ASTM E2218-23 PDF

SIGNIFICANCE AND USE 5.1 The forming limit curve (FLC) is specific to the material sampled. It can change if the material is subjected to cold work or any annealing process. Thus, two samples from a given lot of material can produce different curves if their processing is varied. 5.2 The processing history of the material must be known if the test is to be considered representative of a grade of a product. 5.3 A forming limit curve (FLC) defines the maximum (limiting) strain that a given sample of a sheet metal can undergo for a range of forming conditions, such as deep drawing, plane strain, biaxial stretching, and bending over a radius in a press and die drawing operation, without developing a localized zone of thinning (localized necking) that would indicate incipient failure. 5.3.1 FLCs may be obtained empirically by using a laboratory hemispherical punch biaxial stretch test and also a tension test to strain metal sheet test specimens, from a material sample, from beyond their elastic limit to just prior to localized necking and fracture. 5.3.1.1 Since the location of localized necking and fracture cannot be predetermined, one or both surfaces of test specimens are covered with a pattern of gauge length measurement units, usually as squares or small diameter circles, by a suitable method such as scribing, photo-grid, or electro-etching, and then each test specimen is formed to the point of localized necking, or fracture. 5.3.2 Strains in the major (e1) and minor (e2) directions are measured using individual gauge length measurement units on the pattern in the area of the localized necking or fracture. 5.3.2.1 Test specimens of varied widths are used to produce a wide range of strain states in the minor (e2) direction. 5.3.2.2 The major strain (e1) is determined by the capacity of the material to be stretched in one direction as simultaneous surface forces either stretch, do not change, or compress, the metal in the minor strain (e2) direction. 5.3.2.3 In the ten... SCOPE 1.1 This test method gives the procedure for constructing a forming limit curve (FLC) for a metallic sheet material by using a hemispherical deformation punch test and a uniaxial tension test to quantitatively simulate biaxial stretching and deep drawing processes. 1.1.1 Fig. 1 shows an example of a forming limit curve on a schematic forming limit diagram (FLD). FIG. 1 Schematic Forming Limit Diagram Note 1: The upper curve represents the forming limit curve. Strains below the lower curve do not occur during forming metallic sheet products in the most stamping press operations. Curves to the left of % e2 = 0 are for constant area of the test specimen surface. 1.2 FLCs are useful in evaluating press performance by metal fabrication strain analysis. 1.3 The method applies to metallic sheet from 0.5 mm (0.020 in.) to 3.3 mm (0.130 in.). 1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses after SI units are provided for information only and are not considered standard. 1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.