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【新文速递】2024年3月1日固体力学SCI期刊最新文章

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今日更新:International Journal of Solids and Structures 1 篇,Journal of the Mechanics and Physics of Solids 3 篇,Thin-Walled Structures 4 篇

International Journal of Solids and Structures

A lattice structure with adjustable mechanical behavior constructed by rotating triangles translated out of plane and splicing each other

Ning Zhang, Xiaodong Ma, Yujia Chang, Xiaogeng Tian

doi:10.1016/j.ijsolstr.2024.112740

通过旋转平移出平面的三角形并相互拼接,构建出具有可调机械性能的晶格结构

Lattice structures have been proven to be one of the most promising metamaterials since they can achieve different mechanical properties by tuning the topology of the microstructure. A novel lattice structure is constructed by Rotating triangles Translated out of plane and Splicing each other (RTS) inspired by the topology strategies of rotating and intertwining. The bending defect in the translational triangles is employed to adjust the mechanical behavior to meet the complicated service environment. The structures under different bending angles were fabricated by selective laser melting technology using orientation-insensitive Ti6Al4V material. The quasi-static compression experiments and numerical simulations show that the bending angle can significantly regulate the elastic modulus, yield strength, and plateau stress of the structure. The initial peak stress (i.e. equivalent yield strength) of RTSs can be adjusted to a level comparable to plateau stress through the bending defect, which is meaningful for anti-collision protection. The elastic modulus, the yield strength, and the plateau stress are inversely proportional to the equivalent aspect ratio (a/h) besides the plateau stress of a/h < 0.7. The effect of relative density on the mechanical properties of RTSs is discussed through the Gibson-Ashby model. This suggests the relative elastic modulus is dominated by the stretching behavior of struts, while the relative yield strength is dominated by the bending behavior of struts. Furthermore, a theoretical model of plateau stress is established based on the principle of plastic hinges, and the maximum error with the numerical simulation is less than 11 % at 1 % ≤ ρ¯ ≤ 10 % and a/h = 1. Altogether, this novel lattice structure has favorable elastic–plastic properties compared with the common lattice structures.

晶格结构已被证明是最有前途的超材料之一,因为它们可以通过调整微结构的拓扑结构实现不同的机械特性。受旋转和交织拓扑策略的启发,我们利用旋转三角形平面外平移和相互拼接(RTS)技术构建了一种新型晶格结构。利用平移三角形中的弯曲缺陷来调整机械行为,以适应复杂的使用环境。通过选择性激光熔融技术,使用对取向不敏感的 Ti6Al4V 材料制作了不同弯曲角度下的结构。准静态压缩实验和数值模拟结果表明,弯曲角度能显著调节结构的弹性模量、屈服强度和高原应力。通过弯曲缺陷可以将 RTS 的初始峰值应力(即等效屈服强度)调整到与高原应力相当的水平,这对于防碰撞保护很有意义。除了 a/h < 0.7 的高原应力之外,弹性模量、屈服强度和高原应力都与等效长宽比 (a/h) 成反比。通过 Gibson-Ashby 模型讨论了相对密度对 RTS 机械性能的影响。这表明相对弹性模量由支柱的拉伸行为主导,而相对屈服强度则由支柱的弯曲行为主导。此外,根据塑性铰链原理建立了高原应力理论模型,在 1 % ≤ ρ¯ ≤ 10 % 和 a/h = 1 时,与数值模拟的最大误差小于 11 %。总之,与普通晶格结构相比,这种新型晶格结构具有良好的弹塑性能。


Journal of the Mechanics and Physics of Solids

Plastic deformations and strain hardening in fully dense granular crystals

Ashta Navdeep Karuriya, Francois Barthelat

doi:10.1016/j.jmps.2024.105597

全致密粒状晶体的塑性变形和应变硬化

Granular crystals are intriguing constructs at the intersection between granular matter and architectured materials, offering new combinations of tunable mechanical properties, healing and recyclability. We have recently fabricated and tested strong, fully dense granular FCC crystals based on millimeter size rhombic dodecahedral grains. These “granular metamaterials” display a rich set of mechanisms: Nonlinear deformations, crystal plasticity reminiscent of atomistic mechanisms, shear-induced dilatancy, micro-buckling. Here we present discrete elements simulations of FCC granular crystals, where individual polyhedral grains are discretized with overlapping spheres. After validation with a simple cube-on-cube frictional sliding configuration, we duplicate the triaxial compression experiments on FCC granular crystals. The model captures the strength and micromechanics of deformation of the crystal but overestimates the stiffness because of imperfect contacts in the experiments. We could however use this model to identify the source of strain hardening in the crystal: Kinking of deformation bands, and collision of grains, generate strong obstacles to slip. We also show that below a certain size for the crystal, there is not enough volume to fully develop {111} frictional slip planes, which increases strength significantly. This effect can be used to increase strength by confinement, or in polycrystalline granular materials.

