CN102175136B - Straight tube multi-axis ratchet wheel strain testing system and method - Google Patents
Straight tube multi-axis ratchet wheel strain testing system and method Download PDFInfo
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- CN102175136B CN102175136B CN201010600661.XA CN201010600661A CN102175136B CN 102175136 B CN102175136 B CN 102175136B CN 201010600661 A CN201010600661 A CN 201010600661A CN 102175136 B CN102175136 B CN 102175136B
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Abstract
The invention relates to a straight tube multi-axis ratchet wheel strain testing system and a straight tube multi-axis ratchet wheel strain testing method. A hydraulic servo fatigue tester, a quasi three-point bent clamp and a strain gauge method measurement straight tube are controlled by using a sensor, data are acquired through a multi-channel dynamic strain meter, and results are output through a computer. According to the method, the testing position is flexible, and the load working conditions are diverse; and the method is novel, the design is reasonable, and the data are accurate and reliable. Meanwhile, the multi-channel dynamic strain meter has the characteristics of low drift, low noise and broad frequency response; and the fatigue tester has the functions of presetting, measuring, controlling and automatically recording the testing conditions and the testing parameters and automatically giving an alarm and halting the machine when the test is invalid or abnormal, can be widely applied to test and research of the evolution laws of multi-axis ratchet wheel strain of a pressure straight tube under various complex working conditions such as earthquake or temperature change of fluid in the tube and the like, and can be used for determining the ratchet wheel boundary of the straight tube.
Description
Technical field
The present invention relates under a kind of multiaxis Cyclic Load, the method for the test each position of straight pipeline ratchet strain Temporal Evolution, belongs to straight tube multi-axis ratchet strain measurement system and method.
Background technology
Be subject to during ratchet strain under multiaxis Cyclic Load develops at test straight tube material at present both at home and abroad, more than be the test of pipeline material bar or plates specifications sample being carried out to the strain of multiaxis ratchet, be mainly to utilize extensometer method etc.But there are a lot of problems in this method, first it only considers the ratchet behavior after the stand under load of material own, fail to be effectively used for the impact of research structure on Biaxial ratcheting, its loading condition and type are all limited in addition, and the location of extensometer is fixing all more complicated with staking-out work, it is inaccurate etc. that misoperation very easily produces measurement data.So they can not simulate the accumulation of straight tube in primary stress and the ratchet strain everywhere of secondary stress combination lower straighttube really and accurately, therefore its applicability is poor.Also adopt in addition exciting device as shaking table comes, utilize inertial force that bending load is provided.Although it can carry out directly loading research to straight tube structure, this method, the load range providing is less than normal, and loading type is single, limited to by self larger.Though have recent years scholar also to propose the Biaxial ratcheting of overstrain sheet method test straight tube, still because accuracy of data acquisition is not high enough, test channel finite sum test position is located the limitation such as inaccurate, causes test procedure complexity and result inaccurate.
Summary of the invention
The object of the invention is to propose a kind of test method that can accurately test the ratchet strain evolutionary process of straight pipeline under three-dimensional stress state.This test method has been optimized the whole bag of tricks in the past, utilize imposed load F and the output pressure P of microcomputer combined sensor control hydraulic servo fatigue tester that various complex load operating modes are provided, and adopt strain gauge method measurement straight tube to be subject to the real-time multiaxis ratchet behavior under complex load operating mode.Wherein, between the axial normal stress in the straight tube sample that output pressure P causes and circumference stress, relation can be as follows:
Wherein, σ
zfor the axial normal stress of interior pressure generation; σ
θfor the circumference stress of interior pressure generation; P represents that testing machine provides pressure value in test design; D is the external diameter of straight tube sample; T represents the wall thickness of straight tube sample.
The method test position is flexible, and load working condition is various, and method novelty is reasonable in design, and data accurately and reliably.Simultaneously hyperchannel dynamic strain indicator has low drift and low noise, the wide feature of frequency response; fatigue tester has that test condition, test parameters can be preset, observing and controlling, record automatically; test occurs losing efficacy or when abnormal; the functions such as automatic alarm shutdown; can be widely used under the various complex working conditions of experimental study; as fluid temperature variations in earthquake or pipe etc., the Evolution of the multiaxis ratchet strain of straight tube with pressure, and can be used for determining the ratchet border of straight tube.
