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  • 1960-1964  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    New approach to the autofrettage of high-strength cylinders (1962)
    Springer
    Experimental mechanics 2 (1962), S. 33-40 
    Details
    ISSN: 1741-2765
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The usual method of autofrettage (cold working) for gun tubes utilizes hydraulic pressure applied directly to the bore in order to plastically deform the wall of the tube so that favorable residual-stress patterns are produced. The strength of the tube is effectively increased, providing many associated benefits; however, ultra-high hydraulic pressures are required for high-strength steels since plastic-flow pressure is directly proportional to the yield strength of the material. A new method for the autofrettage of high-strength steel cylinders requiring greatly reduced pressures is developed and described herein. An oversize mandrel is forced through the tube to plastically deform the walls. Three methods of forcing the mandrel are investigated. Mechanical-push swaging is used in the autofrettage of short 5-in. long specimens with pull swaging and hydraulic-push swaging being used on specimens 40 in. long. All specimens are made from 4340 steel heat treated to various strengths. Cylinders with wall ratios ranging from 1.5 to 2.8, yield strengths ranging from 90,000 to 180,000 psi, and percent enlargements at the bore ranging from 1.0 to 5.0 are utilized. An engineering analysis is made investigating such factors as percent enlargement and elastic recovery at the bore, the ratio of pressure required for pushing the mandrel to the yield strength of the material, the effects of various lubricants on the frictional forces involved, and the induced three-dimensional stresses in the cylinder walls. Sach's boring-out technique is used to evaluate induced residual-stress patterns. Strains are recorded with electric-resistance strain gages and the associated dynamic and static instrumentation is described. Results are presented in graph form.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02325691
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Residual stresses in thick-walled cylinders resulting from mechanically induced overstrain (1963)
    Springer
    Experimental mechanics 3 (1963), S. 253-262 
    Details
    ISSN: 1741-2765
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Autofrettage is a process for inducing elastic response in thick-walled cylinders subjected to internal pressures which otherwise cause plastic strains. To extend the use of autofrettage to higher pressure applications and to elminate many of the problems encountered in the use of the conventional process based on the use of direct internal hydrostatic pressure, a new technique has been developed which utilizes the mechanical advantage of a sliding wedge to produce the desired bore enlargement. Since the use of a sliding wedge or mandrel will induce shearing forces at the mandrel-cylinder interface, the resultant residual-stress distribution will differ from that theoretically predicted as characteristic of the direct hydrostatic process. It is the purpose of this work to determine the residual-stress distribution as a function of magnitude of overstrain and diameter ratio, and how it affects the reyielding characteristics of cylinders autofrettaged by this technique. Residual-stress distributions, determined by the Sachs boring-out technique for diameter ratios ranging from 1.5 to 2.3 and for several different magnitudes of overstrain, are shown. The shearing force associated with this technique induces substantial longitudinal residual stresses. The increase in the magnitude of this longitudinal residual stress with overstrain and the resultant decrease in the tangential residual stress are shown and discussed. Hydrostatic reyielding tests of autofrettaged cylinders are used to substantiate the decrease of tangential residual stress with increased overstrain. The substantially lower optimum overstrain as compared to the direct hydrostatic technique is shown and discussed. For optimum overstrain, the elastic strength of cylinders autofrettaged by swaging is comparable to that characteristic of the conventional process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02325841
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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