When bonded joints are subjected to harsh environmental conditions, the interphase, the three-dimensional region surrounding the adhesive/substrate interface, becomes critically important. Frequently, failure occurs in this region after adhesively bonded systems are subjected to elevated temperature oxidative aging. In a previous study, this was found to be the case with a polyimide adhesive bonded to chromic acid anodized (CAA) Ti-6Al-4V. The objective of the current research has been twofold: 1) to investigate the effect of thermal aging on the interphase region of polyimide/titanium adhesive joints, and 2) to evaluate the method used in the current study for durability characterization of other adhesive/substrate systems. The method used in this research has been to characterize the effect of elevated temperature aging on the following systems: 1) Notched coating adhesion (NCA) specimens and 2) bulk samples of dispersed substrate particles in an adhesive matrix. The NCA test has the advantages of an accelerated aging geometry and a mode mix that leads to failure through the interphase, the region of interest. The bulk samples have the advantage of an increased interphase volume and allow for the application of bulk analysis techniques to the interphase, a region that is traditionally limited to surface analysis techniques. The adhesive systems studied consisted of one of two polyimide adhesives, LaRC© PETI-5 or Cytec Fiberite© FM-5, bonded to CAA Ti-6Al-4V. The model filled system consisted of a PETI-5 matrix with amorphous titanium dioxide filler. Through the use of the NCA test, it was determined that bonded specimens made with FM-5 lose approximately 50% of their original fracture energy when aged in air at 177°C for 30 days. This aging temperature is well below the glass transition temperature of the adhesive, 250°C. At the same time, the failure location moves from the anodized oxide layer to the adhesive that is directly adjacent to the substrate surface, the interphase region. Through surface analysis of this region, it is determined that the adhesive penetrates the pores of the CAA surface to a depth of 70 to 100 nm, promoting adhesion at the interface. With aging, the adhesive in the interphase region appears to be weakening, although analysis of the bulk adhesive after aging shows little change. This indicates that adhesive degradation is enhanced in the interphase compared to the bulk. Analysis of the model filled system gave similar information. Specimens containing titanium dioxide filler had glass transition temperatures that were approximately 20°C lower than the neat polyimide samples. In addition, the filled samples contained a significant portion of low molecular weight extractable material that was not present in the neat specimens. The tan delta spectra from dynamic mechanical thermal analysis of the filled specimens exhibited a shoulder on the high-temperature side of the glass transition peak. This shoulder is attributed to the glass transition of the interphase, a distinct phase of the polyimide which is constrained by adsorption onto the filler particle surfaces. As a function of aging time at 177° or 204°C, the shoulder decreases substantially in magnitude, which may relate to loss of adhesive strength between the polyimide and the filler particles. From this research, it has been illustrated that information relating to the durability of adhesively bonded systems is gained using an interfacially debonding adhesive test and a model system of substrate particles dispersed in an adhesive matrix / Ph. D.

Self-consolidating concrete (SCC) has wide use for placement in congested reinforced concrete structures in recent years. SCC represents one of the most outstanding advances in concrete technology during the last two decades. In the current work a great deal of cognizance pertaining to mechanical properties of SCC and comparison of fracture characteristics of notched and unnotched beams of plain concrete as well as using acoustic emission to understand the localization of crack patterns at different stages has been done. An artificial neural network (ANN) is proposed to predict the 28day compressive strength of a normal and high strength of SCC and HPC with high volume fly ash. The ANN is trained by the data available in literature on normal volume fly ash because data on SCC with high volume fly ash is not available in sufficient quantity. Fracture characteristics of notched and unnotched beams of plain self consolidating concrete using acoustic emission to understand the localization of crack patterns at different stages has been done. Considering this as a platform, further analysis has been done using moment tensor analysis as a new notion to evaluate fracture characteristics in terms of crack orientation, direction of crack propagation at nano and micro levels. Analysis of B-value (b-value based on energy) is also carried out, and this has introduced to a new idea of carrying out the analysis on the basis of energy which gives a clear picture of results when compared with the analysis carried out using amplitudes. Further a new concept is introduced to analyze crack smaller than micro (could be hepto cracks) in solid materials. Each crack formation corresponds to an AE event and is processed and analyzed for crack orientation, crack volume at hepto and micro levels using moment tensor analysis based on energy. Cracks which are tinier than microcracks (could be hepto), are formed in large numbers at very early stages of loading prior to peak load. The volume of hepto and micro cracks is difficult to measure physically, but could be characterized using AE data in moment tensor analysis based on energy. It is conjectured that the ratio of the volume of hepto to that of micro could reach a critical value which could be an indicator of onset of microcracks after the formation of hepto cracks.

