Publisher：Materials Today Communications  

A novel high-density pulsed electric current (HDPEC) method is developed to modify the grain-scale microstructure of laser powder-bed fused Ni-based superalloy IN718, which has not been reported in other studies. Rapid micro-residual stress relief and micro-segregation alleviation were achieved without significant grain coarsening which is common in conventional heat treatment. This technique can be an alternative energy-saving post-treatment method for additively manufactured metallic materials, enabling rapid and efficient annealing and solution treatment.

DOI： 10.1016/j.mtcomm.2023.106892

Scopus

Publisher：Engineering Fracture Mechanics  

This study aims to demonstrate the use of a novel treatment approach for fatigue crack healing. High-density pulsed electric currents, which have been widely used for fatigue crack healing of metals, can exert synergistic effects on fatigue crack healing by both compressive stress (owing to the Joule heating) and dislocation motion (owing to the electron wind force). However, these synergistic effects are sometimes weakened by temperature elevations owing to high current densities, failing to efficiently heal fatigue cracks owing to the thermal degradation of metals. In this study, type 316 austenitic stainless steel, which is the most common metallic material, was considered for investigating fatigue crack healing improvement under controlled crack tip temperature elevation owing to the Joule heating induced by multiple high-density pulsed electric currents. Appropriate current parameters such as current density and pulse number under fixed pulse duration were optimized. The results revealed microstructural modifications, such as crack closure with crack bridging, annihilation of slip bands, and material filling near the crack tips, which is promising for fatigue crack healing improvement. The results of fatigue crack growth tests validated these microstructure improvements.

DOI： 10.1016/j.engfracmech.2023.109235

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1016/j.engfailanal.2023.107230

Language：Japanese   Publisher：Vacuum  

The {101} texture of deformed face-centered cubic metals, such as 316 stainless steel and Ni-based alloy Inconel 718, was successfully alleviated by high-density pulsed electric current (HDPEC) treatment. Furthermore, the deformed grains recovered after the HDPEC treatment. The HDPEC induced the rapid dislocation motion and grain refinement that resulted in random grain orientation and equiaxed grain morphology, which led to anisotropy recovery in the deformed metals. This method provides a promising way to modify the microstructure of materials with short time and low cost, after forming or during service.

DOI： 10.1016/j.vacuum.2021.110855

Scopus

Language：Japanese   Publisher：International Journal of Fatigue  

This study evaluated the low-cycle fatigue (LCF) life of type 316 austenitic stainless steel to determine the effect of multiple high-density pulsed electric currents (HDPECs). Fatigue properties were analyzed with the fatigue crack growth (FCG) and LCF tests by considering different conditions of multiple HDPECs and its application. The HDPEC densities of 100, 150 and 200 A/mm2 with application numbers from 1 to 17 times were used. The LCF results were assessed by using fatigue models, and the effectiveness of the application methods was examined. Under the HDPEC density of 200 A/mm2, increasing the number of HDPECs during the period of crack propagation is the best way for delaying FCG. Multiple applications of HDPEC caused a decrease in the length and an increase in the depth of striations in the specimen's fatigue fracture surface, and the degree of ductility was increased thereby leading to the delay in FCG. The proposed conditions pave the way toward improving the LCF life of the material.

DOI： 10.1016/j.ijfatigue.2021.106639

Web of Science

Scopus

Language：Japanese   Publisher：Archive of Applied Mechanics  

The size dependence of central nanovoid embedded in either monocrystalline or polycrystalline high-entropy-alloy (HEA) films under biaxial tension is investigated in this study. Regarding monocrystalline samples, our attention is paid to the proportional increase in the embedded nanovoid with invariant void volume fraction (VVF). The critical stresses in concerned materials at which dislocations start to emit from void under biaxial tension, in an ascending order, are CoCrFeCuNi < CoCrFeMnNi < metal Ni. Lattice distortion appears to facilitate dislocation emission from the void surface in HEAs, which lowers the critical stress compared with the theoretical model. Regarding polycrystalline samples, the size of both the film and embedded nanovoid is kept invariant, whereas grain size of either periodic hexagonal ones or randomly generated ones is allowed to vary. Apart from the random polycrystalline CoCrFeCuNi, the peak stresses of rest polycrystalline samples obey the reverse Hall–Petch effect. Both monocrystalline and polycrystalline CoCrFeMnNi samples fail due to the coalescence with nucleated secondary voids. For the latter, grain boundaries act as primary sites for secondary void nucleation. Unlike HEAs, polycrystalline Ni samples fail due to intergranular cracking instead of void growth and coalescence.

