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Re: OT: Interesting video
From: Don E. Bray
Date: 2013 Dec 17, 02:14 +0000
On Dec 16, 2013, at 06:19 PM, Hewitt Schlereth <hhew36@gmail.com> wrote:
From: Don E. Bray
Date: 2013 Dec 17, 02:14 +0000
This discussion is very correct on the important role which the Liberty ships played on developments in material ductility and fracture mechanics. There was no such field as fracture mechanics before the Liberty ships appeared. Where brittle materials such as ceramics break easily upon flexure, fully ductile materials will bend and deform but not break. We see the benefits of that ductility well demonstrated in this video.
I was mesmerized in 1962 by the action of the expansion joint on the Everglades but at that time I had little knowledge of material properties. Later, much later, teaching mechanics and materials and design at the university level, I was able to integrate these experiences into the classroom lectures.
The examples of ships breaking apart at the docks and failing mostly in the cold North Atlantic is well documented. This led to the development of steels which have a much lower ductile to brittle transition temperature and thus maintain ductile at the low North Atlantic temperatures. Those developments benefitted the aircraft industry, also, and were useful in diagnosing the source of failure in the British Comet airliner.
I am not aware of the situation on the watertight compartments.
DEB
************************************** Astrophysics Primer - Creation to Black Holes http://www.debclltx.com/ Astronomy New Arctic images at http://benbray.com/ Shipping across North Pole 2013 http://news.ca.msn.com/canada/coal-cargo-ship-crosses-northwest-passage-3 Don E. Bray Mail P. O. Box 10315, College Station, Texas 77842-0315 Office/Cellular 979-492-9534
On Dec 16, 2013, at 06:19 PM, Hewitt Schlereth <hhew36@gmail.com> wrote:
Lu, thank you. A niece lives near San Francisco, so a visit to the Jeremiah O'Brien is now on my to-see list.Hewitt
Sent from my iPadThe San Francisco Liberty Ship is the SS Jeremiah O'Brien, docked near Fisherman's Wharf and part of the National Maritime Museum in SF.
In 1994 the O'Brien steamed under her own power to Normandy to mark the 50th anniversary of her participation in the invasion.
She still makes regular trips in SF Bay under her own steam -- but has to be escorted by two tugboats since Liberty ships had but a single engine and an engine failure on the O'Brien could turn her into a uncontrolled ship aimed at a populated waterfront. I also understand that she has a very large turning radius and needs help from the tugs to do a U-turn despite SF Bay being five miles wide.
Long and interesting article on Liberty ships in Wikipedia: http://en.wikipedia.org/wiki/Liberty_ship
including why they were called "Liberty" ships and how individual ships were named.
The article also discusses the ships' proclivity to hull fractures, with at least three splitting in half and sinking (arguably not bad, since over 2700 were built). It turns out that this occurred mostly during winter passages from the US to Britain. The steel in the hulls actually turned from ductile (which would give a little under stress) to brittle (which would snap under stress) at temperatures in the low 30s (Fahrenheit, or a few degrees above 0 C).
It's not clear from the Wikipedia article how the ships were compartmented.
On 12/16/2013 2:19 PM, Jackson McDonald wrote:: http://fer3.com/arc/m2.aspx?i=125773