CN111896399B - Research CFRP (carbon fiber reinforced plastic) constrained heat damage coal sample creep-impact coupling test system and method - Google Patents

Research CFRP (carbon fiber reinforced plastic) constrained heat damage coal sample creep-impact coupling test system and method Download PDF

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CN111896399B
CN111896399B CN202010777349.1A CN202010777349A CN111896399B CN 111896399 B CN111896399 B CN 111896399B CN 202010777349 A CN202010777349 A CN 202010777349A CN 111896399 B CN111896399 B CN 111896399B
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coal
creep
strain
temperature
coal sample
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CN111896399A (en
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李庆文
黄筱
董芳红
杨浩
曹行
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Liaoning University of Technology
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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
    • G01N3/32—Investigating strength properties of solid materials by application of mechanical stress by applying repeated or pulsating forces
    • G01N3/36—Investigating strength properties of solid materials by application of mechanical stress by applying repeated or pulsating forces generated by pneumatic or hydraulic means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
    • G01N1/286—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q involving mechanical work, e.g. chopping, disintegrating, compacting, homogenising
    • 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
    • G01N2203/0001—Type of application of the stress
    • G01N2203/0005—Repeated or cyclic
    • 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
    • G01N2203/003—Generation of the force
    • G01N2203/0042—Pneumatic or hydraulic means
    • G01N2203/0048—Hydraulic means
    • 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
    • G01N2203/0058—Kind of property studied
    • G01N2203/0069—Fatigue, creep, strain-stress relations or elastic constants
    • G01N2203/0071—Creep

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Abstract

The invention discloses a research CFRP (carbon fiber reinforced plastic) constrained thermal damage coal sample creep-impact coupling test system and a method, and belongs to the technical field of underground engineering and mining engineering. The method of the invention comprises the following steps: preparing a coal sample test piece, grouping the coal samples, heating the coal samples, pasting CFRP and strain gauges on the coal samples, and performing a uniaxial compression test; and (3) carrying out a creep impact test on the coal sample by adopting a creep-impact coupling test system, finally analyzing test data, obtaining the optimal CFRP wrapping layer number for resisting creep-impact disturbance according to the increment of the strength improvement of the test piece by different reinforcing layer numbers, and analyzing the influence of thermal damage on the mechanical property of the coal sample for resisting the creep-impact disturbance. The invention can provide reference for the design of the in-situ heat injection exploitation of coal underground gasification, coal underground liquefaction and coal bed gas, optimization of the roadway surrounding rock supporting scheme, and exploration of the aging rupture characteristics of deep coal rock under the action of impact load.

Description

Research CFRP (carbon fiber reinforced plastic) constrained heat damage coal sample creep-impact coupling test system and method
Technical Field
The invention relates to the technical field of underground engineering and mining engineering, in particular to a research CFRP (carbon fiber reinforced plastics) constrained heat damage coal sample creep-impact coupling test system and method.
Background
Along with the increasing depth of coal mining in China, the surrounding rock in the deep part of the coal mine is easily influenced by the environment of three-high and one-disturbance, and the phenomena of water pressure increase, ground temperature increase, coal and gas protrusion, ore pressure impact and the like appear.
Temperature is one of the important factors affecting the physical and mechanical parameters of the coal. Compared with normal temperature, the mechanical parameters of coal and rock such as fracture toughness, strength, elastic modulus and poisson ratio have temperature effect under the high temperature condition. The mining engineering related to temperature such as underground coal gasification, underground coal liquefaction, in-situ heat injection exploitation of coal bed gas and the like has the common characteristics that underground coal is in three-dimensional stress and high-temperature environment. In underground coal gasification, the gasification combustion zone is used as a heat source to generate heat action on surrounding coal and rock mass, and the rock mass is a poor conductor of heat, but the lithology of the coal seam roof and the coal seam floor can be changed under the high-temperature action after long-time action of high temperature. The CFRP has the characteristics of high temperature resistance, high strength, high modulus and the like, and is widely used in the field of reinforced concrete, so that the CFRP is adopted to reinforce the coal pillar, and the mechanical property of the coal pillar can be effectively enhanced.