Le dimensionnement des joints collés est une préoccupation majeure du CNES pour lesapplications spatiales des futurs lanceurs. Pour dimensionner une structure collée, il est nécessaire depouvoir apprécier les caractéristiques mécaniques du joint collé.Dans cette étude, trois adhésifs structuraux ont été sélectionnés (Hysol®EA 9321, Hysol®EA9394 et Hysol EA® 9395). Après leur caractérisation massique, une étude statistique pour mettre enévidence les effets des différents paramètres (vitesse d’essai, géométrie éprouvette, le degré depolymérisation…) a été entreprise.La deuxième étape a pour objectif de fiabiliser l’analyse des essais de fissuration etd’améliorer la compréhension des mécanismes d’endommagement et de propagation de fissure dansles liaisons collées. Trois types d’essai ont été utilisés, à savoir, l’essai Double Cantilever Beam(DCB), pour l’étude du mode I, l’essai End Notched Flexure (ENF), pour le mode II, et l’essai MixedMode Bending (MMB), pour les chargements en mode mixte I/II. Nous avons développé de nouvellesinstrumentations et méthodologies d’analyse. Pour affiner le protocole de test standard, la techniquedite de « backface strain monitoring » a été utilisée. Elle consiste à positionnées des jauges dedéformation sur les surfaces de l’éprouvette de façon à enregistrer l’évolution du signalextensométrique durant la propagation de la fissure. Cette méthode permet une meilleure estimation dela position front de fissure ainsi que l'étude de la répartition des contraintes le long du joint de colle.La corrélation d'images numériques (DIC) a également été utilisée afin de proposer un nouveauprotocole de calibrage de la longueur de fissure et pour comparer un modèle analytique (poutre deTimoshenko sur fondation élastique) avec les résultats expérimentaux. / Adhesive bonding is being strongly considered in space applications CNES as anadvantageous assembly technique for future launchers. Correct design of adhesive joints is of majorconcern. Aerospace adhesives are tough viscoelastic matrices (special epoxy resins) reinforced withnano-, or microparticles. Extended use of adhesive joints in structural applications is limited due to thedifficulties in predicting in-service performance, frequently leading to over-conservative design.Three structural adhesives (Hysol®EA 9321, Hysol®EA 9394 and Hysol®EA 9395) wereselected. After their bulk characterization, statistical studies to highlight effects of different parameterse.g. speed, test piece geometry, degree of polymerization were undertaken.In the second stage, fracture mechanics tests were effected employing: the double cantileverbeam (DCB) configuration (mode I characterisation), the three point bending end-notched flexure(ENF) (mode II) and the mixed-mode bending (MMB) (combined mode I/II loading). Crack growth inbonded joints was investigated in a novel way. To refine standard test protocol, the backface strainmonitoring technique was used. Strain gauges were used to measure the strain on the exposed skin ofthe adherends during crack onset and propagation. This method allows better estimation of the crackfront position as well as fine investigation of the stress distribution along the bondline and in the crackfront vicinity. Digital image correlation (DIC) was also used to compare analytical models, e.g.Timoshenko beam on elastic foundation model with experimental results.

