Exploratory proto-type multi-lug breech block/ring assembly was designed for future projectile launchers. The new geometry redistributes the applied load to several surfaces rather than one surface in conventional breech to react the load. Induced residual stresses from shot peening and overload processes improve fatigue life of the system. In this work, experimental x-ray diffraction residual stress mapping was performed in the lugs of the unaffected portion of a 50% overloaded multi-lug breech ring which was fatigue tested to failure. Finite element modelling of a two-dimensional cross section of the breech block/ring assembly was performed using ABAQUS codes on a Convex C-220 computer. Comparison of experimental residual stresses and FEA predictions showed good agreement in the major features of residual stress distribution, especially in the front lug. While FEA predicted the general characteristics of experimental residual stress distribution, experimental residual stresses were deeper and less compressive.
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