CN109668782A - A method of measurement concrete initial fracture toughness - Google Patents
A method of measurement concrete initial fracture toughness Download PDFInfo
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- CN109668782A CN109668782A CN201811472383.7A CN201811472383A CN109668782A CN 109668782 A CN109668782 A CN 109668782A CN 201811472383 A CN201811472383 A CN 201811472383A CN 109668782 A CN109668782 A CN 109668782A
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- 238000000034 method Methods 0.000 title claims abstract description 29
- 238000005259 measurement Methods 0.000 title description 6
- 238000012360 testing method Methods 0.000 claims abstract description 48
- 230000000977 initiatory effect Effects 0.000 claims abstract description 14
- 238000005336 cracking Methods 0.000 claims abstract description 12
- 239000000945 filler Substances 0.000 claims abstract description 10
- 238000004364 calculation method Methods 0.000 claims abstract description 7
- 239000010687 lubricating oil Substances 0.000 claims abstract description 6
- 239000011248 coating agent Substances 0.000 claims abstract description 4
- 238000000576 coating method Methods 0.000 claims abstract description 4
- 238000004088 simulation Methods 0.000 claims description 5
- 230000008901 benefit Effects 0.000 abstract description 5
- 238000005070 sampling Methods 0.000 abstract description 2
- 238000005520 cutting process Methods 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 238000013001 point bending Methods 0.000 description 4
- 238000010998 test method Methods 0.000 description 4
- 238000006073 displacement reaction Methods 0.000 description 3
- 238000012544 monitoring process Methods 0.000 description 3
- 229910000831 Steel Inorganic materials 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 230000015271 coagulation Effects 0.000 description 2
- 238000005345 coagulation Methods 0.000 description 2
- 238000013480 data collection Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 239000011888 foil Substances 0.000 description 2
- 238000013467 fragmentation Methods 0.000 description 2
- 238000006062 fragmentation reaction Methods 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 239000010959 steel Substances 0.000 description 2
- 241000208340 Araliaceae Species 0.000 description 1
- 235000005035 Panax pseudoginseng ssp. pseudoginseng Nutrition 0.000 description 1
- 235000003140 Panax quinquefolius Nutrition 0.000 description 1
- 238000004026 adhesive bonding Methods 0.000 description 1
- 239000002390 adhesive tape Substances 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000013213 extrapolation Methods 0.000 description 1
- 235000008434 ginseng Nutrition 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000010008 shearing Methods 0.000 description 1
- 239000002689 soil Substances 0.000 description 1
- 238000007655 standard test method Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
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- Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
Abstract
The invention belongs to concrete fracture performance study technical fields in building and hydraulic engineering, provide a kind of method for measuring concrete initial fracture toughness.The test specimen is concrete cube test specimen.Experimental rig is divided into two parts, and first part is antifriction apparatus, includes bottom plate and two layers of antifriction piece.By the smooth contact that antifriction piece and coating lubricating oil realization test specimen and bottom plate are arranged among test specimen and bottom plate.Second part is loading device, includes wooden filler strip, arc loading head, load transducer.Test specimen crack tip strain value is monitored using resistance strain gage, initial cracking load is determined according to the hysteresis of strain value in loading procedure.Initial cracking load is brought into cube initiation angle calculation formula and obtains the initiation angle of concrete.The cube specimen that this method proposes has many advantages, such as in form convenient for making, self weight is smaller, can core boring sampling.
Description
Technical field
The invention belongs to concrete fracture performance study technical fields in building and hydraulic engineering, are related to one kind and are cut by bottom
The method that the cube specimen of seam determines concrete initial fracture toughness.
Background technique
The formation in crack is divided into three phases in concrete structure, be respectively the crack initiation in crack, crack stablize extension and
The unstable propagation in crack.The concept of initiation angle and toughness is proposed using stress intensity factor as the double-K fracture model of parameter,
Initiation angle and toughness are the critical points for distinguishing crack extended mode.In recent years, splitting using initial fracture toughness as standard
Seam growth criterion is widely used, which thinks that crack tip stress intensity factor is greater than material initial fracture toughness
When crack start extension and the extension each time in crack be considered as primary new crack initiation.The initial fracture toughness of material can be considered point
Therefore how the foundation of analysis crack propagation process determines that the initial fracture toughness of material has obtained the extensive of domestic and foreign scholars
Concern.
