CN109781548A - The method of asymmetric three-point bending load test rock combined rupture toughness based on NDB sample - Google Patents
The method of asymmetric three-point bending load test rock combined rupture toughness based on NDB sample Download PDFInfo
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Abstract
The method of asymmetric three-point bending load test rock combined rupture toughness of the present invention offer based on NDB sample, test specimen ontology used is the rectangle deep beam (NDB) with grooving, shape is cuboid, the grooving that height is a is prefabricated at ontology intermediate cross-section, extend to body thickness direction, and runs through body thickness direction front/rear end；Test specimen body length L is 2 times of test specimen body width W, and thickness B is not less than 0.8W.Based on this NDB sample, the present invention provides a kind of methods for being loaded using asymmetric three-point bending and carrying out the pure I type of rock, pure II type and the test of I-II combined rupture toughness, and the application of tensioning and shear load is realized by asymmetrical loading.NDB sample structure used in the present invention is simple, is easy to process using sillar；Load clamp is common three-point bending fixture, it is only necessary to which support asymmetric arrangement, experiment load is extremely convenient, and is able to achieve the I-II combined rupture toughness test of pure I type, pure II type and entire Combined Loading section.
Description
Technical field
The invention belongs to rock fracture toughness testing field, in particular to a kind of rock combined rupture toughness test method.
Technical background
Rock fracture mechanics are that an important subdiscipline, rock fracture toughness characterize rock in rock mechanics subject
Material resists the ability of crackle crack initiation and extension, is to solve rock engineering the very corn of a subject parameter using fracture mechanics, reasonably
Determine that rock fracture toughness is one of main research work of current rock fracture mechanics.
International Society of Rock Mechanics (ISRM) successively suggested 4 kinds of test specimens and corresponding test method to carry out rock I
Type Statical pattern toughness test, comprising: the short pole of chevron notch (SR) sample (1977), herringbone under compact tension specimen load
Chevron notch Brazilian disc (CCNBD) sample of shape grooving three-point bend round bar (CB) sample (1988), radial loaded
Vertical cut slot semi-disc bending (SCB) sample (2014), this 4 kinds of test specimens are penetrated under the load of (nineteen ninety-five) and symmetrical three-point bending
It is to be further processed to obtain on the basis of the core drilled through.SR test specimen initial crack length at a distance from critical crack length compared with
Long, critical load when causing by non-liner revision is close to maximum load.In contrast, CB test specimen initial crack length with face
The distance of boundary's crack length is shorter, and the critical load of non-liner revision is relatively low.And crack propagation is in folding after SR test specimen loaded load
Line is advanced, hence it is evident that deviates middle line.In addition, SR and CB sample also produces the problems such as difficult, experimental facilities and loading system are complicated.
CCNBD test specimen configuration is complicated, is not easy to produce, not can be carried out simplified two dimensional analysis so that test specimen minimum dimensionless stress intensity because
Sub- YminIt must can be demarcated by Three-dimensional numerical calculation.For SCB sample, if from two examinations of a complete disk cutting production
Part can lose some materials as two non-standard semi-discs, the amendment of test result Need Hierarchy Theory；If being processed into standard SCB
Sample, then a disk can only process a test specimen, waste rock material.In addition, American Society Testing and Materials (ASTM)
Unilateral grooving beam (SENB) three point bending test (2001) is provided, it is more that (1986) etc. are tested in disk compact tension specimen (DCT)
Kind configuration test specimen and test method carry out fracture toughness of materials test.
