274 results found
Chavoshi SZ, Jiang J, Wang Y, et al., 2018, Density-based constitutive modelling of P/M FGH96 for powder forging, International Journal of Mechanical Sciences, Vol: 138-139, Pages: 110-121, ISSN: 0020-7403
© 2018 Elsevier Ltd A set of viscoplastic constitutive equations is presented in this study to predict hot compressive deformation behaviour and densification levels of powder metallurgy (P/M) FGH96 nickel-base superalloy during direct powder forging (DPF) process. The constitutive equations make use of the elliptic equivalent stress proposed in porous material models, and unify the evolution of relative density, normalised dislocation density, isotropic hardening and flow softening of the powder compact. A gradient-based optimisation technique is adopted to determine the material constants using the experimental data obtained from Gleeble isothermal uniaxial compression tests of HIPed FGH96 at different temperatures and strain rates. The developed constitutive equations are incorporated into finite element code DEFORM via user-defined subroutine for coupled thermo-mechanical DPF process modelling. The constitutive equations benefiting from the viscoplastic densification model of the calibrated Abouaf, among the six studie d porous material models, compare favourably with the experimental data, while the equations integrating the porous material model of Shima and Oyane provide excellent agreement with experiments in the low density outer region of the powder compact.
Ganapathy M, Li N, Lin J, et 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
Kopec M, Wang K, Politis DJ, et al., 2018, Formability and microstructure evolution mechanisms of Ti6Al4V alloy during a novel hot stamping process, Materials Science and Engineering A, Vol: 719, Pages: 72-81, ISSN: 0921-5093
© 2018 Elsevier B.V. A novel hot stamping process for Ti6Al4V alloy using cold forming tools and a hot blank was presented in this paper. The formability of the material was studied through uniaxial tensile tests at temperatures ranging from 600 to 900°C and strain rates ranging from 0.1 to 5 s −1 . An elongation ranging from 30% to 60% could be achieved at temperatures ranging from 750 to 900°C respectively. The main microstructure evolution mechanisms varied with the deformation temperature, including recovery, phase transformation and recrystallization. The hardness of the material after deformation first decreased with the temperature due to recovery, and subsequently increased mainly due to the phase transformation. During the hot stamping tests, qualified parts could be formed successfully at heating temperatures ranging from 750 to 850°C. The forming failed at lower temperatures due to the limited ductility of the material. At temperatures higher than 900 °C, extensive phase transformation of α to β occurred during the heating. During the transfer and forming, the temperature dropped significantly which led to the formation of transformed β reduction of the formability and subsequent failure. The post-form hardness distribution demonstrated the same tendency as that after uniaxial tensile tests.
Politis DJ, Politis NJ, Lin J, et al., 2018, An analysis of the tooth stress distribution of forged bi-metallic gears, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART C-JOURNAL OF MECHANICAL ENGINEERING SCIENCE, Vol: 232, Pages: 124-139, ISSN: 0954-4062
Shao Z, Bai Q, Li N, et 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
© 2016, © IMechE 2016. The determination of forming limit curves and deformation features of AA5754 aluminium alloy are studied in this article. The robust and repeatable experiments were conducted at a warm forming temperature range of 200 °C–300 °C and at a forming speed range of 20–300 mm/s. The forming limit curves of AA5754 at elevated temperatures with different high forming speeds have been obtained. The effects of forming speed and temperature on limiting dome height, thickness variation and fracture location are discussed. The results show that higher temperatures and lower forming speeds are beneficial to increasing forming limits of AA5754; however, lower temperatures and higher forming speeds contribute to enhancing the thickness uniformity of formed specimens. The decreasing forming speed and increasing temperature result in the locations of fracture to move away from the apexes of formed specimens. It is found that the analysis of deformation features can provide a guidance to understand warm forming process of aluminium alloys.
Xiao W, Wang B, Zheng K, et 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
© 2017 The aim of this research was to investigate the effects of contact pressure and lubrication on the interfacial heat transfer coefficient (IHTC) between AA7075 sheet and H13 tool steel and the in-die quenching performance in hot stamping. Firstly, a series of designed in-die quenching experiments were performed using different contact pressures, 0.05–30 MPa and lubrication conditions to determine the IHTC values using an efficient methodology. Secondly, temperature evolution of the tools and blank during the in-die quenching was investigated. Mechanical properties of material in-die quenched under different process conditions, were measured to determine their relation to quench conditions. The results have shown that IHTC values increased with increasing contact pressure and use of lubricant. A strength level of T6 condition could be obtained using a contact pressure greater than 5 MPa in the lubricated condition.
