Engineering Fracture Mechanics最新文献_第2页

Phase-field approach for precise fracture tracking in anisotropic rocks: Integrating orthotropy-based energy decomposition and two-fold symmetric fracture toughness 在各向异性岩石中精确跟踪断裂的相场方法：整合基于各向同性的能量分解和双重对称断裂韧性

IF 4.7 2区工程技术 Q1 MECHANICS

Engineering Fracture Mechanics

Pub Date : 2024-10-09 DOI: 10.1016/j.engfracmech.2024.110543

Rock formations are known to exhibit material anisotropy, both in terms of elastic and fracture properties. This means that the fracture path in such formations is not a priori known but rather a complex unknown that requires robust numerical techniques to predict accurately. In this context, the phase-field model is considered particularly effective, provided that certain physical considerations are carefully adjusted to align with the physics of the problem. While addressing elastic anisotropy is well-established, the tension–compression asymmetry necessary to inhibit crack interpenetration in phase-field fracture models needs to account for the specific material anisotropy. Additionally, to accurately capture crack propagation, it is critical to simultaneously account for orientation-dependent fracture toughness in such materials. To address this, the present study employs an anisotropic phase-field model that integrates the generalized spectral decomposition proposed in the literature for orthotropic materials with a two-fold symmetric fracture toughness, to predict the fracture trajectories in rock-type samples under fixed mixed-mode loading ratios. While each of the two aspects has primarily been applied to model orthotropic plates under simple tensile and shearing loading conditions in the literature, here we study their applicability in complex loading scenarios. To this end, the experimental data from notched semi-circular specimens of Grimsel Granite undergoing complex mixed-mode loading obtained in our previous work is considered. We focus on two given mode-mixity ratios and perform numerical studies. Our results emphasize the importance of considering this generalized decomposition for phase-field modeling of fracturing in rock-type materials, particularly under loading conditions where the crack might otherwise be unrealistically driven into the compressive region. Although certain features are well captured by considering anisotropy in elasticity alone, our findings demonstrate that incorporating a two-fold symmetric fracture toughness proves to be advantageous for more precise tracking of the fracture path.

众所周知，岩层在弹性和断裂特性方面表现出材料的各向异性。这意味着此类岩层的断裂路径并非先验已知，而是一个复杂的未知数，需要强大的数值技术才能准确预测。在这种情况下，相场模型被认为特别有效，但前提是必须仔细调整某些物理因素，使其与问题的物理特性相一致。虽然弹性各向异性是公认的，但在相场断裂模型中，抑制裂纹相互渗透所需的拉伸-压缩不对称需要考虑特定材料的各向异性。此外，要准确捕捉裂纹扩展，必须同时考虑此类材料随取向变化的断裂韧性。为了解决这个问题，本研究采用了各向异性相场模型，该模型整合了文献中针对具有两重对称断裂韧性的正交材料提出的广义谱分解，以预测岩石类型样本在固定混合模式加载比下的断裂轨迹。虽然这两个方面在文献中主要应用于简单拉伸和剪切加载条件下的各向同性板材模型，但我们在此研究它们在复杂加载情况下的适用性。为此，我们考虑了之前工作中获得的格里姆斯花岗岩缺口半圆试样在复杂混合模式加载下的实验数据。我们将重点放在两个给定的模式混合比上，并进行了数值研究。我们的研究结果强调了考虑这种广义分解对岩石类材料断裂相场建模的重要性，尤其是在加载条件下，否则裂缝可能会不切实际地进入压缩区域。虽然仅考虑弹性各向异性就能很好地捕捉到某些特征，但我们的研究结果表明，加入两重对称断裂韧性证明有利于更精确地跟踪断裂路径。

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引用次数: 0

Investigating tensile failure mechanisms of layered rocks through physical testing and PFC3D analysis 通过物理测试和 PFC3D 分析研究层状岩石的拉伸破坏机制

IF 4.7 2区工程技术 Q1 MECHANICS

Engineering Fracture Mechanics

Pub Date : 2024-10-09 DOI: 10.1016/j.engfracmech.2024.110541

Rocks generally exhibit less resistance to tension compared to shear or compression forces, and tension cracks often precede shear or compression failures. While the mechanical performance of rock layers under compression has been widely described, their tensile behavior is less known.

