GB/T 15970.6-1998 Corrosion of metals and alloys - Stress corrosion testing - Part 6: Preparation and application of pre-cracked specimens
Some standard content:
GB/T 15970.6—1998
This standard is equivalent to the international standard ISO7539-6:1989 "Corrosion of metals and alloys-Stress corrosion testing-Part 6: Preparation and use of pre-cracked specimens".
GB/T15970, under the general title of "Corrosion stress corrosion test for metals and alloys", includes the following parts: Part 1 (GB/T15970.1-1995): General principles of test methods; Part 2 Preparation and application of bent beam specimens; Part 3 (GB/T15970.3-1995): Preparation and application of U-bend specimens; Part 4 Preparation and application of uniaxially loaded tensile specimens; Part 5 (GB/T15970.5-1998): Preparation and application of C-ring specimens; Part 6 (GB/T15970.6-1998): Preparation and application of pre-crack specimens; Part 7 Slow strain rate test;
Part 8 Preparation and application of welding specimens. Parts 2, 4, 7 and 8 will be formulated in succession. Appendix A of this standard is the appendix to the standard.
This standard replaces GB/T12445.1-1990 "Stress Corrosion Test Method for Double Cantilever (DCB) Specimens of High Strength Alloys", GB/T12445.2-1990 "Stress Corrosion Test Method for Pre-cracked Specimens of Cantilever Bending (CANT) of High Strength Alloys", and GB/T12445.3-1990 "Stress Corrosion Test Method for Pre-cracked Specimens of Wedge Open Loading (WOL) of High Strength Alloys" from the date of implementation. This standard was proposed by the former Ministry of Metallurgical Industry.
This standard is under the jurisdiction of the Information Standards Research Institute of the former Ministry of Metallurgy. The drafting unit of this standard: the former General Iron and Steel Research Institute of the Ministry of Metallurgy. The main drafter of this standard: Zhang Xuan.
CB/T15970.6-1998
ISO Foreword
ISO (International Organization for Standardization) is a cross-border joint organization of national standard bodies (IS member groups). The formulation of international standards is formally carried out through ISO) technical committees. Each member body interested in a subject has the right to participate in the technical committee established for that subject. International organizations, governmental and non-governmental organizations that collaborate with ISO may also participate in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
Draft international standards adopted by technical committees are circulated and approved by member bodies before being adopted as international standards by ISO committees. According to ISO procedures, a draft requires at least 75% of the member bodies to vote in favor of it. International Standard ISO75396 was developed by Technical Committee ISO/TC156\Corrosion of Metals and Alloys. ISO7539, under the general title of "Corrosion of Metals and Alloys - Stress Corrosion Testing", includes the following parts: Part 1: General test methods
Part 2: Preparation and application of bent beam specimens Part 3: Preparation and application of U-bend specimens Part 4: Preparation and application of uniaxially loaded tensile specimens Part 5: Preparation and application of C-ring specimens Part 6: Preparation and application of pre-cracked specimens Part 7: Slow strain rate test
Part 8: Preparation and application of welded specimens 778
GB/T15970.6-1 998bzxz.net
1. This series of standards gives the design, preparation and application of different types of specimens for testing in order to evaluate the stress corrosion resistance of metals. This standard is one of the GB/T15970 series of standards. The use of any standard in this series of standards requires reading the relevant provisions of GB/T15970.1. This helps to select appropriate test procedures for specific environments and also helps to provide guidance on the importance of evaluating test results. 779
1 Scope
National Standard of the People's Republic of China
Corrosion stress corrosion testing of metals and alloys Part 6: Preparation and application of pre-cracked specimens of metals and alloys--Stress corrosion testingPart 6:Preparation and use of pre-cracked specimensGB/T 15970. 6— 1998
idt Iso 7539-6:1989
generation hip GB/T12-445.1
GB/3 12145. 2
GB/T 12145.3
1.1 This standard covers the design, preparation, and use of precracked specimens for studying stress corrosion susceptibility. Recommendations for cut-door specimens are given in Appendix A (Standard Appendix). The term "metal" as used in this standard also includes alloys. 1.2 Because of the requirement to maintain elastic restraint at the crack tip, precracked specimens are not suitable for evaluating fine or thin materials such as sheet or wire. They are generally only suitable for evaluating thicker or coarser materials such as thick plates, bars, and forgings. Precracked specimens are also suitable for welded parts. 1.3 Precracked specimens can be The load can be quantitatively applied by using a constant load device or a device that increases the load monotonically, or used in conjunction with a device to produce a constant displacement at the force application point.
