Citation:
A. Abo Al-kheer, M. Eid, Y. Aoues, A. El-Hami, M.G. Kharmanda, A.M. Mouazen, Theoretical analysis of the spatial variability in tillage forces for fatigue
analysis of tillage machines, Journal of Terramechanics, Volume 48, Issue 4, August 2011, Pages 285-295.
Abstract:
This paper presents a new theoretical model to describe the spatial variability
in tillage forces for the purpose of fatigue analysis of tillage machines. The
proposed model took into account both the variability in tillage system
parameters (soil engineering properties, tool design parameters and operational
conditions) and the cyclic effects of mechanical behavior of the soil during
failure ahead of tillage tools on the spatial variability in tillage forces. The
stress-based fatigue life approach was used to determine the life time of
tillage machines, based on the fact that the applied stress on tillage machines
is primarily within the elastic range of the material. Stress cycles with their
mean values and amplitudes were determined by the rainflow algorithm. The damage
friction caused by each cycle of stress was computed according to the Soderberg
criterion and the total damage was calculated by the Miner's law. The proposed
model was applied to determine the spatial variability in tillage forces on the
shank of a chisel plough. The equivalent stress history resulted from these
forces were calculated by means of a finite element model and the Von misses
criterion. The histograms of mean stress and stress amplitude obtained by the
rainflow algorithm showed significant dispersions. Although the equivalent
stress is smaller than the yield stress of the material, the failure by fatigue
will occur after a certain travel distance. The expected distance to failure was
found to be df=0.825×106km. It is concluded that the spatial variability in
tillage forces has significant effect on the life time of tillage machines and
should be considered in the design analysis of tillage machines to predict the
life time. Further investigations are required to correlate the results achieved
by the proposed model with field tests and to validate the proposed assumptions
to model the spatial variability in tillage forces