Sarp Adali | University of KwaZulu-Natal (original) (raw)
Papers by Sarp Adali
SN applied sciences, Mar 6, 2023
Composite Structures, May 1, 2020
Abstract The present study focuses on the mechanical and absorption properties of composites rein... more Abstract The present study focuses on the mechanical and absorption properties of composites reinforced by achatina fulica snail (S-shell) and eggshell particles (E-shell). Epoxy composites of snail and eggshell particles were prepared separately with the filler content ranging from 5 to 20% by weight. Hybrid composites of both fillers were also prepared and assessed. Specimens of the composites and hybrid composites with different percentage weights of the reinforcing materials were fabricated using the resin casting method. Mechanical properties such as tensile strength, Young’s modulus, impact strength, hardness and water absorption properties of the specimens were evaluated experimentally. It was observed that the addition of shell particles improves the mechanical properties of neat epoxy irrespective of the percentage weight of the reinforcement. The mechanical and water absorption properties of composites and hybrid composites varied depending on the amount of the reinforcement. Significantly, hybrid reinforcement by S-shell and E-shell particles offered superior properties in most cases. High percentage weight of calcium carbonate in these naturally sourced fillers and the synergistic effect of the S-shell and E-shells particle fillers can be attributed to high strength, stiffness, and decrease in water uptake of the composites.
WIT transactions on engineering sciences, 1970
Journal of Nanomaterials, Jul 4, 2020
Journal of Bio- and Tribo-Corrosion, Feb 12, 2020
Composites Part C: Open Access
Computer-Aided Civil and Infrastructure Engineering, 1995
ABSTRACT Multiobjective design of a laminated cylindrical shell is obtained with the objectives d... more ABSTRACT Multiobjective design of a laminated cylindrical shell is obtained with the objectives defined as the maximization of axial load and external and internal pressures subject to a strength constraint. The failure under axial load and external pressure may occur by buckling. The ply angle is taken as the design variable. The weighted global criterion method is employed to solve the vector-optimization problem, which involves minimization of the distance to ideal solution vector in L2 metric. A symmetrically laminated and balanced shell is considered as an example. Pareto optimal solutions are given for two- and three-objective design problems, and numerical results are presented in the form of tradeoff curves and surfaces. The effects of problem parameters are investigated, and the results are given for various weighting factors and shape parameters.
Composite Structures, 2000
... field expressible as (8). in which ζ represents x in the two-dimensional problem in ... A fin... more ... field expressible as (8). in which ζ represents x in the two-dimensional problem in ... A finite difference procedure was developed to determine the transient, radially-varying ambient temperature ...Numerical results for the benchmark problem indicate that the third-order theory yields ...
SN applied sciences, Mar 6, 2023
Springer eBooks, 1987
A first-ply failure analysis is given for a symmetric, cross-ply laminate of elliptic shape subje... more A first-ply failure analysis is given for a symmetric, cross-ply laminate of elliptic shape subject to flexural loads. In particular, clamped elliptic laminates under a uniformly distributed load are treated. The effects of fibre type and content, voids and hygrothermal conditions are investigated on the failure load and its location by means of micromechanical relations from which elastic and strength properties of the composite are computed. Numerical results are given in graphical form with a view towards the design of elliptic laminates by means of parametric studies.
International Journal of Mechanical Sciences, Mar 1, 2016
Journal of mechanisms, transmissions, and automation in design, Jun 1, 1983
An antisymmetrically laminated angle-ply plate is optimized with the objectives of minimizing the... more An antisymmetrically laminated angle-ply plate is optimized with the objectives of minimizing the maximum dynamic deflection, maximizing the natural frequencies and/or maximizing the buckling load. The design variables are the fiber orientation and the thickness of individual layers and are computed by using the methods of nonlinear programming. The concept of Pareto optimality is used in formulating the design problem and in reducing the multiple objectives into a single performance index. Numerical results are presented in the form of optimal tradeoff curves which allow the designer to assess the various possibilities open to him before deciding on a certain design. In this sense, the present design is an interactive process.
