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This and the next slide are from a report, AAIB (Farnborough, UK) Bulletin No. 2/96, Ref: EW/A95/6/1, sent to me by Professor Jan Blachut, Department of Mechanical Engineering, The University of Liverpool.
This and the next slide show the geometry of the internal pressure bulkhead (this slide) and the geometry of the local region of the dome where fatigue, fracture and tearing occurred (next slide).
After investigation it was concluded that the local fracturing of the aft pressure dome was caused by fatigue cracks contained within a single bay of the dome that grew under cyclic stress reversals caused partly by repeated local "oil-canning" (local nonlinear "snap-through" buckling) in a previously accidentally inwardly dented dome bay that subsequently "popped" outward and inward with each cabin pressure cycle.
From Farnborough, UK, AAIB Bulletin No. 2/96, Ref: EW/A95/6/1, Information Source: Farnborough AAIB Field Investigation.
"Rear pressure bulkhead construction: The rear pressure bulkhead is a thin shell structure comprising a series of 1 mm (0.040 inch) thick gore panels lapjointed to form a dome-shaped pressure membrane of approximately hemispherical profile, overlaid with a network of doublers and anti-tear straps as shown [here. The cabin pressure is seen by the concave surface of the pressure bulkhead}."
"The bulkhead failure mode: The rapid decompression [during flight] was caused by a [local] failure of the rear pressure bulkhead at the location shown in [this and in the next slide]. [As sketched in the next slide,] the failure comprised a 394 mm (15.5 inches) by 292 mm (11.5 inches) "letterbox" rupture of the pressure membrane at the top of the bulkhead just to the left of the aircraft centreline, immediately inboard of the 150 mm wide doubler which runs around the outer periphery...."
A sketch of the failure, giving approximate sizes and other details, is shown in the next slide.
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