  The occurrence of cracks on the structure of axle box bogie of NT-11 economic
trains operated by PT Kereta Api Indonesia is studied. These axle box bogies
were designed for the maximum speed of 90 km/hour. The current market demand
led to an increase in maximum speed to 110 km/hour. We investigate the effects
of this speed increase in the occurrence of cracks of the axle box bogies.
Based on the data obtained from PT Kereta Api Indonesia, a statistical approach
is first used to see a relationship between the occurrence of cracks and some
parameters, namely the distance to one-way destination, the speed, and the
number of stops that the trains make to arrive at the destination. From this
statistical study, stopping frequency is the most dominant factor that affects
the occurrence of cracks and that the increase in speed leads to an increase in
the crack's occurrence. A mathematical model is then designed to further
describe the effects of this increased velocity on the structure of axle box
bogies. From this model, a resonance analysis is derived and numerical
experiments are carried out. It is shown that the wagon resonance is highly
dependent on the velocity. An example of typical data shows that this resonance
occurs when the train reaches a velocity at approximately 104 km/hour. These
resonance effects are believed to create a larger distance between parts of the
axle box bogie that influence the occurrence of the cracks.
