05-05-2012, 01:17 PM
Impact Testing
Impact Test.ppt (Size: 726 KB / Downloads: 51)
Need for toughness testing
The sudden and complete failure of structures at stress well below their yield strength.
Indicated that other considerations besides the conventional tensile properties must be included during the design of such structures.
Analysis of these failures and reanalysis of previous failures indicated that the fracture usually initiated at “notches”
Design failure: Two rigid member attached at a sharp angle(900 or less).
Fabrication procedure: Weld arc strikes, Tool gouges.
Flaws in the material: Flakes, porosity.
Brittle cleavage fracture
The basic factors which contribute to a brittle cleavage type of fracture are:
The tri-axial state of stress (stress concentration)
A low temperature (often sub zero)
A high strain rate or rapid rate of loading (impact testing)
Factors one and two are responsible for most of the brittle failure
Impact Testing
Dynamic load is applied suddenly- as from the result of a moving pendulum hammer to determine:
Notch toughness of the material.
Ductile to brittle transition temperature.
Two types of notched bar impact test are: