Environmental consideration fatigue

Wei, R. P., Environmental Considerations in Fatigue and Fracture of Constructional Steels, in New Horizons in Construction Materials, Vol. I, H.-Y. Fang, ed., ENVO Publishing Co., Lehigh Valley, PA (1977). 

Generally the selection technique of choice should be that which results in the fastest communication possible. Consideration of factors such as cognitive load [Cress and French, 1994], environmental changes, fatigue, aesthetics, and stability of physical skill often influence the choice of the best selection technique. 

In addition, the use of field fortification samples measures the carefulness factor of the Field Scientist during the field research and allows a Study Director/Manager or distant observer to obtain a quality control estimate on the field portion of the study. For this reason, the field fortification samples are usually meant to be different from laboratory procedural fortifications and are meant to be prepared under field conditions, which are considerably more rigorous than are controlled laboratory conditions. For example, environmental factors such as heat, humidity, wind, human stress, and other human factors such as fatigue to the Field Scientist are an integral part of any field worker exposure/re-entry study. Field fortifications made to matrices under these conditions will test and readily demonstrate the ability of the Field Scientist to perform such a difficult study under trying circumstances. 

Materials selection process can be depicted in terms of Figure 1.40. Materials selection involves many factors that have to be optimized for a particular application. The foremost consideration is the cost of the material and its applicability in the environmental conditions so that integrity can be maintained during the lifetime of the equipment. When the material of construction is metallic in nature, the chemical composition and the mechanical properties of the metal are significant. Some of the important mechanical properties are hardness, creep, fatigue, stiffness, compression, shear, impact, tensile strength and wear. 

Since the strength properties of FRP composites are more sensitive to temperature change at lower temperatures than metals, the in service ambient temperature range must be a consideration in the fatigue design. If the environmental in-service temperature is less than 50°C, fatigue properties may be considered unaffected. 

The problem is complete except for consideration of fatigue effects and of in-use hazards and environmental exposure. The fatigue analysis consists of an examination of the S-N curves for the three materials used, to determine if the lifetime expectancy is adequate for the stress levels used. If there are no S-N data available, the only alternative is a life test on the part or S-N data accumulation for the... 

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