https://orcid.org/0000-0002-5145-8172
Abstract
Welded aluminum light poles are slender structures subjected to cyclic loading due to the response to wind. Fatigue behavior of welded details is dependent upon local stresses influenced by loading, geometric features of connections, and residual stresses. Residual stresses may be tensile or compressive, which may develop in the component because of plastic deformation, application of a temperature gradient, structural transformations, or a combination thereof. Welding during assembly and manufacture results in residual stresses due to localized heating and shrinkage restraint during cooling. In the majority of cases, residual stresses are tensile adjacent to welds and influence crack growth kinetics. Fatigue tests of two different sets of light pole specimens were conducted within the Structures Laboratory of the University of Akron: postweld heat-treated (PWHT) and non–postweld heat-treated (NPWHT). Different fatigue resistance was observed between the two specimens. The steeper gradient was observed for the provided design S–N for the NPWHT, which means the NPWHT specimens failed in the shorter lifetime in comparison with PWHT. Heat treatment is a method for increasing the fatigue resistance of the welded aluminum hand-hole details. A complete residual stress measurement was conducted on both PWHT and NPWHT specimens to understand the influence of heat treatment on the residual stresses and on the fatigue resistance. Residual stress measurements around welded reinforced hand-holes using the incremental hole-drilling approach were reduced using power series and integral methods. Tikhonov regularization was employed to improve results. Larger tensile residual stresses were measured in position 3:00 or 9:00 o’clock reference. Compressive and tensile residual stresses usually appear together in residual stress test results. PWHT procedure increased the compressive residual stresses and does not have a significant effect on the tensile residual stresses locked in welded aluminum details. Therefore, PWHT is useful for increasing the fatigue resistance of welded aluminum details.
