Digital Image Correlation Based Real-Time Fatigue Feedback System Study

Fatigue testing is a specialized form of mechanical testing that is performed by applying cyclic loading to a coupon or structure. Two common forms of fatigue testing are load controlled high cycle and strain controlled low cycle fatigue. Some strain measurement device, such as extensometers, strain gage, that are often used as a feedback sensor on strain controlled fatigue test. However, in applications where strain controlled fatigue testing could face some extreme conditions as well as high temperature and unusual sizing which requires the strain measurement to be nondestructive and full field. While digital image correlation (DIC), an advanced optical measurement technique, has a decent solution on challenges of fatigue testing measurement. The problem is how to turn DIC from a measurement system to a feedback controller unit. Due to the developments in camera and computation techniques, the sequential process can now be performed as a parallel process. That means while the images are streamed from the camera to the computer the correlation and reconstruction can be performed at the same time. In this way results from the correlation system can be used to monitor and control an experiment in real-time. Since the DIC cannot be built in the loading machine, a DAQ device is used to generate the analog trigger signal according to the mode of fatigue testing. A circular feedback system is formed by the connection of a loading machine, DIC and DAQ device. The proposed feedback system can overcome some technical difficulties on fatigue testing. This study is a primary research of the system.