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Evaluating Product Design: Drop Test Simulation

Today, we're going to talk about how to perform a drop test in LS-Dyna. Why do we do drop tests? The main reason is to evaluate how well the product design and the material will perform when exposed to the amount of external impact force.

This type of study is typically done for consumer electronics, but it's very expensive when done experimentally. With real physical products. An experimental drop test may be already too late to correct the actual design. That's the reason why this simulation of our drop test plays a critical role. As we see here, the drop test workflow can be separated into three major parts geometry in material preprocess with automation and solver and post process.

Here is a router drop test example. The first step is to import CAD and engineering data. You can do that in project schematic. First you create a project in LS-Dyna and import CAD to the geometry and also import the material property into the engineering data. After you've done that, you can assign a material property to corresponding parts. Then we will go to connections. All the fasteners and source connections are modeled as bonded contacts. Those things are listed here. Then we will go to the mesh. You need to be careful about mesh is appropriate mesh size and refine some local areas if needed. Next, I'm going to highlight the most important part here is to set up the drop orientations.

Here we introduce the drop test plug in. It's an external add-on to help create a drop orientation conveniently. Here, you just click on the drop test, plug in, and it will create a folder for you. And if you need a drop test, just click on that. If you perform a bore impact analysis, you can do this and you can also perform tip over analysis. So, let's do a drop test. After we click this, it will create this folder for you and ask for the job height or equivalently initial velocity. And you can also set up the friction coefficient and the gap between the rigid wall and the model. So, after you are fine with these settings, you can go to one level down to the real drop orientations. You can set up the drop orientations by these four methods. Vector with two points, global plane, plane with three points and access with two points is very convenient. Let's say we have six drop orientations back. Bottom antenna corner. Front edge. Back edge. With this drug test plug in, we can set up these kinds of different drop orientations. After you finish these settings, you can go to the drop test plugin and export the list to a key file and run it through LS-Run. That's the preprocess of a typical drop test.

Here's the defamation results of six orientation drop tests. Let's focus on the first one and open in LS pre-post. Here's the result from the bottom drop test. We can have a look at the defamation; we can turn on or turn off the mesh. We can look at the stress. Go to fringe component von Mises stress. Here I just hide the cover because the stress on the cover is not that big. So here you can see with the color magenta, this part is much more critical than other parts. We can also look at the other results, like the assessment which had the range. But then you can see the displacement, the counterpoint. We have other results available like acceleration and velocity. And strained components.

Here's another example about cell phone drop tests. Same as before. First step, you can import CAD and engineering data to the projects and then assign the material to the corresponding parts and then match the parts set up to the connections. Here, most connections are bonded contacts. Next step, we're going to set up the drop orientations. We're going to demonstrate how to use drop test, plug in to help you to set up different drop orientations. First you have to go to LS-Dyna, then drop test, plug in, create this folder and create drop tests and look at this kind of property. If the drop height is fine for you, set up the gap and the friction coefficient. If this is fine, we can go to the next step. Create a drop orientation. Let's say we want a corner drop. We just select the corner. It will find the appropriate location for you directly. Because the first point is the gravity center. The second point is the point selected. It was searching for the lowest rigid wall for you. Let's say we want another orientation. Let's say bottom drop. We can use the global plane method. Just set this as back so you can see this as a bottom drop. Let's test another case. For example, we want to create a plane by free points. I just select three points. And then it will form a plane and then it will search for the lowest points on the cell phone and hit the plane you've created. That's about the preprocess of this example.

Next step you can import the LS-Dyna K file, then do post processing. Here are the corner drop test results. You can see the von Mises addressed here. And since this is a corner drop, therefore the corner you will see stress concentration. Besides that, we can also view other results, like effects of plastic strain, first principles, stress, and all other stress components. For the nodal results, we have displacement, velocity, and acceleration. 

Improve the safety and reliability of your consumer electronic products, visit: Ansys LS-DYNA | Crash Simulation Software

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