Advances in Permanent Deformation Modeling of Asphalt Concrete—A Review

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Space-Time Multiscale-Multiphysics Homogenization Methods for Heterogeneous Materials

We present a unified, homogenization framework for computational analysis of heterogeneous materials consisting of multiple length scales, multiple time scales and coupled-multiple physics. The research efforts also addresses the technological issues associated with modeling the morphological details of microstructures with randomly distributed inclusions. The Random Sequential Adsorption (RSA) algorithm is improved to accurately and effectively model the morphological details of materials with randomly distributed inclusions. The proposed algorithm is more robust; computational efficient and versatile in comparison to the existing methods. A temporal homogenization scheme is developed and integrated with the previously developed spatial homogenization theory for fatigue life analysis of heterogeneous materials. The unified space-time multiscale homogenization model is validated for fatigue life prediction of elevated temperature Ceramic Matrix Composites (CMCs). In the final phase of the research a mathematical model for coupled moisture diffusion-mechanical deformation is developed. This model is integrated with the spatial homogenization framework to analyze problems consisting of multiple length scales and coupled-multiple physics. The unified multiscale-multiphysics model is validated for evaluating the degradation of physical and mechanical properties of short glass fiber and carbon fiber filled thermoplastic material systems

Experimental and Numerical Investigation of the Damage Response of Ceramic Matrix Composites.

Ceramic matrix composites (CMCs) are of interest in the aerospace industry due to their ability to retain high stiffness at elevated temperatures. CMC materials are slated to replace metal alloys currently used in the combustion section of aerospace jet engines, leading to weight savings due to the lower density. In this work monotonic tensile tests at room and high temperature are conducted. Three different composite layups are investigated. Mechanics based numerical models based on finite element analyses are developed to predict the damage behavior of CMCs. The energy based crack band model implemented in Abaqus' user subroutines is used to enforce mesh objectivity. Crack densities are predicted with microstructural FEM models including hundreds of fibers. Geometrical inhomogeneities are included in the model in order to represent the microstructure accurately. Crack-paths and stress-strain responses are compared to experimental results. Component level numerical predictions are developed using a multiscale approach referred to as the integrated finite element method (IFEM). In the IFEM, a representative volume element, which includes nonlinear response due to constituent level damage, is embedded within Abaqus user subroutine UMAT. This allows the user to capture the influence of constituent stress-strain relation at the RVE level. Energy based fracture mechanics models are implemented in the constitutive relations of the RVE model. Damage of each constituent within the RVE is predicted. Macroscopic crack paths are predicted and compared to experimental results. In support of IFEM, micromechanics based models are developed to study the effect of fiber packing and other geometrical features on the transverse response of CMC plies. Experiments on CMCs at elevated temperature revealed the existence of fiber debonding and subsequent sliding and pullout of the fibers. A numerical model is developed to predict the fiber debonding using discrete cohesive zone elements (DCZM).PhDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111477/1/pasmey_1.pd

Aging concrete structures: a review of mechanics and concepts

The safe and cost-efficient management of our built infrastructure is a challenging task considering the expected service life of at least 50 years. In spite of time-dependent changes in material properties, deterioration processes and changing demand by society, the structures need to satisfy many technical requirements related to serviceability, durability, sustainability and bearing capacity. This review paper summarizes the challenges associated with the safe design and maintenance of aging concrete structures and gives an overview of some concepts and approaches that are being developed to address these challenges

Numerical simulation of fatigue processes : application to steel and composite structures

