Hand-holes are present within the body of welded aluminum light poles. They are used to provide access to the electrical wiring for both installation and maintenance purposes. Wind is the main loading on these slender aluminum light poles and acts in a very cyclic way. In the field, localized fatigue cracking has been observed. This includes areas around hand-holes, most of which are reinforced with a cast insert welded to the pole. This study is focused on an alternative design, specifically hand-holes without reinforcement. Nine poles with 18 openings were fatigue tested in four-point bending at various stress ranges. Among the 18 hand-holes tested, 17 failed in one way or another as a result of fatigue cracking. Typically, fatigue cracking would occur at either the 3:00 or 9:00 positions around the hand-hole and then proceed to propagate transversely into the pole before failure. Finite element analysis was used to complement the experimental study. Models were created with varying aspect ratios to see if the hand-hole geometry had an effect on fatigue life.
Fracture mechanics can be defined as a methodology that is used to
predict and diagnose failure of a part with some kind of existing crack
or flaw. These models can be used to aid in the examination of
laboratory experiments and possibly give an explanation into its fatigue
life. This study utilized AFGROW as the fracture mechanics software. All
models were used on a previous study conducted on aluminum light poles
containing hand-holes and reinforcement (when applicable). The ultimate
goal of this study was an attempt to replicate the laboratory results
from these previous studies and to gain a deeper understanding of the
failure modality. In total, eight fracture mechanics models were created
to achieve this goal. Of these models, three contained an initial break,
two had a beta correction added, one contained an open hole, and two
were modeled as a plate. From all of the fracture mechanics models,
models containing plates yielded the best results when it came to
replicating lab results. Some finite element analysis (FEA) in ABAQUS
was used in conjunction with the fracture mechanics models.
Welded aluminum light poles often contain hand-holes. These hand-holes are used to give access for electrical wiring installation and maintenance purposes. Wind load may cause light poles to be loaded in a cyclic manner. This cyclic loading can cause localized fatigue cracking around the hand-hole. Fatigue failure around hand-holes has been observed in the field, but studies surrounding the resistance of the hand-holes are few and far between. This study included four-point bending fatigue tests on welded aluminum poles containing hand-holes. Eight welded aluminum specimens, each with two hand-holes, were tested in fatigue. These 16 details were loaded at the same stress range. Each specimen had a slightly different geometry or treatment applied to the hand hole. These different details mimicked traditional reinforced hand holes, similar to those evaluated in previous studies. Changes in the treatment and/or geometry included milling the inside of hole, milling the inside of the hole as well as the cast insert prior to welding, and milling the cast insert itself prior to welding. Among the 16 details tested, 15 failed as a result of fatigue cracking. It was found that specimen failure would originated in the throat of the fillet weld and then proceeded to propagate into the reinforcement ring/casting. A finite element analysis was used in addition to the experimental study.
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