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18-04-2017, 01:33 PM

Hi am Mohamed i would like to get details on fmea of gearbox ppt ..My friend Justin said fmea of gearbox ppt will be available here

jaseela123d · 19-04-2017, 11:57 AM

The FMEA divides the sequence of gear and bearing failures into three distinct stages and examines the contribution of transient torsional events (TTEs) to each failure stage: initiation, propagation, and failure. This section begins with the propagation of cracks.

Propagation

Once a crack has started, the propagation, driven by a cyclic loading, can initiate one of the causes of transient torsional events. Fatigue, therefore crack growth, is the dominant failure mode in the wind turbine gearboxes. The crack may have been initiated by fatigue, a defect, or other pre-existing damages, such as scrap denting or scuffing . TTEs are strongly linked to fatigue failure modes in standards and fault analysis texts. TTE accelerate the growth of cracks, as it is a function of the load . Crack growth velocities tend to increase over time and the remaining material available to support the loads decreases, increasing stress levels in the remaining material.

Steels lacking fracture toughness have lower fatigue lives than the more resistant materials. Hardened bearings, widely used in turbine gearboxes, have low fracture toughness, which increases the risk of fatigue failure. Without propagation, initiation will not cause failure, so reducing the load will slow down and, at times, will stop the spread, thus prolonging the service life of the gearbox.
Failure
This is the third and last stage of the sequence (initiation, propagation, and failure). A clear definition of failure is required for an accurate FMEA. In this analysis, it is said that a gearbox or gearbox component has failed when it meets one or more of the following conditions:
1. A fracture has occurred in one or more parts. The most common examples are inner rings with cracks and broken gear teeth.
2. The wind turbine can not run until the gearbox has been repaired or replaced.
3. Functional failures. For example, the turbine must be declassified to operate with a particular gearbox condition, such as overheating or high gearbox vibration at rated power. In FMEA, functional failure means that the asset works, but it does not operate at a level of performance acceptable to the owner or the user [14].
4. The severity of a failure mode is classified as high or severe in a standard or standard-based fault analysis reference.
5. Component failure means repairs can occur up-tower.
6. Gearbox failure means removal of the gearbox from the tower for repair or rebuild.
7. Catastrophic failure means that the gearbox can not economically undergo repairs or rebuild.

Hardened bearings have low cracking resistance, therefore suppression of TTEs should extend the life of the bearings and reduce the risk of axial cracking. Cyclic loading drives fatigue, but the relationship is not linear. Halving the peak-to-peak amplitude of the transients of the transmission pair reduces their fatigue load by 75% , so it is worth pursuing the life-prolonging potential of RTD devices.

Fatigue is the dominant failure mode in TTE-related gearboxes. Other modes include friction and plastic deformation. Fatigue explores a wide variety of defects, defects and previous damages to initiate failure, which is the first of three distinct stages of failure. Initiation is followed by propagation and, finally, failure. The initiation takes the longest of the three stages, the propagation is faster and the final failure can occur in an instant. The duration of the initiation and growth phases of fatigue failure modes - ranging from the fatigue of bending of the gear teeth to the hertzian fatigue of the support elements - is influenced by a heavy cyclic load such as the resultant Of TTEs. The analysis of the causes and effects of the gearbox failure mode suggests that TTE suppression has a high potential to prolong the initiation and propagation stages of the failure in new, in service and previously damaged transmissions.

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