Aluminum is used as a structural member in marine applications because of its low weight. One challenge is to design against failure of aluminum structures in fire. A parametric study was performed to quantify the effects of parameters on the compression failure of aluminum plates during a fire. A thermo-structural apparatus was designed to perform compression tests on aluminum samples consisting of a compression load frame, a hydraulic system, and electric heaters. The effect of dimensional variation on failure behavior was examined. Aluminum 5083 and 6082 alloys were tested with three thicknesses, two lengths and two widths. Three heat fluxes and various buckling stresses were used. Micro Vicker's hardness values were measured before and after testing to quantify the effect of heating on the strength of the aluminum. In general, lower applied stress resulted in higher failure temperature and longer time to failure. Dimensional variations had a negligible effect on failure behavior. The 5083 alloy has a minimum stress level of 50% of the buckling stress at 10kW/m2 and 10% of the buckling stress at 20kW/m2, while the 6082 alloy has a minimum stress level of 75% of the buckling stress at 10kW/m2 and 25% of the buckling stress at 20kW/m2. The 6082 failed at higher temperatures and longer failure times than the 5083. The presence of insulation on the exposed surface decreased the temperature rise, resulting in longer failure times. Vicker's hardness decreased with heating in general. The results describe the effects of parameters of the failure of aluminum. / Master of Science

Student Number : 0100281N - MSc(Eng) Research Report - School of Civil and Environmental Engineering - Faculty of Engineering and the Built Environment / Many environmental and engineering projects require prediction of the velocity of flow in river channels, in terms of those channel properties and flow characteristics which induce resisting forces or an energy loss to the flow. Relationships such as the Manning, Chézy and Darcy-Weisbach equations have been in use for a century or more. All of them account for resistance with a single coefficient of resistance, and the central problem is evaluation of this coefficient. Experimental results by different researchers have shown that Manning’s n varies strongly with the ratio of flow depth to roughness height. It is constant for values of this ratio above about 4, but increases significantly for lower values. This suggests that the equation is not suitable in its original form for the case of intermediate-scale roughness. The roughness is intermediate-scale if the relative submergence ratio of flow depth to roughness elements height lies between 1 and 4. The influence of the roughness elements on flow resistance in this regime is caused by a combination of both element drag and boundary shear, or friction. The results of an experimental study with hemispherical roughness elements are presented, showing how the roughness element size, spacing and pattern influence flow resistance. For the range of conditions tested, Manning’s n appears to depend on roughness element size, spacing and pattern.

An experimental investigation was undertaken to analyze the behavior of sandwich composite structures exposed to one-sided heating where a debond exists between the unexposed facesheet and core material. Sandwich composites of plain weave E-glass/epoxy facesheets and an end-grain balsa wood core manufactured using the Vacuum Assisted Resin Transfer Molding (VARTM) technique were the only materials analyzed. These were selected due to their current use in naval vessels and the heightened interest in the fire response properties of balsa wood and its utility as a core material. In order to better understand the interfacial behavior, Mode I Double Cantilever Beam (DCB) fracture tests were performed at ambient, 60 C, and 80 C to determine the influence of the decreased Mode I fracture toughness. While ambient testing showed that stable crack growth could be obtained, high temperature tests resulted in considerable damage occurring to the core at the crack-front preventing stable crack growth. This can be attributed to the significant decrease in the balsa core strength and material properties even for small increases in temperature. Additionally, Mode II Cracked Split Beam (CSB) tests were performed at ambient temperature to examine the sliding dominant crack-growth. Again, the occurrence of balsa core damage prevented stable crack-growth and an accurate measurement of Mode II fracture toughness was not obtained. Intermediate-scale compression testing with one-sided heating at two heat flux levels was performed with a custom designed load frame on sandwich composite columns. This enabled the influence of the debond to be measured using a 3D-Digital Image Correlation (DIC) technique spatially linked with a thermographic camera. The DIC allowed for a detailed observation of debond growth and buckling prior to global failure of the test article. A behavior similar to that observed in the Mode I DCB fracture tests occurred: as the interfacial temperature increased, the amount of crack growth decreased. This crack growth was followed by a core failure at the crack-front, triggering a global failure of the test article. This global failure for test articles containing a debond manifested itself primarily as an anti-symmetric post-buckling shape. Test articles with no debond exhibited the typical progression of the out-of-plane displacement profile for a fixed-fixed column. As the out-of-plane displacement increased, core failure ultimately occurred near the gripped region where the zero-slope condition is required, triggering global failure of the no debond test article. These tests highlight that the reduction in strength and material properties of the end-grain balsa wood core significantly outweigh the reduction in interfacial fracture toughness due to the increased temperatures. / Master of Science

