Medical Implant Fatigue Simulation using Ansys Mechanical

Hi everyone, this is Ming Yao from Ozen Engineering. In this video, I will be talking about how we set up a fatigue simulation for a dental implant. This is very typical of many medical device companies.

These companies use ANSYS tools to simulate various types of ASTM, ISO, or ASME testing methods to ensure that their implants, biomedical implants are durable.

The key benefit ANSYS provides here is the ability to model things like nonlinear contacts, which allows us to model accurate fixture interaction as well as component-to-component interaction.

I will start from the beginning by opening up a clean ANSYS Workbench environment and loading in the geometry.

This is an ANSYS Workbench environment that allows us to simulate a wide range of analyses, from structural mechanics to fluid dynamics, electromagnetics, explicit drop simulation, and thermal. So, almost everything ANSYS can do is available in this tool, in this environment.

And we're going to start with just a basic static structural analysis. Here is the geometry we're starting with. We have a number of parts here in the analysis. The implant and the screw, I'm going to set both of these to be a version of titanium.

So, we have a large list of titanium alloys, as well as steel, metal, plastics. Just pick the first two. So, we have a large list of titanium alloys here. The cap, I'll make this out of, let's say, a carbide. Maybe a titanium carbide material.

The fixture, let's see, perhaps it's a polycarbonate or some other type of epoxy plastic material. Maybe we'll just make it a mixture of ABS and polycarbonate. And finally, the load cell here, I'm going to make it a rigid body. This way, we don't have to model the inside of the load cell.

The material properties are all set. If I go into the material section, you can see that my titanium material has an isotropic hardening model as well as fatigue curves. So, we can easily calculate the fatigue characteristics of our implants. Next, we want to set up the contacts.

We want to make sure that the material is not too tight. And finally, we want to make sure that the material is not too tight. So, we're going to put in a few more pieces of metal. And we're going to make sure that the material is not too tight.

We're going to make sure that the material is not too tight. So, you can see that many parts here are screwed in. We want to ensure that the surfaces are properly selected. I'm going to add a couple more surfaces to this. And we'll change the behavior from bonded to frictional.

This one, this is probably glued together, the cap to the implant. This one is also screwed in. So, we'll change that to a frictional contact. And I think it did select all of the surfaces we need. And finally, this one from the top to bottom, we'll make this a frictionless contact.

So, those are the contacts that needed to be set up. I'll set a frictional coefficient of 1. But this depends on your test data and how much friction you think is at those interfaces. These are nonlinear contacts.

One quick way of making sure we have a fast and stable solution is to update the stiffness at each iteration. So, ANSYS can adjust the stiffness to ensure better convergence. Next, let's take a quick look at the mesh here. You can see the mesh is a little bit large on the structure side.

If I hide this part, see the mesh is not bad here, but it's still probably a bit coarse. So, we can select these two parts. Put in a sizing. And that circle is how big the default sizing is for this. So, maybe we cut this down to 2 millimeters. And we can put in a sizing here too.

Maybe 3 millimeters. Or 5 millimeters. Make this fairly coarse. At the contact areas, we want to be a little bit more careful. So, I can drag those into the meshing section. And specify maybe we want to drop the contact area down to 1 millimeter. Generate an updated mesh.

Having a smaller mesh on the contact area gives us more integration and contact points. Which reduces the amount of penetration. And usually leads to a more stable solution as well as a more accurate solution.

The downside to that is as you refine the mesh in the contact region or anywhere, the simulation speed slows down and it takes longer to run an analysis. I'm running the simulation on my 4-core laptop. So, it will take a little bit of time with this much nonlinearity.

But with more cores and more computational resources, it should run faster. So, I'm going to go ahead and run the simulation. And I'm going to go ahead and set up the simulation. And I'm going to go ahead and set up the simulation. Okay, so the mesh is completed. If I hide this part now.

You can see we have smaller mesh. We can probably go a bit smaller than that even. Okay. So, now let's go ahead and set up the simulation. We're going to support this area with fixed support. And we're going to go ahead and set up the simulation. And we're going to move this surface down.

Because this is a rigid body component, we can assign remote displacement. So, it's going to be moving minus 1 millimeter downwards. And we're going to fix all the other degrees of freedom. And now we run the simulation. Oh, it's a nonlinearity analysis. We want to turn on large deflection.

And we want to turn on auto time stepping. Usually, I start with maybe a little bit of time. Maybe 10 or 100. So, maybe 50 here. And usually, 1 into the 6. This allows ANSYS to dynamically adjust the amount of load it's putting on at each point. To calculate so that we get a converged solution.

It takes a while to run the simulation. So, I'm going to jump to this results here. Go ahead and delete all of these results. And go from the beginning. So, this simulation took 500 iterations. And running on my laptop here, it probably took a few minutes. About 60, so 6,000 seconds on my laptop.

So, that's about 600, 100 minutes. And if I go to 1. 5. Scale factor. So, I'm scaling the stress by 1.5 times. Now, we're down to 96, 000. The minimum fatigue is occurring right here. As we'd expect. In the contact area. So, this gives you an idea of the type of simulation we can do.

For a dental implant design. We can do this type of analysis for almost any type of orthopedic implants. Where you're required to undergo various types of testing regimens. What makes this simulation accurate is that we're allowing the text fixture to separate. As it should. From our test material.

And if I look at the contact up here. You will notice the contact area moving around. So, the contact location is sliding as a function of deformation. So, this is true large deformation with nonlinear contacts. Based on the simulation, we can do another type of analysis.

You can see the model is exactly the same. But we've switched to an explicit dynamics model. What this allows me to do is look at an impact simulation. A drop test. On this part. So, let's go ahead and take a look at this video. As I drop a piece of steel on the implant.

You can see the loading here is dynamic. We can understand the maximum deflection. When I drop this piece of steel from 2 meters up. The dental implant deforms by almost 1 millimeter. As is at this maximum location. Here. We can look at the stresses on the screws itself. The implant.

The screw stress. Both. And we can look at various other scenarios. So, it tells me what the maximum stress is. As this dental implant undergoes. An impact. So, if you're finding the need to hammer implants in. And seeing how that behaves inside the body. And where things could potentially break.

This is a great tool for modeling those dynamic events. The setup is very similar. Explicit dynamics. It also takes a while to run. However, the big benefit is that it automatically detects interactions between different bodies. So, I don't have to specify all possibilities for impact.

That's all for the simulation. Hopefully, you enjoyed this analysis. We're finding this very helpful for many of our orthopedic implant customers. So, if you have questions. Please feel free to reach out to us at ozeng.ink. If you like this video. Please subscribe or give a like on YouTube.

Thanks very much. And have a great day. Thank you.