Experimental Study of Large-Diameter Thin-Wall Pressure Vessels - A. J. Durelli and Oth
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Experimental Study of Large-diameter Thin-wall P ressure Vessels Brittle coatings and electrical strain gages are employed to determine stress distribution over surfaces of vessels by A. J. Durelli, J. W. Dally and S. Morse ABSTRACT--An experimental stress analysis of three cylindrical pressure vessels with radius/thickness ratios ranging from 100 to 238 and different head closures is described. Brittle coatings and electrical strain gages were employed to determine stress distributions over the entire outer surface of the vessels. Electrical strain gages alone were used to determine stresses on the inside surface of the vessels. Particular emphasis was placed on determining stress concentrations and on nonlinear effects produced by geometric imperfections. An at- tempt was also made to correlate the failure, which started in the cylindrical portion of the three vessels, with the elastic-stress distribution. It was found that the imperfections in the cylinder were not significant if the vessel was fabricated from a ductile steel. How- ever, if the vessel was constructed from a high-strength but brittle steel, the imperfections significantly lower the bursting strength of the vessel. Introduction The authors believe that a recent investigation they have conducted dealing with large-diameter thin- wall vessels may be of interest to people working in the missile field. Three different vessels were stud- led experimentally in order to determine their stresses and failure characteristics v~hen subjected to internal pressure. The results of the investiga- tion were used as a basis for developing lightweight vessel designs and for evaluating various manufac- turing techniques used in their fabrication. Although the experimental procedure varied some- what in the investigation of each of the three vessels, the following three phases were common to each analysis. First, brittle coatings were applied to de- termine the stress distributions over the entire outer surfaces. Second, certain regions of interest indi- cated by the brittle-coating analysis were instru- mented with electrical-resistance strain gages and A. -=7. Durelli and S. Morse are associated with Armour Research Founda- tion, Chicago, Ill. Dr. Durelli is also Professor of Civil Eng ineer ing a t the Illinois Institute of Technolagy. J. W. Dally, formerly with Armour Re= search Foundation, is now Assistant Professor in Mechanics at Cornell University, Ithaca, N. Y. Pape r presented at 1959 SESA Spring ~Ieeting h e ld in}~Washington, D. C., on May 20-22. the response of these gages was followed within the elastic range of the material. Third, the vessels were pressurized until failure occurred and the load, the location of the failure and the type of the failure were recorded. In this presentation, emphasis will be placed on the experimental procedures and general findings rather than specific results which hold only for a par- ticular vessel. Vessel A Vessel Description Vessel A was about 7 ft long with a diameter of about 28 in. and a wall thickness of abcut 0.110 in, giving an R / t ratio of 128 in the cylindrical portion of the vessel. The forward end of the vessel was hemispherical with a wall thickness of about 0.15 in. and a circular opening at the top. The aft end of the vessel was in the form of a knuckle ring of variable thickness with a large circular opening. In the experimental analysis, both of the openings at the ends of the vessel were closed with flat plates and sealed with O rings. The vessel was fabricated by drawing two ends as cups and welding these two ends together with a circumferential weld. The vessel material was AISI 4130 steel heat treated to a hardness of Rockwell C-37. Tests of a coupon taken longitudinally from the vessel after its failure gave a 0.2% yield strength of 170,000 psi and an ultimate strength of 190,000 psi. An over-all view of the vessel is given in Fig. 7. Two thin skirts welded around the knuckles hide partially the for- ward and aft closures. These skirts are stress free. Outside micrometer measurements at a number of positions about and along the axis of the cylinder indicated ~hat the vessel was not perfectly cylindri- cal. Two types of imperfections occurred. The first type may be defined as "out of roundness," indicating that the vessel is somewhat elliptical in shape rather than circular. The second type may be called "corrugation," indicating local irregularities Experimental Mechanics I 33