Journal of Applied Physics, Nov 15, 1995
The processes of crack growth and dislocation emission induced by the crack tip are investigated.... more The processes of crack growth and dislocation emission induced by the crack tip are investigated. A crystal with cubic lattice of atoms under plane strain conditions is considered. The main principles of the nanofracture mechanics approach employed in this study are outlined. Both ductile and brittle mechanisms of crack growth in the crystal are examined in nano- or interatomic scale. Only the fundamental constants of the classical theory of dislocations are used which include the interatomic spacing, elastic constants, the Schmid friction constant, and the true surface energy of crystal lattice. The efficient solution of the elastic problem for an arbitrary number of dislocations near the crack tip is obtained in terms of complex potential functions. The equilibrium of dislocation pairs near the crack tip during monotonic loading is investigated. It is shown that dislocation generation at the crack tip occurs at certain quantum levels of external load. The magnitude of external load corresponding to crack growth initiation and emission of the first pair of dislocations is calculated. The mathematical problem for an arbitrary N number of dislocation pairs near the crack tip is reduced to a parametric system of N nonlinear equations, where the stress intensity factor of external load KI plays the role of parameter and N the role of discrete time. The minimum value of KI at which the solution of this system of equations exists corresponds to the stress intensity factor at which the Nth pair of dislocations is generated. The numerical method is presented to determine the minimum value of KI. The approximate method of self-consistent field is employed to reduce the order of the system of nonlinear equations. The approximate method is used to calculate the fracture curve KI(lc) relating the value of KI which maintains the crack growth to the crack length increment lc. The exact solution is also studied, and numerical results are given for a crack in an aluminum specimen and involve the quantum levels of external load corresponding to the moments of dislocation generation and the values of the superfine stress intensity factor up to 150 dislocations.
7th AIAA/USAF/NASA/ISSMO Symposium on Multidisciplinary Analysis and Optimization, Aug 22, 1998
Multilayered composite discs rotating with a constant angular velocity are optimized with the obj... more Multilayered composite discs rotating with a constant angular velocity are optimized with the objective of maximizing the rotational speed by determining the fibre orientations and the lamination optimally. The effect of a temperature field is taken into account in the optimization. The design is required to satisfy a given non—failure criterion and in the present study the failure is determined on the basis of first ply failure using the Tsai—Wu strength criterion. Various boundary conditions are considered with the force or displacement conditions being specified on the inner and outer boundaries of the discs. In particular explicit solutions are obtained for free—free, fixed—free and free-fixed boundaries. The discs are modelled as symmetrical and balanced laminates with angle—ply and/or cross—ply layers. Numerical results are given for different combinations of cross—ply and angle—ply laminations. It is shown that the optimal lamination (combination of cross—ply or angle-ply layers) and the optimal fibre orientations depend largely on the boundary conditions and in some cases on the thermal loading.
5th Symposium on Multidisciplinary Analysis and Optimization, Aug 22, 1994
Quite often the values of the elastic constants of composite materials can be estimated with some... more Quite often the values of the elastic constants of composite materials can be estimated with some error due to manufacturing imperfections, defects and misalignments. This introduces some level of uncertainty in the computation of the buckling loads, frequencies, etc. In the present study an ellipsoidal convex model is employed to study the buckling of long cross-ply cylinders subject to external pressure with the material properties displaying uncertain-but-bounded variations around their nominal values. This approach determines the lowest buckling pressure and as such provides a conservative answer. Method of Lagrange multipliers is applied to compute the worst-case variations of the elastic constants and an explicit expression is obtained for the critical buckling pressure for a given level of uncertainty. Expressions for the relative sensitivities of the buckling pressure to uncertain elastic constants are derived.Copyright © 2013 by ASME
Journal of structural mechanics, 1981
ABSTRACT ABSTRACT A curved bar in the form of a circular ring sector is under uniform torsion whe... more ABSTRACT ABSTRACT A curved bar in the form of a circular ring sector is under uniform torsion when acted upon by two equal and opposite forces directed alone the axis passing through the center of the ring and perpendicular to its plane, i.e., forces acting along the axis of rotation. The exact torsion theory can be extended to this case when the material of which the bar consists is cylindri-cally anisotropic, with the axis of anisotropy directed along the axis of rotation and having an elastic symmetry about any plane of the transverse cross section. In this paper, a thin-walled curved bar having the loading conditions and material properties described above is optimized so as to maximize its torsional stiffness. The optimization is carried out with respect to the cross-sectional shape of the bar subject to constraints on the transverse area (single-purpose design) and bending stiffness (multipurpose design). In the special case of an orthotropic material, the angle of inclination of the ortho-tropy axe...
