A nanoindentation investigation of local strain rate sensitivity in dual-phase Ti alloys

Using nanoindentation we have investigated the local strain rate sensitivity in dual-phase Ti alloys, Ti-6Al-2Sn-4Zr-xMo (x=2 and 6), as strain rate sensitivity could be a potential factor causing cold dwell fatigue. Electron backscatter diffraction (EBSD) was used to select hard and soft grain orientations within each of the alloys. Nanoindentation based tests using the continuous stiffness measurement (CSM) method were performed with variable strain rates, on the order of 10−1 to 10−3s−1. Local strain rate sensitivity is determined using a power law linking equivalent flow stress and equivalent plastic strain rate. Analysis of residual impressions using both a scanning electron microscope (SEM) and a focused ion beam (FIB) reveals local deformation around the indents and shows that nanoindentation tested structures containing both α and β phases within individual colonies. This indicates that the indentation results are derived from averaged α/β properties. The results show that a trend of local rate sensitivity in Ti6242 and Ti6246 is strikingly different; as similar rate sensitivities are found in Ti6246 regardless of grain orientation, whilst a grain orientation dependence is observed in Ti6242. These findings are important for understanding dwell fatigue deformation modes, and the methodology demonstrated can be used for screening new alloy designs and microstructures

Railway wheel steel behaviour upon thermo-mechanical loadings

Optimised railway maintenance techniques such as rail grinding and milling, or rail repair welding, are vital to more sustainable rail networks. As demands on the railway increases, the need to better understand the material behaviour during local heating events occurring during maintenance is amplified. Other heating events can occur during operation, for instance during severe block braking. This thesis provides insight into thermal damage resulting from these local heating events on railway wheels, which can lead to altered mechanical properties and changed residual stresses. The material behaviour of the ferritic-pearlitic railway wheel steel ER7T was studied during severe block braking (i.e., slow heating and cooling) at peak temperatures varying between 300 \ub0C and 650 \ub0C. The thermal dilatation was restricted to different degrees between free expansion and full restriction. This study thus explores the combined effect of thermal and mechanical cycling on the mechanical properties and material structure. The experimental results from the thermo-mechanical testing were also used to validate a new constitutive material model for use in FE models to predict severe block braking.\ua0 The second part of the thesis explored the effect of rapid heating and cooling events on the microstructure and residual stress state of railway wheel steel. Localised heating using laser scanning with additive manufacturing equipment was compared to the heating done by scanning with laser welding equipment. This study thus investigated the similarities of different rapid heating (high temperature) processes and the effect of process parameter variations. The results can be used to provide insight into the material behaviour of railway steels during local heating events. Furthermore, it can support the development of more accurate simulations for both operation and maintenance processes

Index to 1984 NASA Tech Briefs, volume 9, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1984 Tech B Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Model-based Design Framework for Shape Memory Alloy Wire Actuation Devices.

While Shape Memory Alloys (SMAs) have exceptional actuation characteristics such as high energy density, silent operation, flexible packaging, etc., they have not found widespread use in commercial applications because of the significant learning curve required of engineers before they are capable of designing actuation devices using this unique material. An SMA actuation device design framework consisting of grammar, design methods, and design process enables engineers of different backgrounds to make efficient and appropriate design decisions in different stages of the design process. A reference SMA actuation device structure built on a generalized actuation device hierarchical structure using the actuation device grammar works as a reference structure to identify and populate device design options, and to model and analyze the device actuation performance as well as to enlighten non-expert engineers about the essential elements of SMA actuation devices. Design methods consisting of modular modeling, model aggregation and performance prediction, and visualization approaches support design decisions to serve diverse stakeholders of actuation device design by exposing the effects of individual device elements not only for SMA actuation devices, but also for a wide range of actuation devices. A multi-stage design process is formalized to help engineers create a detailed design including a three-step decoupled equilibrium design procedure which prevents potential iteration by decoupling the force and deflection of actuation output behavior, and hides the complexity of material and SMA architectural models from engineers while still exposing the impact of design parameters. The design framework makes SMA design knowledge more accessible to engineers with different levels of expertise and roles in device development by systematically organizing and presenting the device grammar, design methods, and design process. A design tool software platform based on the framework enables the creation of computer-aided design tools to support a variety of design tasks, which were demonstrated in two use case examples. By having the SMA actuation device design framework, the acceptance of the SMA actuation technology into both research and commercial applications can be increased to utilize promising SMA actuation benefits, and the device development cycle leading to these applications can be streamlined.PhDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120684/1/wonhekim_1.pd

