Abstract. Forming Limit Curve (FLC) is a well-known tool for the evaluation of failure in sheet metal process. However, its experimental determination and evaluation are rather complex. From theoretical point of view, FLC describes initiation of the instability not fracture. During the last years Digital Image Correlation (DIC) techniques have been developed extensively. Throughout this paper, all the measurements were done using DIC and as it is reported in the literature, different approaches to capture necking and fracture phenomena using Cross Section Method (CSM), Time dependent Method (TDM) and Thinning Method (TM) were investigated. Each aforementioned method has some advantages and disadvantages. Moreover, a cruciform specimen was used in order to cover whole FLC in the range between uniaxial to equi-biaxial tension and as an alternative for Nakajima test. Based on above-mentioned uncertainty about the fracture strain, some advanced numerical failure models can describe necking and fracture phenomena accurately with consideration of anisotropic effects. It is noticeable that in this paper, dog-bone, notch and circular disk specimens are used to calibrate Johnson-Cook (J-C) fracture model. The results are discussed for mild steel DC01.

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A well-known method of materials formability description is the Forming Limit Diagram (FLD). In FLDs/FLC (Forming Limit Curve) a plot of major and minor principal strains in the plane of deformed sheet where necking takes place is represented. The current paper is dealing with anisotropy influence on FLC. This effect is going to be studied with the use of mild steel DC01. Hills anisotropic criterion is considered here and for its application experimental investigation has to be carried out in order to provide input data for the model applied. Uniaxial tensile tests were performed for basic characterisation of sheet samples with the use of contact-less measuring devices. In order to assess the anisotropy experimentally, the specimens were extracted and tested in Rolling Direction (RD), Transverse Direction (TD) and 45° Skew Direction (SD) for the Lankford ratios determination. Detailed stress state description of the material investigated was carried out with the use the stress triaxiality and Lode angle parameter. Therefore, transformations from conventional space into stress state provide a profound insight into the necking phenomenon. According to the experimental and numerical results it was found that it is necessary to take anisotropy effects into account for the material investigated.Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

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During recent years, material characterization based on miniature tensile specimens has been investigated extensively. The Small Punch Test (SPT) is often used for determination of tensile properties but alternative miniature tensile specimen geometries have been suggested due to the limitations of the SPT specimen geometry. However, compared to SPT, the Micro-Tensile Test (M-TT) has a significant advantage since it does not need previous established correlations and enables direct results conversion into standard terms. In this paper, the applicability of the M-TT is investigated for material characterization including Lankford coefficients, hardening laws and stress-strain curves. For this purpose, mild steel DC01 M-TT samples were extracted from sheet in Rolling, Transverse and Diagonal Directions. Moreover, M-TT samples were machined to achieve different thicknesses for indicating thickness effects on strain path.