ASTM B646-97
(Practice)Standard Practice for Fracture Toughness Testing of Aluminum Alloys
Standard Practice for Fracture Toughness Testing of Aluminum Alloys
SCOPE
1.1 This practice provides guidance for testing (a) thin products, of thicknesses equivalent to sheet that is, ([∧lt;=]0.249 in. (6.30 mm)), (b) intermediate thicknesses of plate, forgings, and extrusions, too thin for valid plane-strain fracture toughness testing but too thick for treatment as sheet, that is over 0.249 in. (6.30 mm) and up to 1 to 2 in. (25 to 50 mm), dependent upon toughness level, and (c) relatively thick products where Test Method E399 is applicable. For changes to this specification since the last issue, refer to the Summary of Changes section at the end of the standard.
1.2 This practice addresses the problem of screening tests, recognizing the complexity and expense of making formal fracture toughness measurements on great quantities of production lots, and provides alternatives in the form of simpler, less expensive tests that may be carried out either in a research or production test laboratory.
1.3 The values stated in inch-pound units are to be regarded as the standard.
1.4 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 and health practices and determine the applicability of regulatory limitations prior to use.
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Standards Content (Sample)
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Designation: B 646 – 97
Standard Practice for
Fracture Toughness Testing of Aluminum Alloys
This standard is issued under the fixed designation B 646; 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.
This standard has been approved for use by agencies of the Department of Defense.
INTRODUCTION
Fracture toughness is a key property for a number of aluminum alloys utilized in aerospace and
process industries, but at the current stage of development of fracture test techniques no standard
methods exist to cover a number of the product lines or dimensional ranges involved. Plane-strain
fracture toughness, K , is a keystone of the industry, but for the very tough alloys of principal interest,
Ic
valid measurements can be made only for relatively thick sections. Thus it is necessary to provide this
standard practice for uniform quality control test procedures for the industry, pointing out which
current standards are utilized in specific cases, and providing guidelines where no standards exist.
1. Scope B 645 Practice for Plane Strain Fracture Toughness Testing
of Aluminum Alloys
1.1 This practice provides guidance for testing (a) thin
E 23 Test Methods for Notched Bar Impact Testing of
products, of thicknesses equivalent to sheet that is, (|La0.249
Metallic Materials
in. (6.30 mm)), (b) intermediate thicknesses of plate, forgings,
E 338 Test Method of Sharp-Notch Tension Testing of
and extrusions, too thin for valid plane-strain fracture tough-
High-Strength Sheet Materials
ness testing but too thick for treatment as sheet, that is over
E 399 Test Method for Plane-Strain Fracture Toughness of
0.249 in. (6.30 mm) and up to 1 to 2 in. (25 to 50 mm),
Metallic Materials
dependent upon toughness level, and (c) relatively thick
E 561 Practice for R-Curve Determination
products where Test Method E 399 is applicable. For changes
E 602 Test Method for Sharp-Notch Tension Testing with
to this specification since the last issue, refer to the Summary
Cylindrical Specimens
of Changes section at the end of the standard.
E 616 Terminology Relating to Fracture Testing
1.2 This practice addresses the problem of screening tests,
E 1304 Test Method for Plane-Strain (Chevron Notch)
recognizing the complexity and expense of making formal
Fracture Toughness of Metallic Materials
fracture toughness measurements on great quantities of pro-
2.2 Other Document:
duction lots, and provides alternatives in the form of simpler,
Aluminum Association Bulletin T5, “Fracture Toughness
less expensive tests that may be carried out either in a research
Testing of Aluminum Alloys”
or production test laboratory.
1.3 The values stated in inch-pound units are to be regarded
3. Terminology
as the standard.
3.1 The terminology and definitions in the referenced docu-
1.4 This standard does not purport to address all of the
ments are applicable to this practice.
safety concerns, if any, associated with its use. It is the
3.2 Definitions of Terms Specific to This Standard:
responsibility of the user of this standard to establish appro-
3.2.1 For purposes of this practice, the following descrip-
priate safety and health practices and determine the applica-
tions of terms are applicable in conjunction with Practice E 561
bility of regulatory limitations prior to use.
and use of the compact specimen:
2. Referenced Documents 3.2.2 K —A value of K on the R-curve based on a 25 %
R
secant intercept of the load-crack opening displacement test
2.1 ASTM Standards:
record and the effective crack length at that point that otherwise
B 557 Test Methods of Tension Testing Wrought and Cast
satisfies the remaining-ligament criterion of Practice E 561.
