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<p>Coupon tests provide an efficient way to characterize sheared edge fracture limits with reduced material usage relative to full-scale stamping trials. Sheared edge fracture limits obtained from the commonly employed conical hole expansion test may not be representative of other in-plane deformation modes encountered in stamped components. Accurate prediction of edge cracks requires consideration of the local boundary conditions which can significantly influence the edge fracture limits. This study examines the influence of deformation mode on the&#xa0;residual edge formability for a 3rd-generation 980&#xa0;MPa advanced high&#xa0;strength steel and two hot-rolled MP800 steels with different microstructures. Conical and flat punch hole expansion, in-plane bending, and edge fracture tensile tests were performed after hole punching with 12% clearance. Fracture strains were measured using digital image correlation (DIC) at multiple lengthscales. The MP800 steels showed strong sensitivity to deformation mode with edge thinning limits differing by more than 10%. The 980GEN3 steel showed a limited sensitivity to the applied boundary conditions. The DIC lengthscale also affected the measured edge thinning with absolute differences of up to 20%. Global edge stretch measures were proposed to improve transferability of the&#xa0;fracture limits obtained from these tests to industrial forming conditions. Finite-element simulations of the coupon tests reinforced the importance of accounting for the deformation mode with good agreement between the predicted&#xa0;data and global edge thinning.</p>

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Quantifying Boundary Condition and Lengthscale Effects During Edge Stretching of AHSS

  • 期刊论文

  • 发表日期：

    2026年5月24日

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  • A. Narayanan,
  • R. Northcote,
  • P. Cleary,
  • J. Smith,
  • E. McCarty,
  • M. Quinones,
  • D. Kanelos,
  • C. Butcher

摘要

Coupon tests provide an efficient way to characterize sheared edge fracture limits with reduced material usage relative to full-scale stamping trials. Sheared edge fracture limits obtained from the commonly employed conical hole expansion test may not be representative of other in-plane deformation modes encountered in stamped components. Accurate prediction of edge cracks requires consideration of the local boundary conditions which can significantly influence the edge fracture limits. This study examines the influence of deformation mode on the residual edge formability for a 3rd-generation 980 MPa advanced high strength steel and two hot-rolled MP800 steels with different microstructures. Conical and flat punch hole expansion, in-plane bending, and edge fracture tensile tests were performed after hole punching with 12% clearance. Fracture strains were measured using digital image correlation (DIC) at multiple lengthscales. The MP800 steels showed strong sensitivity to deformation mode with edge thinning limits differing by more than 10%. The 980GEN3 steel showed a limited sensitivity to the applied boundary conditions. The DIC lengthscale also affected the measured edge thinning with absolute differences of up to 20%. Global edge stretch measures were proposed to improve transferability of the fracture limits obtained from these tests to industrial forming conditions. Finite-element simulations of the coupon tests reinforced the importance of accounting for the deformation mode with good agreement between the predicted data and global edge thinning.