The structure-property relationships of epoxy nanocomposites with inorganic layer-structure nanofillers have been studied to obtain the fundamental understanding of the role of nanofillers and the physics of polymer nanocomposites in this dissertation. Several polymer nanocomposite systems with modified montmorillonite (MMT) or α-zirconium phosphate (ZrP) nanofillers were prepared with epoxy matrices of different ductility and properties. The successful nanofiller's exfoliations were confirmed with X-ray diffraction and transmision electronic microscopy (TEM). Dynamic mechanical analysis (DMA) on the prepared epoxy nanocomposites revealed the significant increase in rubbery plateau moduli of the epoxy nanocomposite systems above Tg, as high as 4.5 times, and tensile test results showed improved modulus by the nanofiller addition, while the fracture toughenss was not affected or slightly decreased by nanofillers. The brittle epoxy nanocomposite systems were toughened with core shell rubber (CSR) particles and showed remarkable increase in fracture toughness (KIC) value up to 270%. The CSR toughening is more effective at ductile matrices, and TEM observation indicates that major toughening mechanisms induced by the CSR addition involve a large scale CSR cavitation, followed by massive shear deformation of the matrix.

This thesis work describes a new experimental method for the determination of Mode II (shear) fracture toughness, KIIC of rock and compares the outcome to results from Mode I (tensile) fracture toughness, KIC, testing using the International Society of Rock Mechanics Chevron-Bend method.<br><br>Critical Mode I fracture growth at ambient conditions was studied by carrying out a series of experiments on a sandstone at different loading rates. The mechanical and microstructural data show that time- and loading rate dependent crack growth occurs in the test material at constant energy requirement.<br><br>The newly developed set-up for determination of the Mode II fracture toughness is called the Punch-Through Shear test. Notches were drilled to the end surfaces of core samples. An axial load punches down the central cylinder introducing a shear load in the remaining rock bridge. To the mantle of the cores a confining pressure may be applied. The application of confining pressure favours the growth of Mode II fractures as large pressures suppress the growth of tensile cracks.<br><br>Variation of geometrical parameters leads to an optimisation of the PTS- geometry. Increase of normal load on the shear zone increases KIIC bi-linear. High slope is observed at low confining pressures; at pressures above 30 MPa low slope increase is evident. The maximum confining pressure applied is 70 MPa. The evolution of fracturing and its change with confining pressure is described.<br><br>The existence of Mode II fracture in rock is a matter of debate in the literature. Comparison of the results from Mode I and Mode II testing, mainly regarding the resulting fracture pattern, and correlation analysis of KIC and KIIC to physico-mechanical parameters emphasised the differences between the response of rock to Mode I and Mode II loading. On the microscale, neither the fractures resulting from Mode I the Mode II loading are pure mode fractures. On macroscopic scale, Mode I and Mode II do exist. / Diese Arbeit beschreibt eine neue experimentelle Methode zur Bestimmung der Modus II (Schub) Bruchzähigkeit, KIIC, von Gestein und vergleicht die Ergebnisse mit Resultaten aus Versuchen zur Bestimmung der Modus I (Zug) Bruchzähigkeit, KIC.<br><br>An einer Serie von Versuchen mit verschiedenen Belastungsraten wurde das kritische Modus I Rißwachstum eines Sandsteines untersucht. Die mechanischen Daten zeigen, daß zeit- und belastungsratenabhängiges Rißwachstum in dem Material bei konstantem Energieverbrauch stattfindet. <br><br>Der neu entwickelte Versuchsaufbau zur Ermittlung der Modus II Bruchzähigkeit wurde Punch- Through Shear Test genannt. Die Proben werden aus Bohrkernen hergestellt in deren Endflächen Nuten eingebracht werden. Eine Last auf den Innenzylinder induziert eine Schubspannung. Auf die Mantelfläche der Proben kann ein Umlagerungsdruck aufgebracht werden. Da durch Normalspannungen das Modus I Rißwachstum unterdrückt wird, wird das Modus II Rißwachstum gefördert.<br><br>Die PTS- Probengeometrie wurde bezüglich Nutentiefe, -durchmessers, -breite und des Probendurchmessers optimiert. KIIC steigt bi-linear mit Zunahme des Umlagerungsdruckes an. Ein starker Anstieg ist bis zu Umlagerungsdrücken von etwa 30 MPa zu beobachten, oberhalb ist die Steigung geringer. Bisher wurden Umlagerungsdrücke bis maximal 70 MPa aufgebracht. Die Entwicklung der entstehenden Risse und deren Variation mit Umlagerungsdruck wird beschrieben.<br><br>Ob die Entstehung eines Modus II Risses in Gestein möglich ist, wurde vielfach in der Literatur diskutiert. Der Vergleich der Ergebnisse der Modus I und II Experimente, insbesondere bezüglich der Rißmuster und der Korrelationsanalysen von KIC und KIIC zu physiko-mechanischen Parametern, zeigt die Unterschiede der Reaktion auf Modus I und Modus II Belastung auf. Mikroskopisch gesehen wachsen die Risse weder unter Modus I noch unter Modus II Belastung in einem reinen Modus. Allerdings existieren Modus I und Modus II Risse auf der makroskopischen Betrachtungsebene.