DOI： 10.1007/s00419-021-02100-2

Web of Science

Scopus

Language：Japanese   Publisher：Journal of Materials Science  

Abstract: The effect of high-density pulsed electric current (HDPEC) on the microstructure evolution and corresponding changes in the mechanical properties of the deformed Ni-based alloy Inconel 718 was investigated. After HDPEC treatment, the strain hardening was fully relieved and the ductility recovered correspondingly. The results show that the dislocation density plays a dominant role, and the grain size has a side effect on the strain-hardening relief. Furthermore, the correlation between the mechanical properties and microstructure evolution affected by HDPEC was clarified. HDPEC treatment provides a way to alter the microstructure and thus tailor the mechanical properties of the deformed components. Hence, it is applicable to the metal-forming field to achieve rapid relief of strain hardening and enhance formability. Graphical abstract: [Figure not available: see fulltext.]

DOI： 10.1007/s10853-021-06344-9

Scopus

Language：Japanese   Publisher：Transportation Research Procedia  

A high speed train-track-subgrade vertical coupled dynamic model is developed in frequency domain. In this model, coupling effects between vehicle and track and between track and subgrade are considered. Full vehicle is represented by a rigid body model of a body, two bogies, and four wheelsets connected to each other with springs and dampers. Track and subgrade system are considered as a multilayer beam model connected to each other with springs and damping element. The receptances of track and subgrade system are discussed and receptance contribution of the wheel/rail coupling system are investigated. Combined with the pseudo-excitation method, a solution of the random dynamic response is presented. The random vibration response and transfer characteristics of ballastless track and subgrade system are obtained under track random irregularity when a high speed vehicle runs through. The displacement receptances of rail are higher than the track slab and the subgrade in 10~5000Hz, and that of track slab is more than the subgrade above 30Hz; Frequency ranges of energy distribution of rail vibration are more wide than track slab and subgrade, whereas the vibrations of track slab and subgrade are mainly focused blow 43Hz.

DOI： 10.1016/j.trpro.2017.05.405

Scopus

Language：Japanese   Publisher：Wear  

Wheel/rail contact modelling is essential in railway vehicle dynamic simulation, wheel/rail wear and fatigue. For this purpose, the tiny contact area at wheel/rail interface needs to be carefully investigated. In this paper a Partition Model (P_M) method is proposed to solve the wheel/rail normal contact problem. In the model, the contact region is divided into zones according to different curvature radii of wheel/rail profiles, and each zone is modified by the principle (the normal gaps of contact patch boundaries being equal to each other). For the sake of accuracy, both the iterative algorithms of wheel/rail normal force and elastic compression are also introduced in this model. Three typical test cases are designed to verify the feasibility and accuracy of the proposed method, and the results are compared to those provided by Kalker׳s CONTACT program and Finite Element (FE) method. The results show that the P_M method is fast and accurate for calculating normal contact problems in non-Hertzian cases. The good agreement with CONTACT and finite element method indicates that the capability of P_M method in railway vehicle simulation, wheel/rail wear and fatigue.

