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Application of the expanded distinct element method for the study of crack growth in rock-like materials under uniaxial compression

Lei YANG, Yujing JIANG, Bo LI, Shucai LI, Yang GAO

《结构与土木工程前沿（英文）》 2012年第6卷第2期页码 121-131 doi: 10.1007/s11709-012-0151-0

摘要： The expanded distinct element method (EDEM) was used to investigate the crack growth in rock-like materials under uniaxial compression. The tensile-shear failure criterion and the Griffith failure criterion were implanted into the EDEM to determine the initiation and propagation of pre-existing cracks, respectively. Uniaxial compression experiments were also performed with the artificial rock-like samples to verify the validity of the EDEM. Simulation results indicated that the EDEM model with the tensile-shear failure criterion has strong capabilities for modeling the growth of pre-existing cracks, and model results have strong agreement with the failure and mechanical properties of experimental samples. The EDEM model with the Griffith failure criterion can only simulate the splitting failure of samples due to tensile stresses and is incapable of providing a comprehensive interpretation for the overall failure of rock masses. Research results demonstrated that sample failure primarily resulted from the growth of single cracks (in the form of tensile wing cracks and shear secondary cracks) and the coalescence of two cracks due to the growth of wing cracks in the rock bridge zone. Additionally, the inclination angle of the pre-existing crack clearly influences the final failure pattern of the samples.

关键词： expanded distinct element method (EDEM) crack growth rock-like material tensile-shear failure criterion Griffith failure criterion mechanical and failure behavior

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Progressive failure analysis of notched composite plate by utilizing macro mechanics approach

《结构与土木工程前沿（英文）》 2021年第15卷第3期页码 623-642 doi: 10.1007/s11709-021-0726-8

摘要： In this study, gradual and sudden reduction methods were combined to simulate a progressive failure in notched composite plates using a macro mechanics approach. Using the presented method, a progressive failure is simulated based on a linear softening law prior to a catastrophic failure, and thereafter, sudden reduction methods are employed for modeling a progressive failure. This combination method significantly reduces the computational cost and is also capable of simultaneously predicting the first and last ply failures (LPFs) in composite plates. The proposed method is intended to predict the first ply failure (FPF), LPF, and dominant failure modes of carbon/epoxy and glass/epoxy notched composite plates. In addition, the effects of mechanical properties and different stacking sequences on the propagation of damage in notched composite plates were studied. The results of the presented method were compared with experimental data previously reported in the literature. By comparing the numerical and experimental data, it is revealed that the proposed method can accurately simulate the failure propagation in notched composite plates at a low computational cost.

关键词： progressive failure notched composite plate Hashin failure criterion macro mechanics approach finite element method

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LSSVM-based approach for refining soil failure criteria and calculating safety factor of slopes

Shiguo XIAO; Shaohong LI

《结构与土木工程前沿（英文）》 2022年第16卷第7期页码 871-881 doi: 10.1007/s11709-022-0863-8

摘要： The failure criteria of practical soil mass are very complex, and have significant influence on the safety factor of slope stability. The Coulomb strength criterion and the power-law failure criterion are classically simplified. Each one has limited applicability owing to the noticeable difference between calculated predictions and actual results in some cases. In the work reported here, an analysis method based on the least square support vector machine (LSSVM), a machine learning model, is purposefully provided to establish a complex nonlinear failure criterion via iteration computation based on strength test data of the soil, which is of more extensive applicability to many problems of slope stability. In particular, three evaluation indexes including coefficient of determination, mean absolute percentage error, and mean square error indicate that fitting precision of the machine learning-based failure criterion is better than those of the linear Coulomb criterion and nonlinear power-law criterion. Based on the proposed LSSVM approach to determine the failure criterion, the limit equilibrium method can be used to calculate the safety factor of three-dimensional slope stability. Analysis of results of the safety factor of two three-dimensional homogeneous slopes shows that the maximum relative errors between the proposed approach and the linear failure criterion-based method and the power-law failure criterion-based method are about 12% and 7%, respectively.

