You
are in: Virtual Consultant
> Material Choices > Q3
> Temperature.
The
following should be considered if the composite will experience
temperature extremes. When an organic resin is heated, either
the glass transition temperature,
Tg, will eventually be reached or thermal decomposition will
occur. The properties of organic resins used in composites
are always temperature dependent. Above the Tg, the materials
become softer with lower modulus and strength and in some
cases an increase in susceptibility to moisture absorption.
Composites are rarely used at temperatures above Tg.
In
general:
|
Temperature
Range
|
Effect
|
|
Sub-Zero
|
Fibre-Resin
Debonding
Resin
Hardening
Resin
Microcracking
|
|
Freeze-Thaw
|
Degradation
due to moisture induced swelling and drying.
Aggravated
degradation in the presence of salt due to formation
and expansion of salt deposits
|
|
T
> processing temperature
|
Initial
post cure then thermal degradation
|
 Thermal
decomposition is generally by oxidation. Epoxies are generally
stable up to 150-160°C. Oxidation can lead to a change
of colour, typically a change from pale yellow to rusty brown.
With severe heating or long term use at temperature, oxidation
may lead to microcracks. Phenolics have higher working temperatures
and are thermally stable at 180°C. Oxidation will cause
a hardening and associated change in colour.
|
