High kinetic energy absorption with low back face deformation ballistic composites
Viscoelastic, lightweight composite armor that is resistant to backface deformation, and to a method for evaluating the effectiveness of composite armor in resisting backface deformation. The index of retraction of a composite is determined by evaluating the degree of composite retraction at the site of impact of projectile after movement of the projectile is stopped. The degree of retraction indicates the ability of the composite to resist backface deformation.
1. A viscoelastic, deflection resistant fibrous composite panel comprising a consolidated plurality of non-woven fibrous plies, each of said non-woven fibrous plies comprising a plurality of fibers having a tenacity of at least 35 g/denier and said fibers having surfaces that are greater than 50% free of a fiber surface finish, wherein the fibers of said fibrous composite are coated with a viscoelastic binder material that comprises a polyurethane having a modulus of elasticity of 400 MPa to 2000 MPa, wherein said binder is bonded to the fiber surfaces, and wherein the composite has an index of retraction of at least 17% when impacted by a projectile having sufficient kinetic energy to cause a deflection of the panel at its impact site.
2. The composite panel of claim 1 wherein said fibers are ultra-high molecular weight polyethylene fibers.
3. The composite panel of claim 1 wherein the composite has an index of retraction of at least 23%.
4. The composite panel of claim 1 wherein the panel exhibits retractive behavior wherein the deflection of the panel at the impact site reaches a peak deflection and then partially retracts, wherein a ratio of the peak deflection to the amount of retraction is less than 6.0:1.
5. The composite panel of claim 1 wherein the panel has a short beam shear strength of at least 4 ksi for a composite having a binder content of less than 20 weight %, as determined by ASTM D2334.
6. The composite panel of claim 1 wherein the bond interface between the fiber surface and the viscoelastic binder material has an effective shear modulus of at least 50 MPa as determined by ASTM E143-13.
7. The composite panel of claim 1 wherein said composite panel has an in-plane shear strength between fibrous plies of from about 1 MPa to about 2 MPa.
8. The composite panel of claim 1 wherein said panel has an areal density of at least 1.0 lb/ft 2 and is capable of preventing the penetration of a rifle bullet projectile having an energy level of at least 1500 joules.
9. The composite panel of claim 1 wherein said fibers have been corona treated with an energy flux of from 2 Watts/ft 2 /min to 100 Watts/ft 2 /min.
10. The composite panel of claim 1 wherein said fibers have been plasma treated with an energy flux of 100 W/ft 2 /min or less.
11. A viscoelastic, deflection resistant fibrous composite panel comprising a consolidated plurality of non-woven fibrous plies, each of said non-woven fibrous plies comprising a plurality of fibers having a tenacity of at least 35 g/denier and said fibers having surfaces that are greater than 50% free of a fiber surface finish, wherein the fibers of said fibrous composite are coated with a viscoelastic binder material, wherein said binder is bonded to the fiber surfaces, and wherein the composite has an index of retraction of at least 17% when impacted by a projectile having sufficient kinetic energy to cause a deflection of the panel at its impact site, and wherein the viscoelastic binder material comprises a polyurethane having a modulus of elasticity of from 400 MPa to 2000 MPa, a tensile strength in the range of 10 to 100 MPa, and elongation at failure in the range of 30% to 400% at a temperature between 0° and 60° C. and at a relative humidity of between 0% and 100%.