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Fracture Mechanics on Aluminum Specimens 铝试样的断裂力学
Pub Date : 2021-01-01 DOI: 10.4236/wjm.2021.1112016
Juan Jose Mejia Briseno, Francisco Casanova-del-Angel
ASTM standards for A413 aluminum alloy specimen assays were used based on standard E399-05, with a minimum requirement of three specimens. Linear elastic fracture mechanic testing was carried out in plane strain conditions and fracture toughness of the tested aluminum, critical stress intensity factor was determined. Four specimens with the selected geometry were made, since in the pre-cracking process a non-acceptable propagation of crack may be present, i.e., the crack does not propagate in a parabolic manner. In like manner, the Type SE (B) specimen, that is, a beam subject to bending under a monotonic load, was used. Stress efforts were induced in the experiment, the load mode for such experiments is mode I, determining a temporary value of the K Q apparent stress intensity factor. When such value complies with the validity criteria of E-399 Standard, it becomes the stress intensity factor K IC of material.
A413铝合金试样测定的ASTM标准基于标准E399-05,最低要求为三个试样。在平面应变条件下进行了线弹性断裂力学试验,测定了被试铝的断裂韧性,确定了临界应力强度因子。由于在预裂过程中可能存在不可接受的裂纹扩展,即裂纹不以抛物线方式扩展,因此制作了四个具有选定几何形状的试样。以同样的方式,使用SE (B)型试件,即在单调荷载下弯曲的梁。在实验中诱导应力作用,该实验的加载模式为模式I,确定K Q表观应力强度因子的临时值。当该值符合E-399标准的有效性标准时,即为材料的应力强度因子kic。
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引用次数: 2
On the Orientation of Fractures with Transpressional and Transtensional Wrenches in Pre-Existing Faults 预存断层中具有压扭和张扭的裂缝走向
Pub Date : 2020-11-10 DOI: 10.4236/wjm.2020.1011014
Shuping Chen
The orientation of fractures with transpressional and transtensional wrenches in pre-existing faults has not been quantitatively determined. Based on Coulomb failure criterion and Byerlee’s frictional sliding criterion, this paper has indicated quantitative geometric relationships between the pre-existing fault and the local induced principal stress axes caused by the rejuvenation of the pre-existing fault. For a hidden pre-existing fault with some cohesion, the angles between the local induced principal stress axes and the pre-existing fault quantitatively vary with the applied stress and the cohesion coefficient, the ratio of the thickness of the cover layer to the thickness of the whole wrench body, whether transpressional or transtensional wrenches occur. For a surface pre-existing fault with zero cohesion, the angles between the pre-existing fault and the local induced principal stress axes are related to the rock inner frictional angle regardless of both the applied stress and the cohesion coefficient where transpressional wrenches occur, and the local induced maximum principal stress axis is identical with the applied maximum principal stress axis where transtensional wrenches occur. Therefore, the geometric relationships between the pre-existing faults and their related fractures are defined, because the local induced principal stress axes determine the directions of the related fractures. The results can be applied to pre-existing weak fabrics. They can help to understand and analyze wrench structures in outcrops or subsurface areas. They are of significance in petroleum exploration.
