Publications
409 results found
Ganapathy M, Li N, Lin J, et al., 2015, Analysis of new Gleeble tensile specimen design for hotstamping application, 4th International Conference on New Forming Technology, Publisher: EDP
Hot tensile testing is useful to understand the material behavior at elevated temperatures. Hence it is of utmost importance that the test condition is accurate enough to derive stress-strain data in fully austenitic state and to ensure homogeneous deformation throughout the gauge length of the specimen. But present limitation of standard Gleeble hot tensile sample geometry could not be used to achieve a uniform temperature distribution along the gauge section, thus creating errors of experimental data. In order to understand the effect of sample geometry on temperature gradient within the gauge section coupled electrical-thermal and thermo-mechanical finite element analysis has been carried out using Abaqus, with the use of viscoplastic damage constitutive equations presented by Li [1]. Based on the experimental study and numerical analysis, it was observed that the new sample geometry introduced by Abspoel [2], is able to achieve a better uniformity in temperature distribution along the gauge length; The temperature deviation along the gauge length within 25 ∘C during soaking and 5 ∘C after cooling and onset of deformation); also the strain deformation is found to be almost homogeneous.
Lam ACL, Shi Z, Huang X, et al., 2015, Material modelling for creep-age forming of aluminium alloy 7B04, Publisher: EDP Sciences, ISSN: 2261-236X
This paper presents a study on the creep-ageing behaviour of a peak-aged aluminium alloy 7B04 under different tensile loads at 115oC and subsequently modelling it for creep-age forming (CAF) applications. Mechanical properties and microstructural evolutions of creep-aged specimens were investigated. The material was modelled using a set of unified constitutive equations, which not only captures the material's creep deformation but also takes into account yield strength contributions from solid solution hardening, age hardening and dislocation hardening during creep-ageing. A possible application of the present work is demonstrated by implementing the determined material model into a commercial finite element analysis solver via a user-defined subroutine for springback prediction of creep-age formed plates. A good agreement is observed between the simulated springback values and experimental results. This material model now enables further investigations of 7B04 under various CAF scenarios to be conducted inexpensively via computational modelling.
Gao H, Li N, Ho H, et al., 2015, Determination of a Set of Constitutive Equations for an Al-Li Alloy at SPF Conditions, Materials Today: Proceedings, Vol: 2, Pages: S408-S413, ISSN: 2214-7853
Li X, Li N, Zhu Q, et al., 2015, A Testing System and Method to Generate Forming Limit Diagrams at Elevated Temperatures, CN102749253 B
Wang S, Zhuang W, Cao J, et al., 2015, Micro-mechanics Modeling for Micro-forming Processes, Micromanufacturing Engineering and Technology: Second Edition, Pages: 733-748, ISBN: 9780323311496
The development toward miniaturization of products and devices in metal industries has increased the demand for metallic parts manufactured at micro-scale. This chapter describes an integrated numerical simulation platform, which employs virtual grain generation (VGRAIN) and crystal plasticity finite element simulation technology to aid the forming process design of micro-components. The VGRAIN system generates finite element models of controlled grain tessellation structures, which incorporate material micro-structure information and dedicated intergrain relationships. Micro-deformation of grains was characterized by crystal plasticity theory and implemented via user-defined subroutine VUMAT/UMAT into ABAQUS software. The validity of the integrated numerical simulation platform had been demonstrated through the forming of a micro-pin. The platform had been further used to investigate the initiation and propagation of micro-cracks under complex forming processes.
Liu J, Wang LL, Lee J, et al., 2015, Size-dependent mechanical properties in AA6082 tailor welded specimens, Journal of Materials Processing Technology, Vol: 224, Pages: 169-180, ISSN: 0924-0136
AA6082 tailor welded blanks (TWBs) produced using laser welding and friction stir welding were studiedin this paper. The nominal mechanical properties of welded AA6082 under uniaxial tension conditionswere characterised by evaluating the local properties of the base material, heat affected zone (HAZ) andweld zone. Tensile specimens were machined in the way that the weld line lies perpendicular to theloading axis. Three standard-sized specimens containing varying ratios of weld in the gauge region ofthe specimen were used to determine the size-dependent properties of welded AA6082 in the TWBs.A post-weld strength prediction (PWSP) model, based on the theories of plasticity, has been developedto estimate the post-weld properties of the tailor welded specimens. The model can be used to predictthe post-weld yield strength and the global tensile behaviour of welded AA6082 specimens. Good agreementsbetween the modelling and the experimental results have been obtained, with the yield strengthdeviation less than 6%. It was found that the yield strength increased with increasing dimensions of thetensile specimens. The size-dependent phenomenon was studied and the complex plastic deformationmechanisms have been found to cause the size-dependent phenomenon
Wang X, Ahn J, Bai Q, et al., 2015, Effect of forming parameters on electron beam Surfi-Sculpt protrusion for Ti-6Al-4V, Materials & Design, Vol: 76, Pages: 202-206, ISSN: 0261-3069
The development of electron beam Surfi-Sculpt enables many types of protrusions in a wide range of metallic materials to be tailored. The effect of forming parameters, including heat input and scanning frequency on the quality of protrusions and microstructure evolution was studied. The micro-hardness of heat affected zone was greater than that of the molten zone and parent material. Forming parameters were optimised by comparing the height of the protrusion. This study can provide guidance for an optimum protrusion design.
