Learning Forum

[mdmech.mech]

Hello all,

I have watched the video lecture in Random vibration using ANSYS, 

Video Lecture: 

/courses/index.php/courses/random-vibration-analysis/lessons/how-to-correctly-interpret-psd-results-lesson-3/

In that lecture at 13:41 minutes, the lecturer shows that the equivalent stress plot in GUI is 94.454 MPa and for 3 - sigma it is 283.35 MPa, Here I have doubts. Supposing I have a material yield strength of 250 MPa, can we say that the table will fail because it exceeds the yield strength of the material?

Otherwise, I should see the RMS stress graph values in the (detail window) response PSD graph after extracting them at the particular location.

(An example is shown in the video itself for displacement in X at 14:35 minutes. ) Likewise Should I see the equivalent stress value, compare it to yield strength, and decide whether the design is safe or not?

Thanks

[Ashish Khemka]

Hi,

Yes, if the design doesnot allow the stress to exceed yield then you can consider it failed. But, one should look for the spread of the stress - is the spread local or say through section yielding. 

 

Regards,

Ashish Khemka

[mdmech.mech]

Thanks for the reply, sir. Hence, I should not take RMS values; I have to look for 3-Sigma stress that is 283.35 MPa. Please Confirm

[Ashish Khemka]

No, please use the RMS value. The 3-sigma rules of multiplying the RMS value by 3 gives us a conservative estimate on the upper bound of the equivalent stress.

Regards,

Ashish Khemka

[mdmech.mech]

Sir, When I take RMS value showing in detail window, it is very less, So my design should pass with respect to yield strength, isn't it, please clarify me, I could not able to understand 

[Ashish Khemka]

Hi,

Can you please share the two plots?

Regards,

Ashish Khemka