CN102162778B - Multiple-spindle ratchet wheel strain testing system and method of pipe bend - Google Patents
Multiple-spindle ratchet wheel strain testing system and method of pipe bend Download PDFInfo
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- CN102162778B CN102162778B CN 201010599442 CN201010599442A CN102162778B CN 102162778 B CN102162778 B CN 102162778B CN 201010599442 CN201010599442 CN 201010599442 CN 201010599442 A CN201010599442 A CN 201010599442A CN 102162778 B CN102162778 B CN 102162778B
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- 238000012360 testing method Methods 0.000 title claims abstract description 71
- 238000000034 method Methods 0.000 title claims abstract description 20
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- 238000010998 test method Methods 0.000 claims description 17
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- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 5
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Abstract
The invention relates to a multiple-spindle ratchet wheel strain testing system and method of a pipe bend. The applied load F and output pressure P of a hydraulic servo fatigue testing machine are jointly controlled by a microcomputer and a sensor so as to provide various complex load working conditions, and a real-time multiple-spindle ratchet wheel action of the bend under the complex load working conditions is measured by a stain gauge method; and the variation situation of strain applied to the bend is measured by utilizing the sensor to control the hydraulic servo fatigue testing machine, a clamping fixture auxiliary mechanism and the strain gauge method, data is collected by a multi-channel dynamic strain instrument, and the result is output through the computer. According to the invention, multiple complex load combination working conditions can be provided, the load working conditions and the application range are wide, the measurement position can be adjusted flexibly, namely the strain gauge sticking position can be selected freely according to concrete test designs, and is not restricted by the test conditions; the test result has high accuracy, the data curve is smooth ad stable, and the design is reasonable; and the multi-channel dynamic strain instrument has the characteristics of low drift, low noise and wide frequency response.
Description
Technical field
The present invention relates under a kind of multiaxis Cyclic Load, the method for each position ratchet strain Temporal Evolution of testing conduit elbow belongs to bend pipe multiaxis ratchet strain measurement system and method.
Background technology
Be subjected to during ratchet strain under the multiaxis Cyclic Load develops at the testing conduit Elbow material at present both at home and abroad, more than be the test of Elbow material bar or plates specifications sample being carried out the strain of multiaxis ratchet, mainly be to utilize extensometer method etc.But there are a lot of problems in this method, at first it only considers the ratchet behavior behind the stand under load of material own, fail effectively to be 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 complicated with staking-out work, and it is inaccurate etc. that misoperation very easily produces measurement data.So they can not simulate the accumulation of elbow elbow ratchet strain everywhere under primary stress and secondary stress combination really and accurately, so its applicability is relatively poor.Also adopt in addition exciting device such as shaking table, utilize inertial force that bending load is provided.Although it can directly load research to elbow structure, this method, the load range that provides is less than normal, and loading type is single, and it is larger limited to by self.Though have recent years the scholar also to propose the Biaxial ratcheting of overstrain sheet method test elbow, 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 the test method of the ratchet strain evolutionary process of the accurate testing conduit elbow of a kind of energy under three-dimensional stress state.This test method has been optimized in the past the whole bag of tricks, 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 employing strain gauge method measurement elbow is subjected to the real-time multiaxis ratchet behavior under the complex load operating mode.Wherein, axial normal stress and the circumference stress Relations Among in the elbow sample that causes of output pressure P can be as follows:
Wherein, σ
zBe the living axial normal stress of cutting down output on the bend pipe, MPa; σ
θFor the inner pressure ring of random angle θ corresponding position on the bend pipe to stress, MPa; P represents that testing machine provides pressure value in the test design, MPa; D is the external diameter of elbow sample, mm; T represents the pipe wall thickness of elbow sample, mm; R represents the radius-of-curvature of bend pipe, mm; r
nThe mean radius in expression bend pipe cross section, mm; θ is certain any corresponding central angle on the bend pipe.
The method test position is flexible, and load working condition is various, and method is novel, and reasonable in design, data accurately and reliably.Simultaneously the hyperchannel dynamic strain indicator has low drift and low noise, the wide characteristics of frequency response; fatigue tester has that test condition, test parameters can be preset, observing and controlling, automatic record; test occur to be lost efficacy or when unusual; the functions such as automatic alarm shutdown; can be widely used under the various complex working conditions of experimental study; such as fluid temperature variations in earthquake or the pipe etc., the Evolution of the multiaxis ratchet strain of elbow with pressure, and can be used for determining the ratchet border of channel bend.
