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在单试样卸载柔度法及三曲线法基础上 ,提出了一种更简便的测定金属材料 JR曲线及其条件起裂值的单试样三点柔度法 ,并用该方法测定了 1 Cr1 / 2 Mo钢、1 6Mn R钢和 WCF62钢的 JR曲线及其条件起裂值 ,与标准的多试样法相比 ,误差均在工程许可范围内 相似文献
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单试样三曲线法测定J积分阻力曲线及条件起裂值 总被引:1,自引:0,他引:1
用单试样三曲线法测定了16MnR 钢和某一焊缝金属的 J 积分阻力曲线及其条件起裂值,与标准的多试样测定结果基本吻合.实验表明,单试样三曲线的关联分析反映了带裂纹的三点弯曲试样的宏观断裂物理过程,裂纹的延性扩展符合幂函数规律. 相似文献
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COD阻力曲线的单试样三曲线分析法 总被引:1,自引:0,他引:1
在三曲线分析的基础上,提出了一种新的单试样测定 COD 阻力曲线的方法和步骤,编制了计算机应用程序。用三曲线法测定了 C—Mn 钢,Cr-Mo 钢和一种焊缝金属的 COD 阻力曲线,与标准的多试样法实验结果符合较好。该方法使用方便经济。有推广使用的价值。 相似文献
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在-196 ℃对S30408奥氏体不锈钢的母材和焊缝进行了夏比摆锤冲击实验,采用改进的柔度变化率法得到了低温下不锈钢母材夏比试样的起裂点。结果表明,采用改进的柔度变化率法得到的结果比采用传统的柔度变化率法得到的结果更准确。根据实验得到的载荷-位移曲线,结合采用Schindler法和关键曲线法各自所得结果的优点,得到了不锈钢母材的动态裂纹扩展阻力曲线(动态J-R曲线)。依据不锈钢焊缝在低温动载下的载荷-位移曲线及其断裂特征,通过线弹性断裂力学计算获得其动态断裂韧性。 相似文献
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动态弹塑性断裂韧性测试方法的比较研究 总被引:7,自引:0,他引:7
利用示波冲击试验,对动态弹塑性断裂韧性测试的不同方法(单试样法和多试样法)进行了研究.结果表明,单试样法(柔度变化率)测定材料的动态断裂韧性是一种简单、准确、适合于工程应用的好方法 相似文献
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本文提供了一种可以进行自增强处理的圆筒试样,通过实验用柔度法确定了该试样的表面裂纹的应力强度因子,介绍了含表面裂纹试样的柔度测试技术,导出了柔度与表面裂纹尖端前缘各点的应力强度因子的关系式,该式可作为各种含表面裂纹试样柔度法测表面裂纹 K_1因子的参考,本文还测定了不同自增强程度下,自增强圆筒的表面裂纹疲劳扩展规律。 相似文献
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一种弹塑性材料动态起裂韧度的J表征和测试方法 总被引:4,自引:0,他引:4
在数值计算的基础上提出了一个弹塑性材料动态起裂韧度的J表征和测试方法.这一方法利用自行研制的间接杆-杆型冲击拉伸试验装置,对周边切口的短圆柱试件实施基于一维试验原理的弹塑性材料动态断裂试验;利用试件两端的平均载荷—相对位移曲线(P-δ)或平均载荷-裂纹张开位移曲线(P-△),推广Bice远场公式获得动态J积分;采用柔度变化率法确定裂纹起裂点,从而得到动态起裂韧度JJD.这一方法的优点在于利用P-δ或P-△曲线将外力对试件所做的与裂纹运动无关的质心惯性运动动能近似地从总能量中分离出来,且平均载荷P在起裂前以至失稳扩展前是单调增的,同时试验获得的P-δ和P-△曲线光滑,这使得用J积分作为裂纹尖端的表征参量以及用柔度变化率法确定起裂点和失稳点具有坚实的物理基础. 相似文献
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40Cr材料动态起裂韧性KId()的实验测试 总被引:4,自引:0,他引:4
描述了利用Hopkinson压杆技术加载三点弯曲试样测试40Cr,材料动态起裂韧性KId()的试验方法。试样上的动态载荷历程由Hopkinson杆直接测得,并分别代入动态有限元程序及近似公式求得动态应力强度因子历史;由贴在试样裂尖附近的应变片确定起裂时间,最终确定起裂时的动态应力强度因子值,即动态起裂韧性KId()。试验结果表明:利用Hopkinson压杆技术加载三点弯曲试样测试材料动态起裂韧性的方法是可行的,起裂时,动态有限元的位移法、应力法及近似公式法求得的动态应力强度因子值比较吻合;在本文的载荷速率下,40Cr材料动态起裂韧性KId()与准静态裂韧性KId()相比,降低了约28%。 相似文献
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M. Shamsul Alam Md Emdadul Haque Md Bellal Hossain 《International Journal of Non》2007,42(8):1035-1045
Based on the classical harmonic balance method a new technique is presented to determine higher approximate periodic solutions of the non-linear differential equations. The new method is systematic and simple. The solution covers the general initial value problem (i.e., for while the existing solution is determined for a particular case, especially for . The solution is easily transformed to perturbation solution. The method is used in various non-linear problems possessing second and more than second derivatives. 相似文献
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A variable angle calibration technique for hot wire and hot film X-probes incorporating a new method of interpolation is described here along with measurements in a fully developed turbulent channel flow. Results based on the new method of calibration include the mean velocity profile, Reynolds stress, and probability density distributions for fluctuating velocity components u and and for the flow angle. Also skewness and flatness factors for u and are given. Measurement data were also evaluated using the conventional method. A comparison of both techniques shows that the new method does not yield appreciable differences in statistical flow analyses but is more accurate in measuring rare flow events associated with large flow angles. An extended version of the new method of calibration allowing three dimensional measurements in turbulent flow will be discussed. 相似文献
