1.1本试验方法涵盖了使用静态或准静态载荷条件下的预裂纹试样在高温下测定金属中的蠕变裂纹扩展（CCG）。时间（CCI），t 0.2 初始裂纹扩展a 一、 =从首次施加力和蠕变裂纹扩展速率开始的0.2 mm， 一 或da/dt表示为蠕变裂纹扩展相关参数C*或K的幅值。其中C*定义为从C*（t）和C导出的裂纹尖端应力的稳态测定 t () . 以这种方式导出的裂纹扩展被确定为可用于建模和寿命评估方法的材料特性 () . 1.1.1裂纹扩展相关参数C*，C*（t），C的选择 t 或K取决于材料蠕变特性、试样的几何形状和尺寸。蠕变裂纹扩展试验中通常观察到两种类型的材料行为；蠕变延性 () 蠕变脆性 () . 在蠕变延性材料中，蠕变应变占主导地位，蠕变裂纹扩展伴随着裂纹尖端大量与时间相关的蠕变应变，裂纹扩展速率与C的稳态定义相关 t 或C*（t），定义为C*（参见）。蠕变中- 脆性材料，蠕变裂纹扩展发生在低蠕变延性。因此，随时间变化的蠕变应变与裂纹尖端局部的伴随弹性应变相当或受其支配。在这种稳态蠕变-脆性条件下，C t 或者可以选择K作为相关参数 () . 1.1.2在任何一个试验中，可能存在两个裂纹扩展行为区域 (, ) . 初始瞬态区域，弹性应变占主导地位，蠕变损伤发展，稳态区域，裂纹随时间成比例增长。稳定- 本标准涵盖了状态蠕变裂纹扩展速率行为。此外，还就如何根据初始裂纹扩展期处理瞬态区域提出了具体建议。在稳态期间，da/dt与适当的裂纹扩展速率相关参数之间存在唯一的相关性。 1.1.3在蠕变延性材料中，当整个未开裂韧带发生蠕变变形时，会发生广泛蠕变。这种条件不同于小规模蠕变和过渡蠕变条件 () . 在大范围蠕变的情况下，与裂纹长度和未开裂韧带尺寸相比，蠕变变形主导的区域在尺寸上是显著的。 在小范围蠕变中，只有裂纹尖端局部的未开裂韧带的一小部分经历蠕变变形。 1.1.4广泛蠕变区域中的蠕变裂纹扩展速率通过C*（t）-积分进行关联。C t 参数将小尺度蠕变和过渡蠕变区域中的蠕变裂纹扩展速率关联起来，并根据定义，在扩展蠕变区域中降低到C*（t） () . 因此，在本文件中，定义C*用作稳态广泛蠕变区的相关参数，而C*（t）和/或C t 是描述小尺度蠕变、瞬态和稳态蠕变中瞬时应力状态的参数。 针对不同几何形状推导C*的推荐函数如所示。 1.1.5初始裂纹扩展尺寸a的工程定义 一、 用于量化裂纹发展的初始阶段。该距离为0.2 mm。它已显示 () 试验开始时存在的这段时间可能是试验时间的一个重要时期。在这一早期阶段，裂纹尖端经历了损伤发展以及达到稳定状态之前的应力重新分布。建议将定义为t的初始裂纹扩展期关联起来 0.2 在a 一、 =0.2 mm，当裂纹尖端处于大范围蠕变时，稳态C*，蠕变-脆性条件下为K。C*和K的值应在定义为a的最终指定裂纹尺寸下计算 o +a 一、 其中a o 起始裂纹的初始尺寸。 1.1.6 CCI和CCG试验的推荐试样为标准紧凑拉伸试样C（T）（见），其在恒定载荷条件下承受拉力。U形夹设置如所示（有关详细信息，请参阅）。本程序中测试有效的其他几何形状如所示。 这些是张力CS（T）、中间张力M（T）、单缺口张力传感器（T）、单缺口弯曲传感器（B）和双边缺口弯曲张力传感器（T）。在中，显示了用于测量力线（FLD）裂纹口张开位移（CMOD）处位移的试样侧槽位置，以及电位降（PD）输入和输出引线的位置。拉伸试样的建议载荷为销载荷。中给出了结构、尺寸范围和初始裂纹尺寸及其侧槽程度， () . 样本选择将在中讨论。 1.1.7裂纹尖端的应力状态可能会影响蠕变裂纹扩展行为，并可能导致平面试样中的裂纹前沿隧穿。试样尺寸、几何形状、裂纹长度、试验持续时间和蠕变特性将影响裂纹尖端的应力状态，是决定裂纹扩展速率的重要因素。试样及其侧槽的推荐尺寸范围如所示。已经表明，在该范围内，开裂率不会因材料和荷载条件的范围而变化 () . 这表明，对于相对较短的测试持续时间（少于一年），约束水平在这些几何形状测试中观察到的正常数据分散范围内没有变化。 然而，建议在实验室施加的限制范围内，对不同几何形状、试样尺寸、尺寸和裂纹尺寸的起动器进行试验。在所有情况下，应尽可能通过测试标准C（T）试样来比较上述数据。显然，通过测试上述更广泛的试样类型和条件，可以提高材料裂纹扩展数据的可信度。 1.1.8材料不均匀性、残余应力和材料在温度、试样几何形状和低温下的退化- 力长期试验（主要大于一年）可能会影响裂纹扩展特性的速率 () . 在存在残余应力的情况下，当试样取自具有残余应力场特征的材料或受损材料时，这种影响可能非常显著。例如，焊接件和/或厚铸件、锻造、挤压、部件、塑性弯曲部件和复杂部件形状，在这些情况下，完全消除应力是不可行的。从含有残余应力的此类部件上取下的试样也将含有残余应力，这些残余应力可能因试样制造而改变其范围和分布。 试样本身的提取部分缓解并重新分布了残余应力模式；然而，在接下来的测试中，剩余的幅值仍然会造成显著影响。残余应力叠加在外加应力上，导致裂纹尖端应力强度不同于仅基于外加力或位移的应力强度。试样加工过程中的变形也表明存在残余应力。 1.1.9还应考虑蠕变和裂纹扩展引起的残余应力的应力松弛。 本标准中不包括处理这些变化的具体余量。然而，本文中提出的计算C*的方法使用了试样蠕变位移率来估计C*固有地考虑了上述影响，如已测量的瞬时蠕变应变所反映的。然而，尽管预计高温下的应力松弛可能部分抵消残余应力的影响，但在分析这些类型的试验时仍应格外小心，因为相关参数K和C*如所示。 1.1.10除在恒力下测试的样本外，其他样本的配置和尺寸将涉及进一步的有效性要求。这是通过比较来自推荐测试配置的数据来实现的。然而，如果将数据与从标准试样（如中所述）获得的数据进行比较，并验证了适当的相关参数，则该方法适用于使用其他几何形状。 1.2以国际单位制表示的数值应视为标准。括号中的英寸-磅单位仅供参考。 1.3 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和健康实践，并确定监管限制的适用性。

1.1 This test method covers the determination of creep crack growth (CCG) in metals at elevated temperatures using pre-cracked specimens subjected to static or quasi-static loading conditions. The time (CCI), t 0.2 to an initial crack extension a i = 0.2 mm from the onset of first applied force and creep crack growth rate, a or da/dt is expressed in terms of the magnitude of creep crack growth relating parameters, C* or K. With C* defined as the steady state determination of the crack tip stresses derived in principal from C*(t) and C t () . The crack growth derived in this manner is identified as a material property which can be used in modeling and life assessment methods () . 1.1.1 The choice of the crack growth correlating parameter C*, C*(t), C t , or K depends on the material creep properties, geometry and size of the specimen. Two types of material behavior are generally observed during creep crack growth tests; creep-ductile () and creep-brittle () . In creep ductile materials, where creep strains dominate and creep crack growth is accompanied by substantial time-dependent creep strains at the crack tip, the crack growth rate is correlated by the steady state definitions of C t or C*(t), defined as C* (see ). In creep-brittle materials, creep crack growth occurs at low creep ductility. Consequently, the time-dependent creep strains are comparable to or dominated by accompanying elastic strains local to the crack tip. Under such steady state creep-brittle conditions, C t or K could be chosen as the correlating parameter () . 