PSI - Issue 24

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Lorenzo Bergonzi et al. / Procedia Structural Integrity 24 (2019) 213–224 Lorenzo Bergonzi et al. / Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction This work offers an insight of miniaturized specimen technique development and usage as a viable method to assess materials mechanical properties. Such a methodology is very interesting especial for metal additive manufacturing (AM), where the cost of rough material is quite high and therefore there is great interest in limiting the quantity needed for material characterization. Furthermore, it is described the process of miniaturization of MaCh3D proprietary tensile testing specimen (Bergonzi et al. 2018) in order to use the machine with high performance materials such as metal alloys. Using MaCh3D in AM fabricated metal characterization would make the process more economic efficient, lowering the costs associated to quality assessment as well as enabling punctual monitoring of production directly on the production site.

Nomenclature AM

Additive Manufacturing DMLS Direct Metal Laser Sintering L 0 Initial gauge length S 0 Initial area of cross-section D 0

Initial diameter of the parallel length of a circular test piece

T

Specimen thickness Specimen width Average grain size Imposed displacement

W

s u

T x,y,z

Suppressed translational degree of freedom in x, y or z direction

k s k r Dimensional ratio for sheet specimens Dimensional ratio for round specimens K t Stress concentration factor "#$ Maximum stress on specimen section, excluding heads % Nominal stress on rectilinear section ' Reaction forces FFF Free Filament Fabrication " Maximum tensile stress 1.1. Miniaturized specimen technique

In recent decades, small specimen test technique has been implemented to study post-irradiation structural materials for nuclear reactors or evaluating the residual life of industrial equipment Dyson et al. (2016); Klueh (1985); Lucas (1990); Lucon (2014); Wakai et al. (2011); Xu et al. (2000) In such situations, limited materials are available for testing, due to the volume limits in irradiation testing facility and the necessity for reducing specimen radioactivity, and the requirement for minimum damage of sampling in-service components. Specimen size reduction must be done in such a way to guarantee that the obtained sample geometry is still representative of bulk material mechanical properties. Nonetheless, because of the size effect and other reasons, mechanical properties deduced from some small specimens, can significantly deviate from measured values for standard specimens as reported in many works in literature. A great variety of tensile specimens with different sizes and geometries have been used in different works, mainly to reduce the volume of material needed Liu et al. 2017; LaVan and Sharpe 1999; Sergueeva et al. 2009; Rund et al. 2015; Zhao et al. (2009) or to maintain the test specimen similar in size to structural components, the latter applying especially in the study of micro-mechanics such material characterization of electronic components with dimensions in the order of microns Sharpe (2003). In the vast majority of cases, specimens deviate from the sizes and geometries prescribed by ASTM / ISO standards; moreover, different tensile testing techniques are being used, such