颗粒晶体是颗粒物质和建筑材料之间的交叉点,是一种引人入胜的构造,提供了可调整的机械特性、愈合性和可回收性的新组合。我们最近以毫米大小的菱形十二面体晶粒为基础,制造并测试了强韧、完全致密的粒状 FCC 晶体。这些 "颗粒超材料 "显示出一系列丰富的机制:非线性形变、与原子机制相似的晶体塑性、剪切诱导的扩张、微弯曲。我们在此介绍 FCC 颗粒晶体的离散元模拟,其中单个多面体晶粒用重叠球体离散化。经过简单的立方体对立方体摩擦滑动配置验证后,我们复 制了 FCC 颗粒晶体的三轴压缩实验。该模型捕捉到了晶体的强度和微观变形力学,但由于实验中的不完全接触,高估了刚度。不过,我们可以利用该模型找出晶体应变硬化的根源:变形带的扭结和晶粒的碰撞会产生强大的滑移障碍。我们还表明,在晶体达到一定尺寸以下时,就没有足够的体积来充分形成{111}摩擦滑移面,从而显著提高强度。这种效应可用于通过限制或在多晶颗粒材料中提高强度。


Analytical boundary integral solutions for cracks and thin fluid-filled layers in a 3D poroelastic solid in time and wavenumber domain

Elías R. Heimisson

doi:10.1016/j.jmps.2024.105591

三维孔弹性固体中裂缝和薄流体填充层的时域和波域边界积分解析解

The spectral boundary integral (SBI) method has been widely employed in the study of fractures and friction within elastic and elastodynamic media, given its natural applicability to thin or infinitesimal interfaces. Many such interfaces and layers are also prevalent in porous, fluid-filled media. In this work, we introduce analytical SBI equations for cracks and thin layers in a 3D medium, with a particular focus on fluid presence within these interfaces or layers. We present three distinct solutions, each based on different assumptions: arbitrary pressure boundary conditions, arbitrary flux boundary conditions, or a bi-linear pressure profile within the layer. The bi-linear pressure solution models the flux through a thin, potentially pressurized, leaky layer. We highlight conditions under which the bi-linear SBI equations simplify to either the arbitrary flux or arbitrary pressure SBI equations, contingent on a specific non-dimensional parameter. We then delve into the in-plane pressure effects arising from a shear crack in a poroelastic solid. While such pressurization has been suggested to influence frictional strength in various ways and only occurs in mode II sliding, our findings indicate that a significant portion of the crack face is affected in 3D scenarios. Additionally, we investigate non-dimensional timescales governing the potential migration of this pressurization beyond the crack tip, which could induce strength alterations beyond the initially ruptured area.

频谱边界积分(SBI)方法因其对薄界面或无限小界面的天然适用性,已被广泛应用于弹性和弹力介质中断裂和摩擦的研究。多孔、充满流体的介质中也普遍存在许多这样的界面和层。在这项工作中,我们介绍了三维介质中裂缝和薄层的 SBI 分析方程,尤其关注这些界面或层中的流体存在。我们提出了三种不同的解决方案,每种解决方案都基于不同的假设:任意压力边界条件、任意流量边界条件或层内的双线性压力曲线。双线性压力解决方案对通过薄的、可能受压的泄漏层的通量进行建模。我们重点介绍了双线性 SBI 方程简化为任意通量或任意压力 SBI 方程的条件,这取决于特定的非尺寸参数。然后,我们深入研究了孔弹性固体中的剪切裂缝所产生的面内压力效应。虽然这种加压作用被认为会以各种方式影响摩擦强度,而且只发生在模式 II 滑动中,但我们的研究结果表明,在三维情况下,裂纹面的很大一部分都会受到影响。此外,我们还研究了这种加压可能迁移到裂纹尖端以外的非维度时间尺度,这可能会引起最初破裂区域以外的强度变化。


Ellipticity enhances adhesion strength for contacts under shear loads

Fa Wu, Qingao Wang, Chun Li, Qunyang Li, Huajian Gao

doi:10.1016/j.jmps.2024.105596

椭圆度增强了剪切负荷下接触点的粘附强度

Adhesion under a shear load parallel to the contact interface is a common issue in engineering and biological systems, such as when insects and adhesion devices crawl on vertical walls. A question of interest is whether and how the shear load influences the adhesion behavior between an elliptical flat punch and an elastic medium. Here, we derive lower- and upper-bound limiting analytical solutions to this problem based on the local and global energy balances. Numerical results based on our analytical solution indicate that the lower- and upper-bounds are very close to each other, and their ratio depends only on the ellipse eccentricity in the absence of shear load. The lower-bound solution yields the location of the initial detachment, which is influenced by the contact area, ellipse eccentricity, shear load, and Poisson’s ratio, but not Young’s modulus. The presence of a shear load reduces the pull-off force and can also alter the position where the detachment is nucleated. Furthermore, there exists an optimal elliptical shape that gives rise to the maximum adhesion strength in the presence of a shear load. The theoretical findings are validated through experiments involving the pull-off of a rigid punch from an adhesive polymer substrate subjected to a shear load. The present study sheds insight and may provide helpful guidelines for designing biomimetic adhesive systems.

