Characterizing method based on the welding crack expansion process of metal magnetic memory detection technology
Technical field
The invention belongs to tape welding seam hardware magnetic Non-Destructive Testing field; More particularly; Be a kind of concentrated based on metal magnetic memory signal and parameter variation characteristic detection component internal stress thereof; Quantitatively characterizing crack propagation process and component damage degree methods belong to metal magnetic memory detection range in the Non-Destructive Testing.
Background technology
Ferromagnetic material is widely used in the commercial production because of its excellent mechanical property and cheap price.Fatigue break is the modal a kind of failure mode of ferromagnetic component (particularly weld assembly), and 60% to 80% fatigue break is because the stress of various microcosmic and macroscopic view is concentrated, damage accumulative total causes according to statistics.Welding is the process of a non-equilibrium heating cooling, can produce unrelieved stress through welded structure, and the local location of structure causes significantly stress to concentrate, and under the cyclic loading condition, moves, and just is easy to cause the fatigue damage fracture.Generally speaking, the root that welding crack produces expansion is exactly that the stress of various microcosmic is concentrated, and the suffered load type of waveform of the generation of crackle and expansion and structural member has very big relation in addition.Diagnose the expansion process of crackle in advance through the method for Non-Destructive Testing, find out potential extensions path, extremely important to the fatigure failure of prevention test specimen.
Carry out analysis of fatigue, effectively evaluating stress deformation situation, the limit stress that particularly causes damaging distortion situation just become valuator device and member structural strength and reliability one foundation always.In order to find out maximum machine stress deformation zone timely and accurately; The Russia scholar has proposed the metal magnetic memory detecting method based on material power magneto-coupling effect; Be to utilize the ferrimagnet spontaneous magnetization characteristic under magnetic field of the earth and the stress field acting in conjunction to detect; Can detecting material internal stress concentration zones and stress concentration degree thereof, and then steady hazardous location possibly take place in the existence of definite defective or member.The metal magnetic memory testing instrument device can detect the method phase component of component surface stray field, and the method phase component of this stray field has reflected the degree that the welding crack internal stress is concentrated.Crackle and near zone thereof be the highest place of stress concentration degree often, and the stress that therefore can utilize the metal magnetic memory testing instrument device to detect is concentrated the expansion process that characterizes crackle.
Summary of the invention
The objective of the invention is to overcome the deficiency of prior art; Provide a kind of and can be directed against magnetic signal and characteristic parameter variation characteristic thereof, the low-cycle fatigue damage quantitatively characterizing method that the fatigue damage degree and the crack propagation process of the breach weld assembly under the effect of different loads form carried out quantitatively characterizing based on metal magnetic memory detection technology.
Technical purpose of the present invention is achieved through following proposal:
Technical scheme of the present invention is that technological magnetic memory detection technology is combined with the dynamic stress coefficient of concentration and the fracture damage mechanics of fatigue load; With magnetic memory signal method phase component and its graded situation as the welding joint variable in the damage continuously; Set up a kind of based on metal magnetic memory detection technology to the low-cycle fatigue damage quantitatively characterizing method of breach weld assembly under the different loads form, described method mainly may further comprise the steps:
At first (step 1) is carried out low cycle fatigue test to band breach welded specimen (shown in accompanying drawing 1, test specimen is long to be 2a, and wide is b) under the fatigue load effect of different wave.At the prefabricated crackle of indentation, there (being about 1mm), can predict that crackle can be along the direction expansion perpendicular to weld seam before the experiment perpendicular to weld seam.In the tired loading procedure; Detect the test specimen surface heat zone of influence under the different fatigue cycle index and (measure passage 1; Pass through precrack during measurement) and the magnetic memory signal (normal component of spontaneous stray field intensity) of axis of a weld place (measure passage 2); Promptly obtained the magnetic memory signal of different measuring passage in the crack propagation process, each start line of measuring all is positioned at l place, weld seam left side, and each terminated line of measuring all is positioned at l place, weld seam right side; Be the center with the precrack promptly, equidistant place begins respectively to measure and stop in the left and right sides.
Secondly (step 2), the position P of the magnetic memory signal zero crossing of heat-affected zone and commissure under the extraction different loads cycle index
1(l), P
2(l) and the magnetic memory signal maximal value Hp of commissure
2(y)
Max(shown in accompanying drawing 2) passes precrack, magnetic memory signal zero crossing position P in the tired loading procedure owing to be in the measurement passage of heat-affected zone
1(l) remain unchanged, can be used as reference, judge the zero crossing position of the magnetic memory signal at axis of a weld place according to this.
