Prediction of Stretch Flangeability Limits of Advanced High Strength Steels using the Hole Expansion Test

In this study, the effect of the material anisotropies of hot-rolled high-strength steel sheet on localized deformation behavior in hole expansion test has been investigated experimentally. First, the hole expansion test with the circular hole has been conducted to investigate the effect of anisotropies of material properties on the localized deformation behavior around the hole edge. Next, the hole expansion test with the oval hole has been conducted to investigate the effect of the major axis direction of the oval hole on the localized deformation behavior around the hole edge. As a result, it was clarified that the effect of anisotropies of r-value and n-value on the localized deformation behavior is strong, especially the anisotropy of n-value.

Download Full-text

Influence of Microstructure on Damage in Advanced High Strength Steels

Materials Science Forum ◽

10.4028/www.scientific.net/msf.706-709.925 ◽

2012 ◽

Vol 706-709 ◽

pp. 925-930 ◽

Cited By ~ 12

Author(s):

Frank Hisker ◽

Richard Thiessen ◽

Thomas Heller

Keyword(s):

Work Hardening ◽

Tensile Testing ◽

Failure Modes ◽

Tensile Elongation ◽

High Strength Steels ◽

High Strength ◽

Body Parts ◽

Hole Expansion ◽

Advanced High Strength Steels ◽

Dp Steels

AHSS (Advanced High Strength Steels) combine high strength and good ductility. Their outstanding forming and work-hardening behavior predestines these steels for fabrication of strength relevant structural elements and automobile body parts. To characterize a material, not only tensile, but also hole-expansion and bending behavior are important and help predict the stretch-flange-formability. In this study, detailed analyses of the correlation between these three tests and the damage mechanisms during forming have been performed for selected steels. The results show that for AHSS one should differentiate between “local” and “global” failure. Furthermore, not only are certain materials more sensitive to local or global damage, but also various testing methods tend to provoke either local or global damage. Tensile testing provokes global failure whereas hole-expansion tends to induce local failure. A specimen fails during bending with a mixture of local and global modes. These failure modes are strongly attributed to the microstructure. DP-steels yield high elongation during tensile testing and poorer hole-expansion values. High-resolution EBSD has revealed that the microstructure of DP-steels is sensitive to localized damage, which is compensated by work-hardening around damaged regions and thus shifts the loading to un-hardened regions. This makes DP-microstructures well-suited to tensile loading but sensitive to hole-expansion. CP-steels of comparable strength show poorer tensile elongation and higher hole-expansion ratios due to a microstructure which is not sensitive to localized failure (but has limited capacity for work-hardening). The failure mode in TRIP-steels exhibits a similar character as in DP-steels, but only after the martensitic transformation of retained austenite.

Download Full-text

Description of anisotropic properties of sheet metal based on spline curves and hole expansion test simulation of high-strength steel

International Journal of Solids and Structures ◽

10.1016/j.ijsolstr.2020.07.010 ◽

2020 ◽

Vol 202 ◽

pp. 672-684

Author(s):

Toshiro Amaishi ◽

Hideo Tsutamori ◽

Takeshi Nishiwaki ◽

Takaaki Kimoto

Keyword(s):

Sheet Metal ◽

High Strength Steel ◽

High Strength ◽

Hole Expansion ◽

Anisotropic Properties ◽

Expansion Test ◽

Hole Expansion Test ◽

Spline Curves

Download Full-text

Forming Performance of 800MPa Grade Advanced High Strength Steels

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.455.173 ◽

2013 ◽

Vol 455 ◽

pp. 173-178 ◽

Cited By ~ 2

Author(s):

Mei Zhang ◽

Yu Xiang Ning ◽

Jun Zhang ◽

Zi Wan ◽

Tao Wang

Keyword(s):

High Strength Steels ◽

High Strength ◽

Expansion Ratio ◽

Hole Expansion ◽

Advanced High Strength Steels ◽

Hsla Steels ◽

Blank Holding Force ◽

Hole Expansion Ratio ◽

Test Hole ◽

Springback Behavior

800MPa grade Advanced High Strength Steels (AHSS), including Complex Phase steel CP800 and Ferrite-Bainite steel FB800, were chosen to test the forming performance in different test conditions and compared with the reference traditional high strength low alloy (HSLA) steels HR700LA. Tensile test, hole expansion (HE) test, and HAT shape stamping test were taken to investigate the forming performance of the materials. Test results indicated that the studied 800MPa grade AHSS showed a better strength ductility balance compared with the reference steel. Among all the steels researched, FB800 showed the best hole expansion ratio (HER), and CP800 the worst. Springback angles of AHSS after HAT shape stamping tests were markedly smaller than those of HR700LA steels, though the springback angles of HR700LA decreased continuously with blank holding force (BHF) increasing. Steel FB800, CP800S and CP800B had much better shape stability compared with steels HR700LA. AHSS showed much smaller springback behavior under the same stamping condition, especially for steels CP800-B, FB800-2 and FB800-1. When increasing the BHF to 100KN, AHSS showed the largest springback deformation. Among the three kinds of CP800 steels researched, steel CP800-B indicated outstanding springback restrain trend in BHF further increasing attempt. So, springback behavior could be restricted obviously by using a larger BHF in AHSS CP800B forming operations.

Download Full-text

An Innovative Shearing Process for AHSS Edge Stretchability Improvements

Journal of Manufacturing Science and Engineering ◽

10.1115/1.4005460 ◽

2011 ◽

Vol 133 (6) ◽

Cited By ~ 16

Author(s):

Hua-Chu Shih ◽

Ming F. Shi

Keyword(s):

High Strength Steel ◽

High Strength Steels ◽

High Strength ◽

Straight Edge ◽

Forming Process ◽

Expansion Test ◽

Advanced High Strength Steels ◽

Sheared Edge ◽

Shear Edge

A beveled shear hole piercing process has recently been developed for advanced high strength steel (AHSS). The preliminary results have shown the new process is able to improve the quality of the sheared edge and the edge stretchability of AHSS. The goal of the current study is to optimize the beveled shearing process and identify the optimal shearing conditions for AHSS. Four different advanced high strength steels, including DP600, DP780, TRIP780, and DP980 with various thicknesses together with a conventional high strength steel, HSLA50, are selected in this study. The hole expansion test is used to evaluate the effect of shear edge conditions on the edge stretchability. The results show that an optimal selection of the die clearance and the shearing angle results in a less damaged edge, which significantly delays edge fracture in the forming process and increases the edge stretchability for AHSS. To further validate the advantages of the beveled shearing process in improving the shear edge quality of AHSS, a straight edge shearing device with the capability of adjusting the shearing variables (rake angles and die clearance) with respect to different sheet thicknesses was also developed and built. The edge stretchability of the straight edge sheared specimen was then evaluated using the sheared edge tension test. A similar trend to the beveled shear hole piercing process of AHSS is observed, and a significant improvement in the edge stretchability is also obtained with optimal shearing conditions.

Download Full-text