Constitutive, Formability, and Fracture Characterization of 3rd Gen AHSS with an Ultimate Tensile Strength of 1180 MPa

Abstract

<div class="section abstract"><div class="htmlview paragraph">The superior formability and local ductility of the emerging class of third generation of advanced high-strength steels (3rd Gen AHSS) compared to their conventional counterparts of the same strength level offer significant advantages for automotive lightweighting and enhanced crash performance. Nevertheless, studies on the material behavior of 3rd Gen AHSS have been limited and there is some uncertainty surrounding the applicability of developed methodologies for conventional dual-phase (DP) steels to this new class of AHSS. The present paper provides a comprehensive study on the quasi-static and dynamic constitutive behavior, formability characterization and prediction, and the fracture behavior of two commercial 3rd Gen AHSS with an ultimate strength of 1180 MPa that will be contrasted with a conventional DP1180. The hardening response to large strain levels was determined experimentally using tensile and shear tests and then validated with 3-D simulations of tensile tests. In general, the strain rate sensitivity of the two 3rd Gen AHSS was significantly different as one grade exhibited larger transformation-induced behavior. The in-plane formability of the three 1180 MPa steels determined using Marciniak tests was similar but with a stark contrast in the local formability for the 3rd Gen AHSS. The forming limit curves could be accurately predicted using the experimentally measured hardening behaviour and the modified Bressan-Williams through-thickness shear model. An efficient experimental approach to fracture characterization for AHSS was developed that exploits tool contact and bending to obtain fracture strains on the surface of the specimen by suppressing necking. Miniature conical hole expansion and biaxial punch tests are used along with the VDA 238-100 bend test.</div></div>

Experimental and Numerical Fracture Characterization of DP1180 Steel in Combined Simple Shear and Uniaxial Tension

“…The image scale for the tensile tests was 0.012 mm/pixel, and since the speckle pattern governs the subset size, the subset was fixed at 31 pixels for both geometries. The step size and strain filter were then varied to obtain different VSG sizes using Equation (9). The DIC camera frame rate is especially important in fracture characterization to capture the fracture location.…”

“…It is emphasized that the DP1180 steel used in the study is commercially available. Additional information regarding the characterization of the same lot of DP1180, encompassing its shear behavior, formability, and constitutive properties, can be found in the following works: Khameneh et al [39], Fast-Irvine et al [38], Butcher et al [40], Noder et al [9], and Abedini et al [37,41]. Furthermore, an extensive volume of test data for the same lot of DP1180 steel is publicly available as part of the Numisheet 2022 fracture benchmark on non-linear strain paths [42].…”

“…Novel test methods have been developed to suppress necking instabilities and obtain proportional loading until fracture. Examples include the conical hole expansion and hole tension tests for uniaxial tension [6][7][8], the VDA238-100 v-bend and dihedral punch tests for plane strain tension [9,10], and miniature biaxial punch tests [11,12]. Fracture characterization in simple shear has been challenging due to its high fracture strains and propensity for premature edge cracking in tension [13].…”

Evaluation of Crashworthiness Using High-Speed Imaging, 3D Digital Image Correlation, and Finite Element Analysis

“…The SMM was used to get the post-yield flow stress behaviour. Due to the relatively low anisotropy reported in previous investigations of AHSS grades [16,[29][30][31][32], this article took advantage of the isotropic version of the SMM with a von Mises yield criterion to characterise the material flow behaviour and to calibrate a plane-stress failure locus.…”