Fatigue Crack Growth Rate Data Acquisition System for Linear and Nonlinear Fracture Mechanics Applications

摘要

A computer-based, automated-data-acquisition system was developed for determining fatigue crack growth rate data for both linear and nonlinear fracture mechanics testing. The system hardware employed an HP 9825A Desktop Computer equipped with an HP 6940B Multiprogrammer which digitized the analog test signals (load and displacement) for input to the computer. For linear elastic fracture mechanics (LEFM) testing the crack growth rate, da/dN, is presented as a function of the stress intensity factor range, Delta K. Compliance relationships are used to monitor crack length which is then used to calculate the stress intensity range. For nonlinear fracture mechanics (NLFM) testing, the crack growth rate is related to the rate of potential energy change, or Delta J. Compliance techniques are also employed to monitor crack extension. The results for both analysis methods obtained with the acquisition system are in excellent agreement with results obtained using the more conventional visual and analytical methods. The automated system is superior from a point of speed and consistency, and possesses the accuracy required for valid fatigue crack growth rate (FCGR) testing. Furthermore, the system requires no personal supervision or special specimen preparation and thus would be available for obtaining fatigue crack growth results from test specimens which are subjected to adverse environments which preclude the use of visual measurements. (Author)