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

301 results found

Zheng K, Dong Y, Zheng D, Lin J, Dean TAet al., 2019, An experimental investigation on the deformation and post-formed strength of heat-treatable aluminium alloys using different elevated temperature forming processes, Journal of Materials Processing Technology, Vol: 268, Pages: 87-96, ISSN: 0924-0136

© 2018 Elsevier B.V. Forming at elevated temperatures can significantly increase the ductility of aluminium alloys enabling the manufacture of complex-shaped panel components from sheets. This study describes and investigates two elevated temperature forming processes: Hot Form Quench (HFQ ® ) (Lin et al., 2008) and conventional hot forming (HF) of aluminium alloys, with various material condition and processing parameters in order to advance the understanding of forming characteristics and post-formed strength. High temperature uniaxial tensile tests of AA7075 under HFQ ® and HF conditions were performed to compare the stress-strain behaviors, ductility, and post-formed hardness. The results have shown that the ductility for HFQ ® condition was greater than that for the HF condition when forming temperature was below 400 °C. In addition, typical microstructural evolution, such as the low-melting phase of HFQ ® and precipitation of HF, were identified using fracture morphology observations and used to explain ductility differences exhibited in these processes. Post-formed hardness resulting from HF with different initial alloy temper and forming conditions were determined and compared with those from HFQ ® . Severe reduction in hardness was found for HF using both high quench-sensitive alloy AA7075 and low quench-sensitive alloy AA6082. For the first time, the effects of a variety of influencing factors are investigated systematically, including heating rate, initial alloy, temperature and strain rate, on the high temperature deformation and post-formed strength of heat-treatable aluminium alloys, which contributes to the thorough understanding of the correlation between forming conditions and microstructural evolutions.

JOURNAL ARTICLE

Rong Q, Li Y, Shi Z, Meng L, Sun X, Sun X, Lin Jet al., 2019, Experimental investigations of stress-relaxation ageing behaviour of AA6082, Materials Science and Engineering A, Vol: 750, Pages: 108-116, ISSN: 0921-5093

© 2019 Stress-relaxation ageing behaviour of peak-aged aluminium alloy 6082 (AA6082-T6) has been experimentally investigated with initial loading in both elastic and plastic regions in this study. The stress-relaxation ageing tests with various initial strain levels were carried out at 160 °C for up to 12 h and room temperature tensile tests were performed subsequently. Selected samples have been examined using transmission electron microscopy (TEM) to study microstructural evolution during the process. The results show that the total stress relaxed after 12 h test increases significantly with increasing initial strain levels. The initial strain levels contribute little effect on yield strength evolution during stress-relaxation ageing, as softening from the coarsening of β ′′ precipitates is balanced by hardening from dislocations. Stress-relaxation mechanisms of the material have been analysed on the basis of creep stress exponent. In the elastic region, a creep stress exponent of 3 with a threshold stress of 70.1 MPa has been obtained, indicating a dislocation glide controlled creep mechanism; while in the plastic region, a decreasing threshold stress with increasing initial strain levels has been proposed to achieve a positive creep stress exponent.

JOURNAL ARTICLE

Pan R, Zheng J, Zhang Z, Lin Jet al., 2019, Cold rolling influence on residual stresses evolution in heat-treated AA7xxx T-section panels, MATERIALS AND MANUFACTURING PROCESSES, Vol: 34, Pages: 431-446, ISSN: 1042-6914

JOURNAL ARTICLE

Pan R, Pirling T, Zheng J, Lin J, Davies CMet al., 2019, Quantification of thermal residual stresses relaxation in AA7xxx aluminium alloy through cold rolling, JOURNAL OF MATERIALS PROCESSING TECHNOLOGY, Vol: 264, Pages: 454-468, ISSN: 0924-0136

JOURNAL ARTICLE

Lyu F, Li Y, Huang X, Shi Z, Zeng Y, Lin Jet al., 2019, An investigation of creep age forming of AA7B04 stiffened plates: Experiment and FE modelling, Journal of Manufacturing Processes, Vol: 37, Pages: 232-241, ISSN: 1526-6125

© 2018 Creep age forming (CAF) of aluminium alloy 7B04 (AA7B04) stiffened plates has been experimentally and numerically investigated in this study. Creep-ageing experiments of AA7B04-T651 were conducted under different tensile stress levels at 140 °C for up to 20 h, and a set of unified constitutive equations was calibrated based on the experimental results of the evolutions of creep strain, yield strength and precipitate size, which was implemented into ABAQUS for CAF process modelling. CAF experiments and corresponding simulations of AA7B04 stiffened plates were then carried out and the effect of stiffener height and die radius on springback and yield strength was studied. It was found that the springback percentage decreases with increasing stiffener height and decreasing forming die radius, and the yield strength is slightly lower in the stiffener than in the skin of the CAFed stiffened plates due to stress effect on ageing progression. A good agreement has been achieved between experimental and corresponding FE results, with maximum deviations of 6.7% and 3.3% respectively for springback and yield strength.

