Comparison of Kinetic energy and Strain energy 2

[fruton]

Through conducting a a dynamic implicit analysis using FE I am trying to make an assessment if inertial effects in my model can be ignored. If I were to compare the kinetic energy and strain energy under impact and check that there they are both negligible would this be a good enough indication that I can ignore inertial effects in my model?

Thanks

 

[drawoh]

fruton,

I was under the impression that at the start of impact, there was kinetic energy, and at the end of the impact, it was all strain energy. I would think that kinetic energy would be irrelevant to your analysis. You should be able to read strain and deformation directly from your model, and compare this with your strain energy.

JHG

 

[rb1957]

KE is relevent to an impact problem, though it's hard to see how it can be insignificant ... maybe it is so small that you're saying "clearly, there is no impact".

if your FEA shows negligible stresses in the structure, then you can easily say (depending on the validity of your analysis) that th eimpact has an insignificant affect on the structure.

 

[fruton]

Thank-you very much for your responses.

Drawoh, wouldn't KE become important if it has affect on the impact as rb1957 is suggesting? And what would comparing strain to strain energy show?

rb1957, there is defintely impact in my problem and the stresses are not negligible.

Thanks again.

 

[drawoh]

fruton,

Your kinetic energy is converted into strain energy, hopefully, elastic.

If you know where the impact takes place, you should be able to apply a force there in your model, and read off the resulting deflection.

Strain Energy U = 1/2 F[δ]

JHG

 

[fruton]

Thanks drawoh,

I noticed that strain energy formula is based on tension/compression

http://www.roymech.co.uk/Useful_Tables/Beams/Strain_Energy.html

Not sure if it will apply to my ball in socket type problem?

 

[TERIO]

Strain energy is not only applicable for tension/compression. For an elastic material and a general state of stress/strain the strain energy density (strain energy per unit volume)


1/2[σ]_ij[ε]_ij=1/2([σ]_xx[ε]_xx+[σ]_yy[ε]_yy+[σ]_zz[ε]_zz+2[σ]_xy[ε]_xy+2[σ]_xz[ε]_xz+2[σ]_yz[ε]_yz)

Note: the factor of 2 on the shear strains goes away if you are using engineering shear strain [γ]_ij=2[ε]_ij