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Due to necessary of existence of access opening, inspection paths, installation, entrance and exit doors, etc, creation of cutouts on the vessel structure is unavoidable. On the other hand, composite structures and structural analysis is complex and create cutout and imperfection structure increase these complexity. The aim of this research is to determine the mechanical response of three cutout positions on composite pressure vessels under 30 bar external pressure, so that no buckling and fracture failure occurs. Also, the optimum composite vessel thickness for this condition and cutout effect has been determined in this study. The studied vessels are made from E-Glass fiber and Epoxy matrix. Finite element simulation used to investigate the parameters effect. For this reason, commercial ABAQUS software and linear and non-linear analysis carried out to examine the parameters. To evaluate the simulation results, two composite vessels manufactured and fractured under external pressure. Moreover, the final vessel with three cutouts tested under 30 bar external pressure. The concluded results show that the optimum thickness was 16 mm for vessel with three cutouts and create the cutouts led to decrease buckling pressure. Also, with increasing cutout size the percent of buckling pressure increased.

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ABSTRACT
Equal Channel Angular Pressing (ECAP) is one of the methods of refining and fine-graining metal materials. In this research, ECAP operation was performed on samples of 5182 alloy in 1 to 4 passes at ambient temperature. After implementation of the specimens through ECAP, prepared to obtain mechanical properties such as hardness, tensile and metallography. The results of these experiments showed that the mechanical properties of the packed materials through ECAP have improved compared to the normal state. Using a scanning microscope, it was observed that the average grain size decreased from 131 μm in the initial state to 745 nm after the ECAP process after the fourth pass. The results of hardness test also showed a 213% increase compared to normal.  The increase in yield stress after 4 passes is about 3 times. Finally, the crack growth of these materials under fatigue loading was compared with the non-ECAP mode by creating a suitable pre-crack. It was observed that crack growth is faster in ECAP materials and the failure surface is smoother compared to normal. Also, the deviation of the crack from its path in microstructure materials is less than normal. Finally, by comparing the Experimental results of crack growth with the results of numerical analysis, the accuracy of the numerical results is validated and confirmed.