Sarp Adali - Profile on Academia.edu (original) (raw)

Papers by Sarp Adali

Optimal Design of Laminated Composite Plates for Maximum Buckling Load Using Genetic Algorithm

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2005

An optimization procedure using a genetic algorithm (GA) is proposed to determine the optimal sta... more An optimization procedure using a genetic algorithm (GA) is proposed to determine the optimal stacking sequence of laminated composite plates for the maximum buckling load under several different loadings, such as uniaxial compression, shear, biaxial compression, and the combination of shear and biaxial loadings. A series of optimal design is conducted for composite laminates having different aspect ratios, load conditions, and number of plies. Critical buckling load is taken as fitness function and fibre orientations are taken as design variables. A performance index is introduced to represent the effectiveness of optimal design with respect to worst case design. Then, for uniaxial compression loading, postbuckling behaviour is analysed numerically for the optimally designed composite plates as well as the worst case design composite plate. It shows the outstanding postbuckling performance of one of the optimally designed composite plates against the worst case design composite pla...

SN applied sciences, Mar 6, 2023

In this study we present the interactions of the fundamental frequencies of a nanomanufacturing c... more In this study we present the interactions of the fundamental frequencies of a nanomanufacturing coupled system by exploring the natural frequencies of the subsystems. These nanomanufacturing subsystems function in concert, e.g., a cantilever beam with spring-mass. The individual subsystems are studied under free vibration to generate the natural and buckling frequencies. These subsystems, when under free vibration, generate unique local natural frequencies that interact to form a unique global natural frequency. This allows for greater control and improved sensitivity for scanning and shaping nano surfaces, by allowing selective variation of the local frequency of one system to influence the global system frequencies. In this investigation, a nanobeam with arbitrary boundary conditions is used to model the system and the effects on the parameters of interest are studied. Euler-Bernoulli theory is applied in conjunction with Eringen's theory of nonlocal continuum theory to model the small-scale effects due to the size of the beam under consideration. The coupled equations are solved using separation of variables for the local and global frequencies. The nanobeam is restrained with an adjustable torsional spring and pin at one end. The boundary condition at the free end is a springmass system with axial load. Altering the torsional, transverse spring stiffness and mass increases or decreases the natural frequencies. The motions of the beam and the tip-mass generates a frequency response during contact interactions. The tip response frequency is used to determine the maximum displacements (penetration depth) and accelerations (contact forces) in a sample during nanomanufacturing. Article Highlights 1. Coupled systems exhibit local natural frequencies which contribute to a unique universal natural frequency for the system. 2. The interaction of the local natural frequencies causes an amplification or attenuation in the displacement and acceleration. 3. By manipulating the universal natural frequencies of a nanobeam tool with tip-mass, we can control contact forces.

Studies on the mechanical and absorption properties of achatina fulica snail and eggshells reinforced composite materials

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

The optimal designs of laminated plates subject to non-uniform temperature distributions are give... more The optimal designs of laminated plates subject to non-uniform temperature distributions are given for maximum buckling temperature. The method of solution involves the finite element method based on Mindlin plate theory and numerical optimisation. A computational approach is developed which involves successive stages of solution for temperature distribution, buckling temperature and optimal fibre angle. Three different temperature loadings are considered and various combinations of simply supported and clamped boundary conditions are studied. The effect of plate aspect ratio on the optimal fibre angle and the maximum buckling temperature is investigated.

