Standard Test Method for Crack-Tip Opening Displacement (CTOD) Fracture Toughness Measurement
1.1 This test method covers the determination of critical crack-tip opening displacement (CTOD) values at one or more of several crack extension events. These CTOD values can be used as measures of fracture toughness for metallic materials, and are especially appropriate to materials that exhibit a change from ductile to brittle behavior with decreasing temperature. This test method applies specifically to notched specimens sharpened by fatigue cracking. The recommended specimens are three-point bend [SE(B)] compact [C(T)], or arc-shaped bend [A(B)] specimens. The loading rate is slow and influences of environment (other than temperature) are not covered. The specimens are tested under crosshead or clip gage displacement controlled loading.
1.1.1 The recommended specimen thickness, B, for the SE(B) and C(T) specimens is that of the material in thicknesses intended for an application. For the A(B) specimen, the recommended depth, W, is the wall thickness of the tube or pipe from which the specimen is obtained. Superficial surface machining may be used when desired.
1.1.2 For the recommended three-point bend specimens [SE(B)], width, W, is either equal to, or twice, the specimen thickness, B, depending upon the application of the test. (See 4.3 for applications of the recommended specimens.) For SE(B) specimens the recommended initial normalized crack size is 0.45 ≤ ao/W 0.70. The span-to-width ratio ( S/W) is specified as 4.
1.1.3 For the recommended compact specimen [C(T)] the initial normalized crack size is 0.45 ≤ ao/W 0.70. The half-height-to-width ratio (H/W) equals 0.6 and the width to thickness ratio W/ B is specified to be 2.
1.1.4 For the recommended arc-shaped bend [A(B)] specimen, B is one-half the specimen depth, W. The initial normalized crack size is 0.45 < ao>/W 0.70. The span to width ratio, S/W, may be either 3 or 4 depending on the ratio of the inner to outer tube radius. For an inner radius, r1, to an outer radius, r2, ratio of > 0.6 to 1.0, a span to width ratio, S/W, of 4 may be used. For r 1/r2 ratios from 0.4 to 0.6, an S/W of 3 may be used.
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 and health practices and determine the applicability of regulatory limitations prior to use.
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