The emission of an edge dislocation from a thin-film-covered crack is studied in order to investigate the effects of a passive film on stress-corrosion cracking. The results show that the crack stress field in the film due to the applied loads is enhanced by a harder film or abated by a softer film. For an edge dislocation is the film is harder. Under pure mode II or III loadings a harder thin film makes the dislocation emission easier and a softer film makes the dislocation emission more difficult if the film thickness is smaller than a critical value. The opposite is also true if the film thickness is larger than the critical value. Under pure mode I loadings, however, a harder thin film makes the dislocation emission more difficult and a softer film makes the dislocation emission easier for the two flim thicknesses used in this study.

A three-dimensional parametrized finite element model is established for the nonlinear analysis of the hydraulically expanded tube-to-tubesheet joint. Distribution of the residual contact pressure on the contact surface between the tube and the tubesheet is investigated. It is found that sealing circular bands exist on the contact surface which enhance the sealing of the joint since the residual contact pressures on the sealing circular bands are higher than on other positions. The sealing circular bands are located close to the two ends of the hole when it is not grooved, but they are located at the two brinks of the groove for a grooved hole and in the latter case, the residual contact pressures are even higher, reflecting that the joint with a grooved tube-sheet hole is more capable of sealing. Experiments and finite element calculations for the pull-out force of the joint are also performed for different expansion pressures and groove widths. Results show that with the increase of the groove width, the measured pull-out force increases significantly and becomes larger and larger than the calculated one, which is owing to the scratch on the contact surface between the tube and tubesheet.

Considered is the tandem emission of dislocations and dislocation dipoles from a crack under in-plane shear in one slip system as well as multiple slip systems. Effective stress intensity factors are determined by considering zones of local distortion similar to that in macro-plasticity. The dislocation free zone (DFZ) is also obtained which is analogous to the core region in fracture mechanics. Studied are effects of dislocation emission or development of plastic zone in front of the crack tip on the potential crack propagation based on the strain energy density factor criterion.

In situ tensile tests in a transmission electron microscope (TEM) show that dislocations emitted from a mode II crack tip will form a inverse piled-up group after equilibrium or a double piled-up group when they meet a obstruction, e.g., grain boundary or second phase. A microcrack can initiates in front of the piled-up group of dislocations. Micromechanics analysis shows that dislocations emitted from a mode II blunnt crack tip can form a inverse piled-up or double piled-up group, depending upon the applied stress intensity factor Km, lattice friction stress t f and the distance of the obstruction from the crack tip L, The maximum normal stress in front of the double piled-up group which is located at the direction of a =-64

While many edge dislocations can be emitted from the tip of a Mode I crack, the distribution of these dislocations turns out to be dependent on the number of available slip systems as well as the order of emission. This study deals with the situation in which the edge dislocations are emitted one at a time and along a slip plane in which the shear stress is the largest. The result shows that most of the dislocations are confined in two or four symmetric planes even though 34 slip planes are available. Dislocations are emitted along two symmetric planes until they are almost saturated and then the emission is switched to another two planes nearby. The switching reduces crack tip shielding so that more dislocations are emitted in four planes than if the emission is limited to two planes. There is a dislocation-free zone near the crack tip whose size increases with the critical stress intensity factor for dislocation emission.

In an effort to simulate dislocation distribution around a Mode I crack, edge dislocations are allowed to be emitted from the crack tip along many possible slip planes containing the crack tip. it turned out that the final distribution depends on the order of emission. So the previous paper dealt with the situation in which the emission process is one at a time, namely after one dislocation is emitted the plastic zone is re-equilibrated before the next dislocation is emitted. In this paper, many dislocations are emitted at the same time when the condition is met, namely, when the slip force exceeds the lattice friction for dislocation motion. It is found that the dislocations are more uniformly distributed than the previous case of sequential emission. The shielding effect for the same number of dislocations emitted is less when the dislocations are distributed along more slip planes. The shape of the plastic zone is different from but the size is comparable with the plastic zone based on yon Mises or Tresca criterion. A distinct dislocation-free zone appears when there is a critical stress intensity factor for dislocation emission.