The current study includes experimental approaches as well as computational testing with the three-dimensional Particle Flow Code (PFC3D) to evaluate the effect of layer thickness and mechanical parameters on the strength and failure patterns of layered rocks-like materials under continuous tension.

The Brazilian tensile strength test was conducted on concrete and gypsum specimens. The concrete specimen measured 54 mm in diameter and 27 mm in thickness, resulting in a tensile strength of 1.35 MPa. The gypsum specimen, with the same measurements, had a tensile strength of 0.6 MPa. In addition, uniaxial compressive strength tests were performed on both materials, yielding compressive strengths of 18 MPa for concrete and 6 MPa for gypsum. Our findings indicate that layer thickness and mechanical properties considerably influence failure patterns, tensile strength, and progressive deformation of these materials. The failure modes seen in the layered specimens indicate that the tensile strength ascertained by numerical testing and direct tensile testing is equally accurate. Both the empirical and computational findings are in accordance with the analytical predictions of the failure criterion. In rock engineering, these failure criteria have a high degree of accuracy when it comes to predicting tensile strength and reflecting the failure modes of layered rocks, like layered sandstone, slate, and shale.

与剪切力或压缩力相比，岩石通常表现出较小的抗拉强度，而拉伸裂缝往往出现在剪切力或压缩力破坏之前。目前的研究包括实验方法以及利用三维粒子流代码（PFC3D）进行的计算测试，以评估层厚度和力学参数对连续拉伸条件下层状岩石类材料的强度和破坏模式的影响。混凝土试样直径为 54 毫米，厚度为 27 毫米，抗拉强度为 1.35 兆帕。石膏试样的测量值相同，抗拉强度为 0.6 兆帕。此外，还对两种材料进行了单轴抗压强度测试，结果显示混凝土的抗压强度为 18 兆帕，石膏的抗压强度为 6 兆帕。我们的研究结果表明，层厚度和机械性能在很大程度上影响着这些材料的破坏模式、抗拉强度和渐进变形。分层试样的破坏模式表明，通过数值测试和直接拉伸测试确定的抗拉强度同样准确。经验结果和计算结果都与失效标准的分析预测相一致。在岩石工程中，这些破坏标准在预测抗拉强度和反映层状岩石（如层状砂岩、板岩和页岩）的破坏模式方面具有很高的准确性。

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引用次数: 0

Effects of ultrasonic shot peening followed by surface mechanical rolling on mechanical properties and fatigue performance of 2024 aluminum alloy 表面机械滚压后超声波喷丸强化对 2024 铝合金机械性能和疲劳性能的影响

IF 4.7 2区工程技术 Q1 MECHANICS

Engineering Fracture Mechanics

Pub Date : 2024-10-09 DOI: 10.1016/j.engfracmech.2024.110538

Aiming to improve the mechanical properties and fatigue performance of 2024 aluminum alloy, the experimental investigations on composite treatment consisting of ultrasonic shot peening (USP) followed by surface mechanical rolling (SMR) were carried out. The experimental results were compared with the specimens only treated by USP or SMR in terms of surface roughness, microhardness gradient and microstructure observation. The uniaxial tension test and low cycle fatigue test were conducted on the as-received specimen and the ones treated by USP, SMR and USP/SMR composite treatment, respectively. The tensile mechanical properties were effectively improved by USP. The introduction of SMR following USP can significantly increase the number of cycles to failure. Combining fracture morphology analysis and DEM-FEM coupling simulation of USP/SMR composite treatment, it was concluded that the improvement of tensile mechanical properties is mainly attributed to the synergistic effect of the compressive residual stresses and gradient-structured layer produced by USP, and the decrease in surface roughness resulting from SMR is the main reason for the significant improvement of fatigue performance. This work could provide an insight into the surface strengthening mechanism for USP/SMR composite treatment of materials with respect to the improvement of mechanical properties and fatigue performance.

