1.1 本指南涵盖了无法完全消除应力的铝制品平面应变断裂韧性测试的补充指南。提出了识别残余应力何时可能显著偏离试验结果的指南，以及在试验过程中最小化残余应力影响的方法。本指南还提供了对这些产品测试期间产生的数据进行经验校正和解释的指南。试验方法 E399 是用于铝合金平面应变断裂韧性测试的标准测试方法。 1.2 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的用户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。 1.3 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）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》中确立的国际公认标准化原则制定的。 ====意义和用途====== 4.1 财产 K 集成电路 ，由试验方法确定 E399 或ISO 12135，表征了材料在中性环境中以及在横向塑性流动高约束场（平面应变条件）内承受施加的开启力或力矩的尖锐裂纹存在时的抗断裂能力。A. K 集成电路 该值被认为是与平面应变状态相关的断裂韧性的下限值。 4.1.1 沉淀硬化铝合金产品使用的热淬火工艺可能会在产品中引入显著的残余应力。 5. 机械应力消除程序（拉伸、压缩）通常用于消除形状简单的产品中的这些残余应力。然而，对于具有厚横截面的轧制产品（例如，厚规格板或大型手工锻件）或复杂形状（例如，闭式模锻、复杂开式模锻、阶梯挤压、铸件），完全的机械应力消除并不总是可能的。在其他情况下，在矫直、成型或焊接操作等制造操作期间，可能会无意中将残余应力引入产品。 注1: 就本指南而言，仅考虑了体积残余应力（即通常在热处理淬火过程中产生的类型），而非工程残余应力，例如喷丸或冷孔膨胀产生的残余应力。 4.1.2 从含有残余应力的此类产品上取下的试样本身也将含有残余应力。虽然样本提取行为本身部分缓解和重新分布了原始应力的模式，但剩余的幅度仍然可以明显到足以在测试结果中造成重大误差。 4.1.3 残余应力是叠加在外加应力上的非比例内应力，导致实际裂纹尖端应力强度因子不同于仅基于外加力或位移的应力强度因子，残余应力可能会使韧性测量产生偏差。从概念上讲，裂纹尖端区域的压缩残余应力必须在裂纹尖端经历拉伸应力之前通过施加的力来克服，从而使 K Q 或 K 集成电路 测量到更高的值，可能产生非- 下限韧性值。从数量上讲，这种影响取决于连续变化的残余应力场和相关裂纹尖端响应的应力平衡。相反，拉伸残余应力与施加的力相加，并使测量值产生偏差 K Q 或 K 集成电路 结果为较低值，可能低于材料“真实”韧性能力。 4.1.4 当存在大量残余应力时，使用深边缘缺口试样（如紧凑拉伸C（T））的试验对试样加工过程中的变形特别敏感。 通常，对于此类残余应力由热淬火引起的情况，结果 K 集成电路 或 K Q 结果通常向上偏移（即， K Q 高于在无残余应力试样中实现的值）。膨胀值是由于试样加工过程中残余应力的重新分布以及裂纹前缘可变残余应力引起的过度疲劳预裂纹前缘曲率造成的。 6. 4.2 本指南可用于以下目的: 4.2.1 提供警告标志，表明 K 集成电路 受到残余应力的影响，可能不是断裂韧性的下限值。 4.2.2 提供可用于最小化残余应力对测量断裂韧性值影响的实验方法。 4.2.3 建议可用于将残余应力影响的断裂韧性值修正为近似代表无残余应力偏差试验的断裂韧性值的方法。

1.1 This guide covers supplementary guidelines for plane-strain fracture toughness testing of aluminum products for which complete stress relief is not practicable. Guidelines for recognizing when residual stresses may be significantly biasing test results are presented, as well as methods for minimizing the effects of residual stress during testing. This guide also provides guidelines for an empirical correction as well as interpretation of data produced during the testing of these products. Test Method E399 is the standard test method to be used for plane-strain fracture toughness testing of aluminum alloys. 1.2 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. 1.3 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 ====== 4.1 The property K Ic , determined by Test Method E399 or ISO 12135, characterizes a material's resistance to fracture in a neutral environment and in the presence of a sharp crack subjected to an applied opening force or moment within a field of high constraint to lateral plastic flow (plane strain condition). A K Ic value is considered to be a lower limiting value of fracture toughness associated with the plane strain state. 4.1.1 Thermal quenching processes used with precipitation hardened aluminum alloy products can introduce significant residual stresses into the product. 5 Mechanical stress relief procedures (stretching, compression) are commonly used to relieve these residual stresses in products with simple shapes. However, in the case of mill products with thick cross-sections (for example, heavy gauge plate or large hand forgings) or complex shapes (for example, closed die forgings, complex open die forgings, stepped extrusions, castings), complete mechanical stress relief is not always possible. In other instances residual stresses may be unintentionally introduced into a product during fabrication operations such as straightening, forming, or welding operations. Note 1: For the purposes of this guide, only bulk residual stress is considered (that is, of the type typically created during a quench process for thermal heat treatment) and not engineered residual stress, such as from shot peening or cold hole expansion. 4.1.2 Specimens taken from such products that contain residual stress will likewise themselves contain residual stress. While the act of specimen extraction in itself partially relieves and redistributes the pattern of original stress, the remaining magnitude can still be appreciable enough to cause significant error in the test result. 4.1.3 Residual stress is a non-proportional internal stress that is superimposed on the applied stress and results in an actual crack-tip stress-intensity factor that is different from one based solely on externally applied forces or displacements, and residual stress can bias the toughness measurement. Conceptually, compressive residual stress in the region of the crack tip must be overcome by the applied force before the crack tip experiences tensile stresses, thus biasing the K Q or K Ic measurement to a higher value, potentially producing a non-lower-bound toughness value. Quantitatively, the effect depends on stress equilibrium for the continuously varying residual stress field and the associated crack tip response. Conversely, a tensile residual stress is additive to the applied force and biases the measured K Q or K ic result to a lower value, potentially under-representing the material “true” toughness capability. 4.1.4 Tests that utilize deep edge-notched specimens such as the compact tension C(T) are particularly sensitive to distortion during specimen machining when substantial residual stress is present. In general, for those cases where such residual stresses are thermal quench induced, the resulting K Ic or K Q result is typically biased upward (that is, K Q is higher than that which would have been achieved in a residual stress-free specimen). The inflated values result from the redistribution of residual stress during specimen machining and excessive fatigue precrack front curvature caused by variable residual stresses across the crack front. 6 4.2 This guide can serve the following purposes: 4.2.1 Provide warning signs that the measured value of K Ic has been biased by residual stresses and may not be a lower limit value of fracture toughness. 4.2.2 Provide experimental methods that can be used to minimize the effect of residual stress on measured fracture toughness values. 4.2.3 Suggest methods that can be used to correct residual stress influenced values of fracture toughness to values that approximate a fracture toughness value representative of a test performed without residual stress bias.