SCT试样断裂试验研究

通过对由标准ＣＴ试样发展而来的异形紧凑拉伸（ＳＣＴ）试样的应变测试和断裂试验,证明ＳＣＴ试样能够很好地再现压力容器接管等高应变梯度区的主要特征。其试验结果与实物容器实测结果非常接近,并给出了推荐的高应变区裂纹张开位移（ＣＯＤ）估算式。     

当代合成氨技术的现状及其发展方向

本文前五部分分别发表在本刊1994（3），1995（2），1996（2）（4）及1997（2）期（续五）图29乌达双容器合成塔系统托普索200系列和凯洛格卧式合成塔均系用在一个容器内设置二段以下。今天，优质合金的广泛使用已经使得合成塔受压壳体在400C下操作成为可能，就像耐尔森（Nelson）流程中那样。以布朗合成塔为例，其第二个塔是在人口气体400C且氨浓度为10％下与壳体直接接触。需要特别指出的是焊接方面，即要注意予热质量和焊后热处理，以避免产生裂纹，因为在这种操作条件下曾发生过几次这类事故。卡萨里制氮公司（AmmoniaCasale）的ACA…     

超期服役加氢反应器内壁裂纹原因分析及修复

通过对柴油加氢反应器内壁裂纹的分析,找出反应器内壁产生裂纹的原因,并制定了裂纹修补方案,提出了容器运行中的注意事项。     

带裂纹压力容器的可靠性分析

众所周知 ,按常规设计方法认为是安全的压力容器 ,有时会发生意外的断裂事故 ,其原因在于以材料力学为基础的常规设计方法中 ,假设材料是各向同性的均匀介质 ,而实际上材料的组织并非均匀 ,也非各向同性 ,且有裂纹等缺陷存在。根据统计数字表明 ,容器发生事故的原因大多数由于裂纹所引起 ,这些裂纹在一条件下迅速开裂扩展 ,甚至造成灾难性事故。这是容器发生低应力破坏的根本原因。本文以线弹性断裂力学为基础 ,考虑容器中裂纹的影响 ,利用可靠性分析方法 ,对带裂纹的压力容器的可靠度进行分析讨论 ,从而可了解其可靠程度的大小 ,为带裂纹的…     

在关卧式容器的容积计量问题

化工生产中容器的计量问题是一个既重要又繁琐的问题,可将其划分为两大类：第一类是容器的横截面积Ｓ不随容器高度ｈ发生变化;第二类假设截面积Ｓ为不定值,随着高度ｈ而发生变化,即Ｓ＝Ｆ（ｈ）。例如卧式容器即如是。１　体积计算卧式容器容积Ｖ与高度变化规律为Ｖ＝Φ（ｈ）。如图１所示建立直角坐标系。图１　卧式容器侧视直角坐标系根据微积分知识可知：Ｖ＝∫ｙ０Φ（ｙ）ｄｙ　其中Φ（ｙ）为坐标ｙ处容器的横截面积,设椭圆方程为：ｘ２（ａ２）２＋（ｙ－ｈ２）２（ｈ２）２＝１Φ（ｙ）＝｜２ｘ｜·ｌ　而ｘ＝±１－（ｙ－ｈ２…     

焊接缺陷的应力集中对压力容器低应力脆性断裂的影响

大量的工程实践证明,按照现行容器设计规范,通过全面强度校核所设计的压力容器,只要材料选择适当,并且制造工艺正确,则在正常工作情况下,容器的金属母材部分,一般不会发生破坏。但是,即使如此,容器的焊缝在循环应力作用下仍可能出现裂纹。如果不能及时发现,并作适当处理,裂纹就可发展到失稳扩展的程度,导致突然的容器的低应力脆性断     

含裂纹容器的有限元分析

利用有限元通用软件ANSYS Workbench,建立容器的有限弹性体三维有限元模型,进行地震工况下不同裂纹长度、不同裂纹方向、不同支腿数量和不同容器高度下的应力分析,得到断裂力学中表征裂纹尖端附近应力场,进而得出以下结论:裂纹长轴长度和角度的变化对应力场影响;等效应力值随着裂纹长轴长度的变大显著变大,等效应力最大点随着裂纹长轴长度的变大由长轴边缘移到短轴边缘;等效应力值随着裂纹长轴角度的变大而变化,在22.5°时达到最大;等效应力最大点随着裂纹长轴角度的变大,由长轴边缘移到短轴边缘。     

压力容器的焊接结构设计

引言压力容器焊接质量的好坏对使用的安全性影响极大。据大量的压力容器事故分析:容器的破坏大部分是先在焊缝上产生微裂纹源。随着服役中各种因素的综合作用,促使微裂纹不断扩展,当裂纹扩展到失稳的临界尺寸时,就快速扩展成穿透裂纹,从而导致整个容器的破坏。因此合理、正确的进行压力容器焊接结构设计,是保证压力容器安全可靠的重要前提。     

