Abstract This article focuses on geometrically nonlinear transient analysis of thick deep laminat... more Abstract This article focuses on geometrically nonlinear transient analysis of thick deep laminated composite curved beams with generalized differential quadrature method. Generalized differential quadrature method is coupled with the weak form of the equation of motion. Virtual work principle is used to derive the equation of motion. Spatial derivatives in the equation of motion are expressed with generalized differential quadrature method. Geometric nonlinearity is considered through Green–Lagrange nonlinear strain–displacement relations that are derived using elasticity theory equations. First-order shear deformation theory is used to consider the transverse shear effect. Time integration of the equation of motion is carried out using Newmark average acceleration method. Several problems from the literature are solved with the proposed method and results are compared.
The International Journal of Advanced Manufacturing Technology, Apr 27, 2005
During the production of thin shell plastic parts by injection molding, warpage depending on the ... more During the production of thin shell plastic parts by injection molding, warpage depending on the process conditions is often encountered. In this study, efficient minimization of warpage on thin shell plastic parts by integrating finite element (FE) analysis, statistical design of experiment method, response surface methodology (RSM), and genetic algorithm (GA) is investigated. A bus ceiling lamp base is considered as a thin shell plastic part example. To achieve the minimum warpage, optimum process condition parameters are determined. Mold temperature, melt temperature, packing pressure, packing time, and cooling time are considered as process condition parameters. FE analyses are conducted for a combination of process parameters organized using statistical three-level full factorial experimental design. The most important process parameters influencing warpage are determined using FE analysis results based on analysis of variance (ANOVA) method. A predictive response surface model for warpage data is created using RSM. The response surface (RS) model is interfaced with an effective GA to find the optimum process parameter values.
Journal of Materials Engineering and Performance, Jan 8, 2021
For fitness-for-service assessment of pipeline cracks, it is necessary to examine toughness value... more For fitness-for-service assessment of pipeline cracks, it is necessary to examine toughness values of pipeline steels and their variations with temperature. In this study, experimental values of toughness (KJC) at room temperature have been obtained for base metal (BM), seam weld (SW), and girth weld (GW) in an API X65 gas transportation pipeline in order to investigate the structural integrity of whole structure. The toughness tests employed side-grooved compact tension specimens, obtained from the original pipe, to characterize the resistance to crack extension curves based on the unloading compliance technique. The values of JIC for tested specimens were found, and then, KJC values are obtained using ASTM E1820 guideline as 302, 262, and 166 MPam1/2 for BM, SW, and GW materials, respectively. Charpy V-notch (CVN) impact tests at room and low temperatures were also conducted to determine low-temperature effects on the toughness, and to examine ductile–brittle transition temperature values in the samples under study. The capability of CVN test for prediction of toughness in the tested specimens was also investigated. The error values in using CVN test results are large enough to justify that the CVN test is not suitable for prediction of toughness accurately.
International Journal of Adhesion and Adhesives, Dec 1, 2019
Adhesive joints have found extensive applications in aerospace structures because of important ad... more Adhesive joints have found extensive applications in aerospace structures because of important advantages such as uniform stress distribution, thermal, acoustic and electrical insulation as well as capability of joining dissimilar materials. These joints in aerospace structures frequently experience severe low temperatures. Lack of experimental data in this field motivated the study of the fracture of adhesive joint at low temperatures in this paper. Fracture parameters of carbon-fibre-reinforced polymer-based composites (CFRP) and aluminum bonded joints were investigated in a temperature range of −80 to +22°C. In order to understand the mechanical behavior of different components of the bonded joint, firstly, the components (adhesive, composite, and aluminum) were characterized by conducting tensile tests. Subsequently, specimens of cracked bonded joint were tested at low temperatures in different loading modes (mode I, mode II, and mixed mode I/II). The finite element model of the bonded joint was developed in order to obtain the dimensionless functions of stress intensity factors at lower temperatures. The results showed that a reduction in temperature down to a particular value contributes to improved critical stress intensity factors, while any further reduction in the temperature tends to lower the critical stress intensity factors, eventually leading to decreased fracture energy absorption capacity of the structure. In the final section of this paper, a study on fracture surfaces and fracture mechanisms was performed via macroscopic and scanning electron microscopic (SEM) analyses.
