Occurrence of melting during the solid particle erosion of copper

Copper single crystals were eroded by glass particles at a velocity of 133 m s^?1 and an incidence angle of 30°. After erosion, surfaces and debris were examined by electron microscopy. Clear evidence was obtained for localized melting of the surface layers; this is associated with embedded fragments of erodant. The most likely cause of melting appears to be the smearing of a thin layer of copper between the erodant particle and the embedded fragments. Under such conditions the layer may melt if the rate of heating during impact is sufficiently larger than the rate of thermal conduction through the low conductivity embedded and impacting glass erodant. The implication of these results for other studies and the erosion of two-phase microstructures is discussed.     

Muscle-ligament interactions at the knee during walking.

A two-dimensional mathematical model of the knee is used with gait analysis to calculate muscle, cruciate ligament and tibio-femoral contact forces developed at the knee during normal level walking. Ten normal adult subjects--four females and six males--participated. The knee model is based upon a four-bar linkage comprising the femur, tibia and two cruciate ligaments. It takes account of the rolling and sliding of the femur on the tibia during flexion/extension and the changes in direction of the ligaments and muscle tendons. We considered forces transmitted by six elements: quadriceps, hamstrings, gastrocnemius, anterior and posterior cruciate ligaments, and tibio-femoral contact. The equations of mechanics can be used to determine the absolute values of only three of the knee forces simultaneously, so that twenty limiting solutions of three of the six forces were considered. A limiting solution was rejected if any of the three forces were negative, corresponding to compressive muscle or ligament forces, or tensile contact forces. These constraints always reduced and at times removed the redundancy of the knee structures. The high incidence of predicted single muscle activity, supported by electromyography, suggested that the ligaments play a significant role in load transmission during gait. The temporal patterns of muscle and ligament activity and ligament force magnitudes were sensitive to the choice of model parameters. The analysis showed that each of four possible minimum principles of muscle selection--minimal muscle force, muscle stress, ligament force and contact force--was unlikely to be valid throughout the walking cycle.     

Examining corrosion effects and corrosion/erosion interactions on metallic materials in aqueous slurries

In this paper aspects of the corrosion behaviour of two materials (Co-base Stellite X-40 and austenitic cast iron BS 3468 S2W) under aggressive slurry erosion conditions are considered. Electrochemical techniques are used to assess the rate of corrosion in impingement conditions. The material degradation has been separated into components of mechanical erosion, electrochemical corrosion and interactive effects. It has been shown that the erosion significantly enhances the corrosion rate of both materials and has the effect of moving Stellite X-40 from a passive to an active corrosion regime. However, in terms of the magnitude of the material loss component the effect of corrosion on erosion (often referred to as synergy) is a much more prominent feature for both materials.     

The significance of the erosion parameter and the mechanisms of erosion in single-particle impacts

Single-particle impact studies were performed on 70?30 brass (70%Cu?30%Zn) specimens using a gas gun designed to impact steel balls 3 mm in diameter repeatedly at the same location at a fixed velocity of usually 120 m s^?1 and at angles of 25° and 90° to the target surfaces. Specimens were initially cold worked to varying degrees and the effect of the specimen hardness on the erosion parameter was determined. A factorial experiment was designed to evaluate the statistical significance of the variables involved in the determination of the erosion parameter. It was concluded that the initial level of cold work in the specimen and the kinetic energy of the impacting ball have a significant effect on the erosion parameter. Scanning electron microscopy of the impacted specimens and the erosion debris revealed contributions to erosion from two mechanisms, i.e. flake formation and lip fragmentation. Flake formation is the dominant mode of erosion in normal impact conditions while lip fragmenta     

Electro-mechanical interactions during erosion–corrosion

This study aims to understand the physical processes invoked when solid particle erosion occurs in a corrosive media. The literature on wear-corrosion shows some effort has been placed in qualifying the interactions between erosion and corrosion leading to ‘synergistic’, ‘additive’ and ‘antagonistic’ terms. These terms are difficult to quantify experimentally with multiple experiments being required and generate considerable errors often suggesting these interactive terms are negligible. Hence the current work seeks to investigate these interactions, the errors associated with their measurement and gain understanding of the processes involved by careful examination of microstructural and mechanical property changes of surfaces subjected to erosion–corrosion. Cast nickel–aluminium bronze/NaCl solution has been chosen to study as this system has been studied at Southampton for several years. In situ electrochemical, gravimetric and topographical analyses have been evaluated and discussed using microstructural and hardness measurements.     