1.4 The outstanding advantage of the pre-cracked specimen is that the limit defect size of a component with a known geometry and a known stress can be calculated from the measured data. If the defect size exceeds the limit value, stress corrosion cracking will occur. The pre-cracked specimen can also measure the growth rate of stress corrosion cracks.
2 Referenced standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. When this standard is published, the versions shown are valid. All standards will be revised, and the parties using this standard should explore the possibility of using the latest versions of the following standards. GB/T15970.1—1995 Corrosion stress corrosion test of metals and alloys Part 1: General test methods 3 Definitions
The following definitions and the definitions given in GB/T15970.1 apply to this standard. 3.1 Crack length α The effective crack length is measured from the crack tip to the notch edge of the specimen or to the axis of the loading point, depending on the geometry of the specimen.
3.2 Specimen width W The effective width is measured from the back of the specimen to the notch face or to the loading plane, depending on the geometry of the specimen.
3.3 Specimen thickness B self-explanatory words.
3.4 Reduction in specimen thickness after side notching Bn self-explanatory words. 3.5 Half height of specimen H self-explanatory words.
3.6 Applied load P self-explanatory words.
3.7 Deflection V on the axis of the loading point, self-explanatory words. 3.8 Deflection V from the loading line self-explanatory words. 3.9 Modulus of elasticity E self-explanatory words.
3.10 Stress intensity factor Y
A factor derived from stress analysis for a specimen of a specific geometry. This coefficient will give the State Administration of Quality and Technical Supervision approved 1998-12-07 780
1999-07-01 implementation
GB/T15970.6—1998
related to the stress intensity factor for a certain crack length and load and specimen size. 3.11 Plane strain stress intensity factor K, K, is a function of applied load, crack length and specimen geometry, and has the dimension of stress × length. K, is specifically used to determine the elastic stress field intensity at the crack tip of an open specimen: K: = applied stress·crack length (N·m32) 3.12 Initial stress intensity factor K (self-explanatory term. 3.13 Plane strain fracture toughness K: cK, limit value. Under high constraint conditions of plastic deformation, under the influence of increasing stress intensity, when K: reaches this limit value, rapid crack extension independent of the environment will occur. 3.14 Provisional Kic value KQ When the effective criterion dominated by plane strain is met, KQ=KI: 3.15 Limit stress intensity factor KsCC of stress corrosion cracking sensitivity Under specific test conditions under high constraint conditions of plastic deformation, that is, under plane strain Under the condition of dominant plane strain, when the stress intensity is higher than KIscc, the initiation and extension of stress corrosion cracks will occur: 3.16 Provisional Kiscc value Kascc When the effective criterion of dominant plane strain is met, KasccKrsu. 3.17
Fatigue stress intensity K, plane strain stress intensity corresponding to the maximum stress of fatigue cycle. 3.18 Fatigue stress intensity range △K, self-explanatory words. 90.2% condition stress Rpo.2 self-explanatory words.
3.20 Applied stress α self-explanatory words.
3.21 Geometric correction factor Q self-explanatory words,
3.22 Fatigue load ratio R The algebraic ratio of the minimum load to the maximum load in the fatigue cycle. 3.23 Cracking rate The instantaneous rate of stress corrosion crack extension is determined by continuous crack monitoring method. 3.24 Average crack growth rate The average crack growth rate is obtained by dividing the change in crack length caused by stress corrosion by the test time. 3.25 Orientation of the specimen The fracture plane of the specimen is marked first in the direction of stress application and second in the direction of crack growth. It is represented by three reference axes: X, Y and 7. In addition, B is consistent with the direction of the main working force applied during material processing (short horizontal axis), X is consistent with the grain flow direction (vertical axis), and Y is perpendicular to the X and Z axes (see Figure 6). 4 Principle
4.1 It is difficult to ensure that components do not produce crack-like defects during processing or subsequent use. In view of this, pre-cracked specimens are used. The presence of these defects is sensitive to stress corrosion cracking, while this sensitivity is not obvious in amplitude load tests of smooth specimens for some materials (such as titanium). Applying the principles of linear elastic fracture mechanics, the stress state at the crack tip in pre-cracked specimens or components can be quantitatively determined by means of plane strain stress intensity. 4.2 For specimens with mechanical notches and fatigue precracks, a constant load or displacement of the force application point or a continuously increasing load is applied. The purpose of the test in a chemically aggressive medium is to quantitatively determine the conditions that produce environmentally accelerated crack growth with the help of the stress corrosion critical stress intensity factor Kiscc and the crack growth kinetics. 4.3 Empirical data can be used in design and life prediction. The purpose is to ensure that the stresses in large components are not sufficient to cause environmentally accelerated cracking at pre-existing defects, or to ensure that the crack growth will not cause a risk of instability during the design life or inspection cycle. 5 Specimens
5.1 Overview
