Investigation of Changes in Fatigue Damage Caused by Mean Load under Block Loading Conditions
- After the first phase of loading, the second phase of testing is carried out to obtain the criterion of sample failure.
- The sequence of cycles n1 and n2 is determined, and this load sequence is repeated until the criterion of sample failure is not reached.
2. Stress–Strain Analysis Model
3. Analytical Simulation
- Case A, where the change in K′ and n′ parameters was taken into account for different values of the mean strain em,
- Case B, where the influence of mean strain em on the values of the coefficients K ‘and n′ was omitted, assuming their values to be em = 0.
4. Summary and Conclusions
- When neglecting the effect of the mean strain value on the K′ and n′ parameters and considering only the parameters of the cyclic deformation curve for εm = 0 (symmetric loads), the ratio of the total degree of fatigue damage varied from 10% for εa = 0.2% to 3.5% for εa = 0.6%. The largest differences in the calculation of the ratio of the partial degrees of fatigue damage in relation to the reference case were observed for sequence block n3, where εm = 0.4%.
- When assuming the independence of parameter K′ from the mean strain value, the worst calculation results in relation to the reference Case A were obtained for K′ = 587.7 MPa, where the total degree of fatigue damage was, on average, four times lower than the reference case. For these simulations, the largest calculation inaccuracy was also related to the n3 block load sequence, where the mean strain value was the largest (0.4%).
- When considering the independence of parameter n′ from the mean strain value, the best results in terms of the degree of fatigue damage calculation were achieved for n′ = 0.1507 (obtained for a symmetric load, εm = 0). The differences in the ratios of partial and total degrees of fatigue damage compared to the reference case were in the range of −20% to 4%. Similar results were obtained for Case B, where parameters K′ and n′ characterized the cyclic strain curve for symmetric loads.
- It can be concluded that the third sequence n3, where the biggest mean strain value was applied (εm = 0.4%), led to the largest inaccuracy. A higher value of mean strains, thus, increases the sensitivity of the algorithm toward applied parameters K′ and n′.
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Informed Consent Statement
Data Availability Statement
Conflicts of Interest
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|Step No.||Description of Operation||Equation|
E, Young’s modulus; K′, cyclic strength coefficient; n′, cyclic strain-hardening exponent.
|2.||Input data: εA, εB, εa, and εm|
|3.||alculation of σA for given K′ and n′ (*)|
|(*) Values of the coefficients K′ and n′ depend on the current values of the average strain εm. However, this requires additional tests to determine the functions K′ = f (εm) and n′ = f (εm).|
|4.||alculation of εApl|
|5.||alculation of σa for given K and n obtained for εm = 0|
|6.||alculation of εapl|
|7.||Calculation of mean stress σm|
i refers to the next load sequence
|8.||Resulting parameters (σa, σm)|
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Pawliczek, R.; Lagoda, T. Investigation of Changes in Fatigue Damage Caused by Mean Load under Block Loading Conditions. Materials 2021, 14, 2738. https://doi.org/10.3390/ma14112738
Pawliczek R, Lagoda T. Investigation of Changes in Fatigue Damage Caused by Mean Load under Block Loading Conditions. Materials. 2021; 14(11):2738. https://doi.org/10.3390/ma14112738Chicago/Turabian Style
Pawliczek, Roland, and Tadeusz Lagoda. 2021. "Investigation of Changes in Fatigue Damage Caused by Mean Load under Block Loading Conditions" Materials 14, no. 11: 2738. https://doi.org/10.3390/ma14112738