UC San Diego

There is a growing demand for the usage of composite sandwich structures in the aircraft industry. Aircraft may suffer damage from a variety of impact sources such as ground service equipment, runway debris, bird strike, or hail ice. The damage response of hail ice impacts on composite sandwich structures is not well understood and they can often result in core damage without visually detectable surface damage. This seed damage may grow and lead to large-scale failure of the structure through repetitive operational loading, such as ground-air-ground cycles of aircraft (causes core internal pressurization). Therefore, it is necessary to understand the types of damage that can occur as a result of impacts. This study explores the effect of high velocity hail ice impact on damage formation in lightweight composite sandwich panels, particularly at a level that produces barely visible external damage. Panels consisting of two different facesheet thicknesses (1.19 and 1.87 mm) were impacted at angles of 25, 40, and 90 degrees at speeds of 25 and 50 m/ s. The tests revealed three different core damage modes. Any level of measurable surface damage was an indicator of the presence of internal core damage, but internal damage could also be present without measurable surface damage. Thus, visual inspection alone was not a reliable method of damage detection. No clear relationship was found between impact energy levels and internal damage state since, for example, both 83 and 20.5 J tests produced core fracture, while a 16 J test did not produce any core damage. All core damage occurred at a depth of 3-5 mm from the impact- side facesheet