Generalization of an asymptotic model for constant-rate aerosol reactors

An asymptotic model was previously developed to predictbehaviors of constant-rate aerosol reactors operating with particles in the free-molecular or continuum limits. This model considered the limiting cases of having either condensation or nucleation dominate during a nucleation burst that occurs from steady addition of condensable monomer. In the present article, this model is generalized to allow condensation and nucleation to both be important during a nucleation burst. Criteria are derived to predict the relative magnitudes of nucleation and condensation, and scaling relations are presented for particle number densities, particle sizes, and onset times and durations of nucleation bursts. Comparison of the asymptotic results with numerical integration of the governing equations is favorable both qualitatively and quantitatively.     

Failure analysis: Vapor overheads discharge line for high level radioactive waste evaporator

A 2 in. schedule 40 steel (60.3 mm diameter, 3.91 mm wall) core pipe in an evaporator overheads discharge line broke at several locations downstream from a section of the line that bridges a road. The failure occurred during pump restart. Fish mouth openings that developed along the pipe seams were initiated at lack of fusion defects in the pipe welds. Full drainage of the water from the pipe did not occur when the pump was shut down because such drainage created an upstream vacuum in the piping system. Freezing of water in the pipe (the line was not heat traced) and water hammer during pump restart each contributed to the extensive deformation and tearing observed at the breaks. The weld flaws served as crack initiation sites and the water hammer provided the overpressure that led to the fish mouth fracture. The pipe was replaced and a vacuum break was installed to eliminate the drainage problem.     

Technical note – effects of seaming conditions on external and internal double‐seam characteristics in round metal cans

Canning is the major packaging technology for fully preserved food products. To obtain safe canned foods with extended shelf‐life, the closed cans have to be hermetic. The consistency and quality of the seaming process are crucial to food safety. This note investigates the effects of different seaming conditions (base‐plate pressure and seaming‐roller pressure) on external (seam thickness, seam height) and internal (body hook length, overlap, lid hook length, seam gap and body hook butting) double‐seam characteristics in round metal cans. External double‐seam characteristics were significantly affected by the seaming‐roller pressure during the final closure of the cans. Generally, there were small effects of base‐plate pressure on the external double‐seam characteristics. In contrast, all the investigated double‐seam characteristics were affected significantly by the seaming‐roller pressure, whereas only body hook length and seam gap were significantly affected by the base‐plate pressure. This note illustrates the importance of close control and optimization of the seaming conditions during production of canned foods as a means to reduce the processing induced variability in double‐seam characteristics, and subsequently to obtain safe and high‐quality canned products. Copyright © 2005 John Wiley & Sons, Ltd.     

纳米粒子气溶胶分析系统的建立

纳米粒子气溶胶分析系统对粒径测量的量值可溯源到标准粒子,可进行单分散、多分散样品的测量以及电子分级筛选。该文介绍纳米粒子气溶胶分析系统的基本原理、测量方法和系统组成,总结了所进行的实验研究。并展望了良好的应用前景。     

Failure analysis of steel bearing plates

Steel bearing plates appeared to have failed during service due to wear damage. The subsequent failure analysis revealed that the observed surface damage was the result of widespread plastic deformation and smearing associated with a network of surface crazing, rather than wear. Additionally, the majority of the bearing plates examined met microstructural specifications, although both the carbon and manganese contents were below the specified limits. The deficiencies in carbon and manganese lowered the hardenability of the alloy and may have contributed to the need for an overly severe quench during the heat treatment processing employed during manufacture.     

DP590高强钢双脉冲胶接点焊的工艺研究

针对DP590高强钢薄板, 本文提出一种应用双脉冲电流进行高强钢胶接点焊的连接工艺,通过双脉冲胶接点焊正交试验,研究双脉冲胶接点焊工艺对接头力学性能及显微组织的影响,并应用极差分析获得双脉冲胶接点焊最优工艺参数,对比分析单脉冲和双脉冲胶接点焊接头的力学性能、金相组织、显微硬度.研究表明：双脉冲电流的引入可有效降低胶接点焊过程飞溅的产生,提高胶接点焊工艺的稳定性.其中,电流是影响双脉冲胶接点焊接头力学性能的主要因素.采用双脉冲胶接点焊工艺,可明显细化熔核区的晶粒,熔核区密集分布大量的板条状马氏体,有助于提升焊核区的显微硬度,提高接头的整体韧性和强度.     

