The winLIFE GEARWHEEL&BEARING programme is required in addition to winLIFE BASIC in order to carry out the following calculations. Gear design with the ZAR programme from HEXAGON is integrated in such a way that it is easy to use. A detailed example is documented.

Gear Design

The design of gearing in accordance with DIN 2290 can now be carried out directly with the ZAR programme from HEXAGON. When calculating fatigue life, ZAR is used to calculate the speed and load dependent factors. This allows the use of real collectives, such as those commonly used in the automotive industry.

Fatigue Life of Gearwheels and Bearings

The fatigue of gears occurs in the tooth root due to bending and in the tooth flank due to pitting. Both damage mechanisms occur simultaneously and, depending on the material properties and design, one of the two phenomena will dominate. Since it is not known which effect dominates, both damage possibilities should be analysed when calculating the fatigue life.

Tooth Root Fatigue

Tooth root fatigue results from the dynamic tooth root stress that occurs with every tooth engagement, which can lead to a primary crack and ultimately to tooth fracture. Geometry (notch factor), surface and stress are the decisive influencing variables.

Rules for the application and derivation of Wöhler curves for gears have been derived in standards and research projects, which winLIFE uses as a guide. Of course, users can also use their own data.

Forces on a tooth and resulting stresses in the foot

Tooth Flank Fatigue (Pittings)

The normal force on the tooth surface in the area where there is no sliding movement of the surfaces, but pure rolling, causes Hertzian pressure, which can lead to the formation of pitting.

The fatigue life can be determined using specially calculated S-N curves.

Force on a tooth and the resulting pressure in the tooth flank

Fatigue Life of Antifriction Bearings

Antifriction bearing


The cause of bearing fatigue is similar to the cause of pitting in gearwheels: the Hertzian pressure of the surfaces.

This fatigue life can also be described using S-N curves, and the manufacturers provide data on this. This data is used to estimate the fatigue life.

S-N Curves and their Modifications

Modifications are also common when calculating the fatigue life of bearings and gearwheels, as shown below:

Possible modifications to S-N curves for gearwheels and bearings
Input screen for creating an S-N curve for gearwheels


A S-N curve is generated based on DIN standards or FVA guidelines using the input screen shown above. The data for the antifriction bearings is taken from the manufacturer's catalogues.

Enter a Load Spectrum

The fatigue life of gearwheels and bearings depends on the number of revolutions and the load acting on them - torque or force.

A collective can be imported as a load, e.g. from a measurement (dwell time count). The collective can also be entered manually in the , but this will only be done for very few collective levels due to the effort involved.

Input screen for displaying (and modifying if necessary) the dwell time table (values are given in seconds)


A dwell time must be specified for each element of the speed-torque matrix. As a typical matrix contains hundreds of elements, manual input is very time-consuming and is only used in exceptional cases. Such a matrix is usually taken from a measurement or simulation.

The following figure shows a dwell time matrix as obtained from the winEVA system.  The winLIFE interface is well documented so that a connection to other systems is possible with little effort.

Time proportions of the dwell time of the speed and torque of the gearwheel, shown in a dwell time matrix


The dwell time matrix is automatically converted into a torque-speed or force-speed table. The result for the pinion (gear 1) and gear 2 is shown in the following figure.

Torque as a function of speed for a gearwheel pair

Conversion to the Component

In many cases, the load spectrum available to the user does not match that of the gearwheel. This is often due to the fact that the measurement is usually carried out on easily accessible shafts (input/output). It is therefore necessary to make a conversion to the speeds and torques acting on the gearwheel. In the case of planetary gears, this conversion is often made more difficult by the fact that there are no fixed speed ratios and the direction of transmission also changes.

When dealing with gear wheels, you must also enter other factors for the number of engagements per rotation or specific influences of reversal of stress when dealing with planet gears.

Damage Accumulation

Fatigue life is calculated using linear damage accumulation. The results are detailed in the log file.

Ease of Use

Since the fatigue phenomena of gearwheels and bearings are similar to those of other components, the calculation procedure is also similar to that of the winLIFE BASIC module. A user who is familiar with winLIFE BASIC will quickly become familiar with winLIFE GEARWHEEL&BEARING, as the programme structure and user guidance are similar.