Journal of Nanomaterials, Jul 4, 2020

The possibility of obtaining calcium carbonate nanoparticles from Achatina fulica shell through m... more The possibility of obtaining calcium carbonate nanoparticles from Achatina fulica shell through mechanochemical synthesis to be used as a modifying filler for polymer materials has been studied. The process of obtaining calcium carbonate nanopowders includes two stages: dry and wet milling processes. At the first stage, the collected shell was dry milled and undergone mechanical sieving to ≤50 μm. The shell particles were wet milled afterward with four different solvents (water, methanol, ethylene glycol, and ethanol) and washed using the decantation method. The particle size and shape were investigated on transmission electron microscopy, and twenty-three particle counts were examined using an iTEM image analyzer. Significantly, nanoparticle sizes ranging from 11.56 to 180.06 nm of calcium carbonate was achieved after the dry and wet milling processes. The size particles collected vary with the different solvents used, and calcium carbonate synthesis with ethanol offered the smallest organic particle size with the average size ranging within 13.48-42.90 nm. The effect of the solvent on the chemical characteristics such as the functional group, elemental composition, and carbonate ion of calcium carbonate nanopowders obtained from Achatina fulica shell was investigated. The chemical characterization was analyzed using Fourier transform infrared (FTIR) and a scanning electron microscope (SEM) equipped with an energy-dispersive spectroscope (EDX). The effect of milling procedures on the mechanical properties such as tensile strength, stiffness, and hardness of prepared nanocomposites was also determined. This technique has shown that calcium carbonate nanoparticles can be produced at low cost, with low agglomeration, uniformity of crystal morphology, and structure from Achatina fulica shell. It also proved that the solvents used for milling have no adverse effect on the chemical properties of the nano-CaCO 3 produced. The loading of calcium carbonate nanoparticles, wet milled with different solvents, exhibited different mechanical properties, and nanocomposites filled with methanol-milled nano-CaCO 3 offered superior mechanical properties.

Journal of Bio- and Tribo-Corrosion, Feb 12, 2020

In this study, microhardness and flow strength (tensile) of a shell of an African Giant snail (Ac... more In this study, microhardness and flow strength (tensile) of a shell of an African Giant snail (Achatina Fulica) were studied as a function of indentation load. The influence of loading direction on the hardness of the nacreous and prismatic structure of the shell material was analyzed. The results revealed that microhardness measured on the shell was dependent on the load on the nacreous and prismatic structures. Indentation loading between 50 and 500 kN induced tensile strengths that ranged between 675-1050 and 390-810 MPa on the prismatic and nacreous layers, respectively. In addition, the morphology of the shell surface exhibited an interlocking structure with a large surface for binding to the organic matrix. The observed reinforcement of the shell explained the hardness property of the shell. The improved hardness of the shell implies that it can be beneficiated into filler that may be used to improve the mechanical properties of polymeric composite materials.

Long-term effects of low and high temperatures on the mechanical performance of hybrid FRP composite laminates: Experimental and model assessment

Composites Part C: Open Access

Multiobjective Design of Laminated Cylindrical Shells for Maximum Pressure and Buckling Load

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.

Developments in thermopiezoelasticity with relevance to smart composite structures

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

In this study we present the interactions of the fundamental frequencies of a nanomanufacturing c... more In this study we present the interactions of the fundamental frequencies of a nanomanufacturing coupled system by exploring the natural frequencies of the subsystems. These nanomanufacturing subsystems function in concert, e.g., a cantilever beam with spring-mass. The individual subsystems are studied under free vibration to generate the natural and buckling frequencies. These subsystems, when under free vibration, generate unique local natural frequencies that interact to form a unique global natural frequency. This allows for greater control and improved sensitivity for scanning and shaping nano surfaces, by allowing selective variation of the local frequency of one system to influence the global system frequencies. In this investigation, a nanobeam with arbitrary boundary conditions is used to model the system and the effects on the parameters of interest are studied. Euler-Bernoulli theory is applied in conjunction with Eringen's theory of nonlocal continuum theory to model the small-scale effects due to the size of the beam under consideration. The coupled equations are solved using separation of variables for the local and global frequencies. The nanobeam is restrained with an adjustable torsional spring and pin at one end. The boundary condition at the free end is a springmass system with axial load. Altering the torsional, transverse spring stiffness and mass increases or decreases the natural frequencies. The motions of the beam and the tip-mass generates a frequency response during contact interactions. The tip response frequency is used to determine the maximum displacements (penetration depth) and accelerations (contact forces) in a sample during nanomanufacturing. Article Highlights 1. Coupled systems exhibit local natural frequencies which contribute to a unique universal natural frequency for the system. 2. The interaction of the local natural frequencies causes an amplification or attenuation in the displacement and acceleration. 3. By manipulating the universal natural frequencies of a nanobeam tool with tip-mass, we can control contact forces.

