Due to the very large number of tests offered, descriptions of those most commonly requested have been gathered into the following groups:. ASTM E covers the determination of resistance to fracturing of metallic materials by R-curves using either the center-cracked tension panel M T , the compact specimen C T , or the crack-line wedge-loaded specimen C W , to deliver applied stress intensity factor, K, to the material. An R-curve is a continuous record of toughness development in terms of KR plotted against crack extension in the material as a crack is driven with a continuously increased stress intensity factor, K. R-curves characterize the resistance to fracture of materials during incremental slow-stable crack extension and result from growth of the plastic zone as the crack extends from a sharp notch.
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Standard Test Method for. K-R Curve Determination 1. A number in parentheses indicates the year of last reapproval. A K-R curve is a continuous record of toughness development resistance to crack extension in terms of K R plotted against crack extension in the specimen as a crack is driven under an increasing stress intensity factor, K. The values given in parentheses are for information. It is the responsibility of the user of this standard to establish appro- priate safety and health practices and determine the applica- bility of regulatory limitations prior to use.
Current edition approved Nov. Published November Originally approved in Referenced Documents. K a p p is an engineer- ing estimate of toughness that can be used to calculate residual strength. K a p p depends on the material, specimen size, and specimen thickness and as such is not a material property.
K c depends on the material, specimen size, and specimen thickness and as such is not a material property. Summary of Test Method. Wacker Dr. United States. No further reproductions authorized. The crack is driven forward by continuously or incrementally increasing force or displacement.
Methods of measuring crack extension and of making plastic-zone corrections to the physical crack size are prescribed. Expressions for the calcu- lation of crack-extension force K R are given. Criteria for determining if the specimen conditions are predominantly elastic are provided.
It provides a record of the toughness development as a crack is driven stably under increasing applied stress intensity factor K. For a given material, K-R curves are dependent upon specimen thickness, temperature, and strain rate. The amount of valid K-R data generated in the test depends on the specimen type, size, method of loading, and, to a lesser extent, testing machine characteristics.
The K-R curve may be superimposed on the family of crack driving curves as shown in Fig. The intersection of the crack driving curves with the K-R curve shows the expected effective stable crack extension for each loading condition. N OTE 1—Fixed displacement in crack-line-loaded specimens results in a decrease of K with crack extension.
N OTE 2—With force control, K usually increases with crack extension, and instability will occur at maximum force. Single pin grips can be used on specimens less than mm 12 in. For specimens wider than mm 12 in. Grips should be carefully aligned to minimize the introduction of bending strain into the specimen.
Pin or gimbal. If extra-heavy-gauge, high-toughness materials are to be tested, the suitability of the grip arrangement may be checked using the AISC Steel Construction Manual. Buckling seriously affects the validity of a K analysis and is particularly troublesome when using compliance techniques to determine crack size 7.
It is therefore required that buckling constraints be affixed to the M T and C T specimens in critical regions when conditions for buckling are anticipated. A procedure for the detection of buckling is described in 9.
Unless it can be shown by measurement or analysis that buckling will not occur during a test, buckling. The guides shall be so designed to prevent sheet kinking about the crack plane and sheet wrinkling along the specimen width. Buckling constraints should provide a high stiffness constraint against out-of-plane sheet displacements while minimizing friction. Buckling constraints with additional pressure adjustment capability near the center of the specimen are recommended 6.
Friction between the specimen and the buckling constraints shall not interfere with the in-plane stress distribution in the specimen. A suspension system to prevent the buckling constraint from sliding down the specimen is recommended. It is convenient to use a base plate and cover plate with ports cut at appropriate locations for attaching clip gages and for crack size observations.
Friction between buckling. Care shall be taken to keep lubricants out of the crack. The initial clamping forces between opposing plates should be high enough to prevent buckling but not high enough to change the stress distribution in the region of the crack tip at any time during the test. For small C T specimens, the gage recommended in Test Method E may have a sufficient linear working range to be used. However, testing specimens with W greater than mm 5.
