CN108225904A - The fixture of rocks in direct tension experiment and the test method based on the fixture - Google Patents
The fixture of rocks in direct tension experiment and the test method based on the fixture Download PDFInfo
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- CN108225904A CN108225904A CN201810322299.0A CN201810322299A CN108225904A CN 108225904 A CN108225904 A CN 108225904A CN 201810322299 A CN201810322299 A CN 201810322299A CN 108225904 A CN108225904 A CN 108225904A
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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
- G01N3/02—Details
- G01N3/04—Chucks
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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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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0014—Type of force applied
- G01N2203/0016—Tensile or compressive
- G01N2203/0017—Tensile
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/04—Chucks, fixtures, jaws, holders or anvils
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Abstract
The fixture of experiment and the test method based on the fixture, belong to rock mechanics testing field.The fixture can be directly used for rock three-axis force testing machine, including seaming chuck and push-down head, hollow sliding groove is provided at the top of push-down head, sliding groove includes two pulleys being arranged in parallel movement side, further include two groups of dumbbell shaped wheel shafts and two stretching chain bars, dumbbell shaped wheel shaft includes two slip wheel shafts being connected by tensile axis, the two slide wheel shaft and are able to slide on two pulley movement sides, the one end of every tensile axis respectively with a stretching chain bar is connected, the other end of two stretching chain bars is connected respectively with the both ends of test specimen, further include the wedge clamp being set between two tensile axis, the top length of wedge clamp is more than bottom length, under the action of seaming chuck, wedge clamp can be gradually reduced, with the decline of wedge clamp, two stretch distance between axles increase, two stretch chain bar and are stretched, with tensile test specimen；Suitable for carrying out the test of rock tensile strength.
Description
Technical field
The invention belongs to rock-soil mechanics testing fields, and rock can be realized on conventional rock mechanics machine by being related to one kind
The fixture of direct tensile test and the test method that rock tensile strength test is carried out based on the fixture.
Background technology
The failure mode of rock can be divided into following three classes mostly：Brittle break, ductile fracture and plane of weakness failure by shear.And rock
Stone occurs to destroy mainly as caused by one or more factors in shearing, pressure, pulling force, therefore the tension of study of rocks is strong
Degree has considerable meaning to the failure mode and failure criteria of study of rocks.
It is relatively difficult to rock progress direct tensile test since the tensile strength of rock is smaller, therefore indoor survey at present
The tensile strength of amount rock is mainly carried out by indirect drawing process.Wherein, most widely used method be split the law (bar
Western split the law) measure rock tensile strength.Split the law is to concentrate pressure by applying to its diametric(al) using cylindrical type test specimen
What power was realized, step is simple, easily operated, it is only necessary to which a rock pressure machine can carry out.However, determined by this method
The tensile strength that tensile strength is measured with direct tensile test is difficult to obtain and stretches resultant stress strain song there are certain error
Line.
It is the device that rocks in direct tension experiment is selected in the prior art as shown in Figure 1, is set respectively both sides about 6 in test specimen
Upper end cap 12 and lower endcaps 13 are equipped with, upper end cap 12, which is connected with, stretches chain 15, and 13 bottom of lower endcaps is connect with backing plate 11, test specimen
Fixing groove 14 is connect with backing plate 11, and 11 lower section of backing plate has rigid sleeve 16 to support, and stretches chain 15 bolt and test specimen fixing groove
14 connections, due to there is certain interval between backing plate 11 and the test specimen fixing groove 14 of lower endcaps 13, rigid sleeve 16 cannot be entire
Effective supporting role is played to the weight of test specimen and lower endcaps during experiment.After test specimen institute tension stress reaches peak value,
Under the action of test specimen, lower endcaps 13 below failure mechanics and gravity suffered by the stretching chain 15 of lower part, test specimen occurs to destroy suddenly,
Leading to the rock tensile strength measured at present, there are further errors, and mechanics effect test is also more tired after carrying out peak stress
Difficulty, being fallen there is also the sample after destruction causes the sensors such as extensometer or its interface etc. to be risk of damage to.Although at present
There are some researchs to be improved, but be not avoided that gravity to being generated during rock tensile failure for rock tensile test specimen and fixture
Influence.On the other hand, axially loaded rate need to be reduced in order to test to obtain ess-strain result behind rock peak, tradition is directly drawn
Stretching experiment is controlled by reducing linear variable difference transformer LVDT rates, and reality is difficult to for the equipment that LVDT is not configured
It is tested, and the minimum loading speed of equipment is limited behind existing peak, it is impossible to unlimitedly reduce the loading speed.Therefore, there is an urgent need for one
It kind can effectively reduce gravity and influence, improve result precision and conventional rock forcing press can be utilized and can be in conventional rock
Further reduced on the basis of the minimum loading speed of forcing press loading speed rocks in direct tension intensity and destruction test
Rock straightway testing system and method.
