CN116448596A - Brittle material dynamic fracture parameter test method and electromagnetic falling plate impact test system - Google Patents
Brittle material dynamic fracture parameter test method and electromagnetic falling plate impact test system Download PDFInfo
- Publication number
- CN116448596A CN116448596A CN202310225708.6A CN202310225708A CN116448596A CN 116448596 A CN116448596 A CN 116448596A CN 202310225708 A CN202310225708 A CN 202310225708A CN 116448596 A CN116448596 A CN 116448596A
- Authority
- CN
- China
- Prior art keywords
- sample
- plate
- crack
- dynamic
- strain
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 239000000463 material Substances 0.000 title claims abstract description 28
- 238000009863 impact test Methods 0.000 title claims abstract description 20
- 238000010998 test method Methods 0.000 title description 3
- 238000000034 method Methods 0.000 claims abstract description 41
- 230000005540 biological transmission Effects 0.000 claims abstract description 35
- 238000012360 testing method Methods 0.000 claims abstract description 34
- 230000008569 process Effects 0.000 claims abstract description 12
- 238000004088 simulation Methods 0.000 claims abstract description 10
- 238000010586 diagram Methods 0.000 claims description 11
- 238000012544 monitoring process Methods 0.000 claims description 11
- 239000011435 rock Substances 0.000 claims description 11
- 230000000977 initiatory effect Effects 0.000 claims description 7
- 238000005336 cracking Methods 0.000 claims description 6
- 230000006870 function Effects 0.000 claims description 6
- 230000003028 elevating effect Effects 0.000 claims description 4
- 230000008571 general function Effects 0.000 claims description 4
- 230000001737 promoting effect Effects 0.000 claims description 4
- 229910001369 Brass Inorganic materials 0.000 claims description 3
- 230000009471 action Effects 0.000 claims description 3
- 239000010951 brass Substances 0.000 claims description 3
- 238000012937 correction Methods 0.000 claims description 3
- 238000005259 measurement Methods 0.000 claims description 3
- 230000001902 propagating effect Effects 0.000 claims description 3
- 230000003068 static effect Effects 0.000 claims description 3
- 238000003860 storage Methods 0.000 claims description 3
- 229910000838 Al alloy Inorganic materials 0.000 claims description 2
- 230000003321 amplification Effects 0.000 claims description 2
- 238000003199 nucleic acid amplification method Methods 0.000 claims description 2
- 230000035945 sensitivity Effects 0.000 claims description 2
- 230000007246 mechanism Effects 0.000 description 13
- 238000012545 processing Methods 0.000 description 4
- 239000003973 paint Substances 0.000 description 3
- 229910000831 Steel Inorganic materials 0.000 description 2
- 238000004364 calculation method Methods 0.000 description 2
- 238000006073 displacement reaction Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000005507 spraying Methods 0.000 description 2
- 239000010959 steel Substances 0.000 description 2
- TZCXTZWJZNENPQ-UHFFFAOYSA-L barium sulfate Chemical compound [Ba+2].[O-]S([O-])(=O)=O TZCXTZWJZNENPQ-UHFFFAOYSA-L 0.000 description 1
- 238000005422 blasting Methods 0.000 description 1
- 235000014121 butter Nutrition 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 230000005389 magnetism Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000007557 optical granulometry Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 230000035939 shock Effects 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
Classifications
-
- 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
- G01N3/30—Investigating strength properties of solid materials by application of mechanical stress by applying a single impulsive force, e.g. by falling weight
- G01N3/303—Investigating strength properties of solid materials by application of mechanical stress by applying a single impulsive force, e.g. by falling weight generated only by free-falling weight
-
- 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
- G01N3/06—Special adaptations of indicating or recording means
- G01N3/068—Special adaptations of indicating or recording means with optical indicating or recording means
Abstract
A method for testing the dynamic fracture parameters of brittle materials and an electromagnetic falling plate impact test system comprise the following steps: preparing a sample, debugging an electromagnetic falling plate impact test system, lifting an impact plate to a test height, lifting an incident plate to place the sample between the incident plate and a transmission plate, releasing the impact plate to trigger a high-speed camera and a super-dynamic data acquisition system so as to acquire sample surface images in the same time domain in the dynamic fracture process of the sample and strain signals on the incident plate and the transmission plate, converting the strain signals into stress loading time-course curves, substituting the stress loading time-course curves into an ABAQUS software finite element sample three-dimensional numerical simulation model, and calculating stress intensity factor curves; meanwhile, DIC digital image analysis software is adopted to calculate and analyze the surface images of the sample to obtain the crack breaking moment and crack propagation speed of the sample surface, so that the breaking moment of the tip of the sample center crack is reversely deduced, and the breaking moment of the sample center crack is brought into a stress intensity factor curve to obtain the dynamic fracture starting toughness. Convenient operation and high precision.