Zheng J-H, Pan R, Li C, et al., 2018, Experimental investigation of multi-step stress-relaxation-ageing of 7050 aluminium alloy for different pre-strained conditions, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, Vol: 710, Pages: 111-120, ISSN: 0921-5093
Zhou W, Lin J, Dean TA, et 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 i
Zhou W, Lin J, Dean TA, et al., 2018, Analysis and modelling of a novel process for extruding curved metal alloy profiles, International Journal of Mechanical Sciences, Vol: 138-139, Pages: 524-536, ISSN: 0020-7403
© 2018 An analytical upper-bound-based model for predicting curvature of bent metal alloy profiles obtained through a novel extrusion process, differential velocity sideways extrusion (DVSE), previously proposed by the authors, has been first-time developed. Finite element modelling and simulation and model material experiments, which were validated by extrusion of AA1050, have been performed to determine the geometry of the deformation zone and assess the accuracy of the analytical model. The extrusion force, curvature, and effective strain predicted by the analytical method agreed well with results from experiments and FE simulation. It was shown that the punch with a lower velocity experiences a lower extrusion force, which increases both with increase of its velocity and the extrusion ratio. The extrusion force on the faster punch with a constant velocity v 1 changes quite slightly with the increase of the velocity v 2 of the slower punch. Various values of curvature, which decrease with the increase of the punch velocity ratio v 2 /v 1 and the decrease of the extrusion ratio, can be achieved through the DVSE process. DVSE is a novel process which leads to larger effective strain per pass than that in the equal channel angular extrusion (ECAE).
Bai Q, Mohamed M, Shi Z, et 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
Dong Y, Zheng K, Fernandez J, et 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
Ganapathy M, Li N, Lin J, et al., 2017, Investigation of a new hot stamping process with improved formability and productivity, Pages: 771-776
In order to improve the drawability of boron steel and also to increase the productivity of hot stamping process, a new hot stamping process with pre-cooling has been proposed. Stress-strain behavior at various temperatures was investigated and compared with that in traditional hot stamping processes. Detailed studies were carried out on the strain hardening parameter, n, at different temperatures and deformation rates. To evaluate this concept, hot stamping experiments were performed with both conventional (without pre-cooling) and new process (with pre-cooling) for a scaled down B-Pillar automotive component. The new hot stamping process with pre-cooling was able to produce the B-Pillar at low temperature (500°C) with less thinning than the hot stamping carried out without precooling at high temperature (765°C). Also the in-die quenching time was reduced by about 60%, by adopting the new hot stamping process with pre-cooling, which would increase the productivity significantly for automotive mass production without compromising the part quality.
Ganapathy M, Li N, Lin JG, et 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
Huang X, Wang B, Lin J, et al., 2017, Effect of mandrel diameter on non-circularity of hollow shafts in cross wedge rolling, Pages: 2376-2381
© 2017 The Authors. Published by Elsevier Ltd. Because of the need for lightweight design, the application of hollow shaft parts rapidly increases. The mandrel plays an important role in the process of forming hollow shafts using cross wedge rolling (CWR). This paper presents the experimental and numerical analysis on the effect of the mandrel diameter on non-circularity in CWR for the hollow shafts with mandrel. A thermomechanical finite element (FE) model was developed to simulate the CWR process of hollow shaft. The experiments and numerical analysis suggest that the diameter of mandrel has a great effect on the non-circularity of hollow shafts. During the CWR process, because of the effect of the mandrel, the workpiece is compressed in radial direction and extended along the circumferential direction, which lead to the increase of the non-circularity. With increasing diameters, the workpieces show larger non-circularity. The non-circularity slowly increases when mandrel diameter is small. However, when the mandrel diameter exceeds a certain value, the non-circularity increases rapidly. Besides, the non-circularity of the inner hole is larger than that of the outer circle. According to the strain curves during the forming process, it can be found that circumferential compressive strain plays an important role in the rounding forming stage. Larger compressive strains decrease the non-circularity of the rolled pieces.
Huo Y, Lin J, Bai Q, et 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
Ji H, Liu J, Wang B, et 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
Jiang J, Hooper P, Li N, et al., 2017, An integrated method for net-shape manufacturing components combining 3D additive manufacturing and compressive forming processes, Pages: 1182-1187
© 2017 The Authors. Published by Elsevier Ltd. Additive manufactured (AM) or 3D printed metallic components suffer poor and inconsistent mechanical properties due to the presence of a large number of micro-voids, residual stress and microstructure inhomogeneity. To overcome these problems, a new forming process has been proposed, which effectively combines AM and compressive forming. The aim of this study is to prove the feasibility of this newly proposed method by providing preliminary results. Thus, we compared the tensile performance of hot-forged additive manufactured stainless steel 316L samples to none-hot-forged additive manufactured ones. Significant improvement in mechanical properties has been found in the tensile tests as well hardness test. In addition, our EBSD characterized grain orientation maps at each stage of the process revealed the corresponding microstructure revolution which provides insights into underlying mechanistic.
Kaye MC, Balint D, Lin J, et 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
Kong XX, Li N, O'Keeffe R, et 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
Li N, Zheng J, Zheng K, et al., 2017, A fast ageing method for stamped heat-treatable alloys, WO2017021742 A1
Li Y, Shi Z, Lin J, et 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
Li Y, Shi Z, Lin J, et 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
Liu J, Wang A, Zheng Y, et al., 2017, Hot stamping of AA6082 tailor welded blanks for automotive applications, Pages: 729-734
Friction stir welded (FSWed) AA6082 tailor welded blanks (TWBs), with gauge combinations of 2.0-2.5 and 3.0-5.0 mm, have been prepared and successfully formed into automotive panel components. Experimental results indicated that the post-form strength, in terms of hardness, varied from location to location on the final parts. The strength is highly dependent on the blank gauges, with the average hardness values being HV 110 and HV 98 for the 2.0-2.5 and 3.0-5.0 mm TWB parts, respectively. Conventional FE simulation was built in PAM-STAMP and the prediction results were validated from experimental data in terms of strain distribution and temperature evolution. A typical continuous cooling precipitation (CCP) diagram for AA6082 was implemented into the verified simulation data to explain the strength variations. It is deemed that the temperature history during the stamping and quenching stages has played a major role on the post-form strength of the final parts.
Ma W-Y, Wang B-Y, Lin J-G, et al., 2017, Influence of process parameters on properties of AA6082 in hot forming process, TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, Vol: 27, Pages: 2454-2463, ISSN: 1003-6326
Mohamed M, Lin J, Foster A, et 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.
Mohamed M, Lin J, Foster A, et 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
Rong Q, Shi Z, Li X, et al., 2017, Experimental studies and constitutive modelling of AA6082 in stress-relaxation age forming conditions, Pages: 293-298
© 2017 The Authors. Published by Elsevier Ltd. AA6082 is a popular material for automotive body structure because of its good formability and weldability. In this study, stress relaxation and ageing behaviour of AA6082 at T6 condition were investigated through stress relaxation tests with three different initial stresses at 160 °C for 12 h. Interrupted tests for 1, 3, 5 and 12 h and subsequent uniaxial tensile tests were carried out to investigate the effect of ageing time on yield strength of the material. The results show that after 12 h stress relaxation tests with initial stresses of 173, 198, and 225 MPa, the stresses relaxed were respectively 19.4 %, 24.3 %, and 25.6 % of the initial stresses. Minor change of yield strength of the material throughout the ageing time was observed. Moreover, a set of unified constitutive equations was calibrated to model the stress relaxation behaviour of AA6082 during creep age forming process, and related material constants for the AA6082 were determined. A close agreement between experimental data and computed results has been achieved for stress relaxation behaviour of the material. This study helps to understand the stress relaxation behaviors of AA6082 material, and facilitates the CAF applications of AA6082 material in industrial field.
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, 36th IDDRG Conference on Materials Modelling and Testing for Sheet Metal Forming, Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588
Shao Z, Li N, Lin J, 2017, The optimisation of cruciform specimen for the formability evaluation of AA6082 under hot stamping conditions, Pages: 735-740
The hot stamping and cold die quenching process is increasingly adopted to form complex-shaped structures of sheet metals in the automotive industry. However, it is difficult to obtain formability data of sheet metals under hot stamping conditions by using conventional experimental testing methods. In this study, a novel in-plane biaxial testing system, which is attached to a Gleeble materials thermo-mechanical simulator, had been developed for determining forming limit diagrams (FLDs) under hot stamping conditions. However, there is no standard of cruciform specimen geometries available for this type of biaxial tests. In this paper, the features of thickness reduction in the central region and slots in the arms of a type of cruciform specimen of aluminium alloy 6082 were verified first to increase strain uniformity of the biaxial loading zone on a cruciform specimen, based on the selective heating and cooling method. Finite Element (FE) thermo-electrical and thermo-mechanical models with UAMP and VUMAT subroutines were then implemented in ABAQUS 6.12 to optimise specimen dimensions so that fracture occurs in the concerned central region of the specimen during testing. By the use of the optimised specimen for AA6082 in the biaxial testing system, formability tests under the designated strain paths were conducted at specified hot stamping conditions. Strain fields in the gauge region of the cruciform specimens were measured using the digital image correlation (DIC) system and the experimental results were presented and analysed in order to verify the cruciform specimen design.
Shao Z, Li N, Lin J, et 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
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