Torsional fatigue tests of anodized aluminum rods

Abstract

Fatigue tests in reversed torsion were run on 2024-T351 aluminum-alloy specimens in (1) uncoated state and (2) anodized with 0.3 and 0.05-mil (0.0076- and 0.0013-mm) coatings. Tests on both groups were run at low (20–25 percent), medium (55–60 percent), and high (86–91 percent) relative humidity. One lot of uncoated specimens was tested that had been polished after machining, and one lot of anodized specimens was tested that had been polished before coating. Tests on uncoated and on anodized specimens were run at stress levels of approximately 13,000, 17,000 and 20,000 psi (89.62, 117.2 and 137.9 MPa, respectively). Results of tests on both coated and uncoated specimens showed longer fatigue life at low humidity than at high humidity. Little difference was found between tests at medium and at high humidity. No difference was found between polished and unpolished specimens. With coated specimens, the thickness of coating showed no effect on fatigue life. Comparing the results on coated and uncoated specimens at low humidity, coated specimens had a longer fatigue life. However, at high humidity, there was no significant difference.