Impact ice adhesion strength of stainless steel 304 as determined on a centrifuge test stand

Passive approaches to mitigate accreting ice on aircraft while in-flight (i.e., impact ice) using coatings are actively being investigated. Determination of impact ice adhesion under simulated in-flight conditions however is dependent upon the test method. Tests that slowly form ice (i.e., freezer ice) may not accurately simulate inflight icing (i.e., impact icing) conditions where supercooled water droplets impact a surface at a particular velocity. The Adverse Environment Rotor Test Stand (AERTS) located at the Pennsylvania State University (PSU) is one facility that has demonstrated simulation of impact icing conditions for determination of ice adhesion strength (tau) without sample removal from the ice accretion environment. This facility though is in high demand requiring a significant amount of lead time and capital to obtain tau results neither of which is conducive to exploratory research. As a solution for quick and economic screening of materials in a controlled manner under simulated impact icing conditions, a laboratory-scale ice adhesion test device (AERTS Jr.) was developed by PSU based on the AERTS design under funding from NASA Langley Research Center. To verify operation, a study was conducted using flat stainless steel 304 disks having surface roughness values ranging from 172 to 662 nm as determined by optical profilometry. Tests were conducted under impact icing conditions from -16 to -8 ? with supercooled water droplets having a median volume diameter of 20 mu m that afforded an icing cloud with a liquid water content of approximately 0.30 g/m(3) within the device. For each substrate roughness evaluated, a linear relationship with a correlation coefficient of > 0.97 was obtained for plots of tau vs temperature that followed the known trend of decreasing temperature and increasing r. Plots of tau vs surface roughness also followed the known linear trend of increasing tau with increasing surface roughness at each test temperature. Statistical analysis found that for surfaces of comparable roughness r was similar. The tau at -8 ? obtained on AERTS Jr. was comparable to those obtained for flat disks on AERTS Jr. II, a second generation AERTS Jr. developed for NASA Glenn Research Center, based on calculated values.

Automated summary

Passive approaches to mitigate impact ice on aircraft are actively being investigated, and a laboratory-scale ice adhesion test device (AERTS Jr.) has been developed for quick and economic material screening under simulated impact icing conditions, showing comparable results to previous studies.