Reliability Engineering Snapshot TM

Illustrated Case Studies in the Maintenance Reliability Engineering World of Failure Analysis, Predictive Maintenance, and Non Destructive Evaluation




Machine Design - Case Study No. 127: Undercutting Sharp Flange Corners to Relieve Stress Concentration


View of Shaft with Undercut RadiusWhen mating components must fit tight and prevent the use of a large radius between section changes, consider using an undercut radius to relieve the stress concentration.

The failure of a large 22" diameter shaft was the result of a stress concentration created by a 1/8" radius at a large section change. The failure is showcased in the article "Material Properties - Case Study No. 128: Mine Hoist Shaft Flange Failure at Sharp Radius Stress Concentration." All of the design details are discussed in that article. The figure to the left shows a section transition. The flange diameter in the picture was 42". The white line denotes the perimeter of the flange before the design change. The two white dots denote where material was removed for the undercut radius. The reason the 1/8" radius was used in the first place was because a drum had to fit up tightly to the flange. A large radius between the flange and the shaft would have prevented the drum from fitting snugly up against the flange. The undercut radius relieves the stress concentration caused by the large section change and allows the drum to fit up snugly with the flange along the white line.


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