Meanwhile it is more for the research of compressive strength of rock in the prior art, interior utilizes conventional rock mechanics machine
Measure the technology comparative maturity, and a variety of auxiliary such as acoustic emission test, optical strain measurement occur of compressive strength of rock
Measuring technique, with reflect rock sample when destroying the germinating of crackle, nucleation, extension, perforation until the process of gross fracture.For
The subsidiary function of conventional rock mechanics machine is made full use of, reducing gravity influences, improves result precision and can be with
Loading speed can be reduced using conventional rock forcing press and further on the basis of the minimum loading speed of conventional rock forcing press
Rocks in direct tension intensity and destruction test, need invention one kind that can realize rock on conventional rock mechanics machine
The fixture and test method of direct tensile test measure destructive process of the rock sample in direct tensile test, and can paint
The curve in post-peak area of rock tensile failure is made, to draw rock tensile failure whole English teaching, acquisition more can reaction engineering
Practical Tensile Strength of Rock.
Invention content
The technical problems to be solved by the invention are to overcome rocks in direct tension experiment in the prior art by gravity shadow
Pilot causes result accuracy rate low, and it is straight cannot to provide a kind of rock directly tested on conventional rock forcing press the shortcomings that
The fixture of tension test and the test method based on the fixture are connect, which can be real directly on conventional rock mechanics machine
Existing rocks in direct tension experiment, as a result accuracy rate is high, and can realize that loading speed reduces to obtain by changing the radian of fixture
Obtain Complete Stress-Strain Curve.
The technical solution adopted by the present invention to solve the technical problems is：The fixture of rocks in direct tension experiment, the fixture
Rock three-axis force testing machine is can be directly used for, including seaming chuck and push-down head, hollow slip is provided at the top of push-down head
Slot, sliding groove include two pulleys being arranged in parallel movement side, further include two groups of dumbbell shaped wheel shafts and two stretching chain bars, dumbbell
Shape wheel shaft includes two slip wheel shafts being connected by tensile axis, the two slide wheel shaft and are able to move in two pulleys
Slided on side, every tensile axis respectively with one stretching chain bar one end be connected, two stretching chain bar the other ends respectively with test specimen
Both ends be connected, further include the wedge clamp being set between two tensile axis, it is long that the top length of wedge clamp is more than bottom end
Degree, under the action of seaming chuck, wedge clamp can be gradually reduced, and with the decline of wedge clamp, two stretch distance between axles and increase
Greatly, two stretching chain bars are stretched, so as to fulfill the stretching of test specimen.
Specifically, test specimen is dog-bone, including cylinder body, cylinder body both ends are respectively provided with a discoid test specimen
Pull head, the diameter of test specimen pull head are more than the diameter of cylinder body.
Specifically, sliding groove is rectangular-shape grid structure, it is welded to each other by 12 solid steel tubes, is sliding groove top
A solid fixed block is respectively arranged at portion's four points of connection.
Further, test specimen collet is equipped on the outside of test specimen pull head, latch groove is provided on test specimen collet, is also set on tensile axis
There is latch groove, stretch the steel rod piece that chain bar is high tensile, the both ends for stretching chain bar are both provided with latch groove, by with inserting
The bolt that cotter way matches is connected chain bar is stretched with test specimen pull head and tensile axis respectively.
Further, guide rail is provided at the top of sliding groove, sliding wheel shaft can be free to slide on guide rail.
Specifically, wedge clamp for two it is identical become radian pressing plates, thickness of compressive plate be 4~6mm, wedge clamp bottom
End length is slightly less than the total length that test specimen adds both ends to stretch chain bar, and wedge clamp top length adds both ends drawing chain slightly larger than test specimen
The total length of bar, the side of wedge clamp from bottom end to top as radius of curvature gradually increases, tangent line with it is vertical to angle by
It is decrescence small.
