Experimental Mechanics最新文献_第10页

Comparison of Hall–Petch Law with an Elastic Limit Identification Method Using Kinematic Field Measurements 基于运动场测量的霍尔-佩奇法与弹性极限识别方法的比较

IF 2 3区工程技术 Q2 MATERIALS SCIENCE, CHARACTERIZATION & TESTING

Experimental Mechanics

Pub Date : 2025-01-07 DOI: 10.1007/s11340-024-01140-3

Q. Hu, A. Beaurain, J. F. Witz, A. El Bartali, D. Najjar

Background

Plastic deformation in polycrystalline metals is highly heterogeneous due to the varied microstructure distribution. Although some traditional laws, such as the Hall–Petch law, describe the relationship between microstructure and yield stress, accurately predicting the initial yield stress (hence elastic limit) related to local plasticity activation remains challenging.

Objective

This study proposes a novel approach to identify local elastic limits using full-field strain measurements, avoiding complex constitutive models.

Methods

Full-field kinematic measurements were performed on the heat-treated polycrystalline 316L austenitic stainless steel. By examining the different mechanical responses during elastic and plastic deformation, the onset of plasticity activation for each grain is identified from its grain-average strain evolution, allowing further calculation of the grain-scale elastic limit.

Results

Strain field observations indicate early strain localizations, particularly at twin boundaries and triple junctions. Based on microstructures segmented by ordinary grain and twin boundaries, considering and not considering twins, two different local elastic limits are identified.

Conclusions

The average elastic limit for the case considering twins is closer to the value obtained from the macroscopic stress–strain curve. In addition, the statistical analysis of the classified grain sizes reveals a more pronounced Hall–Petch relationship when twins are considered. These results indicate the necessity of considering twins in identifying the local mechanical properties.

在多晶金属中，由于微观组织分布的不同，塑性变形是高度不均匀的。虽然一些传统的定律，如Hall-Petch定律，描述了微观结构与屈服应力之间的关系，但准确预测与局部塑性激活相关的初始屈服应力（即弹性极限）仍然具有挑战性。目的本研究提出了一种利用全场应变测量来识别局部弹性极限的新方法，避免了复杂的本构模型。方法对热处理多晶316L奥氏体不锈钢进行全场运动学测量。通过研究弹塑性变形过程中不同的力学响应，从晶粒平均应变演化中识别出每个晶粒的塑性激活起始点，从而进一步计算出晶粒尺度的弹性极限。结果应变场观测显示了早期应变局部化，特别是在孪晶界和三联结处。基于普通晶界和孪晶界分割的微观组织，在考虑孪晶界和不考虑孪晶界的情况下，确定了两种不同的局部弹性极限。结论考虑孪晶情况下的平均弹性极限更接近宏观应力-应变曲线。此外，对分类晶粒尺寸的统计分析表明，当考虑双胞胎时，霍尔-佩奇关系更为明显。这些结果表明在确定局部力学性能时考虑孪晶的必要性。

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引用次数: 0

Split-Hopkinson Pressure Bar Testing of Water with Partial Lateral Confinement 部分侧向约束水的劈裂-霍普金森压杆试验

IF 2 3区工程技术 Q2 MATERIALS SCIENCE, CHARACTERIZATION & TESTING

Experimental Mechanics

Pub Date : 2025-01-07 DOI: 10.1007/s11340-024-01134-1

K.S.O. Li, A. Van Lerberghe, A. D. Barr, A. A. Dennis, S. D. Clarke

Background

For the first time, the high-strain-rate behaviour of water is investigated experimentally and validated to LS-DYNA numerical simulations, using Smooth Particle Hydrodynamics (SPH).

Objective

This paper presents the application of a modified split-Hopkinson pressure bar (SHPB) fitted with a partial lateral confinement apparatus on a water specimen.

Method

The lateral confinement is provided by a water reservoir surrounding the specimen. A pressure transducer is installed in the reservoir wall to measure lateral stresses, and a dispersion correction algorithm, SHPB_Processing.py, is utilised to obtain accurate measurements of axial and radial stresses and strains.

Results

Experimental results underscore the capability of the modified apparatus to assess triaxial behaviour of water under high-strain rates. Comparisons with numerical modelling reveal that cohesion between water particles is non-existent, highlighting an intrinsic limitation in numerical modelling.

Conclusion

These results highlight the capability to perform characterisation of fluids under high-strain rates. While limitations in numerical modelling still exist, numerical modelling and experimental testing using the modified apparatus can be applied to characterise fluid behaviour in the future.

本文首次利用光滑颗粒流体力学（SPH）对水的高应变率行为进行了实验研究，并在LS-DYNA数值模拟中进行了验证。目的介绍带局部侧限装置的改进型劈裂霍普金森压杆（SHPB）在水样上的应用。方法通过在标本周围的水库提供侧向约束。在储层壁上安装了一个压力传感器来测量侧向应力，并使用弥散校正算法SHPB_Processing.py来获得轴向和径向应力和应变的精确测量。结果实验结果表明，改进后的装置能够很好地评价水在高应变速率下的三轴特性。与数值模拟的比较表明，水颗粒之间的内聚是不存在的，突出了数值模拟的内在局限性。结论这些结果突出了在高应变速率下对流体进行表征的能力。虽然数值模拟的局限性仍然存在，但使用改进的仪器进行数值模拟和实验测试可以应用于未来的流体行为特征。

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引用次数: 0

On the Cover: A Novel Method to In-Situ Characterize Fatigue Crack Growth Behavior of Nickel Based Superalloys by Laser Thermography 封面上：一种原位表征镍基高温合金疲劳裂纹扩展行为的激光热成像新方法

IF 2 3区工程技术 Q2 MATERIALS SCIENCE, CHARACTERIZATION & TESTING

Experimental Mechanics

Pub Date : 2025-01-07 DOI: 10.1007/s11340-024-01132-3

引用次数: 0

Physics-Informed Neural Network Based Digital Image Correlation Method 基于物理信息神经网络的数字图像相关方法

IF 2 3区工程技术 Q2 MATERIALS SCIENCE, CHARACTERIZATION & TESTING

Experimental Mechanics

Pub Date : 2025-01-07 DOI: 10.1007/s11340-024-01139-w

B. Li, S. Zhou, Q. Ma, S. Ma

Background

Deep Learning-based Digital Image Correlation (DL-DIC) approaches take advantages such as pixel-wise calculation in a full-automatic manner without user's input and improved accuracy in non-uniform deformation measurements. However, DL-DIC still faces accuracy limitations due to the lack of high-precision real-world training data in supervised-learning methods and the need for smoothing noisy solutions in unsupervised-learning methods.

Objective

This paper proposes a DIC solution method based on Physics-Informed Neural Networks (PINN), called PINN-DIC, to address deformation measurement challenges of current DL-DIC in practical applications.

Methods

PINN-DIC utilizes a fully connected neural network, with regularized spatial coordinate field as input and displacement field as output. It applies the photometric consistency assumption as a physical constraint, using grayscale differences between predicted and actual deformed images to construct a loss function for iterative optimization of the displacement field. Additionally, a warm-up stage is designed to assist in iterative optimization, allowing PINN-DIC to achieve high accuracy in analyzing both uniform and non-uniform displacement fields.

Results

PINN-DIC, validated through simulations and real experiments, not only maintained the advantages of other DL-DIC methods but also demonstrated superior performance in achieving higher accuracy than conventional unsupervised DIC and handling irregular boundaries with adjusting the input coordinate field.

Conclusions

PINN-DIC is an unsupervised method that takes a regularized coordinate field (instead of speckle images) as input and achieves higher accuracy in deformation field results with a simple network. It introduces a novel approach to DL-DIC, enhancing performance in complex measurement scenarios.