Currently, common Fracture Mechanics of Concrete test method includes three-point bending beam method and edge splitting method, both at home and abroad
The research achievement of a large amount of scholars has been proven that both methods can measure the initial fracture toughness of concrete.China is 2005
Three-point bending beam method and edge splitting method are included in concrete for hydraulic structure fracture mechanics standard test method by year.Three-point bending beam method can
Relatively easily to determine stable trial curve and then determine fragmentation parameters.But due to the limitation of span-depth radio, big aggregate examination
The volume of part is often larger, this not only to test specimen pour and handling work is made troubles benefit, but also be self-possessed to measurement fracture ginseng
Several influences is also larger.Compared with three-point bending beam method, mainly examination is eliminated or reduced to this method the advantages of edge splitting method
Influence of the part self weight to fragmentation parameters measurement result.But experimental rig is complex, to testing crew operating technology require compared with
It is high.In addition, make different height size wedge-splitting specimen when, if load slot not with the increase of sample dimensions and
Proportional increase, then due to fixture is transmitted to vertical force component on test specimen and test specimen self weight and end reaction collinearly will be
Crack tip generates additional bending moment, generates certain influence to the authenticity of measured fracture toughness.
Summary of the invention
Based on the research achievement in the above concrete fracture field analyzed, and combine applicant long-term, a kind of use is proposed
The method that the cube specimen of bottom edge joint-cutting accurately and easily determines concrete material initial fracture toughness.What this method proposed
Cube specimen has many advantages, such as in form convenient for making, self weight is smaller, can core boring sampling.There is operation in test method
Simplicity is convenient for the advantages that promoting.In addition, applicant obtains determining coagulation by cube specimen based on experimental study and theory analysis
The calculation formula of native initial fracture toughness.
Technical solution of the present invention:
A method of measurement concrete initial fracture toughness passes through a kind of simple test specimen and easy to operate of making
Loading device obtains the initial cracking load of concrete sample, determines concrete in conjunction with the formula being fitted by numerical simulation result
Initial fracture toughness, the specific steps are as follows:
The new test method of the initial fracture toughness of concrete is determined using a kind of cube specimen of bottom joint-cutting, including
Test specimen and experimental rig two parts；
Test specimen is the concrete cube test specimen that bottom middle position is provided with through crack；
Experimental rig is divided into two parts, and first part is antifriction apparatus, includes bottom plate and two layers of antifriction piece；By trying
Two layers of antifriction piece is set among part and bottom plate, and coating lubricating oil realizes that test specimen and the smooth of bottom plate connect between two layers of antifriction piece
Touching；Second part is loading device, includes wooden filler strip, arc loading head and load transducer；Wooden filler strip is three layers of gluing
Plate is made, and length is not less than piece lengths；Arc loading head is to be made of arc cushion block with bloom, table on bloom and arc cushion block
Face is of same size, and arc loading head length is identical as test specimen；
The initial cracking load measured is brought into cube specimen initiation angle calculation formula and obtains the initiation angle of concrete；
Calculation formula are as follows:
Wherein, P is external loads；B is cube specimen side length；A is fracture length；K is stress intensity factor.
Beneficial effects of the present invention: cube concrete sample production of the invention is simple, and test operation is convenient, according to giving
Calculation formula out can directly obtain the initial fracture toughness of concrete.
Detailed description of the invention
Fig. 1 is test specimen and device combination diagram.
In figure: 1 bottom plate；2 first antifriction pieces；3 lubricating oil；4 second antifriction pieces；5 cube specimens；6 wooden filler strips；7 arcs
Shape loading head；8 load transducers.
Specific embodiment
Below in conjunction with attached drawing and technical solution, a specific embodiment of the invention is further illustrated.