Good toughness properties in base and weld material enable the use of duplex stainless steels (DSS) in critical applications. DSS offer high strength compared to common austenitic stainless steels. The high strength can be utilized to reduce the wall thickness and accordingly accomplish reduction of cost, welding time and transportation weight, contributing to ecological and energy savings. Although DSS have been used successfully in many applications the last decades, the full utilisation in pressure vessels has been restricted due to conservative design rules. The consequences of failure in a pressure vessel are often very severe and it is accordingly important to verify a high ductility and fracture toughness. In this study fracture toughness data has been generated that has been used to analyse the brittle failure model in the European pressure vessel code EN 13445. The evaluation of the results has been made successfully by the master curve analysis, previously applied to ferritic steels. The master curve analysis includes calculation of a reference temperature, which can be correlated to an impact toughness transition temperature. A correlation between fracture and impact toughness results is necessary for a practically applicable design code. The heat distribution and austenite reformation have been modelled to verify satisfactory toughness properties in the heat affected zone. A similar model was used to evaluate the nucleation and diffusional growth of sigma phase during isothermal heat treatment or continuous cooling. For future stainless steel development, the availability of satisfactory correlations between composition, microstructure and mechanical properties are essential to optimize alloy design. Stainless steel data has been analysed to find approximate relations between mechanical properties and the chemical composition, grain size, ferrite content, product thickness and solution hardening size misfit parameter. The solution hardening effect was successfully predicted by the Labusch-Nabarro relation and multiple regression analyses were used to evaluate hardening equations for stainless steel. / QC 20100920

Submerged arc welding (SAW) is often the method of choice in pressure vessel fabrication. This process features high production rates, welding energy and/or welding speed and requires minimal operator skill. The selection of appropriate parameters in SAW is essential, not only to optimize the welding process in order to maintain the highest level of productivity, but also to obtain the most desirable mechanical properties of the weld.<p> The focus of this study was to investigate the effect of welding speed on the properties of SA516 Grade 70. Plates of SA516 Gr. 70 steel 17 mm x 915 mm x 122 mm were submerged arc welded with a welding current of 700 A and welding speeds of 15.3, 12.3 and 9.3 mm/s. Following the welding; strength, microstructure, hardness and impact toughness of the specimens were examined. Charpy impact testing was performed according to ASTM E 23 on specimens notched in the weld metal (WM) and in the heat-affected zone (HAZ), to measure the impact toughness. Fractography was performed on broken specimens using optical and scanning electron microscopy in order to correlate the mechanisms of fracture with the impact toughness values.<p> The highest hardness values were in the coarse-grained HAZ followed by the WM with the lowest hardness in the parent metal (PM). The HAZ had higher impact toughness than the WM and PM for all welding speeds. The slowest welding speed (9.3 mm/s) obtained complete penetration and therefore produced the most visually sound weld. The fastest welding speed (15.3 mm/s) had the narrowest HAZ and showed good ductile-to-brittle transition behaviour for both the WM and HAZ specimens, but produced incomplete penetration defects. Welding speed had little affect on the notch toughness of the HAZ with only a 9 J rise in upper shelf energy and an 8 °C drop in the impact transition temperature (ITT) with increased welding speed from 9.3 to 15.3 mm/s. However, for the WM, there was a 63 J drop in the upper shelf energy but also a 41 °C improvement of the ITT between the 9.3 and 15.3 mm/s welding speeds.

