Environmentally Induced Failure

Environmentally induced failures cost industries billions of dollars every year. A 1995 study reported that the cost impact of corrosion to the U.S. economy totaled nearly 300 billion annually, about 4% of the gross domestic product (Kuruvilla, 1999). Corrosion failures are usually caused by electrochemical reactions on the surfaces between the components and the environments. Typically, these corrosion failures occur way into their life cycles, otherwise defined by the loading conditions. They often occur unexpectedly in service. It is paramount to manage corrosion control and assess part corrosion resistance for a critical structural component of a machine. In automotive industries, corrosion management is part of the automotive 

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Although the potential that is applied to microelectronic devices is normally relatively limited (< 5V), very large electric fields can result because of the very small separation distances between conductors. When condensed water and ionie contamination are present between the lines (on the surface of separating insulators), these fields produce undesirable results by means of the three separate, but related mechanisms described next and shown schematically in Figure 4. For reference, these processes are often referred to as electrolytic. An extensive review of this subject was compiled by Steppan et al. [45], The voltage driver is normally externally applied, but another source is the semiconductor junctions that exist within an IC [17], Most environmentally induced failures in ICs that are observed in practice, and especially during accelerated aging, are caused by the applied electrical bias. 

Corrosion also occurs as a result of the conjoint action of physical processes and chemical or electrochemical reactions (1 3). The specific manifestation of corrosion is deterrnined by the physical processes involved. Environmentally induced cracking (EIC) is the failure of a metal in a corrosive environment and under a mechanical stress. The observed cracking and subsequent failure would not occur from either the mechanical stress or the corrosive environment alone. Specific chemical agents cause particular metals to undergo EIC, and mechanical failure occurs below the normal strength (5aeld stress) of the metal. Examples are the failure of brasses in ammonia environments and stainless steels in chloride or caustic environments. 

Environmentally induced cracking consists of (i) stress corrosion cracking (ii) corrosion fatigue and (iii) hydrogen-induced cracking. The general features of these modes of failure are given below ... 

Besides the stress of state in the polymer, environmental stress cracking in polymers involves both solubility and absorption rate phenomena. Sensitizing media that cause ESC can be divided into two categories those that swell or wet the polymer and those that chemically react with the polymer. The medium may be gaseous or liquid. The former mechanism has been the subject of numerous studies and is commonly recognized as the primary cause of the majority of chemically induced failures of polymers. Although both amorphous and semicrystalline polymers are susceptible to ESC, it is well known that amorphous polymers tend to be more at risk. The close packing of chains in the crystalline domains of semicrystalline polymers acts as a barrier to fluid. 

Reproductive failure can be induced by environmental hazards at any level, although most types of infertility have not been linked to environmental factors. Since it is not ethically possible to observe or impose reproductive toxic exposures on human subjects, much of what we believe about the effects of putative toxins are based on the assumption that well-defined spontaneous reproductive failures are accurate surrogates for environmentally induced defects. Spontaneous reproductive failures, together with results from animal experiments, are used as models to predict or to understand the impact of reproductive toxicants on the human system. 

The total cost of material fracture is about 4% of gross domestic product in the United States and Europe (88,89). Fracture modes included in the cost estimates were stress-induced failures (tension, compression, flexure, and shear), overload, deformation, and time-dependent modes, such as fatigue, creep, SCC, and embrittlement. The environmentally assisted corrosion problem is very much involved in the maintenance of the safety and reliability of potentially dangerous engineering systems, such as nuclear power plants, fossil fuel power plants, oil and gas pipelines, oil production platforms, aircraft and aerospace technologies, chemical plants, and so on. Losses because of environmentally assisted cracking (EAC) of materials amount to many billions of dollars annually and is on the increase globally (87). 

In any case, the energy (or stress) required to induce failure under a given set of loading and environmental factors is clearly important. Different test methods may be appropriate, depending on the nature of the application—for example, on whether the polymer may be subjected to a slowly applied stress, to a sudden impact, to a cycling load, and so forth (see Section 1.7). 

Despite the many failures encountered over the last decades in up-scaling photochemical reactions, industrial preparative photochemistry has not lost its image as an attractive tool for the synthesis of fine chemicals. Reaction conditions (solvent, temperature, work-up procedures) are, in general, quite flexible and facilitate implementation of such processes on an industrial scale in terms of environmental protection. In addition, light-induced oxidation processes exhibit a very promising potential for the chemical treatment of contaminated surface and ground waters, as well as for liquid and gaseous industrial waste. 

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