Conservatism in/Limitations of Shock Response Spectrum Analysis 1

[SpaceEngineer4]

Good morning lads. I've noticed that oftentimes some of the senior engineers I've worked with indicate that shock analyses are inherently conservative versus reality. I understand that using modal combination, like SRSS, is conservative generally because it assumes that all modes in are phase. However, other shock analysis approaches like CQC and ROSE account for modal coupling to improve the predictions agreement with reality. My question is regarding how your companies deal with shock analyses. It seems like we're perpetually showing negative margins to the shock analyses and inevitably end up testing the hardware to satisfy customer requirements on most programs. The sticking point is no one ever believes the analysis, and the test is always an "I told you so" and it goes off without a hitch.... what has everyone's experience been with shock testing and analysis? Are there practical recommendations to bring the analysis more in line with reality?

Cheers,
SE4

 

[SWComposites]

FEMs of assemblies are almost always too stiff - no joint flexibility, no damping, no boundary condition flexibility, etc.

To improve your analysis, you should be correlating existing models to existing test data.

 

[Sparweb]

...no slip, no sealant, no gasket...