Specifically, being provided with connecting plate between at the top of two wedge clamps, seaming chuck is acted on connecting plate, passes through company
The effect of power is passed to two pieces of wedge clamps by fishplate bar.
Preferably, seaming chuck be cylindric or rectangular-shape single solid steel briquetting, the size and shape and seaming chuck of push-down head
It is identical.
Another technical solution is used by the present invention solves its technical problem：Rock stretching test method, based on above-mentioned
The fixture of test specimen tension test, includes the following steps：
A. the rock sample of meet the requirements size and quality is selected, records the master data of test specimen, and at the both ends of test specimen
Test specimen collet is pasted, master data includes test specimen internal diameter D2；
B. suitably upper push-down head is selected, and records the quality m of seaming chuck0, push-down head is placed on experiment motor spindle pressure
On head, and sliding groove is placed on push-down head so that testing machine bottom ram, push-down head bottom center and experiment motor spindle pressure
Test specimen, is fixed on the tensile axis of movable pulley between centers of sliding groove by the alignment of head center by stretching chain bar；
C. wedge clamp is vertically filled in and slided among wheel shaft, squeezed wedge clamp from top to down, make wedge clamp and cunning
Driving wheel axis both sides fit closely, and assemble seaming chuck, seaming chuck top center is made to be aligned with testing machine upper pressure head center；
D. the axially mounted Axial extensometer in the middle part of test specimen, the circumferential extensometer of circumferential direction installation, slightly elevated machine displacement are straight
It closely compresses to seaming chuck and machine seaming chuck, is loaded with constant axial displacement loading speed, until experiment terminates, recorded
Related data can measure and obtain rock sample complete stress-strain diagram in drawing process, and record Complete Stress-Strain Relationship of Rock is bent
Wedge clamp and the inclination angle value of tensile axis point of intersection when the stress of line reaches peak value, and peak value inclination value θ is recorded as,
The peak value P of test specimen axial stresscr；
E. rock tensile strength σ is calculated according to the data of recordt=2* (Pcr+m0g)*tanθ/(πD2 2), wherein, PcrFor axis
To the peak value of stress, m0For seaming chuck quality, D2For test specimen diameter, θ is peak value inclination value.
Specifically, test specimen is fixed on the tensile axis of movable pulley between centers of sliding groove by stretching chain bar in step B, have
Body is, connection stretches chain bar respectively on the outside of two test specimen collets, and will stretch the other end of chain bar respectively with a tensile axis phase
Even, stretch and latch groove be reserved on the both ends of chain bar, using the bolt to match with latch groove will stretch chain bar and test specimen collet,
Tensile axis is connected.
The beneficial effects of the invention are as follows：It is simple in structure, it is easily operated, draw direction is converted by traditional vertical direction
Horizontal direction makes gravity and stretching axle power orthogonal, avoids influence of the gravity to stretching axle power, while resitting an exam certainly by seaming chuck
Consider within experiment influence factor, further reduce experimental error, meanwhile, it is loaded by becoming radian wedge shape clamping plate,
When test specimen reaches destruction, test specimen axial rate reaches minimum, can be enterprising on the minimum loading speed basis of conventional rock forcing press
One step reduces loading speed, is conducive to Complete Stress-Strain Curve in complete picture rock drawing process, and it is accurate to improve result of the test
Property；Further, since it directly can realize the direct tensile test of rock in conventional rock mechanics machine, tradition is made full use of
The function of Rock Mechanics Test machine, extends the purposes of conventional rock mechanics machine, and can combine conventional rock mechanical test
The loaded type CT scan of machine, the subsidiary means of acoustic emission monitor(ing) monitor the destructive process of rock, favorably through a variety of ways
In the generation, extension and perforation process of further exploring rock crackle in drawing process.The present invention is suitable for carrying out rock drawing
Stretch strength test.
