Volume 3, Issue 6 (June 2006)
Development of a Circumferentially Throughwall Cracked Tube Specimen for Fatigue Crack Growth Rate Tests
This paper describes the development of a nonstandard specimen geometry for fatigue crack growth rate studies. Most fatigue crack growth rate data, available in open literature, for Alloy 690 and Alloy 600 were developed using standard, thick section C(T) specimens. Recently a need arose to study a circumferentially throughwall cracked tube specimen. The goal of the development was to use this tube specimen to determine any effects of section thickness or grain size on corrosion enhancement of fatigue crack growth rates in a simulated pressurized water reactor (PWR) primary side environment. Along with the final specimen geometry, the stress intensity equation and crack length monitoring equation are discussed. The stress intensity equation was converted to a standard polynomial equation in order to use a conventional automated fatigue crack growth rate software package. Symmetry arguments were made to justify the use of direct current potential drop (DCPD) and the use of the standard Johnson's equations for measuring crack lengths. Also, some discussions of the validity requirements for this geometry are presented such as stress intensity limits to remain with linear elastic fracture mechanics (LEFM) bounds and crack length limits to avoid excess bending stresses. A baseline test program was conducted on Alloy 690 tube specimens in ambient air and these results were compared with literature data. Also, a sensitivity investigation was preformed to determine the error between the polynomial equations developed and the actual equations in literature. The results of this study confirmed that a circumferentially cracked tube specimen could produce valid fatigue crack growth rate data.