Estimation of the Plastic Zone in Fatigue via Micro-Indentation
Abstract
:1. Introduction
2. Materials and Methods
2.1. Aluminium Alloy 2024-T351
2.2. Fatigue Experiment
3. Micro-Indentation Technique
3.1. Description of the Micro-Indentation Experimental Procedure
3.2. Sensitivity Analysis
4. Results and Discussion
4.1. Plastic Zone Estimation
4.2. Preliminary Analysis on S355 Steel
5. Conclusions and Future Research
- The effect of the microstructure has been identified as the main cause of noise for the results. The fact that the size of the indentations is very similar to the hard precipitates of this alloy most likely decreases the quality of the results.
- The results and the sensitivity analysis indicate that for the current alloy, the best results are obtained by achieving a #3 μm surface finish, using 25 gf load for 15 s. Those parameters provide a good trade-off in terms of resolution and quality of each micro-indentation to produce a good enough map that can be used for quantitative analysis of plastic zones.
- The results have also shown that the shape and size can be approximately estimated from the 2D contour maps, as compared to Westergaard’s estimation of the plastic zone. The hardness profiles along the crack growing direction have allowed acceptable estimations of the plastic zone to be made, both for the monotonic and the cyclic plastic zones. For the cases studied, the estimations of the monotonic plastic zones have overall been better than those of the cyclic plastic zone.
- The results indicate that 0.2 mm appears to be the approximate size of the plastic zone that this methodology captures reliably. Plastic zones well below this figure can be spotted but visualisation of size and shape can be difficult.
- Based on previous works, a new criterion is proposed to separate the elastic from the plastic contribution from the micro-hardness measurements which enables us to retrieve the monotonic and the cyclic plastic zone. The current procedure for inferring the plastic zone around a fatigue crack tip is based on the hardening of the material being tested. Accordingly, applying this procedure to materials experiencing low strain hardening will yield less accurate results.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Mn | Si | Cr | Cu | Zn | Pb | Fe | Ti | Mg |
---|---|---|---|---|---|---|---|---|
0.650 | 0.070 | 0.010 | 4.570 | 0.060 | 0.004 | 0.120 | 0.039 | 1.500 |
Yield Stress, σy | 375 MPa |
Ultimate Tensile Stress, σu | 492 MPa |
Young’s Modulus, E | 73 GPa |
Specimen ID | a, mm | ΔKI, MPa√m |
---|---|---|
P1 | 30.40 | 9.91 |
P2 | 37.61 | 20.61 |
P3 | 40.25 | 30.23 |
Sample | Type of PZ | PZexp (mm) | PZtheo (mm) | Error (%) | Difference (mm) |
---|---|---|---|---|---|
P1 | Cyclic | 0.11 | 0.04 | 175 | 0.07 |
Mono | 0.18 | 0.20 | −10.0 | −0.02 | |
P2 | Cyclic | 0.21 | 0.15 | 40.0 | 0.06 |
Mono | 0.69 | 0.75 | −8.00 | −0.06 | |
P3 | Cyclic | 0.35 | 0.34 | 2.94 | 0.01 |
Mono | 1.78 | 1.64 | 8.54 | 0.14 |
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Lopez-Crespo, C.; Cruces, A.S.; Seitl, S.; Moreno, B.; Lopez-Crespo, P. Estimation of the Plastic Zone in Fatigue via Micro-Indentation. Materials 2021, 14, 5885. https://doi.org/10.3390/ma14195885
Lopez-Crespo C, Cruces AS, Seitl S, Moreno B, Lopez-Crespo P. Estimation of the Plastic Zone in Fatigue via Micro-Indentation. Materials. 2021; 14(19):5885. https://doi.org/10.3390/ma14195885
Chicago/Turabian StyleLopez-Crespo, Cristina, Alejandro S. Cruces, Stanislav Seitl, Belen Moreno, and Pablo Lopez-Crespo. 2021. "Estimation of the Plastic Zone in Fatigue via Micro-Indentation" Materials 14, no. 19: 5885. https://doi.org/10.3390/ma14195885