在平行于接触界面的剪切载荷作用下的粘附是工程和生物系统中的一个常见问题,例如昆虫和粘附装置在垂直墙壁上爬行时。我们感兴趣的一个问题是,剪切载荷是否以及如何影响椭圆扁平冲头与弹性介质之间的粘附行为。在此,我们根据局部和全局能量平衡推导出该问题的下限和上限极限分析解。基于分析解的数值结果表明,下限和上限非常接近,在没有剪切载荷的情况下,它们的比值只取决于椭圆的偏心率。下限解法得出了初始脱离的位置,该位置受接触面积、椭圆偏心率、剪切载荷和泊松比的影响,但不受杨氏模量的影响。剪切载荷的存在会降低拉拔力,也会改变脱离成核的位置。此外,存在一种最佳椭圆形,在剪切载荷作用下可产生最大粘附强度。理论研究结果通过实验得到了验证,实验涉及刚性冲头在剪切载荷作用下从粘合聚合物基底上脱落。本研究为设计仿生物粘合剂系统提供了有益的指导。


Thin-Walled Structures

Experimental and numerical study on the behavior of high strength Q960 steel columns after fire exposure

Weiyong Wang, Yameng Li, Zhiruoyu Wang, Shiyun Pang

doi:10.1016/j.tws.2024.111748

火灾暴露后高强度 Q960 钢柱行为的实验和数值研究

High-strength steel exhibits extensive potential in large-span buildings and bridges. Therefore, it is of great significance to clarify its mechanical properties particularly in the realm of post-fire building repair and reconstruction, making it imperative to elucidate its bearing capacity after exposure to elevated temperatures. To comprehensively investigate the overall stability of high-strength Q960 steel columns under high-temperature conditions, a series of axial compression bearing capacity tests are conducted on eight Q960 steel columns—four of which featured H-shaped sections and the remaining four being box-shaped sections. The design of these members considered the effects of slenderness ratio and temperature. At the same time, the residual stress and geometric initial defects of the steel column were measured. Furthermore, the axial compression model for Q960 steel columns, encompassing both room and high-temperature scenarios, was established using the ABAQUS finite element software. This model duly accounted for the influence of residual stress and geometric initial defects. Subsequently, the test outcomes, encompassing horizontal and vertical displacements, ultimate bearing capacity, and failure mode, were compared with the results obtained from finite element analysis. This comparison serves to validate the accuracy of the model while facilitating parameter analysis. The results based on both the finite element analysis and experimental findings, indicate that when employing the Chinese code GB 50,017–2017, the stability coefficient calculation for Q960 steel columns following high-temperature exposure yields satisfactory safety margins. In light of these findings, a calculation method is proposed to accurately predict the stability coefficient of Q960 steel columns in the aftermath of high-temperature conditions, thus offering a reliable approach for assessing the stability bearing capacity of such columns in such scenarios. By comparing with EN 1993–1–12 and ANSI/AISC 360–22, it is found that EN 1993–1–12 has a better prediction effect, while ANSI/AISC 360–22 is conservative when the slenderness ratio is small.

高强度钢在大跨度建筑和桥梁中具有广泛的应用潜力。因此,明确其力学性能具有重要意义,尤其是在火灾后的建筑修复和重建领域,因此阐明其在高温条件下的承载能力势在必行。为了全面研究高强度 Q960 钢柱在高温条件下的整体稳定性,我们对八根 Q960 钢柱进行了一系列轴向压缩承载能力试验,其中四根为 H 型截面,其余四根为箱形截面。这些构件的设计考虑了细长比和温度的影响。同时,还测量了钢柱的残余应力和几何初始缺陷。此外,还使用 ABAQUS 有限元软件建立了 Q960 钢柱的轴向压缩模型,包括室温和高温两种情况。该模型充分考虑了残余应力和几何初始缺陷的影响。随后,将测试结果(包括水平和垂直位移、极限承载能力和失效模式)与有限元分析得出的结果进行了比较。这种比较有助于验证模型的准确性,同时便于进行参数分析。基于有限元分析和实验结果的结果表明,当采用中国规范 GB 50,017-2017 时,Q960 钢柱高温暴露后的稳定系数计算可获得令人满意的安全系数。有鉴于此,本文提出了一种计算方法,用于准确预测 Q960 钢柱在高温条件下的稳定系数,从而为评估此类钢柱在高温条件下的稳定承载能力提供了一种可靠的方法。通过与 EN 1993-1-12 和 ANSI/AISC 360-22 进行比较,发现 EN 1993-1-12 的预测效果更好,而 ANSI/AISC 360-22 在细长率较小时较为保守。


Experimental investigation on the residual bending capacity of carbon fiber corrugated sandwich structures under the repeated impact

Yiyang Liu, Haibo Zhou, Caiyu Yin, Jianbo Chen, Jiayi Liu, Jingxi Liu

doi:10.1016/j.tws.2024.111754

反复冲击下碳纤维波纹夹层结构残余弯曲能力的实验研究

Corrugated sandwich structures are fabricated with carbon fiber-reinforced polymer (CFRP) face sheets and cores. An experimental study was performed to investigate the response of this type of structure to impact loading; specifically, the impact force, energy absorption capacity, and failure mode were explored. The effects of the impact energy and the number of impacts on the corrugated sandwich structure damage were also studied. The failure modes and bending capacities of structures subjected to single or repeated impacts were analyzed. The bending capacities of the composite corrugated sandwich structures were related to the failure states of the panels. When a panel endured multiple impacts, its bending capacity significantly decreased; however, its energy absorption level first increased and then decreased. An empirical relationship between the residual strength factor, the impact energy, and the number of impacts was obtained. The findings of this study can serve as a reference for performance evaluations of marine composite structures subjected to combined impact and bending loading.

波纹夹层结构由碳纤维增强聚合物(CFRP)面片和芯材制成。实验研究调查了这种结构对冲击载荷的响应,特别是冲击力、能量吸收能力和破坏模式。此外,还研究了冲击能量和冲击次数对波纹夹层结构损坏的影响。分析了结构在单次或多次冲击下的破坏模式和弯曲能力。复合波纹夹层结构的弯曲能力与面板的破坏状态有关。当板材承受多次撞击时,其抗弯能力明显下降;然而,其能量吸收水平先上升后下降。研究得出了剩余强度系数、冲击能量和冲击次数之间的经验关系。本研究的结果可作为对承受冲击和弯曲联合载荷的海洋复合材料结构进行性能评估的参考。


Theoretical and numerical investigations on dynamic stability of viscoelastic columns with semi-rigid connections

Jian Deng, Jorge Eliecer Ballesteros Ortega, Kefu Liu, Yanglin Gong

doi:10.1016/j.tws.2024.111758

带半刚性连接的粘弹性柱动态稳定性的理论和数值研究

Dynamic stability of structures is an essential topic in civil engineering analysis and design because collapse of critical structures due to dynamic excitations would cause loss of properties or even fatalities. This paper conducts theoretical analysis and numerical simulation investigations on both stability and responses of viscoelastic columns with semi-rigid connections/supports subjected to axial parametric loads. The equation of motion for the viscoelastic column is derived and decoupled into an ordinary differential equation with periodic coefficients by describing the viscoelasticity as the linear Kelvin-Voigt model. Theoretical analysis is performed by the method of harmonic balance and the approximate boundaries of dynamic stability are obtained. A novel numerical simulation method is proposed to investigate both dynamic stability and vibration responses of viscoelastic columns with semi-rigid connections. The approximate boundaries are calibrated by the numerical results. The effects of the material's viscoelasticity, the supports’ rigidity, damping, and the static and dynamic component loads on the column stability are investigated through the numerical analysis. Two key findings of the study are that the greater the rigidity of the supports, the larger both the natural frequency and the critical dynamic load; and the viscosity of materials has a great positive impact on the dynamic stability of viscoelastic columns. The proposed method can be extended to systems under arbitrary periodic parametric excitations.

结构的动态稳定性是土木工程分析和设计中的一个重要课题,因为动态激励导致的关键结构倒塌会造成财产损失甚至人员伤亡。本文对带有半刚性连接/支撑的粘弹性柱在轴向参数载荷作用下的稳定性和响应进行了理论分析和数值模拟研究。通过将粘弹性描述为线性 Kelvin-Voigt 模型,推导出粘弹性柱的运动方程,并将其解耦为具有周期性系数的常微分方程。利用谐波平衡法进行了理论分析,并得到了动态稳定性的近似边界。提出了一种新的数值模拟方法,用于研究具有半刚性连接的粘弹性柱的动态稳定性和振动响应。数值结果校准了近似边界。通过数值分析,研究了材料的粘弹性、支撑的刚度、阻尼以及静态和动态分量载荷对支柱稳定性的影响。研究的两个主要发现是:支撑刚度越大,固有频率和临界动载荷都越大;材料的粘度对粘弹性柱的动态稳定性有很大的积极影响。所提出的方法可扩展到任意周期参数激励下的系统。


Achievement of High-strength Al/CFRP Hybrid Joint via High-speed Friction Stir Lap Joining and Laser Texturing Pretreatment Parameters Variation

