Composite Structures Having Bondlines with Matched Electrical Conductivity

Abstract

Two composite laminates are joined together by a bondline having portions exposed to the ambient environment. The bondline contains scrim having an electrical conductivity and impedance matched to that of the laminates in order to mitigate effects of lightning strikes.

What is claimed is: 
     
         1 . A composite laminate structure, comprising:
 first and second fiber reinforced plastic resin laminates each having an electrical impedance; and   a structural bondline joining the first and second laminates together, the bondline having an electrical impedance substantially matching the electrical impedance of the first and second laminates.   
     
     
         2 . The composite laminate structure of  claim 1 , wherein:
 the fiber reinforcement in each of the first and second fiber reinforced plastic resin laminates are carbon fibers, and   the structural bondline includes an adhesively impregnated scrim having an electrical impedance that substantially matches the electrical impedance of the first and second laminates.   
     
     
         3 . The composite laminate structure of  claim 1 , wherein at least a portion of the structural bondline is exposed to an ambient environment. 
     
     
         4 . The composite laminate structure of  claim 1 , wherein the first and second laminates and the structural bondline form a T-joint. 
     
     
         5 . The composite laminate structure of  claim 1 , wherein:
 the first and second laminates form part of a fuel tank having an open interior, and   a portion of the structural bondline is exposed to the open interior of the fuel tank.   
     
     
         6 . The composite laminate structure of  claim 1 , wherein the structural bondline includes an adhesively impregnated scrim having an AC conductivity that substantially matches the AC conductivity of the first and second laminates. 
     
     
         7 . A composite laminate structure, comprising:
 a first carbon fiber reinforced plastic laminate having a first electrical impedance;   a second carbon fiber reinforced plastic laminate having a second electrical impedance substantially matching the first electrical impedance; and   an adhesive bondline between the first and second laminates, the adhesive bond including an adhesive and a scrim having a third electrical impedance substantially matching the first and second electrical impedances.   
     
     
         8 . The composite laminate structure of  claim 7 , wherein:
 the first and second laminates form part of a fuel tank having an open interior adapted to store fuel, and   a portion of the adhesive bondline is exposed to the open interior of the fuel tank.   
     
     
         9 . The composite laminate structure of  claim 7 , wherein the first and second laminates and the adhesive bondline form a T-joint. 
     
     
         10 . The composite laminate structure of  claim 7 , wherein:
 each of the first, second and third electrical impedances include a resistive component and a reactive component,   the resistive components are substantially equal, and   the reactive components are substantially equal.   
     
     
         11 . The composite laminate structure of  claim 7 , wherein the scrim is formed of carbon fibers. 
     
     
         12 . The composite laminate structure of  claim 7 , wherein the first and second laminates and the bondline have substantially the same AC conductivity. 
     
     
         13 . A composite aircraft fuel tank having lightning protection, comprising:
 at least a first carbon fiber reinforced plastic laminate wall;   at least a second carbon fiber reinforced plastic laminate wall;   an adhesive bondline joining the first and second laminate walls, the adhesive bondline including an electrically conductive scrim having an electrical impedance substantially matching the electrical impedance of each of the first and second laminate walls.   
     
     
         14 . The composite aircraft fuel tank of  claim 13 , wherein at least a portion of the adhesive bondline is adapted to be exposed to fuel vapors within the fuel tank. 
     
     
         15 . A method of providing lightning protection of for a bond joint between two cured carbon fiber reinforced plastic laminates, comprising:
 installing scrim in the bond joint having an electrical impedance that substantially matches the electrical impedance each of the two carbon fiber reinforced plastic laminates.   
     
     
         16 . The method of  claim 15 , wherein installing the scrim includes impregnating the scrim with an adhesive. 
     
     
         17 . The method of  claim 16 , wherein the adhesive is one of a film adhesive and a paste adhesive. 
     
     
         18 . The method of  claim 15  wherein the scrim is formed of carbon fibers. 
     
     
         19 . The method of  claim 15 , wherein the laminates and the scrim possess substantially the same electrical conductivity. 
     
     
         20 . The method of  claim 16 , wherein installing the scrim in the bond joint includes:
 assembling the two laminates in a T-shaped configuration, and   placing the scrim between an edge of one of the two laminates, and a face of the other of the two laminates.   
     
     
         21 . An aircraft fuel tank having a exposed bond joint produced by the method of  claim 15 . 
     
     
         22 . A method of reducing the electrical potential across an exposed bondline between two carbon fiber reinforced plastic laminates, comprising:
 determining the electrical conductivity of each of the two laminates;   selecting a scrim having an electrical conductivity substantially matching the determined electrical conductivity of each of the two laminates;   installing the scrim and an adhesive between the two laminates;   curing the adhesive.   
     
     
         23 . A method of fabricating a composite structure having an exposed bond protected against lightning strikes, comprising:
 laying up first and second carbon fiber reinforced plastic pre-preg laminates;   curing the first and second pre-preg laminates;   joining the first and second cured laminates with a bond joint, including
 selecting a scrim having an electrical impedance substantially matching the electrical impedance of each of the first and second laminates, 
 impregnating the scrim with a bonding adhesive, 
 installing the impregnated scrim between the first and second laminates to form a bondline, and 
 curing the adhesive.