关键词： slope stability safety factor failure criterion least square support vector machine

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钨合金的冲击拉伸行为及其本构和断裂判据的表述

张宝,丁淳彤,刘宝华,陈雪莲

《中国工程科学》 2003年第5卷第3期页码 44-50

摘要：

利用飞轮式Hopkinson拉杆实验技术对钨质量分数为93% 的钨合金在-50～100℃温度范围、应变率ε=10²～10³s^-1区间的动态拉伸性态进行了测试，提供了相应的σ-ε曲线和最大拉伸失效应变，并以此为依据建立了该合金动态拉伸行为的本构关系，提出了该合金受动载发生塑性失稳以致发生拉断的判据。利用断口分形分析理论，对试件拉伸断口微观特征所作的分析和对宏观力学性态实验所作的结论给予了有力的支持。

关键词：动态拉伸本构模型钨合金断裂失效判据

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Deformation control criterion of shield tunnel under lateral relaxation of soft soil

《结构与土木工程前沿（英文）》 2023年第17卷第5期页码 780-795 doi: 10.1007/s11709-023-0944-3

摘要： Metro shield tunnels under the lateral relaxation of soil (LRS) are susceptible to significant lateral deformations, which jeopardizes the structural safety and waterproofing. However, deformation control standards for such situations have not been clearly defined. Therefore, based on a specific case, a model test is conducted to realize the LRS of a shield tunnel in a sandy stratum to reveal its effect on segment liners. Subsequently, a deformation control criterion is established. The LRS is simulated by linearly reducing the loads applied to the lateral sides of the segment structure. During lateral unloading, the lateral earth pressure coefficient on the segment decreases almost exponentially, and the structural deformation is characterized by horizontal expansion at the arch haunches and vertical shrinkage at the arch vault and arch bottom. Based on the mechanical pattern of the segment structure and the acoustic emission, the deformation response of a segment can be classified into three stages: elastic and quasi-elastic, damage, and rapid deformation development. For a shield tunnel with a diameter of approximately 6 m and under the lateral relaxation of sandy soil, when the ellipticity of the segment is less than 2.71%, reinforcement measures are not required. However, the segment deformation must be controlled when the ellipticity is 2.71% to 3.12%; in this regard, an ellipticity of 3% can be used as a benchmark in similar engineering projects.

关键词： shield tunnel lateral relaxation of soil deformation control criterion of segment structure model test

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合龙段底板分层破坏抗裂设计方法研究

林海峰,张冬冬,赵启林

《中国工程科学》 2012年第14卷第5期页码 106-112

摘要：

针对悬浇预应力混凝土箱梁桥合龙段底板在合龙索张拉过程中经常发生分层破坏的现象，介绍了混凝土多种破坏准则，并从理论上指出最大拉应力准则不适用于箱梁桥合龙段的底板抗裂设计，而应该采用双向应力状态下的混凝土强度破坏准则。选取多座典型破坏桥梁与未发生破坏桥梁为研究对象，建立了桥梁结构的三维实体有限元模型，得出合龙段底板预应力管道之间的竖向应力与纵向应力，进而利用不同混凝土破坏准则分别对典型桥梁的应力状态及安全性做了预测，并与桥梁实测结果进行了对比，证明了理论分析的正确性。研究结论可为同类桥梁的抗裂设计提供参考。

关键词：桥梁工程底板有限元法破坏准则双向应力

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Integrated management of cardiac failure: the cardiac failure clinic

null

《医学前沿（英文）》 2011年第5卷第1期页码 20-25 doi: 10.1007/s11684-011-0106-1

摘要：

The prevalence of the risk factors and the risk of cardiac failure are both increasing in China. This might be the consequence of the changes of the life conditions (emigration to the urban areas, changes in the diet and life style, lack of physical exercise, etc.). The wide range of clinical presentations of cardiac failure (acute or chronic) and of therapeutic approaches (medical or surgical) makes necessary the integration within the same structure of the various experts involved in the diagnosis and the treatment of cardiac diseases. Technologic and human resources required to offer all the options represent a multifaceted commitment which should be focused optimally in dedicated centers. In these centers, collaboration should replace competition between the medical and the surgical cardiac specialists. Development of team work should permit to optimize the cost efficacy of the treatments. Most of all, such a structure will facilitate the translation of innovative therapies between the research centers and clinical facilities.

