A new method of high-temperature strain measurement

A new technique for measuring strain at temperatures from room temperature to at least 3000 K has been developed and evaluated. The system was developed for measuring strain during studies of the short-time (seconds to minutes), high-temperature mechanical properties of materials heated by self resistance, but it has general applicability. The technique consists of optically tracking two small ceramiccement targets on the specimen with a digital line scan camera. The targets are illuminated with a laser and viewed through a narrow-band (1-nm) interference filter which eliminates specimen thermal radiation. Experimental testing of the system has been performed on stainless steel and graphite at temperatures up to 1477 K and 3000 K, respectively. With the present lens arrangement, the strain measurement system has a maximum displacement range of 4.24 mm and an overall inaccuracy at temperature of ±4.14 μm. The unique features of this system are: (1) the sensitivity to variations in light level in the tracking range has been substantially reduced; (2) the system is dynamic in that it can operate during heatup and on short-time scales; (3) the nodules are stable and have no adverse effects on the test results; and (4) the system is reliable and easy to use.