Technical scheme of the present invention is as follows:
Straight tube multi-axis ratchet test macro of the present invention, utilizes sensor control hydraulic servo fatigue tester, accurate 3 curved jigs and strain gauge method to measure straight tube, by hyperchannel dynamic strain indicator image data, through computer export result.
Described sensor control hydraulic servo fatigue tester comprises oil press, and testing machine loads upper chuck, lower dop and oil hose; Sensor control hydraulic servo fatigue tester is realized and being pressed in different and the composite condition of moment of flexure loads, and test condition, test parameters can be preset, observing and controlling, record automatically, test occur losing efficacy or when abnormal automatic alarm shut down.
Described straight tube is: be provided with two straight tube pipe plugs at the two ends of a straight tube; A wherein sealing completely; Other end straight tube pipe plug is provided with a tapped through hole along the axial center of pipe, as logical hydraulic fluid port; Fill after oil, will lead to hydraulic fluid port and be connected with three-way connection threaded one end, in three-way connection place setting pressure table Real Time Observation straight tube overpressure situation, three-way connection opposite side is connected with oil transporting appliance.
Straight tube multi-axis ratchet strain testing method of the present invention: foil gauge is affixed on to straight length sample 3 outside surfaces everywhere; Then cavity straight tube is filled with to oil, until fill, be connected with straight tube 3 filling oily connecting hose 10 one end, flexible pipe 10 other ends are connected with oil press 12 by quick connector again, then pass through to change oil press liquid level control straight tube internal pressure by sensor and the microcomputer that software is housed; By straight tube everywhere the each foil gauge lead-in wire of foil gauge lead-in wire and temperature compensation material place carry out exact connect ion by each joint on wire and front terminal block according to corresponding relation; Lower loading blocks 17 and the lower loading crossbeam 18 of dop 16 fixing accurate 3 angle coupling tools under recycling fatigue tester; Bearing pin is installed and is located each clamping plate position and upper loading crossbeam 7; Finally utilize microcomputer and test control software, by inputting different operating loading, utilize the interior pressure of sensor control straight tube and testing machine to load moment of flexure and carry out the test of multiaxis ratchet.Finally adopt hyperchannel dynamic strain indicator 11 Real-time Collection straight tube sample strain evolution everywhere situations, and data-switching is stored in main control computer 28.
Foil gauge is two-way right angle foil gauge, and the location optimization that is affixed on straight tube is in the middle of straight tube, and taking centre as the position, equidistant a few place of point, in each position of posting foil gauge, rotates 180 degree along hoop, sticks respectively foil gauge.
Described hyperchannel dynamic strain indicator comprises amplifier circuit 30, front terminal block 25 and input adapter 26, and rear out splice going splice 29, power supply 27, pci data collector and main control computer 28 form; Foil gauge ultra-weak electronic signal is changed and imported by front terminal block 25 input adapters 26, and through amplifying circuit 30, faint change in electric is amplified, by pci data collector 28, this electric signal is changed into digital signal demonstration and is stored in main control computer 28.
Described accurate 3 curved jigs comprise lower loading blocks 17, lower loading crossbeam 18, connect journal stirrup a14 and journal stirrup b19 at its two ends, fix and locate again the large-scale clamping plate 1 in two ends by bearing pin b15 and bearing pin c20, these clamping plate fasten bit test straight tube 3 by bolt 2, then utilizing small-sized clamping plate 9 and bolt 8 to be fixed on straight tube 3 apart from pipeline section center equidistant, and be connected with upper loading crossbeam 7 and upper load bar 6 by bearing pin a4.
Can be described in detail as follows for the present invention:
First required according to test design, foil gauge is affixed on to straight length sample 3 outside surfaces everywhere; Then cavity straight tube is filled with to oil, until fill, be connected with straight tube 3 filling oily connecting hose 10 one end, flexible pipe 10 other ends are connected with oil press 12 by quick connector again, then pass through to change oil press liquid level control straight tube internal pressure by sensor and the microcomputer that special software is housed.By straight tube everywhere the each foil gauge lead-in wire of foil gauge lead-in wire and temperature compensation material place carry out exact connect ion by each joint on wire and front terminal block according to corresponding relation.Lower loading blocks 17 and the lower loading crossbeam 18 of dop 16 fixing accurate 3 angle coupling tools under recycling fatigue tester, install bearing pin 4,15 and 20 according to test design and locate each clamping plate position and upper loading crossbeam 7.Finally utilize microcomputer and test control software, by inputting different operating loading, utilize the interior pressure of sensor control straight tube and testing machine to load moment of flexure and carry out the test of multiaxis ratchet.