在已有的断层中,经扭扭和经扭扭的裂缝方向尚未定量确定。基于库仑破坏准则和Byerlee摩擦滑动准则,给出了既有断层与既有断层回春引起的局部诱发主应力轴之间的定量几何关系。对于具有一定内聚力的隐伏先存断层,无论是否发生横扭或张扭,局部诱发主应力轴与先存断层之间的夹角随外加应力和内聚力系数、覆盖层厚度与整个扳手体厚度之比而定量变化。对于零黏聚的地表先存在断层,无论施加应力和发生扭扭的黏聚系数如何,断层与局部诱发主应力轴的夹角与岩石内摩擦角有关,局部诱发最大主应力轴与发生扭扭的最大主应力轴相同。因此,由于局部诱导主应力轴决定了相关裂缝的方向,因此确定了已存在断层与其相关裂缝之间的几何关系。研究结果可以应用于已有的脆弱织物。它们可以帮助理解和分析露头或地下区域的扳手结构。它们在石油勘探中具有重要意义。
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引用次数: 3
Maximum Interval of Stability and Convergence of Solution of a Forced Mathieu’s Equation 一类强迫Mathieu方程解的稳定性和收敛性的最大区间
Pub Date : 2020-11-10 DOI: 10.4236/wjm.2020.1011015
E. Eze, U. E. Obasi, R. N. Ujumadu, Grace Ihuoma Kalu
This paper investigates the maximum interval of stability and convergence of solution of a forced Mathieu’s equation, using a combination of Frobenius method and Eigenvalue approach. The results indicated that the equilibrium point was found to be unstable and maximum bounds were found on the derivative of the restoring force showing sharp condition for the existence of periodic solution. Furthermore, the solution to Mathieu’s equation converges which extends and improves some results in literature.
结合Frobenius方法和特征值方法,研究了一类强迫Mathieu方程解的稳定性和收敛性的最大区间。结果表明,平衡点是不稳定的,恢复力导数存在最大边界,证明周期解存在的尖锐条件。此外,Mathieu方程解的收敛性推广和改进了文献中的一些结果。
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引用次数: 0
Collisions in Classical Mechanics in Terms of Mass-Momentum “Vectors” with Galilean Transformations 经典力学中质量-动量“矢量”与伽利略变换的碰撞
Pub Date : 2020-10-12 DOI: 10.4236/wjm.2020.1010011
A. Ogura
We present the usefulness of mass-momentum “vectors” to analyze the collision problems in classical mechanics for both one and two dimensions with Galilean transformations. The Galilean transformations connect the mass-momentum “vectors” in the center-of-mass and the laboratory systems. We show that just moving the two systems to and fro, we obtain the final states in the laboratory systems. This gives a simple way of obtaining them, in contrast with the usual way in which we have to solve the simultaneous equations. For one dimensional collision, the coefficient of restitution is introduced in the center-of-mass system. This clearly shows the meaning of the coefficient of restitution. For two dimensional collisions, we only discuss the elastic collision case. We also discuss the case of which the target particle is at rest before the collision. In addition to this, we discuss the case of which the two particles have the same masses.
我们提出了质量-动量“矢量”在一维和二维经典力学中用伽利略变换分析碰撞问题时的有用性。伽利略变换将质心和实验室系统中的质量-动量“矢量”连接起来。我们证明,只要来回移动两个系统,我们就能得到实验室系统的最终状态。与通常解联立方程的方法不同,这提供了一种简单的方法。对于一维碰撞,在质心系统中引入了恢复系数。这清楚地说明了恢复系数的含义。对于二维碰撞,我们只讨论弹性碰撞的情况。我们还讨论了目标粒子在碰撞前处于静止状态的情况。除此之外,我们还讨论了两个粒子具有相同质量的情况。
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引用次数: 1
A Simple Theory of Asymmetric Linear Elasticity 非对称线性弹性的一个简单理论
Pub Date : 2020-09-22 DOI: 10.4236/wjm.2020.1010012
Ze-hua Qiu
Rotation is antisymmetric and therefore is not a coherent element of the classical elastic theory, which is characterized by symmetry. A new theory of linear elasticity is developed from the concept of asymmetric strain, which is defined as the transpose of the deformation gradient tensor to involve rotation as well as symmetric strain. The new theory basically differs from the prevailing micropolar theory or couple stress theory in that it maintains the same basis as the classical theory of linear elasticity and does not need extra concepts, such as “microrotation” and “couple stresses”. The constitutive relation of the new theory, the three-parameter Hooke’s law, comes from the theorem about isotropic asymmetric linear elastic materials. Concise differential equations of translational motion are derived consequently giving the same velocity formula for P-wave and a different one for S-wave. Differential equations of rotational motion are derived with the introduction of spin, which has an intrinsic connection with rotation. According to the new theory, S-wave essentially has rotation as large as deviatoric strain and should be referred to as “shear wave” in the context of asymmetric strain. There are nine partial differential equations for the deformation harmony condition in the new theory; these are given with the first spatial differentiations of asymmetric strain. Formulas for rotation energy, in addition to those for (symmetric) strain energy, are derived to form a complete set of formulas for the total mechanical energy.