Description of the drawings
Fig. 1 is the structure diagram for the device that existing direct tensile test is selected；
Fig. 2 is the structure diagram of fixture in the present invention；
Fig. 3 is the structure diagram A-A section plan views of fixture in the present invention；
Fig. 4 is the structure diagram of wedge clamp in the present invention；
Fig. 5 is the structure diagram for implementing rock tension test in the present invention on testing machine；
Fig. 6 is the structure diagram of dog-bone sample in the present invention；
Wherein, 11 be backing plate, and 12 be upper end cap, and 13 be lower endcaps, and 14 be test specimen fixing groove, and 15 is stretch chain, and 16 are
Rigid sleeve, 1 is seaming chuck, and 2 be wedge clamp, and 3 is slide wheel shaft, and 4 be sliding groove, and 5 be push-down head, and 6 be test specimen, and 7 is draw
Chain bar is stretched, 8 be tensile axis, and 61 be cylinder body, and 62 be test specimen pull head.
Specific embodiment
Below in conjunction with the accompanying drawings, detailed description of the present invention technical solution.Conventional rock forcing press described in text, that is, common rock
Stone forcing press.
The fixture of rocks in direct tension experiment as shown in figures 2-3, including seaming chuck 1 and push-down head 5,5 top of push-down head
Hollow sliding groove 4 is provided with, sliding groove 4 includes two pulleys being arranged in parallel movement side, further includes two groups of dumbbell shaped wheel shafts
And two stretching chain bars 7, dumbbell shaped wheel shaft include two slip wheel shafts 3 being connected by tensile axis 8, it is preferred that movable pulley
It is connected between axis 3 and tensile axis 8 with bolt, distance should be slightly bigger than sliding groove between two slip wheel shafts of every group of dumbbell shaped wheel shaft
The distance on two pulley movement sides makes the two slide wheel shaft and is able to slide on two pulley movement sides, every stretching
The one end of axis 8 respectively with a stretching chain bar 7 is connected, and the other end of two stretching chain bars 7 is connected respectively with the both ends of test specimen, also wraps
The wedge clamp 2 being set between two tensile axis 8 is included, the top length of wedge clamp 2 is more than bottom length, in seaming chuck 1
Under the action of, wedge clamp 2 can be gradually reduced, with the decline of wedge clamp 2, two 8 spacing of tensile axis increases, two drawings
It stretches chain bar 7 to be stretched, so as to fulfill the stretching of test specimen.
Seaming chuck is cylindric or rectangular-shape single solid steel briquetting, and when installation causes seaming chuck center and rock mechanics experiment
Machine seaming chuck center is aligned.As long as in test seaming chuck can press against wedge clamp and walk downward, push-down head can cushion sliding groove
Just meet condition.The size and shape of push-down head are identical with seaming chuck, in order to purchase and process.
Sliding groove 4 can select rectangular-shape grid structure formula, be welded to each other by 12 solid steel tubes.Cuboid has
There are 12 sides, therefore use 12 steel pipe manufacturing sliding grooves, other connection modes may be used, but in view of connection fixed effect
It is good, preferably with welding.The length of sliding groove should be greater than test specimen and both ends be added to stretch the total length of chain bar, and need to reserve certain distance
It is slided for sliding wheel shaft.The width of push-down head is more than the width of sliding groove, can realize and sliding groove is erected on push-down head,
A solid fixed block is respectively arranged at 4 top four points of connection of sliding groove, it is such as solid in four pieces of sliding groove apex welding
Bloom slides to avoid wheel shaft is slided from sliding groove.In order to control the slide-and-guide for sliding wheel shaft, set at the top of sliding groove
There is guide rail, sliding wheel shaft can be free to slide on guide rail.
Considered based on pulling force, stretch the steel rod piece that chain bar 7 is high tensile, the both ends for stretching chain bar are both provided with inserting
Cotter way, by being connected chain bar is stretched respectively with test specimen pull head and tensile axis with the bolt that latch groove matches.Rod piece both sides with
Bolt connects test specimen collet and stretches steel shaft, preferably compression helical spring respectively, and it is straight to substitute tradition using compression helical spring
Connect the rigid sleeve of cupping machine use.There is a pin clamp in the middle part of tensile axis and stretching chain bar, being inserted into bolt makes the two solid
It is fixed.
