Engine Valve Stresses.


An axisymmetric model of a typical engine valve has been made and analysed with FEA. Instructions about how to set up an axisymmetric model are in the tutorial that accompanies the student edition of PTC Pro/Engineer and Mechanica.
The valve was constrained in the 'Y' direction by the edge defining the valve seat. This shows very small areas of higher stresses which are probably numerical effects and not significant.
Note that this model was inadvertantly set up with inch lbmass units and would not convert to MKS so it was run in the original units. However while this needs to be considered when considering actual stress values, it does not affect the stress concentration values given.

The valve had 3 circumferential grooves near the top of the stem to hold the collet and spring retainer, 0.0015 units diameter in a stem diameter of 0.008 units with a valve head diameter of 0.040 units and a total length of 0.1 units)
The model assumed a load (of 100 units) in the positive 'Y' direction was applied around the top semi-circular groove in the stem.
The theoretical tensile stress in the stem is: 1.989e6.

The von Mises stress plots below indicate that the maximum stress concentration effects of these grooves was a maximum of about 2.3.
When the maximum principal stress plot is examined (not shown here) the stress concentration factor of the grooves is 3.
The stress concentration, on a maximum principal stress plot (not shown here) where the stem joins the head, where a 0.0075 unit radius was used, is much lower, about 1.6 times that of the mean stress in the stem. (1.3 on the von Mises plot).

Plot of von Mises stresses in stem by grooves.

Plot of von Mises stresses at radius of stem and head.

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David Grieve 5th February 2003.