关键词： cardiac failure cardiac transplantation mechanical circulatory support

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煤与瓦斯突出潜在危险区（带）预测

鲜学福,许江,王宏图

《中国工程科学》 2001年第3卷第2期页码 39-46

摘要：

煤矿的生产和实践证明，发生在矿井中的动力现象具有分区和成带的特点。文章探讨了把煤、岩和瓦斯作为一个体系，采用力学方法的划分问题。根据对煤岩复合样及含瓦斯煤样在复杂应力状态下力学性质的分析，基于对Drucker-prager理论的修正和完善，建立了它们的断裂判据，并给出了计算稳定性系数和潜在弹性应变能密度的公式，提出了按这两个指标划分煤与瓦斯突出潜在危险区（带）的基本方法。

关键词：矿井中的动力现象煤与瓦斯突出潜在危险区（带）断裂判据稳定性系数弹性应变能密度

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Experimental research on ductile fracture criterion in metal forming

Song YU, Weiming FENG

《机械工程前沿（英文）》 2011年第6卷第3期页码 308-311 doi: 10.1007/s11465-011-0233-z

摘要：

Ductile fracture criterion is key limitation parameter in material forming. Accuracy predicting surface and internal failure in plastic deformation process affects on the technology design of workpiece and die greatly. Tension, compression, torsion and shearing test on 45# steel are utilized for providing the experimental values of the critical values at fracture, and 11 widely used ductile fracture criterion are selected to simulate the physical experiments and their relative accuracy for predicting and quantifying fracture initiation sites are investigated. The comparing results show that metal forming process under high triaxiality can be estimated successively using both Normalized Cockcroft-latham and the Brozzo ductile fracture criteria, but the Ayada and general Rice-Tracey model work very well for the low triaxiality cases.

关键词： ductile fracture criteria metal forming process material experiment stress triaxiality

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A new fracture criterion for peridynamic and dual-horizon peridynamics

Jinhai ZHAO, Hesheng TANG, Songtao XUE

《结构与土木工程前沿（英文）》 2018年第12卷第4期页码 629-641 doi: 10.1007/s11709-017-0447-1

摘要： A new fracture criterion based on the crack opening displacement for peridynamic (PD) and dual-horizon peridynamics (DH-PD) is proposed. When the relative deformation of the PD bond between the particles reaches the critical crack tip opening displacement of the fracture mechanics, we assume that the bond force vanishes. A new damage rule similar to the local damage rule in conventional PD is introduced to simulate fracture. The new formulation is developed for a linear elastic solid though the extension to nonlinear materials is straightforward. The performance of the new fracture criterion is demonstrated by four examples, i.e. a bilateral crack problem, double parallel crack, monoclinic crack and the double inclined crack. The results are compared to experimental data and the results obtained by other computational methods.

关键词： Castigliano’s theorem breaking energy critical extension XFEM COD PD-COD

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Bending failure performance of a shield tunnel segment based on full-scale test and numerical analysis

《结构与土木工程前沿（英文）》页码 1033-1046 doi: 10.1007/s11709-023-0973-y

摘要： This study focuses on the bending failure performance of a shield tunnel segment. A full-scale test was conducted to investigate deformation and failure characteristics. During the loading, the bending failure process can be divided into four stages: the elastic stage, working stage with cracks, failure stage, and ultimate stage. The characteristic loads between contiguous stages are the cracking, failure, and ultimate loads. A numerical model corresponding to the test was established using the elastoplastic damage constitutive model of concrete. After a comparative analysis of the simulation and test results, parametric studies were performed to discuss the influence of the reinforcement ratio and proportion of tensile longitudinal reinforcement on the bearing capacity. The results indicated that the change in the reinforcement ratio and the proportion of tensile longitudinal reinforcement had little effect on the cracking load but significantly influenced the failure and ultimate loads of the segment. It is suggested that in the reinforcement design of the subway segment, the reinforcement ratio and the proportion of tensile longitudinal reinforcement can be chosen in the range of 0.7%–1.2% and 49%–55%, respectively, allowing the segment to effectively use the reinforcement and exert the design strength, thereby improving the bearing capacity of the segment.