The test method that above-mentioned ISRM and ASTM suggests is chiefly used in I type fracture toughness testing, however in practical rock engineering
In, rock fracture subjects a variety of loadings such as I type, II type and the compound load of I/II.For Accurate Prediction rock fracture
Extension, it is necessary to accurate measurement rock combined rupture toughness.SENB test specimen is loaded by asymmetric three-point bending load/four-point bending
The test of I/II combined rupture can be realized, but its length is very big, causes breaking load small, therefore traditional SENB test specimen is more suitable for
Metal group material carries out fracture toughness testing, is not optimal selection for the fragile materials such as rock and concrete.CB sample with
There are similar problems for SENB sample.Although CCNBD and SCB test specimen can be realized by adjusting the methods of fracture dip and fracture length
From pure I type to the entire Combined Loading section of pure II type I/II combined rupture toughness test, but as previously mentioned, test specimen (especially
It is large scale test specimen) processing difficulties.Center-cracked Brazilian disc (CSTBD) sample and center vertical crack platform Brazilian disc
(CSTFBD) sample configuration is simple, realizes that pure I type, pure II type and the compound fracture toughness testing of I/II only need to pass through change
The angle of loading direction and centre burst.However, existing research is pointed out, disc-like sample is carrying out large dimension specimen fracture toughness
Processing difficulties when test.The unilateral grooving deep beam test specimen (NDB) that Chinese patent ZL201510397736.1 is proposed is split using inclination
Line and asymmetrical load are realized to be loaded using simple test specimen configuration, the test of convenient I/II combined rupture toughness, but compound disconnected
Dipping fracture is needed when splitting toughness and II type fracture toughness testing, high inclination-angle crackle is prefabricated, and there are difficulty.And the subtle mistake at inclination angle
Difference, bring test result error are very big.Therefore this method is higher to experimental implementation and test specimen requirement on machining accuracy, and tests
Result precision is difficult to control and ensures.
As previously mentioned, the samples difficulty such as processing large scale SR, CB, CCNBD and SCB is extremely prominent；In comparison, as
This kind of non-circular test specimen for being configured only need cutting action that can process required size from sillar of SENB, NDB, it is more operational.But
It is that, in order to realize Combined Loading, the sample of the configurations such as traditional SENB, NDB needs to split using complicated load or prefabricated inclination
Seam, this requires sample level of processing and loading device all higher.Therefore, research is configured simple, easy processing and load is easy
New Rock combined rupture toughness measuring technology has important more practical value.
Summary of the invention
It is an object of the invention to be directed to the deficiency of existing rock combined rupture toughness measuring technology, propose that one kind is based on
The method of the asymmetric three-point bending load test rock combined rupture toughness of NDB sample, utilizes non-inclined (vertical) crack NDB
Sample realizes the fracture toughness testing of pure I type, pure II type and the compound section load of entire I/II, and it is prefabricated to avoid Incline Crack
The problem that precision prescribed is high and the prefabricated difficulty of high inclination-angle crackle is big, test accuracy is easily controllable and ensures.
The method of the invention, using NDB sample, the NDB sample ontology is cuboid, is provided in ontology by ontology
The midline position of lower end surface is open and the vertical grooving parallel with the direction thickness B, the front and back end in the direction grooving impenetrating thickness B
Face, test specimen body length L are 2 times of test specimen body width W, and specimen thickness B is not less than 0.8W, and the depth of grooving is a, and 0.3W
≤a≤0.7W；
The present invention loads the pure I type of rock that carries out, pure II type and the survey of I-II combined rupture toughness using asymmetric three-point bending
Examination, three-point bending left support abutment and grooving center interplanar distance are S1, right support abutment and grooving center interplanar distance are S2, and S2≤S1；?
Grooving length a is selected in the range of 0.3≤a/W≤0.7, and in 0.4≤S1Left support abutment and centreline space are determined in the range of/W≤0.9
Away from S1, adjust right support abutment and centreline space away from specimen width ratio S2/ W value is from S1/ W starts to gradually reduce, until obtaining pure II
The corresponding S of type2Until, different loads multiplicity is obtained with this；It is marked comprehensively using finite element numerical program-ABAQUS/ANSYS etc.
