Day 7 – Some Like It HOT!

One of the many issues in utilizing composite materials has to do with the anticipated temper range in which the structure is expected to operate. In all cases, it’s the ability of the resin system to maintain its physical properties throughout the operating environment. Too cold equals too brittle and subject to fracture, too hot and the resin will exceed its Tg – Glass Transition Temperature.

The Tg of a resin system is the temperature at which a polymer resin will begin to change from a hard glass-like state to a soft rubber-like state. The selection of the resin to be used in any given application must ensure that the Tg of the resin will be well above the maximum temperature it could ever be exposed to.

For ultra-high temperature exposure and ultra-high performance such as would be found in a jet engine exhaust nozzle, Ceramic Matrix Composites (CMC’s) or Carbon-Carbon Composites (C-C) are used to deflect heat away from the surrounding components. Pictured here are the ceramic heat deflecting plates lining the exhaust nozzle of a General Electric F414 turbojet engine as fitted to the F-18 Super Hornet fighter.

Oxide-ceramic matrix composites are typically made from a blend of aluminium oxide (AL2O3) and silicon dioxide (SiO2). This material can easily withstand temperatures in excess of 1000 deg. C!

New high-temp ceramic materials are in development all the time. Now available as a pre-preg known as Cerapreg? from Insovolta AG in Austria.