space-qualified polyimide Kapton films impacted by simulated hypervelocity debris. The effect of the simulated debris was studied using X-ray microtomography ...
Characterisation of the Effect of Simulated Space Debris on Polymers Using X-ray Microtomography 1,2
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R. Verker , P.K. Pranzas , F. Beckmann , T. Donath , A. Schreyer , N. Eliaz and E. Grossman 1
Space Environment Division, Soreq NRC, Yavne 81800, Israel Department of Solid Mechanics, Materials and Systems, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel 3 Institute for Materials Research, GKSS Forschungszentrum, Max-Planck-Str. 1, 21502 Geesthacht, Germany 2
The aggressive space environment present in Low Earth Orbit (LEO) at altitudes ranging from 200 to 700 km restricts the number of space-qualified materials and reduces the service life of polymers used in space technologies. The predominant environmental species in LEO responsible for polymers degradation are Atomic Oxygen (AO), UV radiation and space debris particles. Hypervelocity space debris impacts can lead to degradation of satellite performance and, in extreme cases, might cause a total loss of a spacecraft. The increase in space debris population provides the motivation for this study, which focuses mainly on the structure and mechanical behaviour of space-qualified polyimide Kapton films impacted by simulated hypervelocity debris. The effect of the simulated debris was studied using X-ray microtomography which provides three-dimensional information of the damaged area by reconstructing a series of two-dimensional absorption images. It allows the characterisation of structures larger than 1 µm. For the simulation of spacecraft hypervelocity debris with dimensions ranging from 10 to 100’s µm and impact velocities of up to 3 km/s, the Laser-Driven Flyer (LDF) method was used. Impact effects on the internal three-dimensional microstructure of Kapton are studied by means of the synchrotron radiation-based X-ray absorption micro computerized tomography (µ-CT) [1]. The measurements were performed at beamline BW2, using a photon energy of 24 keV and an effective pixel size of 1.5 µm. Figure 1 shows a top-view cut just below the surface of a 125 µm-thick Kapton sample impacted by 2.9 km/s flyers. Figure 2 and 3 show two-dimensional cuts through the three-dimensional image of the impacted Kapton. The white regions are aluminum particles imbedded in the polymer at the displayed depth. The dark areas are holes created by the impacts [2].
100 µm Figure 1: Top-view cut just below the surface of a 125 µm-thick Kapton foil impacted by 2.9 km/s flyers.
100 µm Figure 2: Two-dimensional cut through the three-dimensional µ-CT image of the impacted Kapton.
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Figure 3: A spall created by the impact is evident and used to estimate the fracture strain.
These results provide information on size and distribution of the flyers. It is evident that the cloud of aluminum flyers created by the LDF system is composed of several small particles, each of the order of few tens of micrometers in size. Figure 3 shows a cross-section of the impacted sample, revealing – besides of the observed holes – also the formation of longitudinal cracks (i.e., spalls). These cracks originate from debris impacts and the related spallation process. Using this image the engineering fracture strain and the strain rate can be calculated.
References [1] D. Tadic, F. Beckmann, K. Schwarz, and M. Epple, Biomaterials 25, 3335 (2004) [2] R. Verker, N. Eliaz, I. Gouzman, S. Eliezer, M. Fraenkel, S. Maman, F. Beckmann, K. Pranzas, and E. Grossman, Acta. Mat. 52, 5539 (2004)