JOURNAL ARTICLE

Shao Z, Jiang J, Lin J, 2018, Feasibility study on direct flame impingement heating applied for the solution heat treatment, forming and cold die quenching technique, JOURNAL OF MANUFACTURING PROCESSES, Vol: 36, Pages: 398-404, ISSN: 1526-6125

JOURNAL ARTICLE

Lin J, Axinte D, 2018, Professor Trevor A. Dean and his contribution to the Journal, International Journal of Machine Tools and Manufacture, Vol: 133, Pages: 1-3, ISSN: 0890-6955

JOURNAL ARTICLE

Li Y, Yang YL, Rong Q, Shi Z, Lin J, Said Ret al., 2018, Effect of initial temper on mechanical properties of creep-aged Al-Cu-Li alloy AA2050

© The Authors, published by EDP Sciences, 2018. The evolution of mechanical properties of a third generation Al-Cu-Li alloy, AA2050, with different initial tempers (T34 and as-quenched (WQ)) during creep-ageing has been investigated and analysed in this study. A set of creep-ageing tests under 150 MPa at 155 °C for up to 24 h was carried out for both initial temper conditions and tensile tests were performed subsequently to acquire the main mechanical properties of the creep-aged alloys, including the yield strength, ultimate tensile strength (UTS) and uniform elongation. Precipitation behaviour of the T34 and WQ AA2050 alloys has been summarised and successfully explains the detailed evolutions of the obtained mechanical properties of the alloy with these two initial tempers during creep-ageing. The results indicate that the T34 alloy can be a better choice for creep age forming (CAF) process compared with WQ alloy, as it provides better yield strength and uniform elongation properties concurrently after creep-ageing. In addition, a work hardening rate analysis has been carried out for all the creep-aged alloys, helping to reveal the detailed dislocation/precipitates interaction mechanisms during plastic deformation in the creep-aged T34 and WQ AA2050 alloys.

CONFERENCE PAPER

Rong Q, Li Y, Sun X, Shi Z, Meng L, Lin Jet al., 2018, Experimental studies of the efficient use of flexible tool in creep age forming

© The Authors, published by EDP Sciences, 2018. Application of a newly developed flexible forming tool to creep age forming (CAF) process has been investigated in this study. The flexible tool mainly consists of sparsely distributed forming pins, splines and elastomeric sheet. The effect of key factors related to the forming tool on the shape of the formed parts has been studied through various CAF experiments. The key factors investigated in this study include: the interval between forming pins, the arrangement of pins, the accuracy requirement of pin height and the material of splines. It has been found that reducing the interval between pins can efficiently smooth the shape of CAFed plates. The feasibility of asymmetric arrangement of pins has been proven, which can decrease the number of used pins, reduce tool weight, and increase efficiency. The forming results are very sensitive to the pin height, thus the experimental set-up error should be carefully controlled. Additionally, compared with mild steel, spring steel is more suitable as the spline material.

CONFERENCE PAPER

Kopec M, Wang K, Wang Y, Wang L, Lin Jet al., 2018, Feasibility study of a novel hot stamping process for Ti6Al4V alloy

© The Authors, published by EDP Sciences, 2018. To investigate the feasibility of a novel hot stamping process for the Ti6Al4V titanium alloy using low temperature forming tools, mechanical properties of the material were studied using hot tensile tests at a temperature range of 600 - 900°C with a constant strain rate of 1s-1. Hot stamping tests were carried out to verify the feasibility of this technology and identify the forming window for the material. Results show that when the deformation temperature was lower than 700°C, the amount of elongation was less than 20%, and it also had little change with the temperature. However, when the temperature was higher than 700°C, a good ductility of the material can be achieved. During the forming tests, parts failed at lower temperatures (600°C) due to the limited formability and also failed at higher temperatures (950°C) due to the phase transformation. The post-form hardness firstly decreased with the temperature increasing due to recovery and then increased due to the phase transformation. Qualified parts were formed successfully between temperatures of 750 - 850°C, which indicates that this new technology has a great potential in forming titanium alloys sheet components.

