Alireza Khalifeh

By Alireza Khalifeh

Stress corrosion cracking (SCC) is the formation and growth of crack through materials subjected to tensile stress and a specific corrosive medium. It can lead to unexpected sudden failure of normally ductile metals. Metal-environment combinations susceptible to cracking are specific. This means that all environments do not cause SCC on all of the alloys. Additionally, the environments that cause this kind of cracking have little corrosion effect on the alloy in normal conditions. In certain states, unwanted environmental and metallurgical changes have occurred and provide the metal-environment combination sensitive to SCC. The SCC sites on the metal surfaces may not be visible by visual inspection, while metal parts are being filled with microscopic cracks. These invisible cracks progress rapidly and lead the component and structures to catastrophic failures. In this chapter, the incidence of SCC on important industrial alloys from the chemical, metallurgical, and mechanical point of view is discussed.

Part of the book: Failure Analysis

By Alireza Khalifeh

Stress corrosion cracking is a phenomenon associated with a combination of tensile stress, corrosive environment and, in some cases, a metallurgical condition that causes the component to premature failures. The fractures are often sudden and catastrophic, which may occur after a short period of design life and a stress level much lower than the yield stress. It can also occur after several years of satisfactory services due to operating errors and changing process conditions. Two classic cases of stress corrosion cracking are seasonal cracking of brass in ammoniacal environment and sensitization and stress corrosion cracking of stainless steels in existence of chlorides, caustic, and polythionic acid. Presence of crack and other defects on the material surfaces accelerates the fracture processes. Therefore, when designing components, the role of imperfections and aggressive agents together must be taken into account. The fracture mechanic introduces a material characteristic namely fracture toughness or K ISCC = σ πa = σ π a , which properly describes the fracture behavior of materials in such conditions. The main objective in writing of this chapter is to present scientific findings and relevant engineering practice involving this phenomenon.

Part of the book: Engineering Failure Analysis

By Alireza Khalifeh

This chapter deals with the fatigue fracture of the materials under cyclic loadings. Components of structures and machines may be subjected to cyclic loads and the resulting cyclic stress that can lead to microscopic physical damage and fracture of the materials involved. It has been seen at a stress well below the ultimate strength, this microscopic damage can accumulate under action of cyclic loadings until it develops into a crack that leads to final separation of the component. In addition, the material inherently has cracks and other microscopic defects that grow due to cyclic loads and lead to fracture of machine or structure parts. The failures are more often sudden, unpredictable and catastrophic which may occur after a short period of design life. The main objective in writing this chapter is to present scientific findings and relevant engineering practice involving materials fatigue failures.

Part of the book: Failure Analysis

By Alireza Khalifeh, Habib Danesh Manesh and Abolghasem Dehghan

The satisfactory design of the components is highly dependent on the adequate knowledge of the material behavior and operational conditions. For the structures under earthquakes, often this information is not available, is incomplete or inaccurate, and leads to increases the risk of the possible failures. The extensive brittle fracture of steel structures during the Northridge earthquake (USA, 1994) and Kobe earthquake (Japan, 1995) highlighted many of these deficiencies. The investigations have shown that the failures were caused by combination effects of high strain rate, welding defects, welding residual stress, and seismic loads. In this chapter, the effects of strain rates on mechanical properties of steel materials have been discussed. Welding defects act as cracks and cause the structures to fail at loads lower than design stress. Thus, the issue has been evaluated from the view point of failure mechanics. Welding processes produced residual stresses in the weldments. These regions have higher stresses triaxiality and will be prone to brittle fracture. Therefore, the role of residual stresses in the failure of steel structures is well expressed. The contents given in this chapter can be of great help in preventing the failure of structures during an earthquake and the occurrence of human and financial losses.

Part of the book: Advances in Structural Integrity and Failure