PSI - Issue 68

Lars A. Lingnau et al. / Procedia Structural Integrity 68 (2025) 303–309 L. A. Lingnau et al. / Structural Integrity Procedia 00 (2025) 000–000

305

3

strain generated hydrostatic stress in the forming zone, leading to the development of forming-induced ductile damage. After extrusion, the billet diameter (d 1 ) was measured to be 23.4 mm. To regulate the amount of damage induced, different shoulder opening angles were used. Specifically, shoulder opening angles of 2α = 90° and 2α = 30° were employed during the extrusion process. The choice of shoulder opening angle affects the hydrostatic stress states along the central axis, thereby influencing the degree of forming-induced ductile damage. The full forward rod extrusion was carried out on a triple-acting hydraulic drawing press with a maximum punch force of 2600 kN and a punching speed of 10 mm/s.

Table 1. Chemical composition of 16MnCrS5 steel, all data in wt%. C Si Mn P

S

Cr

Fe

16MnCrS5 steel

0.14 0.14 0.19

< 0.40 1.10

0.010

0.027 0.020 0.035

0.80 0.80 1.10

bal. bal. bal.

Min. Max.

-

1.00 1.30

-

DIN EN 10084

0.40

0.035

The specimen geometry was designed to ensure comparable levels of strain hardening and residual stress, even under varying forming process parameters. The specimens were machined from the formed semi-finished products. Hering (Hering and Tekkaya (2020)) showed that machining does not significantly alter the damage state or the distribution of forming-induced ductile damage within the specimen. Fig. 1 provides details on the specimen geometry used in this study, as well as the extraction position of the specimens from the workpiece after full forward rod extrusion.

Fig. 1. Fatigue specimen geometry and removal area from the component formed via full forward rod extrusion (all dimensions in mm) based on Lingnau (Lingnau et al. (2024)).

2.2. Fatigue testing setup To distinguish the influence of forming-induced ductile damage on the fatigue performance constant amplitude fatigue tests were conducted on a Walter + Bai LFV-T250 T2500 HH servo-hydraulic axial-torsional testing system at a test temperature of T = 20 °C. These tests were conducted with a total strain amplitude of ε a,t = 0.01, a strain ratio of R = 1, and a test frequency of f = 0.01 Hz, combined with superimposed torsion controlled by an angular amplitude of θ = 10° at a frequency of f = 0.01 Hz (Fig. 3a)). To investigate the influence of the phase shift, which represents the phase angle between cyclic axial and torsional loading a phase shift of d = 90° was applied (Fig. 3b)).