Minimum Material Bend Radius

[gutboy17]

I'm trying to find a reliable resource for minimum bend radius for various materials. I'm currently working on a problem of a 2024-T3 formed sheet metal panel that is cracking at one of the panel edges. The panel isn't heavily loaded and it is in a relatively low vibration environment, so I was initially perplexed. I started to review the drawing and the sheet thickness is .04" and the bend radius are .12". So, looking at my old reliable design slide rule I noticed that the minimum bend radius for the above material is .25". Running this question by another designer, and his slide rule has the minimum bend radius at .12". I couldn't find anything in the Machinery HNDBK 26, so I was wondering if someone else had another resource.

 

[TVP]

The recommended bend radius for 2024-T3 Al sheet that is 1 mm thick (0.04") is 3T to 4T, which would be 3-4 mm (0.12-0.16"). References for this are ASM Alloy Digest data sheet and "How To Design Metal Stampings" by Dayton Rogers Mfg. Co. This data is for a 90 degree bend.