Aluminum- and Magnesium-Alloy Products
3.2.3 K —A value of K on the R-curve based on the
R
max
maximum load value of the load-crack opening displacement
This practice is under the jurisdiction of ASTM Committee B-7 on Light Metals
and Alloys, and is the direct responsibility of Subcommittee B07.05 on Testing.
Current edition approved Oct. 10, 1997. Published May 1998. Originally Annual Book of ASTM Standards, Vol 03.01.
published as B 646 – 78. Last previous edition B 646 – 94. Available from The Aluminum Association, 750 3rd Ave., New York, NY
Annual Book of ASTM Standards, Vol 02.02. 10017.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
B 646
test record and the effective crack length at that point that center-slotted panels in accordance with Practice E 561, as
otherwise satisfies the remaining-ligament criterion of Practice modified by this practice, are recommended for screening and
E 561. The K value is used when the 25 % secant intercept quality control purposes as described in 7.3. The sharp notch
R
max
occurs at a point after the maximum load is reached. Charpy screening test in accordance with Test Methods E 23
3.2.4 For purposes of this practice, the following descrip- may also be applied for correlative purposes.
tions of terms are applicable in conjunction with the chevron 6.1.3 For relatively thick high-strength products, plane-
notch (short-rod and short-bar) Test Method E 1304. strain fracture toughness tests in accordance with Test Method
E 399 as supplemented by Practice B 645 are recommended.
4. Summary of Practice
For further guidelines, refer to Practice B 645; no further
4.1 This practice provides guidelines for the selection of
description is covered herein.
tests for the evaluation of the fracture toughness properties of 6.1.4 For screening tests of relatively thick high-strength
aluminum alloys, particularly for quality assurance and mate-
products, tension tests of sharply notched cylindrical speci-
rial release purposes, including: mens and the associated correlations with plane-strain fracture
4.1.1 Center-slotted panel testing of sheet products in ac-
toughness as determined in accordance with Test Method
cordance with Practice E 561, M(T) specimen procedures. E 399 and are recommended, as described in 8.2.3. Additional
4.1.2 Screening tests of sheet products in accordance with
alternative screening tests that are recommended for relatively
Test Method E 338. thick products are the chevron notch (short-rod and short-bar)
4.1.3 Plane-strain fracture toughness tests in accordance
test described in Test Method E 1304 and 8.2.1 and the sharp
with Test Method E 399. notch Charpy screening test in accordance with Test Methods
4.1.4 Intermediate thickness fracture toughness tests in E 23 and 8.2.4.
accordance with Practice B 645 and Test Method E 399.
6.1.5 For intermediate thicknesses of high-strength prod-
4.1.5 Intermediate thickness fracture toughness tests in ucts, too thin for valid plane-strain fracture toughness testing
accordance with Practice E 561 using the C(T) (compact
but too thick for large panel testing in accordance with Practice
specimen) and a 25 % secant-intercept value concept, desig- E 561, a modification of compact specimen testing in accor-
nated as K , as a single value or discrete point evaluation of
dance with Test Method E 399 as described in Practice B 645
R
the crack-growth resistance curve (R-curve). and Section 9 is recommended. For such intermediate thick-
4.1.6 Screening tests of both intermediate and relatively
ness products, three additional alternative tests exist. They are
thick materials using the chevron notch (short-rod or short-bar) as follows: a direct measure of fracture toughness using
Test Method E 1304.
Practice E 561 and the K concept as described in 9.2.1.1, the
R
4.1.7 Screening tests for a range of thickness from about same screening tests suggested for thick products involving the
0.1-in. (2.54 mm) upward using the sharp notch Charpy test as
chevron notch (short-rod or short-bar) test as described in Test
covered in Test Methods E 23. Method E 1304 and 8.2.1 and the sharp notch Charpy test in
4.1.8 Screening tests of thick materials in accordance with
accordance with Test Methods E 23 and 8.2.4.
Test Method E 602. 6.2 It is pointed out that there are no current standard
recommendations for toughness testing of relatively low-
5. Significance and Use
strength aluminum alloys which display large-scale yielding
5.1 This practice is provided to develop and maintain
even in the presence of extremely large cracks in very thick
uniformity in practices for the evaluation of the toughness of
sections. Such cases must be dealt with individually on a
aluminum alloys, particularly with regard to quality assurance
research basis using tests selected from program needs and
and material release to specifications.
anticipated design criteria. A typical case for general guidance
5.2 It is emphasized that the use of these procedures will not
is given in the literature.
alter the validity of data determined with specific test methods,
7. Fracture Toughness of Thin Sections
but provides guidance in the interpretation of test results (valid
or invalid) and guidance in the selection of a reasonable test 7.1 If a complete and precise measure of the fracture
procedure in those instances where no standard exists today. toughness of sheet or of sections of an extruded, welded, or
forged shape equal to or less than 0.249 in. (6.30 mm) in
6. Selection of Test Procedures
thickness is required, the crack-resistance curve should be
6.1 The following methods are recommended for individual
measured in accordance with Practice E 561.
