PSI - Issue 77

Bastian Roidl et al. / Procedia Structural Integrity 77 (2026) 119–126 Author name / Structural Integrity Procedia 00 (2025) 000 – 000

121

3

Table 1 - Printing parameters differ for the skin and for the core regions. Segment Skin

Core 370 1400 0.112 0.050 Core 190

Power [W] Speed [mm/s]

200 800

Hatch spacing [mm] Spot size [µm] Layer height [mm]

0.112

140

0.025

Subsegment Scan trajectory

Surface

Subsurface

Equidistant to surface

Zig-zag

Chessboard

Domain

Into a depth of approx. 0.3 mm

Into a depth of approx. 2.5 mm

The rest

H

A

G

Fig. 1

Specimens A have the cross-sectional area of 63.6 mm 2 , G-specimens have the area of 10.2 mm², and H-specimens 30.5 mm².

2.2. Tensile test results Prior to dynamic test, tensile tests were carried out on a Hegewald & Peschke tensile testing machine at OTH Amberg Weiden with a 20 kN load cell and a built-in extensometer in order to gain initial insights into the material properties of the specimens. For these preliminary tests, experiments were conducted on 10 specimens. The average values from these measurements result in elongation to failure of 5%, tensile strength of 393 MPa, and yield strength of 229 MPa, with only minor scatter among the measured values. 2.3. Fatigue experiments Fatigue tests were carried out at three different sites, the Free University of Bozen-Bolzano, CTU in Prague and OTH Amberg-Weiden. For tests at OTH and CTU, the fatigue specimens were designed with a machined head incorporating a M18x1 thread to allow attachment to an Amsler HFP 422 resonant pulsator equipped with a 100 kN load cell (testing frequency ranging from 90 Hz up to 120 Hz based on the specimen geometry). The specimens with the G geometry were tested at the Free University of Bozen-Bolzano, using a STEP Lab UD04 machine with a 5 kN load cell with fixed testing frequency of 35 Hz. Six test series were analyzed. Two different load ratios — fully reversed (R = -1) and tension-tension (R = 0.1) have been applied to draw conclusions about the influence of mean stress. The specimens were tested with the focus set on the region of lifetimes between 10,000 and 1,000,000 cycles. The fatigue tests conducted in this study were terminated upon reaching any of the following criteria: • A decrease in testing frequency of more than 10 Hz, • A variation in load amplitude exceeding ±0.5 kN, • A shift in static load beyond ±0.5 kN, • Completion of 10⁷ cycles, at which point the specimen was classified as a run -out. Run-out specimens were subsequently subjected to an additional fatigue test with at least double the original load amplitude to further assess their behavior. Kohout- Věchet (K&V) model of the S-N curve [13] is described as follows: = [ ∙ + + ] . (1)