CLTE Linear Thermal Expansion Coefficient Tests

Any material under the influence of increasing temperature begins to expand. This causes significant changes in dimensions, part warping, or internal stress. Linear coefficient of thermal expansion (CLTE) is a material property that characterizes the ability of a plastic to expand under the influence of temperature rise. Applied tests show how dimensionally stable a part under development will remain under temperature changes.

The most widely used international standards for measuring the linear (linear) coefficient of thermal expansion in plastics are:

• ASTM D696-16 Standard test method for linear coefficient of thermal expansion of plastics from minus 30 degrees to plus 30 degrees with a vitreous silica dilatometer
• ASTM E228-17 Standard test method for linear thermal expansion of solid materials with a push rod dilatometer
• ASTM E831-19 Standard test method for linear thermal expansion of solid materials by thermomechanical analysis
• ISO 11359-2 Plastics - Thermomechanical analysis (TMA) - Part 2: Determination of linear coefficient of thermal expansion and glass transition temperature
• ASTM E289-17 Standard test method for linear thermal expansion of rigid solids by interferometry

These standards cover materials in the form of thermoplastics and thermoset materials, filled or unfilled, sheets or molded parts.

The main techniques used for coefficient of thermal expansion measurements are: dilatometry, interferometry, and thermomechanical analysis.

• In the dilatometry technique, the sample is heated in an oven and the displacement of the sample tips is transmitted to a sensor via the push rod. This technique is widely used. Push rods can be of glassy silica type, high purity alumina type or isotropic graphite type. This technique is defined in ASTM D696 and ASTM E228 standards.
• In the thermomechanical analysis method, measurements are made using a thermomechanical analyzer consisting of a sample holder and a probe that transmits changes in length to a transducer that converts the movements of the probe into an electrical signal. This method is defined in ASTM E831 and ISO 11359-2 standards.
• In the interferometry method, with optical interference techniques, the displacement of the sample tips is measured in terms of the number of wavelengths of monochromatic light. The sensitivity is significantly higher than dilatometry, but above 700 degrees interferometry is not used as the technique relies on optical reflection of the sample surface. This method is defined in the ASTM 289 standard.

Our organization also provides CLTE linear thermal expansion coefficient testing services.