Failure mode and fatigue behavior of weld-bonded lap-shear specimens of magnesium and steel sheets

Failure modes and fatigue behaviors of ultrasonic spot welds in lap-shear specimens of magnesium AZ31B-H24 and hot-dipped-galvanized mild steel sheets with and without adhesive were investigated. The spot welded specimens failed from the kinked crack growth mode. The adhesive-bonded specimens failed from the cohesive failure through the adhesive and the kinked crack growth through the magnesium sheet. The weld-bonded specimens failed from the cohesive failure through the adhesive, the interfacial failure through the spot weld, and the kinked crack growth through the magnesium sheet. The estimated fatigue lives for the adhesive-bonded and weld-bonded specimens failed from the kinked crack growth mode are lower than the experimental results.     

Low velocity axial impact crushing performance of empty recyclable metal beverage cans

This paper focuses on the axial impact crushing behaviour of recyclable empty metal beverage cans available in the market. The idea is to make a macro foam (sacrificial cladding structure) out of these cans to protect the main load bearing members of civil engineering structures from the air blast load. Axial drop weight tests have been conducted to understand the crushing characteristics and the corresponding energy absorption of a single empty beverage can in detail. To conduct such tests a small-scale drop weight test set-up has been designed and manufactured. The deformation mechanisms and the corresponding energy absorption of the beverage cans were studied in detail for different initial impact velocities (1.4 m/s, 2.2 m/s, 3.1 m/s, 3.8 m/s, 4.4 m/s and 4.9 m/s). Furthermore, an analytical model is proposed to calculate the crushing parameters of empty metal beverage cans. The results from the analytical model are compared and validated with the experimental results.     

Evaluation of Can Microseam Resistance when Submitted to Mechanical Abuse

Microseaming is a significant technological development in the can manufacturing process that has been employed in the packaging of tomato processed products in Brazil. It was developed by the Brazilian company Grupo Kramer in 1990. Due to its reduced dimensions in relation to the traditional can closing system, i.e. the conventional double seam, microseam mechanical resistance as well as its capability to guarantee package integrity when submitted to processing and distribution remain questionable. In this study microseam resistance was compared to conventional double seam resistance when submitted to mechanical abuse through a standardized impact on the seam region positioned at angles of 45 and 67°. As evaluation parameters of closing integrity loss after impact swelling resulting from the cans external contact with a bacterial suspension, internal vacuum loss and can centre depth changes were used. The microseam presented a performance comparable to the conventional double seam for the impact at 45°, whereas at 67° its performance was found to be superior. This superior microseam performance can be credited to its being more malleable, i.e., to its greater capability of deforming itself when submitted to a puncture-type impact, to its more compact structure and to the type of deformation resulting from this type of impact.     

Failure analysis of an AM 350 steel bellows

The failure of an AM 350 steel bellows, which was to be used in the control rod drive mechanism (CRDM) of the fast breeder test reactor (FBTR), was noticed during helium leak testing. The leak test was carried out before performance testing in a test rig. Visual examination of the leak area did not indicate any obvious defect. Stereo microscopy and optical microscopy indicated the presence of pits. A few of these pits had propagated through the thickness. EDAX of the corrosion products revealed the presence of chlorides. The exposure of the bellows to a marine atmosphere during a storage period of 13 years was suspected to have caused the pitting.     

基于模型修正的钢管焊接结构焊缝损伤识别

摘要：本文提出了一种基于模型修正的钢管焊接结构焊缝损伤识别方法。利用从发射台骨架试验模型获取的模态参数,选择识别结果中精度较好的模态频率作为模型修正的基准频率。通过对待修正参数的灵敏度分析,运用ANSYS和MATLAB软件对有限元模型进行了修正。以实测模态和计算模态之间的误差建立一个带约束边界非线性最小二乘目标函数,将损伤识别问题转化为优化问题,并采用信赖域方法求解该优化问题。以有限元模型焊接结点单元组弹性模量的降低模拟焊缝损伤,并假定了两种损伤工况,通过对发射台骨架模型的数值仿真及试验研究,结果表明本文提出的损伤识别方法识别效果较为理想,为解决这种复杂焊接结构焊缝损伤识别问题提供了新的思路。     

Failure analysis of a cast steel railway wheel

The failure analysis of a broken railway pearlitic cast steel railway wheel, which was involved in a train derailment, has been investigated. The fractographic results near the fracture origin of the wheel have been compared to the regions of stable (fatigue) and unstable crack propagation of cast steel fracture toughness samples. The macro and microfractographic features of the broken wheel did not show any evidence of the occurrence of a fatigue mechanism, indicating that its fracture was caused by transgranular cleavage fracture, as a consequence of the train derailment.     

Failure analysis of ferritic stainless steel locking ring

A locking ring made of Ferritic stainless steel, fitted in a pressure gauge, failed after the service of seven years. The mode of failure was analyzed by using Scanning Electron Microscope and optical microscope. A finite element model proposed in this work demonstrated the stress distribution in different regions of the locking ring. It was observed that the ring failed in the same region where the maximum stresses were predicted. Furthermore, a detailed study on the mode of failure found that the failure occurred in stress corrosion cracking conditions.     

