Main Article Content
Failure may result from mechanical or chemical reactions of structural materials with aggressive environment, moisture or other impact, or as a consequence of reducing the surface energy of the body. Problems in calculating the impact of the aggressive environment on the extension of cracks are solved by introducing a stress intensity factor that is treated as a material/environment system constant. The reduced toughness depends on the adsorbed chemical substance that is a function of the concentration and time in which the cracked material is exposed to aggressive fluid (lubricant, tribology matter). The choice of material is very important for structures operating in salty environments. Fatigue also occurs as a result of temperature change (principally varies in regions of low and high temperature). At low temperature a relatively stable composition and structure are retained (increased service life), and at high temperatures, various phase transformations are present (aging, creep and recrystallization), where as a rule tensile and fatigue strength both decrease. These aspects of crack propagation due to cyclic loading or environmental impact highlight the significance of fatigue in the integral design, including tribology aspects.