Publications
409 results found
Huo YM, Wang BY, Bai Q, et al., 2014, Viscoplastic damage constitutive modelling of high-speed railway axle steel 25CrMo4, Pages: 679-686, ISSN: 1013-9826
Ductile damage inadvertently exists in the steel during hot tension. The ductile damage during hot forming directly influences the mechanical properties of 25CrMo4 steel for high-speed railway axle. To investigate the grain growth/refinement rule and damage features of 25CrMo4 in hot forming, grain growth test and grain refinement test were conducted using the thermal-mechanical simulator Gleeble-1500. In the grain growth test, the specimens were compressed to ensure that the initial austenitic grain size was small enough, then held at the deformation temperatures (1223K, 1273K, 1323K and 1373K) for 0min, 10min, 20min and 30min, respectively, to study the grain growth rule. In the grain refinement test, the specimens were stretched to different strain level at three temperatures (1313K, 1373K and 1433K) with two strain rates of 1.0/s and 10.0/s to study the grain refinement rule. The micro-voids and micro-cavities were found in tensile specimens during grain refinement test. Based on damage evolution mechanisms, damage constitutive equations are formulated to model the evolution of micro-voids and micro-cavities for 25CrMo4 under hot forming conditions. Partial experiment data were used to determine the material constants in damage constitutive equations by using the Genetic Algorithm (GA) method. To validate the model, the experimental data and computed curves of effective stress and grain size were compared. Close agreements were found between the experimental and prediction results. The developed viscoplastic damage equations are able to characterize the deformation behaviour of 25CrMo4 in hot tension process.
Bai Q, Lin J, Tian G, et al., 2014, A novel forming process for powder metallurgy of superalloys, Pages: 833-839, ISSN: 1013-9826
Powder metallurgy (PM) of nickel-based superalloys has been used for a wide range of products owing to their excellent special properties in processing and applications. Typical processes for high performance PM superalloys include hot isostatic pressing, hot extrusion and hot isothermal forging. Hot isostatic pressing is normally conducted at a high temperature, by using a low pressure for a long time in a closed vessel, resulting in high cost and low product efficiency. In this paper a novel forming process, i.e. direct powder forging for powder metallurgy of superalloys has been proposed. In this process, the encapsulated and vacuumed powder is heated up to the forming temperature and forged directly to the final shape, by using a high forming load for a very short time. Direct powder forging is a low-cost and energy-saving process compared to conventional PM processes, and in addition, press machines of conventional forging can be used for direct powder forming process. In direct powder forging it is important to control the relative density of the deformed part since the existence of voids could reduce the mechanical strength and fatigue life. In this paper, feasibility tests of direct powder forging are presented. Microstructure, relative density and hardness of the formed specimen were studied.
Politis NJ, Politis DJ, Davies CM, et al., 2014, An experimental and numerical investigation into forming force reduction in precision gear forging, Pages: 165-173, ISSN: 1013-9826
A significant factor in the cost of industrial machinery for precision forging is the maximum load required to fully forge the final shape of components. Typically in a precision forging process, the required load increases greatly towards the end of the stroke. This study focuses on reducing the final sharp increase in load encountered in a typical closed die forging setup. A technique of reducing the peak load in the forging of gears is proposed, named the Peripheral Relief (PR) method. A gear forging tool set has been designed and manufactured. A number of experimental trials have been performed using model materials to investigate the force reduction technique. An efficient and simplified FE model has been developed to evaluate the effects of the PR method. The experimental load characteristics are compared to the simulated results. The method has been found, both numerically and experimentally, to significantly reduce the peak load encountered at the end of the forging stroke compared to current closed die forging techniques.