5.1.1 All large ranges of standard specimen geometries used in fracture toughness tests can be used. The specific type of specimen may vary depending on the shape and strength of the raw material, the sensitivity of the material to stress corrosion cracking, and the purpose of the test. 5.1.2 The basic requirement is that the size must meet the conditions of triaxial stress (plane strain) dominated. Under this condition, plastic deformation is limited near the crack tip. Experience in fracture toughness tests shows that in order to measure the correct Kic value, the crack length α and thickness B of the specimen cannot be less than 2.5 (Kc/Rpu.2). To ensure sufficient restraint, large specimens should be used as much as possible, with α and B at least equal to 4 (K1c/Rpm.2). From the point of view of fracture mechanics, the minimum specimen thickness that can obtain a constant Kis value cannot be specified at this time. During stress corrosion, the presence of an aggressive environment can reduce the plasticity value associated with fracture and therefore with the size required to limit plastic deformation. However, in order to reduce the risk of insufficient constraint, a specification similar to that used in fracture toughness tests is recommended, namely; a and B are not less than 2.5 (Kic/Rpo.2)2
and preferably not less than 4 (Kic/Rpn.2)2
where K is the stress intensity applied in the test. The final determined limit stress intensity value should replace K in formula (1) to verify its validity.
5.1.3 If the specimen is to be used to determine Ksrc, the initial specimen size may be based on an estimate of the material's KIscc (it is best to estimate the Kiscc value higher at the beginning, so a larger specimen than is actually needed is used). In actual use, if the thickness of the material used does not meet the valid conditions, the same thickness of the specimen may be used for the test, as long as it can be clearly stated that the measured limit stress intensity KQsC: is only relevant to this special application. When it is necessary to determine the behavior of stress corrosion crack growth as a function of stress intensity, the specimen size should be determined by the highest stress intensity estimated for the crack growth rate. 5.1.4 Two basic types of specimens can be used: a) specimens for constant displacement tests, which are self-loaded using loading bolts; b) specimens for constant load tests, which require external loading devices. 5.1.5 Self-loaded constant displacement specimens are more economical because they do not require external loading devices. In addition, this type of specimen is compact and convenient for exposure tests in actual working environments. This type of specimen can generate stress corrosion cracks from fatigue pre-cracks, so it can be used to determine Kiscc. In this case, a group of specimens must be used to accurately determine the limit value, or to find Ks through the termination value of crack extension. Because under constant displacement test conditions, the stress intensity gradually decreases with the expansion of the crack. Therefore, in principle, a single specimen is sufficient to measure Kiscc, but in fact, considering the shortcomings of the constant displacement method described in Article 5.1.6, it is often recommended to use several specimens (not less than 3). 5.1.6 Disadvantages of constant displacement specimens:
a) External load can only be measured indirectly through the change of displacement; b) Oxides or corrosion products generated in the crack can wedge the crack surface, thereby changing the applied displacement and load values, and can also block the crack mouth, thereby hindering the entry of corrosive media and reducing the accuracy of crack length measurement using the resistance method; c) Crack bifurcation, blunting or crack deviation from the propagation surface will cause the measured crack arrest and invalid data; d) When the crack growth rate is lower than a certain value, the crack is considered to have stopped, and this value is difficult to accurately determine; e) During crack growth, elastic relaxation of the loading system can cause increased displacement and generate higher loads than expected; f) Over time, plastic relaxation in the specimen can cause the specimen load to be lower than expected; g) Loading in the test environment is sometimes impossible, which will slow down the initiation of cracks in subsequent tests. 5.1.7 The advantage of constant load tests is that they can accurately and quantitatively represent stress parameters. Since crack propagation results in an increase in the opening displacement, the likelihood of the oxide film blocking and expanding the crack is low. The determination of the crack length can be conveniently carried out using a number of continuous monitoring methods. The geometry of the constant load specimen can be chosen within a wide range, depending on the shape of the test material, the available experimental equipment and the purpose of the test. This means that crack propagation can be studied under bending or tensile loading conditions, and the specimens can be used to determine Kiscc or to determine the crack growth rate. In the former, a group of specimens with prefabricated fatigue cracks are used to determine the initiation of stress corrosion cracks on fatigue precracks. In order to avoid unnecessary incubation periods, the constant load specimens can be loaded after they have been placed in the test medium. 5.1.8 The main disadvantages of the constant load test are the high cost and large size. This is related to the need to use an external loading system. For bending specimens, the test can be carried out on a relatively simple cantilever beam testing machine, but for specimens loaded in tension, a constant load creep rupture testing machine or similar testing machine is required. In this case, in order to minimize the cost, the specimens can be loaded in series using a loading chain, which prevents the specimens from breaking and then unloading. The bulky loading system means that constant load tests are difficult to carry out under the actual operating medium conditions, but the tests can be carried out in the medium discharged by the actual operating system. 5.2 Specimen design and evaluation
Figure 1 shows the geometric shapes of some pre-cracked specimens used in stress corrosion tests. 5.2.1 Constant load specimens can be of two different types: a) the type in which the stress intensity increases with the crack length; b) the type in which the stress intensity is virtually independent of the crack length. 782
GB/T15970.61998
Specimens of type a) are suitable for determining Ksc and studying the crack growth rate as a function of K. Specimens of type b) are suitable for basic research such as the mechanism of stress corrosion.
