This work describes the creation of detailed FEM models of the selected area. Primarily is focused on the process of creating a detailed FEM model of the part of airplane using the static condensation. This work also contains a description of the process stress analysis of part of the fuselage of the airplane EV-55 Outback.

This research explores the nearly untapped research area of the analysis of fracture mechanics in residual stress zones. This type of research has become more prevalent in the field in recent years due to the increase in prominence of residual stress producing processes. Such processes include additive manufacturing of metals and installation procedures that lead to loads outside the anticipated standard operating load envelope. Abaqus was used to generate models that iteratively advanced toward solving this problem using the compact tensile specimen geometry. The first model developed in this study is a two-dimensional fracture model which then led to the development of an improved three-dimensional fracture model. Both models used linear elastic fracture mechanics to determine the stress intensity factor (K) value. These two models were verified using closed-form equations from linear elastic fracture mechanics. The results of these two models validate the modeling techniques used for future model iterations. The final objective of this research is to develop an elastic-plastic fracture mechanics model. The first step in the development of an elastic-plastic fracture model is a three-dimensional quasi-static model that creates the global macroscale displacement field for the entire specimen geometry. The global model was then used to create a fracture submodel. The submodel utilized the displacement field to reduce the model volume, which allowed a higher mesh density to be applied to the part. The higher mesh density allowed more elements to be allocated to accurately represent the model behavior in the area local to the singularity. The techniques used to create this model were validated either by the linear elastic models or by supplementary dog bone prototype models. The prototype models were run to test model results, such as plastic stress-strain behavior, that were unable to be tested by just the linear elastic models. The elastic-plastic fracture mechanics global quasi-static model was verified using the plastic zone estimate and the fracture submodel resulted in a J-integral value. The two-dimensional linear elastic model was validated within 6% and the three-dimensional linear elastic model was validated within 0.57% of the closed-form solution for linear elastic fracture mechanics. These results validated the modeling techniques. The elastic-plastic fracture mechanics quasi-static global model formed a residual stress zone using a Load-Unload-Reload load sequence. The quasi-static global model had a plastic zone with only a 0.02-inch variation from the analytical estimate of the plastic zone diameter. The quasi-static global model was also verified to exceed the limits of linear elastic fracture mechanics due to the size of the plastic zone in relation to the size of the compact specimen geometry. The difference between the three-dimensional linear elastic fracture model J-integral and the elastic-plastic fracture submodel initial loading J-integral was 3.75%. The J-integral for the reload step was 18% larger than the J-integral for the initial loading step in the elastic-plastic fracture submodel. / Master of Science / Additive manufacturing, sometimes referred to as 3-D printing, has become an area of rapid innovation. Additive manufacturing methods have many benefits such as the ability to produce complex geometries with a single process and a reduction in the amount of waste material. However, a problem with these processes is that very few methods have been created to analyze the initial part stresses caused by the processes used to additive manufacture. Finite element methods are computer-based analyses that can determine the behavior of parts based off prescribed properties, shape, and loading conditions. This research utilizes a standard fracture determination shape to leverage finite element methods. The models determine when a crack will form in a part that has process stresses from additive manufacturing. The model for crack initiation was first developed in two dimensions, neglecting the thickness of the part, using a basic material property definition. The same basic material property definition was next used to develop a crack initiation model in three dimensions. Then a more advanced material property definition was used to capture the impact of additive manufacturing on material properties. This material property definition was first used to establish the part properties as it relates to part weakening due to additive manufacturing. A higher accuracy model of just the crack development area was produced to determine the crack initiation properties of the additive manufactured part. Methods previously confirmed by testing were used to validate the models produced in this research. The models demonstrated that under the same loading parts with initial processes stresses were closer to fracture than parts without initial stresses.

Es wird ein auf der Submodelltechnik basierender Ansatz vorgestellt, mit dem Cord-Elastomer-Verbunde, speziell die Balgwände von Luftfedern, einer detaillierten FE-Analyse zugänglich gemacht werden können. Dieser Ansatz beinhaltet ein Globalmodell, das die gesamte Luftfeder abbildet, und zwei Submodelle, die sich auf bestimmte Ausschnitte der Balgwand konzentrieren.

