Definition - What does Precracked Specimen mean?
A precracked specimen is a notched sample metal that is used to measure the propagation of cracks in an effective manner. It is a preferred method to evaluate crack propagation during corrosion fatigue.
It is a measurement involving velocity of crack propagation in order to assess corrosion fatigue even further. With precracked specimens, cracking tends to occur at the point of the notch. The notch is considered to realistically represent inconsistencies that are often introduced to metals during welding or processing and allows for the assessment of fatigue cracking.
Corrosionpedia explains Precracked Specimen
Corrosion fatigue typically takes place within a corrosive environment. It is the mechanical degradation of substances under cyclic loading and corrosion. Almost all structures in engineering go through alternating stress and harmful environments. The environment plays a vital role in influencing high strength matter’s fatigue.
Materials with particularly high strength make use of precracked specimen testing, so that the strength and fatigue crack behavior can be assessed. Fractures in materials can be promoted by recurrent slip bands, pitting and other factors. Corrosion fatigue can be decreased through alloy additions, cathodic protection or inhibition.
During testing under normal fatigue involving smooth specimens, more than 90% is used in the nucleation of the crack, with the remaining in its propagation. Crack nucleation in corrosion fatigue is assisted by corrosion itself. Generally, 10% of life is enough at this stage, while the rest is spent on the propagation of cracks. Hence, it will be more beneficial to measure the behavior of crack propagation at corrosion fatigue stages. Fracture mechanics use precracked specimens to measure the propagation of cracks. Much importance is given to the velocity of crack propagation to evaluate corrosion fatigue.