Is a Tear-Type Corner Relief Ever an Acceptable Substitute for a Standard Bend Relief on a Closed Corner?

Yes, and on a closed corner it's often the better choice. A tear relief lets the material rip a controlled crack at the intersection of two bend lines instead of routing a clean obround cutout where there's no room for one. Two flanges closing up against each other usually leave no space for a standard relief without weakening both flanges at once.

Why closed corners are different

A standard bend relief works by cutting material away before the bend so the flange has a free edge to stretch into. That's easy on an open edge. A closed corner is two bends meeting at 90 degrees with no free edge between them. The metal at that intersection has to stretch in two directions at once as both flanges form.

There's no obround you can cut there without opening a gap in the finished corner, which usually defeats the point of a closed corner.

The tear relief accepts a small, controlled crack at the vertex instead. It's a deliberate feature, not a flaw sneaking through. The crack propagates a short predictable distance and stops, because the stress concentration that drove it disappears once the bend is formed.

What makes a tear relief work instead of fail

The crack has to be short and has to have somewhere to stop. That depends on ductility and thickness.

A tear relief on a soft aluminum or cold rolled steel part in a light gauge behaves itself. The material yields and the crack self-limits. Push the same closed corner into a harder temper, a thicker section, or a tighter bend radius, and the crack doesn't stop where you need it to. It keeps running. Now you've got a split corner instead of a tight one.

This is a judgment call that depends on gauge, material, and radius, not a rule you apply blind. If you're not confident the crack will self-arrest, don't gamble on it. Fall back to an open-style relief with a small gap, or redesign the corner as a two-piece joint.

What to put on the drawing

Call it out explicitly on the print rather than leaving the choice to whoever runs the flat pattern software. Most sheet metal CAD has a closed-corner option that defaults to tear or rip, and that default can get applied without anyone on the design side actually deciding it's right for that material and gauge.

Put a note on the print: closed corner, tear relief acceptable, or the opposite if you need the corner to stay intact and are willing to accept the stretched look of an open relief.

DigiForge's sheet metal line runs laser cutting, press-brake forming and PEM insertion, with a 2-week standard lead time and a cut tolerance of ±0.13 mm. Corner relief style doesn't move either of those numbers, but it's worth flagging in your model notes before the file goes out for quote, since it changes how the flat pattern gets laid out.