Betts C, Balint D, Lin J, 2014, In-situ micro-tensile testing and X-ray micro-tomography based FE modeling of open-cell metal foam struts and sandwich panels, 8th International Conference on Porous Metals and Metallic Foams, Publisher: ELSEVIER SCIENCE BV, Pages: 197-202, ISSN: 2211-8128
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- Citations: 3
Mohamed M, Lin J, Foster A, et al., 2014, A new test design for assessing formability of materials in hot stamping, 11th International Conference on Technology of Plasticity (ICTP), Publisher: ELSEVIER SCIENCE BV, Pages: 1689-1694, ISSN: 1877-7058
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- Citations: 14
El Fakir O, Wang L, Balint D, et al., 2014, Predicting effect of temperature, strain rate and strain path changes on forming limit of lightweight sheet metal alloys, 11TH INTERNATIONAL CONFERENCE ON TECHNOLOGY OF PLASTICITY, ICTP 2014, Vol: 81, Pages: 736-741, ISSN: 1877-7058
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- Citations: 18
Huo YM, Wang BY, Lin JG, et al., 2013, Damage mechanisms research for the high-speed railway axle steel 25CrMo4 during hot cross wedge rolling, Dongbei Daxue Xuebao/Journal of Northeastern University, Vol: 34, Pages: 1625-1629, ISSN: 1005-3026
The approximate analysis method is used to make clear the damage mechanisms during cross wedge rolling. Hot tension and compression of 25CrMo4 specimens were implemented under three temperatures (1040, 1100 and 1160°C) and two strain rates (1.0 and 10.0 s-1) on thermal-mechanical simulator. The true stress-strain curve and microstructure was obtained and compared under tension and compression condition. Some conclusions can be drawn: The recovery and recrystallization leads to the softening mechanism during compression, and the plastic damage leads to the softening mechanism during tension. Plastic damage undergoes three phases: nucleation, growth and coalescence, whose type involves grain boundary damage and inclusion damage. Streamline is some place where refined grain, grain boundary damage and inclusion damage are apt to take place. The inclusion damage consists of that at grain boundary and inside grain. The axial tension stress is the main damage in high-speed railway axle during cross wedge rolling.
Afshan S, Balint D, Farrugia D, et al., 2013, A new experimental method for identifying the conditions necessary for diffusion bonding in free cutting steels, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, Vol: 586, Pages: 25-30, ISSN: 0921-5093
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- Citations: 4
Kaye M, Puncreobutr C, Lee PD, et al., 2013, A new parameter for modelling three-dimensional damage evolution validated by synchrotron tomography, ACTA MATERIALIA, Vol: 61, Pages: 7616-7623, ISSN: 1359-6454
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- Citations: 17
Fu L, Wang BY, Lin JG, et al., 2013, Constitutive model coupled with dislocation density for hot deformation of 6111 aluminum alloy, Beijing Keji Daxue Xuebao/Journal of University of Science and Technology Beijing, Vol: 35, Pages: 1333-1339, ISSN: 1001-053X
The hot deformation behavior of 6111 aluminum alloy was investigated by high-temperature tensile testing on a Gleeble-1500 thermal-mechanical simulator at deformation temperatures of 350, 450, 550°C and strain rate of 0.1, 1, 10 s-1. It is shown that the flow stress of the aluminum alloy decreases when the temperature rises but increases when the strain rate increases, and the hot deformation behavior transfers from a strain-hardening deformation stage to a steady-state deformation stage. A unified viscoplastic constitutive model coupled with dislocation density was established in consideration of the effects of strain, temperature and strain rate on the flow stress. Material constants in the constitutive model were solved through a genetic algorithm. Predicted true stress-true strain curves calculated by this model are in good agreement with experimental data.