The present thesis aims at advancing an innovative computational methodology that simulates steel and composite material fracture under cyclic loading following a phenomenological approach, with calibration from both small scale and large scale testing. This work addresses fatigue processes ranging from high cycle to ultra-low-cycle fatigue. An assessment of the current state of the art is done for all the different fatigue types. Following, for ultra-low cycle fatigue a new constitutive law is proposed and validated with experimental results obtained on small scale samples. Industrial applications are shown for a large diameter straight pipe under monotonic loading conditions and for a bent pipe under cyclic loading. Emphasis is made on the capacity of the model to represent different failure modes depending on the loading conditions. The research regarding this part has been used in the frame of the European Project: ¿Ultra low cycle fatigue of steel under cyclic high-strain loading conditions¿ (ULCF). Regarding high cycle fatigue, a classic damage model is presented in combination with an automatic load advancing strategy that saves computational time when dealing with load histories of millions of cycles. Numerical examples are shown in order to demonstrate the capabilities of the advancing strategy and a validation of the model is done on small scale samples. A new constitutive model is presented for Low Cycle Fatigue that uses the classic plasticity and damage theories and simultaneously integrates both processes in the softening regime. The capabilities of the model are shown in numerical examples. Finally, the high cycle fatigue damage model is applied to the constituents of a composite material and the structural behaviour is obtained by means of the serial/parallel rule of mixtures. Validation of the constitutive formulation is done on pultruded glass fiber reinforced polymer profiles.La presente tesis propone una metodología innovadora para la simulación numérica de la rotura de materiales metálicos y compuestos sometidos a cargas cíclicas. El enfoque es fenomenológico y la formulación se calibra con resultados experimentales obtenidos en especímenes a pequeña escala y con experimentos a gran escala. Este trabajo abarca procesos de fatiga desde alto número de ciclos hasta muy bajo número de ciclos. Una evaluación del estado del arte hasta el momento se ha llevado a cabo para los diferentes tipos de fatiga. A continuación, se propone una nueva ley constitutiva para la fatiga de muy bajo número de ciclos y se presenta la validación con resultados experimentales obtenidos en especímenes a escala pequeña. El modelo constitutivo se ha probado en dos aplicaciones industriales: una tubería de gran diámetro bajo condiciones de carga monótonas y una tubería doblada a un ángulo de 90 grados sometida a cargas cíclicas. Se ha enfatizado la capacidad del modelo de reproducir diferentes modos de rotura dependiendo de las condiciones de carga. El trabajo referente a este modelo se ha usado en el marco del proyecto europeo: ¿Fatiga de muy bajo número de ciclos del acero bajo grandes deformaciones cíclicas¿. Respecto a la fatiga de alto número de ciclos, se presenta un modelo clásico de daño combinado con una estrategia automatizada de avance en la carga por número de ciclos. La estrategia conduce a un ahorro en tiempo de computación cuando se aplican millones de ciclos de carga. Las capacidades y particularidades de la estrategia de avance en la carga se enseñan en una serie de ejemplos numéricos. El modelo se valida con resultados experimentales obtenidos en especímenes a pequeña escala. Un nuevo modelo constitutivo se presenta para la fatiga de bajo número de ciclos que se basa en las teorías básicas de plasticidad y daño y que integra simultáneamente las ecuaciones de ambos procesos en el régimen de ablandamiento. Las capacidades del modelo se enseñan a través de ejemplos numéricos. Finalmente, se estudia la aplicación del modelo de daño para fatiga de alto número de ciclos en los componentes de materiales compuestos. El comportamiento estructural del material compuesto se obtiene a través de la teoría de mezclas serie/paralelo. La formulación se valida con resultados experimentales obtenidos en perfiles de GFRP.Postprint (published version

Multiscale Damage Modelling of Notched and Un-Notched 3D Woven Composites With Randomly Distributed Manufacturing Defects

This work proposes a stochastic multiscale computational framework for damage modelling in 3D woven composite laminates, by considering the random distribution of manufacturing-induced imperfections. The proposed method is demonstrated to be accurate, while being simple to implement and requiring modest computational resources. In this approach, a limited number of cross-sectional views obtained from micro-computed tomography (µCT) are used to obtain the stochastic distribution of two key manufacturing-induced defects, namely waviness and voids. This distribution is fed into a multiscale progressive damage model to predict the damage response of three-dimensional (3D) orthogonal woven composites. The accuracy of the proposed model was demonstrated by performing a series of finite element simulations of the un-notched and notched tensile tests (having two different hole sizes) for resin-infused thermoplastic (Elium®) 3D woven composites. Excellent correlation was achieved between experiments and the stochastic finite element simulations. This demonstrates the effectiveness of the proposed stochastic multiscale model. The model successfully captured the stochastic nature of tensile responses (ultimate tensile strength and stiffness), damage modes (matrix damage and fibre failure), and initiation and propagation of transverse cracks in thermoplastic 3D woven composites, consistent with experimental observation. The stochastic computational framework presented in this paper can be used to guide the design and optimization of 3D textile composite structures

