Methods for diverting lightning current from skin fasteners in composite, non-metallic structures

Patent metadata

Field	Value
Publication number	US-9912137-B2
Application number	US-201514875297-A
Country	US
Kind code	B2
Filing date	Oct 5, 2015
Priority date	Oct 5, 2015
Publication date	Mar 6, 2018
Grant date	Mar 6, 2018

Abstract

A multilayer composite structure with integrated fastener-to-conductive layer surface lightning protection interconnection employs a conductive layer with an inner surface and a plurality of chamfered recesses forming countersinks in an outer surface. A carbon-fiber reinforced plastic (CFRP) composite layer is disposed on the inner surface of the conductive layer and conforms to the surface shape. A plurality of holes extend through the plurality of chamfered recesses in the conductive layer and the adjoining CFRP composite layer in a manner such that the conductive layer defines a countersink portion extending into the openings of the plurality of holes. The chamfered recesses in the conductive layer provides an electrically conductive surface area that contacts conductive countersunk fasteners installed within the plurality of holes to enable current sharing between groups of neighboring fasteners.

First claim

What is claimed is:

1. A multilayer composite structure with integrated fastener-to-conductive layer surface lightning protection interconnection comprising:
a conductive layer, with a plurality of preshaped conical chamfered recesses with inner and outer surfaces forming countersinks; and
one or more carbon fiber reinforced plastic (CFRP) composite layers disposed on and conforming to the inner surface of the plurality of preshaped conical chamfered recesses of the conductive layer; and
a plurality of holes extending through the plurality of chamfered recesses in the conductive layer and the adjoining CFRP composite layer in a manner such that each of the plurality of preshaped conical chamfered recesses in the conductive layer defines a countersink portion extending into openings of related holes in the plurality of holes,
whereby extension of the conductive layer into the preshaped conical chamfered recesses provide an electrically conductive surface area defining conical countersinks extending into each hole that contacts heads of conductive countersunk fasteners installed within the plurality of holes.

2. The multilayer composite structure with integrated fastener-to-conductive layer surface lightning protection interconnection as defined in claim 1 further comprising a fiberglass or surfacing film layer cocured over the outer surface of the conductive layer, said fiberglass or surfacing film layer removed from the preshaped conical chamfered recesses.

3. The multilayer composite structure with integrated fastener-to-conductive layer surface lightning protection interconnection as defined in claim 1 further comprising an adhesive layer integrated with the conductive layer between the conductive layer and the CFRP composite layer, said conductive layer, adhesive layer and the CFRP composite layer cocured on a shaped tool.

4. The multilayer composite structure with integrated fastener-to-conductive layer surface lightning protection interconnection as defined in claim 1 further comprising a plurality of conical washers inserted into the chamfered recesses.

5. The multilayer composite structure with integrated fastener-to-conductive layer surface lightning protection interconnection as defined in claim 4 wherein a conical head of each fastener conductively engages each conical washer.

6. The multilayer composite structure with integrated fastener-to-conductive layer surface lightning protection interconnection as defined in claim 1 wherein the conductive layer comprises a wire mesh.

7. The multilayer composite structure with integrated fastener-to-conductive layer surface lightning protection interconnection as defined in claim 6 wherein the wire mesh comprises an expanded metal foil, selected from the set of copper, nickel or aluminum.

8. The multilayer composite structure with integrated fastener-to-conductive layer surface lightning protection interconnection as defined in claim 7 wherein the expanded metal foil has thickness from 0.001 to 0.005 inch.