Description
Technical Field
The invention relates to a method for testing dynamic fracture parameters of brittle materials and an electromagnetic falling plate impact test system.
Background
Brittle materials, such as rock, concrete and the like, have very important roles in researching the dynamic fracture parameters and breaking mechanisms under strong shocks such as blasting, impact and the like. The dynamic fracture toughness comprises dynamic fracture toughness and dynamic expansion toughness, and is used as an important parameter index for evaluating the engineering stability of the rock mass.
At present, a Hopkinson bar test method based on a small-size sample is mostly adopted in a dynamic fracture toughness solution, and then a recommended formula is adopted to calculate the dynamic fracture toughness of the material. When the impact test is carried out by adopting the small-size sample, the stress wave is reflected back and forth for 3-5 times in the sample before the rock is damaged, and the stress state of the crack tip can be changed when the stress wave is reflected back from the boundary of the sample and reaches the crack tip, but the actual engineering rock mass is very large, and the rock mass is damaged in the process of unidirectional stress wave propagation under the power disturbance, so that the dynamic test of the small-size sample cannot be good for researching the actual rock mass working condition.
Disclosure of Invention
The invention aims to provide a method for testing dynamic fracture parameters of brittle materials.
In order to solve the technical problems, the invention adopts the following technical scheme: a method for testing the dynamic fracture parameters of brittle materials comprises,
preparing a sample, wherein the sample is a large-size side-opened triangular single-crack plate speckle sample, a triangular groove is formed in the middle of the top of the sample, a straight groove is formed by continuously extending downwards from the sharp corner of the triangular groove, and a speckle pattern layer is arranged on the surface of the sample at least in the area right below the triangular groove;
step two, debugging an electromagnetic falling plate impact test system, wherein the electromagnetic falling plate impact test system comprises an impact plate, an incident plate and a transmission plate which are sequentially and linearly distributed from top to bottom, and further comprises a high-speed camera for shooting images of a spot diagram layer on the surface of the sample, and a super-dynamic data acquisition system for respectively acquiring strain signals on the incident plate and the transmission plate, wherein the super-dynamic data acquisition system comprises strain gauges, super-dynamic strain gauges and oscilloscopes which are respectively attached to the incident plate and the transmission plate, the impact plate is lifted to a test height, and the incident plate is lifted so that the top of the sample is upwards placed between the incident plate and the transmission plate;
releasing the impact plate, and synchronously triggering a high-speed camera and a super-dynamic data acquisition system to acquire sample surface images in the same time domain in the dynamic fracture process of the sample and strain signals on the incident plate and the transmission plate;
converting the strain signals on the incident plate and the transmission plate into stress loading time-course curves based on a one-dimensional stress wave theory, and substituting the stress loading time-course curves into an ABAQUS software finite element sample three-dimensional numerical simulation model to calculate stress intensity factor curves; meanwhile, calculating and analyzing the surface image of the sample by adopting D I C digital image analysis software to obtain the crack breaking moment and crack propagation speed of the sample surface, and reversely deducing the breaking moment of the crack tip of the sample center; and (3) bringing the fracture moment of the sample center crack into a stress intensity factor curve to obtain the dynamic fracture toughness.
The invention further aims to provide the electromagnetic drop plate impact test system for implementing the method for testing the dynamic fracture parameters of the brittle materials.
In order to solve the technical problems, the invention adopts the following technical scheme: the utility model provides an electromagnetism falling plate impact test system, includes guide rail, workstation, still including setting up impact plate in the guide rail, be used for absorbing after the circular telegram electromagnetic plate, incident plate, transmission board, still including being used for promoting the first elevating system of electromagnetic plate, be used for promoting the second elevating system of incident plate, set up in the sample is directly ahead be used for taking the high-speed camera of sample surface spot diagram layer department image, the collection respectively incident plate with the super dynamic data acquisition system of transmission board strain signal, super dynamic data acquisition system is including pasting respectively establish incident plate with strain gauge on the transmission board, with the super dynamic strain gauge of strain gauge voltage signal amplification, gather stress signal and the oscilloscope of storage, high-speed camera and the oscilloscope is connected with the workstation respectively.
The scope of the present invention is not limited to the specific combination of the above technical features, but also covers other technical features formed by any combination of the above technical features or their equivalents. Such as those described above, and those disclosed in the present application (but not limited to) having similar functions, are replaced with each other.
Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages:
(1) The dynamic fracture test is carried out by adopting a large-size sample, and when the stress wave propagates to the bottom end of the sample and then is reflected to the tip end of the crack, the crack is cracked, so that the influence of the reflected tensile wave can be avoided, and the fracture failure mechanism under the impact load of the large-volume engineering rock mass can be studied.
(2) The sample has simple structure, convenient processing and manufacturing, and the test process does not need a mold.
(3) The method adopts a digital image combined test-numerical method to study the expansion speed and fracture toughness in the crack fracture process, and has the advantages of non-contact measurement, small interference, high dynamic fracture parameter solving precision and simple and feasible operation method.
Drawings
FIG. 1 is a flow chart of a method for testing dynamic expansion parameters of a crack-containing sample under impact load in an embodiment of the invention;
FIG. 2 is a schematic view of a large-size side-opening triangular single-slit plate speckle sample according to an embodiment of the invention;
FIG. 3 is a schematic view of a large-size side-opened triangular single-slit plate speckle sample shooting surface speckle in an embodiment of the invention;
FIG. 4 is a schematic diagram of an electromagnetic drop plate impact loading system in an embodiment of the invention;
FIG. 5 is a graph showing load time course applied to both ends of a sample according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of crack extension path monitoring point placement in an embodiment of the invention;
FIG. 7 is a graph of monitoring point x-direction strain time course in an embodiment of the present invention;
FIG. 8 is a schematic diagram of an ABAQUS three-dimensional numerical calculation model in an embodiment of the invention;
FIG. 9 is a graph of the time course of the ABAQUS solving for stress intensity factors in an embodiment of the invention;
FIG. 10 is a graph of fracture dynamic fracture toughness for an embodiment of the present invention;
wherein: 1. a guide rail; 2. a workstation; 3. an impingement plate; 4. an incident plate; 5. a transmissive plate; 6. a sample; 7. a second lifting mechanism; 71. a second motor; 72. a second lifting frame; 73. a third sling; 8. a super dynamic data acquisition system; 81. a strain gage; 82. a super dynamic strain gauge; 83. an oscilloscope; 9. a high speed camera.
Detailed Description
In order to more clearly explain the objects, technical solutions and advantages of the present invention, the following description will fully explain the implementation process of the present invention by referring to the embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
The present invention will be described in detail with reference to the accompanying drawings.
As shown in fig. 1, the method for testing the dynamic fracture parameter of the brittle material under impact load according to the embodiment of the invention comprises the following steps:
step one: a speckle pattern layer was formed on the surface of the crack tip in the propagation region by using a large-sized side-cut triangular single-crack plate speckle sample 6.
Step two, debugging an electromagnetic falling plate impact test system, lifting an impact plate 3 to a test height, lifting an incidence plate 4 so that the top of a sample 6 is upwards placed between the incidence plate 4 and a transmission plate 5, and then lowering the incidence plate 4;
step three: and (3) performing impact test on the sample 6, acquiring strain signals on the incident plate 4 and the transmission plate 5 through a super dynamic data acquisition system 8 in the test, and synchronously acquiring image photos of the surface of the sample 6 through a high-speed camera 9.
Step four: based on the photo taken by the high-speed camera 9, calculating a strain field and a displacement field of the tip of the surface crack by adopting D I C digital image analysis software, and reversely pushing the center fracture moment according to the stress wave propagation rule to calculate the crack propagation speed; and converting the strain signals acquired by the super-dynamic data acquisition system 8 into stress loading time-course curves, substituting the stress loading time-course curves into ABAQUS finite element software to perform numerical calculation, obtaining stress intensity factor time-course curves of the surface crack tips, and obtaining the dynamic fracture toughness of the rock materials according to the dynamic fracture moment of the cracks.
Step five: and the influence of the space time difference of stress wave propagation is considered, and the dynamic expansion toughness is obtained after correction by adopting a universal function, so that the precision is higher.
The testing method comprises the following detailed steps:
firstly, preparing a sample 6, wherein the sample 6 is a large-size side-opened triangular single-crack plate speckle sample 6, and a single crack refers to a chamfer groove in the middle of the top of the sample 6, and a sharp angle of the chamfer groove continuously extends downwards to form a straight groove, so that the crack growth in an impact test is guided. And a spot diagram layer is arranged in the area of the surface of the sample 6, which is positioned right below the chamfer groove, and is used for collecting expansion cracks of the surface of the sample 6 in impact test by a high-speed camera 9. The sample 6 may be a brittle material such as rock or concrete, and has a length W of 200mm, a height H of 325mm, a thickness B of 30mm, a straight groove depth a of 30mm, a straight groove width of 1.5mm, and side lengths L of 62.5mm on both sides of the top triangular groove, as shown in FIG. 2.
