Vibrational entropy and microstructural effects on the thermodynamics of partially disordered and ordered Ni3V

Samples of Ni3V were prepared with two microstructures: (1) with equilibrium D022 order, and (2) with partial disorder (having a large D022 chemical order parameter, but without the tetragonality of the unit cell). For both materials, we measured the difference in their heat capacities from 60 to 325 K, inelastic neutron-scattering spectra at four values of Q at 11 and at 300 K, and Young's moduli and coefficients of thermal expansion. The difference in heat capacity at low temperatures was consistent with a harmonic model using the phonon density of states (DOS) curves determined from the inelastic neutron-scattering spectra. In contrast, at temperatures greater than 160 K the difference in heat capacity did not approach zero, as expected of harmonic behavior. The temperature dependence of the phonon DOS can be used to approximately account for the anharmonic contributions to the differential heat capacity. We also argue that some of the anharmonic behavior should originate with a microstructural contribution to the heat capacity involving anisotropic thermal contractions of the D022 structure. We estimate the difference in vibrational entropy between partially disordered and ordered Ni3V to be Spdis -Sord =(+0.038±0.015)kB /atom at 300 K

The use of hypermedia to increase the productivity of software development teams

Rapid progress in low-cost commercial PC-class multimedia workstation technology will potentially have a dramatic impact on the productivity of distributed work groups of 50-100 software developers. Hypermedia/multimedia involves the seamless integration in a graphical user interface (GUI) of a wide variety of data structures, including high-resolution graphics, maps, images, voice, and full-motion video. Hypermedia will normally require the manipulation of large dynamic files for which relational data base technology and SQL servers are essential. Basic machine architecture, special-purpose video boards, video equipment, optical memory, software needed for animation, network technology, and the anticipated increase in productivity that will result for the introduction of hypermedia technology are covered. It is suggested that the cost of the hardware and software to support an individual multimedia workstation will be on the order of $10,000

Doctor of Philosophy

dissertationMany states are implementing Accelerated Bridge Construction (ABC) methods to reduce traffic delays due to bridge construction. One such method is the use of precast concrete full-depth panels to construct bridge decks. The grouted transverse joint between precast concrete deck panels is the most vulnerable element of the bridge deck system. To extend the longevity of bridge decks it is imperative to improve the integrity of the grouted transverse joint. The focus of this research is to compare different methods to protect, strengthen, and analyze the capacity of the grouted transverse joint. This is done through four separate papers focusing on: the protection of the joint using different overlay systems; the capacity and behavior of the transverse joint using Fiber Reinforced-Polymers (FRP) composite rods at different posttensioning levels; finite element modeling of the transverse joint under concentrated truck tire loads; and an analytical approach, comparing the applied concentrated truck tire load with the capacity of the joint. Minimal research has been done on the capacity of the joint under concentrated loads, which are the majority of the loads applied to bridge decks. No previous research has been provided using Carbon FRP rods for posttensioning of the transverse bridge deck joint. Several observations, conclusions and recommendations were found with this research. It was found that overlay systems reduce the chloride intrusion for the transverse joint between full depth precast bridge deck panels. Posttensioning across the iv transverse joint provided increased joint shear transfer capacity and will impede deck cracking, and therefore lead to longer useful life of the bridge deck. The use of carbon FRP rods for posttensioning is beneficial in improving the integrity of the joint. Prior to the initial joint cracking the deck behaved monolithically which leads to the simpler design methods for the design and distribution methods of concentrated loads acting on the deck. The proposed effective distribution width of 36 in. was acceptable in the design of the transverse joint precast bridge decks under concentrated loads