Journal of Materials Engineering and Performance, 2021
For fitness-for-service assessment of pipeline cracks, it is necessary to examine toughness value... more For fitness-for-service assessment of pipeline cracks, it is necessary to examine toughness values of pipeline steels and their variations with temperature. In this study, experimental values of toughness (KJC) at room temperature have been obtained for base metal (BM), seam weld (SW), and girth weld (GW) in an API X65 gas transportation pipeline in order to investigate the structural integrity of whole structure. The toughness tests employed side-grooved compact tension specimens, obtained from the original pipe, to characterize the resistance to crack extension curves based on the unloading compliance technique. The values of JIC for tested specimens were found, and then, KJC values are obtained using ASTM E1820 guideline as 302, 262, and 166 MPam1/2 for BM, SW, and GW materials, respectively. Charpy V-notch (CVN) impact tests at room and low temperatures were also conducted to determine low-temperature effects on the toughness, and to examine ductile–brittle transition temperature values in the samples under study. The capability of CVN test for prediction of toughness in the tested specimens was also investigated. The error values in using CVN test results are large enough to justify that the CVN test is not suitable for prediction of toughness accurately.
In this study, predictive hydrocode simulations are coupled with approximate optimization (AO) me... more In this study, predictive hydrocode simulations are coupled with approximate optimization (AO) methodology to achieve successive design automation for a projectile-Whipple shield (WS) system at hypervelocity impact (HVI) conditions. Successive design methodology is first applied to find the most dangerous threat for a given WS design by varying the shape and orientation of a projectile while imposing constraints on the
The hydroxyl groups of the polyphenols are capable to act as reducing agent for reduction reactio... more The hydroxyl groups of the polyphenols are capable to act as reducing agent for reduction reaction. The effect of drying temperature, extraction temperature and extraction duration were evaluated using central composite design which consists of 20 experimental runs. Response surface methodology (RSM) was used to estimate the optimum parameters in extracting polyphenols from the palm leaves. The correspondence analysis of the results yielded a quadratic model which can be used to find optimum conditions of extraction process. The optimum extraction condition of drying temperature, extraction temperature and extraction duration are 70°C, at 70°C of 10 minutes, respectively. Total polyphenols were determined by application of the Folin-Ciocalteu micro method and the extract was found contain of 8 mg GAE/g dry palm leaves at optimum conditions.
Abstract Aeroelastic stability of tapered/skew variable stiffness composite cantilevered plates a... more Abstract Aeroelastic stability of tapered/skew variable stiffness composite cantilevered plates are considered in the current study at flutter and post-flutter regions. The variable stiffness behavior is obtained by altering the fiber angles continuously according to a selected curvilinear fiber path function in the composite laminates. Flutter speed, limit cycle oscillations (LCOs), and bifurcation diagrams of tapered/skewed plates are obtained at two different fiber path functions. Nonlinear structural model is utilized based on the virtual work principle. Fully nonlinear Green’s kinematic strain relations are used to account for the geometric nonlinearities and the first order shear deformation theory (FSDT) is employed to generalize the formulation for the case of moderately thick plates including transverse shear effects. One prominent target of the present study is to determine how the variable stiffness parameters affect the nonlinear behavior. Consequently, one may find the best fiber path with improved flutter and post-flutter characteristics for tapered/skew plates in supersonic flow. First order linear piston theory is used to model the aerodynamic loading. In order to get a reliable solution, the Generalized Differential Quadrature (GDQ) method is employed. Moreover, time integration of the equations of motion is carried out using the Newmark’s average acceleration technique. It will be shown that taperness/skewness as well as variable stiffness lamination parameters have significant effects on the aeroelastic stability margins. In addition, the post-critical behavior is found to be periodic or quasi-periodic at all the presented simulations with no specific route to chaos.
Yuzey puruzlulugu, frezeleme islemlerinin performansinin degerlendirilmesinde goz onune alinabile... more Yuzey puruzlulugu, frezeleme islemlerinin performansinin degerlendirilmesinde goz onune alinabilecek en onemli kriterlerden biridir. Bir frezeleme isleminde, yuzey puruzlulugune etki eden parametreler, uygulanan operasyon tipine ve uretilen malzeme cinsine gore degisiklik gostermektedir. Bu calisma, Inconel 718 gibi super alasimli bir malzemenin duz uclu kesicilerle frezelenmesi sonucu olusan yuzey puruzlulugunun yapay sinir aglariyla tahmin edilerek bir puruzluluk modeli olusturulmasini kapsar. Toplam 81 deney, kesici kataloglarindan secilen kesme parametreleriyle kesme sivri.' kullanarak yapilmistir. Deneylerden elde edilen puruzluluk degerleri, optik olcum metoduna gore calisan yuzey puruzluluk cihaziyla olculmustur. Ileri beslemeli bir yapay sinir agi, islenen yuzeylerden elde edilen puruzlulugu tahmin etmek icin kullanilmistir. Kesme hizi (Vi), ilerleme (fz), eksenel kesme derinligi (an) ve radyal kesme derinligi (at) gibi parametreler, yapay sinir aginin giris katmanin'...
Dynamic analysis of composite doubly curved panels with variable thickness subjected to different... more Dynamic analysis of composite doubly curved panels with variable thickness subjected to different pulse types using Generalized Differential Quadrature method (GDQ) is presented in this study. Panels with variable thickness are used in the construction of aerospace and marine industry. Giving variable thickness to panels can allow the designer to get optimum structural efficiency. For this reason, estimating the response of variable thickness panels is very important to design more reliable structures under dynamic loads. Dynamic equations for composite panels with variable thickness are obtained using virtual work principle. Partial derivatives in the equation of motion are expressed with GDQ and Newmark average acceleration scheme is used for temporal discretization. Several examples are used to highlight the effectiveness of the proposed method. Results are compared with finite element method. Effects of taper ratios, boundary conditions and loading type on the response of compos...
In this paper geometrically nonlinear static behavior of laminated composite hollow super-ellipti... more In this paper geometrically nonlinear static behavior of laminated composite hollow super-elliptic beams is investigated using generalized differential quadrature method. Super-elliptic beam can have both oval and elliptic cross-sections by adjusting parameters in super-ellipse formulation (also known as Lamé curves). Equilibrium equations of super-elliptic beam are obtained using the virtual work principle. Geometric nonlinearity is taken into account using von-Kármán nonlinear strain-displacement relations. Spatial derivatives in strains are expressed with the generalized differential quadrature method. Transverse shear effect is considered through the first-order shear deformation theory. Static equilibrium equations are solved using Newton-Raphson method. Several composite super-elliptic beam problems are solved with the proposed method. Effects of layer orientations of composite material, boundary conditions, ovality and ellipticity on bending behavior are investigated.
Bu calismada tabakali kompozit levha ve panellerin dusuk carpma hizlarindaki nonlineer dinamik da... more Bu calismada tabakali kompozit levha ve panellerin dusuk carpma hizlarindaki nonlineer dinamik davranisi Genellestirilmis Diferansiyel Kuadrature (Generalized Differential Quadrature) yontemi ile incelenmektedir. Sistemin dinamik denklemleri Virtuel is ilkesi ile elde edilmektedir. Duzleme dik dogrultudaki kalinlik etkisi 1. mertebe kayma deformasyon teorisi ile dikkate alinmaktadir. Buyuk yer degistirmeler Von-Karman nonlineer birim sekil degisimleri ile dikkate alinmaktadir. Konumsal turevler Genellestirilmis Diferansiyel Quadrature yontemi ile zaman integrasyonu da Newmark metodu ile hesaplanmaktadir. Onerilen metotla bircok carpma problemi cozulmus ve literaturdeki sonuclarla karsilastirilmistir. Onerilen metodun carpma problemlerinin incelenmesinde etkili ve verimli bir yontem oldugu gosterilmistir.
