A hybrid method is presented which permits calculation of residual stresses in a swage autofrettaged tube including Bauschinger effect. The results are generally supported by three types of available experimental evidence by comparing “equivalent” swage and hydraulic autofrettage tubes having the same level of overstrain. Radial slitting of the swaged tube is predicted to show a greater opening angle than its hydraulic equivalent. Fatigue lifetime of the swaged tube is predicted to be significantly higher than the hydraulic case. Re-pressurization of the equivalent tubes is predicted to produce initial re-yielding at the same pressure in both cases. Analysis of results shows that permanent strains in the swaged tube are expected to appear at a pressure level below that for the hydraulic tube.
A pressure vessel, which was designed and tested under laboratory conditions for tens of thousands of cycles, failed in service after only a few cycles. Thousands of oscillatory pressure reversals were measured at each loading. However, the predominance of the stress amplitudes were well below the critical threshold values necessary to initiate fatigue cracking. Analysis demonstrated that the disparity between lab cycling and field loading conditions could not be explained simply by mechanical loading alone. Further investigation into the problem revealed that an extremely aggressive environment, the by-products of the internal combustion from within the pressure vessel, along with high temperatures, pressures, and other sources of high tensile loading all contributed to the short fatigue life of the vessel.
This report describes a finite element analysis of the breech closure for the 155 mm Cannon M199, which is normally mounted on the Towed Howitzer M198. In this configuration it has has an excellent record for reliability in the field and is easy to service. However when the breech is used in an ammunition test environment, some maintenance problems exist. The analysis is for a 9 body problem with 13 contact surfaces and was solved for both static and dynamic load cases. The two dynamic loads were of similar shape with different loading times. The 9 bodies in the model include, a facility mount, four major structural components, the obturator seal and 3 minor components. The results show that the major components are normally subjected to quasi-static loading but under fast `pressure spike' loadings, the dynamic effect can be important. This is particularly true for the contact between minor components which can show extreme behavior with the fast loading rates.
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