以收集足够的数据进行统计分析。不幸的是,这些方法无法解释由微观结构引起的材料性能的局部纳米级变化,因为它们测量每个测试样品的单个平均性能。在这项工作中,我们使用AM Inconel 718作为模型系统,开发了一种新的方法,将通过纳米压痕获得的纳米机械性能与通过电子背散射衍射(EBSD)获得的微观结构相关联。通过将从每个压痕获得的机械性能与用EBSD测量的相应结晶方向相关联,我们计算了每个取向的加权平均硬度和模量。这使我们能够生成描述力学性质和结晶方向之间关系的逆性质图。在计算零件模量和硬度时,我们的方法得出的结果与文献一致。此外,它可以有效地捕捉微观结构中纳米级性能的变化。该方法的主要优点是能够快速测试单个AM零件并生成用于统计分析的大型数据集。该方法补充了现有的宏观表征技术,有助于提高AM零件的性能预测,并有助于AM技术的更广泛应用。
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引用次数: 0
Creating Geometric Imperfections in Thin-Walled Structures using Acoustic Excitation 利用声激励在薄壁结构中产生几何缺陷
IF 2.6 4区 工程技术 Q2 Engineering Pub Date : 2023-06-16 DOI: 10.1115/1.4062746
Jennifer Xue, Zheren Baizhikova, R. Ballarini, Tian Chen
Thermomechanical buckling of slender and thin-walled structural components happens without warning and can lead to catastrophic failure. Similar phenomena are observed during plasmolysis (contraction of a plant cell’s protoplast) and rupture of viral capsids. Analytical formulas derived from stability analyses of elastic plates, cylinders, and shells that do not account for the effects of random geometric imperfections introduced during the manufacturing process or biological growth may vastly over-estimate buckling capacity. To ensure structural safety the formulas must therefore be combined with empirical data to define “knock down factors” which are in turn used to establish safety factors. Towards improved understanding of the role of imperfections on mechanical response, ingenious methods have been used to fabricate and test near-perfectly hemispherical shells and those containing dimple-like defects. However, a method of inducing imperfections in the form of randomly-shaped surfaces remains elusive. We introduce a protocol for realizing such imperfect shells and measuring the pressure required to buckle them. Silicone is poured onto an elastomeric mold under an acoustic excitation, which can be either random sound, or if desired the same as the modal frequency of the mold. Illustrative micro-Computed-Tomography images and buckling pressure experiments of a nearly-perfect shell and an imperfect one show that the method is effective in introducing randomly-shaped imperfections of significant magnitudes. This proof-of-concept study demonstrates that the experimental results when combined with computational simulations can lead to improved understanding of stochastic buckling phenomena.
细长薄壁结构构件的热力学屈曲在没有预警的情况下发生,可能导致灾难性的破坏。在质解(植物原生质体的收缩)和病毒衣壳的破裂过程中也观察到类似的现象。从弹性板、圆柱和壳的稳定性分析中得出的分析公式,如果没有考虑到在制造过程或生物生长过程中引入的随机几何缺陷的影响,可能会大大高估屈曲能力。因此,为了确保结构安全,这些公式必须与经验数据相结合,以确定“击倒因子”,然后再用于建立安全系数。为了更好地理解缺陷对机械响应的作用,人们采用了巧妙的方法来制造和测试近乎完美的半球形外壳和含有韧窝状缺陷的外壳。然而,一种以随机形状表面的形式诱导缺陷的方法仍然难以捉摸。我们介绍了一种实现这种不完美外壳的协议,并测量了使它们弯曲所需的压力。在声音激励下,将硅树脂倒入弹性体模具中,声音激励可以是随机声音,也可以是与模具模态频率相同的声音。近完美壳和不完美壳的微计算机层析成像和屈曲压力实验表明,该方法在引入显著大小的随机形状缺陷方面是有效的。这一概念验证研究表明,当实验结果与计算模拟相结合时,可以提高对随机屈曲现象的理解。
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引用次数: 0
On Jump Discontinuities in Internal Forces of Flexible Structures Carrying Moving Subsystems 承载运动子系统的柔性结构内力的跳跃不连续
4区 工程技术 Q2 Engineering Pub Date : 2023-06-15 DOI: 10.1115/1.4062628
Bingen Yang, Hao Gao
Abstract Combined systems, which are flexible structures carrying moving subsystems, are seen in various applications. Due to structure–subsystem interactions, the structure in a combined system encounters jump discontinuities in its internal forces (such as the bending moment and shear force of a beam). Accurate estimation of such jump discontinuities is important to the performance, safety, and longevity of a combined system. Because of the time-varying nature and complexity of structure–subsystem interactions, conventional series solution methods experience slow convergence, and the Gibbs phenomenon in computation and the improved series expansion methods are limited to certain proportionally damped continua under moving forces and moving oscillators. In this paper, a novel modified series expansion method (MSEM) is proposed to resolve the aforementioned issues with the existing series solution methods. Through the introduction of a jump influence function, the proposed method produces fast-convergent series solutions and accurately predicts the jump discontinuities without the Gibbs phenomenon. The MSEM is applicable to structures with nonproportional damping and subject to arbitrary boundary conditions, and it can easily manage general M-DOF moving subsystems having multiple contact points with a supporting structure. As an important result of this investigation, a mathematical proof of the convergence of the MSEM-based solutions is given for the first time. Additionally, two numerical examples are presented to demonstrate the accuracy, efficiency, and versatility of the proposed MSEM in modeling and analysis of combined systems.