Computers & Structures, Mar 1, 1995
Abstract A finite element formulation for the analysis of laminated composite plates based on a h... more Abstract A finite element formulation for the analysis of laminated composite plates based on a higher order theory is presented. Different types of finite elements which take into account transverse shear and normal deformation are developed. The degrees of freedom of the nodal points of these elements are independent of the number of layers. The applications of the elements to the bending of laminated plates with various loading and boundary conditions are given and numerical results are obtained. The accuracy of the elements is assessed by comparing the solutions obtained using the proposed elements with those obtained using the three-dimensional elasticity theory and with the closed-form solutions available in the literature. It is shown that the present approach reduces the number of unknown variables for the same degree of accuracy and extends the field of application of the finite element method. The finite elements proposed are highly efficient and accurate, and may easily be incorporated into existing finite element codes.
Journal of Pressure Vessel Technology-transactions of The Asme, Nov 1, 1997
Finite element solutions are presented for the optimal design of hemispherically and flat-capped ... more Finite element solutions are presented for the optimal design of hemispherically and flat-capped symmetrically laminated pressure vessels subjected to external pressure. The effect of vessel length, radius, and wall thickness, as well as bending-twisting coupling and hybridization on the optimal ply angle and buckling pressure are numerically studied. Comparisons of the optimal fiber angles and maximum buckling pressures for various vessel geometries are made with those for a hybrid pressure vessel. The well-known golden section method is used to compute the optimum angle in each case.
Engineering Optimization, 1992
The optimal ratio of the thickness of a low-stiffness fiber composite material to the total thick... more The optimal ratio of the thickness of a low-stiffness fiber composite material to the total thickness is determined for sandwich hybrid laminates. The objective of optimization is to maximize the fundamental frequency or the separation between two adjacent frequencies of the laminate subject to a mass or thickness constraint. The sandwich plate is constructed as an antisymmetric, angle-ply laminate which has outer layers made of a high-stiffness fiber composite material and inner layers of a low- stiffness fiber composite material. Such hybrid constructions produce cost-effective structures by making maximum use of expensive fibers. Optimal hybridization further increases the efficiency of the construction by determining the best thicknesses of layers containing high and low stiffness fibers. Comparative numerical results are given in graphical form for boron/glass hybrid and non-hybrid laminates. In the maximum fundamental frequency problem, the optimal laminate configuration is found to be a hybrid one for all ply angles. In the maximum frequency separation problem, the hybrid or non-hybrid configurations can be the optimal designs depending on the ply angles. The design variable is observed to display several jump discontinuities with respect to ply angles in the frequency separation problems. Comparative studies of hybrid and non-hybrid laminates indicate that the results for the hybrid case do not always fall in between those of the non-hybrid cases.
SN applied sciences, Mar 6, 2023
Composite Structures, May 1, 2020
Abstract The present study focuses on the mechanical and absorption properties of composites rein... more Abstract The present study focuses on the mechanical and absorption properties of composites reinforced by achatina fulica snail (S-shell) and eggshell particles (E-shell). Epoxy composites of snail and eggshell particles were prepared separately with the filler content ranging from 5 to 20% by weight. Hybrid composites of both fillers were also prepared and assessed. Specimens of the composites and hybrid composites with different percentage weights of the reinforcing materials were fabricated using the resin casting method. Mechanical properties such as tensile strength, Young’s modulus, impact strength, hardness and water absorption properties of the specimens were evaluated experimentally. It was observed that the addition of shell particles improves the mechanical properties of neat epoxy irrespective of the percentage weight of the reinforcement. The mechanical and water absorption properties of composites and hybrid composites varied depending on the amount of the reinforcement. Significantly, hybrid reinforcement by S-shell and E-shell particles offered superior properties in most cases. High percentage weight of calcium carbonate in these naturally sourced fillers and the synergistic effect of the S-shell and E-shells particle fillers can be attributed to high strength, stiffness, and decrease in water uptake of the composites.
WIT transactions on engineering sciences, 1970
Journal of Nanomaterials, Jul 4, 2020
Journal of Bio- and Tribo-Corrosion, Feb 12, 2020
Composites Part C: Open Access
Computer-Aided Civil and Infrastructure Engineering, 1995
ABSTRACT Multiobjective design of a laminated cylindrical shell is obtained with the objectives d... more ABSTRACT Multiobjective design of a laminated cylindrical shell is obtained with the objectives defined as the maximization of axial load and external and internal pressures subject to a strength constraint. The failure under axial load and external pressure may occur by buckling. The ply angle is taken as the design variable. The weighted global criterion method is employed to solve the vector-optimization problem, which involves minimization of the distance to ideal solution vector in L2 metric. A symmetrically laminated and balanced shell is considered as an example. Pareto optimal solutions are given for two- and three-objective design problems, and numerical results are presented in the form of tradeoff curves and surfaces. The effects of problem parameters are investigated, and the results are given for various weighting factors and shape parameters.
