Deformation and failure mechanisms of metallic additively manufactured triply periodic minimum surface structures

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The advantageous use of topologically optimized, light-weight cellular structures in industry often requires cunning and flexible production technologies, such as additive manufacturing (AM). AM allows for an optimization of the geometry e.g. with respect to a reduced weight of the component. However, it sometimes possesses reduced mechanical stability and performance caused by naturally introduces defects at the microscopic (single strut), mesoscopic (unit cell) and macroscopic (whole lattice structure) scale. It is therefore imperative to well understand the deformation and failure mechanisms of such complex structures at all of the three length scales. The proposed project aims at understanding the deformation and failure mechanisms of metallic AM Triply Periodic Minimum Surface (TPMS) structures. Our approach is based on a combination of advanced characterization, data-driven, and model-based methodologies. On the one hand, we aim to investigate the geometric features and mechanical behavior of these structures using experimental data (namely ex- and in-situ X-ray Computed Tomography, XCT). On the other hand, this knowledge will be generalized using simulation models to predict the mechanical behavior (stiffness, load bearing capacity) of untested TPMS structures. Advanced Bayesian techniques combined with a random field representation of geometrical defects and constitutive parameters are used to determine both systematic manufacturing deficiencies in the geometry as well as the spatial distribution of model parameters including an uncertainty quantification to predict the accuracy of the model prediction. The optimization and further development of in-situ XCT imaging and experimental data analysis methods are a precondition for the application of improved model calibration techniques that directly use the complete deformation field obtained from the digital volume correlation. There are a few mechanisms contributing to the deformation and damage of TMPS structures, some linked to the raw material (microstructure), some to the manufacturing parameters (micro- and mesoscopic effects, e.g. manufacturing defects), and some to the geometrical features (nominal geometry, wall thickness deviation). In the project, those effects are analyzed: we will identify geometrical defects and subsequently analyze the material behavior (e.g. (an-)isotropy). To derive realistic and comprehensive insights, two loading scenarios will be studied: compression (widely applied for AM cellular structures) and torsion (novel). As an ultimate achievement, the identification the deformation and failure mechanisms will allow specifying the most relevant design and manufacturing parameter contributing to the mechanical behavior and predicting the mechanical performance and its uncertainty directly by a simulation model directly incorporating manufacturing defects.