组合系统是一种承载运动子系统的柔性结构,有着广泛的应用。由于结构-子系统的相互作用,组合系统中的结构在其内力(如梁的弯矩和剪力)中遇到跳跃不连续。准确估计这种跳变不连续对组合系统的性能、安全性和使用寿命至关重要。由于结构-子系统相互作用的时变性质和复杂性,传统的级数解方法收敛速度慢,计算中的吉布斯现象和改进的级数展开方法仅限于运动力和运动振子作用下的一定比例阻尼连续体。本文提出了一种改进的级数展开法(MSEM)来解决现有级数求解方法存在的上述问题。通过引入跳变影响函数,该方法能产生快速收敛的级数解,并能准确预测跳变不连续而不出现吉布斯现象。该方法适用于具有非比例阻尼和任意边界条件的结构,能够方便地管理具有多个接触点和支撑结构的一般多自由度运动子系统。作为本研究的一个重要成果,本文首次给出了基于msem的解的收敛性的数学证明。此外,给出了两个数值算例,以证明所提出的MSEM在组合系统建模和分析中的准确性、效率和通用性。
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引用次数: 0
A cavity-based micromechanical model for the shear band failure in metallic glasses under arbitrary stress states 基于空腔的任意应力状态下金属玻璃剪切带破坏微观力学模型
IF 2.6 4区 工程技术 Q2 Engineering Pub Date : 2023-06-09 DOI: 10.1115/1.4062724
Yanfei Gao
Deformation and fracture of metallic glasses are often modeled by stress-based criteria which often incorporate some sorts of pressure dependence. However, detailed mechanisms that are responsible for the shear band formation and the entire damage initiation and evolution process are complex and the origin of such a pressure dependence is obscure. Here we argue that the shear band formation results from the constitutive instability, so that the shear-band angle and arrangements can be easily related to the macroscopic constitutive parameters such as internal friction and dilatancy factor. This is one reason for the observed tension-compression asymmetry in metallic glasses. The free volume coalescence leads to precipitous formation of voids or cavities inside the shear bands, and the intrinsic “ductility” is therefore governed by the growth of these cavities. Based on a generalized Stokes-Hookean analogy, we can derive the critical shear-band failure strain with respect to the applied stress triaxiality, in which the cavity evolution scenarios are sharply different between tension-controlled and shear/compression-dominated conditions. This is another possible reason for the tension-compression asymmetry. It is noted that diffusive-controlled cavity growth could also be the rate-determining process, as suggested by the recent measurements of shear-band diffusivity and viscosity that turn out to satisfy the Stokes-Einstein relationship. This constitutes the third possible reason for the tension-compression asymmetry.
金属玻璃的变形和断裂通常采用基于应力的准则来建模,这些准则通常包含一些压力依赖性。然而,导致剪切带形成和整个损伤发生和演化过程的详细机制是复杂的,而且这种压力依赖性的来源尚不清楚。本文认为剪切带的形成是本构失稳的结果,因此剪切带的角度和排列可以很容易地与内摩擦和剪胀系数等宏观本构参数联系起来。这是在金属玻璃中观察到的拉压不对称的一个原因。自由体积聚并导致剪切带内的空洞或空腔的急剧形成,因此这些空腔的生长控制了固有的“延性”。基于广义Stokes-Hookean类比,我们可以推导出相对于应力三轴性的临界剪切带破坏应变,其中在拉伸控制和剪切/压缩主导的条件下,空腔演化情景明显不同。这是拉压不对称的另一个可能原因。值得注意的是,扩散控制的空腔生长也可能是速率决定过程,正如最近对剪切带扩散率和粘度的测量所表明的那样,它们最终满足斯托克斯-爱因斯坦关系。这构成了拉压不对称的第三个可能原因。
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引用次数: 0
Mechanics of tunable adhesion with surface wrinkles 具有表面褶皱的可调粘附力学
IF 2.6 4区 工程技术 Q2 Engineering Pub Date : 2023-06-07 DOI: 10.1115/1.4062699
Teng Zhang
Surface wrinkles have emerged as a promising avenue for the development of smart adhesives with dynamically tunable adhesion, finding applications in diverse fields, such as soft robots and medical devices. Despite intensive studies and great achievements, it is still challenging to model and simulate the tunable adhesion with surface wrinkles due to roughened surface topologies and pre-stress inside the materials. The lack of a mechanistic understanding hinders the rational design of these smart adhesives. Here we integrate a lattice model for nonlinear deformations of solids and nonlocal interaction potentials for adhesion in the framework of molecular dynamics to explore the roles of surface wrinkles on the adhesion behaviors. We validate the proposed model by comparing wrinkles in a neo-Hookean bilayer with benchmarked results and reproducing the analytical solution for cylindrical adhesion. We then systematically study the pull-off force of the wrinkled surface with varied compressive strains and adhesion energies. Our results reveal the competing effect between the adhesion induced contact and the roughness due to wrinkles on enhancing or weakening the adhesion. Such understanding provides guidance for tailoring material and geometry as well as loading of the wrinkled surfaces for different applications.
