共查询到20条相似文献,搜索用时 15 毫秒
1.
We consider the process of deformation and fracture of an oval ring modeling the behavior of a long cylindrical shell subjected to distributed external pressure. The shell deformation is studied in both the presence and absence of an aggressive medium. The hypothesis of nonlinear viscosity with a singular component is taken for the constitutive relation used to estimate the metal characteristics. This relation allows for the difference between the tensile and compression strength of the material. The singularity permits taking into account not only the nonlinear viscosity but also instantaneous fracture characteristics. We show that an aggressive medium can substantially decrease the shell operation life. 相似文献
2.
The contour method is applied in an innovative manner to measure the distribution of hoop residual stress in a large martensitic-ferritic steel pipe containing a multi-pass girth weld. First, a novel one-step wire electro-discharge machining cut is conducted to divide the pipe lengthways into two halves. The deformation of the cut halves is then measured and analysed in a way that simultaneously gives maps of hoop stress across the wall thickness on both sides of the pipe and automatically accounts for through-thickness hoop bending effects and how they may vary along the pipe. Finally the contour method results are combined with X-ray diffraction residual stress measurements using the principle of superposition to determine the distribution of the axial and radial residual stresses in the pipe. It is thereby demonstrated how the distribution of three direct components of the residual stress tensor in a welded pipe can be readily determined using a “hybrid” contour measurement approach. 相似文献
3.
腐蚀管道的剩余强度计算方法研究 总被引:7,自引:0,他引:7
对目前国内外常用规范进行归纳和总结,得到5种常用方法:ASME-B31G, DM方法,
Wes-2805-97, CVDA-84和$J$积分方法. 本文将BP神经网络和遗传算法相结合,得到一种新
的神经网络,并将这种神经网络成功用于计算腐蚀管道的剩余强度和最大允许注水压力. 通
过示例分析,对7种常用规范和本文提出的改进的遗传神经网络方法进行了比较,得到下面
结论:不同计算方法计算得到的剩余强度和最大允许注水压力相差较大,Wes-2805-97规范、
ASME-B31G规范、CVDA-84规范等都比J积分方法计算得到的剩余强度和最大允许注水压力
偏大、偏保守;DM断裂力学方法计算得到的剩余强度和最大允许注水压力比J积分偏小、
偏危险;J积分方法和基于J积分方法的改进的遗传神经网络方法计算结果比较接近,比较
适中,可以认为是计算剩余强度和最大允许注水压力较好的方法. 相似文献
4.
In the present paper, the problem of propagation of collapsing cylindrical shock wave in an ideal gas permeated by a transverse magnetic field with infinite electrical conductivity is investigated. Here it is assumed that the medium ahead of the shock front is uniform and at rest. Also, its counter pressure concerning the motion of the wave front is neglected. This problem admits a self similar solution of second kind. The similarity exponent has been computed by solving a nonlinear eigenvalue problem and integrating numerically the self-similar equations for various values of adiabatic heat exponent and Cowling number. Numerical computations have been performed to determine the flow field behind the shock wave. The influence of magnetic field strength and adiabatic heat exponent on the flow parameters for various cases is presented. 相似文献
5.
The evolution and the steady-state structure of gasdynamic disturbances in a thermodynamically nonequilibrium gas are investigated both analytically and numerically. It is shown that in a medium with negative viscosity steady-state structures different from those in an equilibrium medium can exist. The conditions of existence of stationary shock waves with a discontinuous front and a smooth increase or decrease in the amplitude behind the front, waves with an oscillatory structure, and a stationary self-wave pulse with a power-law trailing front are determined.Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 5, 2004, pp. 181–191. Original Russian Text Copyright © 2004 by Makaryan and Molevich. 相似文献
6.
The paper addresses a fracture problem for an orthotropic cracked plate made of a material with different tensile and compressive
strengths and subjected to biaxial loading. The problem is solved using a micromechanical fracture model proposed earlier
by the authors. It is assumed that the fracture of the material in the fracture process zones at the crack front is described
by the Gol’denblat–Kopnov failure criterion. Strength curves for an orthotropic cracked plate with different strength and
fracture-toughness parameters are plotted 相似文献
7.
