Based on increment loading & changeable rigidity method and using three-dimensional non-linear finite element method and the elasticity-plasticity damage constitutive relation, the law of the effect of three different by-stage excavation scheme for multi-step excavation process on the stress disturbing, the plastic dissipation energy, the plastic region and the displacement around opening had been simulated and analyzed, and the project of excavation orders had been optimized and there were important engineering value.

The non-differentiability of the plastic dissipation calculated through the Von-Mises yield function leads to convergence difficulties when using mathematical programming to solve upper bound limit analysis of pipe elbow.

This problem is avoided replacing the plastic dissipation by the strain energy of a ficticious elastic-plastic material with a nearly infinite Young modular.

Cyclic plastic dissipated energy and fractional dimension methods are applied to lifetime prediction of zirconium and zircaloy-4. A power relationship is obtained between plastic dissipated energy, fractional dimension and fatigue lifetime.

The rolling of the substrates on rollers allows control of the plastic dissipation during substrate bending and prevents dissipation associated with substrate unbending.

Mechanical analysis shows that control of plastic dissipation in substrates remains effective, as long as the ratio of the plate thickness to the roller radius is large enough to prevent wound-up.

The higher the strain rate sensitivity is, the larger amount of the external work is transformed into plastic dissipation energy than into cohesive energy, which delays the cohesive zone rupturing.

In this case, the plastic dissipation energy decreases and the cohesive dissipation energy increases which accelerates the cohesive zones debonding.

It is shown explicitly in the case of mode III that solutions with logarithmic singularity produce negative plastic dissipation in the plastic reloading sector.

The low cycle fatigue behaviors of zirconium and zircaloy-4 at room temperature, 400℃ and 600℃ have been investigated. The macroscopic stress response curves show that the cyclic deformation behavior of hexagonal zirconium and zircaloy-4 is characterized by three stages of cyclic hardening, saturation and cyclic softening. Hexagonal metals are sensitive to loading history, just like plane-slip materials. Cyclic plastic dissipated energy and fractional dimension methods are applied to lifetime prediction of...

The low cycle fatigue behaviors of zirconium and zircaloy-4 at room temperature, 400℃ and 600℃ have been investigated. The macroscopic stress response curves show that the cyclic deformation behavior of hexagonal zirconium and zircaloy-4 is characterized by three stages of cyclic hardening, saturation and cyclic softening. Hexagonal metals are sensitive to loading history, just like plane-slip materials. Cyclic plastic dissipated energy and fractional dimension methods are applied to lifetime prediction of zirconium and zircaloy-4. A power relationship is obtained between plastic dissipated energy, fractional dimension and fatigue lifetime. The deformation mechanism analysis shows that the possible deformation modes of zirconium and its alloys include prismatic, pyramidal and basal slipping, and twinning.

Low cycle fatigue lifetime curves of zirconium and zircaloy-4 at room temperature and 400 ℃ were measured, respectively. Cyclic plastic dissipated energy and fractal dimension of fracture surfaces are selected as damage variable to evaluate the fatigue lifetime. The accumulated formula of plastic dissipated energy is established on the basis of considering cyclic deformation character of zirconium and zircaloy-4. The test results indicate that the relationship between cyclic plastic dissipated energy and fatigue...

Low cycle fatigue lifetime curves of zirconium and zircaloy-4 at room temperature and 400 ℃ were measured, respectively. Cyclic plastic dissipated energy and fractal dimension of fracture surfaces are selected as damage variable to evaluate the fatigue lifetime. The accumulated formula of plastic dissipated energy is established on the basis of considering cyclic deformation character of zirconium and zircaloy-4. The test results indicate that the relationship between cyclic plastic dissipated energy and fatigue lifetime fits power law. Fractal analysis of fracture surface shows that the relationship between fractal dimension and fatigue lifetime can be also expressed as power law. An empirical formula describing the relationship between dissipated energy, fractal dimension and fatigue lifetime, D ≈ 0.027 lnN f + 1.099 ≈0.120 lnWpf- 0.025, is obtained, and their physical mechanism is discussed thermodynamically.

Fatigue tests and transmission electron microscope(TEM) observation were performed to examine the characterization of microplasticity developed during high cycle fatigue in 2Cr13 steel.The specimens were being elasticity deformation under three special cycle loads before fatigue crack initiation and elastic modulus were not being changed.The characterization of local microplastic deformation was observed in specimens at half fatigue life cycles.There were many kinks in parallel screw dislocations and some screw...

Fatigue tests and transmission electron microscope(TEM) observation were performed to examine the characterization of microplasticity developed during high cycle fatigue in 2Cr13 steel.The specimens were being elasticity deformation under three special cycle loads before fatigue crack initiation and elastic modulus were not being changed.The characterization of local microplastic deformation was observed in specimens at half fatigue life cycles.There were many kinks in parallel screw dislocations and some screw dislocation meshes existed in a crisscross configuration.Prismatic loops and gliding loops were formed and piled up around M\-3C or M\-2C carbides in some areas.Dislocation cells were formed at some areas at fatigue life cycles.TEM observation of tensile test of the specimens after half life fraction revealed the mechanisms of the crack initiation and propagation.Microcracks initiated at carbides and propagated along the cell walls or the lath boundaries.The local microplasticity dissipation during high cycle fatigue had brought about local damage in 2Cr13 steel.It needed a little plastic work for the cracks growth through these damage regions.Characterization of Microplasticity Da mage Developed during High Cycle Fatigue in