ASTM D696-24 pdf download

ASTM D696-24 pdf download,Standard Test Method for Coefficient of Linear Thermal Expansion of Plastics Between 30°C and +30°C with a Vitreous Silica Dilatometer.

1.1 This test protocol is designed for the assessment of the linear thermal expansion coefficient in plastics that have an expansion coefficient in excess of 1 µm/(m·°C), employing a glassy silica dilatometer. The plastics being tested must demonstrate a minimal level of creep or elastic strain rate, or a combination of both, during the test conditions and the forces applied, to guarantee that the measurement accuracy is not adversely affected by these characteristics.

1.1.1 When testing at temperatures deviating from 30°C and +30°C, it is necessary to utilize Test Method E228.

1.1.2 The methodology is not appropriate for materials characterized by exceptionally low thermal expansion coefficients (below 1 µm/(m·°C)). In scenarios involving extremely low thermal expansion, it is recommended to employ interferometric or capacitive measurement techniques.

1.1.3 An alternative, widely adopted technique is thermomechanical analysis, as outlined in Test Method E831. This method facilitates the evaluation of the property across a spectrum of scanned temperatures.

1.2 The thermal expansion of plastics comprises a reversible component, with superimposed length changes due to fluctuations in moisture content, curing procedures, the exhaustion of plasticizers or solvents, stress relief, phase transformations, and various other factors. The primary goal of this test protocol is to ascertain the linear thermal expansion coefficient, while attempting to isolate these factors as much as possible. Generally, it is not practical to entirely negate the influence of these factors. As a result, this test protocol is anticipated to yield an estimated value of the actual thermal expansion.