Effect of Anisotropic Yield Functions on the Accuracy of Hole Expansion Simulations for 590 MPa Grade Steel Sheet

Advanced Structured Materials

2015

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A servo-controlled tension-internal pressure testing machine with an optical 3D deformation analysis system (ARAMIS , GOM) was used to measure the multiaxial plastic deformation behavior of a high-strength steel sheet with a tensile strength of 590 MPa for a strain range from initial yield to fracture. Tubular specimens were fabricated by roller bending and laser welding the as-received flat sheet materials. Many linear stress paths in the first quadrant of the stress space were applied to the tubular specimens to measure the forming limit curve (FLC), forming limit stress curve (FLSC), and forming limit plastic work per unit volume (FLPW) of the as-received sheet material in addition to the contours of plastic work and the directions of the plastic strain rates. Differential hardening behavior was observed; the shapes of the work contours constructed in the principal stress space changed with an increase in plastic work. The observed differential hardening behavior was approximated by changing the material parameters and the exponent of the Yld2000-2d yield function as functions of the reference plastic strain. Marciniak-Kuczyński-type forming limit analyses were performed using both the differential hardening model and isotropic hardening models based on the Yld2000-2d yield function. It was found that the material model that is capable of reproducing both the work contours and the directions of the plastic strain rates measured for a strain range close to the fracture limit can give a more effective constitutive model for accurately predicting the FLC, FLSC, and FLPW.T. Hakoyama JSPS Research Fellow (Doctoral Course Students),

Section: Introductionmentioning

confidence: 63%

Effect of Biaxial Work Hardening Modeling for Sheet Metals on the Accuracy of Forming Limit Analyses Using the Marciniak-Kuczyński Approach

Hakoyama

Advanced Structured Materials

2015

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“…Regarding the biaxial tensile testing machines proposed in literature, see [10]. It should be noted that the biaxial tensile test method using a cruciform test piece has proven to be useful for accurately detecting and modeling the deformation behavior of sheet metals under biaxial tension and consequently improves the predictive accuracy of FEA for springback in stretch-bending [11], hole expansion in HSS sheet [12][13], surface deflection in automotive body panels [14], and hydraulic bulge forming of 6000 series aluminum alloy sheets [15]. A cruciform test piece is useful for biaxial load-unload tests of sheet metals [16] [17].…”

Section: Biaxial Tensile Testing Methods Using a Cruciform Test Piece mentioning

confidence: 99%

Multiaxial Stress Tests for Metal Sheets and Tubes for Accurate Material Modeling and Forming Simulations

2014

Acta Metall Slovaca

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This paper is a review of the mechanical testing methods developed by the author's research group: multiaxial stress test methods using a cruciform test piece and a tubular test piece. The former is useful for small strain ranges under several percent while the latter is useful for larger strain ranges (from yielding to fracture). These test methods are useful to determine appropriate materials model for performing accurate metal forming simulations. Special attention is given to the measurement and modeling of the anisotropic plastic deformation behavior of sheet metals commonly used in industry and to the validation of the material models based on phenomenological yield functions for large plastic strain ranges. The effects of material models used in metal forming simulations on the improvement of the predictive accuracy for forming defects are also discussed.Keywords: anisotropy; finite element analysis; formability; material model; mechanical test; sheet metal forming; yield function IntroductionThe establishment of trial-and-error-less manufacturing enhanced by forming simulation methods such as finite element analysis (FEA) is strongly desired in industry to shorten the product development period and reduce costs for prototype manufacturing. Improvement of the predictive accuracy for defect formation (such as fracture and springback) using FEA is key to realizing trial-and-error-less manufacturing. A material model is one of the key factors that affect the accuracy of FEA [1][2]. In metal forming processes, materials are subjected to multiaxial stress states and stress reversals. Therefore, the validity of the material models used in FEA should also be checked by multiaxial stress tests and stress reversal tests [3]. This paper reviews advanced material test methods for metal sheets and tubes to determine accurate material models for use in metal forming simulations. Special attention is given to the anisotropic plastic deformation behavior of lightweight metals, such as high-strength steels (HSS), aluminum alloys, and pure titanium sheets commonly used in industry, and to the validation of the material models based on anisotropic yield functions determined for large plastic strain ranges. Additionally, the effects of the material models on the improvement of the predictive accuracy of the forming simulations are discussed.

“…These methods were used to experimentally determine a proper material model for tubular and sheet materials. It was demonstrated that the selection of an appropriate yield function improves the accuracy of defect prediction in forming simulations of stretching, 13) minute surface deflection, 14) stretch flange forming, 15,16) and hydraulic bulge forming. 17) Recently, Suzuki 18) conducted hole expansion forming experiments and a finite element analysis (FEA) of a solute-strengthened 440-MPa hot-rolled steel sheet (sheet thickness: 2.0 mm) and a precipitationstrengthened 590-MPa hot-rolled steel sheet (sheet thickness: 2.3 mm) and found that a higher-order yield function is superior to Hill's quadratic yield function in predicting the thickness distribution.…”

Section: Materials Modeling Of Hot-rolled Steel Sheet Considering Differential Hardening and Hole Expansion Simulationmentioning

confidence: 99%

Material Modeling of Hot-Rolled Steel Sheet Considering Differential Hardening and Hole Expansion Simulation

Nomura¹,

2022

ISIJ Int.

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The elastoplastic deformation behavior of a 440-MPa hot-rolled steel sheet subjected to many linear stress paths is precisely measured using biaxial tensile tests with cruciform specimens (ISO 16842: 2014) and multiaxial tube expansion tests to determine appropriate material models for finite element analysis (FEA). It is found that the Yld2000-2d yield function correctly reproduces the contours of plastic work and the directions of the plastic strain rates. Differential hardening (DH) models are determined by varying the values of the exponent and material parameters for the Yld2000-2d yield function as functions of the reference plastic strain. Moreover, a finite element analysis of hole expansion in the test material is performed. The DH model correctly predicts the minimum thickness position, which matches the fracture position of the specimen in the experiment.