The spot diagram layer making method specifically comprises the following steps: and (3) spraying white paint on the surface of the crack propagation direction area of the sample 6, and after the white paint is dried, covering the surface of the sample 6 by using a 0.3mm round hole plate, and spraying black paint on the surface of the sample 6 through the perforated plate to manufacture black spots, wherein the effect is shown in figure 3.
The second step, an electromagnetic falling plate impact test system is adopted to perform impact test on the sample 6, as shown in fig. 4, the test system is designed according to the SHPB principle, and mainly comprises a guide rail 1 and a workstation 2 which are arranged in the vertical and horizontal direction, an impact plate 3 which is arranged in the guide rail 1, an electromagnetic plate which is arranged on the guide rail 1 and absorbs the impact plate 3 after being electrified, an incident plate 4 and a transmission plate 5, a first lifting mechanism for lifting the electromagnetic plate, a second lifting mechanism 7 for lifting the incident plate 4, a high-speed camera 9 which is arranged right in front of the sample 6 and is used for shooting an image picture at a spot diagram layer of the surface of the sample 6, and a super-dynamic data acquisition system 8 for acquiring strain signals of the incident plate 4 and the transmission plate 5, wherein the super-dynamic data acquisition system 8 comprises a strain gauge 81 which is respectively stuck on the incident plate 4 and the transmission plate 5, a super-dynamic strain gauge 82 which amplifies the voltage signals of the strain gauge 81, an oscilloscope 83 which acquires and stores the stress signals, a voltage stabilizing source, and a resistor, and the like. The high-speed camera 9 and the oscilloscope 83 are connected to the workstation 2, respectively. The electromagnetic plate, the first lifting mechanism and the second lifting mechanism are respectively connected with the control unit and independently control the electric action and the like. As shown in fig. 4, the structure of the second lifting mechanism 7 comprises a second lifting frame 72 arranged on steel frames at two sides of the guide rail 1, a second motor 71 arranged on the second lifting frame 72, and at least two second lifting ropes 73 with upper ends respectively connected with the second lifting frame 72, wherein the lower ends of the second lifting ropes 73 are respectively connected with the incident plate 4. The second motor 71 can drive the second lifting frame 72 to move upwards or downwards along the steel frame after being powered. The structure of the first lifting mechanism refers to the second lifting mechanism 7. The first lifting mechanism and the electromagnetic plate are not shown in fig. 4, and the state shown in fig. 4 is a schematic diagram of the state that the impact plate 3 falls on the top of the incident plate 4 after the electromagnetic plate is powered off.
The incident plate 4 had a size of 300mm long, a height of 3000mm, a thickness of 30mm, and the transmissive plate 5 had a size of 300mm long, a height of 1000mm, and a thickness of 30m, all of which were composed of a density of 2800kg/m 3 The LY12CZ aluminum alloy with the elastic modulus of 72GPa, the Poisson ratio of 0.33 and the P wave speed of 5500m/s is prepared.
In order to reduce the dispersion effect of the stress wave, a brass plate with a section smaller than the section area of the incident plate 4 is placed on top of the incident plate 4. During the test, the motor control switch and the electromagnet control switch of the first lifting mechanism are turned on, at the moment, the electromagnet has magnetism through alternating current, the impact plate 3 is lifted to the test design height through the lifting electromagnet, the motor control switch of the second lifting mechanism 7 is turned on to lift the incident plate 4, a thin layer of butter is uniformly coated on two end faces of the sample 6, which are in contact with the incident plate 4 and the transmission plate 5, then the sample 6 is gently placed between the incident plate 4 and the transmission plate 5, and the impact height and the super-dynamic data acquisition system 8 are well debugged.
Thirdly, acquiring strain signals and image photos in the test
The electromagnet control switch is turned off, at this time, the oscilloscope 83 and the high-speed camera 9 automatically trigger and start to synchronously collect signals and take pictures, the impact plate 3 freely falls down to impact the top of the incidence plate 4 to generate a plane compression stress wave, the plane stress wave is partially reflected back to the incidence plate 4 after passing through the incidence plate 4 and is partially transmitted to the sample 6 to realize dynamic loading of the sample 6, the stress wave propagates in the sample 6 to reach the top of the transmission plate 5 to be emitted and transmitted again, and thus, the loading signals of the stress wave are posted on the incidence plate 4 and the transmission plate 5 to collect voltage signals by the strain gauge 81. Because the collected voltage signal is very tiny, the voltage signal is amplified by the super dynamic strain gauge 82 and transmitted to the digital storage oscilloscope 83 for collecting and storing the strain signal.
