Compression of an Aluminum Foam

The deformation of foams under mechanical load is a complex process that is influenced by different types of deformation simultaneously. Plastic deformation and buckling of foam struts, for example, play an important role. The comprehensive characterization of the deformation of a foam is, therefore, not possible using classical compression tests.

Luckily, the new in-situ computed tomography (CT) technology widens the scope of these tests. For this, the deformation is performed inside the CT and is observed with a series of consecutive scans. This method offers exciting new insights into the behavior of cellular materials, such as foams.

Together with our partner Tescan, we took up the challenge of performing a compression test on an open-cell aluminum foam during an in-situ CT and subsequently simulating the process with GeoDict. We proceeded in the following steps:

• Scanning of two foam samples by in-situ CT (by Tescan)
• Analysis of the scans with GeoDict (by Math2Market GmbH)
• Implementation of a simulation model based on the first scan with GeoDict (by Math2Market GmbH)
• Verification of the simulation model on the second scan with GeoDict (by Math2Market GmbH)

What was the result?

• An in-situ CT scan provides fascinating insights into the deformation of foams.
• The deformation of the foam is very well reproduced by the simulation in GeoDict.
• Experiments and simulation do not compete, but complement each other perfectly instead.
• Working together in a highly motivated team of experts is always fun.

What does this mean for our customers?

• All findings and solutions to challenges are used to improve the GeoDict software.
• The user can calculate the mechanical properties of foams using GeoDict.
• Any user can work together with our experts and solve completely new research challenges with GeoDict

First, the scans were imported into GeoDict and segmented. Animations of the deformation simulation were created using the video capabilities in GeoDict.

The open-cell foam used was manufactured by Recemat and is made of aluminum 99.7, with an estimated pore diameter of 2.5 mm and a porosity of 95%.

The pores were identified with a watershed algorithm using the PoroDict module of GeoDict. This identification works perfectly, even though the cells of the foam samples are quite open. Only pores that do not intersect the domain boundary were analyzed, since pores that are cut off at the boundary distort the results.

The mechanical simulations were performed using the CT scans of the uncompressed samples. ElastoDict uses the FFT-based voxel solver FeelMath, which means that the mechanical simulation can be performed directly on the CT scan without the need for mesh generation. In addition, this solver allows simulation of large compressions of foams, which is often a challenge with standard FE-based solvers.

The foam is made of Al 99.7. The simulation of scan 1 showed that the mechanical properties corresponding to heat treatment H112 are the most suitable. That means that the Young's modulus is 70 GPa, the yield strength is 23 MPa, and the elongation at break is 23%. These properties were represented by a bilinear hardening law and then, also used for the simulation of scan 2.

For the simulation, a compression of 35% was specified and symmetrical boundary conditions were defined. The tangential boundaries were assumed to be stress-free. The specimens were only slightly larger than the scanned area, so it can be assumed that the specimen could expand to the sides during compression.