Composite Structures, 2000
... field expressible as (8). in which ζ represents x in the two-dimensional problem in ... A fin... more ... field expressible as (8). in which ζ represents x in the two-dimensional problem in ... A finite difference procedure was developed to determine the transient, radially-varying ambient temperature ...Numerical results for the benchmark problem indicate that the third-order theory yields ...
SN applied sciences, Mar 6, 2023
Springer eBooks, 1987
A first-ply failure analysis is given for a symmetric, cross-ply laminate of elliptic shape subje... more A first-ply failure analysis is given for a symmetric, cross-ply laminate of elliptic shape subject to flexural loads. In particular, clamped elliptic laminates under a uniformly distributed load are treated. The effects of fibre type and content, voids and hygrothermal conditions are investigated on the failure load and its location by means of micromechanical relations from which elastic and strength properties of the composite are computed. Numerical results are given in graphical form with a view towards the design of elliptic laminates by means of parametric studies.
International Journal of Mechanical Sciences, Mar 1, 2016
Journal of mechanisms, transmissions, and automation in design, Jun 1, 1983
An antisymmetrically laminated angle-ply plate is optimized with the objectives of minimizing the... more An antisymmetrically laminated angle-ply plate is optimized with the objectives of minimizing the maximum dynamic deflection, maximizing the natural frequencies and/or maximizing the buckling load. The design variables are the fiber orientation and the thickness of individual layers and are computed by using the methods of nonlinear programming. The concept of Pareto optimality is used in formulating the design problem and in reducing the multiple objectives into a single performance index. Numerical results are presented in the form of optimal tradeoff curves which allow the designer to assess the various possibilities open to him before deciding on a certain design. In this sense, the present design is an interactive process.
Journal of Applied Physics, Nov 15, 1995
The processes of crack growth and dislocation emission induced by the crack tip are investigated.... more The processes of crack growth and dislocation emission induced by the crack tip are investigated. A crystal with cubic lattice of atoms under plane strain conditions is considered. The main principles of the nanofracture mechanics approach employed in this study are outlined. Both ductile and brittle mechanisms of crack growth in the crystal are examined in nano- or interatomic scale. Only the fundamental constants of the classical theory of dislocations are used which include the interatomic spacing, elastic constants, the Schmid friction constant, and the true surface energy of crystal lattice. The efficient solution of the elastic problem for an arbitrary number of dislocations near the crack tip is obtained in terms of complex potential functions. The equilibrium of dislocation pairs near the crack tip during monotonic loading is investigated. It is shown that dislocation generation at the crack tip occurs at certain quantum levels of external load. The magnitude of external load corresponding to crack growth initiation and emission of the first pair of dislocations is calculated. The mathematical problem for an arbitrary N number of dislocation pairs near the crack tip is reduced to a parametric system of N nonlinear equations, where the stress intensity factor of external load KI plays the role of parameter and N the role of discrete time. The minimum value of KI at which the solution of this system of equations exists corresponds to the stress intensity factor at which the Nth pair of dislocations is generated. The numerical method is presented to determine the minimum value of KI. The approximate method of self-consistent field is employed to reduce the order of the system of nonlinear equations. The approximate method is used to calculate the fracture curve KI(lc) relating the value of KI which maintains the crack growth to the crack length increment lc. The exact solution is also studied, and numerical results are given for a crack in an aluminum specimen and involve the quantum levels of external load corresponding to the moments of dislocation generation and the values of the superfine stress intensity factor up to 150 dislocations.
7th AIAA/USAF/NASA/ISSMO Symposium on Multidisciplinary Analysis and Optimization, Aug 22, 1998
Multilayered composite discs rotating with a constant angular velocity are optimized with the obj... more Multilayered composite discs rotating with a constant angular velocity are optimized with the objective of maximizing the rotational speed by determining the fibre orientations and the lamination optimally. The effect of a temperature field is taken into account in the optimization. The design is required to satisfy a given non—failure criterion and in the present study the failure is determined on the basis of first ply failure using the Tsai—Wu strength criterion. Various boundary conditions are considered with the force or displacement conditions being specified on the inner and outer boundaries of the discs. In particular explicit solutions are obtained for free—free, fixed—free and free-fixed boundaries. The discs are modelled as symmetrical and balanced laminates with angle—ply and/or cross—ply layers. Numerical results are given for different combinations of cross—ply and angle—ply laminations. It is shown that the optimal lamination (combination of cross—ply or angle-ply layers) and the optimal fibre orientations depend largely on the boundary conditions and in some cases on the thermal loading.