Crashworthiness, Occupant Protection and Biomechanics in Transportation Systems, 2001
Optimum crashworthiness design of the vehicle rail structure is one of the crucial tasks in desig... more Optimum crashworthiness design of the vehicle rail structure is one of the crucial tasks in designing crashworthy vehicles that render better occupant protection. The usual trial-and-error approach in selecting the optimum design parameters, in order to maximize the energy absorbing capacity of the rail structure, is computationally expensive and cumbersome; particularly when there are several design parameters to be properly selected. Optimization methods can be used to automate the search for the optimum design parameters. In the current research, an efficient design optimization methodology is presented and utilized to obtain optimum crashworthiness design of the energy-absorbing rail structures. The methodology adopted in this research makes use of Design of Experiments (DOE) based approximation methods, numerical optimization algorithms and structural analysis software. The design optimization approach has been devoted to structural impact applications. The nonlinear explicit F...
Abstract Present study deals with large displacement transient dynamic response of truncated coni... more Abstract Present study deals with large displacement transient dynamic response of truncated conical panels made of Porous Functionally Graded Materials (P-FGMs) using Generalized Differential Quadrature (GDQ) method. In this study, geometric non-linearity is taken into consideration through Green-Lagrange non-linear strain-displacement relations. First order shear deformation theory (FSDT) is utilized to take transverse shear effects into account. Virtual work principle is used to derive the equation of motion. The solution methodology utilizes GDQ method for spatial discretization of the variables. Newmark average acceleration method is implemented in time integration. Effects of different types of porosity distribution, porosity ratio and conical parameters on non-linear transient behavior of truncated conical panels are investigated for functionally graded material made of Zirconia/Aluminum (ZrO2/Al) considering various volume fraction coefficients.
In this study, natural frequencies and vibrational mode shapes of variable stiffness composite sk... more In this study, natural frequencies and vibrational mode shapes of variable stiffness composite skewed plates are optimized applying a genetic algorithm. The variable stiffness behavior is obtained by altering the fiber angles continuously according to two selected curvilinear fiber path functions in the composite laminates. Fundamental frequency and related mode shapes of the plates are optimized for two different fiber path functions using the structural model obtained based on the virtual work principle. A three-layer composite skewed plate with four types of boundary conditions and different plate geometries is considered as case study in this research. Diverse sweptback angles as well as different aspect ratios are considered as various plate geometries. The present study aims to calculate the best fiber path with maximized fundamental frequency or in-plane strengths for a composite skewed plate. The generalized differential quadrature method of solution is employed to solve the governing equations of motion. Moreover, the linear kinematic strain assumptions are used, and the first-order shear deformation theory is employed to generalize the formulation for the case of moderately thick plates including transverse shear effects. Numerical results demonstrate the effect of the fiber angles, boundary conditions, and diverse geometries on the natural frequencies of the composite plate. The optimal fiber angles of each layer are presented for the above cases in free vibration analysis. It is verified that the application of optimized curvilinear fibers instead of the traditional straight fibers introduces a higher degree of flexibility, which can be used to adjust frequencies and mode shapes.
Abstract In the present study, the fundamental natural frequencies of curvilinear fiber composite... more Abstract In the present study, the fundamental natural frequencies of curvilinear fiber composite skew and taper cylindrical panels are optimized applying genetic algorithm (GA). Later, the fundamental amplitude-dependent nonlinear frequency behavior of the optimized curved fiber layup configurations is studied and compared with the reference unidirectional fiber layup. The variable stiffness behavior is obtained by altering the fiber angles continuously according to the curvilinear fiber path function in the composite laminates. A nonlinear structural model is utilized based on the virtual work principle. Green’s nonlinear kinematic strain relations are used to account for the geometric nonlinearities and the first-order shear deformation theory (FSDT) is adopted to generalize the formulation for the case of moderately thick cylindrical panels including transverse shear deformations. The goal is to determine how the variable stiffness parameters affect the linear and nonlinear free vibration behavior of the skew and taper cylindrical panels. Consequently, one may find the optimum fiber path with improved structural characteristics for the cylindrical panel. Eight-layered composite skew and taper cylindrical panels at two different boundary condition sets are considered in this research. Generalized Differential Quadrature (GDQ) method of solution is employed to solve the nonlinear governing equations of motion. Numerical results demonstrate the degree of effectiveness for fiber angle paths, boundary conditions, and geometrical non-uniformities on the fundamental frequencies of the cylindrical panel. Eventually, optimum fiber angles of each layer in free vibration analysis are presented.