In the exploitation process of the deep coal seam, the coal and the rock are easily affected by the impact such as blasting tunneling, mechanical vibration and the like, and creep deformation of the coal and the rock is more easily caused under the long-term load effect. Therefore, in consideration of the environment where the underground coal is located, the underground coal pillar is subjected to high temperature, ground stress caused by upper and lower strata and impact force caused by blasting tunneling, and a test method capable of simulating the high temperature, ground stress and impact load of the coal pillar is needed.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a creep-impact coupling test system and a creep-impact coupling test method for researching CFRP (carbon fiber reinforced plastic) constrained thermal damage coal samples, which can provide references for the design of in-situ heat injection exploitation schemes of underground coal gasification, underground coal liquefaction and coalbed methane.
In order to solve the technical problems, the invention adopts the following technical scheme:
a creep-impact coupling test system comprising: roof, balancing weight, weight tray, support steel column, hydraulic jack, load sensor, load collector, bottom plate, hoist engine, strain gauge, strain acquisition instrument and computer.
The support steel column is provided with a sliding groove, three ends of the balance weight are provided with sliding blocks, and the sliding blocks on the balance weight are in sliding connection with the sliding groove on the support steel column.
The heavy hammer is connected with the winch through a central pulley fixed on the top plate and a steel rope; the weight tray and the balance weight are connected through three small pulleys and a large pulley which are fixed on the top plate by steel ropes, and the balance weight is controlled to apply pressure to the test piece by increasing or decreasing the number of the weights on the weight tray;
the three small pulleys are distributed around the central pulley in a regular triangle shape, correspond to the three end parts of the balance weight, and are fixed at positions on the top plate, corresponding to the weight plates; the large pulley and the winch are arranged at the opposite side of the central pulley, and the central pulley, one small pulley of the three small pulleys and the large pulley are sequentially arranged at a straight line position; in order to avoid the intersection between the wires, the wire between the winch and the central pulley does not pass through the small pulley.
The strain acquisition instrument controls the strain gauge to acquire strain data in real time and transmits the data to the computer; the computer sends a control instruction to the winch by analyzing the strain data, and the winch drives the heavy hammer to apply impact disturbance to the balance hammer.
The middle part of the balance weight is a hemispherical groove, so that the test piece is convenient to be impacted uniformly.
The load sensor is arranged at the upper part of the hydraulic jack, and a test piece to be detected is placed on the load sensor; the load collector controls the load sensor to collect the load of the test piece, and transmits load data to the computer for simulating working conditions in different stages.
On the other hand, the invention also provides a method for researching the mechanical properties of the CFRP-restrained heat-damaged coal sample by adopting the creep-impact coupling test system, which comprises the following steps:
step 1: collecting and manufacturing coal samples under different heat injuries, and carrying out reinforcing treatment on the coal samples under different heat injuries to different degrees, wherein the process is as follows:
step 1.1: collecting coal blocks from a deep mine, firstly polishing the coal blocks to a standard coal sample, and ensuring the coal sample to be polished smoothly so as to ensure clean and pollution-free surface;
step 1.2: dividing the coal samples into a plurality of groups, wherein the number of each group is consistent, and heating the coal samples in different groups in a mode of increasing the temperature;
step 1.3: and (3) after standing the heated coal samples to normal temperature, respectively pasting CFRP strips with different layers on the outer surfaces of each group of coal samples for reinforcement.
The standard coal sample is any one of standard cuboid with the length-to-width ratio of 1:1:2 or standard cylinder with the height-to-diameter ratio of 2:1, and the test piece can be replaced by a concrete column test piece and a rock column test piece;
the temperature range for heating the different groups of coal samples is 100-500 ℃.
