Fatigue Crack Growth Behavior of TC-128-B Steel Under Variable Amplitude Loading

Railroad tank cars are exposed to a high degree of variable amplitude loading that is comprised of both tensile compressive cycles. In order to consistently and accurately predict this type of loading, material properties, usage, and load interaction models must be used in concert. The objective of this study is to present the methodology necessary to generate tank car specific spectrum crack growth life prediction models. Experimental fatigue crack growth data from this project and previous efforts provided the baseline data necessary to develop NASGRO® models and predict simplified over-load and under-load experiments. The methods were then advanced to predict spectrum crack growth experimental data representative of tank car usage. The results show that significant amounts of compressive loads in the tank car spectra essentially negate the need for a tensile stress based load interaction model. In order to provide consistently conservative prediction, the most basic model must be implemented instead of the more elaborate retardation models.