A method of measurement concrete initial fracture toughness provides a kind of simple sample type of production and operation side
Just loading device is determined with obtaining the initial cracking load of concrete sample in conjunction with the formula being fitted by numerical simulation result
The initial fracture toughness of concrete, the specific steps are as follows:
The new test method that the initial fracture toughness of concrete is determined using a kind of cube specimen of bottom joint-cutting, is related to
Test specimen and experimental rig two parts；Test specimen is concrete cube test specimen, side length 150mm, and in test specimen bottom middle position
The through crack that length is 45mm, width is 2mm is set；Experimental rig is divided into two parts, and first part is antifriction apparatus, includes
Bottom plate and two layers of PVC antifriction piece, base-plate is having a size of long 400mm, wide 400mm, thick 40mm.By in test specimen and bottom plate
Between setting PVC antifriction piece and coating lubricating oil realize test specimen and bottom plate smooth contact.Lower layer PVC antifriction piece (antifriction piece 1) ruler
Very little is long 300mm, wide 200mm, thick 0.4mm, and upper layer PVC antifriction piece (antifriction piece 2) is thick having a size of long 200mm, wide 150mm
0.4mm.Second part is loading device, includes wooden filler strip, arc loading head, 30t load transducer.Wooden filler strip is three layers
Glued board is made, width 20mm, and with a thickness of 3~4mm, length is not less than piece lengths.Arc loading head use radius for
The steel arc cushion block and bloom of 75mm forms, and the high 20mm of steel arc cushion block, bloom is identical as cushion block upper surface width, horizontal
Section is as shown in Figure 1, arc loading head length is identical as test specimen.
(1) test specimen makes
Cube concrete sample is made using standard cube die trial, release agent is coated in die inside, pours coagulation
Soil, vibration compacting are sent into standard curing room in 10 minutes after pouring, and temperature is 20 DEG C, relative humidity 95%.After 24 hours
Demoulding is sent into standard curing room and is conserved to taking out after 28 days after demoulding.
Test specimen is stood for 24 hours after taking out in laboratory environment, cuts out 2mm in test specimen bottom middle position using cutting machine
Width, the through crack of 45mm high, schematic diagram are as shown in Figure 1.
(2) experimental rig
It is loaded using 300t electro-hydraulic servo testing machine.Antifriction piece 1 is laid in test machine bottom board center and with transparent
Adhesive tape is fixed along surrounding, and lubricating oil is uniformly applied to the upper surface of antifriction piece 1.By antifriction piece 2 along test machine bottom board middle line pair
Title is laid in the upper surface of antifriction piece 1 and away from each 1mm of middle line, and the bubble between antifriction piece up and down is discharged.Concrete sample is put
Being placed on antifriction piece 2 keeps test specimen or so fracture surface concordant respectively at the edge of antifriction piece 2.Above concrete sample from bottom to top according to
Secondary is wooden filler strip, arc loading head, 30t load transducer.
(3) load and monitoring scheme
(3.1) loading scheme
It connects loading device (load transducer, arc loading head), Adjustment Tests machine keeps arc loading head and filler strip uniform
Contact, prevents bias-load.Using displacement loading mode, broken with the test specimen that is loaded onto of the speed continuous uniform of 0.024mm/min
It is bad.To prevent testing machine to be damaged, stop loading if vertical shearing displacement reaches 5mm.
(3.2) monitoring scheme
Test specimen crack tip strain value is monitored using resistance strain gage, is determined according to the hysteresis of strain value in loading procedure
Split load.Before load, 1 foil gauge, ruler for drawing grids are each side pasted at the position 5mm in the crack tip of test specimen front and rear surfaces
Very little is 10mm × 2mm, foil gauge is connected to data collection system, the strain in real-time monitoring loading procedure.Biography is connected simultaneously
Sensor and data collection system record loading complete process load and strain data in real time.
(4) data processing
(4.1) determination of initial cracking load
After the test, load-strain curve is drawn according to test data, straining corresponding load at hysteresis point is
Load is split, the initial cracking load as the test specimen is averaged by the initial cracking load that 4 groups of data obtain.