旋转是反对称的,因此不是以对称为特征的经典弹性理论的相干元素。从非对称应变的概念发展了一种新的线弹性理论,该理论被定义为变形梯度张量的转置,涉及旋转和对称应变。新理论与主流的微极理论或耦合应力理论的基本不同之处在于,它与经典的线弹性理论保持着相同的基础,不需要额外的概念,如“微旋转”和“耦合应力”。新理论的本构关系,即三参数胡克定律,来源于各向同性非对称线弹性材料的定理。导出了简明的平移运动微分方程,给出了相同的P波速度公式和不同的S波速度公式。引入自旋导出了旋转运动微分方程,自旋与旋转有着内在的联系。根据新理论,S波本质上具有与偏应变一样大的旋转,在不对称应变的情况下应被称为“剪切波”。在新理论中,变形协调条件有九个偏微分方程;这些是用非对称应变的第一次空间微分给出的。除了(对称)应变能的公式外,还导出了旋转能的公式,以形成一套完整的总机械能公式。
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引用次数: 4
Two Problems of Time Entering Respectively the Relativistic Mechanics and Electron Transport in Quantum Theory 时间分别进入的两个问题——量子理论中的相对论力学和电子输运
Pub Date : 2020-09-22 DOI: 10.4236/wjm.2020.1010013
S. Olszewski
In the relativistic mechanics, we calculate a minimal distance between the time scale of a one-dimensional motion having a larger velocity and the time scale of a similar motion with a lower velocity. Concerning the quantum theory, we demonstrate that mechanical parameters entering the electron motion in the Bohr hydrogen atom can provide us with a correct size of the time interval entering the Joule-Lenz law for the emission energy between two neighbouring quantum levels of the atom.
在相对论力学中,我们计算了具有较大速度的一维运动的时间尺度与具有较低速度的类似运动的时间标尺之间的最小距离。关于量子理论,我们证明了进入玻尔氢原子中电子运动的机械参数可以为我们提供进入焦耳-伦茨定律的时间间隔的正确大小,用于原子的两个相邻量子能级之间的发射能量。
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引用次数: 0
γ-Ray Irradiation Effect on MCF Rubber Solar Cells with both Photovoltaics and Sensing Involving Semiconductors Fabricated under Magnetic and Electric Fields 磁场和电场下制备的MCF橡胶太阳能电池的γ射线辐照效应
Pub Date : 2020-08-31 DOI: 10.4236/wjm.2020.108008
K. Shimada, Ryo Kato, Ryo Ikeda, H. Kikura, H. Takahashi
For cases in which a robot with installed solar cells and a sensor operates in a nuclear reactor building or in space for extravehicular activity, we require elastic and extensible solar cells. More than two different types of sensing are also required, minimally with photovoltaics and built-in electricity. Magnetic compound fluid (MCF) rubber solar cells are made of rubber, so they are elastic and extensible as well as sensitive. To achieve flexibility and an effective photovoltaic effect, MCF rubber solar cells must include both soluble and insoluble rubbers, Fe3O4, TiO2, Na2WO4∙2H2O, etc. On the basis of this constitution, we propose a consummate fabrication process for MCF rubber solar cells. The characteristics of these cells result from the semiconductor-like role of the molecules of TiO2, Fe3O4, Ni, Na2WO4∙2H2O, polydimethylsiloxane (PDMS), natural rubber (NR), oleic acid, polyvinyl alcohol (PVA), water and magnetic cluster involved in the MCF rubber. Their tendencies can be deduced by synthesizing knowledge about the enhancement of the reverse-bias saturation current IS and the diode ideality factor N, with conventional knowledge about the semiconductor affected by γ-irradiation and the attenuation of the photon energy of γ-rays.
