AEROSPACE STRUCTURES

Impact experiments against a rigid barrier were performed on 1/7-scale models of a generic munitions structure to determine the environment to which the adaption kit (AK) is subjected in accidental axial and side impacts. In axial impacts, the AK experiences an oscillatory acceleration caused by bending vibration in the bulkhead plate to which the AK is attached, and a steady acceleration caused by axial plastic collapse of the shell structure. In side impacts, the shell and ring deform plastically near the impact point. At low speed (5 m/s), the load to the plate is dominated by the forces from one or two bolts that also deform plastically near the impact point. At high speeds, the load on the plate is dominated by the second (plastic) impact produced as the plate continues its forward motion into the inside surface of the shell.

Experiments were performed to determine the damage caused by impulsive loads on the surface of an aircraft fuselage. Both full-scale and 1/3-scale model fuselage sections were tested by first damaging them with explosive loading and then statically measuring the strength remaining in the damaged sections. The full-scale structures were right circular cylinders 4 ft in diameter and 4 ft long; the scale models were 16 in. in diameter and 16 in. long. Construction was semimonocoque with aluminum skin riveted to longitudinal stringers and circumferential frames. It was found that a load with 10% greater (scaled) impulse was required in the scaled experiments to produce damage that was similar to that produced in the full-scale experiments. In the static tests of the damaged cylinders, the remaining strength of the scale model was 13% less than that of the full-scale structures. The construction cost of a 1/3-scale model was approximately 1/8 that of a full-scale structure. Test costs were similarly reduced; one man could install the scale models on the test fixture, but a crane was needed with the full-scale cylinders.

Experiments were performed on 6061-T6 aluminum 30.5-cm-diameter cylindrical shells representing sections of a liquid-fueled booster using the spray-lead-at-target (SPLAT) technique to produce an impulsive load with a half-cosine distribution. Damage modes and critical loads were determined for unpressurized and pressurized shells with and without internal fluid for a range of radius-to-thickness ratios and length-to-diameter ratio. Sheet explosive tests were performed on 50-cm-diameter filament-wound composite bottles representing subscale solid-fueled rocket motors. The bottles were partially filled with an inert fuel simulant and pressurized to the nominal operating pressure. Critical response modes and lethal loads were determined as a function of case material, fuel thickness, and fuel geometry.