Due to light weight and high stiffness in bending, composite tubes are increasingly used in automobile, printing, sport and aerospace industries. Modeling and design of these tubes are the goal of this research. For this purpose, finite element analyses were performed by ABAQUS software. For analyses of these tubes a general knowledge about various failure criteria are required. These criteria are introduced in this thesis and among those; Puck criterion which is one of best failure theories of this materials is used. Besides this criterion, degradation equations have been implemented in UMAT subroutine that leads to a nonlinear solution. This nonlinear solution gives us a better behavior of composite material based on experimental parameters. Bending stiffness of laminated composite tubes is determined experimentally using four-point bending test. Effects of tube inner radius and stacking sequence and fiber orientation of the walled thickness laminate, 0° ply location and fiber material on bending stiffness and strength of composite tubes are studied. This project presents a unique and comprehensive comparison between the predictions of internationally recognized failure theories for fiber-reinforced polymer-composite laminates by the World-Wide Failure Exercise (WWFE). Whereby, 15 of the leading theories for predicting failure in composite laminates have been tested against experimental evidence. It is essential to distinguish between fiber failure and inter-fiber failure by separate failure criteria. After crack initiation, the stiffnesses of the affected plies degrade gradually with increasing load, until fiber fracture in one ply provokes ultimate failure of the laminate. Various theories and their originators or their colleagues are carefully selected to cover a wide range of lay-ups, materials and in-plane loading conditions. . When IFF occurs in a layer, the stiffness of this layer is lowered and part of its load is transferred to other layers of the laminate, leading that layer to higher stresses and potentially to further failure. The comparison has been performed through 14 carefully selected test cases by the World-Wide Failure Exercise, which includes biaxial strength envelopes for a range of unidirectional and multi-directional laminates, and stress–strain curves for a range of multi-directional laminates, loaded under uniaxial or biaxial conditions. The predictions and experimental data have been compared in a systematic and detailed manner, to identify the strengths and weaknesses of each theory, together with a ranking of the overall effectiveness of each theory.. Key words: Composite material, Puck criteria, Tube, FEA, ABAQUS, four-point bending test, subroutine, UMAT, degradation