Yuchun Liu, Xinbo Wang, Li Zhou, Hongyun Zhao, Xiaohui Han, Caiwang Tan, Xiaoguo Song

doi:10.1016/j.tws.2024.111762

通过高速摩擦搅拌搭接和激光纹理预处理参数变化实现高强度铝/CFRP 混合接头

This paper presents the achievement of a high-strength Al/CFRP hybrid joint through a high-speed friction stir lap joining process, combined with variations in laser surface texturing pretreatment parameters. The study examined the impact of laser surface texturing parameters by varying the depth, interval distance and width of the laser texture. By adjusting laser texturing parameters, the softened PA66 was fully infused into the textured grooves on the aluminum surface, leading to a significant reduction in interfacial voids and cracks in Al/CFRP. The preliminary tensile shear test showed that the hybrid joint broke at the CFRP base material, indicating that the laser texturing exhibited excellent Al/CFRP interface strengthening ability. Further compression shear tests were applied to reveal the actual interfacial load-carrying performance for comparison. The maximum shear strength of 25.5(+0.7)(−1.34) MPa was achieved at a joining speed of 3000 mm/min. Additionally, a mathematical model was proposed to assess the strengthening impact of laser texturing parameters, considering micro-texture geometry and interfacial defects. The tearing of PA66, detachment of carbon fibers, and the breakage of carbon fibers were the three primary types of fracture modes identified at the Al/CFRP interface. The joining mechanism revealed that both mechanical interlocking and the chemical bonding of Al-O-C contributed to the increase in joint shear strength. This study presents a credible method for producing high-strength Al/CFRP lightweight structures.

本文介绍了通过高速搅拌摩擦搭接工艺,并结合激光表面纹理预处理参数的变化,实现了高强度铝/CFRP 混合接头。研究通过改变激光纹理的深度、间隔距离和宽度,考察了激光表面纹理参数的影响。通过调整激光纹理参数,软化的 PA66 被完全注入铝表面的纹理沟槽中,从而显著减少了铝/CFRP 的界面空隙和裂纹。初步拉伸剪切试验表明,混合接头在 CFRP 基材处断裂,这表明激光纹理加工具有出色的铝/CFRP 界面强化能力。进一步的压缩剪切试验揭示了界面的实际承载性能,以供比较。在 3000 mm/min 的连接速度下,达到了 25.5(+0.7)(-1.34) MPa 的最大剪切强度。此外,考虑到微纹理几何形状和界面缺陷,还提出了一个数学模型来评估激光纹理参数对强化的影响。PA66 的撕裂、碳纤维的脱落和碳纤维的断裂是在 Al/CFRP 接口上发现的三种主要断裂模式。连接机理表明,Al-O-C 的机械互锁和化学键合都有助于提高连接剪切强度。这项研究为生产高强度 Al/CFRP 轻质结构提供了一种可靠的方法。




来源:复合材料力学仿真Composites FEM
ACTMechanicalSystemFluxInspire振动断裂复合材料碰撞非线性化学建筑海洋裂纹理论材料仿生
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首次发布时间:2024-11-06
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【新文速递】2024年3月3日固体力学SCI期刊最新文章

