Papers by Author: Tatsuo Inoue

Abstract: A phenomenological mechanism of transformation plasticity is discussed, in the first part of the paper, why the transformation plastic deformation takes place under a stress level even lower than the characteristic yield stress of the material: This is principally based on the difference in thermal expansion coefficient of mother and new phases. Some calculated data of induced stress and strain depending on applied stress are represented. Bearing in mind that it is also a kind of plastic strain, a unified plastic flow theory is derived by introducing the effect of progressing new phase into the yield function of stress, temperature and plasticity related parameters. Thus obtained strain rate reveals to include the transformation plastic part in addition to thermo-mechanical plastic components. Application of the theory is carried out to simulate some complicated cases of varying stress and temperature, and the results are compared with experimental data.

Abstract: Phenomenological mechanism of transformation plasticity is proposed in the first part of the paper by use of simple model why stress in mother phase increases to reach yielding due to progressing new phase and to induce plastic deformation even under small applied stress. Based on the discussion, a unified constitutive model including transformation-induced and ordinal thermomechanical plastic strain rates by introducing an effect of varying phases during phase transformation into yield function. Thus derived constitutive equation is applied to describe strain response under varying temperature and stress with some discussions as well as metallo-thermo-mechanical simulation of quenching.

Abstract: Laser peening without protective coating (LPwC) has been applied to metallic materials using low energy pulses of a Q-switched and frequency-doubled Nd:YAG laser. Compressive residual stresses of several hundred megapascals were imparted on the surface of the materials. Redistribution of the residual stress in the top surface due to thermal loading was evaluated non-destructively by synchrotron radiation of SPring-8. Accelerating stress corrosion cracking (SCC) tests showed that LPwC prohibited SCC of sensitized materials. LPwC largely prolonged the fatigue lives of titanium alloys, aluminum alloys and austenitic stainless steels.

Abstract: Strategy and function of a new developed FEM code COSMAP(COmputer Simulation of MAterial Process) for surface hardening during of thermo-mechanical processing, including heat treatment, carbonizing and nitriding, is briefly introduced in this paper. The simulation code is developed based on the metallo-thermo-mechanical theory considering the coupled equations of diffusion, heat conduction, inelastic stresses and kinetics of phase transformation. Some examples of simulation and the experimental verification for carbonized quenching, carbonizednitrided- quenching process of a cylinder and ring as well as a gear are illustrated, and comparison of the simulated values of distortion, residual stresses and profile of induced phases with the experimental data is made with some discussions.

Abstract: Mechanism of transformation plasticity (TP) is discussed from continuum mechanics viewpoint, and derivation of TP law from the unified thermo-mechanical and transformation plasticity constitutive equation. Result of identified TP coefficient for a chromium steel (JIS SCr420) by use of multi-functional testing machine is introduced as one of the material data together with other data to the simulation of a quenching process by use of newly developed code COSMAP. The simulated distribution of temperature, phases and stress/distortion are compared with the experimentally measured values to verify the accuracy.

Abstract: As one of the activities carried out by our group of IMS-VHT (Virtual Heat Treatment tool for monitoring and optimising HT process), results of a benchmark project on the simulation of carburized quenching process is summarized. Several programs available for taking into account the metallo-thermo-mechanical coupling had been employed for the simulation for a cylinder, ring as well as a helical gear by use of common data of material properties and cooling characteristics. Comparison of the simulated values of distortion, residual stresses and profile of induced phases with the experimental data is made with some discussions.

Abstract: The three-year activities of Japanese IMS-VHT (virtual heat treatment tool for monitoring and optimising heat treatment process) project are summarized in collaboration with international VHT program. A brief introduction of the developed code and the results of a simulation of the carburized-quenching process of a cylinder, ring, and helical gear are described by using accumulated databases of material characteristics and cooling conditions. A trial to optimizing the heat treatment (HT) process by using a database system is presented based on collected data of practical cases. The goal of this project is to optimize the process, such as gas-carburizing followed by quenching into oil, and to accumulate heat treatment data to create a knowledge-based database.