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

321 results found

Li Y, Shi Z, Lin J, 2019, Experimental investigation and modelling of yield strength and work hardening behaviour of artificially aged Al-Cu-Li alloy, Materials and Design, Vol: 183, ISSN: 0264-1275

The yield strength and work hardening properties of an Al-Cu-Li alloy AA2050 after artificial ageing have been experimentally investigated and modelled in this study. Uniaxial tensile stress-strain curves of the alloy artificially aged for up to 500 h have been acquired and evolutions of main precipitates during ageing have been summarised to elucidate the underlying mechanisms of the observed mechanical properties, such as yield strength and work hardening behaviour. Work hardening analysis with Kocks-Mecking plots has been performed to analyse the shearing-to-bypassing transition progress of the aged alloy and it has been found that the transition does not occur at the peak-ageing state. A new mechanism-based unified constitutive model, comprising three sub-models, has been developed to simultaneously predict the evolutions of microstructures, yield strength and work hardening properties of the artificially aged AA2050. It is the first unified model covering a wide range of artificial ageing conditions from under-ageing to over-ageing, providing an effective tool for performance prediction of the aged alloys for industrial applications. The model has the generic feature and could be applied to artificial ageing of other 2xxx series aluminium alloys with dominant T1 precipitates.

Journal article

Zheng J-H, Dong Y, Zheng K, Dong H, Lin J, Jiang J, Dean TAet al., 2019, Experimental investigation of novel fast-ageing treatments for AA6082 in supersaturated solid solution state, JOURNAL OF ALLOYS AND COMPOUNDS, Vol: 810, ISSN: 0925-8388

Journal article

Zheng K, Zhu L, Lin J, Dean TA, Li Net al., 2019, An experimental investigation of the drawability of AA6082 sheet under different elevated temperature forming processes, Journal of Materials Processing Technology, Vol: 273, ISSN: 0924-0136

The performed research has, for the first time, investigated and compared the drawability of AA6082 at a comparable temperature range between two elevated temperature forming processes: termed (i)Low Temperature Hot Form and Quench (LT-HFQ®)or pre-cooled HFQ®, patented by Adam et al. (2015)and (ii)Direct Heating Aluminium Forming (DHAF)which represents a refinement of conventional warm forming targeting a higher temperature range. A series of uniaxial tensile and cylindrical deep drawing experiments were conducted. According to uniaxial tensile test results, the most obvious work-hardening and reasonable ductility was observed under LT-HFQ® at a deformation temperature of 350 °C and strain rate of 1 s−1, which can enhance drawability. For deep drawing experiments, it was found that preheating conditions of each process prior to forming significantly affected forming characteristics and post-formed hardness of the alloy; both the achieved maximum Draw ratio (DR)and limit Blank Holding Force (BHF)at some specific process parameters were increased under LT-HFQ®. Forming speed and temperature had significant effects on alloy deformation and thus drawability for both processes. In addition, by evaluating the post-formed hardness, process drawability and microstructural evolutions under different processes were simultaneously analyzed.

Journal article

Zhou W, Li Y, Shi Z, Lin Jet al., 2019, An analytical solution for elastic buckling analysis of stiffened panel subjected to pure bending, International Journal of Mechanical Sciences, Vol: 161-162, ISSN: 0020-7403

In this study, an analytical solution has been developed for the elastic buckling analysis of stiffened panels subjected to pure bending, and the effect of main geometric parameters of the stiffened panels on buckling strength has been investigated. A simplified model of stiffened panels has been proposed for buckling analysis, where an elastically built-in boundary condition replaces the skin's effect on buckling of the stiffened panels. The equilibrium method with a conventional rigid skin assumption and a new flexible skin assumption is developed for the simplified model to analytically capture the buckling behaviour of the stiffened panels. To consider the non-rigid rotation effect of flexible skin on buckling of stiffened panels, a new parameter, the effective width of stiffened panels, has been introduced, and a finite element (FE) assisted method has been employed to obtain its value for different stiffened panels. The results show that the flexible skin assumption significantly enhances the accuracy of buckling strength prediction compared with the conventional rigid skin assumption, and the maximum difference between analytical results and corresponding FE simulations is decreased from 12.2% with rigid skin assumption to only 3.9%. Based on the proposed analytical solution, effects of main geometric parameters of the stiffened panels (the stiffened panel length and width, the stiffener height, and the ratio of the skin thickness to the stiffener thickness) on their buckling coefficients have been discussed. Increasing stiffened panel length and/or reciprocal of stiffener height leads to an initial abrupt decrease of the buckling coefficient until reaching a stable level. When the stiffened panel width increases, the buckling coefficient first increases and then remains stable, whereas increasing thickness ratio leads to the increase of the buckling coefficient.

