Crack Initiation and Propagation Simulations for ManTen and
RQC100 Steel Keyhole Notched Specimens Tested by the Fatigue Design
& Evaluation Committee of SAE 2020-01-0191
In the 1970s the Fatigue Design and Evaluation Committee of SAE tested 57 "Keyhole"
notched specimens with three different variable amplitude(VA) histories
using two materials; a lower strength ManTen steel and a higher strength
boron steel RQC-100. Recordings were made of not only initiation and
final fracture cycles but also a record of the advance of the cracks during
the propagation phase. In this work the initiation fatigue life is predicted
using the usual method of plasticity correction at the notch followed by
a Palmgren-Miner summation of damage with mean stress correction. The emphasis
of the study is on simulating the crack propagation results. For that phase
the ASME da/dN vs. DeltaK lines augmented by Hasegawa et al's lines and
thresholds for negative R ratios, were used specifically to help predict the
propagation for one of the VA histories that had a significant negative mean.
The open source crack propagation simulation program applied a material
memory model to determine the crack advance on a reversal by reversal basis.
The resulting crack advance plots are compared with the experimental observations.
Results are presented for the constant amplitude tests and for all three VA histories
used to test the two materials.