Failure criteria for Composite beams. 1

[sharpedge]

Hello, 'm abit new to this forum and I would be glad if some one would answer my question.

I am doing some elastic stress analysis on composite beams, and I am new at this, I am not so sure of which failure criteria is best to apply. Personally I feel that Rankine and St. Venant(Maximum principal stress and strains)is out of the way.But then 'm not too sure which of the other three ( Tresea, Hencky and Von misses, and Beltrami& Haigh) is best for complex elstic failure analysis.

 

[dik]

There are deflection issues, flexural strength issues, shear failure of any composite action connectors, failure of the decking/concrete component of the composite member, steel stresses being a composite of the shored/unshored construction, Working Stress/Limit States design, etc.

Dik

 

[Qshake]

Dik - I beleive this question deals with composite material and not concrete on steel with shear (nelson) studs.

There are a number of failure criteria for composite sections and one of the most common is the Tsai-Hill formulation which is probably most like the Von Mises criterion.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[dik]

Thanks, Qshake...

Dik

 

[brep]

I'm not sure there is a a simple answer to this - certainly from industry experience I have found that failure criteria such as Tsai-Hill, Tsai-Wu etc are used by some, and absolutely NOT used by others.

The most common in my experience is Maxiumum Strain. It is the opinion of many in aerospace that this is all you need...

 

[GBor]

I would agree with brep, but to use it, you have to know the strain characteristics of your material. This is true no matter which theory you use, but generally, I believe strain-related criteria are considered more reliable. I don't believe there is any one "perfect" criteria that will accurately predict all potential failure modes...be careful.

 

[sharpedge]

Thanks for all your response. My opinion has always viewed failure due to bending is better predicted using strain related criteria. However since in composite, one is likely going to get elastic coupling of some sort, 'm not too sure which failure criteria will accurately predict the failure mode.
Any comments would be appreciated.

 

[SWComposites]

What type of composite material are you using? What shape beam? How is it loaded? What is the application?

 

[sharpedge]

Thank you all for your comtribution,
SWComposites (Aerospace),...I am using Glass fibre Reinfroced Plastci (GFRP) and I am looking at two beam shapes specifically.
1.Box beam 2. I-shaped Beam.
I am particularly investigating their Elastic coupling and not so sure what failure critieria to use to examine the beam when it fails due to the bending-twist or strech-twist coupling.
Thanks,