The development of organic photovoltaics (OPVs) has attracted a lot of attention due to their potential to create a low cost flexible solar cell platform. In general, an OPV is comprised of a number of layers of thin films that include the electrodes, active layers and barrier films. Thus, with all of the interfaces within OPV devices, the potential for failure exists in numerous locations if adhesion at the interface between layers is inherently low or if a loss of adhesion due to device aging is encountered. To date, few studies have focused on the basic properties of adhesion in organic photovoltaics and its implications on device reliability. In this dissertation, we investigated the adhesion between interfaces for a model multilayer barrier film (SiNx/PMMA) used to encapsulate OPVs. The barrier films were manufactured using plasma enhanced chemical vapor deposition (PECVD) and the interfacial fracture toughness (Gc, J/m2) between the SiNx and PMMA were quantified. The fundamentals of the adhesion at these interfaces and methods to increase the adhesion were investigated. In addition, we investigated the adhesive/cohesive behavior of inverted OPVs with different electrode materials and interface treatments. Inverted OPVs were fabricated incorporating different interface modification techniques to understand their impact on adhesion determined through the interfacial fracture toughness (Gc, J/m2). Overall, the goal of this study is to quantify the adhesion at typical interfaces used in inverted OPVs and barrier films, to understand methods that influence the adhesion, and to determine methods to improve the adhesion for the long term mechanical reliability of OPV devices.

Submerged arc welding (SAW) is often the method of choice in pressure vessel fabrication. This process features high production rates, welding energy and/or welding speed and requires minimal operator skill. The selection of appropriate parameters in SAW is essential, not only to optimize the welding process in order to maintain the highest level of productivity, but also to obtain the most desirable mechanical properties of the weld.<p> The focus of this study was to investigate the effect of welding speed on the properties of SA516 Grade 70. Plates of SA516 Gr. 70 steel 17 mm x 915 mm x 122 mm were submerged arc welded with a welding current of 700 A and welding speeds of 15.3, 12.3 and 9.3 mm/s. Following the welding; strength, microstructure, hardness and impact toughness of the specimens were examined. Charpy impact testing was performed according to ASTM E 23 on specimens notched in the weld metal (WM) and in the heat-affected zone (HAZ), to measure the impact toughness. Fractography was performed on broken specimens using optical and scanning electron microscopy in order to correlate the mechanisms of fracture with the impact toughness values.<p> The highest hardness values were in the coarse-grained HAZ followed by the WM with the lowest hardness in the parent metal (PM). The HAZ had higher impact toughness than the WM and PM for all welding speeds. The slowest welding speed (9.3 mm/s) obtained complete penetration and therefore produced the most visually sound weld. The fastest welding speed (15.3 mm/s) had the narrowest HAZ and showed good ductile-to-brittle transition behaviour for both the WM and HAZ specimens, but produced incomplete penetration defects. Welding speed had little affect on the notch toughness of the HAZ with only a 9 J rise in upper shelf energy and an 8 °C drop in the impact transition temperature (ITT) with increased welding speed from 9.3 to 15.3 mm/s. However, for the WM, there was a 63 J drop in the upper shelf energy but also a 41 °C improvement of the ITT between the 9.3 and 15.3 mm/s welding speeds.

Geopolymers (GPs) are a new class of inorganic polymers that have been considered as good candidate materials for many applications, including fire resistant and refractory panels, adhesives, and coatings, waste encapsulation material, etc. The aim of this study is to establish relationship between structural and mechanical properties of geopolymers with different chemical compositions. The metakaolin-based geopolymers were prepared by mechanically mixing metakaolin and alkaline silicate aqueous solutions to obtain samples with SiO2/Al2O3 molar ratio that ranges from 2.5 to 5, and Na/Al or K/Al atomic ratios equal to 1. Geopolymer samples were cured in a laboratory oven at 80°C and ambient pressure for different times in the sealed containers. Structural characterization of the samples with different chemical compositions was carried out using X-Ray Diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, Nuclear Magnetic-Resonance (NMR) spectroscopy and Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS). The mechanical characterization included Micro-indentation, Vickers indentation and fracture toughness measurement, as well as compressive testing. It was found that structure and mechanical properties of GPs depend on their chemical composition. The Na-GPs with ratio 3 have a highest compressive strength and Young‘s modulus of 39 MPa and 7.9 GPa, respectively. The results of mechanical testing are discussed in more detail in this thesis and linked to structural properties of processed geopolymers.

