Localized forming limit analysis of substrate-supported metals: Influence of yield-dependent necking bound angle

2021 ◽  
pp. 095440542110573
Author(s):  
Ali Bandizaki ◽  
Asghar Zajkani ◽  
Saeed Moulood
Keyword(s):  
Anisotropy Parameter ◽  
High Strength Steels ◽  
High Strength ◽  
Theoretical Models ◽  
Plastic Instability ◽  
Forming Limit ◽  
Yield Criteria ◽  
Advanced High Strength Steels ◽  
Theory Application ◽  
Stress States

In this paper, the influence of functional elastomeric substrate-supported layers for enhancing potential resistance capability against localized plastic failure of advanced high strength steels is considered based on a localized necking model of vertex theory. Application of this structure leads to postponing the plastic instability of the metallic part. By defining diffuse and localized modes of deformation in a general framework, the theoretical models are developed to predict necking limits at several stress states. In addition, the results of the Hookean and neo-Hookean elastomers are compared in terms of strain hardening with the anisotropy parameter of Hill’s yield criteria. Since necking band angle (NBA) is a principal factor for the necking prediction, its effect on bifurcation events is evaluated specifically for different ratios of stress rate, and quadratic and non-quadratic yield criteria. This analysis is performed by proposing a supported and yield-dependent necking bound angle (YD-NBA). All considerations are done by providing equilibrium conditions governed over the NBA. Finally, obtained results indicate good agreements between several theoretical considerations and experimental data.

Effect of Strain Paths on Formability Evaluation of TRIP Steels

2010 ◽  
Vol 89-91 ◽  
pp. 214-219 ◽  
Author(s):  
David Gutiérrez ◽  
A. Lara ◽  
Daniel Casellas ◽  
Jose Manuel Prado
Keyword(s):  
Strain Path ◽  
High Strength Steels ◽  
High Strength ◽  
Test Method ◽  
Forming Limit ◽  
Trip Steels ◽  
Advanced High Strength Steels ◽  
Strain Paths ◽  
Analysis System

The Forming Limit Diagrams (FLD) are widely used in the formability analysis of sheet metal to determine the maximum strain, which gives the Forming Limit Curve (FLC). It is well known that these curves depend on the strain path during forming and hence on the test method used to calculate them. In this paper, different stretching tests such as the Nakajima and the Marciniak tests were performed, with different sample geometries to obtain points in different areas of the FLD. An optical analysis system was used, which allows following the strain path during the test. The increasing use of advanced high-strength steels (AHSS) has created an interest in determining the mechanical properties of these materials. In this work, FLCs for a TRIP steel were determined using Nakajima and Marciniak tests, which revealed different strain paths depending on the type of test. Determination of the FLCs was carried out following the mathematical calculations indicated in the ISO 12004 standard and was also compared with an alternative mathematical method, which showed different FLCs. Finally, the tests were verified by comparing the strain paths of the Nakajima and Marciniak tests with a well-known mild steel.

Experimental Study on Shear Fracture of Advanced High Strength Steels

2008 ◽  
Author(s):  
Hua-Chu Shih ◽  
Ming F. Shi
Keyword(s):  
Computer Simulations ◽  
Shear Fracture ◽  
High Strength Steels ◽  
High Strength ◽  
Thickness Ratio ◽  
Forming Limit ◽  
Forming Limit Curve ◽  
Advanced High Strength Steels ◽  
Stretch Bending ◽  
Type Of Fracture

Fracturing in a tight radius during stretch bending has become one of the major manufacturing issues in stamping advanced high strength steels (AHSS), particularly for those AHSS with a tensile strength of 780 MPa or higher. Computer simulations often fail to predict this type of fracture, since the predicted strains are usually below the conventional forming limit curve. In this study, a laboratory stretch-forming simulator (SFS) is used to simulate the stretch bending of AHSS in stamping to develop a possible failure criterion for use in computer simulations. The SFS simulates the stamping process when sheet metal is drawn over a die radius with tension applied. Various sizes of die radius are used during the experiment, and the shear fracture phenomenon can be recreated using this test for a given material and gauge. It is found that shear fracture depends not only on the radius-to-thickness ratio but also on the tension/stretch level applied to the sheet. The experimental data show that a critical radius-to-thickness ratio for shear fracture exists for any given material and gauge, but this ratio is not unique and it depends upon the amount of tension imposed during the bending.

Forming Limit Curves and Forming Limit Stress Curves for Advanced High Strength Steels

2013 ◽  
Vol 773-774 ◽  
pp. 109-114 ◽  
Author(s):  
Sansot Panich ◽  
Frédéric Barlat ◽  
Vitoon Uthaisangsuk ◽  
Surasak Suranuntchai ◽  
Suwat Jirathearanat
Keyword(s):  
Yield Criterion ◽  
Flow Behavior ◽  
Constitutive Models ◽  
High Strength Steels ◽  
High Strength ◽  
Forming Limit ◽  
Advanced High Strength Steels ◽  
Hardening Law ◽  
Limit Stress ◽  
Forming Limit Curves

Experimental and numerical investigations using Forming Limit Curve (FLC) and Forming Limit Stress Curve (FLSC) were carried out for two Advanced High Strength Steel (AHSS) grades DP780 and TRIP780. The forming limit curves were experimentally determined by means of Nakazima stretching test. Then, both FLC and FLSC were analytically calculated on the basis of the Marciniack-Kuczinsky (M-K) model. The yield criteria Barlat2000 (Yld2000-2d) were employed in combination with the Swift and modified Voce strain hardening laws to describe plastic flow behavior of the AHS steels. Hereby, influence of the constitutive models on the numerically determined FLCs and FLSCs were examined. Obviously, the forming limit curves predicted by the M-K model applying the Yld2000-2d yield criterion and Swift hardening law could fairly represent the experimental limit curves. The FLSCs resulted from the experimental data and theoretical model were also compared.

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.

scholarly journals Hydrogen-related challenges for the steelmaker: the search for proper testing

2017 ◽  
Vol 375 (2098) ◽  
pp. 20160408 ◽  
Author(s):  
R. G. Thiessen
Keyword(s):  
Standardized Test ◽  
High Strength Steels ◽  
High Strength ◽  
Advanced High Strength Steels ◽  
Passenger Safety ◽  
Transportation Sector ◽  
Wide Range ◽  
Increased Sensitivity ◽  
Stress States ◽  
Increased Strength

The modern steelmaker of advanced high-strength steels has always been challenged with the conflicting targets of increased strength while maintaining or improving ductility. These new steels help the transportation sector, including the automotive sector, to achieve the goals of increased passenger safety and reduced emissions. With increasing tensile strengths, certain steels exhibit an increased sensitivity towards hydrogen embrittlement (HE). The ability to characterize the material's sensitivity in an as-delivered condition has been developed and accepted (SEP1970), but the complexity of the stress states that can induce an embrittlement together with the wide range of applications for high-strength steels make the development of a standardized test for HE under in-service conditions extremely challenging. Some proposals for evaluating the material's sensitivity give an advantage to materials with a low starting ductility. Despite this, newly developed materials can have a higher original elongation with only a moderate reduction in elongation due to hydrogen. This work presents a characterization of new materials and their sensitivity towards HE. This article is part of the themed issue ‘The challenges of hydrogen and metals’.

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