why notch is provided on specimun
Answers
During the 1960’s, the nature of the notch acuity was strongly debated. and a sharper acuity was recommended. Atthe same time, the introduction of linear elastic fracture mechanics led to the use of pre-cracked Charpy specimens. However the introduction of this kind of specimen has never supplanted the use of the traditional Charpy V notch. The initial U notch recommended by Charpy has been progressively discarded. In the 1970s, the adoption of the fracture mechanics concept led to the evaluation of fracture toughness via the use of Charpy impact tests in terms of the critical stress intensity factor or the critical strain energy release rate. This approach requires that the critical load is suitably evaluated and the free oscillations experienced by the specimen during impact are understood. The recent introduction of Notch Fracture Mechanics has provided a promising tool for this problem. In this approach, there is no fundamental difference between fracture emanating from a notches or a crack. However, the effective fracture stress is sensitive to stress field conditions and particularly to relative stress gradient. It is interesting to notice that Charpy implicitly suggested that the specific work for fracture is a measure of fracture toughness. He termed this Resilience. This parameter is now realised as an energy fracture criterion in the form of JIC
The notch serves as stress and more concentration zone as some materials are known to be sensitive to some materials than the others hence necessary in specimun provision.
In dimension, the depth and tip of the notch is very important in the specimen .
Notches actually fixes some instance where you want your specimen not to succeed