Abstract This article focuses on geometrically nonlinear transient analysis of thick deep laminat... more Abstract This article focuses on geometrically nonlinear transient analysis of thick deep laminated composite curved beams with generalized differential quadrature method. Generalized differential quadrature method is coupled with the weak form of the equation of motion. Virtual work principle is used to derive the equation of motion. Spatial derivatives in the equation of motion are expressed with generalized differential quadrature method. Geometric nonlinearity is considered through Green–Lagrange nonlinear strain–displacement relations that are derived using elasticity theory equations. First-order shear deformation theory is used to consider the transverse shear effect. Time integration of the equation of motion is carried out using Newmark average acceleration method. Several problems from the literature are solved with the proposed method and results are compared.
The International Journal of Advanced Manufacturing Technology, Apr 27, 2005
During the production of thin shell plastic parts by injection molding, warpage depending on the ... more During the production of thin shell plastic parts by injection molding, warpage depending on the process conditions is often encountered. In this study, efficient minimization of warpage on thin shell plastic parts by integrating finite element (FE) analysis, statistical design of experiment method, response surface methodology (RSM), and genetic algorithm (GA) is investigated. A bus ceiling lamp base is considered as a thin shell plastic part example. To achieve the minimum warpage, optimum process condition parameters are determined. Mold temperature, melt temperature, packing pressure, packing time, and cooling time are considered as process condition parameters. FE analyses are conducted for a combination of process parameters organized using statistical three-level full factorial experimental design. The most important process parameters influencing warpage are determined using FE analysis results based on analysis of variance (ANOVA) method. A predictive response surface model for warpage data is created using RSM. The response surface (RS) model is interfaced with an effective GA to find the optimum process parameter values.
Journal of Materials Engineering and Performance, Jan 8, 2021
For fitness-for-service assessment of pipeline cracks, it is necessary to examine toughness value... more For fitness-for-service assessment of pipeline cracks, it is necessary to examine toughness values of pipeline steels and their variations with temperature. In this study, experimental values of toughness (KJC) at room temperature have been obtained for base metal (BM), seam weld (SW), and girth weld (GW) in an API X65 gas transportation pipeline in order to investigate the structural integrity of whole structure. The toughness tests employed side-grooved compact tension specimens, obtained from the original pipe, to characterize the resistance to crack extension curves based on the unloading compliance technique. The values of JIC for tested specimens were found, and then, KJC values are obtained using ASTM E1820 guideline as 302, 262, and 166 MPam1/2 for BM, SW, and GW materials, respectively. Charpy V-notch (CVN) impact tests at room and low temperatures were also conducted to determine low-temperature effects on the toughness, and to examine ductile–brittle transition temperature values in the samples under study. The capability of CVN test for prediction of toughness in the tested specimens was also investigated. The error values in using CVN test results are large enough to justify that the CVN test is not suitable for prediction of toughness accurately.
International Journal of Adhesion and Adhesives, Dec 1, 2019
Adhesive joints have found extensive applications in aerospace structures because of important ad... more Adhesive joints have found extensive applications in aerospace structures because of important advantages such as uniform stress distribution, thermal, acoustic and electrical insulation as well as capability of joining dissimilar materials. These joints in aerospace structures frequently experience severe low temperatures. Lack of experimental data in this field motivated the study of the fracture of adhesive joint at low temperatures in this paper. Fracture parameters of carbon-fibre-reinforced polymer-based composites (CFRP) and aluminum bonded joints were investigated in a temperature range of −80 to +22°C. In order to understand the mechanical behavior of different components of the bonded joint, firstly, the components (adhesive, composite, and aluminum) were characterized by conducting tensile tests. Subsequently, specimens of cracked bonded joint were tested at low temperatures in different loading modes (mode I, mode II, and mixed mode I/II). The finite element model of the bonded joint was developed in order to obtain the dimensionless functions of stress intensity factors at lower temperatures. The results showed that a reduction in temperature down to a particular value contributes to improved critical stress intensity factors, while any further reduction in the temperature tends to lower the critical stress intensity factors, eventually leading to decreased fracture energy absorption capacity of the structure. In the final section of this paper, a study on fracture surfaces and fracture mechanisms was performed via macroscopic and scanning electron microscopic (SEM) analyses.
