300MW锅炉汽包接管角焊缝缺陷安全评定

运用我国“压力容器缺陷评定规范”CVDA-1984及英国“Guide on methods for assessing the acceptability of flaws in metallic structures”BS7910-1999,对300MW锅炉汽包接管缺陷安全性进行评定。汽包接管缺陷评定所需的汽包各运行工况温度场、应力场,通过有限元计算获得。评定结果表明：在设计工况下的30年服役期内,该锅炉汽包接管现有缺陷不会引发一次性脆性断裂,汽包现有缺陷扩展不会对安全运行构成威胁,汽包现有缺陷可不进行返修处理而继续安全运行。     

Modelling the wetting of a solid occlusion by a liquid film

We investigate in this work how the presence of an occlusion affects the dynamics of the wetting front of a liquid film draining down a vertical surface. This numerical study is developed in the context of the lubrication approximation. Through a parametric study, we show that depending on the asymptotic film thickness and the fluid properties, there exists a critical substrate contact angle below which separation of the contact line from the occlusion wall is observed which results in the appearance of a dry zone in the wake of the occlusion. In analogy with external aerodynamics, we also show that a sharp corner in the occlusion can induce this contact line separation. Our numerical results also highlight the importance of the occlusion wettability on the morphology of the wetting front suggesting a possible mechanism to control and mitigate the often undesirable fingering instability.     

Chain rupture and tensile deformation of polyamide 6 fibers

Summary The tensile deformation of polyamide 6 fibers gives rise to irreversible changes of its tensile properties, which apparently arise from chain rupture. This molecular failure process is usually analyzed by means of the ESR-spectroscopy. The number of ruptured chains, as obtained by this method, is, however, much too small to account for the changes of the tensile properties and for the observed strong decrease of the average molecular weight. Based on studies on energy dissipation, on structural as well on spectroscopical investigations we come to the conclusion that chain rupture is mainly responsible for the irreversible changes of the tensile properties. The dissipation of energy can be accounted for in terms of the energy release on chain rupture and energetic interactions with neighboring segments, in agreement with the data on the molecular weight decrease. The spectroscopically determined number of ruptured chains is governed by a fast recombination of the free radicals.

---

Zusammenfassung Eine Deformation von Polyamid 6 Fasern führt zu irreversiblen Veränderungen in den mechanischen Eigenschaften, die offensichtlich durch Kettenbrüche verursacht werden. Dieser molekulare Versagensprozeß wird gewöhnlich mittels der ESR-Spektroskopie analysiert. Die hierdurch erhaltene Anzahl an Kettenbrüchen ist jedoch viel zu gering, um sowohl die Veränderungen in den mechanischen Eigenschaften als auch die starke Abnahme des mittleren Molekulargewichtes erklären zu können. Auf der Grundlage unserer Untersuchungen zur Energiedissipation, aus Streuexperimenten und spektroskopischen Untersuchungen kommen wir zu dem Schluß, daß Kettenbrüche für die Veränderungen der Eigenschaften allein verantwortlich sind. Die Energiedissipation läßt sich vollständig auf die Energiefreisetzung beim Kettenbruch und energetische Wechselwirkungen mit umgebenden Segmenten zurückführen, in Einklang mit den Ergebnissen zur Molekulargewichtserniedrigung. Die spektroskopisch bestimmte Anzahl an Kettenbrüchen wird durch eine schnelle Rekombination der freien Radikale beeinträchtigt.

     

Surfactant accumulation within the top foam layer due to rupture of external foam films

The analysis of processes taking place in a steady pneumatic (dynamic) foam shows the possibility of different modes of surfactant accumulation within the top layers of bubbles due to rupture of external foam films. An increasing surfactant concentration within the top layers promotes the stabilisation of bubbles and the foam as a whole. Considering the balance of surfactant and water during the bursting of films it is possible to estimate the accumulated surfactant loss caused by a downwards flow through the Plateau borders of the subsurface bubble layer. This effect depends on the particular conditions, especially on the surfactant activity and concentration of the surfactant, water volume fraction in the foam and size of foam bubbles. The process of surfactant accumulation in the top foam bubble layer can be complicated due to the removal of part of the accumulated surfactant through transport with droplets spread out during bubble bursting.     

