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Stress field near circular-arc interface crack tip based on electric saturation concept

Longchao DAI, Xinwei WANG

《机械工程前沿（英文）》 2009年第4卷第3期页码 320-325 doi: 10.1007/s11465-009-0042-9

摘要： Within the framework of nonlinear electroelasticity, the anti-plane problem of a circular-arc interfacial crack between a circular piezoelectric inhomogeneity and an infinite piezoelectric matrix subjected to a far-field uniform loading is investigated by an electrical strip saturation model, the complex variable method, and the method of analytical continuation. Explicit closed form expressions for the complex potentials in both the matrix and the inclusion, and the stress intensity factor at the crack tip are presented. Comparison with some related solutions based on the linear electroelastic theory shows the validity of the present solutions

关键词： piezoelectric material arc crack strip saturation stress intensity factor

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Mixed mode properties of CNT reinforced composites using Arcan test rig

Jacob MUTHU

《结构与土木工程前沿（英文）》 2015年第9卷第4期页码 397-404 doi: 10.1007/s11709-015-0321-y

摘要： Composite materials reinforced with carbon nanotubes were mechanical tested using Arcan test rig under Mode-I, Mode-II and mixed mode loading conditions to obtain their fracture properties. The butterfly composite specimens were fabricated with 0.02, 0.05 and 0.1 wt % CNTs. The polyester/CNT composite was fabricated using VRTM (Vacuum Resin Transfer Molding) where the CNTs were first functionalised to reach an optimum properties. Arcan test rig was designed and fabricated to work with the Shimadzu testing machine. The results show that the functionalised CNTs have improved the fracture behavior by acting as bridge between the cracked face. In addition, the fracture properties were not improved for the higher weight fraction of 0.1 wt% CNTs.

关键词： CNT composites Arcan test rig stress intensity factor

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An investigation on prevalent strategies for XFEM-based numerical modeling of crack growth in porous media

《结构与土木工程前沿（英文）》 2021年第15卷第4期页码 914-936 doi: 10.1007/s11709-021-0750-8

摘要： Crack growth modeling has always been one of the major challenges in fracture mechanics. Among all numerical methods, the extended finite element method (XFEM) has recently attracted much attention due to its ability to estimate the discontinuous deformation field. However, XFEM modeling does not directly lead to reliable results, and choosing a strategy of implementation is inevitable, especially in porous media. In this study, two prevalent XFEM strategies are evaluated: a) applying reduced Young’s modulus to pores and b) using different partitions to the model and enriching each part individually. We mention the advantages and limitations of each strategy via both analytical and experimental validations. Finally, the crack growth is modeled in a natural porous media (Fontainebleau sandstone). Our investigations proved that although both strategies can identically predict the stress distribution in the sample, the first strategy simulates only the initial crack propagation, while the second strategy could model multiple cracks growths. Both strategies are reliable and highly accurate in calculating the stress intensity factor, but the second strategy can compute a more reliable reaction force. Experimental tests showed that the second strategy is a more accurate strategy in predicting the preferred crack growth path and determining the maximum strength of the sample.

关键词： numerical modeling extended finite element method porous media crack growth stress intensity factor

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The formation mechanism and the influence factor of residual stress in machining

null

《机械工程前沿（英文）》 2014年第9卷第3期页码 265-269 doi: 10.1007/s11465-014-0311-0

摘要：

Residual stresses generated in cutting process have important influences on workpiece performance. The paper presents a method of theoretical analysis in order to explicate the formation mechanism of residual stresses in cutting. An important conclusion is drawn that the accumulated plastic strain is the main factor which determines the nature and the magnitude of surface residual stresses in the workpiece. On the basis of the analytical model for residual stress, a series of simulations for residual stress prediction during cutting AISI 1045 steel are implemented in order to obtain the influences of cutting speed, depth of cut and tool edge radius on surface residual stress in the workpiece. And these influences are explained from the perspective of formation mechanism of residual stress in cutting. The conclusions have good applicability and can be used to guide the parameters selection in actual production.

关键词： residual stress analytical model strain plastic cutting parameter

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太阳电池填充因子随日照强度变化的理论分析与计算

丁金磊,程晓舫,翟载腾,查珺,茆美琴

《中国工程科学》 2007年第9卷第6期页码 82-87

摘要：

根据太阳电池直流模型和最大功率点数学条件，推出短路电流、开路电压、最大功率点电流和电压以及填充因子随日照强度变化的数学关系式；并选取２个电池分别计算出在不同日照强度下上述电池参数随日照强度的变化率。验证了短路电流和最大功率点电流是近似跟日照强度成正比，开路电压和最大功率点电压是近似跟日照强度的自然对数成正比。并提出了填充因子随日照强度的变化关系不具有简单的函数形式，而对不同的太阳电池其变化关系也迥异。最后用Multisim的模拟结果检验了理论分析计算的正确性。

