Strain gage evaluation with four-point bending at moderate temperatures

This paper describes the application of the traditional four-point bending technique to conduct strain gage performance tests at moderate temperatures. The tests measure the apparent strain, linearity, drift, creep and hysteresis behavior to ascertain the reliability of strain gages to be used in the testing of experimental cylindrical vessels subjected to thermal loading. The four-point bending rig was designed to take advantage of the advances in personal computer datalogging and graphical processing software. The test rig is designed to provide a thermal barrier to minimize the heat losses and thermal isolation of the test beam while maintaining structural continuity. A low wattage and lightweight electric foil heater incorporating a precise temperature controller minimizes weight and enhances temperature stability. Gage performance data on five candidate strain gages at temperatures ranging from ambient to 215°C (419°F) are presented, and the evaluation procedure is outlined. The strain gage with the most acceptable performance was identified within the validity limits from ambient to a temperature of 215°C and from zero to a maximum strain of 1000 .