
38 Process Techniques for Engineering High-Performance Materials
The investigation determined that both the production process and the
design were faulty. During assembly, rivets were punched through multiple
layers of aluminum sheet in a single step. This was faster and easier than
drilling a clean hole and inserting the rivet in a second operation. The tech-
nique produced irregular holes, which initiated fatigue cracks. The postcrash
design change also eliminated the square window frames, which amplied
the stress on the fasteners. The picture above shows the redesigned passen-
ger windows of the later models. To this day, airliners have rounded ...