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Exploding Dough And Fun With Carrots 

February 22nd 2013

by Tony Abbey, NAFEMS Training Manager


Welcome to my first blog for NAFEMS and an unusual title.  

It has been a very busy two weeks travelling and teaching the NAFEMS “Introduction to FEA” class in the UK and Holland. As usual each class was very different - depending on the background of the client company and the individuals attending. Both classes were fun, I always enjoy meeting fellow engineers and talking about FEA and engineering. Two or three days working with a group gives a great opportunity to find out about everyone’s background, what aspects of analysis they are involved with and the engineering behind the products or process.

It is a privilege to have this opportunity and I have 

been able to learn a great deal about a broad range of industrial sectors and their individual requirements and challenges. It has also given me a good insight into the changing nature of analysis over the years. And it certainly has changed. All the classes now have a wide span of engineers who are working with FEA; no longer a roomful of gurus who view FEA as an end in itself – there is a much broader, younger and questioning audience.
There is more discussion about aspects of idealization that we took for granted 20 years ago – why not just ‘pour’ elements into the CAD model and get on with the job. Good question, and I will revisit that in further blogs.

There is much more discussion about interface with CAD – can it be done effectively in a particular client’s environment, can we improve it? Again much scope for discussion in future blogs. There is also a very clear shift away from the traditional level of checking and manual verification, that is a concern and a reason for emphasizing this aspect on every course.

Anyway, back to the curious blog title. I like to give a lot of practical examples of structures and their behaviour during the class. One of those revolves around torsion in a shaft. A somewhat dry subject, with a curious pattern of shear flow running in a spiral manner around the shaft. That is difficult to picture, so I cheat and use an example from off the supermarket shelf. In my home city of Los Angeles the use of ready-made dough in tubes, for bagels and other goodies is very common. My wife uses these a lot and as an engineer I of course play with the things. They have a helical join along the tube – like a loo roll, and when twisted they shear along the join and fail. The resulting loud explosive pop is very satisfying and quite addictive – like bubble wrap. My wife has more loose dough than she needs as it is habit forming!

On many classes I get very blank stares and then have to explain the exploding dough tube. I do suggest a quick trip to the supermarket to try it out – of course you should buy any you pop! I am going to do a YouTube video one of these days just to prove I am not making it up.  During this week’s class in Holland I explained all this. The next day I was delighted when one of the attendees came up with a tube of Dutch croissant dough in a tube! So we had a live class demonstration and it was very satisfying – not quite the same ‘bang’ as the US version, probably due to EU regulations!

I am tempted to take a tube into every class – but I am not sure what customs would say to my stash of explosive tubes…

What about the carrot? Again one of the classroom examples – a nice fresh carrot shows a similar type of torsional shear failure as a steel bar! I don’t carry carrots around either, but I was delighted when a young lady on the class produced her ‘experimental’ two halv

So, some homework folks … take your carrot, exploding dough and mix carefully!es of a carrot. Her boyfriend was a little bemused apparently – but what a great sport and it helped to make a fun class.

Until next time,

Regards,

Tony

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