Date of Publication:  2000 (?)

Sponsoring Agency:  U.S. Department of Transportation, Federal Railroad Administration, Volpe National Transportation Systems Center

Abstract:

As part of an effort to apply damage tolerance concepts to railroad tank cars, the fatigue crack growth (FCG) behavior of two lots of TC-128B (similar to A612 Grade B steel) steel was investigated. Advanced test control strategies were used to optimize testing, resulting in twenty-one FCG datasets using thirteen specimens. In addition to the material lot difference, variables assessed include load ratio (R = 0.1, 0.6 and -1.0), orientation (L-T and L-S) and, indirectly, crack growth test technique (K-decreasing, -increasing, constant-Kmax with increasing-Kmin). The two material lots yielded essentially identical FCG properties for both low and high R-ratio. The influence of R-ratio was slight, on the order of a 50 percent increase in growth rate at the higher 0.6 R-ratio when compared to low R-ratio conditions. The in-plane orientation (L-T) exhibits a growth rate approximately two times (2x) faster than the through-thickness orientation (L-S). Furthermore, constant Kmax test results suggest that the fatigue crack growth threshold is approximately 2-3 ksi
in and 3-4 ksi
in for the L-T and L-S orientation, respectively. Finally, the data generated for TC-128B in the two orientations tested (a) agrees well with A612-Gr. B data extracted from the literature and (b) exhibits slightly slower growth rates than a generalized FCG response derived for common structural and low alloy steels.

No. of Pages:  10