Technical scheme of the present invention is as follows:
Elbow multiaxis ratchet test macro of the present invention, utilize sensor control hydraulic servo fatigue tester, jig auxiliary body and strain gauge method to measure the strain variation situation of elbow stand under load, by hyperchannel dynamic strain indicator image data, through the computer export result.
Described sensor control hydraulic servo fatigue tester comprises oil press (11), and testing machine loads upper chuck (1), lower dop (10) and oil hose; Sensor control hydraulic servo fatigue tester realizes pressing in different and the composite condition of moment of flexure loads, and test condition, test parameters can be preset, observing and controlling, automatic record, test occur losing efficacy or when unusual automatic alarm shut down.
Described elbow sample is: the two ends of a channel bend (15) and two straight connectors (14) be connected 16) a separately end be connected by weld seam; The separately other end of two straight connectors then respectively at two pipe plugs (12) be connected 19) weld seam connects; Two pipe plug sidewall locations have all had a tapped through hole (13), as the logical hydraulic fluid port of turnover, be beneficial to gas in the pipe is effectively discharged, and prevent that a large amount of bubbles are stranded in tube chamber, impact pressurization effect; After filling oil, one of them logical hydraulic fluid port is connected with three-way connection (17) threaded one end, in three-way connection place setting pressure table (18) Real Time Observation elbow sample internal pressure situation; Another logical hydraulic fluid port (13) then connects with the oil hose that is connected oil press.
Channel bend multiaxis ratchet method of testing of the present invention: foil gauge is affixed on elbow sample (5) maximal bending moment position outside surface everywhere; Then cavity elbow sample is filled with oil, until fill, connecting hose one end that to fill again oil is connected with elbow sample (5), the flexible pipe other end is connected with oil press (11) by quick connector, controls elbow sample internal pressure by sensor and the microcomputer that software is housed by changing oil press (11) liquid level again; Foil gauge lead-in wire and each foil gauge lead-in wire of temperature compensation material place carry out exact connect ion by each joint on wire and the front terminal block according to corresponding relation everywhere with the elbow sample; Subsequently the elbow sample is threaded with lower loading blocks (7) with upper loading blocks (4), and between them, adds the aluminium pad, make between loading blocks and the elbow sample displacement transmit continuous; Then upper loading blocks (4) and lower loading blocks (7) are passed through respectively the hinged of bearing pin (3) and (8) realization and upper load bar (2) and lower load bar (9); Fixing upper load bar (2) and the lower load bar (9) that loads auxiliary body of recycling fatigue tester upper chuck (1) and lower dop (10); Utilize at last microcomputer and test control software, by inputting different operating loading, utilize the interior pressure of sensor control elbow sample and testing machine to load moment of flexure and carry out the test of multiaxis ratchet.Adopt hyperchannel dynamic strain indicator (6) Real-time Collection elbow sample strain evolution everywhere situation, and data-switching is stored in the main control computer (23).
Foil gauge is two-way right angle foil gauge, relates to altogether 10 positions herein; Wherein, curved side in the definition elbow (i.e. 0 degree position) is position 1, outside sweep side (i.e. 180 degree positions) is position 9, centre position, both sides between inner edge and the outer rim is defined as respectively position 7 (90 degree position) and position 10 (90 degree position), to between the 90 degree positions, respectively paste a slice foil gauge every 15 degree at 0 degree, correspondence position 2 is to the position 6 respectively, 90 degree to 180 degree centre positions paste a slice foil gauge, i.e. position 8 (135 degree position).
Described hyperchannel dynamic strain indicator comprises amplifier circuit (25), front terminal block (20) and input adapter (21), rear out splice going splice (24), power supply (22), pci data collector and main control computer (23) form; The foil gauge ultra-weak electronic signal is changed by front terminal block (20) and input adapter (21) importing, and through amplifying circuit (25) faint change in electric is amplified, change this electric signal into digital signal by pci data collector (23) and show and be stored in main control computer (23).
Described jig auxiliary body comprises load bar (2) and lower load bar (9), upper loading blocks (4) and lower loading blocks (7), hinged by bearing pin (3) and (8) between load bar and the loading blocks, loading blocks and elbow sample (5) are threaded connection, during connection, add the right quantity aluminium backing between the two, the warranty test displacement is transmitted continuously.
