**1. Introduction**

The austenitic stainless steel AISI 316L is one of the most utilized constructional materials for various parts in the power industry and beyond. It was investigated in the conventional wrought state [1], while it has been loaded in tension, torsion, and even combinations of both. Nevertheless, it is increasingly utilized in the additively manufactured form [2], as it opens new possibilities. This was the motivation for the conference paper [3], which is the forerunner of this further extended paper. Stainless steel 316L (SS316L) may be optimized and applied in an organic shape or can even serve as a custom made part or machine element utilized in the repair or reconstruction of a structure, where commercial products are not available or are hardly producible by conventional manufacturing, such as machining. Various process parameters used during the additive

**Citation:** Koˇrínek, M.; Halama, R.; Fojtík, F.; Pagáˇc, M.; Krˇcek, J.; Krzikalla, D.; Kocich, R.; Kunˇcická, L. Monotonic Tension-Torsion Experiments and FE Modeling on Notched Specimens Produced by SLM Technology from SS316L. *Materials* **2021**, *14*, 33. https:// dx.doi.org/10.3390/ma14010033

Received: 27 November 2020 Accepted: 21 December 2020 Published: 23 December 2020

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manufacturing of SS316L have been examined [4,5]. One of the important outputs are the mechanical properties [6,7] or porosity [8]. The building direction also plays a vital role [9], and the final surface roughness is of particular interest [10]. It is well known that printing the layer by layer and natural cooling from the bottom directly lead to the formation of residual stresses in the material. The influence of the scanning strategy on the resulting residual stresses was also intensively studied for SS316L in recent years [11–13]. There are many studies available, which are focused on mechanical properties research, including anisotropy induced by the selective laser melting (SLM) process in the literature. However, there is still missing information about the plasticity of SS316L prepared by SLM under various multiaxial stress states. To simulate critical loading states and nonstandard events in technical practice, it is important to realize the necessary monotonic experiments using biaxial testing machines. This is an important motivation for research in the field of multiaxial plasticity.

This paper presents new results for the deformation response obtained during monotonic multiaxial loading of specimens made from SS316L, produced by SLM technology in the "as printed" state. Almost all specimens were printed in the vertical direction to prevent the effect of residual stresses. Due to the character of the specimens that contain notches, the digital image correlation (DIC) method was used. The DIC method is a progressive optical-numerical method suitable for 3D analysis of structural components under uniaxial and multiaxial loading in the full-field [14,15]. Averaged characteristics gained in this experimental study with DIC measurements were used for the validation of a numerical model based on the finite element method (FEM).
