Material properties missing?
Material properties missing?
(OP)
Hi all,
This is a first time in a few years (since about 2nd year uni!) I have to look at materials properties in detail. I have been doing a bunch of research into a few Polypropylene (20% GF and MF) and Nylon 6 (30% GF)materials for a particular application. What I have been finding though is that most of the data sheets available on the web (from MatWeb, IDES, and even the supplier websites themselves), seem to have data missing.
For example yield stress, poissons ratio or tensile strength will be commonly missing.
I am wondering how yield stress can be left out unless the material doesn't have a defined yield point in its stress-strain curve? And if the material doesn't have a defined yield stress how do you approximate it for the purposes of simple FEA or hand calcs? or should I just use the UTS given?
Also if poissons ratio is not given should I just use the 0.3 to 0.5 range and compare results? Or is there somewhere that standard poissons ratios are defined that I should be using?
Thanks in advance!
James
This is a first time in a few years (since about 2nd year uni!) I have to look at materials properties in detail. I have been doing a bunch of research into a few Polypropylene (20% GF and MF) and Nylon 6 (30% GF)materials for a particular application. What I have been finding though is that most of the data sheets available on the web (from MatWeb, IDES, and even the supplier websites themselves), seem to have data missing.
For example yield stress, poissons ratio or tensile strength will be commonly missing.
I am wondering how yield stress can be left out unless the material doesn't have a defined yield point in its stress-strain curve? And if the material doesn't have a defined yield stress how do you approximate it for the purposes of simple FEA or hand calcs? or should I just use the UTS given?
Also if poissons ratio is not given should I just use the 0.3 to 0.5 range and compare results? Or is there somewhere that standard poissons ratios are defined that I should be using?
Thanks in advance!
James





RE: Material properties missing?
Usually flexure properties are of more importance in plastics. If they are loaded in tension they will creep, even at low loads.
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: Material properties missing?
That said you can use 0.35 for Poisson's Ratio which is typical of most materials though the range is what you stated of 0.3 - 0.5. You will find that varying the ratio will not greatly affect your results.
Yield stress and tensile are another matter. This will vary more material to material and plays a more important role in your analysis. I would suggest two approaches. First, if you have a specific material and vendor in mind call or email their Tech Support and request the info. The larger suppliers usually have this information (esp. tensile) in some analysis for their top customers but don't/didn't publish it because (a)the values didn't compare well against competition (b)the datasheet was done as a preliminary datasheet before all testing was completed and never updated or (c) the time and money to perform testing isn't valued enough by the supplier. The second approach is to find a similar grade that has the necessary data and use that. The accuracy here is less but if you are doing preliminary analysis this will put you in the ballpark.
RE: Material properties missing?
thanks for the responses.
EdStainless - the application I am working on is a temporary support for the building industry and is a metal part replacement. Its predominant loads are in tension - so for my particular case this is more important than flexure. I am curious though why is flexure generally more important for plastics? - Do you mean simply that most applications for plastics involve bending usually?
Also to help with creep (and strength in general) we have been looking at glass filled reinforcing of 20-30% - does this sound reasonable?
Plastx - ok so for data sheets manufactuers mightn't list Yield stress because the application it was intended for might have only been concerned with UTS for example. or it cost too much ;). Have tried both approaches so far with a sizeable vendor still not coming up with any more numbers (even given a 200 tonne/year volume estimation!) - hence have been looking for close enough grades - although I have seen some fairly different numbers for seemingly similar grades.
Thanks again
James
RE: Material properties missing?
Mike
RE: Material properties missing?
When you injection mold reinforced plastics you get some directionality of properties. this is a function of how much reinforcement, fiber length, and molding practice.
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: Material properties missing?
Ed - thanks for the clarification.
Cheers
James
RE: Material properties missing?
http://www.vydyne.com/pages/product_info.asp
RE: Material properties missing?
Cheers
James