CONFERENCE PAPER

Li Y, Shi Z, Lin J, Yang Y-L, Saillard P, Said Ret al., 2018, Effect of machining-induced residual stress on springback of creep age formed AA2050 plates with asymmetric creep-ageing behaviour, INTERNATIONAL JOURNAL OF MACHINE TOOLS & MANUFACTURE, Vol: 132, Pages: 113-122, ISSN: 0890-6955

JOURNAL ARTICLE

Shao Z, Lin J, Ganapathy M, Dean Tet al., 2018, Experimental and modelling techniques for hot stamping applications, Procedia Manufacturing, Vol: 15, Pages: 6-13, ISSN: 2351-9789

Hot stamping techniques have been developed for the production of complex-shaped components since the 1970s, increasingly used for the automotive industry. The application of these techniques includes hot stamping of boron steel for critical automobile safety components, and solution heat treatment, forming and cold die quenching (HFQ®) for forming complex-shaped high strength aluminium panels of automobile bodies and chassis structures. The developed forming techniques need dedicated experimental testing methods to be improved for characterising the thermomechanical behaviour of materials at the hot stamping conditions, and advanced materials modelling techniques to be developed for hot stamping applications. In this paper, requirements for thermomechanical tests and difficulties for hot stamping applications are introduced and analysed. The viscoplastic modelling techniques have been developed for hot stamping applications. Improved experimental methods have been proposed and used in order to obtain accurate thermomechanical uniaxial tensile test data and determine forming limits of metallic materials under hot stamping conditions.

JOURNAL ARTICLE

Li Y, Shi Z, Yang Y-L, Lin J, Said Ret al., 2018, Experimental and numerical study of creep age forming of AA2050 plates with sparse multi-point flexible forming tool, Metal Forming 2018, 17th International Conference on Metal Forming, Publisher: Elsevier, Pages: 1016-1023, ISSN: 2351-9789

Creep age forming of an Al-Cu-Li alloy (AA2050-T34) with an asymmetric tension/compression creep-ageing behaviour has been experimentally and numerically investigated in this study. Creep age forming experiments of plates with different thicknesses have been carried out to form doubly curved shapes using a recently developed sparse multi-point flexible forming tool. Corresponding FE model for creep age forming, incorporating the material model that describes the stress-strain relation and asymmetric creep-ageing behaviour of the alloy, has been developed through PAM-STAMP. The flexible forming tool can generate various tool shapes for creep age forming and is ideal for innovative trials. Stress concentration was found in some forming pin areas of the loaded plate. With larger initial loaded plastic strain and higher creep strain generated in these local areas, bumps may occur in formed shapes after creep age forming under certain circumstances. It is shown that the FE model is able to predict the formed shape accurately for thicker plates and can be used for tool set-up optimisation.

CONFERENCE PAPER

Xiao W, Wang B, Zheng K, Zhou J, Lin Jet al., 2018, A study of interfacial heat transfer and its effect on quenching when hot stamping AA7075, ARCHIVES OF CIVIL AND MECHANICAL ENGINEERING, Vol: 18, Pages: 723-730, ISSN: 1644-9665

JOURNAL ARTICLE

Politis DJ, Politis NJ, Lin J, Dean TAet al., 2018, A review of force reduction methods in precision forging axisymmetric shapes, INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TECHNOLOGY, Vol: 97, Pages: 2809-2833, ISSN: 0268-3768

JOURNAL ARTICLE

Zheng J-H, Lin J, Lee J, Pan R, Li C, Davies CMet al., 2018, A novel constitutive model for multi-step stress relaxation ageing of a pre-strained 7xxx series alloy, INTERNATIONAL JOURNAL OF PLASTICITY, Vol: 106, Pages: 31-47, ISSN: 0749-6419

JOURNAL ARTICLE

Chung T-F, Yang Y-L, Hsiao C-N, Li W-C, Huang B-M, Tsao C-S, Shi Z, Lin J, Fischione PE, Ohmura T, Yang J-Ret al., 2018, Morphological evolution of GP zones and nanometer-sized precipitates in the AA2050 aluminium alloy, International Journal of Lightweight Materials and Manufacture, ISSN: 2588-8404

JOURNAL ARTICLE

Shao Z, Li N, Lin J, Dean TAet al., 2018, Strain measurement and error analysis in thermo-mechanical tensile tests of sheet metals for hot stamping applications, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART C-JOURNAL OF MECHANICAL ENGINEERING SCIENCE, Vol: 232, Pages: 1994-2008, ISSN: 0954-4062

JOURNAL ARTICLE

Pan R, Shi Z, Davies CM, Li C, Kaye M, Lin Jet al., 2018, An integrated model to predict residual stress reduction by multiple cold forging operations in extra-large AA7050 T-section panels, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART B-JOURNAL OF ENGINEERING MANUFACTURE, Vol: 232, Pages: 1319-1330, ISSN: 0954-4054

JOURNAL ARTICLE

Chung T-F, Yang Y-L, Huang B-M, Shi Z, Lin J, Ohmura T, Yang J-Ret al., 2018, Transmission electron microscopy investigation of separated nucleation and in-situ nucleation in AA7050 aluminium alloy, ACTA MATERIALIA, Vol: 149, Pages: 377-387, ISSN: 1359-6454

JOURNAL ARTICLE

Li Y, Shi Z, Lin J, Yang Y-L, Saillard P, Said Ret al., 2018, FE simulation of asymmetric creep-ageing behaviour of AA2050 and its application to creep age forming, INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, Vol: 140, Pages: 228-240, ISSN: 0020-7403

JOURNAL ARTICLE

Zheng K, Lin J, Wu G, Hall RW, Dean TAet al., 2018, EXPERIMENTAL INVESTIGATION AND MODELLING OF HOT FORMING B4C/AA6O61 LOW VOLUME FRACTION REINFORCEMENT COMPOSITES, JOURNAL OF THEORETICAL AND APPLIED MECHANICS, Vol: 56, Pages: 457-469, ISSN: 1429-2955

JOURNAL ARTICLE

Zhou W, Lin J, Dean TA, Wang Let al., 2018, Analysis and modelling of a novel process for extruding curved metal alloy profiles, INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, Vol: 138, Pages: 524-536, ISSN: 0020-7403

JOURNAL ARTICLE

Chavoshi SZ, Jiang J, Wang Y, Fang S, Wang S, Shi Z, Lin Jet al., 2018, Density-based constitutive modelling of P/M FGH96 for powder forging, INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, Vol: 138, Pages: 110-121, ISSN: 0020-7403

JOURNAL ARTICLE

Kopec M, Wang K, Politis DJ, Wang Y, Wang L, Lin Jet al., 2018, Formability and microstructure evolution mechanisms of Ti6Al4V alloy during a novel hot stamping process, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, Vol: 719, Pages: 72-81, ISSN: 0921-5093

JOURNAL ARTICLE

Zhou W, Lin J, Dean TA, Wang Let al., 2018, Feasibility studies of a novel extrusion process for curved profiles: Experimentation and modelling, International Journal of Machine Tools and Manufacture, Vol: 126, Pages: 27-43, ISSN: 0890-6955

© 2017 The work described in this paper concerns a novel method for directly forming curved profiles/sections from billets in one extrusion operation using two opposing punches. Its mechanics are based on internal differential material flow, and it has been given the acronym, differential velocity sideways extrusion (DVSE). A tool set enabling sideways extrusion to be performed using opposing punches moving with different velocities was used for a series of experiments in which punch velocity ratio and extrusion ratio were process parameters. Plasticine was used as a model work-piece material and a series of compression tests were undertaken, to determine its constitutive properties and gain an estimate of work-piece die friction for use in process simulation. Curvature of extrudate can be controlled and varied using a difference between the velocities of the two punches, defined by velocity ratio. Greater curvature is achieved with lower velocity ratio. Curvature is also dependent on extrusion ratio, an increase in which increases curvature, although curvature is less sensitive to it than to velocity ratio. The extent of work-piece flow velocity gradient across the die exit orifice, which causes curvature, has been identified. Severe plastic deformation of the extrudate occurs in a way similar to channel angular extrusion (CAE), thus a greatly promoted effective strain level is achieved, though it is not always uniform across a section. The inner bending region of an extrudate experiences maximum localised effective strain, which decreases with decrease in curvature. To the authors' knowledge this is the first publication in which extrudate curvature is deliberately induced using opposing punches with differential velocities. Although only fixed velocity ratio values have been used in the work described in this paper the ability to change during operation exists and the process has the potential for the production of a profile with different curvature along it

JOURNAL ARTICLE

Zhou W, Shi Z, Lin J, 2018, Upper bound analysis of differential velocity sideways extrusion process for curved profiles using a fan-shaped flow line model, International Journal of Lightweight Materials and Manufacture, Vol: 1, Pages: 21-32, ISSN: 2588-8404

JOURNAL ARTICLE

Ganapathy M, Li N, Lin J, Abspoel M, Bhattacharjee Det al., 2018, A Novel Grip Design for High-Accuracy Thermo-Mechanical Tensile Testing of Boron Steel under Hot Stamping Conditions, EXPERIMENTAL MECHANICS, Vol: 58, Pages: 243-258, ISSN: 0014-4851

JOURNAL ARTICLE

Shao Z, Bai Q, Li N, Lin J, Shi Z, Stanton M, Watson D, Dean Tet al., 2018, Experimental investigation of forming limit curves and deformation features in warm forming of an aluminium alloy, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART B-JOURNAL OF ENGINEERING MANUFACTURE, Vol: 232, Pages: 465-474, ISSN: 0954-4054

JOURNAL ARTICLE

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