Micromechanical Failure Analysis of Elliptic, Cross-ply Laminates under Flexural Loads

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

Dynamic stability of viscoelastic rectangular plates under a uniformly distributed tangential fol... more Dynamic stability of viscoelastic rectangular plates under a uniformly distributed tangential follower load is studied. Two sets of boundary conditions are considered, namely, clamped in one boundary and free in other boundaries (CFFF) and two opposite edges simply supported and other two edges free (SFSF). By considering the Kelvin-Voigt model of viscoelasticity, the equation of motion of the plate is derived. The differential quadrature method is employed to obtain the numerical solution and it is verified against known results in the literature. Numerical results are given for the real and imaginary parts of the eigenfrequencies to investigate the divergence and flutter instabilities. It is observed that the type of stability differs for CFFF and SFSF plates indicating the strong influence of the boundary conditions on the dynamic stability of viscoelastic plates. In particular it is found that CFFF plates undergo flutter instability and SFSF plates divergence instability. One consequence is that SFSF plates become unstable at a load less than the load for CFFF plates as the effects of viscoelasticity as well as the aspect ratio are found to be minor for SFSF plates.

Multiobjective Design of an Antisymmetric Angle-Ply Laminate by Nonlinear Programming

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.

Dislocation generation and crack growth under monotonic loading

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.

Design optimization of composite rotating discs under multiple loads

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

The minimum deflection design of thick laminated sandwich plates is given based on a higher-order... more The minimum deflection design of thick laminated sandwich plates is given based on a higher-order theory of plates and shells which includes the effects of the normal and shear deformation. Results are given for both isotropic and transversely isotropic surface layers with an isotropic core material. The design variable is the total surface layer thickness for a symmetric configuration. The higher-order theory is implemented using dedicated symbolic computation routines developed in the C programming language. The analysis is incorporated into an optimization algorithm to determine the optimal thicknesses of the surface layers for the minimum deflection design of three-layered sandwich shells. Numerical results are given for shells under sinusoidal loading and the effects of various input parameters are investigated.

Uncertainty Analysis of a Cross-Ply Composite Cylinder Subject to External Pressure by Convex Modeling

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

Optimization of a Thin-Walled, Anisotropic Curved Bar for Maximum Torsional Stiffness∗

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...

Finite elements based on shear and normal deformation theory for the analysis of laminated composite plates

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.

Optimal Design of Laminated Cylindrical Pressure Vessels for Maximum External Pressure

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.

Optimal Design of Laminated Composite Plates for Maximum Buckling Load Using Genetic Algorithm

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2005

An optimization procedure using a genetic algorithm (GA) is proposed to determine the optimal sta... more An optimization procedure using a genetic algorithm (GA) is proposed to determine the optimal stacking sequence of laminated composite plates for the maximum buckling load under several different loadings, such as uniaxial compression, shear, biaxial compression, and the combination of shear and biaxial loadings. A series of optimal design is conducted for composite laminates having different aspect ratios, load conditions, and number of plies. Critical buckling load is taken as fitness function and fibre orientations are taken as design variables. A performance index is introduced to represent the effectiveness of optimal design with respect to worst case design. Then, for uniaxial compression loading, postbuckling behaviour is analysed numerically for the optimally designed composite plates as well as the worst case design composite plate. It shows the outstanding postbuckling performance of one of the optimally designed composite plates against the worst case design composite pla...

SN applied sciences, Mar 6, 2023

In this study we present the interactions of the fundamental frequencies of a nanomanufacturing c... more In this study we present the interactions of the fundamental frequencies of a nanomanufacturing coupled system by exploring the natural frequencies of the subsystems. These nanomanufacturing subsystems function in concert, e.g., a cantilever beam with spring-mass. The individual subsystems are studied under free vibration to generate the natural and buckling frequencies. These subsystems, when under free vibration, generate unique local natural frequencies that interact to form a unique global natural frequency. This allows for greater control and improved sensitivity for scanning and shaping nano surfaces, by allowing selective variation of the local frequency of one system to influence the global system frequencies. In this investigation, a nanobeam with arbitrary boundary conditions is used to model the system and the effects on the parameters of interest are studied. Euler-Bernoulli theory is applied in conjunction with Eringen's theory of nonlocal continuum theory to model the small-scale effects due to the size of the beam under consideration. The coupled equations are solved using separation of variables for the local and global frequencies. The nanobeam is restrained with an adjustable torsional spring and pin at one end. The boundary condition at the free end is a springmass system with axial load. Altering the torsional, transverse spring stiffness and mass increases or decreases the natural frequencies. The motions of the beam and the tip-mass generates a frequency response during contact interactions. The tip response frequency is used to determine the maximum displacements (penetration depth) and accelerations (contact forces) in a sample during nanomanufacturing. Article Highlights 1. Coupled systems exhibit local natural frequencies which contribute to a unique universal natural frequency for the system. 2. The interaction of the local natural frequencies causes an amplification or attenuation in the displacement and acceleration. 3. By manipulating the universal natural frequencies of a nanobeam tool with tip-mass, we can control contact forces.

