Correlation between Fractal Dimension and Areal Surface Parameters for Fracture Analysis after Bending-Torsion Fatigue
Abstract
:1. Introduction
2. Materials and Methods
2.1. Fatigue Test Materials and Campaign
2.2. Fracture Surface Topography Measurement
3. Results and Discussion
3.1. Measurement Results
3.2. Individual Fracture Zones
3.3. Statistical Dependencies of Fractal Dimensions
3.4. Fracture Surface Parameters for Extremal Fractal Dimensions Cases
3.5. Relationship between Df and Areal Surface Parameters
3.6. Material and Loading Model Based on Fracture Surface Topography
4. Conclusions
- For all investigated specimens, the largest values of Df are for bending, slightly lower for torsion, and the smallest for combined loads;
- The size distribution of peaks and valleys is well described by the fractal theory;
- The highest sensitivity of the Df parameter occurs for pure bending in ring-notched specimens;
- Surface topography parameter values such as areal parameters Sx, volume parameters Vx and core height parameter Sk are significantly inversely related to the fractal dimension Df;
- Using Narrow Neural Network, it has been found a 6th degree type model, with the best fit arithmetical mean height Sa to fractal dimension Df, with a coefficient of determination R2 equal to 0.905;
- The obtained results show that the fracture surface topography is a function of the loading condition, which affects the fracture mechanisms;
- Material and loading parameter P shows a rather good fit to fractal dimension Df, with R2 = 0.637, but different loading methods and materials still cause some discrepancies;
- The fractal dimension analysis of the total area method can be extended to other materials under bending-torsion fatigue;
- The presented results indicate that using only fractal dimension Df in a function of r is an inaccurate approach to clearly analyse the conditions under which the specimen was damaged. It should be mentioned that, apart from the r parameter other factors have an important impact on the fatigue crack mechanisms. However, the fracture surface morphology recaptures important stages of the fatigue crack process. Fractal dimension, in connection with other ratios of fractography, can be an effective tool for comprehensive failure analysis;
- The proposed method can be applied to the prediction of fracture behaviour and the cracking process in cases dependent on the loading conditions and features of the material.
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
Nomenclature
Df | - | fractal dimension |
E | GPa | Young’s modulus |
P | 1/mm | material and loading parameter |
r | - | loading stress ratio |
R | - | stress ratio |
R2 | - | coefficient of determination |
Sa | µm | arithmetical mean height |
Sk | µm | core height |
Smr1, Smr2 | % | areal material ratio |
Sp | µm | maximum peak height |
Spk | µm | reduced peak height |
Sq | µm | root mean square height |
Sv | µm | maximum pit height |
Svk | µm | reduced dale height |
Sz | µm | maximum height |
Vmc | mm³/mm² | core material volume |
Vmp | mm³/mm² | peak material volume |
Vvc | mm³/mm² | core void volume |
Vvv | mm³/mm² | pit void volume |
σmax | MPa | maximum normal stress |
σy | MPa | Yield stress |
