experimental stress distribution was compared with a model based on Tresca's yield criterion for a solid cylinder under internal pressure.
Microhardness test can be used as a qualitative test for inferring residual stresses in components (Kokubo, 1932; Pharr et al., 1994; Tosha, 2002).
Researchers observed that the surface microhardness increases due to presence of compressive residual stresses, whilst the surface microhardness decreases due to presence of tensile residual stresses. Another qualifying test for envisaging the presence of residual stresses in an autofrettaged cylinder is the measurement of opening angle due to radial cut through the wall of the cylinders (Parker et al., 1983;
Parker and Underwood, 1998). When a radial cut is made through the wall of the autofrettaged cylinder, the cylinder opens by an angle which is a direct measure of pure bending moment ‘locked-in’ to the cylinder. It can be demonstrated that the experimentally measured opening angle matches with the released bending moments locked into the cylinder based upon stress analysis and thus confirming the presence of residual stresses.
stress intensity factor was calculated for straight as well as elliptical fronted longitudinal crack and the fatigue life was evaluated using Paris law (Paris and Erdogan, 1963). Results were compared with the available experimentally determined fatigue lives. It was observed that the non-hardening material model provides acceptable results. Rees (1991a) also carried out the fatigue life prediction of autofrettaged cylinder for closed-end conditions modifying number of available stress intensity factors (Underwood, 1972; Bowie and Freese, 1972; Pu and Hussain, 1979; Throop, 1970; Parker and Farrow, 1981) and then incorporating in Paris law.
Author considered elliptical crack geometry for the analysis and in order to incorporate the crack geometry, the available stress intensity factors were modified accordingly. Comparing the results with the fatigue life of non-autofrettaged cylinder, author observed a significant increase in the fatigue life of autofrettaged cylinder for a range of working pressures. Also, comparing the results with experiments, author found that the result provided by modified stress intensity factor of Bowie and Freese (1972) is more consistent with the fatigue life observed in autofrettaged cylinders. In a later paper, Rees (1991b) combined the stress intensity factors of Bowie and Freese (1972) and Banks-Sills and Marmur (1989) to calculate the fatigue lives of plain and rifled-bored cylinders for both non-autofrettaged and autofrettaged conditions in a similar manner considering the straight-fronted and elliptical-fronted longitudinal crack.
A fracture mechanics-based fatigue life analysis was developed by Underwood and Parker (1995) for pressurized thick-walled autofrettaged cylinders with one or several semi-elliptical-shaped axial grooves at the inner radius. The fatigue life for a crack initiating at the root of the groove was calculated for various cylinder, groove and crack configurations and for different material yielding conditions. Authors compared their result with laboratory life of A723 thick-walled cylinders resulting from cyclic hydraulic pressurization.
Koh (1996) carried out a finite element fatigue test simulation of autofrettaged thick-walled cylinders with an external groove under pulsating pressure. Life estimations of the cylinders were made by using a local strain approach, which is based on a local strain calculation and a fatigue damage relation.
Author observed that the estimated fatigue lives were within factors of 2−4, compared with the experimental fatigue lives determined from the simulation fatigue tests. The fatigue life design of thick-walled autofrettaged pressure vessel with external groove using computer aided engineering techniques was carried out by Koh et al. (1997). He carried out the shape optimization of the external grooves and fatigue life estimation of the vessel using ANSYS finite element package. Koh (2000) also predicted the fatigue life of cross-bored autofrettaged cylinder using linear elastic finite element analysis. The fatigue analysis of autofrettaged components using FEM was carried out by Thumser et al. (2002) incorporating strain dependent Bauschinger effect. The calculated residual stress field was used to evaluate the endurance limit of the component. Authors calculated the necessary stress intensity factors due to loading and residual stresses using the weight function method.
Parker and Underwood (1998) studied the effect of fatigue lives in autofrettaged cylinders, which they have corrected for the Bauschinger effect.
Considering the analysis of Parker and Underwood (1998) further, Troiano et al. (2003) estimated the fatigue lives for all cylinders using Paris law. They observed that the higher strength material always provides longer fatigue life. The fatigue life analysis of autofrettaged cylinders based on experimental loading-unloading stress- strain characteristic was carried out by Jahed et al. (2006a). A longitudinal surface crack emanating from the bore was assumed for the analysis. Authors employed weight function method developed by Bueckner (1970) and Rice (1972) to evaluate the stress intensity factor. The stress intensity factor was then used in Paris law to estimate the fatigue life. It was observed that the fatigue life is increased by a factor of 2.11 at 10% autofrettage to 4.96 at 90% autofrettage. Farhangdoost and Aliakbari (2011) carried out a comparison of the fatigue lives of autofrettaged and non- autofrettaged aluminum cylinder with outer to inner radii ratio 2. They conducted experiments and carried out numerical simulation in ABAQUS to estimate the fatigue lives. Authors observed that the fatigue life of the autofrettaged cylinder is more than the non-autofrettaged cylinder for a range of working pressures. Recently, Ma et al. (2015) studied the influence of Bauschinger effect on the stress intensity
factors of a semi-elliptical crack in determining the fatigue life of autofrettaged cylinders.