---

In this study, the first mode of stress intensity factor of semi-elliptical circumferential crack in the outer surface of a cylinder with radius to thickness ratio of 30, is investigated. The cylinder is applied in semi-submersible drilling platforms. First, the stress field of the cylinder under thermal and mechanical loads is extracted based on semi couple thermo-elastic equations. Then, the weight functions are derived for deepest and surface points using three reference loads results. Explicit expressions of stress intensity factors for surface and deepest points are presented using thermo-elastic stress field and the weight functions of the cracked cylinder. The results obtained by proposed weight functions and those obtained by finite element method and those presented in the literatures have a good accuracy. The interaction effects of thermal and mechanical loads on the stress intensity factors are studied. The results show that with increasing load ratio, the dimensionless stress intensity factors of deepest and surface points, decrease and increase, respectively.

---

In this paper, the stress intensity factor for a longitudinal semi-elliptical crack in the internal surface of a thick-walled cylinder is derived analytically and numerically. The cylinder is assumed enough long and subjected to the axisymmetric cooling thermal shock on the internal surface. The uncoupled thermoelasticity governing equations for an uncracked cylinder are solved analytically. The non-dimensional hyperbolic heat equation is solved using separation of variables method. The weight function method is implemented to obtain the stress intensity factor for the deepest and surface points of the crack. Results show the different behavior of the crack under hyperbolic thermal shock. At a short time after the thermal shock, the stress intensity factor at the deepest point –especially for shallow cracks- for hyperbolic model is significantly greater than Fourier one. The stress intensity factor at the deepest point is greater as the crack is narrower for both models. Unlike mechanical loading, the greatest stress intensity factor may occur at the surface point. According to the results, assumption of adequate heat conduction model for structure design under transient thermal loading is critical.

---

Thick-walled cylindrical vessels are specially used in oil, chemical, nuclear and military industries in order to withstand internal pressure. The presence of the compressive residual stress in the walls increases the bursting pressure and fatigue life. Autofrettage processes and radial interference in multilayer cylinders are among the conventional methods of creating residual stresses in the pressure vessels. In order to achieve higher strength and fatigue life, the combination of these processes is also considered. J integral method is a suitable criterion for evaluating the crack parameters in elastic and elastoplastic strain fields. In this research, distribution of the J integral along the semi-elliptical crack front on the inner surface of the interferenced two-layered cylinder with closed end has been studied. Inner layer was autofrettaged. Burst pressure was determined based on the fracture toughness criterion (J_ΙC). Also, the effects of the autofrettage percent, radial interference; depth, angle and aspect ratio of the crack on the J integral and burst pressure variations have been investigated. The inner and outer layers of the cylinder were made of 7075-T6 aluminum alloy. The periodic nonlinear hardening behavior of this alloy has been predicted using Chabooche model. The validity of the results and their accuracy were examined