1.1 该试验方法给出了通过使用半球形变形冲压试验和单轴拉伸试验来定量模拟双轴拉伸和深拉过程来构建金属片材的成形极限曲线（FLC）的程序。 1.1.1 图1 示出了在示意性成形极限图（FLD）上的成形极限曲线的示例。 图1 成形极限示意图 注1: 上部曲线表示成形极限曲线。在大多数冲压机操作中，在形成金属片材产品的过程中不会出现低于下曲线的应变。%左侧的曲线 e 2. =0表示试样表面的恒定面积。 1.2 FLC可用于通过金属制造应变分析来评估冲压性能。 1.3 该方法适用于0.5毫米（0.020英寸）至3.3毫米（0.130英寸）的金属薄板。 1.4 以国际单位制表示的数值应视为标准。 国际单位制后括号中给出的值仅供参考，不被视为标准值。 1.5 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的使用者有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。 1.6 本国际标准是根据世界贸易组织技术性贸易壁垒委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认的标准化原则制定的。 ====意义和用途====== 5.1 成形极限曲线（FLC）是特定于取样材料的。如果材料经过冷加工或任何退火工艺，它可能会发生变化。 因此，如果处理方式不同，来自给定批次材料的两个样品可以产生不同的曲线。 5.2 如果要将测试视为产品等级的代表，则必须了解材料的加工历史。 5.3 成形极限曲线（FLC）定义了给定的金属板样品在一系列成形条件下所能承受的最大（极限）应变，如深冲、平面应变、双轴拉伸和冲压和模拉操作中半径范围内的弯曲，而不会产生表明初始失效的局部减薄区（局部颈缩）。 5.3.1 FLC可以通过使用实验室半球形冲头双轴拉伸试验和拉伸试验从材料样品应变金属板试样，从超过其弹性极限到刚好在局部颈缩和断裂之前，根据经验获得。 5.3.1.1 由于局部颈缩和断裂的位置无法预先确定，因此通过适当的方法，如划线、照相等，用标距长度测量单位的图案覆盖试样的一个或两个表面，通常为正方形或小直径圆形- 网格，或电蚀刻，然后将每个试样形成到局部颈缩或断裂的点。 5.3.2 主要菌株( e 1. )和次要( e 2. )在局部颈缩或断裂区域的图案上使用单独的标距长度测量单元来测量方向。 5.3.2.1 不同宽度的试样用于产生较小范围的应变状态( e 2. )方向。 5.3.2.2 主要菌株( e 1. )由材料在一个方向上拉伸的能力决定，同时的表面力在较小的应变下拉伸、不改变或压缩金属( e 2. )方向。 5.3.2.3 在拉伸试验变形过程中( e 2. )均为阴性，且试样在厚度和宽度上均变窄。 5.3.3 这些应变绘制在成形极限图（FLD）上，并绘制成形极限曲线（FLC）以连接测量的最高值 e 1. 和 e 2. 包括良好数据点的应变组合。 5.3.3.1 当良好数据点和边缘数据点之间存在混合且没有明确区别时，建立最佳拟合曲线，以遵循最大良好数据点作为FLC。 5.3.4 成形极限是在最大主应变下确定的( e 1. )在颈缩之前获得。 5.3.5 FLC定义了在形成金属片材产品时有用变形的极限。 5.3.6 众所周知，FLC会随着材料（特别是在制造材料的加工操作过程中产生的机械或可成形性）和金属板厚度的变化而变化。 5.3.6.1 应变硬化指数( n 值），在测试方法中定义 电子646 ，影响成形极限。A高 n 该值将提高极限主应变( e 1. )，在正的小应变条件下允许更多的拉伸( e 2. > 0). 5.3.6.2 塑性应变比( r 值），在测试方法中定义 第517页 ，会影响材料的深冲能力。A高 r 值将移动较小的应变( e 2. )进入FLD左侧较不严重的区域 哦 ( e 2. <0），从而允许对给定的主要应变进行更深的拉伸( e 1. ). 5.3.6.3 材料的厚度将影响FLC，因为较厚的试样具有更多的体积来响应成形过程。 5.3.6.4 用于确定FLC的钢板产品的性能 图3 包括 n 价值和 r 价值 5.3.7 FLC可作为材料应变分析的诊断工具，并已用于评估冲压操作和材料选择。 5.3.8 FLC为与顺序冲压操作形成的零件上的应变分布进行比较提供了图形基础。 5.3.9 通过该方法获得的FLC遵循恒定比例应变路径，其中存在标称固定的主应变比( e 1. )至次要( e 2. )应变。 5.3.9.1 没有中断加载或应变逆转，但随着试样接近颈缩或断裂，应变率可能会减慢。 5.3.9.2 FLC可用于保守预测一整类材料的性能，前提是 n 价值 r 所使用的材料的尺寸、值和厚度是该类别的代表。 5.3.10 复杂的成形操作中，应变路径发生变化，或者应变在金属板厚度上不均匀，可能会产生与通过该方法获得的成形极限不一致的极限应变。 5.3.11 材料对塑性变形响应的表征可能涉及断裂应变以及颈缩的开始。这些菌株高于FLC。 5.3.12 FLC不适合批量质量保证测试，因为它是特定于为确定成形极限而测试的材料样品的。

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 % e 2 = 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. ====== 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 ( e 1 ) and minor ( e 2 ) 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 ( e 2 ) direction. 5.3.2.2 The major strain ( e 1 ) 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 ( e 2 ) direction. 5.3.2.3 In the tension test deformation process, the minor strains ( e 2 ) are negative, and the test specimen is narrowed both through the thickness and across its width. 5.3.3 These strains are plotted on a forming limit diagram (FLD), and the forming limit curve (FLC) is drawn to connect the highest measured e 1 and e 2 strain combinations that include good data points. 