DOI： 10.1016/j.wear.2016.07.001

Scopus

Language：Japanese   Publisher：Tiedao Xuebao/Journal of the China Railway Society  

Thermal damage due to wheel-rail contact is one of the main failure modes of wheel-rail system in heavy-haul railway. When a heavy haul train accelerates, slide may occur on the contact surface between the wheel and the rail, which will lead to higher wheel-rail temperature rise. The rise of the temperature to a certain value will cause the phase change of the wheel/rail materials, which will lead to the cracks, scratches and stripping damage on the surface of the wheel and rail. The rail was viewed as a semi-elastic space. Firstly, a wheelset axial slice projection method was used to calculate wheel/rail contact geometry, then the wheel-rail contact elastic method was used to obtain the wheel/rail contact patch and normal contact stress. Finally, the wheel-rail normal contact stress obtained was applied to the semi-elastic space model of the rail. A computer program to predict the thermal effects of the wheel-rail contact was compiled with Matlab software to analyze the generation location, depth and distribution of the martensite of the rail top. The temperature field of the rail was investigated under the conditions of different wheel-set lateral displacements, different wheel speeds, different friction coefficients and different relative sliding velocity of the wheel-rail system. The results showed that the dramatic thermal effects due to wheel/rail sliding contact may cause the rise of the temperature to austenization to form crisp and rigid martensite. The results also showed that it is feasible to study the thermal effect of the wheel/rail contact using elastic half-space hypothesis.

DOI： 10.3969/j.issn.1001-8360.2016.07.012

Scopus

Language：Japanese   Publisher：Progress in Civil, Architectural and Hydraulic Engineering - Selected Papers of the 4th International Conference on Civil, Architectural and Hydraulic Engineering, ICCAHE 2015  

Thermal damage caused by wheel-rail contact is one of the main failure modes of wheel-rail system in heavy-haul railway. When a heavy haul train is running, the adhesion and slip of wheel-rail contact will lead to wheel-rail temperature rise which can reduce the adhesion between the wheel-rail and also can lead to the cracks, scratches, and stripping damage on the surface of the wheel-rail. First, a wheel set axial slice projection method is used to calculate wheel-rail rigid contact point; then, a virtual penetration method and Kalker’s FASTSIM Program are used to calculate wheel/rail contact stress, which can better reflect the real wheel-rail contact status; and then, a moving heat source is used to simulate the movement of the wheel on the rail; finally, the rail thermal effect is calculated. A wheel-rail contact thermal effects analysis program is compiled using Matlab software. The temperature field was analyzed on the basis of wheel-set lateral displacement, wheel speed, and the creepage of wheel-rail. The results show that the temperature of rail surface is high on the condition of wheel-rail rolling contact, and the material parameters changes along with the temperature changes should be considered when calculating wheel-rail thermal contact coupling.

Scopus

Language：Japanese   Publisher：Vehicle System Dynamics  

Searching for the contact points between wheels and rails is important because these points represent the points of exerted contact forces. In order to obtain an accurate contact point and an in-depth description of the wheel/rail contact behaviours on a curved track or in a turnout, a method with improved accuracy in three dimensions is proposed to determine the contact points and the contact patches between the wheel and the rail when considering the effect of the yaw angle and the roll angle on the motion of the wheel set. The proposed method, with no need of the curve fitting of the wheel and rail profiles, can accurately, directly, and comprehensively determine the contact interface distances between the wheel and the rail. The range iteration algorithm is used to improve the computation efficiency and reduce the calculation required. The present computation method is applied for the analysis of the contact of rails of China (CHN) 75kg/m and wheel sets of wearing type tread of China's freight cars. In addition, it can be proved that the results of the proposed method are consistent with that of Kalker's program CONTACT, and the maximum deviation from the wheel/rail contact patch area of this two methods is approximately 5%. The proposed method, can also be used to investigate static wheel/rail contact. Some wheel/rail contact points and contact patch distributions are discussed and assessed, wheel and rail non-worn and worn profiles included.