Journal article

Chavoshi S, Tagarielli V, Shi Z, Lin J, Wang S, Jiang J, Dear J, Nikbin Ket al., Predictions of the mechanical response of sintered FGH96 powder compacts, Journal of Engineering Materials and Technology, ISSN: 0094-4289

This paper presents predictions of the response of sintered FGH96 Ni-based superalloy powder compacts at high temperature, obtained by analysis of 3D representative volume elements generated by both X-ray tomography and a virtual technique. The response ofthe material to a multiaxial state of stress/strain for porosities as large as 0.3 is explored, obtaining the yield surfaces and their evolution as well as scaling laws for both elastic and plastic properties. The two modelling approaches are found in good agreement. The sensitivity of the predictions to particle size, inter-particle friction, applied strain rate,and boundary conditions is also examined.

Journal article

Chung TF, Yang YL, Shiojiri M, Hsiao CN, Li WC, Tsao CS, Shi Z, Lin J, Yang JRet al., 2019, An atomic scale structural investigation of nanometre-sized η precipitates in the 7050 aluminium alloy, Acta Materialia, Vol: 174, Pages: 351-368, ISSN: 1359-6454

Using high-angle-annular-dark-field (HAADF) scanning-transmission-electron microscopy (STEM), we have investigated η-precipitates in the Al-Zn-Mg-Cu (AA7050) aluminium alloy. The HAADF STEM images taken along the zone axes of [101¯0]η, [12¯10]η, and [0001]η illustrated the projected atomic-scale configurations of η-MgZn2 crystal. The precipitates developed in layer-by-layer growth, supplied with precursors such as Zn, Cu, and Mg, which were solute atoms segregated around the η/Al interfaces due to the higher lattice strain energy. Stacking faults and defect layers composed of flattened hexagons were frequently observed along the zone axes of [12¯10]η and [101¯0]η, respectively, and their formation was elucidated, similarly taking into account the layer-by-layer growth. Occasional coalescence between two precipitates yielded a complicated boundary or a twin-like boundary. Based on the differences in orientation relationships between η-types and the Al matrix reported to date, two new types of η precipitates have been recognized and named η4' and η12.

Journal article

Zheng K, Dong Y, Zheng J-H, Foster A, Lin J, Dong H, Dean TAet al., 2019, The effect of hot form quench (HFQ (R)) conditions on precipitation and mechanical properties of aluminium alloys, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, Vol: 761, ISSN: 0921-5093

Journal article

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

Journal article

Dragatogiannis DA, Kollaros D, Karakizis P, Pantelis D, Lin J, Charitidis Cet al., 2019, Friction stir welding between 6082 and 7075 aluminum alloys thermal treated for automotive applications, Materials Performance and Characterization, Vol: 8

Copyright © 2019 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. The automotive industry demands ecofriendly manufacturing processes and lightweight structures and materials to reduce CO2emissions and decrease weight and fuel consumption while optimizing overall performance. Aluminum alloys in the 7xxx and 6xxx series offer high potential for weight reduction in automotive and other transportation industries. 7xxx aluminum alloys have the best strength performance among all commercial aluminum alloys. Alloys in the 6xxx series generally have medium-to-high strength, high corrosion resistance, and good formability. Alloys in both the 7xxx and 6xxx series are strengthened by heat treatment. The increased strength-to-weight ratio and the thermal treatment processing open thepossibilitytouse thesealloysaspossible alternative materials instead of steel in the automotive industry for the fabrication of car body parts. However, their poor formability and weldability are the main drawbacks when these alloys are considered as substitutes of steel and other dissimilar joints during the fabrication of car body parts and the production chain. Recently, Hot Forming and in-die Quenching (HFQ), a patented hot stamping process, has been introduced to manufacture complex-shaped high-strength heat-treatable aluminum alloys. The work describedinthis articleisanexperimental investigation of the weldability between AA6082 and AA7075 by Friction Stir Welding (FSW) that considers thermal treatmentsused during HFQ for automotive applications. The aforementioned FSW base metals, 6082 and 7075, are heat treated according to the solution heat treatment adopted during HFQ to evaluate the effect of the HFQ thermal cycle on the quality of the produced joints. Optical microscopy has been used to characterize the microstructure of the produced joints. The defect-free welded joints are characterized by good mechanical mixing between the joined mater

