Cracks in wheel disc

[ajayputta]

Could some one tell me the causes for cracks to develop at the ventillation holes of a truck wheel disc. Could this be due to overloading of the wheel. The cracks start at the vent hole and extend towards the weld between the disc and rim.

Thanx in advance.

 

[GregLocock]

Yes, this is a classic failure mode for steel wheels. It is /probably/ a fatigue crack. Options are to reduce the loading, reduce the number of cycles, improve the material spec, make the spider thicker or redesign the holes to reduce the stress raisers. The cracks can be initiated at cracks caused by the punching process, if the tool was blunt, for instance.

Is this an in-service failure (how old is the wheel)? or is it a rig or durability test failure?

Cheers

Greg Locock

 

[ajayputta]

Thanks very much. To clarify your questions, this is a failue during running ( for say 6 months or 50000 km.) and not during the test. Infact the wheels pass the tests with a very large margin.

Thanks

 

[GregLocock]

Then your test is not harsh enough. Cracks after 6 months in service are totally unnacceptable. Sorry about that.
Cheers

Greg Locock

 

[kins]

There are many reasons which cause these failures.
Failure within 6 months (50000) of running is not acceptable.
One of the reason for the failure might be overloading of the vehicle.
Punching of the vent holes creates Stress concentration in this region. So a better vent hole shape which brings down the stress levels have to be considered. The process followed to make these vent holes (punching) must be looked. Any problem during this operation has to be rectified.Stress relieving has to be done.

The material specification must also be checked.
The test load you consider should represent the actual loads the vehicle experiences during its operation.

 

[717]

Yes, crack at vent holes is one of the very common "Failure patterns" observed during the cornering fatigue testing of wheel rims. It seems that in this particular case the failure has occured due to overloading. The fatigue life can be improved by changing the shape / size of vent holes or changing the raw material or by removing the sharpness of the edges of vent hole to reduce the stress concentration.

 

[ajayputta]

Thanks for the insight friends. May I know:

1. What causes excessive cornering fatigue on the wheels.

2. Details of the CFT test.

3. What are the effects of torsion caused due to sudden acceleration & braking on the wheel.

4. Effects of tire wear & ply pattern on the wheel. We notice that the vehicles are fitted with a mixture of cross & radial ply tires, 10.20 & 11R20 sizes and at various wear levels.

Thanks

 

[717]

1) During cornering the wheel is subjected to a bending moment. When an overloaded vehicle takes a sharp turn at very high speed, this may cause excessive fatigue.

2)CFT is basically to simulate the condition mentioned at point 1.

3)This mainly causes stresses in the rim /disc joint area. There is a test known as radial fatigue test ( or drum test ) to simulate this.

4) No comments.