压力容器剩余寿命预测

压力容器是与众多行业密切相关的关键通用设备,同时,压力容器又是具有高度爆炸危险地特种设备,压力容器的安全运行至关重要。压力容器在制造和使用的过程中会产生大量的裂纹缺陷,这些裂纹的存在严重影响容器可靠性,有必要对压力容器进行安全评定和疲劳寿命预测。论文通过对疲劳多裂纹的萌生、扩展机理的研究,提出了关于含多裂纹的压力容器疲劳寿命预测的数学模型。该模型在对容器剩余寿命的预测中考虑了裂纹在扩展的过程中由于其应力场变化导致其裂纹尖端应力强度因子变化的情况,较基于单一裂纹扩展的寿命预测结果更加准确。     

书讯

《压力容器的焊接结构设计》出版发行,本书根据大量的压力容器事故分析,容器的破坏大部分是由焊缝上微裂纹源,不断扩展,当裂纹扩展到失稳的临界尺寸时,就快速扩展成穿透裂纹,从而导致整个容器的破坏。因此合理正确的进行压力容器焊接结构设计是保证压力容器安全可靠的重要前提。《压力容器的焊接结构设计》由专门技术人员编写。主要内容有:压     

Crack development behavior in thermally sprayed anti-oxidation coating under repeated thermal-oxygen coupling environment

The crack development behavior in thermally sprayed anti-oxidation coating was investigated after long-term and short-term oxidation with repeated thermal cycles from 1500 °C to room temperature. According to the distribution characteristics, the formed cracks can be divided into three types: type-A cracks with multi-directional features, type-B cracks originated from the inner interface bulges and type-C cracks initiating at surface oxide layer. Based on the analytical math models (blunt crack model and interface roughness model), the maximum stress at different positions was evaluated from the perspective of inner interface roughness, uneven oxide film, original microcracks and gathering micropores. The original vertical type-A cracks are most dangerous due to the highest crack tip stress. However, the micropore distribution or appropriate interface may promote transformation of vertical type-A cracks to less dangerous horizontal type-A cracks. This study on crack development behavior provides a fundamental insight and further avenues to optimize the composition and structure of thermally sprayed ceramic coating.     

Ф1200mm尿素合成塔裂纹原因分析

针对Ф1200mm尿素合成塔全面检验过程中发现的裂纹缺陷,对裂纹形态和产生原因进行了分析,认为分别属于焊接延迟裂纹、应力腐蚀裂纹和腐蚀疲劳裂纹。     

Propagation Behavior of Machining Cracks in Delayed Fracture

The propagation behavior of machining-induced cracks in silicon nitride was investigated by conducting constant-stress and constant-stress-rate tests. A dye-impregnation technique that forced a palladium nitrate solution into the cracks gave clear evidence of subcritical crack growth of machining cracks in suspended constant-stress test specimens. The fracture origin before subcritical crack growth usually consisted of a series of small cracks within an elongated semielliptical envelope. The dye-impregnation results gave evidence that some of the elemental cracks had coalesced during subcritical crack growth. It was hypothesized that coalescence might explain an initially higher crack-growth rate suggested by constant-stress-rate tests.     

Quantifying the effects of crack width,tortuosity, and roughness on water permeability of cracked mortars

The existing service-life prediction models rarely account for the effect of cracks on mass transport and durability of concrete. To correct this deficiency, transport in fractured porous media must be studied. The objective of this paper is to quantify the water permeability of localized cracks as a function of crack geometry (i.e., width, tortuosity, and surface roughness). Plain and fiber-reinforced mortar disk specimens were cracked by splitting tension; and the crack profile was digitized by image analysis and translated into crack geometric properties. Crack permeability was measured using a Darcian flow-thru cell. The results show that permeability is a function of crack width square. Crack tortuosity and roughness reduce the permeability by a factor of 4 to 6 below what is predicted by the theory for smooth parallel plate cracks. Although tortuosity and roughness exhibit fractal behavior, their proper measurement is possible and results in correct estimation of crack permeability.     

Effect of residual stresses to the crack path in alumina/zirconia laminates

Laminates with alternating layers are well known from nature. The strongly bonded alumina/zirconia (Al₂O₃/ZrO₂) layers can combine high fracture resistance with high strength and stiffness when properly tailored. The presence of compressive residual stresses formed in Al₂O₃ layers can suppress and deflect cracks propagating through the layers. The crack path is governed by both the elastic properties and the internal stress field of individual layers. The laminates with various layer-thickness ratios ranging from 0.1 to 3 were used to investigate the effect of residual stresses and influence of crack formation pattern on the crack path development. The indentation surface cracks observed in various alumina-zirconia laminates exhibit the same crack deflection independently on the level of internal stresses. The crack deflection observed on the fracture surfaces of bending specimens was related to the indentations cracks. The complicated crack path was explained experimentally by 3D reconstruction with the support of numerical simulations.     

