Session: 01-04-01: Advances in Aerospace Structures

Paper Number: 101265

101265 - Buckling Load Optimization of Variable Thickness and Stiffness Composite Plate Using Fem and Semi-Analytical Method 

INTRODUCTION

Optimized structures with lightweight designs are a basic requirement for aerospace structures. Thin skin composites are utilized in such structures owing to their strength-to-weight benefits. Additionally, varying the fiber angle in the composite structures allows for design with localized stiffness variation. Stiffness variation, especially in bending can also be achieved by varying local thickness. In this study, we attempt to improve the buckling performance of the thin skin structures by combining the fiber angle variation and thickness variation spatially across a panel. Two approaches are used for the study, first a numerical approach using the Finite Element pseudo-mesh approach. Second a semi-analytical approach. With both approaches, the objective is to increase buckling load while minimizing the weight of uni-axially and bi-axially loaded panels.

2.            METHODS

The problem is divided into composite fiber angle variation and thickness variation, where numerical and semi-analytical analyses were performed for two types to be combined for a full composite panel with varied thickness profiles.

2.1          Fiber angle variation (FEM)

Fiber angle variation-based optimization is performed where the stiffness of the panel is calculated through the fiber angle at each localized location. FEM analysis was performed using Abaqus by defining the fiber angle at each stress mesh element. After performing an initial analysis with a constant stiffness composite panel, the generated input file generated was modified for varying stiffness panels. The variation of stiffness was performed manually at the manufacturing (pseudo) mesh level and further interpolated using quadratic shape functions generating an input file to be sent to Abaqus for further processing. The obtained buckling value result was optimized using the Gradient Descent method to optimize the stiffness across the plate geometry.

2.2          Thickness variation (FEM)

Like fiber angel variation, a constant thickness plate was numerically solved in FEM (Abaqus), and using the same manufacturing mesh technique a variable thickness panel was generated to update the input file for FEM analysis of the variable thickness panel.

2.3          Semi-Analytical Analysis

Analytical analysis on the stability of thin plates under minimum potential energy consideration was performed using the Ritz method to derivate the governing differential equation for variable stiffness and variable thickness cases. Both cases separately analyzed approximating double Fourier series for the deflection function and solving the eigenvalue problem to calculate the critical buckling load for the plate.

The buckling load was optimized using the Gradient Descent method to optimize for efficient stiffness and thickness variation over the plate.               

3.            Work in Progress

With the completion of analytical and FEM optimization for composite plate, the FEM analysis for thickness variation is also completed. Further work is being expanded on the analysis of the semi-analytical method for thickness variation. The final paper will include an analysis of the composite plate and thickness variation plate separately with a combined analysis of fiber angle and thickness variation and its influence on the buckling load.

 

Presenting Author: Sandesh Amgai The University of Texas at Arlington

Presenting Author Biography: Sandesh Amgai is a graduate student at the University of Texas at Arlington pursuing his doctoral program in Aerospace Engineering. He has completed his Bachelor's degree from the University of Texas at Arlington majoring in Mechanical Engineering with a minor in Nuclear Engineering. Mr. Amgai's primary field of research is focused on the analysis and manufacturing of composite structures using Automated Fiber Placement technology. He is working under the tutelage of Dr. Paul Davidson, at the Laboratory of Advanced Manufacturing, Materials, and Analysis (LAMMA). Besides academia, Mr. Amgai is a member of the Graduate Student Council (GSC) at the university, which is an official voice and governing body of the entire graduate student community.

Authors:

Jeegar Vallabhbhai Patel University of Texas at Arlington
Sandesh Amgai The University of Texas at Arlington
Paul Davidson University of Texas at Arlington