Journal of Materials Engineering and Performance, 2021
For fitness-for-service assessment of pipeline cracks, it is necessary to examine toughness value... more For fitness-for-service assessment of pipeline cracks, it is necessary to examine toughness values of pipeline steels and their variations with temperature. In this study, experimental values of toughness (KJC) at room temperature have been obtained for base metal (BM), seam weld (SW), and girth weld (GW) in an API X65 gas transportation pipeline in order to investigate the structural integrity of whole structure. The toughness tests employed side-grooved compact tension specimens, obtained from the original pipe, to characterize the resistance to crack extension curves based on the unloading compliance technique. The values of JIC for tested specimens were found, and then, KJC values are obtained using ASTM E1820 guideline as 302, 262, and 166 MPam1/2 for BM, SW, and GW materials, respectively. Charpy V-notch (CVN) impact tests at room and low temperatures were also conducted to determine low-temperature effects on the toughness, and to examine ductile–brittle transition temperature values in the samples under study. The capability of CVN test for prediction of toughness in the tested specimens was also investigated. The error values in using CVN test results are large enough to justify that the CVN test is not suitable for prediction of toughness accurately.
In this study, predictive hydrocode simulations are coupled with approximate optimization (AO) me... more In this study, predictive hydrocode simulations are coupled with approximate optimization (AO) methodology to achieve successive design automation for a projectile-Whipple shield (WS) system at hypervelocity impact (HVI) conditions. Successive design methodology is first applied to find the most dangerous threat for a given WS design by varying the shape and orientation of a projectile while imposing constraints on the
The hydroxyl groups of the polyphenols are capable to act as reducing agent for reduction reactio... more The hydroxyl groups of the polyphenols are capable to act as reducing agent for reduction reaction. The effect of drying temperature, extraction temperature and extraction duration were evaluated using central composite design which consists of 20 experimental runs. Response surface methodology (RSM) was used to estimate the optimum parameters in extracting polyphenols from the palm leaves. The correspondence analysis of the results yielded a quadratic model which can be used to find optimum conditions of extraction process. The optimum extraction condition of drying temperature, extraction temperature and extraction duration are 70°C, at 70°C of 10 minutes, respectively. Total polyphenols were determined by application of the Folin-Ciocalteu micro method and the extract was found contain of 8 mg GAE/g dry palm leaves at optimum conditions.
Abstract Aeroelastic stability of tapered/skew variable stiffness composite cantilevered plates a... more Abstract Aeroelastic stability of tapered/skew variable stiffness composite cantilevered plates are considered in the current study at flutter and post-flutter regions. The variable stiffness behavior is obtained by altering the fiber angles continuously according to a selected curvilinear fiber path function in the composite laminates. Flutter speed, limit cycle oscillations (LCOs), and bifurcation diagrams of tapered/skewed plates are obtained at two different fiber path functions. Nonlinear structural model is utilized based on the virtual work principle. Fully nonlinear Green’s kinematic strain relations are used to account for the geometric nonlinearities and the first order shear deformation theory (FSDT) is employed to generalize the formulation for the case of moderately thick plates including transverse shear effects. One prominent target of the present study is to determine how the variable stiffness parameters affect the nonlinear behavior. Consequently, one may find the best fiber path with improved flutter and post-flutter characteristics for tapered/skew plates in supersonic flow. First order linear piston theory is used to model the aerodynamic loading. In order to get a reliable solution, the Generalized Differential Quadrature (GDQ) method is employed. Moreover, time integration of the equations of motion is carried out using the Newmark’s average acceleration technique. It will be shown that taperness/skewness as well as variable stiffness lamination parameters have significant effects on the aeroelastic stability margins. In addition, the post-critical behavior is found to be periodic or quasi-periodic at all the presented simulations with no specific route to chaos.
