Experimental and theoretical investigations of stiffened and unstiffened composite panels under uniform transversal loading

Diploma Thesis , 2003 , 102 Pages , Grade: 1,0

Engineering - Mechanical Engineering

With the increased use of composite materials in various structural applications, the subject of analysing the properties of composite unstiffened and stiffened panels has received widespread attention. Laminated panels are considered as the basic modules of high performance boats, aircraft and many other complex structures, which require less specific weight, better durability, and excellent damage tolerance and are often subject to air-blast loading or under water shock. The failure mode of fibre reinforced composite materials is rather more complex than that of isotropic material. This is because of the different properties of fibres and matrix the composite is made of. There has been a number of failure theories developed since the first industrial usage of composites in the early 1980s. Those theories are based on different failure criteria and often just cover some special set up. In the last years computer simulations based on FEA were set up to predict the failure of composites. Because there is only few experimental data available for comparison, the need for experimental investigations of composites is big.
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Inhaltsverzeichnis (Table of Contents)

• 1. INTRODUCTION
• 2. BASICS OF COMPOSITE STRUCTURES
• 2.1 COMMON FIBRES
• 2.2 GLASS FIBRE
• 2.3 COMMON MATRICES
• 2.4 EPOXY MATRIX
• 2.5 FIBRE - MATRIX INTERACTION
• 2.6 FAILURE TYPES OF COMPOSIte Materials
• 2.6.1 Micro Failure Mechanism
• 2.6.2 Macro Failure Mechanism
• 3. EXPERIMENTAL INVESTIGATION OF A CANTILEVER BEAM
• 3.1 SETUP AND PROCEDURE
• 3.2 RESULTS AND DISCUSSION
• 3.3 E-MODULUS
• 3.4 CONCLUSION
• 4. EXPERIMENTAL INVESTIGATION OF COMPOSITE PANELS
• 4.1 PROBLEM STATEMENT
• 4.1.1 Commonly Used Methods and Former Experiments
• 4.1.2 Method Adopted
• 4.2 SPECIMEN PROPERTIES
• 4.2.1 Sample Preparation
• 4.2.2 Stiffeners
• 4.2.3 Sensor Setup
• 4.3 EXPERIMENTAL PROGRAM AND INSTRUMENTATION
• 4.4 Test ResulTS AND ANALYSIS
• 4.4.1 Panel-1, no Stiffener
• 4.4.2 Panel-2, one Stiffener
• 4.4.3 Panel-3, two Stiffeners
• 4.5 DISCUSSION
• 4.5.1 Panel-1, no Stiffener
• 4.5.2 Panel-2, one Stiffener
• 4.5.3 Panel-3, two Stiffeners
• 4.6 DISCUSSION AND ERRORS
• 5. LAMINATE THEORY FOR THE UNSTIFFENED PANEL
• 5.1 ELASTIC PROPERTIES
• 5.2 ANALYTIC APPROACH WITH KNOWN FORMULAS
• 5.3 LAMINA STRENGTH AND Failure TheorIES
• 5.3.1 Lamina Strength and Failure Mechanism
• 5.3.2 Failure Theories
• 5.4 LAMINATE STRENGTH AND FAILURE
• 5.4.1 First Ply Failure
• 5.4.2 Ultimate Laminate Failure
• 6. FINITE ELEMENT ANALYSIS
• 6.1 SETUP
• 6.2 RESULTS
• 6.2.1 Panel-1, no Stiffener
• 6.2.2 Panel-2, one Stiffener
• 6.2.3 Panel-3, two Stiffeners
• 6.3 DISCUSSION AND ERRORS
• 7. COMPARISON
• 7.1 DEFLECTIONS
• 7.2 STRAINS
• 7.3 FAILURES AND STRESSES
• 8. CONCLUSION

Zielsetzung und Themenschwerpunkte (Objectives and Key Themes)

This thesis aims to analyze the behavior of stiffened and unstiffened composite panels subjected to uniform transversal loading. The research investigates both experimental and theoretical aspects of the problem, focusing on the load-deflection response, strain distribution, and failure mechanisms.

• Experimental investigation of a cantilever beam
• Experimental investigation of composite panels with different stiffeners
• Laminate theory for the unstiffened panel
• Finite element analysis of the composite panels
• Comparison of experimental and theoretical results

Zusammenfassung der Kapitel (Chapter Summaries)

• Chapter 1 introduces the subject of stiffened and unstiffened composite panels and sets the stage for the research conducted in this thesis.
• Chapter 2 discusses the basics of composite structures, covering topics like common fibers, matrices, and the interaction between fibers and matrices. The chapter also explores different failure types in composite materials, including micro and macro failure mechanisms.
• Chapter 3 details an experimental investigation of a cantilever beam made from composite material. The chapter covers the setup and procedure of the experiment, the results obtained, and a discussion of the E-modulus and failure mechanisms.
• Chapter 4 delves into the experimental investigation of composite panels with different stiffener configurations. It outlines the problem statement, the specimen properties, the experimental program, and the analysis of the test results. This chapter examines the load-deflection behavior, strain distribution, and failure modes of panels with varying stiffness.
• Chapter 5 presents a laminate theory for the unstiffened panel, focusing on its elastic properties and applying analytical approaches with known formulas to analyze the panel's strength and failure behavior. The chapter also explores lamina strength and failure theories, including first ply failure and ultimate laminate failure.
• Chapter 6 covers the finite element analysis of the composite panels. It describes the setup of the analysis, presents the obtained results for different stiffener configurations, and discusses the discrepancies between the simulated and experimental results.
• Chapter 7 compares the experimental and theoretical results obtained throughout the thesis. This chapter examines the deflections, strains, and failures observed in the experiments and compares them with the predictions of the laminate theory and finite element analysis.

Schlüsselwörter (Keywords)

Composite panels, stiffeners, transversal loading, experimental investigation, laminate theory, finite element analysis, load-deflection response, strain distribution, failure mechanisms.

• Grade: 1,0
• Author: Dr.-Ing. Jan Brökel (Author)
• Publication Year: 2003
• Pages: 102
• Catalog Number: V114919
• ISBN (eBook): 9783640150984
• ISBN (Book): 9783640151073
• Language: English
• Tags: Experimental