One of the big challenges in Additive Manufacturing for Aerospace is understanding the material properties to an extent that the process can be used for flight critical applications. This process can take years or even decades for more complex processes. Additive manufacturing holds great promise for the aerospace industry and these characterization efforts are underway as we speak. Below is a quick overview of what this means and how it is accomplished.
What is Material Characterization?
According to Wikipedia “Characterization, when used in materials science, refers to the broad and general process by which a material’s structure and properties are probed and measured. It is a fundamental process in the field of materials science.” At a high level what it means is that for a specified material you need to understand how the material performs mechanically so that you can predict its performance during design.
Why is this so important?
Engineers will design components to a known value for mechanical properties. Designs are tested in simulation software prior to use and then the validation is performed on the actual parts to reduce cost and minimize time. It’s a lot less expensive to run a simulation of a part than creating a testing rig. If the engineer does not know these properties then they expose themselves to an unnecessary risk that no aerospace company is willing to take.
What is used today?
Originally started by the US government, the MMPDS (Metallic Materials Properties Development Standardization) is the gold standard for design allowable related to metals. Engineers still refer to this handbook today to understand tensile strength, fatigue, and other material properties that can be used in designs.
Why doesn’t AM apply?
The properties that are shown in the MMPDS are for specific material processing techniques. AM is a completely different way to process metal. That drives you to a characterization of both the process and the material.
How does this get done?
Testing, testing, and testing. The MMPDS standard drives you to test 10 coupons from 10 lots. The most important item to keep in mind during a characterization effort is to hold all your
variables constant. That will allow you to isolate the results and ensure repeatability. When undergoing a characterization effort, you want to understand the goals of the testing, the constraints, and the variables. Based on this information you can optimize the design of your builds and experiments to deliver the maximum amount of testing data while minimizing the coupons tested. In a future blog post, we’ll discuss examples of this.
Material characterization is an essential part of the aerospace industry and is the first step in using Additive Manufacturing in aerospace applications. Be sure to check our blog for future updates on the subject and as always we welcome questions.