FRP characteristics

[EmnaFati]

Hi everyone,
I'am a little confused,after a discussion with mu superior at work ,I 'am working on an FRP piping system , the vendor gave us these values:
- Young's modulus - axial : 13000 MPa
- Young's modulus - radial : 20000 MPa
- Poisson's ratio (principal): 0.4
- Poisson's ratio (secondary): 0.58
I konw that (please correct me if I am wrong ) Ea*Va/h = Eh*Vh/a ; Vh/a =Poisson's ratio of the strain in the axial direction resulting from a stress in the hoop direction and Va/h =Poisson's ratio of the strain in the hoop direction resulting from a stress in the axial direction. It's the principal poisson's ratio ( Va/h) which I need to use in CAESAR II input, which is equal to Eh/Ea*Vh/a BUT my superior told me that:
First : "Ea/Eh*Vh/a" this expression is not the same as the principal poisson's ratio
Second: "Ea/Eh*Vh/a" can't be 0.4, he said that it must be between 0.2 and 0.3 for FRP piping material
Third : Vh/a is always less than Va/h
I am pretty sure he is wrong since he didn't state any ressources but what he said raised some questions on my mind:
What are the usual min and max poisson's ratio values for FRP ?
Is there any relation between Vh/a Va/h like one should be less than the other ?

Thank you all in advance (I am a native English speaker so I may made some mistakes )

 

[LittleInch]

Each vendor has their own numbers as the wind angle and resin varies, but my understanding has always been that the simple hoop stress to axial stress issue is a ratio of around 0.6, i.e. when the pipe is pressurized the axial stress is high, which means that normally the system is always in tension, even up to quite a high differential temperature, once you put pressure inside it of a reasonable value.

FRP isn't like steel so the normal ratios and norms don't apply.

Last time we just gave it to the vendor to do the stress analysis as it was taking our normal steel based analysts too long to figure it all out and it also pushed responsibility onto the vendor.....

Come to think of it do you mean GRE or is this something like flexsteel?



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[zdas04]

You did not specify pipe size. Looking at a data sheet for Ameron Centron Series 2000 and Series 3000 and Series 4000 FRP (Series 5000 and 7000 have different values), they show primary Poisson's ratio for their small (1" and 1.5") and large (8-16") pipe at 21°C as 0.56, while the 2-6" is 0.26 (secondary ratios are 0.37 and 0.21 respectively). The Young's modulus numbers are similar to what you reported, but again they vary considerably from one pipe size to another (and are much different at elevated temperatures).

I've never seen anyone try to model FRP with something like Caesar II, because most failures in FRP are related to localized stresses that are far lower than the bulk stresses that Caesar II can analyze. If a rock falls on the pipe from the edge of the ditch it will bruise the pipe--the pipe will pass hydro and visual inspection, but over time (3-10 years is common) the damaged fibers will rub together and eventually leak. Caesar II cannot predict the incidence of rocks falling off the spoil pile. My experience with hundreds of miles of this stuff (all buried) is that traditional stress analysis is a significant waste of time--the failure modes are markedly non-traditional. On a pipe rack the results may be different.

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[LittleInch]

I've done it in Caesar II and they introduced a special module relatively recently to allow it to be analysed for things like bends, tees, valves and supports.

I do agree with zdas though - the failures I've seen were either abrasion due to the large deflections in buried pipe when pressure was applied then relaxed, then applied.... A small stone might take 10 years, but it will bore a hole in it like a drill bit.

construction and handling damage not spotted at the time but appeared months and years later was also the cause of many leaks.

It has its place, but it's not the easiest of materials to either analyse or work with.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.