今日更新:International Journal of Solids and Structures 1 篇,Journal of the Mechanics and Physics of Solids 1 篇,International Journal of Plasticity 1 篇,Thin-Walled Structures 2 篇International Journal of Solids and StructuresPneumatically tunable adherence of elastomeric soft hollow pillars with non-circular contactsGuangchao Wan, Wanliang Shandoi:10.1016/j.ijsolstr.2024.112736具有非圆形触点的弹性软空心支柱的气动可调附着力Dynamically tunable interfacial dry adhesion plays a significant role in numerous biological functions and industrial applications. Among various strategies, pneumatics-activated adhesive devices draw much attention due to their distinct advantages such as fast speed, reliable performance, large adhesion tunability and easily accessible materials. To understand and predict adhesion strength of pneumatics-activated adhesives, it is necessary to examine their interfacial mechanics that is nonlinearly coupled with the large deformation of the devices under pressure. However, previous studies have only focused on axisymmetric cases in which the outline of the contact area is circular, whereas the tunable adherence of non-circular contact controlled by pneumatics remains elusive. In this work, through a combination of experiments and simulations, we study the effect of non-circular contact geometry on tunable dry adhesion of pressure-activated soft hollow pillars. Specifically, elliptical, square, and rectangular contact shapes are considered and their effects on tunable adhesion of the soft hollow pillars are compared to that of circular contact geometry thoroughly. The results show that soft hollow pillars with elliptical, square, and rectangular contact surfaces demonstrate rich interfacial delamination behaviors that depend on the contact outline geometry and internal pressure. Among all contact geometries, elliptical contact has the highest adhesion tunability yet requires lowest activating pressure owing to the non-uniform curvature distribution of the contact outline. However, when the eccentricity increases, the elliptical contact has reduced tunability of adhesion caused by the contact of opposing sides of the sidewall upon buckling. For square and rectangular contacts, they have the lowest adhesion tunability and need higher activating pressure than those of circular and elliptical contact since the 90-degree edges of the sidewall prohibit buckling instability. Our findings greatly broaden the design space of pneumatics-activated adhesive devices by adding the contact geometry of the soft hollow pillars as a new design parameter, which can provide valuable guidance to tunable adhesive design for various applications in manufacturing and robotics.动态可调的界面干附着力在众多生物功能和工业应用中发挥着重要作用。在各种策略中,气动激活粘合剂装置因其速度快、性能可靠、粘合力可调节性大和材料易得等独特优势而备受关注。要了解和预测气动活化粘合剂的粘合强度,有必要研究其界面力学,因为界面力学与设备在压力下的大变形呈非线性耦合。然而,以往的研究只关注接触区域轮廓为圆形的轴对称情况,而由气动控制的非圆形接触的可调粘附性仍然难以捉摸。在这项工作中,我们通过实验和模拟相结合的方法,研究了非圆形接触几何形状对压力激活的软空心支柱的可调干附着力的影响。具体来说,我们考虑了椭圆形、正方形和长方形接触形状,并将它们对软质空心柱可调粘附性的影响与圆形接触几何形状的影响进行了彻底比较。结果表明,具有椭圆形、正方形和矩形接触面的软质空心支柱表现出丰富的界面分层行为,这些行为取决于接触轮廓几何形状和内部压力。在所有接触几何形状中,椭圆形接触具有最高的粘附可调性,但由于接触轮廓的曲率分布不均匀,所需的启动压力也最低。然而,当偏心率增大时,椭圆形触点的粘附可调性会降低,原因是弯曲时侧壁的对立面会发生接触。对于方形和矩形触点,由于侧壁的 90 度边缘阻碍了屈曲不稳定性,因此它们的附着力可调性最低,所需的激活压力也高于圆形和椭圆形触点。我们的发现大大拓宽了气动激活粘合装置的设计空间,增加了软质空心支柱的接触几何形状作为新的设计参数,这将为制造和机器人领域各种应用的可调粘合剂设计提供有价值的指导。Journal of the Mechanics and Physics of SolidsExploring static responses, mode transitions, and feasible tunability of Kagome-based flexible mechanical metamaterialsJian Li, Ronghao Bao, Weiqiu Chendoi:10.1016/j.jmps.2024.105599探索基于 Kagome 的柔性机械超材料的静态响应、模式转换和可行的可调谐性We consider the static responses of the uniaxially compressed flexible mechanical metamaterials, which integrate soft hinges and rigid bodies, constructed from the Kagome lattice. First, we experimentally find that the static responses of the regular-Kagome-based structure significantly differ from those of the twisted-Kagome-based structure with a very small twisting angle. Following this, we establish a theoretical model, which is combined with the deflated continuation algorithm for bifurcation analysis, to delve into the static responses and potential bifurcation behavior of these structures. We then experimentally and numerically investigate the mode transitions between various stable modes, and systematically study the role of the twisting angle in the occurrence of bifurcations. Our findings indicate that mode transitions can be feasibly realized according to the calculated bifurcation diagrams. They also provide direct evidence of a crucial physical mechanism that the transition between different stable deformation states can occur through multiple pathways but must pass through at least one unstable deformation state. Moreover, by introducing the twisting angle or stiff defects, the response of the structure can be modulated, thereby enhancing the programmability and tunability of Kagome-based flexible mechanical metamaterials. Our research also reveals that novel phenomena such as meta-beam buckling and multi-phase dominated deformations can be triggered within these flexible structures, which offers valuable insights for future metamaterial designs and applications.