DOI： 10.1080/00423114.2015.1066508

Scopus

Language：Japanese   Publisher：Tiedao Xuebao/Journal of the China Railway Society  

As wheel-rail contact stress has great influence on wheel-rail wear and rolling contact fatigue, precise calculation of wheel-rail contact points and contact stress is crucial. First of all, based on the standard profile of the wheel-rail running surface in heavy-haul railway, an improved axial slice projection method was used to locate precisely and effectively all the contact points between the wheel and the rail. Then, the wheel-rail contact elastic compression was introduced to locate wheel-rail contact patch. Thirdly, the method of a precise calculation of the wheel-rail contact stress was used to calculate wheel-rail contact normal stress considering the effect of the yaw angle and the roll angle on the motion of the wheelset. Results showed that the wheelset axial slice projection method for locating wheel-rail contact point was accurate, direct, and comprehensive when wheel-rail multipoint contact was located and wheel-rail contact stress was calculated. With the change of the lateral displacement and the yaw angle of the wheelset, the wheel-rail contact patch showed a non-elliptical shape. In one side of track with shorter radius of curvature where wheel rim and rail gauge angle contacted, the maximum value of whee-rail normal contact stress could reach 3 400 MPa; In the other side of track, the wheel-rail normal contact stress was less than 2 000 MPa. When the lateral displacement of the wheelset was set from 0 to 3 mm, the increase of the yaw angle of the wheelset led to the decrease of the right wheel-rail contact patch area and increase of the corresponding wheel-rail normal contact stress. When the lateral displacement of the wheelset was set from 4 to 9 mm, the increase of the yaw angle of the wheelset led to the increase of the right wheel-rail contact patch area and decrease of the corresponding wheel-rail normal contact stress. The increase of the yaw angle of the wheelset was conducive to the left wheel-rail contact. But the influence was minor.

DOI： 10.3969/j.issn.1001-8360.2015.06.003

Scopus

Language：Japanese   Publisher：Applied Acoustics  

Slab tracks are common track structures in high-speed railways. In this study, a vehicle/slab track interaction model is developed based on vehicle-track coupling dynamics theory, and composite track elements are used to rapidly model the finite element equations of the slab track based on the stationary value theory of total potential energy. In the model, the rail is represented as a discretely-supported infinite beam, the slab and the base are considered as continuously-supported free beams, and the connections of the track structure are modelled as viscoelastic spring-damping elements. The composite track element method effectively derives the equations of motion with high or low degrees of freedom by increasing or decreasing the number of track elements; therefore, it can be applied to the dynamic analysis of the track and to investigate the dynamic responses of the slab track system, including the rail, pad, slab, Cement asphalt mortar (CA mortar) and base. The equations of motion of the vehicle system are also proposed using the finite element method. The vehicle system and the slab track system interact through the vertical wheel/rail force, which is approximated using Hertz contact theory. The dynamic responses of a slab track subjected to moving vehicle loads are analysed using dynamic simulations and are compared with another classic simulation method. The effects of random track irregularity and vehicle velocity on the dynamic responses of the slab track system are discussed.

DOI： 10.1016/j.apacoust.2015.05.009

Scopus

Language：Japanese   Publisher：CM 2015 - 10th International Conference on Contact Mechanics of Wheel / Rail Systems  

Wheel/rail contact problem is an important part of railway vehicle dynamic simulation, wear and fatigue. In order to understand these problems, the tiny contact area needs to be investigated, a Partitions Model (P-M) is proposed to solve wheel/rail contact problem in this paper. In the present model, the contact zone is divided into some zones according to the different curvature radius of wheel/rail profile, and each contact patch is modified by using the principle which to ensure the normal gap of contact patch boundary point is equal. The iteration of wheel/rail normal contact force and elastic compression is also be considered to ensure results accurately. Then, a validation of the P-M method for normal problem computing on three test cases is proposed, and the results are assessed using Kalker's CONTACT program. Some comprision results shows that the present method is fast and reliable for calculating normal contact problem on non-Hertzian cases. The P-M results give very good agreement with the result of Kalker's CONTACT program, so it can be used for railway vehicle-track dynamics simulation.

Scopus

Language：Japanese   Publisher：Applied Mechanics and Materials  

Wheel-rail contact stress is foundation of the relationship between wheel and rail, and also an important basis for investigating further wear, surface damage and other problems of wheel and rail system. A three dimension elastic-plastic wheel/rail contact model is established using non-linear finite element method. The changes of wheel/rail normal contact stress, Mises stress and elastic-plastic deformations are analyzed under different conditions in heavy haul railway. A method is provided for a foundation of the future study of wheel-rail contact wear, fatigue and cracks germination and development in this paper.

DOI： 10.4028/www.scientific.net/AMM.638-640.1128

Scopus

Event date： 2015.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Hangzhou   Country：China