Betts C, Balint D, Lin J, 2013, The effect of morphological imperfections on damage in 3D FE analysis of open-cell metal foam core sandwich panels, INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, Vol: 75, Pages: 377-387, ISSN: 0020-7403
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- Citations: 1
Zhou J, Wang B, Lin J, et al., 2013, Optimization of an aluminum alloy anti-collision side beam hot stamping process using a multi-objective genetic algorithm, ARCHIVES OF CIVIL AND MECHANICAL ENGINEERING, Vol: 13, Pages: 401-411, ISSN: 1644-9665
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- Citations: 54
Yang H, Davies CM, Lin J, et al., 2013, Prediction and assessment of springback in typical creep age forming tools, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART B-JOURNAL OF ENGINEERING MANUFACTURE, Vol: 227, Pages: 1340-1348, ISSN: 0954-4054
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- Citations: 3
Fu L, Wang B, Meng Q, et al., 2013, Factors affecting quality in hot stamping of aluminum alloy, Zhongnan Daxue Xuebao (Ziran Kexue Ban)/Journal of Central South University (Science and Technology), Vol: 44, Pages: 936-941, ISSN: 1672-7207
A finite element model was established for hot stamping of aluminum alloy, and the factors affecting quality were investigated including initial blank temperature, stamping velocity, blank holder force (BHF) and friction coefficient. The reliability of finite element simulation was proved by the hot stamping experiments of aluminum alloy. The results indicate that initial blank temperature of 400-500°C is feasible in hot stamping. The quality will be weakened with the increase of stamping velocity, however, the effects are limited when certain extents are exceeded. Fracture occurs when BHF is more than 15 kN. Good lubrication is necessary for hot stamping of aluminum alloy. Forming will be successful while friction coefficient is less than 0.15.
Karimpour M, Balint DS, Rzepiejewska-Malyska KA, et al., 2013, An inverse method for extracting the mechanical properties of the constituent materials of a multilayer from nanoindentation data, COMPUTATIONAL MATERIALS SCIENCE, Vol: 68, Pages: 384-390, ISSN: 0927-0256
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- Citations: 11
Afshan S, Balint D, Lin J, et al., 2013, Micromechanical Modelling of Void Healing, Advanced Structured Materials, Pages: 1-8
Predicting effective consolidation or level of remnant porosity for a range of steel grade (function of solidification regime), billet size, pass schedule/roll design and thermo-mechanical conditions has always been an important issue for steel producers as it will affect the mechanical properties of final products (strength, ductility, etc.). It is known that partial or complete recovery of strength in such porous materials can be obtained by pore closure and diffusive healing processes at elevated temperature. This study investigates the elimination of porosity through two stages of void closure and healing. An Abaqus/UMAT has been developed for the analysis of the material porosity elimination process including two stages of void closure and healing. The model uses the Gurson-Tvergaard (GT) model under compression to predict the void closure. The closure model parameters were calibrated by an optimisation technique using a representative volume element concept. Then a healing model based on a combination of diffusion bonding, creep and plasticity was implemented as a UMAT subroutine and finally the whole behaviour of the material was controlled using a status check method developed in this work.
Betts C, Balint D, Lin J, 2013, An Investigation of the Mechanical Properties of Open Cell Aluminium Foam Struts: Microtensile Testing and Modelling, Advanced Structured Materials, Pages: 53-63
A microtensile test procedure has been developed to directly determine the mechanical properties of individual metal foam struts. The results reveal that the measured strut properties display a considerable reduction in elastic stiffness compared to the typical value of 70 GPa for aluminium alloys. A realistic finite element modelling procedure of the as-tested struts has been established, using X-ray micro-tomography scans of the undeformed struts, to assess the reasons for this reduction in stiffness. The material model in the FE simulations was established using a damage model that comprises of a set of continuum mechanics-based viscoplastic damage constitutive equations. The equations were calibrated with the microtensile test data and implemented into ABAQUS through the user defined subroutine VUMAT. The prime factor in the recorded reduction in stiffness was found to be slippage between the grips and the strut during testing.
Bai Q, Lin J, Dean TA, et al., 2013, Modelling of dominant softening mechanisms for Ti-6Al-4V in steady state hot forming conditions, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, Vol: 559, Pages: 352-358, ISSN: 0921-5093
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- Citations: 75
Zhan L, Lin J, Huang M, 2013, Study on springback behavior in creep age forming of aluminium sheets, Advanced Science Letters, Vol: 19, Pages: 75-79, ISSN: 1936-6612
Multi-step finite element simulation procedures have been developed using the commercial FE solver MSC.MARC for the study of springback in creep age forming (CAF) of aluminium sheets. A set of mechanism-based unified constitutive equation set has been implemented into MSC.MARC via the user defined subroutine, CRPLAW, to describe the interaction between precipitation hardening and creep behaviour of the AA7055 during CAF. The effects of ageing time, curvature and work-piece thickness, amount of load, loading rate on springback are studied. Some important conclusions are drawn: the longer the ageing time, the less the springback, but the influence declines with the increasing of ageing time; single curvature tool causes higher springback than double curvature tool; the amount of load and loading rate in creep age forming do not change the amount of springback significan y; for the same tool shapes, the thicker sheet has lower springback. In the end, the effect of loading patterns, he uniform pressure loading and the end clamping loading, on the spatial variation of springback are studied. The ults show that the end clamping loading has a little lower springback than the uniform pressure loading. © 2013 American Scientific Publishers All rights reserved.
