PSI - Issue 34

Zoltan Major et al. / Procedia Structural Integrity 34 (2021) 191–198 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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2. Experiments 2.1. Materials and Specimens

Two cylindrical test specimen configurations (hollow cylindrical (CH) and bulk notched cylindrical specimens (BNC)), with approx. the same nominal cross-section, were produced at cirp GmbH (Heimsheim, Germany) using an EOS Formiga SLS machine (EOS GmbH, Krailling, Germany). The printing orientation is vertical (parallel to the faces and perpendicular to the symmetry axis (90°)) and horizontal (perpendicular to the faces and parallel to the symmetry axis (0°)). The specimens are shown in both printing position in Fig. 1. Similar specimen geometry is used for fatigue testing of rubbers [Alshuth, 2002; Abraham, 2005].

Fig. 1. Cylindrical test specimen configurations (a) printing orientation vertical (90°); (b) printing orientation parallel (0°).

These cylindrical specimens can be tested under axial (tensile/compressive) loading and under torsional loading with different boundary conditions at the top face of the specimens. Recent investigations are focused on the axial loading (tension/compression) but follow-up investigations will also utilize a wide complexity of multiaxial (axial/torsional (shear)) loading conditions. 2.2. Test parameters and equipment The following test parameters have been varied during the investigation: • Material grades; PA12 (PA 2200 - Polyamide 12) and TPU (EOS TPU 1301), • Hollow cylindrical (HC) and bulk notched cylindrical specimens (BNC), • 0° (parallel) and 90° (perpendicular) printing direction relative to the symmetry axis of the specimens, • Monotonic tensile tests with testing rates 0.1 mm/s, 1 mm/s, 10 mm/s, 100 mm/s at RT; • Cyclic tensile tests with R = 0.1 (tension/tension) and R = -1 (tension/compression), at a frequency of f=5 Hz at T=23 °C and • Specimens with and without surface treatment The monotonic tests at various loading rates have been performed on a servohydraulic testing machine (MTS Damper Test System, MTS Systems, Minneapolis, USA), the cyclic fatigue tests were carried out on an electromechanical testing machine (TAinstruments, ElectroForce 3500, Minneapolis, USA). The same self-designed and home-made fixture with corresponding adapter was used for both tests. 3. Results Monotonic tests First, the results of the monotonic tensile tests are described and discussed. Load-displacement curves of PA12 and TPU for 0.1 mm/s are plotted in Fig. 2. The differences in the stress-strain curve and thus in the corresponding tensile