PSI - Issue 57

8

Ahmad Qaralleh et al. / Procedia Structural Integrity 57 (2024) 649–657 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

656

Fig. 9 (a-d) presents lifetime estimates for both constant and variable amplitudes, considering load ratios R = -1 and R = 0. These estimates are based on stress hypotheses, namely, von Mises and the 1 st principal stress, using damage parameters P RAM and P RAJ . The estimates incorporate cyclic material properties obtained from strain-controlled tests and the incremental step test. The calculated data points are compared with experimental results.

a.)

d.)

10 2 10 40 50 60 70 Force Amplitude F a [kN] (log) 40 50 60 70 Force Amplitude F a [kN] (log) 20 30 10 20 30

10 40 50 60 70 Force Amplitude F a [kN] (log) R F = 0 k = 6 N k = 4·10 5 F a,k = 16 kN T S = 1:1.01 20 30

R F = -1 k = 6 N k = 1·10 6 F a,k = 17.3 kN T S = 1:1.1

von Mises Max Principal P RAM P RAJ P RAM P RAJ

von Mises Max Principal P RAM P RAJ P RAM P RAJ

CA IST

CA IST

10 2

10 3

10 4

10 5

10 6

10 7

10 3

10 4

10 5

10 6

10 7

Cycles to failure N (log)

Cycles to failure N (log)

c.)

e.)

10 40 50 60 70 Force Amplitude F a [kN] (log) 20 30

R F = -1 k = 7 N 10 7 = 1·10 7 F a, 10 7 = 31 kN T S = 1:1.13

R F = 0 k = 6 N = 3·10 6 F a,3·10 6 = 27.7 kN T F = 1:1.08

von Mises Max Principal P RAM P RAJ P RAM P RAJ

von Mises Max Principal P RAM P RAJ P RAM P RAJ

CA IST

CA IST

10 2

10 3

10 4

10 5

10 6

10 7

10 2

10 3

10 4

10 5

10 6

10 7

Cycles to failure N A (log)

Cycles to failure N (log)

Fig. 9 Comparison between experimental and calculated fatigue lifetime. a.) CAL R= -1; b.) CAL R= 0; c.) VAL R= -1; d.) VAL R= 0

The FKM guideline nonlinear approach yielded weak estimation for the material's fatigue lifetime, primarily due to the significant influence of load time history and unaddressed transient behavior. The results obtained were conservative. However, the employment of P RAM with the material properties obtained from the constant amplitude loading yielded acceptable results compared to other different variants considered. The local strain approach assumes that the material's behavior can be represented by its stabilized response. This assumption does not accurately describe the transient behavior observed in the examined material. Thus, the estimated fatigue life may be ambiguous and not truly indicative of the material's fatigue life in realistic applications. 6. Conclusion The comprehensive experimental study on the steering knuckle made of bainitic steel provided valuable insights into its cyclic behavior. The observed hardening effects, the transition from linear-elastic to elastic-plastic stress-strain behavior, and the influence of higher loads on material response were all significant findings. The material has shown