A comparison of liquid impact erosion and cavitation erosion

A comparison has been made between the response of several metals and alloys to multiple liquid jet impact and their response to ultrasonically induced cavitation. For the single-phase metals and alloys, namely aluminum, iron, Al-1%Cu, Al-1%Mg and Cu-30%Zn, the failure mechanism is the same for the two techniques. However, there are significant differences for Al-4%Cu and Al-9%Mg. The former alloy fails in cavitation by the growth of macroscopic fatigue-like striated pits, whereas under liquid impact the fracture appears more like transcrystalline cleavage. The differences in the Al-9%Mg alloy are even more dramatic: under cavitation the surface becomes covered with macroscopic striated pits, whereas under liquid impact failure is intercrystalline. Although the magnitude and duration of the pressure pulses produced by the two techniques are similar, all the materials studied required three to four orders of magnitude more impacts by avitation than by liquid impact for a given amount of erosion. The greater erosive power of the liquid impact is attributed to the shearing effects of lateral flow of the liquid after impact.     

Introduction to the microscopy of erosion

Erosion of materials by the impact of small solid particles, by the impact of liquid drops and by cavitation in a liquid is discussed. Erosion arising from these three sources is described, terminology is defined, and the methods available for erosion testing in the laboratory are reviewed. A brief discussion is presented of the microscopical techniques which have been used to study erosion, and some of their advantages and drawbacks are outlined.     

Enhanced sampling for lipid-protein interactions during membrane dynamics

The inflexible concept of membrane curvature as an independent property of lipid structures is today obsolete. Lipid bilayers behave as many-body entities with emergent properties that depend on their interactions with the environment. In particular, proteins exert crucial actions on lipid molecules that ultimately condition the collective properties of the membranes. In this review, the potential of enhanced molecular dynamics to address cell-biology problems is discussed. The cases of membrane deformation, membrane fusion, and the fusion pore are analyzed from the perspective of the dimensionality reduction by collective variables. Coupled lipid-protein interactions as fundamental determinants of large membrane remodeling events are also commented. Finally, novel strategies merging cell biology and physics are considered as future lines of research.     

Analysis of boiler-tube erosion by the technique of acoustic emission Part I. Mechanical erosion

This paper investigates the mechanical erosion of the metal tubes in bagasse-fired boilers with the aid of the acoustic emission technique. By studying the material removal under various collision conditions, the paper analyzes the dependence of the erosion wear upon the impact angle, velocity, size and concentration of the particles. It was found that the material removal mechanisms were mainly dependent on the particle collision angle and fell into four regimes characterized by rubbing and scratching, cutting and cracking, forging and extrusion as well as sputtering and adhesion. The highest wear rate took place with the cutting and cracking mechanism when the particle collision angle was in the range of 20–30°. The variation of the acoustic emission energy confirmed the conclusions. Finally, three simple formulae were developed to show the dependence of the erosion wear upon the main erosion parameters.     

Investigation into erosion rate of AISI 4340 steel during wire electrical discharge turning process

Wire electrical discharge turning (WEDT) process was developed to generate cylindrical form on any electrically conductive material applied in aerospace and automotive industry. The mechanism of metal removal in WEDT process is by means of successive spark discharge. Each spark results in the formation of crater. In the present work, a new model is proposed to predict the erosion rate of each spark for a given discharge energy. A new method is proposed to measure the crater depth from 2D roughness profile of the machined component. The proposed model is validated by conducting experiments on AISI 4340 steel and the results obtained are presented in the paper. It is observed that the results are in close proximity with the experimental values at low discharge energy. The stochastic erosion mechanism of WEDT process is analyzed using scanning electron microscope images of spark eroded wire. Using the proposed model the erosion rate can be controlled and better surface characteristic of machined surface can be achieved.     

