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Technical Paper

A Novel Approach for Generating a Full-Range Tensile Stress-Strain Curve

A new method has been developed to measure full stress-strain curves using Digital Image Correlation (DIC) for Advanced High Strength Steels (AHSS). With the post-necking strain measured by the built in-house DIC system during tensile tests, stress-strain data for AHSS beyond uniform elongation up to fracture can be determined. In this paper, the technique to generate full stress-strain curves by DIC is introduced. The measured stress-strain curves are compared with those obtained by extrapolation methods. The measured stress-strain data generated by the new method is validated by finite element analysis (FEA).
Technical Paper

Characterization of Edge Fracture in Various Types of Advanced High Strength Steel

In vehicle crash events there is the potential for fracture to occur at the processed edges of structural components. The ability to avoid these types of fractures is desired in order to minimize intrusion and optimize energy absorption. However, the prediction of edge cracking is complicated by the fact that conventional tensile testing can provide insufficient data in regards to the local fracture behavior of advanced high strength steels. Fracture prediction is also made difficult because there can be inadequate data on how the cutting processes used for hole piercing and blanking affect the edge condition. In order to address these challenges, research was undertaken to analyze edge fracture in simple test pieces configured with side notches and center holes. Test specimens were made from a number of advanced high strength steels including 590R (C-Mn), 780T (TRIP), 980Y (dual phase) and hot stamp 1500 (martensitic).
Journal Article

Determination of Forming Limit and Fracture Limit Curves Using Digital Image Correlation

Forming limit curve (FLC) and fracture forming limit curve (FFLC) are valuable tools for failure prediction in forming simulation and die try-out in press shops. In this paper, methods are presented to determine FLC and FFLC for sheets of advanced high strength steels (AHSS) using digital image correlation (DIC). Dome tests were conducted on AHSS specimens using DIC system for strain measurement. For generating FLCs, two approaches are introduced to determine the onset of localized necking by analyzing the strain history at critical locations, one of which has been implemented into the commercial DIC software Vic-3D (Correlated Solution inc.). For determination of FFLC, a method for measuring fracture strains based on the strain path evolution is presented. The measured FLCs for several AHSS were compared to the FLCs using ISO 12004-2, and conventional North American experimental measurements and empirical equations.
Journal Article

Measurement of Fracture Strains for Advanced High Strength Steels (AHSS) Using Digital Image Correlation

Predicting fracture behavior of Advanced High Strength Steels (AHSS) on both manufacturing and crash simulations is becoming more and more important with the wide use of AHSS in automotive industry. The accurate measurement of fracture strains is a critical input for predicting failure in FEA simulations. It is well known that fracture is a highly localized behavior and fracture strain is gauge or size dependent. In this paper, a full field measurement technique, Digital Image Correlation (DIC), is employed to measure gauge-dependent fracture strains for several Advanced High Strength Steels (AHSS) under tensile test conditions and Limit Dome Height (LDH) tests. Applications of the fracture strains for FEA simulation are discussed.
Technical Paper

Study on Metal Sheet Ductile Fracture using Square Punch Test

This study introduces a new practical calibration approach of ductile fracture models by performing square punch tests on metal sheets. During square punch tests, ductile fracture occurs at either the corner of die or punch radius when applying different clamping loads and lubrication conditions. At the corner of die radius, in-plane pure shear is induced at the intersection between the side-walls and the flange by combined tension and compression. On the other hand, the material at the corner of the punch radius is under combined bending and biaxial tension. The material studied in this paper is advanced high strength steel (AHSS) DP780 from ArcelorMittal. Isotropic J2 plasticity model with mixed Swift-Voce hardening rule is calibrated from uniaxial tensile tests.