Hello,
I have been making a FEA static analysis of composite vehicle. The structure is sandwich. I have found the safety factor for carbon faceplates, it equals 2 (for working conditions which are static and short- lasting). But I cant find safety factor for foam core (in particular it is PVC). Do you know it? And if so, could you tell the reference for that (this analysis is for engineering degree thesis)?
Thank you for helping me.
If no one can provide a good reference I would find a component made with PVC foam core and estimate how thick it is, and then simulate this to ‘reverse engineer’ the safety factor. You can then make a sanity check … If you are making a car chassis and it says 5mm thickness, this is too thin, if it says 50mm, this is too thick. If you justify your decisions you should gain lots of marks for this, as it shows you are looking at the right factors.
Oh, another thought… If you simulate with factor 1.0 and factor 10, and it makes little difference, if you justify picking a figure in the middle this should also earn marks.
I know of some safety factors used in the marine industry for balsa and PVC foam cores, specifically from the ABS “Rules for Building and Classing High-Speed Craft” Part 3 (free for download at: http://ww2.eagle.org/en/rules-and-resources/rules-and-guides.html). Table 7 on Page 86 provides inverted safety factors based on minimum core shear strength. Basically, for cross-linked PVC the safety factor is 2.5, but can be reduced to 1.8 if shear elongation exceeds 40%.
Nice info, those numbers and this thread will be logged by the ol’ grey matter for future reference!
To: Jonty
I’m not sure what you are talking about because safety factors are estimated after experimental research. In order to know a correct value I should make first a car with a e.g. value of four (for safety factor of foam). Then if nothing bad happens with car I can decrease it to three. If nothing bad happens I can reduce it to 2.5 and so on…
I don’t understand how it is possible to obtain that figure with simulator. If I key in SF value of 1 and change it to value of X, then failure criterion for foam will decrease approx. X times (I mean it that failure criterion as a reserve factor). So the ratio of failure criteria will always be moreless constant.
Anyway, Thank you!
My suggestion is that if you know the max rated loading of a component, and from the thicknesses of skins and core you calculate the strength then you can derive a SF from this; If the strength is 2x greater than failure loading, then that says 2x SF.
Anyway, it was a work-around suggestion, which is invalid since tgundberg provided a nice source!