Fatigue relevant road surface statistics

Klas Bogsjo

Road roughness is a major source of fatigue in vehicles.
It is therefore interesting to study characteristics
of road irregularities in order to improve vehicle durability. 
This study compares different methods to create synthetic random road
profiles. The comparison is made from a fatigue damage point of view,
i.e. how much fatigue damage the synthetic roads cause  compared to
actual measured roads. Vehicles travelling along actual and synthetic
roads are simulated with a simple one-wheeled vehicle model equipped
with linear springs and dampers. Damage assessments are based on the 
Palmgren-Miner hypothesis, Basquin's relation and Rainflow counting.
The result suggests that actual roads cause a
more damage than synthetic Gaussian roads, due to occasional road transients,
such as bumps and holes, which cause large loads on the vehicle.
Thus, an assumption Gaussian road level distribution 
is very questionable.