Autofrettage process analysis of a compound cylinder based on the elastic-perfectly plastic and strain hardening stress-strain curve

Abstract

The autofrettage process enhances the carrying capacity and fatigue lifetime of pressure vessels by increasing their residual stress. A compound cylinder was introduced in order to increase residual stress. An autofrettaged compound cylinder can resist a higher pressure than a single cylinder having the same dimension. This residual stress can be measured through experimental or calculation processes. In this study, residual stress analysis of an autofrettaged compound cylinder was conducted. The elastic-perfectly plastic and strain hardening models were investigated. The residual stress distribution of the autofrettaged compound cylinder with shrink fit tolerance was predicted. Shrink fit is a very efficient way to extend compressive residual stress. The compressive residual stress of the strain-hardening model is smaller than that of the elastic-perfectly plastic model because of the Bauschinger effect. The compressive residual stress of the strain hardening model decreased by up to 80% overstrain level.

Design Optimization of Compound Cylinders Subjected to Autofrettage and Shrink-Fitting Processes

“…The unknown model coefficient vector {a} can be identified through regression analysis in order to minimize the error between the true response (obtained using finite element model) and its approximation using the response surface method. In other words, for a given design vector of {x} evaluated at design points generated by DOE process with n number of experiments, one may write [20] fyg ¼ ½Xfag þ feg (6) In which fŷg ¼ ½Xfag represents approximate response vector, {y} is the true response vector obtained by the finite element analysis, and [X] is the n  p design matrix. The problem is now to find the unknown coefficient vector {a} that minimizes the error{e}.…”

“…Thus, introducing compressive residual stresses near the bore can reduce the overall level of tensile stresses experienced at the bore area which has direct effect on fatigue life. Shrink-fit and autofrettage processes applied individually or in combination have been effectively used to induce favorable compressive residual hoop stresses [1][2][3][4][5][6]. In autofrettage process which typically applied in monoblock cylinders, the pressure is increased to a prescribed value under which the region near bore area undergoes plastic deformation while the remaining area is still under elastic deformation.…”

“…In the autofrettage process, the maximum induced compressive residual hoop stress is mainly limited due to the Bauschinger effect which causes reduction of compressive yield strength of the material in the yielded zone [2,3]. Combination of shrink-fit and autofrettage applied to layered cylindrical shells seems to be effective to remedy the limitations associated with these processes and thus to be able to produce better residual stress distribution through the thickness of the compound cylinder [4][5][6]. Due to many parameters involves, such as sequence of combination, thickness of layers, autofrettage pressure, and radial inference, design optimization of these multilayer cylinders become of paramount importance to provide optimal residual stress distribution.…”

A comparative study of thermal and hydraulic autofrettage

“…As a technology for increasing the pressure carrying capacity and enhancing fatigue life of cylinders, the conventional hydraulic and swage autofrettage have received significant attention of the researchers. Detailed analytical, numerical and experimental analysis of the hydraulic autofrettage has been carried out by many researchers, e.g., [1][2][3][4][5][6]. The analytical solution of the swage autofrettage is difficult due to its transient and localized nature; however, many researchers have investigated the process experimentally and computationally using commercially available finite element packages [7][8][9][10][11].…”

Residual stress analysis of swage autofrettaged gun barrel via finite element method

“…Perl et al [2,3] evaluated the effects of different shocks on semi-elliptical surfaces and stress intensity factor formations on thick-walled cylinders. Lee et al [4] evaluated residual stresses in autofrettage pressure vessels. Parker et al [5] represented the material model for gun barrels using the A723 gun steel material, explained the nonlinear behavior of this material, and examined three different armament gun tubes and investigated the material behavior of these tubes.…”