Red to blue

Some research has a very long incubation time.  Last month, we published a short paper that describes the initial results of research that started just after I arrived in Liverpool in 2011.  There are various reasons for our slow progress, including our caution about the validity of the original idea and the challenges of working across discipline boundaries.  However, we were induced to rush to publication by the realization that others were catching up with us [see blog post and conference paper].  Our title does not give much away: ‘Characterisation of metal fatigue by optical second harmonic generation‘.

Second harmonic generation or frequency doubling occurs when photons interact with a non-linear material and are combined to produce new photons with twice the energy, and hence, twice the frequency and half the wavelength of the original photons.  Photons are discrete packets of energy that, in our case, are supplied in pulses of 2 picoseconds from a laser operating at a wavelength of 800 nanometres (nm).  The photons strike the surface, are reflected, and then collected in a spectrograph to allow us to evaluate the wavelength of the reflected photons.  We look for ones at 400 nm, i.e. a shift from red to blue.

The key finding of our research is that the second harmonic generation from material in the plastic zone ahead of a propagating fatigue crack is different to virgin material that has experienced no plastic deformation.  This is significant because the shape and size of the crack tip plastic zone determines the rate and direction of crack propagation; so, information about the plastic zone can be used to predict the life of a component.  At first sight, this capability appears similar to thermoelastic stress analysis that I have described in Instructive Update on October 4th, 2017; however, the significant potential advantage of second harmonic generation is that the component does not have to be subject to a cyclic load during the measurement, which implies we could study behaviour during a load cycle as well as conduct forensic investigations.  We have some work to do to realise this potential including developing an instrument for routine measurements in an engineering laboratory, rather than an optics lab.

Last week, I promised weekly links to posts on relevant Thermodynamics topics for students following my undergraduate module; so here are three: ‘Emergent properties‘, ‘Problem-solving in Thermodynamics‘, and ‘Running away from tigers‘.

 

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Ramblings on equality

By David Samuel, User:Hellodavey1902 – Own work, CC BY-SA 3.0,

I had some time to spare in Oxford last week and visited the Treasury in the Weston Library again (see my post entitled ‘The Red Crane‘ on July 26th, 2017).  I was amazed to be confronted by an eight-hundred year-old copy of the Magna Carta.  No fuss, no fanfare, just sitting there behind a glass screen as close as you are to your screen as you read this blog.  But the Bodleian Library has four copies of the Magna Carta; so, maybe it’s nothing special to them!  This one is slightly dogged-eared, or to be more precise, rodent-nibbled – there were a couple of small holes where an animal had gnawed it while it was folded up and stored at Osney Abbey from its issue following King John’s death in 1217 until the Abbey’s dissolution in 1539.  The equivalent documents in the USA, the declaration of independence, the constitution and the bill of rights, are housed in the grandiose building on the National Mall, shown in the picture.

After the Weston Library Treasury, I went to the bookshop next door and could not resist buying a couple of books: ‘Signs Preceding the End of the World‘ by Yuri Herrara and ‘The Wandering Falcon‘ by Jamil Ahmad.  Hopefully, I will not succumb to tsundoku (see my post on ‘Tsundoku‘ on May 24th, 2017) and will eventually read these novels.  BTW – you can read the Magna Carta here.

It’s October and the start of university term, which also means that once again I am teaching thermodynamics to first-year undergraduate students. I have blogged on thermodynamics frequently; so, I am going to provide links to these posts during the next couple of months.  Primarily for those of my undergraduate students who find their way to this blog, but hopefully these links will also be of interest to regular readers. My opening lecture set thermodynamics in the context of the more familiar sciences as described in my post entitled ‘And then we discovered thermodynamics‘ on February 3rd, 2016.  Last week’s lecture started with the Zeroth Law of Thermodynamics, which I have discussed in two posts entitled ‘All things being equal‘ on December 3rd, 2014 and ‘Lincoln on equality‘ on February 6th, 2013 – now I’ve gone in a full circle, if somewhat shakily!

Instructive Update

Six months ago I wrote about our EU research project, called INSTRUCTIVE, and the likely consequences of Brexit for research [see my post: ‘Instructive report and Brexit‘ on March 29th, 2017].  We seem to be no closer to knowing the repercussions of Brexit on research in the UK and EU – a quarter of EU funding allocated to universities goes to UK universities so the potential impacts will hit both the UK and EU.  Some researchers take every opportunity to highlight these risks and the economic benefits of EU research; for instance the previous EU research programme, Framework Programme 7, is estimated to have created 900,000 jobs in Europe and increased GDP by about 1% in perpetuity.  However, most researchers are quietly getting on with their research and hoping that our political leaders will eventually arrive at a solution that safeguards our prosperity and security.  Our INSTRUCTIVE team is no exception to this approach.  We are about half-way through our project and delivered our first public presentation of our work at the International Conference on Advances in Experimental Mechanics last month.  We described how we are able to identify cracks in metallic structures before they are long enough to be visible to the naked eye, or any other inspection technique commonly used for aircraft structures.  We identify the cracks using an infra-red camera by detecting the energy released during the formation and accumulation of dislocations in the atomic structure that coalesce into voids and eventually into cracks [see my post entitled ‘Alan Arnold Griffith‘ on April 26th, 2017 for more on energy release during crack formation].  We can identify cracks at sub-millimetre lengths and then track them as they propagate through a structure.  At the moment, we are quantifying our ability to detect cracks forming underneath the heads of fasteners [see picture] and other features in real aerospace structures; so that we can move our technology out of the laboratory and into an industrial environment.  We have a big chunk of airplane sitting in the laboratory that we will use for future tests – more on that in later blog posts!

INSTRUCTIVE is an EU Horizon 2020 project funded under the Clean Sky 2 programme [project no. 686777] and involves Strain Solutions Ltd and the University of Liverpool working with Airbus.

Statistics on funding from http://russellgroup.ac.uk/news/horizon-2020-latest-statistics/and https://www.russellgroup.ac.uk/media/5068/24horizon-2020-the-contribution-of-russell-group-universities-june-201.pdf

For other posts on similar research topics, see ‘Counting photons to measure stress‘ on November 18th, 2015 and ‘Forensic engineering‘ on July 22nd, 2015.

Pebbles – where are yours?

The picture shows a little collection of pebbles and a shell that sits on the desk in my office.  There are similar collections in various locations at home and some of my coats have a pebble permanently in one pocket – there’s even a shell on the dashboard of our car.  They have all been picked up during walks on beaches [see my post entitled ‘Take a walk on the wild side‘ on 26th August 2015] and serve as reminders of the ‘slowness’ enjoyed on vacation [see my post ‘Slow down, breathe your own air‘ on December 23rd, 2015].  Barbara Hepworth owned a similar collection of stones that you can see in the Hepworth Wakefield.  On the subject of this habit she wrote in 1961: ‘Many people select a stone or a pebble to carry for the day.  The weight and form and texture felt in our hands relates us to the past and gives us a sense of a universal force.  The beautifully shaped stone, washed up by the sea, is a symbol of continuity, a silent image of our desire for survival, peace and security.’  I could not express it better so I didn’t try.

The quote is from a contribution to the film Barbara Hepworth directed by John Read, BBC TV, 1961 and can be found in Barbara Hepworth: Writings and Conversations, edited by Sophie Bowness, London: Tate Publishing, 2015.

Airborne urban mobility

Pop.Up_copyright Italdesign 2

At the Airbus PhD workshop that I attended a couple of weeks ago [see my post entitled Making Engineering Work for Society on September 13th 2017], Axel Flaig, Head of Airbus Research and Technology, gave us an excellent opening presentation describing their vision for the future.  Besides their vision for the next generation of passenger aircraft with reductions in CO2, NOx and noise emissions of 75%, 90% and 65% respectively against 2000 levels by 2050, they are also looking at urban air mobility.  We have 55 megacities [cities with a population of more than 10 million] and it is expected that this will increase to 93 by 2035 [see my post entitled ‘Hurrying Feet in Crowded Camps’ on August 16th, 2017].  These megacities are characterized by congestion and time-wasted moving around them; so, Airbus is working on designs for intra-city transport that takes us off the roads and into the air.  Perhaps the most exciting is the electric Pop.up concept that is being developed with Italdesign.  But, Airbus are beyond concepts: they have a demonstrator single-seater, self-pilot vehicle, the Vahana that will fly in 2017 and a multi-passenger demonstrator scheduled to fly in 2018.

Soon, we will have to look left, right and up before we cross the road, or maybe nobody will walk anywhere – though that would be bad news for creative thinking [see my post on ‘Gone Walking’ on 19th April 2017], amongst other things!

 

Image from http://www.airbus.com/newsroom/press-releases/en/2017/03/ITALDESIGN-AND-AIRBUS-UNVEIL-POPUP.html where there is also a video.