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Coefficient of Moisture Expansion (CME) - CME is defined as the fractional increase in strain per unit mass variation due to the moisture desorption or absorption. The CME is determined by measuring the moisture content change and the strain change between two moisture equilibrium states. The CME is needed in the design and construction of high stability structural applications. Precision Measurements and Instruments Corporation PMIC has extensive experience measuring the CME in composite plates, tubes and honeycomb structures with a wide variety of sizes, and shapes, temperatures and humidities.

The moisture change is measured using a balance with a resolution of 10-4 g. The strain change is measured with a unique hanging sample dilatometer, developed by engineers at PMIC. This dilatometer uses Linear Variable Differential Transformers (LVDTs) to monitor length change. The dilatometer has a maximum resolution of 3*10-6 in.

PMIC has the ability to make real time strain and percent moisture change under many different environmental conditions between 0% RH to 95% RH and at temperatures ranging from 25°C to 85°C. Axial and transverse expansions of panels as well as hoop and axial moisture expansion of tubes are made with this system. Our test procedures allow the calculation of Fickian and non-Fickian diffusion coefficients.

Relevant ASTM standards utilized are:

• ASTM C272 Water Absorption of Core materials for Structural Sandwich Constructions
• ASTM C481 Laboratory Aging of Sandwich Constructions
• ASTM C271 Density of Core Materials for Structural Sandwich Constructions
• ASTM E104 Maintaining Constant Relative Humidity by Means of Aqueous Solutions
• ASTM D570 (1988) Water Absorption of Plastics
• ASTM D5229/ D5229M Moisture Absorption Properties and Equilibrium Conditioning of Polymer Matrix Composite Materials.

PMIC is also developing advanced test techniques combining microbalance and remote displacement measuring systems for hygro-thermo-elasticity characterization.

Please contact us with your Moisture Expansion based requirements.