Changes in the coefficient of thermal expansion in stressed Gilsocarbon graphite

The thermal expansion coefficient (CTE) of Gilsocarbon graphite samples has been measured using strain gauges whilst the samples were subject to either tensile or compressive static loading. Compressive loading increased the CTE from ∼5.4 × 10−6 K−1 to ∼8 × 10−6 K−1 for a compressive load of −50 MPa, whilst tensile loading decreased the CTE to ∼4 × 10−6 K−1 for a tensile load of 12 MPa. There was also found to be corresponding changes to CTE perpendicular to the loading direction. Independent measurements on other samples using clip gauge extensometers were shown to support the strain gauge results. It is considered that the mechanism for this behaviour is related to closure of micro-cracks under load.