基于深度学习的数字图像相关（DL-DIC）方法具有自动计算像素的优点，无需用户输入，并且在非均匀变形测量中提高了精度。然而，由于有监督学习方法缺乏高精度的真实训练数据，以及无监督学习方法需要平滑噪声解，DL-DIC仍然面临精度限制。目的提出一种基于物理信息神经网络（PINN）的DIC求解方法，即PINN-DIC，解决当前DL-DIC在实际应用中的变形测量难题。方法spinn - dic采用全连接神经网络，以正则化空间坐标场为输入，位移场为输出。该方法将光度一致性假设作为物理约束，利用预测变形图像与实际变形图像的灰度差构建损失函数，对位移场进行迭代优化。此外，还设计了一个预热阶段，以协助迭代优化，使PINN-DIC在分析均匀和非均匀位移场时都能达到高精度。结果通过仿真和实际实验验证，spinn -DIC不仅保持了其他DL-DIC方法的优点，而且在获得比传统无监督DIC更高的精度和通过调整输入坐标场处理不规则边界方面表现出了优越的性能。结论spinn - dic是一种以正则化坐标场（而不是散斑图像）作为输入的无监督方法，通过简单的网络可以获得更高精度的变形场结果。它引入了一种新的DL-DIC方法，提高了复杂测量场景中的性能。

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引用次数: 0

Editorial: Message from the Incoming Editor-in-Chief 社论：来自即将上任的总编辑的信息

IF 2 3区工程技术 Q2 MATERIALS SCIENCE, CHARACTERIZATION & TESTING

Experimental Mechanics

Pub Date : 2025-01-03 DOI: 10.1007/s11340-024-01133-2

J. Wang

引用次数: 0

X-Ray Tomography-Based Characterization of the Porosity Evolution in Composites Manufactured by Fused Filament Fabrication 基于x射线层析成像的熔融长丝复合材料孔隙演化表征

IF 2 3区工程技术 Q2 MATERIALS SCIENCE, CHARACTERIZATION & TESTING

Experimental Mechanics

Pub Date : 2024-12-13 DOI: 10.1007/s11340-024-01124-3

A. Lingua, F. Sosa-Rey, N. Piccirelli, D. Therriault, M. Lévesque

Background

Fused filament fabrication delivers composites with incomplete interface bonding prone to delaminate under loading due to the non-isothermal molecular entanglement during deposition.

Objective

We aim to localize the mesoscale porosity in 3D-printed composites and quantify its volumetric growth under loading to investigate whether incomplete filament adhesion can lead to delamination.

Methods

We measured the porosity volumic content by X-ray tomography testing. To distinguish between damage nucleated at the crack tip and mesoscale interface delamination, we quantified the local, 3D strain concentration region size at the crack tip by 2D digital image correlation of slice images over orthogonal planes.

Results

Through image segmentation, we observed that the mesoscale porosity resulting from the deposition process clustered at the filament interfaces and doubled from roughly 7% to 14% from an applied opening load of 700 N to 1400 N due to the stress concentration at the filament interfaces. Digital image correlation emphasized the strain concentration over a reduced area at the notch, up to the damage nucleation for an applied load of 1400 N, before the sudden brittle failure.

Conclusion

The presented contactless characterization technique emphasizes that mesoscale porosity concentrates at the filament interface, which is a critical delamination nucleation site under loading. This fracture mechanism is even more severe for high-performance composites such as carbon fiber reinforced PEEK.

熔融长丝制造提供的复合材料具有不完全的界面键合，由于在沉积过程中的非等温分子纠缠，在负载下容易分层。目的定位3d打印复合材料的中尺度孔隙率，量化其在载荷下的体积增长，以研究不完全的纤维粘附是否会导致分层。方法采用x射线层析成像法测定孔隙度体积含量。为了区分裂纹尖端的损伤成核和中尺度界面分层，我们通过正交平面上切片图像的二维数字图像相关来量化裂纹尖端的局部三维应变集中区域尺寸。结果通过图像分割，我们观察到沉积过程导致的中尺度孔隙率聚集在细丝界面处，并且由于细丝界面处的应力集中，当施加700 N至1400 N的开口载荷时，中尺度孔隙率从大约7%增加到14%。数字图像相关强调了缺口减小区域上的应变集中，在施加1400 N载荷的情况下，直到损伤成核，然后才发生突然脆性破坏。结论所提出的非接触表征技术强调了细丝界面处的中尺度孔隙度集中，而细丝界面是加载作用下脱层成核的关键部位。对于高性能复合材料，如碳纤维增强PEEK，这种断裂机制甚至更为严重。