Finite element simulation for the cold-joining of high power connectors

A method for the Finite-Element (FE) simulation of the Cold-Joining-Process (CJP) of massive copper contacts is developed in this thesis. The standard procedure for the calculation of interference fit connectors is not applicable to the joining process of massive copper components, since the contact area builds up in a context of considerable plastic deformation and high frictional loads. The new FE model not only shortens and optimizes the design cycle for novel High-Power-Connectors (HPCs), but also allows a deeper understanding of the CJP and the connector. The FE model is rolled out to real HPCs. The comparison between calculated and real features of the connector nails down the validity of the simulation. By means of this real example the capability of the new simulation method to set the ground for the design of future CJCs is demonstrated.Im Rahmen dieser Arbeit wird eine neue Methode zur Beschreibung von massiven Kupfer-Einpresskontakte entwickelt. Die Berechnung von Pressverbänden nach DIN 7190 ist bei der Auslegung von massiven Kupferkontakten nicht anwendbar da während des Fügevorganges hohe Verformungsgrade und Reibspannungen auftreten. Das neue Modell bietet nicht nur verkürzte und effiziente Auslegungszyklen für neue Hochleistungskontakte (HLK) an, sondern vertieft auch das Grundverständnis des Fügeprozesses und der Kontakteigenschaften. Nach einer kurzen Motivation des Themas und einer Einführung in die kalte Kontaktiertechnik, werden im dritten Kapitel die Grundlagen der experimentellen Arbeiten sowie der Simulationsmethoden erarbeitet. Die Herausforderungen bei der Modellierung von Fügeprozessen liegen in der Materialbeschreibung und Reibungscharakterisierung. Deshalb werden die beiden Themen in zwei eigenständigen Kapiteln vorgestellt, ausgehend vom jeweiligen Stand der Technik bis zur Validation der entwickelten Methoden und Modelle. Das vierte Kapitel beschäftigt sich mit der Materialbeschreibung und beinhaltet zwei neue Methoden zur bauteilnahen Ermittlung der Fließeigenschaften von Kupferwerkstoffen. Das Reibverhalten in einem Einpressvorgang wird im fünften Kapitel untersucht. Hierzu wurde ein neuer Prüfstand zur Ermittlung von Reibkoeffizienten und Beschreibung der auftretenden Verschleißmechanismen aufgebaut. Die Materialbeschreibung und die Reibungscharakterisierung sind eng miteinander verknüpft. Beide Modelle wurden deshalb in ein Finiten-Elementen (FE)-Tool zusammengeführt, um die komplexen Wechselwirkungen beschreiben zu können. Für eine genaue aber mit möglichst wenig Aufwand verbundene FE-Beschreibung von Einpressvorgängen werden Richtlinien erarbeitet und vorgeschlagen. Auf Basis des FE-Modells werden neue Hochstromkontakte entwickelt. Über den Vergleich der simulierten und der realen Eigenschaften wurde das Modell erfolgreich validiert und seine Aussagekraft eindrücklich nachgewiesen.A method for the Finite-Element (FE) simulation of the Cold-Joining -Process (CJP) of massive copper contacts is developed in this thesis. The standard procedure for the calculation of interference fit connectors is not applicable to the joining process of massive copper components, since the contact area builds up in a context of considerable plastic deformation and high frictional loads. The new FE model not only shortens and optimizes the design cycle for novel High-Power-Connectors (HPCs), but also allows a deeper understanding of the CJP and the connector. After a short introduction into the cold-joining technology and its relevance, the experimental details for the CJP and the general settings of the FE model are presented in the third chapter, as well as an overview of characteristic CJPes. The main challenges of the FE simulation of CJPes arise in the fields of material and friction characterization. Therefore each of the two areas will be developed in a separate chapter, beginning with the state of the art in the field, and ending with the assessment of the impact of the new methodology developed. The fourth chapter addresses the material characterization and includes two novel methods for the determination of flow curves and the characterization of the inhomogeneity at punched edges. The friction behavior during cold-joining is studied in chapter five. A new test bench is developed for the determination of friction coefficients and the study of wear disposition. Both material properties and friction behavior showed to be closely connected and interdependent. To cope with this complex interaction, both models were integrated in a FE tool. Guidelines are developed and proposed for an accurate FE representation of a certain CJP with the minimum modeling complexity. The FE model is rolled out to real HPCs. The comparison between calculated and real features of the connector nails down the validity of the simulation. By means of this real example the capability of the new simulation method to set the ground for the design of future CJCs is demonstrated

Mechanical characterization of fiber reinforced concretes subjected to freezing temperature

Este trabajo final de grado evalua el comportamiento de hormigón reforzado con fibras metalicas y de polimeros a temperaturas bajas.This bachelor thesis evaluates the behaviour of concrete reinforced with steel and polymeric fibers at low temperatures

Performance evaluations of latex-modified and silica fume modified concrete overlays for bridge decks