Can believe for the present invention and to be described as follows:
In this test method, foil gauge should be chosen 90 degree perpendicular type foil gauges, can test everywhere hoop and axial strain value, can draw the evolution situation of different moments of flexure place elbow ratchet strain simultaneously.
Test method of the present invention can record under different interior pressures and the moment of flexure composite condition, the stable situation of the ratchet strain of the maximum ratchet strain location of elbow sample, and can determine method in conjunction with the ratchet border, determine the test ratchet boundary graph of various elbows.
Concrete elbow sample is comprised of three parts, and one is 90 degree elbows, and the 2nd, the straight connector of each long 0.1m (14) and (16), wherein straight connector (16) pipe side has a through hole, and is connected with three-way connection (17) weld seam, as vent port; Three is that two each length are straight tube pipe plug (12) and (19) of 0.1m; Pipe plug (12) be connected 19) with straight connector (14) be connected 16) adopt butt-weld to be connected; Wherein the pipe side position of a pipe plug (12) is designed with a tapped through hole, as logical hydraulic fluid port; Another pipe plug (19) sealing; After filling oil, will be welded with three-way connection (17) and locate setting pressure table (18) Real Time Observation elbow cavity pressure situation; Threaded hole (13) links to each other with the oil hose that is connected oil press (11), presses in realizing to load.
The multi-spindle hydraulic servo fatigue tester comprises oil press (11), and testing machine loads upper chuck (1), lower dop (10), and oil hose.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, automatic record, losing efficacy appears in test or when unusual, 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, automatic record; test occur to be lost efficacy or when unusual, automatic alarm is shut down.
Described anchor clamps auxiliary body comprises load bar (2) and lower load bar (9), upper loading blocks (4) and lower loading blocks (7), hinged by bearing pin (3) and (8) between load bar and the loading blocks, loading blocks and elbow sample (5) are threaded connection, during connection, add the right quantity aluminium backing between the two, the warranty test displacement is transmitted continuously.This supplementary card lamps structure is simple, and is reasonable in design, can realize accurately that the design moment of each position of elbow is symmetrical, and the place provides maximal bending moment load in the middle of elbow, has guaranteed the accuracy of experimental measurement.
Described hyperchannel dynamic strain indicator (6) comprises amplifier circuit (25), front terminal block (20) and input adapter (21), rear out splice going splice (24), power supply (22), pci data collector and main control computer (23) form.Its Main Function is the foil gauge ultra-weak electronic signal to be changed imported by front terminal block (20) input adapter (21), and through amplifying circuit (25) faint change in electric is amplified, change this electric signal into digital signal by pci data collector (23) and show and be stored in main control computer (23).Its principle is, amplifier (25) inside provides High Precision Low Temperature to float the 5V bridge and presses and two Low Drift Temperature precision resistances, and resistance is 120 ohm.Only need external two 120 ohm of foil gauges, namely a foil gauge and a temperature compensation foil gauge can consist of 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 elbow 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 (23) 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 namely foil gauge pastes the position and can select arbitrarily according to concrete test design, and condition restriction is not put to the test; And the test result precision is high, and data and curves is smooth steadily, and is reasonable in design.In addition, the hyperchannel dynamic strain indicator has low drift and low noise, the wide characteristics of frequency response.Improve fatigue tester and have that test condition, test parameters can be preset, observing and controlling, automatic record, test occurs losing efficacy or when unusual, the functions such as automatic alarm shutdown.The anchor clamps supplementary structure can be realized the elbow symmetrically and evenly gradient distribution of moment of flexure everywhere, and the position applies maximal bending moment therebetween.
Description of drawings
Fig. 1 is described test method supplementary structure synoptic diagram;
Fig. 2 is hyperchannel dynamic strain indicator amplifying circuit electrical bridge principle figure;
Fig. 3 is elbow sample 3 structural design synoptic 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 bend sample of this measurement of test method to be subjected to multiaxis ratchet behavior gained hoop strain-axial strain graph of a relation under the multiaxis Cyclic Load;
Fig. 7 is the stagnant ring figure of a kind of stainless steel bend sample of measurement of test method multiaxis ratchet behavior gained loaded load-hoop strain for this reason;
Fig. 8 for this reason the hoop ratchet strain at 1 place, position of a kind of stainless steel bend sample of measurement of test method and axial ratchet strain with circulation number of turns variation relation figure;
Among the figure: 1 upper grip, load bar on 2,3 bearing pin a, loading blocks on 4,5 elbow samples, 6 hyperchannel strain datas test acquisition system, 7 times loading blocks, 8 bearing pin b, 9 times load bars, 10 lower clamps, 11 multiaxis hydraulic fatigue machines, 12 pipe plug a, 13 oil supply holes, 14 straight connector a, 1590 degree elbows, 16 straight connector b, 17 three-way connections, 18 precision pressure gauges, 19 pipe plug b, 20 front terminal blocks, 21 input adapters, 22 power supplies, 23PCI data acquisition unit and main control computer, 24 rear out splice going splices, 25 amplifier circuits.
