Hamidreza Yazdani Sarvestani

Stress analysis of thick orthotropic cantilever tubes under transverse loading

In this work, a new high-order displacement-based method is proposed to investigate stresses and strains in thick arbitrary laminated orthotropic cantilever straight tubes under transverse loading. The most general displacement field of elasticity for an arbitrary thick laminated orthotropic straight tube is developed. A layer-wise method is employed to analytically determine the local displacement functions and stresses under transverse loading. The accuracy of the proposed method is subsequently verified by comparing the theoretical results with experimental data, finite-element method (FEM), and Lekhnitskii solution. The results show good agreement. In addition, high efficiency in terms of computational time is shown when the proposed method is used as compared with FEM. Finally, several numerical examples for stress and strain distributions in various thick cantilever composite straight tubes subjected to transverse loading are discussed.

Investigation of Through-Thickness Stresses in Composite Laminates Using Layerwise Theory

In this study, an analytical method is developed to exactly obtain the interlaminar stresses near the free edges of laminated composite plates under the bending moment based on the reduced form of elasticity displacement field for a long laminate. The analytical and numerical studies were performed based on the Reddy’s layerwise theory for the boundary layer stresses within cross-ply, symmetric, angle-ply, and general composite laminates. Finally, a variety of numerical results are presented for the interlaminar normal and shear stresses along the interfaces and through thickness of laminates near the free edges. The results showed high stress gradient of interlaminar normal and shear stresses near the edges of laminates.

Analysis of Free Edge Stresses in Composite Laminates Using Higher Order Theories

This paper presents the determination of the interlaminar stresses close to the free edges of general cross-ply composite laminates based on higher order equivalent single-layer theory (HESL). The laminates with finite dimensions were subjected to a bending moment, an axial force, and/or a torque for investigation. Full three-dimensional stresses in the interior and the boundary-layer regions were determined. The computed results were compared with those obtained from Reddy’s layerwise theory. It was found that HESL theory predicts precisely the interlaminar stresses near the free edges of laminates. Besides, high efficiency in terms of computational time is obtainable when HESL theory is used as compared with layerwise theory. Finally, various numerical results were presented for the cross-ply laminates. Also design guidelines were proposed to minimize the edge-effect problems in composite laminates.

Effects of layup sequences on stresses of thick composite cantilever tubes

In this study, a new simple-input displacement-based method is used to study effects of layup sequences on stresses, strains, and deformations of thick laminated orthotropic cantilever straight tubes under transverse loading. Three-dimensional stress distributions are obtained based on the most general displacement field of elasticity. A layer-wise theory which includes the full three-dimensional constitutive relations is used. A non-dimensional simple coefficient is introduced to compare interlaminar radial stresses of different layup sequences. Finally, some design guidelines are proposed to consider effects of layup sequences of laminated thick composite tubes subjected to shearing load.In this study, a new simple-input displacement-based method is used to study effects of layup sequences on stresses, strains, and deformations of thick laminated orthotropic cantilever straight tubes under transverse loading. Three-dimensional stress distributions are obtained based on the most general displacement field of elasticity. A layer-wise theory which includes the full three-dimensional constitutive relations is used. A non-dimensional simple coefficient is introduced to compare interlaminar radial stresses of different layup sequences. Finally, some design guidelines are proposed to consider effects of layup sequences of laminated thick composite tubes subjected to shearing load.

Curved nanotube structures under mechanical loading

Configuration of carbon nanotube (CNT) has been the subject of research to perform theoretical development for analyzing nanocomposites. A new theoretical solution is developed to study curved nanotube structures subjected to mechanical loadings. A curved nanotube structure is considered. A nonlocal displacement-based solution is proposed by using a displacement approach of Toroidal Elasticity based on Eringens theory of nonlocal continuum mechanics. The governing equations of curved nanotube structures are developed in toroidal coordinate system. The method of successive approximation is used to discretize the displacement-based governing equations and find the general solution subjected to bending moment. The numerical results show that all displacement components increase with increasing the nonlocal parameter. The present theoretical study highlights the significance of the geometry and nonlocal parameter effects on mechanical behavior of nanotube structures.

Nonlocal theory to analyse nanotube structures under tension

Because nanocomposites have found augmented use in many industries, the analytical solutions are required to be developed. This paper presents the development of a new analytical method for studying nanotube structures under tension using layer-wise and Eringen theories. Two opposite ends of tubes are subjected to normal forces. Nonlocal governing differential equations are derived and presented. The theoretical developments determine the effect of the geometric and nonlocal constitutive relations for single-walled nanotubes (SWNTs), double-walled nanotubes (DWNTs), and multiwalled nanotubes (MWNTs) under tension loading. It is observed that all displacement components increase with the increase in the nonlocal parameter.

Prediction of Interlaminar Stresses of an Unsymmetric Cross-Ply Laminate Using Layerwise and Higher-Order Equivalent Single-Layer Theories

In the present study, the layerwise theory (LWT) and the first-order shear deformation theory (FSDT) are used to analyze analytically the interlaminar stresses near the freeedges of a general (symmetric and unsymmetric) cross-ply composite laminate subjected to bending. The FSDT is employed to determine the global deformation parameters appearing in the displacement fields. The LWT is then utilized to determine the local interlaminar stresses within the boundary layer regions of laminates. To assess the obtained results from the LWT in conjunction with FSDT, the interlaminar stresses are also computed using higher-order equivalent single-layer theory (HESL) available in the literature. Comparison of results for edge-effect problems of several cross-ply laminates indicates high stress gradients of interlaminar normal and shear stresses near the edge of laminates. Also, LWT can predict interlaminar stresses more accurate than HESL.

Mechanical Behavior of Laminated Composite Curved Tubes

The stress analysis on thick laminated composite curved tubes subjected to pure bending moment is performed by proposing a high-order displacement-based method. The most general displacement field of elasticity for thick laminated composite curved tubes is developed by employing a displacement approach of toroidal elasticity and a layerwise method. The accuracy of the proposed method is verified by comparing the numerical results obtained using the proposed method with finite element method (FEM).

Effects of lay-up sequence in thick composite tubes for helicopter landing gears

Analysis and design of composite helicopter landing gears are challenges. Cross tubes of helicopter landing gears consist of straight tubes at the middle and curved tubes at the sides. In this work, to simulate ground handling, thick laminated composite straight tubes subjected to pure bending moments are studied using a new high-order simple-input analytical method. The accuracy of the proposed method is subsequently verified by comparing the numerical results obtained using the proposed method with finite element method and experimental data. The results show good agreement. High efficiency in terms of computational time is achieved when the proposed method is used as compared with finite element method. In addition, a simple non-dimensional coefficient is proposed to predict interlaminar radial stresses of thick composite straight tubes.