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The usual time domain Boundary Element Method (BEM) contains fundamentalsolutions which are convoluted with time-dependent boundary data andintegrated over the boundary surface. Here, a new approach for theevaluation of the convolution integrals, the so-called OperationalQuadrature Methods developed by Lubich, is presented. In thisformulation, the convolution integral is numerically approximated by aquadrature formula whose weights are determined using the Laplacetransform of the fundamental solution and a linear multisep method. Tostudy the behaviour of the method, the numerical convolution of afundamental solution with a unit step function is compared with theanalytical result. Then, a time domain Boundary Element formulationapplying the Operational Quadrature Methods is derived. For thisformulation only the fundamental solutions in Laplace domain arenecessary. The properties of the new formulation are studied with anumerical example. 相似文献
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IntroductionLet Yn beasequenceofi.i.d .randomvariablesonaprobabilityspace(Ω ,T ,P)andletSn =∑ni=1Yi.Bennett( 1 962 ) [1]andHoeffding ( 1 963) [2 ]respectivelystudysumsofindependentrandomvariablesandgiveimportantprobabilityinequalitiesundertheconditionwhichYi,1 ≤i≤narebound… 相似文献
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In this work, an enhanced treatment of the solid boundaries is proposed for smoothed particle hydrodynamics with implicit time integration scheme (Implicit SPH). Three types of virtual particles, i.e., boundary particles, image particles and mirror particles, are used to impose boundary conditions. Boundary particles are fixed on the solid boundary, and each boundary particle is associated with two fixed image particles inside the fluid domain and two fixed mirror particles outside the fluid domain. The image particles take the flow properties through fluid particles with moving least squares (MLS) interpolation and the properties of mirror particles can be obtained by the corresponding image particles. A repulsive force is also applied for boundary particles to prevent fluid particles from unphysical penetra- tion through solid boundaries. The new boundary treatment method has been validated with five numerical examples. All the numerical results show that Implicit SPH with this new boundary-treatment method can obtain accurate results for non-Newtonian fluids as well as Newtonian fluids, and this method is suitable for complex solid boundaries and can be easily extended to 3D problems. 相似文献
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Uncertainty in calculating vorticity from 2D velocity fields using circulation and least-squares approaches 总被引:1,自引:0,他引:1
The most common method for determining vorticity from planar velocity information is the circulation method. Its performance has been evaluated using a plane of velocity data obtained from a direct numerical simulation (DNS) of a three dimensional plane shear layer. Both the ability to reproduce the vorticity from the exact velocity field and one perturbed by a 5% random uncertainty were assessed. To minimize the sensitivity to velocity uncertainties, a new method was developed using a least-squares approach. The local velocity data is fit to a model velocity field consisting of uniform translation, rigid rotation, a point source, and plane shear. The least-squares method was evaluated in the same manner as the circulation method. The largest differences between the actual and calculated vorticity fields were due to the filter-like nature of the methods. The new method is less sensitive to experimental uncertainty. However the circulation method proved to be slightly better at reproducing the DNS field.The least-squares method provides additional information beyond the circulation method results. Using the correlation
