This study presents the first stage of a multi-scale numerical framework designed to predict the non-linear constitutive behavior of metal-composite interfaces in titanium-graphite fiber metal laminates. Scanning electron microscopy and x-ray diffraction techniques are used to characterize the baseline physical and chemical state of the interface. The physics of adhesion between the metal and polymer matrix composite components are then evaluated on the atomistic scale using molecular dynamics simulations. Interfacial mechanical properties are subsequently derived from these simulations using classical mechanics and thermodynamics. These molecular-level property predictions are used in a companion study to parameterize a continuum-level finite element model of the interface by means of a traction-separation constitutive law. Extension of the proposed approach to other dissimilar metal-or metal oxide-polymer interfaces is also discussed.

This article presents experimental and numerical results regarding the bolt bearing strength of titanium—graphite (TiGr) fiber metal laminate joints as a function of joint geometry, in particular the edge—distance ratio. The measured strength values are used to examine the influence of the laminate constituent materials and optimize the joint geometry. Additionally, a finite element model of the bolt bearing test procedure is introduced; incorporating a three-dimensional progressive failure constitutive model for the fiber-reinforced composite layers. Model validation is accomplished through comparison with experimentally obtained TiGr joint bearing results in terms of loading history, measured strength, and deformed sample geometry.

This paper presents a finite element model used to predict the bearing strength of hybrid titanium composite fibermetal laminates. The model is used to examine the effects of material parameters such as titanium content and edgedistance ratio on specific bearing strength. In addition, a three-dimensional progressive failure user material subroutine is implemented into the commercial finite element code ABAQUS to model stiffness degradation in the graphite-polyimide layers of the hybrid laminate. These results are used to optimize the fiber-metal laminate layup by determining to the ideal tradeoff between joint strength and structural weight.= characteristic element length E 11 = composite modulus along the fiber axis E 22 = composite modulus transverse to the fiber axis f fc = Hashin fiber compression failure initiation f ft = Hashin fiber tension failure initiation f mc = Hashin matrix compression failure initiation f mt = Hashin matrix tension failure initiation G f = fiber fracture energy G m = matrix fracture energy G 12 = shear modulus fiber-matrix direction G 23 = shear modulus for the matrix-matrix direction h = laminate thickness J = material Jacobian P b = bearing load S lt = shear strength for a unidirectional lamina S UD = undamaged material compliance matrix t = pseudotime value at the current finite element analysis increment u i = displacement measured at node (i) 12 = Poisson's ratio for the fiber-matrix direction 23 = Poisson's ratio for the matrix-matrix direction w fc = degradation variable for the fiber compression failure mode w ft = degradation variable for the fiber tension failure mode w mc = degradation variable for the matrix compression failure mode w mt = degradation variable for the matrix tension failure mode X c = compressive strength in the fiber direction for a unidirectional lamina X t = tensile strength in the fiber direction for a unidirectional lamina Y c = compressive strength transverse to the fiber direction for a unidirectional lamina Y t = tensile strength transverse to the fiber direction for a unidirectional lamina t = difference between successive pseudotime increments " = differential strain change between increments " ij = strain state " init ij = tensile strain component at failure " init ij = compressive strain component at failure b = bearing stress ij = stress state ys = yield strength

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This study presents a multiscale numerical framework designed to predict the nonlinear constitutive behavior of metal-composite interfaces in titanium-graphite fiber metal laminates. Molecular-level property predictions derived in a separate analysis are used to parameterize a finite element model of the interface by means of a traction-separation constitutive law. Additional continuum-level energy dissipation and progressive failure phenomena are implemented into commercial finite element software through a user-defined material subroutine. Results obtained from this multiscale interface model are compared against experimental measurements of titanium-graphite fiber metal laminates in a short-beam shear loading configuration. The model predictive accuracy and its application to other bonded metal-composite systems are subsequently discussed.