Andraž Maček

Accurate representation of plastic anisotropy is essential for reliable sheet metal forming simulations. However, calibration of advanced anisotropic yield functions typically relies on multiple mechanical tests performed along different loading directions and under various multiaxial stress states. The extensive experimental effort required conflicts with the short lead times demanded by industry. Moreover, many of the stress states that need to be characterized are not relevant to the forming process of interest. Material Testing 2.0 (MT2.0) addresses these limitations by reducing the experimental burden while enabling the design of application-specific experiments that reproduce the stress states encountered during the target forming process. In this paper, we demonstrate the potential of the MT2.0 approach for the efficient and targeted calibration of the widely used Yld2000-2d anisotropic yield function for sheet metals. The proposed methodology requires only a single heterogeneous biaxial tensile test, thereby significantly reducing the required experimental effort. Furthermore, the experiment is specifically designed to probe the first quadrant of the stress space, which is relevant for the targeted forming applications. To this end, a novel cruciform specimen is designed to identify all anisotropy parameters through inverse analysis based on full-field strain measurements. The specimen geometry provides complementary information on the plastic anisotropic response by combining regions subjected to predominantly uniaxial tension along the rolling, transverse, and diagonal directions with regions experiencing biaxial tension. The design minimizes strain gradients, ensuring reliable Digital Image Correlation (DIC) measurements and comparable plastic strain levels across the informative regions. The performance of the identification scheme, based on Finite Element Model Updating (FEMU), is assessed using synthetic DIC data to quantify parameter sensitivity, identifiability, and robustness against measurement noise. For the proposed MT2.0 approach, it is demonstrated that a physically motivated parameterization of the Yld2000-2d yield function significantly improves parameter identifiability. The method is benchmarked against a state-of-the-art calibration procedure for a low-carbon steel sheet, relying on biaxial tensile tests performed under seven different stress ratios. The inversely identified anisotropic yield locus closely reproduces the benchmark response. These findings demonstrate the feasibility of reliable single-test identification of planar plastic anisotropy. Furthermore, they highlight that efficient and robust MT2.0 specimen designs must be developed in conjunction with the selected inverse identification method and full-field measurement technique.

Accurate representation of plastic anisotropy is essential for reliable sheet metal forming simulations. However, calibration of advanced anisotropic yield functions typically relies on multiple mechanical tests performed along different loading directions and under various multiaxial stress states. The extensive experimental effort required conflicts with the short lead times demanded by industry. Moreover, many of the stress states that need to be characterized are not relevant to the forming process of interest. Material Testing 2.0 (MT2.0) addresses these limitations by reducing the experimental burden while enabling the design of application-specific experiments that reproduce the stress states encountered during the target forming process. In this paper, we demonstrate the potential of the MT2.0 approach for the efficient and targeted calibration of the widely used Yld2000-2d anisotropic yield function for sheet metals. The proposed methodology requires only a single heterogeneous biaxial tensile test, thereby significantly reducing the required experimental effort. Furthermore, the experiment is specifically designed to probe the first quadrant of the stress space, which is relevant for the targeted forming applications. To this end, a novel cruciform specimen is designed to identify all anisotropy parameters through inverse analysis based on full-field strain measurements. The specimen geometry provides complementary information on the plastic anisotropic response by combining regions subjected to predominantly uniaxial tension along the rolling, transverse, and diagonal directions with regions experiencing biaxial tension. The design minimizes strain gradients, ensuring reliable Digital Image Correlation (DIC) measurements and comparable plastic strain levels across the informative regions. The performance of the identification scheme, based on Finite Element Model Updating (FEMU), is assessed using synthetic DIC data to quantify parameter sensitivity, identifiability, and robustness against measurement noise. For the proposed MT2.0 approach, it is demonstrated that a physically motivated parameterization of the Yld2000-2d yield function significantly improves parameter identifiability. The method is benchmarked against a state-of-the-art calibration procedure for a low-carbon steel sheet, relying on biaxial tensile tests performed under seven different stress ratios. The inversely identified anisotropic yield locus closely reproduces the benchmark response. These findings demonstrate the feasibility of reliable single-test identification of planar plastic anisotropy. Furthermore, they highlight that efficient and robust MT2.0 specimen designs must be developed in conjunction with the selected inverse identification method and full-field measurement technique.

Material Testing 2.0 (MT2.0) couples full‑field deformation measurements (Digital Image Correlation, DIC) with inverse identification methods (Virtual Fields Method, VFM) to extract constitutive parameters from a small number of heterogeneous experiments. This paper presents the Cut‑Clamp‑Play concept: an integrated industrial MT2.0 solution that unifies specimen design, automated testing hardware, and a computationally efficient VFM identification chain to deliver fast, user‑friendly sheet‑metal characterization. A perforated cruciform specimen is optimized for parameter identifiability of the Yld2000‑2d anisotropic yield function and used in a single biaxial test. A working prototype has been built at KU Leuven and used to collect representative DIC data; the measured displacement/strain response is double‑symmetric, confirming correct mechanical operation. Projected and early prototype results indicate that the Cut‑Clamp‑Play approach can reduce operator actions by roughly 70% and produce identification results within one hour for typical sheet‑metal cases, while further work is required to make the fully automated “Play” stage robust for industrial deployment.

This paper revisits the long-standing question of how to fully characterise the in-plane plastic anisotropy of sheet metals without assembling evidence from multiple standardised tests. The central idea is pragmatic: a single, well-designed heterogeneous biaxial experiment can replace the conventional combination of uniaxial and equibiaxial tests if the specimen and the inverse identification method are co-designed to (i) activate informative stress states and (ii) maintain low strain gradients for accurate digital image correlation measurements. The proposed cruciform specimen is deliberately conceived as a benchmark configuration for full-field inverse identification, with known locations and stress-strain states at which relevant material information is embedded. The approach is coupled with a Finite Element Model Updating framework, enabling all anisotropy parameters of the YLD2000-2d model to be identified from a single full-field dataset. Sensitivity and identifiability analyses demonstrate that a physically based parameter formulation significantly improves the conditioning of the inverse problem. Virtual experimentation confirms the robustness and accuracy of the proposed “one-test” identification strategy.

The accuracy of numerical predictions in sheet metal processes involving multiaxial stress–strain states (e.g., blanking, riveting, and incremental forming) heavily depends on the characterisation of plastic anisotropy under multiaxial loading conditions. A fully calibrated 3D plastic anisotropy model is essential for this purpose. While in-plane material behaviour can be conventionally characterised through uniaxial and equi-biaxial tensile tests, calibrating out-of-plane material behaviour remains a significant challenge. This behaviour, governed by out-of-plane shear stress and associated material parameters, is typically described by out-of-plane shear yielding. These parameters are notoriously difficult to determine, leading researchers to frequently assume isotropic behaviour or identical shear parameters for in-plane and out-of-plane responses. Although advanced calibrations may utilise crystal plasticity modelling, there remains a critical need for macro-mechanical characterisation methods. This paper presents an out-of-plane shear testing and material characterisation procedure based on full-field strain measurements using digital image correlation (DIC). Strains within the shear zone are measured via DIC and employed in the Finite Element Model Updating (FEMU) to identify out-of-plane shear parameters of a 2.42 mm thick, cold-rolled AW5754-H22 aluminium alloy sheet, using the Yld2004-18p yield criterion. Given that the characteristic strain response at this scale may be influenced by local crystal structure behaviour on the surface, this paper evaluates the feasibility of such measurements. Finally, to test the validity of the full-field-based approach, the FEMU-identified parameters are compared against results obtained through a classical optimisation procedure based on force-elongation measurements from the shear zone.