Ko DC, Lin J, Yanagimoto J, et al., 2015, Advanced forming technology for lightweight components: From theory to application, Advances in Mechanical Engineering, Vol: 2014, ISSN: 1687-8132
Lin J, 2015, Fundamentals of materials modelling for metals processing technologies: Theories and applications, ISBN: 9781783264964
This book provides a comprehensive introduction to the unique theory developed over years of research on materials and process modelling and its application in metal forming technologies. It starts with the introduction of fundamental theories on the mechanics of materials, computational mechanics and the formulation of unified constitutive equations. Particular attention is paid to elastic-plastic formulations for cold metal forming and unified elastic-viscoplastic constitutive equations for warm/hot metals processing. Damage in metal forming and numerical techniques to solve and determine the unified constitutive equations are also detailed. Examples are given for the application of the unified theories to solve practical problems encountered in metal forming processes. This is particularly useful to predict microstructure evolution in warm/hot metal forming processes. Crystal plasticity theories and modelling techniques with their applications in micro-forming are also introduced in the book. The book is self-contained and unified in presentation. The explanations are highlighted to capture the interest of curious readers and complete enough to provide the necessary background material to further explore/develop new theories and applications.
Wang B, Li Z, Zheng M, et al., 2015, Modelling and experimental research in hot precision forging of shaft gear, 4th International Conference on New Forming Technology (ICNFT), Publisher: E D P SCIENCES, ISSN: 2261-236X
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- Citations: 1
Zheng K, Lin J, Politis DJ, et al., 2015, An experimental investigation for macro-textured tool in hot stamping, 4th International Conference on New Forming Technology (ICNFT), Publisher: E D P SCIENCES, ISSN: 2261-236X
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- Citations: 1
Shi Z, Lam ACL, Yang H, et al., 2014, Creep-age forming AA2219 plates with different stiffener designs and pre-form age conditions: Experimental and finite element studies, Journal of Materials Processing Technology, Vol: 219, Pages: 155-163, ISSN: 1873-4774
Creep-age forming (CAF) is one of the relatively new forming techniques that has been proven viable for the production of extra-large integral airframe structures. However, experimental studies on forming stiffened structures under creep-ageing conditions remain scarce. In this work, 200 mm × 48 mm integrally stiffened plates of aluminium alloy 2219 have been formed on an end clamp device that has a bending radius of 156 mm and creep-aged at 175 °C for 18 h. Three different stiffener designs, namely the beam stiffened, waffle and isogrid plates, are tested alongside the flat plates. Utilisation of PTFE pocket fillers and intermediate sheets to reinforce and protect stiffeners during forming operation is found effective as demonstrated by the defect-free formed parts with smooth curvature. Springback of the plates ranged from 12.2 to 15.7% in the experimental studies for different stiffener designs. Using the CAF material constants determined for this alloy, corresponding finite element models have been developed and experimentally validated using the measured profiles of the creep-age formed plates. Up to 6.3% difference in springback is observed when forming workpieces with different pre-form age condition alone.
El Fakir O, Wang L, Balint D, et al., 2014, Numerical study of the solution heat treatment, forming, and in-die quenching (HFQ) process on AA5754, International Journal of Machine Tools and Manufacture, Vol: 87, Pages: 39-48, ISSN: 0890-6955
An FE model of the solution heat treatment, forming and in-die quenching (HFQ) process was developed. Good correlation with a deviation of less than 5% was achieved between the thickness distribution of the simulated and experimentally formed parts, verifying the model. Subsequently, the model was able to provide a more detailed understanding of the HFQ process, and was used to study the effects of forming temperature and speed on the thickness distribution of the HFQ formed part. It was found that a higher forming speed is beneficial for HFQ forming, as it led to less thinning and improved thickness homogeneity.
