Zahit Mecitoğlu

Nonlinear Structural Response of Laminated Composite Plates Subjected to Blast Loading

We are concerned with the theoretical analysis of the laminated composite plates exposed to normal blast shock waves as well as presenting correlation between the theoretical analysis and the experimental results of the strain time histories. The laminated composite plate is clamped at all edges. On the theoretical side of the study, dynamic equations of the plates are derived by the use of the virtual work principle within the framework of the Love theory of plates. The geometric nonlinearity effects are taken into account with von Karman assumptions. Then the governing equations of the laminated plate are solved by the Runge-Kutta-Verner method. A new displacement function is considered for the theoretical solution of the blast-loaded clamped plate. Furthermore, finite element modeling and analysis for the blast-loaded composite plates are presented. On the experimental side of the study, tests have been carried out on the laminated composite plates with clamped edges for two different blast loads. The results of theoretical and finite element methods are compared with the experimental results. Theoretical and finite element analyses results are in a good agreement. There is a qualitative agreement between the analyses and experimental results in the first load case. The predicted peak strains and response frequency are in an agreement with the experimental results for first load case. Thus the theoretical solution may be used for providing material in the preliminary design stage. There is a difference between the analysis and experimental results in the second load case because of the extremely large deflections. In this study the effects of loading conditions, geometrical properties, and material properties are separately examined on the dynamic behavior, as well.

Nonlinear Damped Vibrations of a Laminated Composite Plate Subjected to Blast Load

This research deals with the derivation and solution of nonlinear dynamic equations of a clamped laminated plate exposed to blast load including structural damping effects. Dynamic equations of the plate are derived by the use of the virtual work principle. The geometric nonlinearity effects are taken into account with the von Karman large deflection theory of thin plates. An appropriate approximate solution is assumed for the space domain considering the finite element analysis results for the large deformation static analysis of the laminated plate. The Galerkin method is used to obtain the nonlinear differential equations in the time domain. These nonlinear differential equations include structural damping effects. The finite difference method is applied to solve the system of coupled nonlinear equations. The results of the theoretical analysis are compared with the experimental results. Good agreement is found for the peak values and frequencies. Effects of aspect ratio and damping on the dynamic response of the plate are examined. The damping coefficient greatly affects the nonlinear dynamic response.

Governing equations of a stiffened laminated inhomogeneous conical shell

This study presents the dynamic equations of a stiffened composite laminated conical thin shell under the influence of initial stresses. The governing equations of a truncated conical shell are based on the Donnell-Mushtari theory of thin shells including the transverse shear deformation and rotary inertia. The extension-bending coupling is considered in the derivation. The composite laminated conical shell is also reinforced at uniform intervals by elastic rings and/or stringers. The stiffening elements are relatively closely spaced, and therefore the stiffeners are smeared out along the conical shell. The inhomogeneity of material properties because of temperature, moisture, or manufacturing processes is taken into account in the constitutive equations. A generalized variational theorem is derived so as to describe the complete set of the fundamental equations of the conical shell. Next, the uniqueness is examined in solutions of the dynamic equations of the conical shell, and the boundary and initial conditions are shown to be sufficient for the uniqueness in solutions. The equations of the laminated composite conical shell are solved by the use of the finite difference method as an illustrative example. The accuracy of results is tested by certain earlier results, and a good agreement is found.

Dynamic Response of Composite Cylindrical Shells to Shock Loading

In this paper, dynamic response of composite cylindrical shells subjected to shock loading is studied analytically. The equations of motion are based on Sanders theory of thin shell. The effects of transverse shear deformation and rotatory inertia are taken into account. The circular cylindrical thin shell with simply supported ends is subjected to a shock load, represented by an axially symmetric moving load at a constant speed along the longitudinal direction. The governing equations are solved analytically using the Assumed-Modes Method. The influences of geometrical parameters and composite material properties of circular cylindrical shells on the dynamic response are studied.