As shown in figure 4, wedge clamp 2 for two it is identical become radian pressing plates, thickness of compressive plate be not easy it is blocked up, preferably 4
~6mm, wedge clamp bottom length should be slightly less than the total length that test specimen adds both ends to stretch chain bar, and preferably 290mm, top length should
Slightly larger than the total length that test specimen plus both ends stretch chain bar, preferably 310mm, the side of wedge clamp is from bottom end to top with curvature
Radius gradually increases, and tangent line is gradually reduced with vertical to angle.In front of test specimen and one piece of wedge clamp is filled at rear respectively.On
Pressure head bottom surface size is slightly larger than two pieces of wedge clamp spacing, it can be achieved that applying pressure to two pieces of wedge clamps simultaneously using seaming chuck
So that wedge clamp declines, in addition it is also possible to be provided with connecting plate between at the top of two wedge clamps, seaming chuck acts on company
On fishplate bar, connecting plate is parallel with seaming chuck bottom surface, and the effect of power is passed to two pieces of wedge clamps by connecting plate.
As shown in figure 5, the fixture of rocks in direct tension experiment can be directly used for rock three-axis force testing machine, by test specimen
Experiment can be carried out by being fixed in three-axis force experimental machine by components such as wedge-shaped clamping plate and sliding grooves.Pass through the fixture energy
By the load that the load conversion of vertical direction that testing machine applies is horizontal direction, gravity is eliminated as much as in rocks in direct tension
Test the influence generated in the process.In addition, by using become radian wedge clamp to control loading speed, with experiment into
The loading velocity of row horizontal direction is slower and slower, so as to reach loading maximum value when rock tensile test specimen is up to destruction.
As shown in fig. 6, test specimen is dog-bone, including cylinder body 61,61 both ends of cylinder body are respectively provided with a disk
The characteristics of test specimen pull head 62 of shape, circular cross-section, is uniform force, can bear the active force of bigger, comes from force analysis
It says, circular stress is more reasonable than other shapes uniformly, and the phenomenon that being not in stress concentration improves result accuracy.Test specimen
The diameter of pull head 62 is more than the diameter of cylinder body 61, and the universality based on test toolss selects following parameter：Cylinder body 61
Height for 90~110mm, a diameter of 28~32mm, test specimen pull head 62 is discoid, a diameter of 48~54mm.It can be used
It is bonded or welded mode and test specimen pull head 62 is connected on 61 both ends of cylinder body, based on the small consideration of small and error in length is deformed, preferably
Bonding way.
Rocks in direct tension test method is carried out on conventional rock mechanics machine based on above-mentioned fixture, including following step
Suddenly：
(1) it samples.
In this example, sampling work is unfolded in the underground power house of Sichuan Province's Pubugou Hydropower Station, chooses 1# tailwater tunnels
Granite, be named as biotite monzonitic granite, hereinafter referred to as Pubugou Project granite.Rock sample is visually observed as in canescence
Coarse grain inequigranular structure, massive structure, rock constituents are mainly quartzy (grey), and potassium feldspar (flesh pink), plagioclase is (greyish white
Color) and less dark minerals, the distribution of mineral constituent it is less uniform.Middle coarse grain seriate hypidiomorphic granular is viewed as under microscope
Structure, massive structure.Rock constituents are mainly made of two kinds of feldspars, quartz and a small amount of biotite.Part has stronger fragmentation.
(2) test specimen is prepared.
The Pubugou Project granite core or sillar chosen from scene are machined into directly in use for laboratory drilling machine or lathe etc.
Diameter is 50mm, is highly the standard specimen of 100mm, and ratio of height to diameter is (2 ± 0.2), in the middle part of test specimen of polishing later, until being in the middle part of test specimen
Diameter 30mm, the cylinder body of height 90mm, test specimen pull head is diameter 60mm, the prolate test specimen of height 5mm, forms dog-bone
Test specimen.It is designed to that dog-bone test specimen in order to stretch, provides tensile stress.Sample preparation standard reference《GB50266-2013 engineering rocks
Body test method standard》Etc. relevant regulations carry out, with grinding machine process surface of test piece, be less than test specimen two ends face nonparallelism
0.05mm；Test specimen upper and lower side diameter difference is less than 0.3mm；Surface of test piece should be smooth, and avoid generating due to irregular surface answers
Power concentration phenomenon.
(3) process is tested.
