structural analysis with moving parts

[kasak985]

hello to all

I find myself in the grip with an analysis of a bicycle pedal

essentially the pedal has a pin inserted inside. the tree is fixed while the pedal turns through the balls.
on the pedal I should apply a load of 1000n.

so I would have a load on a rotating pedal around a fixed shaft
the purpose of the analysis is to check the stress tree, then it will follow a fatigue analysis.

How can I set the problem in workbench?? I tried with joint, displacement but I'm confused and lost..

Thank you very much...:redface:

♪

 

[kasak985]

Suppose we have a very simple cinematism such as a bicycle pedal, now, we imagine to impose above the pedal a load over the pedal.. .

which form should I use.. .
the dynamic rigid doesn't allow me to get a stress like out-put.
static structural, with remote dispacement?
dynamic structural does not seem appropriate to me because we do not talk about impact phenomena. .

please. . .

 

[stefano.garbin]

He uses a static and a little brain!
in the case of a pedal pin is not very wrong assuming that the maximum of the force is explicated when the pedivella is inclined by 45° forward downwards.
then the pedal pin almost never goes into "tiro", so you have a fatigue with r=0.
1000n are few. the norm seems to me to predict 1200n, but it is easy to get even to 1800n.
dimensional well the pedal pin because if it breaks it is easy that the cyclist gets very bad.

 

[eih64]

I'll tell you right away that what you call a "simple pedal" is all but simple.

You have to decide what you want to do. and as first advice I tell you parts from a simple static analysis (1 load frame). the elastic module is that of the materials in play. in this first phase (as I perceive you "novice") I would leave aside the bearing (which works in compression not traction and ...) ... use a load "bearing load" ... and with due attention you will have a discreet representation of the phenomenon. .

Good job.
nb.. simplifies the problem

 

[kasak985]

Thank you very much for your help.. .

cmq I am trying to simplify while remaining within the static structural. I checked the test in the regulations..the load is applied on the pedal at a distance on the shaft, so I have circumvented the problem so:

-Express the pedal
-divided the static structural in 8 step
- applied the load on the surface of the bearings of the tree (which will be bering load)
-for each step the force is oriented according to the rotation angle by simple sen cos of the relative angle between pedal and shaft


However, yesterday I rolled up to study the rigid dynamics and transient structural.... Now, with regard to the rigid dynamic, I managed to replicate the cinematism of the pedal through joint and joint load. However in rigid environment you can not get stresses.

then once replicated the mechanism with rigid dynamics two are the roads I could undertake:
1) In rigid dynamics use "joint probe" to determine the resulting force on the joint during the motion of the mechanism. .
to this point copio take off the table of the reused of the joint probe as force of a static structural performed to several step
at this point remains the problem that I cannot apply the load on the surface of the pedal in the rigid dynamics and therefore the resulting force in the joint probe is not true.:mixed:
2)At the bottom of the rigid dynamics set a transient structural at this point the system should premise me to impose a pressure on the pedal but I do not know why the solution does not converge. : office: added:
http://www.youtube.com/watch?v=mrgs5ec_8-yhttp://www.youtube.com/watch?v=dk7fkdk0jj4I know that I should stop at the structural situation, but the boss wants to see the shaft that deforms under the pressure of the pedal in rotation, says that in the past they have already done these things...addirittura will follow the modeling of a cyclist acting on the pedal to create mini movies. . .Will other programs for cinemas with applied loads? ? ?I did 4:00 last night to study how to fully simulate this mechanism. . .

thanks good weekend:redface:

♪

 

[kasak985]

I'll tell you about this problem. .

I practically did everything with transient structural
set:

- the tree with fixed joint
- the pedal with revolute joint
-joint load for revolute joint
-pressure on the pedal, value according to regulations
-free

is exactly as I said in the previous message in green, with the difference that to bring everything to convergence I reduced the time step to 5e-3 sec.. .
the results look good, corresponding with tests received. . .

question: could all this not be done in static structural?? :frown::frown:

thank you very much...:wink:

 

[stefano.garbin]

The approach I suggested you tried?
He's not very refined, but I'm convinced he's not so wrong. . .

 

[kasak985]

I tried different structural analyses, I did them all without pedals.

In fact, as you recommended, the city bike standard under fatigue test indicates to apply on the tree a load of 1300 n, when the pedivella is 45° from the horizontal, with a frequency of 25hz, at a distance of 65mm from the pedivella itself.

However, the tree in question has a hole in the axis with the pedivella, so when the load is applied to 0° it finds a reduction of material.
static analysis on the tree had a load applied according to regulatory distance, but I also tried to put it on the bearing surfaces to replicate a condition of use.

then the legislation also provides a test of dynamic durability, at this point the pedal is fixed and the shaft is set in motion by a reducing motion, in this situation I need a dynamic analysis.. .even if I have cmq set static multistep analysis with loads that change direction to each step. I set this test with dynamic analysis the way I said in the previous mess.

dynamic analysis seems to be very expensive from the computational point of view, for a 140000 elements of goes also on the 10 hours or more (with bcsoption,, incore,13000), actually simulate everything with simple static analysis would be ideal. .
However I am very interested in the field of dynamic analysis in ansys....I am now entering this field...so the questions would be endless... .- one on all is that if I go well in workbench with the transient structural, for the structures that provide parts in relative movement, and explicit dynamics for impacts and so on ..or do there exist other methods for the moving parts mutual?

- I have read pages and help pages for these two modules but I still don't have to be clear in what case you use one or the other... .

Thank you. .

luca:redface: