MECHANICAL TESTING

Charpy Impact Utilizing Pre-Cracked Samples - ASTM E 812

"Standard Test Method for Crack Strength of Slow-Bend Precracked Charpy Specimens of High-Strength Metallic Materials"
The test method employs a Charpy specimen provided with a sharp notch terminating in a fatigue crack tested in three-point bending using fixtures that minimize the contribution of friction forces to the measured applied load. The maximum load in the test is recorded and the crack strength is determined from this value and the original dimensions of the specimen using the simple-bend equation.

The crack strength does not provide a quantitative measure of fracture resistance that could be used in the design of structures. However, experience with a number of high-strength alloys has shown that the ratio of the crack strength to the 0.2% tensile yield strength sc /sYS or to the tensile ultimate strength, sc /s UT, can be correlated with KIc / s YS or with KIc / s UT, respectfully, where KIc is the plane-strain fracture toughness in accordance with Test Method E399. The lower-strength limits of useful correlations established by the presently available data are: for steel s YS = 1378 MPa (200 ksi) for aluminum alloys s YS = 275.6 MPa (40 ksi), and the titanium alloys s YS = 826 MPa (120 ksi).

Correlations of this type can be useful for the following purposes:
In research and development of materials, to study the effects of such variables as composition, heat treatment, mechanical processing, etc., where a ranking of materials in terms of their plane-strain fracture toughness KIc may be useful.

For specifications of acceptance and manufacturing quality control and for service evaluation to compare the resistance to plane-strain fracture of a number of materials that are otherwise suitable for an application; provided that a "calibration relation" can be established between sc and KIc over a range of toughness of interest.

Index of Mechanical Testing