Armed Polite Society
Main Forums => The Roundtable => Topic started by: Hawkmoon on February 05, 2021, 06:47:24 PM
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Bulk carrier snaps in half due to a wave on the Black Sea.
https://www.youtube.com/watch?v=4mgRb3G5elg
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No, I don't see it every day, but I did see it once before. =)
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Isn't that the theory of the Exxon valdez...it got caught between waves somehow that wasn't supposed to happen, because the channel it was in did something funky with the waves.
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Isn't that the theory of the Exxon valdez...it got caught between waves somehow that wasn't supposed to happen, because the channel it was in did something funky with the waves.
No. The Exxon Valdez was out of the channel and hit a reef.
FWIW I've been on a boat that took some nasty seas and cracked, but it wasn't catastrophic, and we made port and welded her up. That's one of the reasons correct ballasting is important.
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That is a theory I've heard of what happened to the Edmund Fitzgerald.
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Didn't they end up adding a reinforcing band of steel to each side of Liberty Ship hulls during WWII to keep this from happening to them?
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Didn't they end up adding a reinforcing band of steel to each side of Liberty Ship hulls during WWII to keep this from happening to them?
Yes. The British riveted ships didn't have a problem but the American Liberty ships were welded, and in the extreme cold of the North Atlantic they suffered from embrittlement.
https://en.wikipedia.org/wiki/Liberty_ship
Hull cracks
Early Liberty ships suffered hull and deck cracks, and a few were lost due to such structural defects. During World War II there were nearly 1,500 instances of significant brittle fractures. Twelve ships, including three of the 2,710 Liberties built, broke in half without warning, including SS John P. Gaines,[20][21] which sank on 24 November 1943 with the loss of 10 lives. Suspicion fell on the shipyards, which had often used inexperienced workers and new welding techniques to produce large numbers of ships in great haste.
The Ministry of War Transport borrowed the British-built Empire Duke for testing purposes.[22] Constance Tipper of Cambridge University demonstrated that the fractures did not start in the welds themselves, but were due to low temperature embrittlement of the steel used;[23] the same steel used in riveted construction did not have this problem. She discovered that the ships in the North Atlantic were exposed to temperatures that could fall below a critical point at which the steel changed from being ductile to becoming brittle, allowing cracks to start easily.[24] The predominantly welded hull construction allowed small cracks to propagate unimpeded, unlike in a hull made of separate plates riveted together. One common type of crack nucleated at the square corner of a hatch which coincided with a welded seam, both the corner and the weld acting as stress concentrators. Furthermore, the ships were frequently grossly overloaded, increasing stresses, and some of the problems occurred during or after severe storms at sea that would have placed any ship at risk. Minor revisions to the hatches and various reinforcements were applied to the Liberty ships to arrest the cracking problem. The successor Victory ship used the same steel, with improved design to reduce potential fatigue.
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Per Hawkmoon re Liberty ships:
One common type of crack nucleated at the square corner of a hatch which coincided with a welded seam, both the corner and the weld acting as stress concentrators.
With respect to the De Havilland Comet crashes the sharp corners of the windows (among other things) concentrated stresses during pressurization and depressurization, leading to catastrophic failures:
Both of these locations feature sharp right hand corners which cause local areas of high stress-concentration that provide very benign conditions for crack initiation and propagation under fatigue loading.
https://aerospaceengineeringblog.com/dehavilland-comet-crash/
(https://fugahumana.files.wordpress.com/2012/06/window.jpg)
I know they use transparent plastic models of parts under polarized light to reveal stress concentration points in the part.
Terry, 230RN
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Per Hawkmoon re Liberty ships:
With respect to the De Havilland Comet crashes the sharp corners of the windows (among other things) concentrated stresses during pressurization and depressurization, leading to catastrophic failures:
(https://fugahumana.files.wordpress.com/2012/06/window.jpg)
I know they use transparent plastic models of parts under polarized light to reveal stress concentration points in the part.
Terry, 230RN
According to this video I just came across newer research shows it wasn't the sharp corners of the windows that was the source of the problem, the engineers actually designed the windows to prevent that issue before hand, but rather the way they punched the holes for the rivets around the windows and the way they did the fatigue testing hid the problem.
https://www.youtube.com/watch?v=2rvx-r2itrE
Jump to the part about the rivet holes https://youtu.be/2rvx-r2itrE?t=557
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According to this video I just came across newer research shows it wasn't the sharp corners of the windows, the engineers actually designed the windows in a way to fix that problem before hand, but rather the way they punched the holes for the rivets around the windows and the way they did the fatigue testing hid the problem.
https://www.youtube.com/watch?v=2rvx-r2itrE
Jump to the part about the rivet holes https://youtu.be/2rvx-r2itrE?t=557
Aw, shucks. The square window thing was probably the only bit of aviation trivia (I thought) I knew. =(