A comparison of Charpy and Izod Impact Tests.
The impact test has been used extensively in mechanical testing of steel products, in research, and in procurement specifications for over three decades. Where correlations with fracture mechanics parameters are available, it is possible to specify CVN (Charpy V-notch) toughness values that would ensure elasticplastic or plastic behavior for fracture of fatigue cracked specimens subjected to minimum operating temperatures and maximum in service rates of loading.
The notch behavior of the face-centered cubic metals and alloys, a large group of nonferrous materials and the austenitic steels can be judged from their common tensile properties. If they are brittle in tension, they will be brittle when notched, while if they are ductile in tension they will be ductile when notched, except for unusually sharp or deep notches (much more severe than the standard Charpy or Izod specimens). Even low temperatures do not alter the characteristic of these materials to a greater extent. In contrast, the behavior of the ferritic steels under notch conditions cannot be predicted from their properties as revealed by the tension test. For the study of these materials the Charpy and Izod type tests are accordingly very useful. Some metals that display normal ductility in the tension test may nevertheless break in brittle fashion when tested or when used in the notched condition. Notched conditions include constraints to deformation in directions perpendicular to the major stress, or multi axial stresses, and stress concentrations. It is in this field that the Charpy and Izod tests prove useful for determining the susceptibility of steel to notch brittle behavior though they cannot be directly used to appraise the serviceability of a structure.
Izod impact test machine
Izod Impact test
The izod test involves the striker, the testing material, and the pendulum. The striker is fixed at the end of the pendulum. The test material is fastened at a vertical position at the bottom, and the notch is facing the striker. The striker swings downward, hitting the test material in the middle, at the bottom of it’s swing, and is left free at the top. The notch is placed to concentrate the stress, and provoke delicate failure. It lowers distortion and decreases the ductile fracture.
The test is done easily and quickly to examine the quality of the materials, and test whether it meets the specific force of impact properties.
Charpy Impact test
The Charpy method includes striking an appropriate test material with a striker fastened at the end of a pendulum. The test material is secured horizontally in place at both ends, and the striker hits the center of the test material, behind a machined notch. The notch is positioned away from the striker, fastened in a pendulum. The test material usually measures 55x10x10 millimeters. The Charpy method has a machined notch across one of the larger faces. There are two types of charpy notch, a V-notch or a U-notch. The V-notch, or the AV-shaped notch, measures 2 millimeters deep, with a 45 degree angle and 0.25 millimeter radius, parallel to the base. The U-notch, or keyhole notch, is 5 millimeters deep notch, with a 1 millimeter radius at the bottom of the notch. Higher speeds and collision energy could be achieved in a vertical style fall. This method proved to be reliable, and gave qualitative collision data.
Charpy impact test machine
- In the Izod method, the test material is placed in a vertical position, while in the Charpy method, the test material is placed horizontally.
- The notch in the Izod test is facing the striker, fastened in a pendulum, while in the charpy test; the notch is positioned away from the striker
- No standards are available for conversion from Charpy impact values to Izod impact values