为了改善 2024 铝合金的机械性能和疲劳性能，对由超声波喷丸强化（USP）和表面机械滚压（SMR）组成的复合处理进行了实验研究。实验结果在表面粗糙度、显微硬度梯度和显微结构观察方面与只经过 USP 或 SMR 处理的试样进行了比较。对原样试样和经 USP、SMR 及 USP/SMR 复合处理的试样分别进行了单轴拉伸试验和低循环疲劳试验。USP 有效改善了拉伸机械性能。在 USP 之后引入 SMR 可以显著增加失效循环次数。结合对 USP/SMR 复合处理的断口形貌分析和 DEM-FEM 耦合模拟，可以得出结论：拉伸机械性能的改善主要归因于 USP 产生的压残余应力和梯度结构层的协同效应，而 SMR 导致的表面粗糙度降低是疲劳性能显著改善的主要原因。这项工作有助于深入了解 USP/SMR 复合处理材料在改善机械性能和疲劳性能方面的表面强化机制。

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引用次数: 0

A data-driven ductile fracture criterion for high-speed impact 数据驱动的高速冲击韧性断裂标准

IF 4.7 2区工程技术 Q1 MECHANICS

Engineering Fracture Mechanics

Pub Date : 2024-10-05 DOI: 10.1016/j.engfracmech.2024.110525

Data-driven methods based on machine learning (ML) models offer new approaches for characterizing the fracture behavior of advanced elastoplastic materials. In this paper, a ML-based data-driven ductile fracture criterion is proposed to characterize the fracture behavior of elastoplastic materials under high-speed impact loading conditions. To reduce the required training dataset and enhance the predictability capability, several assumptions are used. Firstly, utilizing the decoupled assumption, two separate artificial neural network (ANN) models are employed to establish the fundamental fracture model and characterize the strain rate effect of ductile fracture behavior, respectively. In addition, the enhanced method with a logarithmic function is introduced to improve predictability capability of the proposed data-driven criterion under unknown high strain rates. To establish a complete numerical implementation framework, an enhanced rate-dependent data-driven constitutive model and a compatible numerical implementation algorithm are additionally introduced. Eventually, to assess the applicability of the proposed data-driven fracture criterion, numerical simulations of notched specimens and ballistic impact conditions of Ti-6Al-4V material are conducted, respectively. These investigation results demonstrate the effectiveness of the proposed data-driven ductile fracture criterion.

基于机器学习（ML）模型的数据驱动方法为表征先进弹塑性材料的断裂行为提供了新方法。本文提出了一种基于 ML 的数据驱动韧性断裂准则，用于表征高速冲击加载条件下弹塑性材料的断裂行为。为了减少所需的训练数据集并提高预测能力，本文使用了几个假设。首先，利用解耦假设，采用两个独立的人工神经网络（ANN）模型分别建立基本断裂模型和表征韧性断裂行为的应变率效应。此外，还引入了具有对数函数的增强方法，以提高所提出的数据驱动准则在未知高应变率下的预测能力。为了建立一个完整的数值实施框架，还引入了与速率相关的增强型数据驱动构成模型和兼容的数值实施算法。最后，为了评估所提出的数据驱动断裂准则的适用性，分别对 Ti-6Al-4V 材料的缺口试样和弹道冲击条件进行了数值模拟。这些研究结果证明了所提出的数据驱动韧性断裂准则的有效性。

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引用次数: 0

A rate-dependent crack bridging model for dynamic fracture of CNT-reinforced polymers 依赖速率的 CNT 增强聚合物动态断裂裂缝桥接模型

IF 4.7 2区工程技术 Q1 MECHANICS

Engineering Fracture Mechanics

Pub Date : 2024-10-05 DOI: 10.1016/j.engfracmech.2024.110535

Carbon nanotubes (CNTs) improve the fracture toughness of polymer-based matrix composites by bridging the crack growth path. This research presents a finite element (FE) rate-dependent crack bridging model of Mode-I dynamic crack growth in CNT-reinforced polymers accounting for rate of loading and rapid crack growth. Two distinct CNT bridging and matrix cracking damage mechanisms are taken into account in the fracture process zone (FPZ) accounting for the dissipation of fracture energy. A viscoelastic-viscoplastic material model is adapted for the matrix phase to capture the strain rate effects. The crack in the matrix phase is modeled using cohesive zone elements characterized by experimental data. A rate-dependent traction-separation law obtained from CNT pull-out simulation at relevant crack opening speeds is used to simulate the CNT bridging in the FPZ. Considering the given traction-separation law as a constitutive equation, the CNTs are replaced with non-linear spring elements to facilitate the FE simulation of crack bridging with numerous CNTs in the FPZ. The proposed rate-dependent FE model for crack bridging enables the study of the effect of key CNT factors such as length, orientation, waviness, volume fraction, and agglomeration on fracture energy dissipation at various crack speeds. The developed model can simultaneously consider the interactive effects of all CNT parameters which is useful for considering all processing-induced uncertainties in analyzing the effects of CNTs on the dynamic fracture toughness of nanocomposites.

碳纳米管（CNT）通过桥接裂纹生长路径提高了聚合物基复合材料的断裂韧性。本研究提出了一种有限元（FE）速率依赖性裂纹桥接模型，用于计算 CNT 增强聚合物中 Mode-I 动态裂纹生长的加载速率和快速裂纹生长。在断裂过程区（FPZ）考虑了两种不同的 CNT 桥接和基体开裂破坏机制，并考虑了断裂能量的耗散。基体相采用粘弹性-粘塑性材料模型，以捕捉应变速率效应。基体相中的裂缝使用以实验数据为特征的内聚区元素建模。在相关的裂缝张开速度下，通过 CNT 拔出模拟获得的随速率变化的牵引分离定律用于模拟 FPZ 中的 CNT 桥接。将给定的牵引力分离定律视为一个构成方程，用非线性弹簧元件代替 CNT，以方便对 FPZ 中众多 CNT 的裂纹桥接进行有限元模拟。所提出的依赖速率的裂纹桥接 FE 模型可以研究 CNT 的长度、取向、波形、体积分数和聚集等关键因素在不同裂纹速度下对断裂能量耗散的影响。所开发的模型可同时考虑所有 CNT 参数的交互影响，有助于在分析 CNT 对纳米复合材料动态断裂韧性的影响时考虑所有加工引起的不确定性。

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引用次数: 0

A novel subsurface damage model in diamond wire sawing of silicon wafers 金刚石线锯硅片时的新型表层下损伤模型

IF 4.7 2区工程技术 Q1 MECHANICS

Engineering Fracture Mechanics

Pub Date : 2024-10-05 DOI: 10.1016/j.engfracmech.2024.110534

The subsurface damages (SSDs) generated during fixed abrasive diamond wire sawing (DWS) of silicon wafers can reduce the fracture strength and increase the breakage probability of these wafers. It is crucial to accurately evaluate these SSDs. A theoretical model of SSD depth is developed for the fixed abrasive DWS of silicon wafers considering the size effects of material properties, micro-geometries of abrasive grits, and inclination/interaction effects of subsurface cracks. A series of silicon wafers are processed, and the silicon material properties, diamond wire parameters, and surface/subsurface morphologies of silicon wafers are measured. The model is experimentally validated and then used to study the effects of processing parameters on inclination/interaction effects, cutting behaviors, and SSDs. The results show that the model has a relative error of less than 5.0% after revealing that the inclination/interaction parameters, cutting behavior parameters, and SSD depth almost follow a normal distribution, with a maximum distribution probability ranging from 30% to 50%. The average inclination angle is approximately 30°, the average cutting depth is in the range of one to two hundred micrometers, the average load is a few millinewtons, and the SSD depth is in the range of a few micrometers. With an increasing density of abrasive grit, a decreasing feed rate, or an increasing wire speed, the interaction effect becomes more pronounced, while the inclination angle, cutting depth, load, active grit ratio, and SSD depth decrease. When the protrusion height increases, or the half sharpness angle or tip radius of abrasive grit decreases, there is an increase in the cutting depth, load, active grit ratio, or SSD depth. The inclination angle decreases as the protrusion height, half sharpness angle, or tip radius increases. This research helps to understand the cutting mechanism and evaluate the SSDs during the DWS of silicon wafers.

固定磨料金刚石线锯（DWS）切割硅晶片时产生的表层下损伤（SSD）会降低这些晶片的断裂强度并增加其破损概率。准确评估这些 SSD 至关重要。考虑到材料特性的尺寸效应、磨料磨粒的微观几何形状以及次表层裂纹的倾斜/相互作用效应，针对硅晶片的固定磨料 DWS 建立了 SSD 深度理论模型。对一系列硅片进行了加工，并测量了硅材料特性、金刚石线参数和硅片表面/次表面形态。该模型经过实验验证，然后用于研究加工参数对倾斜/相互作用效应、切割行为和 SSD 的影响。结果表明，该模型的相对误差小于 5.0%，因为它揭示了倾斜/相互作用参数、切割行为参数和固态沉积深度几乎遵循正态分布，最大分布概率在 30% 至 50% 之间。平均倾角约为 30°，平均切削深度在一到两百微米之间，平均载荷为几毫牛，SSD 深度在几微米之间。随着磨粒密度的增加、进给率的降低或线速度的提高，相互作用效应会变得更加明显，而倾斜角、切割深度、负载、有效磨粒比和 SSD 深度则会减小。当突出高度增加，或磨粒的半锐角或尖端半径减小时，切割深度、负荷、活性磨粒比率或 SSD 深度都会增加。倾斜角随着突出高度、半锐角或刀尖半径的增加而减小。这项研究有助于了解切割机制，并评估硅晶片 DWS 过程中的 SSD。

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引用次数: 0

Fracture performance and cracking mechanism of large-particle size hydraulic asphalt concrete at different temperatures 大粒径水工沥青混凝土在不同温度下的断裂性能和开裂机理

IF 4.7 2区工程技术 Q1 MECHANICS

Engineering Fracture Mechanics

Pub Date : 2024-10-04 DOI: 10.1016/j.engfracmech.2024.110530

This study investigates the fracture properties of large-particle size hydraulic asphalt concrete (LPSHAC) at various temperatures using pre-cracked trabecular bending tests and digital image correlation (DIC). Results show that temperature significantly affects LPSHAC’s fracture properties, with the energy release rate and J-integral fracture toughness increasing initially and then decreasing as temperature rises. Horizontal strain better characterizes damage progression at higher temperatures. Crack curvature coefficients at 0 °C and 20 °C increased by 8.2 % and 30.1 % compared to that at −20 °C, while the aggregate fracture area ratio rose as the temperature decreased from 20 °C to −20 °C.

本研究采用预裂小梁弯曲试验和数字图像相关性（DIC）技术，研究了大粒径水工沥青混凝土（LPSHAC）在不同温度下的断裂性能。结果表明，温度对 LPSHAC 的断裂性能有很大影响，能量释放率和 J-积分断裂韧性最初会增加，然后随着温度的升高而降低。水平应变能更好地表征高温下的损伤发展。与零下 20 摄氏度时相比，0 摄氏度和 20 摄氏度时的裂缝曲率系数分别增加了 8.2% 和 30.1%，而随着温度从 20 摄氏度降至零下 20 摄氏度，总断裂面积比也随之上升。

引用次数: 0

Study on fracture behaviour of pipeline girth welds based on curved wide plate specimens: Experimental and numerical analysis 基于弧形宽板试样的管道环缝焊缝断裂行为研究：实验和数值分析

IF 4.7 2区工程技术 Q1 MECHANICS

Engineering Fracture Mechanics

Pub Date : 2024-10-04 DOI: 10.1016/j.engfracmech.2024.110522

Understanding the fracture characteristics and strain capacity of pipelines with girth welds under external loads is crucial for evaluating pipeline safety. The use of curved wide plate (CWP) specimens closely resembling full-scale (FS) pipelines in geometry provides a more realistic representation of crack tip constraint states compared to small-size fracture toughness test specimens in laboratory settings. This study aims to investigate the ductile fracture characteristics of center cracks on the outer surface of girth welds in high-grade steel pipelines under external loads through large-scale CWP tensile tests and advanced numerical simulations. Tensile tests were conducted on CWP specimens using a kiloton tensile testing machine, with double crack opening displacement (COD) gauge monitoring crack mouth opening displacement (CMOD), and high-precision displacement sensors and strain gauges tracking deformation and strains at various positions. The study yielded significant experimental results, and a finite element (FE) model of the CWP was developed using the nonlinear finite element method (FEM) to validate the experimental data against simulation results. The FE model was then used to investigate the influence of material properties on crack propagation resistance and driving force curves. A method for determining the ultimate tensile strain capacity (UTSC) of pipelines based on actual material fracture toughness was proposed. This research contributes valuable experimental data for further exploration of fracture behaviour in large-scale pipeline girth welds and offers insights for safety evaluations of such welds.

了解带有环缝焊缝的管道在外部载荷作用下的断裂特性和应变能力对于评估管道安全至关重要。与实验室环境中的小尺寸断裂韧性测试样本相比，使用几何形状与全尺寸 (FS) 管道非常相似的弧形宽板 (CWP) 试样能更真实地反映裂纹尖端的约束状态。本研究旨在通过大规模 CWP 拉伸试验和先进的数值模拟，研究高等级钢制管道环缝外表面中心裂纹在外部载荷作用下的韧性断裂特征。使用千吨级拉伸试验机对 CWP 试样进行了拉伸试验，使用双裂缝张开位移（COD）计监测裂缝口张开位移（CMOD），使用高精度位移传感器和应变计跟踪不同位置的变形和应变。研究得出了重要的实验结果，并使用非线性有限元法（FEM）建立了 CWP 的有限元（FE）模型，以根据模拟结果验证实验数据。然后利用有限元模型研究了材料特性对裂纹扩展阻力和驱动力曲线的影响。根据实际材料的断裂韧性，提出了一种确定管道极限拉伸应变能力（UTSC）的方法。这项研究为进一步探索大型管道环缝焊缝的断裂行为提供了宝贵的实验数据，并为此类焊缝的安全评估提供了启示。

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引用次数: 0

Influence mechanism of initial mechanical damage on concrete permeability and tunnel lining leakage 初始机械损伤对混凝土渗透性和隧道衬砌渗漏的影响机理

IF 4.7 2区工程技术 Q1 MECHANICS

Engineering Fracture Mechanics

Pub Date : 2024-09-30 DOI: 10.1016/j.engfracmech.2024.110531

The stress state is not effectively considered in existing studies when researching the permeability evolution of concrete with initial mechanical damages, causing ambiguity in the influence mechanism of initial mechanical damage on tunnel lining leakage. This deficiency can lead to significant uncertainty in predicting the probability and evaluating the consequences of tunnel leakage diseases, further affecting the formulation of relevant prevention strategies. Therefore, mechanical damage is induced to concrete specimens by subjecting them to certain stress levels, and triaxial compression seepage tests are subsequently conducted to study the influence of initial mechanical damage on permeability evolution and macrocracks. Furthermore, the relationship between microcrack characteristics and concrete permeability is studied, ultimately revealing the influence mechanism of initial mechanical damage on tunnel lining leakage. Research results indicate that the concrete permeability decreases first, becomes stable, and then continuously increases during testing, and is positively related to changes in horizontal deformation ratio. When the damage-inducing stress reaches 80% of the uniaxial compressive strength (UCS), the impact of initial mechanical damage on concrete permeability increases significantly. The increase in initial mechanical damage can lead to a significant rise in permeability, even when the crack volume is in a compacted state. Additionally, cracks on the surface of the specimen become clearly visible when the test terminates, once the damage-inducing stress reaches 85% UCS. Two factors contribute to the gradual increase in concrete permeability with the rise in initial damage-inducing stress. Firstly, microcracks inside the concrete gradually widen and propagate. Secondly, the microcracks resulting from the initial damage progressively enlarge due to water pressure during the triaxial compression seepage test. Influenced by the blockage of seepage channels, concrete permeability can occasionally decrease during testing. The accidental load induces the gradual propagation of microcracks inside the mechanically damaged concrete. Then, the rebound deformation of concrete after the removal of the accidental load causes the closed microcracks to reopen significantly, leading to an increase in permeability and subsequent tunnel lining water leakage.

