DIY Network

Composite Panel Composite Panel From "Trade School" episode DTRS-108

Figure A

In this episode of Trade School, we follow the education of aviation technology student Sean Hulit through his Airframe and Power Plant courses at school (figure A). Aviation technicians maintain, repair and rebuild almost all facets of today’s aircraft. Due to stringent industry regulations and the enormous responsibility to flight crews and passengers, only the most dedicated of students can make the grade.

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Until a few years ago, most airplane components were crafted with aluminum. In recent years, the industry has shifted to the use of carbon fiber materials. These materials are lighter, easier to work with, and have as much inherent strength as their aluminum predecessors, resulting in a more efficient aircraft. Today, carbon fiber materials are used in virtually all parts of the aircraft structure.

In this segment, we join Sean at his Advanced Composites class where his instructor Tim Guerrero guides him through a basic skills project (figure B). Today, Sean fabricates a small fiberglass panel, typically used to build or repair modern airplane components (figure C). This composite "sandwich" is also used in boat and spa construction. An exact ratio of resin to fiber is critical to harness the strength of the panel.

Figure B

Figure C

Materials:
Fiberglass cloth
Kevlar fabric
Teflon peel-py
Cotton bleeder coth
Nomex honeycomb core
Epoxy resin and sow hardener

Basic Tools:
Wood tongue depressor
Paintbrush
Vacuum press
Scissors
Razor blade
Band saw

• Sean begins by taking inventory of his materials (figure D). The "recipe" for this fiberglass "sandwich" calls for epoxy resin coupled with a hardening agent, two sections of Kevlar (the same material used to make bulletproof vests), four sections of fiberglass cloth, one section of fire-retardant honeycomb core, four sections of Teflon peel-ply and two sections of cotton bleeder cloth. For this project, all the sections are pre-cut into small squares.

• To make the required mixture called a resin matrix, Sean combines equal parts of resin and a hardening agent (figure E). Making sure not to incorporate any air, he slowly stirs the matrix in a plastic cup using a wood tongue depressor.

  Figure D

  Figure D

  
  

• Next Sean builds up half the panel on a sheet of plastic film. He orients a sheet of Kevlar fabric across his work area so that the direction of the weave, or "warp" runs left to right (figure F). (To help orient the pieces, he pre-marked the warp with a marker). Then, using a clean paintbrush, he coats a thin layer of the matrix on the Kevlar. He brushes with the direction of the warp for better resin penetration (figure G).

  Figure F

  Figure G

  
  

• Next, he adds a fiberglass cloth over the Kevlar. This time, he orients the warp at a 45-degree angle. Crossing the weaves in this manner is critical for adding strength to the panel. He repeats wetting the fiberglass with the resin matrix. He adds a second fiberglass cloth over the first orienting the warp another 45-degrees (figure H). Again, he wets this with matrix.

• Then, after removing the plastic wrap, he centers the stack over the honeycomb so that the Kevlar layer contacts the honeycomb (figure I).

  Figure H

  Figure I

  
  

• Sean completes the build-up by making a second stack using the same procedure described above. He sandwiches the honeycomb between the two stacks.

  In the next segment, Sean cures the panel with vacuum pressure and heat.
  

  ALSO IN THIS EPISODE:
  	Composite Panel
  	The Curing Process
  	Timing Radial Engine Valves
  	Web Extra: Where Are They Now? (Sean Hulit)