Non-Destructive Testing for Ageing Management of Nuclear Power Components

Worldwide a renaissance of the nuclear industry is obviously taken place and many countries favour nuclear power as one reliable opportunity to generate electrical energy at very low CO2 generating rates in order to avoid the green house effect in the earth atmosphere. However, since 1986 when the Tschernobyl accident was happening, nearly nowhere new nuclear power plants were established. The People Republic of China, India and in the last decade Japan, Finland and France are the exception. In other words, existing supply chains of former manufacturers were mainly destroyed or have changed its technical application field. Furthermore, a lot of technical expertise was lost as younger generations were influenced politically to find its interest in other scientific areas other than in nuclear physics or nuclear engineering. Even if we can observe today a change in mind in many countries concerning the acceptance of nuclear power the question seriously is to answer: Will we find enough well skilled technicians to reliably build all the planned nuclear power plants in the future? Therefore, life extension of existing plants the more plays an important role. This is truer as we have learnt in the last decades how many potential we have for life time extension even if we take into account ageing phenomena concerning the materials as thermal ageing, fatigue and neutron embrittlement when we think at steel components in the primary circuit; as there are the reactor pressure vessel, heat exchangers, surge line, pressurizer vessel, main cooling pumps and pipe lines. However, as in different countries life extension to an over all life time of 80 years is in discussion in future we have to take into account the infrastructure, i.e. bridges nearby, important for fluid traffic, emergency current generators, the concrete components of the containment and the cooling towers but also ageing phenomena of electric cable insulation, etc. Within these life time extension strategies the methodology of a continuously applied ageing management worldwide is seen as an important measure to guarantee nuclear safety. Besides the application of standardised non-destructive testing (NDT) technology during inservice inspection trials in order to perform a diagnosis of the material states online structural health monitoring of components by enhanced and intelligent NDT-sensors and sensor-networks will play a forthcoming future role. In Germany actually code-accepted procedures to perform ageing management were finally discussed and approved by the authorities. However, research and development in the last decade in the Nuclear Safety Research Programme of the German Ministry for Economy and Technology was continuously performed in order to develop and qualify NDT-technology for characterisation of ageing phenomena. The here presented chapter describes the objectives of this research and the final results obtained. In any case, the methodology of the micromagnetic NDT procedures was especially developed. This methodology is suitable for materials characterisation of magnetisable steels in terms of determination of mechanical properties. There are many similarities between movements of dislocations under mechanical loads and pinning of this lattice defects at vacancies, precipitates, grain and phase boundaries, contributing to the strength of the material and the movement of magnetic domains under magnetic loads, i.e. when the material is magnetised in a hysteresis loop. The methodology of the Micromagnetic, Multiparameter, Microstructure and Stess Analysis (3MA) is discussed which on a wide basis of different diverse as well as redundant information allows the sensitive materials characterisation. In case of a Cu-rich steel alloy precipitation hardening is discussed in combination with thermal ageing. It is shown that superimposed fatigue loads will enhance the thermal ageing effect. Fatiguing of austenitic stainless steel under some conditions is combined with phase transformation from the face-centred-cubic (fcc) lattice to body-centred-cubic (bcc) martensitic phase which is ferromagnetic of nature. Where the carbon content is low enough to avoid the phase transformation other NDT techniques based on electric conductivity effects or ultrasonic wave propagation phenomena have to be applied. 3MA is sensitive to characterise neutron embrittlement in pressure vessel materials. Material of western pressure vessel design as well as of Russian design were characterised which shows that a new NDT technology for inservice inspection of the pressure vessel wall from the id-surface can be developed

Index to 1981 NASA Tech Briefs, volume 6, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1981 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences