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Thermomechanical Constitutive Models of Shape Memory Polymers and Their Composites 形状记忆聚合物及其复合材料的热力学本构模型
IF 14.3 1区 工程技术 Q1 Engineering Pub Date : 2022-11-08 DOI: 10.1115/1.4056131
Wei Zhao, Liwu Liu, X. Lan, J. Leng, Yanju Liu
Shape memory polymers (SMPs) and SMP composites (SMPCs) have been widely employed in several fields and exhibit excellent self-actuation, deformation, and self-adaption. Establishing reasonable constitutive models is vital for understanding the shape memory mechanism and expanding its applications. Moreover, the mechanical response of SMPs under different conditions can be predicted, facilitating their precise control. The internal mechanism for the shape memory behavior in most SMPs is thermal actuation. This study reviews the theories of thermally actuated SMPs, rheological and phase transition concept models, and models combining the rheology and phase transition concept. Furthermore, the constitutive models of particulate-reinforced SMPCs, carbon-fiber-reinforced SMPCs, and the buckling behavior of SMPCs are summarized. This study is expected to help solve the remaining issues rapidly and contribute to the establishment of rational constitutive models for SMPs and SMPCs.
形状记忆聚合物(SMPs)和形状记忆复合材料(smpc)具有良好的自致动、变形和自适应性能,已广泛应用于多个领域。建立合理的本构模型对于理解形状记忆机理和扩大形状记忆的应用具有重要意义。此外,还可以预测smp在不同条件下的力学响应,便于对其进行精确控制。在大多数smp中,形状记忆行为的内部机制是热致动。本文综述了热驱动SMPs的理论、流变和相变概念模型,以及流变和相变概念相结合的模型。总结了颗粒增强、碳纤维增强复合材料的本构模型以及复合材料的屈曲行为。本研究将有助于快速解决剩余问题,并有助于建立合理的smp和smpc本构模型。
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引用次数: 5
What Is the Internal Pressure That Initiates Damage in Cementitious Materials during Freezing and Thawing? A Micromechanical Analysis 在冻融过程中引起胶凝材料损伤的内部压力是什么?微观力学分析
IF 14.3 1区 工程技术 Q1 Engineering Pub Date : 2022-11-05 DOI: 10.3390/applmech3040074
J. Timothy, Alexander Haynack, T. Kränkel, C. Gehlen
Damage induced by repetitive freezing and thawing processes is one of the critical factors that affect concrete durability in cold climates. This deterioration process manifests as surface scaling and internal damage. The damage processes are governed by physicochemical mechanisms that are active across multiple scales. In this contribution, we present a novel multiscale theoretical framework for estimating the critical pressure required for microcrack initiation during freezing and thawing of cementitious mortar. Continuum micromechanics and fracture mechanics is used to model the phenomena of microcrack initiation and growth. Damage at the microscale is upscaled to the level of the specimen using multilevel homogenization. The critical pressure is estimated using poromechanics at the microscopic scale. A theoretical analysis shows that in the frozen state, the material can resist higher pressures. As a consequence, the material is more susceptible to damage during thawing. The micromechanical predictions are within the range of the predictions obtained by electrokinetic theory.