El Fakir O, Chen S, Wang L, et al., 2013, Numerical Investigation on the Hot forming and Cold-Die Quenching of an Aluminium-Magnesium Alloy into a Complex Component, LIGHT METALS TECHNOLOGY 2013, Vol: 765, Pages: 368-372, ISSN: 0255-5476
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- Citations: 6
Das S, Ji S, El Fakir O, et al., 2013, Melt Conditioned Twin Roll Casting (MC-TRC) of Thin Mg-Alloy Strips for Direct Stamping of Mg Components, LIGHT METALS TECHNOLOGY 2013, Vol: 765, Pages: 170-+, ISSN: 0255-5476
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- Citations: 5
Sun C, Bai Q, Lin J, et al., 2013, The Effect of Process and Model Parameters in Temperature Prediction for Hot Stamping of Boron Steel, ADVANCES IN MECHANICAL ENGINEERING, ISSN: 1687-8132
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- Citations: 2
Zhang P, Karimpour M, Balint D, et al., 2012, Three-dimensional virtual grain structure generation with grain size control, MECHANICS OF MATERIALS, Vol: 55, Pages: 89-101, ISSN: 0167-6636
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- Citations: 21
Zhang P, Karimpour M, Balint D, et al., 2012, Cohesive zone representation and junction partitioning for crystal plasticity analyses, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Vol: 92, Pages: 715-733, ISSN: 0029-5981
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- Citations: 10
Zhang P, Karimpour M, Balint D, et al., 2012, A controlled Poisson Voronoi tessellation for grain and cohesive boundary generation applied to crystal plasticity analysis, 21st International Workshop on Computational Mechanics of Materials (IWCMM), Publisher: ELSEVIER SCIENCE BV, Pages: 84-89, ISSN: 0927-0256
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- Citations: 59
Liu G, Zhu Q, Zhu G, et al., 2012, A Testing System and Method to Generate Forming Limit Diagrams at Elevated Temperatures, CN102749253 A
Fu L, Wang BY, Meng QL, et al., 2012, Comparison of thinning features of a hot and cold stamped aluminium B-pillar model for passenger cars, Advanced Materials Research, Vol: 562-564, Pages: 234-237, ISSN: 1022-6680
To overcome low formability and springback problems in forming aluminium panel parts, a novel process of hot stamping is introduced in this paper. It is good plasticity and low deformation resistance when aluminum alloys under high temperature, which makes it possible to form complex parts such as B pillars. Finite element method is used to analysis the thinning regions in this part, it can be acquired that the quality of the part in hot stamping is better than in cold stamping. © (2012) Trans Tech Publications, Switzerland.
Lin J, Balint D, Pietrzyk M, 2012, Microstructure Evolution in Metal Forming Processes, Publisher: Woodhead Publishing, ISBN: 9780857090744
Recent research on the mechanisms, modeling, and control of microstructure evolution during metal forming processes are provided.
Chen Y, Zhuang W, Wang S, et al., 2012, Investigation of FE Model Size Definition for Surface Coating Application, CHINESE JOURNAL OF MECHANICAL ENGINEERING, Vol: 25, Pages: 860-867, ISSN: 1000-9345
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- Citations: 3
Liu B, Lang L, Zeng Y, et al., 2012, Forming characteristic of sheet hydroforming under the influence of through-thickness normal stress, JOURNAL OF MATERIALS PROCESSING TECHNOLOGY, Vol: 212, Pages: 1875-1884, ISSN: 0924-0136
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- Citations: 26
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