The effect of stress state on ductility in the moderate stress triaxiality regime of medium and high strength steels

2012 ◽  
Vol 65 (1) ◽  
pp. 203-212 ◽  
Author(s):  
Imad Barsoum ◽  
Jonas Faleskog ◽  
Shivinandan Pingle
Keyword(s):  
Stress State ◽  
Stress Triaxiality ◽  
High Strength Steels ◽  
High Strength ◽  
Moderate Stress

Failure Strain Criterion Accounting for the Effect of Material Strength

2021 ◽  
Author(s):  
N. Baghous ◽  
I. Barsoum
Keyword(s):  
Stress State ◽  
Ultimate Strength ◽  
Failure Criterion ◽  
Stress Triaxiality ◽  
Ductile Failure ◽  
High Strength Steels ◽  
Local Failure ◽  
Material Strength ◽  
Lode Parameter ◽  
Steel Grades

Abstract The objective of this study is to investigate the effect of the Lode parameter on different material strengths. Recent work has shown that ductile failure highly depends on the stress state characterized by both the stress triaxiality T and the Lode parameter L, which is related to the third deviatoric stress invariant. Thus, for six different steel grades, two different specimen geometries were manufactured to account for two different Lode parameters (L = −1 and L = 0), whereas T is controlled by introducing different sized notches at the center of the specimens. By performing tensile experiments and running finite element simulations, the ductile failure loci of the six materials showed variations between the two specimen geometries, indicating that the failure highly depends on the stress state characterized by both T and L. This indicates the need to reassess the ductile local failure criterion in the ASME codes that only accounts for T as a stress state measure. A Lode sensitivity parameter LS is defined based on the experimental results and revealed that the steel grades with ultimate strength higher than a certain threshold value (450 MPa) exhibit sensitivity to the Lode parameter, and the results showed that the LS increases with increase in the ultimate strength of the steel grade. The results were incorporated to enhance the original ASME local failure criterion by accounting for T, L, and LS to accurately assess ductile failure in high-strength steels.

scholarly journals Stress state dependency of unloading behavior in high strength steels

2017 ◽  
Vol 207 ◽  
pp. 179-184 ◽  
Author(s):  
Satoshi Sumikawa ◽  
Akinobu Ishiwatari ◽  
Jiro Hiramoto ◽  
Fusahito Yoshida ◽  
Till Clausmeyer ◽  
...  
Keyword(s):  
Stress State ◽  
High Strength Steels ◽  
High Strength ◽  
State Dependency

Fracture Characterisation by Butterfly-Tests and Damage Modelling of Advanced High Strength Steels

2021 ◽  
Vol 883 ◽  
pp. 294-302
Author(s):  
Bernd Arno Behrens ◽  
Kai Brunotte ◽  
Hendrik Wester ◽  
Matthäus Dykiert
Keyword(s):  
Stress State ◽  
Shear Fracture ◽  
Pure Shear ◽  
Testing Machine ◽  
High Strength Steels ◽  
High Strength ◽  
Fracture Initiation ◽  
Forming Limit ◽  
Advanced High Strength Steels ◽  
Damage Models

Advanced High Strength Steels (AHSS) are widely used in today's automotive structures for lightweight design purposes. FE simulation is commonly used for the design of forming processes in automotive industry. Therefore, besides the description of the plastic flow behaviour, also the definition of forming limits in order to efficiently exploit the forming potential of a material is required. AHSS are prone for crack appearances without prior indication by thinning, like exemplary shear fracture on tight radii and edge-fracture, which can not be predicted by conventional Forming Limit Curve (FLC). Stress based damage models are able to do this. However, the parameterisation of such models has not yet been standardised. In this study a butterfly specimen geometry, which was developed at the Institute for Forming Technology and Machines (IFUM), was used for a stress state dependent fracture characterisation. The fracture behaviour of two AHSS, CP800 and DP1000, at varied stress states between pure shear and uniaxial loading was characterised by an experimental-numerical approach. For variation of the stress state, the specimen orientation relative to the force direction of the uniaxial testing machine was orientated at different angles. In this way, the relevant displacement until fracture initiation was determined experimentally. Subsequently, the experimental tests have been numerically reproduced giving information about the strain and stress evolution in the crack impact area of the specimen for the experimentally identified fracture initiation. With the help of this testing procedure, two different stress-based damage models, Modified Mohr-Coulomb (MMC) and CrachFEM, were parameterised and compared.

