Piston pin is subjected to both shear and bending loads. I need some clarity in this scenario to complete my paper. The system runs at a wide range of RPMs , so fatigue also may be one of the major causes.
Are you looking for design considerations or typical real world failure mechanisms? Shear and bending are your two major design considerations, keeping in mind that your shear loads are fully reversing.
Assuming a pin properly designed for the intended application loads, typical real world failures are usually lubrication or engine overspeed related. An engine suffering from detonation (pre-ignition) can also contribute to failure.
You should also keep in mind the natureof the cyclic variation of heat transfer to the material of the pin resulting from combustion and friction. The loading is also cycling as you know when the power stroke starts the connecting rod angle will change from left to right. This will cause a sudden thrust on the pin which produce a noticeable piston slap if there is any appreciable clearance.
For typical real world failure , one of the reason for failure is fatigue loading. We carry out pressure pulsation test of the entire crank case to validate the crank. We can use the actual piston and its pin and carry out the same test to validate the design. In real world failure the metallurgical aspect has to be also verified like hardness and its homogeneity.
According to me, adhesive wear can be the cause of failure of the gudgeon or piston pin. Why I am telling this because the piston pin is fully in contact with the connecting rod bushing and the locking snap ring. Adhesive wear form between two contacting surfaces. Adequate lubrication can mitigate the cause.
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