Ett företag som tillverkar hydrauliska snabbkopplingar har genom regelbundna kvalitetsprover upptäckt att vissa låskulor till snabbkopplingarnas låsmekanism plötsligt fått en bristande kvalité och spricker vid belastning. Låskulorna är gjorda av rostfritt stål och har en viktig funktion i låsmekanismen. Om de spricker vid användning kan det leda till konsekvenser med materiella skador eller personskador. Företaget vill förekomma eventuella kvalitetsproblem och måste därför säkerställa att låskulorna har rätt hållfasthet. Låskulorna köps in från en underleverantör och företaget vill därför utveckla en provmetod som provar låskulornas materialegenskaper när de levereras till fabriken. Arbetet i denna rapport syftar till att hjälpa företaget utveckla en sådan provmetod. Ett första steg är att undersöka orsaken till att låskulorna spricker. Materialanalyser utförs av ett materiallaboratorium för att fastställa vilka faktorer i materialet som orsakar brott i låskulorna. Analyserna visar att låskulorna sannolikt spricker på grund av en ökad sprödhet i materialet. Sprödheten beror på att martensiten i materialet är dåligt anlöpt samt en stor mängd karbider. Med orsaken till sprickorna fastställd undersöks befintliga metoder för materialprovning. En provmetod måste prova materialet i färdigtillverkade låskulor eftersom låskulornas tillverkningsprocess påverkar materialegenskaperna. Många av de standardiserade provmetoderna är dock svåra att tillämpa på låskulorna med anledning av låskulornas geometri och små dimensioner. En form av slagprov och pressprov utförs på låskulorna. Ett av syftena med proven är att undersöka om de är lämpliga att använda som provmetod. Genom proven framträder olika materialegenskaper för olika låskulor. Resultaten är dock inte jämförbara låskulorna emellan och proven anses inte vara lämpliga som provmetod. Även ett utmattningsprov utförs på låskulorna genom en upprepande belastning i en snabbkoppling. Detta prov är inte heller lämpligt att använda som provmetod då provet är mycket tidskrävande samt att det finns vissa osäkerheter kring provresultatet. I detta arbete undersöks även två nyligen framtagna provmetoder för kulor till kullager och möjligheten att tillämpa dessa provmetoder på låskulorna. I undersökningen jämförs de båda provmetoderna med avseende på utförande samt framtagning av provkropp. Även en spänningsanalys av en låskula belastad i en snabbkoppling utförs för att ta reda på i vilket område av låskulan de maximala spänningarna uppstår. Undersökningen ger att enbart en provmetod är intressant för fortsatt arbete.   Den provmetod som föreslås i detta arbete kallas "the notched ball test" (NBT). Provmetoden innebär att en djup och smal skåra bearbetas i en låskula som sedan belastas med en tryckande kraft vinkelrätt mot skåran tills brott uppstår. Den maximala spänningen som verkar vid brottet beräknas med en enkel ekvation och används som mått för låskulans hållfasthet. Provmetoden är lämplig då den går att utföra med befintlig utrustning på företaget, den provar materialet i färdigtillverkade låskulor samt i samma område som de maximala spänningarna i en låskula belastad i en snabbkoppling uppstår. NBT nyttjar även dragspänningar vilket är fördelaktigt när sprödhet ska upptäckas i ett material. För att fastställa hur olika materialegenskaper samt geometrier för provkroppen påverkar provresultaten utförs en djupare analys av provmetoden. Analysen ger även vilka geometrier som bör användas vid utförandet av NBT samt värdet för den konstant som används vid beräkning av brottspänningen. Praktiska prov av NBT utförs inte i detta arbete men rapporten innefattar slutsatser om provmetoden och rekommendationer till företaget hur ett fortsatt arbete med NBT kan utföras. / A company that manufactures hydraulic quick-couplings has discovered through regular quality checks that the quality of some of the locking balls for the locking mechanism in the quick couplings suddenly has become insufficient and the locking balls rupture under load. The locking balls are made of stainless steel and if they rupture during usage the consequences can be material damage or even personal injury. The company wants to prevent any quality problems and must therefore ensure that the strength of the locking balls is sufficient. The locking balls are purchased from a subcontractor and the company would therefore like to develop a method for strength testing locking balls delivered to the factory. This thesis aims to help the company in developing such a method.  