1.1.2 In any one test, two regions of crack growth behavior may be present (, ) . The initial transient region where elastic strains dominate and creep damage develops and in the steady state region where crack grows proportionally to time. Steady-state creep crack growth rate behavior is covered by this standard. In addition specific recommendations are made in as to how the transient region should be treated in terms of an initial crack growth period. During steady state, a unique correlation exists between da/dt and the appropriate crack growth rate relating parameter. 1.1.3 In creep ductile materials, extensive creep occurs when the entire uncracked ligament undergoes creep deformation. Such conditions are distinct from the conditions of small-scale creep and transition creep () . In the case of extensive creep, the region dominated by creep deformation is significant in size in comparison to both the crack length and the uncracked ligament sizes. In small-scale-creep only a small region of the uncracked ligament local to the crack tip experiences creep deformation. 1.1.4 The creep crack growth rate in the extensive creep region is correlated by the C*(t)-integral. The C t parameter correlates the creep crack growth rate in the small-scale creep and the transition creep regions and reduces, by definition, to C*(t) in the extensive creep region () . Hence in this document the definition C* is used as the relevant parameter in the steady state extensive creep regime whereas C*(t) and/or C t are the parameters which describe the instantaneous stress state from the small scale creep, transient and the steady state regimes in creep. The recommended functions to derive C* for the different geometries is shown in is described in. 1.1.5 An engineering definition of an initial crack extension size a i is used in order to quantify the initial period of crack development. This distance is given as 0.2 mm. It has been shown () that this period which exists at the start of the test could be a substantial period of the test time. During this early period the crack tip undergoes damage development as well as redistribution of stresses prior reaching steady state. Recommendation is made to correlate this initial crack growth period defined as t 0.2 at a i = 0.2 mm with the steady state C* when the crack tip is under extensive creep and with K for creep brittle conditions. The values for C* and K should be calculated at the final specified crack size defined as a o + a i where a o initial size of the starter crack. 1.1.6 The recommended specimens for CCI and CCG testing is the standard compact tension specimen C(T) (see ) which is pin-loaded in tension under constant loading conditions. The clevis setup is shown in (see for details). Additional geometries which are valid for testing in this procedure are shown in. These are the C-ring in tension CS(T), middle tension M(T), single notch tension SEN(T), single notch bend SEN(B), and double edge notch bend tension DEN(T). In, the specimens side-grooving position for measuring displacement at the force-line (FLD) crack mouth opening displacement (CMOD) and also and positions for the potential drop (PD) input and output leads are shown. Recommended loading for the tension specimens is pin-loading. The configurations, size range and initial crack size and their extent of side-grooving are given in of, () . Specimen selection will be discussed in. 1.1.7 The state-of-stress at the crack tip may have an influence on the creep crack growth behavior and