Fourth step, stress loading time curve and image photo processing
The super dynamic strain gauge 82 in this embodiment is eight channels, the oscilloscope 83 is four channels, the maximum acquisition frequency is 100MHz, and the relationship between the voltage signal and the strain signal is:
wherein DeltaU is the measured voltage, U is the bridge supply voltage, in this embodiment 2 volts, n 1 And n 2 Gain coefficients of the super dynamic resistance strain gauge and oscilloscope 83, respectively, this test n 1 ＝1000，n 2 ＝10，K S For the sensitivity coefficient of the strain gage 81, K S ＝2.1。
According to the one-dimensional stress wave propagation theory, the stress loading time course curve loaded at the two ends of the sample 6 can be calculated according to the following formula:
in sigma top (t) and sigma bot (t) stress loading time curves of the top and bottom ends of the sample 6, respectively, A is the cross-sectional areas of the incident plate 4 and the transmissive plate 5, A s For sample 6 cross-sectional area, A si For the cross-sectional area of the triangular open end of sample 6, E p For the elastic modulus of the entrance plate 4 and the transmission plate 5 ε i (t)、ε r (t) and ε t (t) an incident wave strain time-course curve, a reflected wave strain time-course curve and a transmitted wave strain time-course curve, respectively. The stress loading curve of this embodiment is shown in fig. 5.
The image photo analysis is realized by DIC digital image analysis software, 8 monitoring points are arranged at equal intervals along the crack tip extension path of the sample 6 to measure the x-direction strain information of the position, the arrangement mode of the monitoring points is shown in figure 6, and the crack initiation moment of the crack extended to the corresponding surface crack of the sample 6 is determined by finding the strain curve inflection point according to the following mode.
Wherein K (t) is a curve inflection point ε x Is the x-direction strain.
The change of the displacement x-direction strain of the 8 monitoring points along with the shooting frame number is shown in fig. 7, and the propagation speed v of the crack can be obtained according to the distance between the monitoring points.
According to the embodiment of the invention, a method of combining test and numerical values is adopted to solve the dynamic fracture toughness, and an ABAQUS finite element software is adopted to establish a three-dimensional numerical simulation model of the sample. As shown in FIG. 8, the three-dimensional numerical simulation model of the sample adopts 1/4 node singular units to simulate the singularities of crack tips, wherein the unit types of the crack tip areas are C3D15 units, and the other areas are C3D20 units. Substituting the stress loading time course curve obtained by the impact test into an ABAQUS software finite element sample three-dimensional numerical simulation model to calculate a stress intensity factor curve, reversely pushing out the breaking moment of the central crack of the sample 6 according to the breaking moment of the surface crack of the sample 6 obtained by image photo processing, and carrying the stress intensity factor curve to obtain the dynamic fracture initiation toughness.
Correction
Since the crack initiation starts first from the center of the specimen 6, the moment of fracture of the stress wave propagating to the i-th layer element in the thickness direction of the crack front is:
wherein t is f Time of cracking of sample 6 surface crack, B i V is the distance from the ith layer unit to the surface of the sample 6 in the thickness direction of the crack front P Is the stress wave propagation velocity.
The stress intensity factor profile along the thickness direction, i.e. the z-direction, is also symmetrical due to the symmetry of the geometric model, constraints and loads. Starting from the z-direction center, when using a 2.5mm cell size, only 7 stress intensity factor histories need to be calculated, as shown in FIG. 9.
After the fracture moments of different positions of the front edge of the crack in the z direction are determined, the fracture moments are brought into a stress intensity factor curve, and the fracture starting toughness of the crack can be obtained. As shown in Table 1, K I ' is dynamic stress intensity factor of different points of crack front obtained by cracking at the same time in z direction, t f K is the cracking time corresponding to different points of the front edge of the crack in the z direction Ι And (3) the dynamic stress intensity factors corresponding to the cracking of the points at different positions of the front edge of the z-direction crack calculated according to the formula (5).
Table 1 below shows the dynamic stress intensity factors obtained by experiments when cracking occurs at different points of the front edge of the crack in the thickness z direction.
TABLE 1
As can be seen, the dynamic fracture toughness at the center point of the crack front of the three-dimensional numerical simulation model of the sample is 7.082 MPa-m 1/2 The dynamic fracture toughness obtained is 6.593 MPa.m as calculated by the fracture initiation at the center of the crack front 1/2 The relative error was 7.42%. Therefore, when the z-direction crack front is cracked at different positions, the propagation time in the thickness z-direction has a large influence on the measurement result, and consideration should be given.
