Fragment Barrier Reports

SRI International is performing research under contract to FAA to protect critical aircraft components against fragments resulting from uncontained failure of a turbine engine. The following reports and papers in PDF format are available from this research:

1. "Lightweight Fragment Barriers for Commercial Aircraft" presented at the 18th International Symposium on Ballistics, San Antonio, Texas (November 1999) [680 Kb]
   The ballistic resistance of woven high-strength polymer fabrics to aircraft engine fragments was evaluated. Gas gun tests were performed to determine the relative effectiveness of Kevlar, Spectra, and Zylon and the effect on ballistic performance of fragment sharpness, fabric gripping conditions, and fabric areal density. A computational fabric model was constructed based on yarn geometry and properties and weave configuration. The model was implemented in LS-DYNA3D to simulate impact tests and elucidate the effect of yarn density and fabric gripping conditions. Full-scale tests on an aircraft fuselage section showed that a few plies of Zylon fabric glued to the insulation package within the fuselage wall.
    
2. "Full-Scale Tests of Lightweight Fragment Barriers on Commercial Aircraft", DOT/FAA/AR-99/71, (November 1999) [1.3 Mb]
   SRI performed full-scale fabric barrier tests on an aircraft fuselage at the Navy Air Warfare Center in China Lake, CA. The tests examined the effects of polymer material, number of plies, location of the fabric within the fuselage wall, and gripping arrangements.
    
3. "Improved Barriers to Turbine Engine Fragments: Interim Report I," DOT/FAA/AR-99/8, I, (June 1999) [10.0 Mb]
   The ballistic performance of various barriers of Zylon (polybenzoxazole, PBO) fabric was measured in gas gun tests using fragment simulating projectiles. Failure mechanisms and effects of multiple fabric plies and gripping mode were investigated. Absorbed kinetic energy appears to increase linearly with fabric areal density. It was found that a layer of fabric glued to the interior wall panel absorbed considerable energy at very low added weight. To assist in model development, quasi-static penetration tests were performed with a tensile machine in conjunction with a video camera to elucidate the phenomenology and evolution of fabric failure. Tensile properties of Zylon yarn were measured at several strain rates. The framework of a fabric model was constructed and simple impacts were simulated to demonstrate efficacy.
    
4. "Improved Barriers to Turbine Engine Fragments: Interim Report II," DOT/FAA/AR-99/8, II, (May 1999) [1.2 Mb]
   Several numerical problems were solved associated with modeling the crimped geometry and interaction of woven yarns. The model behaved properly in simple simulations of single yarn response to axial and transverse loads. Laboratory and field site tests were performed to provide data for developing and validating the computational model. The ballistic response of fabrics to fragment impact was evaluated, the phenomenology of fabric deformation and failure was elucidated in quasi-static penetration tests, and the tensile properties of yarns and fibers were measured. Three high-strength polymer materials were examined: PBO (Zylon), aramid (Kevlar), and polyethylene (Spectra).
    
5. "Improved Barriers to Turbine Engine Fragments: Interim Report III," DOT/FAA/AR-99/8, III, (May 2001) [20.5 Mb]
   Full-scale fragment impact tests on a commercial aircraft fuselage confirmed that barriers made from high-strength polymer fabrics in the fuselage wall could prevent penetration into the cabin. A computational capability is now being developed to enable efficient design of fabric fragment barriers. A mathematical model of woven fabric made from Zylon polybenzazoles (PBO), Kevlar, or Spectra was constructed using the data and observations from laboratory tests to measure yarn tensile and friction properties, quasi-static penetration tests to measure the evolution and phenomenology of fabric deformation and failure, and projectile impact tests to measure effects of fabric material, mesh density, boundary conditions (how a fabric is gripped), and projectile sharpness. The model was implemented in the LS-DYNA3D finite element code and used to simulate the failure behavior of yarns and fabrics under impact scenarios. The resulting insights are assisting barrier design. A simplified version of the computational model is being developed to enhance its usefulness to the commercial aircraft industry in designing engine fragment barriers.
    
