Hello everybody,
I am working on Transient dynamic analysis of a simple Single Lap Shear (SLS-like) specimen in Ansys (please find the image attached). The model has a crack as shown. In transient analysis, I use a non-linear contact between the crack faces. Boundary conditions are
1. I fix a part of the bottom plate
2. Global acceleration of 1g (m/s*s) is applied in 'y' direction on all bodies at a single frequency of 180 Hz (non-eigen frequency) as below
Load = 9.81*sin(2*3.14159*180*time) (pi in radian)
3. I extract the displacement (Uy) and normal stress (Sy) at an edge point (P) on the specimen. Materials are linear elastic isotropic.
Frequency of displacement response is exactly 180 Hz (same as input freq), but the frequency of stress response is 360 Hz (exactly double the input freq). The same is also evident from a Fourier plot of both the responses. This is perplexing me.
The problem is also reproducible for different frequencies. I am not able to understand why and how this can happen??
It would be really helpful if somebody could help me understand it.
Thank you in advance for your time.
Have nice day.!
Regards,
Shree
Dear Dr. Gravenkamp,
Thank you for the answer.
- "From your graph, I wonder whether the chosen time step is small enough to capture such high frequencies" --- Do you say that because, the displacement and stress curves are not smooth and do not look like perfect sinusoids?? If that is the case, I would like to inform you that, increasing the number of sub-steps (reducing time step) did not change the response qualitatively. Still same behaviour is seen for both stress and displacement
- "I would first make sure that the displacement results are converged with respect to both the spatial discretization and the time step" --- I do not completely understand that. :( :(
Thank you again for your time.
Shree
Dear Mr. Méndez-Esteban ,
I understand your point. But my material model is linear elastic isotropic. I do not see how tension-compression asymmetry can occur. I understand that Ansys identifies more frequency because of the shorter peaks. Wondering why it happens only for stress plot and not displacement (perhaps because load is acceleration and so displacement is not affected) ?? Bit confusing.. :(
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