As shown in Figure 3, two-way right angle foil gauge is affixed on to straight length outer surface position 1 to position 10; 1 place, position is pipe interlude maximal bending moment sectional position, for measuring the strain evolution situation of straight tube outer wall " the most dangerous " position; In addition, at each 135mm place from straight tube sample centre position to both sides, the each a slice foil gauge that pastes in position 3 and position 9, whether the ratchet strain evolution situation that this design can be studied symmetrical moment of flexure section is consistent; Position 3, the 40mm of being all separated by between position 5 and position 7, this design is the distribution situation changing with moment of flexure amplitude in order to study straight tube ratchet strained situation; Meanwhile, in each position of posting foil gauge, rotate 180 degree along hoop, stick respectively foil gauge, be position 2, position 4, position 6, position 8 and position 10, this design can be studied same moment of flexure amplitude place, the difference of the ratchet strain evolution situation between hoop diverse location.Foil gauge pastes position and can require to select arbitrarily separately according to test design, and condition restriction is not put to the test.
In this test method, due to straight tube centre position suffered circulation moment of flexure amplitude maximum, and constantly reduce to two ends along straight tube from centre, thus foil gauge should be covered near centre position, especially straight tube centre position, i.e. maximal bending moment place; Foil gauge should be chosen 90 degree perpendicular type foil gauges, can test hoop and axial strain value everywhere, can draw the evolution situation of different moments of flexure place straight tube ratchet strain simultaneously.
Test method of the present invention, can record under different interior pressures and moment of flexure composite condition, the stable situation of ratchet strain of the maximum ratchet strain location of straight tube, and can determine method in conjunction with ratchet border, determine the test ratchet boundary graph of various straight tubes.
Concrete straight tube sample is made up of two parts, and the one, the straight length 22 of long 1m; Two is two long straight tube pipe plugs 21 and 23 for 0.1m.Wherein pipe plug 21 seals completely; Other end straight tube pipe plug 23 is designed with a tapped through hole along the axial center of pipe, as logical hydraulic fluid port; Because logical hydraulic fluid port bore is larger, therefore do not need the pore that begins to rehearse; Fill after oil, will lead to hydraulic fluid port and be connected with three-way connection 24 threaded one ends, in three-way connection place setting pressure table 13 Real Time Observation straight tube overpressure situation, three-way connection opposite side with oil transporting appliance; Pipe plug 21 adopts butt-weld to be connected with 23 with straight length 22.
Multi-spindle hydraulic servo fatigue tester comprises oil press 12, and testing machine loads upper chuck 5, lower dop 16, and oil hose 10.This testing machine is a kind of improved multiaxle fatigue experimental machine; the composite condition that can realize different interior pressures and moment of flexure loads; and test condition, test parameters by multiaxial experiment control software can preset, observing and controlling, record automatically, losing efficacy appears in test or when abnormal, automatic alarm is shut down.
Multiaxial experiment control software can realize imposed load as shown in Figure 5, apply interior pressure, cycle index, cycle period, loading waveform, load that the test parameterss such as starting phase angle are preset, observing and controlling, record automatically; losing efficacy appears in test or when abnormal, automatic alarm is shut down.
Described accurate 3 curved jigs comprise lower loading blocks 17, lower loading crossbeam 18, connect journal stirrup a14 and journal stirrup b19 at its two ends, fix and locate again the large-scale clamping plate 1 in two ends by bearing pin b15 and bearing pin c20, these clamping plate fasten bit test straight tube 3 by bolt 2, then utilizing small-sized clamping plate 9 and bolt 8 to be fixed on straight tube 3 apart from each 75mm place, pipeline section center, and be connected with upper loading crossbeam 7 and upper load bar 6 by bearing pin a4.This supplementary card lamps structure is simple, reasonable in design, and the design moment that can accurately realize the each position of straight tube is symmetrical, and provides maximal bending moment load in pipeline section middle, has ensured the accuracy of experimental measurement.
