Experimental FCGR Measurements

The method was based on an ultrasonic monitoring of the growing crack, schematically shown in Fig. 10.9 with a WOL compact specimen. The procedure was used to permit either semi-automatic or completely automatic monitoring of the crack growth behavior and had a sensitivity of about 0.25 mm. Today, direct visual measurements of the crack size have been substituted by indirect readings based on the specimen compliance. This is measured by a clip gauge mounted on 

10 Fracture Mechanics Approach to Fatigue Crack Propagation 

Another example of FCGR measurements obtained with 1 WOL specimens is given in Fig. 10.14 for a high strength steel type 4340, with 910 MPa yielding and 1,400 MPa ultimate strength [25]. The equation interpolating the experimental data is 

Interesting enough, the strength of the material seems not influence the FCGR that has the same exponent 2.5 of the NiMoV previously seen. 

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Fig. 11.19 Experimental measurements of the surface roughness in a Ti-6Al-4 V alloy heat hardened to three different strength and subjected to different AK that result in different FCGR,...

The reason is not known, but it is an experimental result that must be reported. Finally, Fig. 12.25 [27] presents the FCGR, da/dN, measured on aluminum alloy, type 6061-T6, specimens welded by modified indirect electric arc (MEA). The tensile properties of the base material, HAZ and weld metal are shown in Fig. 12.25 [27]. It can be seen how the strength properties of the HAZ are poor compared to that of the weld metal and, in particular, of the base material. Nevertheless, the higher FCGR, da/dN, is that of the weld metal followed by the HAZ and base material. The FCGR, da/dN, obeys to a Paris law relationship Fig. 12.26... 

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