Yuzey puruzlulugu, frezeleme islemlerinin performansinin degerlendirilmesinde goz onune alinabile... more Yuzey puruzlulugu, frezeleme islemlerinin performansinin degerlendirilmesinde goz onune alinabilecek en onemli kriterlerden biridir. Bir frezeleme isleminde, yuzey puruzlulugune etki eden parametreler, uygulanan operasyon tipine ve uretilen malzeme cinsine gore degisiklik gostermektedir. Bu calisma, Inconel 718 gibi super alasimli bir malzemenin duz uclu kesicilerle frezelenmesi sonucu olusan yuzey puruzlulugunun yapay sinir aglariyla tahmin edilerek bir puruzluluk modeli olusturulmasini kapsar. Toplam 81 deney, kesici kataloglarindan secilen kesme parametreleriyle kesme sivri.' kullanarak yapilmistir. Deneylerden elde edilen puruzluluk degerleri, optik olcum metoduna gore calisan yuzey puruzluluk cihaziyla olculmustur. Ileri beslemeli bir yapay sinir agi, islenen yuzeylerden elde edilen puruzlulugu tahmin etmek icin kullanilmistir. Kesme hizi (Vi), ilerleme (fz), eksenel kesme derinligi (an) ve radyal kesme derinligi (at) gibi parametreler, yapay sinir aginin giris katmanin'...
Dynamic analysis of composite doubly curved panels with variable thickness subjected to different... more Dynamic analysis of composite doubly curved panels with variable thickness subjected to different pulse types using Generalized Differential Quadrature method (GDQ) is presented in this study. Panels with variable thickness are used in the construction of aerospace and marine industry. Giving variable thickness to panels can allow the designer to get optimum structural efficiency. For this reason, estimating the response of variable thickness panels is very important to design more reliable structures under dynamic loads. Dynamic equations for composite panels with variable thickness are obtained using virtual work principle. Partial derivatives in the equation of motion are expressed with GDQ and Newmark average acceleration scheme is used for temporal discretization. Several examples are used to highlight the effectiveness of the proposed method. Results are compared with finite element method. Effects of taper ratios, boundary conditions and loading type on the response of compos...
In this paper geometrically nonlinear static behavior of laminated composite hollow super-ellipti... more In this paper geometrically nonlinear static behavior of laminated composite hollow super-elliptic beams is investigated using generalized differential quadrature method. Super-elliptic beam can have both oval and elliptic cross-sections by adjusting parameters in super-ellipse formulation (also known as Lamé curves). Equilibrium equations of super-elliptic beam are obtained using the virtual work principle. Geometric nonlinearity is taken into account using von-Kármán nonlinear strain-displacement relations. Spatial derivatives in strains are expressed with the generalized differential quadrature method. Transverse shear effect is considered through the first-order shear deformation theory. Static equilibrium equations are solved using Newton-Raphson method. Several composite super-elliptic beam problems are solved with the proposed method. Effects of layer orientations of composite material, boundary conditions, ovality and ellipticity on bending behavior are investigated.
Bu calismada tabakali kompozit levha ve panellerin dusuk carpma hizlarindaki nonlineer dinamik da... more Bu calismada tabakali kompozit levha ve panellerin dusuk carpma hizlarindaki nonlineer dinamik davranisi Genellestirilmis Diferansiyel Kuadrature (Generalized Differential Quadrature) yontemi ile incelenmektedir. Sistemin dinamik denklemleri Virtuel is ilkesi ile elde edilmektedir. Duzleme dik dogrultudaki kalinlik etkisi 1. mertebe kayma deformasyon teorisi ile dikkate alinmaktadir. Buyuk yer degistirmeler Von-Karman nonlineer birim sekil degisimleri ile dikkate alinmaktadir. Konumsal turevler Genellestirilmis Diferansiyel Quadrature yontemi ile zaman integrasyonu da Newmark metodu ile hesaplanmaktadir. Onerilen metotla bircok carpma problemi cozulmus ve literaturdeki sonuclarla karsilastirilmistir. Onerilen metodun carpma problemlerinin incelenmesinde etkili ve verimli bir yontem oldugu gosterilmistir.
