Difficulty in the delayed fracture test
of sprayed coatings is that we cannot detect small cracks hidden under the coating.
The fracture test
is performed on a material testing system (MTS) servohydraulic testing machine [see Figure 5(a)].
Moreover, the net flexural strength, [f.sub.flex], can be theoretically calculated as follows using (500 x 100 x 100 mm) prism specimens used in fracture test
Most of the clustered events in Test 1 are localized around the notch tip, with a vertical extension expected in the mode I fracture test
. Similarly, in Test 2, although the individual events were dispersed on the 2D projection plane, the hierarchical clustering analysis extracted the fracture location from a cloud of AE events (Figs.
The basic configuration of the fracture test
is the same as in Figure 3.
Effect of shot peening on the delayed fracture of QT-treated spring steel (Almen strip) and maraging steel were studied by both the conventional delayed fracture test
(DFT) and step-wise strain increase (SSI) method assisted by AE technique.
Another fatigue fracture test
of a compact tension (CT) specimen also showed a change of fracture type from TG- to IG-fracture at around [K.sub.max] of 8 MPa[square root of m], above which both the fast crack propagation and high AE generation rates were detected.
For proposing more common models, three granites of different grain size distribution were used for fracture test
under triaxial compression at two different loading rates of 27.5 and 2.5 MPa/min, respectively.
As ASTM D5045 specifies, the maximum load for precracking was limited to prevent plastic deformation effects in the static fracture test
. Under this load limit, the ratio between the initial crack length (a) and the specimen width (W), a/W, was controlled to be ~0.4 to 0.6 by tapping a liquid-nitrogen-chilled razor blade into the wedge.
Indentation fracture test
using spherical indenter gives us much useful information about micro-fracture.
A longitudinal video extensometer was used to measure the specimen deformation without touching the fracture test