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ASTM D696 Standard Test Method for Coefficient of Linear Thermal Expansion of Plastics Between −30°C and 30°C with a Vitreous Silica Dilatometer
Last updated April 24, 2025
ASTM D696 Standard Test Method for Coefficient of Linear Thermal Expansion of Plastics Between −30°C and 30°C with a Vitreous Silica Dilatometer
ASTM D696 standard outlines a consistent technique for measuring the coefficient of linear thermal expansion (CLTE) of plastics within the range −30°C to 30°C with a vitreous silica dilatometer. This property is essential to assess how plastic materials expand or shrink with a temperature change, influencing their performance in practical applications. A precise measurement of CLTE aids engineers in developing components that preserve structural integrity with changing thermal environments. With the help of standardized equipment and environmental conditions, ASTM D696 attains comparability and reproducibility of outcomes. Comprehending this testing procedure is instrumental in ensuring quality control, investigations, and choice of material within industries that operate from motor cars to aeronautics.
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ASTM D696 Introduction
Plastics undergo dimensional variations with temperature, and the amount of these changes is characterized using the coefficient of linear thermal expansion (CLTE). ASTM D696 provides a method for its measurement between temperatures of −30°C and 30°C. The test is performed on a vitreous silica dilatometer, a very stable device that can pick up tiny changes in sample lengths as the samples are subjected to controlled variations in temperature. The technique applies to both semi-crystalline and amorphous thermoplastics and thermosets, so engineers and materials scientists can assess the consistency of the performance of plastics in thermally dynamic conditions.
ASTMD696 Test Method
Temperature Control
The sample is cooled or warmed at a steady rate between the range of −30°C and 30°C in a liquid bath or environmental chamber.
Measurement Procedure
The length of the plastic sample is measured constantly by the dilatometer as temperature varies.
Calculation of CLTE
The variation of length per unit length per degree of temperature variation is computed through a standard formula.
ASTMD696 Equipment and Sample Preparation
Vitreous Silica Dilatometer
Very stable equipment with very little thermal expansion is utilized to determine length change with high accuracy.
Sample Dimensions
Generally, cylindrical or rectangular samples of known sizes are employed to fill the dilatometer tube precisely.
Preconditioning
The sample is conditioned to the standard environment (typically 23°C, 50% RH) for 40 hours to allow it to equilibrate in moisture.
ASTMD696 Results and Interpretation
The linear coefficient of thermal expansion is measured in mm/mm/°C (or µm/m/°C). Results generally demonstrate a straight-line relationship throughout the temperature range of interest. Data variability might be an indicator of material uniformity, residual stress, or lack of full conditioning. Elevated CLTE is indicative of extreme expansion with temperature, which will restrict a plastic’s use for precision applications. The repeatability of result is critical, and statistical procedures can be applied to confirm consistency across specimens or batches.
Comparison studies of D696 and ISO 11359 indicate variations in apparatus as well as temperature range. Other standards that pertain to the subject include ASTM E831 for thermomechanical properties and ASTM D3386 for thermal conductivity. Papers addressing dimensional stability, thermal fatigue, and composite response to thermal cycling further enhance the comprehension of CLTE.
Applications of ASTMD696 in Industry
The D696 test method is extensively applied across industries where thermal stability is a requirement. For the automotive industry, plastic components close to engines or HVAC components have to survive thermal cycling. In aerospace, materials for cabin interior and structural components are chosen for their well-predictable expansion behavior. The electronics industry depends on low-CLTE plastics for circuit boards and enclosures to avoid warping. Even in consumer products, plastics in appliances or outdoor items are expansion tested to ensure durability and fitment. Therefore, this standard is very important in guaranteeing product reliability under temperature extremes.