Issue 43

F. Berto et alii, Frattura ed Integrità Strutturale, 43 (2018) 1-32; DOI: 10.3221/IGF-ESIS.43.01 21 setup time and the use of tools (Fig. 26). This digital workflow prompts a product development process and structural property prediction without physical testing, only utilizing advanced simulation based methods for both, structural optimization and failure prevention. Figure 26: Complex component obtained by AM processes. With AM, however, a significant problem arises in these methodologies. In conventional manufacturing technologies, one utilizes a given material with defined and well-known material properties and removes material to obtain the desired geometry. In contrast, the material properties in AM evolve during the fabrication process. Geometry and material properties are closely related, every change in the geometry will change the way the AM machine performs its building routine affecting the toolpath and ultimately the properties of the resulting solid. Parts are no longer isotropic, in some cases not fully dense, surfaces are rough and there is a high change of inclusions, impurities and inhomogeneities, all related to the underlying manufacturing strategy, which, in turn, is dependent on the input geometry. We face a dilemma; on the one hand, we possess a technology that is undoubtedly of high potential and can fulfil the needs of modern digital manufacturing, which enables the manufacturing of unprecedented complex designs in an economic fashion. On the other hand, we cannot guarantee that these parts will withstand complex loading scenarios because of the still poor and/or poorly known material properties as well as the failure criteria allowing their prediction in place to date and an accurate design considering the structural integrity is fully guaranteed. Utilizing modern AM, the aim is to create digital material designs fulfilling stringent requirements of aerospace, automotive and biomedical applications. The latest topology optimization routines can be used and developed further for better usability and better interaction with the AM manufacturing process chain. Specifically, it is possible to work on improving the interfaces between the topology optimization routine and its compatibility to solid modelling. This will enable easy downstream processing. Further, it is necessary to optimize the tessellation routines streamlining the entire development process and allowing smooth transition between the individual steps of the process. Further, it is important to optimize support structures. These are necessary for attaching AM parts to the building platform to ensure dimensional accuracy. These support elements can be considered as part of the optimization routine maximizing speed and minimizing failure already happening in the building process. To develop experimental and theoretical understanding of the fatigue and fracture behavior of these advanced geometric complex components is then a fundamental step for taking advantage of AM processes in structural components. To date, this assessment and the quality assurance of AM components is not accurate as microstructural features as well as the specific mechanical/cracking behavior of AM materials cannot be modelled effectively due to their building strategy determined microstructural configuration. For complex AM components, no specific design criteria are in place considering stress concentration phenomena arising from geometrical discontinuities/features. Further, no fatigue data generated by testing such geometrical discontinuous AM metals can be found in the technical literature. It remains a very