Dental fatigue test implants

[Riccardo1990]

Good morning to all, I am a mechanical engineer of bologna and work in dental field
I am designing a new dental implant and before going to production I am trying to perform a static test, according to the law uni en iso 14801, to verify the seal of the entire structure. the system is composed: - plant (inserted in the sleeve/support of brown brass);
- an angled ram fixed by a screw at the plant itself;
- a titanium carbide cap (cemented on the black moncone);
- steel cylinder simulating an actuator/pistone.I'm studying half the surface to simplify the simulation. I have set the materials (earned directly from the granta software) so I am sure of their validity, I have simplified the entire structure with spaceclaim, I have put in contact the components so that there are no interference or compnetrations and finally I have put the constraints:
- fixed support: put to the brass support (brown)
- displacement: null shift in the direction of symmetry (long z) figure below
- Bolt pretension: screw pretension calculated with the motosh formula
- remote displacement: between the spherical and piston cap (contacted with a frictionless) so that during the pretension of the screw, rams + hood + piston come down together I'm breaking down static simulation in two steps:
1) only the pretension of the screw (piston + cap does not contribute energyly, on them there are no efforts; therefore when the screw puts in pretension moncone and plant the other two follow only the moncone in the descent, since the hood is cemented)
2) application of force by the actuator on the structure "altered already from the pretension"

in the first phase I managed to make the accounts square, during the pretension of the screw, the moncone drops in the plant of 0.17mm (exactly as in reality), carrying behind hood and piston (it is as if there were, in fact there are neither efforts nor energy on the components)
in the second phase, when I apply the remote force on the piston, it happens that the piston and the cap lose the contact and the piston starts from the initial condition and not from that "altered" from the screw. in a few words the initial point of the second phase must coincide with the end of the first. Moreover the piston must move only vertically and the spherical cap, during the descent flows without friction on the piston in a few words there is first the pretension of the screw and then the application of force with active pretension.
I'm almost sure it's a matter of system constraints and I'm not succeeding in setting them properly, I always get stuck with simulation.

I apologize for the long description
waiting for your answer, I wish you a good day
richer

 

[cacciatorino]

I don't know about the cad or the fem you're using, but there's definitely a log file somewhere that says exactly how the simulation stopped, and why. I think it's a good starting point for a simulation setup.

 

[Riccardo1990]

Good morning
the simulation I am doing with ansys mechanical pro, release 2024

 

[F_Ingrasciotta]

hi, at first impact I would tell you that the "remote displacement" used on the division surface is wrong, there you have to insert a symmetry that will block you both the movements and rotations of the knots on that plane.

in the second phase, when I apply the remote force on the piston, it happens that the piston and the cap lose the contact and the piston starts from the initial condition and not from that "altered" from the screw. in a few words the initial point of the second phase must coincide with the end of the first. Moreover the piston must move only vertically and the spherical cap, during the descent flows without friction on the piston

that part non l'ho ben capita on this.

 

[cacciatorino]

hi, at first impact I would tell you that the "remote displacement" used on the division surface is wrong, there you have to insert a symmetry that will block you both the movements and rotations of the knots on that plane.


I don't quite understand this part.

in practice he wants to take the solution of the first step (planning of the capsule on the pin) as a starting point for the second step. I hope I understand correctly. Perhaps you should use "soft spring" to make the arrangement of the upper punch without the system being labile.

 

[F_Ingrasciotta]

practically if I well understood the situation is:

-step0-> no load and contact bodies
- step1 -> precarious and therefore open contact
-step2 -> preload+force with the capsule starting from the initial situation.

at this point instead of the "remote force", which identifies a step 0 force application point identified in space (and therefore there remains for the whole simulation), I would use a pressure on the cap cap, making sure that the force resulting from the pressure is equal to the force.

using a symmetrical remember to use such a pressure to get half the force you want.

 

[Riccardo1990]

hi, at first impact I would tell you that the "remote displacement" used on the division surface is wrong, there you have to insert a symmetry that will block you both the movements and rotations of the knots on that plane.


I don't quite understand this part.

in the second part of the simulation, I put on the piston a remote force of 80n, which should move the piston vertically (it should not contain rotations -->probably a remote disp should also be added. on the displacement of the piston, I do not know) this force is transmitted on the cap that, together with the moncone, will be slightly flexed. the contact point, during the application of the load, varies slightly, but the pieces are always in contact. Unfortunately I can't set the maintenance of the contact between the cap and the piston. I put a frictionless contact (spherical cord and piston), which inside it already contains the information to keep the surfaces united, but so it is not.

"You have to put in a symmetry that will block both the movements and rotations of the knots on that floor" I don't really understand.

greetings

 

[Riccardo1990]

in practice he wants to take the solution of the first step (planning of the capsule on the pin) as a starting point for the second step. I hope I understand correctly. Perhaps you should use "soft spring" to make the arrangement of the upper punch without the system being labile.

accurately

I'm trying to replicate this simulation. in the video however apply a remote displacement of 1mm (according to me it is too much in reality, but it's okay so), while I have the chewing force of 80n (which in theory is 160n but I'm studying symmetry and therefore consider it half). Moreover, its moncone is already screwed into the plant, while I use a bolt pretension (step 1) and force application (step 2)

 

[F_Ingrasciotta]

"You have to put in a symmetry that will block both the movements and rotations of the knots on that floor" I don't really understand.

there is the specific "simmetrie" command and then choose whether "symmetry or asymmetry". for more details of what it is I refer you to the slides of the course I followed to the unipi (for the symmetry see from slide 6), here the link.

in the second part of the simulation, I put on the piston a remote force of 80n, which should move the piston vertically (it should not contain rotations -->probably a remote disp should also be added. on the displacement of the piston, I do not know)

reading the various answers you gave me I understood a little better the situation, for the piston why do not create a prismatic guide? at the moment, in addition to the constraints on the symmetry plane, you did not provide any other bond, so the piece is free to move. if only a vertical movement must be allowed with a certain force, you must properly bind it.

 

[Riccardo1990]

Okay.
Thank you for your suggestions and try to apply them.
I have only one doubt:
how do I maintain the bond between piston and spherical cap? in the first phase I remember that the pretension of the vine (in dark green) drags behind all the upper structure (winned with remote disp. (clear green). doing so the pieces are bound to move on the x-y plan. until here everything works correctly and the structure drops by 0.17mm on x-y plane. in the second phase, when I apply the force (I try to put the prismatic guide as you suggested so that you can move only vertically) the piston will have to start working from the new condition/position inherited from point 1 (see that it fell by 0.17) and remaining in contact with the cap for the whole simulation. the cap will have to move as in the video that I have attached

Thank you very much

 

[F_Ingrasciotta]

how do I maintain the bond between piston and spherical cap?

uses a "no separation" contact instead of "frictionless" so as to make linear analysis (the frictionless makes you non-linear analysis) and with the indicated contact always maintains the normal connection to the surface even if tangential translation without friction is guaranteed.

to this link find the explanation of the contacts well made.

in the second phase, when I apply force (I try to put the prismatic guide as you suggested so that you can move only vertically) [...]

honestly the prismatic guide I would put it from the beginning, otherwise in the first step the piston remains labile.

 

[Riccardo1990]

You gave me some really interesting tips, I try to apply them to the system
I'll let you know when I make the simulation.
Thank you very much

 

[F_Ingrasciotta]

You gave me some really interesting tips, I try to apply them to the system
I'll let you know when I make the simulation.
Thank you very much

Have you had a way to make the simulation?