Journal article

Li Y, Yang Y-L, Rong Q, Shi Z, Lin J, Said Ret al., 2019, Effect of initial tempers on mechanical properties of creep-aged AA2050, Manufacturing Review, Vol: 6, ISSN: 2265-4224

The evolution of mechanical properties of a third-generation Al–Cu–Li alloy, AA2050, with different initial tempers (as-quenched WQ, naturally aged T34 and peak-aged T84) during creep-ageing has been investigated in this study. A set of creep-ageing tests was carried out under 150 MPa at 155 °C with different durations for all 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 and uniform elongation. The evolution of these mechanical properties during creep-ageing has been discussed in association with precipitation behaviour of AA2050 alloys with different initial tempers. The results indicate that the T34 alloy is the best choice for creep age forming (CAF) applications among these initial tempers, as it provides better yield strength and uniform elongation concurrently after creep-ageing. In addition, a work hardening rate analysis has been carried out for all the creep-aged alloys, helping to understand the detailed dislocation/precipitate interaction mechanisms during plastic deformation in the creep-aged AA2050 alloys with WQ, T34 and T84 initial tempers.

Journal article

Zhou W, Yu J, Lin J, Dean TAet al., 2019, Manufacturing a curved profile with fine grains and high strength by differential velocity sideways extrusion, International Journal of Machine Tools and Manufacture, Vol: 140, Pages: 77-88, ISSN: 0890-6955

For structural and aerodynamic reasons, curved profiles are widely used in the transport industry for manufacturing lightweight structures. In the present work, a curved AA1050 bar with fine grains and high strength was manufactured by a novel forming technique, differential velocity sideways extrusion (DVSE). The evolution of grain structure and micro-texture during DVSE and the mechanical properties of the formed bar were studied, and the grain refinement mechanism was revealed. Due to the severe strains arising in the process, (greater than that for conventional one pass equal channel angular extrusion), significant grain refinement in the curved bar (grain size ∼3 μm) was achieved from the original billet (grain size ∼357 μm) in one extrusion operation. Coarse band-like structures containing subgrains with low angle boundaries in the shearing zone gradually transformed into fine shear band-like structures containing equiaxed (sub)grains with a mixture of low and high angle boundaries. The fine shear band-like structures inclined approximately along the shear intersection planes. Severe plastic deformation induced a high dislocation density that initiated subgrain walls with low angle boundaries, which gradually transformed into grain boundaries with high misorientation, indicating that refinement of AA1050 grains in the DVSE process is due mainly to continuous dynamic recrystallization (cDRX). Due to the appearance of greater effective strain on the inner bend of the extruded bar, the grain refinement degree and high angle boundary fraction of the material on the inner bend are slightly greater than those of the material on the outside. DVSE resulted in a weak C-type shear-texture component which can be determined by a proper rotation of the negative simple shear texture. Compared with the billet, significant increase of the hardness, yield strength and ultimate tensile strength by 134.8%, 354.0% and 116.8% respectively was achieved in the formed c

Journal article

Li Y, Rong Q, Shi Z, Sun X, Meng L, Lin Jet al., 2019, An accelerated springback compensation method for creep age forming, International Journal of Advanced Manufacturing Technology, Vol: 102, Pages: 121-134, ISSN: 0268-3768

Springback compensation is essential for tool design in creep age forming (CAF) process. In this study, a new accelerated springback compensation method integrating springback mechanism of a plate with creep-ageing behaviour of materials has been developed for CAF tool design to manufacture both singly and varyingly curved products. Springback compensation curves that relate the objective shapes and springback compensated shapes by their curvature, stress and strain states have been established, based on the numerical solution of springback behaviour of CAF process. For singly curved products, a one-step springback compensation method is proposed with reference to the springback compensation curves, and its effectiveness has been demonstrated by CAF test with a peak-aged aluminium alloy AA6082-T6. For products with varying curvatures, an accelerated method is developed for CAF tool design by integrating springback compensation curves with finite element (FE) assisted displacement adjustment techniques. The new accelerated method can significantly improve the tool design efficiency for CAF process when compared with conventional displacement adjustment techniques and has been verified by CAF manufacture of a varyingly curved product with AA6082-T6 material. The new accelerated springback compensation method developed in this study can be used for efficient tool design for CAF process of various products.

Journal article

Li Y, Shi Z, Rong Q, Zhou W, Lin Jet al., 2019, Effect of pin arrangement on formed shape with sparse multi-point flexible tool for creep age forming, International Journal of Machine Tools and Manufacture, Vol: 140, Pages: 48-61, ISSN: 0890-6955

The effect of forming pin arrangement on formed shape accuracy with sparse multi-point flexible (SMPF) tool has been experimentally and numerically investigated for creep age forming (CAF) process. An analytical method has been introduced to predict shape, stress and strain distributions of blanks loaded by SMPF tool with different pin configurations. Experiments and FE simulations of loading and CAF processes by SMPF tool with various pin number/interval conditions have been performed and the formed shapes after loading and CAF have been quantitatively analysed. The results show that increasing pin numbers in SMPF tool decreases shape errors and stress variations in the loaded blank, leading to lower deflections of the formed blank after CAF. With increasing pin numbers, the formed shape approaches the shape formed with corresponding surface tool. The shape error percentage in loaded blanks is significantly enlarged after CAF with SMPF tool, from 3% to more than 20% for singly-curved tool shapes with aluminium alloy 6082, and detailed value varies with tool shapes. Stresses in loaded blanks directly affect CAFed shapes and it has been found for the first time that there is a same stress discrepancy level between loaded blanks with SMPF tool and corresponding surface tool to achieve a particular shape accuracy after CAF with different tool shapes. It is proposed that the stress discrepancy parameter in loaded blanks can be used as a new and more efficient design criterion for pin arrangement in SMPF tool for CAF process. In addition, an asymmetric pin pattern, which reduces half of pins in SMPF tool and increases efficiency, has been proposed and its effectiveness for CAF process has been tested and discussed.

Journal article

Li Y, Shao Z, Rong Q, Shi Z, Balint D, Sun X, Meng L, Lin Jet al., 2019, Development of similarity-based scaling criteria for creep age forming of large/extra-large panels, The International Journal of Advanced Manufacturing Technology, Vol: 101, Pages: 1537-1551, ISSN: 0268-3768

A scaling method is developed for the creep age forming (CAF) process to downscale manufacturing of large/extra-large panels to lab-scale experimental trials for industrial application. Similarity theory is applied to identify both the geometrical and physical (non-geometrical) similarities between large-size prototypes and scaled-down models in all process stages of CAF, including loading, stress-relaxation and unloading (springback). A constitutive model is incorporated into the theory in order to identify the similarity in the highly non-linear stress-relaxation behaviour for aluminium alloy plates during CAF, and to obtain the effective scaling criteria for the CAFed plates after springback. The method was demonstrated by scaling down CAF manufacturing of both singly curved and doubly curved large plates under both proportional and non-proportional geometrical scaling conditions. The analytical results of the scaling method and numerical results obtained by CAF FE modelling were found to be in good agreement. Scaling diagrams linking the key deformation (springback) and structural (flexural rigidity) variables to scaling ratios under both proportional and non-proportional conditions were generated, and the developed scaling diagrams have been validated by corresponding CAF experiments. The scaling method developed in this study provides guidance on the design of scaled-down CAF experimental trials and will be used in the practical CAF process of large/extra-large panels.

