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Skid Loader Attachment Analysis

Hi everybody.

I am designing a rapid attach system for the bucket of a skid steer loader (see picture below), taking inspiration from the commercial systems.

In the second picture you can see how this system work: there a contact surface between the bucket and the tach.

So there is a contact zone and of sure I should do a non-linear quasi static analysis; however since I would not do a non linear analysis I ask you if there is another way to get a solution.

I've already done a non linear analysis but I can't validate the results since this kind of analysis should be quite instable. So I'd like to find another way (with linear analysis) just to compare the results.
Thanks in advance for your help

Best Regards

Stefano

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Altair Forum User

Hi Stefano,

What type of contact did you use for quasi static analysis and can you explain what do you mean by 'Quite unstable results'? Maybe this is because of unstable contacts or under-constrained model (just guessing)

With linear static analysis you can use freeze contacts or try with spring elements

Altair Forum User

Hi Prakash

At first thanks for your fast reply!

When I talk about instability I mean that this kind of analysis has to do some iteration (it isn't static). So if I change, for example, master and slave contacts it doesn't converge. Or if I change the value in discret (from default to s2s) it doesn't converge. So I don't have the full control of the analysis.

Then Prakash I attach two different results, obtained by modeling the entire lift group (see model.jpg):

1- The first attempt consists in contact with static friction coefficient and the results are shown in the second picture. Slave contact=tach; master=bucket; non-linear quasi static analysis.
2 - The second attempt consists in a linear analysis with freeze contacts. Same master and slave.

The results are completely different. In my opinion the contact model is closer to real situation than the freeze one. But at the same time I am not sure that results of non linear analysis are correct.

Thanks and regards.

Stefano

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Altair Forum User

Hi Stefano,

This is expected as having freeze is similar to having rigids.

When using contacts there are set of rules. Choose the slave entities:

considerably smaller than their counter part.

· strongly curved compared to the other part of the contact pair.

· not as stiff as the other part, especially if the other part is even rigid.

· that have a considerably finer mesh than their counter part.

DISCRET = N2S is recommended if the slave entity is a set of grids (nodes) or a set of solid elements.

Altair Forum User

Hi Prakash

Very well...So I could modify my model to obtain more accurate results, by following your suggestion, in non linear analysis.

But what about linear? You talked about spings elements..could they solve the problem?

Altair Forum User

Stefano,

Springs are again linear in nature and could not give right results. I would suggest you to modify your non linear anlaysis set up

Altair Forum User

Ok Prakash

I will modify my non linear analysis...to validate the model I could do another analysis in which I could remove the bucket (so there are no more contact zones) and I could apply the load directly on the surfaces representing the contact area....What do you think about it?

Altair Forum User

Stefano,

It may not be a practical approach but you can give it a try.

Altair Forum User

Ok Prakash....but I'd like to be sure about results obtained by non linear analysis....anyway I will attach new results as soon as it will be ready!!!

Altair Forum User

Hi Prakash... I will send you by transfer link my last model...I used two different types of contact:

1 - freeze for the upper side of tach and bucket

2 - slide for the rest contacts (when you will see the model everything will be clearer).

The analysis doesn't seem to converge.

If you can please check the model...

Thanks and regards.

Altair Forum User

Stefano,

Thank you, I will have a look at it and I will share my feedback with you soon.