Structural composite material for acoustic damping

Abstract

A composite material for acoustic or mechanical damping, comprising a plurality of layers of fibrous material embedded in a solid material. The solid material layers are interspersed by perforated films of viscoelastic polymer.

1 . A composite material for acoustic or mechanical damping, comprising: a plurality of layers of fibrous material embedded in a structural matrix material; a layer of viscoelastic high polymer material between consecutive layers of fibrous material, said layer of viscoelastic polymer material being bonded to the adjacent layers of fibrous material embedded in the structural matrix material, characterized in that the layer of viscoelastic polymer material is perforated, whereby the structural matrix material is continuous through the perforations between the adjacent layers of fibrous material embedded in a structural matrix material.  
     
     
         2 . A composite material according to  claim 1  wherein the perforations occupy 5-50% of the area of the layer of viscoelastic polymerial material.  
     
     
         3 . A composite material according to  claim 1 , wherein the structural matrix material comprises a resin.  
     
     
         4 . A composite material according to  claim 1 , wherein the viscoelastic polymer material comprises one of: polyurethane, polyester, polyethylene, PVC and copolymers.  
     
     
         5 . A composite material according to  claim 1 , wherein the fibrous material is glass fiber matting.  
     
     
         6 . A composite material according to  claim 1 , wherein a pure epoxy/glass fiber or metal, layer is located on one surface of the composite material.  
     
     
         7 . A method for producing a composite material for acoustic or mechanical damping, comprising the steps of: 
 providing at least one first, fibrous, layer impregnated with a first structural matrix material;    stacking the at least one first, fibrous, layer on a former;    providing at least one second layer comprising a viscoelastic polymer material;    stacking the at least one second layer on the stack of the first, fibrous, layer(s);    providing at least one third, fibrous, layer impregnated with a second structural matrix material;    stacking the at least one third layer on the stack of first and second layers; and    simultaneously heating and compressing the resulting stack of first, second and third layers to cause the material of the second layer(s) to bond with the first and third layers, further comprising the step of perforating the second layer(s) prior to the step of stacking the second layer(s), whereby the structural matrix material is continuous through the perforations between the adjacent layers of fibrous material embedded in the structural matrix material.    
     
     
         8 . A method according to  claim 7  wherein the step of perforating comprises forming perforations with occupy 5-50% of the area of the second layer(s).  
     
     
         9 . A method according to  claim 7 , wherein the viscoelastic polymer film material comprises one of: polyurethane, polyester, polyethylene, PVC and copolymers.  
     
     
         10 . A method according to  claim 7 , wherein the step of heating and compressing is performed by enclosing the stack in a heat-shrinking material, and then heating the stack and the heat-shrinking material.  
     
     
         11 . A method according to  claim 10  wherein the heat shrinking material is polyamide tape.  
     
     
         12 . A method according to  claim 7 , wherein the first and/or second structural matrix material comprises an epoxy, polyester or phenolic resin; or polyurethane.  
     
     
         13 . A method according to  claim 7 , wherein the structural matrix material(s) includes thermo setting material, and the step of heating and compressing is effective to harden the thermosetting material.  
     
     
         14 . A method according to  claim 7 , wherein the fibrous layers comprise glass fiber matting.  
     
     
         15 . A method according to  claim 7 , further comprising the step of selecting the direction of the fibers and fiber types in the fibrous layers to provide a desired combination of structural strength, stiffness and damping properties.  
     
     
         16 . A method according to  claim 7 , further comprising the step of providing a pure epoxy/glass fiber or metal layer, on one surface of the composite material.  
     
     
         17 . A method according to  claim 7 , wherein the layer of viscoelastic polymer material comprises a thermoplastic material, and the heating and compressing step is effective to diffuse or intermingle the thermoplastic material into the structural matrix material.  
     
     
         18 .- 20 . (canceled)