FATIGUE CRACK INITIATION STUDIES USING FLASH PHOTOMICROGRAPHY--PART I EXPERIMENTAL EQUIPMENT AND PROCEDURE
An automatic system has been developed to take flash photomicrographs of the roots of notches in flat, doubly-notched specimens during low-cycle fatigue tests to determine the cyclic time of crack initiation. The photomicrographs are taken periodically during the test usually at 50- or 100-cycle intervals until a well-defined crack has formed at the notch root and extends across the full thickness of the specimen. For analyzing the film record, each frame of the developed negative is projected on a screen starting at the last frame on the film, and the well-defined crack is traced backward in "time", frame by frame to its initiation. A crack is judged to have initiated when it is visible in one frame and not evident on the frame just preceding. Cracks with a surface length on the specimen of approximately 0.001 inch and an opening of 0.0001 inch are easily visible in the project images. In the report, the system is described in sufficient detail so that it may be duplicated by others. Possible modifications of the system are suggested for additional applications in fatigue studies and sample photomicrographs are also shown. Experimental results, using this system, will be described in a separate report.
- Sponsored by the U.S. Army Material Command, Washington, D.C. 20315.
Army Materials and Mechanics Research CenterWatertown, MA USA 02172
- Papirno, R
- Parker, B S
- Publication Date: 1971-12
- Features: References;
- Pagination: 19 p.
- TRT Terms: Cracking; Fatigue cracking; Fatigue tests; Measuring instruments
- Uncontrolled Terms: Crack propagation
- Old TRIS Terms: Crack formation; Photomicrography
- Subject Areas: Marine Transportation; Materials;
- Accession Number: 00035645
- Record Type: Publication
- Source Agency: Ship Structure Committee
- Report/Paper Numbers: D/A 1T061102B32A
- Files: TRIS
- Created Date: Oct 13 1972 12:00AM