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Öğe Bending, buckling and free vibration analyses of shallow-to-deep FG curved sandwich beams using a global-local refined shear deformation theory(Elsevier Science Inc, 2023) Lezgy-Nazargah, M.; Karamanli, Armagan; Vo, Thuc P.This paper investigates the bending, vibration, and buckling behaviour of functionally graded (FG) curved sandwich beams using a global-local refined shear deformation theory. Material properties of these beams are varied through the thickness according to the power-law distribution. A beam element with a combination of Hermite cubic and quadratic Lagrange shape functions is developed to solve the problems. The obtained results are compared with the results from finite element software (ABAQUS), and other higher-order beam theories. It can be observed that the present model can predict accurately static, vibration, and buckling responses of both shallow and deep FG sandwich beams with arbitrary boundary conditions.Öğe Bending, buckling and free vibration behaviours of 2D functionally graded curved beams(Elsevier Science Inc, 2023) Karamanli, Armagan; Wattanasakulpong, Nuttawit; Lezgy-Nazargah, M.; Vo, Thuc P.The flexural, free vibration and buckling responses of 2D-FG curved beams with various shear deformation theories are presented by using finite element model. Their material properties via both directions (length and thickness) are varied with power-law distribution. A two-node beam element satisfying C1 continuity requirement is employed to solve the problems. Various problems including isotropic, 1D- and 2D-FG curved beams are analysed and the obtained results are verified with those available in the literature. Comprehensive parameter examinations are carried out to depict the effects of gradation indexes in both directions, open angles, end conditions and aspect ratios on structural behaviours of 2D-FG curved beams.Öğe Comprehensive analysis of bio-inspired laminated composites plates using a quasi-3D theory and higher order FE models(Elsevier Sci Ltd, 2024) Karamanli, Armagan; Vo, Thuc P.; Eltaher, Mohamed A.A comprehensive study is carried out by employing various finite element models (FEMs) for the bending, buckling stability and free vibration analyses of bio-inspired helicoidal composite plates with various lamination schemes. A higher order quasi-3D kinematic plate theory is developed to include a shear deformation effect. The variational formulation of the problem is exploited to derive the equations of motion, element stiffness, geometrical stiffness, and mass matrices based on a non-conforming rectangular element. Three different finite elements models are derived based on non-conforming elements with different number of nodes and degree of freedom. The developed finite element model has been validated with those found in the open literature. The effects of boundary condition, lamination scheme, orthotropy ratio and aspect ratio on the mechanical response of the bio-inspired helicoidal composite plates are examined. Notably, for the lamination schemes investigated in this study, no shear locking phenomenon was observed in the analyses conducted using these FEMs. Dimensionless centre deflections, critical buckling loads and fundamental frequencies of bio-inspired helicoidal composite plates vary depending on the type of lamination scheme, boundary condition and aspect ratio. The new orientation schemes can replace the traditional ones to overcome the shear singularity and overcome the delamination defects.Öğe Finite element formulation of metal foam microbeams via modified strain gradient theory(Springer Science and Business Media Deutschland GmbH, 2022) Karamanlı, Armağan; Vo, Thuc P.; Civalek, ÖmerSize-dependent behaviours of metal foam microbeams with three different porosity distribution models are studied in this paper. Based on the finite element model, a normal and shear deformation theory has been employed for the first time to investigate their structural behaviours by using modified strain gradient theory and considering the effects of variable material length scale parameter. The equations of motion and boundary conditions of system are derived from Hamilton’s principle. Finite element models are presented for the computation of deflections, vibration frequencies and buckling loads of the metal foam microbeams. The verification of proposed models is carried out with a comparison of the numerical results available in the literature. Calculations using the different parameters reveal the effects of the porosity parameters (distribution and coefficient), small size, boundary conditions and Poisson’s ratio on the displacements, frequencies and buckling loads of metal foam microbeams. Some benchmark results of these structures for both models (modified couple stress theory and modified strain gradient theory with constant and variable material length scale parameter) and with/without Poison’s effect are provided for future study. © 2022, The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature.Öğe Higher order finite element models for transient analysis of strain gradient functionally graded microplates(Elsevier, 2023) Karamanli, Armagan; Vo, Thuc P.; Civalek, OmerIn the study, three different higher order finite element models (HOFEMs) are developed to perform the transient analysis of functionally graded (FG) microplates subjected to different dynamic loads, namely, sinusoidally distributed step and exponential blast loads. A normal and shear deformable plate theory with five unknowns is used to present displacement field and modified strain gradient theory is employed for small-scale effect. A rectangular four-noded element and Newmark's method is used to solve transient analysis of FG microplates. The effects of boundary condition, type of dynamic loading, thickness to material length parameter, aspect ratio, gradient index and CPU time are investigated. It is found that two of the HOFEMs developed based on the C1 and C2 continuity requirements produced almost same numerical results. However, the one with 36 unknows per element yields slightly different results than the others. The HOFEM satisfying the C1 continuity requirement consumes the minimum computational time.