Success of acid fracturing depends on uneven etching along the fracture surfaces caused by heterogeneities such as variations in local mineralogy and variations in leakoff behavior. The heterogeneities tend to create channeling characteristics, which provide lasting conductivity after fracture closure, and occur on a scale that is neither used in laboratory measurements of acid fracture conductivity, which use core samples that are too small to observe such a feature, nor in typical acid fracture simulations in which the grid block size is much larger than the scale of local heterogeneities. Acid fracture conductivity depends on fracture surface etching patterns. Existing acid fracture conductivity correlations are for random asperity distributions and do not consider the contribution of channels to the conductivity. An acid fracture conductivity correlation needs the average fracture width at zero closure stress. Existing correlations calculate average fracture width using dissolved rock equivalent width without considering the effect of reservoir characteristics. The purpose of this work is to develop an intermediate-scale acid fracture model with grid size small enough and the whole dimension big enough to capture local and macro heterogeneity effects and channeling characteristics in acid fracturing. The model predicts pressure field, flow field, acid concentration profiles, and fracture surface profiles as a function of acid contact time. By extensive numerical experiments with the model, we develop correlations of fracture conductivity and average fracture width at zero closure stress as a function of statistical parameters of permeability and mineralogy distributions. With the model, we analyzed the relationships among fracture surface etching patterns, conductivities, and the distributions of permeability and mineralogy. From result analysis, we found that a fracture with channels extending from the inlet to the outlet of the fracture has a high conductivity because fluid flow in deep channels needs a very small pressure drop. Such long and highly conductive channels can be created by acids if the formation has heterogeneities in either permeability or mineralogy, or both, with high correlation length in the direction of the fracture, which is the case in laminated formations.

A thermo-structural model was developed to predict the failure of compressively loaded fiber-reinforced polymer (FRP) laminates during fire. The thermal model was developed as a one-dimensional heat and mass transfer model to predict the thermal response of a decomposing material. The thermal properties were defined as functions of temperature and material decomposition state. The thermal response was used to calculate mechanical properties. The structural model was developed with thermally induced bending caused by one-sided heating. The structural model predicts out-of-plane deflections and compressive failure of laminates in fire conditions. Laminate failure was determined using a local failure criterion comparing the maximum combined compressive stress with the compressive strength. Intermediate-scale one-sided heating tests were performed on compressively loaded FRP laminates. The tests were designed to investigate the effect of varying the applied stress, applied heat, and laminate dimensions on the structural response. Three failure modes were observed in testing: kinking, localized kinking, and forced-response deflection, and were dependent on the applied stress level and independent of applied heating. The times-to-failure of the laminates followed an inverse relationship with the applied stress and heating levels. The test results were used to develop a relationship which relates a non-dimensionalized applied stress with a non-dimensionalized slenderness ratio. This relationship relates the applied stress, slenderness ratio, and temperature of the laminate at failure and can be used to determine failure in design of FRP laminate structures. The intermediate-scale tests were also used to validate the thermo-structural model with good agreement. / Master of Science