and a vorticity threshold criteria to identify regions of rigid rotation (or eddies), the rigid rotation component of the least-squares method indicates these same regions.The authors thank Dr. Michael Rogers of NASA Ames Research Center for supplying the DNS fields. In addition, Professor Ellen Longmire at the University of Minnesota asked how else might one calculate vorticity other than the circulation method and prompted this investigation. 相似文献
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Interval finite difference method for steady-state temperature field prediction with interval parameters 总被引:1,自引:0,他引:1
A new numerical technique named interval finite difference method is proposed for the steady-state temperature field prediction with uncertainties in both physical parameters and boundary conditions. Interval variables are used to quantitatively describe the uncertain parameters with limited information. Based on different Taylor and Neumann series, two kinds of parameter perturbation methods are presented to approximately yield the ranges of the uncertain temperature field. By comparing the results with traditional Monte Carlo simulation, a numerical example is given to demonstrate the feasibility and effectiveness of the proposed method for solving steady-state heat conduction problem with uncertain-but-bounded parameters. 相似文献
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Towards a new partially integrated transport model for coarse grid and unsteady turbulent flow simulations 总被引:1,自引:0,他引:1
A new two-equation model is proposed for large eddy simulations (LESs) using coarse grids. The modeled transport equations are obtained from a direct transposition of well-known statistical models by using multiscale spectrum splitting given by the filtering operation applied to the Navier–Stokes equations. The model formulation is compatible with the two extreme limits that are on one hand a direct numerical simulation and on the other hand a full statistical modeling. The characteristic length scale of subgrid turbulence is no longer given by the spatial discretization step size, but by the use of a dissipation equation. The proposed method is applied to a transposition of the well-known k- statistical model, but the same method can be developed for more advanced closures. This approach is intended to contribute to non-zonal hybrid models that bridge Reynolds-averaged Navier–Stokes (RANS) and LES, by using a continuous change rather than matching zones. The main novelty in the model is the derivation of a new equation for LES that is formally consistent with RANS when the filter width is very large. This approach is dedicated to applications to non-equilibrium turbulence and coarse grid simulations. An illustration is made of large eddy simulations of turbulence submitted to periodic forcing. The model is also an alternative approach to hybrid models. PACS 47.27.Eq 相似文献
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This paper continues the discussions to a class of method for solving problems with random boundary notches and/or cracks in references by C. Ouyang in [1] (See also [2] and [3]). Using the basic method given in this reference as well as some further developments. We develop here a new effective computational method for solving random deep boundary notches and/or cracks. The actual numerical computations given in this paper show that the present method is quite workable and the results obtained have enlarged the contents of Handbook of Stress Intensity Factors given by G. C. Sih.Project supported by the Science Funds of Chinese Academy of Sciences. 相似文献