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: 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: Methods, systems, and apparatuses for determining a flexibility value K of a fastener. An illustrative system includes a test apparatus including three straps with a strain gauge coupled to each strap. A fastener, such as a bolt, is installed through the straps, with a tensile or compressive force then applied to the test apparatus. Responsively, the strain gauges generate signals indicative of elastic deformation of the straps. The signals are transmitted to a signal processor, which may display deformation values, or alternatively, may process the signals to calculate the value K. The elastic deformation values acquired from the strain gauges, together with cross sectional area and elastic moduli of the straps, are entered into a calculation which applies a predetermined relationship to arrive at the value K. The test apparatus may be a stand-alone device for use in calculating the value K.

Abstract: A finite element method for predicting crack opening and propagation entails defining a succession of overlapping interface elements at a potential crack plane, each element having a bound node pair and side node pairs spaced from the bound node pair to sense approach of a crack. An energy-based fracture mechanics criterion determines whether release occurs at the bound nodes and, if so, the displacement between the bound nodes is calculated based on a strain softening law. The process is repeated for each element in sequence.

Abstract: A finite element method for predicting crack opening and propagation entails defining a succession of overlapping interface elements at a potential crack plane, each element having a bound node pair and side node pairs spaced from the bound node pair to sense approach of a crack. An energy-based fracture mechanics criterion determines whether release occurs at the bound nodes and, if so, the displacement between the bound nodes is calculated based on a strain softening law. The process is repeated for each element in sequence.