Opening, crack mouth

A compliance crack detection curve as shown in Figure 5 was first constructed using the load displacement records obtained from the fracture tests. This compliance is based on the crack mouth opening displacement and is thus not to be confused with the compliance of the... 

TABLE 2—Calculated crack mouth opening and load-line compliance calibrations for modified compact bolt-loaded specimen [30]. 

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). 

Bearing Ball 2 contains an artificial C-crack and another small surface feature. The artificial C-crack, shown in Fig. 4b, has a chord length of 1.32 mm with a radius of 0.745 mm, and a crack mouth opening at middle arc of <0.7 pm. The markings for the C-crack and the surface feature also consist of four Vicker s indents and located -6.5 mm from the corresponding features. 

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. 

The centrally-notched beams spanned 450 mm, with a distance between the concentrated loads of 150 mm. A monitoring system of 14 gauges was used. Values of loading, crack mouth opening, deflection under the load, position of the crack tip, and six surface strains ahead of the notch were simultaneously recorded and thereupon processed by an EPSON QX-10 computer (Fig.l). 

Figure 1. Position of the gauges used for monitoring the behaviour of the beams in flexure. Channels 9" to 11 yield information on deflections, 1 , 12 and 13 on the crack mouth opening, 2 to 7 on surface strains ahead of the notch, 8 on the position of the crack tip, and 0 and 15 on the load intensity.

Crack mouth opening displacement and fracture surface energy for RefC specimens tested at about 126 days... 

Crack mouth opening displacements and fracture surface specimens tested at 100, 174 and 405 days... 

Specimen Crack mouth opening displacement Fracture surface energy y. 

In spite of the scatter a non-linear correlation can be observed in a graph relating the crack mouth opening displacement at ultimate load to the... 

Pairs of curves of load-deflection (F-f) and load-crack mouth opening displacement (F-v) or F-f and v-f were obtained using a tensometric dynamometer displacement gauges and 2 X-Y recorders. It is noted that as a rule, the ascending branch of the F-f diagram is approximately linear up to approximately the maximum (critical) load F. Descending branches asymptotically tended to the deflection axis (Fig. 1). This can always be observed when the dead weight influence is absent. 

Figtire 2 Load-deflection and crack mouth opening displacement-deflection curves of concrete A3 and bend beam scheme. 

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