Theory and Numerical Modeling of Geomechanical Multi-material Flow

Multi-material flow describes a situation where several distinct materials separated by sharp material interfaces undergo large deformations. The research presented in this paper addresses a particular class of multi-material flow situations encountered in geomechanics and geotechnical engineering which is characterized by a complex coupled behavior of saturated granular material as well as by a hierarchy of distinct spatial scales. Examples include geotechnical installation processes, liquefaction-induced soil failure, and debris flow. The most attractive numerical approaches to solve such problems use variants of arbitrary Lagrangian–Eulerian descriptions allowing interfaces and free surfaces to flow through the computational mesh. Mesh elements cut by interfaces (multi-material elements) necessarily arise which contain a heterogeneous mixture of two or more materials. The heterogeneous mixture is represented as an effective single-phase material using mixture theory. The paper outlines the specific three-scale mixture theory developed by the authors and the MMALE numerical method to model and simulate geomechanical multi-material flow. In contrast to traditional flow models which consider the motion of multiple single-phase materials or single multi-phase mixture, the present research succeeds in incorporating both the coupled behavior of saturated granular material and its interaction with other (pure) materials.DFG, 76838227, Numerische Modellierung der Herstellung von Rüttelinjektionspfähle

Multiscale Failure Analysis of Laminated Composite Panels Subjected to Blast Loading Using FEAMAC/Explicit

This preliminary report demonstrates the capabilities of the recently developed software implementation that links the Generalized Method of Cells to explicit finite element analysis by extending a previous development which tied the generalized method of cells to implicit finite elements. The multiscale framework, which uses explicit finite elements at the global-scale and the generalized method of cells at the microscale is detailed. This implementation is suitable for both dynamic mechanics problems and static problems exhibiting drastic and sudden changes in material properties, which often encounter convergence issues with commercial implicit solvers. Progressive failure analysis of stiffened and un-stiffened fiber-reinforced laminates subjected to normal blast pressure loads was performed and is used to demonstrate the capabilities of this framework. The focus of this report is to document the development of the software implementation; thus, no comparison between the results of the models and experimental data is drawn. However, the validity of the results are assessed qualitatively through the observation of failure paths, stress contours, and the distribution of system energies

Impact damage prediction in carbon fiber-reinforced laminated composite using the matrix-reinforced mixing theory

The impact damage tolerance of fiber-reinforced laminated composite materials is a source of concern, mainly due to internal induced damage which causes large reductions on the strength and stability of the structure. This paper presents a procedure based on a finite element formulation that can be used to perform numerical predictions of the impact induced internal damage in composite laminates. The procedure is based on simulating the composite performance using a micro-mechanical approach named matrix-reinforced mixing theory, a simplified version of the serial/parallel mixing theory that does not require neither the iterative procedure nor the calculation of the tangent stiffness tensor. The numerical formulation uses continuum mechanics to simulate the phenomenon of initiation and propagation of interlaminar damage with no need to formulate interface elements, resulting in a computationally less demanding formulation. To demonstrate the capability of numerical procedure when applied to a low-velocity impact problem, numerical results are compared with the experimental ones obtained in a test campaign performed on 44 laminates specimens subjected to an out-of-plane and concentrated impact event, according to ASTM test method. Results are in good agreement with experimental data in terms of delamination onset and the internal spatial distribution of induced damage

Constitutive model for fibre-reinforced composite materials exposed to high temperature