Described hyperchannel dynamic strain indicator 11 comprises amplifier circuit 30, front terminal block 25 and input adapter 26, and rear out splice going splice 29, power supply 27, pci data collector and main control computer 28 form.Its Main Function is that foil gauge ultra-weak electronic signal is changed and imported by front terminal block 25 input adapters 26, and through amplifying circuit 30, faint change in electric is amplified, by pci data collector 28, this electric signal is changed into digital signal demonstration and is stored in main control computer 28.Its principle is, amplifier 30 inside provide High Precision Low Temperature to float 5V bridge and press and two Low Drift Temperature precision resistances, and resistance is 120 ohm.Only need external two 120 ohm of foil gauges, a foil gauge and a temperature compensation foil gauge, can form Wheatstone bridge.Because Wheatstone bridge (claiming again wheatstone bridge) is a kind of accurately instrument of measuring resistance; Because the distortion of sample stand under load will cause straight tube all directions generation everywhere strain, cause that foil gauge resistance changes, the electric signal of this faint variation amplifies through Wheatstone bridge and it changes digital signal record in main control computer 28 the most at last.
The invention has the advantages that, Various Complex load combinations operating mode can be provided, load working condition and applied range, test position can be adjusted flexibly, and foil gauge pastes position and can select arbitrarily according to concrete test design, and condition restriction is not put to the test; And test result precision is high, data and curves is smooth steadily, reasonable in design.In addition, hyperchannel dynamic strain indicator has low drift and low noise, the wide feature of frequency response.Improve fatigue tester and have that test condition, test parameters can be preset, observing and controlling, record automatically, test occurs losing efficacy or when abnormal, the functions such as automatic alarm shutdown.Accurate 3 curved supplementary structures can be realized the straight tube distribution of gradient symmetrically and evenly of moment of flexure everywhere, and apply maximal bending moment in centre position.Therefore, the method can be widely used under various complex working conditions, the experimental test of the single shaft of straight tube and the strain of multiaxis ratchet.
Brief description of the drawings
Fig. 1 is described test method supplementary structure schematic diagram;
Fig. 2 is hyperchannel dynamic strain indicator amplifying circuit electrical bridge principle figure;
Fig. 3 is straight tube sample 3 structural design schematic diagram;
Fig. 4 is strain measurement system 11 structural representations;
Fig. 5 is that multiaxis ratchet test control software program is carried out block diagram;
Fig. 6 utilizes a kind of stainless steel straight tube of this measurement of test method to be subject to the multiaxis ratchet behavior gained hoop strain-axial strain graph of a relation under multiaxis Cyclic Load;
Fig. 7 is the stagnant ring figure of a kind of stainless steel straight tube multi-axis ratchet behavior gained loaded load-hoop strain of measurement of test method for this reason;
Fig. 8 for this reason the hoop ratchet strain at 2 places, position of a kind of stainless steel straight tube of measurement of test method and axial ratchet strain with circulation number of turns variation relation figure;
In figure: 1 large-scale clamping plate, 2 large-scalely load dop under crossbeam, 8 small-sized bolts for clamping plate, 9 small-sized clamping plate, 10 oil hoses, 11 hyperchannel strain datas test acquisition systems, 12 multiaxis hydraulic fatigue machines, 13 accurate oil pressure gauges, 14 journal stirrup a, 15 bearing pin b, 16 testing machines, 17 times loading blocks, load crossbeam, 19 journal stirrup b, 20 bearing pin c 18 times on load bar, 7 on bolt, 3 straight tube samples, 4 bearing pin a, 5 testing machine upper chucks, 6 for clamping plate.21 pipe plug a, 22 straight lengths, 23 pipe plug b, 24 three-way connections.25 front terminal blocks, 26 input adapters, 27 power supplies, 28PCI data acquisition unit and main control computer, 29 rear out splice going splices, 30 amplifier circuits.
