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991.
992.
Yun-Jae Kim 《Engineering Fracture Mechanics》2004,71(2):173-191
This paper presents experimental validation of two reference stress based methods for circumferential cracked pipes. One is the R6 method where the reference stress is defined by the plastic limit load. The other is the enhanced reference stress method, recently proposed by the authors, where the reference stress is defined by the optimised reference load. Using 38 published pipe test data, the predicted maximum instability loads according to both methods are compared with the experimental ones for pipes with circumferential through-thickness cracks and with part circumferential surface cracks. It is found that the R6 method gives conservative estimates of the maximum loads for all cases. Ratios of the experimental maximum load to the predicted load range from 0.54 to 0.98. On the other hand, the proposed method gives overall closer maximum loads than R6, compared to the experimental data. However, for part through-thickness surface cracks, the estimated loads were slightly non-conservative for four cases, and possible reasons are fully discussed. 相似文献
993.
994.
995.
周铣加工表面形貌仿真新算法 总被引:3,自引:0,他引:3
考虑主轴偏心,基于周铣过程中刀具切削刃上任意点与工件相对运动的轨迹方程和周铣过程几何特征,构造出可以求解周铣加工表面上任意一点形貌高度值的三维表面形貌仿真算法,并给出了相应的仿真算例。该算法无需对刀齿进行微段离散,并且不依赖于工件网格划分,加工表面上任意一点形貌高度值的计算次数等于刀具齿数,具有通用性好、运算速度快、结果准确度高的特点。 相似文献
996.
U. Kamachi Mudali H. S. Khatak Baldev Raj M. Uhlemann 《Materials and Manufacturing Processes》2004,19(1):61-73
It is well known that the addition of nitrogen to steels and stainless steels enhances the passivity and localized corrosion resistance, in addition to improving the mechanical properties. Selective alloying of surfaces of steels and stainless steels with nitrogen could also enhance the corrosion resistance and improve the mechanical properties without affecting the bulk properties. Techniques like ion implantation, laser alloying, nitriding, etc. can be effectively used to introduce very high levels of nitrogen. In addition, these techniques can also produce modified surfaces with novel microstructures to further improve the properties. The surface alloying methods also provide an opportunity to selectively nitrogenate the surface of finished components in order to obtain better properties. The review highlights the techniques, modifications and the properties obtained further. 相似文献
997.
Leonard J. Borucki Thomas Witelski Colin Please Peter R. Kramer Donald Schwendeman 《Journal of Engineering Mathematics》2004,50(1):1-24
Statistical models are presented to describe the evolution of the surface roughness of polishing pads during the pad-conditioning process in chemical-mechanical polishing. The models describe the evolution of the surface-height probability-density function of solid pads during fixed height or fixed cut-rate conditioning. An integral equation is derived for the effect of conditioning on a foamed pad in terms of a model for a solid pad. The models that combine wear and conditioning are then discussed for both solid and foamed pads. Models include the dependence of the surface roughness on the shape and density of the cutting tips used in the conditioner and on other operating parameters. Good agreement is found between the model, Monte Carlo simulations and with experimental data. 相似文献
998.
Maximum stress intensity factors of a surface crack usually appear at the deepest point of the crack, or a certain point along
crack front near the free surface depending on the aspect ratio of the crack. However, generally it has been difficult to
obtain smooth distributions of stress intensity factors along the crack front accurately due to the effect of corner point
singularity. It is known that the stress singularity at a corner point where the front of 3 D cracks intersect free surface
is depend on Poisson's ratio and different from the one of ordinary crack. In this paper, a singular integral equation method
is applied to calculate the stress intensity factor along crack front of a 3-D semi-elliptical surface crack in a semi-infinite
body under mixed mode loading. The body force method is used to formulate the problem as a system of singular integral equations
with singularities of the form r
−3 using the stress field induced by a force doublet in a semi-infinite body as fundamental solution. In the numerical calculation,
unknown body force densities are approximated by using fundamental density functions and polynomials. The results show that
the present method yields smooth variations of mixed modes stress intensity factors along the crack front accurately. Distributions
of stress intensity factors are indicated in tables and figures with varying the elliptical shape and Poisson's ratio. 相似文献
999.
Oxidation behaviour of the near α-titanium alloy IMI 834 was investigated over a range of temperatures, from 600–800°C, in
air. Specimens were solution-treated in the α + β and β phase fields for 1 h and 1/2 h, respectively and cooled in air to
room temperature. The solution treated samples were subjected to stabilization treatment at 700°C for 2 h, followed by cooling
in air. Oxidation behaviour of these samples was studied from 600–800°C in air, for 50 h. The morphology of the scales formed
was examined by SEM and the phases present in the scales were characterized by X-ray diffraction. While there was little oxidation
at 600°C, the rate of oxidation increased at higher temperatures. In general, the rate of oxidation was found to be more in
the α + β treated condition than that in the β treated one. The results are discussed in terms of the characteristics of the
oxide film formed under different conditions. 相似文献
1000.
A. P. Fröba L. Penedo Pellegrino A. Leipertz 《International Journal of Thermophysics》2004,25(5):1323-1337
Light scattering by thermally excited capillary waves on liquid surfaces or interfaces can be used for the investigation of viscoelastic properties of fluids. In this work, the simultaneous determination of surface tension and liquid kinematic viscosity of n-pentane by surface light scattering (SLS) on a gas–liquid interface was carried out. The experiments are based on a heterodyne detection scheme and signal analysis by photon correlation spectroscopy (PCS). Measurements were performed under saturation conditions over a wide temperature range from about 233 to 363 K. For the whole temperature range the total uncertainty of the liquid kinematic viscosity and surface tension is estimated to be better than 1.0 and 1.2, respectively. The results obtained corroborate the reliability of the SLS technique for the determination of thermophysical properties. 相似文献