(4.2) calculating of initiation angle
According to numerical simulation as a result, determining cube initiation angle calculation formula using the method for data fitting.It adopts
With the displacement extrapolation techniques provided in ANSYS software come calculating stress strength factor, for simulation fracture tip each point stressSingularity moves to the node in each side of the isoparametric elements around crack tip at 1/4 branch by splitting tip.Pass through
Adjust test specimen the high when sample dimensions of different seams (seam is high than being 0.05~0.95, interval 0.01, test specimen side length be 50mm~
2000mm is spaced 50mm), fitting obtains the stress intensity factor expression formula suitable for cube specimen:
P external loads (kN)；B cube side length (mm)；A fracture length (mm)；K stress intensity factor (MPamm1/2)；
Formula is brought into when P is initial cracking load obtains initiation angle Kini。
(5) result
Obtain the load-strain curve of loading complete process；Determine concrete initial cracking load；Obtain accurate concrete crack initiation
Toughness.
Claims (1)
1. a kind of method for measuring concrete initial fracture toughness, by it is a kind of make simple test specimen and it is easy to operate plus
It carries and sets, obtain the initial cracking load of concrete sample, determine concrete in conjunction with the formula being fitted by numerical simulation result
Initial fracture toughness, which is characterized in that specific step is as follows:
This method includes test specimen and experimental rig two parts；
Test specimen is the concrete cube test specimen that bottom middle position is provided with through crack；
Experimental rig is divided into two parts, and first part is antifriction apparatus, includes bottom plate and two layers of antifriction piece；By in test specimen and
Two layers of antifriction piece is set among bottom plate, and coating lubricating oil realizes the smooth contact of test specimen and bottom plate between two layers of antifriction piece；
Second part is loading device, includes wooden filler strip, arc loading head and load transducer；Wooden filler strip is three layers of glued board system
At length is not less than piece lengths；Arc loading head is to be made of arc cushion block with bloom, and bloom and arc cushion block upper surface are wide
Spend identical, arc loading head length is identical as test specimen；
The initial cracking load measured is brought into cube specimen initiation angle calculation formula and obtains the initiation angle of concrete；It calculates
Formula are as follows:
Wherein, P is external loads；B is cube specimen side length；A is fracture length；K is stress intensity factor.
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| Application Number | Priority Date | Filing Date | Title |
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| CN201811472383.7A CN109668782B (en) | 2018-12-04 | 2018-12-04 | Method for measuring fracture initiation fracture toughness of concrete |
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| CN201811472383.7A CN109668782B (en) | 2018-12-04 | 2018-12-04 | Method for measuring fracture initiation fracture toughness of concrete |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110487578A (en) * | 2019-08-28 | 2019-11-22 | 湘潭大学 | Girder construction damnification recognition method based on end reaction and strain |
| CN110501126A (en) * | 2019-08-28 | 2019-11-26 | 湘潭大学 | Girder construction damnification recognition method based on end reaction and amount of deflection curvature |
| CN111610099A (en) * | 2020-07-08 | 2020-09-01 | 郑州大学 | Rubber concrete fracture performance analysis method based on temperature and humidity changes |
| CN113325164A (en) * | 2021-06-04 | 2021-08-31 | 大连理工大学 | Method for analyzing three-dimensional expansion process of concrete I-shaped crack |
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110487578A (en) * | 2019-08-28 | 2019-11-22 | 湘潭大学 | Girder construction damnification recognition method based on end reaction and strain |
| CN110501126A (en) * | 2019-08-28 | 2019-11-26 | 湘潭大学 | Girder construction damnification recognition method based on end reaction and amount of deflection curvature |
| CN111610099A (en) * | 2020-07-08 | 2020-09-01 | 郑州大学 | Rubber concrete fracture performance analysis method based on temperature and humidity changes |
| CN111610099B (en) * | 2020-07-08 | 2022-08-02 | 郑州大学 | Rubber concrete fracture performance analysis method based on temperature and humidity changes |
| CN113325164A (en) * | 2021-06-04 | 2021-08-31 | 大连理工大学 | Method for analyzing three-dimensional expansion process of concrete I-shaped crack |
| CN113325164B (en) * | 2021-06-04 | 2022-08-09 | 大连理工大学 | Method for analyzing three-dimensional expansion process of concrete I-shaped crack |
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