Fracture Toughness of Advanced Structural Ceramics: Applying ASTM C1421

Abstract

The three methods of determining the quasi‐static Mode I fracture toughness (KIc) (surface crack in flexure—SC, single‐edge precracked beam—PB, and chevron‐notched beam—VB) found in ASTM C1421 were applied to a variety of advanced ceramic materials. All three methods produced valid and comparable KIc values for the Al2O3, SiC, Si3N4, and SiAlON ceramics examined. However, not all methods could successfully be applied to B4C, ZrO2, and WC ceramics due to a variety of material factors. The coarse‐grained microstructure of one B4C hindered the ability to observe and measure the precracks generated in the SC and PB methods while the transformation toughening in the ZrO2 prevented the formation of the SC and PB precracks and thus made it impossible to use either method on this ceramic. The high strength and elastic modulus of the WC made it impossible to achieve stable crack growth using the VB method because the specimen stored a tremendous amount of energy prior to fracture. Even though these methods have passed the rigors of the standardization process there are still some issues to be resolved when the methods are applied to certain classes of ceramics. It is recommended that, when appropriate, at least two of these methods be employed to determine the KIc, especially when a new or unfamiliar ceramic is being evaluated.

Application of ASTM C1421 to WC-Co fracture toughness measurement

“…Table 2 shows the fracture toughness values from the SC and PB methods in ASTM C1421 and the Palmqvist method in ISO 20,879. The SCF method was successfully used to determine the fracture toughness of a "binderless" WC material [44], but similar success could not be achieved on the composition containing 10% Co. This was due to the absence of a suitable precrack forming under the Knoop indentation in the 10% Co material.…”

“…The material properties of the studied compositions, as determined for this effort, are described in Table 1, which also includes information on the "binderless" WC from Cercom 5 [44] for comparison. Table 2 shows the fracture toughness values from the SC and PB methods in ASTM C1421 and the Palmqvist method in ISO 20,879.…”

“…These results will be combined with the results from a binderless WC [44] to determine the applicability of the different fracture toughness methodologies to this class of materials.…”

“…The standard is also supported by a standard reference material, (SRM) 2100 2 [43], which can be used to verify that an investigator is conducting each of the three methods properly. The three techniques in ASTM C1421 have been used to determine the toughness of a "binderless" WC material [44]. Testing showed that the SC and PB methods produced acceptable, but slightly different, values.…”

Compositions Optimization of Antang Corundum for Developing Advanced Ceramic

“…It is on this note that the research seeks to formulate a beneficiated alumina (via froth floatation) for the development of ceramic for armour application and compare with an established ceramics of CoorsTek Ceramics; AD-series. CoorsTek Ceramics is well known in the field of ballistics and it has been effectively used by researchers: Swab et al, 2014;Serjouei et al, 2014;Bourne et al, 2007;Sarva et al, 2007;Fawaz et al, 2004;Shih et al, 1998;Bless et al, 1996. CoorsTek AD-85 alumina was specifically referred as the material has alumina content (Al2O3-85%) close to the main starting material (Antang corundum alumina).…”