For the dynamic expansion toughness in the crack expansion process, according to the dynamic fracture mechanics theory, the dynamic stress intensity factor of the crack expanding at any speed under the action of dynamic load is equal to the general function of the instantaneous crack tip multiplied by the stress intensity factor of the static crack tip at the place, namely:
wherein K is I d (t) represents the dynamic stress intensity factor, K, of a crack propagating at a speed v at time t I 0 (t,a j ) Representing the instantaneous length a of a motion crack j And j is the number of the monitoring point.
The approximate formula of the generic function k (v) is:
wherein V is R For sample 6 material rayleigh wave velocity, h is a function of elastic wave velocity:
wherein V is P And V S The wave velocities of the P wave and S wave of the material of the sample 6 are respectively.
According to the method, the dynamic expansion toughness of the crack when expanding to any position can be calculated, and as shown in fig. 10, the specific method comprises the following steps: at the established crack propagation length a j In the ABAQUS finite element sample three-dimensional numerical simulation model, a stress intensity factor curve K under the crack length at the moment is obtained by calculating an input load curve I 0 (t,a j ) The crack propagation speed calculated by the digital image method is substituted into formula (7) to calculate the universal function K (v), and then the dynamic stress intensity factor curve K of the crack is obtained according to formula (6) I d (t) whereby the dynamic propagation toughness during crack initiation can be determined.
The invention discloses a novel method for testing the dynamic fracture parameters of brittle materials, which is based on digital image processing and combines a test-numerical method, so that the crack growth speed, the dynamic fracture toughness and the expansion toughness of the brittle materials such as rock and the like under impact load can be accurately measured. The method is convenient to operate, high in solving precision and suitable for the research of the dynamic fracture whole process of the crack.
The above-mentioned method is only an embodiment of a dynamic fracture parameter testing process with a configuration including a single crack, and is only for illustrating the technical concept and features of the present invention, so that those skilled in the art can understand the content of the present invention and implement it according to the same, and it is not intended to limit the scope of the present invention, and any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present invention are included in the scope of the present invention.
Claims (10)
1. A method for testing the dynamic fracture parameters of brittle materials comprises the following steps:
preparing a sample (6), wherein the sample (6) is a large-size side-opened triangular single-crack plate speckle sample (6), a chamfer groove is formed in the middle of the top of the sample (6), a straight groove is formed by continuously extending downwards from the sharp corner of the chamfer groove, and a speckle pattern layer is arranged on the surface of the sample (6) at least in the area right below the chamfer groove;
step two, debugging an electromagnetic drop plate impact test system, wherein the electromagnetic drop plate impact test system comprises an impact plate (3), an incident plate (4) and a transmission plate (5) which are sequentially and linearly distributed from top to bottom, a high-speed camera (9) for shooting images of a spot diagram layer on the surface of a sample (6) and a super-dynamic data acquisition system (8) for respectively acquiring strain signals on the incident plate (4) and the transmission plate (5), wherein the super-dynamic data acquisition system (8) comprises a strain gauge (81), a super-dynamic strain gauge (82) and an oscilloscope (83) which are respectively stuck on the incident plate (4) and the transmission plate (5), the impact plate (3) is lifted to a test height, and the incident plate (4) is lifted to place the sample (6) between the incident plate (4) and the transmission plate (5);
releasing the impact plate (3), and synchronously triggering a high-speed camera (9) and a super-dynamic data acquisition system (8) to acquire surface images of the sample (6) in the same time domain in the dynamic fracture process of the sample (6), and strain signals on the incident plate (4) and the transmission plate (5);
converting the strain signals on the incident plate (4) and the transmission plate (5) into stress loading time-course curves based on a one-dimensional stress wave theory, substituting the stress loading time-course curves into an ABAQUS software finite element sample three-dimensional numerical simulation model, and calculating stress intensity factor curves; meanwhile, calculating and analyzing the surface image of the sample (6) by adopting DIC digital image analysis software to obtain the crack breaking moment and crack propagation speed of the surface of the sample (6), and reversely deducing the breaking moment of the center crack tip of the sample (6); the dynamic fracture toughness can be obtained by bringing the fracture moment of the central crack of the sample (6) into a stress intensity factor curve.
2. The method for testing the dynamic fracture parameters of the brittle material according to claim 1, wherein: the relation between the voltage signal and the strain signal generated by the strain gauge (81) is as follows:
wherein ε (t) is a strain signal, deltaU is a measured voltage, U is a bridge supply voltage, n 1 And n 2 Gain factors, K, of the super dynamic resistance strain gauge and oscilloscope (83), respectively S Is the strain gage sensitivity coefficient.
