Crack Mouth Opening Displacement CMOD

In general, the experimental approach to the problems of crack propagation in non-linear and non-elastic materials is based on the observation and recording of behaviour of specimens with initial notches, and COD measurements were developed by several authors. Later, crack tip opening displacement (CTOD) was determined as a function of crack mouth opening displacement (CMOD) (Velasco et al. 1980), which was directly measured and recorded, for example, according to EN ISO 12737 1999 and ASTM E 399-06 (2006), (cf. Figure 10.5). 

WOL Type T specimen is wedge bolt-loaded as shown in Fig. 15.19. Type X specimen is no longer used. The development process continued till the introduction of the third type of specimen worldwide known as the Compact C(T) specimen of Fig. A.9c. Today the C(T) type specimen is the most used one in fracture mechanics applications. However, WOL Type T specimen is still used in see applications for measuring the stress intensity threshold Kj -cc (see Sect. 15.5). The h a/w) and V(a/w) functions for the calculation of the corresponding K and A for types WOL-T and C(T) specimens are listed in the following [6]. The symbols refer to Fig. A.9b and c for types WOL-T and C(T) specimens, respectively. A represents the crack mouth opening displacement (CMOD), i.e., the displacement measured at the notch opening on the specimen surface, as shown in Fig. A.9. 

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