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    A comparative study on crashworthiness of thin-walled tubes with functionally graded thickness under oblique impact loadings
    (Taylor and Francis Ltd., 2019) Baykasoğlu, Cengiz; Baykasoğlu, Adil; Tünay, Merve
    The main objective of this study is to investigate the effects of functionally graded thickness (FGT) patterns and cross-sectional shapes (i.e. circular, square and hexagonal) on crashworthiness performance of thin-walled tubes under multiple impact loading angles (0°–30°) by using the nonlinear explicit finite-element (FE) method. In order to show the efficiency of FGT tubes under different impact loading angles, the crashworthiness performances of the FGT tubes are also compared with their uniform thickness (UT) counterparts. At this point, the FGT and UT tubes are designed to have the same height, average cross-section area and weight. In addition, a multigene genetic programming (MGP)-based procedure is first time presented in literature for crashworthiness prediction of thin-walled structures under different impact loadings. To ensure the accuracy of the numerical models, the FE models are validated against both theoretical and experimental results in literature. The results demonstrated that the cross-sectional shapes, gradient exponents and impact loading angles effect the crashworthiness performances of thin-walled tubes, significantly. The simulation results showed that the FGT tubes have a superior crashworthiness performance compared to their UT counterparts especially at high impact loading angles due to the fact that FGT makes possible more folds to be formed and significantly increases the global buckling resistance of tubes. In particular, the SEA values of FGT tubes can reach 93% higher values than that of UT counterparts. The results also showed that the FGT tubes with square cross-section have generally lower energy absorption performance compared with circular and hexagonal ones. Especially, the square FGT tubes have up to 31% lower the SEA values than hexagonal and circular tubes. It is also revealed that the proposed MGP approach is able to predict the crashworthiness parameters with high accuracy. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.
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    Energy absorption of circular aluminium tubes with functionally graded thickness under axial impact loading
    (Taylor and Francis Ltd., 2015) Baykasoğlu, Cengiz; Tünay, Merve
    The main objective of this study is to investigate the effects of thickness-gradient patterns on energy absorption characteristics of aluminium-based circular tubes under axial impact loading. Functionally graded thickness (FGT) enables to obtain variable stiffness throughout the length of a structure; thus, it provides more efficient control of the crashworthiness parameters when compared with traditionally designed uniform thickness (UT) counterparts. In order to investigate the crash behaviour of FGT tubes, different thickness-gradient patterns are introduced to the axial direction of the tubes and then impact with a fixed rigid wall is simulated by using the nonlinear explicit finite element (FE) method. To show the efficiency of FGT tubes, crashworthiness performance of the FGT tubes are compared with their UT counterparts at the same weight. The effects of thickness range and aspect ratio of the tubes on their crash behaviours are also investigated. The simulation results show that the FGT tubes have superior crashworthiness performance than that of their UT counterparts and the crashworthiness parameters of the FGT tubes can be controlled and improved with the appropriate selection of geometric parameters of the tubes. © 2014 Taylor & Francis.