基于C8051F002单片机设计的雷达液位信号分配器

设计一种基于C8051F002单片机的雷达液住信号分配器，该分配器的主要功能是完成与FCU（雷达液位现场接线单元）和二次仪表之间的通信。文章在介绍雷达液位信号分配系统的工作原理基础上，着重介绍了该分配器与FCU之间采用基于MODBUS通信协议实现的串行通信，和与二次仪表之间的SMBUS总线通信。同时给出该分配器的软硬件设计原理。在实际应用中，该分配器可以准确快速的实现液位信号的分配。     

On modeling the deformations and tool-workpiece interactions during machining metal matrix composites

Significance of application of metal matrix composites (MMCs) in various industries has already been demonstrated. In order to address the challenges faced during machining MMCs, development of novel modeling techniques for understanding the mechanics of the process is crucial. This paper presents a new approach towards finite element modeling of MMC machining process to facilitate the analysis of plastic deformations. Transient Lagrangian modeling is used with adaptive remeshing control in order to reduce the effects of mesh distortions on accurate estimation of plastic deformation during machining. The thorough understanding of MMC plastic deformations, which is achieved using the developed model, is an asset in analysis of MMC behavior during the process.     

On the mechanism of wet abrasive erosion

A method of testing wet abrasive erosion is presented, together with its mechanism. Many factors have been investigated, including abrasive particle size, velocity and test duration, etc. It is suggested that wet abrasive erosion may be divided into two sub-groups — high stress wet abrasive erosion and low stress wet abrasive erosion. It is found that the effect of corrosion plays an important role in wet abrasive erosion of ferrous metals, and adding a corrosion inhibitor can mitigate it considerably.     

Aerodynamic effects in the erosion process

Experimental investigations of velocity effects on the erosion of a ductile material by aerodynamically entrained solid particles indicate that erosion varies with the fourth power of velocity in normal or 90° impacts. For smaller angles of attack the exponent is less than 4 but greater than 2. Previous quantitative erosion models do not predict these high exponent values. In this study the two-phase fluid mechanical system is analyzed and an analytical expression is presented that predicts particle impact speeds varying with the square of the fluid free stream speed in normal impacts. It is shown that the high values found experimentally are the result of aerodynamic effects alone.     

Analysis of particulate erosion

A general analysis is developed for the erosion of materials whereby material is removed through a process of erosion pit nucleation and growth. This model is applicable to a variety of materials exposed to liquid drop impingement and impingement by rounded solid particles. A fundamental limitation of the model is that material removal has to occur as a preferential process.     

Alveolar macrophage-T cell interactions during Th1-type sarcoid inflammation

Sarcoidosis is an immunomediated, multisystem disorder of unknown cause(s) characterized by a heightened Th1 immune response that leads to an uncontrolled granuloma formation at sites of disease activity. The past few years have seen outstanding advances in the understanding of immunological and molecular events involved in the pathogenesis of this disease. The idea is that several cytokines and chemokines, which are secreted at sites of disease activity, participate in granuloma formation. This paper describes recent data that have clarified some of the events that govern the development of the hypersensitivity reaction during sarcoidosis. In particular, we will review recent evidence indicating that a complex relationship exists between the macrophage/lymphocyte cellular axis and the tissue networks of cytokines.     

Particle size threshold in the erosion of metals

It is postulated that erosive metal loss in the velocity range above 70 m s^?1 requires that the deformed material under the particle be heated to a high temperature. The particle size below which the erosion rate drops appreciably is then calculated assuming that it is the diameter range below which heat is carried away so rapidly by conduction that this temperature rise cannot occur. Good agreement between predictions and experimental data is obtained.