Coefficient of Linear Thermal Expansion

Understanding Coefficient of Linear Thermal Expansion ASTM E831, ASTM D696, ISO 11359

Coefficient of Linear Thermal Expansion (CLTE) is an important material property that determines the expansion or contraction rate of a material as a function of temperature changes. This property can be used to design materials and structures that can withstand thermal stress and prevent failures. ASTM E831, ASTM D696, and ISO 11359 are the standards used to measure the CLTE by TMA or dilatometer.

The TMA test involves placing the specimen in a holder at room temperature, measuring its height with a probe, and heating it in a furnace at a specified rate, usually ten degrees per minute. The dilatometer test requires placing the sample in the apparatus at room temperature, positioning and zeroing the height gauge, and measuring the movement of the sample from -30°C to +30°C in a temperature bath. Both tests produce a graph that shows the expansion rate of the material with temperature changes.

The specimen size for the TMA test should be between 2 and 10 mm in length and no larger than 10 mm in lateral dimension. The specimen must be flat on both ends. For the dilatometer test, the sample size should be approximately 12.7mm (0.5") wide x 75mm (3") long.

The data obtained from the test allows for the calculation of the coefficient of linear thermal expansion between the desired temperature ranges. The equipment used for the test includes a Thermomechanical Analyzer, a dilatometer, and an Instrulab PRT.

In conclusion, the CLTE is an essential material property that can be determined using the TMA or dilatometer tests. Understanding the expansion/contraction characteristics of materials is crucial for designing structures and selecting materials that can withstand thermal stress and prevent failures. The ASTM E831, ASTM D696, and ISO 11359 standards provide guidelines for testing and determining the CLTE of a material.