反复冻融过程引起的损伤是影响寒冷气候条件下混凝土耐久性的关键因素之一。这种劣化过程表现为表面结垢和内部损伤。损伤过程是由物理化学机制控制的,这种机制在多个尺度上都是活跃的。在这一贡献中,我们提出了一个新的多尺度理论框架,用于估计胶凝砂浆冻结和融化过程中微裂纹萌生所需的临界压力。用连续体细观力学和断裂力学模拟了微裂纹的萌生和扩展。使用多级均质化技术将微尺度的损伤提升到试样的水平。利用孔隙力学在微观尺度上估计临界压力。理论分析表明,在冻结状态下,材料可以抵抗更高的压力。因此,这种材料在解冻过程中更容易受到破坏。微力学预测在电动力学理论预测的范围内。
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引用次数: 2
Local Stability in the Process of Excavation Located in High Permeability Saturated Sand of Diaphragm Wall Construction 高渗透饱和砂土连续墙开挖过程中的局部稳定性研究
IF 14.3 1区 工程技术 Q1 Engineering Pub Date : 2022-10-31 DOI: 10.3390/applmech3040072
Yuhang Liu, Linchun Wei, Yanfei Zhu, X. Zhuang
The stability of the slurry trench is very important in the construction of the underground diaphragm wall. In the current research, the local instability of the slurry trench is mainly investigated after the excavation of a unit slot is completely completed. However, the local stability in the process of excavation has received little attention. In this paper, the local stability in the process of excavation located in high permeability strata of diaphragm wall construction is investigated. A slurry infiltration experiment was carried out to investigate the distribution of the excess pore pressure in the high permeability strata, which can determine the effective support pressure. Then, the local stability of the slurry trench in the process of excavation located in high permeability saturated sand is calculated. The results show that the same types of sand according to the design code cannot be simply treated to have the same permeability and similar distribution of the excess pore pressure, since whether the filter cake can be formed and the quality of the filter cake are the key factors to determine the distribution of the excess pore pressure. This is also crucial for the local stability in the process of excavation located in high permeability saturated sand. It is suggested that attention should be paid to the local stability in the process of excavation located in high permeability strata when the slurry infiltration mode is the pure permeable zone.
浆液槽的稳定性在地下连续墙施工中起着至关重要的作用。在目前的研究中,主要研究的是单元槽开挖完成后泥浆槽的局部失稳。然而,基坑开挖过程中的局部稳定问题却很少受到重视。本文对位于高渗透地层的连续墙施工开挖过程中的局部稳定性进行了研究。通过浆体入渗试验,研究了高渗透地层中超孔隙压力的分布规律,从而确定了有效支护压力。在此基础上,对高渗透饱和砂土开挖过程中浆槽的局部稳定性进行了计算。结果表明:按设计规范处理的同类型砂土,不能简单地认为其渗透率相同、超孔隙压力分布相似,滤饼能否形成、滤饼质量好坏是决定超孔隙压力分布的关键因素。这对于高渗透饱和砂土开挖过程中的局部稳定也是至关重要的。建议当浆体入渗方式为纯透水区时,应注意位于高渗透地层的开挖过程中的局部稳定性。
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引用次数: 0
Stiction and Friction of Nano- and Microtextured Liquid Silicon Rubber Surface Formed by Injection Molding 注射成型液态硅橡胶纳米和微织构表面的粘滞和摩擦
IF 14.3 1区 工程技术 Q1 Engineering Pub Date : 2022-10-31 DOI: 10.3390/applmech3040073
C. Koplin, Dennis F. Weißer, A. Fromm, M. Deckert
The use of cross-linking polymers such as liquid silicone rubber (LSR) can replicate serviceable surfaces with nano- and microstructures via the injection molding process. Laser ablation can be used to introduce microstructures into molding tools, while nanostructures are generated via PVD coating processes on the tools. This is why nanostructures are built using self-organized layer growth. The aim of this study was to generate evidence of direction-dependent coefficients of friction of elastomeric surfaces in dry or lubricated contact in boundary friction. Models of the dry friction of elastomeric surfaces, such as Schallamach waves or stick-slip cycles, were used to describe the friction modulation of such surfaces. Assumptions for model contacts against smooth partners, both dry and with lubrication, as well as assumptions for the interaction of structures with smooth surfaces, were investigated. It was found that for elastomer surfaces with Shore hardness 50, nanostructures are suitable for creating a direction-dependent friction increase in static and sliding friction. Friction reductions with defined microstructures are possible if their periodicity seems to interact with the wavelength of possible Schallamach waves. The choice of lubrication determines the forced wetting of the contact, but due to the structuring, there is a continuous transition to mixed friction.
