ASTM E 21 covers tension testing methods to determine yield strength, tensile strength, elongation and reduction of area of metals at elevated temperatures. Specimen sizes described in ASTM E 8 are usually suitable for testing to E 21. According to E 21, specimens should be round whenever the material dimensions allow for this geometry--exceptions are for sheet or strip type materials. As in E 8, the ratio of gage length to diameter should be 4. Care should be taken to ensure that the load is applied as axially as possible. To facilitate this, E 21 recommends using threaded ends in round specimens or suitable end geometry to meet this requirement. When a rectangular specimen is used and when there is enough material, elongated shoulder ends can be used to permit gripping outside the furnace. ASTM E 21 requires a testing machine that complies with the accuracy specified in ASTM E 4, along with grips and a heating device that uses an electrical resistance or radiation mechanism. The air surrounding the specimen should be at atmospheric pressure conditions. A class B-2 extensometer, according to E 83, should be used when the yield strength is being determined.
To guarantee accurate results, our series of universal testing machines meet or exceed the accuracy specifications requested by ASTM E 21. When testing rectangular type specimens up to 350 °C (660 °F), our recommended solution includes a set of high-temperature mechanical wedge action grips with flat serrated faces. In the case of round specimens, we use V-serrated faces. Above the mentioned temperature, we have success using tension pull rods with specimen holders with female threads that match the specimen ends. In regards to the heating device, for temperature ranges up to 600 °C ( 1110 °F) we typically use our Series 3119 environmental chambers, and for temperatures above 1200 °C (2200 °F) our suggested solution is a furnace, such as the model SF-16 3-zone split furnace.
Instron offers effective extensometry solutions for tensile testing of metals. Our extensometers meet or exceed the accuracy classifications as stated in ASTM E 83. We suggested using our W-E440 series of high temperature axial extensometers for tests up to 540 °C (1000 °F) in an environmental chamber. Our model RT-214 extensometer provides an effective solution for tests up to 1100 °C (2000 °F).