5.2.2 Constant load specimens with increased K can be subjected to tensile or bending loads. Depending on the design, tensile loaded specimens are mainly subjected to tensile stress at the crack tip (similar to the central crack plate type of far tensile specimens) or contain a significant bending stress component (like the crack line loaded specimens such as compact tension). This significant bending stress at the crack tip can adversely affect the stability of the crack path in stress corrosion testing and can promote crack bifurcation in some materials. Bend specimens can be loaded in three-point or four-point or cantilever bending arrangements.
Constant load
K increase
Tensile loading
Distant tensile
Center plate
Crack line bending
Close reading tensile
C-shaped specimen
Bending loading
Distant bending
Three-point bending
Four-point bending
Cantilever beam
Distant bending
Double torsion plate
Crack line bending
Tower-shaped double cantilever
Stress intensity factor coefficient used in the literature Constant displacement
K reduction
Crack line bending
Influence
T-stem loading
(T-WOL)
Figure 1 Geometry of pre-cracked specimen in stress corrosion test (Wa)
No influence
Double cantilever
5.2.3 Constant K constant load specimens can be subjected to torsion loads, such as double torsion single crack plate specimens, or tensile loads, such as constant value double cantilever specimens. Although loaded in tension, the latter specimens produce crack line bending, which makes the crack propagation tend to deviate from the plane. This phenomenon can be suppressed by the side grooves.
5.2.4 Constant displacement specimens are usually self-loaded by means of a loading bolt installed on one arm of the specimen against the fixed platform of the other arm. Or two bolts on the two arms are self-loaded relative to each other. Two types can be used: 783
GB/T 15970.6—1998
a) (Wa) Influence specimens. For example, T-wedge open loading (T-WOL) specimens. This specimen affects the stress field at the crack tip because the end face is close to the crack tip.
b) (Wa) Non-influence specimens, such as double cantilever beam DCB specimens. The end face of this type of specimen is far away from the crack tip, thus ensuring that the end face position has almost no effect on the stress field at the crack tip. 5.2.5 The above-mentioned geometric specimens have unique advantages and are widely used in stress corrosion experiments. These advantages are: a) Cantilever beam bending specimens, easy to process. Used for constant load, low test cost; b) Compact tensile (CTS) specimens, used for constant load tests, with minimal material requirements; c) Self-loaded double cantilever beam (DCB) constant displacement specimens, convenient for testing under field conditions; d) T-wedge open loading (T-WOI) constant displacement specimens, which are also self-loaded specimens and require the least amount of material in the test: e) In order to study the radial expansion of longitudinal cracks under constant load conditions, the thick-walled cylinder is processed into (shaped specimens). The design details of the above-mentioned various standard specimens are shown in Figures 2a to e. B±0.8%
2W+5mm
Width=W
ThicknessB-0.5W
0.1Maximum
Notch width N=0.065W (if W exceeds 25mm) or: 1.5mm (if W is less than or equal to 25mm) Effective length l=0.25~0.45W
Effective crack length a=0.45~0.55W
Figure 2a) Proportional dimensions and tolerances of cantilever beam test specimens 781
0. 2%w TA
Root radius
0.1Maximum
Net width=W
Total width C=1. 25 W
Thickness R=0. 5 W
Half height H= 0. 6 W
Hole diameter D=0.25W
Half of the distance between the outer edges of the hole F=1.6DNotch width N=0.065WMaximum
Effective notch length l=0.250.40W
Effective crack length a=0.45~0.55W
GB/T15970.6—1998
Figure 2b) Proportional dimensions and tolerances of compact tensile specimens 0.4/
Half height=H
Thickness B-２H
Net width W=10HMinimum
Total width CW+d
Screw diameter d-0.75HMinimum
Notch width N0.14HMaximum
Effective notch length l=2 H
GB/T15970.6-1998
60°Nominal
Dart nail surface radius 12.5~50
