Mcdonnell Douglas Corporation

Eugene R Speakman

In this fastening system two or more layers of material are fastened together by inserting a hollow sleeved fastener such as a rivet or a bolt into the hole in a high interference fit to expand the hole radially. The sleeve is configured either as a collar and a straight shank or as an angled upper portion combined with a shank for counterbored applications. The intersections between either the collar and the shank or the angle portion and the staight shank are designed with an enlarged radius such that when the sleeve is expanded after the insertion of the fastener inside of it, this radius is expanded, which in turn stress coins the adjacent edge of the hole in the layers. This localized stress coining as well as the hoop stress in the hole surrounding the hole dramatically increases the fatigue strength of the fastened layers in a structure assembly.

Interference fit bolt and sleeve

In this fastening system two or more layers of material are fastened together by inserting a hollow sleeved fastener such as a rivet or a bolt into the hole in a high interference fit to expand the hole radially. The sleeve is configured either as a collar and a straight shank or as an angled upper portion combined with a shank for counterbored applications. The intersections between either the collar and the shank or the angle portion and the straight shank are designed with an enlarged radius such that when the sleeve is expanded after the insertion of the fastener inside of it, this radius is expanded, which in turn stress coins the adjacent edge of the hole in the layers. This localized stress coining as well as the hoop stress in the hole surrounding the hole dramatically increases the fatigue strength of the fastened layers in a structure assembly.

Method of installing interference fit sleeved fasteners having radiused

This interference fit bearing is divided into an outer and an inner bearing assembly. The outer bearing assembly has an outside radial dimension measured from the center of the bearing which is at least 0.002 inches larger than the opening into which it will be interference fit. The inside radial dimension of the outer bearing assembly will be larger than the outer radial dimension of the inner bearing assembly prior to insertion of the bearing into the receiving hole in the interference fit. When the outer and inner bearing assemblies of the interference fit bearing are pressed into the hole in the receiving load bearing element, the compression of the bearing by the receiving hole will act to force the outer bearing assembly into the proper tolerance fit with the inner bearing assembly of the bearing. At the same time the receiving hole is prestressed by the interference fit which will dramatically decrease fretting and stress corrosion which would otherwise occur under cyclic loads in the load bearing element at its interface with the bearing.

Interference fit bearings

A stress coining tool for fatigue life extension of the wall of an aperture in a metallic structural member, in the form of a rigid elongated member having a plurality of annular olive-like protuberances of a progressively larger diameter from one end of the member, and an additional olive-like protuberance of a smaller diameter than the largest protuberance, such additional protuberance located on the opposite side of the largest protuberance from the other protuberances. The diameter of the largest annular protuberance is such that the material forming the wall of the aperture is displaced radially elastically and plastically an amount to provide stress coining and to minimize stress concentration in the wall of the aperture. The additional olive-like protuberance to the rear of the largest protuberance is of a diameter such that the latter protuberance functions as a guide to permit passage of the tool back through the aperture without causing any further plastic deformation of the wall of the aperture. The elongated member is provided with a serrated pole stem which permits attachment of the tool to a rivet gun in conjunction with a mechanism thereon for rapid force vibration of the tool to impact it through the aperture, and then to impact it back through the aperture.

Stress-coining apparatus and method

Liner bushings and bearing assemblies are securely captured within their receiving holes by a new staking system. The inner and outer surfaces of the webs of metal adjacent the actual staking groove which are to be bent over or staked are fabricated such that these surfaces are substantially parallel to each other over the majority of the surfaces. The staking process is advantageously accomplished by use of a self-aligning staking anvil which has a gap in its circumference in order that the tool may conform exactly to the staking groove. Additionally a master matching gauge ensures proper installation.

Staking system

Fretting caused by movement of adjacent structural members at high stress is prevented by providing a tetrafluoroethylene layer between the moving surfaces. The tetrafluoroethylene may be applied directly to the mating surfaces of parts or on the surfaces of shim stock inserted therebetween.

Structure to retard fretting and method of manufacture

A rivet for joining a plurality of structural members having a cylindrical shank and a head with a conical undersurface, flared uniformly outwardly from the shank, an upper surface that is generally similar to the minor portion of a filled torus, sliced normal to its centerline and an outer edge therebetween which is rounded adjacent the conical undersurface and cylindrical adjacent the upper surface. When being installed in a workpiece aperture to form a joint, the rivet head coldflows to assume adequate expansion into the aperture while becoming generally flush to the workpiece surface so rivet head shaving is not required.

Crowned flush head rivet

A stress coining fastened joint, for minimizing stress concentration in a wall of an aperture in a metallic structural member, the tool being a rigid elongated shaft adapted for forcible insertion through the aperture. The shaft has end portions and is provided with a plurality of different diameter, annular protuberances spaced intermediate the end portions. The largest of the protuberances has a diameter of such predetermined relationship to the diameter of the aperture, that upon a forced insertion thereof through the aperture the material forming the wall of the aperture is displaced radially substantially the difference between the diameter of the largest protuberance and the diameter of the aperture. The displaced material will thereafter rebound approximately one-half of the initial displacement. The stress coining tool may be combined with a conventional fastener to provide a simultaneous stress coining and fastening operation.

Stress coining tool fastened joint

A bushing for use in high strength materials where fatigue failure is a problem. The bushing is cylindrical and includes a circumferential lubrication groove on its inner surface while fillets and smooth transition surfaces are used to transition between the major cylindrical surfaces of the bushing and the housing. The bushing is pressed into the housing which is an interference fit therewith to reduce stress concentrations. Lubricant is provided to the circumferential lubrication groove by means of a passageway which may include a smooth wall annulus placed in a stepped hole in the housing and retained in the hole by a hollow screw which extends to the area of lubrication. A standard lubrication fitting is threaded into the annulus to provide means for connection to conventional lubricant supplying apparatus.

Fatigue bushing assembly

A riveted joint employing a rivet having a cylindrical shank and a head with a conical undersurface, flared uniformly outwardly from the shank and truncated by an upper surface that is generally similar to the minor portion of a filled torus, sliced normal to its centerline. When being installed in a workpiece aperture to form the joint, the rivet head cold-flows to assume adequate expansion into the aperture while becoming generally flush to the workpiece surface so rivet head shaving is not required.

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Fullerton, CA, United States of America

Eugene R Speakman