(step 3) once more; Because the stress concentration degree of crack tip is higher than other zones; At the highest region of stress concentration, stray field normal component zero crossing is so can analyze the propagation law of crack tip in loading procedure according to the zero point position of magnetic memory signal.The position coordinates of the magnetic memory signal zero crossing of commissure is P during with the N time fatigue and cyclic
2(l)
NBe variable, set up and characterize crack tip and fixed position P
1(l) displacement difference is than expression formula, promptly
When | L|≤5% just shows the magnetic memory signal zero crossing position P that measures passage 2
2(l)
NWith the magnetic memory signal zero crossing position P that measures passage 1
1(l) approaching more, crackle is along the position expansion of vertical weld.
(step 4) is analyzed crack initiation extension phase the stress here according to the maximal value of weld seam magnetic memory signal and is concentrated situation, the degree of injury of prediction test specimen at last.The magnetic memory signal maximal value H of commissure during with the N time fatigue and cyclic
2(Y)
Max NAs variable, set up the expression model of weld assembly injury tolerance,
As the standard of weighing the welding piece fatigue damage.H wherein
2(y)
Max 0Expression loads the maximal value of the detected magnetic memory signal in preceding commissure, works as D
NRepresented that major injury, D took place in the commissure at>=2.0 o'clock
NThe degree of injury of the big more member of value big more.
The present invention adopts the stress of heat-affected zone and commissure stray field under the metal magnetic memory technology for detection different fatigue cycle index to concentrate; Through the expansion process of the quantitative sign crack tip of the variation of magnetic memory signal null position, with the degree of injury of test specimen in the maximal value quantitatively characterizing crack propagation process of magnetic memory signal and its intensity gradient.
Description of drawings
The Workpiece structure synoptic diagram of Fig. 1 the present invention test
The magnetic memory signal curve map of heat-affected zone and commissure under Fig. 2 different loads cycle index, wherein the position of the magnetic memory signal zero crossing of heat-affected zone and commissure is respectively P
1(l), P
2(l) and the magnetic memory signal maximal value Hp of commissure
2(y)
Max
Sample dimensions synoptic diagram in Fig. 3 embodiment of the invention
The magnetic memory signal curve map of heat-affected zone and commissure under the different loads cycle index in Fig. 4 embodiment of the invention 1
The magnetic memory signal curve map of heat-affected zone and commissure under the different loads cycle index in Fig. 5 embodiment of the invention 2
Embodiment
Further specify technical scheme of the present invention below in conjunction with specific embodiment.A kind of method based on crack propagation process and degree of injury in metal magnetic memory technology and the characteristic parameter sign welded structure thereof; Under same stress ratio effect; Fatigue load adopts square wave fatigue load and triangular wave fatigue load respectively, the size of test specimen (mm) as shown in Figure 3:
Embodiment 1: fatigue load is selected square wave load, and stress ratio is 0.5, maximum load 120KN, minimum load 60KN
1, band breach welding piece is carried out torture test under the condition of setting, before the experiment indentation, there prefabricated perpendicular to weld seam, be about the crackle of 1mm; In the tired loading procedure, with the magnetic memory signal of metal magnetic memory technology for detection test specimen heat-affected zone and commissure.Extract the position P of the zero crossing of the magnetic memory signal of heat-affected zone and commissure under the N time cycle index then
1(l), P
2(l)
NMagnetic memory signal maximal value Hp with the commissure
2(y)
Max N(shown in accompanying drawing 4) wherein is in the magnetic memory signal zero crossing position P of heat-affected zone
1(l)=40.
The position coordinates of the magnetic memory signal zero crossing of commissure is P (l) during 2, according to the N time fatigue and cyclic
NBe variable, calculate the crack tip displacement difference than (as shown in table 1 below).After cycle index is greater than 10000 times, | the magnetic memory signal zero crossing position that L|≤2.5 show the commissure is approaching with predetermined cracking position, and weld seam is along the direction expansion of vertical weld, with predict the outcome consistent.
Table 1
Cycle index |
500 |
1000 |
1500 |
2000 |
2500 |
3000 |
4000 |
5500 |
6000 |
7500 |
L |
20 |
15 |
15 |
14.5 |
13.5 |
12 |
10 |
10 |
10 |
7.5 |
Cycle index |
8500 |
9500 |
10500 |
11500 |
13000 |
14500 |
15000 |
15500 |
17000 |
16530 |
L |
5 |
2.5 |
2.5 |
2.5 |
2.5 |
2.5 |
0 |
0 |
0 |
0 |
Cycle index |
17500 |
18500 |
19030 |
19500 |
20040 |
21000 |
22000 |
23500 |
24500 |
25500 |
L |
0 |
0 |
-2.5 |
-2.5 |
-2.5 |
-2.5 |
-2.5 |
-2.5 |
-2.5 |
-2.5 |
The magnetic memory signal maximal value H of commissure during 3, with the N time fatigue and cyclic
2(y)
Max NAs variable, calculate weld assembly injury tolerance (as shown in table 2 below), as the standard of weighing the welding piece fatigue damage.As N>After 10000 times, D
N>=2 show member generation major injury, D
NThe degree of injury of the big more member of value big more.
