ASTM C1421-99

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Designation: C 1421 – 99
Standard Test Methods for
Determination of Fracture Toughness of Advanced Ceramics
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at Ambient Temperature
This standard is issued under the fixed designation C 1421; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope K for a material can be functions of environment, test rate
Ivb
and temperature.
1.1 These test methods cover the fracture toughness deter-
1.5 These test methods are intended primarily for use with
mination of K (precracked beam specimen), K (surface
Ipb Isc
advanced ceramics which are macroscopically homogeneous.
crack in flexure), and K (chevron-notched beam specimen) of
Ivb
Certain whisker- or particle-reinforced ceramics may also meet
advanced ceramics at ambient temperature. The fracture tough-
the macroscopic behavior assumptions.
ness values are determined using beam specimens with a sharp
1.6 These test methods are divided into three major parts
crack. The crack is either a straight-through crack (pb), or a
and related sub parts as shown below. The first major part is the
semi-elliptical surface crack (sc), or it is propagated in a
main body and provides general information on the test
chevron notch (vb).
methods described, the applicability to materials comparison
NOTE 1—The terms bend(ing) and flexure are synonymous in these test
and qualification, and requirements and recommendations for
methods.
fracture toughness testing. The second major part is composed
1.2 These test methods determine fracture toughness values
of annexes that provide procedures, specimen design, precrack-
based on a load and crack length measurement (pb, sc), or a
ing, testing, and data analysis for each method. Annex A1
load measurement and an inferred crack length (vb). In general,
describes suggested test fixtures, Annex A2 describes the pb
the fracture toughness is determined from maximum load.
method, Annex A3 describes the sc method, and Annex A4
Load and displacement or an alternative (for example, time)
describes the vb method. The third major part consists of three
are recorded for the pb specimen and vb specimen.
appendices detailing issues related to the fractography and
1.3 These test methods are applicable to materials with
precracking used for the sc method.
either flat or with rising R-curves. The fracture toughness
Main Body Section
measured from stable crack extension may be different than Scope 1
Referenced Documents 2
that measured from unstable crack extension. This difference
Terminology (including definitions, orientation and symbols) 3
may be more pronounced for materials exhibiting a rising
Summary of Test Methods 4
Significance and Use 5
R-curve.
Interferences 6
NOTE 2—One difference between the procedures in these test methods Apparatus 7
Specimen Configurations, Dimensions and Preparations 8
and test methods such as Test Method E 399, which measure fracture
General Procedures 9
toughness, K , by one set of specific operational procedures, is that Test
Ic
Report (including reporting tables) 10
Method E 399 focuses on the start of crack extension from a fatigue
Precision and Bias 11
precrack for metallic materials. In these test methods the test methods for
Annexes
advanced ceramics make use of either a sharp precrack formed via bridge
Test Fixture Geometries A1
loading (pb) or via Knoop indent (sc) prior to the test, or a crack formed Special Requirements for Precracked Beam Method A2
Special Requirements for Surface Crack in Flexure Method A3
during the test (vb). Differences in test procedure and analysis may cause
Special Requirements for Chevron Notch Flexure Method A4
the values from each test method to be different. Therefore, fracture
Appendices
toughness values determined with these methods cannot be interchanged
Precrack Characterization, Surface Crack in Flexure Method X1
with K as defined in Test Method E 399 and may not be interchangeable
Ic
Complications in Interpreting Surface Crack in Flexure Precracks X2
with each other.
Alternative Precracking Procedure, Surface Crack in Flexure X3
Method
1.4 These test methods give fracture toughness values, K ,
Ipb
K , and K , for specific conditions of environment, test rate 1.7 Values expressed in these test methods are in accordance
Isc Ivb
with the International System of Units (SI) and Practice E 380.
and temperature. The fracture toughness values, K ,K , and
Ipb Isc
1.8 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1
responsibility of the user of this standard to establish appro-
This test method is under the jurisdiction of AST
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