I get a different behavior when I select different numbers of loading steps

Hi


I am doing a simple compression test simulation of a mortar cube. It has been defined using solid65 element and as far as I know everything in this aspect works fine. However, I have noticed some peculiarities. The load imposed is a negative vertical displacement, if I only use one loading step, I get a non linear behavior of the element. However, if I utilize more loading steps but the final value is the same as the case before, I get a completely different behavior, In some cases it even remains in the linear range. As I am doing a static structural modelling I understand that each load step is applied statically, so there should not be any concerns regarding a loading speed or rate. I would like to ask your opinion about this, maybe there is something I am misunderstanding regarding loading steps.


Thank you very much for your help.

Answers

  • danielshawdanielshaw Forum Coordinator

    Do you have the load step applied or ramped applied? If the load is step applied in a non-linear solution, the results may be different than if the load is ramped applied. Also, do you have automatic time stepping active? 

  • KaiKai Forum Coordinator

    Hi @19yuuki91 , can you explain what you mean by linear range and nonlinear range? Did you turn on large deflection under analysis settings? Do you have any screenshots to show the results discrepancies?

  • Do you have the load step applied or ramped applied? If the load is step applied in a non-linear solution, the results may be different than if the load is ramped applied. Also, do you have automatic time stepping active?

    Hi @danielshaw, thanks for your answer and I apologize for the lack of specificity in my question. Automatic time stepping in on. The next screenshots show the load being applied in one step and in 100 steps, both reaching the same maximum value. In both cases the load (displacement) was applied using tabular data, if the displacement is applied as constant, which then makes it appear as ramped then there is no solution convergence.


    I did a comparison of both behaviors (the results of 1 step vs 100 steps) and as you can see there is a slight difference towards the end. Additionally, they both have different values of max strain. Do you think it has to do with the "length" of the load step that is causing this difference? As I have discovered with your inquire is that indeed I do not understand the difference when a load is applied using tabular data or ramped. Thank you very much for your help and I apologize if my problem ends un being trivial.


    Best regards

  • 19yuuki9119yuuki91 Member
    edited September 24

    Hi @19yuuki91 , can you explain what you mean by linear range and nonlinear range? Did you turn on large deflection under analysis settings? Do you have any screenshots to show the results discrepancies?

    Hi @Kai, thanks for your answer. My model does not have large deflections on. I apologize for not being specific enough, with @danielshaw 's comment, I realized that there is a difference when the displacement is applied as ramped or in tabular data. For more details please look at my comment replying to @danielshaw.


    Best regards

  • KaiKai Forum Coordinator

    Hi @19yuuki91 , I recommend that you turn on large deflection in order to get more accurate results. The results look suspicious, for example, I don't understand why the orange line (100 steps) is a polyline towards the end. Instead, strain should always increase.

  • Hi @Kai, thanks again for taking your time and providing an answer. I turned large deflections on and it still presents that weird behavior where the curve goes back and forth. That makes me think that I might have an error in another part of my model. I will check other aspects of it and comeback with my findings, if I am able to detect any error. Thank you

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