13th International Conference on the Technology of Plasticity (ICTP 2021): Constitutive Behavior II
Program Organizers: Glenn Daehn, Ohio State University; Libby Culley, The Ohio State University; Anupam Vivek, Ohio State University; Jian Cao, Northwestern University; Brad Kinsey, University of New Hampshire; Erman Tekkaya, TU Dortmund; Yoshinori Yoshida, Gifu University

Tuesday 9:15 AM
July 27, 2021
Room: Virtual: Room D
Location: Virtual

Session Chair: Toshihiko Kuwabara, Tokyo University of Agriculture and Technology


Experimental Study and Modelling of Stress Relaxation Ageing Behaviour and Post-form Mechanical Properties in Creep Age Forming of Al-Zn-Mg Alloy: Yong Li1; Fenggong Lyu2; Zhusheng Shi1; Yuansong Zeng2; Xia Huang2; Jianguo Lin1; 1Imperial College London; 2AVIC Manufacturing Technology Institute
    The stress relaxation ageing behaviour and post-form mechanical properties of an Al-Zn-Mg alloy, AA7B04, have been experimentally investigated and modelled. Stress relaxation ageing tests were carried out under different initial stress levels and durations at 165 °C and subsequent tensile tests were performed at room temperature. The detailed effects of stress and time on stress relaxation and main post-form mechanical properties (yield strength, ultimate tensile strength and uniform elongation) have been analysed and discussed. Based on the results and analysis, a set of unified constitutive equations has been developed for the first time to simultaneously predict stress relaxation ageing behaviour of the aluminium alloy during creep age forming (CAF) process and the main mechanical properties of the products after CAF. The model is comprised of three sub-models, including microstructure, stress relaxation ageing and post-form mechanical properties, and has successfully predicted corresponding behaviour. The developed model provides an effective tool to not only predict the forming process, but also support possible industrial applications for CAF products.

Accurate Modelling of Flow Stress of AISI1025 at Room Temperature and Its Application to Precision Forging Simulation: ManSoo Joun1; Mohd Kaswandee Razali1; JeongBuk Byun1; KwangHee Lee2; 1Gyeongsang National University; 2Pungkang, HoaSeong
    This paper evaluates and criticizes the Swift model of expressing strain hardening behaviours of metals at room temperature using an experimental tensile test and its FE prediction. A concept of reference flow stress curve composed of two ranges of strain divided by the true strain at the necking point is proposed, which predicts tensile test exactly from the standpoint of engineering and is thus employed to evaluate the Swift model. It has been shown that it has a weak point in describing the flow stress of typical strain hardening material with emphasis on necking. An improved Swift model is applied to obtain accurate flow stress of a commercial steel AISI1025 and it is employed to simulate a sequence of cold forging processes by precision complete analysis for process and die optimal design in terms of die life, which should be conducted under an accurate analysis model.

Stress-relaxation Age Forming of A Component with Complex and Large Curvatures: Simulation and Manufacturing: Qi Rong1; Zhusheng Shi1; Yong Li2; Jianguo Lin1; 1Imperial College London; 2Beihang University
    Stress-relaxation age forming (SRAF) of a panel component (820*300*3 mm) with complex and large curvatures has been simulated and corresponding SRAF test of an Al-Mg-Si alloy, AA6082-T6, has been carried out in this study. An FE model is established to simulate the stress-relaxation ageing (SRA) behaviour of AA6082 during SRAF at various stress levels, for the first time, ranging from elastic to plastic regions and a unified constitutive model for SRA of the material has been implemented into finite element (FE) software ABAQUS via the user-defined subroutine CREEP. An optimised tool surface was determined from FE simulation through springback predication and compensation and was used for manufacturing test. A good agreement of the formed shape has been achieved between the FE simulation and the SRAF test, with a maximum shape error below 4 mm, satisfying the industrial requirement. Hardness results from the formed plate show insignificant change of strength during SRAF, in good agreement with the simulation. The effects of the initial plastic strain and creep strain generated during loading and stress-relaxation stages on the formed shape have also been analysed.

Cancelled
Rate Dependent Hardening Behavior of Autobody Sheet Metals in Tension and Compression: Hoon Huh1; 1KAIST
    This paper is concerned with evaluation of rate-dependent hardening behaviors of auto-body sheets with novel tension and compression testing devices. Hardening behaviors in tension and compression are indispensable for accurate numerical simulation of sheet metal forming and subsequent spring-back as well as crashworthiness. Novel in-plane tension and compression testing devices are developed with a servo-hydraulic testing machine to obtain tensio-compression hardening curves of auto-body steel sheets at intermediate strain rates ranging from 0.001 s−1 up to 100 s−1. With the testing devices specially developed, hardening behaviors are evaluated in tension-compression for mild steel sheets, TRIP980, TWIP980 steel sheets and magnesium alloy at various strain rates ranging from 0.001 s−1 to 100 s−1 in terms of the flow stress considering the Bauschinger effect and the permanent softening. It is observed that the stress offset is dependent on the inherent characteristics of steel sheets as well as the strain rates.