Studies on the mechanical and absorption properties of achatina fulica snail and eggshells reinforced composite materials

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

The optimal designs of laminated plates subject to non-uniform temperature distributions are give... more The optimal designs of laminated plates subject to non-uniform temperature distributions are given for maximum buckling temperature. The method of solution involves the finite element method based on Mindlin plate theory and numerical optimisation. A computational approach is developed which involves successive stages of solution for temperature distribution, buckling temperature and optimal fibre angle. Three different temperature loadings are considered and various combinations of simply supported and clamped boundary conditions are studied. The effect of plate aspect ratio on the optimal fibre angle and the maximum buckling temperature is investigated.

Journal of Nanomaterials, Jul 4, 2020

The possibility of obtaining calcium carbonate nanoparticles from Achatina fulica shell through m... more The possibility of obtaining calcium carbonate nanoparticles from Achatina fulica shell through mechanochemical synthesis to be used as a modifying filler for polymer materials has been studied. The process of obtaining calcium carbonate nanopowders includes two stages: dry and wet milling processes. At the first stage, the collected shell was dry milled and undergone mechanical sieving to ≤50 μm. The shell particles were wet milled afterward with four different solvents (water, methanol, ethylene glycol, and ethanol) and washed using the decantation method. The particle size and shape were investigated on transmission electron microscopy, and twenty-three particle counts were examined using an iTEM image analyzer. Significantly, nanoparticle sizes ranging from 11.56 to 180.06 nm of calcium carbonate was achieved after the dry and wet milling processes. The size particles collected vary with the different solvents used, and calcium carbonate synthesis with ethanol offered the smallest organic particle size with the average size ranging within 13.48-42.90 nm. The effect of the solvent on the chemical characteristics such as the functional group, elemental composition, and carbonate ion of calcium carbonate nanopowders obtained from Achatina fulica shell was investigated. The chemical characterization was analyzed using Fourier transform infrared (FTIR) and a scanning electron microscope (SEM) equipped with an energy-dispersive spectroscope (EDX). The effect of milling procedures on the mechanical properties such as tensile strength, stiffness, and hardness of prepared nanocomposites was also determined. This technique has shown that calcium carbonate nanoparticles can be produced at low cost, with low agglomeration, uniformity of crystal morphology, and structure from Achatina fulica shell. It also proved that the solvents used for milling have no adverse effect on the chemical properties of the nano-CaCO 3 produced. The loading of calcium carbonate nanoparticles, wet milled with different solvents, exhibited different mechanical properties, and nanocomposites filled with methanol-milled nano-CaCO 3 offered superior mechanical properties.

Journal of Bio- and Tribo-Corrosion, Feb 12, 2020

In this study, microhardness and flow strength (tensile) of a shell of an African Giant snail (Ac... more In this study, microhardness and flow strength (tensile) of a shell of an African Giant snail (Achatina Fulica) were studied as a function of indentation load. The influence of loading direction on the hardness of the nacreous and prismatic structure of the shell material was analyzed. The results revealed that microhardness measured on the shell was dependent on the load on the nacreous and prismatic structures. Indentation loading between 50 and 500 kN induced tensile strengths that ranged between 675-1050 and 390-810 MPa on the prismatic and nacreous layers, respectively. In addition, the morphology of the shell surface exhibited an interlocking structure with a large surface for binding to the organic matrix. The observed reinforcement of the shell explained the hardness property of the shell. The improved hardness of the shell implies that it can be beneficiated into filler that may be used to improve the mechanical properties of polymeric composite materials.

Long-term effects of low and high temperatures on the mechanical performance of hybrid FRP composite laminates: Experimental and model assessment

Composites Part C: Open Access

Multiobjective Design of Laminated Cylindrical Shells for Maximum Pressure and Buckling Load

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.

