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The dynamic axial crushing response of circular tubes made of unidirectional carbon fiber‐epoxy composite was investigated numerically applying a new approach to the modeling of the delamination process. In the proposed approach, delamination (interface damage) was modeled by inserting isotropic resin plies capable of damage. They are tied to the adjacent laminae and replace the commonly used surface‐based cohesive model. Two multi‐layer models of laminated tubes having cross‐ply and angle‐ply stacking sequences were simulated using stacked conventional shell elements layers to capture the crushing response and intralaminar and interlayer damage of laminated tubes. The progressive failure analysis in Abaqus/Explicit was utilized to model the successive damage of both the interface and laminae. Both the intralaminar layers and isotropic resin layers were modeled by the conventional reduced integration shell element (S4R). The suggested modeling technique offers some advantages compared to the main‐stream interface modeling of the axial impact of laminated tubes. The computational cost is reduced and yet accurate predictions are obtained. The FE models based on the proposed delamination approach were validated by experimental test results obtained by the authors for cross‐ply and angle‐ply tubes subjected to a low‐velocity impact.

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In this study, vibration behavior of orthotropic cylindrical shells with variable thickness is investigated. Based on linear shell theory and applying energy method and using spline functions, free vibration relations are derived for shell with variable thickness and curvature. Frequency parameter and mode shapes are found after solving the frequency Eigenvalue equation. Effects of variable thickness along axial and circumferential directions of the shell on its frequency parameter are studied and compared against each other. Shell thickness is assumed to be varied in a parabolic profile along both directions. Also, frequency parameters for both circular and parabolic curvatures along circumferential direction are investigated and results are compared together. In addition, effect of variable thickness on the mode shapes is studied.