Coefficient of moisture expansion  – CME

Aircraft and spacecraft components often require a high degree of dimensional stability. To evaluate polymeric composite materials for aerospace applications, it is necessary to determine the coefficient of moisture expansion (CME). CME is defined as the ratio of change in strain to mass variation due to moisture desorption or absorption.

AAC determines CME by measuring the length change and mass loss of samples in situ in vacuum. The length variation is measured using two laser interferometers, one focused on the front and one on the rear end of the sample, that is thermally stabilized with a thermostat. The mass loss is measured using a high-resolution balance operated in a vacuum chamber and recorded online.

The AAC CME test method offers the advantage of highly accurate measurement within a few days, compared to the typical weeks or months required for other methods. AAC measures mass loss in a vacuum with an accuracy of 1 µg and length change with an accuracy of 10nm.

Coefficient of Moisture Expansion is typically of interest in

• Aerospace
• Aeronautics
• Polymer industry
• Nuclear Reactors