Aircraft Engine Fragment Barrier

Overview

ARA teamed with SRI International to perform research sponsored by the FAA to design barriers to protect critical aircraft components against fragments resulting from uncontained failure of a turbine engine. Review of DoD armor technology indicated that advanced high-strength polymers have the best combination of low weight and high ballistic resistance for practical barriers. We are using these advanced materials to develop practical fragment barriers in commercial aircraft by generating ballistic data and building computational capabilities for barrier design.

Laboratory impact experiments on high-strength polymer fabrics have helped establish the failure mechanism of fabrics and to conceptualize fragment barrier designs that mitigate the hazards of uncontained engine fragments. Experiments were also performed to measure the material and failure properties of yarns used to develop finite element models of fabric response. Large-scale fragment impact experiments on barrier structures were performed to verify the effectiveness of the barriers and to validate the computational model. As a results of this investigation, we expect to deliver to the FAA information and software on advanced materials that will enable airframers and others to design and evaluate lightweight engine fragment barriers.

Fragment Barrier Designs

The goal of this research is to develop the necessary technology to design and develop barriers capable of protecting critical aircraft components against fragments resulting from uncontained failure of a turbine engine. Fuselage impact tests examined the placement of high-strength fabric ballistic barriers within the fuselage walls, as shown in Figure 1, to mitigate the hazard from fragments released in an uncontained engine burst.

Migration Design Concept

Figure 2 illustrates the concept of hazard mitigation. The solid black line shows cumulative number of fragments above a given kinetic energy. There are many fragments with energies above 300 ft-lbs and only a few fragments with energies above 3,000 ft-lbs.

Fuselage impact experiments measured the effectiveness of the fuselage wall in stopping fragments. As shown by the light blue lines, the fuselage wall, at a weight of 1.48 lb/sq. ft., stops all fragments with energies below 350 ft-lbs. As shown by the pink lines, a single layer of zylon fabric, weighing only 0.03 lb/sq. ft., stopped fragments with energies below 750 ft-lbs. As shown by the dark blue lines, three layers of Zylon fabric, weighing only 0.10 lb/sq.ft., stopped fragments with energies as high as 3,600 ft-lbs. This was more than 10 times the amount of energy absorbed by the unfortified fuselage wall, at an increase in weight of only about six percent.

Figure 1 - Fragment Barrier Design.

Figure 2 - Mitigation Design Concept.