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Lode Parameter Dependence and Quasi-Unilateral Effects in Continuum Damage Mechanics: Models and Applications in Metal Forming
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Lode Parameter Dependence and Quasi-Unilateral Effects in Continuum Damage Mechanics: Models and Applications in Metal Forming

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Abstract:

This work concerns with two successive modifications of the Lemaitre's damage model tomeet the requirements of formability prediction for today's modern steels. The first one is the quasiunilateraldamage evolution which modifies the damage driving force by scaling the elastic energyrelease rate due to compressive principal stress components. The second one is the shear modificationby which the damage rate is multiplied by a normalized maximum shear stress dependent factor.With the assumption of non-rotating principal axes of deformation, proportional strain paths and rigidplasticity, closed form expressions for the isochronous fracture surfaces are derived for each modelvariant and resulting surface plots at various spaces are compared. The findings show that the formermodification not only remedies the pathological reflective symmetry of the fracture surface acrossthe plane with vanishing stress triaxiality ratio, but also allows hindering fracture under uniaxialcompression. The latter modification by adding a direct Lode parameter dependence to the damageevolution function allows prediction of premature fracture at generalized shear stress states, a conditionobserved for certain advanced high strength metallic sheets. Parameter calibration is realized foreach model variant using the experimental data from the literature. It is shown that the fracture modelwith both the shear modification and the quasi-unilateral enhancement shows the best fitting quality.Finally, the models are implemented as user subroutines for ABAQUS/EXPLICIT and used in predictionof initiation and propagation of cracks for a series of deep-drawing punch tests. A good agreementwith the outputs reported in the literature is observed in terms of the shear damage occurrence zonesas well as corresponding punch force-displacement diagrams.

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Periodical:

Key Engineering Materials (Volumes 651-653)

Pages:

187-192

DOI:

https://doi.org/10.4028/www.scientific.net/KEM.651-653.187

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Online since:

July 2015

Authors:

Celal Soyarslan*, Helmut Richter, Swantje Bargmann

Keywords:

Continuum Damage Mechanics, Ductile Fracture, Lode Parameter Dependence, Metal Forming, Quasi-Unilateral Damage

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© 2015 Trans Tech Publications Ltd. All Rights Reserved

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