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引用次数: 0

Dissimilar Material Joining via Interlocking Metasurfaces 通过互锁超表面连接异种材料

IF 2 3区工程技术 Q2 MATERIALS SCIENCE, CHARACTERIZATION & TESTING

Experimental Mechanics

Pub Date : 2024-12-10 DOI: 10.1007/s11340-024-01127-0

B. Elbrecht, B. Young, B. Clark, P. Noell

Background

The integration of dissimilar materials poses a significant challenge in engineering, necessitating innovative solutions for robust and reliable joining. Interlocking metasurfaces (ILMs) are a new joining technology comprising arrays of autogenous features patterned across two surfaces that interlock to form robust structural joints.

Objective

This study elucidates the factors influencing the tensile performance of ILM joints formed between dissimilar materials.

Methods

We employed parametric optimization to identify optimal unit cell geometries for maximal yield strength based on the hypothesis that the elastic tensile properties of the materials are the primary determinants of tensile performance. Experimental validation was performed by mechanically testing the theorized optimal ILM geometry and a range of ILM geometries to capture the overall behavior trends of joints between two additively manufactured polymers, VeroPureWhite (VW) and RGDA8430-DM (8430).

Results

Experimental validation of optimized designs revealed that additional factors, e.g. flexural strength and localized plasticity, also strongly influenced the tensile performance of T-slot ILMs joining dissimilar materials. The proposed optimal design remained the best performer.

Conclusions

This study demonstrates the viability of ILMs as a joining method for dissimilar materials. ILMs can join dissimilar materials with no loss in joint yield strength compared to joints composed solely of the weaker of the two constitutive materials. ILMs demonstrated their potential as a versatile and effective joining technology in diverse engineering applications.

不同材料的集成在工程中提出了重大挑战，需要创新的解决方案来实现坚固可靠的连接。互锁超表面（ilm）是一种新的连接技术，包括在两个表面上形成互锁的自特征阵列，以形成坚固的结构连接。目的探讨影响不同材料间ILM关节抗拉性能的因素。方法基于材料的弹性拉伸性能是拉伸性能的主要决定因素这一假设，采用参数优化方法确定最大屈服强度的最佳单元胞几何形状。通过机械测试理论上的最佳ILM几何形状和一系列ILM几何形状来进行实验验证，以捕获两种增材制造聚合物VeroPureWhite （VW）和RGDA8430-DM（8430）之间关节的整体行为趋势。结果优化设计的实验验证表明，抗弯强度和局部塑性等附加因素也对t型槽ilm连接不同材料的拉伸性能有很大影响。所提出的最优设计仍然是最佳的。结论本研究证明了ILMs作为异种材料连接方法的可行性。与仅由两种本构材料中较弱的材料组成的接头相比，ilm可以连接不同的材料而不会损失接头的屈服强度。在不同的工程应用中，ilm展示了其作为一种通用而有效的连接技术的潜力。

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引用次数: 0

Research on a New Exponential Function Weighted Averaging Method Used for Full-Gradient Strain Measurement of DIC 基于指数函数加权平均的DIC全梯度应变测量新方法研究

IF 2 3区工程技术 Q2 MATERIALS SCIENCE, CHARACTERIZATION & TESTING

Experimental Mechanics

Pub Date : 2024-12-10 DOI: 10.1007/s11340-024-01125-2

X. Song, C. Zhou, K. Xiong

Background

In the implementation of Digital Image Correlation (DIC), several post-processing methods have been developed to calculate reliable strain field. Nevertheless, achieving effective and easy-to-implement strain measurement for full-gradient strain fields continues to be a challenge.

Objective

The widely used pointwise least square (PLS) method is hard to get a balance between smoothing and accuracy when dealing with different deformation fields. A large strain calculation window may lead to over-smoothing, whereas a small strain calculation window may be insufficient to suppress noise.

