Papers by Author: Jalil Rezaeepazhand

Abstract: This paper presents the similarity conditions between aeroelastic instability (flutter) and the free vibration frequency of cross-ply laminated plate. The method is based upon the direct use of governing equation of the system. Both complete and partial similarities are discussed. This approach, the natural frequency analysis of models and prototype is used to predict the flutter boundary of laminated plate. The results present herein indicate that there are some constrains such as geometry of the model, model material, and stacking sequence of laminates in designing a model with complete similarity. As working with complete similar scale model is usually difficult, some certain types of distortion (distortion in number of plies, and stacking sequence) are considered. According to the results, cross ply composite models can be found which have this ability to predict flutter boundary of the prototype accurately using free vibration data.

Abstract: Electrorheological (ER) fluids are a kind of smart material whose rheological properties can be controlled by an external electric field. In the present paper, the transient vibration of a rectangular three layer sandwich plate with electrorheological fluid core is analyzed based on the classical plate theory. The Bingham plastic model is used to consider the post-yield behavior of ER fluid. The structure is modeled using a finite element method. Hamilton’s principle is employed to derive the finite element equations of motion. The constant average acceleration scheme is used to integrate the equations of motion. The effects of change in electric field and core thickness on the structure settling time and its natural frequencies are studied for various boundary conditions. The results show that the thickness of the core layer and the electric field strength has significant effects on damping behavior of the sandwich plate. When the applied electric field increases a linear decay in transient response of the structure is observed. It is also found that the electric field changes have no influence on the system natural frequencies.

Abstract: This study describes the establishment of similarity conditions among structural systems. The main objective of this research is to study the applicability of similitude theory in establishing necessary similarity conditions for designing scaled down models for predicting the vibration behavior of delaminated composite beam-plates. The results presented herein indicate that, for vibration response of delaminated plates, based on structural similitude, a set of scaling laws can be found to establish necessary structural similitude and design rules for small scale models. For models with the same material properties and stacking sequence as prototype, distorted models with different delamination length than those of prototype can predict the behavior of the prototypes with good accuracy.

Abstract: This study investigates the application of laminated composite patches for enhancement of flutter behavior of perforated metallic plates repaired with an external composite patch. Due to material anisotropy and discontinuity in geometry involved in flutter analysis of repaired plates, closed form solutions are practically unobtainable. Numerical studies using commercial finite element software were conducted to investigate the effects of variation in lamination parameters on the flutter boundary of perforated plates repaired with cross-ply composite patches. Both ply-level and sub-laminate level configurations are investigated. Presented results illustrate that flutter boundaries of perforated plates can be changed by choosing proper stacking sequence for composite patches.

Abstract: The performance of perforated metallic plates repaired with laminated composite patches is presented in this study. A square aluminum plate with a central circular cutout is considered as a damaged structural element. Numerical studies using commercial finite element code were conducted to investigate the effects of variation in laminate parameters such as number of plies, fiber orientation, and stacking sequences on free vibration responses of the repaired plates. Particular emphasis is placed on the effect of imperfect bonding (patch debonding). A quantitative measure for the effectiveness of the composite patches parameters is taken to be the relative change in natural frequencies of the deboned patches compare to the patches with perfect bonding. The results presented herein indicated that, vibration response of a repaired perforated metallic plate is affected by the number of plies, stacking sequences of the patch and the quality of bonding between the patch and the base plate.

Abstract: A significant amount of research has been conducted on the buckling behavior of delaminated composite laminates. However, none of the investigations has been focused on establishing similarity and scaling laws for buckling response of composite laminated with delamination. The main objective of this study is to demonstrate the applicability of similitude theory in designing scaled down models for predicting the buckling behavior of delaminated laminated beam subjected to uni-axial compression. The results presented herein indicate that, for buckling response of delaminated beam-plates, based on structural similitude, a set of scaling laws can be found which use to develop design rules for small scale models. For models with the same material properties and stacking sequence as prototype, distorted models with different number of delaminations, delamination length and depth than those of the prototype can predict the behavior of the prototypes with good accuracy.

Abstract: Performance level and life span of existing structural elements can be increased by repair and strengthening of these structural elements using advanced composite materials.The performance of damaged metallic plates reinforced with fiber-reinforced polymer composite materials (composite patch) are presented in this study. A square aluminum plate with a central circular cutout is considered as a damaged structural element. Numerical studies using commercial finite element code were conducted to investigate the effects of variation in patch geometries and lamination parameters on buckling responses of repaired plates. The varying laminate parameters such as, fiber angles and stacking sequences are considered in this study. A quantitative measure for the effectiveness of the composite patches is taken to be the relative change in buckling loads of the reinforced plates compare to those of the perfect one. The results presented herein indicated that, for buckling response of a repaired metallic plate with central cutout, a set of laminated composite patches with different shape and stacking sequences can be found which improve load carrying capacity of damaged plates.

Abstract: The high stress concentration at the edge of a non-circular shaped cutout is of practical importance in designing of the engineering structures. These types of cutout usually are evaluated either experimentally or numerically. In this paper an attempt is made to formulate a simple analytical method for stress analysis in perforated composite plates with non-circular cutouts. The stress concentration of isotropic and composite perforated plates with variety of centrally located non-circular cutout was investigated. Numerical evaluation using commercial finite element code, were conducted to evaluate the analytical results. Parametric studies were conducted to investigate the effects of variation in cutout shape, bluntness, and material properties on the location and the value of the maximum stress in plates subjected to uni-axial tension load. The results presented herein, indicated that the maximum stress in perforated isotropic/composite plates can be significantly change by using proper material properties, cutout shapes and bluntness.