Effect of crack opening on the local diffusion of chloride in inert materials

The paper addresses the problem of the effect of crack opening on the ability of chloride ions to diffuse along a crack. Experimental tests are carried out on an inert material (brick) to prevent crack self-healing. A mechanical expansive core is used to generate cracks of constant width across the thickness of the sample. Five cracked specimens with crack openings ranging from 21 to 128 μm were exposed to a chloride solution for 10 h and then removed to determine the total chloride concentration perpendicular to the crack path. The results show that crack opening significantly influences the ability of chloride ions to diffuse along a crack. Indeed, the chloride profiles indicate impediment of chloride-diffusion capacity in cracks less than 53 μm in width. It was found that this crack-opening threshold agrees with the critical crack opening measured in a uniaxial tensile test that characterizes the interaction phenomena between the fracture surfaces.     

Morphology of Vickers Indent Flaws in Soda–Lime–Silica Glass

The subsurface structure of Vickers indents in soda–lime–silica glass was investigated using confocal microscopy and conventional microscopy. It was determined that the lateral cracks that form beneath the indentation site propagate away from the surface. The median/radial (MR) crack system was found to be semielliptical in shape. The growth of the lateral and MR cracks was found to be codependent such that the depth of the lateral crack limited the depth of the MR crack, and the presence of the MR crack caused deflections in the direction and increased the extent of lateral crack growth.     

Crack growth angle prediction of an internal crack under mixed mode load for unfilled elastomer using the strain energy density factor

This article investigates the prediction of the crack growth angle of an existing internal crack under mixed mode loading at the crack tip for an unfilled ethylene propylene diene terpolymer rubber (EPDM). For the realization of mixed mode loading, the cracks of the uniaxial loaded specimens were oriented with different angles to the loading direction. The energy density factor was used as a potential criterion for determining the crack growth angle. The determination of the strain energy density factor was carried out simulatively in Abaqus. The second-order Ogden model was used to describe the rubber-like material behavior. The relative local minimum of the strain energy density factor provides the possible growth angle. The experimental investigations show that the initial cracks grow orthogonally to the loading direction for the different crack orientation angles. For the crack orientation angle parallel to the load direction, the crack growth was observed because the strong stretching of the specimen caused strong necking in the crack region. The crack growth for the remaining crack orientation angles were induced due to shear loading at the crack tip. The predictive angle of different crack orientation angles shows very good accordance to the measured crack growth angles.     

Vertical crack distribution effect on the TBC delamination induced by crack growth from the ceramic surface and near the interface

The propagation of vertical crack on the surface of thermal barrier coatings (TBCs) may affect the interface cracking and local spallation. This research aims to establish a TBC model incorporating multiple cracks to comprehensively understand the effects of vertical crack distribution on the coating failure. The continuous TGO growth and ceramic sintering are together introduced in this model. The influence of the vertical crack spacing and non-uniform distribution on the stress state, crack driving force, and dynamic propagation is examined. Moreover, the influence of coating thickness on the crack growth driving is also explored. The results show that large spacing will lead to early crack propagation. The uniform distribution of vertical cracks can delay the spallation. When the spacing is less than 4 times ceramic coat thickness, the cracking driving force will come in a steady-state stage with the increase of vertical crack length. Prefabrication of vertical cracks with spacing less than 0.72 mm on the coating surface can greatly decrease the strain energy. The results in this study will contribute to the construction of an advanced TBC system with long lifetime.     

Modification of ultrasonic transducers to study crack propagation in vinyl polymers,supported by SEM technique

Detecting defects in various industrial products remains a challenging task in the industry. Researchers are constantly working to improve detection techniques and tools for various defects, particularly cracks. Many industrial structures suffer from cracks. The selection of a suitable technique and/or tool is based upon the tested structures and the accuracy of the technique and/or tool. The work's novelty is the development of a fully accurate, simple, and safe ultrasonic tool for precisely scanning cracks. A pen-shaped cone was added to the ultrasonic transducers to improve their performance. Different crosshead speeds and annealing techniques were used to cause cracks on medium density polyethylene (MDPE) and poly-methyl-methacrylate (PMMA) polymer plates with specific dimensions. Cone reduced the front diameter of the transducers from 12 to 2 mm (cone tip diameter). It improved the transducers by giving them new properties such as a small near field, a collimated beam, high sensitivity, and high wave reflection. The modified transducers tracked the cracks at discrete sequential sites, where the ultrasonic velocity was measured to determine the crack speed, critical crack speed, dynamic stress intensity factor, and crack branching phenomenon. Additionally, ultrasonic attenuation was measured in order to accurately determine crack growth behavior, the crack's neck zone, and the crack growth dependency on both plate thickness and annealing. Scanning electron microscope (SEM) images revealed crack propagation in polymer plates. The results of ultrasonic testing and SEM evaluations were consistent. This guaranteed that the modified transducers could scan cracks accurately.