共查询到12条相似文献,搜索用时 15 毫秒
1.
Grzegorz Robak 《Fatigue & Fracture of Engineering Materials & Structures》2020,43(9):2006-2023
The article discusses the problem related to estimating fatigue life of elements containing stress concentrators. The algorithm for estimating fatigue life presented in this work uses a fictitious ray based on the Neuber method. The proposed algorithm takes into account the variability of microstructural length, which depends on the number of failure cycles. The function thus obtained can be used to select the appropriate value for this length, which simplifies the calculation procedure needed to estimate fatigue life. In addition, this work includes an analysis of the impact of variable cutout geometry on the value of the support coefficient. As a result, it was possible to extend the application of this concept to lower fatigue life values and to structural elements with different notch geometries. The method was verified by performing experiments using elements made of three steel grades. A good correlation between calculation and experimental results was obtained. 相似文献
2.
C. Linder F. Armero 《International journal for numerical methods in engineering》2007,72(12):1391-1433
This paper presents new finite elements that incorporate strong discontinuities with linear interpolations of the displacement jumps for the modeling of failure in solids. The cases of interest are characterized by a localized cohesive law along a propagating discontinuity (e.g. a crack), with this propagation occurring in a general finite element mesh without remeshing. Plane problems are considered in the infinitesimal deformation range. The new elements are constructed by enhancing the strains of existing finite elements (including general displacement based, mixed, assumed and enhanced strain elements) with a series of strain modes that depend on the proper enhanced parameters local to the element. These strain modes are designed by identifying the strain fields to be captured exactly, including the rigid body motions of the two parts of a splitting element for a fully softened discontinuity, and the relative stretching of these parts for a linear tangential sliding of the discontinuity. This procedure accounts for the discrete kinematics of the underlying finite element and assures the lack of stress locking in general quadrilateral elements for linearly separating discontinuities, that is, spurious transfers of stresses through the discontinuity are avoided. The equations for the enhanced parameters are constructed by imposing the local equilibrium between the stresses in the bulk of the element and the tractions driving the aforementioned cohesive law, with the proper equilibrium operators to account for the linear kinematics of the discontinuity. Given the locality of all these considerations, the enhanced parameters can be eliminated by their static condensation at the element level, resulting in an efficient implementation of the resulting methods and involving minor modifications of an existing finite element code. A series of numerical tests and more general representative numerical simulations are presented to illustrate the performance of the new elements. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
3.
A numerical solution of the inverse problem of the gravitational field at a single point is obtained using six field elements
for a point, a spherical cap, a differential spherical sector and a vertical segment. In the system of six equations obtained,
the unknowns are the mass of the body, the depth of its center, and the second, third, and fourth degree moments. The accuracy
of the solution of this system is ten times higher than when using three field elements.
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Translated from Izmeritel’naya Tekhnika, No. 5, pp. 3–8, May, 2007. 相似文献
4.
不同脱乙酰度壳聚糖的制备及结构性能的研究 总被引:6,自引:0,他引:6
壳聚糖目前是天然可降解医用材料的研究热点,但因脱乙酰度(D.D.)为60%~80%的壳聚糖难于制备,国内外对不同脱乙酰度壳聚糖的生物相容性研究少见报导.探索了不同脱乙酰度壳聚糖的制备工艺及D.D.对壳聚糖结构和性能的影响,为进一步研究不同脱乙酰度壳聚糖降解产物对内皮细胞行为的影响做准备.方法:以高脱乙酰度壳聚糖为原料制备中、低脱乙酰度壳聚糖,用酸碱滴定法测定D.D.,粘度法测定分子量,傅利叶红外光谱和X射线衍射法分析晶体结构.结果:制备得到的壳聚糖D.D.分别为54%、61%、63%、70%、80%;D.D.降低使壳聚糖分子量增加,结晶度降低,水溶性和成膜性能改善.表明在乙酰化反应中控制均相条件和乙酸酐用量,能解决D.D.在60%~80%间的壳聚糖难制备的问题. 相似文献
5.
C. K. Lee R. E. Hobbs 《International journal for numerical methods in engineering》1997,40(24):4547-4576
A series of numerical tests is carried out employing some commonly used finite elements for the solution of 2-D elastostatic stress analysis problems with an automatic adaptive refinement procedure. Different kinds of elements including Lagrangian quadrilateral and triangular elements, serendipity quadrilaterals, incompatible elements and hybrid elements have been tested. It is found that for a general problem involving compressible material and when a moderate accuracy of the final solution is sought, the nine-node Lagrangian (L9) element will be the most effective element, while when an extremely accurate solution is needed, higher order Lagrangian quadrilaterals or triangles will be a suitable choice. However, if only linear elements are available, the well known 5βI linear hybrid element is the best choice. © 1997 John Wiley & Sons, Ltd. 相似文献
6.
