Imperial College London

ProfessorJianguoLin

Faculty of EngineeringDepartment of Mechanical Engineering

Head/Professor in Mechanics of Materials Division
 
 
 
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Contact

 

+44 (0)20 7594 7082jianguo.lin

 
 
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Assistant

 

Miss Valerie Crawford +44 (0)20 7594 7083

 
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Location

 

524City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

257 results found

Zheng JH, Pan R, Li C, Zhang W, Lin J, Davies CMet al., 2018, Experimental investigation of multi-step stress-relaxation-ageing of 7050 aluminium alloy for different pre-strained conditions, Materials Science and Engineering A, Vol: 710, Pages: 111-120, ISSN: 0921-5093

© 2017 A novel insight into the whole two-step stress relaxation ageing process during T74 multi–step ageing treatment (120 °C for 6 h and subsequently 177 °C for 7 h), which is typically experienced by extra-large aircraft components that contain high residual stresses, has been established. Stress relaxation ageing (SRA) tests, tensile tests and transmission electron microscopy (TEM) were performed on AA7050 samples to determine the relationship between internal microstructure and macroscopic behaviour during the stress relaxation and precipitate evolution process. Samples were subjected to SRA at different initial stresses (220–360 MPa) after being pre-strained to different extents (i.e. 0%, 1%, 3%). Room temperature tensile tests were then performed on interrupted SRA test specimens to examine the corresponding strengthening phenomenon. TEM was performed on a selection of peak–aged and T74 over–aged samples to study the precipitate distribution. At 120 °C typical stress relaxation behaviour was observed and the data follow ed a logarithmic curve. Subsequently at 177 °C, dislocation–creep dominated stress relaxation behaviour, with no apparent threshold stress, was observed. The absence of a threshold stress at 177 °C may be attributed to the continuous over-ageing phenomenon. The effect of pre-deformation levels and initial stresses on SRA has also been investigated. Pre-stretching, which creates uniformly distributed dislocations, promotes stress relaxation and ageing. No significant influence of initial stress level on SRA was observed at 120 °C, but noticeable effects were seen at 177 °C. The calculated stress exponent n at 177 °C is found independent of the initial stresses. These findings provide clear scientific guidance for residual stress reduction during the multi-step ageing process of AA7050 and provide the basis for residual stress prediction models.

JOURNAL ARTICLE

Bai Q, Mohamed M, Shi Z, Lin J, Dean Tet al., 2017, Application of a continuum damage mechanics (CDM)-based model for predicting formability of warm formed aluminium alloy, INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TECHNOLOGY, Vol: 88, Pages: 3437-3446, ISSN: 0268-3768

JOURNAL ARTICLE

Dong Y, Zheng K, Fernandez J, Li X, Dong H, Lin Jet al., 2017, Experimental investigations on hot forming of AA6082 using advanced plasma nitrocarburised and CAPVD WC: C coated tools, JOURNAL OF MATERIALS PROCESSING TECHNOLOGY, Vol: 240, Pages: 190-199, ISSN: 0924-0136

JOURNAL ARTICLE

Ganapathy M, Li N, Lin J, Abspoel M, Bhattacharjee Det al., 2017, A Novel Grip Design for High-Accuracy Thermo-Mechanical Tensile Testing of Boron Steel under Hot Stamping Conditions, Experimental Mechanics, Pages: 1-16, ISSN: 0014-4851

© 2017 The Author(s) Achieving uniform temperature within the effective gauge length in thermo-mechanical testing is crucial for obtaining accurate material data under hot stamping conditions. A new grip design for the Gleeble Materials-Simulator has been developed to reduce the long-standing problem of temperature gradient along a test-piece during thermo-mechanical tensile testing. The grip design process comprised two parts. For the first part, the new design concept was analysed with the help of Abaqus coupled Thermal-Electric Finite element simulation through the user defined feedback control subroutine. The second part was Gleeble thermo-mechanical experiments using a dog-bone test-piece with both new and conventional grips. The temperature and strain distributions of the new design were compared with those obtained using the conventional system within the effective gauge length of 40 mm. Temperature difference from centre to edge of effective gauge length (temperature gradient) was reduced by 56% during soaking and reduced by 100% at 700 °C. Consequently, the strain gradient also reduced by 95%, and thus facilitated homogeneous deformation. Finally to correlate the design parameters of the electrical conductor used in the new grip design with the geometry and material of test-piece, an analytical relationship has been derived between the test-piece and electrical conductor.

