INTERFACE MECHANICS OF LAYERED COMPOSITE BEAM-TYPE STRUCTURES
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In this study, improved analytical models are developed to characterize interface behavior of layered composite beam-type structures. The mechanics models of the bonded interface with and without adhesive layer are established, from which the interface fracture, delamination buckling, free vibration and stress analysis across the adhesive layer of corresponding interface are studied. By modeling an interface cracked bi-layer composite beam as two Timoshenko's sub-beams, elegantly simple but theoretically rigorous methods for computing the interface stresses and interface crack tip deformations are summarized, from which the distinguished levels of accuracy from different joint models in capturing the crack tip deformations are illustrated. Based on the flexible joint model, closed-form solutions of energy release rate (ERR) of four-point bending fracture specimens are first provided, and the experiment of wood-FRP bond interfaces under mode-II and mixed mode fracture is evaluated. An improved one-dimensional (1-D) analytical model is then developed to analyze the buckling behavior of a delaminated bi-layer composite beam-column. By accounting for the global deformations of the intact region, the present model is capable of capturing the buckling mode shape transitions from global, to global-local coexistent, and to local buckling for asymmetric delamination buckling as the interface delamination increases. An improved vibration analysis is further developed to evaluate the free vibration behavior of delaminated bi-layer composite beams. Besides including the delamination tip deformations, the contact and friction effects between the delaminated sub-layers are accounted for by employing the piecewise linear spring model and the linear bridging model. Frequencies and mode shapes are then solved through a boundary eigen-value problem. An improved adhesively-bonded joint model is finally proposed to study the interface stress distributions in the plated beams with moderately-thick adhesive layer. Both the shear and normal stresses along different adherend-adhesive interfaces are assumed to be different, and the adhesive layer is modeled as a simplified 2-D elastic continuum, from which the closed-form expressions of interface stresses are then obtained. The improvement of the proposed model over other existing theoretical models is demonstrated by disclosing the shear and normal stress variations across the adhesive thickness direction.