τmax | MPa | maximum shear stress |
MSE | - | Mean Squared Error; is the square of the RMSE |
MAE | - | Mean Absolute Error; is always positive and similar to the RMSE, but less sensitive to outliers |
PCA | - | Principal Component Analysis |
RMSE | - | Root Mean Square Error; is always positive and its units match the units of response |
Appendix A
10HNAP Steel | 2017-T4 Aluminium Alloy | S355J2 Steel | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Df | Sq | Sz | Sa | r | Df | Sq | Sz | Sa | r | Df | Sq | Sz | Sa | r |
2.28 | 34 | 216 | 28 | 0.00 | 2.18 | 347 | 2490 | 236 | 0.00 | 2.16 | 332 | 1133 | 295 | 0.00 |
2.27 | 35 | 236 | 29 | 0.00 | 2.20 | 351 | 2020 | 261 | 0.00 | 2.21 | 185 | 859 | 148 | 0.00 |
2.23 | 31 | 301 | 25 | 0.00 | 2.23 | 279 | 1820 | 217 | 0.00 | 2.31 | 46 | 383 | 35 | 0.00 |
2.27 | 39 | 341 | 31 | 0.00 | 2.21 | 418 | 2970 | 252 | 0.00 | 2.17 | 305 | 1073 | 266 | 0.00 |
2.28 | 39 | 236 | 34 | 0.00 | 2.17 | 637 | 2830 | 524 | 0.00 | 2.12 | 510 | 1483 | 463 | 0.00 |
2.28 | 32 | 276 | 26 | 0.00 | 2.20 | 401 | 2780 | 291 | 0.00 | 2.17 | 1180 | 4510 | 1020 | 0.00 |
2.33 | 29 | 182 | 25 | 0.00 | 2.24 | 411 | 3060 | 322 | 0.00 | 2.14 | 141 | 1420 | 93 | 0.00 |
2.26 | 32 | 243 | 26 | 0.00 | 2.27 | 189 | 1180 | 153 | 1.00 | 2.17 | 347 | 2490 | 236 | 0.00 |
2.28 | 46 | 269 | 37 | 0.00 | 2.15 | 141 | 1420 | 93 | 1.00 | 2.17 | 351 | 2020 | 261 | 0.00 |
2.35 | 39 | 269 | 32 | 0.00 | 2.12 | 242 | 2580 | 143 | 1.00 | 2.15 | 223 | 1057 | 159 | 1.00 |
2.30 | 41 | 271 | 31 | 0.00 | 2.15 | 311 | 2680 | 156 | 1.00 | 2.13 | 526 | 3160 | 408 | 1.00 |
2.13 | 180 | 998 | 141 | 1.00 | 2.14 | 279 | 1820 | 217 | 0.42 | 2.16 | 306 | 1502 | 247 | 0.28 |
2.11 | 269 | 1360 | 216 | 1.00 | 2.06 | 418 | 2970 | 252 | 0.18 | 2.04 | 1390 | 5394 | 1202 | 0.28 |
2.12 | 208 | 1210 | 160 | 1.00 | 2.07 | 637 | 2830 | 524 | 0.39 | 2.13 | 227 | 1182 | 193 | 0.21 |
2.15 | 198 | 996 | 160 | 1.00 | 2.10 | 401 | 2780 | 291 | 0.42 | 2.13 | 209 | 1312 | 169 | 0.21 |
2.15 | 206 | 1120 | 160 | 1.00 | 2.07 | 411 | 3060 | 322 | 0.18 | 2.1 | 547 | 1898 | 461 | 0.16 |
2.09 | 278 | 1570 | 226 | 1.00 | 2.12 | 867 | 3150 | 747 | 0.18 | 2.06 | 1370 | 5211 | 1172 | 0.46 |
2.11 | 327 | 1500 | 272 | 1.00 | 2.11 | 526 | 3160 | 408 | 0.39 | 2.12 | 218 | 1498 | 137 | 0.29 |
2.12 | 272 | 1370 | 219 | 1.00 | 2.11 | 574 | 3270 | 429 | 0.44 | 2.08 | 619 | 2404 | 520 | 0.29 |
2.15 | 183 | 1130 | 146 | 1.00 | - | - | - | - | - | 2.14 | 191 | 1035 | 142 | 0.29 |
2.13 | 180 | 1030 | 134 | 1.00 | - | - | - | - | - | 2.07 | 914 | 3621 | 802 | 0.34 |
2.09 | 230 | 1310 | 186 | 0.50 | - | - | - | - | - | 2.08 | 607 | 2419 | 519 | 0.34 |
2.12 | 160 | 1200 | 117 | 0.50 | - | - | - | - | - | 2.19 | 281 | 1509 | 222 | 0.24 |
2.09 | 373 | 1620 | 311 | 0.50 | - | - | - | - | - | 2.17 | 282 | 1977 | 189 | 0.18 |
2.11 | 190 | 1010 | 150 | 0.50 | - | - | - | - | - | 2.18 | 328 | 1464 | 293 | 0.28 |
2.09 | 437 | 1760 | 380 | 0.50 | - | - | - | - | - | 2.07 | 547 | 1960 | 503 | 0.24 |
2.09 | 489 | 2180 | 416 | 0.50 | - | - | - | - | - | 2.13 | 1180 | 5017 | 907 | 0.24 |
2.16 | 433 | 1820 | 370 | 0.50 | - | - | - | - | - | 2.12 | 408 | 1765 | 327 | 0.42 |
2.09 | 522 | 2060 | 452 | 0.50 | - | - | - | - | - | 2.15 | 544 | 1771 | 463 | 0.42 |