JOURNAL ARTICLE

Ganapathy M, Li N, Lin JG, Abspoel M, Bhattacharjee Det al., 2017, Test-Piece and Test-Rig Designs to Obtain High Accuracy Experimental Data for Boron Steel at Hot Stamping Conditions, 3rd International Conference on Advanced High Strength Steel and Press Hardening (ICHSU), Publisher: WORLD SCIENTIFIC PUBL CO PTE LTD, Pages: 109-113

CONFERENCE PAPER

Huo Y, Lin J, Bai Q, Wang B, Tang X, Ji Het al., 2017, Prediction of microstructure and ductile damage of a high-speed railway axle steel during cross wedge rolling, JOURNAL OF MATERIALS PROCESSING TECHNOLOGY, Vol: 239, Pages: 359-369, ISSN: 0924-0136

JOURNAL ARTICLE

Ji H, Liu J, Wang B, Tang X, Lin J, Huo Yet al., 2017, Microstructure evolution and constitutive equations for the high-temperature deformation of 5Cr21Mn9Ni4N heat-resistant steel, JOURNAL OF ALLOYS AND COMPOUNDS, Vol: 693, Pages: 674-687, ISSN: 0925-8388

JOURNAL ARTICLE

Kaye MC, Balint D, Lin J, Farrugia Det al., 2017, Test-piece design for experimental and numerical evaluation of damage in relation to spatial triaxial stress inversion, INTERNATIONAL JOURNAL OF DAMAGE MECHANICS, Vol: 26, Pages: 588-607, ISSN: 1056-7895

JOURNAL ARTICLE

Kong XX, Li N, O'Keeffe R, Lin JGet al., 2017, Experimental Investigation on the Accuracy of Uniaxial Tensile Data of AA6082 Under HFQ (R) Conditions, 3rd International Conference on Advanced High Strength Steel and Press Hardening (ICHSU), Publisher: WORLD SCIENTIFIC PUBL CO PTE LTD, Pages: 390-394

CONFERENCE PAPER

Li N, Zheng J, Zheng K, Lin J, Davies Cet al., 2017, A fast ageing method for stamped heat-treatable alloys, WO2017021742 A1

PATENT

Li Y, Shi Z, Lin J, Yang Y-L, Rong Qet al., 2017, Extended application of a unified creep-ageing constitutive model to multistep heat treatment of aluminium alloys, MATERIALS & DESIGN, Vol: 122, Pages: 422-432, ISSN: 0264-1275

JOURNAL ARTICLE

Li Y, Shi Z, Lin J, Yang Y-L, Rong Q, Huang B-M, Chung T-F, Tsao C-S, Yang J-R, Balint DSet al., 2017, A unified constitutive model for asymmetric tension and compression creep-ageing behaviour of naturally aged Al-Cu-Li alloy, INTERNATIONAL JOURNAL OF PLASTICITY, Vol: 89, Pages: 130-149, ISSN: 0749-6419

JOURNAL ARTICLE

Mohamed M, Lin J, Foster A, Dean T, Dear Jet al., 2017, Formability investigation using a new test design for hot stamping processes, International Journal of Materials and Product Technology, Vol: 54, Pages: 3-19, ISSN: 0268-1900

© 2017 Inderscience Enterprises Ltd. Hot stamping is widely used in the forming of lightweight automotive panel components. The process optimisation requires knowledge of constitutive relations of work-piece material but assessment of formability of materials in hot stamping conditions is exceptionally challenging. A testing method and corresponding specimen design are developed in this paper for evaluating formability of materials in hot stamping conditions. A series of tests have been carried out for AA6082 aluminium alloy, at different forming rates and failure modes have been analysed. A set of stress-state dependent damage equations for AA6082 is introduced and this has been input into the FE code, ABAQUS. An FE model is developed and validated from the experimental results. Failure modes at particular forming conditions are predicted and designed specimen shapes are optimised for different forming conditions. It is concluded that work-piece design is related to ductility for hot stamping conditions and recommendations for work-piece design are given.

