The wear of a wall due to the erosive effect of particle impacts is a complex function of particle impact, particle and wall properties. For nearly all metals, erosion is found to vary with impact angle and velocity according to the relationship [63]:
 | (6–89) |
where 
is a dimensionless mass, 
is the particle impact velocity and 
is a dimensionless function of
the impact angle. The impact angle is the angle in radians between
the approaching particle track and the wall. The value of the exponent, 
, is generally
in the range 2.3 to 2.5 for metals.
Finnie’s model of erosive wear [64] relates the rate of wear to the rate
of kinetic energy of impact of particles on the surface, using 
:
 | (6–90) |
where:
 | (6–91) |
