Eann Patterson

Eann Patterson

Engineer, educator & author. I hold the AA Griffith Chair in Structural Materials & Mechanics at the University of Liverpool. Read my blog at RealizeEngineering.Wordpress.com to find out more.

Location Liverpool


  • I am sorry to hear that you feel it is beyond you. You should be follow later steps without having understood these worked examples. So, keep going!

  • I cannot find the error in the pdf. Can you tell me more?

  • Yes, there are quite a few parallels. I have posted a couple of posts on my blog on this topic. See, for example:

  • Yes, I am planning to start a new PhD project on fracture properties of timber next academic year which, in part, is motivated by the increase use of timber in tall buildings.

  • Yes, there certainly used to be - I remember seeing it when I was much younger. I think it's the one next to Battersea Park?

  • Thank you. It would be good to see some more designs!

  • Thank you for spotting the typos. I found two and have corrected them.

  • This a bit too much information; but it's good to hear that you have got set up to try out FEA.

  • It might be that most ancient structures fell down long ago and the only ones left are the very best. I expect that the best modern day ones will also survive for centuries. However, it is very expensive to design everything to survive for thousands of years!

  • Yes, this approach is being used in a wide range of engineering fields, such as aerospace engineering.

  • Yes, it is why troops break step but you wouldn't expect a random collection of pedestrians to produce the same effect.

  • Here is a quick link to the collection of editorials mentioned in the audio clip: http://journals.sagepub.com/topic/collections/sdj-1-golden_anniversary_editorials/sdj

  • I am glad you found the course rewarding. I hope to see you again either on-line or on one of our campuses in Liverpool, London or Suzhou.

  • I have not come across that particular programme. There are lots of integrated analysis systems for structures. Some of them are specialised for particular industries, such as aerospace or civil engineering, others are more generalised.

  • If the probability of failure is high then we need to redesign the structure to lower the probability. This might mean doing tests or research to remove some of the unknowns.

  • Yes, it does appear to act in a similar way to drilling a hole to stop a crack, except that the crack is not arrested. The crack's advance is slowed down but we have not managed to arrest a crack in this way.

  • I am still reading comments on previous weeks so if you ask questions I will try to answer them.

  • Welcome to the course. We are in the last week which is week 5; however, I am scanning through comments made in other weeks, so feel free to ask questions or make comments and one of us will answer them. I hope you make it to the end before it closes to free admission in three weeks time!

  • Yes, but be careful with the word 'show' because some deflections might so small as to be invisible with the naked eye.

  • I'm not sure whether that's poor design or your technique, or a bit of both?

  • We use the LISA code when we are teaching a short course on structural integrity to scientists. Its a free download at http://www.lisa-fet.com/

    I have never tried it on an iMAC.

  • I have co-authored one book entitled 'The Entropy Vector: Connecting Science and Business' with Bob Handscombe. We wrote it a long time ago. See: http://www.worldscientific.com/worldscibooks/10.1142/5365

    However, it does not deal with this subject directly. I wrote a piece for the Citizens of Everywhere project a few months ago...

  • I don't follow what you mean.

  • Maybe some types of tofu would work as an alternative. Though I have not tried it in this experiment and would not recommend using the stinky tofu that I have come across in Taiwan!

  • No. Yield line analysis assumes possible collapse modes for a structure based on the formation of plastic hinges or yield lines. It does deal with the fracture of the material.

  • if you are in France, you should try Cantal or Comte cheese.

  • I don't know. Before I could answer, I would need to know a lot more about the geometry of the structure, the materials and loading conditions. So I am hoping yours was a rhetorical question?

  • If you want even more heavy reading material, then some of our work on cracks in titanium has been published under the title: Quantitative measurement of plastic strain field at a crack tip, by Y Yang, M Crimp, RA Tomlinson & EA Patterson in the Proceedings of the Royal Society A, 468:2399-2415, 2012. A download is available at...

  • Some of latest research was published last year in the journal: Experimental Mechanics under the title: High temperature vibratory response of Hastelloy-X: stereo-DIC measurements and image decomposition, by RB Berke, CM Sebastian, R Chona, EA Patterson & J Lambros. It's currently available as a free download from the publishers if you want some extra heavy...

  • By coincidence I wrote next week's post for my blog about GIGO. So, yes I agree.

  • Yes, that's a nice example but I fear we might be revealing our age.

  • Yes, titanium has a material response similar to steel and aluminium but offers higher performance per unit mass. However, as you point out, it is expensive. We have been performing research on fatigue crack growth in titanium though not connected to the work on hypersonic flight mentioned above.

  • Yes, the gradient of the elastic portion of the stress-strain curve and the yield point will change with temperature. The level of change varies from one material to another. So this has to be accounted for in the design of aircraft. We are currently working the behaviour of aircraft panels during hypersonic flight when temperatures up to 2000 degrees can...

  • No, see my response to your earlier comment.

  • I didn't say that bonds break and re-form in elastic deflections. Dislocation movement and bond breaking then re-forming are associated with permanent or plastic deformation. However, plastic deformation can be very local in a structure so that the remainder of the structure behaves elastically. It is rare for an entire structure to transition from elastic...

  • Yes. Digital computers might be able to handle a large number of variables but the creative process of generating innovative designs still requires our analogue brains and graphical representations, such as Mohr's circles, allow us to interprete the analysis and understand the stress system.

  • Yes, you are right. It is missing. Our graphic designer will work on it later today.

  • Surely, if the water forms a thin film then it is no longer a droplet. A droplet is a very small drop and by definition a drop is 'a small round or pear-shaped portion of liquid that hangs or falls or adheres to a surface' according to the OED.

  • I had already used the bungee cord in another example and want something different to avoid confusion...

  • We don't have an acoustic room or recording studio so we have to make do with what's available. I want to show the steps involved in the analysis rather than the short-cuts that will only work in specific circumstances.

  • I can't answer that question. Universities make proposals to FutureLearn for new courses but as far as I am aware there is no grand plan. The choice available to you depends on what the educators fancy producing.

  • Thank you. I have made the corrections.

  • We are somewhat constrained by the platform we are using. Our use of audio steps was an experiment and hence the platform and format is not optimised for it. However, FutureLearn have already made changes to help us present the audio steps; so hopefully we will be able to make additional changes in the future. Thank you for the feedback.

  • Redundancy means 'the inclusion of extra components which are not strictly necessary to functioning, case of failure in other components' according to the Oxford English Dictionary. In this case, the bag is stable on the floor and the strap is unnecessary, and hence redundant, until the strap is used to lift the bag clear of the floor.

    When the bag is in...

  • Thank you

  • The horizontal axis is the distance along the beam and the vertical axis is the shear force acting internally within the beam. Listen to our Q&A session this week for some more explanation of shear forces.

  • If we think in terms of an elemental shape, such as a cube, then a shear force causes a rotation of one face relative to another. The result is that the cube is no longer a cuboid because its faces are no longer mutually perpendicular. In fact, we measure shear strain in terms of the change in angle between the faces; but, that's a whole new topic that perhaps...

  • It depends on how heavy it is relative to the forces being applied. In many cases the self-weight of the structure is not significant compared to the forces applied to it.

  • Yes, I think that is correct and is why you tension it in the first place.

  • You can if you want to and you would get the same answer as for the z-direction.

  • Yes, in thin-walled structures it is usually assumed that txt is negligible.

  • Shear forces often generating a deformation associated with layers of material attempting to slide past one another. However, when pressure is applied to an object, it is does not necessarily generate a bending moment. Pressure applied on a column might just produce a compressive stress without any bending.

  • The analysis deals with the work done by the external or applied force. Inside the bar this work done is converted into strain energy and stored in the molecular structure of the material. If the deformation of the bar is elastic, i.e. reversible, then the strain energy can be released and it is conventional to think of it in terms of energy rather than...

  • Less than, if it is to be classified as thin-walled.

  • I have mentioned in another step: 'The Stone Skeleton: structural engineering of masonry architecture' by Jacques Heyman published by Cambridge University Press [http://www.cambridge.org/gb/academic/subjects/engineering/civil-and-geotechnical-engineering/stone-skeleton-structural-engineering-masonry-architecture?format=PB&isbn=9780521629638#69djY5LMDRz3Xt8C.97]

  • Well, I am sorry that you find me dull. Yes, the curriculum does follow the traditional syllabus of an introductory course in Mechanics of Solids; because, that's exactly what it is!

    One of the 'O's in MOOCs stands for open, i.e. the course is free, which means that there is no budget. The small expenditure involved in making this course was justified on...

  • Yes, you could have used symmetry. However, I wanted to show how the analysis is performed and so I chose a relatively simple example. If you want to test your skills, then make it asymmetric by making one end of the plank built-in (for example, embedded in concrete).

  • Yes, thank you for spotting the typos. I have corrected them in the article and pdf.

  • Well-spotted! Thank you. I have corrected the typo. I apologise for any confusion caused.

  • I am not sure that I follow your logic but I don't think it is correct. Membrane structures only experience in-plane shear and their resistance to it is related to the shear strength of the material.

    We need to distinguish between domes and membrane structures - they may appear to be geometrically similar but the loading conditions are different. I have...

