Temperature Effect on Fracture Toughness of PMMA (Perspex)

[mikex24]

what is the temperature effect on fracture toughness on PMMA (Perspex)?. I have done in lab yesterday a fracture toughness test to measure the K1c value of this material at room temperature. The tutor tell us to find what will be the affect of doing the same test, but with different temperatures. Same test at 193.15 kelvin and the same test at 373.15 kelvin. I am thinking that on 193 kelvin the material will be very brittle and at 373.15 will be very ductile. So at the fisrt case the material will cracked very easy and at the second case the material will not cracked but maybe extend like a rubber. I need some more information about this to make clear in my mind the effect of different temperatures for this material(PMMA-Perspex).

 

[Studiot]

Remember Google is your friend,

http://www.springerlink.com/content/t785h65200758w65/

 

[mikex24]

thank you for the reply, unfortunately i can't open that file. i have to buy it. do you have the ability to download it? thanks

 

[Studiot]

We did a fracture toughness test on PMMA and the result of K1c was 1.6 MPa.sqrt (m). The question is to discuss, how the data would change if the test was conducted at -193.15 Klevin or +373.15 Kelvin?.

I think we should return this discussion to the thread for the benefit of others, and those who might also offer contributions.

I also wonder if your lab was about straddling the ductile - brittle transition. there is lots on google about this. The example picture shows nylon, not pmma but you might look around a bit.


http://www.google.co.uk/imgres?imgu...&sa=X&ei=RANfTbrDFoKp8AOKkrBa&ved=0CFIQ9QEwBw

 

[mikex24]

yes, the tutor told us that the word ''GLASS TRANSITION-Tg'' will help us to answer the question. but i am not familiar with these so any help from you will help me.

 

[Studiot]

I have asked others to look in as it's gone midnight here, meanwhile google

brittle - ductile transition (or the other way round)

It basically says that as a material gets colder there is a temperature below which fracture occurs by brittle failure and above which failure occurs by ductile failure.

If you plot the specific failure energy with temperature you get the characteristic S shaped curve, as shown in my link, with the transition temp at the steep near vertical part. The lower brittle energy corresponds to K₁C.

 

[mikex24]

... i get some idea. The tutor also asked from us to find the Tg temperature of this material. i have found it in a book that the Tg temp is 373.15. If someone can give me some idea of what the tutor would expect to see from me about the K1c and Tg temp. thank you

 

[Astronuc]

thank you for the reply, unfortunately i can't open that file. i have to buy it. do you have the ability to download it? thanks

One should be able to save the first page of that article cited by Studiot. It actually shows the K_IC value as a function of temperature.

The fracture toughness (and ductility) normally improves with increasing temperature. PMMA does over a narrow range ~360 to 380K. But it falls off after that.

PMMA also gets increased K_IC as a function of decreasing temperature below 333 K.

In general, metals show a decreasing K_IC with decreasing temp.
http://www.sv.vt.edu/classes/MSE2094_NoteBook/97ClassProj/exper/mcmurtry/www/matt.html

It would be interesting to see if one's own measurements are consistent.

Some universities have a subscription to Springer journals.

See if one can find - "Time-temperature dependent fracture toughness of PMMA." Journal of Materials Science 10 (8): 1381-1393.

 

[Rafa]

All polymers material have a Tg . This is the temperature where the thermal eneergy is sufficient to break the secundary bondig between polimer chain. If temperature is higher than Tg then the material can "fluid", in this case Kic almost hasn`t sense because the material is little "solid" . The fracture toughness can be applied to metalic materials and you can extrapolate (with luck) to other soid materials but a polymer at temperature higher than Tg is not a solid material