ASTM C1421-18

ASTM C1421-18 - 1.1.2018

Significance and Use

5.1 Fracture toughness, K_Ic, is a measure of the resistance to crack extension in a brittle material. These test methods may be used for material development, material comparison, quality assessment, and characterization.

5.2 The pb and the vb fracture toughness values provide information on the fracture resistance of advanced ceramics containing large sharp cracks, while the sc fracture toughness value provides this information for small cracks comparable in size to natural fracture sources. Cracks of different sizes may be used for the sc method. If the fracture toughness values vary as a function of the crack size it can be expected that K_Isc will differ from K_Ipb and K_Ivb. Table 1 tabulates advantages, disadvantages, and applicability of each method.

1. Scope

1.1 These test methods cover the fracture toughness, K_Ic, determination of advanced ceramics at ambient temperature. The methods determine K_Ipb (precracked beam test specimen), K_Isc (surface crack in flexure), and K_Ivb (chevron-notched beam test specimen). The fracture toughness values are determined using beam test specimens with a sharp crack. The crack is either a straight-through crack formed via bridge flexure (pb), or a semi-elliptical surface crack formed via Knoop indentation (sc), or it is formed and propagated in a chevron notch (vb), as shown in Fig. 1.

1.6 Values expressed in these test methods are in accordance with the International System of Units (SI) and IEEE/ASTM SI 10.

1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.9 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

2. Referenced Documents

C1161-18(2023)	Standard Test Method for Flexural Strength of Advanced Ceramics at Ambient Temperature
C1322-25	Standard Practice for Fractography and Characterization of Fracture Origins in Advanced Ceramics
E4-24	Standard Practices for Force Calibration and Verification of Testing Machines
E112-25e1	Standard Test Methods for Determining Average Grain Size (Includes all amendments and changes 9/9/2026).
E177-26a	Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods (Includes all amendments and changes 5/14/2026).
E337-15(2023)	Standard Test Method for Measuring Humidity with a Psychrometer (the Measurement of Wet- and Dry-Bulb Temperatures)
E691-23	Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
E740-03	Standard Practice for Fracture Testing with Surface-Crack Tension Specimens
E1823-26a	Standard Terminology Relating to Fatigue and Fracture Testing (Includes all amendments and changes 8/27/2026).
IEEE/ASTM SI 10	Standard for Use of the International System of Units (SI) (The Modern Metric System)
NIST SRM 2100	Fracture Toughness of Ceramics Available from National Institute of Standards and Technology (NIST), 100 Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http://www.nist.gov.