JOURNAL ARTICLE

Mohamed M, Lin J, Foster A, Dean T, Dear Jet al., 2017, Formability investigation using a new test design for hot stamping processes, INTERNATIONAL JOURNAL OF MATERIALS & PRODUCT TECHNOLOGY, Vol: 54, Pages: 3-19, ISSN: 0268-1900

JOURNAL ARTICLE

Shao Z, Li N, Lin J, 2017, The comparison of two continuum damage mechanics-based material models for formability prediction of AA6082 under hot stamping conditions, ISSN: 1742-6588

© Published under licence by IOP Publishing Ltd. The hot stamping and cold die quenching process has experienced tremendous development in order to obtain shapes of structural components with great complexity in automotive applications. Prediction of the formability of a metal sheet is significant for practical applications of forming components in the automotive industry. Since microstructural evolution in an alloy at elevated temperature has a large effect on formability, continuum damage mechanics (CDM)-based material models can be used to characterise the behaviour of metals when a forming process is conducted at elevated temperatures. In this paper, two sets of unified multi-axial constitutive equations based on material's stress states and strain states, respectively, were calibrated and used to effectively predict the thermo-mechanical response and forming limits of alloys under complex hot stamping conditions. In order to determine and calibrate the two material models, formability tests of AA6082 using a developed novel biaxial testing system were conducted at various temperatures and strain rates under hot stamping conditions. The determined unified constitutive equations from experimental data are presented in this paper. It is found that both of the stress-state based and strain-state based material models can predict the formability of AA6082 under hot stamping conditions.

CONFERENCE PAPER

Shao Z, Li N, Lin J, Dean Tet al., 2017, Formability evaluation for sheet metals under hot stamping conditions by a novel biaxial testing system and a new materials model, INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, Vol: 120, Pages: 149-158, ISSN: 0020-7403

JOURNAL ARTICLE

Wang A, Zhong K, El Fakir O, Liu J, Sun C, Wang L-L, Lin J, Dean TAet al., 2017, Springback analysis of AA5754 after hot stamping: experiments and FE modelling, INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TECHNOLOGY, Vol: 89, Pages: 1339-1352, ISSN: 0268-3768

JOURNAL ARTICLE

Wang LL, Dean T, Lin JG, 2017, Innovation, Development and Implementation of the HFQ (R) Process, 3rd International Conference on Advanced High Strength Steel and Press Hardening (ICHSU), Publisher: WORLD SCIENTIFIC PUBL CO PTE LTD, Pages: 289-300

CONFERENCE PAPER

Wang S, Fang S, Shi Z, Jiang J, Zhou X, Lin Jet al., 2017, Direct powder forging of PM nickel-based superalloy: densification and recrystallisation, INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TECHNOLOGY, Vol: 88, Pages: 2661-2670, ISSN: 0268-3768

JOURNAL ARTICLE

Wu P, Wang B, Lin J, Zuo B, Li Z, Zhou Jet al., 2017, Investigation on metal flow and forming load of bi-metal gear hot forging process, INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TECHNOLOGY, Vol: 88, Pages: 2835-2847, ISSN: 0268-3768

JOURNAL ARTICLE

Zheng K, Lee J, Lin J, Dean TAet al., 2017, A buckling model for flange wrinkling in hot deep drawing aluminium alloys with macro-textured tool surfaces, INTERNATIONAL JOURNAL OF MACHINE TOOLS & MANUFACTURE, Vol: 114, Pages: 21-34, ISSN: 0890-6955

JOURNAL ARTICLE

Zheng K, Lee J, Politis DJ, Li N, Lin J, Dean TAet al., 2017, An analytical investigation on the wrinkling of aluminium alloys during stamping using macro-scale structural tooling surfaces, INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TECHNOLOGY, Vol: 92, Pages: 481-495, ISSN: 0268-3768

JOURNAL ARTICLE

Zheng K, Politis DJ, Lin J, Dean TAet al., 2017, An experimental and numerical investigation of the effect of macro-textured tool surfaces in hot stamping, International Journal of Material Forming, Vol: 10, Pages: 241-254, ISSN: 1960-6206

© 2015, The Author(s). This paper presents a method of increasing draw-ability of materials in hot stamping processes using forming tools with macro-scale textures on the tool surfaces. Firstly, a series of tool texture designs and orientations were presented and a test programme was designed for the experimental investigation. Top-hat shape drawing experiments in cold and hot stamping conditions were conducted to evaluate the effect of macro-scale tool surface textures on the material drawing. Texture directional and texture feature effects of the blankholders on the draw-ability of the material have been investigated. A finite element model of the top-hat drawing process with textured tool surfaces has been established and validated from experimental data. Further FE process modelling has been carried out and the effects of texture features and forming speed have been studied. The relationships between texture designs and material drawing results have been analysed. The developed FE model can provide a guide to design the geometry of tool textures and optimise the hot stamping process parameters.