products and situations: 7.2 For quality assurance or material release purposes, the
6.1.1 For products in sheet thicknesses, that is nominally
critical (or maximum) stress intensity factor for monotonically
|La0.249 in. (6.30 mm), the measurement of critical stress loaded M(T) panels tested in general accordance with Practice
intensity factor (Kc) associated with a monotonically loaded
E 561 is recommended as the index of fracture toughness. This
center-slotted panel tested in general accordance with Practice
value is designated K for purposes of this practice.
c
E 561 for center-cracked tension (M(T)) specimens is recom-
7.2.1 The recommended specimen size is 16 in. (405 mm)
mended, as described in 7.2.
6.1.2 For products in sheet thicknesses, the use of tension
Kaufman, J. G., and Kelsey, R. A., “Fracture Toughness and Fatigue Properties
tests of sharply edge-notched specimens in accordance with
of 5083-0 Plate and 5183 Welds for Liquefied Natural Gas Applications,” Properties
Test Method E 338, and the corresponding correlations of such
of Materials for Liquefied Natural Gas Tankage, ASTM STP 579, ASTM, 1975, pp.
data with the critical stress-intensity factors from tests of 138–158.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
B 646
wide with 15 in. (380 mm) being an acceptable minimum tension specimen tested in accordance with Test Method E 602
width. The initial crack length, 2a shall be equal to one quarter and the sharp notch Charpy test with root radius <0.001-in.
o
of the width, W; that is, 2a /W 5 0.25 with a tolerance (0.0254 mm) tested in accordance with Test Methods E 23.
o
of +0.0125 W − OW. The center-slot length may be either 8.2.1 Chevron notch (short-rod or short-bar) specimens.
fatigue-cracked or machine-notched, as long as the ends of any 8.2.2 Standard chevron notch (short-rod or short-bar) speci-
machined slot are sharpened with a jeweler’s saw or sharp mens 1.00-in. (25.4-mm) in diameter or 1.00 in. (25.4-mm)
notching tool. wide are recommended.
7.2.2 Specimen widths less than 15 in. (381 mm) may be 8.2.2.1 Use of the Chevron notch (short-rod or short-bar)
used for quality assurance or lot release testing, but it must be specimen test method is strongly recommended for screening
recognized that the maximum or critical stress intensity factor purposes. This test can be a direct measure of K and as a
isd ependent upon the interaction of the crack-driving force, a replacement or an alterntive to Test Method E 399. Two
function of specimen width, and the crack-resistance curve, so relatively attractive features of the chevron notch (short-rod or
the value is specimen width (as well as thickness) dependent. short-bar) method are fatigue precracking is not required and
The value will decrease with decreasing specimen width, all small overall test volume.
other factors being identical. 8.2.2.2 The stress intensity value, K , determined in
IvM
7.2.3 Except when specifically stated, test to measure K accordance with Test Method E 399, Annex 1, has been shown
c
with such specimens shall be made with face stiffeners to to correlate rerasonably well with plane-strain fracture tough-
prevent buckling above or below the center slot. ness and if a suitable correlation has been established for the
7.2.4 The K value shall be calculated at the maximum load alloy/temper/product in question, the value may be used as a
c
by the use of the secant or polynomial equation for M(T) lot release criterion. Additional background and guidance on
panels given in Practice E 561. The half crack length used in such use is presented in Section 10 and in the literature.
the K-expression shall be the effective crack length, a ,atthe 8.2.3 Sharp cylindrically notched tension specimen.
e
maximum load point calculated using the compliance expres- 8.2.3.1 While both standard specimens, ⁄2 in. (12.5 mm)
sion for M(T) panels in Practice E 1561. If, as sometimes and 1 in. (27 mm) in diameters, are used for quality control
happens, there is considerable crack extension at maximum testing, the 1 ⁄16-in. (27-mm) specimen is generally more cost
load, the point at which the load first reaches the maximum effective particularly for very tough alloys and tempers, be-
shall be used in the crack length calculations. cause of the greater sensitivity to differences in fracture
toughness at high toughness levels.
NOTE 1—K is sometimes confused with the apparent fracture tough-
c
8.2.3.2 The ratio of sharp-notch strength to tensile yield
ness, which is usually designated K or K . The apparent fracture
app co
strength has been shown to correlate reasonably well with
toughness differs from K in that the initial half crack length, a , is used
c o
in the K-expression instead of the effective crack length.
...
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