Crack imaging

The tensile tests have been accompanied by acoustic emission (AE) registration, fuU-field surface strain-mapping (SM), progressive crack imaging at different load levels and micrographic inspection of the cross-sections of samples. The results of testing have been reported in [108,109]. 

Koutsopoulos, H.N. and Downey, A.B. (1993) Primitive-based classification of pavement cracking images. ASCE Journal of Transportation Engineering, 119, 402-418. 

Figure 9.4 Crack image processing, after Brandt and Kasperkiewicz (2003).

Li T, Almond DP, Rees DAS (2011) Crack imaging by scatming pulsed laser spot thermography. NDT E Int 44(2) 216-225... 

Figure 632 SEM of PEFC catalyst layer with relatively large scale macro cracking. (Image by Soowhan Kim, Penn State Fuel Cell Dynamics and Diagnostics Lab.)...

The major drawback of this identification method, as used to date, is that only a part of the useful information contained into original Bscan image, i.e. segmented Bscan image, is used for defect characterization. Moreover, it requires the availability of defect classification information (i.e. if the defect is volumetric or planar, e.g. a crack or a lack of fusion), which, generally, may be as difficult to obtain as the defect parameters themselves. Therefore, we... 

Figure 4 A radiographic image of a welded joint (defect transversal crack), a Original image, b Edge image (only the defect is maintained).

Figure 7 New photothermal camera versus penetrant testing on a crack (width 5 pm) at the surface of Fig 4. part The large arrow shows that the PT indication almost extinguishes at thinner width (approx. I pm) locations along the crack the photothermal signal does not. The bottom little arrow indicates a place where the crack splits in two, which is not revealed on the PT image because of the spreading of the penetrant liquuid.

Figure 4 Elements of a Crack Detection Window of an Image Processing Program...

Figure 4 presents such a crack indication in the A-Scan-image. The respective A-Scan for a flawless blade is shown in figure 5. In every case the echo from the comer serves as an indication of a good coupling. 

The system uses a remote controlled manipulator system whieh scans the volume of interest. It also positions the x-ray source and x-ray camera at different angles relative the crack and create projection images of the craek. By using a tomographic reconstruction of these images a 3-D representation of the crack can be used for analysis and sizing. 

Thermal imaging is sensitive to iafrared radiation that detects temperature changes over the surface of a part when heat has been appHed. Thermal diffusion ia a soHd is affected by variatioa ia composition or by the preseace of cracks, voids, delamiaatioas, etc the effects are detected by surface temperature changes. Defects cannot be detected if their depth below the surface is more than two to three times their diameter. Nondestmctive testing has been primarily used for composites and analysis of adhesive bonds or welds. Several studies are documented ia the Hterature (322—327). 

Figure 8 shows the SEM images with a low level of strain (50%). It is clear that even with a low-strain level defects are initiated in the sulfur cured system with the formation of large cracks at the boundary layer between the two phases. However, in the peroxide cured system the mechanism of crack initiation is very different. In the latter case the NR-LDPE interface is not the site for crack initiation. In this case, stress due to externally applied strains is distributed throughout the matrix by formation of fine crazes. Furthermore, such crazes are developed in the continuous rubber matrix in a direction... 

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