2.07 | 400 | 1880 | 324 | 0.50 | - | - | - | - | - | 2.08 | 595 | 2642 | 479 | 0.55 |
- | - | - | - | - | - | - | - | - | - | 2.08 | 524 | 2471 | 405 | 0.55 |
- | - | - | - | - | - | - | - | - | - | 2.13 | 539 | 2135 | 488 | 0.33 |
- | - | - | - | - | - | - | - | - | - | 2.12 | 334 | 2204 | 247 | 0.55 |
- | - | - | - | - | - | - | - | - | - | 2.08 | 525 | 1811 | 495 | 0.26 |
- | - | - | - | - | - | - | - | - | - | 2.12 | 475 | 1601 | 417 | 0.23 |
- | - | - | - | - | - | - | - | - | - | 2.16 | 339 | 1309 | 282 | 0.60 |
- | - | - | - | - | - | - | - | - | - | 2.14 | 357 | 1242 | 312 | 0.23 |
- | - | - | - | - | - | - | - | - | - | 2.21 | 182 | 1055 | 154 | 0.33 |
- | - | - | - | - | - | - | - | - | - | 2.17 | 376 | 1473 | 293 | 0.15 |
- | - | - | - | - | - | - | - | - | - | 2.2 | 282 | 1265 | 221 | 0.31 |
- | - | - | - | - | - | - | - | - | - | 2.16 | 399 | 1248 | 348 | 0.18 |
- | - | - | - | - | - | - | - | - | - | 2.13 | 382 | 1182 | 339 | 0.39 |
- | - | - | - | - | - | - | - | - | - | 2.21 | 1130 | 4510 | 915 | 0.21 |
- | - | - | - | - | - | - | - | - | - | 2.15 | 595 | 3260 | 458 | 0.26 |
- | - | - | - | - | - | - | - | - | - | 2.16 | 989 | 3860 | 803 | 0.26 |
- | - | - | - | - | - | - | - | - | - | 2.2 | 867 | 3150 | 747 | 0.16 |
- | - | - | - | - | - | - | - | - | - | 2.15 | 574 | 3270 | 429 | 0.18 |
- | - | - | - | - | - | - | - | - | - | 2.14 | 189 | 1180 | 153 | 0.26 |
- | - | - | - | - | - | - | - | - | - | 2.17 | 242 | 2580 | 143 | 0.16 |
- | - | - | - | - | - | - | - | - | - | 2.18 | 311 | 2680 | 156 | 0.16 |
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Material | Reference | ||
---|---|---|---|
10HNAP | 0; 0.5; 1 | −1 | [14] |
S355J2 | 0; 0.16–0.6; 1 | −1 | [39] |
2017-T4 | 0; 0.18–0.44; 1 | −1; −0.5; 0 | [40] |
Specimen | Entire Fracture | Initiation | Propagation |
---|---|---|---|
10HNAP (r = 0) | 2.280 | 2.230 | 2.224 |
S355J2 (r = 0.18) | 2.170 | 2.088 | 2.176 |
2017-T4 (r = 0) | 2.300 | 2.180 | 2.172 |
Loading Mode | Averaged Fractal Dimension | ||
---|---|---|---|
10HNAP | 2017-T4 | S355J2 | |
Bending (B) | 2.28 | 2.20 | 2.18 |
Torsion (T) | 2.13 | 2.17 | 2.14 |
Bending-Torsion (B-T) | 2.10 | 2.10 | 2.13 |
Parameter | Specimen | ||
---|---|---|---|
10HNAP | 2017-T4 | S355J2 | |
Df max. | B | B | B |
Df min. | B-T | B-T | B-T |
Sa max. | B-T | B-T | B-T |
Sa min. | B | T | T |
RMSE | R2 | MSE | MAE |
---|---|---|---|
202.66 | 0.31 | 41072 | 145.98 |
Curve Fitting, General Model Gaussian | Goodness of Fit |
---|---|
f(x) = a × exp(−((x − b)/c)2) | SSE: 8383 |
Coefficients: | R2: 0.637 |
a = 76.3 | Adjusted R2: 0.6294 |
b = 2.435 | RMSE: 9.345 |
c = 0.1918 |
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Macek, W. Correlation between Fractal Dimension and Areal Surface Parameters for Fracture Analysis after Bending-Torsion Fatigue. Metals 2021, 11, 1790. https://doi.org/10.3390/met11111790
Macek W. Correlation between Fractal Dimension and Areal Surface Parameters for Fracture Analysis after Bending-Torsion Fatigue. Metals. 2021; 11(11):1790. https://doi.org/10.3390/met11111790
Chicago/Turabian StyleMacek, Wojciech. 2021. "Correlation between Fractal Dimension and Areal Surface Parameters for Fracture Analysis after Bending-Torsion Fatigue" Metals 11, no. 11: 1790. https://doi.org/10.3390/met11111790