One known example was the cargo hold openings on Liberty ships which originally had 90º corners. These initiated cracks, with at least one Liberty breaking into two. Later ones were built with rounded corners.
However, the examples of Caravelle, L1011 and DC6 / 7 do suggest to me that the shape itself is less important than its construction. I believe that Bishop did specify Redux alone, but management demanded a cautious "belt and braces" construction. It is sadly ironic that this cautious approach was what led to the failures.