Determine the infinitude no dimension method Y at the specimen crack tip under asymmetrical loadingI、YIIWith the nonsingular stress of nondimensionalization
T*, and obtain pure II type and load corresponding S2, then pass through three-point bending fixture graduated scale adjusting right support abutment interval S2, adjusted
The front end spacing and rear end spacing of two supports are not much different in 1%, and with should all be used between identical left support abutment in group experiment
Away from S1。
Further, before rock fracture toughness test of the present invention, finite element numerical program-ABAQUS/ANSYS is utilized
Deng comprehensive infinitude no dimension method Y for demarcating the specimen crack tip under asymmetrical loadingI、YIIWith the non-surprise of nondimensionalization
Different stress T*, and obtain pure II type and load corresponding S2, the specific steps are as follows:
(1) corresponding numerical value peg model is established.Using finite element numerical software for calculation, the two dimension for establishing test specimen ontology is several
What model, it is assumed that rock material is linear elastic materials and assigns test specimen elastic parameter, and grid division (is set as plane strain later
Unit), and at left support abutment restraint joint (node is the contact point of left support abutment and sample in two-dimensional geometry model) it is vertical and
Horizontal displacement, vertical displacement is constrained at right support abutment, and seaming chuck load(ing) point applies reference mode load p (vertical).It is acted in load P
Under, the test specimen I type and II type stress strength factor KI, KIIIt may be expressed as: with nonsingular T stress
Infinitude no dimension method Y is released according to (1)-(3) formula is counterI、YIIWith the following institute of the nonsingular stress T* of dimensionless
Show:
(2) it is based on step (1) described numerical model, uses " dichotomy " constantly to reduce S in calculating2Value.When calculating
The load multiplicity M arrivedeNear 1, error is no more than 10-4Magnitude, can be approximately considered and reach the fracture of pure II type
The support spacing for realizing pure II type load is obtained, what is be calculated the results are shown in Table 1.Wherein, load multiplicity is given by:
1 difference a/W of table, difference S1S when test specimen described in/W realizes the fracture of pure II type2The size of/W
(3) the right support abutment spacing based on (1) described numerical model method for building up and (2) described acquisition determines needed for test
Grooving length a and left support abutment interval S1, right support abutment spacing is from S1According to the step pitch of setting gradually reduce to table 1 determine it is critical
S2, infinitude no dimension method Y is calculated one by oneIAnd YIIAnd the nonsingular stress T* of dimensionless.Further, of the present invention
Method is further comprising the steps of:
(4) front end face in test specimen body thickness direction draws the auxiliary line of three vertical directions, wherein an auxiliary line position
In on the center line of test specimen ontology front end face, two other auxiliary line is distributed in two sides, the spacing etc. between adjacent two auxiliary lines
In left and right support and center line interval S1And S2。
(5) by the auxiliary line on ruler and test specimen ontology front end face, test specimen is installed on testing stand, before making test specimen ontology
Three auxiliary lines on end face, intermediate auxiliary line alignment load load pressure head, and the auxiliary line of two sides is directed at seat pivot.
(6) Adjustment Tests machine, which makes it load pressure head and test specimen, gentle touchdown, is finally checked test specimen riding position,
Confirm errorless rear installation LVDT displacement sensor.
(7) using the control load of LVDT displacement sensor, operation rock mechanics experiment machine loads test specimen, until test specimen is broken
It is bad to lose bearing capacity completely.
(8) according to the peak load and I/II type infinitude no dimension method Y in experimentI/YIIAs follows
Calculate rock combined rupture toughness:
Further, the rate that operation rock mechanics experiment machine loads test specimen is preferably lower than 0.2mm/min, to avoid examination
Test it is possible that any dynamic effect.
Further, load load pressure head (3) is that pole structure loads pressure head, and the support (4), (5) are pole
Structural bearings, upper pole pressure head contour are parallel with grooving median plane.
Further, the angle in two faces of test specimen ontology arbitrary neighborhood is 90 ° ± 0.5 °；One direction of test specimen ontology is any
The cross dimensions deviation of two positions is no more than 0.1mm.
Further, the length L of test specimen ontology is preferably not less than 10 times of rock particles size, and is not less than 76mm.
Further, the length L control of test specimen ontology is 2 times of body width W, and error is no more than 0.04W.
Further, thickness B is not less than 0.8 times of body width W, and is not less than 30mm；The notch width b is less than
1mm。
The production method of test specimen of the present invention for the pure I type of rock, pure II type and the test of I-II combined rupture is such as
Under:
(1) sample is cut.It will tentatively be cut, processed from the sillar of engineering site or field acquisition with rock cutter
At test specimen ontology 10mm at least bigger than required size (length).It can be more if thering is blade cutting machine to be used to process rock sample
The distance of two blades is easily adjusted for controlling the thickness cut every time, it is more convenient to process.