1) sample preparation：It is 227.87g with electronics balance measurement test specimen quality, height of specimen 105.21mm, test specimen outer diameter
48.68mm, test specimen diameter D2For 30.09mm, it is 2.64g/cm to calculate and obtain Sample density3Test specimen complies with standard, and records above-mentioned
Data.Test specimen collet is bonded on the outside of test specimen pull head with epoxy resin AB glue and is put into constant temperature oven in test specimen two ends later
In be heated to colloid solidification.Test specimen collet is a kind of existing plastic clamp, in traditional tension test also can use arrive, collet
On have latch groove, for stretch chain connection.After test specimen cooling, examination is connected with the stretching chain bar side of the reserved latch groove in both ends
Wheel shaft is slided in part collet, side connection, is inserted into bolt and connects and check whether bolt connection is close.
2) placing component：Select two a diameter of 120mm, the pressure head of height 30mm, respectively as seaming chuck and push-down head,
Weighing obtains monolithic pressure head quality as 2.663kg, and push-down head bottom center is aligned with testing machine bottom ram center；It selects real
The heart steel pipe structure rectangular-shape grid structure sliding groove, sliding groove overall dimensions be length 350mm, width 200mm, height
Sliding groove is placed on push-down head by 200mm, and slip groove bottom rectangular centre is made to be aligned with push-down head bottom ram center.
3) rock sample is placed：The test specimen that step 1) obtains is being slided together with stretching chain bar and slip wheel shaft device
On slot, moderate lubrication oil is smeared on sliding groove, pushes and slides wheel shaft, checks whether test specimen entirety can be on solid sliding groove
It is free to slide.Bottom 290mm, top 310mm are selected, wedge clamp is vertically filled in slip wheel shaft by the wedge clamp of thickness 5mm
Centre, in front of rock sample and one piece of wedge clamp is respectively filled at rear.Wedge clamp is suitably squeezed from top to down, makes wedge pressure
Plate is fitted closely with sliding wheel shaft both sides, assembles seaming chuck, seaming chuck top center is made to be aligned with testing machine upper pressure head center.
4) it tests：The axially mounted Axial extensometer in the middle part of rock sample, the circumferential extensometer of circumferential direction installation.Slightly elevated machine
Device displacement is closely compressed until seaming chuck and machine seaming chuck, later with the constant axial displacement loading speed of 0.005mm/min
It is loaded, terminates until breaking test occurs, record related data, related data herein includes using on paper when destroying
Ruler draws tangential angle, and with the wedge clamp that protractor measures and the angle of inclination of tensile axis point of intersection, can
It measures and obtains rock sample complete stress-strain diagram in drawing process.Record the axial stress of Complete Stress-Strain Relationship of Rock curve
Reach that peak value is wedge clamp and the angle of inclination of tensile axis point of intersection is 15 °, and be recorded as peak value inclination value θ, such as Fig. 2
Shown in middle B points, the peak value P of axial stresscrFor 13.137kN, above-mentioned stress all refers to the axial stress that rock sample is subject to.
(5) result of calculation.Rock tensile strength is calculated according to the data of record
σt=2* (Pcr+m0g)*tanθ/(πD2 2)=2* (13.137+2.663*9.8/1000) * 1000*tan (15 °)/
(π*30.092)=48MPa wherein, PcrFor the peak value of axial stress, m0For seaming chuck quality, D2For test specimen diameter, θ inclines for peak value
Angle value.
In order to improve result precision, it can repeatedly measure and average.
Claims (10)
1. the fixture of rocks in direct tension experiment, which is characterized in that including seaming chuck (1) and push-down head (5), push-down head (5) top
Portion is provided with hollow sliding groove (4), and sliding groove (4) moves side including two pulleys being arranged in parallel, further includes two groups of dumbbells
Shape wheel shaft and two stretching chain bars (7), dumbbell shaped wheel shaft include two slip wheel shafts (3) being connected by tensile axis (8), this
Two are slided wheel shaft and are able to slide on two pulley movement sides, and every tensile axis (8) respectively stretches chain bar (7) with one
One end is connected, and two other ends for stretching chain bar (7) are connected respectively with the both ends of test specimen, further include and are set to two tensile axis
(8) wedge clamp (2) between, the top length of wedge clamp (2) are more than bottom length, under the action of seaming chuck (1), wedge
Shape pressing plate (2) can be gradually reduced, with the decline of wedge clamp (2), two tensile axis (8) spacing increases, two drawing chains
Bar (7) is stretched, so as to fulfill the stretching of test specimen.