Journal article

Zheng J-H, Pan R, Wimpory RC, Lin J, Li C, Davies CMet al., A novel manufacturing process and validated predictive model for high-strength and low-residual stresses in extra-large 7xxx panels, Materials & Design, ISSN: 0264-1275

A novel manufacturing process, enabling the production of high quality (i.e. with low and controllable residual stress distributions and good mechanical properties) T-section 7xxx panels, has been established. This process provides a solution to residual stress induced distortion problems, which greatly concerns a range of industries and especially the aircraft industry. This process consists of three sequential steps — water quenching (WQ), cold rolling (CR) and constrained ageing (CA). The effectiveness of this process was experimentally verified, through applying this process to laboratory sized 7050 T-section panels. The RS was measured by neutron diffraction and X-ray techniques, in addition to deflections and hardness at each processing stage. An integrated Finite Element (FE) model, including all three steps, was developed to simulate this manufacturing process and predict both the RS and the final strength distributions. It has been concluded that this novel process can effectively reduce the residual stresses from ±300 MPa to within ±100 MPa and produce T-section panels with required mechanical properties (i.e. hardness: ~159 HV10). A cold rolling level of 1.5% was found most appropriate. The residual stress and yield strength distributions were accurately predicted by FE, providing a valuable prediction tool to process optimization for industrial applications.

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

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 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, 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

Residual stresses (RS) are often induced through quenching of aluminum alloys and present a potential risk of developing crack or distortion in subsequent manufacturing processes. Study of methods to minimise the RS in quenched components is of practical importance. In this paper, cold rolling (CR) has been carried out to remove the RS in quenched AA7050 blocks. The CR effect on relaxing RS in quenched AA7050 blocks has been evaluated via the neutron diffraction (ND), X-ray diffraction (XRD) and contour techniques. The results reveal that although CR transforms near-surface residual stresses from large compression to large tension along the rolling direction, it results in remarkable RS relief in the core part of the material. An integrated finite element model for RS evolution through the CR process was put forward and has been validated by the experimental results.

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

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

Ganapathy M, Li N, Lin J, Abspoel M, Bhattacharjee Det al., 2019, Experimental investigation of a new low-temperature hot stamping process for boron steels, International Journal of Advanced Manufacturing Technology, ISSN: 0268-3768

© 2019, The Author(s). This paper demonstrates the promise of a new low-temperature hot stamping process with pre-cooling for 22MnB5 boron steels. It is the first time for the new process being successfully implemented for producing an automotive demonstrator component assisted with thorough experimental studies. The studies mainly include hot forming experiments carried out on an industrial prototyping line, post-form examinations, and in-die quenching tests. Automotive B-Pillar components with two designed drawing depths (50 and 64 mm) were hot stamped at a wide range of temperatures and forming speeds, through both the conventional hot stamping processes and the new processes with pre-cooling applied. For the as-formed B-Pillars, 3D shape scanning was conducted to investigate the thickness distribution of the components; uniaxial tensile testing, hardness testing, and scanning electron microscopes (SEM) observation were conducted to assess the final mechanical properties and microstructures. To understand the benefit of the low-temperature hot stamping in reducing cycle time, a separate set of in-die quenching experiments were designed and carried out, with combinations of three different process parameters: workpiece start quenching temperature, initial tool temperature, and die-workpiece contact pressure. The results of this work confirmed that low-temperature hot stamping could be performed successfully in producing complex-shaped components, such as automotive B-Pillars, with much reduced cycle time.

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

The solution heat treatment, forming and cold die quenching (HFQ) process has been developed and adopted for forming high strength complex-shaped components of light alloys in the automotive industry. In order to exploit and increase the competitiveness of this technology, production cycle time and manufacturing costs need to be reduced to enable high productivity and energy efficiency. This can be realised by reducing the cycle time for heating a metallic sheet to its solution heat treatment temperature during the HFQ process, and by decreasing post ageing time. Rapid heating methods are capable of providing a solution to be integrated into this novel forming technique of HFQ. This paper presents feasibility study on the adoption of the direct flame impingement (DFI) heating method that has a high potential for non-ferrous blanks to achieve higher heating rate in HFQ processes, compared to convection heating in a conventional furnace. The adaptability of DFI heating for HFQ process has been validated, in terms of capability of high heating rate, quality of surface layer examination and lap-shear strength measurement of bonded samples.

