Cracks in metals

Based upon a piezoelectric 1-3-composite material, air-bome ultrasonic probes for frequencies up to 2 MHz were developped. These probes are characterized by a bandwidth larger than 50 % as well as a signal-to-noise ratio higher than 100 dB. Applications are the thickness measurement of thin powder layers, the inspection of sandwich structures, the detection of surface near cracks in metals or ceramics by generation/reception of Rayleigh waves and the inspection of plates by Lamb waves. 

Symposium on Stress-corrosion Cracking in Metals, Amer. Soc. Test. Mater.-Amer. Inst. Min. (Metall.) Engrs., Philadelphia (1944)... 

P. Manolatos, M. Jerome, and J. Galland, in Hydrogen Transport Cracking in Metals, Ed. by A. Turnbull, Institute of Materials, London, 1995, p. 155. 

The photophysical phenomena of fluorescence and phosphorescence have found varied applications in fluorescent tube lights, X-ray and TV screens, as luminescent dials for watches, as optical brighteners in white dress materials, as paints in advertisement hoardings which show enhanced brilliance by utilizing fluorescence, for detection of cracks in metal work, for tracing the course of river through caves, as microanalytical reagents, and so on. 

Radiography - An x-ray based technique used for detecting flaws in materials, for example, voids and cracks in metals. 

Glass is a classic example atomic bonds can stretch (elasticity) or rupture, but typically do not reform. In metals, atomic bonds can slide and reform, a phenomenon described by dislocation theory this gives rise to energy dissipation, which makes it much more difficult to propagate a crack in metals. 

D. O. Sprowls, Evaluation of stress-corrosion cracking, in Metals Handbook, in Corrosion, vol. XIII, ASM International, Metals Park, OH, 1987, pp. 245—282. 

C-H. Hseuh and A. G. Evans, Residual stresses and cracking in metal/ceramic systems for microelectronics packaging, J. Am. Ceram. Soc., 68 (1985) 120-6. 

Directly exposed X-ray films are used for what are known as industrial applications such as searching for cracks in metal objects, for example oil pipelines. The films can be made handleable in light by packaging with hght-opaque materials. An improvement in efficiency can be achieved by placing the film, in particular the coated side, next to a screen made from a heavy metal such as lead. The screen absorbs X-rays more effectively than the film providing primary electrons some of which can expose the film. This indirect exposure supplements that achieved by direct exposure. 

Stresses induced by electromigration, in conjunction with those produced by thermal fluctuations, collectively lead to diffusion of vacancies and inelastic deformation processes which cause stress-voiding and slit cracking in metal interconnects (Sanchez et al. (1992) and Joo and Thompson (1997)). Such failure processes are also strongly influenced by the crystallo-... 

Metal-Ceramic Interfaces, Pergamon, Oxford, 1990, p. 63. Coupled Atomistic-Continuum Calculations of Near Interface Cracking in Metal/Ceramic Composites. 

Fig. 32. Analogy between local bond flaws and cracks in metallic skins.

Kermani, M.B., Hydrogen cracking and its mitigation in the petroleum industry, Proceedings of the Conference on Hydrogen Transport and Cracking in Metals, 1994, pp. 1-8. 

Environmental-stress cracking (ESC) which is essentially the same as stress-corrosion cracking in metals... 

Tokaji, K., Ogawa, T. The growth of microstructurally small fatigue cracks in metals. ESIS 13, Mechanical Engineering Publication, London, pp. 85-99 (1992)... 

Cracks Detection of cracks in metals covered with dielectric coatings without the need for removal... 

The preceding examples refer to one-dimensional situations. When bond flaws are assessed in two dimensions, the need for the bond to always be stronger than the adherends becomes abundantly clear. If the adherends are stronger than a properly processed bonded joint with no defects, any large defect or damage acquires the characteristics of a through crack in metallic skins, as explained in O Fig. 44.24. 

Some of the papers referenced do this for rubber, nylon and tooth dentins. Peterlin, Zhurkov et al. and Becht have also made quantitative measures of bond rupture. In answer to your second question, our experimental evidence (J. Polym. Sci. A-1, 7, 2125 (1969) indicates only a small fraction of the total work of fracture can be attributed to primary bond rupture. The remainder may be attributed to secondary bond rupture, plastic and viscoelastic deformation somewhat analogous to work of plastic deformation at the tip of a crack in metals. 

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