The Fabrication and Mechanical Properties of Continuous Fiber Composite Lattice Structures

Doctoral Thesis / Dissertation , 2016 , 292 Pages

Engineering - Aerospace Technology

The primary aim of this research work is to examine the mechanical properties per weight density of novel core materials for use in sandwich panels. Composite lattice core sandwich structures with relative densities in the range of 3% to 35% were manufactured and tested under quasi-static compression loading conditions. Collapse strength, failure mechanisms and energy absorption characteristics of the lattice structures have been evaluated. Since these core material shapes are unique, research involved developing suitable manufacturing methods. The study started by looking at introducing simple through thickness lattice structure into PET foam cores. This was achieved by drilling the foam material, glass fibers were then inserted into the perforations. The panel was then infused with resin using the vacuum assisted resin transfer molding process. This was then extended to look at the possibility of removing the core by adopting a-lost mold manufacturing procedure that would leave a free-standing lattice structure. This involved inserting reinforcing fiber tows through holes in wax blocks. Following infusion with an epoxy resin and subsequent post curing, the preforms were heated to a temperature above that required to melt the wax, leaving well-defined lattice structures based on vertical, pyramidal, modified-pyramidal, octet configurations and others based on what are termed BCC, BCCz, FCC and F2BCC designs. Compression tests showed that the strength of individual struts and the corresponding cores increases with strut diameter and fiber volume fraction. Smaller diameter struts failed in buckling, whereas the larger diameter columns failed in a crushing mode involving high levels of energy absorption. Truss core structures with 4 mm diameter columns, based on 28% fiber volume fractions offered specific energy absorption values above 70 kJ/kg. Compression tests on the four lattice structures based on BCC, BCCz, FCC and F2BCC designs indicated that the F2BCC lattice offered the highest compression strength of approximately 12 MPa. Although, when normalized by relative density, the BCCz lattice structure out-performed the three remaining structures. The specific energy absorption values of the lattices were relatively high, ranging from 44 kJ/kg for the BCC lattice to 80 kJ/kg for the BCCz structure. Similarly, the specific compression strengths of some of the lattices have been shown to be superior to those of more traditional core materials. [...]

Inhaltsverzeichnis (Table of Contents)

• Abstract
• Nomenclature
• Chapter 1: Introduction
  • 1.1 Background
  • 1.2 Literature Review
  • 1.3 Aims and Objectives
  • 1.4 Thesis Organization
• Chapter 2: Fabrication Procedures
  • 2.1 Introduction
  • 2.2 Manufacturing Through-Thickness Lattice Core Structures in Foam
  • 2.3 Fabrication of Free-Standing Lattice Core Structures
  • 2.4 Lattice Structures Manufactured using the Lost-Mold Technique
  • 2.5 Conclusion
• Chapter 3: Mechanical Characterization
  • 3.1 Introduction
  • 3.2 Experimental Procedure
  • 3.3 Compression Testing of Foam Core Structures
  • 3.4 Compression Testing of Free-Standing Lattice Core Structures
  • 3.5 Compression Testing of Lattice Structures Manufactured using the Lost Mold Technique
  • 3.6 Conclusion
• Chapter 4: Analytical Modeling
  • 4.1 Introduction
  • 4.2 Analytical Prediction of Elastic Properties
  • 4.3 Analytical Prediction of Compression Collapse Strength
  • 4.4 Conclusion
• Chapter 5: Numerical Modeling
  • 5.1 Introduction
  • 5.2 Finite Element Modeling of Lattice Structures
  • 5.3 Results and Discussion
  • 5.4 Conclusion
• Chapter 6: Conclusions and Future Recommendations
  • 6.1 Conclusions
  • 6.2 Future Recommendations
• References
• Appendix

Zielsetzung und Themenschwerpunkte (Objectives and Key Themes)

This research investigates the mechanical properties of novel core materials for use in sandwich panels. The primary objective is to examine the mechanical properties per weight density of these materials. The study focuses on manufacturing and testing composite lattice core sandwich structures with a range of relative densities under quasi-static compression loading conditions.

• Fabrication and testing of lattice core structures with varying densities and geometries.
• Examination of the mechanical properties, including collapse strength, failure mechanisms, and energy absorption characteristics.
• Development of suitable manufacturing methods for unique lattice core structures.
• Comparison of the mechanical performance of various lattice structures with traditional core materials.
• Development of analytical and numerical models to predict the mechanical behavior of lattice structures.

Zusammenfassung der Kapitel (Chapter Summaries)

The thesis begins with an introduction providing background information on the use of lattice structures in sandwich panels and a review of relevant literature. Chapter 2 focuses on the fabrication procedures for different types of lattice core structures, including the development of a 'lost mold' manufacturing technique. Chapter 3 presents the results of mechanical characterization experiments, including compression testing of foam core structures, free-standing lattice core structures, and lattice structures manufactured using the lost mold technique. Chapter 4 delves into the analytical modeling of lattice structures, including predictions of elastic properties and compression collapse strength. Chapter 5 provides a detailed analysis of the numerical modeling using finite element methods and compares these results with analytical predictions and experimental data. While the conclusion of the thesis is not included in this preview, Chapter 6 likely provides a comprehensive summary of the findings and suggests future research directions.

Schlüsselwörter (Keywords)

This research focuses on the fabrication and mechanical properties of lattice structures for use in sandwich panels. Key themes include: lattice structures, sandwich structures, mechanical properties, resin infusion, finite element, composites, VARTM, unidirectional fiber, and energy absorption. The study explores various manufacturing techniques, including the lost mold method, and uses experimental data to investigate the impact of factors such as strut diameter, fiber volume fraction, and geometry on the mechanical performance of these structures. The research also involves the development of analytical and numerical models to predict and analyze the mechanical behavior of lattice structures.

• Course: Aerospace Engineering
• Author: Hassan Ziad Jishi (Author)
• Publication Year: 2016
• Pages: 292
• Catalog Number: V345395
• ISBN (eBook): 9783668355910
• Language: English
• Tags: fabrication, mechanical, properties, continuous, fiber, composite, lattice, structures