The first edition of the international calculation method for micropitting, ISO TR 15144-1:2010, was just
published last December. It is the first official international calculation method to check for the risk of
micropitting ever published. Years ago, AGMA published a method for the calculation of the specific oil film
thickness containing some comments about micropitting, and the German FVA published a calculation
method based on intensive research results. The FVA and the AGMA are close to the ISO TR. However the
calculation of the micropitting safety factors is new.
In this paper the ISO TR 15144 will be explained briefly. The technical report presents two calculation rules,
method A and B. Method A needs as input the Hertzian pressure on every point of the tooth flank. This is
based on an accurate calculation of the meshing of the gear pair considering tooth and shaft deflections to get
the load distribution over the flank line in every meshing position. Such a calculation is very time consuming
when using an FEM tool. Alternatively specific analytical programs which are commercially available (such as
LDP, RIKOR, KISSsoft) may be used. In either case, the use of Method A without such an advanced tool is
impossible. Method B is much simpler; the load distribution is defined for different cases as spur or helical
gears, with and without profile modifications. Method B can be programmed as standalone software, may be
even in Excel. However, a restriction, which arose in the last meeting of the ISO working group responsible for
this topic, limits considerably the application of method B: If gears with profile modification have to be verified,
the tip relief Ca must correspond exactly to a proposed value Ceff. If not, the method for gears without any
profile modifications has to be used. As modern gear design implies profile modifications of different kinds,
this is a critical limitation for the application of method B in ISO TR 15144.