“A\ planes are parallel and perpendicular to each other, with a deviation within the range of 0.002H (H is the reading value). 2\B\ points on each plane are equidistant from the top and bottom of the surface, with a deviation within the range of 0.001H (H is the reading value). 3 The center line of the screw is perpendicular to the center line of the specimen, with a deviation of 1°. The material of the screw is the same as that of the specimen; the fine thread teeth are square or hexagonal heads. Figure 2c) Proportional dimensions and tolerances of double cantilever specimens 786
Thickness—B
Net width W=2.55B
Total width C=3.20B
Half height H=1. 24 B
Hole diameter D=0.718B±0.003B
Effective notch length 1=0.77B
Notch width N=0.06B
Screw diameter T=0.625B
GB/T15970.6-1998
RO.05±0.025
60°±2
The surfaces are parallel and perpendicular to each other, with a deviation within 0.002H (H is the reading value). The center line of the screw is perpendicular to the center line of the specimen, with a deviation of 1°. 2
3The material of the screw is the same as that of the specimen; the fine thread is a square or hexagonal head. %H
Figure 2d) Dimension proportions and tolerances of T-shaped wedge-shaped open loading specimens mm
Net width = W
Thickness B = 0.50W 0.01W
GB/T15970.6—1998
Hole axis to inner diameter tangent X = 0.50W ± 0.005W Notch width N = 1.5 Minimum mm 0.1W Maximum) Notch depth 10.3W
Hole axis to specimen surface Z - 0.25W ± 0.01W Hole axis to outer surface T = 0.25W ± 0.01W Hole diameter D = 0.25W ± 0.005W
Note: All surfaces are parallel and perpendicular, with a deviation within 0.002W (W is the reading value), the "E\ surface is perpendicular to the "Y\ surface, with a deviation within 0.02W (W is the reading value).
Figure 2e) Dimensional proportions and tolerances of C-shaped specimens 5.2.6 If necessary, for example, when it is difficult to accurately control the initiation and/or propagation of fatigue cracks, it is advisable to use a specimen with a herringbone notch as shown in Figure 3. If necessary, the angle of this notch can be increased from 90° to 120°. 5.2.7 Where it is necessary to determine the crack opening displacement, such as when a deflection is applied to a constant displacement specimen, the notch for mounting the extensometer can be machined into a notch as shown in Figure 4a). The notch can be screwed or glued to the opposite sides of the specimen notch, as shown in Figure 4b): Figure 4c) shows a detailed view of a suitable tapered beam extensometer. 788250.40W
Effective crack length a=0.45~0.55W
GB/T15970.6—1998
Figure 2b) Proportional dimensions and tolerances of compact tensile test specimens 0.4/
Half height=H
Thickness B-２H
Net width W=10HMinimum
Total width CW+d
Screw diameter d-0.75HMinimum
Gap width N0.14HRoot maximum
Effective gap length 1=2H
GB/T15970.6-1998
60°Nominal|| tt||Dart nail surface radius 12.5~50
“A\ surfaces are parallel and perpendicular to each other, with a deviation within a range of 0.002H (H is the reading value). 2\B\ points on each surface are equidistant from the top and bottom of the surface, with a deviation within a range of 0.001H (H is the reading value). 3 The center line of the screw is perpendicular to the center line of the specimen, with a deviation of 1°. The material of the screw is the same as that of the specimen; the fine thread teeth are square or hexagonal heads. Figure 2c) Proportional dimensions and tolerances of double cantilever specimens 786
Thickness—B
Net width W=2.55B
Total width C=3.20B
Half height H=1. 24 B
Hole diameter D=0.718B±0.003B
Effective notch length 1=0.77B
Notch width N=0.06B
Screw diameter T=0.625B
GB/T15970.6-1998
RO.05±0.025
60°±2
Surfaces are parallel and perpendicular to each other , the deviation is within 0.002H (H is the reading value). The center line of the screw is perpendicular to the center line of the specimen, with a deviation of 1°. 2
3 The material of the screw is the same as that of the specimen; the fine thread is a square or hexagonal head. %H
Figure 2d) Dimension ratio and tolerance of T-shaped wedge-shaped open loading specimen mm
Net width = W
Thickness B = 0.50W0.01W
G B/T15970.6—1998
Hole axis to inner diameter tangent X=0.50W±0.005W Notch width N=1.5 minimum mm (0.1W maximum) Notch depth 10.3W
Hole axis to specimen surface Z-0.25W±0.01WHole axis to outer surface T=0.25W±0.01WHole diameter D=0.25W±0.005W
Note: All surfaces are parallel and perpendicular, with a deviation within 0.002W (W is the reading value), and the "E\ surface is perpendicular to the "Y\ surface, with a deviation within 0.02W (W is the reading value).
