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The paper reports analytical solutions valid for residual stresses in cylindrical pressure vessels subjected to autofrettage. The material behavior is thought of as obeying a generic monotonic [sigma] -- [epsilon] curve and exhibiting the Bauschinger effect during the unloading phase. Under linear and power-hardening conditions, the solution is given in an explicit form. The circumstances under which it is possible to apply the superposition principle also in the presence of localized plasticity are clearly identified. When possible, the final stresses can be obtained by using in an appropriate manner the stress expressions related to the loading phase. Finally, the influence on residual stresses, both of the hardening law and of the shape of the unloading [sigma] -- [epsilon] curve, is discussed. [DOI: 10.1115/1.1425809] Keywords: Autofrettage, Residual Stress, Bauschinger Effect, Nonlinear Stress, Pressurized Vessels

In the recent past, Atzori and Lazzarin proposed a diagram able to include the geometrical effects on the fatigue limit of defects, short cracks, long cracks and U-shaped notches of whatever severity. The diagram shows that defect sensitivity and notch sensitivity can be considered as two sides of the same medal, thus creating a bridging between Linear Elastic Fracture Mechanics and Notch Mechanics. The fundamental material parameter, dependent on the load ratio, necessary to define the diagram is the El Haddad-Smith-Topper length parameter a0 defined by the plain material fatigue limit and the threshold value of the mode I stress intensity factor for long cracks. It is worth noting that a0 does not contain any geometry-related parameter. The diagram has been validated in the past against a number of experimental results and has been subsequently extended to sharp and blunt V-shaped notches, dependent on their absolute dimensions. After summarising the theory supporting the approach, some application examples relevant to both defect and notch sensitivity will be given

The existence of three-dimensional effects at cracks has been known for many years, but understanding has been limited, and for some situations still is. Understanding improved when the existence of corner point singularities and their implications became known. Despite increased understanding, three-dimensional effects are sometimes ignored in situations where they may be important. The purpose of the present investigation is to study by means of accurate 3D finite element (FE) models a coupled fracture mode generated by anti-plane loading of a straight through-the-thickness crack in linear elastic discs. The results obtained from the highly accurate finite element analyses have improved understanding of the behaviour of through cracked discs under anti-plane loading. The influence of plate bending is increasingly important as disc thickness decreases. It appears that a new field parameter, probably a singularity, is needed to describe the stresses at the disc surfaces. Calculation of the strain energy density (SED) in a control volume at the crack tip shows that the position of the maximum SED is a function of disc thickness.

Byline: Paolo Livieri, Filippo Berto, Paolo Lazzarin This paper deals with fatigue life assessments of welded rectangular hollow sections made of steels and aluminium alloys, in a T-joint configuration, carried out by means of a local stress approach. The welded toe region is modelled like a sharp V-notch with an opening angle of 135 and the intensity of the asymptotic stress distributions is quantified by means of the Notch Stress Intensity Factors (NSIFs). In order to carefully evaluate the NSIFs of hollow sections welded in a T-joint configuration, some Three-Dimensional (3D) Finite Element (FE) analyses are firstly carried out. Afterwards, the NSIFs are used to evaluate the mean value of the strain energy density over a semicircular sector of radius RC at the welded toe. The radius RC is thought of as a material-dependent parameter. The experimental values of fatigue life are compared with those predicted by two previously scatter bands curves recently reported in the literature for welded joints made of structural steel and aluminium alloy. These curves were drawn by using mainly fatigue data obtained from cruciform and T-shaped welded joints. Although the analyses reported here represent only a first attempt to extend an energy-based approach to 3D hollow section joints, the comparison shows that a quite satisfactory assessment of the fatigue life can also be obtained for this type of welded joints. The agreement is good for welded joints made of structural steel, whereas the predictions are found to be in the safe direction for welded joints made of aluminium.