Interview with Dr. Andrew Harrison
German Aerospace Center – Institute of Vehicle Concepts
r-LightBioCom’s project partner Deutsches Zentrum für Luft- und Raumfahrt (DLR) – German Aerospace Center is responsible for characterising composite properties at lab scale and generating a validated and automated numerical material calibration process. The first material test campaign is currently in progress. We had the opportunity to interview Dr. Andrew Harrison, researcher at DLR who is leading all the project-related work, and gained fascinating insights.
Q: Andrew, after 1.5 years into the project, the first comprehensive material test characterisation campaign is being conducted at DLR’s Institute of Vehicle Concepts in Stuttgart, Germany. Please tell us what this test campaign is aiming at.
A: The test campaign is aiming to identify key mechanical performances of various materials as part of the r-LightBioCom project. The tests will be used to create a database of material properties for use in the Coupled Ecological Optimisation (CEO) framework while also providing insights to identify the ideal composite developed within r-LightBioCom for each use case.
We are currently testing core materials via compression tests. These core materials are a mixture of foams and metal honeycombs, thermoplastics, and bio-based materials such as paper and wood. In the future, the testing campaign will be extended to the bio-based composites produced in r-LightBioCom.
Figure 1. Examples of various core materials, e.g. aluminium foam, nomex and paper honeycombs, for dynamic material characterisation.
Q: What methods and techniques do you use for characterising these materials? Which tools and instruments are indispensable for such tests?
A: The laboratory is using a universal testing machine to ascertain key mechanical properties of materials under quasi-static test conditions, while impact loading and dynamic properties (such as rate dependency) are obtained through use of a pendulum impact machine. The main output of each test are force-displacement curves, which are used to calculate key performance indicators of the material, for example the stiffness and failure properties.
Q: Which material properties are particularly critical for applications envisaged in r-LightBioCom?
A: The testing campaign will show the key mechanical properties for r-LightBioCom’s use cases, such as the stiffness, strength and failure points of the materials. It will also illustrate how the different rates of loading affect the said key properties observed through quasi-static testing.
Figure 3. Measurement and preparation of core-specimens for characterisation.
Q: What challenges have you encountered so far?
A: The testing campaign is running smoothly. However, one particular challenge is replicating the material performance, provided by the testing campaign, into a material description used by finite element modelling techniques. The response of honeycomb structures under compressive loading has a unique curve that provides distinctive challenges to reproduce in a digital material description while retaining computation efficiency, accuracy, and robustness.
DLR is currently exploring further material descriptions and design parameters that will extend the capabilities of the automated material characterisation process that feed directly into the reduced order modelling strategy and CEO of r-LightBioCom.
Q: Could you briefly describe what a typical test looks like in your current campaign?
A: To begin with, a typical test with pre-prepared specimens involves ensuring correct alignment of the test specimen within the holding device of the testing machine. The test machine starting parameters are then set, for instance, pre-load for quasi-static compression or the contact angle for the pendulum dynamic impacts. The cameras are set to record throughout the entire test duration for qualitative analysis and the test is performed until the end criteria is reached.
Videos, left: Paper honeycomb dynamic compression test at 1.5m/s; right: Deformation of Paper honeycomb under 3.5m/s impact loading
Figure 5. Contact angle of the impactor on the core-specimen in the 4a Impetus.
Q: Finally, please tell us how material characterisation impacts the development of new technologies.
A: Material characterisation is pivotal for the development of new technologies to ensure that the materials meet the required criteria for their application. To implement new materials, the performance of the material throughout its lifetime must be known to ensure environmental protection, safety and quality.
In addition to this, by performing extensive tests, the influencing factors to the material properties can be identified and leveraged in development and innovations of new technologies for industrial application.
Andrew, thank you for taking the time to share your insights and experiences with us. We wish you continued success with your upcoming tests and will keep our readers updated on r-LightBioCom’s future developments.