关键词： shield tunnel bearing capacity failure mechanism segment reinforcement

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Overview on acute-on-chronic liver failure

null

《医学前沿（英文）》 2016年第10卷第1期页码 1-17 doi: 10.1007/s11684-016-0439-x

摘要：

Liver failure (LF) is defined as severe dysfunction in hepatic synthesis, detoxification, and metabolism induced by various etiologies. Clinical presentation of LF typically includes severe jaundice, coagulation disorder, hepatic encephalopathy, and ascites. LF can be classified into acute LF, acute-on-chronic LF (ACLF), and chronic LF. ACLF has been demonstrated as a distinct syndrome with unique clinical presentation and outcomes. The severity, curability, and reversibility of ACLF have attracted considerable attention. Remarkable developments in ACLF-related conception, diagnostic criteria, pathogenesis, and therapy have been achieved. However, this disease, especially its diagnostic criteria, remains controversial. In this paper, we systemically reviewed the current understanding of ACLF from its definition, etiology, pathophysiology, pathology, and clinical presentation to management by thoroughly comparing important findings between east and west countries, as well as those from other regions. We also discussed the controversies, challenges, and needs for future studies to promote the standardization and optimization of the diagnosis and treatment for ACLF.

关键词： liver failure chronic liver failure acute-on-chronic liver failure diagnosis prognosis treatment

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Surficial stability analysis of soil slope under seepage based on a novel failure mode

《结构与土木工程前沿（英文）》 2021年第15卷第3期页码 712-726 doi: 10.1007/s11709-021-0729-5

摘要： Normally, the edge effects of surficial landslides are not considered in the infinite slope method for surficial stability analysis of soil slopes. In this study, the limit stress state and discrimination equation of an infinite slope under saturated seepage flow were analyzed based on the Mohr-Coulomb strength criterion. Therefore, a novel failure mode involving three sliding zones (upper tension zone, middle shear sliding zone, and lower compression zone) was proposed. Accordingly, based on the limit equilibrium analysis, a semi-analytical framework considering the edge effect for the surficial stability of a soil slope under downslope seepage was established. Subsequently, the new failure mode was verified via a numerical finite element analysis based on the reduced strength theory with ABAQUS and some simplified methods using SLIDE software. The results obtained by the new failure mode agree well with those obtained by the numerical analysis and traditional simplified methods, and can be efficiently used to assess the surficial stability of soil slopes under rainwater seepage. Finally, an evaluation of the infinite slope method was performed using the semi-analytical method proposed in this study. The results show that the infinite slope tends to be conservative because the edge effect is neglected, particularly when the ratio of surficial slope length to depth is relatively small.

关键词： soil slope seepage surficial failure mode stress state edge effects

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一种损伤演化方程的建立和几种层裂准则的推导

曹结东,李永池

《中国工程科学》 2006年第8卷第1期页码 40-45

摘要：

通过唯象分析和细观统计相结合的方法建立了一种韧性材料的损伤演化方程，从物理上对方程中的参数进行了合理的解释，并以此为依据推导了材料的便于工程应用的几种层裂准则，根据准则总结了一些有意义的层裂规律；通过层裂实验和数值模拟相结合的方法来确定材料参数，计算结果与实验结果较好的一致性验证了所建的损伤演化方程和推导的层裂准则是合理的，决定材料参数的方法是有效的。

关键词：损伤演化方程层裂准则数值模拟

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Study of high-strength CFRP bolted joints with failure- monitoring cone washers

Tsukasa KATSUMATA, Yoshihiro MIZUTANI, Akira TODOROKI, Ryosuke MATSUZAKI

《机械工程前沿（英文）》 2011年第6卷第3期页码 272-276 doi: 10.1007/s11465-011-0231-1

摘要：

To increase the strength of carbon-fiber-reinforced plastic (CFRP) bolted joints, a method to increase the friction force between carbon-fiber-reinforced plastic members was proposed. The increase in failure load for the proposed joint was confirmed in finite-element method analyses and joint tests. Additionally, the feasibility of damage monitoring using surface strains of the cone washer was demonstrated.

关键词： composite bolted joint failure monitoring finite-element method