PSI - Issue 54

Jürgen Bär et al. / Procedia Structural Integrity 54 (2024) 188–195 Author name / Structural Integrity Procedia 00 (2019) 000–000

189

2

Radius coordinate of the normal vector � Relative Potential, P i = U i /U 0,i with i=1,2,3 Mean relative Potential, P mean = 1/3 ꞏ (P 1 +P 2 +P 3 ) Potential with i=1,2,3 Z-coordinate of the normal vector � Angle coordinate of the normal vector �

n

P i

P mean

Parameter of the Tiedemann equation related to the slope of the curve Parameter of the Tiedemann equation related to the curvature of the curve

r

t

U i y 0

Half distance between the welding points of the wires for the potential measurement

z

Angle of the crack initiation site relative to potential 1, φ = 180°- φ ’

φ

φ ’

1. Introduction The failure of components under cyclic loading cannot be adequately predicted to date. In general, the cyclic lifetime can be divided into 3 phases: crack initiation, propagation of short cracks and propagation of long cracks (Schijve 2003). The investigation of all three phases in one experiment is difficult, because mostly different sample geometries and measurement methods have to be used to investigate the different processes. For detection of crack initiation and the measurement of the crack length different methods are available (Bjørheim et al. 2022; Si et al. 2020). Unfortunately, the location of the incipient crack must be known for all measurement methods that can be automated, and in addition, most methods are restricted to flat specimens. In case of round specimen an automated detection of crack initiation is possible using AC or DC potential drop methods, but the measurement of the crack size is only possible when the crack initiation site is known. Recent investigations by Hartweg and Bär (Hartweg und Bär 2019) as well as Nahbein and Bär (Nahbein und Bär 2022) have shown that the crack location can be detected by using a multiple potential measurement on round specimens. In this paper a method is presented which allows the determination of the crack depth in round specimens independent of the position of the crack on the circumference. 2. Experimental details The experiments were performed on round specimen with a diameter of 20 mm of the high alloyed steel X2CrNi 19-11 (AISI 304L). A circumferential notch with a radius of 4 mm and a depth of 3 mm was machined into the specimens (figure 1a). For the measurement with three potential probes copper wires with a diameter of 0.22 mm were laser welded to the circumference of the specimen with an angle of 120° in between (figure 1b) directly at the border of the notch as shown in figure 1c.

a

b

c

Fig. 1. (a) specimen geometry; (b) position of the potential probes on the circumference; (c) location of the potential probes near the notch.