PSI - Issue 79

Daniel Hofferberth et al. / Procedia Structural Integrity 79 (2026) 313–321

320

of v = 0.092 – 0.096 for alternating and v = 0.069 – 0.079 for pulsating loading [Hofferberth10]. The individual scatter of the S-N curves is shown as error-lines.

9 12 15 18 21 24 27 30

scatter band

v N=10 6 =0.065

regression line

v N=10 6 =0.068

6

Bonded specimens Experimental value at N = 10 6 load cycles

R  = -1 R  = 0

 2 =  1 (V 90%,1 /V 90%,2 ) v

3

0.01 Local stress amplitude [MPa] 0.1

1

10

100

1000

V 90% [mm³]

Fig. 8: Highly stressed volume diagram for the bonded specimens

� � � � �� � �� %, � � �� %, � � �

(4)

With the conversion of equation (4), the endurable local stress amplitude  2 of an individual component, like a magnet, can be calculated, equation (5). � � � � � �� %, � � �� %, � � � (5) With the determined slopes and the endurable local stress amplitudes ���� � 444 MPa and ��� � 555 MPa for a reference volume of �� & � 1 � , the fatigue strength of bonded magnets can be assessed. 4. Conclusion Due to the use of rare-earth elements in many applications, design, and, above all, recycling strategies are becoming increasingly important. For sustainable assessment of bonded magnetic components, the knowledge of fatigue behavior and common assessment approaches is important and part of the HARMONY project. The fatigue tests, performed with bonded specimens without subsequent magnetization (reference S-N curves), showed only a small influence of aging on the fatigue behavior, which leads to the application of a common evaluation of the individual fatigue tests. However, it is evident that mean stresses have a higher influence on fatigue behavior, resulting in mean stress sensitivities between 0.64 < M ≤ 0.78. With the knowledge of the mean stress sensitivity, the notch concentration factor and the highly stressed volume V 90% , necessary information for an assessment of individual components are available. In further studies, the influence of magnetization on fatigue behavior will be further investigated. Acknowledgements The work was performed within the HARMONY Project, co-funded by the European Union Call HORIZON-CL4 RESILIENCE-01-09 – Recyclability and resource efficiency of Rare Earth based magnets (IA). References Kuguel, R., 1960. The highly stressed volume of material as a fundamental parameter in the fatigue strength of metal members, Theor. Appl Fract. Mech 1960, 169, pp. 1 – 18 Sonsino, C. M., 1993. Zur Bewertung des Schwingfestigkeitsverhaltens von Bauteilen mit Hilfe örtlicher Beanspruchungen, Konstruktion 45 (1993), pp. 25 – 33