Tensile tests and fractography of MLI TeflonTM (FEP) outer surface layer retrieved during the Hubble Space Telescope (HST) second servicing mission were performed as part of the effort to investigate the failure mechanism of the MLI observed during the second service mission. The fracture surfaces of a tensile test sample as well as a bend-cracked sample were also analyzed for comparison purpose. The surface morphology of the Teflon and aluminum was compared with that of a pristine sample. Fractography analysis shows that the samples exhibit three kinds of distinctive fracture surfaces, although the material has been severely embrittled in space. They are classified as shear fracture, fibrous fracture and smooth fracture based on the fracture surface morphology. The shear fracture is due to a cut by scissors or other cutting devices. Bending and/or tension of the sample during the handling created the fibrous fracture. The smooth fracture occurred in space. The fracture that occurred in space can not be duplicated by tension and/or bending of the embrittled samples. This indicates that cracks were probably developed and propagated very slowly in the material under the influence of the radiation and/or other environmental effects and relatively low stresses and/or stress intensity factors. This 'slow crack growth' property of Teflon material has never been studied.
Mechanical properties and fractography of MLI FEP from the HST second service mission
1998
13 Seiten, 4 Quellen
Aufsatz (Konferenz)
Englisch
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