V. E. Dontsov V. E. Nakoryakov A. A. Chernov 《Journal of Applied Mechanics and Technical Physics》2007,48(3):346-360
The evolution of a shock wave and its reflection from a wall in a gas-liquid medium with dissolution and hydration are experimentally
investigated. Dissolution and hydration behind the front of a moderate-amplitude shock wave are demonstrated to be caused
by fragmentation of gas bubbles, resulting in a drastic increase in the area of the interphase surface and in a decrease in
size of gas inclusions. The mechanisms of hydration behind the wave front are examined. Hydration behind the front of a shock
wave with a stepwise profile is theoretically analyzed.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 3, pp. 58–75, May–June, 2007. 相似文献
8.
Mihaela Popescu 《Acta Mechanica Sinica》2009,25(3):311-318
This paper presents a computational model for the fluid dynamics in a fractured ductile pipe under high pressure. The pressure profile in front of the crack tip, which is the driving source of crack propagation, is computed using a nonlinear wave equation. The solution is coupled with a one dimensional choked flow analysis behind the crack. The simulation utilizes a high order optimized prefactored compact-finite volume method in space, and low dispersion and dissipation Runge-Kutta in time. As the pipe fractures the rapid depressurization take place inside the pipe and the propagation of the crack-induced waves strongly influences the outflow dynamics. Consistent with the experimental observation, the model predicts the expansion wave inside the pipe, and the reflection and outflow of the wave. The model also helps characterize the propagation of the crack dynamics and fluid flows around the tip of the crack. 相似文献
9.
This paper analyzes the effect of the time-dependent shape of a load pulse on the spall strength of materials. Within the framework of a classical one-dimensional scheme, triangular pulses with signal rise and decay portions and with no signal rise portions considered. Calculation results for the threshold characteristics of fracture for rail steel are given. The possibility of optimization of fracture by selecting a loading time with the use of an introduced characteristic of dynamic strength (pulse fracture capacity) is demonstrated. The study is carried out using a structure–time fracture criterion. 相似文献
10.
We obtain analytical approximations to the probability distribution of the fracture strengths of notched one-dimensional rods and two-dimensional plates in which the stiffness (Young’s modulus) and strength (failure strain) of the material vary as jointly lognormal random fields. The fracture strength of the specimen is measured by the elongation, load, and toughness at two critical stages: when fracture initiates at the notch tip and, in the 2D case, when fracture propagates through the entire specimen. This is an extension of a previous study on the elastic and fracture properties of systems with random Young’s modulus and deterministic material strength (Dimas et al., 2015a). For 1D rods our approach is analytical and builds upon the ANOVA decomposition technique of (Dimas et al., 2015b). In 2D we use a semi-analytical model to derive the fracture initiation strengths and regressions fitted to simulation data for the effect of crack arrest during fracture propagation. Results are validated through Monte Carlo simulation. Randomness of the material strength affects in various ways the mean and median values of the initial strengths, their log-variances, and log-correlations. Under low spatial correlation, material strength variability can significantly increase the effect of crack arrest, causing ultimate failure to be a more predictable and less brittle failure mode than fracture initiation. These insights could be used to guide design of more fracture resistant composites, and add to the design features that enhance material performance. 相似文献
11.
制作高强钢特征试件,在压、弯应力共同作用下进行疲劳断裂试验;结合疲劳辉纹产生机理,采用降载勾线法在试件断面制造出“海滩状花纹”;利用CAD软件描绘断面形貌并测量裂纹长度,用Newman-Raju理论进一步研究表面裂纹扩展的规律,并与试验值比较.结果表明降载勾线法可以解决高强度钢表面裂纹不易测量及断面难以观测到疲劳辉纹的问题;采用Newman-Raju公式模拟压弯组合应力下表面裂纹扩展形貌是合适的,但由此计算的疲劳寿命偏于保守.另外,当压弯应力比值较小时,计算扩展形貌时压应力可以忽略,而计算疲劳寿命时压应力不可忽略. 相似文献
12.
Numerical simulation of hydraulic fracture crack propagation 总被引:1,自引:0,他引:1
The plane problem of crack motion in an elastic medium under the pressure of a viscous fluid is considered. Under the condition of a constant fluid flow rate, the fluid is injected at the center of the crack. Contrary to other formulations of the problem, this paper attempts to take into account a possible fluid lag behind the crack tip. The resulting numerical solution is compared with a semianalytic one. It is found that the proposed numerical model can be used to predict the characteristics of a hydraulic fracture crack formed in a medium of a prescribed strength. 相似文献
13.
