Elastic v Plastic

[studiot]

As I was refitting the soft plastic debris catch plate to my hole punch, I reflected how often we use and rely on the elastic properties of so called plastic materials.

If they genuinely operated as a plastic material there would be instant failure of the component.

Comments ?

Edited November 22, 2021 by studiot

[swansont]

What manner of failure? breaking, or deformation? Given that the latter is a plastic property, the former shouldn’t be expected. But if it were maximally able to undergo plastic deformation (the necessary force approaches zero), it would deform under its own weight, which is hardly useful. So that just means there is a threshold force that needs to be applied. 

[studiot]

1 hour ago, swansont said:

What manner of failure? breaking, or deformation? Given that the latter is a plastic property, the former shouldn’t be expected. But if it were maximally able to undergo plastic deformation (the necessary force approaches zero), it would deform under its own weight, which is hardly useful. So that just means there is a threshold force that needs to be applied. 

There was no failure in my case.

That is my point.

The metal mechanism of the punch has a soft plastic catch plate for the punched paper disks that is fitted underneath by stretching it slight over the base of the metal frame.

Clearly it had to be only stretched in the elastic region or it would not the snap back into position, gripping the frame.
Taking it into the plastic region would result in a permanent set so it no longer gripped its place tightly.

 

I was simply reflecting on how many plastic cases of many items and gadgets these days rely on this.

[mistermack]

On 11/22/2021 at 11:42 AM, studiot said:

As I was refitting the soft plastic debris catch plate to my hole punch, I reflected how often we use and rely on the elastic properties of so called plastic materials.

If they genuinely operated as a plastic material there would be instant failure of the component.

Comments ?

I was once part of an argument with some completely non-scientific friends, and they were constantly referring to "plastic" in the wrong way. (for me, we'd had a few drinks). So I got all superior on them, and declared, "you don't even know what plastic means!!".  So they said, "go on then tell us", and I declared, "plastic is the opposite of elastic !!"   They roared with laughter, and I suddenly realised how ridiculous it sounded. Technically orrect but still ridiculous. 

As far as the above question goes, I believe that plastic is called plastic, because it's acting as a plastic when it's heated, moulded and then cooled. It goes from liquid to plastic to elastic solid during the process. 

Of course the vast range of plastics means that some are much more elastic than others when cooled. Like the virtually unbreakable rulers that we used to have at school.  

[studiot]

13 hours ago, mistermack said:

I was once part of an argument with some completely non-scientific friends, and they were constantly referring to "plastic" in the wrong way. (for me, we'd had a few drinks). So I got all superior on them, and declared, "you don't even know what plastic means!!".  So they said, "go on then tell us", and I declared, "plastic is the opposite of elastic !!"   They roared with laughter, and I suddenly realised how ridiculous it sounded. Technically orrect but still ridiculous. 

As far as the above question goes, I believe that plastic is called plastic, because it's acting as a plastic when it's heated, moulded and then cooled. It goes from liquid to plastic to elastic solid during the process. 

Of course the vast range of plastics means that some are much more elastic than others when cooled. Like the virtually unbreakable rulers that we used to have at school.  

 

Thank you for your thoughts.

The general public use the noun  plastic to refer to materials which have the property of plasticity.
Plasticity is the correct scientific noun which refers to a well defined property, which may or may not be invoked to the application of heat.
 

Science uses the adjective plastic (as I did with my catchplate) to refer to nouns that have the specific property.

The property is that makes a material plastic is a mechanical property of they way it responds (mechanically) to stress, not a thermal property per se.

Plasticity is not the 'opposite' of elasticity, it is just one of many possible responses.

The principle responses being, elasticity, plasticity and brittleness.

Most materials exhibit all three at different stress levels and or stress time rates.

[dimreepr]

On 11/22/2021 at 11:42 AM, studiot said:

Comments ?

Define plastic.

Is it a material or an attitude? 

Edited November 30, 2021 by dimreepr

[mistermack]

18 minutes ago, dimreepr said:

Define plastic.

Is it a material or an attitude? 

It's a type of surgery. 

[dimreepr]

16 minutes ago, mistermack said:

It's a type of surgery. 

Dear Doctor, do I feel better?

[StringJunky]

I use 'plastic' in terms of ability to be permanently deformed, and 'elastic'  as the ability to reform to the original physical state.

Edited November 30, 2021 by StringJunky

[Peterkin]

Plasticity is the property that allows a material to be shaped and deformed by some outside agency. If the new form is temporary, and the material can be re-formed into some other shape, it retains its plasticity and is still plastic.  If the shape is retained permanently, it has lost its plasticity and become rigid or flexible or elastic. 

Elasticity is the property that allows a material to be stretched by some outside agency - can be extended in a single plane, and thus become thinner. But when the force stretching it is removed, it retracts to its original shape. When it has been stretched and stressed beyond the ability to retract, it has lost its elasticity and is no longer elastic.

I should think materials commonly referred-to as  plastics can be found at any given point in their respective life-cycles in any of their various states of plasticity and/or elasticity. Similarly, a dead rubber band or waist-band is still called an elastic - only it's a name, not a description.

Edited November 30, 2021 by Peterkin

[studiot]

2 hours ago, StringJunky said:

I use 'plastic' in terms of ability to be permanently deformed, and 'elastic'  as the ability to reform to the original physical state.

 

1 hour ago, Peterkin said:

Plasticity is the property that allows a material to be shaped and deformed by some outside agency. If the new form is temporary, and the material can be re-formed into some other shape, it retains its plasticity and is still plastic.  If the shape is retained permanently, it has lost its plasticity and become rigid or flexible or elastic. 

Elasticity is the property that allows a material to be stretched by some outside agency - can be extended in a single plane, and thus become thinner. But when the force stretching it is removed, it retracts to its original shape. When it has been stretched and stressed beyond the ability to retract, it has lost its elasticity and is no longer elastic.

I should think materials commonly referred-to as  plastics can be found at any given point in their respective life-cycles in any of their various states of plasticity and/or elasticity. Similarly, a dead rubber band or waist-band is still called an elastic - only it's a name, not a description.

 

Thank you both for staying on topic, a practice that seems unfashionable these days.  +1

 

Yes you have the essence of the original difference between the two, though there is a lot more to it these days.

[StringJunky]

6 minutes ago, studiot said:

 

 

Thank you both for staying on topic, a practice that seems unfashionable these days.  +1

 

Yes you have the essence of the original difference between the two, though there is a lot more to it these days.

Fire away.  

[studiot]

1 hour ago, StringJunky said:

Fire away.  

Not sure what you are looking for ?

[mistermack]

On 11/30/2021 at 4:54 PM, StringJunky said:

I use 'plastic' in terms of ability to be permanently deformed,

That IS plastic surgery !