can cause crack-front tunneling in plane-sided specimens. Specimen size, geometry, crack length, test duration and creep properties will affect the state-of-stress at the crack tip and are important factors in determining crack growth rate. A recommended size range of test specimens and their side-grooving are given in in. It has been shown that for this range the cracking rates do not vary for a range of materials and loading conditions () . Suggesting that the level of constraint, for the relatively short term test durations (less than one year), does not vary within the range of normal data scatter observed in tests of these geometries. However it is recommended that, within the limitations imposed on the laboratory, that tests are performed on different geometries, specimen size, dimensions and crack size starters. In all cases a comparison of the data from the above should be made by testing the standard C(T) specimen where possible. It is clear that increased confidence in the materials crack growth data can be produced by testing a wider range of specimen types and conditions as described above. 1.1.8 Material inhomogenities, residual stresses and material degradation at temperature, specimen geometry and low-force long duration tests (mainly greater that one year) can influence the rate of crack growth properties () . In cases where residual stresses exist, the effect can be significant when test specimens are taken from material that characteristically embodies residual stress fields or the damaged material. For example weldments, and/or thick cast, forged, extruded, components, plastically bent components and complex component shapes where full stress relief is impractical. Specimens taken from such component that contain residual stresses will likewise contain residual stresses which may have altered is their extent and distribution due to specimen fabrication. Extraction of specimens in itself partially relieves and redistributes the residual stress pattern; however, the remaining magnitude can still cause significant effects in the ensuing test. Residual stress is superimposed on applied stress and results in crack-tip stress intensity that is different from that based solely on externally applied forces or displacements. Distortion during specimen machining can also indicate the presence of residual stresses. 1.1.9 Stress relaxation of the residual stresses due to creep and crack extension should also be taken into consideration. No specific allowance is included in this standard for dealing with these variations. However the method of calculating C* presented in this document which used the specimens creep displacement rate to estimate C* inherently takes into account the effects described above as reflected by the instantaneous creep strains that have been measured. However extra caution should still be observed with the analysis of these types of tests as the correlating parameters K and C* shown in even though it is expected that stress relaxation at high temperatures could in part negate the effects due to residual stresses. 1.1.10 Specimen configurations and sizes other than those listed in which are tested under constant force will involve further validity requirements. This is done by comparing data from recommended test configurations. Nevertheless, use of other geometries are applicable by this method provided data are compared to data obtained from standard specimens (as identified in ) and the appropriate correlating parameters have been validated. 1.2 The values stated in SI units are to be regarded as the standard. The inch-pound units given in parentheses are for information only. 1.3 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 and health practices and determine the applicability of regulatory limitations prior to use.