Journal article

Pan R, Zheng J, Zhang Z, Lin Jet al., 2018, 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

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 Y-L, 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, 5th International Conference on New Forming Technology - ICNFT 2018, Publisher: EDP Sciences, ISSN: 2261-236X

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

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

© 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

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, 5th International Conference on New Forming Technology - ICNFT 2018, Publisher: EDP Sciences, ISSN: 2261-236X

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

Jiang J, qinmeng L, 2018, Static recrystallization study on pure aluminium using crystal plasticity finite element and phase-field modelling, Metal Forming 2018, Publisher: Elsevier, Pages: 1800-1807, ISSN: 2351-9789

In-depth understanding of the recrystallization process in alloys is critical for generating desirable small grains and weak textured microstructure, which provides high strength and toughness for metal formed parts. The manufacturing industry has a high demand for a valid computational model to accurately predict the level of recrystallization and recrystallized grain size under different strain paths and temperatures. However, current understanding and numerical calculation have not been linked properly for a reliable, physically based model to simulate the deformation and annealing process. Our phase-field model coupled with crystal plasticity simulations, which is based on the theory of stored energy minimization, enables a reliable prediction on the microstructure evolution under different processing routes. We hope that this modelling work provides a solution for the prediction of some long standing microstructure formation problems.

Conference paper

Huang H, Wang B, Lin J, Zhu Cet al., 2018, Simulation of austenite formation of 60Si2CrA steel using internal state variable model, 17th International Conference on Metal Forming, Publisher: Elsevier BV, Pages: 1872-1878, ISSN: 2351-9789

Conference paper

Li J, Wang B, Lin J, Fang S, Wang S, Zhu Cet al., 2018, Investigation on evolution of the alpha phase during cross wedge rolling of TC6 blade perform, 17th International Conference on Metal Forming, Publisher: Elsevier BV, Pages: 168-175, ISSN: 2351-9789

Conference paper

Lane C, Shao Z, Zheng K, Lin Jet al., 2018, Effect of the thickness reduction of specimens on the limit strains in thermomechanical tensile tests for hot-stamping studies, Manufacturing Review, Vol: 5, ISSN: 2265-4224

Sheet metal formability under hot stamping conditions has been evaluated using a novel planar testing system developed previously, being used within a Gleeble machine. Nevertheless, the specimen design with the central recess was not standardised, and the thickness reduction was not applied to the dog-bone type of specimen for testing at the uniaxial straining state. In this paper, effect of thickness reduction of dog-bone specimens on limit strain measurement under hot stamping conditions is investigated, and two types of dog-bone specimens without and with central recess are presented. Thermomechanical uniaxial tensile tests were performed at various deformation temperatures and strain rates, ranging from 370-510 °C and 0.01-1/s, respectively, by using the developed biaxial testing system in the Gleeble. The distributions of temperature and axial strain along gauge region of the two types of specimen were measured and compared. The specimen with consistent thickness had a better uniformity of temperature and strain distributions, compared to that with thickenss reduction. Forming limits for both types of specimen were also determined using the section-based international standard method. It is found that the accuracy of the calculation of forming limits based on the use of specimen with thickness reduction was highly dependent on the selection of the stage of the deformation of the specimen.

Journal article

Zhang R, Shao Z, Lin J, 2018, A review on modelling techniques for formability prediction of sheet metal forming, International Journal of Lightweight Materials and Manufacture, Vol: 1, Pages: 115-125, ISSN: 2588-8404

With an increasing demand for lightweight design of vehicles in automotive and aircraft industries, sheet metals with low density and high strength have been widely and intensively used in forming lightweight structural panel components. Formability is a critical material property in describing deformation ability of sheet metals, and it is usually evaluated by a forming limit diagram (FLD) determined at various forming conditions. FLDs for metallic material are usually obtained experimentally, which is time-consuming and costly. Numbers of theoretical and numerical models have been developed and used to predict the formability of sheet metals. These modelling techniques are primarily developed based on bifurcation theory, geometrical imperfection theory and continuum damage mechanics. This paper covers a comprehensive review of modelling methods used for the formability prediction of lightweight materials for sheet metal forming applications.

Journal article

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