Structural Analysis of Fatigue Cracking in an Injector Body

In the early prototype of CELECT (Cummins' electronically controlled injector), the fatigue cracks were initiated in the injector body at the intersection of a drilled hole of 2.5 mm diameter and a hemispherical valve pocket. It was believed that the high stress concentration at the intersection produced by over 139 MPa fuel pressure caused the fatigue failure. A three dimensional finite element model was built using the ANSYS program to calculate the stress concentration factor for the new, improved design. A three dimensional photoelastic model was built as validation of the finite element analysis. The photoelastic analysis using the stress freezing method showed good agreement with the finite element analysis. The analyses showed that the stress concentration factor of the intersection without a chamfer was 1.5 as compared with 1.3 stress concentration factor with a chamfer. Engine tests further demonstrated the validity of the proposed design.