High temperature strain gage

Claim 1

A STRAIN MEASURING APPARATUS FOR TEST MATERIAL SUBJECTED TO STRESS COMPRISING IN COMBINATION: (A) A PAIR OF ELECTRICALLY CONDUCTIVE FLEXIBLE LEAVES MADE OUT OF THE SAME MATERIAL AS THE TEST MATERIAL, EACH OF SAID LEAVES HAVING THEIR END PORTIONS MOUNTED ON THE TEST MATERIAL AT SPACED APART LOCATIONS AND IN SUCH A WAY THAT SAID LEAVES ARE LOCATED PARALLEL WITH ONE ANOTHER AND THEIR MIDDLE PORTIONS ARE OPPOSITELY CURVED AND IN CONTACT WITH ONE ANOTHER, SAID LEAVES FLEXING AWAY FROM ONE ANOTHER WHEN A TENSILE FORCE IS APPLIED TO SAID TEST MATERIAL THUS EFFECTING A SEPARATION OF SAID MIDDLE PORTIONS; (B) ELECTRICAL HEATER ELEMENTS INSTALLED ADJACENT TO SAID LEAVES FOR SELECTIVELY HEATING SAID LEAVES; (C) ELETRICAL POWER AND CONTROL MEANS ELECTRICALLY CONNECTING SAID LEAVES AND SAID HEATER ELEMENTS FOR ENERGIZING SAID ELECTRICAL HEATER ELEMENTS UPON SEPARATION OF SAID MIDDLE PORTIONS TO EFFECT A TEMPERATURE RISE IN SAID LEAVES CAUSING THEM TO EXPAND AND FLEX TOWARD ONE ANOTHER UNTIL SAID MIDDLE PORTIONS REESTABLISH CONTACT WITH ONE ANOTHER AND DEENERGIZE SAID HEATER ELEMENTS; (D) COMBINED THERMAL SENSING MEANS AND STRAIN INDICATOR MEANS CONNECTED TO SAID LEAVES AND THE TEST MATERIAL FOR SENSING THE TEMPERATURE DIFFERENCE BETWEEN SAID LEAVES AND THE MATERIAL AND FOR CONVERTING SAID DIFFERENCE INTO A STRAIN INDICATION.