CN101126799A - Method for monitoring fatigue damage using ferromagnetic materials surface stray magnetic field signal - Google Patents
Method for monitoring fatigue damage using ferromagnetic materials surface stray magnetic field signal Download PDFInfo
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Abstract
The utility model discloses a method utilizing a stray magnetic field signal monitoring the damage of ferromagnetic, which belongs to the magnetic nondestructive inspection field. Ferromagnetic components do not have measurable strain in early stages of service, with difficulty to evaluate damage. The utility model, inspected material and smooth plantlike standard fatigue specimens have the same heat treatment state, and are demagnetized through high temperature, so as to get the pure initial magnetic state. And then a constant rate is imposed to pull the tension fatigue load, every stray magnetic field normal component of the surface inspecting components is unloaded corresponding to scheduled cycles, the slope Ks of different magnetic cycle curves is extracted, the critical value of the slope Ksc is determined, and the mapping relationship between the slope Ks before fatigue crack and fatigue cycles N is established. The measured components by the same value are inspected, and the measured slope Ks of the magnetic curve is compared with the critical value of the slope Ksc, and then the fatigue damage can be determined. The utility model has the advantages that the utility model has simple operation and accurate inspecting results, and dynamic monitoring the early fatigue damage of the ferromagnetic components in the unloaded state can be achieved.
Description
Technical field
The present invention relates to a kind of method of utilizing spontaneous surface stray magnetic field signal evaluation to bear the ferromagnetic parts fatigue damage degree of fatigue load, belong to the magnetic nondestructive testing field.
Background technology
Ferromagnetic material has characteristics such as good intensity, hardness, plasticity, toughness as a kind of ferromagnetic substance, is widely used in industrial every field.Many critical components all are to be made by ferromagnetic material in the mechanized equipment, and these parts much are under the work condition environment that alternate load acts on repeatedly, and fatigue failure is their topmost failure modes.
Fatigure failure is a retardation destructive process slowly, normally takes place under the alterante stress effect that is lower than yield limit, and no obvious plastic yield has disguise on the macroscopic view during destruction, often causes catastrophic effect.Therefore, the residual life of the ferromagnetic component of monitoring ferromagnetic material fatigue damage degree, and then prediction in real time is focus and the difficult point problem that academia and engineering circle are paid close attention to always,
When fatigue crack had produced and reached certain size, conventional Dynamic Non-Destruction Measurement such as supercritical ultrasonics technology, eddy-current method, osmosis, magnetic particle method can be found defective.And the incipient fatigue damage stage before macroscopical fatigue crack occurs owing to there is not the variation of tangible microcosmic and macroscopical physical parameter, is detected very difficulty.It is acoustic emission that current detection at this stage is used more, and acoustic emission realizes the dynamic monitoring to the ferromagnetic material fatigue damage by the acoustic signals that the variation of " monitoring " design of part emits.Though acoustic emission phenomenon as far back as the fifties have been found that but because must load when detecting, problem such as ground unrest interference limited its practical application.
In addition, there is report to adopt magnetic nondestructive testing in recent years, detect the ferromagnetic material faulted condition as magnetic Barkhausen noise method, magnetosonic shooting method etc., these methods also are in the fundamental research stage on the one hand, still immature, need when they detect on the other hand member is magnetized, need additional magnetizing equipment and demagnetizer.
Be in the ferromagnetic component in the environment of terrestrial magnetic field, be subjected to the influence of terrestrial magnetic field and load, its surface can produce spontaneous stray magnetic field signal, at present by detecting the normal component H of this stray magnetic field
p(y) zero point and combined magnetic field gradient maximal value k can qualitatively judge the position that ferromagnetic material stress is concentrated, promptly potential hazardous location.This technology metal magnetic memory technology that is otherwise known as.
In the prior art, application number 200410067574.7 is only arranged, the detection method of the Chinese invention patent of publication number CN1603812A---remanent fatigue life of vehicle retired crankshaft, propose at first to use the dangerous position that eddy-current technique detects decommissioning crankshaft, there is crackle to exist as finding, thinks that then its residual life is not enough to keep next life cycle; Under the condition that does not have crackle to produce, applied metal magnetic memory technique detects the stress deformation situation at this position, and whether estimate its residual life according to the mapping relations between stress deformation situation and the residual life is enough to keep life cycle next time.This method at be the retired automobile crane of scrapping, purpose is the stress deformation situation according to its dangerous position, considers whether to have manufacturing feasibility again.And for the ferromagnetic component that bears fatigue load in the military service process, because fatigue load is usually less than the yield limit of material, especially in early days be on active service the stage, the dangerous position of ferromagnetic component measurable strain can not occur, is difficult to utilize stress and the degree of injury that is out of shape the status evaluation ferromagnetic material.And said method does not propose the clear and definite stress deformation situation and the mapping relations of residual life.
Summary of the invention
The objective of the invention is to invent a kind of novel detection method that can under unloaded state, realize dynamic monitoring ferromagnetic component fatigue damage degree.
