Scale-Bridging of Elasto-Plastic Microstructures using Statistically Similar Representative Volume Elements

Die vorliegende Arbeit behandelt die numerische Modellierung des mechanischen Verhaltens mikroheterogener Materialien, wobei das Hauptaugenmerk auf Dualphasenstähle gelegt wird. Ihr makroskopisches Verhalten wird durch die Interaktion der Einzelphasen auf mikrostruktureller Ebene geprägt. Der Einfluss der Morphologie einer realistischen Mikrostruktur kann durch die Verwendung von repräsentativen Volumenelementen (RVEs) unter Anwendung der FE²-Methode direkt in die Materialmodellierung einbezogen werden. Dabei entsteht für RVEs, die als Ausschnitte einer realen Mikrostruktur konstruiert werden, ein enormer Rechenaufwand. Eine Reduzierung des Aufwands ist durch die Verwendung von statistisch ähnlichen RVEs (SSRVEs) möglich. Diese sind durch Ähnlichkeit in Bezug auf bestimmte statistische Maße definiert und liefern gleichzeitig Gleichartigkeit des mechanischen Verhaltens. Die verschiedenen Aspekte der Konstruktion von SSRVEs sind ein Schwerpunkt dieser Arbeit. Es wird gezeigt, dass SSRVEs die mechanischen Eigenschaften der realen Mikrostruktur widerspiegeln und damit ihre Verwendung im Rahmen der FE² -Methode ermöglicht wird. Die Simulation makroskopischer Eigenschaften basierend auf polykristallinen RVEs wird gezeigt. Diese ermöglichen die Beschreibung polykristalliner Materialien, welche von ihrer mikrostrukturellen Textur geprägt werden.The present work deals with the numerical modeling of the mechanical behavior of microheterogeneous materials, with a focus on dual-phase steel. The macroscopic behavior of this material is largely influenced by an interaction of the microstructural constituents. The influence of the morphology of a real microstructure can be included in the material modeling by the application of a suitable representative volume element (RVE) in a direct micro-macro homogenization scheme (also known as FE²-method). However, the use of sections of a real microstructure as an RVE can lead to huge computational costs. A cost reduction can be achieved by the application of statistically similar RVEs (SSRVEs). They are governed by similarities of selected statistical measures with respect to a real microstructure and show a comparable mechanical behavior. The different aspects in the construction method are a main focus of this work. It is shown that SSRVEs can resemble the mechanical behavior of a real DP steel microstructure appropriately, which permits their use in FE²-simulations instead of real microstructures. Aiming for a description of polycrystalline materials governed by texture, the simulation of macroscopic properties based on polycrystalline RVEs is shown

The NASTRAN theoretical manual (level 16.0)

The manual is a commentary on the NASTRAN computer program, introducing the program to all interested persons. The manual's most important function is to present the developments of the analytical and numerical procedures that underlie the program. This manual is one of the four manuals which document the NASTRAN computer program

Fluid-structure interaction of submerged shells

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.A general three-dimensional hydroelasticity theory for the evaluation of responses has been adapted to formulate hydrodynamic coefficients for submerged shell-type structures. The derivation of the theory has been presented and is placed in context with other methods of analysis. The ability of this form of analysis to offer an insight into the physical behaviour of practical systems is demonstrated. The influence of external boundaries and fluid viscosity was considered separately using a flexible cylinder as the model. When the surrounding fluid is water, viscosity was assessed to be significant for slender structural members and flexible pipes and in situations where the clearance to an outer casing was slight. To validate the three-dimensional hydroelasticity theory, predictions of resonance frequencies and mode shapes were compared, with measured data from trials undertaken in enclosed tanks. These data exhibited differences due to the position of the test structures in relation to free and fixed boundaries. The rationale of the testing programme and practical considerations of instrumentation, capture and storage of data are described in detail. At first sight a relatively unsophisticated analytical method appeared to offer better correlation with the measured data than the hydroelastic solution. This impression was mistaken, the agreement was merely fortuitous as only the hydroelastic approach is capable of reproducing-the trends recorded in the experiments. The significance of an accurate dynamic analysis using finite elements and the influence of physical factors such as buoyancy on the predicted results are also examined

Finite element analysis of bonded crack retarders for integral aircraft structures

