ASTM C1421

ASTM C1421 – Standard Test Methods for Determination of Fracture Toughness of Advanced Ceramics at Ambient Temperature

Description:

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.

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.