ASTM E561-15a
K-R曲线测定的标准试验方法

Standard Test Method for KR Curve Determination

被代替

标准号

ASTM E561-15a

发布

2015年

发布单位

美国材料与试验协会

替代标准

ASTM E561-19

当前最新

ASTM E561-23

 

 

引用标准

ASTM E1823 ASTM E399 ASTM E4

适用范围

5.1 The K_R curve characterizes the resistance to fracture of materials during slow, stable crack extension and results from the growth of the plastic zone ahead of the crack as it extends from a fatigue precrack or sharp notch. It provides a record of the toughness development as a crack is driven stably under increasing applied stress intensity factor K. For a given material, K_R curves are dependent upon specimen thickness, temperature, and strain rate. The amount of valid K_R data generated in the test depends on the specimen type, size, method of loading, and, to a lesser extent, testing machine characteristics.

5.2 For an untested geometry, the K_R curve can be matched with the crack driving (applied K) curves to estimate the degree of stable crack extension and the conditions necessary to cause unstable crack propagation (2). In making this estimate, K_R curves are regarded as being independent of initial crack size a_o and the specimen configuration in which they are developed. For a given material, material thickness, and test temperature, K_R curves appear to be a function of only the effective crack extension Δa_e (3).

5.2.1 To predict crack behavior and instability in a component, a family of crack driving curves is generated by calculating K as a function of crack size for the component using a series of force, displacement, or combined loading conditions. The K_R curve may be superimposed on the family of crack driving curves as shown in Fig. 1, with the origin of the K_R curve coinciding with the assumed initial crack size a_o. The intersection of the crack driving curves with the K_R curve shows the expected effective stable crack extension for each loading condition. The crack driving curve that develops tangency with the K_R curve defines the critical loading condition that will cause the onset of unstable fracture under the loading conditions used to develop the crack driving curves.

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