隔膜电解体系内苯酚降解效果的研究 总被引:9,自引:0,他引:9
制备了碳、聚四氟乙烯质量比为4:1的C/PTFE气体扩散电极,并将其作为阴极与Ti/RuO2阳极构成电解槽,在阴阳极之间放置纯棉隔膜,在0.1mol/L Na2SO4溶液中电解20分钟,阴极室HO2-浓度为56mg/L.将隔膜电解槽应用于苯酚的电催化氧化,研究了阴、阳极协同作用电催化氧化降解水中苯酚的效果.实验结果表明,在电解反应初期,苯酚去除效率及COD和TOC的去除率随着电解时间的增加而增大,电解80分钟后,三者的变化趋势减缓,电解100分钟后,阴极室、阳极室苯酚的去除率分别为92%、97%;阴、阳极室COD去除率分别达到86%、70%;TOC去除率分别达到84%、68%.阴极室内,氧在阴极还原生成的碱性过氧化氢(HO2-)导致苯酚的矿化效果优于阳极的氧化作用. 相似文献
7.
We propose a procedure of regularization of the computational scheme used to find stresses and the strength index by the method of boundary elements, which enables one to perform the numerical analysis of bodies with thin coatings, including the cases of multilayer and composite coatings, and present the numerical results obtained for a cutting tool of VK6 hard alloy with TiN monocoating 6 m in thickness. 相似文献
8.
V. P. Legeza 《Strength of Materials》2005,37(2):214-224
We consider the dynamic behavior of a nonlinear vibroprotective system with roller damper of low-frequency oscillations. By using the Ritz averaging method, we deduce the equation of the amplitude-frequency characteristic of the nonlinear system. A new graphic method is proposed for the determination of the parameters of adjustment of the roller damper.__________Translated from Problemy Prochnosti, No. 2, pp. 136 – 150, March – April, 2005. 相似文献
9.
We consider the inverse problem of thermoelasticity for an isotropic medium containing a cavity of unknown shape and subjected
to the action of mechanical and thermal loads. Nonlinear equations are deduced for the geometric parameters of an ellipsoidal
equistressed cavity. Similar relations for mechanical loads obtained by the other authors follow from the constructed equations
as special cases. The numerical analysis is performed and the relationship between the values of the loads and the parameters
of the cavity is investigated. The stresses on the equistressed surface of the cavity are found and the influence of temperature
on the relationship between the parameters of loads and the geometric characteristics of the equistressed cavity is analyzed.
__________
Translated from Problemy Prochnosti, No. 1, pp. 121–131, January–February, 2007. 相似文献
10.
采用了十一醇为萃取剂,吡咯烷二硫代甲酸铵(APDC)为络合剂的分散液液微萃取浮动溶剂固化-石墨炉原子吸收光谱法(DLLME-SFO-GFAAS)测定水体样品中痕量金属离子的分析方法,对实验条件进行了优化,改进了传统萃取方法中试剂用量大、手续繁琐、易交叉感染等不足。同时对方法测量检出限及回收率进行试验,结果表明在优化的实验条件下铜、镉、铅的检出限分别0.03μg/L、0.03μg/L和0.01μg/L,加标回收率在95.3%--102.4%,方法准确、可靠。 相似文献
11.
Yu. G. Korobeinikov G. V. Trubacheev A. V. Fedorov 《Journal of Engineering Physics and Thermophysics》2009,82(1):65-68
The kinetics of convective drying (regeneration) of different types of adsorbents-dessicants with different geometric parameters
has been studied. It is shown that adsorbents of a “channel” (cellular) type have a long constant-rate stage of drying, whereas
a granulated polydisperse adsorbent is mainly dried at a variable rate. Adsorbents having a maximum water yielding capacity
have been revealed. It has been established that the velocity of a drying gas flow substantially influences the process of
moisture extraction from all types of adsorbents. In order to describe the kinetic curves of the given phenomenon, a model
of a relaxation kinetic equation that quite satisfactorily describes the kinetics of drying of the adsorbents studied was
used.
Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 82, No. 1, pp. 65–68, January–February, 2009. 相似文献
12.
Extending the Possibilities of Quantitative Determination of SIL – a Procedure Based on IEC 61508 and the Markov Model with Common Cause Failures
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Robert Pilch 《Quality and Reliability Engineering International》2017,33(2):337-346
Generalized equations for calculating the probability of failure on demand (PFD) in accordance with the IEC 61508 standard and a model based on Markov processes, taking into account common cause failures, are proposed in this paper. The solutions presented in the standard and in many references concentrate on simple k‐out‐of‐n architectures. The equations proposed in the standard concern cases for n ≤ 3. In safety‐related systems applied in industry, architectures of a number of elements n larger than three often occur. For this reason, a generalized equation for calculating PFD was proposed. For cases presented in the standard, the proposed equation provides identical results. The presented simplified Markov model allows the determination of the system availability (A(t)) and unavailability (1–A(t)) as well as their values in the steady state (A and 1–A). This model can be an alternative method of PDF calculations for various k‐out‐of‐n architectures with self‐diagnostic elements. Calculations performed according to the proposed models provide very similar results. The developed models are suitable for practical implementations in calculations of the safety integrity level. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献