A relatively new fracture toughness testing method called Straight Notched Disc Bending (SNDB) was used before for fracture testing of Ankara Andesite and Afyon Marble cores. In this work to investigate the applicability of the new method to other rock types. With a preliminary notch of 10 mm, straight notched disc type specimens with a diameter of 75 mm were loaded by three-point bending loads. Investigation of effect of specimen height on the stress intensity factor and fracture toughness was carried out. Specimen heights (B) between 18 &ndash / 67 mm were tried for andesite and marble cylindrical specimens. Loading span, that is span/radius (S/R) ratio was changed between 0.6 - 0.9 for andesite specimens. Stress intensity factor for specimens was computed with ABAQUS program. Stress intensity factor was found to increase with increasing specimen diameter for a fixed span/radius ratio. Stress intensity factor decreased with increasing specimen height. Changing span was found to have no significant effect on fracture toughness of andesite. Fracture toughness was significantly lower for specimens with smaller height. The suggested testing height interval for this type of specimens was between height/diameter ratios of 0.49 &ndash / 0.64. Results were compared to the results obtained by a well-known specimen geometry named semi-circular bend specimens (SCB) under three-point bending. SCB tests produced lower values for fracture toughness for both rock types. Fracture toughness was 0.99 MPa&amp / #8730 / m for Ankara Andesite and 0.70 MPa&amp / #8730 / m for Afyon Marble.

In this study, by considering different mechanical properties such as wear resistance and toughness of two different metal alloys in design and production stages, bi-metal casting technique was used for producing composite material which will be a solution for the cracking and wear problem in coal crushing hammer heads. The failure analysis of the classical hammer heads which are made from Hadfield steels (austenitic steel) showed that there are crack formations through austenitic grains and also the phase transformation from austenite to martensite is not completed until the material consumed its life. Thermal analysis is the basic technique in this study to determine the solidification conditions. By using thermocouples with a suitable set-up, the cooling curves of the materials which were used in bi-metal casting had been taken and analysed. By using these cooling curve data with a written software program which is based on Newton Thermal Analysis, the solid fraction values by time and by temperate were obtained. According to these values, the interface was investigated by changing experimental conditions and solid fractions. At the last part of the study, a new approach was tried in white cast iron production.

The aim of this study is to investigate the deterioration in mechanical integrity of the collagen network in bovine bone with aging, which are related to fracture toughness. Age-related changes in collagen molecular structures formed by non-enzymatic glycation were examined and indentation fracture technique was used as a method for measuring the microstructural toughness of cortical bone. Microcrack propagation characteristics of bone for fragility were also studied. Young and old group of bovine cortical bone specimens were grouped into 2 as ribosylated and non-ribosylated which were rested in solutions for four weeks. Series of indentations were made on bone specimen groups for each of five masses 10g, 25g, 50g, 100g and 200g for 10 sec to detect the effect of applied indentation load. The applied load was increased to 300g, 500g, 1000g and 2000g for 10 sec to be able to make microcracks. Series of indentations were made on bone specimen groups for each of five durations 5sec, 10sec, 20sec, 30sec for 100g to study the effect of indentation duration. Specimens were examined in the wet and dry state while studying the factors effecting microhardness measurement. Microhardness values measured by 10g of load for 10sec were indifferent between the ribosylated and non-ribosylated groups in the young and old bovine bone pointing that this load is not indicative of the structural collagen changes. Loads of 25g, 50g, 100g and 200g for 10 sec were able to differ ribosylated bone from non-ribosylated bone for the young and old bovine bones. Degree of microhardness increased with increased incubation period. Microhardness of dry specimens being either ribosylated or non-ribosylated were found to be statistically higher than wet specimens in young and old bone except for 10g for 10sec. It has been shown that the calculated fracture toughness measured by the indentation method is a function of indentation load. Additionally, effect of indentation size might have resulted in a higher toughness measurement for higher indent loads with longer cracks even if the toughness is not actually higher.Methods using indentation technique has difficulty in relating the resistance to crack growth to the Mode I fracture toughness definition.Indentation fracture toughness allows sampling only one point on the R&shy / curve methods and was not considered as successful for assessing materials with rising R&shy / curve. Toughness is ranked incorrectly among riboslated and non-ribosylated bovine bone by this technique. Presence of extrinsic toughening mechanisms including crack bridging due to uncracked ligaments and collagen fibers were directly observed by scanning electron microscope. Ribosylated bone was found to have lower number of collagen bridging compared ton on-ribosylated bovine bone.As a summary, indentation fracture method by Vickers indentation in bone is a method for measuring the fracture toughness.