Figure 2e) Dimension proportions and tolerances of C-shaped specimens 5.2.6 If necessary, for example, when it is difficult to accurately control the initiation and/or propagation of fatigue cracks, a herringbone notch specimen as shown in Figure 3 may be used. If necessary, the angle of the notch can be increased from 90° to 120°. 5.2.7 Where crack opening displacement is to be determined, such as when deflection is applied to a constant displacement specimen, the notch for mounting the extensometer can be machined into a notch as shown in Figure 4a), which can be screwed or glued to the opposite sides of the specimen notch, as shown in Figure 4b). Figure 4c) shows a detailed diagram of a suitable tapered beam extensometer. 788250.40W
Effective crack length a=0.45~0.55W
GB/T15970.6—1998
Figure 2b) Proportional dimensions and tolerances of compact tensile test specimens 0.4/
Half height=H
Thickness B-２H
Net width W=10HMinimum
Total width CW+d
Screw diameter d-0.75HMinimum
Gap width N0.14HRoot maximum
Effective gap length 1=2H
GB/T15970.6-1998
60°Nominal|| tt||Dart nail surface radius 12.5~50
“A\ surfaces are parallel and perpendicular to each other, with a deviation within a range of 0.002H (H is the reading value). 2\B\ points on each surface are equidistant from the top and bottom of the surface, with a deviation within a range of 0.001H (H is the reading value). 3 The center line of the screw is perpendicular to the center line of the specimen, with a deviation of 1°. The material of the screw is the same as that of the specimen; the fine thread teeth are square or hexagonal heads. Figure 2c) Proportional dimensions and tolerances of double cantilever specimens 786
Thickness—B
Net width W=2.55B
Total width C=3.20B
Half height H=1. 24 B
Hole diameter D=0.718B±0.003B
Effective notch length 1=0.77B
Notch width N=0.06B
Screw diameter T=0.625B
GB/T15970.6-1998
RO.05±0.025
60°±2
Surfaces are parallel and perpendicular to each other , the deviation is within 0.002H (H is the reading value). The center line of the screw is perpendicular to the center line of the specimen, with a deviation of 1°. 2
3 The material of the screw is the same as that of the specimen; the fine thread is a square or hexagonal head. %H
Figure 2d) Dimension ratio and tolerance of T-shaped wedge-shaped open loading specimen mm
Net width = W
Thickness B = 0.50W0.01W
G B/T15970.6—1998
Hole axis to inner diameter tangent X=0.50W±0.005W Notch width N=1.5 minimum mm (0.1W maximum) Notch depth 10.3W
Hole axis to specimen surface Z-0.25W±0.01WHole axis to outer surface T=0.25W±0.01WHole diameter D=0.25W±0.005W
Note: All surfaces are parallel and perpendicular, with a deviation within 0.002W (W is the reading value), and the "E\ surface is perpendicular to the "Y\ surface, with a deviation within 0.02W (W is the reading value).
Figure 2e) Dimension proportions and tolerances of C-shaped specimens 5.2.6 If necessary, for example, when it is difficult to accurately control the initiation and/or propagation of fatigue cracks, a herringbone notch specimen as shown in Figure 3 may be used. If necessary, the angle of the notch can be increased from 90° to 120°. 5.2.7 Where crack opening displacement is to be determined, such as when deflection is applied to a constant displacement specimen, the notch for mounting the extensometer can be machined into a notch as shown in Figure 4a), which can be screwed or glued to the opposite sides of the specimen notch, as shown in Figure 4b). Figure 4c) shows a detailed diagram of a suitable tapered beam extensometer. 788
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