This standard specifies the method for safety assessment of welded joints according to the brittle fracture principle. This standard is applicable to non-austenitic steel welded structures. It is mainly used for brittle fracture assessment of plane defects such as cracks or crack-like defects in fusion welded joints. JB/T 5104-1991 Assessment of brittle failure of welded joints JB/T5104-1991 Standard download decompression password: www.bzxz.net

Mechanical Industry Standard of the People's Republic of China
Evaluation of Brittle Failure of Welded Joints
1 Main Content and Scope of Application
This standard specifies the method for safety assessment of welded joints according to the brittle fracture principle. JB/T 5104-91
This standard is applicable to non-austenitic steel welded structures. It is mainly used for brittle fracture assessment of plane defects of cracks or crack-like cracks in fusion welded joints.
2 Reference standards
GB 2308
Test method for determining ductile fracture toughness of metallic materials using J resistance curve GB2651
GB3323
GB 4161
GB 9447
JB4291
Tensile test method for welded joints
Radiography and quality classification of steel fusion welded butt joints Test method for plane strain fracture toughness Kic of metallic materials Test method for fatigue crack growth rate of welded joints Test method for COD of welded joints
3 Terms and main symbols
3.1 Terms
Penetration defects
Defects that penetrate the thickness of the plate.
b. Internal defects
Internal defects that do not appear on the plate surface.
C. Surface defects
Defects that do not penetrate the thickness of the plate and appear on the surface. 3.2 Symbols of geometric parameters
W--specimen width;
plate thickness,
angular deformation:
hmisalignment;
half length of through crack; half length of long axis of internal crack; equivalent crack size;
critical crack size;
initial crack size;
surface crack depth; half length of internal crack depth; half length of surface crack length:
N cycles After N cycles, the half length of the penetration crack;
After N cycles, the surface crack depth; the half length of the internal crack depth; b
Approved by the Ministry of Machinery and Electronics Industry of the People's Republic of China on 1991-07-15. 274
Implemented on 1992-07-01
After N cycles, the surface crack half length,
The half length of the original defect:
The half width of the original defect:
JB/T 5104—
The distance from the edge of the internal defect to the corresponding free surface; The distance from the edge of the surface defect in the depth direction to the other corresponding free surface; The minimum distance between the edges of the two defects:
The minimum distance between two parallel defect surfaces.
The units of the above parameters are mm.
3.3 Symbols of mechanical parameters
E—elastic modulus;
yield strength;
tensile strength:
flow stress;
—total tensile stress;
bending stress
tensile stress;
welding residual stress;
the units of the above parameters are N/mm.
Poisson's ratio:
-total tensile strain,
-strain concentration factor.
3.4 ​​Symbols of fatigue parameters
maximum equivalent mean stress.
minimum equivalent mean stress.
Aa-—stress amplitude αmx—Omin
The above parameters are in N/mm2
R—stress ratio amin/amax
3.5 Symbols of fracture mechanics parameters
-crack tip opening displacement (COD);
critical COD;
crack initiation COD;
COD value when the stable crack extension is 0.05mm.: m maximum COD;
The above parameters are in mm.
-corresponding integral value
JR——J integral determined by resistance curve
J integral value corresponding to the stable crack extension of 0.05mm: The above parameters are in N/mm.
Kr-Opening stress intensity factor
-Plane strain fracture toughness:
Kaax\-corresponds to Ki of arax;
Kmin-corresponds to K of min
AKKmxKmin stress intensity factor amplitude.
JB/T 5104-91
The above parameters are in N/mm2
da/dN-crack growth rate, in mm/week;-crack growth rate formula du/dN=（K\ constant C,n-
4 Necessary data for evaluation
4.1 Size, location and direction of defects or quasi-defects. 4.2 Location, structural shape or weld shape of defects. 4.3 Stress when there is no defect in the location of defects. 4.4 Defect Fracture toughness of the material where the sinkhole exists (: or Ji, Kic). 4.5 Chemical composition and mechanical properties of the parent material and the joint. 4.6 Operating temperature of the structure.
5 Standardization of sinkhole size
For plane defects such as lack of fusion, lack of penetration, undercut and cracks, the defect size should be standardized and evaluated. For welding defects that cannot be identified, they should be treated as cracks.
5.1 Defect Standardization Flowchart
Medical sinkhole image detection
Single Defects
[Defect normalization
Multiple defects
Defect normalization
The interference factor determines the composite defect, including
interference of adjacent defects, the relationship between defects and free
surface, and reclassifies after compounding
to determine the equivalent of a single defect. The size of the crack is α, c, 6, such as shear expansion
through crack
[Partial crack ab
surface crack.b|| tt||Determine the equivalent crack size
Defect normalization flow chart
5.2 Defect normalization
5.2.1 Normalization of penetration defects
a When the free surface is a straight line
b When the free surface is a curve
Determination of penetration defect size
5.2.2 Normalization of internal defects
Normalization of surface defects
Free surface is a straight line
JB/T 5104-91
Fig.3 Determination of internal defect size
Semi-elliptical defect
Semi-circular defect
.b Free surface is a curve
Fig.4 Determination of surface defect size
5.3 Interference and combination of adjacent defects
Case of A>B
P,=min(Pi)
Elliptical defect
bCase of A≤B
Pl=min(Pi)
Circular defects
Mutually interfere with each other according to the normalized defects. When adjacent defects interfere, the interfering defects should be combined into a single defect. The interference conditions are shown in Figure 5. S. has two values. If the evaluated joint a>500N/mm, S. Take 3a1, 3c1z If the evaluated joint mouth, ≤500N/mm2, S. Take 2a1.2c1o277
JB/T 5104-—91
When 2a=21+2c2+S2
It is a penetration defect
If SWhen (2c1+ 2c2+S)>2b2, it is a Hertzian defect. When a≥(2b+b+), when a12b1+b2+S, it is a semi-fine defect. When a12b1+b2+S, it is a semi-rat defect. When (2a12a2F3)<(2a12a2F3>, it is a sugar exhaustion defect. When (26+2+$)=(2a1+2a*+S), it is a shape adjustment. When 28=21+2h+$z
2a 2b1+ 26++S?
c=2±6+S2
+)>2(+2+$2 when
is a semi-assisted blood-shaped hard depression
+$,)≤2(+262+$+) when
when 2+2
is a semi-complementary defect
Figure 5 Interference and combination of adjacent defects
5.4 Interference close to the free surface
JB/T 5104—91
5.4.1 Composite when an internal defect interferes with a free surface If α>(2+P)
/If P≤P
If a2+P
6=20+P
Semi-conformal surface defect
Semi-conformal surface defect
Figure 6 Interference between an internal defect and a free surface 5.4.2
2 Composite when an internal defect interferes with two free surfaces (including normalized defects) If P,≤P.
Through-through defect
Figure? Internal defects and interference between two free surfaces 5.4.3
Composite of surface defects and interference with another surface Ps0.3m
2a= 2c' +6
Figure 8 Interference between surface defects and another surface
5.5 Composite of non-coplanar defects when they interfere with each other
5.5.1 If the welded joint a≤500N/mm2 and d≤2α or 2c, it shall be treated as coplanar; if the joint 0,>500N/mm2 and d≤3a or 3c, it shall be treated as coplanar. See Article 5.4. 5.5.2 The position of non-coplanar defects after composite shall be determined at the larger defect. 5.6 Calculation size of oblique defects
Calculate according to the projection size of the original defect in the direction of the principal stress. 5.7 Calculation of equivalent crack size a
Calculate according to the accuracy requirements of the project being assessed and the figures and tables in Appendix A. 279
6 Determination of material properties
JB/T 5104--91
6.1 Yield strength of welded joints. Determination is in accordance with GB2651. 6.2 Expression of crack growth rate of welded joints du/dN=(K\ small constant (\ according to (i117 provisions 6.3 Fracture toughness value COD determination.
6.3.1 COD used for evaluation is.
6.3.2 In the absence of data, 8.80.05 or even m values ​​may be used, but the party being evaluated must agree and should be clearly recorded in the report 6.3.38, 8. The test shall be in accordance with the provisions of JB4291. 6.3.4 The fracture toughness of other fracture criteria such as J.Kic can be used to convert COD values, and the conversion relationship The error must be estimated and explained, and its fracture toughness value Kic is in accordance with the provisions of YB947, and J. is in accordance with the provisions of GB2308. Mechanical conditions
Mechanical conditions refer to the stress or strain value acting on the defect. 7.1 Internal stress caused by external load
The internal stress caused by external load is calculated based on no defects and no manufacturing deviations. All stress and strain values ​​should be considered in the design. Under normal circumstances, it is impossible for the cross section to be subjected to uniform force, so this part of the stress is decomposed into tensile stress α and bending stress w. The stress of this part of the defect is defined as:||tt ||d=ot+abow
The strain at the defect is defined as:
ea/E+aow/E
Where: E-
Elastic modulus:
Coefficient determined by the type of defect, see Table 1. Determination of Table 1ab
Type of defect
Through defect
Internal defect
Surface defect
Defect on the tensile stress side
Defect on the compressive stress side
If (α+a)≥, other appropriate methods can be used 7.2 Welding residual stress
When evaluating the defects of welded joints, residual stress after welding must be considered. The stress at the defect is defined as:
The strain at the defect is defined as:
e2-areg
Wu Zhong: a.
The coefficient related to the type of welding defect and its location is shown in Table 2. ub
Defect type
Penetration defect
Internal defect
Surface defect
JB/T 5104—91
Table 2 a value
Defects parallel to the weld
Defects perpendicular to the weld
7.2.1 If the welded structure is subjected to overall tempering to eliminate residual stress, a. is taken as 0.3. Angle
Defects parallel to the weld
7.2.2 If the welded structure is subjected to local tempering to eliminate residual stress, a. is determined by the measured value. 7.2.3 If the welded structure is not subjected to stress relief treatment, α is taken as 1.7.3 Stress concentration caused by joint shape
Defects perpendicular to the weld
Because the joint geometry is discontinuous due to the welding process, it is necessary to consider the presence of stress concentration and strain concentration at the defect location. The stress of this part of the defect is:
G-(K,-1)α
The strain condition of this part of the defect is:
ey --(Kt-1)e
The value of K is shown in Appendix B.
7.4 Determination of mechanical conditions
7.4.1 Stress
2 StrainWww.bzxZ.net
e=er+e2+e3
8 Fracture assessment
8.1 Stress intensity assessment
The actual service stress of the static section of the defective part shall be less than or equal to 0.7 times the flow stress α of the material at that part, where α. =+). Whether a certain safety factor is added to the service stress depends on the importance of the product. 8.2 Fracture assessment
8.2.1 COD method assessment
The COD fracture parameter expression is given by formula (9)8=2elementae.
8-a(e+e)
Where: Determined according to Chapter 5;
e determined according to Chapter 7.
0. 6e/e,1 -
e/e,>1
When it is evaluated as an allowable defect, it shall be determined in accordance with Chapter 6. 8.2.2 Stress intensity factor method
When the total stress α at the defect site is less than or equal to 0.6 times the yield stress of the welded joint, the stress intensity factor can be calculated using formulas (11) to (13).
Through crack
Internal crack
a)~element a
JB/T 5104—91
Surface crack
In formulas (11), (12) and (13), the definitions and calculations of Y, 0, yao and F are shown in Appendix A. When Ki≤0.6Kic, it is evaluated as an allowable defect. 9 Fatigue crack growth of defect size
9.1 The growth of fatigue crack in welded joints subjected to fatigue loads is calculated by dudN=·(AK)”. 9.1.1 Determination of AK
Through crack
Internal crack
Surface crack
AK-YAGVRa
The definitions and calculations of Y, 2, *, and F in formulas (14), (15), and (16) are shown in Appendix A 9.1.2 Determination of fatigue crack an
an value is solved by formula (17):
N(n-2)c yuan 2Ag
2agl-sign
9.2 For welded joints subjected to fatigue loads, if there is no condition to conduct tests, the estimation of fatigue crack growth can be carried out according to Appendix C. 9.3 Evaluation
After the u value of fatigue crack growth is determined, the aw value is used as the new defect size and evaluated according to Article 8. 282
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