Provided by the present invention is a kind of normal component H that utilizes the stray magnetic field of the ferromagnetic component spontaneous generation in surface
p(y) signal can be by H
p(y) slope K of signal curve
sVariation determine the fatigue life cycle N (being fatigue lifetime) of member experience, and then can predict its residual life, realize estimating the target of ferromagnetic material fatigue damage degree.
The present invention is achieved through the following technical solutions:
1) employing becomes tabular smooth standard tensile sample with the material of the identical material of tested ferromagnetic component, heat treatment regime according to tested member carries out final thermal treatment to standard sample, the maximum heating temperature of Technology for Heating Processing surpasses the Curie-point temperature of material, makes the standard specimen surface obtain pure initial magnetic state; Wherein final thermal treatment is the thermal treatment of carrying out before using after the test specimen finishing.
2) the vertical test specimen of Magnetic Sensor surface, according to fixing lift-off value, the detection line on scanning standard test specimen surface respectively obtains the normal component H of detection line surface stray magnetic field under the test specimen original state
p(y) signal; Spacing for tabular smooth the detection line of standard does not have specific (special) requirements.
3) set the torture test parameter, carry out torture test, fatigue and cyclic is to pre-determined number N, utilize Magnetic Sensor, according to the 2nd) go on foot described method, with identical fixedly lift-off value, each detection line on scanning standard test specimen surface obtains stray magnetic field normal component signal under this cycle index; N normal root really considers that according to the bimetry of test specimen the convenience that detects is definite.Fatigue experiment parameter concrete in step 3) will require according to the difference of test specimen to set.
4) repeating step 3), rupture until test specimen; The magnetic signal that Magnetic Sensor records in above-mentioned steps is handled as calculated, sets up detection line surface stray magnetic field normal component H
p(y) with the relation curve of fatigue life cycle N;
5) extract detection line magnetic slope of a curve K under the different cycle indexes
s, set up slope K
sWith the corresponding relation curve of cycle index N, the critical slope value K before the sample fatigure failure that settles the standard
Sc, set up the preceding K of fatigue crack initiation
s-N mapping relations formula;
6) with step 2) used Magnetic Sensor, according to step 2) identical lift-off value, according to the preset time H of the tested component surface detection line of continuous monitoring at interval
p(y) signal, the signal of collection is handled as calculated, extracts magnetic slope of a curve K
s, with the K that obtains
sValue and the 5th) the critical slope value K that determines in the step
ScContrast, K
s〉=K
ScThe time, think that fatigue crack germinates, ferromagnetic component is about to destroy, and adopts new structural member to replace; K
s＜K
ScThe time, think that then member still is in the early fatigue stage, according to step 5) K
s-N mapping relations formula is determined the fatigue damage degree of member.
Described different cycle index lower surface stray magnetic field normal component H
p(y) the test specimen that is measured as records under unloaded state.
The Magnetic Sensor measuring accuracy of using is equal to or higher than 1A/m.
The method that the present invention determines is for the metal magnetic memory technology is introduced new detection parameter---detection line magnetic slope of a curve K
sThis detection parameter is to utilize the information of ferromagnetic material self emission to characterize the degree of incipient fatigue damage.
The present invention need not extrinsic motivated magnetic field and demagnetizer in testing process, do not need any pre-service is done on the test specimen surface, detect easy, testing result precision height, good reproducibility.Even the test specimen unloading, this magnetic signal still exists, and is easy to realize the fatigue damage degree of dynamic monitoring ferromagnetic material.
Description of drawings
Fig. 1 is for detecting test specimen and detection line synoptic diagram
Fig. 2 is detection line magnetic rate of curve K
sWith cycle index N graph of a relation
Embodiment
The present invention realizes by following measure:
Tested construction material is the 18CrNiWAVA steel, and the metal magnetic memory testing instrument device is the EMS-2003 type.
At first, select the ferromagnetic material 18CrNiWAVA steel identical for use, make tabular smooth fatigue sample according to national standard with tested member material.Heat treatment regime according to tested member carries out final thermal treatment to standard sample, is 8 * 10 in vacuum tightness
-1Be heated to 860 ℃ in the vacuum heat treatment furnace of the WZC-30 type of Pa, be incubated 30 minutes, oil quenching, 180 ℃ of tempering then, water-cooled obtains pure initial magnetic state to room temperature.
Secondly, go out 2 parallel detection lines at test specimen length 240mm surface marking, detect line length 100mm, two line perpendicular separations are apart from 10mm, as shown in Figure 1.
Adopt the EMS-2003 metal magnetic memory testing instrument, its Magnetic Sensor is based on Hall unit, and accuracy of detection is 1A/m.The vertical test specimen of sensor surface, lift-off value 1mm scans two detection lines respectively in straightaway mode (direction of scanning is shown in Fig. 1 arrow), gathers the normal component signal of test specimen original state lower surface stray magnetic field, through the Origin software processes, obtain H under the original state
p(y) value distributes.