A first step is to investigate the cause of the locking balls rupture. Material analyses are executed by a material laboratory in order to determine what features in the material that causes the ruptures. The analyses shows that rupture is probably caused by an increased brittleness in the material and the brittleness is a consequence of less tempered martensite and a high amount of carbides. With the cause of rupture determined, existing methods for testing material properties is studied. It is important that strength testing is carried out with test specimens prepared from the actual locking balls. Otherwise the influence of the locking balls manufacturing process on the material properties is not taking into account. Many of the standardized methods for testing material properties, however, are hard to apply to the locking balls due to the geometry and small dimensions of the locking balls. A kind of impact test and compression test is performed. One of the purposes with the tests is to investigate if they are adequate for strength testing the locking balls. The results of the tests, however, are not suitable for comparison. Also, a fatigue test of the locking balls is performed by a repetitive loading of a quick coupling. The fatigue test is, however, time consuming and there are uncertainties in the test results. None of these tests is considered suitable as a strength testing method. In this thesis, two recently developed methods for strength testing ceramic balls and the possibility to apply these methods on the locking balls is studied. The study includes an analysis of the stress distribution in a locking ball under load to determine in which region the highest stresses occur. The study provides that only one of the methods is suitable for the locking balls due to differences in preparing the test specimen and which region of the locking ball that is tested in each method. The strength testing method that is proposed in this thesis is called the notched ball test (NBT). In NBT a long and narrow notch is cut in a locking ball which is then loaded in compression perpendicular to the notch until rupture occurs. The maximum stress acting at the rupture is calculated and used to determine the strength of the locking ball. NBT is suitable because it can be performed with existing equipment at the company, the test specimen is prepared from actual locking balls and the test uses tensile stresses which is an advantage when brittleness is to be detected in a material. An analysis of NBT is performed to determine how material properties and different notch geometries is affecting the test results. The analysis also gives some recommendations for notch geometries that should be used when performing NBT as well as a constant that is used when calculating the maximum stress. Practical experiments of NBT are not carried out in this thesis. Instead, conclusions regarding NBT and recommendations for the company on how they should proceed with NBT are given.

The studies in this dissertation mainly utilize planar antennas for ultra-wideband antenna designs not only on the investigation of antenna performance but also towards exploiting attractive features of ultra-wideband antennas for practical applications, such as WMAN access-point antennas, omnidirectional WiMAX access-point antennas, band-notched UWB (Ultra-wideband, 3.1 ~ 10.6 GHz) antennas, and so on. To begin with, the effects of the ground-plane size and the asymmetrical ground plane on ultra-wideband antennas are studied in Chapter 2. Following up, from the conclusive results, an antenna for WMAN operation in access-point applications and an omnidirectional monopole for USB wireless network card device are proposed and analyzed. Characteristics of ultra-wideband antenna radiation in relation to the antenna's width for obtaining omnidirectional radiation are addressed. In Chapter 3, several ultra-wideband access-point antennas are presented for achieving good omnidirectional radiation in the azimuthal plane across the bandwidth. Furthermore, in Chapter 4, band-notching techniques are applied to ultra-wideband antennas for avoiding the interference between the UWB and the WLAN systems.

Bulk metallic glasses (BMGs) are a new class of structural materials and exhibit unique combinations of mechanical properties. As a result, their mechanical behavior has been an active area of scientific pursuit in the recent past and considerable emphasis has been paid to understand plastic deformation in them. It is now well accepted that shear transformation zones (STZs), aided by free volume, are the fundamental carriers of plasticity. At a microscopic level, deformation at low temperatures and high stresses tends to localize into shear bands. Most BMGs posses high fracture toughness despite high yield strengths and poor global ductility. However, the micro-mechanisms of fracture and fatigue in this new class of materials are not fully understood yet. The overall objective of this study is to provide insights into the fracture and fatigue response of amorphous alloys, which is important both from scientific and technological perspectives. The key questions we seek to answer through this study are the following. Do amorphous alloys undergo a ductile-brittle transition (DBT), and if so what are the reasons for it? What are the parameters that influence fatigue crack