(2) polishing sample.The test specimen after preliminary working is polished on one side using grinding machine, then makees benchmark using the face polished
Four faces that face is polished normal thereto, the face parallel with datum level of finally polishing is to required thickness.When being polished using grinding machine, every time
The depth of cut is preferably less than 1mm.The angle in two faces of test specimen ontology arbitrary neighborhood after processing is completed should be controlled at 90 ° ± 0.5 °, this
The cross dimensions deviation of one direction of body any two position is preferably no more than 0.1mm.
(3) prefabricated crack.Sample bottom middle position be recommended to use thickness less than 0.3-0.5mm diamond blade or
Very thin scroll saw is machined directly into required fracture length.The crack that formation length is a is cut, and crack is vertical with lower end surface.It cuts
In slot prefabrication process, each depth of cut is preferably less than a/10.
Compared with prior art, the invention has the following advantages:
1, the method for the invention carries out rock combined rupture toughness using the vertical grooving NDB sample under asymmetrical loading
Test, enrich rock fracture toughness measuring technology system.
2, NDB test specimen structure used in the present invention is simple, is easy to carry out cutting processing using sillar, avoid limited in size
Drill core on sillar, it is easy to process, it is low to raw material shape requirement, and without complicated load or prefabricated dipping fracture
Achieve that Combined Loading, it is of less demanding to sample level of processing and loading device.Therefore, the method for the present invention is a kind of test specimen structure
Shape is simple, easy processing makes and loads easy New Rock combined rupture toughness measuring technology.
3, compared to the scheme of ZL 201510397736.1, test specimen of the present invention and test method are only cut test specimen is vertical
In the case of slot, by adjusting the interval S of left and right support and centreline space1、S2With fracture length a, pure I type, pure II type can be realized
And the I/II combined rupture toughness test in entire combined rupture section.The vertical grooving of component greatly simplifies test specimen processing
Difficulty can be completed test specimen using common cutting machine and process, avoids the difficulty of processing of cutting dipping fracture, especially overcome
When slanted angle β, especially β > 60 ° the shortcomings that test specimen processing difficulties, while solving to bring survey because of the inclined mismachining tolerance of test specimen β
The big problem of test result error, and loading method is simple, it is easy to accomplish.
5, the scheme compared to ZL 201510397736.1 and traditional SENB test specimen, test specimen of the present invention and test side
Method, smaller using support spacing, so that crack tip stress concentration degree is smaller, breaking load is bigger, test result reliability
It is higher.
6, compared with traditional SENB sample, the present invention can avoid two big defects of SENB test specimen, i.e., asymmetric 3 points curved
Song load needs to pass through mobile crack position and realizes the test of I/II combined rupture, cannot achieve pure II type load；Four-point bending is real
Test the program relative difficulty for realizing pure II type load.
7, piece lengths L and width W ratio used in the present invention are 2.0 ± 0.04, and the thickness of test specimen meets B >=0.8W,
Experimental condition does not set the upper limit in the case where allowing, and the upper limit of tradition SENB specimen thickness B and piece lengths L ratio is 2/9.Cause
This, test specimen of the present invention wants short and thick compared to traditional SENB test specimen, and more composite rock fracture toughness testing requires
Plane strain condition.
8, it is also convenient to cooperation sound emission during the three point bending test of test specimen of the present invention and non-contact answers
Become tracking and the measurement of crack forward position rock deformation that test macro DIC carries out fracture propagation process.
9, it is of the present invention can also be used in other brittleness and quasi-brittle material (such as: concrete, PMMA, ceramics and glass
Deng) Plane Strain Fracture Toughness test.
Detailed description of the invention
Fig. 1 is the test specimen structural schematic diagram of the present invention for rock fracture toughness test；
Fig. 2 is the main view of the test specimen of the present invention for rock fracture toughness test；
Fig. 3 is the side view of the test specimen of the present invention for rock fracture toughness test；
Fig. 4 is the top view of the test specimen of the present invention for rock fracture toughness test；
Fig. 5 is the test specimen of the present invention for rock fracture toughness test on the testing stand of rock mechanics experiment machine
Scheme of installation and loading figure.