我们考虑了单轴压缩柔性机械超材料的静态响应,这种超材料将软铰链和刚体结合在一起,由卡戈米晶格构建而成。首先,我们通过实验发现,基于常规卡戈米结构的静态响应与基于扭曲卡戈米结构的极小扭曲角的静态响应存在显著差异。随后,我们建立了一个理论模型,并将其与用于分岔分析的放气延续算法相结合,深入研究了这些结构的静态响应和潜在分岔行为。然后,我们通过实验和数值方法研究了各种稳定模式之间的模式转换,并系统地研究了扭转角在分岔发生中的作用。我们的研究结果表明,根据计算出的分岔图,模式转换是可以实现的。它们还直接证明了一种重要的物理机制,即不同稳定变形状态之间的转换可以通过多种途径发生,但必须至少经过一种不稳定变形状态。此外,通过引入扭转角或刚性缺陷,可以对结构的响应进行调制,从而增强基于 Kagome 的柔性机械超材料的可编程性和可调性。我们的研究还揭示了在这些柔性结构中可以触发元梁屈曲和多相主导变形等新现象,这为未来的超材料设计和应用提供了宝贵的启示。International Journal of PlasticityQuantifying Dislocation Drag at High Strain Rates with Laser-Induced Microprojectile ImpactQi Tang, Mostafa Hassanidoi:10.1016/j.ijplas.2024.103924 利用激光诱导微弹丸冲击量化高应变速率下的位错拖曳力As deformation rate increases, the thermally activated dislocation glide gives way to a continuous glide of dislocations governed by their interactions with phonons. Understanding the dislocation-phonon drag regime is critical for designing metallic materials for extreme deformations rates. However, it has proven challenging to study empirically, partly due to the resource intensive nature of the experimental approaches targeting this regime. Here, we develop an impression-based experimental approach combining laser-induced microprojectile impact (Hassani et al., 2020a) and spherical nanoindentation to characterize the dislocation-phonon drag regime. We also utilize a physically based constitutive framework that, when integrated our experimental measurements, can quantify the dislocation-phonon drag regime. We isolate the effect of dislocation-phonon drag by leveraging the similar deformation geometries and length scales but different operative mechanisms during spherical nanoindentation and microprojectile impact. We discuss mechanistic contributions to the plastic work for microprojectile impacts in a range of impact velocities producing strain rates up to 109 s−1. We also develop a deformation mechanism map focused on the transition from thermal activation to dislocation drag for a model FCC metal, copper.随着形变速率的增加,热激活的位错滑行让位于位错与声子相互作用下的连续滑行。了解差排-声子阻力机制对于设计适用于极端变形率的金属材料至关重要。然而,事实证明对其进行经验研究具有挑战性,部分原因是针对该机制的实验方法需要大量资源。在此,我们开发了一种基于压痕的实验方法,结合激光诱导微弹丸冲击(Hassani 等人,2020a)和球形纳米压痕来表征位错-声子阻力机制。我们还利用了一个基于物理的构成框架,该框架与我们的实验测量相结合,可以量化差排-声子阻力机制。我们利用球形纳米压痕和微弹丸冲击过程中相似的变形几何形状和长度尺度以及不同的作用机制,分离出差排-声子阻力的影响。我们讨论了在一系列冲击速度(应变率高达 109 s-1)下微弹丸冲击塑性功的机理贡献。我们还绘制了一张变形机理图,重点关注模型 FCC 金属铜从热激活到位错拖曳的转变过程。Thin-Walled StructuresData-Driven PSO-CatBoost Machine Learning Model to Predict the Compressive Strength of CFRP- Confined Circular Concrete SpecimensNima Khodadadi, Hossein Roghani, Francisco De Caso, El-Sayed M. El-kenawy, Yelena Yesha, Antonio Nannidoi:10.1016/j.tws.2024.111763预测 CFRP 承压圆形混凝土试件抗压强度的数据驱动型 PSO-CatBoost 机器学习模型This work articulates the development of a sophisticated machine-learning model for the prediction of compressive strength in Carbon Fiber-Reinforced Polymer Confined-Concrete (CFRP-CC) specimens. Despite extensive empirical studies conducted over the last three decades, prevailing predictive models predominantly rooted in linear or nonlinear regression analyses are constrained by their dependency on limited data scopes. Addressing this deficiency, our research delineates the formulation of an innovative Particle Swarm Optimization- Categorical Boosting (PSO-CatBoost) algorithm, underpinned by an expansive database encompassing 916 experimental outcomes from 116 scholarly articles, spanning the period from 1991 to mid-2023. This innovative approach effectively combines the strengths of Particle Swarm Optimization and the CatBoost algorithm. It carefully evaluates various vital factors that affect the compressive strength of CFRP-CC. The uniqueness of our approach is further accentuated through the application of SHapley Additive exPlanations (SHAP) and Permutation Feature Importance (PFI) methodologies, thereby elucidating the relative importance of each contributory feature. In an unprecedented comparative analysis, the PSO-CatBoost model is rigorously benchmarked against six contemporary machine learning paradigms: CatBoost, XgBoost, AdaBoost, GBoost, Extra Trees, and Random Forest. Furthermore, this model is assessed against six empirical models for further comparison. The model exhibits superior predictive efficacy, evidenced by an exemplary coefficient of determination R-squared of 0.9847, surpassing the methodologies. This research introduces a new predictive model for CFRP-CC and represents a significant shift in concrete research, moving towards a more sophisticated, data-driven, and machine learning-focused methodology. This work thus establishes a new benchmark in the predictive modeling realm for CFRP-CC compressive strength, offering a robust and comprehensive analytical tool for both researchers and practitioners in the field. Lastly, a graphical user interface was designed for modeling the compressive strength of CFRP-CC to facilitate practical use.