使用交联聚合物,如液体硅橡胶(LSR),可以通过注射成型工艺复制具有纳米和微结构的可用表面。激光烧蚀可以在模具中引入微结构,而PVD涂层可以在模具上产生纳米结构。这就是为什么纳米结构是用自组织层生长来构建的。本研究的目的是产生证据的方向依赖的摩擦系数的弹性表面在干或润滑接触的边界摩擦。弹性体表面的干摩擦模型,如沙拉赫波或粘滑循环,被用来描述这种表面的摩擦调制。研究了模型与光滑伙伴接触的假设,包括干燥和润滑,以及光滑表面结构相互作用的假设。研究发现,对于邵氏硬度为50的弹性体表面,纳米结构适合在静摩擦和滑动摩擦中产生方向相关的摩擦增加。如果确定微观结构的周期性似乎与可能的沙拉马赫波的波长相互作用,则摩擦减小是可能的。润滑的选择决定了接触的强制润湿,但由于结构的原因,存在向混合摩擦的连续过渡。
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引用次数: 0
Shear Band Control for Improved Strength-Ductility Synergy in Metallic Glasses 提高金属玻璃强度-延性协同效应的剪切带控制
IF 14.3 1区 工程技术 Q1 Engineering Pub Date : 2022-10-18 DOI: 10.1115/1.4056010
Z. Sha, Y. Teng, L. H. Poh, T. Wang, Huajian Gao
Aside from ultrahigh strength and elasticity, metallic glasses (MGs) possess a number of favorable properties. However, their lack of dislocation based plastic deformation mechanisms in crystalline metals and the resulting loss of ductility have restricted the engineering applications of MGs over the last 60 years. This review aims to provide an overview of deformation and failure mechanisms of MGs via formation and propagation of shear bands (SBs), with an emphasis on the control of SBs to promote strength-ductility synergy. With this goal in mind, we highlight some of the emerging strategies to improve the ductility of MGs. Topics covered include post-processing techniques such as pre-compression, heterogeneity tuning, and rejuvenation, with a primary focus on recent progresses in structural design based methods including nanoglasses, notched MGs, and MG nanolattices, as future innovations towards strength-ductility synergy beyond the current benchmark ranges.
除了超高的强度和弹性外,金属玻璃(mg)还具有许多有利的性能。然而,由于在结晶金属中缺乏基于位错的塑性变形机制以及由此导致的延性损失,限制了mg合金在过去60年的工程应用。本文旨在通过剪切带(SBs)的形成和传播,概述mggs的变形和破坏机制,并强调控制剪切带以促进强度-延性协同。考虑到这一目标,我们强调了一些新兴的策略,以提高mg的延展性。涵盖的主题包括后处理技术,如预压缩、非均质调谐和回弹,主要关注基于结构设计方法的最新进展,包括纳米玻璃、缺口MG和MG纳米晶格,作为超越当前基准范围的强度-延性协同的未来创新。
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引用次数: 7
Design and Fabrication of Untethered Light-Actuated Microbots in Fluid for Biomedical Applications 生物医学流体中无系留光驱动微型机器人的设计与制造
IF 14.3 1区 工程技术 Q1 Engineering Pub Date : 2022-10-17 DOI: 10.3390/applmech3040071
Md. Faiyaz Jamil, Mishal Pokharel, Kihan Park
Untethered mobile robots at the micro-scale have the ability to improve biomedical research by performing specialized tasks inside complex physiological environments. Light-controlled wireless microbots are becoming the center of interest thanks to their accuracy in navigation and potential to carry out operations in a non-invasive manner inside living environments. The pioneering light-engineered microbots are currently in the early stage of animal trials. There is a long way ahead before they can be employed in humans for therapeutic applications such as targeted drug delivery, cancer cell diagnosis, tissue engineering, etc. The design of light-actuated microbots is one of the challenging parts along with the biocompatibility and precision control for in vivo applications. Recent progress in light-activated microbots has revealed a few innovative design concepts. In this study, we presented a framework on the different aspects with a comparative analysis of potential designs for the next generation of light-controlled microbots. Utilizing numerical simulations of fluid-structure interactions, limiting design elements of the microbots are addressed. We envision that this study will eventually facilitate the integration of robotic applications into the real world owing to the described design considerations.
