Re: do you agree with it???

William Lu wrote:
> Dear ALL, 
> Yesterday, my manager told me that I had used a wrong
> material to conducted my structural analysis
> of a rotating turbine blade (including airfoil,and the disk 
> supporting it). He said, however, the predicted stress value based on
> the wrong material should be the same as what we can see using the
> right material. Only frequencies and modal shapes need to be 
> re-calculated.
> It surprised me a lot!!! Can you guys agree with my manager's 
> words? If so, pls. detail the resons. He may have some hints on the
> wrong material and right material that we should use, for example,
> even they are different material, but they have very close 
> Densities, and Youngs modules, my point is, ideally, the stress will
> absolutely depend on the material, right? can you imagine that a 
> rotating steel turbine and a rotating wooden turbine have
> exactly the same stress? It is so strange!
>
> This could be a very funny problem, forgive  me if you think so.
> thanks,

The material's modulus won't matter if the structure is determinate.
But if the structure is indeterminate with different materials, then
the modulii will matter in determining the load paths.

An individual turbine blade is determinate.