对于安装了太阳能电池和传感器的机器人在核反应堆建筑或太空中进行舱外活动的情况,我们需要弹性和可扩展的太阳能电池。还需要两种以上不同类型的传感,最低限度地使用光伏和内置电力。磁性复合流体(MCF)橡胶太阳能电池是由橡胶制成的,因此它们具有弹性、可扩展性和敏感性。为了实现灵活性和有效的光伏效应,MCF橡胶太阳能电池必须包括可溶性和不可溶性橡胶、Fe3O4、TiO2、Na2WO4∙2H2O等。在此基础上,我们提出了一种完善的MCF橡胶太阳电池制造工艺。这些电池的特性是由TiO2、Fe3O4、Ni、Na2WO4∙2H2O、聚二甲基硅氧烷(PDMS)、天然橡胶(NR)、油酸、聚乙烯醇(PVA)、水和MCF橡胶中涉及的磁性团簇分子的半导体样作用产生的。它们的趋势可以通过综合关于反向偏置饱和电流IS和二极管理想因子N的增强的知识,以及关于受γ辐射影响的半导体和γ射线光子能量衰减的传统知识来推导。
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引用次数: 2
Star Formation in Self-Gravitating Molecular Cloud: The Critical Mass and the Core Accretion Rate 自引力分子云中的恒星形成:临界质量和核心吸积率
Pub Date : 2020-05-29 DOI: 10.4236/wjm.2020.105005
G. M. Kumssa, S. B. Tessema
Understanding how stars form in molecular clouds is one of the ongoing research areas in astrophysics. Star formation is the fundamental process to which our current understanding remains incomplete due to the complexity of the physics that drives their formation within molecular clouds. In this article theoretical modelling of the lowest possible mass of the cloud needed for collapse and the core accretion rate has been presented for the molecular cloud collapsing under its gravity. In many of previous studies the critical mass of star forming cloud under its gravity has been modelled using kinetic energy and gravitational potential energy. However, we test the effect of thermodynamic efficiency factor together with other physical processes in describing the critical mass, and controlling or triggering the rate of mass falling onto the central core. Assuming that, the ratio of radiation luminosity to gravitational energy released per unit time of the collapsing MC is less than unity. Following this conceptual framework we have formulated the critical mass and the core accretion rate of the self-gravitating molecular cloud.
了解恒星如何在分子云中形成是天体物理学正在进行的研究领域之一。恒星形成是一个基本过程,由于分子云中驱动恒星形成的物理复杂性,我们目前对这一过程的理解仍然不完整。在这篇文章中,已经提出了分子云在其重力作用下坍缩所需的云的最低可能质量和核心吸积率的理论模型。在之前的许多研究中,恒星形成云在其重力作用下的临界质量已经使用动能和引力势能进行了建模。然而,我们测试了热力学效率因子与其他物理过程在描述临界质量以及控制或触发质量落在中心核心上的速率方面的影响。假设,坍缩MC每单位时间释放的辐射光度与引力能之比小于1。根据这个概念框架,我们已经公式化了自引力分子云的临界质量和核心吸积率。
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引用次数: 1
Residual Stress Consideration in Fatigue Damage of Offshore Wind Turbine Monopiles: To Be or Not to Be? 海上风电单桩疲劳损伤的残余应力考虑:是还是不是?
