Abstract: Examples described herein relate to apparatuses and methods for predicting strength of a coupon of composite material. A first critical damage event and strain and stress distributions of the coupon is determined by performing a finite element analysis (FEA) of a finite element model of the coupon. The first critical damage event is associated with the strain and stress distributions. The strain and stress distributions are received as inputs to at least one surrogate model. A final load corresponding to a final failure of the coupon is determined using the at least one surrogate model.

Abstract: A method of forming a composite structure including coupling a plurality of components together forming a joint: wherein the plurality of components are oriented to form a radius gap therebetween: forming a filler structure that includes a closed cell foam core that has a porosity within a range defined between about 20 percent and about 40 percent by volume of the closed cell foam core and wherein the closed cell foam core is formed from a silicone-based material. The method also includes positioning the filler structure in the radius gap: and applying at least one of heat or pressure to the plurality of components and the filler structure.

Abstract: A method of analyzing the durability of a structure. Load-controlled testing is performed on samples of a composite material of the structure to relate critical strain invariants of the material to cyclic rates of strain invariant accumulation and frequencies associated with the cyclic rates. The material is characterized based on effective properties of the material, including the cyclic rates of strain invariant accumulation. Laminate properties and a geometrical definition of the structure are used to obtain a parametric model. Material characterizations are used to determine model element frequency responses to applied load conditions. Each element's frequency responses and critical strain invariants are used to determine whether damage is indicated at the element. Progression of damage is tracked and accounted for in the model.

Abstract: A method of predicting the strength characteristics of a composite laminate may include loading a structural model of a composite laminate formed of a material system. The method may additionally include comparing strain invariants from loading the composite laminate to critical strain invariant values of the material system. The method may also include identifying as a first significant event (FSE) a strain invariant of the matrix and/or the fibers reaching a critical strain invariant value.

Abstract: A composite structure is provided. The composite structure includes a plurality of components coupled together forming a joint, wherein the plurality of components are oriented such that a gap is defined at least partially therebetween. A filler structure is positioned in the gap, and the filler structure includes a closed cell foam core.

Abstract: A composite structure is provided. The composite structure includes a plurality of components coupled together forming a joint, wherein the plurality of components are oriented such that a gap is defined at least partially therebetween. A filler structure is positioned in the gap, and the filler structure includes a closed cell foam core.

Abstract: A method of predicting the strength characteristics of a composite laminate may include loading a structural model of a composite laminate formed of a material system. The method may additionally include comparing strain invariants from loading the composite laminate to critical strain invariant values of the material system. The method may also include identifying as a first significant event (FSE) a strain invariant of the matrix and/or the fibers reaching a critical strain invariant value.

Abstract: A composite structure is provided. The composite structure includes a plurality of components coupled together forming a joint, wherein the plurality of components are oriented such that a gap is defined at least partially therebetween. A filler structure is positioned in the gap, and the filler structure includes a closed cell foam core.

Abstract: A method of analyzing the durability of a structure. Load-controlled testing is performed on samples of a composite material of the structure to relate critical strain invariants of the material to cyclic rates of strain invariant accumulation and frequencies associated with the cyclic rates. The material is characterized based on effective properties of the material, including the cyclic rates of strain invariant accumulation. Laminate properties and a geometrical definition of the structure are used to obtain a parametric model. Material characterizations are used to determine model element frequency responses to applied load conditions. Each element's frequency responses and critical strain invariants are used to determine whether damage is indicated at the element. Progression of damage is tracked and accounted for in the model.

Abstract: A method of analyzing the durability of a structure. Load-controlled testing is performed on samples of a composite material of the structure to relate critical strain invariants of the material to cyclic rates of strain invariant accumulation and frequencies associated with the cyclic rates. The material is characterized based on effective properties of the material, including the cyclic rates of strain invariant accumulation. Laminate properties and a geometrical definition of the structure are used to obtain a parametric model. Material characterizations are used to determine model element frequency responses to applied load conditions. Each element's frequency responses and critical strain invariants are used to determine whether damage is indicated at the element. Progression of damage is tracked and accounted for in the model.

Abstract: A fiber reinforced resin composite includes a coating on the fibers that improves load transfer between the fibers and the surrounding resin matrix.

Abstract: A method of analyzing the durability of a structure. Load-controlled testing is performed on samples of a composite material of the structure to relate critical strain invariants of the material to cyclic rates of strain invariant accumulation and frequencies associated with the cyclic rates. The material is characterized based on effective properties of the material, including the cyclic rates of strain invariant accumulation. Laminate properties and a geometrical definition of the structure are used to obtain a parametric model. Material characterizations are used to determine model element frequency responses to applied load conditions. Each element's frequency responses and critical strain invariants are used to determine whether damage is indicated at the element. Progression of damage is tracked and accounted for in the model.

Abstract: Thermoplastic welding is an emerging technology targeted at significantly reducing the manufacture of aerospace structure by eliminating fasteners and the touch labor associated with fasteners to prepare, install, and inspect the assemblies. Thermoplastic welds, however, suffer from significant residual tensile strain caused by differences in the coefficient of thermal expansion between the carbon fiber reinforced composite laminates and the unreinforced weld. We alleviate this strain by adding fiber reinforcement to the weld using a structural susceptor which is a laminate of alternating layers of thermoplastic resin and fiber reinforcement sandwiching a conventional metal susceptor. A further advantage of the structural susceptor is the ability to peel it in selected locations to fill the gap between the laminates, eliminating costly profilometry of the faying surfaces and the associated problem of resin depletion where machining occurred to match the faying surfaces.

Abstract: Thermoplastic welds suffer from significant residual tensile strain caused by differences in the coefficient of thermal expansion between the carbon fiber reinforced composite laminates and the unreinforced weld. A structural susceptor alleviates this strain by adding fiber reinforcement to the weld. A structural susceptor is a laminate of alternating layers of thermoplastic resin and fiber reinforcement sandwiching a conventional metal susceptor. A further advantage of the structural susceptor is the ability to peel it in selected locations to fill the gap between the laminates, eliminating costly profilometry of the faying surfaces and the associated problem of resin depletion where machining occurred to match the faying surfaces.