Defect size

Nair, S., S. Udpa, and L. Udpa, (1993), Radial basis functions network for defect sizing . Review of Progress in QNDE, Vol. 12, 1993, pp. 819-825... 

For defect sizing by TOED, use of L waves involves a penalty in resolution of almost a factor of two at a given frequency because of difference in velocity as compared to shear waves and use of SV waves runs into difficulties because of the mode conversion problems. Further, problems due to couplant thickness variations, surface roughness affects, beam skewing and distortion problems in anisotropic welds can also be expected. On the contrary, SH waves are not affected... 

Considering the success of detecting crack tip echoes from defects at the near probe surface, future work will deal with the detection and sizing of defects on the far probe surface. Future work also relates to carrying out defect sizing in anisotropic austenitic stainless steel welds and... 

Manual ultrasonic testing offers the advantages of low equipment cost combined with the flexibility of the human operator to provide good access and complex scanning capability. However, a total reliance on the capabilities of the ultrasonic technician to visualise the physical situation leads to a number of drawbacks, including lack of accuracy and consistency of defect size and location measurements, lack of verification that the required scan coverage has been fully achieved, and lack of consistency in flaw classification. A further disadvantage is that the ultrasonic data is not permanently recorded there is therefore no opportunity for the data to be re-examined at a later date if required. 

The ERS may not be misunderstood as being the defect s real size, since it only considers the portion of sound being reflected by the defect, and therefore the influences of the shape, the surface condition and the orientation of the defect are not taken into consideration. Unfortunately a lot of criticism was loaded onto the DGS method, because exactly this mistake was made in the early days of the DGS technique, and many people described the DGS-method as a technique for defect sizing". 

For many years, the technical capabilities of standard NDT methods did not allow for this approach. If NDT would have produced quantitative data on defect size from the beginning, it is highly probable that current acceptance criteria for weld defects would have used this information. Acceptance criteria would have been completely different from what they are... 

One of the most important appHcations of LEFM is to estimate the critical crack or defect size which causes fast fracture to occur. This occurs when the value of iCin a stmcture becomes equal to the plain strain fracture toughness, of the material the critical crack size, for a given stress and fracture toughness, is then given by equation 31. 

From this therefore it is evident that the failure stress, ductile/brittle transitions which may be observed in plastics. According to line B, as the fiaw size decreases the failure stress tends towards infinity. Clearly this is not the case and in practice what happens is that at some defect size ([Pg.132]

MN/m estimate Ae maximum defect size which could be tolerated in Ae material if it is to last for at least 1 year. 

The critical defect size in the material may be calculated from... 

In the case of the ASME codes for nuclear pressurised components, the questions of fatigue design and of flaw evaluation are dealt with separately in ASME Section III and Section XI Appendix A, respectively. The design S-A curve for machined butt welds typical of thick section pressurised components is set at a factor of two on stress range or twenty on cyclic life, whichever is more conservative, below the mean of S-N data developed on smooth cylindrical specimens in air. (A somewhat similar design curve obtained by a different method from experimental S-A data for machined butt welds is given in British Standard 5500.) These safety factors are intended to encompass any adverse influence of minor weld defects, size effects, data scatter and environment. As far as environmental effects are... 

The peak profile analysis techniques allow separating the intrinsic and extrinsic causes producing peak broadening and shift. Accurate peak profile analysis requires the instrumental broadening well characterized and, in general, significantly smaller than the one due to sample defects (size and strain). New high quality X-ray sources and... 

Vosikovsky, O., Macecek, M., and Ross, D.J. Allowable defect sizes in a sour crude oil pipeline for corrosion fatigue conditions, International Journal of Pressure Vessels and Piping, 13,197-226,1983. 

M. Birch, R. G. Brown and J. E. Brocklehurst, Dcfinning the Effective Inherent Defect Size of Graphite for Fracture Mechanics Applications, Extended Abstracts and Program-16th Biennial Conference on Carbon, Pub. American Carbon Society, 1983, pp 404405. 

The strength a of a brittle material is proportional to the fracture toughness KIC and indirectly proportional to the square root of the highest defect size Vfl in the loaded volume a =Y -Kic/yfa (Y is a geometry factor). For optimisation a must be reduced and KIC increased. Whilst the reduction of a is possible by optimising all the processing steps (Sect. 5), an improvement of KIC is mainly possible by microstructural engineering (Sect. 6). 

The best approach, however, consists of controlling the defect size and geometry and taking into account the corresponding stress-field inhomogeneity. This is realized in the frame of linear elastic fracture mechanics (LEFM), which was first applied to metals and ceramics and then adapted with success to polymers (Williams, 1984). 

The mean critical defect size (c), calculated from the Griffith equation,107108 increases markedly with increasing spinel content (Fig. 14.7). For 0.5 pm in situ spinel composites, the defect size increases up to -20%, and then decreases slightly with further additions of spinel. However, for the preformed spinel composites there is a gradual increase in defect size up to 30% spinel additions. The increase in defect size is in general much more marked at 20%, in... 

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