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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 used was a Hewlett Packard (HP) 9825A desktop computer equipped with an HP 6940B multiprogrammer.
For linear elastic fracture mechanics (LEFM) testing, the crack growth rate da/dN is presented as a function of the stress intensity factor range ΔK. 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 ΔJ. Compliance techniques are also used to monitor crack extension.
The results of both analysis methods obtained with the acquisition system for aluminum alloys 2124-T851 and 7075-T73 (Unified Numbering System [UNS] A92124 and A97075) 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 crack growth 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 that are subjected to adverse environments which preclude the use of visual measurements.
Research engineerMember of ASTM, University of Dayton Research Institute, Dayton, Ohio
Stock #: JTE11233J