Step 2: taking a coal sample with the same CFRP layer number from each group, applying pressure to the coal sample longitudinally until the coal sample is destroyed, actually measuring to obtain a stress-strain curve of each group of coal samples and obtaining peak intensity sigma on the curve p ；
Step 3: to simulate the conditions of different stages, three values less than the peak strength sigma are chosen on the stress-strain curve p Is denoted as stress intensity sigma A 、σ B Sum sigma C ；
Step 4: attaching strain gauge to coal sample and placing the strain gauge on load sensor of creep-impact coupling test system, and obtaining stress intensity sigma in step 3 A And carrying out a step-by-step loading creep test, simultaneously applying n times of cyclic impact disturbance with the frequency f at the constant-speed creep stage of each corresponding creep stage until the coal sample is subjected to instability damage after a plurality of creep stages, and recording the creep-impact disturbance strength applied when the coal sample is subjected to instability damage, wherein the process is as follows:
step 4.1: a plurality of strain gauges are vertically and circumferentially stuck outside a CFRP strip of a coal sample, the coal sample is placed on a load sensor, and the coal sample is lifted to the bottom of a light-touch balance weight through a hydraulic jack, so that the condition that the coal sample is subjected to load to generate fine damage before a test is avoided;
step 4.2: the weights on the weight tray are reduced, so that the balance weight pressurizes the coal sample, the load collector controls the load sensor to collect the load born by the coal sample, load data are transmitted to the computer, and meanwhile, the number of the weights is adjusted to control the loading value on the coal sample at the stress sigma A ；
Step 4.3: the strain acquisition instrument controls the strain gauge to acquire strain data of the coal sample in real time, the data is transmitted to the computer, and the computer analyzes the strain data;
step 4.4: when the strain meets the constant-speed creep condition, a computer sends a control instruction to a winch, and the winch drives a heavy hammer to apply n times of cyclic impact disturbance with the frequency f to the balance hammer;
the constant-speed creep meeting condition is that dε/dt=Ω, ε is a strain value, t is time, dε/dt is a strain value in unit time, Ω is a constant;
step 4.5: and after each stage of creep is completed, loading is continued, the same time is passed after each loading, and n times of cyclic impact disturbance with the frequency f are applied in the constant-speed creep stage.
Step 5: repeating the step 4 to obtain the coal samples with the same CFRP layer number in different groups, namely under different heat damages, at the stress intensity sigma A 、σ B Sum sigma C The stress-strain diagram below and the creep-impact disturbance strength applied when the instability is broken;
step 6: repeating the steps 2 to 5 until obtaining stress-strain images of the coal samples in the same group, namely under the same heat damage degree and different CFRP layer numbers, and creep-impact disturbance strength applied when the coal samples are unstable and damaged;
step 7: and comparing the stress-strain diagram of the coal samples with different CFRP layers and the creep-impact disturbance intensity applied during the destabilization damage under the same heat damage degree and the same loading stress in the same group, obtaining the CFRP wrapping layer number with optimal creep-impact disturbance resistance according to the increment of the strength improvement of the test piece by different reinforcing layers, and analyzing the influence of the heat damage on the mechanical property of the coal samples for resisting the creep-impact disturbance.
The beneficial effects of adopting above-mentioned technical scheme to produce lie in: the method and the system provided by the invention are easy to operate, can effectively measure the mechanical properties of the CFRP-like passively constrained thermally damaged coal sample under creep-impact coupling, set different temperatures and divide the CFRP layer number for testing in a variable control mode, and obtain the CFRP wrapping layer number optimally resisting creep-impact disturbance according to the increment of the strength improvement of the test piece by different reinforcing layer numbers. The invention can provide reference for the design of the in-situ heat injection exploitation of coal underground gasification, coal underground liquefaction and coal bed gas, optimization of the roadway surrounding rock supporting scheme, and exploration of the aging rupture characteristics of deep coal rock under the action of impact load.
Drawings
FIG. 1 is a block diagram of a creep-impact coupling test system in accordance with an embodiment of the present invention;
FIG. 2 is a schematic diagram of a connection mode of a weight tray and a counterweight according to an embodiment of the invention;
FIG. 3 is a flow chart of a method for studying CFRP-like constrained heat damage to the mechanical properties of a coal sample in an embodiment of the invention;
FIG. 4 is a schematic view of a coal-like CFRP wrap and strain gauge arrangement in accordance with an embodiment of the present invention;
FIG. 5 is a top view of FIG. 4 in an embodiment of the invention;
FIG. 6 is a graph showing stress-strain curves in an embodiment of the invention;
FIG. 7 is a schematic diagram of a coal sample stress situation according to an embodiment of the present invention;
FIG. 8 is a schematic diagram of a step-wise loading creep test according to an embodiment of the present invention.
Detailed Description
The following describes in further detail the embodiments of the present invention with reference to the drawings and examples. The following examples are illustrative of the invention and are not intended to limit the scope of the invention.
In this embodiment, a creep-impact coupling test system, as shown in fig. 1, includes: the device comprises a top plate 1, a balance weight 2, a heavy hammer 3, a weight 4, a weight tray 5, a supporting steel column 6, a hydraulic jack 7, a load sensor 8, a load collector 9, a bottom plate 10, a winch 11, a strain gauge 12, a strain collector 13 and a computer 14.
