A “Toolbox” for Forensic Engineers

Failure Due to Manufacturing Faults 135
Figure 5.4 Scanning electron micrographs of rivet fracture: (A) ¥20; (B) ¥55;
(C) ¥6000.
The side panels were sheets of aluminum alloy that were attached to one
another and the frame by riveting along vertical lap joints incorporating tophat
channel sections to act as stiffeners. All the failures involved the “unzipping”
of the vertical lap joint between the first and second sheets in from the
end of the container. The rivets had sheared across at the interface without
causing any tearing or ovality of the rivet holes. Figure 5.4 shows three SEM
views of a typical fracture surface at various magnifications. These are clearly
single shear overstress fractures. A rivet was also sectioned, polished and
etched for microstructural examination. This confirmed the shearing mode,
as evident in Figure 5.5, by the way the grain structure has flowed adjacent
to the fractured edge. The above interpretation explains the lack of any
stretching of the holes in the sheet on either side of the rivets, so the investigation
concentrated on what might be wrong with the rivets.