5th Symposium on Multidisciplinary Analysis and Optimization, Aug 22, 1994
Quite often the values of the elastic constants of composite materials can be estimated with some... more Quite often the values of the elastic constants of composite materials can be estimated with some error due to manufacturing imperfections, defects and misalignments. This introduces some level of uncertainty in the computation of the buckling loads, frequencies, etc. In the present study an ellipsoidal convex model is employed to study the buckling of long cross-ply cylinders subject to external pressure with the material properties displaying uncertain-but-bounded variations around their nominal values. This approach determines the lowest buckling pressure and as such provides a conservative answer. Method of Lagrange multipliers is applied to compute the worst-case variations of the elastic constants and an explicit expression is obtained for the critical buckling pressure for a given level of uncertainty. Expressions for the relative sensitivities of the buckling pressure to uncertain elastic constants are derived.Copyright © 2013 by ASME
Journal of structural mechanics, 1981
ABSTRACT ABSTRACT A curved bar in the form of a circular ring sector is under uniform torsion whe... more ABSTRACT ABSTRACT A curved bar in the form of a circular ring sector is under uniform torsion when acted upon by two equal and opposite forces directed alone the axis passing through the center of the ring and perpendicular to its plane, i.e., forces acting along the axis of rotation. The exact torsion theory can be extended to this case when the material of which the bar consists is cylindri-cally anisotropic, with the axis of anisotropy directed along the axis of rotation and having an elastic symmetry about any plane of the transverse cross section. In this paper, a thin-walled curved bar having the loading conditions and material properties described above is optimized so as to maximize its torsional stiffness. The optimization is carried out with respect to the cross-sectional shape of the bar subject to constraints on the transverse area (single-purpose design) and bending stiffness (multipurpose design). In the special case of an orthotropic material, the angle of inclination of the ortho-tropy axe...
Computers & Structures, Mar 1, 1995
Abstract A finite element formulation for the analysis of laminated composite plates based on a h... more Abstract A finite element formulation for the analysis of laminated composite plates based on a higher order theory is presented. Different types of finite elements which take into account transverse shear and normal deformation are developed. The degrees of freedom of the nodal points of these elements are independent of the number of layers. The applications of the elements to the bending of laminated plates with various loading and boundary conditions are given and numerical results are obtained. The accuracy of the elements is assessed by comparing the solutions obtained using the proposed elements with those obtained using the three-dimensional elasticity theory and with the closed-form solutions available in the literature. It is shown that the present approach reduces the number of unknown variables for the same degree of accuracy and extends the field of application of the finite element method. The finite elements proposed are highly efficient and accurate, and may easily be incorporated into existing finite element codes.
Journal of Pressure Vessel Technology-transactions of The Asme, Nov 1, 1997
Finite element solutions are presented for the optimal design of hemispherically and flat-capped ... more Finite element solutions are presented for the optimal design of hemispherically and flat-capped symmetrically laminated pressure vessels subjected to external pressure. The effect of vessel length, radius, and wall thickness, as well as bending-twisting coupling and hybridization on the optimal ply angle and buckling pressure are numerically studied. Comparisons of the optimal fiber angles and maximum buckling pressures for various vessel geometries are made with those for a hybrid pressure vessel. The well-known golden section method is used to compute the optimum angle in each case.
Engineering Optimization, 1992
The optimal ratio of the thickness of a low-stiffness fiber composite material to the total thick... more The optimal ratio of the thickness of a low-stiffness fiber composite material to the total thickness is determined for sandwich hybrid laminates. The objective of optimization is to maximize the fundamental frequency or the separation between two adjacent frequencies of the laminate subject to a mass or thickness constraint. The sandwich plate is constructed as an antisymmetric, angle-ply laminate which has outer layers made of a high-stiffness fiber composite material and inner layers of a low- stiffness fiber composite material. Such hybrid constructions produce cost-effective structures by making maximum use of expensive fibers. Optimal hybridization further increases the efficiency of the construction by determining the best thicknesses of layers containing high and low stiffness fibers. Comparative numerical results are given in graphical form for boron/glass hybrid and non-hybrid laminates. In the maximum fundamental frequency problem, the optimal laminate configuration is found to be a hybrid one for all ply angles. In the maximum frequency separation problem, the hybrid or non-hybrid configurations can be the optimal designs depending on the ply angles. The design variable is observed to display several jump discontinuities with respect to ply angles in the frequency separation problems. Comparative studies of hybrid and non-hybrid laminates indicate that the results for the hybrid case do not always fall in between those of the non-hybrid cases.