According to the one-dimensional stress wave propagation theory, the stress loading time course curve loaded at two ends of the sample (6) can be calculated according to the following formula:
in sigma top (t) and s bot (t) is stress loading time curves of the top end and the bottom end of the sample (6), A is the cross-sectional area of the incident plate (4) and the transmission plate (5), as is the cross-sectional area of the sample (6), asi is the cross-sectional area of the triangular opening end of the sample (6), and Ep is the elastic modulus of the incident plate (4) and the transmission plate (5), epsilon i (t)、ε r (t) and ε t (t) incident wave responses respectivelyA time-varying profile, a reflected wave strain profile, and a transmitted wave strain profile.
3. The method for testing the dynamic fracture parameters of the brittle material according to claim 1, wherein: the DIC digital image analysis software is used for photographing the surface image of the sample (6), a plurality of monitoring points are arranged at equal intervals along the crack propagation path of the sample (6) to measure the strain information of the monitoring points in the horizontal x direction, strain curve inflection points are found out to determine the crack initiation time when the crack propagates to the corresponding surface crack of the sample (6),
wherein K (t) is the inflection point of the curve epsilon x For the x-direction strain,
according to the set distance between adjacent monitoring points, the crack propagation speed v can be obtained,
the crack initiation starts from the center of the sample (6) at first, and the stress wave propagates to the fracture moment t of the ith layer unit in the thickness direction of the crack front i The method comprises the following steps:
wherein t is f At the time of cracking the surface crack of the sample (6), B i V being the distance of the ith layer unit in the width direction of the crack front from the surface of the specimen (6) P Is the propagation speed of the stress wave of the sample (6).
4. A method for testing a dynamic fracture parameter of a brittle material according to claim 3, characterized in that: for the dynamic expansion toughness in the crack expansion process, according to the dynamic fracture mechanics theory, the dynamic stress intensity factor of the crack expanding at any speed under the action of dynamic load is equal to the general function of the instantaneous crack tip multiplied by the stress intensity factor of the static crack tip at the place, namely:
wherein K is I d (t) represents a dynamic stress intensity factor, K, of the crack propagating at the crack propagation velocity v at the time t I 0 (t,a j ) Representing the instantaneous length a of a motion crack j The static stress intensity factor j is the number of the monitoring point, and the approximate formula of the general function k (v) is as follows:
wherein V is R For sample (6) material rayleigh wave velocity, h is a function of elastic wave velocity:
wherein V is P And V S The wave velocities of the P wave and the S wave of the material of the sample (6) are respectively.
5. The method for testing the dynamic fracture parameters of the brittle material according to claim 1, wherein: when the crack front is cracked at different positions, the propagation time in the thickness direction influences the measurement result, so that a three-dimensional numerical simulation model of the sample under different crack propagation lengths is established to calculate a stress intensity factor curve, and then the dynamic propagation toughness in the crack breaking process can be obtained through general function correction.
6. The method for testing the dynamic fracture parameters of the brittle material according to claim 1, wherein: the three-dimensional numerical simulation model of the sample adopts 1/4 node singular units to simulate the singularities of crack tips, the unit types of the crack tip areas are C3D15 units, and the other areas are C3D20 units.
7. The method for testing the dynamic fracture parameters of the brittle material according to claim 1, wherein: the incident plate (4) and the transmission plate (5) have densities of 2800kg/m respectively 3 The incidence plate (4) is made of LY12CZ aluminum alloy with the elastic modulus of 72GPa, the Poisson ratio of 0.33 and the P wave speed of 5500m/s, and the size of the incidence plate is 300mm long, the height of 3000mm and the thickness of 30mm; the length of the transmission plate (5) is 300mm, the height is 1000mm, and the thickness is 30m.
8. The method for testing the dynamic fracture parameters of the brittle material according to claim 1, wherein: the side opening single-crack triangular speckle plate sample (6) is made of rock or concrete, the length W of the side opening single-crack triangular speckle plate sample (6) is 200mm, the height H is 325mm, the thickness B is 30mm, the depth a of a straight groove is 30mm, the width of the straight groove is 1-2mm, the side lengths L of two sides of a top triangular groove are 62.5mm respectively, and the speckle pattern layer comprises a white underlayer sprayed on the downward expansion direction area of an inverted triangular crack on the surface of the sample (6) and a plurality of black specks distributed on the white underlayer.
9. The method for testing the dynamic fracture parameters of the brittle material according to claim 1, wherein: the top of the incidence plate (4) is fixed with a brass plate with a section smaller than the section area of the incidence plate (4), and the upper end face and the lower end face of the sample (6) contacted with the incidence plate (4) and the transmission plate (5) are respectively and uniformly coated with a brass layer.