Design and Manufacturing of a Composite Drive Shaft

In this study, a composite drive shaft for heavy commercial vehicles is designed and manufactured. The carbon/epoxy composite material is used for the shaft tube and the end joints are made of steel. The material properties of the carbon/epoxy composite are obtained by performing coupon tests. The shaft tube is modeled using ANSYS finite element software. The static, buckling and modal analysis are achieved to obtain the Tsai-Wu strength ratio, the critical buckling torque and free vibration frequencies, respectively. The shaft tube is manufactured by using filament winding method. The steel end connections are bonded to the shaft tube during the filament winding process.

Numerical investigation of stepped concentric crash tubes subjected to axial impact: The effects of number of tubes

The purpose of this study is to examine the energy absorption characteristics of stepped concentric crash tubes subjected to an axial impact load. The stepped concentric tubes with circular cross section are analyzed numerically by using LS-DYNA. The total mass and volume are kept constant when the number of tubes is increased. As the number of concentric tubes is increased, it is observed a smooth transition of the peak forces during the impact. Also increasing the number of tubes reduces the maximum peak force and leads to a reduction of the initial peak force due to lower wall thickness of the tubes.

Active vibration control of a laminated composite plate subjected to blast load

Purpose – The purpose of this paper is to develop a structural vibration control system by using a state observer which estimates system states using displacements measured from sensors.Design/methodology/approach – Friedlanders exponential decay function is used for expressing the blast load model. A semiloof shell element is developed in order to account for piezoelectric effects. The composite plate is discretized by using the semiloof shell elements, and stiffness and mass matrices of the plate are obtained from the finite element model. In order to reduce the degrees of freedom of the finite element model, mode summation method is used with weighted modal vector including initial dominant modes in the dynamic behavior.Findings – The structural vibrations are suppressed successfully and in an optimal way by using a state observer control system which estimates system states using displacements measured from sensors.Originality/value – This paper shows, for the first time, that vibrations of a cantile...

FREE VIBRATIONS OF A CONICAL SHELL WITH TEMPERATURE-DEPENDENT MATERIAL PROPERTIES

This article presents an analysis of the free vibrations of a truncated conical thin shell subjected to thermal gradients. The governing equations of the shell are based on the Donnell-Mushtari theory of thin shells. Simply supported and clamped boundary conditions are considered at both ends of truncated conical shell. Temperature loading due to supersonic flow is assumed to vary along the meridian and across the thickness of the shell Hamiltons principle is used to derive the appropriate governing equations of a conical shell with temperature-dependent material properties. The shell material has a kind of inhomogeneity due to the varying temperature load and temperature dependency of material properties. The resulting differential equations are solved numerically using the collocation method. The results are compared with certain earlier results. The influence of temperature load on the vibration characteristics is examined for the conical shells with various geometrical properties.

Crashworthiness Optimization of Nested And Concentric Circular Tubes Using Response Surface Methodology And Genetic Algorithm

In this study crashworthiness optimization of nested and concentric circular tubes under impact loading is performed by coupling Finite Element model, Response Surface Models and Genetic Algorithm. Specific Energy Absorption SEA and Crash Force Efficiency CFE are used in crashworthiness optimization since these criteria are important indicators for evaluating crashworthiness performance. Length and thickness of three concentric tubes as well as radius of one tube are adopted as design variables which are effective parameters on SEA and CFE. To reduce the computational cost of the optimization procedure, simple and computationally cheap Response Surface Models are created to replace finite element analyses in further calculations. The Non‐dominated Sorting Genetic Algorithm –II NSGAII is applied to obtain the Pareto optimal solutions. Optimization results are presented for different selected designs that indicate relative importance of multi‐objective functions. Results show that the total weight of the vehicles can be reduced by using nested tubes comparing to single tubes with identical masses. These designs can be adopted for use in practice.

Flutter Analysis of A Laminated Composite Plate with Temperature Dependent Material Properties

Panel flutter is a self-excited oscillating phenomenon and involves interactions among elastic, inertia, and aerodynamic forces in supersonic flow. The panel flutter differs from wing flutter only in that the aerodynamic force resulting from the airflow acts only on one side of the panel. In the framework of small deflection linear structural theory, there is a critical speed of the airflow (or dynamic pressure λcr) beyond which the panel motion becomes unstable and grows exponentially with time.