The Sensitivity to the Lode Parameter in Ductile Failure of Tubular Steel Grades

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
I. Barsoum ◽  
M. A. Al-Khaled
Keyword(s):  
Stress State ◽  
Ultimate Strength ◽  
Stress Triaxiality ◽  
Ductile Failure ◽  
High Strength ◽  
Pressure Vessels ◽  
Electron Microscopic ◽  
Lode Parameter ◽  
Steel Grades ◽  
Failure Locus

Ductile failure in steels is highly controlled by the stress state, characterized by the stress triaxiality (T) and the Lode parameter (L). The ASME Boiler and Pressure Vessel Code requires pressure vessels to be designed to resist local ductile failure. However, the standard does not account for the Lode parameter dependence in its failure locus. In this study, the influence of the stress state, characterized T and L, on the ductility of ASME tubular product steel grades is investigated. Two seamless pipes of midstrength carbon steel SA-106 Gr. B and high-strength superduplex steel SA-790 were considered. Ring specimen geometries for plane strain (PS) stress state (L = 0) and tensile stress (TS) state (L = −1) are utilized to establish the ductile failure locus in terms of T and L for the two steels. The experimental results (EXP) show that the effect of the Lode parameter on the failure locus for the SA-106 Gr. B steel is insignificant, whereas for the SA-790 steel, the effect is rather significant. A parameter SL is introduced in order to quantify the sensitivity of the failure locus to the Lode parameter. It is found that for materials with ultimate strength lower than about 550 MPa, the sensitivity to L is insignificant (SL ≈ 1), whereas for materials with ultimate strength higher than 550 MPa, the sensitivity to L could be significant (SL > 1). Scanning electron microscopic (SEM) analysis of the fracture surfaces revealed that the sensitivity to L is closely associated with the rupture micromechanisms involved.

A Stress-State Related Void Coalescence Criterion and its Validation

2010 ◽  
Vol 44-47 ◽  
pp. 2656-2660
Author(s):  
Zeng Tao Chen ◽  
Rahul Datta
Keyword(s):  
Stress State ◽  
Volume Fraction ◽  
Cell Model ◽  
Stress Triaxiality ◽  
High Strength Steels ◽  
Void Volume Fraction ◽  
Void Volume ◽  
Void Coalescence ◽  
Element Analysis ◽  
Critical Void

We propose a new critical void volume fraction (fc) criterion that identifies the onset of void coalescence based on the stress state of the material as compared to the definition of the phenomenological criterion by Tvergaard and Needleman [1], where void coalescence is predicted based merely on a constant value for critical void volume fraction. The new fc criterion is obtained using the finite element analysis of the unit cell model of clustered voids. Validation of this new criterion is done by implementing the new coalescence criterion into the Gurson-Tvergaard-Needleman (GTN) [1-3] model and simulating the ductile fracture experiment of a series of angularly notched sheet samples of dual phase (DP), advanced high strength steels (AHSS). A methodology has been devised to construct a stress triaxiality-based void coalescence criterion. Validation of the methodology has been performed using tensile tests of angularly notched samples of DP490 AHSS. Experimental data is compared with FE simulations in order to verify the dependency of void coalescence on stress triaxiality.

Features of welding technology for pipes from high-strength steels

2017 ◽  
Vol 7 (6) ◽  
pp. 54-59
Author(s):  
Nikolay G. Goncharov ◽  
◽  
Oleg I. Kolesnikov ◽  
Alexey A. Yushin ◽  
◽  
...  
Keyword(s):  
High Strength Steels ◽  
High Strength ◽  
Welding Technology
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