A la pàgina XIX del Sumari manquen: la pàgina 333: "Original publications" i les pàgines 335 a 361 "Bibliography"The high strength-weight ratio of composite materials have made them one of the best materials for the design of light-weight structures. However, its special complexity has made them not suitable for the design of structures with a relative complexity or with numerous structural component and pieces. Hence, the importance in the development of adequate constitutive models which allow simulating the micro-macro scale interaction of composites, and to address the intrinsic and natural flexibility of composites that is not as relevant in traditional materials. Meanwhile, the mechanical development of these materials is a mature research branch with more than four groundbreaking decades of life, this is not certainly met at the thermo-mechanical level which is still in an early stage and, consequently, limiting the extensive use of composites in real world and complex structures, particularly structures in which a strong and detailed fulfilment of fire criteria is necessary. E.g., this is the very situation in the large-length ship design sector, where the share in the market for ships built using composite material, tends to be very reduced and closely accompanied by tools which serve to perform structural health monitoring, in order to palliate, the amount of high uncertainty of the present thermo-mechanical response, found in the design of these structures. The present thesis focuses on the development, formulation-wise and computational implementation, of a numerical model in order to predict the non-linear constitutive behaviour of fibre-reinforced plastic (FRP) composites exposed to thermal degradation due to high temperatures. This very model is cemented in the groundbreaking development of constitutive mechanical formulations specially tailored for composites also known as rule of mixtures -- in this present context, the formulation is the so-called serial-parallel rule of mixtures -- which establish a set of closure equations to obtain the suitable micro-macro scale interaction of the composite structure and, at the same time, to take into account the characterisation of the internal and state variables of the constituent phases. Apart, the ultimate objective of this thesis, in this special context -- where a structure is under thermal loads or, what is the same, exposed to fire -- it is mandatory to develop a consistent formulation and tool to perform what is referred to as a fire collapse assessment analysis. The utilisation of a more sophisticated thermal degradation or pyrolysis formulation, based on the present existing formulations, will be employed in order to obtain the internal and state variables of the thermal degradation process. Thus, the outcome of this analysis will serve as means to obtain the unknown thermal state of the structure and complete the thermo-mechanical analysis. The formulation of the thermo-mechanical problem is adapted to be used in laminated non-linear constitutive shells. The use of shells is a necessity for the right optimisation of the computational cost of analysing structures with a high number of structural reinforcements or divisions, such as the ones that appear regularly during the ship design process of large ship structures.Per als materials compostos, la seva relació esforç-pes elevada ha fet d'ells un dels millors materials per al disseny d'estructures lleugeres. No obstant això, la seva especial complexitat, fa d'ells un difícil treball quan es tracta del disseny d'estructures amb una certa complexitat, o, en l'existència de nombroses divisions estructurals i peces. En conseqüència, el desenvolupament de models constitutius adients és de vital importància, en especial aquells que permeten la simulació de la interacció per la micro-macro escala dels compostos, i que resolguin la flexibilitat natural i intrínseca d'aquests materials avançats, qüestió que no és tan rellevant per al disseny de materials tradicionals. Mentrestant, el desenvolupament de teories mecàniques per aquests materials es troba ja a la seva maduració, amb més de quatre dècades de descobriments en aquesta branca. D'altra banda, en qüestions que involucren l'anàlisi termo-mecànica, el paradigma es considera relativament verd, el qual limita l'aplicació extensiva dels compostos en aplicacions pràctiques i d'estructures complexes, de fet, és particularment limitant en el disseny d'estructures que requereixen del compliment d'exigents i detallats criteris relatius al foc. E.g., això mateix succeeix en el disseny d'embarcacions de grans eslores, on la quota de mercat dels vaixells construïts mitjançant materials compostos sol ser reduïda, i estretament acompanyada per eines de monitoratge de la integritat estructural, per així poder pal·liar la gran incertesa vinculada a la resposta termo-mecànica, fruit de les capacitats del disseny comercial actual. L'actual tesi se centra en el desenvolupament, de manera teòrica, i amb corresponent implementació computacional, d'un model numèric capaç de predir el comportament no-linear constitutiu de compostos plàstics amb fibra embedida (FRP) quan aquests són exposats a altes temperatures i en conseqüència a la degradació tèrmica. Aquest mateix model està inspirat en els desenvolupaments, pioners i excepcionals, de models constitutius mecànics, els quals estan pensats per a compostos. Aquestes teories formen part de la família de les regles