<br><font size=2 face="Arial">"Interesting, Gray. Would you also discuss some details about chopped filler (say 1/16" to 1/2" chop length) and continuous strand filler? Also how material stiffness and impact resistance are affected?"</font>
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<br><font size=2 face="Arial">MattK</font>
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<br><font size=2 face="sans-serif">Chopped fibers actually work well. A chopped fiberglass of about 1.0" can approach most of the properties of continuos fiberglass(as long as the fiber volume is sufficient). Shorter fiber such as 0.5" and 0.25" increase most of the properties of neat epoxy resin also. In essence they are long enough to transfer some load through the matrix. An 8% by weight chopped fiberglass in epoxy looks like wet cat hair. Pack enough fiber in (fiber volumes greater than 30%) and even a<b> FILLET</b> can now transfer load and can become useful. Of course all of this is way too much for our applications.</font>
<br><font size=2 face="sans-serif">Chopped fibers suck in my industry because we need absolute predicability. Not knowing exactly how the fiber is oriented or what the void volume is is impossible to analyze (FEA). Chopped fiber is never as good or as light as continuous fiber. Chopped fiber does not give you "Maximum efficiency of materials" which means it is too heavy to rely on. On Aeroslave planes, I mix 3-4% chopped carbon fiber to beef up the microballoon-epoxy corner fill material.</font>
<br><font size=2 face="sans-serif">First thing I had to learn to do when transitioning from building missiles to building pattern planes is not to build it too strong. Remember.....If you cannot break it then you made it <b>too heavy</b>!<br>
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Gray Fowler<br>
Principal Chemical Engineer<br>
Composites Engineering</font>