微型无绳移动机器人能够在复杂的生理环境中执行特殊任务,从而改善生物医学研究。光控无线微型机器人由于其导航精度和在生活环境中以非侵入性方式进行操作的潜力,正成为人们感兴趣的中心。这种开创性的光工程微型机器人目前正处于动物试验的早期阶段。要将它们应用于人类的治疗应用,如靶向药物输送、癌细胞诊断、组织工程等,还有很长的路要走。光驱动微型机器人的设计是具有挑战性的部分之一,以及生物相容性和体内应用的精度控制。光激活微型机器人的最新进展揭示了一些创新的设计概念。在这项研究中,我们提出了一个不同方面的框架,并对下一代光控微型机器人的潜在设计进行了比较分析。利用流体-结构相互作用的数值模拟,解决了微型机器人的限制设计元素。我们设想,由于所描述的设计考虑,这项研究最终将促进机器人应用与现实世界的集成。
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引用次数: 2
Undamped Free Vibration Analysis of Functionally Graded Beams: A Dynamic Finite Element Approach 功能梯度梁无阻尼自由振动分析:一种动力有限元方法
IF 14.3 1区 工程技术 Q1 Engineering Pub Date : 2022-10-07 DOI: 10.3390/applmech3040070
A. Gee, S. M. Hashemi
A Dynamic Finite Element (DFE) method for coupled axial–flexural undamped free vibration analysis of functionally graded beams is developed and subsequently used to investigate the system’s natural frequencies and mode shapes. The formulation is based on the Euler–Bernoulli beam theory and material grading is assumed to follow a power law variation through the thickness direction. Using the closed-form solutions to the uncoupled segments of the system’s governing differential equations as the basis functions of approximation space, the dynamic, frequency-dependent, trigonometric interpolation functions are developed. The interpolation functions are used with the weighted residual method to develop the DFE of the system. The resulting nonlinear eigenvalue problem is then solved to determine the coupled natural frequencies. Example elements using DFE, Finite Element Method (FEM) and the Dynamic Stiffness Method (DSM) are implemented in MATLAB for testing, verification, and validation. Good agreement was observed and the DFE formulation exhibited superior convergence performance compared to the FEM.
提出了一种用于功能梯度梁轴-弯耦合无阻尼自由振动分析的动态有限元方法,并将其用于研究系统的固有频率和模态振型。该公式基于欧拉-伯努利梁理论,并假设材料分级在厚度方向上遵循幂律变化。利用系统控制微分方程不耦合段的封闭解作为近似空间的基函数,建立了动态的、频率相关的三角插值函数。利用插值函数和加权残差法建立了系统的DFE。然后求解得到的非线性特征值问题以确定耦合固有频率。在MATLAB中使用DFE、有限元法(FEM)和动刚度法(DSM)实现实例单元进行测试、验证和验证。与有限元法相比,DFE公式具有较好的收敛性能。
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引用次数: 1
A Review of Techniques for Measuring the Biot Coefficient and Other Effective Stress Parameters for Fluid-Saturated Rocks 饱和流体岩石Biot系数及其他有效应力参数测量技术综述
IF 14.3 1区 工程技术 Q1 Engineering Pub Date : 2022-10-07 DOI: 10.1115/1.4055888
H. Kasani, A. Selvadurai
Predicting the behavior of a saturated rock with variations in pore fluid pressure during geo-energy production and storage, deep geological disposal of nuclear wastes, etc. is carried out using the isothermal theory of poroelasticity that incorporates Biot's effective stress principle. Several experimental methods for determining Biot's effective stress parameter have been documented in the literature. The original definition of Biot's effective stress is constantly being extended to account for non-linear and inelastic behavior of the rock. The objective of this study is to review the fundamentals of the original experimental approach for determining Biot's coefficient and other developments, their advantages and disadvantages, and include several case studies. Current techniques are based on different premises: jacketed and unjacketed bulk moduli or compressibility values; volume changes of the bulk and pore fluid from a drained triaxial test on a saturated sample; isotropic-isochoric compression tests on a saturated sample; matching volumetric strains or failure envelopes for dry and saturated samples; variations of rock properties, such as volumetric strain, permeability, compressional and shear wave velocities, with respect to confining stress and pore pressure; estimation of the Biot coefficient from other poroelastic parameters; and approximation of the dry bulk modulus or unjacketed bulk modulus of the rock from mineralogical compositions or ultrasonic wave velocities. This article discusses variations in Biot's effective stress coefficients produced using the different techniques and how factors such as pore geometry, test conditions, stress path, and test temperature affect the Biot's coefficient.
