Creo Community Challenge November 2023: Simulating a Drop Test
The November 2023 Creo Community Challenge was simulation based:
Many products have requirements regarding the ability to survive multiple drops from a given height. Your challenge is to simulate a drop test in Creo. Many people have a technique for simulating drops. If you don’t, how would you create one? You can use Creo Ansys Simulation, Creo Simulation Live, Creo Simulate, Mechanism Design Extension (MDX), Mechanism Dynamics Option (MDO), or any other module you see fit.
We only had one submission this month. Upon reflection, there are a few potential reasons for this. Licensing is a big one; people might not have access to the more advanced licenses. If they don’t have access, then they likely lack expertise. But most of all, even though they seem simple, drop tests are hard.
I first simulated drop tests in the defense industry and later supported them for consumer electronics. Anyone who has a smartphone or a kid knows there are a thousand ways to drop an object. MIL-STD-810G specifies that an object has to be dropped from a height of four feet onto concrete-backed plywood 26 times, including eight corners, six faces, and 12 edges. The latest version of the standard has increased the height to six feet, changed the material to steel, and specifies three scenarios: logistic transit drop, tactical transit drop, and severe tactical transit drop.
That’s a lot to test. On top of that, simulating a drop is harder than it sounds. Let’s take a look at a few techniques.
The submission
User Hadardor wins the challenge with a cylinder that rolls down a ramp, hits and knocks over a wall, and falls into a U-shaped channel in the Mechanism Dynamics Option (MDO). The cylinder is assembled with a planar connection. The impact is possible due to cam-follower connections with liftoff enabled. A 3D contact connection enables the cylinder to push the wall over, which itself has a pin connection. The simulation was completed with a dynamic analysis with gravity and friction enabled.
This is a fun simulation to watch. Head over to the PTC Community to download and run the model for yourself.
My first drop test
Back in the 1990s, I had to simulate a drop test for a container for surface-to-air missiles. Our resources were extremely limited since computers weren’t that powerful. Your models could not have many elements and nodes, and you had to make lots of idealizations.
We applied a three-point constraint to the end opposite the impact. Then we applied a high acceleration load over a very short duration where the container would land. We ran the equivalent of Creo Simulate’s Dynamic Shock analysis in NASTRAN. I wasn’t happy with the approach, but I believed it was the best we were capable of at the time.
NxRev simulation
In the late 2000s, I worked for NxRev, a Value Added Reseller (VAR) for PTC products and services. My manager and colleague Roberto Sanchez developed a drop test for a flip phone. The assembly contains a variety of connections between the phone and empty placeholder components, including pin, cylinder, planar, and ball. It has cam-follower connections for each of the corners and the ground. It uses a damper and gravity in a dynamic analysis to make the phone tumble. I posted a video of the analysis on the community page.
Use the knowledge base
As a user, I am in the PTC Knowledge Base all the time. During the course of the challenge, I decided to see what was available for drop tests. I found three separate documents. One even has model files you can download. The documents are quite old, written for Mechanica with dated Pro/ENGINEER images. However, the techniques are still valid. This should remind people that the
Knowledge Base should be the first stop for people approaching new design, simulation, and manufacturing problems.
What’s next
That’s six different approaches to the same problem. The good news is that people have a variety of tools available to them in Creo for making sure their products meet requirements.
The next challenge will return to our roots with something design-oriented that everyone should be able to participate in. In the meantime, I encourage everyone to check out the Knowledge Base to see what hidden gems you can find.