Embodiment
The present invention realizes the reversed bending of interior pressure pipe part by utilizing multiaxle fatigue experimental machine to be equipped with accurate three Dian Wan jig auxiliary bodies, and utilizes accurate foil gauge to measure the ratchet strain of straight tube sample.Instrument that this test method is used comprises design straight tube sample 3, multiaxle fatigue experimental machine 12, hyperchannel dynamic strain measurement instrument 11 and other auxiliary body.Described design straight tube sample 3 is mainly made up of two parts, the one, the straight length 22 of long 1m, two is two long straight tube pipe plugs 21 and 23 for 0.1m, wherein pipe plug 21 seals completely, and other end straight tube pipe plug 23 centers have a tapped through hole as logical hydraulic fluid port, and this logical hydraulic fluid port is connected with three-way connection 24 one end, can setting pressure table 13 at three-way connection, Real Time Observation straight tube overpressure situation, the three-way connection other end is connected with oil transporting appliance, pipe plug 21 and 23 and straight length 22 by being welded to connect; The effect of pipe plug 21 and 23 is the straight tube samples 3 that can bear oil pressure in order to form airtight cavity with straight length 22, to make.Described multi-spindle hydraulic servo fatigue tester 12 comprises that testing machine loads upper chuck 5, lower dop 16, and oil hose 10, described accurate three Dian Wan jig auxiliary bodies comprise lower loading blocks 17, lower loading crossbeam 18, connect journal stirrup a 14 and journal stirrup b 19 at its two ends, fix and the large-scale clamping plate 1 in two ends, location by bearing pin b 15 and bearing pin c 20 again, these clamping plate fasten bit test straight tube 3 by bolt 2, then utilizing small-sized clamping plate 9 and bolt 8 to be fixed on straight tube 3 apart from each 75mm place, pipeline section center, and be connected with upper loading crossbeam 7 and upper load bar 6 by a bearing pin 4, wherein, foil gauge Position Design as shown in Figure 3, the effect of auxiliary body is mainly that straight tube sample 3 is accurately fixed on to multiaxle fatigue experimental machine 12 in location, realize the stretching of testing machine or compressive load F are transformed into Moment at straight tube sample 3, obtain the Bending moment distribution effect in accurate 3 curved tests, this is due in the time that large-scale clamping plate 1 retrain straight tube sample 3, the axial displacement herein of straight tube sample is zero, the stretching that testing machine applies or compressive load F will make straight tube sample 3 produce obvious displacement amount of deflection, for keeping total system dynamic balance, so produce obviously along the axial stretching of straight tube sample or compression method stress in pipeline, as shown in Figure 3, according to theory of mechanics of materials, its bending normal stresses computing formula is as follows:
Wherein, F is testing machine imposed load; L is straight tube sample 3 length, is 1m herein; M represents the moment of straight tube sample 3 maximal bending moment positions; W
zrepresent the module of anti-bending section of straight tube sample 3; D is the internal diameter of straight tube sample 3; D represents the external diameter of straight tube sample 3; σ
zmaxrepresent the maximum deflection normal stress value of the maximum moment of flexure section of straight tube sample 3.
Described hyperchannel strain data test acquisition system 11 comprises amplifier circuit 30, front terminal block 25 and input adapter 26, and rear out splice going splice 29, power supply 27, pci data collector and main control computer 28 form.Its Main Function is that foil gauge ultra-weak electronic signal is changed and imported by front terminal block 25 input adapters 26, and through amplifying circuit 30, faint change in electric is amplified, by pci data collector 28, this electric signal is changed into digital signal demonstration and is stored in main control computer 28.Its principle is, amplifier 30 inside provide High Precision Low Temperature to float 5V bridge and press and two Low Drift Temperature precision resistances, and resistance is 120 ohm.Only need external two 120 ohm of foil gauges, a foil gauge and a temperature compensation foil gauge, can form Wheatstone bridge.Because Wheatstone bridge (claiming again wheatstone bridge) is a kind of accurately instrument of measuring resistance; Because the distortion of sample stand under load will cause straight tube all directions generation everywhere strain, cause that foil gauge resistance changes, the electric signal of this faint variation amplifies through Wheatstone bridge and it changes digital signal record in main control computer 28 the most at last.
Its amplifying circuit principle as shown in Figure 2, R
1, R
2known measuring resistance, R
svariable standard resistance, R
xit is measured resistance.B, connects galvanometer between D.Connect after circuit, galvanometer does not generally show zero, and B is described, 2 current potentials of D are unequal, by regulating R
s, make no current in galvanometer pass through (I
k=0), now electric bridge reaches balance.
The condition of bridge balance is B, and 2 current potentials of D equate, so have:
I
1R
1＝I
2R
2，I
xR
x＝I
sR
s (6)
Again
I
1＝I
x，I
2＝I
s (7)
So have:
Owing to being the output of voltage bridge, can draw:
Work as U
bD=0 o'clock, bridge balance, obtained: R
2r
x=R
1r
s(10)
Again due in resistance strain measurement, must consider temperature compensation, thereby metering circuit the arm-type or symmetric form such as can only adopt, therefore according to the situation difference of alternate arm coupling, its output will there will be following three kinds of situations:
1. pair output symmetric circuit
From upper figure, now have:
R
2＝R
S＝R
R
1＝R
X＝R′ (11)
Work as R
2change amount be Δ R and Δ R < < R:
Definition
k is foil gauge sensitivity coefficient herein.Have so:
Relation in this kind of situation that Here it is between Voltage-output and strain.
2. the symmetrical output circuit of pair power supply
Now have: R
2=R
1=R (14)
R
x＝R
s＝R′ (15)
Work as R
2change amount have while being Δ R and Δ R < < R:
Can ignore Δ R item:
3. equal arm bridge output
Now have: R
1=R
2=R
x=R
s=R (18)
Work as R
2change amount have while being Δ R and Δ R < < R:
This shows that output voltage is directly proportional to causing the mechanical strain ε that foil gauge resistance changes, what dynamic strain indicator used described in this test method is to the symmetrical output circuit of power supply.
The enforcement of this test method, first required according to test design, as shown in Figure 3, two-way right angle foil gauge is affixed on to straight length outer surface position 1 to position 10; 1 place, position is pipe interlude maximal bending moment sectional position, for measuring the strain evolution situation of straight tube outer wall " the most dangerous " position; In addition, at each 135mm place from straight tube sample centre position to both sides, the each a slice foil gauge that pastes in position 3 and position 9, whether the ratchet strain evolution situation that this design can be studied symmetrical moment of flexure section is consistent; Position 3, the 40mm of being all separated by between position 5 and position 7, this design is the distribution situation changing with moment of flexure amplitude in order to study straight tube ratchet strained situation; Meanwhile, in each position of posting foil gauge, rotate 180 degree along hoop, stick respectively foil gauge, be position 2, position 4, position 6, position 8 and position 10, this design can be studied same moment of flexure amplitude place, the difference of the ratchet strain evolution situation between hoop diverse location.Measure the ratchet strain evolution situation of other position as wish, foil gauge position can be changed as required voluntarily.
Then, cavity straight tube sample 3 is filled with to oily, until fill, while filling with oil, should strictly control oil-feed speed, otherwise form bubble in Yi Guan, affect the effect of pressurizeing in the future; Be connected with three-way connection 24 on straight tube sample 3 filling oily connecting hose 10 one end, pressure is born in the design of connecting hose should be greater than the required interior pressure of test, guarantees trouble free service again; The flexible pipe other end is connected with the interior pressure passageway of fatigue tester 12 by quick connector, then the load F value of being controlled straight tube internal pressure value P and straight tube sample being applied by sensor and the microcomputer that independently developed multiaxial loading Control experiment software is housed; When pressurization, constant pressing speed, unsuitable too fast, as inner pressure curve increases as being in time linear, illustrate that in straight tube, bubble is less, filling oil quality is better; As inner pressure curve is obvious non-linear increase in time, illustrate that in pipe, bubble is more, pressurization difficulty, filling oil quality is not good, may need again to fill with oil debugging.This is because interior pressure causes bubble in chamber obviously to be compressed, and more liquid oils enters straight tube sample and fills the bubble volume reducing, and makes inner pressure curve be non-linear.
As normal in the effect of pressurizeing, each joint on wire and front terminal block 25 is carried out to exact connect ion according to corresponding relation; After having connected, should whether normal controlling if checking that each foil gauge connects reading on microcomputer 28, whether there is short circuit, the situation such as open circuit or foil gauge signal fluctuation is larger; As occur above-mentioned various extremely, and may be between foil gauge lead-in wire, to insulate badly, or lead-in wire and wire bonds poor quality, cause showing on microcomputer foil gauge abnormal signal.
The straight tube test specimen that adopts this measurement of test method the to bear constant internal pressure multiaxis ratchet strain evolutionary process under Moment that circulated: dynamic strain indicator should carry out automatic clear and input foil gauge sensitivity coefficient in the time using for the first time.Strain is covered on straight tube outside surface key axial and circumferential everywhere, straight tube test specimen interior pressure in conjunction with the multiaxis operating loading effect of moment of flexure under produce distortion, the foil gauge resistance that is closely covered on straight tube outside surface is by the axial deformation along with straight tube test specimen and circumferential deformation and change, cause the variation of the outside electric bridge microvolt of Hui Sitong magnitude voltage signals, and carry out voltage amplification through direct current amplifier, obtain positive and negative 10V voltage input hyperchannel AD plate and carry out AD conversion.Finally can axially converting digital signal output display or storage on main control computer to circumferential strain value and prepare against subsequent treatment straight tube test specimen by AD plate.