Trends in aircraft design and manufacture are towards the reduction of manufacturing cost and structural weight while maintaining high level of safety. These reductions can be achieved by using integral structures. However, integral structures lack redundant structural members, hence fail safety is not guaranteed. Bonded selective reinforcements (straps) can obviate this problem and improve the damage tolerance capability of integral structures, although increase the design di±culties. The objective of this research is to develop an effective analysis method to predict the fatigue crack growth (FCG) life of integral structures reinforced by bonded crack retarders, determine the effectiveness of the reinforcements, and assess the important strap design parameters. The main mechanisms that influence the crack propagation have been identified, modelled, and discussed. When a crack propagates in the panel skin, bonded straps delay the fracture growth by exerting bridging forces at the crack tip. Nevertheless damage also affects the strap due to the stiffness mismatch and high stress concentration, and the strap/substrate interface is affected by a progressive delamination that advances together with the substrate crack and limits the strap bridging action. Tensile thermal residual stresses (TRS) in the cracked substrate, caused by the adhesive cure process, act to open the crack and hence increase the growth rate. Last but not least, secondary bending caused by the non-symmetric configurations induces a stress gradient along the crack front. This reduces the effectiveness of the bridging action and causes a curved crack front. An enhanced 2D FE modelling technique that takes into account of these mechanisms and their interactions has been developed and implemented in a computerprogram that interfaces the commercial code NASTRAN. This program is used to calculate the stress intensity factors and the FCG life of bonded strap reinforced integral structures. This modelling technique has been validated for a wide range of test samples in terms of TRS and their redistribution with crack propagation, disbond areas, and FCG lives. The FCG life of a large scale integral skin-stringer panel reinforced by various bonded straps has also been predicted and compared with the experiments. Numerical predictions have shown good agreement with the experimental measurements. Parametric studies have been conducted to understand the effectiveness of different strap configurations on crack growth retardation; these include different strap materials, strap dimensions and locations on the substrate. A design tool has been developed aimed at achieving optimal crack retarder design in terms of prescribed fatigue life target and minimum structural weight. In conclusion, a novel modelling tool has been developed, the effectiveness of bonded straps in retarding fatigue crack growth has been demonstrated and, following the parametric analysis, the most important parameters in the design of bonded straps have been identified.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The NASTRAN User's Manual Level 16.0 and Supplement

The user's manual is restricted to those items related to the use of NASTRAN that are independent of the computing system being used. The features of NASTRAN described include: (1) procedures for defining and loading a structural model and a functional reference for every card that is used for structural modeling; (2) the NASTRAN data deck, including the details for each of the data cards; (3) the NASTRAN control cards that are associated with the use of the program; (4) rigid format procedures, along with specific instructions for the use of each rigid format: (5) procedures for using instructions for the use of each rigid format; (5) procedures for using the NASTRAN plotting capability; (6) procedures governing the creation of DMAP programs; and (7) the NASTRAN diagnostic messages. The NASTRAN dictionary of mnemonics, acronyms, phrases, and other commonly used NASTRAN terms is included along with a limited number of sample problems

Deformation behaviour of a concrete gravity dam based on monitoring data and numerical simulation

Deformation behaviour is a key index for evaluating the health state of concrete dam structures in long-term service. Under regular loading conditions, dam’s deformation behaviour can be preliminary depicted using monitoring data. Physically well-founded numerical simulation of the dam’s deformation behaviour provides an efficient approach to comprehend the effects of different external loads. In this work, an advanced numerical model based on monitoring data and thermal-structural coupled analysis is developed for a concrete gravity dam, the Rappbode Dam, to gain insight into the current deformation behaviour of the dam under usual and unusual load conditions. Firstly, a graphical visualisation of the monitoring data, including air temperature, water temperature, water level in the reservoir, uplift water pressure at the dam base, temperature interior the dam body and horizontal displacements, is presented to illustrate ambient loading conditions and structural responses of deformation behaviour. Secondly, based on mesh accuracy analysis which considers the different element types and mesh densities, a functional finite element model of the dam-foundation system is generated with appropriate mesh, enabling the thermal analysis of time-varying temperature distributions and structural analysis of deformation behaviour. Thirdly, based on the thermal analysis, a transient heat transfer model is calibrated to describe the thermal transfer process from the ambient environment to the dam and to present the time-varying temperature distribution within the dam body. The initial condition in the transient thermal analysis is investigated to acquire a rational primary temperature distribution in the dam. The thermal properties of the dam’s concrete are back analysed based on the concrete temperature from thermometers. The time-dependent air temperature and water temperatures are considered to specify boundary conditions. Lastly, in structural analysis, by investigating the displacement response under the loads of temperature distribution within the dam body, the hydrostatic pressure, uplift pressure and self-weight, mechanical material parameters are back analysed based on the measurements. Hence, material parameters of the dam’s concrete are updated to the present operational phase, therewith an advanced numerical model of the dam is developed. In terms of recorded usual loading conditions, computed results are aligned with measured results of displacements. With the aid of the advanced numerical model of the dam, the thermal effect due to time-varying temperature distribution, structural effect due to water-level variation and simultaneous effect are investigated under usual and unusual loading conditions. The results show that thermal displacements at different points are in phase with each other despite the phase shift in temperatures from each other. Hydrostatic pressure is more significant than uplift water pressure in determining the structural displacement. The thermal effect dominates the displacement at the dam crown, while the effect due to water level begins to dominate with the decrease of elevation. The results from an example of an unusual load case indicate enlarged ranges of displacement variations and warn of areas with possible cracks in the dam.Das Verformungsverhalten ist ein Schlüsselindex bei der Bewertung des Zustands einer Staumauer im Langzeiteinsatz. Unter regelmäßigen Belastungsbedingungen kann es anhand von Überwachungsdaten dargestellt werden. Physikalisch fundierte numerische Simulationen des Verformungsverhaltens der Staumauer bieten einen effizienten Ansatz, um die Auswirkungen verschiedener externer Belastungen zu erfassen. In dieser Arbeit wird ein fortschrittliches numerisches Modell auf der Grundlage von Überwachungsdaten und thermisch-strukturell gekoppelten Analysen für eine Staumauer, die Rappbodetalsperre, entwickelt, um einen Einblick in das aktuelle Verformungsverhalten der Staumauer unter regulären und ungewöhnlichen Lasteinwirkungen zu gewinnen. Zunächst werden Überwachungsdaten wie die Lufttemperatur, die Wassertemperatur, der Wasserspiegel im Speicher, der Sohlwasserdruck, die Betontemperatur innerhalb der Staumauer und die horizontalen Verschiebungen grafisch dargestellt, um die Eigenschaften der externen Lasteinwirkungen sowie die strukturellen Reaktionen des Verformungsverhaltens zu veranschaulichen. Anschließend werden geeignete Netze für das funktionale Finite-Elemente-Modell der Rappbodetalsperre erzeugt, dessen Genauigkeit durch die Untersuchung verschiedener Elementtypen und Netzfeinheiten gewährleistet wird. Das funktionale Finite-Elemente-Modell ermöglicht eine transiente thermische und eine strukturelle Analyse. Die transiente thermische Analyse der Temperatur erlaubt es, die Randbedingungen als variierende Umgebungstemperatur mit der Zeit zu spezifizieren und die Temperaturverteilung innerhalb der Staumauer für jeden Zeitpunkt zu berechnen. Die Spezifizierung der Anfangsbedingungen in der transienten thermischen Analyse wird untersucht, um eine rationale primäre Temperaturverteilung in der Staumauer zu erhalten. Abschließend werden die Eigenschaften des Staumauerbetons anhand der Beton-Temperaturmessungen innerhalb der Staumauer und Verschiebungen analysiert, indem das Verschiebungsverhalten unter den Belastungen der Temperaturverteilung innerhalb des Staukörpers, des hydrostatischen Drucks, des Auftriebsdrucks und des Eigengewichts untersucht wird. Dementsprechend wird ein fortschrittliches numerisches Modell der Staumauer entwickelt, deren Materialparameter des Staumauerbetons auf die gegenwärtige Betriebsphase aktualisiert und angepasst sind. Im Hinblick auf die üblichen Belastungsbedingungen werden gute Übereinstimmungen zwischen den berechneten und gemessenen Ergebnissen der Verschiebungen nachgewiesen. Mittels des fortgeschrittenen numerischen Modells der Staumauer werden die thermische, die strukturelle und die gesamte Verschiebung unter gewöhnlichen und ungewöhnlichen Belastungsbedingungen untersucht. Durch die Ergebnisse wird deutlich, dass trotz der Phasenverschiebung der Temperaturen voneinander die thermischen Verschiebungen an verschiedenen Stellen in der Staumauer in Phase zueinander liegen. Der hydrostatische Druck ist für die Bestimmung der strukturellen Verschiebung von größerer Bedeutung als der Sohlwasserdruck. Der thermische Effekt dominiert die Verschiebung an der Staumauerkrone, und mit der Abnahme der Höhe beginnt der Effekt des Wasserspiegels zu dominieren. Die Ergebnisse eines Beispiels für einen ungewöhnlichen Belastungszustand weisen auf erweiterte Verschiebungen hin und warnen vor möglichen Rissen in der Mauerköper

Computational Modelling of Concrete and Concrete Structures

Computational Modelling of Concrete and Concrete Structures contains the contributions to the EURO-C 2022 conference (Vienna, Austria, 23-26 May 2022). The papers review and discuss research advancements and assess the applicability and robustness of methods and models for the analysis and design of concrete, fibre-reinforced and prestressed concrete structures, as well as masonry structures. Recent developments include methods of machine learning, novel discretisation methods, probabilistic models, and consideration of a growing number of micro-structural aspects in multi-scale and multi-physics settings. In addition, trends towards the material scale with new fibres and 3D printable concretes, and life-cycle oriented models for ageing and durability of existing and new concrete infrastructure are clearly visible. Overall computational robustness of numerical predictions and mathematical rigour have further increased, accompanied by careful model validation based on respective experimental programmes. The book will serve as an important reference for both academics and professionals, stimulating new research directions in the field of computational modelling of concrete and its application to the analysis of concrete structures. EURO-C 2022 is the eighth edition of the EURO-C conference series after Innsbruck 1994, Bad Gastein 1998, St. Johann im Pongau 2003, Mayrhofen 2006, Schladming 2010, St. Anton am Arlberg 2014, and Bad Hofgastein 2018. The overarching focus of the conferences is on computational methods and numerical models for the analysis of concrete and concrete structures