[pt] Critérios de fadiga multiaxial para vida infinita tinham por objetivo apenas avaliar a ocorrência de fratura em um componente mecânico quando submetido a carregamentos multiaxiais totalmente reversíveis. Carpinteri e Spagnoli propuseram uma modificação em seu próprio modelo, substituindo por outros parâmetros os limites de resistência à fadiga em flexão f−1 e torção t−1 para ensaios totalmente reversíveis, introduzindo na equação uma variável nf que permitiu realizar uma previsão de vida em fadiga finita. O objetivo do presente estudo é verificar experimentalmente a consistência dessa modificação. A metodologia consistiu em obter experimentalmente curvas de Wohler para tração e torção referentes ao aço DIN 42CrMo4 a fim de obter os parâmetros m e m(asterisco), que são os coeficientes angulares das mesmas em escala log-log, produzindo meios para a aplicação do critério. Como o equacionamento do modelo não apresenta solução analítica, foi desenvolvido uma solução numérica para obter junto ao critério uma previsão teórica de vida em fadiga. Adicionalmente, o estudo busca discutir acerca de uma possível relação direta entre amplitude de tensão normal, amplitude de tensão cisalhante e número de ciclos para falha. O modelo em si apresentou consistência parcial com os experimentos, tendo sido assertivo nos ensaios de torção pura, mas discrepante em ensaios de tração pura. Para carregamentos combinados, houve razoável precisão em dois casos e grande dispersão em outra, mas a avaliação final depende de mais pontos experimentais. / [en] Infinite-life multiaxial fatigue criteria had only the ability to evaluate whether or not fatigue failure is to occur to a mechanical componente once subjected to multiaxial fatigue loadings. Carpinteri e Spagnoli proposed a modification to their own model, substituting both fully reversed bending and torsion fatigue endurance limits, f1 and t−1 respectively, introducing into the equation a new variable nf, allowing the model to predict the fatigue-life of the mechanical component. The main goal of the presente study is to assess the accuracy of the modified model via experiments. The research methodology consisted in determining m and m (asterisk), which are the slopes of the S-N curves for fully reversed bending and torsion experiments on regards to DIN 42CrMo4 steel when plotted into a log-log scale, providing means to apply the model. Since there is no analytic solution to the model, the criterion s equation has to be solved numerically. Furthermore, the present study discusses the possibility of a direct relation between amplitude of normal stress, amplitude of shear stress and number of cycles to failure. The modified Carpinteri & Spagnoli s criterion proved itself to be partially consistent, presenting both accurate predictions of torsional fatigue-life and discrepant results for axial loadings. For combined loadings, the model provided two consistent results while another experimental point was proved far off. The final assessment on regards to the model s accuracy depends on more experimental points.

<p>  </p> <p>There has been a growing interest within the aerospace industry for shifting towards a digital twin approach, for reliable assessment of individual components during the product lifecycle - across design, manufacturing, and in-service maintenance, repair & overhaul (MRO) stages. The transition towards digital twins relies on continuous updating of the product lifecycle datasets and interoperable exchange of data applicable to components, thereby permitting engineers to utilize current state information to make more-informed downstream decisions. In this thesis, we primarily develop a framework to store, track, update, and retrieve product lifecycle data applicable to a serialized component, its features, and individual locations. </p> <p>From a structural integrity standpoint, the fatigue performance of a component is inherently tied to the component geometry, its material state, and applied loading conditions. The manufacturing process controls the underlying material microstructure, which in turn governs the mechanical properties and ultimately the performance. The processing also controls the residual stress distributions within the component volume, which influences the durability and damage tolerance of the component. Hence, we have demonstrated multiple use cases for fatigue life assessment of critical aerospace components, by using the developed framework for efficiently tracking and retrieving (i) the current geometric state, (ii) the material microstructure state, and (iii) residual stress distributions.</p> <p>Model-based definitions (MBDs) present opportunities to capture both geometric and non-geometric data using 3D computer-aided design (CAD) models, with the overarching aim to disseminate product information across different stages of the lifecycle. MBDs can potentially eliminate error-prone information exchange associated with traditional paper-based drawings and improve the fidelity of component details, captured using 3D CAD models. However, current CAD capabilities limit associating the material information with the component’s shape definition. Furthermore, the material attributes of interest, viz., material microstructures and residual stress distributions, can vary across the component volume. To this end, in the first part of the thesis, we implement a CAD-based tool to store and retrieve metadata using point objects within a CAD model, thereby creating