Methods

A new exponential function and the exponential function weighted averaging (EFWA) method are proposed. The shape of the exponential function can be either sharp-topped or flat-topped, allowing the EFWA method to either preserve or smooth the original strain results. A straightforward and effective selection strategy for parameters of the exponential function is also provided, enabling the EFWA method to achieve self-adaptive post-processing.

Results

The calculation examples of synthetic images indicate that, the proposed EFWA method can consistently yield high measurement accuracy for unidirectional and multi-directional complex deformation fields and exhibits superior spatial resolution compared to the PLS method. The minimum Metrological Efficiency Indicator (MEI) value for the EFWA method is 1.72, compared to 4.67 for original results and 5.10 for the PLS method. The results of a tensile experiment carried out on an open-hole specimen indicate that, after the EFWA method is implemented, the strain results in areas away from the hole are effectively smoothed and the strain results in areas around the hole are preserved.

Conclusions

The proposed EFWA method can achieve effective and easy-to-implement strain measurement for full-gradient strain fields.

在数字图像相关（DIC）的实现过程中，为了计算可靠的应变场，已经发展了几种后处理方法。然而，对全梯度应变场进行有效且易于实施的应变测量仍然是一个挑战。目的应用广泛的逐点最小二乘（PLS）方法在处理不同变形场时难以在平滑性和准确性之间取得平衡。较大的应变计算窗口可能导致过度平滑，而较小的应变计算窗口可能不足以抑制噪声。方法提出了一种新的指数函数和指数函数加权平均法。指数函数的形状可以是尖顶的，也可以是平顶的，这使得EFWA方法可以保留或平滑原始应变结果。给出了一种简单有效的指数函数参数选择策略，使EFWA方法能够实现自适应后处理。结果合成图像的计算实例表明，与PLS方法相比，EFWA方法对单向和多向复杂变形场均具有较高的测量精度，且具有更好的空间分辨率。EFWA方法的最小计量效率指标（MEI）值为1.72，而原始结果为4.67，PLS方法为5.10。在裸眼试件上进行的拉伸试验结果表明，采用EFWA方法后，孔外区域的应变结果得到有效平滑，孔周围区域的应变结果得到保留。结论EFWA方法可以实现全梯度应变场的应变测量，且测量方法简单易行。

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引用次数: 0

Characterization of Environmental Stress Cracking in Polymers Through a Modified Bent Strip Test Method 用改进弯条试验方法表征聚合物的环境应力开裂

IF 2 3区工程技术 Q2 MATERIALS SCIENCE, CHARACTERIZATION & TESTING

Experimental Mechanics

Pub Date : 2024-12-09 DOI: 10.1007/s11340-024-01129-y

Y. Zhang, L. Wu, B. Jar, X. Xing

Background

The environmental stress cracking resistance (ESCR) of polymers is characterized most conveniently by the bent strip method standardized as ASTM D1693. The method has, however, suffered from poor reproducibility of the ESCR results.

Objective

In this study we propose modifications on the standardized method to reduce the variability of the ESCR results.

Methods

The notch is introduced to the specimens with the aid of automate testing machine instead of manual notching. The proposed method is then applied for a systematic investigation on the influence notch offset distance, notch inclination angle, notch depth on the environmental stress cracking behavior of polyethylene material.

Results

The results reveal interesting phenomenon that crack initiation occurs at the interior point between the endpoint and the middle of the notch, instead of at the middle point of the notch, where the maximum stress or strain is located. Finite element simulation has been conducted to elucidate root cause of this phenomenon. It has been found that the crack initiates at a point that is very close to the position of the maximum stress triaxiality, although the crack initiation position shifts slightly toward the position of the maximum stress or strain.

Conclusions

As a result, the crack initiation is controlled by the stress, strain and stress triaxiality, but stress triaxiality plays a dominant role in the initiation of environmental stress cracking.