9. A multilayer composite structure with integrated fastener-to-conductive layer surface lightning protection interconnection comprising:
a conductive layer, with a plurality of preshaped conical chamfered recesses with inner and outer surfaces forming countersinks; and
one or more carbon fiber reinforced plastic (CFRP) composite layers disposed on and conforming to the inner surface of the plurality of preshaped conical chamfered recesses of the conductive layer; and

a plurality of holes extending through the plurality of chamfered recesses in the conductive layer and the adjoining CFRP composite layer in a manner such that each preshaped conical chamfered recesses in the conductive layer defines a countersink portion extending into openings of the plurality of holes, wherein the plurality of holes are sized to receive shafts of a plurality of fasteners in a clearance fit;
whereby the preshaped conical chamfered recesses in the conductive layer provide an electrically conductive surface area that contacts heads of conductive countersunk fasteners installed within the plurality of holes, said clearance fit of the shafts and holes encouraging current transition at the heads of the conductive countersunk fasteners to the conductive layer through higher resistance due to the clearance fit between the shafts and composite layers adjacent the shafts.

10. An integrated fastener surface lightning protection interconnection comprising:
a carbon fiber reinforced plastic (CFRP) composite structure having a hole with a countersink;
a conical washer inserted in the countersink wherein the conical washer has a thickness of 0.001 to 0.005 inch; and:
a fastener received with a clearance fit in the hole, a conical head of the fastener conductively engaging the conical washer wherein the fastener head is titanium and the conical washer is corrosion resistant steel (CRES) whereby any electrical discharge attaching to the head of the fastener is dissipated in a discharge path primarily through the composite layers in an outer portion of the composite structure extending adjacent from the fastener head.

11. A method of forming a multilayer composite structure with integrated fastener-to-conductive layer surface lightning protection interconnection comprising the steps of:
laying a conductive layer over a tool having a plurality of raised conical-shaped features, to form a plurality of preshaped chamfered recesses in the conductive layer with inner and outer surfaces forming countersinks;
laying at least one carbon-fiber reinforced plastic (CFRP) composite layer over the conductive layer conforming to the inner surface of the plurality of preshaped conical chamfered recesses of the conductive layer;
cocuring the CFRP and conductive layer on the tool;
machining a plurality of holes through the plurality of preshaped conical chamfered recesses in the conductive layer and the adjoining composite layer in a manner such that the preshaped conical chamfered recesses in the conductive layer define countersinks extending into openings of the plurality of holes and exposes a conductive surface of the conductive layer; and,
inserting fasteners into the plurality of holes;
wherein the extensions of the conductive layer into the preshaped conical chamfered recesses in the countersinks in the conductive layer provides an electrically conductive surface area defining conical countersinks extending into each hole that contacts the conductive countersunk heads of the fasteners installed within the plurality of holes.

12. The method as defined in claim 11 wherein the conductive layer comprises a wire mesh and further comprising laying an adhesive layer between the wire mesh and the at least one CFRP layer.

13. The method as defined in claim 12 wherein the wire mesh wherein the conical washer has a thickness of between 0.001 and 0.005 inches.

14. The method as defined in claim 11 further comprising inserting conical washers into the chamfered recesses prior to inserting the fasteners into the plurality of holes.

15. The method as defined in claim 11 wherein the step of machining a plurality of holes comprises machining a plurality of holes for clearance fit of fasteners.

16. A method of forming a multilayer composite structure with integrated fastener-to-conductive layer surface lightning protection interconnection comprising the steps of:
laying a fiberglass layer on a tool having a plurality of raised conical-shaped features;
laying a wire-mesh conductive layer over the fiberglass layer, to form a plurality of chamfered recesses in the wire-mesh condu

Assignees

• Boeing Co

Inventors

• Le Quynhgiao
• Morgan Jeffrey Denys
• Greegor Robert B
• Whiting Brent A

Classifications

• B29C70/545 Primary

  Perforating, cutting or machining during or after moulding · CPC title

• B32B7/12

  using interposed adhesives or interposed materials with bonding properties · CPC title

• H02G13/80 Primary

  Discharge by conduction or dissipation, e.g. rods, arresters, spark gaps · CPC title

• F16B37/14

  Cap nuts; Nut caps or bolt caps · CPC title

• B32B2605/18

  Aircraft · CPC title