Diaphragm rupture. Impingement by a conically-nosed, ram-accelerator projectile

The effect of diaphragm rupture by a conically-nosed projectile on the gasdynamics related to ram accelerator operation was experimentally and numerically studied. The experiments were conducted using a 25-mm-bore ram accelerator. Either air or nitrogen was used as the test gas. Using a high-speed image converter camera, it was observed that during the process of the diaphragm rupture a region with strong radiation developed between the diaphragm and the approaching projectile/sabot. This radiating region corresponds to the shock-heated gas which is originated from a precursory shock wave driven by the accelerating projectile/sabot. The flow around the projectile upon entering the test section by rupturing the diaphragm was visualized by holographic interferometry. During the diaphragm rupture, the system of oblique shock waves around the conical nose of the projectile was seen undisturbed on the downstream side of the diaphragm. Under the same condition as the experiment, numerical simulation was conducted using GRP (Generalized Riemann Problem) scheme which was extended to the computation of compressible flow fields bounded by moving surfaces. Two diaphragm rupture models were examined: (1) the diaphragm deformed by wrapping tightly around the moving projectile; (2) the diaphragm was ruptured instantly at the moment the projectile touched the diaphragm. Comparing these models with the experimentally visualized flow, the former was found to express the diaphragm rupture process much better than the latter. Received 9 February 1998 / Accepted 9 September 1998     

Three‐point bending tests. Part II: An improved formula for the modulus of rupture and numerical simulations

The goal of this paper is to analyze analytical and numerically, from several perspectives, the modulus of rupture (MOR) for brittle materials, studying the bending test of three points which is normally used in laboratory to calculate it. In particular, we will give four different approaches to the MOR: through the classical theory of beams; by means of the one‐ and three‐dimensional numerical simulations; and by using an improved expression to the MOR obtained through its asymptotic analysis. Finally, we will present these methodologies for cylindrical and rectangular beams made of porcelain. Copyright © 2011 John Wiley & Sons, Ltd.     

Point defect generation,nano-void formation and growth. II. Criterion for ductile failure

Using the derived relation for point defect generation according to a new constitutive relation, the notion of nano-void formation at grown-in nano-particles is examined and its consequences deduced as the nano-voids grow in size with continued deformation. Assuming that void growth is due only to point defect accumulation, the analysis of fracture strains in tension of natural-aged AA6111 suggests that coalescence by micro-plastic activity occurs when the void diameter becomes about one third of the evolving inter-void spacing. Hence, the derived limit strain to incipient void-coalescence is inversely proportional to the square root of point defect generation as determined from the stress–strain data. Using this criterion, failure prediction maps can be constructed for strain modes of plane-strain and balanced bi-axial to result in the outer bounds of the forming limit diagram. Trial examinations with AA5754 and AA3003 show great promise.     

网络结构的边毁裂度

在毁裂度的基础上,研究图的边的毁裂度.通过优化组合、归纳假设的方法界定了图的边毁裂度的值,如笛卡尔积图:Pm×Pn,Pm×Cn,Cm×Cn,Km×Kn,并界定了G=G1×G2的边毁裂度的界.最后给出了一些基本图,如路、圈、星图、完全二部图Km,n的线图边毁裂度.     

An improved nonlocal Gurson model for plastic porous solids,with an application to the simulation of ductile rupture tests

In recent work, the author and co-workers have developed a new methodology to delocalize the damage in Gurson model for porous ductile materials. The motivation was to rectify the difficulties connected to the excessive damage smoothing arising in the practical use of the original damage delocalization method. The new approach consists of delocalizing the logarithm of the damage instead of the damage itself. The relevance of the new method to avoid mesh size effects and satisfactorily reproduce typical ductile fracture experiments are explored in this work.