ASTM C1421 Fracture Toughness at ambient temperature

Scope:

ASTM C1421 test quantitatively measures fracture toughness (KIc) of various ceramic specimens in surrounding temperature. This test is a collection of three tests – precracked beam test specimen (KIpb), chevron notched beam test specimen (KIvb), and surface crack in flexure (KIsc). All the three methods are based principally on using the existence of a sharp, real crack for detecting any crack extension. Performing  all the three tests is essential as the result obtained by one cannot give precise measurements. However, depending on various R-curve possibilities, certain specific tests are preferred over others. For small-crack fracture toughness, KIsc method is prevalent while for longer-cracks KIvb test results have proven better. The KIpb test reflects either for short or long-crack length depending upon precracking conditions. While for ceramic specimens with a flat (no) R-curve, all three tests are expected to be the same. Tests conducted by ASTM C1421 deliver specific fracture values that depend upon rate, temperature, and surrounding environment.

Test Procedure:

ASTM C1421 involves application of force on a given ceramic specimen in three or four point flexure. The ceramic test specimen can either have a crack before the tests (pb, sc) or develop one during the loading (vb). At least five cycles of measurement of each testing condition must be performed. It is advisable for the sc test specimens to be only tested in four-point fixtures.

Sample size:

For the precracked beam method in ASTM C1421, the test specimen must have a cross-section of 3 mm by 4 mm. While for the surface crack in flexure method, in addition to having a similar cross-section it must also have a length of 25 mm or greater.
The chevron notch flexure method needs cubic samples of different dimensions.

Data:

Data analysis of ASTM C1421 uses values conveyed in accordance with the International System of Units (SI) and IEEE/ASTM SI10. All the values are to be taken in SI units.

Keywords:

Ceramics, flexural strength, ASTM C1421

Conclusion:

Hence, ASTM C1421 is a standard test method for determination of fracture toughness of advanced ceramics at ambient temperature.