Piston pin boss stress

[HarleyE30]

Hi everyone,

Attached is an image of an initial piston design (bosses are huge so I can initially see where material can be removed). Also please ignore the irregular shape of the piston, it's not for a normal application!

The FEA is simulating the loading in the upwards direction (piston is upside down in image), which would be produced by the gudgeon pin, reacting to the gas force in the cylinder (80 Bar ). The load is applied as a bearing load in the appropriate direction

As you can see, the major stress area is the edge of the pin bore. This piston is aluminium (modelled as AL 6061). Max stress at this point is 101 MPa. Would this be a concern? Is the mesh too large perhaps?

Any advice appreciated, thanks.

 

[inline6]

what/where is the axial restraint? perhspa the op can show the applied load and applied restraint?

if understand the design the contact pressure in the boss should react against the gas pressure on the face of the piston? i might be wrong given it has been stated as not normal design but should the gas pressure be on the circular face at the bottom?

to me the high stress looks like it due to the flexibility of the crown, i base this off of the deformed shape.

when dealing with close fitting pins the lateral contraction of the bore must be considered as the bore can pinch the pin

 

[loki3000]

slightly offtopic:
is it difficult to get a position like this @car manufacturer if you are a mech engineer (and not for instance a motorsport engineer that some universities offer) with nonlinear mechanics/ strength of materials (FEA) orientation?
or is that kind of work available if you do a phd?

i would kill for a job like that.

 

[ivymike]

I'd suggest you try getting in at a consultancy first (ricardo, avl, fev, etc) and then see if you can play that into an OEM role. alternatively you may have luck w/smaller engine manufacturers like Cummins, Cat, Deere.

 

[nchanga]

HarleyE30,

Have you subtracted the force needed to accelerate the piston towards the crank? Some of the combustion force is accelerating the piston so will not go into the pin. cheers, derek

 

[loki3000]

ivymike, is the same for suspension analysis (i.e. consultants are the best bet)? i am two countries south of germany.

 

[ivymike]

I really have no idea - but automotive companies do hire engineers from somewhere.