Abstract: A fastening system comprises a fastener, a washer, and a collar. The fastener has a shaft extending through a hole in a composite panel. The washer is concentrically positioned on the shaft between a head of the fastener and the composite panel. The washer comprises an enlarged bore facing the composite panel. The enlarged bore is one of a chamfered bore or a countersunk bore. The collar secures the fastener relative to the composite panel.

Abstract: An apparatus is provided for predicting propagation of a crack in a structure. A finite element model is provided that represents the layers of the structure by meshes of elements having interfaces defined between adjacent elements in orthogonal potential crack planes. Overlapping interface elements are defined at the interfaces and include a plurality of node pairs spaced apart along multiple interfaces and having a node cluster therebetween that includes bound node pairs. The nodes of each node pair are coincident with respective nodes of the adjacent elements on opposite sides of the interface. An analysis of the finite element model under an external load is performed in which a crack tip is established at a node cluster. A strain energy release rate between the nodes of the bound node pairs of the node cluster is calculated and based thereon propagation of the crack is identified.

Abstract: A fastening system comprises a fastener, a washer, and a collar. The fastener has a shaft extending through a hole in a composite panel. The washer is concentrically positioned on the shaft between a head of the fastener and the composite panel. The washer comprises an enlarged bore facing the composite panel. The enlarged bore is one of a chamfered bore or a countersunk bore. The collar secures the fastener relative to the composite panel.

Abstract: An open-channel stiffener for stiffening a panel has a bonding flange for bonding the stiffener to the panel through a bondline formed between the bonding flange and the panel to form a stiffened panel. The open-channel stiffener has a cross-sectional shape that aligns, or substantially aligns, a shear center of the stiffener with a centroid of the stiffener and aligns the shear center proximate an edge of the bondline, and removes the need for a radius filler noodle. A plurality of perforations may be formed through the bonding flange to permit an adhesive to wick into the perforations and create a mechanical interlock between the bonding flange and the panel.

Abstract: An apparatus is provided for finite element modeling and analysis of a structural product. A pre-processing system may produce a finite element model of a structural product including component parts joined by a fastener. The finite element model may represent the product by respective meshes of elements including shell or solid elements for the component parts, and beam and spring elements for the fastener in which at least one spring element has an axial offset from the shell or solid elements with respect to an axis of the fastener. A processing system may perform a finite element method (FEM) failure analysis of the finite element model under an external load that is transferable from the component parts to the fastener. The FEM failure analysis may produce an output that indicates a behavior of the fastener, and the FEM failure analysis may predict a component failure rate of the fastener based on the behavior.

Abstract: An open-channel stiffener for stiffening a panel has a bonding flange for bonding the stiffener to the panel through a bondline formed between the bonding flange and the panel to form a stiffened panel. The open-channel stiffener has a cross-sectional shape that aligns, or substantially aligns, a shear center of the stiffener with a centroid of the stiffener and aligns the shear center proximate an edge of the bondline, and removes the need for a radius filler noodle. A plurality of perforations may be formed through the bonding flange to permit an adhesive to wick into the perforations and create a mechanical interlock between the bonding flange and the panel.

Abstract: An apparatus is provided for predicting propagation of a crack in a structure. A finite element model is provided that represents the layers of the structure by meshes of elements having interfaces defined between adjacent elements in orthogonal potential crack planes. Overlapping interface elements are defined at the interfaces and include a plurality of node pairs spaced apart along multiple interfaces and having a node cluster therebetween that includes bound node pairs. The nodes of each node pair are coincident with respective nodes of the adjacent elements on opposite sides of the interface. An analysis of the finite element model under an external load is performed in which a crack tip is established at a node cluster. A strain energy release rate between the nodes of the bound node pairs of the node cluster is calculated and based thereon propagation of the crack is identified.

Abstract: An apparatus is provided for finite element modeling and analysis of a structural product. A pre-processing system may produce a finite element model of a structural product including component parts joined by a fastener. The finite element model may represent the product by respective meshes of elements including shell or solid elements for the component parts, and beam and spring elements for the fastener in which at least one spring element has an axial offset from the shell or solid elements with respect to an axis of the fastener. A processing system may perform a finite element method (FEM) failure analysis of the finite element model under an external load that is transferable from the component parts to the fastener. The FEM failure analysis may produce an output that indicates a behavior of the fastener, and the FEM failure analysis may predict a component failure rate of the fastener based on the behavior.

Abstract: A composite structure having a base charge and an outer channel charge is provided. The outer channel charge has an inner radius and an outer radius. A charge of plies adjacent to the inner radius reduces the inner radius.

Abstract: A composite structure having a base charge and an outer channel charge is provided. The outer channel charge has an inner radius and an outer radius. A charge of plies adjacent to the inner radius reduces the inner radius.