Fig. 6 is that the test specimen of the present invention for rock fracture toughness test is in fracture length a and specimen width W ratio
I type infinitude no dimension method Y when 0.3INumerical result；
Fig. 7 is that the test specimen of the present invention for rock fracture toughness test is in fracture length a and specimen width W ratio
II type infinitude no dimension method Y when 0.3IINumerical result；
Fig. 8 is that the test specimen of the present invention for rock fracture toughness test is in fracture length a and specimen width W ratio
T* numerical result when 0.3；
Fig. 9 is that the test specimen of the present invention for rock fracture toughness test is in fracture length a and specimen width W ratio
I type infinitude no dimension method Y when 0.5INumerical result；
Figure 10 is the test specimen of the present invention for rock fracture toughness test in fracture length a and specimen width W ratio
II type infinitude no dimension method Y when being 0.5IINumerical result；
Figure 11 is the test specimen of the present invention for rock fracture toughness test in fracture length a and specimen width W ratio
T* numerical result when being 0.5；
Figure 12 is the test specimen of the present invention for rock fracture toughness test in fracture length a and specimen width W ratio
I type infinitude no dimension method Y when being 0.7INumerical result；
Figure 13 is the test specimen of the present invention for rock fracture toughness test in fracture length a and specimen width W ratio
II type infinitude no dimension method Y when being 0.7IINumerical result；
Figure 14 is the test specimen of the present invention for rock fracture toughness test in fracture length a and specimen width W ratio
T* numerical result when being 0.7.
Specific implementation method
The test specimen of the present invention for rock fracture toughness test and rock fracture toughness are surveyed below by embodiment
Method for testing is described further.
In following each embodiments, it is that microcomputer universal testing machine (uses that rock fracture toughness, which tests testing equipment used,
815 rock mechanics experiment machine of MTS can also), the three-point bending fixture for using equipment included；To in addition to load in test procedure
The parameters such as displacement be zeroed out operation after start to test, time t, load p, machine are mainly acquired during test and is displaced
It is displaced with LVDT.Totally 4 groups of load test, every group four times, experimental data is averaged.
In following each embodiments, using the long L=200mm of test specimen, width W=100mm, thickness B=80mm, crack length a=
50mm, left support abutment and center line interval S1=60mm, crackle surface load p=10kN.Based on ABAQUS numerical simulation, according to
Formula demarcates infinitude no dimension method, as a result as follows:
Table 2 a/W=0.5, S1/ W=0.6 numerical value calibration result
Embodiment 1
Deep beam test specimen described in the present embodiment for rock fracture toughness test, is shown in Fig. 1~4, test material is sandstone, institute
Stating test specimen ontology 1 is cuboid, is provided on ontology along ontology lower end face thickness B direction center line mouth, prolongs to body interior
It stretches, and runs through the grooving 2 of body thickness direction front/rear end, piece lengths L is 200mm, and width W is 100mm, and thickness B is
80mm；Grooving length a is 50mm (a/W ratio is 0.5), and fracture dip β is 90 °.Rock fracture test is carried out with above-mentioned test specimen
It operates as follows:
1) left support abutment and center line interval S are adjusted according to three-point bending fixture graduated scale1With right support abutment and centreline space away from
S2, so that S1For 60mm, S2For 6.5mm, the front end spacing and rear end spacing of two supports adjusted are not much different in 1%；
2) auxiliary line that three vertical directions are drawn in test specimen front end face a, wherein auxiliary line is located in test specimen front end face
On heart line, two other auxiliary line is distributed in two sides, the spacing of two auxiliary lines in left and right and center line be respectively 60mm and
6.5mm；
3) by the ruler that width is 12mm that test specimen is flat-pushing to ideal position after auxiliary line is finished, and pass through auxiliary line
The center of two support poles (4) of calibration clamp, (5) and loading end pole (3), avoids test specimen skew from causing excessive test
Error places test specimen；
4) adjustment that testing machine carries out micro-displacement is manually controlled, first relatively rapid top is reinforced by remote controler and is filled
It sets adjusting to be moved to above test specimen and then turn down speed, so that upper end pressure head and test specimen have gentle touchdown；LVDT is displaced and is passed
Sensor moves on to required position and installs；
5) using the control load of LVDT displacement sensor, loading speed 0.05mm/min operates rock mechanics experiment machine and opens
Begin to test, collected peak load PcrFor 17.0kN.
I type infinitude no dimension method Y is obtained by table 2I=0.00217, II type infinitude no dimension method YII=-
0.487025, it is known that angle β is 90 °, S1For 60mm, S2To be pure II type fracture when 6.5mm, therefore, according to what is recorded in test
Peak load PcrAnd YIIThe sandstone II type fracture toughness being calculated are as follows:
Embodiment 2
Deep beam test specimen described in the present embodiment for rock fracture toughness test, is shown in Fig. 1~4, test material is sandstone, institute
Stating test specimen ontology 1 is cuboid, is provided on ontology along ontology lower end face thickness B direction center line mouth, prolongs to body interior
It stretches, and runs through the grooving 2 of body thickness direction front/rear end, piece lengths L is 200mm, and width W is 100mm, and thickness B is
80mm；Grooving length a is 50mm (a/W ratio is 0.5), and fracture dip β is 90 °.Rock fracture test is carried out with above-mentioned test specimen
It operates as follows:
1) left support abutment and center line interval S are adjusted according to three-point bending fixture graduated scale1With right support abutment and centreline space away from
S2, so that S1For 60mm, S2For 20mm, the front end spacing and rear end spacing of two supports adjusted are not much different in 1%；
2) auxiliary line that three vertical directions are drawn in test specimen front end face a, wherein auxiliary line is located in test specimen front end face
On heart line, two other auxiliary line is distributed in two sides, and the spacing for controlling two auxiliary lines and center line is respectively 60mm and 20mm；
3) by the ruler that width is 12mm that test specimen is flat-pushing to ideal position after auxiliary line is finished, and pass through auxiliary line
The center of two support poles (4) of calibration clamp, (5) and loading end pole (3), avoids test specimen skew from causing excessive test
Error places test specimen；
4) adjustment that testing machine carries out micro-displacement is manually controlled, first relatively rapid top is reinforced by remote controler and is filled
It sets adjusting to be moved to above test specimen and then turn down speed, so that upper end pressure head and test specimen have gentle touchdown；LVDT is displaced and is passed
Sensor moves on to required position and installs；
5) using the control load of LVDT displacement sensor, loading speed 0.05mm/min operates rock mechanics experiment machine and opens
Begin to test, collected peak load PcrFor 23.5kN.
I type infinitude no dimension method Y is obtained by table 2I=0.52048, II type infinitude no dimension method YII=-
0.287631, it is known that angle β is 90 °, S1For 60mm, S2For 20mm, Shi Wei I-II Mixed Mode Fracture.Therefore, remember according in test
The peak load P of recordcrAnd YI、YIIThe sandstone I-II Mixed Mode Fracture toughness being calculated are as follows:
Embodiment 3
Deep beam test specimen described in the present embodiment for rock fracture toughness test, is shown in Fig. 1~4, test material is sandstone, institute
Stating test specimen ontology 1 is cuboid, is provided on ontology along ontology lower end face thickness B direction center line mouth, prolongs to body interior
It stretches, and runs through the grooving 2 of body thickness direction front/rear end, piece lengths L is 200mm, and width W is 100mm, and thickness B is
80mm；Grooving length a is 50mm (a/W ratio is 0.5), and fracture dip β is 90 °.Rock fracture test is carried out with above-mentioned test specimen
It operates as follows:
1) left support abutment and center line interval S are adjusted according to three-point bending fixture graduated scale1With right support abutment and centreline space away from
S2, so that S1For 60mm, S2For 40mm, the front end spacing and rear end spacing of two supports adjusted are not much different in 1%；
2) auxiliary line that three vertical directions are drawn in test specimen front end face a, wherein auxiliary line is located in test specimen front end face
On heart line, two other auxiliary line is distributed in two sides, and the spacing of left and right two auxiliary lines to center lines is respectively 60mm and 40mm；
3) by the ruler that width is 12mm that test specimen is flat-pushing to ideal position after auxiliary line is finished, and pass through auxiliary line
The center of two support poles (4) of calibration clamp, (5) and loading end pole (3), avoids test specimen skew from causing excessive test
Error places test specimen；
4) adjustment that testing machine carries out micro-displacement is manually controlled, first relatively rapid top is reinforced by remote controler and is filled
It sets adjusting to be moved to above test specimen and then turn down speed, so that upper end pressure head and test specimen have gentle touchdown；LVDT is displaced and is passed
Sensor moves on to required position and installs；
5) using the control load of LVDT displacement sensor, loading speed 0.05mm/min operates rock mechanics experiment machine and opens
Begin to test, collected peak load PcrFor 14.0kN.