As normal in each foil gauge signal, dop 16 under the lower loading blocks 17 of accurate 3 angle coupling tools and lower loading crossbeam 18 use fatigue testers is fixed, and bearing pin 4,15 and 20 is installed for locating each clamping plate 9 positions and upper loading crossbeam 7, straight tube sample 3 is fixed on accurate three Dian Wanqi jig auxiliary bodies the most at last, prepares to test; Wherein, be installed before straight tube sample, should be on straight tube sample foil gauge paste district and auxiliary body's fixed area is divided certain density grid, be convenient to accurate location, ensure that loading position is accurate, load distributes as test design, in addition, after off-test, also can change by observing mesh shape, judge straight tube entirety and local deformation situation.
Finally, utilize multiaxial loading Control experiment software in microcomputer 28, as shown in Figure 5, by inputting interior pressure value P (unit, MPa), imposed load F (unit, kN), sets cycle period (unit, s), cycle index, the test parameterss such as data sampling frequency (1Hz is to 1000Hz) and loading waveform (triangular wave or sine wave), carry out straight tube and are subject to the multiaxis ratchet strain evolution test under interior pressure and circulation moment of flexure combination acting in conjunction; In addition, in test Protection parameters hurdle, set imposed load, interior pressure and displacement stroke Protection parameters, prevent that straight tube sample deformation is excessive; As imposed load, interior pressure or displacement stroke exceed Protection parameters, when test is carried out, and load, interior pressure or displacement stroke reach after protection value, no longer increase or decline, and ignore test setting value, program ejects dialog box and reports to the police, and auto stop, and interior pressure and load autostable are offloaded to zero; In addition, test load F, interior pressure P, test is carried out the time, cycle index, the hoop strain of each position and axial strain are all recorded in the local hard drive of main control microcomputer automatically by setpoint frequency, in order to deriving and processing.
For example, for realizing constant internal pressure P=20MPa and circulation imposed load F=± 30kN, cycle period is 30s, and initial operating mode is P=20MPa, the complex combination operating mode of F=0kN, in should selecting, press hurdle in multiaxial loading Control experiment software, in setting, press lower limit and be 20MPa, in setting, pressing cycle period is 30s, and selecting to load waveform is triangular wave, setting cycle index is 500, and selecting to load phasing degree is 0 degree; And then select imposed load hurdle, set on imposed load and be limited to 30kN, under be limited to-30kN, and to set the load cycle cycle be also 30s, selecting to load waveform is triangular wave, setting cycle index is also 500, selecting to load phasing degree is 0 degree.Wherein, cycle index, loads the parameters such as waveform and cycle period and all can need to change setting according to self test design.
Be that 0MPa is to 20MPa as realized interior pressure P range of DO, constant imposed load F=30kN, cycle period is 30s, initial operating mode is P=0MPa, the composite condition of F=0kN, in multiaxial loading Control experiment software select in pressure hurdle, in setting, press and be limited to 20MPa, under be limited to 0MPa, in setting, pressing cycle period is 30s, selecting to load waveform is triangular wave, and setting cycle index is 500, and setting and loading phasing degree is 270 degree; And then select imposed load hurdle, set on imposed load and be limited to 30kN, under be limited to-30kN, and to set the load cycle cycle be also 30s, selecting to load waveform is triangular wave, setting cycle index is also 500, selecting to load phasing degree is 0 degree.Wherein, cycle index, loads the parameters such as waveform and cycle period and all can need to change setting according to self test design.
For example, utilize this measurement of test method the straight tube sample of a kind of austenitic stainless steel Z2CND18.12N be subject to the multiaxis ratchet behavior under constant internal pressure 20MPa and cyclic loading ± 30kN effect, now the multi-axis stress state of the each sectional position of straight tube sample can calculate by aforementioned formula (1) to formula (5).For example, the suffered moment of flexure maximum in straight tube sample midsection, now, in 2 places, position, press the constant axial normal stress producing to be:
the constant circumference stress that interior pressure produces is:
and cyclic loading F=± 30kN can obtain according to formula (3), equivalent cycle moment of flexure is:
bringing formula (5) into must bending method stress be:
therefore the normal stress at foil gauge position 1 and 2 places, position is: mean stress is 84.4MPa, and stress amplitude is ± 373.7MPa; 2 times of the mean stresses of circumference stress are to the mean stress of normal stress, and its stress amplitude is relevant with normal stress amplitude, and concrete outcome complexity, does not discuss.
