Fractographic method

The specimens were cut from the plate in two directions longitudinal and transverse to the rolling direction. The welded joint specimens were cut transverse to the weld. The notch in the welded joint specimens was made in the plane parallel to the weld direction. Tests were conducted at room temperature and at 77 K. The topographical features of the fracture surfaces of notched specimens were revealed by the fractographic method and with a scanning electron microscope (SEM). 

Harmuth H, Bradt RC. Investigation of refractories brittleness by fracture mechanical and Fractographic methods. Interceram Ref Refractories Man. 2010. 

Fractographic analyses of CF must be improved, including quantitative measurement of crack surface crystallography [119], and computerized image analysis methods to characterize and reconstruct the CF process [120]. 

The SCF method uses a very small precrack introduced by a Knoop indenter. This method of relying on the material s brittleness to cause small surface precracks to form underneath an indention is unique to ceramics. The precrack is small and on the order of real flaws in ceramics. Thus, fractographic techniques, and some care and skill, are needed to see and measure the size of the precrack. Both the cracks depth and the width must be measured for the SCF precrack. Crack detection and the size measurement is aided by purposely tilting the test specimen 1 /2° relative to the indenter so that the precrack and fast fracture regions are not coplanar. As a result, the precrack in some materials is easy to discern, even with a low power stereo binocular microscope. In other materials, a careful examination with a scanning... 

Figure 11. SEM fractograph after Kic measurement by the SEPB method for a SiC whisker-SiaN4 composite (density 98XTD).

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