I type infinitude no dimension method Y is obtained by table 2I=1.031894, II type infinitude no dimension method YII=-
0.100698, it is known that angle β is 90 °, S1For 60mm, S2For 40mm, therefore Shi Wei I-II Mixed Mode Fracture is remembered according in test
The peak load P of recordcrAnd YIIThe sandstone I-II Mixed Mode Fracture toughness being calculated are as follows:
Embodiment 4
Deep beam test specimen described in the present embodiment for rock fracture toughness test, is shown in Fig. 1~4, test material is sandstone, institute
Stating test specimen ontology 1 is cuboid, is provided on ontology along ontology lower end face thickness B direction center line mouth, prolongs to body interior
It stretches, and runs through the grooving 2 of body thickness direction front/rear end, piece lengths L is 200mm, and width W is 100mm, and thickness B is
80mm；Grooving length a is 50mm (a/W ratio is 0.5), and fracture dip β is 90 °.Rock fracture test is carried out with above-mentioned test specimen
It operates as follows:
1) left support abutment and center line interval S are adjusted according to three-point bending fixture graduated scale1With right support abutment and centreline space away from
S2, so that S1For 60mm, S2For 60mm, the front end spacing and rear end spacing of two supports adjusted are not much different in 1%；
2) auxiliary line that three vertical directions are drawn in test specimen front end face a, wherein auxiliary line is located in test specimen front end face
On heart line, two other auxiliary line is symmetrically distributed in two sides, and the spacing between adjacent two auxiliary lines is 60mm；
3) by the ruler that width is 12mm that test specimen is flat-pushing to ideal position after auxiliary line is finished, and pass through auxiliary line
The center of two support poles (4) of calibration clamp, (5) and loading end pole (3), avoids test specimen skew from causing excessive test
Error places test specimen；
4) adjustment that testing machine carries out micro-displacement is manually controlled, first relatively rapid top is reinforced by remote controler and is filled
It sets adjusting to be moved to above test specimen and then turn down speed, so that upper end pressure head and test specimen have gentle touchdown；LVDT is displaced and is passed
Sensor moves on to required position and installs；
5) using the control load of LVDT displacement sensor, loading speed 0.05mm/min operates rock mechanics experiment machine and opens
Begin to test, collected peak load PcrFor 10.5kN.
I type infinitude no dimension method Y is obtained by table 2I=1.372582, II type infinitude no dimension method YII=0,
Know that angle β is 90 °, S1For 60mm, S2For 60mm, Shi Weichun I type fracture, therefore, according to the peak load recorded in test
PcrAnd YIThe sandstone I type fracture toughness being calculated are as follows:
Claims (10)
1. the method for the asymmetric three-point bending load test rock combined rupture toughness based on NDB sample, which is characterized in that make
With NDB sample, the NDB sample ontology is cuboid, be provided in ontology by ontology lower end surface midline position opening and with
The parallel vertical grooving in the direction thickness B, the front/rear end in the direction grooving impenetrating thickness B, test specimen body length L are test specimen sheet
2 times of body width W, specimen thickness B are not less than 0.8W, and the depth of grooving is a, and 0.3W≤a≤0.7W；
The pure I type of rock that carries out, pure II type and the test of I-II combined rupture toughness, three-point bending are loaded using asymmetric three-point bending
Left support abutment and grooving center interplanar distance are S1, right support abutment and grooving center interplanar distance are S2, and S2≤S1；In 0.3≤a/W≤0.7
Grooving length a is selected in range, and in 0.4≤S1Left support abutment and center line interval S are determined in the range of/W≤0.91, adjust right branch
Seat and centreline space away from specimen width ratio S2/ W value, from S1/ W starts to gradually reduce, until obtaining the corresponding S of pure II type2For
Only, different loads multiplicity is obtained with this；Wherein, right support abutment interval S is adjusted by three-point bending fixture graduated scale2, after adjustment
Two supports front end spacing and rear end spacing be not much different in 1%, and with group experiment in should all use identical left support abutment
Interval S1。
2. method according to claim 1 comprehensively, which is characterized in that marked using finite element numerical program-ABAQUS/ANSYS etc.