Raugei M, El Fakir O, Wang L, et al., 2014, Life cycle assessment of the potential environmental benefits of a novel hot forming process in automotive manufacturing, JOURNAL OF CLEANER PRODUCTION, Vol: 83, Pages: 80-86, ISSN: 0959-6526
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- Citations: 42
Betts C, Balint D, Lee J, et al., 2014, In situ microtensile testing and X-ray microtomography-based finite element modelling of open-cell metal foam struts and sandwich panels, JOURNAL OF STRAIN ANALYSIS FOR ENGINEERING DESIGN, Vol: 49, Pages: 592-606, ISSN: 0309-3247
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- Citations: 9
Politis DJ, Lin J, Dean TA, et al., 2014, An investigation into the forging of Bi-metal gears, JOURNAL OF MATERIALS PROCESSING TECHNOLOGY, Vol: 214, Pages: 2248-2260, ISSN: 0924-0136
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- Citations: 33
Zhou J, Wang B-Y, Lin J-G, et al., 2014, Forming defects in aluminum alloy hot stamping of side-door impact beam, TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, Vol: 24, Pages: 3611-3620, ISSN: 1003-6326
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- Citations: 35
Bai Q, Lin J, Jiang J, et al., 2014, A study of direct forging process for powder superalloys, Materials Science and Engineering A - Structural Materials Properties Microstructure and Processing, Vol: 621, Pages: 68-75, ISSN: 0921-5093
Li N, Sun C, Guo N, et al., 2014, Damage Investigation of Boron Steel at Hot Stamping Conditions, Procedia Engineering, Vol: 81, Pages: 1744-1749, ISSN: 1877-7058
The uniaxial tension tests of 1500 MPa boron steel at strain rates of 0.01-5.0 s-1 and temperatures of 550-850 °C were performed. Considering the difference between the deformation necking cross section and the centre measuring section of specimen, a correction method of measuring strain and temperature at necking cross section are developed. For the method, the deformation of necking cross section was obtained which approximate for the trapezoidal change law near the necking zone. The stress strain curves are corrected based on the correction method of the strain and by considering temperature correction. A set of unified constitutive equations has been developed and calibrated. Correlation between the corrected and predicted true stress data from the constitutive equation is presented. The correlation coefficient is 0.969, and the absolute average relative error is 3.73% in the range of allowable experimental conditions.
Li N, Lin J, Dean TA, et al., 2014, Materials Modelling for Selective Heating and Press Hardening of Boron Steel Panels with Graded Microstructures, Procedia Engineering, Vol: 81, Pages: 1675-1681, ISSN: 1877-7058
Kardoulaki E, Lin J, Balint D, et al., 2014, Investigation of the effects of thermal gradients present in Gleeble high-temperature tensile tests on the strain state for free cutting steel, JOURNAL OF STRAIN ANALYSIS FOR ENGINEERING DESIGN, Vol: 49, Pages: 521-532, ISSN: 0309-3247
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- Citations: 21
Li N, Lin J, Dean TA, et al., 2014, Concept Validation for Selective Heating and Press Hardening of Automotive Safety Components with Tailored Properties, Key Engineering Materials, Vol: 622-623, Pages: 1124-1131, ISSN: 1013-9826
A new strategy termed selective heating and press hardening, for hot stamping of boron steel parts with tailored properties is proposed in this paper. Feasibility studies were carried out through a specially designed experimental programme. The main aim was to validate the strategy and demonstrate its potential for structural optimisation. In the work, a lab-scale demonstrator part was designed, and relevant manufacturing and property-assessment processes were defined. A heating technique and selective-heating rigs were designed to enable certain microstructural distributions in blanks to be obtained. A hot stamping tool set was designed for forming and quenching the parts. Demonstrator parts of full martensite phase, full initial phase, and differentially graded microstructures have been formed with high dimensional quality. Hardness testing and three point bending tests were conducted to assess the microstructure distribution and load bearing performance of the as-formed parts, respectively. The feasibility of the concept has been validated by the testing results.
Shao Z, Bai Q, Lin J, 2014, A novel experimental design to obtain forming limit diagram of aluminium alloys for solution heat treatment, forming and in-die quenching process, Key Engineering Materials, Vol: 622-623, Pages: 241-248, ISSN: 1013-9826
© (2014) Trans Tech Publications, Switzerland. Solution heat treatment, forming and in-die quenching (HFQ) is a patented process to form complex shape metal components at a high efficiency and a low cost. Conventional experiment approaches to determine forming limit curves (FLCs) at different strain paths are not applicable for the HFQ forming process. A novel biaxial tensile test rig is designed to overcome the difficulties and determine the FLCs at high temperatures based on the commercial Gleeble machine. This test device employs the circle plate and connecting rod mechanism in order to achieve different strain states, such as uniaxial tension, plane strain and biaxial tension. Resistance heating and air cooling are adopted to obtain an isothermal environment and to control cooling rates in Gleeble respectively. The designs of the cruciform specimen for this test are also introduced in this paper.