6. "Improved Barriers to Turbine Engine Fragments: Interim Report IV," DOT/FAA/AR-99/8, IV, (June 2002) [3.7Mb]
   This interim technical report describes the progress made during year 3 of SRI International's Phase II effort to develop a computational capability for designing lightweight fragment barriers for commercial aircraft. Fabrics of high-strength polymers have been shown to be excellent candidates for these barriers. A series of large-scale fragment impact tests was performed at SRI.s remote test site to characterize the resistance of full-scale fabric barriers to realistic fragment impact and provide data for model calibration and verification. These tests have demonstrated the importance of allowing material failure to occur near the held corners of a fabric barrier, but not allowing the corner to detach from the fuselage frame. In addition, SRI designed and implemented laboratory tests to characterize the cut resistance of the fabric yarns to sharp blades. Results show a strong effect of the slicing angle upon the energy absorbed during yarn failure. Simulations using the detailed computational fabric model showed the effectiveness of holding the fabric at the corners. A time-efficient, user-friendly design model for fabric barriers is being developed. The model, previously calibrated against small-scale gas gun tests, was used to simulate the large-scale fabric impact tests. The results of the simulations showed that the current model is stiffer and stronger than the measured response of the fabric.
    
7. "Improved Barriers to Turbine Engine Fragments: Interim Report V," DOT/FAA/AR-99/8, V, (June 2002) [3.7Mb]
   This final annual technical report describes the progress made during year 4 of the SRI International Phase II effort to develop a computational capability for designing lightweight fragment barriers for commercial aircraft. Fabrics of high-strength polymers have proven to be excellent candidates for these barriers. Previous large-scale fragment impact testing of corner peg-mounted fabric barriers indicated that the failure of the fabric around the pegged hole was a significant factor in the barrier's effectiveness. Thus, SRI designed and implemented a laboratory test to characterize fabric failure behavior in the vicinity of a pegged hole. A series of these fabric corner failure tests in both Zylon and Kevlar fabrics determined that significant energy can be absorbed in corner tearing. These tests also showed the effects of various parameters on this energy. SRI then performed a second series of large-scale fragment impact tests at its remote test site, using stand-alone fabric barriers attached to a rigid frame through pegs near the four corners. The pegged corner holes were positioned far enough from the fabric edges to allow significant corner tearing without complete corner detachment. Tests revealed a relatively small effect of fragment roll angle and a large effect of impact location (with respect to the center of the barrier) upon the ballistic efficiency of the barrier. In some cases, Kevlar could be as effective as (or more effective than) Zylon, due to the larger fraction of impact energy consumed in producing corner tearing. A considerable database of large-scale fragment impact tests into Zylon and Kevlar fabric ballistic barriers is now available for fabric computational model refinement and verification.

   A simplified finite element fabric model has been developed for use as a design tool for choosing or evaluating parameters for fragment barriers. The design tool uses a continuum description of the fabric, and the calculations run quickly (about 10 min for a 3000-element simulation of a gas-gun test using 6 processors on a Linux cluster) and easily, allowing evaluation of changes in size of fabric, number of layers, and method of gripping. The reliability of the model was evaluated by performing computational simulations of push tests, laboratory gas gun impact tests, and large-scale impact tests of Zylon fabric. The computed deformation and failure behavior and the energy absorbed by the fabric during penetration agreed with measurements to within about 20% for most cases. This report also discusses limitations of the model in its current state.

8. "Finite Element Design Model for Ballistic Response of Woven Fabrics," presented at the 2001 International Ballistics Symposium, Interlaken, Switzerland [87 kb]
   A computational capability is described for designing lightweight fabric barrier systems to protect aircraft against fragments from an engine burst. A model of the deformation and failure of yarns and woven fabric under impact was developed, using data and observations from experiments. When implemented in the shell elements of the LS-DYNA3D finite element code, the model computed residual energies of fragments accelerated against fabric targets in agreement with measurements from laboratory gas gun tests. Computational simulations with this model can assist the engineer in specifying such design variables as yarn pitch, number of fabric plies, gripping conditions, and loads applied to the supporting structure.

Contact Us
Don Shockey
Director, Center for Fracture Physics
Phone: 650-859-2587
Email: donald.shockey@sri.com