I am currently conducting research on the buckling of thin plates and simulating a range of materials in abaqus. It seems according to my results that Aluminium gives a higher buckling load compared to CFRP. Can someone let me know if this is correct.Thank you.
Hi,
I don't think there is a yes or no answer to your question as formulated.
The buckling load depends on the material's elastic constants and geometry. Supposing you refer to identical plate length, width and thickness for both materials, as well as identical boundary conditions, only the elastic constants are relevant.
For aluminium, only one modulus and the Poisson's ratio are required since the material is isotropic. On the other hand, the CFRP material is most likely anisotropic and possibly all elastic constants are relevant. However, these elastic constants will depend on the composite laminate stacking sequence (position, thickness and orientation of its plies) as well as on what type of resin and fibres are used and the fibre volume ratio.
It is thus possible that, due for example to the very weak transverse stiffness of a unidirectional composite plate, it could buckle at a lower load under some circumstances. However, in other circumstances and for other laminates, the opposite could be found.
Note, however, that a quasi-isotropic CFRP laminate is casually referred to as 'black aluminium' as its effective elastic constants are close to those of aluminium. One would thus expect that such a laminate would buckle at a similar load to an aluminium plate (all other things being equal).
Hope this helps.
Laurent
Akshay,
Further to Laurent's comments, if we assume that both the CFRP and Aluminium structures have same lengths and boundary conditions then the over riding factor that will determine the comparative bucking performance of the two materials will be their flexural stiffness (noting that CFRP is tuneable).
The approximate flexural stiffness is proportional to (E x Thickness cubed)
As CFRP often has a higher stiffness and a significantly lower density (I.e Larger T), then from a specific weight perspective I would expect that a CFRP structure would be significantly better at resisting buckling.
Refer a paper of interest?
Regards,
David
Thank you both for the feedback.
my project involves the buckling of thin plates as well as stiffened plates. its a simply supported on all sides square with dimensions in metres of 0.4*0.4*0.01.
i have conducted my research for Aluminium and steel for both. i now want to start the analysis on abaqus for CFRP. it seems that the CFRP gives much lower buckling load for the thin plate compared to the Aluminium. i simuluated both (0/90)s and (90/0)s where the latter gave the better buckling load. Can you propose a better orientation that i could use please.
Hi,
First, you can find analytical solutions for many cases (assumoing symetric laminates) in books like Kollar and Springer Mechanics of Composite Structures (Cambridge University Press).
Basically, you want to have the highest value of the D matrix (bending stiffness matrix). For a laminate of N plies and where K is the ply index and [Qbar] is the reduced and transformed lamina stiffness matrix:
[Dij] = 1/3 Sum_K=1:N ( [Qbar_ij]_K (z_K3 - z_(k-1)3) )
However, each of these terms are not independent and their effect will be greater or lesser depending on the loading conditions so it is not so simple to tell what laminate is best for any situation.
Based on a quick check of the analytic solutions, there should not be a significant difference between [0/90]s and [90/0]s. However, a quasi isotropic [0/90/+-45]s would yield about 50% higher buckling load than your cross-ply laminates and a [+/-45]s would be twice as strong as the cross-ply.
Best regards,
Laurent
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