10. The electromagnetic drop impact test system for implementing the brittle material dynamic fracture parameter testing method of any of claims 1-9, characterized in that: including guide rail (1), workstation (2), still including setting up impact plate (3) in guide rail (1), be used for absorbing behind the circular telegram impact plate (3) electromagnetic plate, incident plate (4), transmission board (5), still including being used for promoting first elevating system of electromagnetic plate, be used for promoting second elevating system (7) of incident plate (4), set up in sample (6) the place ahead be used for taking sample (6) surface spot diagram layer department image high-speed camera (9), gather respectively incident plate (4) with super dynamic data acquisition system (8) of transmission board (5) strain signal, super dynamic data acquisition system (8) are including pasting respectively establish incident plate (4) with strain gauge (81) on transmission board (5), with super dynamic strain gauge (82) of strain gauge (81) voltage signal amplification, gather stress signal and oscilloscope (83) of storage, high-speed camera (9) and oscilloscope (83) are connected with workstation (2) respectively.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202310225708.6A CN116448596A (en) | 2023-03-10 | 2023-03-10 | Brittle material dynamic fracture parameter test method and electromagnetic falling plate impact test system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202310225708.6A CN116448596A (en) | 2023-03-10 | 2023-03-10 | Brittle material dynamic fracture parameter test method and electromagnetic falling plate impact test system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN116448596A true CN116448596A (en) | 2023-07-18 |
Family
ID=87126653
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202310225708.6A Pending CN116448596A (en) | 2023-03-10 | 2023-03-10 | Brittle material dynamic fracture parameter test method and electromagnetic falling plate impact test system |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN116448596A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116818567A (en) * | 2023-08-30 | 2023-09-29 | 北京建筑大学 | Dynamic impact damage mechanical property evaluation method for brittle solid material |
-
2023
- 2023-03-10 CN CN202310225708.6A patent/CN116448596A/en active Pending
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116818567A (en) * | 2023-08-30 | 2023-09-29 | 北京建筑大学 | Dynamic impact damage mechanical property evaluation method for brittle solid material |
| CN116818567B (en) * | 2023-08-30 | 2023-11-14 | 北京建筑大学 | Dynamic impact damage mechanical property evaluation method for brittle solid material |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US11041789B2 (en) | Integrated system and method for in-situ 3-axis scanning and detecting defects in object under static and cyclic testing | |
| CN106948389B (en) | Soil pressure and displacement visual two-dimensional test system for soil retaining structure | |
| CN116448596A (en) | Brittle material dynamic fracture parameter test method and electromagnetic falling plate impact test system | |
| US20210088432A1 (en) | Apparatus and method for performing an impact excitation technique | |
| JP6860256B1 (en) | Equipment for testing the impact resistance of beam column structural members | |
| CN112326786B (en) | Metal plate stress detection method based on electromagnetic ultrasonic Lamb wave S1 modal group velocity | |
| CN107102057B (en) | Magnetic field-based cable-stayed bridge cable fatigue damage monitoring system and method | |
| CN201285359Y (en) | Reliability in-situ evaluation system for thin film material on flexible electronic substrate | |
| JPH0621783B2 (en) | Fatigue / remaining life evaluation method for machine parts | |
| Shi et al. | Analysis of crack propagation in nuclear graphite using three-point bending of sandwiched specimens | |
| CN112649312A (en) | Drop hammer impact test device for realizing medium-low speed impact loading | |
| CN110987791A (en) | System and test method for determining normal bonding parameters of steel plate and concrete | |
| CN109632487A (en) | A kind of qualitative test method of interior rock internal strain field under load effect | |
| CN210892981U (en) | Surface roughness measuring device | |
| US10473552B1 (en) | Test artifact for non-destructive evaluation | |
| CN107449828B (en) | A kind of rock-fill concrete structure space compactness inspection method and evaluation method | |
| Franke et al. | Strain analysis of wood components by close range photogrammetry | |
| CN115901498A (en) | Dynamic crack arrest toughness testing device and method for brittle material | |
| JP2003207432A5 (en) | ||
| RU2596694C1 (en) | Method of measuring length of cracks and speed of its development in bent and stretched elements of structures | |
| RU2302622C2 (en) | Mode of measuring of hardness of metallic samples | |
| Scott et al. | Method for quantifying percentage wood failure in block-shear specimens by a laser scanning profilometer | |
| CN111487128A (en) | Device and method for describing compression shear damage of concrete-surrounding rock bonding surface | |
| CN111323476A (en) | Crack direction judgment method based on force magnetic effect | |
| Lilienthal et al. | Fracture process zone in crystalline rock: effect of specimen size and shape |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination |