Tag Archives: mechanics

Holes

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Holes, little circular ones. There are billions of them in engineering machines and structures. There are more than a million in a jumbo jet alone. Some of them are filled with fasteners, such as bolts and rivets, others are empty to allow fluids to flow through a surface. Load passing through a structure has to flow around holes, especially when they are empty, and the contours of stress bunch up around a hole to form a stress concentration. For a small hole in a very large plate, the stress on the circumference of the hole is three times the level found in the absence of the hole. This concentration increases for bigger holes or smaller plates, so that holes are a potential source of failure – that’s why sheets of stamps are perforated with lines of holes.

A hole can also stop a failure. For instance a crack extending under repeated loading will often stop when it grows into a hole because the ‘sharpness’ of the crack tip is blunted by the roundness of the hole. Engineers sometimes deliberately drill a hole at a crack tip to arrest its progress. So, holes can be both an engineer’s friend and foe.

Conflict Resolution

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conflict pyramidEngineers need to be experts in resolving conflicts…

Every man-made device that moves required energy to make it and uses energy when it moves. Heavier devices have greater inertia than small ones and hence more energy is needed to set them in motion – think about peddling an old-fashioned steel-framed bike compared to a modern alloy one. So, designing for sustainability requires engineers to minimise the quantity of raw materials and energy used to manufacture a device AND to minimize its weight if the device moves as part of its function.

Now, here comes the conflict.

Sustainability also implies that devices should have a long, maintenance-free service life so that resources used in maintenance and replacement are minimized. Service life is usually limited by fatigue and, or wear and the probability of these failure mechanisms occurring can be reduced by lowering stress levels. However, stress is inversely proportional to cross-section area and so can be reduced by adding material, i.e. increasing the mass of the device which will also increase its inertia, or resistance to motion. The probability of failure can be reduced by using stronger, more sophisticated materials that are lightweight and almost always more expensive, e.g. composites. Customers also want performance and additional expense might be acceptable if it is accompanied by additional performance – some people will pay for a carbon-fibre frame for their bicycle. Elegant engineering design requires resolution of the conflict between cost, safety and reliability, performance and sustainability.

This is why engineers are trained in conflict resolution or as it is more commonly known: problem-solving.

100 Everyday Engineering Examples

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bookletsSTOP PRESS – more than 100 Everyday Engineering Examples published in more than 40 lesson plans on a new webpage.

I have been including 5E lesson plans as part my recent posts.  These lesson plans are primarily for people teaching first-year engineering undergraduates, which is pulling me away from the intended focus of this blog. So, I have decided to publish all of the lesson plans that I have written & edited on a separate page.  There are more than 100 Everyday Engineering Examples in the more than forty lesson plans.  If that is not enough Everyday Engineering Examples then you can find more at ENGAGE

Now back to Realizing Engineering – we live in an almost entirely engineered world. Engineers, as a profession, are so good at their job that most people are unaware of their influence on society.  Look around you. Engineers will have designed the machines and transport infrastructure to supply most of what you can see as well as what you are probably sitting in and on.

The Royal Academy of Engineering has produced an ebook to expand on this theme of ‘Engineering in Society’ for first year engineering undergraduates but I think its suitable for anyone considering a career in Engineering.

Slam dunk

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CIMG0176Here is another lesson plan for use in teaching engineering science.  This one is based on the stress generated by a slam dunk in basketball.  Sports provide many potential Everyday Examples but caution needs taken in selecting them because not all students are interested in or participate in sports.  Research has shown that the context of examples should be familiar to all students in a class.  Otherwise students will be worrying about the context and will not be listening to the explanation of the engineering science.  Examples will be perceived as tedious intellectual exercises unless that allow questions to be posed that have interesting or useful answers.  Student motivation is closely linked to their perception of the usefulness of the exercise.

When Everyday Examples are set in a familiar context and yield fruitful outcomes, then the level of student engagement and learning is not influenced by the level of difficulty.  So there is no need to idealise a scenario to an elementary problem prior to applying engineering principles.  And here is the proverbial slam dunk, instructors who successful incorporate appropriate Everyday Examples into their lectures are likely to be rated more highly by their students, regardless of the associated level of difficulty.

Lesson plan: 5EplanNoS9_eccentric_loading

See the Everyday Examples page on this blog for more lesson plans and more background on Everyday Examples.