A Discrete Approach to Describe the Kinematics between Snow and a Tire Tread

The objective of this study is to develop a simulation technique that enables
to describe the interactions between snow and a moving surface. The develop-
ments of this study are focused on the application of the interactions between
a tire tread and a snow-covered road.
Contrary to a continuum mechanics approach snow is considered to exist of
discrete grains which are allowed to bond and collide with each other. There-
fore, a discrete approach based on the extended Discrete Element Method is
applied to the snow. Micro-mechanical models are developed to describe the
deformational behaviour of snow. The micro-mechanical models describe the
deformation and growth of the bonds between grains as well as the contact
behaviour of snow grains on the grain-scale. Further, the age of a snow sample,
the temperature and deformation rate applied are taken into account by the de-
veloped models. The deformational behaviour of snow under brittle and ductile
loading rates is validated with experimental data of common measurements in
the field of snow mechanics. The simulation results successfully recapture the
macro- and micro-scale deformation behaviour of snow and enable to identify
the primary deformation mechanism in charge at the different loading rates,
densities and temperatures.
However, this approach allows treating individual snow grains during loading
due to a rolling tire and predicting both position and orientation of grains. The
micro-mechanical response of each snow grain in contact with the structure of
the tire surface generates a global impact that defines the interaction forces be-
tween the snow and the tire surface, which simultaneously indicate the strength
of traction. In order to predict the elastic deformation of the tire surface the
Finite Element Method is employed.
A coupling method is developed between the discrete approach to characterise
snow and the finite element description of the tire tread. The coupling method
compensates quite naturally the shortages of both numerical methods. Further,
a fast contact detection algorithm has been developed to spare valuable com-
putation time. The coupling approach was successfully tested and validated
with a small scale application but also with the large scale application of tire
- soil interaction. The large-scale simulation results of tire - soil interactions
showed to be accurate in comparison to similar traction measurements.
Finally, the interaction of snow with rigid and deformable tread parts has been
studied in accordance to friction measurements of the field of tire mechanics.
The results show the ability of the simulation technique to describe the targeted
interactions and give valuable insight into the underlying mechanisms.