Monthly Archives: November 2015

Unexpected bad news for turkeys is defined as the probability of something happening multiplied by consequences of its occurrence.  Engineers expend considerable time and effort in reducing the consequences of the quite probable such as ensuring the passenger compartment of a car will remain largely intact during a crash.  The installation of automatic breaking systems on some cars is also an attempt to reduce the probability of an impact, i.e. the occurrence of a crash.  It is difficult to anticipate the very low probability event with catastrophic consequences and so cars are not designed to deal with meteors dropping out the sky or even elevated highways collapsing in an earthquake.   These are what Nassim Taleb, labels Black Swan events but would perhaps be better named after another bird, the more humble turkey.  An American turkey is fed daily by a friendly human and has no idea in November that Thanksgiving is about happen with fatal consequences, or substitute December and Christmas for a British turkey.  From the turkey’s perspective everything is fine down on the farm until it isn’t; in other words, the very low probability event with catastrophic consequences occurs.  From the farmer’s perspective, turkey for dinner at Thanksgiving is close to a certainty, i.e. a probability of one.  The problem for engineers designing machines is to have the perspective of the farmer and not the turkey.

Happy Thanksgiving to my American readers!


Nassim Nicholas Taleb, The Black Swan – the impact of the highly probable, London: Penguin Books, 2008.

Counting photons to measure stress

TSA pattern around a crack propagating from the left with its tip in the centre.

TSA pattern around a crack propagating from the left with its tip in the centre.

Some might find it strange that I am teaching thermodynamics when my research expertise is in structural materials and mechanics. However, the behaviour of structures is largely controlled by energy and how they absorb, store and release it; while thermodynamics is the study of energy flows and transformations, so there is a connection. In my research group, we exploit this connection in a technique for measuring stress fields in components by monitoring the temperature changes that occur when a component is loaded. In Thermoelastic Stress Analysis (TSA) as it is known, we use very sensitive infrared cameras to monitor the cyclic variations of temperature that occur when cyclic load is applied to a material. The temperature changes are of the order of milli-Kelvin, that’s thousandths of a degree, and are positive with negative, or compressive stress and negative with tensile stress. What we are actually measuring is the rate of change in the release of photons by atoms as they are pushed closer together in compression or pulled further apart in tension; but that’s another story and takes us into physics.

An exciting feature of this technique is that as a crack evolves new surfaces are formed which releases energy as heat. We can detect not only the stress field around the crack but also the heat released during the formation of the crack prior it being visible and its subsequent growth.


Greene, R.J., Patterson, E.A., Rowlands, R.E., 2008, ‘Thermoelastic stress analysis’, in Handbook of Experimental Mechanics edited by W.N. Sharpe Jr., Springer, New York.

Yang, Y., Crimp, M., Tomlinson, R.A., Patterson, E.A., 2012, Quantitative measurement of plastic strain field at a fatigue crack tip, Proc. R. Soc. A., 468(2144):2399-2415.

Patki, A.S., Patterson, E.A., 2010, ‘Thermoelastic stress analysis of fatigue cracks subject to overloads’, Fatigue and Fracture of Engineering Materials and Structures, 33(12):809-821.


Free: Energy! Thermodynamics in Everyday Life

sunTalking to camera is difficult…

For the last few weeks I have been spending a considerable proportion of my working hours in front of a camera shooting video clips for a MOOC, a Massive Online Open Course. The first results of this effort and those of my colleagues Matt O’Rourke and Rob Lindsay in the University’s Centre for Lifelong Learning are now available as a trailer. The initial reviews were ‘cool’ and ‘awesome’, so go ahead and watch it!

Innovation to support learning

Some people have commented on the lack of pedagogical foundation in many MOOCs. However, I think we are being quite innovative in the following ways:

  • we are using an established pedagogy, 5Es (see the next paragraph for more explanation),
  • we have designed three do-it-at-home laboratory exercises,
  • the five-week MOOC will run in parallel with the delivery of the traditional course to first year undergraduates in Liverpool and,
  • the traditional lectures will be repeated at the university’s campus in London two evenings each week.

The lectures in London will allow students living around London to meet each other and me, as well as, of course, experience the energy of the live delivery of the course.

For students worldwide (and in London)

If you are a student who has or is struggling with elementary Thermodynamics then register for the free MOOC which will start in February 2016. I will cover the curriculum content of most ‘A’ level modules and introductory undergraduate courses in Thermodynamics. If you are in London and would like to attend the lectures then contact me and I will send you more details.

For teachers/instructors anywhere

If you are a teacher, tutor or lecturer then consider bringing it to the attention of your students. I will be taking a different approach to the traditional way of teaching classical thermodynamics based on my experience teaching at the University of Liverpool using the Everyday Engineering examples featured on this blog together with the 5Es approach to lecture or lesson plans. If you would like to use it in parallel with your own lectures then get in touch with me so that we can talk about synchronization.


The 5Es are Engage (the students), Explore (the topic), Explain (the principles underpinning the topic), Elaborate (using the principles to analyse the topic) and Evaluate (ask the students to evaluate their learning by performing some analysis). The course has been well-received by students and nearly a thousand have taken it over last four years. This year we are making into a five-week MOOC so that thousands more can learn using it.


Real life thermodynamics

Bybee RW, Taylor JA, Gardner A, van Scotter P, Powell JC, Westbrook A & Landes N, The BSCS 5E Instructional model: origins, effectiveness and applications, BSCS Colorado Srings, 2006.

Sian Bayne & Jen Ross, The pedagogy of the MOOC: the UK view,  Higher Education Academy, 2014

Paul Stacy, The pedagogy of MOOCs,

Talk to people not computers

liverpoolplayhouseRecently, we went to see the Glass Menagerie by Tennessee Williams at the Liverpool Playhouse.  There is a wonderful line in it ‘People go to the movies instead of moving’ when Tom Wingfield comments on everyone living life vicariously through the action-packed life of Hollywood stars.  The play was written in the 1940s long before the advent of smart phones.  Nowadays people interact with their smart phones rather than with the people around them but still live vicariously through the lives of celebrities.  Recent research has found that many people today would actually prefer to deal with computers that appear to understand them rather than with other people, according to Richard Waters.  This is a shame because one of the things that makes humans different to computers is our ‘inbuilt propensity for social interaction’.  Computers are unlikely ever to replicate our emotions, curiosity, irrationality or creativity (See my post entitled ‘Engineers are slow, error-prone…‘ on April 29th, 2015).  So put down your phone or switch off your computer and interact with your fellow human beings.


Richard Waters, Jobs for droids, Essay in Financial Times, Weekend 17/18 October 2015