Table 2
Cycle index |
500 |
1000 |
1500 |
2000 |
2500 |
3000 |
4000 |
5500 |
6000 |
7500 |
D |
1 |
1.071 |
1.25 |
1.375 |
1.339 |
1.357 |
1.339 |
1.393 |
1.393 |
1.696 |
Cycle index |
8500 |
9500 |
10500 |
11500 |
13000 |
14500 |
15000 |
15500 |
17000 |
16530 |
D |
1.732 |
1.786 |
1.946 |
2.143 |
2.232 |
2.321 |
2.679 |
2.839 |
2.857 |
3.036 |
Cycle index |
17500 |
18500 |
19030 |
19500 |
20040 |
21000 |
22000 |
23500 |
24500 |
25500 |
D |
3.214 |
3.393 |
3.572 |
3.518 |
3.554 |
3.69 |
3.929 |
4.107 |
4.214 |
4.339 |
Embodiment 2: fatigue load is selected triangular wave load, and stress ratio is 0.5, maximum load 120KN, minimum load 60KN
1, band breach welding piece is carried out torture test under the condition of setting, before the experiment indentation, there prefabricated perpendicular to weld seam, be about the crackle of 1mm; In the tired loading procedure, with the magnetic memory signal of metal magnetic memory technology for detection test specimen heat-affected zone and commissure.Extract the position P of the zero crossing of the magnetic memory signal of heat-affected zone and commissure under the N time cycle index then
1(l), P
2(l)
NMagnetic memory signal maximal value Hp with the commissure
2(y)
Max N(shown in accompanying drawing 5) wherein is in the magnetic memory signal zero crossing position P of heat-affected zone
1(l)=40.
The position coordinates of the magnetic memory signal zero crossing of commissure is P (l) during 2, according to the N time fatigue and cyclic
NBe variable, calculate the crack tip displacement difference than (as shown in table 3 below).After cycle index is greater than 9500 times, | L|≤5 show that the magnetic memory signal zero crossing position of commissure is approaching with predetermined cracking position, and weld seam is along the direction expansion of vertical weld.
Table 3
Cycle index |
1000 |
1500 |
2000 |
2500 |
3000 |
4070 |
4500 |
5500 |
L |
47.5 |
42.5 |
37.5 |
20 |
20 |
15 |
10 |
10 |
Cycle index |
6500 |
7040 |
8000 |
9500 |
10000 |
11500 |
14500 |
15000 |
L |
10 |
7.5 |
7.5 |
5 |
5 |
5 |
2.5 |
0 |
Cycle index |
15500 |
16000 |
16500 |
17000 |
17500 |
18000 |
|
|
L |
0 |
2.5 |
2.5 |
0 |
0 |
0 |
|
|
The magnetic memory signal maximal value H of commissure during 3, with the N time fatigue and cyclic
2(y)
Max NAs variable, calculate weld assembly injury tolerance (as shown in table 4 below), as the standard of weighing the welding piece fatigue damage.After N is greater than 5500 times, D
N>=2 show member generation major injury, D
NThe degree of injury of the big more member of value big more.
Table 4
Cycle index |
1000 |
1500 |
2000 |
2500 |
3000 |
4070 |
4500 |
5500 |
D |
1 |
1.310 |
1.310 |
1.476 |
1.476 |
1.595 |
1.571 |
2.381 |
Cycle index |
6500 |
7040 |
8000 |
9500 |
10000 |
11500 |
14500 |
15000 |
D |
2.381 |
2.476 |
2.5 |
2.381 |
2.381 |
2.381 |
3.095 |
2.667 |
Cycle index |
15500 |
16000 |
16500 |
17000 |
17500 |
18000 |
|
|
D |
2.929 |
3 |
2.952 |
2.857 |
2.810 |
3.214 |
|
|
More than the present invention has been done exemplary description; Should be noted that; Under the situation that does not break away from core of the present invention, the replacement that is equal to that any simple distortion, modification or other those skilled in the art can not spend creative work all falls into protection scope of the present invention.