Embodiment
The present invention is by utilizing the multiaxle fatigue experimental machine to be equipped with the reversed bending that jig auxiliary body realizes interior pressure pipe part, and utilizes accurate foil gauge to measure the ratchet strain of elbow sample.Instrument that this test method is used comprises design elbow sample 5, multiaxle fatigue experimental machine 11, hyperchannel dynamic strain measurement instrument 6 and other auxiliary body.Described design elbow sample 5 mainly is comprised of three parts, one is 90 degree elbows, the 2nd, and the straight connector of each long 0.1m (14) and (16), wherein straight connector (16) pipe side has a through hole, and be connected with three-way connection (17) weld seam, as vent port; Three is that two each length are straight tube pipe plug (12) and (19) of 0.1m; Pipe plug (12) be connected 19) with straight connector (14) be connected 16) adopt butt-weld to be connected; Wherein the pipe side position of a pipe plug (12) is designed with a tapped through hole, as logical hydraulic fluid port; Another pipe plug (19) sealing; After filling oil, will be welded with three-way connection (17) and locate setting pressure table (18) Real Time Observation swan neck internal pressure situation; Threaded hole (13) links to each other with the oil hose that is connected oil press (11), presses in realizing to load.Described multi-spindle hydraulic servo fatigue tester 11 comprises that testing machine loads upper chuck 1, lower dop 10, and oil hose; Described jig auxiliary body comprises load bar 2 and lower load bar 9, and upper loading blocks 4 and lower loading blocks 7 are hinged by bearing pin 3 and 8 between them; Wherein, the foil gauge Position Design as shown in Figure 3; The effect of auxiliary body mainly is that elbow sample 5 accurately is fixed in multiaxle fatigue experimental machine 11 in the location, realization is transformed into Moment at elbow sample 5 with stretching or the compressive load F of testing machine, moment of flexure not only can produce circumference stress on elbow, also can produce axial stress.By the circumference stress that moment of flexure causes at elbow, the each point place is different in same cross section, and the circumference stress in the outside is maximum in the neutral axis place; And the axial stress that is caused at elbow by moment of flexure, as circumference stress, the each point place is not identical on the same cross section, but its symbol is identical with circumference stress, and size is 1/3～1/2 of this circumference stress.As shown in Figure 3, according to theory of mechanics of materials, its bending normal stresses computing formula is as follows:
Wherein, F is the testing machine imposed load, N; L
BB 'Presentation graphs 3 mid point B are to the length of electric B ', i.e. distance between section A-A center and the jig, and mm, M represent the moment of elbow sample 5 maximal bending moment positions (being elbow interlude cross section), Nmm; W
zThe module of anti-bending section of expression elbow sample 5 midsection A-A, mm
3D is the internal diameter of elbow sample 5, mm; D represents the external diameter of elbow sample 5, mm; σ
ZmaxThe maximum deflection normal stress value at the moment of flexure section A-A place of the maximum of expression elbow sample 5, MPa.