Öğe Prediction compressive strength of cement-based mortar containing metakaolin using explainable Categorical Gradient Boosting model(Elsevier Ltd, 2022) Nguyen, Ngoc-Hien; Tong, Kien T.; Lee, Seunghye; Karamanlı, Armağan; Vo, Thuc P.Although machine learning models have been employed for the compressive strength (CS) of cement-based mortar containing metakaolin, it is difficult to understand how they work due to “black-box” nature. In order to explain the involved mechanism, Categorical Gradient Boosting (CatBoost) model with feature importance, feature interaction, partial dependence plot (PDP) and SHapley Additive exPlanations (SHAP) is proposed in this paper. A dataset consisting of 424 samples with six input variables is used to build the CatBoost model, which has optimal performance by tuning a set of seven hyper-parameters using sequential model-based optimization. Five quantitative measures (R2, MAE, RMSE, a10-, a20-index) are employed to evaluate the accuracy and the obtained results are superior to the previous study. It is from feature importance that the most significant input variable involving the CS is water-to-binder ratio, followed by age of specimen and cement grade. The strongest feature interaction is between water-to-binder ratio and metakaolin. A comprehensive parametric study is carried out via SHAP and PDP to investigate the effects of all input variables on the CS of cement-based mortar.Öğe Super learner machine-learning algorithms for compressive strength prediction of high performance concrete(John Wiley and Sons Inc, 2022) Lee, Seunghye; Nguyen, Ngoc-Hien; Karamanlı, Armağan; Lee, Jaehong; Vo, Thuc P.Because the proportion between the compressive strength of high-performance concrete (HPC) and its composition is highly nonlinear, more advanced regression methods are demanded to obtain better results. Super learner models, which are based on several ensemble methods including random forest regression (RFR), an adaptive boosting (AdaBoost), gradient boosting machine (GBM), extreme gradient boosting (XGBoost), light gradient boosting machine (LightGBM), categorical gradient Boosting (CatBoost), are used to solve this complicated problem. A grid search method is employed to determine the best set of hyper-parameters of each ensemble algorithm. Two super learner models, which combine all six models or select the top three effective ones as the base learners, are then proposed to develop an accurate approach to estimate the compressive strength of HPC. The results on four popular datasets show significant improvement of the proposed super learner models in terms of prediction accuracy. It also reveals that their trained models always perform better than other methods since their errors (MAE, MSE, RMSE) are always much lower and values of R2 are higher than those of the previous studies. The proposed super learner models can be used to provide a reliable tool for mixture design optimization of the HPC. © 2022 The Authors. Structural Concrete published by John Wiley & Sons Ltd on behalf of International Federation for Structural Concrete.Öğe Transient analysis of bio-inspired shear and normal deformable laminated composite plates using a higher-order finite element model(Taylor & Francis Inc, 2024) Karamanli, Armagan; Vo, Thuc P.; Eltaher, Mohamed A.A study based on the transient responses of bio-inspired helicoidal laminated composite plates is performed by using a higher-order finite element model (HOFEM) consisting of the thickness stretching effect. The obtained results show good agreement with those available in the open literature. The shear locking phenomena is not inspected by employing the developed HOFEM for the helicoidal lamination schemes. The effects of path of the concentrated moving load, lamination scheme, boundary condition, speed, aspect and orthotropy ratios on the transient responses are investigated. Dynamic dimensionless center deflections and dynamic amplification factors are affected by considering not only the lamination scheme but also the path of the load, boundary condition, orthotropy and aspect ratios.Öğe Transient dynamics of 2D-FG porous microplates under moving loads using higher order finite element model(Elsevier Ltd, 2023) Karamanlı, Armağan; Eltaher, Mohamed A.; Thai, Son; Vo, Thuc P.This study presents the higher order finite element model to explore the transient vibration of two-dimensional functionally graded (2D-FG) porous microplate under harmonic moving loads, that can be helped in design of nanoplate devices such as NEMS, nanofilters, nanoresonators, and nanoswitches. A normal and shear deformable plate theory with five unknowns is exploited with the modified couple stress theory to portray the kinematic relations, constitutive stress–strain equations, and size-dependence effect. This complicated problem is investigated for the first time based on Newmark's method to obtain time history analysis of 2D-FG porous microplates having in-plane inhomogeneity. In-plane displacements and stretching component of the transverse displacement are interpolated by using Bogner-Fox-Schmit rectangular element with four degrees of freedom (DOF) for each node satisfying the C1 continuity requirement. In addition, bending and shear components of the transverse displacement are presented by a nonconforming rectangular element with six DOF for each node satisfying the C2 continuity requirement. Various boundary conditions are considered to evaluate the influences of the thickness to material length parameter, aspect ratio, gradient index in two directions, material loss due to porosity in two directions, load velocity parameter and load excitation frequency ratio. It is revealed based on the results that dynamic deflections of 2D-FG porous microplates are significantly affected by the variation of the analysis parameters mentioned above. © 2022 Elsevier Ltd