Rotorblätter von Windenergieanlagen (WEA) weisen häufig lange vor dem Erreichen der prognostizierten Lebensdauer von 20 bis 30 Jahren Risse in der Blattschale auf. Die Folge sind aufwendige Reparaturen am installierten und schwer zugänglichen Rotorblatt und der kostenintensive Nutzungsausfall durch den Stillstand der WEA. Als mögliche Initiatoren für die Schäden in der Blattschale der Rotorblätter gelten fertigungsbedingte Imperfektionen. Für die Untersuchung des Einflusses dieser Imperfektionen auf das Ermüdungsverhalten der Rotorblätter wurde an der BAM (Bundesanstalt für Materialforschung und -prüfung) ein Prüfstand für statische und zyklische Versuche von Schalensegmenten im intermediate scale entwickelt und betrieben. Die untersuchten Schalensegmente in Sandwichbauweise sind der Rotorblattschale von WEA im Hinblick auf die Strukturmechanik, die Halbzeuge, den Laminataufbau und dem eingesetzten Fertigungsverfahren ähnlich. Als Imperfektionen wurden verschiedenen Variationen von Lagenstößen in die Hautlagen und Schaumstöße mit Breitenvariation in den Stützkern reproduzierbar eingebracht. Die Überwachung des Schädigungszustandes während der Schwingversuche unter realistischen Lastszenarien erfolgt über eine kombinierte in situ Schädigungsüberwachung mittels passiver Thermografie und Felddehnungsmessung. Mit den durchgeführten Schwingversuchen, der begleitenden Überwachung des Schädigungszustandes sowie dem validierten FEM-Modell ließen sich die Schadensinitiation und die signifikante Reduktion der Lebensdauer durch die eingebrachten Imperfektionen zweifelsfrei nachweisen. Die abgeleiteten Designregeln liefern für die Ingenieurpraxis wichtige Konstruktionshinweise und unterstützen die betriebssichere Auslegung von gekrümmten Sandwichkonstruktionen wie beispielsweise WEA-Rotorblätter.:1 Einleitung 1.1 Motivation 1.2 Zielsetzung 2 Stand der Technik 2.1 Grundlagen FKV-Werkstoffe 2.2 Rotorblätter von Windenergieanlagen 2.2.1 Rotorblattfertigung im SCRIMP-Verfahren 2.2.2 Typische fertigungsbedingte Imperfektionen im Rotorblatt 2.2.3 Lasten am Rotorblatt 2.2.4 Rotorblattprüfung und Komponentenversuche 2.3. Schalentheorie von monolithischen und Sandwichstrukturen 2.3.1 Analytische Betrachtung orthotroper Schalen 2.3.2 Versagensverhalten von Sandwichstrukturen unter Druckbelastung 2.3.3 Analytische Beschreibung des Stabilitätsversagens von Sandwichstrukturen 2.4 Strukturverhalten von Sandwichstrukturen unter statischen und zyklischen Lasten 2.5 Versagenskriterium für monolithisches Laminat nach Puck 2.6 Ermüdungsverhalten monolithischer Winkel-Mehrschichtverbunde 2.7 Materialcharakterisierung der GFK-Decklagen 2.7.1 Statische Materialkennwerte der GFK-Decklagen 2.7.2 Schwingversuche zur Ermittlung der Wöhlerkurve der GFK-Decklagen 2.7.3 Lineare Schädigungsakkumulation zur Berechnung der Schadensbeiträge 2.7.4 Schädigungsmechanismen bei statischer Schub-Zug-Beanspruchung 2.7.5 Im RHV-Schwingversuch erfasste Schädigungsmechanismen 2.8 In situ Überwachung des Schädigungszustandes mittels zerstörungsfreier Prüfung 2.8.1 In situ Überwachung - Optische Felddehnungsmessung 2.8.2 In situ Überwachung – passive Thermografie 3 Versuchsplanung 3.1 Schalenprüfstand für Substrukturen-Versuche 3.1.1 Anforderungen an den Schalenprüfstand 3.1.2 Konstruktion und Umsetzung 3.1.3 Integrierte Zustandsüberwachung 3.2 Der Schalenprüfkörper für Substrukturen-Versuche 3.2.1 Schalenprüfkörper – Auslegung 3.2.2 Schalenprüfkörper - Fertigungsverfahren 3.2.3 Schalenprüfkörper - Eingebrachte Imperfektionen 4 Statische und zyklische Versuche an Schalenprüfkörpern 4.1 Statische Versuche an Schalenprüfkörpern 4.1.1 Mit der Felddehnungsmessung detektierte Prüfkörperverformung 4.1.2 Detektierte Z-Verschiebung mittels Felddehnungsmessung 4.1.3 Diskussion der detektierten Verformung des Schalenprüfkörpers 4.1.4 Fazit – statische Druckversuche an Sandwichschalen 4.2 Numerische Abbildung des Schalenprüfkörpers 4.2.1 Nichtlineare Stabilitätsanalyse - Schalenprüfkörper ohne Imperfektion 4.2.2 Validierung des im FEM-Schalenmodell modellierten komplexen Verformungsverhaltens unter statischer Axiallast 4.2.3 FEA – laminatschichtweise Analyse der Anstrengung (Zfb, Puck) 4.2.4 Diskussion FEM-Schalenmodell 4.3 Schwingversuche an Schalenprüfkörpern 4.3.1 Referenzprüfkörper – Einstufen-Schwingversuch 4.3.2 Referenzprüfkörper – Zweistufen-Schwingversuch 4.3.3 Referenzprüfkörper - lokaler Steifigkeitsabfall im Mehrstufen-Schwingversuch 4.3.4 Referenzprüfkörper: Fazit der Ein- und Mehrstufen-Schwingversuche 4.3.5 Zweistufen-Schwingversuche an Prüfkörpern mit Imperfektionen 4.3.6 Im Mehrstufen-Schwingversuch erreichte Lastspielzahlen 4.3.7 Nachweis der Schadensinitiierung - Ansatz zur erweiterten Auswertung der passiven Thermografie 5 Diskussion der Ergebnisse 5.1 Diskussion der statischen Schalenversuche 5.2 Diskussion der Schwingversuche von Schalenprüfköpern 5.2.1 Schadensakkumulationsprozess der Sandwich-Schalenprüfkörper unter Zug-Druck-Wechsellast 5.2.2 Lastspielzahlen: Vergleich Material- und Substrukturen-Versuche 5.2.3 Anstrengung: Vergleich Material- und Substrukturen-Versuche 5.2.4 Angewendete ZfP-Verfahren: Sichtprüfung, passive Thermografie und Felddehnungsmessung 5.3 Diskussion der Skalierung auf die Blattschale realer Rotorblätter 6 Ausblick 7 Zusammenfassung Literaturverzeichnis Abbildungsverzeichnis Tabellenverzeichnis Anhang