Developments in thermopiezoelasticity with relevance to smart composite structures

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

In this study we present the interactions of the fundamental frequencies of a nanomanufacturing c... more In this study we present the interactions of the fundamental frequencies of a nanomanufacturing coupled system by exploring the natural frequencies of the subsystems. These nanomanufacturing subsystems function in concert, e.g., a cantilever beam with spring-mass. The individual subsystems are studied under free vibration to generate the natural and buckling frequencies. These subsystems, when under free vibration, generate unique local natural frequencies that interact to form a unique global natural frequency. This allows for greater control and improved sensitivity for scanning and shaping nano surfaces, by allowing selective variation of the local frequency of one system to influence the global system frequencies. In this investigation, a nanobeam with arbitrary boundary conditions is used to model the system and the effects on the parameters of interest are studied. Euler-Bernoulli theory is applied in conjunction with Eringen's theory of nonlocal continuum theory to model the small-scale effects due to the size of the beam under consideration. The coupled equations are solved using separation of variables for the local and global frequencies. The nanobeam is restrained with an adjustable torsional spring and pin at one end. The boundary condition at the free end is a springmass system with axial load. Altering the torsional, transverse spring stiffness and mass increases or decreases the natural frequencies. The motions of the beam and the tip-mass generates a frequency response during contact interactions. The tip response frequency is used to determine the maximum displacements (penetration depth) and accelerations (contact forces) in a sample during nanomanufacturing. Article Highlights 1. Coupled systems exhibit local natural frequencies which contribute to a unique universal natural frequency for the system. 2. The interaction of the local natural frequencies causes an amplification or attenuation in the displacement and acceleration. 3. By manipulating the universal natural frequencies of a nanobeam tool with tip-mass, we can control contact forces.

Micromechanical Failure Analysis of Elliptic, Cross-ply Laminates under Flexural Loads

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

Dynamic stability of viscoelastic rectangular plates under a uniformly distributed tangential fol... more Dynamic stability of viscoelastic rectangular plates under a uniformly distributed tangential follower load is studied. Two sets of boundary conditions are considered, namely, clamped in one boundary and free in other boundaries (CFFF) and two opposite edges simply supported and other two edges free (SFSF). By considering the Kelvin-Voigt model of viscoelasticity, the equation of motion of the plate is derived. The differential quadrature method is employed to obtain the numerical solution and it is verified against known results in the literature. Numerical results are given for the real and imaginary parts of the eigenfrequencies to investigate the divergence and flutter instabilities. It is observed that the type of stability differs for CFFF and SFSF plates indicating the strong influence of the boundary conditions on the dynamic stability of viscoelastic plates. In particular it is found that CFFF plates undergo flutter instability and SFSF plates divergence instability. One consequence is that SFSF plates become unstable at a load less than the load for CFFF plates as the effects of viscoelasticity as well as the aspect ratio are found to be minor for SFSF plates.

Multiobjective Design of an Antisymmetric Angle-Ply Laminate by Nonlinear Programming

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.

Dislocation generation and crack growth under monotonic loading

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.

Design optimization of composite rotating discs under multiple loads

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

The minimum deflection design of thick laminated sandwich plates is given based on a higher-order... more The minimum deflection design of thick laminated sandwich plates is given based on a higher-order theory of plates and shells which includes the effects of the normal and shear deformation. Results are given for both isotropic and transversely isotropic surface layers with an isotropic core material. The design variable is the total surface layer thickness for a symmetric configuration. The higher-order theory is implemented using dedicated symbolic computation routines developed in the C programming language. The analysis is incorporated into an optimization algorithm to determine the optimal thicknesses of the surface layers for the minimum deflection design of three-layered sandwich shells. Numerical results are given for shells under sinusoidal loading and the effects of various input parameters are investigated.

Uncertainty Analysis of a Cross-Ply Composite Cylinder Subject to External Pressure by Convex Modeling

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

Optimization of a Thin-Walled, Anisotropic Curved Bar for Maximum Torsional Stiffness∗

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...

Finite elements based on shear and normal deformation theory for the analysis of laminated composite plates

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.

Optimal Design of Laminated Cylindrical Pressure Vessels for Maximum External Pressure

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.