FE Investigation into Manufacturing- and Design-Related Issues Contributing to the Failure of a Climbing Treestand
Keywords:Treestand, Manufacturing defect, dynamic overload, aluminum weld, forensic engineering
The foot platform of a climbing treestand fractured while a user was standing on it in the process of secur-ing his harness to a tree. Analysis of the frame’s fracture surface revealed a manufacturing defect in the form of a ¼-inch diameter hole next to the fracture area, likely created during the welding process. To prove that this defect was the proximate cause of the treestand’s failure (under reasonably expected and foreseeable use conditions), a series of tests on exemplar treestands as well as finite element analysis were performed. It was concluded that the defect reduced the fracture toughness of the treestand by 40%. In addition, it was found that the manufacturer failed to account for additional stress caused by dynamic loading experienced during normal use. The authors opined that both the reduced strength and the omission of dynamic loading in the de-sign resulted in the treestand’s frame failure. Appropriateness of the manufacturer’s reliance on users always wearing their full body harness is also discussed. This paper examines the contribution of the drilled hole to the integrity and suitability of the ASTM-required Factor of Safety (FOS) of 2.
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