这项工作阐明了如何开发一种复杂的机器学习模型,用于预测碳纤维增强聚合物密实混凝土(CFRP-CC)试样的抗压强度。尽管在过去三十年中进行了大量的实证研究,但主要植根于线性或非线性回归分析的主流预测模型因其对有限数据范围的依赖性而受到限制。针对这一不足,我们的研究阐述了一种创新的粒子群优化-分类提升(PSO-CatBoost)算法,该算法以一个庞大的数据库为基础,该数据库涵盖了从 1991 年到 2023 年中期的 116 篇学术论文中的 916 项实验结果。这一创新方法有效地结合了粒子群优化和 CatBoost 算法的优势。它仔细评估了影响 CFRP-CC 抗压强度的各种重要因素。通过应用 SHapley Additive exPlanations(SHAP)和 Permutation Feature Importance(PFI)方法,进一步突出了我们方法的独特性,从而阐明了每个贡献特征的相对重要性。在前所未有的比较分析中,PSO-CatBoost 模型与六种当代机器学习范式进行了严格的基准比较:CatBoost、XgBoost、AdaBoost、GBoost、Extra Trees 和 Random Forest。此外,该模型还与六个经验模型进行了评估,以作进一步比较。该模型表现出卓越的预测功效,其判定系数 R 方为 0.9847,超越了各种方法,堪称典范。这项研究为 CFRP-CC 引入了一个新的预测模型,代表了混凝土研究领域的重大转变,即向更复杂、数据驱动和以机器学习为重点的方法转变。因此,这项工作在 CFRP-CC 抗压强度预测建模领域建立了一个新的基准,为该领域的研究人员和从业人员提供了一个强大而全面的分析工具。最后,为了便于实际使用,还设计了 CFRP-CC 抗压强度建模的图形用户界面。Enhancing bond performance of CFRP-steel epoxy-bonded interface by electrospun nanofiber veilsFurui Zhu, Lu Ke, Zheng Feng, Jiale Zhou, Chuanxi Li, Rundan Zhangdoi:10.1016/j.tws.2024.111765利用电纺纳米纤维纱提高 CFRP-钢环氧树脂粘结界面的粘结性能The epoxy-bonded interfaces between carbon fiber reinforced polymer (CFRP) and steel usually have insufficient strength and toughness, and the toughening of bonded interface is a key problem for the usage of CFRP in steel structures. In this study, electrospun nanofiber veils were first proposed to enhance the bond performance of CFRP-steel epoxy-bonded interfaces. Firstly, shear tests were conducted on neat epoxy and nano-modified single-lap aluminum-aluminum joints to determine the optimal areal density and number of layers of nanofiber veils, as well as the optimal curing processes. Then, a series of neat epoxy and nano-modified CFRP-steel double-lap joints with different bond lengths were tested to investigate the size effect of the bond behavior. The displacement and strain field evolution of the joints were captured by the digital image correlation (DIC) technique, allowing for visualization of the detailed failure process. The failure modes, load-displacement curves, CFRP strain distributions, and bond-slip relationships of the CFRP-steel joints were obtained. Both the tests on aluminum-aluminum and CFRP-steel joints show that the optimal modification strategy is incorporating 3 layers of nanofiber wels with an areal density of 4.5 g/m2, with 5 h room-temperature and 2 h 80°C high-temperature curing. The primary failure mode of CFRP-steel joints is CFRP delamination accompanied by CFRP-adhesive interface or steel-adhesive interface debonding. The bond strengths of the modified joints with 3 layers of 1.5 g/m2 and 4.5 g/m2 nanofiber veils are increased by 7% and 25% compared to those of un-modified joints, respectively. The 4.5 g/m2 nanofiber veils modified bonded interface has an effective bond length of about 152 mm, with a corresponding ultimate bearing capacity of 117 kN. Different from the triangular (brittle) shape of most neat epoxy interfaces, the nano-modified interfaces have trapezoidal (ductile) bond-slip relationships, providing superior cracking resistance. Moreover, a comparison with the bond strength of SiO2 nano-particles and carbon nanotubes (CNTs) modified joints revealed that nanofiber veil modification comes to higher bond strength in most cases. The proposed electrospun nanofiber veil modification technique provides a great insight into the interfacial toughening of CFRP-steel composite structures.碳纤维增强聚合物(CFRP)与钢之间的环氧树脂粘结界面通常强度和韧性不足,粘结界面的增韧是碳纤维增强聚合物在钢结构中应用的关键问题。本研究首次提出了电纺纳米纤维纱来增强 CFRP 与钢环氧树脂粘结界面的粘结性能。首先,对纯环氧树脂和纳米改性单层铝-铝接头进行了剪切试验,以确定纳米纤维网的最佳面积密度和层数,以及最佳固化工艺。然后,测试了一系列具有不同粘接长度的纯环氧树脂和纳米改性 CFRP-钢双搭接接头,以研究粘接行为的尺寸效应。通过数字图像相关(DIC)技术捕捉了接头的位移和应变场演变,从而实现了详细失效过程的可视化。获得了 CFRP-钢接头的破坏模式、载荷-位移曲线、CFRP 应变分布和粘结-滑移关系。铝-铝和 CFRP-钢接头的测试表明,最佳改性策略是加入 3 层面积密度为 4.5 g/m2 的纳米纤维,并进行 5 小时室温固化和 2 小时 80°C 高温固化。CFRP 与钢接头的主要失效模式是 CFRP 分层,同时伴有 CFRP 粘接界面或钢粘接界面脱粘。与未改性接头相比,使用 3 层 1.5 g/m2 和 4.5 g/m2 纳米纤维纱的改性接头的粘接强度分别提高了 7% 和 25%。4.5 g/m2 纳米纤维纱改性粘接界面的有效粘接长度约为 152 mm,相应的极限承载能力为 117 kN。与大多数纯环氧树脂界面的三角形(脆性)不同,纳米改性界面具有梯形(韧性)的粘结滑移关系,从而提供了优异的抗开裂性能。此外,与二氧化硅纳米颗粒和碳纳米管(CNTs)改性接头的粘接强度相比,纳米纤维面纱改性在大多数情况下具有更高的粘接强度。所提出的电纺纳米纤维面纱改性技术为 CFRP-钢复合材料结构的界面增韧提供了重要的启示。来源:复合材料力学仿真Composites FEM

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