Amplitude Definition DIfficulty

[mechdrive1]

Hello,

I am facing difficulty with respect to amplitude definition. My model consists of four steps with different step times in which load and angular velocity are applied and they vary in each step respectively. The load is applied in the form of pressure. My problem in the model is that the load will induce continuous displacement of the object on which it is applied in experiments, but I am not able to observe the same thing in the numerical model instead I am observing that the load is applied at the beginning of the step which causes a certain amount of displacement in the object and then the object remains in the same position for remaining part of the step. I was initially defining the load without any amplitude definition but then I used the tabular type amplitude definition which is as follows:
0.0001, 1., 0.0005, 1., 0.001, 1., 0.005, 1., 0.01, 1., 0.05, 1., 0.1, 1., 0.2, 1.

This amplitude is only for the first step which is of 0.2 s. The next three steps are of 0.12s, 0.18s, and 0.2s respectively. The load in the first step is 5kN then it changes to 4kN, 5kN, 6kN in the next three steps respectively. The load is to remain constant during individual steps and is applied right at the beginning. I have started with 1e-4 because the time increment starts with 1.8e-4.

I have gone through the ABAQUS documentation, specifically the amplitude section in Analysis User's guide but my questions still remain unanswered.

Is my amplitude definition wrong? How do I ensure that my load causes a continuous displacement of the object? Should I be using some other amplitude type or use absolute data in the amplitude definition?

Thanks in advance!
Ankit

 

[Mustaine3]

Your load is constant. In a static analysis this means, that Abaqus will calculate the reaction to the load when it is applied, so at the beginning. Afterwards the load does not change and so does the reaction.

Maybe you should increase the load with a linear curve.

 

[mechdrive1]

Mustaine3,

Thank you for the suggestion. Can you please elaborate more on how I can increase the load with a linear curve? Do you mean I should be increasing linearly from some non-zero value to my final value of 5kN throughout the step?

Regards,
Ankit

 

[Mustaine3]

Defining amplitudes is very simple and explained in the manual, so I will not explain it. See Abaqus Users Manual 34.1.2 Amplitude curves

Btw. the linear amplitude (Ramp) is the default in static analysis. So maybe you don't have to define it yourself.

 

[mechdrive1]

I resolved the issue of gradual application of load. As has been mentioned in other similar posts, you just have to give the first and last data points and then abaqus automatically linearly interpolates between them. However, specifying a few additional data points seems to have worked too but not for a high number of data points (>6).