Described hyperchannel strain data test acquisition system 6 comprises amplifier circuit 25, front terminal block 20 and input adapter 21, and rear out splice going splice 24, power supply 22, pci data collector and main control computer 23 form.Its Main Function is the foil gauge ultra-weak electronic signal to be changed by front terminal block 20 input adapters 21 import, and through amplifying circuit 25 faint change in electric is amplified, change this electric signal into digital signal by pci data collector 23 and show and be stored in main control computer 23.Its principle is, amplifier 25 inside provide High Precision Low Temperature to float the 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, namely a foil gauge and a temperature compensation foil gauge can consist of 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 elbow sample 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 23 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 the D.After connecting circuit, galvanometer does not generally show zero, and B is described, 2 current potentials of D are unequal, by regulating R
S, make in the galvanometer no current by (I
K=0), this moment, electric bridge reached 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 be the output of voltage bridge, can draw:
Work as U
BD=0 o'clock, bridge balance namely obtained: R
2R
X=R
1R
S(10)
Again owing in the resistance strain measurement, must consider temperature compensation, thereby metering circuit the arm-type or symmetric form such as can only adopt, so different according to the situation of alternate arm coupling, following three kinds of situations will appear in its output:
1. to the output symmetric circuit
By upper figure as can be known, have this moment:
R
2＝R
S＝R
R
1＝R
X＝R′ (11)
Work as R
2The change amount be Δ R and Δ R＜＜R, then:
Definition
K is the foil gauge sensitivity coefficient herein.Have so:
Relation in this kind situation that Here it is between Voltage-output and the strain.
2. to the symmetrical output circuit of power supply
Have this moment: R
2=R
1=R (14)
R
x＝R
s＝R′ (15)
Work as R
2The change amount be Δ R and Δ R＜＜have during R:
Can ignore Δ R item, then:
3. equal arm bridge output
Have this moment: R
1=R
2=R
X=R
S=R (18)
Work as R
2The change amount be Δ R and Δ R＜＜have during R:
This shows that output voltage is directly proportional with causing the mechanical strain ε that the foil gauge resistance changes, what the described dynamic strain indicator of this test method used is to the symmetrical output circuit of power supply.
The enforcement of this test method, at first required according to test design, as shown in Figure 3, two-way right angle foil gauge is affixed on 10 positions, wherein, elbow inner edge side (i.e. 0 degree position) is position 1, outer edge side (i.e. 180 degree positions) is position 9, centre position between inner edge and the outer rim is defined as position 7 (90 degree position) and position 10 (90 degree position), in order effectively to compare the ratchet strain evolution situation of these several specific positions like this, spend between the positions to 90 at 0 degree, respectively paste a slice foil gauge every 15 degree, correspondence position 2 to position 6,90 degree paste a slice foil gauge between 180 degree positions respectively, be position 8 (135 degree position), this design can draw from the inboard to the outside along the ratchet strain evolution regularity of distribution of hoop.
Then, cavity elbow sample 5 is filled with oily, until fill, should strictly control oil-feed speed when filling with oil, otherwise form bubble in the Yi Zaiguan, affect the effect of pressurizeing in the future; Flexible pipe one end that will be connected with oil press 11 again is connected with oil-in 13 on the elbow sample 5, and pressure is born in the design of connecting hose should greater than the required interior pressure of test, guarantee trouble free service; The load F value of controlling elbow sample internal pressure value P and the elbow sample being applied by sensor and the microcomputer that independently developed multiaxial loading Control experiment software is housed again; During pressurization, constant pressing speed, unsuitable too fast, increase as being in time linear such as inner pressure curve, illustrate that then bubble is less in the elbow sample, the filling oil quality is better; Be in time obvious non-linear increase such as inner pressure curve, illustrate that bubble is more in the pipe, the pressurization difficulty, the filling oil quality is not good, may need again to fill with the oil debugging.This is because interior pressure causes that bubble is obviously compressed in the chamber in, and more liquid oils enters the elbow sample and fills the bubble volume that reduces, so that inner pressure curve is non-linear.
As the effect of pressurizeing is normal, and each joint on wire and the front terminal block 20 is carried out exact connect ion according to corresponding relation; Connect finish after, should check whether each foil gauge connects reading normal, short circuit whether occurs at control microcomputer 23, the situation such as open circuit or the foil gauge signal fluctuation is larger; As occur above-mentioned various unusually, may be that insulation is bad between the foil gauge lead-in wire, or lead-in wire and wire bonds poor quality, cause demonstration foil gauge abnormal signal on the microcomputer.
The elbow test specimen that adopts this measurement of test method the to bear constant internal pressure multiaxis ratchet strain evolutionary process under the Moment that circulated: dynamic strain indicator should carry out automatic clear and input foil gauge sensitivity coefficient when using for the first time.Strain is covered on the elbow sample outside surface key axial and circumferential everywhere, the elbow test specimen produces distortion in interior pressure under in conjunction with the multiaxis operating loading effect of moment of flexure, the foil gauge resistance that closely is covered on elbow sample outside surface will be along with the axial deformation of elbow test specimen and circumferential deformation and is changed, 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 the AD conversion.At last can axially converting digital signal output display or storage on main control computer to the circumferential strain value and prepare against subsequent treatment the elbow test specimen by the AD plate.
