I used to suffer from tsundoku but now I am almost cured… Tsundoku is a Japanese word meaning ‘the constant act of buying books but never reading them’. I still find it hard to walk into a good bookshop and leave without buying a small pile of books. I did it early this month in the Camden Lock Books and left with ‘The New Leaders‘ by Daniel Goleman, ‘What we talk about when we talk about love‘ by Raymond Carver and ‘The Fires of Autumn‘ by Irène Némirowsky. I will probably read all of these three books over the coming months so it was not really an act of tsundoku. But, it’s perhaps only because there are so few really good bookshops left that I don’t buy more in a year than I can read. Although this is not quite true in my professional life, because I have started buying books on-line and the pile of unread books in my office is growing; so I am not completely cured of tsundoku. Actually, all researchers are probably suffering from it because we collect piles of research papers that we never read – in part because we can’t keep up with the 2.5 million papers published every year. And, it’s growing by about 5% per annum, according to Sarah Boon; perhaps, because there are more than 28,000 scholarly journals publishing peer-reviewed research. Of course, that’s what happens if you measure research productivity in terms of papers published – it’s a form of Goodhart’s law [see my post entitled ‘Goodhart’s Law‘ on August 6th, 2014].
As a student, in the run up to exams, I used to enjoy going out walking in the hills on my own. This approach to exam preparation probably surprised my fellow students. While other walkers that I came across probably thought I was mad because, in an age before mobile phones, they would see me talking to myself; because, as I walked, I was reciting material that I needed to learn for the next exam. This technique worked for me but I have hesitated to recommend such behaviour to my students. Now, I’ve discovered that psychologists have found that cognitive performance is improved in young adults while walking at a comfortable, relaxed speed. This is probably connected to the neurogenesis that I wrote about in my post entitled ‘Gone walking’ on April 19th, 2017.
So, as the examination season is underway in many universities, I thought I should pass on my rather eccentric approach to exam revision. No doubt, I’ll discover that I wasn’t so eccentric after all but none of us dared share such an unconventional approach to exam preparation.
Susan Greenfield, A Day in the Life of the Brain, London: Allen Lane, 2016.
Leadership is like shepherding – selfless and most of the time you have to stand back and watch. You show them where to forage [provide the vision], you take care of their health and welfare, you protect them against predators [threats] and you worry about them. But, when all of that’s done, you watch from a distance and feel proud of them.
If you would like to discuss ideas about leadership in science and technology then join us towards the end of this month for a CPD module on Scientific Impact and Reputation, which is part of our Science and Technology Leadership programme at the University of Liverpool in London.
While we were walking in the Lake District [see my post ‘Gone Walking’ on April 19th, 2017] I read ‘The Shepherd’s Life’ by James Rebank. Rebank describes how his flock is hefted to the land. ‘Heft’ is a word used in Northern England and Scotland, and means to become accustomed and attached to an area of pasture. In our modern society people tend to become accustomed and attached to cities. A few weeks earlier Nilanjana Roy, writing in the FT Weekend on April 8/9, wrote about the growing belief that national identity is an outdated and insufficient concept, whereas cities reflect the common identities of their inhabitants and have been home to peoples of diverse origin and belief for centuries. Many of us who travel frequently have a map in our heads of cities in which we feel comfortable, happy to return, accustomed or ‘hefted’. Roy calls it ‘a map of belonging’ – the cities that your spirit chimes with the most. Mine would probably include Liverpool, Ottawa, Santa Fe and Taipei [see my posts entitled ‘Out and about‘ and ‘Crash in Taipei: an engineer’s travelogue‘ on December 7th, 2016 and November 19th, 2o14 respectively]. To which cities do you feel ‘hefted’?
Alan Arnold Griffith was a pioneer in fracture mechanics who studied mechanical engineering at the University of Liverpool at the beginning of the last century. He earned a Bachelor’s degree, a Master’s degree and a PhD before moving to work for the Royal Aircraft Establishment, Farnborough in 1915.
He is famous for his study of failure in materials. He observed that there were microscopic cracks or flaws in materials that concentrated the stress. And he postulated that these cracks were the source of failure in a material. He used strain energy concepts to analyse the circumstances in which a crack or flaw would propagate and cause failure of a component. In order to break open a material, we need to separate adjacent atoms from one another, and break the bonds between them. This requires a steady supply of energy to do the work required to separate one pair of atoms after another and break their bonds. It’s a bit like unpicking a seam to let out your trousers when you’ve put on some weight. You have to unpick each stitch and if you stop working the seam stays half undone. In a material with a stress raiser or concentration, then the concentration is quite good at delivering stress and strain to the local area to separate atoms and break bonds. This is fine when external work is being applied to the material so that there is a constant supply of new energy that can be used to break bonds. But what about, if the supply of external energy dries up, then can the crack continue to grow? Griffith concluded that in certain circumstances it could continue to grow.
He arrived at this conclusion by postulating that the energy required to propagate the crack was the work of fracture per unit length of crack, that’s the work needed to separate two atoms and break their bond. Since atoms are usually distributed uniformly in a material, this energy requirement increases linearly with the length of the crack. However, as the crack grows the material in its wake can no longer sustain any load because the free surface formed by the crack cannot react against a load to satisfy Newton’s Law. The material in the wake of the crack relaxes, and gives up strain energy [see my post entitled ‘Slow down time to think (about strain energy)‘ on March 8th, 2017], which can be used to break more bonds at the crack tip. Griffith postulated that the material in the wake of the crack tip would look like the wake from a ship, in other words it would be triangular, and so the strain energy released would proportional to area of the wake, which in turn would be related to the crack length squared.
So, for a short crack, the energy requirement to extend the crack exceeds the strain energy released in its wake and the crack will be stable and stationary; but there is a critical crack length, at which the energy release is greater than the energy requirements, and the crack will grow spontaneously and rapidly leading to very sudden failure.
While I have followed James Gordon’s lucid explanation of Griffith’s theory and used a two-dimensional approach, Griffith actually did it in three-dimensions, using some challenging mathematics, and arrived at an expression for the critical length of crack. However, the conclusion is the same, that the critical length is related to the ratio of the work required for new surfaces and the stored strain energy released as the crack advances. Griffith demonstrated his theory for glass and then others quickly demonstrated that it could be applied to a range of materials.
For instance, rubber can absorb a lot of strain energy and has a low work of fracture, so the critical crack length for spontaneous failure is very low, which is why balloons go pop when you stick a pin in them. Nowadays, tyre blowouts are relatively rare because the rubber in a tyre is reinforced with steel cords that increase the work required to create new surfaces – it’s harder to separate the rubber because it’s held together by the cords.
By the way, James Gordon’s explanation of Griffith’s theory of fracture, which I mentioned, can be found in his seminal book: ‘Structures, or Why Things Don’t Fall Down’ published by Penguin Books Ltd in 1978. The original work was published in the Proceedings of the Royal Society as ‘The Phenomena of Rupture and Flow in Solids’ by AA Griffith, February 26, 1920.