Tuesday 7 July 2015


I was born in the aftermath of WWII; 9 years after Hiroshima my parents were still recovering from the life-changing trauma of their 20s. A lot of their close friends were dead and I think they were somewhat surprised to have survived. They never talked about their experiences, for example, through the 50s and 60s. But WWII was 'in the air' when I was growing up: we used to play at being fighter aircraft: arms out, run around like a mad thing making engine sounds and occasionally shouting budda-budda-budda. There was a lot of regular carnage in the war, but those challenging times provided a number of problems that couldn't be solved with a bomb or bayonet. Although of course The Bomb provided some mighty challenging intellectual problems as anyone who has read Richard Feynman's memoirs can tell. I'm thinking of Turing and Enigma; Wald and Armour; Habbakuk and Pykrete; and liberty ships.

Liberty ships? These were the solution to trans-Atlantic traffic after much of the pre-war merchant fleet had been sunk. 2,700 of these work-horses were built between 1941 and the end of the war to the same design: Length 135m; Beam 17.5m; Draft 8.5m; Capacity 10,900 tons. At the start, liberty ships took 230 days to build but this was shaved down to an eye-opening 113 hours between laying down the keel and launch for the SS Robert E Peary. That was a never-repeated stunt - typical construction times were reduced to 6 weeks - and a launched hull was still a long way from useful work, but you get my drift: more shipping was needed yesterday and double up about it! One of the design features by which ship-building could be expedited was to use welded rather than rivetted joints. Another was regular economies of scale: you can put together the second and third ship quicker than the first if they are built to precisely the same design.  It's the same with Ikea flat-packs nowadays.

I've written before about the accidental destruction of a handful of liberty ships - nearly 90% of them survived the war intact. Like Ernest Worthing losing two parents, when a second liberty ship hogged itself to death, the Ministry of Supply instituted an investigation, chaired by Prof John Baker, head of Engineering at Cambridge. But the real expert in metals, their crystal structure and the response to  deformation was Constance Tipper, and she was co-opted by Baker to do the real work. He later said "Her vigor in prosecuting her work in an extremely male preserve will always be remembered and admired". The novel welded joints were fingered but Tipper showed that the brittle fracture was an intrinsic fault of the steel. Although it was agreed that the fractures, once started, could propagate more easily across a welded than a rivetted joint. It turned out that the specs for the steel were such that below a certain temperature, the plates behaved more like cast iron [brittle] and much less like mild steel [ductile, flexible]. Worryingly this critical threshold temperature was very likely to be encountered in the Atlantic in Winter. The eponymous Tipper Test was used to ensure adherence to new higher specs on the steel used in American shipyards.  It's a nice engineering problem - the design must use the minimum amount of steel (there's a war on) commensurate with effective function with an engineer's margin for safety in conditions a bit outside 'normal'.  It took a smart woman to get some data and analyse it, rather than rounding up the usual suspects.  She wrote it all up as The Brittle Fracture Story which is available from Amazon for $150. The fact that so many liberty ships survived the war having delivered their multiples of 10,000 tons to a beleaguered Britain is due in part to her intervening to change the standards of the materials.

Constance Tipper is almost invisible on the interweb - there is only one photograph of her which looks like it was taken when she graduated in Natural Science in 1915 - she scraped a Third! but went on to land a DSc from U London (1926) and ScD from U Cambridge (1949).  In 1923, her boss was invited to give a series of prestigious lectures to the Royal Society and he arranged for co-delivery of the lectures by a colleague CF Elam.  Everything was fine until CF Elam turned out to be Constance Fligg Elam.  Both the speakers had been invited to the RS dining club afterwards, but women were not allowed to sully the salt with their hormones and silly chatter. Apprised of the boys' predicament, she graciously declined the invitation "I am sorry to have given you so much trouble, but it is my misfortune rather than my fault that I do not happen to be a man. I felt very much honoured on receiving your invitation although I realised that it had been sent under a misunderstanding." and received a box of chocolates in return -
"I say Haldane, don't girls like chocolates?"
"Damned if I know, Rutherford, didn't have any girls at Eton".

In 1994, Newnham College planted a sweet chestnut Castanea sativa in the grounds to celebrate Tipper's 100th birthday in 1994, it is known as the Tipper Tree. I hope at least some of the young Newnham women Tipper Hat when they go past. She died the following year.

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