The multiple factors such as power of the shape that the choosing of lift-off value will be taken all factors into consideration ferromagnetic component, size, surface quality, stray magnetic field are determined.Lift-off value is little, and promptly sensor is near surface, accuracy of detection height.In the present embodiment, at the sensor of our present usefulness, early-stage Study result shows that after lift-off value surpassed 10mm, the signal of collection was with regard to some distortion, and surpassing 15mm will influence testing result, can cause erroneous judgement.Therefore in concrete test, select lift-off value 1mm.
Then, test specimen is applied the permanent width of cloth draw fatigue load, maximum stress σ
Max=560MPa, stress ratio R=0, frequency f=10Hz.After test specimen is loaded into predetermined cycle index, test specimen is taken off in unloading, test specimen is positioned on the non magnetic three-dimensional platform along North and South direction, and the probe of being controlled metal magnetic memory testing instrument by the automatically controlled scanning support of three-dimensional moves according to fixed form along detection line, obtains each detection line surface H
p(y) data, magnetic signal is sent into Computer Processing, obtains this cycle index lower surface stray magnetic field normal component and distributes.Repeat above-mentioned steps, obtain test specimen surface stray magnetic field normal component distribution plan under the different cycle indexes, rupture until test specimen.Extract the magnetic rate of curve K under the different cycle indexes
sValue is made K
sRelation curve between value and the cycle index N as shown in Figure 2.Determine slope critical value K
Sc=1.8; Adopt polynomial expression to fit K
sMapping relations between the-N:
K
s＝1.12213+0.38358N-0.0977N
2+0.0097N
3 (1)
At last, detect the 18CrNiWA steel member of identical condition of heat treatment, delimit detection line according to the working condition of member.Respectively early stage, mid-term in life-span, later stage under arms, tested member unloading is placed Magnetic Sensor lift-off value 1mm, each detection line of scanning in the manner described above, the H on acquisition member surface along North and South direction
p(y) signal through the Origin software processes, extracts magnetic rate of curve K
sThe value, multiply by modifying factor after, with K
Sc=1.8 contrasts are judged to have or not fatigue crack initiation, as germinating fatigue crack, then think this member near end of lifetime, adopt new part to replace this member; As fatigue crack initiation not, then determine the fatigue cycle life N that it has experienced according to (1) formula, determine whether this member needs to adopt high-new Surface-micromachining process to repair.
Claims (3)
1. a method of utilizing the ferromagnetic materials surface stray magnetic field signal monitoring fatigue damage is characterized in that, may further comprise the steps:
1) employing becomes tabular smooth standard tensile sample with the material of the identical material of tested ferromagnetic component, heat treatment regime according to tested member carries out final thermal treatment to standard sample, the maximum heating temperature of Technology for Heating Processing surpasses the Curie-point temperature of material, makes the standard specimen surface obtain pure initial magnetic state;
2) the vertical test specimen of Magnetic Sensor surface, according to fixing lift-off value, the detection line on scanning standard test specimen surface respectively obtains the normal component H of detection line surface stray magnetic field under the test specimen original state
p(y) signal
3) set the torture test parameter, carry out torture test, fatigue and cyclic is to pre-determined number N, utilize Magnetic Sensor, according to the 2nd) go on foot described method, with identical fixedly lift-off value, each detection line on scanning standard test specimen surface obtains stray magnetic field normal component signal under this cycle index;
4) repeating step 3), rupture until test specimen; The magnetic signal that Magnetic Sensor records in above-mentioned steps is handled as calculated, sets up detection line surface stray magnetic field normal component H
p(y) with the relation curve of fatigue life cycle N;
5) extract detection line magnetic slope of a curve K under the different cycle indexes
s, set up slope K
sWith the corresponding relation curve of cycle index N, the critical slope value K before the sample fatigure failure that settles the standard
Sc, set up the preceding K of fatigue crack initiation
s-N mapping relations formula;
6) with step 2) used Magnetic Sensor, according to step 2) identical lift-off value, according to the preset time H of the tested component surface detection line of continuous monitoring at interval
p(y) signal, the signal of collection is handled as calculated, extracts magnetic slope of a curve K
s, with the K that obtains
sValue and the 5th) the critical slope value K that determines in the step
ScContrast, K
s〉=K
ScThe time, think that fatigue crack germinates, ferromagnetic component is about to destroy, and adopts new structural member to replace; K
s＜K
ScThe time, think that then member still is in the early fatigue stage, according to step 5) K
s-N mapping relations formula is determined the fatigue damage degree of member.
2. method according to claim 1 is characterized in that: described different cycle index lower surface stray magnetic field normal component H
p(y) the test specimen that is measured as records under unloaded state.
3. method according to claim 1 is characterized in that: the Magnetic Sensor measuring accuracy of using in the described method is equal to or higher than 1A/m.
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| CN108362769A (en) * | 2018-03-01 | 2018-08-03 | 沈阳工业大学 | A kind of non-contact weak magnetic detection method of crack initiation area stress |
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