Advice on Constraints / Tipps von Constraints

Alle Fragen zu: Vernetzung, Materialien, Lasten, Randbedingungen und Elementparameter /
All questions to: meshing, materials, boundary conditions and element properties

Moderatoren: ccad, mz15, auroraIco, Lehrstuhl

Antworten
whpthomas
Newbie
Beiträge: 3
Registriert: Mo 11. Mai 2015, 03:52

Advice on Constraints / Tipps von Constraints

Beitrag von whpthomas »

Advice on Constraints

I have a part that I need to test. The part is fixed at two locations that are constrained in the X and Z planes, but should be free to move in the Y direction and rotate around axis X. A third location has a -7400N force applied in the Z direction without any other constraint. The material is 6061 T6 aluminium.

At the moment I am just using X,Y,Z constraints on one location and an X,Z constraint on the other. However this appears to prevent the object from rotating freely around X at the first location. Is there any way to implement this?

Tipps von Constraints

Ich habe einen Teil , die ich brauche , um zu testen . Das Teil wird an zwei Stellen , die in der X- und Z-Ebene beschränkt sind festgelegt, sondern sollte sich frei in der Y-Richtung bewegen und drehen sich um die Achse X. Eine dritte Lage hat ein in der Z-Richtung angewandt -7400N Kraft keine andere Beschränkung . Das Material ist 6061 T6 Aluminium.

Im Moment bin ich nur mit X , Y, Z Einschränkungen für einen Standort und ein X, Z -Einschränkung auf der anderen. Aber dies scheint das Objekt frei dreht um X an der ersten Stelle zu verhindern. Gibt es eine Möglichkeit , dies zu implementieren?
201505131_190518-CapturFiles-small.jpg
FEA with two constraint locations and one force location
(142.84 KiB) 343-mal heruntergeladen
ChriDin
Alumni
Beiträge: 25
Registriert: Di 29. Apr 2014, 14:52

Re: Advice on Constraints / Tipps von Constraints

Beitrag von ChriDin »

Dear whpthomas,

unfortunately you have to fix all directions at one point, just as you did, in order to solve your calculation. Actually we do not know enough about this component to give good advice on your problem. Maybe you can explain the part a little bit more precisely. What´s its real behavior? What function is it supposed to carry out?

If you want, you can also upload your project folder with an explanation and we think about the constraints.

Kind regards,

Christian
whpthomas
Newbie
Beiträge: 3
Registriert: Mo 11. Mai 2015, 03:52

Re: Advice on Constraints / Tipps von Constraints

Beitrag von whpthomas »

This part is a component in a running training bicycle http://run4.com.

The part is a stirrup that connects the crank arm to the pedal. It is currently hammer forged in 6061-T6 and we are looking at having it squeeze cast (liquid metal forged) in A356.2-T6. The force applied is 2.8g x 130kg x 2 margin of safety. The load force changes direction throughout the operating cycle so I have performed several FEA tests with the matching loads for these different angles. So far the part passes FEA, but essentially its like its been bolted tight at the fixed point and only free to move at the other points. So what I have done is perform separate tests and switch the fixed location between each of the three locations to see which causes the most load.
whpthomas
Newbie
Beiträge: 3
Registriert: Mo 11. Mai 2015, 03:52

Re: Advice on Constraints / Tipps von Constraints

Beitrag von whpthomas »

Actually, I think I came up with a workable solution. The two top locations were constrained on the X and Z planes and the bottom (pedal) location constrained in Y plane with the force applied to -Z. This allows the top bearings to flex relative to the pedal force at the bottom. I think the thing I didn't realise is that you need a few sets of nodes at each location so you can apply different constraints to them. Thanks for your feedback - much appreciated.
ChriDin
Alumni
Beiträge: 25
Registriert: Di 29. Apr 2014, 14:52

Re: Advice on Constraints / Tipps von Constraints

Beitrag von ChriDin »

Dear whpthomas,

thanks for your post.
Do not hesitate to ask us, if there are further questions.
Kind regards

Christian
GvTT
Newbie
Beiträge: 4
Registriert: Do 11. Jun 2015, 09:33

Re: Advice on Constraints / Tipps von Constraints

Beitrag von GvTT »

Hi,

as for simple loadcases I would suggest a minimum clamping approach:

The way I understand your part/problem, it's pretty mich like a crank of a bicycle.

With the given load you can calculate manually the resulting forces on the crank-shaft.
This gives you the chance to set the part into a force-equilibrium.
Theoretically the part would not move... , but show the right tensions.

Now you can clamp it at any arbitrary node, ideally x,y,z displacement in one nore,
z,y displacement in another and and z displacement in a thirt node (these 3 nodes must be on a plane, not a line).

If these restrains are (almost) force free, your loadcase if complete, the influence of the clamping ist minimal.
By this you get a nicefeedback if you understood your loads correctly and you avaind any wrong clampings.

Kind regards
GvTT
Antworten