FRP plate thermal expansion

[JeremyBraggPE]

I am looking for pracitical guides to analyzing an frp plate, otherwise knows as sheet molding compound. In this case the plate is partially fixed and temperature change is causing some out of plane distortion. Does anybody know of any resources that are not completely theoretical? I can likely obtain any material data I need such as coefficient of thermal expansion. Thanks in advance!!

 

[RPstress]

Thermal behaviour can be predicted by classical laminate theory. The Laminator (

http://www.thelaminator.net/)

is my usual recommendation for a cheap ($29) way to do this. For a plate with an even, well defined distribution of fiber this should be reasonably reliable.

SMC will likely be largely quasi-isotropic using fairly short fibers. If you cannot measure basic mechanical properties you can estimate them using methods detailed at

http://home.comcast.net/~brandihampson/cd/index.html

and

http://www.mse.mtu.edu/~drjohn/my4150/.

Unsure what you mean by resources that are not completely theoretical.

For a plate with somewhat complicated constraints, you probably need to use some simple linear structural-thermal finite element analysis using orthotropic plate elements.

 

[JeremyBraggPE]

Thanks for the response! I will check out these links.

By "not completely theoretical" I am referring to a couple of articles I purchased from the Journal of Thermal Stresses. Theory were bogged down with theory and integrations to the point where I got very little practical information in terms of how to solve my problem.

I am working on a FEA, but am struggling somewhat in setting my boundary conditions. Essentially I have a plate that is fixed to the ground by anchors and the plate is thicker around the perimeter which is providing a lot of stiffness. It is challenging, but I am getting there.

 

[allcomposites]

Out of plane deformations are related to material properties and thermal cycle. To analyze geometrical distortions on SMC you need to know resin shrinkage, glass transition temperature and CTE. Also, you must record the temperature evolution at upper and lower mould platens (and from center to periphery). This is key since in-plane heat flux is usually dominant for high speed manufacturing as SMC.

You can use any FE software dedicated to composites. However note that part-mould contact has to be modeled to properly predict warp-in (if you clamp the part it will change the ratio of internal stresses versus part deformation). There are few FEA packages dedicated to this problem (COMPRO, LUSAS, etc).

 

[RPstress]

allcomposites has addressed deformation during manufacture. Such process modelling is very difficult. The usual method is experience + trial and error...

If your problem is for service rather than manufacture then it should be approachable using traditional structural design methods. I would recommend careful use of linear FE with the appropriate othotropic materials (a geometric non-linear check would probably be worth doing). Establishing the thermal properties with confidence is tricky. Even if you can measure them it's hard to get carbon composite values accurately, and hard to be sure that what you measure is appropriate to all of your part.

 

[JeremyBraggPE]

Thanks you both for this great input.

I feel that there is a relationship of the slenderness ratio of the cross section to what is occuring. That the ratio is so high the compressive strength has dropped off considerably.