Combined effects of impact damage and moisture exposure on composite radome dielectric properties

Katherine Berkowitz, Ogheneovo Idolor, Mark Pankow, Landon R Grace

Research output: Chapter in Book/Report/Conference proceedingConference contribution

2 Scopus citations

Abstract

The ability of radar signals to pass unimpeded through the protective structure of a polymer composite aircraft radome is heavily influenced by the properties of the composite. This study investigated the material dielectric response - a proxy for radar transparency - to atmospheric moisture contamination subsequent to physical damage from simulated hail impact. Representative radome composites were damaged through impact followed by moisture exposure. Twelve-ply quartz-fiber reinforced bismaleimide (BMI) laminates were impacted at four different energy levels using a drop tower to simulate hail damage. The relative permittivity was measured before and after impact using a split-post dielectric resonator operating at 2.48 GHz. To determine the effects of impact and subsequent moisture contamination, a sample from each energy level and four undamaged samples were fully dried and then contaminated with water via immersion over 15 days to simulate long-term exposure to humid air and precipitation post-impact. A direct correlation was found between impact energy level and relative permittivity at all levels of absorbed water, independent of exposure time. At 0.787 % water content by weight, the 12 J impact caused a 10.28 % overall increase in relative permittivity from the dry, impacted state and a 6.06 % increase relative to unimpacted samples at the same water concentration. This result suggests a higher ratio of free, high-relative-permittivity water corresponding to higher impact energy levels, consistent with the formation of microfractures in the composite from impact and the preferential absorption of water into this new free volume. Water within this free volume behaves as bulk water; relative permittivity is significantly increased due to absence of rotational restriction of the molecular dipole caused by interactions with the polymer network in undamaged material. Thus, the detrimental effect of atmospheric moisture on composite radar transparency is significantly exacerbated by the formation of microscale damage from impact at the energy levels expected from routine hail encounters, even at equivalent total moisture content.

Original languageEnglish (US)
Title of host publicationSAMPE Long Beach 2018 Conference and Exhibition
PublisherSoc. for the Advancement of Material and Process Engineering
Volume2018-May
ISBN (Electronic)9781934551271
StatePublished - Jan 1 2018
Externally publishedYes
EventSAMPE Long Beach 2018 Conference and Exhibition - Long Beach, United States
Duration: May 21 2018May 24 2018

Other

OtherSAMPE Long Beach 2018 Conference and Exhibition
CountryUnited States
CityLong Beach
Period5/21/185/24/18

ASJC Scopus subject areas

  • Materials Science(all)
  • Mechanics of Materials
  • Mechanical Engineering

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  • Cite this

    Berkowitz, K., Idolor, O., Pankow, M., & Grace, L. R. (2018). Combined effects of impact damage and moisture exposure on composite radome dielectric properties. In SAMPE Long Beach 2018 Conference and Exhibition (Vol. 2018-May). Soc. for the Advancement of Material and Process Engineering.