利用结合Biot有效应力原理的孔隙弹性等温理论,预测了饱和岩石在地能源生产和储存、核废料深层地质处置等过程中孔隙流体压力变化的行为。几种确定Biot有效应力参数的实验方法已在文献中记录。为了考虑岩石的非线性和非弹性特性,Biot有效应力的原始定义不断得到扩展。本研究的目的是回顾确定Biot系数的原始实验方法的基本原理和其他发展,它们的优点和缺点,并包括几个案例研究。目前的技术基于不同的前提:夹套和非夹套的体积模量或压缩性值;饱和试样排水三轴试验中体积和孔隙流体的体积变化饱和试样的各向同性等时压缩试验匹配干燥和饱和样品的体积应变或失效包络;岩石性质的变化,如体积应变、渗透率、纵波和横波速度,相对于围应力和孔隙压力;从其他孔隙弹性参数估计Biot系数;并根据矿物成分或超声波波速近似计算岩石的干体模量或无夹套体模量。本文讨论了使用不同技术产生的Biot有效应力系数的变化,以及孔隙几何形状、测试条件、应力路径和测试温度等因素如何影响Biot系数。
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引用次数: 5
A Novel Technique for Temporarily Repair and Improvement of Damaged Pin Joint Support Bores 一种临时修复和改进损伤销钉连接支撑孔的新技术
IF 14.3 1区 工程技术 Q1 Engineering Pub Date : 2022-10-06 DOI: 10.3390/applmech3040069
Ø. Karlsen, H. Lemu, I. Berkani
Damaged support bores due to wear and ovality can be critical for a machine and its operation, in addition to representing a safety problem and risk of pin breakage. It can be a costly operation to perform the required repairs in between planned service periods, especially because of the unplanned down time. A joint with a standard cylindrical pin will often experience wear and ovality in the support bore surfaces, and at some point, repairs will have to be performed. This study investigates and compares five options when a joint with a cylindrical pin has reached a severe level of wear and ovality, outside its planned service stop. The work involved testing the viability of 3D scanning of the damaged bore surface, 3D printing of a metal bushing, and inserting the bushing into the damaged joint. In addition, two pin solutions, i.e., a standard cylindrical pin and an expanding pin type, were installed into the repaired joint, loaded, and the strain on the pin ends close to the supports was measured. For the sake of comparison, the supports had both smooth circular bore and severe wear and ovality. It was concluded that it is possible to produce and install the 3D-printed bushing insert without major problems; the insert had satisfactory capability during test loading, and it most probably represents a good solution when it comes to the reduction in unwanted downtime during unplanned repairs of damaged joints.
