Residual Stress in a Swage Autofrettaged Steel Cylinder with Semi-Circular Mid-Wall Channels
ARMY ARMAMENT RESEARCH DEVELOPMENT AND ENGINEERING CENTER WATERVLIET NY BENET LABS
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X-ray diffraction residual stress distribution analysis was performed for a swage autofrettaged, thick-walled, A723 steel compound cylinder with axial semi-circular mid-wall channels. Because of the existence of high stress gradient components in the stress distribution, the effect of spatial resolution and the x-ray beam spread function were investigated. Experimental stress measurements were compared with results from Trescas model of a partially autofrettaged solid cylinder. Measured residual stresses were interpreted using an ABAQUS finite element model. Our experimental results verified most features of the predicted hoop stress distribution, including the high stress gradients and compressive stresses near the channel root areas. However, significantly reduced compressive stress levels were observed both near the bore and near the channel roots. An overestimate of fatigue lifetime could result if the reduction of compressive stresses observed experimentally were not taken into account. In solid autofrettaged cylinders, reduction of compressive stresses near the bore has been attributed to the Bauschinger effect. However, there is no analytical model incorporating the Bauschinger effect in the current geometry. This work demonstrated that the introduction of the semi-circular channels in a solid cylinder significantly modified the magnitude and location of stress fields. Both the bore and the channel roots are critical sites for stress concentration. Our analysis further determined that the channel roots were the most critical sites where cracks and failure should occur. Fatigue test results verified that cracking and failure occurred at the channel roots.
- Metallurgy and Metallography