A. M. Lokoshchenko V. V. Nazarov 《Journal of Applied Mechanics and Technical Physics》2007,48(4):542-546
The problem of the long-term strength of an extended thick-walled tube containing a corrosive medium in the internal cavity
is solved. The diffusion of this medium into the tube material is analyzed. The diffusion equation is solved approximately
by introducing the diffusion front, and the error of the solution is estimated. The dependence of the time of fracture of
the tube on the variable tensile stress and the concentration of the medium filling the cavity is obtained.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 4, pp. 88–93, July–August, 2007. 相似文献
14.
The residual strength of a cracked unidirectional fiver reinforced metal matrix composite is studied. We propose a bridging model based on the Dugdale strip yielding zones in the matrix ahead of the crack tips that accounts for ductile deformations of the matrix and fiber debonding and pull-out in the strip yielding zone. The bridging model is used to study the fracture of an anisotropic material and its residual strength is calculated numerically. The predicted results for a SiC/titanium composite agree well with the existing experimental data. It is found that a higher fiber bridging stress and a larger fiber pull-out length significantly contribute to the composite's residual strength. The composite's strength may be more notch-insensitive than the corresponding matrix material's strength depending on several factors such as fiber-matrix interface properties and the ratio of the matrix modulus to an ‘effective modulus’ of the composite. 相似文献
15.
针对管道试件规格不同所要求的焊接工艺不一致问题,讨论P91钢中厚壁管对接接头所要求的双人对称焊形式下的焊接残余应力分布规律.基于ANSYS分析软件,以双移动高斯热源结合单元生死技术,利用顺序耦合方法得到P91钢中厚壁管焊接残余应力.讨论热处理工艺对于P91钢中厚壁管焊接残余应力的影响.结果表明,由于焊接工艺在环向位置上的结构反对称性使得焊接残余应力在环向上呈反对称分布;即便经过较高温度的预热处理,没有焊后热处理时最大等效应力仍超过屈服极限;进行焊后整体热处理的P91钢中厚壁管焊接残余应力得到了有效的改善,平均应力数值下降了60%~70%. 相似文献
16.
17.
18.
This work presents experimental observations of the characteristic fracture process of tempered glass. Square specimens with
a side length of 300 mm, various thicknesses and a residual stress state characterized by photoelastic measurements were used.
Fracture was initiated using a 2.5 mm diamond drill and the fragmentation process was captured using High-Speed digital cameras.
From the images, the average speed of the fracture front propagation was determined within an accuracy of 1.0%. Two characteristic
fragments were found to form on each side of the initiation point and are named “Whirl-fragments” referring to the way they are generated. An earlier estimation of the in-plane shape of the fracture front is corrected and
a hypothesis on the development for the fracture front is offered. The hypothesis is supported by investigations of the fragments
using a Scanning Electron Microscope (SEM) which also revealed a micro scale crack bridging effect. 相似文献
19.
We present results of high-pressure micromodel visualizations of pore-scale fluid distribution and displacement mechanisms
during the recovery of residual oil by near-miscible hydrocarbon gas and SWAG (simultaneous water and gas) injection under
conditions of very low gas–oil IFT (interfacial tension), negligible gravity forces and water-wet porous medium. We demonstrate
that a significant amount of residual oil left behind after waterflooding can be recovered by both near-miscible gas and SWAG
injection. In particular, we show that in both processes, the recovery of the contacted residual oil continues behind the
main gas front and ultimately all of the oil that can be contacted by the gas will be recovered. This oil is recovered by
a microscopic mechanism, which is strongly linked to the low IFT between the oil and gas and to the perfect spreading of the
oil over water, both of which occur as the critical point of the gas–oil system is approached. Ultimate oil recovery by near-miscible
SWAG injection was as high as near-miscible gas injection with SWAG injection using much less gas compared to gas injection.
Comparison of the results of SWAG experiments with two different gas fractional flow values (SWAG ratio) of 0.5 and 0.2 shows
that fractional flow of the near-miscible gas injected simultaneously with water is not a crucial factor for ultimate oil
recovery. This makes SWAG injection an attractive IOR (improved oil recovery) process especially for reservoirs, where continuous
and high-rate gas injection is not possible (e.g. due to supply constraint). 相似文献