Crashworthiness, Occupant Protection and Biomechanics in Transportation Systems, 2001
Optimum crashworthiness design of the vehicle rail structure is one of the crucial tasks in desig... more Optimum crashworthiness design of the vehicle rail structure is one of the crucial tasks in designing crashworthy vehicles that render better occupant protection. The usual trial-and-error approach in selecting the optimum design parameters, in order to maximize the energy absorbing capacity of the rail structure, is computationally expensive and cumbersome; particularly when there are several design parameters to be properly selected. Optimization methods can be used to automate the search for the optimum design parameters. In the current research, an efficient design optimization methodology is presented and utilized to obtain optimum crashworthiness design of the energy-absorbing rail structures. The methodology adopted in this research makes use of Design of Experiments (DOE) based approximation methods, numerical optimization algorithms and structural analysis software. The design optimization approach has been devoted to structural impact applications. The nonlinear explicit F...
Abstract Present study deals with large displacement transient dynamic response of truncated coni... more Abstract Present study deals with large displacement transient dynamic response of truncated conical panels made of Porous Functionally Graded Materials (P-FGMs) using Generalized Differential Quadrature (GDQ) method. In this study, geometric non-linearity is taken into consideration through Green-Lagrange non-linear strain-displacement relations. First order shear deformation theory (FSDT) is utilized to take transverse shear effects into account. Virtual work principle is used to derive the equation of motion. The solution methodology utilizes GDQ method for spatial discretization of the variables. Newmark average acceleration method is implemented in time integration. Effects of different types of porosity distribution, porosity ratio and conical parameters on non-linear transient behavior of truncated conical panels are investigated for functionally graded material made of Zirconia/Aluminum (ZrO2/Al) considering various volume fraction coefficients.
In this study, natural frequencies and vibrational mode shapes of variable stiffness composite sk... more In this study, natural frequencies and vibrational mode shapes of variable stiffness composite skewed plates are optimized applying a genetic algorithm. The variable stiffness behavior is obtained by altering the fiber angles continuously according to two selected curvilinear fiber path functions in the composite laminates. Fundamental frequency and related mode shapes of the plates are optimized for two different fiber path functions using the structural model obtained based on the virtual work principle. A three-layer composite skewed plate with four types of boundary conditions and different plate geometries is considered as case study in this research. Diverse sweptback angles as well as different aspect ratios are considered as various plate geometries. The present study aims to calculate the best fiber path with maximized fundamental frequency or in-plane strengths for a composite skewed plate. The generalized differential quadrature method of solution is employed to solve the governing equations of motion. Moreover, the linear kinematic strain assumptions are used, and the first-order shear deformation theory is employed to generalize the formulation for the case of moderately thick plates including transverse shear effects. Numerical results demonstrate the effect of the fiber angles, boundary conditions, and diverse geometries on the natural frequencies of the composite plate. The optimal fiber angles of each layer are presented for the above cases in free vibration analysis. It is verified that the application of optimized curvilinear fibers instead of the traditional straight fibers introduces a higher degree of flexibility, which can be used to adjust frequencies and mode shapes.
Abstract In the present study, the fundamental natural frequencies of curvilinear fiber composite... more Abstract In the present study, the fundamental natural frequencies of curvilinear fiber composite skew and taper cylindrical panels are optimized applying genetic algorithm (GA). Later, the fundamental amplitude-dependent nonlinear frequency behavior of the optimized curved fiber layup configurations is studied and compared with the reference unidirectional fiber layup. The variable stiffness behavior is obtained by altering the fiber angles continuously according to the curvilinear fiber path function in the composite laminates. A nonlinear structural model is utilized based on the virtual work principle. Green’s nonlinear kinematic strain relations are used to account for the geometric nonlinearities and the first-order shear deformation theory (FSDT) is adopted to generalize the formulation for the case of moderately thick cylindrical panels including transverse shear deformations. The goal is to determine how the variable stiffness parameters affect the linear and nonlinear free vibration behavior of the skew and taper cylindrical panels. Consequently, one may find the optimum fiber path with improved structural characteristics for the cylindrical panel. Eight-layered composite skew and taper cylindrical panels at two different boundary condition sets are considered in this research. Generalized Differential Quadrature (GDQ) method of solution is employed to solve the nonlinear governing equations of motion. Numerical results demonstrate the degree of effectiveness for fiber angle paths, boundary conditions, and geometrical non-uniformities on the fundamental frequencies of the cylindrical panel. Eventually, optimum fiber angles of each layer in free vibration analysis are presented.
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Papers by Hasan Kurtaran