Strain-Based Continuum Damage Mechanics Model for Predicting FLC of AA5754 under Warm Forming Conditions

Mohamed, Mohamed; Shi, Zhusheng; Lin, Jixing; Dean, Trevor; Dear, John P.

doi:10.4028/www.scientific.net/amm.784.460

Cited by 9 publications

(8 citation statements)

References 15 publications

(15 reference statements)

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“…Based the previous studies [41,54], a set of unified viscoplastic constitutive equations are formulated as below:…”

Section: Constitutive Equationsmentioning

confidence: 99%

“…Viscoplasticity theory can also be used for analysis on forming processes at elevated temperatures and a dislocation-based viscoplasticdamage model had been proposed by Lin et al [40] since microstructural evolution at elevated temperatures has a great effect on formability of an alloy. This theory can be developed to predict forming limits of metals for hot stamping applications [41]. and should be controlled precisely to maintain a supersaturated solid solution without grain degradation in a specimen.…”

Section: Introductionmentioning

confidence: 99%

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Formability evaluation for sheet metals under hot stamping conditions by a novel biaxial testing system and a new materials model

Shao

Lin

et al. 2017

International Journal of Mechanical Sciences

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Published: Z. Shao, N. Li, J. Lin, T. Dean, 2017, Formability evaluation for sheet metals under hot stamping conditions by a novel biaxial testing system and a new materials model, Int. J. Mech. Sci., 120, pp149-158. AbstractHot stamping and cold die quenching has been developed in forming complex shaped structural components of metals. The aim of this study is the first attempt to develop unified viscoplastic damage constitutive equations to describe the thermo-mechanical response of the metal and to predict the formability of the metal for hot stamping applications. Effects of parameters in the damage evolution equation on the predicted forming limit curves were investigated. Test facilities and methods need to be established to obtain experimental formability data of metals in order to determine and verify constitutive equations. However, conventional experimental approaches used to determine forming limit diagrams (FLDs) of sheet metals under different linear strain paths are not applicable to hot stamping conditions due to the requirements of rapid heating and cooling processes prior to forming. A novel planar biaxial testing system was proposed before and was improved and used in this work for formability tests of aluminium alloy 6082 at various temperatures, strain rates and strain paths after heating, soaking and rapid cooling processes. The key dimensions and features of cruciform specimens adopted for the determination of forming limit under various strain paths were developed, optimised and verified based on the previous designs and the determined heating and cooling method [1]. The digital image correlation (DIC) system was adopted to record strain fields of a specimen throughout the deformation history. Material constants in constitutive equations were determined from the formability test results of AA6082 for the prediction of forming limit of alloys under hot stamping conditions. This research, for the first time, enabled forming limit data of an alloy to be generated at various temperatures, strain rates and strain paths and forming limits to be predicted under hot stamping conditions.

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“…Based the previous studies [41,54], a set of unified viscoplastic constitutive equations are formulated as below:…”

Section: Constitutive Equationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Formability evaluation for sheet metals under hot stamping conditions by a novel biaxial testing system and a new materials model

Shao

Lin

et al. 2017

International Journal of Mechanical Sciences

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“…Lin et al (2014) were the first to develop a CDM-based constitutive model to predict FLCs for sheet metals under hot stamping conditions under the assumption of plane-stress conditions, coupled with a damage variable to characterise the extent of necking. Since an FLC is constructed using limit strains, Mohamed et al (2015) modified this damage variable, replacing the stress components with strain components to model the effect of the stress or strain state on the damage evolution. The modified damage variable in multiaxial form is expressed as (Mohamed et al, 2015):…”

Section: Cdm-based Damage Variablesmentioning

confidence: 99%

“…Since an FLC is constructed using limit strains, Mohamed et al (2015) modified this damage variable, replacing the stress components with strain components to model the effect of the stress or strain state on the damage evolution. The modified damage variable in multiaxial form is expressed as (Mohamed et al, 2015):…”

Section: Cdm-based Damage Variablesmentioning

confidence: 99%

A CDM-based unified viscoplastic constitutive model of FLCs and FFLCs for boron steel under hot stamping conditions

Zhang

Shi

Yardley

et al. 2022

International Journal of Damage Mechanics

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Forming limit curves (FLCs), which are constructed using the limit strains at localised necking, are the most widely used tools for the evaluation of the formability of sheet metals. Fracture forming limit curves (FFLCs) are more recently developed, complementary tools for formability evaluation which are instead constructed using the limit strains at fracture. Since the formability depends strongly on forming conditions such as strain state, temperature and strain rate, models for predicting FLCs and FFLCs are essential for the optimisation and further application of hot forming processes in which these forming conditions vary significantly with both position and time. However, no model has so far been developed to predict FFLCs either alone or in conjunction with FLCs for sheet metals such as boron steel under hot stamping conditions. In this study, a set of unified viscoplastic constitutive equations for the prediction of both FLCs and FFLCs based on continuum damage mechanics (CDM) has been formulated from a set of recently developed constitutive equations for dislocation-based hardening, in combination with two novel coupled variables characterising the accumulated damage leading to localised necking and fracture. The novel variables take into account the effects of strain state, temperature and strain rate on the formability of sheet metals. The material constants in the CDM-based constitutive equations have been calibrated using experimental data comprising true stress-true strain curves and limit strains of a 22MnB5 boron steel obtained at a range of temperatures and strain rates. Investigation of the effect of varying selected parameters in the coupled damage variables on the resulting computed FLCs and FFLCs has demonstrated the flexibility of the model in enabling curves of different shapes and numerical values to be constructed. This indicates the potential of the CDM-based constitutive model for application to other materials for warm or hot stamping processes.

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“…In the metal sheet forming process, it is usually assumed that the sheet is in plane stress state as the stress in the thickness direction is extremely small [27]. Then, uniaxial constitutive model usually needs to be extended to multiaxial constitutive model considering the variation of stress state and strain path during metal sheet deformation [28].…”

Section: Constitutive Modelingmentioning

confidence: 99%

Behaviors and modeling of thermal forming limits of AA7075 aluminum sheet

Xiao

Wang

2020

Archiv.Civ.Mech.Eng

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The aluminum hot stamping process has been widely studied to produce lightweight parts in automobile industry. As forming limit of aluminum sheet at elevated temperatures plays a vital role in judging stamping formability, this study aims at experimentally investigating the forming limits and establishing a constitutive model to predict them. In this study, isothermal deformation test (Nakajima test) of AA7075 was conducted to determine its forming limits at temperatures of 300-450 °C and stamping speeds of 13-40 mm/s. Based on the experimental results, a constitutive model considering continuum damage mechanics was established to predict the forming limits under different deformation conditions. It was found that the formability of the material is best at 400 °C, and a higher strain rate can improve formability slightly. The comparisons between model predictions and experimental results were evaluated; results indicated a good prediction accuracy of the model in describing forming limits of AA7075 at elevated temperatures. Moreover, comparison between different studies on the thermal forming limits of AA7075 was discussed in detail.

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Strain-Based Continuum Damage Mechanics Model for Predicting FLC of AA5754 under Warm Forming Conditions

Cited by 9 publications

References 15 publications

Formability evaluation for sheet metals under hot stamping conditions by a novel biaxial testing system and a new materials model

Formability evaluation for sheet metals under hot stamping conditions by a novel biaxial testing system and a new materials model

A CDM-based unified viscoplastic constitutive model of FLCs and FFLCs for boron steel under hot stamping conditions

Behaviors and modeling of thermal forming limits of AA7075 aluminum sheet

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