Home > Research > High Temperature Testing
A 20 Kilohertz Optical Strain Gage for High Temperature Testing
Materials used in aircraft jet engines must withstand large forces applied at high frequencies at high temperatures. The University of Michigan has a test machine that can simulate this hostile environment for superalloy specimens that are 3 inches long and 3/8 inch in diameter. Professor Sharpe has developed an optical system that can measure the strain in the center of these specimens while they are being tested. Two tiny reflective markers are placed on the specimen 0.008 inches apart. When illuminated with a laser, interference fringes are generated that are related to the elongation between the markers, i.e. the local strain of the specimen. Motion of these fringes is monitored with high-speed photodetectors and a modern laboratory computer.
This system, whose development was supported by the Defense Advanced Projects Agency is the first of its kind anywhere and will enable strain measurement under many unique and difficult test conditions.
Figure 1. The optical strain gage system on at black plate attached to a test machine at the University of Michigan
Figure 2. A superalloy specimen glowing red at 1000°C (1832°F) while undergoing cyclic loading at 20,000 cycles per second. The red dot on the specimen is from the laser of the optical strain gage.