STRAIN-GAUGE EVALUATION WITH 4-POINT BENDING AT MODERATE TEMPERATURES

This paper describes the application of the traditional four-point ben ding technique to conduct strain gage performance tests at moderate te mperatures. The tests measure the apparent strain, linearity, drift, c reep and hysteresis behavior to ascertain the reliability of strain ga ges to be used in the testing of experimental cylindrical vessels subj ected to thermal loading. The four-point bending rig was designed to t ake advantage of the advances in personal computer data-logging and gr aphical processing software. The test rig is designed to provide a the rmal barrier to minimize the heat losses and thermal isolation of the test beam while maintaining structural continuity. A low wattage and l ightweight electric foil heater incorporating a precise temperature co ntroller minimizes weight and enhances temperature stability. Gage per formance data on five ''candidate'' strain gages at temperatures rangi ng from ambient to 215 degrees C (419 degrees F) are presented, and th e evaluation procedure is outlined. The strain gage with the most acce ptable performance was identified within the validity limits from ambi ent to a temperature of 215 degrees C and from zero to a maximum strai n of 1000 mu epsilon.