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Thread: Elastic/Plastic Deformation

  1. #1 Elastic/Plastic Deformation 
    Time Lord zinjanthropos's Avatar
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    Dec 2005
    Driving in my car
    Was reading up on some science of ordinary things and stumbled across this: Person(s) claiming that tall office buildings get taller at night, once everyone has gone home and their combined weight is removed. I checked it out and someone confirmed and even provided a measurement of 1.5 mm. That was disputed by many people in the know. Anyway it led me to this article on elastic/plastic deformation.

    Elastic meaning material under stress returning to original shape once stress removed and Plastic meaning a permanent deformation. With that in mind I remembered a term I used to hear called memory. So I'm wondering if memory & elastic are one and the same? Is elastic deformation really what it implies since it's only temporary, has what's under stress really been deformed if it can return to original shape? People who design buildings, do they actually allow for any plastic deformation within structures or is it "bend but don't break"?

    What about overall strength? When elastic deformation takes place, does the affected material lose strength, as in molecular bonds?

    All that belongs to human understanding, in this deep ignorance and obscurity, is to be skeptical, or at least cautious; and not to admit of any hypothesis, whatsoever; much less, of any which is supported by no appearance of probability...Hume
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  3. #2  
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    Feb 2018
    Couple of words. Stress is the force applied. Strain is the deformation that occurs when stress is applied. Resilience is the tendency (time and amount) it has to return to it's original shape after stress is removed. Elasticity is how much resilience it has. Plasticity is how much resilience it doesn't have. The reason for specific terms is that coefficients are applied to the terms in engineering for specific materials and structure so that mathematical principles can be applied to simplify complex structures. Repeated stress causes fatigue, eventually breakage. Metal memory is when metals return to a previous shape when some stress like heat is applied. That's because the crystalline structure deforms and stores energy but doesn't release it until some stress like heat or shock causes the crystal structure to mobilize enough to return to its previous shape. They are subject to fatigue too.

    But buildings expand more in the heat of the day than they are compressed by the weight of people.

    Last edited by doitright; December 22nd, 2018 at 05:29 AM.
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