High-Cycle Constant Amplitude Fatigue Life Variability of Welded Round HSS Y-Joints

The variability in fatigue life estimates for welded pipe joints commonly found in overhead transportation sign support structures has not been characterized to the level necessary for generating accurate fatigue life predictions for these structures. Cracking found in existing sign support structures demands that this variability be quantified to understand the impetus for these cracks. The primary goal of this thesis was to quantify the variability in the fatigue life of welded round HSS Y-joints. This thesis includes an intensive study on the fatigue life variability of HSS Y-joints in steel and aluminum structures. It also includes a detailed discussion with illustration of experimental fixturing, specimen fabrication, material characteristics, statistical analysis of fatigue testing results, a comparison of experimental failures to typical transportation sign support structure failures, and current design equations for fatigue life prediction. Observations made during the experimental effort illustrate the importance of material selection in the fatigue life of HSS Y-joints. All fabrication of components, besides the test specimens, and testing, besides metal composition tests were conducted by either myself or other Marquette University faculty and staff