Thermal Stress

[TomCJ]

I'm currently working on a problem which involves looking at the stress involved on the material during the heating phase,

the Scenario is If I have two heaters, one heater producing a greater output than the other (i.e heater 1 = 50watts, heater 2 = 100 watts), although they both provide the same total energy in the end to raise the objects temperature by a set amount, Heater 2 will just heat the object up X times faster than heater 1. this part I understand

The part that confuses me is this;

If I work out the total stress for example is 100 pascals, how can I put that in terms of Heater 1 and heater 2 stress, As we know the faster you heat an object up the greater the stress on the object? compared to when an object is heated slowly

Is it fair to say if heater 1 takes 10 seconds to heat the object up you can divide the total stress by the heating time so
100/10 = 10

and if heater 2 takes 5 seconds to heat the object up you can do the same thing?
100/5 = 20


This would result in heater 2 producing twice the stress on the object compared to heater 1?

To Summarise Im asking how can I link stress to heating time?

Thanks in advance for any help

 

[TomCJ]

secondly if this is true would it also be correct in staying as long as this average was below the objects breaking stress it would not fail even though the total stress may give a number larger than the breaking stress for the material?

 

[MintJulep]

No.

 

[IRstuff]

Is this for school?

What is this stress arising from? When you understand that, then you'll know how to answer your question.

TTFN
faq731-376

 

[TomCJ]

The stress would be arising from the change in temperature across the piece of material,

So firstly I would need to find out if there is a temperature difference between the heated side of the material and the non heated side of the material?

If there was no temperature difference and the materials temperature rose uniformly then there would be no stress?

If there was a temperature difference then there would be a stress with in the material?

thanks for the pointer so far IRstuff hopefully my answer here is what you were suggesting

 

[IRstuff]

The other thing to consider is the Biot number of the material. Is the material so thermally conductive that the transferred heat is immediately distributed throughout the material? In which case, there is minimal stress.

TTFN
faq731-376

 

[TomCJ]

After reading my first question I feel slightly embarrassed as to what I asked and understand completely why, what I said was incorrect, After looking at what I had calculated I had actually found my answer but didn't realise until I went through my results a third time