由于磨损和椭圆度造成的支撑孔损坏对机器及其操作来说是至关重要的,除了代表安全问题和销断裂的风险。在计划的服务周期之间执行所需的维修可能是一项成本高昂的操作,特别是因为存在计划外停机时间。带有标准圆柱销的接头在支撑孔表面经常会出现磨损和椭圆形,在某些情况下,必须进行维修。本研究调查并比较了五种选择,当带有圆柱销的接头在其计划服务停止外达到严重磨损和椭圆度水平时。这项工作包括测试受损孔表面3D扫描的可行性,金属衬套的3D打印,以及将衬套插入损坏的接头。另外,将标准圆柱销和膨胀销两种销方案安装在修复节点内,加载后,测量靠近支座的销端应变。为了便于比较,支架既有光滑的圆孔,也有严重的磨损和椭圆度。得出的结论是,可以生产和安装3d打印衬套插件,而不会出现重大问题;在测试加载期间,该插件具有令人满意的性能,并且在对损坏的接头进行计划外维修期间,它很可能是减少不必要停机时间的良好解决方案。
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引用次数: 0
Application-Oriented Digital Image Correlation for the High-Speed Deformation and Fracture Analysis of AISI 1045 and Ti6Al4V Materials 面向应用的数字图像相关技术在AISI 1045和Ti6Al4V材料高速变形和断裂分析中的应用
IF 14.3 1区 工程技术 Q1 Engineering Pub Date : 2022-10-05 DOI: 10.3390/applmech3040068
L. Gerdes, S. Berger, J. Saelzer, Pascal Franck, Ramon Helwing, A. Zabel, F. Walther
In order to achieve realistic simulations of the chip formation, high quality input data regarding the flow stress and damage behavior of the materials are required. The split Hopkinson pressure bar (SHPB) test setup for the characterization of highly dynamic material properties offers a suitable method for generating high strain rates, similar to those in the chip formation zone. However, the strain measurement in SHPB is usually performed by means of strain gauges. This leads to an unreliable evaluation of strain rate and flow stress/shear flow stress in the case of an inhomogeneous material deformation, since this method presents the total strain whilst excluding local deformations. Inhomogeneous deformations are induced deliberately in special shear specimens, as they are also observed in the investigated cylindrical specimens. The present work deals with this issue by providing two additional measurement techniques, which are applied in SHPB tests for cylindrical specimens made of AISI 1045 and Ti6Al4V. To enable a local strain resolution, digital image correlation (DIC) is applied to high-speed images of the deformation process. In order to allow for the detection of shear bands in the specimens, a deep-learning-based approach is presented. The two measurement methods (strain gauges and DIC) are compared and discussed. In particular, the findings regarding the inhomogeneous deformation of Ti6Al4V allow for future improvements in the result quality of SHPB tests. The presented algorithm shows promising predictions for shear band detection and creates the basis for an automated evaluation of shear sample results, as well as an AI-based pre-selection of frames for the DIC evaluation of SHPB tests.
为了实现切屑形成的真实模拟,需要关于材料的流动应力和损伤行为的高质量输入数据。用于表征高动态材料性能的分离式霍普金森压力棒(SHPB)测试装置提供了一种合适的方法来产生高应变率,类似于切屑形成区的应变率。然而,SHPB中的应变测量通常是通过应变片进行的。这导致在不均匀材料变形的情况下,应变率和流动应力/剪切流动应力的评估不可靠,因为这种方法给出了总应变,同时排除了局部变形。非均匀变形是在特殊剪切试样中引起的,因为它们也在所研究的圆柱形试样中观察到。目前的工作通过提供两种额外的测量技术来处理这个问题,这两种技术应用于由AISI 1045和Ti6Al4V制成的圆柱形试样的SHPB测试。为了实现局部应变分辨率,将数字图像相关(DIC)应用于变形过程的高速图像。为了检测试件中的剪切带,提出了一种基于深度学习的方法。对应变片和DIC两种测量方法进行了比较和讨论。特别是,关于Ti6Al4V的不均匀变形的研究结果允许未来改进SHPB测试的结果质量。所提出的算法显示了对剪切带检测的有希望的预测,并为剪切样品结果的自动评估以及基于人工智能的帧预选SHPB测试的DIC评估奠定了基础。
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引用次数: 1
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Applied Mechanics Reviews
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