Corrosion fatigue in metals has been defined as the

Chapter , Problem 9.19

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Corrosion fatigue in metals has been defined as the simultaneous action of cyclic stress and chemical attack on a metal structure. In the study Effect of Humidity and Several Surface Coatings on the Fatigue Life of 2024-T351 Aluminum Alloy, conducted by the Department of Mechanical Engineering at Virginia Tech, a technique involving the application of a protective chromate coating was used to minimize corrosion fatigue damage in aluminum. Three factors were used in the investigation, with 5 replicates for each treatment combination: coating, at 2 levels, and humidity and shear stress, both with 3 levels. The fatigue data, recorded in thousands of cycles to failure, are presented here. (a) Perform an analysis of variance with = 0.01 to test for significant main and interaction effects. (b) Make a recommendation for combinations of the three factors that would result in low fatigue damage. Shear Stress (psi) Coating Humidity 13,000 17,000 20,000 Uncoated Low (2025% RH) 4580 10,126 1341 6414 3549 5252 897 1465 2694 1017 361 466 1069 469 937 Medium (5060% RH) 2858 8829 10,914 4067 2595 799 3471 685 810 3409 314 244 261 522 739 High (8691% RH) 6489 5248 6816 5860 5901 1862 2710 2632 2131 2470 1344 1027 663 1216 1097 Chromated Low (2025% RH) 5395 2768 1821 3604 4106 4035 2022 914 2036 3524 130 841 1595 1482 529 Medium (5060% RH) 4833 7414 10,022 7463 21,906 1847 1684 3042 4482 996 252 105 847 874 755 High (8691% RH) 3287 5200 5493 4145 3336 1319 929 1263 2236 1392 586 402 846 524 751