Forming limit diagrams with the existence of through-thickness normal stress

Assempour, Ahmad; Nejadkhaki, Hamid Khakpour; Hashemi, Ramin

doi:10.1016/j.commatsci.2010.02.013

Cited by 81 publications

(42 citation statements)

References 27 publications

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“…On the other hand, the plastic-strain increments in the orthotropic symmetry axes frame (x,y,z) are determined from Equation 6, which depends upon the effective plasticstrain increment and the yield function partial derivatives. The later are obtained by applying the consistency condition, df = 0, to the Ferron's yield function defined in the form of Equations 9 and 10, that is: (17) and then, by defining the terms dx 1 , dx 2 and dα as a function of the variables (x 1 ,x 2 ) along with the help of the relations sin 2 α = σ xy /x 2 and cos 2α = (σ x -σ y )/(2x 2 ), which provides: (18) Where: the yield function partial derivatives 35 orthotropic yield criterion plotted in the principal stress space (σ 1 ,σ 2 ) normalized by the equibiaxial yield stress (σ b ) as a function of the orientation angle (α) between the principal stress axes and the in-plane orthotropy directions.…”

Section: Constitutive Equationsmentioning

confidence: 99%

“…For instance, predictions in good agreement with experimental results have been obtained in the case of aluminum alloys [9][10] with the yield criteria proposed by Barlat et al 11 , Karafillis and Boyce 12 and Barlat et al 13 . The effects of the through-thickness normal and shear stress components have also been taken into account within the framework of the M-K model, see the recent works [14][15][16][17][18] . These out-of-plane effects are not negligible in some sheet metal forming processes, such as hydroforming and incremental sheet forming, where significant through-thickness compressive stress components may take place.…”

Section: Introductionmentioning

confidence: 99%

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Experimental analysis and theoretical predictions of the limit strains of a hot-dip galvanized interstitial-free steel sheet

2013

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In this work, the formability of a hot-dip galvanized interstitial-free (IF) steel sheet was evaluated by means of uniaxial tensile and Forming Limit Curve (FLC) tests. The FLC was defined using the flat-bottomed Marciniak's punch technique, where the strain analysis was made using a digital image correlation software. A plastic localization model was also proposed wherein the governing equations are solved with the help of the Newton's method. The investigated hot-dip galvanized IF steel sheet presented a very good formability level in the deep-drawing range consistent with the measured Lankford values. The predicted limit strains were found to be in good agreement with the experimental data of the hot-dip galvanized IF steel sheet owing to the definition of the localization model geometrical imperfection as a function of the experimental surface roughness evolution and, in particular, to the yield surface flattening near to the plane-strain stress state authorized by the adopted yield criterion.

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Section: Constitutive Equationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Experimental analysis and theoretical predictions of the limit strains of a hot-dip galvanized interstitial-free steel sheet

2013

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“…Then, by using the obtained information from the nominal zone, computations of the groove region were performed. The computations in this paper are based on the work of Assempour et al 1 Thus, readers could find more explanations and detailed procedure of the generalized FLD computations and FLD verifications in this reference. 1 …”

Section: Summary Of the Generalized Fld Computationmentioning

confidence: 99%

“…This technique was developed at least six decades ago. 1 In recent years, there has been an accelerating growth in the production of hydroformed products. Regarding process features and various blanks, hydroforming can be classified into sheet hydroforming and tube hydroforming.…”

Section: Introductionmentioning

confidence: 99%

Forming limit diagram of tubular hydroformed parts considering the through-thickness compressive normal stress

Hashemi

Abrinia

Assempour

et al. 2014

Proceedings of the Institution of Mechanical Engineers, Part L:

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In this study, the effect of a compressive normal stress has been considered in the determination of forming limit diagrams and forming limit stress diagrams to predict neck initiation failure in tube hydroforming of T-shaped parts. Computation of the forming limit diagrams and FLSDs is based on the generalized Marciniak and Kuczynski method to consider the existence of through-thickness compressive normal stress. The proposed forming limit diagrams and FLSDs were used in conjunction with ABAQUS/EXPLICIT finite element simulations to predict the onset of necking in tube hydroforming of T-shaped part. The amount of calibration pressure and axial feeding required to produce an acceptable part in finite element method was compared to published experimental data, and a satisfactory agreement between the FEM and test results has been achieved. Therefore, the present approach can be used as a reliable criterion to design tube hydroforming processes and reduce the number of costly trials.

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“…To include shear or thickness stresses, the traditional instability theories have been extended to non-planar stress states, by Eyckens et al [4], Allwood et al [5], Banabic et al [6], Assempour et al [7] and van den Boogaard et al [8]. Their calculations predict enhanced forming limits due to the stabilizing effect of out-of-plane shear and thickness stresses.…”

Section: Introductionmentioning

confidence: 99%

Physically Based Criterion for Prediction of Instability under Stretch-Bending of Sheet Metal

Perdahcıoğlu

Hou²,

Boogaard

2015

KEM

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Abstract. This research focuses on the prediction of the forming limit of certain Advanced High Strength Steel grades under stretch-bending conditions. For these types of steels it is experimentally observed and shown that when there is a bending component added to the main membrane deformation the formability predicted by the regular FLCs underestimate the material behavior. Due to the added effects of thickness stress due to contact and small radius bending as well as bending stresses, a through-thickness stress gradient forms which gives additional stability to the material beyond the forming limits determined by tests that generate mostly uniform membrane deformation. It is observed experimentally and by the detailed simulations that the cross-sectional stability is not lost instantaneously but gradually. A surface dent forms first on the outer surface and progresses in a stable manner towards the contact side since on the contact side the material has still potential to harden. This process delays the localization of the strains and stabilizes the formation of the local neck. For the prediction of this phenomenon theoretically and using shell elements, a modified incremental form of the maximum tension stability criterion is proposed to be applied at integration points through thickness. It is shown that with this criterion the phenomenon of gradual loss of stability can be captured during stretch-bending with shell elements.

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Forming limit diagrams with the existence of through-thickness normal stress

Cited by 81 publications

References 27 publications

Experimental analysis and theoretical predictions of the limit strains of a hot-dip galvanized interstitial-free steel sheet

Experimental analysis and theoretical predictions of the limit strains of a hot-dip galvanized interstitial-free steel sheet

Forming limit diagram of tubular hydroformed parts considering the through-thickness compressive normal stress

Physically Based Criterion for Prediction of Instability under Stretch-Bending of Sheet Metal

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