JOURNAL ARTICLE

Zuo B, Wang B, Li Z, Li N, Lin Jet al., 2017, An investigation of involute and lead deflection in hot precision forging of gears, INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TECHNOLOGY, Vol: 88, Pages: 3017-3030, ISSN: 0268-3768

JOURNAL ARTICLE

Fang S, Shi Z, Bai Q, Jiang J, Wang SY, Lin JGet al., 2016, An investigation of direct powder forging of nickel superalloy FGH96, Pages: 793-799, ISSN: 1013-9826

© 2016 Trans Tech Publications, Switzerland. Powder metallurgy (PM) nickel-based superalloy has been widely used in high temperature applications and is most commonly manufactured using hot isostatic pressing (HIP). However, HIP is an expensive process and takes a long time at high temperature which leads to the formation of networks of prior particle boundaries (PPBs). In this study, a recently developed processing method-direct powder forging (DPF) was employed to produce a PM nickel-based superalloy component, using a single acting hydraulic press under normal atmosphere. EBSD study has been conducted for its microstructure, grains size distribution, and grain boundary misorientation; and mechanical testing has been carried out for its hardness and tensile properties at room temperature and 650°C. It has been found that the DPFed material has reached full density in the whole component. Networks of PPBs have been broken in the direct powder forged FGH96 alloy. Compared with HIPed FGH96 alloy, the DPFed material has a substantially higher recystallisation nucleation degree and more recrystallised sub-grains. After heat treatment, the tensile properties of the direct powder forged FGH96 alloy match or surpass those of the material produced by HIP plus isothermal forging.

CONFERENCE PAPER

Feng J, Wang S, Guo Lin J, 2016, Multi-resolution material hardening law for CPFE micro-forming analysis, Pages: 232-239, ISSN: 1013-9826

© 2016 Trans Tech Publications, Switzerland. A new multi-resolution slip system-based material hardening law has been developed for micro-forming simulation using Crystal Plasticity Finite Element (CPFE) Approach. Material hardenings are formulated based on global and local hardening of dislocations for each slip system and defined with distinct physical meaning. Plasticity is assumed to arise solely from crystalline slip and the overall mechanical response with any crystallographic system, such as FCC, BCC, etc, can be addressed by a local hardening parameter, x, from 0 (pure anisotropic) to 1 (fully isotropic). No interaction matrix is necessary, since the latent hardening can be realized by the hardening factor , x , and the new dislocation density based hardening law can be implemented into existing FE software efficiently. The proposed equations are an extension of the existing hardening law from macro mechanics descriptions down to micro mechanics level, therefore unified constitutive equations had been established at multiscale resolution. Some features of the proposed hardening law will be demonstrated with a single cubic crystal under tension load.

CONFERENCE PAPER

Ji H, Liu J, Wang B, Lin J, Tang Xet al., 2016, The process parameters effect of ovality in cross wedge rolling for hollow valve without mandril

© The Authors, published by EDP Sciences, 2016. This paper presents the experimental and numerical results of the effect process parameters on ovality in cross wedge rolling (CWR) for hollow engine valve without mandrel. Numerical simulation model for ovality was established by means of the rigid-plastic finite element modeling (FEM) method for hollow engine valve. The experiments and numerical analyses suggest that the following parameters represent the best conditions for CWR of hollow engine valve: 30°-34° for the forming angle(α), 5°-7° for the stretching angle(β), 0.2-0.3mm for the mold void width(L), and 65%-70% for the area reduction(Ψ).

CONFERENCE PAPER

Kardoulaki E, Lin J, Balint D, Farrugia Det al., 2016, A study on the effect of stress state on damage evolution in hot deformation of free cutting steels using double notched bars, PHILOSOPHICAL MAGAZINE, Vol: 96, Pages: 2176-2203, ISSN: 1478-6435

JOURNAL ARTICLE

Li N, Lin J, Balint DS, Dean TAet al., 2016, Experimental characterisation of the effects of thermal conditions on austenite formation for hot stamping of boron steel, JOURNAL OF MATERIALS PROCESSING TECHNOLOGY, Vol: 231, Pages: 254-264, ISSN: 0924-0136

JOURNAL ARTICLE

Li N, Lin J, Balint DS, Dean TAet al., 2016, Modelling of austenite formation during heating in boron steel hot stamping processes, JOURNAL OF MATERIALS PROCESSING TECHNOLOGY, Vol: 237, Pages: 394-401, ISSN: 0924-0136

JOURNAL ARTICLE

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