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Neben Reifen, Riemen und Schläuchen zählen speziell auch die Balgwände von Luftfedern zu den Kompositen, da deren weiche Elastomermatrix zur Verstärkung Gewebelagen aus textilen Corden enthält. Diese Verstärkungsträger bestehen aus miteinander verzwirnten Garnen, die ihrerseits einen Zwirn aus polymeren Filamenten darstellen. Luftfederbälge weisen dementsprechend eine hochkomplexe innere Geometrie auf und sind zudem durch stark anisotropes, nichtlineares Materialverhalten gekennzeichnet. Für die strukturmechanische Simulation von Luftfedern mit der Finite-Elemente-Methode (FEM) werden in der vorliegenden Arbeit neuartige, hochauflösende Modelle entwickelt, die diesen Eigenschaften Rechnung tragen. Zunächst wird ein mathematisches Modell formuliert, das die verzwirnte Geometrie von Corden auf allgemeinen räumlichen Bahnkurven beschreibt und mithilfe dessen sich auch die lokale Orientierung der Filamente bestimmen lässt. Zur konstitutiven Modellierung des Filamentmaterials wird zudem ein transversal isotropes, hyperelastisches Materialmodell so modifiziert, dass bei Druckbelastung in Filamentrichtung nur noch die der Regularisierung dienende, isotrope Grundsteifigkeit zum Tragen kommt. Das Geometriemodell der Corde ist die Basis für deren dreidimensionale Abbildung in FE-Netzen von Luftfederbälgen. Als erster Schwerpunkt wird ein auf zyklischer Symmetrie basierendes Streifenmodell entwickelt, das die Cordgeometrie im gesamten Balg vollständig auflöst. Ein besonderes Augenmerk gilt dabei der Generierung konformer Netze, um die Grenzflächen zwischen Matrix und Corden exakt darzustellen. Das Streifenmodell ermöglicht somit detaillierte Analysen zur lokalen Verteilung von Spannungen und Verzerrungen im Inneren der Balgwand. Als zweiter Schwerpunkt wird diese Art der Modellierung auf einen kleinen rechteckigen Ausschnitt der Balgwand übertragen. Dieser Teppich ist als Submodell konzipiert, das Verschiebungen für seine Schnittränder aus einem vereinfachten Globalmodell bezieht und demzufolge die Analyse allgemeiner, nicht axialsymmetrischer Lastfälle möglich macht. Abschließend werden die Modelle anhand einer Rollbalgluftfeder für Busanwendungen eingehend untersucht und einem Praxistest zum Vergleich zweier Konstruktionsvarianten unterzogen. / Tires, belts, hoses and, in particular, air spring bellows are regarded as composites due to layers of reinforcing textile cords that are embedded in a soft elastomer matrix. These cords are produced by twisting yarns which, for their part, represent a twisted structure of polymeric filaments. Hence, air spring bellows feature a highly complex internal geometry as well as strongly anisotropic, nonlinear material behavior. For structural simulations of air springs by means of the finite element method (FEM), new high resolution models are developed here, which reflect all the aforementioned properties. At first, a mathematical model capable of representing the twisted geometry of cords on three-dimensional curves is introduced, which also allows to derive local filament orientations. For the constitutive description of filament material, a transversally isotropic, hyperelastic material model is modified so that only the small isotropic stiffness introduced for regularization remains in case of compressive loads in filament direction. The cord geometry model serves as the basis for their three-dimensional representation in FE meshes of air spring bellows. Firstly, the focus lies on developing a slice model relying on cyclic symmetry, which takes cord geometry into account throughout the entire bellows. Special emphasis is put on building conforming meshes in order to incorporate all material interfaces explicitly. As a result, the slice model allows for detailed analyses of local stress and strain distribution inside the bellows. Secondly, this type of modeling is applied to a rectangular section of the bellows. This carpet is conceived as a submodel acquiring the displacements to be imposed on its cut faces from a simplified global model, and therefore provides the opportunity to analyze general load cases not complying with axial symmetry. Based on a rolling lobe air spring used in bus applications, both models are examined thoroughly and, at last, subjected to a practical test comparing two different designs.