Modal analysis on nonlinear material
Modal analysis on nonlinear material
(OP)
I have a certain amount of experience doing modal analyses and other vibrational analyses on metal structures using NX NASTRAN. However, my company is evaluating a proposal to do modal analyses on some composite parts.
Their material is highly nonlinear, basically plastic. Can anybody enlighten me about the sorts of issues this might cause ?
It seems to me that the material's vibrational modes would also be nonlinear, and would depend on amplitude as well as frequency. Am I wrong ?
Their material is highly nonlinear, basically plastic. Can anybody enlighten me about the sorts of issues this might cause ?
It seems to me that the material's vibrational modes would also be nonlinear, and would depend on amplitude as well as frequency. Am I wrong ?





RE: Modal analysis on nonlinear material
If you are interested in the dynamic response of this type of structure I think you will have to do a nonlinear dynamic analysis using direct integration methods to obtain meaningful results......
Ed.R.
RE: Modal analysis on nonlinear material
RE: Modal analysis on nonlinear material
RE: Modal analysis on nonlinear material
I mention this only to point out that a modal analysis can still have something to offer about the behavior of this struture when subjected to these lower force levels. It's limited, but it can still be useful.
RE: Modal analysis on nonlinear material
If you are trying to predict frequencies to avoid then this approach is perfectly acceptable.
If you get into a scenario where there is some resonance, however small, then watch out. Even if the resonance is small to begin with because the damping is good, the material will begin to heat up. When the material heats up, the material will soften and it's modulus and natural frequency will drop.
If you are lucky the softening will take its frequency away from the driving frequency and it will calm down and cool down. If you are unlucky and the reduction in modulus takes it nearer the driving frequency then it will vibrate more, heat up more, soften more and actively hunt down the driving frequency. Soon after it will dissintegrate from either excessive strains or thermal degradation.
gwolf
RE: Modal analysis on nonlinear material
My problem is further complicated by the fact that some of these panels are lying on a rigid floor, and are being deflected out of plane. Even to do a static analysis, I'd have to do it nonlinear with contact surfaces, etc.
It looks like a plain old Eigenvalue analysis is out the window.
RE: Modal analysis on nonlinear material