associations to spatial locations within the component. The tool is illustrated for storage and retrieval of bulk residual stresses developed during the manufacturing of a turbine disk component, acquired from process modeling and characterization. Further, variations in residual stress distribution owing to process model uncertainties have been captured as separate instances of the disk’s CAD models to represent part-to-part variability as an analogy to track individual serialized components for digital twins. The propagation of varying residual stresses from these CAD models within the damage tolerance analysis performed at critical locations in the disk has been demonstrated. The combination of geometric and non-geometric data inside the MBD, via storage of spatial and feature varying information, presents opportunities to create digital replica or digital twin(s) of actual component(s) with location-specific material state information.</p> <p>To fully realize a digital twin description of components, it is crucial to dynamically update information tied to a component as it evolves across the lifecycle, and subsequently track and retrieve current state information. Hence, in the second part of the thesis, we propose a dynamic data linking approach to include material information within the MBDs. As opposed to storing material datasets directly within the CAD model in the previous approach, we externally store and update the material datasets and create data linkages between material datasets and features within the CAD models. To this end, we develop a model-based feature information network (MFIN), a software agnostic framework for linking, updating, searching, and retrieving of relevant information across a product’s lifecycle. The use case of a damage tolerance analysis for a compressor bladed-disk (blisk) is demonstrated, wherein Ti-6Al-4V blade(s) are linear friction welded to the Ti-6Al-4V disk, comprising well-defined regions exhibiting grain refinement and high residuals stresses. By capturing the location-specific microstructural information and residual stress fields at the weld regions, this information was accessed within the MFIN and used for downstream damage tolerant analysis. The introduction of the MFIN framework facilitates access to dynamically evolving as well as location-specific data for use within physics-based models.</p> <p>In the third part of thesis, we extend the MFIN framework to enable a physics-based, microstructure sensitive and location-specific fatigue life analysis of a component. Traditionally, aerospace components are treated as monolithic structures during lifing, wherein microstructural information at individual locations are not necessarily considered. The resulting fatigue life estimates are conservative and associated with large uncertainty bounds, especially in components with gradient microstructures or distinct location-specific microstructures, thereby leading to under usage of the component’s capabilities. To improve precision in the fatigue estimates, a location-specific lifing framework is enabled via MFIN, for tracking and retrieval of microstructural information at distinct locations for subsequent use within a crystal plasticity-based fatigue life prediction model. A use case for lifing dual-microstructure heat treated LSHR turbine disk component is demonstrated at two locations, near the bore (fine grains) and near the rim (coarse grains) regions. We employ the framework to access (a) the grain size statistics and (b) the macroscopic strain fields to inform precise boundary conditions for the crystal plasticity finite-element analysis. The illustrated approach to conduct a location-specific predictive analysis of components presents opportunities for tailoring the manufacturing process and resulting microstructures to meet the component’s targeted requirements.</p> <p>For reliably conducting structural integrity analysis of a component, it is crucial to utilize their precise geometric description. The component geometries encounter variations from nominal design geometries, post manufacturing or after service. However, traditionally, stress analyses are based on nominal part geometries during assessment of these components. In the last part of the thesis, we expand the MFIN framework to dynamically capture deviations in the part geometry via physical measurements, to create a new instance of the CAD model and the associated structural analysis. This automated workflow enables engineers for improved decision-making by assessing (i) as-manufactured part geometries that fall outside of specification requirements during the materials review board or (ii) in-service damages in parts during the MRO stages of the lifecycle. We demonstrate a use case to assess the structural integrity of a turbofan blade that had experienced foreign object damage (FOD) during service. The as-designed geometry was updated based on coordinate measurements of the damaged blade surfaces, by applying a NURBS surface fit, and subsequently utilized for downstream finite-element stress analysis. The ramifications of the FOD on the local stresses within the part are illustrated, providing critical information to the engineers for their MRO decisions. The automated flow of information from geometric inspection within structural analysis, enabled by MFIN, presents opportunities for effectively assessing products by utilizing their current geometries and improving decision-making during the product lifecycle.</p>