initiation in amorphous alloys and whether fatigue life can be improved by surface treatments? A related question is whether the BMGs are susceptible to deformation-induced crystallization (DIC). A Zr-based BMG, Zr41.2Ti13.75Cu12.5Ni10Be22.5 was utilized to conduct this study. By comparing the fracture and fatigue behaviors in the as-cast and annealed states {annealing was carried out below the glass transition temperature (Tg) because of established embrittlement effects}, we seek to provide answers for the questions posed above. We begin by examining the influence of temperature on the toughness of BMGs. Impact toughness measurements show that the annealed samples, which are brittle at room temperature, recover the lost toughness beyond a critical temperature (TDB) and exhibit a sharp DBT. However, the hardness remains unaffected across the TDB. Fractography reveals nano-scale patterning and cleavage fracture in the brittle state, while the formation of thick vein-patterns and shear fracture are characteristics of the ductile state of the annealed samples. We explore various micro-mechanistic possibilities for explaining the features of this transition, including a critical Poisson’s ratio-toughness correlation. Next, to understand the origins of fatigue crack initiation, we study the un-notched fatigue response of as-cast and sub-Tg annealed Zr-based BMG specimens. Because of embrittlement and nano-crystallization at the crack initiation region, the annealed specimens exhibit a lower fatigue life than the as-cast specimens. Shot-peening of the as-cast specimens did not exhibit significant improvement in their fatigue performance because of competing effects between the compressive residual stress field (CRSF) and deformation-induced softening. To further investigate surface and repeated loading effects, the tribological response of the as-cast Zr-based BMG was compared with specimens annealed above and below the Tg. A good correlation between the hardness (increasing as a function of the annealing temperature) and wear rate was obtained. The formation and peeling of the oxide layer formed during testing was the primary wear mechanism in all the specimens. Lastly, crystallization was observed within the deformed region of the as-cast Zr-based BMG repeatedly scratched with a sharp diamond indenter. But, transmission electron microscopy (TEM) does not reveal any evidence of crystallization within the indents formed within an electron transparent film formed by laser deposition of the as-cast Zr-based BMG. Absence of crystallization in deformed regions obtained by designing critical experiments, which avoid artifacts generated during sample preparation, suggests that the occasional observation of DIC might be an exception rather than the rule in BMGs.

Tato Diplomová práce se zabývá vlivem vyztužení na mechanické vlastnosti materiálu pro přípravu snímatelných náhrad. Pro testování byly použity tři sady vzorků: PMMA pryskyřice, PMMA pryskyřice s Dentapreg Mesh výztuží a PMMA pryskyřice vyztužena zesilující síťkou z nerezové oceli.Pro měření chování vzorků při statickém a dynamickém namáhání byl použit třibodový ohybový test a Charpy rázové kladivo. Viskoelastické vlastnostzi byly měřeny dynamicko-mechanickou analýzou (DMA). Skenovací elektronová mikroskopie (SEM) byla použita k charakterizaci lomových ploch. Během statického namáhání vzorků výztuž nehraje důležitou roli v porovnání s nevyztuženou pryskyřicí. Nicméně byl pozorován opačný trend při dymanickém namáhání, kde efekt výzruže rostl v řadě PMMA pryskyřice – síťka z nerezové oceli – Dentapreg Mesh.

In this article the correlation between the average molar mass and the melt flow rate (MFR) is achieved. Based on the example of Polyoxymethylene (POM) it is shown that a high average molar mass is associated with a low MFR (high viscosity). On the basis of this dependency, the mechanical properties of static and dynamic tensile strength, elastic modulus, hardness and notched impact strength are investigated. It was found that the characteristic values of static tensile strength, elastic modulus and hard-ness increase with increasing MFR (decreasing viscosity). On the other hand the dynamic long-term properties and notched impact strengths decrease with increasing MFR. / Im Beitrag wird der Zusammenhang zwischen der mittleren molaren Masse und des Schmelzfließindex (MFR) hergestellt. Dabei wird am Beispiel von Polyoxymethylen (POM) ersichtlich, dass eine hohe mittlere molare Masse mit einem geringen MFR (hochviskos) einhergeht. Basierend auf dieser Abhängigkeit werden die mechanischen Eigenschaften statische und dynamische Zugfestigkeit, E-Modul, Härte sowie Kerbschlagzähigkeit untersucht. Dabei konnte festgestellt werden, dass die Kenngrößen statische Zugfestigkeit, E-Modul und Härte mit steigendem MFR (abnehmende Viskosität) zunehmen. Die dynamischen Langzeiteigenschaften und Kerbschlagzähigkeiten sinken hingegen mit zunehmendem MFR.

