AIRCRAFT ENGINE FRAGMENT BARRIERS

SRI International is performing research under contract to FAA to protect critical aircraft components against fragments resulting from uncontained failure of a turbine engine. As part of this program we are performing laboratory tests to characterize the response and overall strength of advanced materials for use in fragment barriers. The laboratory tests include gas gun impact tests, described below, as well as quasistatic penetration (push) tests and yarn material properties tests.

GAS GUN TESTS

In the gas gun tests, fragment-simulating impactors (weighing 25 to 100 g) were launched at velocities up to 100 m/s into targets roughly 6 in. (15 cm) square. Views from the high-speed camera recordings for two of these tests are shown below tests. The energy absorbed is calculated from the change in velocity of the impactor.

[215 Kb Quicktime Movie] 80 m/s impact into aircraft interior wall panel

[215 Kb Quicktime Movie] Same velocity with Zylon fabric glued to impact side of panel

BALLISTIC RESULTS FOR DIFFERENT MATERIALS

These tests demonstrated that aramids (Kevlar), polyethylenes (Spectra), and polybenzoxazole (Zylon) absorb more than 5 times more kinetic energy per weight than aluminum fuselage skin (Al-2024T3). The specific energy absorbed (SEA—which we define as the energy absorbed per unit areal density) of a typical Zylon weave was 15 times greater than that of aluminum!

Gas gun impact tests were performed to investigate the effect on the SEA of weave tightness, number of fabric plies, impactor sharpness, and fabric boundary conditions (how the fabric is held—tightly gripped on 2 or 4 edges, or glued to a rigid panel). How the fabric is gripped and the impactor sharpness strongly affects the SEA, as shown below for 25-g impactor at 80 m/s into single-ply Zylon 35x35 targets.

EFFECT OF FRAGMENT SHARPNESS AND
FABRIC GRIPPING CONDITIONS

These tests have shown the potential for implementing the fabric barriers in aircraft fuselages, and have aided in the development of a computational model for simulating impact and penetration of fabric targets. More detailed results of these tests, as well as some larger-scale fabric impact tests performed by SRI in conjunction with NAWC-China Lake, can be found the reports.