Most of the concrete bridge decks in the cold regions undergo severe reinforcement corrosion due to the transport of chloride ions within the concrete by application of deicing salts on bridge decks in the winter. As a result, protective concrete overlays of about 2-inch thickness are applied on bridge decks. Concrete overlays provide: (1) protection against heavy traffic and the further infiltration of the chloride ions; (2) skid resistance surface; and (3) uniform appearance to extend the service life of bridge decks. Despite these advantages, concrete overlays undergo premature delaminations, edge curling, and corner lifting due to expansion/shrinkage of concrete, temperature changes, and repetitive truck loading.;This research work is a part of Phase-II component of a large-scale project sponsored by WVDOH which is focused on the performance evaluation of Latex Modified Concrete (LMC) and Silica Fume Modified Concrete (SFMC) overlays on Type K substrate concrete deck prototypes. This work evaluated four prototype slabs in two stages with each slab of plan size 1829 mm. (6 ft.) by 2438 mm. (8 ft.). In Stage-I, two bi-layer deck slabs were constructed with the same LMC overlay but with two different bonding conditions. Considering the better bonding condition from Stage-I, Stage-II consisted of two bi-layer deck slabs that were constructed with LMC overlay on one slab and SFMC overlay on the other. Pull-Off testing was conducted at different ages for assessing the bond performance of the overlays. The differential length change and differential temperature developed at the interface were continuously monitored using concrete embedment gages and thermocouple loggers, respectively. Debonding due to corner lifting was monitored by installing displacement transducers (LVDT) connected to a data acquisition system. Ultrasonic Pulse Velocity (UPV) testing was conducted to compare the delamination profile at the interface between different types of slabs. Simultaneously with the UPV tester, an oscilloscope was connected to record the time-domain waveform, which was converted into a power spectrum for analysis.;The Stage-I study showed that at 5% level of significance, both the interface bond strength of the LMC slab with and without bonding slurry were similar. However, the other critical delamination parameters such as differential length changes at the interface and vertical displacement due to corner lifting were much less when bonding slurry was incorporated. Also, the time-domain waveform of LMC with bonding slurry showed less attenuation of wave through the interface compared to no-slurry LMC. Further, the frequency spectrum analysis displayed that LMC with bonding slurry had higher peak magnitude compared to LMC without bonding slurry. Based on the results, the use of bonding slurry was preferred for the Stage-II study. This study showed that in-situ pull-off/bond strength results and nature of failure varied widely due to presence of local voids, compaction, and consolidations.;In Stage-II study where the bonding slurries were used for each case, the results showed that the bond strength values of slab with LMC overlay were higher than those of the slab with SFMC overlay, at 5% level of significance as analyzed by three-way ANOVA. The vertical displacement due to corner lifting was found to be lower for the slab with LMC overlay. The time-domain signal indicated that the amplitudes of LMC overlay were higher compared to those of SFMC overlay. Further, the power spectrum analysis showed that LMC had higher magnitude of peaks both at center and edge compared to SFMC overlays indicating the strength of the signals were stronger for LMC compared to SFMC.;The overall conclusion of this study is that the bonding slurry has positive effect to reduce delamination and corner lifting; and when slurry is used, the LMC has advantages over SFMC, although both overlay types are viable options. A full-scale study is required in order to conclude the findings and finally develop a performance based specifications for the overlays for the state of West Virginia

Carbon fiber reinforced latex modified concrete for bridge deck overlays

Latex modified concrete deck overlay systems are used nationwide. However, cracking, spalling and delamination have been observed both in the case of old and new bridge deck construction. Such problems have also been observed even before a newly constructed bridge deck has been opened to traffic.;In this investigation, the effect of reinforcing Latex Modified Concrete (LMC) with carbon fibers is examined. The study focuses on formulation of the mix design and laboratory test methods to evaluate the potential of using Carbon Fiber Reinforced Latex Modified Concrete (CFLMC) for bridge deck overlays. A tension test method of concrete was perfected during the course of this research.;At a low volume fraction of 0.15% (ratio of the volume of carbon fibers to the volume of concrete), CFLMC showed an average increase of 26% in strain to failure compared to LMC, in a direct tension test. Besides an average 17% increase in ultimate flexural strength, the stress strain curves also show an average increase of 43% in failure strain under flexure. Improvements in strain to failure or ductility have the potential to reduce cracking in overlays. Fracture tests predict the fracture toughness of CFLMC to have an average improvement of 27%, compared to LMC

Application of ultra high performance concrete (UHPC) as a thin-bonded overlay for concrete bridge decks

As transportation infrastructure across the globe approaches the end of its service life, new innovative materials and applications are needed to sustainably repair and prevent damage to these structures. Bridge structures in the United States in particular are at risk as a large percentage will be reaching their design service lives in the coming decades. Superstructure deterioration occurs due to a variety of factors, but a major contributor comes in the form of deteriorating concrete bridge decks. Within a concrete bridge deck system, deterioration mechanisms can include spalling, delaminations, scaling from unsuitable material selection, freeze-thaw damage, and corrosion of reinforcing steel due to infiltration of chloride ions and moisture. This thesis presents findings pertaining to the feasibility of using UHPC as a thin-bonded overlay on concrete bridge decks, specifically in precast bridge deck applications where construction duration and traffic interruption can be minimized, as well as in cast-in-place field applications. UHPC has several properties that make it a desirable material for this application. These properties include post-cracking tensile capacity, high compressive strength, high resistance to environmental and chemical attack, negligible permeability, negligible dry shrinkage when thermally cured, and the ability to self consolidate. The compatibility of this bridge deck overlay system was determined to minimize overlay thickness and dead load without sacrificing bond integrity or lose of protective capabilities. A parametric analysis was conducted using a 3D finite element model of a simply supported bridge under HS-20 truck and overload. Experimental tests were conducted to determine the net effect of UHPC volume change due to restrained shrinkage and tensile creep relaxation. The combined effects from numerical models and test results were then considered in determining the optimum overlay thickness for cast-in-place and precast applications