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environmental stress fracture
In materials science, environmental stress fracture or environment assisted fracture is the generic name given to premature failure under the influence of tensile stresses and harmful environments of materials such as metals and alloys, composites, plastics and ceramics.
Metals and alloys exhibit phenomena such as stress corrosion cracking, hydrogen embrittlement, liquid metal embrittlement and corrosion fatigue all coming under this category. Environments such as moist air, sea water and corrosive liquids and gases cause environmental stress fracture. Metal matrix composites are also susceptible to many of these processes.
Plastics and plastic-based composites may suffer swelling, debonding and loss of strength when exposed to organic fluids and other corrosive environments, such as acids and alkalies. Under the influence of stress and environment, many structural materials, particularly the high-specific strength ones become brittle and lose their resistance to fracture. While their fracture toughness remains unaltered, their threshold stress intensity factor for crack propagation may be considerably lowered. Consequently, they become prone to premature fracture because of sub-critical crack growth. This article aims to give a brief overview of the various degradation processes mentioned above.
==Stress corrosion cracking==
Stress corrosion cracking is a phenomenon where a synergistic action of corrosion and tensile stress leads to brittle fracture of normally ductile materials at generally lower stress levels. During stress corrosion cracking, the material is relatively unattacked by the corrosive agent, but fine cracks form within it. This process has serious implications on the utility of the material because the applicable safe stress levels are drastically reduced in the corrosive medium. Season cracking and caustic embrittlement are two stress corrosion cracking processes which affected the serviceability of brass cartridge cases and riveted steel boilers respectively.
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