Normal such as each foil gauge signal, then the elbow sample is threaded with lower loading blocks (7) with upper loading blocks (4), and between them, adds the aluminium pad, make between loading blocks and the elbow sample displacement transmit continuous; Then upper loading blocks (4) and lower loading blocks (7) are passed through respectively the hinged of bearing pin (3) and (8) realization and upper load bar (2) and lower load bar (9); Fixing upper load bar (2) and the lower load bar (9) that loads auxiliary body of recycling fatigue tester upper chuck (1) and lower dop (10) prepared to test; Wherein, be installed before the elbow sample, should be on the elbow sample foil gauge paste the district and auxiliary body's fixed area is divided certain density grid, be convenient to accurate location, guarantee that loading position is accurate, load distributes such as test design, in addition, after the off-test, also can change by observing mesh shape, judge elbow sample integral body and local deformation situation.
At last, utilize multiaxial loading Control experiment software in the microcomputer 28, as shown in Figure 5, by inputting interior pressure value P (unit, MPa), (unit kN), sets cycle period (unit to imposed load F, s), cycle index, the test parameterss such as data sampling frequency (1Hz is to 1000Hz) and loading waveform (triangular wave or sine wave) are carried out the elbow sample and tested by the multiaxis ratchet strain evolution under interior pressure and the 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 the elbow sample deformation is excessive; Such as imposed load, interior pressure or displacement stroke surpass Protection parameters, when test is carried out, and load, after interior pressure or displacement stroke reach the protection value, no longer increase or decline, ignore the 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 all are 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=± 20kN, cycle period is 30s, and initial operating mode is P=20MPa, the complex combination operating mode of F=0kN, press the hurdle in should in multiaxial loading Control experiment software, selecting, press lower limit in the setting and be 20MPa, pressing cycle period in setting is 30s, and selecting to load waveform is triangular wave, setting cycle index is 500, and selecting to load the phasing degree is 0 degree; And then select the imposed load hurdle, and set on the imposed load and be limited to 20kN, lower being limited to-20kN, and to set the load cycle cycle also be 30s, selecting to load waveform is triangular wave, setting cycle index also is 500, selects to load the phasing degree and is 0 and spend.Wherein, cycle index loads the parameters such as waveform and cycle period and all can change setting according to self test design needs.
As realizing that interior pressure P range of DO is that 0MPa is to 20MPa, constant imposed load F=20kN, cycle period are 30s, and initial operating mode is P=0MPa, the composite condition of F=0kN, press the hurdle in then in multiaxial loading Control experiment software, selecting, press in the setting and be limited to 20MPa, the lower 0MPa that is limited to, pressing cycle period in setting is 30s, selecting to load waveform is triangular wave, and setting cycle index is 500, and setting and loading the phasing degree is 270 degree; And then select the imposed load hurdle, and set on the imposed load and be limited to 20kN, lower being limited to-20kN, and to set the load cycle cycle also be 30s, selecting to load waveform is triangular wave, setting cycle index also is 500, selects to load the phasing degree and is 0 and spend.Wherein, cycle index loads the parameters such as waveform and cycle period and all can change setting according to self test design needs.
For example, utilize this measurement of test method the elbow sample of a kind of austenitic stainless steel Z2CND18.12N be subjected to multiaxis ratchet behavior under constant internal pressure 17.5MPa and the cyclic loading ± 20kN effect, this moment, the multi-axis stress state of each sectional position of elbow sample can calculate by aforementioned formula (1) to formula (5).For example, the suffered moment of flexure of elbow sample midsection A-A is maximum, and at this moment, the constant axial normal stress of cutting down output living in 2 places, position is:
In the living constant circumference stress of cutting down output be:
And cyclic loading F=± 20kN can get according to formula (3), and the equivalent cycle moment of flexure is:
Bringing formula (5) into must bending method stress be:
So the normal stress at foil gauge position 1 and 2 places, position is: mean stress is 73.9MPa, and stress amplitude is ± 160.9MPa; 2 times of the mean stresses of circumference stress are to the mean stress of normal stress, and its stress amplitude is relevant with the normal stress amplitude, is about 2 times to 3 times of normal stress, and concrete outcome is complicated, does not discuss, and can draw by FEM (finite element) calculation.
