Masakazu Takagaki

Coupled Analysis of Induction Hardening Considering Induction Heating, Thermal Elasto-viscoplastic Damage, and Phase Transformation

The coupled computational procedure of the induction heating, the thermal conduction, the thermal elasto-viscoplastic damage, and the phase transformation analysis has been developed for the induction hardening analysis of steel machine parts. The validity of the proposed computational procedure has been illustrated by conducting the induction hardening analysis of a circular bar and a notched circular bar.

Fatigue Crack Modeling and Simulation Based on Continuum Damage Mechanics

Numerical simulation of fatigue crack propagation based on fracture mechanics and the conventional finite element method requires a huge amount of computational resources when the cracked structure shows a complicated condition such as the multiple site damage or thermal fatigue. The objective of the present study is to develop a simulation technique for fatigue crack propagation that can be applied to complex situations by employing the continuum damage mechanics (CDM). An anisotropic damage tensor is defined to model a macroscopic fatigue crack. The validity of the present theory is examined by comparing the elastic stress distributions around the crack tip with those obtained by a conventional method. Combined with a nonlinear elasto-plastic constitutive equation, numerical simulations are conducted for low cycle fatigue crack propagation in a plate with one or two cracks. The results show good agreement with the experiments. Finally, propagations of multiply distributed cracks under low cycle fatigue loading are simulated to demonstrate the potential application of the present method.

Estimation of Crack Propagation by The Analysis of Thermal Fatigue Based on Local Approach Fracture

Local approach to fracture based on continuum damage mechanics and finite element method is a powerful method to estimate fatigue strength, which can reduce computing time and cost for the analysis of fatigue crack initiation and propagation. In the present study, this approach has been applied to the analysis of the behaviors of circular cracks in stainless steel pipes under thermal cyclic loading. The obtained solutions have been compared with the experimental results to discuss the accuracy of uncoupled, locally-coupled and fully-coupled approaches. A new technique to remove the mesh-dependence of the solutions has been proposed and its validity has been discussed through numerical studies on the low-cycle fatigue crack propagation.

Fatigue Damage Analysis of Reactor Vessel Model Under Repeated Thermal Loading

The local approach to fracture based on continuum damage mechanics and the finite element method has been applied to the low-cycle fatigue damage and fracture behavior of a nuclear reactor vessel model subjected to repeated thermal loading due to the alternate inflow of high-temperature and low-temperature liquid sodium. The viscoplastic strain based on the creep plasticity isotropic hardening theory with damage evolution is used in the analysis. The calculated results for the neibourhood of intake nozzle and the conical body have been compared with the experimental results. The calculated results considering the difference of mechanical properties of parent metal, weld metal and heat-affected zone have corresponded well with the experimental results for the initiation and propagation of thermal fatigue cracks.