Este trabalho aborda uma investigação numérica-experimental sobre o comportamento à fratura por clivagem de um aço de alta resistência e baixa liga ASTM A572 Grau 50 usando corpos de prova SE(B) em configurações padronizadas e não padronizadas, incluindo a configuração PCVN não padronizada. O principal objetivo desse estudo é contribuir para o desenvolvimento de um procedimento de ensaio de tenacidade à fratura aplicável a geometrias SE(B) com distância entre apoios variável (S/W) e carregada sob configuração de flexão por 3 e 4 pontos. O objetivo secundário, mas não menos importante, é investigar os efeitos da geometria e do modo de carregamento sobre as distribuições dos dados de tenacidade à fratura medidas experimentalmente e suas implicações na caracterização da dependência da tenacidade em relação à temperatura baseada na metodologia da curva mestra. Com base nesses propósitos, é fornecido um novo e extenso conjunto de fatores plásticos eta (?p) aplicáveis às geometrias SE(B) não padronizadas para estimar os valores de tenacidade à fratura, incluindo a integral J e o parâmetro CTOD, medidos experimentalmente em termos de registros de carga e deslocamento. A fim de facilitar o contato com os demais protocolos de ensaios, é também fornecido um novo conjunto de fatores rotacionais plástico (rp) para determinar o CTOD baseado no modelo da rótula plástica. Os ensaios de tenacidade à fratura, realizados em diversas geometrias SE(B) com distância entre apoios variável (S/W) extraídas na direção transversal (T-L) de uma chapa de aço ASTM A572 Grau 50, fornecem os dados de tenacidade à fratura por clivagem em termos da integral-J medida no ponto de instabilidade, Jc. Os resultados experimentais mostram um potencial efeito da geometria do corpo de prova e do modo de carregamento sobre os valores de Jc, os quais podem ajudar a mitigar os efeitos da perda de restrição plástica frequentemente observada em corpos de prova de pequenas dimensões. A aplicação exploratória para determinar a temperatura de referência, T0, a partir da metodologia da curva mestra também fornece um suporte adicional para o uso de corpos de prova SE(B) não padronizados como uma alternativa geométrica nos procedimentos rotineiros de avaliação de tenacidade à fratura, incluindo o uso de corpos de prova de pequenas dimensões nas medições de tenacidade quando a disponibilidade limitada de material e a capacidade de carregamento da máquina são as principais preocupações. / This work addresses a numerical-experimental investigation on the cleavage fracture behavior of an ASTM A572 Grade 50 high strength, low alloy structural steel using standard and non-standard SE(B) specimens, including a non-standard PCVN configuration. The main purpose of this study is to contribute to the development of a fracture toughness test procedure applicable to bend geometries with varying specimen span over width ratio (S/W) and loaded under 3-point and 4-point flexural configuration. The secondary purpose, but none the less important, is to investigate the effects of geometry and loading mode on experimentally measured fracture toughness data distributions and implications for the characterization of the temperature dependence of toughness based on the Master Curve methodology. Based on these purposes, a large new set of plastic ?-factors applicable to these non-standard bend geometries which serve to estimate the experimentally measured toughness values in terms of load-displacement records, including the J-integral and the crack tip opening displacement (CTOD), is provided. In order to facilitate contact with other test protocols, a new set of rotational factors, rp, to determine the CTOD based on the plastic hinge model is also described. Fracture toughness testing conducted on various bend geometries with varying specimen span (S/W) extracted in the T-L orientation from an A572 Grade 50 steel plate provides the cleavage fracture resistance data in terms of the J-integral at cleavage instability, Jc. The experimental results show a potential effect of specimen geometry and loading mode on Jc-values which can help mitigating the effects of constraint loss often observed in smaller fracture specimens. An exploratory application to determine the reference temperature, T0, derived from the Master Curve methodology also provides additional support for using non-standard bend specimens as an alternative specimen geometry in routine fracture assessments, including the use of small-scale fracture specimens to measure fracture toughness properties when limited material availability and test machine capacity are of major concern are of major concern.

The aim is to propose solutions to the new bridge construction due to its unsatisfactory compared to the existing bridge reconstruction project . There are three studies bridging and selected variant trapezoidal plate further processed static opinion. The design was judged by the ultimate limit states and usability. Partial assessments were made for the anchoring system, anchorage area , unravels notched bars and store design to support .