Huo Y, Wang B, Lin J, et al., 2014, Modeling of austenitic grain growth of 25CrMo4 steel for the high-speed railway axle during hot working, INDIAN JOURNAL OF ENGINEERING AND MATERIALS SCIENCES, Vol: 21, Pages: 371-378, ISSN: 0971-4588
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- Citations: 2
Zhu HX, Zhang P, Balint D, et al., 2014, The effects of regularity on the geometrical properties of Voronoi tessellations, PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS, Vol: 406, Pages: 42-58, ISSN: 0378-4371
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- Citations: 23
Lin J, Mohamed M, Balint D, et al., 2014, The development of continuum damage mechanics-based theories for predicting forming limit diagrams for hot stamping applications, INTERNATIONAL JOURNAL OF DAMAGE MECHANICS, Vol: 23, Pages: 684-701, ISSN: 1056-7895
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- Citations: 65
Kardoulaki E, Lin J, Balint D, et al., 2014, Triaxiality effect on material damage evolution in hot rolling, Pages: 1041-1048, ISSN: 1013-9826
High temperature tensile tests have been conducted on double-notched bars (DNBs) of varying notch acuity ratios (a/R), achieving a range of triaxiality, to evaluate the effect of stress state on edge cracking in hot rolling of free cutting steel. The conditions of the tensile tests are selected to physically simulate hot rolling condition of as-cast material to wrought structure. All experiments were conducted using a Gleeble 3800 thermo-mechanical testing system. The aim here is to develop a qualitative relationship between the activated damage mechanisms with respect to different stress states (arising from the sample geometry). Double-notch bars have been selected for this investigation as they enable the optical examination of the pre-failure mechanisms, captured in the unbroken notched area. The damage features have been observed at the notch areas and different damage mechanisms have been identified for different stress state deforming at different temperatures.
El Fakir O, Das S, Stone I, et al., 2014, Solution heat treatment, forming and in-die quenching of a commercial sheet magnesium alloy into a complex-shaped component: Experimentation and FE simulation, Key Engineering Materials, Vol: 622-623, Pages: 596-602, ISSN: 1013-9826
Interest in lightweight materials, particularly magnesium alloys, has increased significantly with rising efficiency requirements in the automotive sector. Magnesium is the lightest available structural metal, with a density approximately 35% lower than that of aluminium. The potential is great for magnesium to become a primary material used in future low carbon vehicle structures; however, there are significant obstacles, namely low ductility and formability, particularly at room temperature. The aim of this work is to present the feasibility of using the solution Heat treatment, Forming, and in-die Quenching (HFQ) process to produce complex shapes from a sheet magnesium alloy, and to use the results to verify a simulation of the process developed using commercial FE software. Uniaxial tensile tests were initially conducted to establish the optimum parameters for forming the part. Stamping trials were then carried out using these parameters, and a simulation set up modelling the forming operation. It was shown that the HFQ process could be used to form a successful component from this alloy, and that a good match was achieved between the results of the forming experiments and the simulation.
Bai Q, Lin J, 2014, Application of finite element method in hot forming of titanium alloy aircraft engine blades, Hangkong Cailiao Xuebao/Journal of Aeronautical Materials, Vol: 34, Pages: 62-71, ISSN: 1005-5053
Titanium alloys are widely used in the precision hot forged engine blades for aircraft. Applications of hot forging for engine blades of titanium alloys are discussed. Finite element (FE) modelling has been extensively used to ensure a better understanding of the hot forming process. This review paper provides an overview of current research development on hot forging FE modelling for engine blades: material constitutive modelling, heat transfer definition and friction characteristics are among the most important aspects to ensure an accurate FE prediction. It is concluded that FE modelling studies and analysis are needed to create predictive physically-based models which should be in good agreement with reliable experimental results when investigating the effects of many parameters on hot forging of titanium alloys.
Lam AC, Lin J, 2014, A validated analytical solution for the two-dimensional bending of aluminium plates under creep-ageing conditions, Pages: 1107-1116, ISSN: 1013-9826
An analytical method suitable for modelling the creep-age forming (CAF) of doubly curved aluminium plates is presented. This new mechanics model combines an efficient numerical integration method with a robust set of CAF constitutive equations that has been experimentally validated with AA7055 at a CAF condition. Corresponding finite element simulations show good agreement with the analytical results. Using the validated analytical model to investigate a threestage CAF process (loading, creep-ageing, and unloading), through-thickness strain distributions are studied for aluminium plates that have been subjected to different creep-ageing time. A creep activation point (CAP) is revealed and a correlation is found between the two parameters introduced in this work - The normalised location of CAP, ZCAP and normalised bend ratio, β. More specifically, a linear relationship is found between β and ZCAP, which indicates that the onset of creep strain, and hence the sizes of the pure elastic core and the outer creep region, can be readily predictable within the limits of study. It is now possible to simulate two-dimensional bending CAF processes for aluminium alloys that have non-spherical precipitates.
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