Experimental and computational study of hypervelocity impact on brittle materials and composites

Retrieval and analysis of space-exposed surfaces from Low Earth Orbit (LEO) can lead to an improved understanding of the space debris and micrometeoroid particulate environment. A large volume of data has been accumulated from analysis of space-exposed ductile materials, including the LDEF satellite. The Hubble Space Telescope (HST) and EURECA solar arrays provide a large, new source of information on the LEO particulate flux. Below a certain crater diameter, these solar arrays are equivalent to semi-infinite brittle material targets and thus the impact crater fluxes are analogous to impact fluxes on returned lunar rocks and Apollo/Gemini windows. An extensive shot programme has been executed onto glass, aluminium and spacecraft honeycomb (used as exterior spacecraft wall and solar array support structure). The data supplement the large database of brittle material hypervelocity impact tests used in this thesis. These data have been used to (i) develop new, target-dependent, empirically-determined brittle material damage equations, (ii) derive a conversion factor between the brittle material ,) conchoidal diameter( D, and the ballistic limit in aluminium for a particular exposure and shielding history (Fmax)a, nd (iii) investigatet he ballistic limit of spacecrafth oneycomb. In addition, the response of brittle materials to, hypervelocity impact has been explored via hydrocode modelling, including the implementation and validation of the Johnson-Holmquist brittle material model at velocities beyond the experimental calibration regime. The converted semi-infinite brittle material fluxes from the HST and EURECA solar arrays have been directly compared with both an experimentally-measured LDEF mean flux and a modelled flux prediction for meteoroids (excluding space debris). The solar array fluxes are in good agreement with the LDEF data and modelling results for F. greater than 20-30 μm. Below this value of F,,,, the data do not reproduce the space debris flux enhancement shown by LDEF.