Rotating Bending Fatigue Microscopic Fracture Characteristics and Life Prediction of 7075-T7351 Al Alloy
Abstract
:1. Introduction
2. Materials and Methods
2.1. Material
2.2. Mechanical Testing
2.3. Three-Parameter Weibull Distribution Function
3. Discussion
3.1. Fractography Analysis
3.2. Scattering Analysis of Fatigue Data
3.3. Fatigue Life Prediction and Reliability Analysis
4. Conclusions
- The relation between the stress intensity factor ΔK and the fatigue life Nf presents a monotone decreasing rule, and their empirical formula is obtained.
- For the same stress amplitude, the scattering degree of the fatigue data is caused primarily by the number of fatigue crack initiation sites and the fatigue crack propagation area fraction.
- The characteristic life under some stress amplitude for a small sample (such as n = 3) can be predicted effectively based on the parameter m calculated from the large sample (such as n = 8) under just 1–2 stress amplitudes, which can greatly decrease the number of test samples.
Acknowledgments
Author Contributions
Conflicts of Interest
Abbreviation
b | scale parameter in Weibull distribution function |
predication value of characteristic life | |
c | location parameter in Weibull distribution function |
d, L | the geometry parameters of sample |
F(x) | Weibull distribution function |
g | the acceleration of gravity (9.8 m/s2) |
h | coating thickness |
ΔK | stress intensity factor (MPa·m1/2) |
m | shape parameter in Weibull distribution function |
n | experimental number |
Nf | cyclic numbers of failure |
α | stress concentration factor (1.08) |
σ | engineering stress amplitude (MPa) |
R | stress ratio |
Ra | surface roughness |
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Material | E (GPa) | µ | HRB | Residual Stress (MPa) | σ0.2 (MPa) | σb (MPa) | δ (%) |
---|---|---|---|---|---|---|---|
Uncoated 7075-T7351 | 70.5 | 0.30 | 94.9 | 0 | 465 | 528 | 14.6 |
Coated (h = 10 μm) 7075-T7351 | 253 | 0.24 | 88.7 | −198 (±11) |
Testing Stress | No. 1 | No. 2 | No. 3 | No. 4 | No. 5 | No. 6 | No. 7 | No. 8 |
---|---|---|---|---|---|---|---|---|
×105 | ×105 | ×105 | ×105 | ×105 | ×105 | ×105 | ×105 | |
113.3 MPa | 0.051 (deleted) | 2.381 | 2.897 | 4.210 | 5.808 | 7.552 | 8.126 | 189.429 (deleted) |
133.3 MPa | 0.043 (deleted) | 1.239 | 2.294 | 2.710 | 3.100 | 4.656 | 6.885 | 8.749 |
166.7 MPa | 0.616 | 0.748 | 0.891 | 0.896 | 1.180 | 1.432 | 1.869 | 2.081 |
181.6 MPa | 0.115 | 0.289 | 0.322 | 0.522 | 0.699 | 0.802 | 1.212 | 1.667 |
204.0 MPa | 0.167 | 0.216 | 0.245 | 0.305 | 0.422 | 0.575 | 0.596 | 0.609 |
Testing Stress | m | b (×105) | Characteristic Life (×105) | Arithmetic Mean Life (×105) | Prediction Life by Lognormal Distribution (F(x) = 50%) (×105) |
---|---|---|---|---|---|
113.3 MPa | 1.03 | 5.879 | 5.177 | 5.162 | 4.668 |
133.3 MPa | 1.12 | 4.881 | 4.319 | 4.233 | 3.520 |
166.7 MPa | 1.02 | 1.325 | 1.216 | 1.214 | 1.117 |
181.6 MPa | 1.11 | 0.820 | 0.722 | 0.704 | 0.531 |
204.0 MPa | 1.05 | 0.440 | 0.394 | 0.392 | 0.352 |
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Yang, H.; Zhang, Z.; Tan, C.; Ito, M.; Pan, P.; Wang, X. Rotating Bending Fatigue Microscopic Fracture Characteristics and Life Prediction of 7075-T7351 Al Alloy. Metals 2018, 8, 210. https://doi.org/10.3390/met8040210
Yang H, Zhang Z, Tan C, Ito M, Pan P, Wang X. Rotating Bending Fatigue Microscopic Fracture Characteristics and Life Prediction of 7075-T7351 Al Alloy. Metals. 2018; 8(4):210. https://doi.org/10.3390/met8040210
Chicago/Turabian StyleYang, Huihui, Zhihao Zhang, Changhao Tan, Makoto Ito, Pan Pan, and Xishu Wang. 2018. "Rotating Bending Fatigue Microscopic Fracture Characteristics and Life Prediction of 7075-T7351 Al Alloy" Metals 8, no. 4: 210. https://doi.org/10.3390/met8040210