  • I don't think that this is correct. Both direct and shear forces lead to displacements and misalignment means 'the incorrect arrangement or position of something in relation to something else', which could also be the result of a direct force.

    If we think in terms of an elemental shape, such as a cube, then a shear force causes a rotation of one face...

  • Yes, that's right.

  • References replaced.

  • Did you mean plain or milk chocolate? In my experience, milk chocolate digestives are more likely to stick together in the packet; but, that might be because we prefer plain and so the milk chocolate ones end up being stored for longer.

  • I think this discussion is going off topic and is irrelevant because it does not change the conclusion drawn from the worked example.

  • Yes and yes.

  • When you press your flat hands together, by applying pressure perpendicular to your palms, then you are applying a direct compressive force to your palms which get squeezed and squash out sideways a little. However, you touch your flat hands firmly together and attempt to slide one past the other, then you are applying a shear force to your palms and you can...

  • I hope that you enjoy the book.

  • I have added a couple of photos of the last demonstrations with the sheet of paper; for those who have struggled to imagine what was being described or to perform it themselves.

  • Maybe. See how it works out for you. You might be interested in my blog posting this week on 'Listening with your eyes shut', at https://realizeengineering.wordpress.com/2017/05/31/listening-with-your-eyes-shut/

  • Hello and welcome to those that have joined the course recently. We are just about to start week 3 but I will continue to scan through, and respond to, the comments and questions in the earlier weeks. So, feel free to ask questions or make comments as you catch up with us. Good luck and I hope you enjoy the course.

  • I will address this issue in this week's Q&A. It would be helpful to me and other learners if you could think about what you want to ask and phrase your questions succinctly.

  • Yes, your point about efficient use of material is appropriate. However, the point about Hooke's necklace is that does not result in a hemisphere, except in special circumstances.

  • This is like the question last week on whether you could use something other than cheese. And, my answer is the same. I tried several materials and loading methods to find one that was reasonably straightforward - newspaper and pencils was the combination that I gave me the best results. But, yes you could get it to work with other materials, e.g. writing...

  • Stay with us! The calculus will not get any harder. And, you should be able to appreciate the principles even if you can't follow the mathematics.

  • We assumed that the loads were static or constant with respect to time. If you walk, run or jump then the load on your femur is not constant with time, and this introduces an additional level of stress that we will look at in week 4.

  • Maybe your plastic egg-cup deformed to fit your beautiful egg.

  • You've got it; though it's a shame to reveal the magic.

  • Yes, I think you are right.

  • And how was your boiled egg?

  • Tell me more and I might be able to help...

  • I would not say 'the same as' but 'is reacted by' or they are in equilibrium with one another. And, yes when the tube reaches its ultimate limit, an explosion is a possible outcome; but split and a leak without an explosion is also possible.

  • I have altered the text of the article to clarify the issue, i.e. that under the direct forces only the cube will deform but remain a cuboid.

  • Perhaps the confusion arises because the Edinburgh institute was called the School of Arts of Edinburgh.

  • You did nothing wrong! I made a transcription error and did not spot my error in proof-reading. Thank you for highlighting it. I have updated the article and the pdf.

  • Yes, you could do all that you suggest; perhaps you would like to post pictures and your results on the media wall? However, the learning from your more complicated version would not be significantly more than from my simple one. And, most people don't have a fisherman's or butcher's scale, or graduated weights and so the experiment becomes inaccessible to...

  • I am not a cellist so I would defer to an expert on this subject. However, I think the strings only have a steel core, which would explain why they are lighter than you expect. However, considering them to be anything other than solid steel, would make this question more complicated than was appropriate at this stage of the course; so, I chose to ignore that...

  • Whilst I have no objection to you reading ahead, it would be helpful if we could keep the discussion in each step relevant to that step; otherwise, it will end in chaos, which is not conducive to most people's learning.

  • Thank you for your correction of my terminology. You are correct but I chose to simplify matters for this course and so I hope you will accept my decision to not change the first paragraph.

  • Welcome. We have just started week 2 but I will continue to browse through comments on week 1, so feel free to ask questions and I, or someone else, will answer them.

  • Judgment calls are necessary in most real experiments. So, I hope I am also teaching you some experimental skills, too!

  • Nice examples. But could you post pictures on the media wall as well as?

  • Yes and thank you!

  • It is neither!

  • There will be more in week 4 on the force-extension curves and changes in behaviour as a material approached failure.

  • Both!

  • Thank you for spotting the typo. I have corrected it and I apologise for the confusion caused.

  • No, in general a membrane will generally be in tension but the tension is cause by a pressure difference across the membrane rather than the other structural components as in a tensegrity structure.