Determine the infinitude no dimension method Y at the specimen crack tip under asymmetrical loadingI、YIIWith the nonsingular stress of nondimensionalization
T*, and obtain pure II type and load corresponding S2, steps are as follows:
(1) it establishes corresponding numerical value peg model: using finite element numerical software for calculation, establishing the two-dimensional geometry mould of test specimen ontology
Type, it is assumed that rock material is linear elastic materials and assigns test specimen elastic parameter, later grid division, and section is constrained at left support abutment
Point is vertical and horizontal displacement, constrains vertical displacement at right support abutment, seaming chuck load(ing) point applies reference mode load p, makees in load P
Under, the test specimen I type and II type stress strength factor KI, KIIIt may be expressed as: with nonsingular T stress
Infinitude no dimension method Y is released according to (1)-(3) formula is counterI、YIIIt is as follows with the nonsingular stress T* of dimensionless:
(2) it is based on step (1) described numerical model, uses " dichotomy " constantly to reduce S in calculating2Value；When the load being calculated
Lotus multiplicity MeNear 1, error is no more than 10-4Magnitude, it is believed that reached the fracture of pure II type, can be obtained and realize pure II type
The support spacing of load, wherein load multiplicity is given by:
(3) the right support abutment interval S based on step (1) described numerical model method for building up and step (2) described acquisition2, determine test
Required grooving length a and left support abutment interval S1, right support abutment spacing is from S1It gradually reduces according to the step pitch of setting to S2, count one by one
Calculate infinitude no dimension method YIAnd YIIAnd the nonsingular stress T* of dimensionless.
3. method according to claim 2, which is characterized in that further comprising the steps of:
(4) front end face in test specimen body thickness direction draws the auxiliary line of three vertical directions, wherein an auxiliary line is located at examination
On the center line of part ontology front end face, two other auxiliary line is distributed in two sides, and the spacing between adjacent two auxiliary lines is equal to a left side
Right support abutment and center line interval S1And S2；
(5) by the auxiliary line on ruler and test specimen ontology front end face, test specimen is installed on testing stand, test specimen ontology front end face is made
On three auxiliary lines, intermediate auxiliary line alignment load loads pressure head, and the auxiliary line of two sides is directed at seat pivot；
(6) Adjustment Tests machine, which makes it load pressure head and test specimen, gentle touchdown, is finally checked test specimen riding position, is confirmed
LVDT displacement sensor is installed after errorless；
(7) using the control load of LVDT displacement sensor, operation rock mechanics experiment machine loads test specimen, until test specimen has destroyed
Bearing capacity is lost entirely；
(8) according to the peak load and I/II type infinitude no dimension method Y in experimentI/YIIIt can calculate as follows
Rock combined rupture toughness:
4. method according to claim 3, which is characterized in that in 0.4W≤S1Become within the scope of≤0.9W and 0.3W≤a≤0.7W
Change left support abutment and center line interval S1With penetration of fracture a, step (1)~(8) in claim 3 are repeated.
5. method according to claim 4, which is characterized in that implement the rate that rock mechanics experiment machine loads test specimen
0.2mm/min should be lower than.
6. method according to claim 4, which is characterized in that load load pressure head (3) is that pole structure loads pressure head,
The support (4), (5) are pole structural bearings, and upper pole pressure head contour is parallel with grooving median plane.
7. any claim the method in -6 according to claim 1, which is characterized in that two faces of test specimen ontology arbitrary neighborhood
Angle be 90 ° ± 0.5 °；The cross dimensions deviation of one direction of test specimen ontology any two position is no more than 0.1mm.
8. any claim the method in -6 according to claim 1, which is characterized in that the length L of test specimen ontology is preferably not
Less than 10 times of rock particles size, and it is not less than 76mm.
9. any claim the method in -6 according to claim 1, which is characterized in that the length L of test specimen ontology is ontology
2 times of width W, error are no more than 0.04W.
10. any claim the method in -6 according to claim 1, which is characterized in that thickness B is not less than body width W
0.8 times, and be not less than 30mm；The notch width b is less than 1mm.
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