Report just arrived from METL
To remind us, Dewey Vicknair's labels
The cut section
The initiation point
METL's summary as bold bullet points
• The fracture surface near the center of the barrel wall showed quasi-cleavage and transgranular brittle fracture. The inner and outer diameter surfaces displayed ductile dimpling features, indicative of overload.
• Ductile dimpling was observed along the inner and outer diameters of the barrel as well as near the suspected initiation site. No microscopic indicators of fatigue were observed.
• The suspected initiation site showed a large cavity surrounded by what appeared to be voids left by inclusions.Initiation point cleavage. No low cycle fatigue striations.
• The braze was extensively contaminated, particularly near the suspected initiation site.
• The contamination in the braze was ferrous and appeared to be heavily oxidized.
"The braze was examined at high magnifications. The region where contamination was observed was consistent with ferrous, oxidized debris. The braze material was consistent with a copper-zinc braze filler. Substantial contamination was observed throughout the inner braze surface. Cross-sections from the good and bad braze areas were taken and showed substantial difference in compositions between the braze material and the contaminated regions."Oxidized debris = burned steel
Good braze
Bad braze with manganese sulfide inclusions
Oxidized steel with inclusions
Unanswered questions:Would the chamber have burst without the over-pressure shell?
Is the top rib extension wedge brazed to the thin medial barrel wall a design defect, or was this a manufacturing error?
Did the use of 2 3/4” shells in a 2 9/16” chamber add to the over-pressure?
The once fired Cheddite hulls are a full 2 3/4”. Sherman Bell's study of 2 3/4” shells in 2 1/2” chambers with a 7/16” forcing cone showed a rise in pressure from 228 psi to 1216 psi compared to 2 3/4” chambers with a 1” forcing cone.
More thoughts to follow. Feel free to contribute meaningful opinions.