气溶胶光学厚度的双角度多光谱反演方法研究

给出了利用角度和光谱两方面信息进行气溶胶光学厚度反演的方法,依据反演方法要求研制了机载双角度多光谱大气辐射计,并通过航空模拟实验验证了用其进行空间对地气溶胶光学厚度反演的可行性。实验结果显示,利用双角度和多光谱的方法,可以摆脱传统方法对地面反射率数据的依赖,在一般区域能够实现实时空间对地气溶胶光学厚度的反演,从而显示出了该方法在对卫里光学遥感数据校正和研究全球气溶胶对气候影响上的潜力。     

电网设备线夹开裂原因

某电力公司变电站用铝合金设备线夹在运行过程发生批次开裂事故,通过宏观观察、断口分析、化学成分分析、力学性能测试、冷冻模拟试验等方法,对设备线夹的开裂原因和开裂机理进行了分析.结果表明:设备线夹焊缝存在焊接缺陷,导致焊缝强度下降;设备线夹接线管底部存在积水空间,寒冷天气下积水结冰,体积膨胀,使焊缝承受设计工况外的负载而过...     

装甲钢焊缝区抗弹防护性能初步探讨

目的 初步探索装甲钢焊缝区的抗弹防护性能并提出防护能力提升措施。方法 通过对装甲钢焊接结构进行组织性能分析及抗弹性能测试,获得焊接对装甲车辆抗弹防护性能的影响规律,并对装甲车辆抗弹防护能力提升对策进行讨论。结果 装甲钢接头焊缝区宽度达到46 mm,焊缝中心硬度低于312HV,较母材区硬度降低40%以上;抗弹性能测试结果表明,焊缝区的抗弹性能较母材区的显著衰减,为提升装甲车辆整体抗弹防护能力,针对焊缝区薄弱点从焊接工艺控制、结构优化、加装防护组件3个方面进行讨论,并提出了相应的防护对策。结论 装甲钢焊缝区是抗弹防护的薄弱点,需通过一系列的防护措施减少焊缝区正面中弹概率,提高装甲车辆服役期间的抗弹防护能力。     

椭球壳液压胀形过程焊缝建模方式的研究

为了研究焊缝区域有限元建模方式对椭球壳胀形过程轴长变化规律的影响,提出3种焊缝建模方式:即完整焊缝模型,粗略焊缝模型与无焊缝模型。首先进行初始轴长比为1.8的椭球壳的液压胀形实验研究,得到轴长随内压力的变化规律。其次进行了3种建模方式的椭球壳胀形过程的数值模拟,对比数值模拟和实验过程轴长变化规律,分析建模方式对模拟精度的影响。结果表明:在变形初期,3种建模方式的模拟精度相近,尺寸偏差均小于4%;但是在变形中后期,无焊缝模型的模拟精度较差,最大尺寸偏差达15%;粗略焊缝模型和完整焊缝模型都能较好地预测轴长的变化规律,且尺寸偏差不超过5%。综上所述,粗略焊缝模型既能简化建模方式,又能较好地预测椭球壳胀形过程轴长的变化规律。     

Failure analysis of a SAE 4340 steel locking bolt

Several SAE 4340 steel locking bolts used to assemble speed reducer housings fractured after a few hours of operation. Micrographic and macrographic analyses, scanning electron microscopy techniques, tensile, impact and hardness testing were used to fully characterize the component and material properties. Stress calculations were performed using both Neuber analysis and Finite Element Analysis (FEA) and the results were compared. Cracks nucleated at the root of the last engaged thread due to a combination of high local stresses in this region, surface defects, non-uniformity of the thread root and low toughness of the material. After nucleation, the crack propagated by fatigue until the catastrophic failure.     

Failure analysis of steel silos subject to wind load

Steel constructed are made of thin-walled cylindrical shells. They are widely used in various food and agriculture industries for storing granular solids, liquids, and bulk food. The present research study was completed to determine the structural behavior of thin-walled silo when subjected to wind load. The study included determination of deformational behavior of a large field silo and development of a finite element model. This experimental part of the study comprises a challenging full-scale test on 14.55 m diameter and 23.27 m high steel silo located in the open farm land near Bothwell in the province of Ontario, Canada. The finite element model was then developed for undertaking wind analysis to study the effect of different parameters such as different geometric dimensions, stiffener patterns, and wind girders on the wind-induced buckling strength of steel silos made of corrugated steel. Both linear and geometrically nonlinear buckling analyses were carried out to determine the critical wind speed for corrugated steel silos. The study found that the wind girders, also known as wind rings, significantly increase the buckling strength of the silo. This study found that the critical buckling wind speeds of the field silo specimen have increased by about 44%. Further, the optimum location for the addition of wind rings was found to be near the roof of the silo.