Temperature measurement and calibration in small punch creep testing machines and equipment

Abstract

Serious lifetime estimation of machinery working in the power industry is conditioned by knowledge of an actual state of used construction materials. Determination of degradation degree by detection of mechanical properties of materials at machine parts used in operating conditions without the necessity of stopping operation of the apparatus and machine component disintegration in the past has led to the development of miniaturized test specimens associated with the emergence of special test procedures and methods. One of these methods is the small punch test (SPT) performed at room, low or elevated temperatures. Just testing temperature is one of the most important test parameters. The accuracy of measurement of this variable is a basic condition of repeatability, compatibility and comparability of the measured testing results. Very small specimen size, the way how it is stored in the heating system, the prescribed tolerance of measurement accuracy determines the way of measuring and controlling its temperature. One possible way of measuring specimen temperature is using a thermocouple directly touching its surface in the test process. However, this method is influenced by the unequal heat conduction between the specimen and the punch with the push pin in an upper direction and the cartridge sitting in the rod within the lower direction. How to determine the real specimen temperature in control systems of SPUTT500 testing machine is the subject of this paper.

Keywords

• lifetime
• temperature
• calibration
• thermocouple
• small punch creep testing