The test operation flow process as mentioned above, obtain the elbow sample situation of the axial and hoop ratchet strain Temporal Evolution of position everywhere, the strain measurement result can be by curve or data representation out, the wherein concrete outcome in elbow centre position such as Fig. 6, Fig. 7 and shown in Figure 8.Wherein, the ratchet strain definition is as follows:
In the formula, ε
Max, ε
MinBe respectively maximum, minimum strain in the once circulation, ε
0Be initial elasticity strain (only having pressure load to do the time spent) that because the initial elasticity strain is very little, and for the load controlled circulation, afterwards each time circulation Elastic strain is not accumulated, and is usually ignored during calculating.
From Fig. 6 to Fig. 8, can find out, the stress-strain of sample stagnates and encircles line smoothing, without unusual catastrophe point, along with the increase of cycle index time, the hoop ratchet answers apparition to increase, but the axial ratchet strain is not obvious, and the 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 the elbow sample and is subjected to the multiaxis Cyclic Load.
Claims (3)
1. elbow multiaxis ratchet method of testing is characterized in that foil gauge is affixed on elbow sample (5) maximal bending moment position outside surface everywhere; Then the cavity elbow is filled with oil, until fill, connecting hose one end that to fill again oil is connected with elbow sample (5), and the flexible pipe other end is connected with oil press (11) by quick connector, controls the elbow internal pressure by sensor and the microcomputer that software is housed by changing the oil press liquid level again; Foil gauge lead-in wire and each foil gauge lead-in wire of temperature compensation material place carry out exact connect ion by each joint on wire and the front terminal block according to corresponding relation everywhere with elbow; Again the elbow sample is threaded with upper loading blocks (4) and lower loading blocks (7) in the anchor clamps auxiliary body respectively, and between them, adds the aluminium pad, make between loading blocks and the elbow sample displacement transmit continuous; Then upper loading blocks (4) and lower loading blocks (7) are passed through respectively the hinged of the realization of the first bearing pin (3) and the second bearing pin (8) and upper load bar (2) and lower load bar (9); Recycling fatigue tester upper chuck (1) and lower dop (10) have been fixed described upper load bar (2) and the lower load bar (9) of the anchor clamps auxiliary body of loading effect; Then utilize microcomputer and test control software, by inputting different operating loading, utilize the interior pressure of sensor control elbow and testing machine to load moment of flexure and carry out the test of multiaxis ratchet, adopt at last hyperchannel dynamic strain indicator (6) Real-time Collection elbow sample strain evolution everywhere situation, and data-switching is stored in the main control computer (23).
2. the method for claim 1, it is characterized in that foil gauge is two-way right angle foil gauge, the position that is affixed on elbow is cross section, elbow centre position, two-way right angle foil gauge is affixed on 10 positions, wherein, elbow inner edge side i.e. 0 degree position is position 1, outer edge side i.e. 180 degree positions is position 9, it is that 90 degree positions and position 10 are-90 degree positions that centre position between inner edge and the outer rim is defined as position 7, in order effectively to compare the ratchet strain evolution situation of these several specific positions like this, spend between the positions to 90 at 0 degree, respectively paste a slice foil gauge every 15 degree, correspondence position 2 to position 6,90 degree paste a slice foil gauge between 180 degree positions respectively, and namely position 8 is 135 degree positions.
3. the method for claim 1, it is characterized in that described hyperchannel dynamic strain indicator comprises amplifier circuit (25), front terminal block (20) and input adapter (21), rear out splice going splice (24), power supply (22), pci data collector and main control computer (23); The foil gauge ultra-weak electronic signal is changed by front terminal block (20) and input adapter (21) importing, and through amplifying circuit (25) faint change in electric is amplified, then by rear out splice going splice (24), the electric signal that amplifies after processing is reached pci data collector (23), this electric signal is changed into the digital signal demonstration and is stored in main control computer (23).
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| CN108844701A (en) * | 2018-06-05 | 2018-11-20 | 陕西科技大学 | Space bending test platform based on oil pipeline |
| CN108760473B (en) * | 2018-07-28 | 2020-11-06 | 中国石油天然气集团有限公司 | Method and test device for testing tensile property of flexible composite pipe |
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| CN201141828Y (en) * | 2007-12-15 | 2008-10-29 | 中国石油化工股份有限公司胜利油田分公司采油工艺研究院 | Simulation experiment device for bending deformation of highly deviated well column |
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