关键词：太阳电池日照强度输出特性填充因子

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强度理论与实验现象

刘大斌,韩文坝,蔡冰清,韩晓东

《中国工程科学》 2007年第9卷第12期页码 44-52

摘要：用四大经典理论、莫尔强度理论和质点平衡强度理论的准则和强度条件，对单向拉压、二向拉压、纯扭转等已被认定的实验现象进行对比，对低、中碳钢重新做了纯扭转求最大屈服剪应力实验。发现质点平衡强度理论的符合率较高，13个实验中的有12个符合。尤其是拉伸—剪切使剪切破坏试验变得容易，压缩—剪切使剪切破坏试验变得困难的实验现象与质点平衡强度理论完全符合；莫尔强度理论也只有当拉伸和压缩极限强度不同时才能符合；其他强度理论都与此实验不符合。特别是当三向等应力拉伸（或压缩）时第三强度理论出现相当应力为零；三向等应力拉伸（或压

关键词：强度理论实验现象屈服现象应力状态

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以土体应力状态计算边坡安全系数的方法

王国体

《中国工程科学》 2006年第8卷第12期页码 80-84

摘要：

土坡的稳定分析一直是沿着条分法的思路发展的。由于对土体应力状态条件的忽视和条分法本身的缺陷，使得条分法得到的安全系数在工程中的应用面临激烈的挑战。土体不同条件下的应力状态表现为K₀效应和变化，它对坡体的安全度影响不可忽视。笔者以考虑土体应力状态为条件，应用土的库伦强度定律和摩尔-库伦准则，推导出平面土坡的安全系数计算公式，与条分法的安全系数对比结果说明这种方法具有概念明确、计算简便、定性可靠的重要特点，可以直接提供于工程应用和参考。

关键词：侧应力系数K₀ 初始应力状态稳定安全系数公式

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液力传动箱上箱体强度分析与优化

刘传峰,田爱琴

《中国工程科学》 2008年第10卷第5期页码 70-74

摘要：

计算机模拟模型分析法是机械设计开发的革命，运用有限元分析法可有效地规避设计风险和失误。对液力传动箱上箱体进行三维建模,提出了力学分析模型，将两个方案进行了有限元分析对比，指导设计方案的改进，提出最终解决方案，解决了设计难题。

关键词：液力传动箱力学模型有限元分析应力图静强度疲劳强度

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Parametric equations for notch stress concentration factors of rib–deck welds under bending loading

《结构与土木工程前沿（英文）》 2021年第15卷第3期页码 595-608 doi: 10.1007/s11709-021-0720-1

摘要： The effective notch stress approach for evaluating the fatigue strength of rib–deck welds requires notch stress concentration factors obtained from complex finite element analysis. To improve the efficiency of the approach, the notch stress concentration factors for three typical fatigue-cracking modes (i.e., root–toe, root–deck, and toe–deck cracking modes) were thoroughly investigated in this study. First, we developed a model for investigating the effective notch stress in rib–deck welds. Then, we performed a parametric analysis to investigate the effects of multiple geometric parameters of a rib–deck weld on the notch stress concentration factors. On this basis, the multiple linear stepwise regression analysis was performed to obtain the optimal regression functions for predicting the notch stress concentration factors. Finally, we employed the proposed formulas in a case study. The notch stress concentration factors estimated from the developed formulas show agree well with the finite element analysis results. The results of the case study demonstrate the feasibility and reliability of the proposed formulas. It also shows that the fatigue design curve of FAT225 seems to be conservative for evaluating the fatigue strength of rib–deck welds.

关键词： notch stress concentration factor rib–deck weld parametric analysis regression analysis parametric equation

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论混凝土坝的几个重要问题

朱伯芳

《中国工程科学》 2006年第8卷第7期页码 21-29

摘要：

目前我国在建混凝土坝的高度、数量、规模均居世界第一位，文章就混凝土坝技术的几个重要问题进行讨论：（1）结束“无坝不裂”历史的关键技术；（2）应用氧化镁混凝土筑坝的两种指导思想和两种实践结果；（3）混凝土强度等级应用于混凝土坝欠妥，坝工混凝土仍以采用混凝土标号为宜；（4）我国特高拱坝的抗压安全系数偏低，应适当提高。（5）拱坝有限元等效应力问题。

关键词：混凝土坝裂缝混凝土标号抗压安全系数有限元等效应力

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Influence of sprinkler irrigation droplet diameter, application intensity and specific power on flower

Yisheng ZHANG, Delan ZHU

《农业科学与工程前沿（英文）》 2017年第4卷第2期页码 165-171 doi: 10.15302/J-FASE-2017145

摘要： To determine the main parameters of droplet strike damage and avoid flower injury due to the unsuitable practices during sprinkler irrigation, an indoor experiment of irrigation droplet impact on cyclamen was conducted. The influences of different parameters such as droplet diameter, application intensity, specific power on flower strike damage was analyzed using Image Pro-Plus software to compute strike damage area and define damage level by sense-analysis. The results showed that a damage area of <1% represents a safe irrigation level, 1%–3% slight damage level, 3%–6% moderate damage level, and>6% heavy damage level. Equations of application intensity, specific power with sprinkler irrigation time and flower injury ratio were regressed against parameters which cause impact damages. The results indicated that specific power has a significant correlation with injury, and flower damage area increased as the increasing of the value of specific power for the same irrigation time. Application intensity was also correlated with injury when the droplet diameter was larger than 1 mm. When the duration of sprinkler irrigation was 1, 5 and 10 min, the threshold of impinging damage of application intensity was 25.30, 5.01 and 1.64 mm·h and the specific power was 0.467×10 , 9.340×10 and 3.110×10 W·m . These results provide a reference for determining the suitable values of sprinkler properties in operation design.