This gage is inserted into a machined hole. The diameter d i , is the gage span 2 Y used in the calibration. Detail drawings of the gage are given in Fig. Radius of the attachment tip should be less than the radius of the circular knife edge in the specimen. However, other types of gages used over different span lengths are equally acceptable provided the precision and accuracy requirements are retained. For example, the conventional clip gage of Test Method E may be used with screw attached knife edges spanning the crack at a chosen span 2 Y.
When using the. This is the actual deformation measurement point, not the gage length of the clip gage itself. If force is sustained at given increments so that the crack stabilizes, physical crack size can be determined within 0. A video or CCD camera recording system may also be useful for determining in-plane strain distribution and out-of-plane dis- placements Specimen unloading compliance values are substituted into the appropriate calibration curve or compliance expression to determine physical crack size a p.
In this case, effective crack size can be computed by adding the plastic zone size at each measurement point. Crack size is determined from compliance measurements using the compliance equations or tables for the specimen tested as described in Section Compliance calibration curves have been developed for. The choice of specimen type depends on the amount of material available, the type of test to be run, and the type of equipment available.
Ideally, the K-R curve should not depend on the specimen type, although the amount of valid K-R curve generated will depend on the specimen type and size. If the material is highly anisotropic, it may be preferable. The following sections provide information about each specimen type. Test-to-test vari- ability in K-R curves also depends on the material being tested. It is recommended that at least duplicate tests on multiple lots of material be performed when developing design data.
For quality assurance testing, a single test can be performed. Methods for estimating specimen size to ensure predominantly. Specimen Compliance Measurement Requirements. This section provides background and require- ments for the use of compliance techniques. The loading compliance technique and the calibration information are used to determine effective crack size a e directly. The crack size is automatically corrected for the plastic-zone and these values of a e can be used directly in the appropriate stress intensity factor solutions to determine K R.
Unloading compliance can also be used to determine physical crack size a p. In this technique, the speci- men compliance is measured during periodic load reversals.
Methods for determining invalid data points are provided in subsequent sections of the method. It is advisable to have a root radius at the ends of the notch of 0. Fatigue precracking is highly recommended and may be omitted only if it has been demonstrated for the material and thickness of interest that the machined notch root radius effectively simulates the sharpness of a fatigue precrack.
The starter notch should be extended by fatigue precrack not less than 1. The procedure for precracking is given in Testing Procedures, Section 9. In this case, the length requirement between the innermost gripping points is relaxed to 1. The machined notch length shall be between 0. The machined notch must lie within the envelope shown in Fig.
A fatigue precrack shall be initiated from each end of the starter notch using the procedure in 9. The fatigue precrack shall extend from the starter notch by at least 1. The original crack size, 2 a o machined notch plus fatigue precrack shall be within the range of 0. Section 11 is the dimension from the specimen centerline to the crack tip. This assumes that the crack is perfectly symmetrical with respect to the specimen centerline.
In practice, this is the half of the average tip-to-tip crack length measurement. This can be done by attaching knife edges to the specimen with screws or cement to accept a commercial clip gage or the one shown in Fig. The specimen can also be machined with integral knife edges using tapered holes as shown in Fig.
M T specimen, the net section stress based on the physical crack size must be less than the yield strength of the material at the test temperature. The M T specimen width W and original crack size a o should be selected to provide valid K R data up to effective crack extension values of interest. In general, a wider specimen will provide valid data up to a larger value of effective crack extension than a narrow specimen. As a guide, a specimen 27 r Y wide and with an original crack size 2 a o of 0.
It therefore is desirable to have an estimate of the maximum value of K R expected in the test before designing the specimen. As an aid, the following table lists minimum recommended M T sizes for assumed ratios of K R m a x to yield strength. Length A.
ASTM E561 – K-R Curve Determination Testing
Historical Version s - view previous versions of standard. Work Item s - proposed revisions of this standard. More E It provides a record of the toughness development as a crack is driven stably under increasing applied stress intensity factor K.
Standard Test Method for K-R Curve Determination