Flow Behavior and Processing Map of a Nickel-based Superalloy during Hot Plastic Deformation Process: Baoyun Zhang1; Shuo Huang2; Wenyun Zhang2; Beijiang Zhang2; Yongquan Ning1; 1Northwestern Polytechnical University; 2Central Iron and Steel Research Institute
    Nickel-based superalloys have been widely used to produce high performance components in advanced engine. In present research, isothermal compression tests of GH4065A Nickel-based superalloy were conducted at deformation temperatures of 1020-1140°C and strain rates of 0.001-1.0s-1. The deformation temperature and strain rate have a significant effect on the true stress-strain curves, from which the intrinsic connection between the flow stress and deformation behavior can be systematically studied. The apparent activation energy of deformation was calculated to be 454.5kJ/mol at the strain of 0.65 when the flow stress was steady. Meanwhile, the constitutive equation was constructed for modeling the hot plastic deformation of this superalloy. Based on the microstructure observation, the influence of hot processing parameters on microstructure has been deeply explored. Moreover, the microstructural mechanism during hot plastic deformation was revealed, which can provide the optimization of hot forging process for manufacturing high performance components in advanced engine.

Hot Deformation Behavior and Constitutive Modeling of a Novel Ni-based Superalloy: Hao Yu1; Qi Liu1; Hao Yang1; Baoyun Zhang1; Bingchao Xie1; Yongquan Ning1; 1Northwestern Polytechnical University
    Ni-based superalloys are widely used to manufacture the key components in gas turbine engine,since their superior mechanical properties at elevated temperature.In present work, hot deformation behavior of a novel Ni-based superalloy was investigated by compression test at temperatures of 1020-1140℃ and strain rates of 0.001-10s-1.At low temperature and high strain rates, the flow stress rapidly increased to a peak value due to work hardening.However, at high temperature and low strain rates, the flow curves exhibited typical dynamic softening stage. The hot deformation activation energy of the studied superalloy is determined to be 735.5KJ/mol, and a strain compensated Arrhenius type constitutive equation is obtained.Comparison of the predicted and experimental values, the developed constitutive equation can accurately describe the deformation mechanism and the flow behavior.Meanwhile, the influence of hot processing parameters on microstructure has been deeply explored, which can optimize the process parameters for manufacturing key components in gas turbine engine.

Constitutive Model and Plate Forging Ability of 5052 Aluminum Alloy under Different Temperatures: Lin Qiquan1; Yantao Li1; Dong Wenzheng1; Wang Zhigang2; 1Xiangtan University; 2Gifu University
    The paper was concerned with plate forging of Al5052. Biaxial tensile tests were conducted to obtain the rheological behavior and stress-strain curve of Al 5052 under warm temperature. An FEM model utilizing the data mentioned above was proposed to simulate the solid boss process of Al5052 by sheet-bulk forming. It was interesting to find out that boss height and forming defects vary with the combination of process parameters. Thus five factors and four level orthogonal experiment table was designed to study the effect of counter-punch force, boss diameter, boss radius, initial sheet thickness and friction coefficient on boss height and dimple defect. The results indicated that boss diameter and counter-punch force play the most important role on the boss height and defect, respectively. Finally, the corresponding experiments were consistent with the numerical prediction results.

Analysis of Creep Behavior of Magnesium Alloy Sheet (AZ31B) in Warm Forming: JaeHyeong Yu1; Chang-Whan Lee1; 1Seoul National University of Science and Technology
    In this study, spring-back of magnesium alloy sheet in V-bending was observed according to holding time in the die set and plastic deformation at warm forming conditions. Also, the creep behavior of the magnesium alloy sheet was investigated in the numerical simulation to analyze the spring-back. At room temperature, the spring-back is 28.11° and 24.99° at holding time of 0 and 1000sec respectively. Also, at 250°, the spring-back is 11.46° and 1.12° at holding time of 0 and 1000sec respectively. The results indicate that creep recovery occurs by increasing holding time in the die set during the warm forming. The experiment was conducted at different punch radius R(1, 2, 4, 5mm) to analyze the effect of creep recovery velocity on the spring-back during V-bending operation. Furthermore, Microstructure observations were conducted for detail insight into the results.

Effect of Short Pulsed-current on Stress Relaxation in Uniaxial Tensile Test: Ichsan Indhiarto1; Qiu Zheng2; Tetsuhide Shimizu1; Tsuyoshi Furushima2; Ming Yang1; 1Tokyo Metropolitan University; 2University of Tokyo
    Electricity assisted metal forming, especially using pulsed-current, was demonstrated to promote drop in flow stress and improving formability. To investigate the effect of pulsed-current on stress relaxation, an uniaxial tensile test was conducted with different pulsed-current parameters by changing its pulse-width and frequency. Employed short pulse width was in range of microsecond, while the frequency was arranged under 1 kHz. Different level of temperature was employed to consider effect from joule heating. Stress relaxation in tensile test was repeated at constant strain interval at 3% strain. This research present analysis of stress relaxation influenced by time-dependent parameter of short pulsed-current