Impact damage to laminated composite aircraft structures, when subjected to in-flight impact by hailstones, can be extensive internally while exhibiting low external visual detectability. Basic research studies have established methods for determining minimum aircraft skin thickness to be resistant from hailstone impacts. Fundamental study of ice behavior and properties enabled establishment of finite element based modeling simulation which accurately represents the ice during impact.
Conventional methods for evaluating blast loads on structures require the use of explosives and remote test facilities. Although detonating charges provides the most realistic test conditions for understanding blast effects, non-explosive techniques such as shock tubes and gas guns are popular alternatives to recreate (simulate) blast events in a safe, controlled lab environment. Some advantages include repeatable, consistent application of loads, no fire and debris cloud obscuring high speed camera observation, and limited shockwaves which can damage sensors and equipment. Generally, these non-explosive methods test smaller specimens and/or produce limited impulse levels. This research activity has developed a non-explosive methodology for applying representative blast loads onto large-sized (e.g., 610 x 610 mm or greater) flexible composite panels using fast (25 m/s) servo-hydraulic actuators tuned to match the specific impulse of an equivalent explosive charge. Control of the applied impulse loading and time-dependent characteristics of the pulse are controlled using “pulse-shaping” techniques and spatial-tuning of the impact mass distribution.