聚合物的抗环境应力开裂性（ESCR）最方便的表征方法是ASTM D1693标准的弯曲条法。然而，该方法存在ESCR结果重复性差的问题。目的在本研究中，我们提出了对标准化方法的修改，以减少ESCR结果的可变性。方法利用自动测试机在试样上划槽，代替人工划槽。应用该方法系统研究了缺口偏移距离、缺口倾角、缺口深度对聚乙烯材料环境应力开裂行为的影响。结果发现了一个有趣的现象，即裂纹发生在缺口端点和中间之间的内部点，而不是最大应力或应变所在的缺口中间点。通过有限元模拟来阐明这一现象的根本原因。研究发现，裂纹起裂点非常接近最大应力三轴位置，但裂纹起裂位置向最大应力或应变位置略微偏移。结论环境应力裂纹的起裂受应力、应变和应力三轴性的控制，但应力三轴性在环境应力裂纹的起裂中起主导作用。

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引用次数: 0

Evolving Properties of Biological Materials Captured via Needle-Based Cavity Expansion Method 利用针基腔膨胀法捕获的生物材料的不断变化的特性

IF 2 3区工程技术 Q2 MATERIALS SCIENCE, CHARACTERIZATION & TESTING

Experimental Mechanics

Pub Date : 2024-12-04 DOI: 10.1007/s11340-024-01128-z

H. M. Varner, S. K. Naghibzadeh, K. C. Spaeth, A. Klein, T. Cohen

Background

The mechanical properties of biological tissues change over time and with disease progression. Quantifying these mechanical properties can thus be instrumental for medical diagnosis and for evaluation of tissue viability for transplant. However, soft and biological materials are exceptionally challenging to mechanically characterize using conventional testing methods, which are hindered by limitations of sample size, fixturing capabilities, and sample preparation.

Objective

We hypothesize that Volume Controlled Cavity Expansion (VCCE) is well-suited to capture subtle mechanical differences in biological tissue. The objective of this work is therefore twofold: first, we seek to quantify how stiffness of liver and gelatin evolve with age. In achieving this understanding, we aim to demonstrate the precision of VCCE in measuring subtle changes in the mechanical properties of biological tissues.

Methods

Performing VCCE tests over 15 days in samples of gelatin and liver (porcine and bovine), we track the evolving pressure-volume response and deformation limits of the materials.

Results

In both materials, we observed time-dependent variation of the stiffness and fracture thresholds. In gelatin VCCE repeatably captured stiffening over time, which was correlated with a higher fracture stress. This was in contrast to observations in bovine liver, where stiffening corresponded to a lower fracture stress. Porcine liver initially stiffened, then reversed this trend and relaxed.

Conclusion

Through this work we show that liver and gelatin stiffen with age, and that this trend is measurable via VCCE. These results highlight the utility of VCCE and call attention to the need for a new class of mechanism based constitutive models that are capable of capturing variations in material over time with a minimal number of parameters.

生物组织的力学特性随时间和疾病进展而改变。因此，量化这些机械特性可以用于医学诊断和评估移植组织的生存能力。然而，软材料和生物材料的机械特性是非常具有挑战性的，使用传统的测试方法，这是由限制的样本量，固定能力和样品制备阻碍。目的我们假设体积控制腔扩张（VCCE）非常适合捕捉生物组织中细微的力学差异。因此，这项工作的目标是双重的：首先，我们试图量化肝脏和明胶的硬度如何随着年龄的增长而变化。为了达到这种理解，我们的目标是证明VCCE在测量生物组织机械特性的细微变化方面的精度。方法对明胶和肝脏（猪和牛）样品进行15天的VCCE测试，跟踪材料的压力-体积响应和变形极限的变化。结果在两种材料中，我们观察到刚度和断裂阈值随时间的变化。在明胶中，VCCE随着时间的推移反复捕获硬化，这与较高的断裂应力相关。这与牛肝脏的观察结果相反，在牛肝脏中，硬化对应于较低的断裂应力。猪肝最初是僵硬的，然后逆转这一趋势，放松下来。结论肝脏和明胶随着年龄的增长而变硬，这一趋势可以通过VCCE测量。这些结果突出了VCCE的实用性，并引起人们对一类新的基于机制的本构模型的关注，这些模型能够以最少的参数捕获材料随时间的变化。

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引用次数: 0