Test operation flow process is described above, obtain the straight tube sample situation of the axial and hoop ratchet strain Temporal Evolution of position everywhere, strain measurement result can be by curve or data representation out, and wherein the concrete outcome in straight tube centre position is as Fig. 6, shown in Fig. 7 and Fig. 8.Wherein, ratchet strain definition is as follows:
In formula, ε
max, ε
minbe respectively maximum, minimum strain in once circulation, ε
0for initial elasticity strain (only having pressure load to do the used time), because initial elasticity strain is very little, and for load controlled circulation, each circulation Elastic strain afterwards is not accumulated, and when calculating, is conventionally ignored.
From Fig. 6 to Fig. 8, can find out, the stagnant ring line smoothing of stress-strain of sample, without abnormal catastrophe point, along with the increase of cycle index time, hoop ratchet answers apparition to increase, but axial ratchet strain is not obvious, and ratchet rate of strain is initially larger, constantly reduce subsequently, and final hoop ratchet strain is tending towards stable, this is with ratchet behavior essential characteristic and other scholar's result of study was consistent in the past.Therefore, think multiaxis ratchet behavior when this test method can be tested preferably straight tube and is subject to multiaxis Cyclic Load.
Claims (4)
1. straight tube multi-axis ratchet method of testing, is characterized in that foil gauge to be affixed on straight length sample (3) outside surface everywhere; Then cavity straight tube is filled with to oil, until fill, be connected with straight tube (3) filling oily connecting hose (10) one end again, flexible pipe (10) other end is connected with oil press (12) by quick connector, then passes through to change oil press liquid level control straight tube internal pressure by sensor and the microcomputer that software is housed; The each corresponding foil gauge lead-in wire at arbitrary straight tube place of the same material that straight tube foil gauge lead-in wire and temperature compensation everywhere used, goes up each joint by the front terminal block (25) of wire and hyperchannel dynamic strain indicator and carries out exact connect ion according to corresponding relation; Lower loading blocks (17) and the lower loading crossbeam (18) of fixing accurate 3 the angle coupling tools of dop (16) under recycling fatigue tester; Bearing pin is installed and is located each clamping plate position and upper loading crossbeam (7); Then utilize microcomputer and test control software, by inputting different operating loading, utilize the interior pressure of sensor control straight tube and testing machine to load moment of flexure and carry out the test of multiaxis ratchet, finally adopt hyperchannel dynamic strain indicator (11) Real-time Collection straight tube sample strain evolution everywhere situation, and data-switching is stored in main control computer (28).
2. the method for claim 1, is characterized in that foil gauge is two-way right angle foil gauge, is affixed on the centre position of straight tube, with apart from equidistant some positions, this straight tube centre position, and in each position of posting foil gauge, rotate 180 degree along hoop, stick respectively foil gauge.
3. the method for claim 1, it is characterized in that described hyperchannel dynamic strain indicator comprises amplifier circuit (30), front terminal block (25) and input adapter (26), rear out splice going splice (29), power supply (27), pci data collector and main control computer (28); Foil gauge ultra-weak electronic signal is changed and imported by front terminal block (25) input adapter (26), and through amplifier circuit (30), faint change in electric is amplified, by pci data collector, this electric signal is changed into digital signal demonstration and is stored in main control computer (28).
4. the method for claim 1, it is characterized in that described accurate 3 angle coupling tools comprise lower loading blocks (17), lower loading crossbeam (18), connect journal stirrup a(14 at lower loading crossbeam (18) two ends) and journal stirrup b(19), again by bearing pin b(15) and bearing pin c(20) the fixing and location large-scale clamping plate in two ends (1), these clamping plate fasten bit test straight tube (3) by the first bolt (2), then utilizing small-sized clamping plate (9) and the second bolt (8) to be fixed on straight tube (3) apart from pipeline section center equidistant, and by bearing pin a(4) be connected with upper loading crossbeam (7) and upper load bar (6).
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