5.3.3.1 When there is intermixing and no clear distinction between good and marginal data points, a best fit curve is established to follow the maximum good data points as the FLC. 5.3.4 The forming limit is established at the maximum major strain ( e 1 ) attained prior to necking. 5.3.5 The FLC defines the limit of useful deformation in forming metallic sheet products. 5.3.6 FLCs are known to change with material (specifically with the mechanical or formability properties developed during the processing operations used in making the material) and the thickness of the sheet metal. 5.3.6.1 The strain hardening exponent ( n value), defined in Test Method E646 , affects the forming limit. A high n value will raise the limiting major strain ( e 1 ), allowing more stretch under positive minor strain conditions ( e 2 > 0). 5.3.6.2 The plastic strain ratio ( r value), defined in Test Method E517 , affects the capacity of a material to be deep drawn. A high r value will move the minor strain ( e 2 ) into a less severe area to the left of the FLD o ( e 2 < 0), thus permitting deeper draws for a given major strain ( e 1 ). 5.3.6.3 The thickness of the material will affect the FLC since a thicker test specimen has more volume to respond to the forming process. 5.3.6.4 The properties of the steel sheet product used in determining the FLC of Fig. 3 included the n value and the r value. 5.3.7 FLCs serve as a diagnostic tool for material strain analysis and have been used for evaluations of stamping operations and material selection. 5.3.8 The FLC provides a graphical basis for comparison with strain distributions on parts formed by sequential press operations. 5.3.9 The FLC obtained by this method follows a constant proportional strain path where there is a nominally fixed ratio of major ( e 1 ) to minor ( e 2 ) strain. 5.3.9.1 There is no interrupted loading, or reversal of straining, but the rate of straining may be slowed as the test specimen approaches necking or fracture. 5.3.9.2 The FLC can be used for conservatively predicting the performance of an entire class of materials provided the n value, r value, and thickness of the material used are representative of that class. 5.3.10 Complex forming operations, in which the strain path changes, or the strain is not homogeneous through the metal sheet thickness, can produce limiting strains that do not agree with the forming limit obtained by this method. 5.3.11 Characterization of a material's response to plastic deformation can involve strain to fracture as well as to the onset of necking. These strains are above the FLC. 5.3.12 The FLC is not suitable for lot-to-lot quality assurance testing because it is specific to that sample of a material which is tested to establish the forming limit.