现有研究在研究初始力学损伤混凝土渗透性演变时，并未有效考虑应力状态，导致初始力学损伤对隧道衬砌渗漏影响机理的模糊性。这一缺陷会给隧道渗漏病害的概率预测和后果评估带来很大的不确定性，进一步影响相关防治策略的制定。因此，通过对混凝土试件施加一定的应力水平，诱导其产生机械损伤，然后进行三轴压缩渗流试验，研究初始机械损伤对渗透性演变和大裂缝的影响。此外，还研究了微裂缝特征与混凝土渗透性之间的关系，最终揭示了初始机械损伤对隧道衬砌渗漏的影响机理。研究结果表明，在试验过程中，混凝土渗透率先降低、稳定后持续上升，并与水平变形比的变化呈正相关。当损伤诱导应力达到单轴抗压强度（UCS）的 80% 时，初始机械损伤对混凝土渗透性的影响显著增加。即使裂缝体积处于密实状态，初始机械损伤的增加也会导致渗透率显著上升。此外，当破坏应力达到 85% UCS 时，试验结束时试样表面的裂缝会变得清晰可见。有两个因素导致混凝土渗透性随着初始破坏诱导应力的增加而逐渐增加。首先，混凝土内部的微裂缝会逐渐扩大和扩展。其次，在三轴压缩渗水试验中，由于水压的作用，初始破坏产生的微裂缝逐渐扩大。受渗水通道堵塞的影响，混凝土的渗透性在试验过程中偶尔会降低。意外荷载会导致机械损伤混凝土内部的微裂缝逐渐扩展。然后，事故荷载移除后混凝土的回弹变形会使闭合的微裂缝重新明显打开，从而导致渗透性增加，进而造成隧道衬砌渗漏水。

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引用次数: 0

Mode-I fracture failure mechanism of 3-D braided composites under low-velocity wedge-loaded impact 低速楔形载荷冲击下三维编织复合材料的 I 型断裂失效机理

IF 4.7 2区工程技术 Q1 MECHANICS

Engineering Fracture Mechanics

Pub Date : 2024-09-30 DOI: 10.1016/j.engfracmech.2024.110533

Mode-I low-velocity impact fracture very often happens during the lifetime service of fiber-reinforced composites. Three-dimensional braided carbon fiber/epoxy composites (3DBC) have higher fracture toughness than laminate, while the Mode-I fracture is also an important behavior. Here we report the Mode-I fracture of 3DBC under low-velocity impact. A single cleavage triangle (SCT) specimen was prepared for the Mode-I impact test. A high-speed camera was used to capture images of the fracture initiation and growth. The inner damages were observed using X-ray microcomputed tomography (Micro-CT). The fracture behaviors were also compared among three braided angles and three impact energies. We found that the crack propagation follows the path of the crimped yarn. The propagation direction changes upon reaching interweaved points. The energy absorption at rupture increases as the braiding angle. A finite element analysis (FEA) model was developed to analyze the internal crack propagation behaviors and failure mechanisms. The fracture mechanisms of 3DBC have been compared between the tests and the FEA results. It was found the braided angle of 45°has a higher impact fracture toughness than the can 10°, 20° and 30° samples.

在纤维增强复合材料的使用寿命期间，经常会发生 Mode-I 低速冲击断裂。三维编织碳纤维/环氧复合材料（3DBC）比层压板具有更高的断裂韧性，而Mode-I断裂也是一种重要行为。在此，我们报告了三维编织碳纤维/环氧树脂复合材料在低速冲击下的 Mode-I 断裂情况。我们制备了一个单劈三角形（SCT）试样用于 Mode-I 冲击试验。我们使用高速相机捕捉了断口萌发和生长的图像。使用 X 射线微计算机断层扫描（Micro-CT）观察内部损伤。我们还比较了三种编织角度和三种冲击能量下的断裂行为。我们发现，裂纹沿着卷曲纱线的路径传播。在到达交织点时，裂纹的传播方向会发生变化。断裂时的能量吸收随着编织角度的增加而增加。我们建立了一个有限元分析（FEA）模型来分析内部裂纹的扩展行为和断裂机制。测试结果与有限元分析结果比较了 3DBC 的断裂机制。结果发现，与 10°、20° 和 30°样品相比，45°编织角的冲击断裂韧性更高。

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引用次数: 0