Pub Date : 2020-04-22 DOI: 10.4236/wjm.2020.104004
A. A. Oyeniran, D. S. Aziaka
The purpose of this paper was to investigate the impact of residual stresses on fatigue damage of offshore wind turbine monopiles by numerical analysis approach using ABAQUS software, a finite element analysis (FEA) tool. Three monopile models with the same dimension (within standard range) have been developed in ABAQUS and partitioned circumferentially into equal rings. Longitudinal partitions have been rotated through 180° as obtainable in practice. Characteristic loads typical of a real life offshore wind turbine environment have been applied to all three models, with tensile and compressive residual stresses applied as additional loads at the critical weld region to the first and second models while the third model had no additional load. With zero boundary conditions applied in all six degrees of freedom, the simulation has been run for 107 cycles of wind and wave loads as recommended in standards in each case. Stress results obtained from the critical weld region in the three models showed that the presence of tensile residual stresses equal to the material yield stress contributed a maximum 0.05% to fatigue damage of the monopile when compared with results from the model with no residual stress while the presence of compressive residual stresses with the magnitude of the yield stress of the material caused a gain of 0.06% in fatigue life by similar comparison, indicating negligible contribution of residual stresses to the stress build up in the critical weld region, thus suggesting that the magnitude of the residual stress as high as the yield stress of the material of the monopile is not large enough to cause the monopile to open up in the axial direction.
利用有限元分析工具ABAQUS软件,采用数值分析方法研究了海上风电机组单桩的残余应力对疲劳损伤的影响。在ABAQUS中建立了三个相同尺寸(在标准范围内)的单桩模型,并将其按周划分为相等的环。在实践中,纵向隔板可以旋转180°。在这三种模型中都应用了实际海上风力涡轮机环境的典型特征载荷,在第一和第二种模型的关键焊接区域施加了拉伸和压缩残余应力作为附加载荷,而第三种模型没有附加载荷。在所有六个自由度均采用零边界条件的情况下,模拟运行了107个周期的风浪荷载,每种情况下均按标准建议进行。三种模型临界焊缝区域的应力结果表明,与不存在残余应力的模型结果相比,存在等于材料屈服应力的拉伸残余应力对单桩疲劳损伤的贡献最大为0.05%,而存在与材料屈服应力大小相当的压残余应力对单桩疲劳寿命的贡献最大为0.06%。表明残余应力对临界焊缝区域应力积累的贡献可以忽略不计,从而表明残余应力的大小与单桩材料的屈服应力一样高,不足以导致单桩在轴向打开。
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引用次数: 2
Analysis of the Behavior of a Square Plate in Free Vibration by FEM in Ansys Ansys有限元法分析方形板的自由振动特性
Pub Date : 2020-03-19 DOI: 10.4236/wjm.2020.102002
Pascal Kuate Nkounhawa, D. Ndapeu, B. Kenmeugne, T. Beda
In the realization of mechanical structures, achieving stability and balance is a problem commonly encountered by engineers in the field of civil engineering, mechanics, aeronautics, biomechanics and many others. The study of plate behavior is a very sensitive subject because it is part of the structural elements. The study of the dynamic behavior of free vibration structures is done by modal analysis in order to calculate natural frequencies and modal deformations. In this paper, we present the modal analysis of a thin rectangular plate simply supported. The analytical solution of the differential equation is obtained by applying the method of separating the variables. We are talking about the exact solution of the problem to the limit values. However, numerical methods such as the finite element method allow us to approximate these functions with greater accuracy. It is one of the most powerful computational methods for predicting dynamic response in a complex structure subject to arbitrary boundary conditions. The results obtained by MEF through Ansys 15.0 are then compared with those obtained by the analytical method.
在机械结构的实现中,实现稳定性和平衡是土木工程、力学、航空、生物力学等领域的工程师经常遇到的问题。板的行为研究是一个非常敏感的课题,因为它是结构元素的一部分。通过模态分析对自由振动结构的动力特性进行研究,以计算其固有频率和模态变形。本文对简支矩形薄板进行了模态分析。应用分离变量的方法得到了微分方程的解析解。我们讨论的是极限值问题的精确解。然而,诸如有限元法的数值方法允许我们以更高的精度近似这些函数。它是预测复杂结构在任意边界条件下的动力响应的最强大的计算方法之一。然后将MEF通过Ansys 15.0获得的结果与通过分析方法获得的结果进行比较。
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引用次数: 6
期刊
力学国际期刊(英文)
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