Hypervelocity impact damage response and characterization of thin plate targets at elevated temperatures

The performance of a typical International Space Station (ISS) shield against the meteoroid and orbital debris (M/OD) impact threat is generally modeled by damage equations for the outer shield and the rear pressure wall. In their current forms, these damage equations neglect the on-orbit temperature extremes witnessed by the ISS. To address IF and HOW temperature extremes affect the performance of the ISS' typical M/OD shield, a comprehensive study was undertaken that investigated hole diameters in .063" thick 6061-T6 aluminum targets impacted at velocities from ∼2-7 km/s at 20°C, 110°C, and 210°C.;Robust graphical and analytical analyses confirmed the existence of a statistically significant temperature effect, i.e., hole diameters in heated targets were larger than those in room temperature targets. A new temperature-dependent model was found via multivariable regression analysis that incorporates a linear velocity term and a temperature term based on a form of the cumulative distribution function.;Numerical modeling of hypervelocity impacts (HVI) into elevated temperature targets was also performed to determine whether or not currently available material and failure models can adequately simulate the differences observed between room and elevated temperature target hole diameters. Statistical analyses showed that AUTODYN simulated the heated data almost as well as the room temperature data. However, the slightly worse Goodness of Fit (GOF) values between the heated empirical vs. simulated comparisons suggest that the simulations do not completely account for the observed temperature effect.;A series of materials tests and observations were carried out on the post-impacted target plates to help explain the empirical data results with respect to material variability and deformation features. Rockwell B and K macro-hardness tests revealed that the hardness values for the targets impacted at 110°C were statistically significantly higher compared to those targets impacted at 20°C and 210°C. Since hole diameters are expected to increase with target temperature, this observation suggests that a less ductile failure mode was involved for the 110°C holes compared to the room temperature and 210°C holes. Polished micrographs of select 110°C impact hole cross-sections support the idea that these targets failed in spall in a less ductile manner compared to the 20°C and 210°C targets.;Current orbital debris (OD) environment predictions are based, in large part, on in-situ damage of spacecraft surfaces, but do not relate observed surface damage to their temperature at the time of the impact. A first-order prediction was calculated to quantify how much elevated temperature bumpers could potentially affect ORDEM2000 flux predictions, and ultimately the risk of impact. By failing to take into account that larger hole diameters are created in heated targets, ORDEM2000 potentially overestimates the risk of impact by particles in the 3mm range of the environment by at least 68%. These calculations show that, in this range, a small error in predicted particle diameter can result in a significant difference in the predicted orbital debris particle flux and risk of impact. To the extent that these effects are true for other spacecraft surfaces, spacecraft designs may be over-conservative due to an overprediction of large particles in the OD environment.