Figure 7: Improper seat design and anchorage
caused damage to seats inside the bus Figure 8: Bus floor made of plywood
Figure 9: Diagram of front axle with bolts Figure 10: Two high tensile bolts for axle
connection found at the site
was brake failure when the bus was travelling
downhill. However, the poor structural integrity of
the bus contributed to the increased fatality and
injury severity. The steel structure of the bus was
highly rusted. The seat anchorage was found to
be very weak. The coach builder used screws and
bolts to attach the seats to the bus floor and the
bus floor was made of plywood with a reinforced
wooden structure. Figures 7 and 8 show the
typical anchorage failures in the bus. Only four
seats remained attached to the floor and those
too, loosely. front axle was detached because of failure of the
high tensile bolts connecting the axle with the
front suspension assembly as shown in Figures 9
and 10. The failed bolts found from the bus axle
and at the crash site were examined using SEM
and Energy Dispersive X-Ray (EDX) to determine
the main mode of failure, the base material
of the bolt and the overall quality of the bolt.
Similar analysis with the original bolt from the
chassis manufacturer was also undertaken. The
examination results show that the axle bolts failed
due to multiaxial tensile and shear loads from
impact. The EDX result indicated that the bolts
consisted of non-standard material composition
as the Carbon (C) contents were unusually
higher than in standard cast iron compositions.
Moreover, the presence of voids in the bolts
caused internal stress concentration on the
sample microstructure, which could lead to failure.
When the result was compared to the original
bolt, it was revealed that substandard and lower
2. Vehicle Component Failure
It is very rare for a vehicle axle to be detached
during a crash. Nevertheless, in one high-profile
crash case investigated by MIROS, the front axle
of a bus was found to be detached upon impact
with a concrete barrier. Based on analysis, the
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