表面褶皱已成为开发具有动态可调附着力的智能粘合剂的一条很有前途的途径,在软机器人和医疗设备等不同领域都有应用。尽管进行了深入的研究并取得了巨大的成就,但由于粗糙的表面拓扑结构和材料内部的预应力,建模和模拟具有表面褶皱的可调粘附仍然具有挑战性。缺乏对机械的理解阻碍了这些智能粘合剂的合理设计。在分子动力学的框架下,我们集成了固体非线性变形的晶格模型和粘附的非局部相互作用势,以探索表面褶皱对粘附行为的作用。我们通过将新胡克双层中的褶皱与基准结果进行比较来验证所提出的模型,并重现圆柱形粘附的分析解。然后,我们系统地研究了具有不同压缩应变和粘附能的褶皱表面的拉脱力。我们的结果揭示了粘附诱导的接触与皱纹引起的粗糙度之间的竞争效应,从而增强或削弱了粘附性。这种理解为剪裁材料和几何形状以及为不同应用加载褶皱表面提供了指导。
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引用次数: 0
Bounds on the Poisson's ratios of diamond-like structures 类金刚石结构泊松比的界
IF 2.6 4区 工程技术 Q2 Engineering Pub Date : 2023-06-07 DOI: 10.1115/1.4062700
Yi Liu, Chunbo Zhang, Hang Yang, Enlai Gao
Poisson's ratios of diamond-like structures, such as cubic C, Si, and Ge, have been widely explored because of their potential applications in solid-state devices. However, the theoretical bounds on the Poisson's ratios of diamond-like structures remain unknown. In this paper, we have derived analytical expressions for the minimum and maximum Poisson's ratios, as well as the Poisson's ratios averaged by three different schemes (i.e., Voigt, Reuss, and Hill averaging schemes). These expressions are based on the correlation between macroscopic elastic constants and microscopic force constants of diamond-like structures, and are solely a function of a dimensionless quantity (λ) that characterizes the ratio of mechanical resistances between angle bending and bond stretching. Based on these expressions, we have determined the bounds on the Poisson's ratios, as well as the minimum and maximum Poisson's ratios, and the Poisson's ratios averaged by the three schemes mentioned above. Specifically, these bounds are (−1, 4/5), (−1, 1/5), (0, 4/5), (−1, 1/2), (−1/3, 1/2), and (−2/3, 1/2), respectively. These results were well supported by atomistic simulations. Mechanism analyses demonstrated that the diverse Poisson's behaviors of diamond-like structures result from the interplay between two deformation modes (i.e., bond stretching and angle bending). This work provides the roadmap for finding interesting Poisson's behaviors of diamond-like structures.