关键词： application intensity damage floriculture flowers specific power sprinkler irrigation

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Impact of inter-fuel substitution on energy intensity in Ghana

Boqiang LIN, Hermas ABUDU

《能源前沿（英文）》 2020年第14卷第1期页码 27-41 doi: 10.1007/s11708-019-0656-5

摘要： Energy intensity and elasticity, together with inter-fuel substitution are key issues in the current development stage of Ghana. Translog production and ridge regression are applied for studying these issues with a data range of 2000–2015. The current energy dynamics reveal the expected inverse relationship: higher energy intensity and lower elasticity with economic growth. There are evidences of energy-economic challenges: high energy cost, inefficiency and backfire rebound effect. The implications are higher energy losses in the system, more consumption of lower-quality energy together with low energy technology innovation. Energy is wasted and directly not productive with economic activities. It is observed further that the higher energy intensity invariably increases CO emission because approximately 95% of total energy is derived from hydrocarbons and biomass. An inter-fuel substitution future scenario design was further conducted and the results were positive with growth, lower energy intensity, and improved energy efficiency. Therefore, government and energy policymakers should improve energy efficiency, cost, and productiveness. That is, they should change energy compositions and augment energy technology innovation, thus, increasing renewable share to 15% by 2026, reducing wood and charcoal by about 69%, and increasing natural gas to about 776%. Energy policymakers should enhance the installation of smart energy, cloud energy solution, tokenization of energy system and storage.

关键词： energy intensity energy elasticity inter-fuel substitution prospects energy contribution Translog production approach ridge regression

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Dynamic mechanism for the decline of China’s energy intensity during the 11th FYP (Five-Year Plan)

Minghui LI

《能源前沿（英文）》 2011年第5卷第3期页码 237-249 doi: 10.1007/s11708-010-0130-x

摘要： From 2006 to 2009, the aggregate energy intensity of China fell by 14.38%, which means that China has made substantial progress towards its goal of achieving approximately a 20% reduction in energy intensity during the period of the 11th FYP (Five-Year Plan). This paper describes some new properties of the mechanism for the decrease in China’s energy intensity since the beginning of the 11th FYP. First, compared with the period of the 10th FYP, technical, structural, and residential energy-savings have been improved to a certain extent. Secondly, unlike the dynamic mechanism before 2000, technical energy savings have been the main driver of momentum since the beginning of the 11th FYP. Next, although structural energy savings are not the main factor, they are still a key factor for the decrease in energy intensity. Finally, residential energy savings are still a stable driver of momentum for the decline in China’s energy intensity.

关键词： energy intensity structural energy savings technical energy savings

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Efficiency of scalar and vector intensity measures for seismic slope displacements

Gang WANG

《结构与土木工程前沿（英文）》 2012年第6卷第1期页码 44-52 doi: 10.1007/s11709-012-0138-x

摘要： Ground motion intensity measures are usually used to predict the earthquake-induced displacements in earth dams, soil slopes and soil structures. In this study, the efficiency of various single ground motion intensity measures (scalar ) or a combination of them (vector ) are investigated using the PEER-NGA strong motion database and an equivalent-linear sliding-mass model. Although no single intensity measure is efficient enough for all slope conditions, the spectral acceleration at 1.5 times of the initial slope period and Arias intensity of the input motion are found to be the most efficient scalar for flexible slopes and stiff slopes respectively. Vector can incorporate different characteristics of the ground motion and thus significantly improve the efficiency over a wide range of slope conditions. Among various vector considered, the spectral accelerations at multiple spectral periods achieve high efficiency for a wide range of slope conditions. This study provides useful guidance to the development of more efficient empirical prediction models as well as the ground motion selection criteria for time domain analysis of seismic slope displacements.

关键词： seismic slope displacements intensity measures empirical prediction

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A family of non-conforming crack front elements of quadrilateral and triangular types for 3D crack problems using the boundary element method

Guizhong XIE, Fenglin ZHOU, Hao LI, Xiaoyu WEN, Fannian MENG

《机械工程前沿（英文）》 2019年第14卷第3期页码 332-341 doi: 10.1007/s11465-019-0540-3

摘要： This study focuses on establishing non-conforming crack front elements of quadrilateral and triangular types for 3D crack problems when the dual boundary element method is applied. The asymptotic behavior of the physical variables in the area near the crack front is fully considered in the construction of the shape function. In the developed quadrilateral and triangular crack front elements, the asymptotic term, which captures the asymptotic behavior of the physical variable, is multiplied directly by the conventional Lagrange shape function to form a new crack front shape function. Several benchmark numerical examples that consider penny-shaped cracks and straight-edge crack problems are presented to illustrate the validity and efficiency of the developed crack front elements.

关键词： Taylor expansion crack front elements stress intensity factors dual boundary element method