Christmas Ornament Safety with Ansys Explicit Dynamics

By Spencer Crandall

Around this time each year, families around the world gather to decorate their Christmas trees. Unfortunately, we’ve all lost an ornament to a clumsy family member, a domestic pet, or a sagging tree. In the spirit of protecting the sentimental ornaments in our lives, we’re going to use Ansys to discuss the topic of safely decorating with glass ornaments. We’ll do this by using the Ansys drop test wizard ACT extension to look at a representative glass ornament falling from varying heights. We’ll go over some simple considerations during setup, material models available, and ultimately what height you can safely drop a glass ornament and expect it to survive.

Jumping right into the tools that we’ll need to run this drop test analysis; we can go into our ACT manager and make sure that the Mechanical Drop Test Wizard ACT extension is loaded.

Figure 1: Drop Test Wizard ACT Extension

Figure 2: Ornament Geometry

Next up will be finding the proper materials for our model. Thankfully, Ansys includes a library of explicit material models, which we can use in lieu of hunting down the complex, rate-dependent, brittle response, material properties that we will need. We will be using the Floatglass material, which uses the Johnson-Holmquist Strength model. This material model will allow us to show plasticity and damage along with material fracture.

Moving into the explicit module inside of Ansys Workbench, we’ll launch the Drop Test Wizard, which will expedite the setup process. This can be found in the Environment context menu when you have the Explicit Dynamics object selected in the outline.

Figure 3: Context Menu Drop Test Wizard

1. Using the Drop Test Wizard we can complete the following steps:
2. Orientation of the target surface and imported geometry
3. Creation of the target surface
4. Meshing
5. Set initial velocity based on drop height
6. Set analysis end time and analysis preference to Drop Test
7. Establish body interaction contact behavior (frictionless or frictional)

Figure 4: Completed Model Setup

With the setup described, we can iterate on our drop height until our glass ornament experiences a failure as shown in the following GIFs (click on each to play).

Figure 5: 40 Inch Drop Height

Figure 6: 41 Inch Drop Height

Figure 7: 96 Inch Drop Height (Just for fun)

Our analyses indicate that you can safely hang your glass ornaments no higher than 40 inches. Keeping that height restriction in mind will help you and yours keep safety at the forefront of all your Christmas tree decorating parties.

This post focuses primarily on the basic application of the explicit dynamics drop test wizard ACT extension. If you’re interested in a more in-depth overview of explicit dynamics in Ansys then I would recommend reviewing our previous two-part blog post or YouTube video:

Blog Post: https://blogs.rand.com/randsim/2020/11/explicit-dynamics-and-ansys-part-i.html

YouTube Video: https://www.youtube.com/watch?v=J1FJGENPf1k