de barreges, en particular, la formulació escollida és la famosa regla de barreges sèrie-paral·lel, la qual estableix un conjunt d'equacions de tancament per així obtenir l'adequada interacció del material compost a la micro-macro escala. Aquesta formulació, a la mateixa vegada, té en compte la caracterització i evolució de tant variables internes com d'estat, per a les constitutives, en aquest context es tractaria de la fibra i la matriu. Per una altra banda, l'objectiu últim d'aquesta tesi, dins d'aquest context particular, on una estructura és sotmesa a càrregues tèrmiques, o en altres paraules, s'exposa al foc, és de forçosa necessitat el desenvolupament d'una formulació consistent i una eina capaç de verificar el que es podria batejar com una anàlisi de col·lapse al foc. L'ús d'una formulació més sofisticada per la degradació tèrmica o piròlisi, basada en formulació existent, serà empleat per així aconseguir les variables internes i d'estat dels processos de degradació tèrmica. En conseqüència, els resultats d'aquesta anàlisi tèrmica serveixen per a obtenir el desconegut estat tèrmic de l'estructura, la distribució de temperatura a través de l'espessor del laminat, i complementar l'anàlisi del model termo-mecànic. La formulació del problema termo-mecànic és adaptada per ser usada en làmines no lineals de materials compostos. Fer servir làmines és una necessitat per a la correcta optimització del cost computacional derivat de l'anàlisi d'estructures amb un alt nombre de reforços o divisions, anàlisis que són freqüentment trobats dins del procés del disseny d'embarcacions de grans eslores.Para los materiales compuestos, su relación esfuerzo-peso elevada ha hecho de ellos uno de los mejores materiales para el diseño de estructuras ligeras. No obstante, su especial complejidad, hace de ellos un arduo trabajo cuando se trata del diseño de estructuras con una cierta complejidad, o, en la existencia de numerosas divisiones estructurales o piezas. Consecuentemente, el desarrollo de modelos constitutivos adecuados es de importancia, en especial aquellos que permiten la simulación de la interacción para la micro-macro escala de los compuestos, y que resuelven la flexibilidad natural e intrínseca de estos materiales avanzados, cuestión que no es tan relevante para el diseño de materiales tradicionales. Mientras tanto, el desarrollo de teorías mecánicas para estos materiales se encuentra en su madurez, con más de cuatro décadas de hallazgos en esta rama. En contraposición, en cuestiones que atañen el análisis termo-mecánico, el paradigma se encuentra relativamente verde, lo cual limita la aplicación extensiva de los compuestos en aplicaciones prácticas y estructuras complejas, de hecho, es particularmente limitante en el diseño de estructuras que requieren del cumplimiento de exigentes y detallados criterios relativos al fuego. E.g., esto mismo sucede en el diseño de embarcaciones de grandes esloras, donde la cuota de mercado de los buques construidos mediante materiales compuestos suele ser reducida, y estrechamente acompañada por herramientas de monitorización de la integridad estructural, para así poder paliar la gran incertidumbre vinculada a la respuesta termo-mecánica, fruto de las capacidades del diseño comercial actual. La actual tesis se centra en el desarrollo, de manera teórica, y con su correspondiente implementación computacional, de un modelo numérico capaz de predecir el comportamiento no-lineal constitutivo de compuestos plásticos con fibra embebida (FRP) cuando estos son expuestos a altas temperaturas y en consecuencia a la degradación térmica. Este mismo modelo está inspirado en los desarrollos, pioneros y excepcionales, de modelos constitutivos mecánicos, las cuales están pensadas para compuestos. Estas teorías forman parte de la familia de las reglas de mezclas, en particular, la formulación escogida es la renombrada regla de mezclas serie-paralelo, la cual establece un conjunto de ecuaciones de cierre para así obtener la adecuada interacción del material compuesto en la micro-macro escala. Esta formulación, a su misma vez, tiene en cuenta la caracterización y evolución de tanto variables internas como de estado, para las fases constituyentes, en este contexto se trataría de la fibra y la matriz. Por otra banda, el objetivo último de esta tesis, dentro de este contexto particular, donde una estructura se somete a cargas térmicas, o, en otras palabras, se expone al fuego, es de forzosa necesidad el desarrollo de una formulación consistente y una herramienta capaz de verificar lo que se puede acuñar como un análisis de colapso al fuego. El uso de una formulación más sofisticada para la degradación térmica o pirolisis, basada en formulación existente, será empleado para así obtener las variables internas y de estado de los procesos de degradación térmica. En consecuencia, los resultados de este análisis térmico sirven para obtener el desconocido estado térmico de la estructura, la distribución de temperatura a través del espesor del laminado, y complementar el análisis termo-mecánico. La formulación del problema termo mecánico es adaptada para ser usada en láminas no lineales de materiales compuestos. Usar láminas es una necesidad para la correcta optimización del coste computacional derivado del análisis de estructuras con un alto número de refuerzos o divisiones, análisis que son frecuentemente encontrados en el proceso de diseño de embarcaciones de grandes esloras.Postprint (published version