Environmental enhancement

One of the conclusions from the 1992 United Nations Conference on Environment and Development in Rio de Janeiro (the Earth Summit) was the urgent need to find a more sustainable way of life, based on careful use of resources and a reduction in environmental emissions. There was also a call to move towards a model in which environmental enhancement is fully integrated with economic development. The consequences of this summit have been far-reaching not least by the fact that, in Europe and elsewhere, environmental protection requirements are now integrated into many policies rather than being separate pieces of legislation. Indeed Article 2 of the EC treaty states that the Community shall. .. promote throughout the Community harmonious, balanced and sustainable development of economic activities This may be viewed as the first step towards... 

Additional tests are planned to determine the effect of test frequency on the crack growth rate range where the transition occurs. On the basis of similar results in environmentally enhanced crack growth in metal alloys, the growth rate transition would be expected to decrease with increasing test frequency. 

Figure 7.1. Schematic illustration of the sequential processes for environmental enhancement of crack growth by gaseous (a) and aqueous (b) environments. Embrittlement by hydrogen is assumed, and is schematically depicted by the metal-hydrogen-metal bond.

Subcritical Crack Growth Environmentally Enhanced Crack Growth under Sustained Loads (or Stress Corrosion Cracking)... 

Figure 8.7. Block diagram showing the various processes that are involved, and their relationships, in the environmental enhancement of crack growth.

The rate of environmentally enhanced crack growth is essentially inversely proportional to the time required to cover (or for the environment to react) with an increment of newly exposed crack surface. It is estimated based on the time required for the environment to fully react with an increment of newly produced crack surface, or in terms of the rate of supply of the environment and the rate of consumption (surface reaction) namely, mass balance. 

Miller, C. F., Ph.D. Dissertation, Chemical Aspects of Environmentally Enhanced Crack Growth in Ni-Based SuperaUoys, Lehigh University (March 2001). 

Modeling of Environmentally Enhanced Fatigue Crack Growth Response... 

Environmentally enhanced crack growth results from a sequence of processes and is controlled by the slowest process in the sequence. ... 

Gao, M., Dwyer, D. J., and Wei, R. P., Niobium Enrichment and Environmental Enhancement of Creep Crack Growth in Nickel-Base Superalloys, Scripta Metall. et Mater., 32, 8 (1995), 1169-1174. 

Gao, M., Dunfee, W., Wei, R. P., and Wei, W., Environmentally Enhanced Thermal-Eatigue Cracking of a Gamma-Based Titanium Aluminide Alloy, Proceedings of 124th International Symposium on Gamma Titanium Aluminides VII Microstructure and Mechanical Behavior, Las Vegas, NV, Y.-W. Kim, et ah, eds.. The Minerals, Metals and Materials Society, Warrendale, PA (1995), 911-918. 

Freiman SW, Wiederhom SM, Mecholsky Jr. JJ. Environmentally enhanced fracture of glass a historical perspective. Journal of the American Ceramic Society 2009 92(7) 1371-1382. 

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