类金刚石结构(如立方C、Si和Ge)的泊松比由于其在固态器件中的潜在应用而被广泛探索。然而,类金刚石结构泊松比的理论界限仍然未知。在本文中,我们导出了最小和最大泊松比的解析表达式,以及三种不同方案(即Voigt、Reuss和Hill平均方案)平均的泊松比。这些表达式基于类金刚石结构的宏观弹性常数和微观力常数之间的相关性,并且仅仅是表征角度弯曲和键拉伸之间的机械阻力比的无量纲量(λ)的函数。基于这些表达式,我们确定了泊松比的边界,以及最小和最大泊松比,以及由上述三种方案平均的泊松比。具体而言,这些边界分别为(−1,4/5)、(−1、1/5)、(0,4/5。这些结果得到了原子模拟的有力支持。机理分析表明,类金刚石结构的不同泊松行为是两种变形模式(即键拉伸和角弯曲)相互作用的结果。这项工作为寻找类金刚石结构有趣的泊松行为提供了路线图。
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引用次数: 0
Non-quadratic strain gradient plasticity theory and size effects in constrained shear 约束剪切中的非二次应变梯度塑性理论及尺寸效应
IF 2.6 4区 工程技术 Q2 Engineering Pub Date : 2023-06-07 DOI: 10.1115/1.4062698
M. Kuroda, A. Needleman
A previously proposed strain gradient plasticity theory is extended to incorporate a non-quadratic power law function of the plastic strain gradient in the free energy expression with an exponent of N + 1. The values of N are taken to vary from N = 1 to N = 0. A simple shear problem of a metal layer between rigid boundaries is analyzed. Two stages of plastic deformation are considered. In stage I, the plastic strain is taken to be zero at the boundaries. Stage I ends when a specified magnitude of the plastic strain gradient is attained at the boundaries. In stage II, the magnitude of the plastic strain gradient at the boundaries is fixed at the specified value. With N = 0, a critical plastic strain gradient cannot be specified at the boundaries because the plastic strain gradient is infinite at the boundaries. The theory with N = 0 predicts a constant plateau stress immediately after initial yield, and the dependence of the plateau stress on the layer thickness can fit experimentally observed plateau stress values. However, with N = 0, a stress gap occurs between the initial yield stress and the plateau stress. The theory with 0 < N = 1 and with stage II also can reproduce the experimentally observed dependence of the plateau stress on the layer thickness for any value of N in that range, with an appropriate value of critical plastic strain gradient at the boundaries. The solution for 0 < N = 1 includes that for N = 0 as a limiting case.
将先前提出的应变梯度塑性理论扩展为在指数为N+1的自由能表达式中包含塑性应变梯度的非二次幂律函数。N的值在N=1到N=0之间变化。分析了刚性边界之间金属层的一个简单剪切问题。考虑了塑性变形的两个阶段。在阶段I中,将边界处的塑性应变取为零。当在边界处获得指定大小的塑性应变梯度时,阶段I结束。在第二阶段,边界处的塑性应变梯度的大小固定在指定值。当N=0时,不能在边界处指定临界塑性应变梯度,因为塑性应变斜率在边界处是无限的。N=0的理论预测在初始屈服后立即出现恒定的平台应力,并且平台应力对层厚度的依赖性可以拟合实验观察到的平台应力值。然而,当N=0时,在初始屈服应力和平台应力之间出现应力间隙。对于该范围内的任何N值,0<N=1和阶段II的理论也可以再现实验观察到的平台应力对层厚度的依赖性,在边界处具有适当的临界塑性应变梯度值。0
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引用次数: 1
Fracture Resistance of Chemo-mechanically Coupled Solid Solutions 化学机械耦合固溶体的抗断裂性能
IF 2.6 4区 工程技术 Q2 Engineering Pub Date : 2023-06-07 DOI: 10.1115/1.4062697
Xueju Wang, Mu Lu, Min Zhou, S. Xia
Fracture in solid solutions, such as electrodes for lithium-ion batteries and fuel cells, is mediated by intricate interactions between solid-state diffusion and crack propagation. In this work, we developed a composition-dependent cohesive zone model and integrated it with a chemo-mechanical coupling constitutive model to study the fracture mechanisms of solid solutions. The computational framework was used to investigate the effective fracture properties of chemo-mechanically coupled solid solutions over a wide range of crack growth velocities and compositional dependence of intrinsic fracture energy. The results revealed an important characteristic crack velocity, which is set by the ratio of the diffusivity to the intrinsic fracture energy and dictates the effective fracture resistance of the material. We also applied the model to study the fracture behavior of two-phase lithiated silicon (Si) and germanium (Ge) nanostructures as candidate high-capacity anodes for next-generation lithium-ion batteries, and showed that Ge nanostructures are more fracture resistant than their Si counterparts. The computational study presented here provides important insights for the rational design, operation, and mechanical testing of chemo-mechanically active material systems for their use in energy storage and conversion.
锂离子电池和燃料电池电极等固溶体的断裂是由固态扩散和裂纹扩展之间复杂的相互作用介导的。在这项工作中,我们建立了一个成分依赖的内聚区模型,并将其与化学-力学耦合本构模型相结合,以研究固溶体的断裂机制。该计算框架用于研究化学-机械耦合固溶体在宽裂纹扩展速度范围内的有效断裂特性以及固有断裂能的成分依赖性。结果表明,裂纹速度是材料的有效抗断裂能力的重要特征,它由材料的扩散率与断裂能之比决定。我们还应用该模型研究了两相锂化硅(Si)和锗(Ge)纳米结构作为下一代锂离子电池候选高容量阳极的断裂行为,结果表明,Ge纳米结构比Si纳米结构更耐断裂。本文提出的计算研究为化学-机械活性材料系统的合理设计、操作和机械测试提供了重要的见解,以用于能量存储和转换。
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引用次数: 0
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