2. fixture as described in claim 1, which is characterized in that test specimen is dog-bone, including cylinder body (61), cylinder master
Body (61) both ends are respectively provided with a discoid test specimen pull head (62), and the diameter of test specimen pull head (62) is more than cylinder body (61)
Diameter.
3. fixture as described in claim 1, which is characterized in that sliding groove (4) is rectangular-shape grid structure, solid by 12
Steel pipe is welded to each other, and a solid fixed block is respectively arranged at the four points of connection of sliding groove (4) top.
4. fixture as described in claim 1, which is characterized in that test specimen collet is equipped on the outside of test specimen pull head, is set on test specimen collet
Latch groove is equipped with, latch groove also is provided on tensile axis, stretches the steel rod piece that chain bar is high tensile, stretches the both ends of chain bar
Latch groove is both provided with, by being connected chain bar is stretched respectively with test specimen pull head and tensile axis with the bolt that latch groove matches.
5. fixture as described in claim 1, which is characterized in that guide rail is provided at the top of sliding groove, sliding wheel shaft can lead
It is free to slide on rail.
6. fixture as described in claim 1, which is characterized in that wedge clamp (2) is two identical change radian pressing plates,
Thickness of compressive plate is 4~6mm, and wedge clamp bottom length is slightly less than the total length that test specimen adds both ends to stretch chain bar, wedge clamp top
End length adds both ends to stretch the total length of chain bar slightly larger than test specimen, and the side of wedge clamp is from bottom end to top with radius of curvature
Gradually increase, tangent line are gradually reduced with vertical to angle.
7. fixture as claimed in claim 6, which is characterized in that connecting plate is provided between at the top of two wedge clamps, on
Pressure head is acted on connecting plate, and the effect of power is passed to two pieces of wedge clamps by connecting plate.
8. fixture as described in claim 1, which is characterized in that seaming chuck is cylindric or rectangular-shape single solid steel briquetting, under
The size and shape of pressure head are identical with seaming chuck.
9. rocks in direct tension test method, which is characterized in that based on as described in any claim in claim 1~8
The fixture of rocks in direct tension experiment, includes the following steps：
A. the rock sample of meet the requirements size and quality is selected, records the master data of test specimen, and paste at the both ends of test specimen
Test specimen collet, master data include test specimen internal diameter D2；
B. suitably upper push-down head is selected, and records the quality m of seaming chuck0, push-down head is placed in testing machine bottom ram,
And sliding groove is placed on push-down head so that in testing machine bottom ram, push-down head bottom center and testing machine bottom ram
The heart is aligned, and test specimen is fixed on the tensile axis of movable pulley between centers of sliding groove by stretching chain bar；
C. wedge clamp is vertically filled in and slided among wheel shaft, squeezed wedge clamp from top to down, make wedge clamp and movable pulley
Axis both sides fit closely, and assemble seaming chuck, seaming chuck top center is made to be aligned with testing machine upper pressure head center；
D. the axially mounted Axial extensometer in the middle part of test specimen, the circumferential extensometer of circumferential direction installation, slightly elevated machine displacement is until upper
Pressure head is closely compressed with machine seaming chuck, is loaded with constant axial displacement loading speed, until experiment terminates, record is related
Data can measure and obtain rock sample complete stress-strain diagram in drawing process, record Complete Stress-Strain Relationship of Rock curve
Wedge clamp and the inclination angle value of tensile axis point of intersection when stress reaches peak value, and it is recorded as peak value inclination value θ, test specimen
The peak value P of axial stresscr；
E. rock tensile strength σ is calculated according to the data of recordt=2* (Pcr+m0g)*tanθ/(πD2 2), wherein, PcrIt is answered to be axial
The peak value of power, m0For seaming chuck quality, D2For test specimen diameter, θ is peak value inclination value.
10. method as claimed in claim 9, which is characterized in that test specimen is fixed on sliding groove by stretching chain bar in step B
Movable pulley between centers tensile axis on, specifically, connection stretches chain bar respectively on the outside of two test specimen collets, and chain bar will be stretched
The other end be respectively connected with a tensile axis, stretch and latch groove be reserved on the both ends of chain bar, utilize what is matched with latch groove
Bolt is connected chain bar is stretched with test specimen collet, tensile axis.
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