The supporting steel column 6 is provided with a sliding groove 6-1, three ends of the counter weight 2 are provided with sliding blocks, and the sliding blocks on the counter weight are in sliding connection with the sliding groove 6-1 on the supporting steel column.
The heavy hammer 3 is connected with the winch 11 through a central pulley 1-1 fixed on the top plate and a steel rope; the weight tray 5 and the balance weight 2 are connected through three small pulleys 1-2 and big pulleys 1-3 fixed on the top plate by steel ropes, the connection condition is shown in figure 2, and the balance weight 2 is controlled to apply pressure to a test piece by increasing or decreasing the number of weights 4 on the weight tray 5;
the three small pulleys 1-2 are distributed around the central pulley 1-1 in a regular triangle, and correspond to the three ends of the balance weight 2, and the large pulleys 1-3 are fixed on the top plate at positions corresponding to the weight tray 5, as shown in figure 2; the big pulley 1-3 and the hoist 11 are arranged at the opposite side of the central pulley 1-1, and the central pulley 1-1, one small pulley 1-2 of the three small pulleys and the big pulley 1-3 are sequentially arranged at a straight line position as shown in figure 2; to avoid the intersection between the wires, the wire between the hoist 11 and the center pulley 1-1 on the plane does not pass through the small pulley 1-2.
The strain acquisition instrument 13 controls the strain gauge 12 to acquire strain data in real time and transmits the data to the computer 14; the computer 14 sends a control command to the winch 11 by analyzing the strain data, and the winch 11 drives the heavy hammer 3 to apply impact disturbance to the balance weight 2.
The middle part of the balance weight 2 is provided with a hemispherical groove, so that a test piece is convenient to be impacted uniformly.
The load sensor 8 is arranged at the upper part of the hydraulic jack 7, and a test piece to be detected is placed on the load sensor 8; the load collector 9 controls the load sensor 8 to collect the load born by the test piece, and transmits load data to the computer 14 for simulating working conditions at different stages.
On the other hand, the invention also provides a method for researching the mechanical properties of the CFRP-restrained heat-damaged coal sample by adopting the creep-impact coupling test system, wherein the flow is shown in the figure 3, and the method comprises the following steps:
step 1: collecting and manufacturing coal samples under different heat injuries, and carrying out reinforcing treatment on the coal samples under different heat injuries to different degrees, wherein the process is as follows:
step 1.1: collecting coal blocks from a deep mine, firstly polishing the coal blocks to a standard coal sample, and ensuring the coal sample to be polished smoothly so as to ensure clean and pollution-free surface;
in the embodiment, the coal briquette is processed into a standard cylinder with the diameter of 50mm multiplied by 100mm (diameter multiplied by height), the method is specifically implemented in such a way that the protruding part on the surface of the coal sample test piece is polished and leveled by an angle grinder, the floating ash on the surface is removed by sand paper, the protruding part on the surface is flattened by a cutting machine, the corner is polished into an arc shape, and the coal sample needs to be polished smoothly and has clean and pollution-free surface.
Step 1.2: dividing the coal samples into a plurality of groups, wherein the number of each group is consistent, and heating the coal samples in different groups in a mode of increasing the temperature;
in this embodiment, coal samples with similar densities are selected for grouping, a high-temperature reinforcing group, a high-temperature non-reinforcing group, a normal-temperature reinforcing group and a normal-temperature non-reinforcing group are set, a plurality of high-temperature reinforcing groups and high-temperature non-reinforcing groups can be set according to temperature, a high-temperature reinforcing group and a normal-temperature reinforcing group can be set according to the number of layers of the strip, and at least 7 coal samples are set in each group. Heating the coal samples in the high-temperature reinforced group and the high-temperature unreinforced group by adopting a resistance furnace, wherein the heating temperature can be 100 ℃, 200 ℃, 300 ℃, 400 ℃ and 500 ℃. And (3) putting the coal sample into the furnace according to the temperature components, starting a power supply, adjusting the temperature to be controlled to a corresponding temperature value, keeping the temperature for 4 hours after the temperature is raised to the set temperature, and naturally cooling to the room temperature in the furnace.
Step 1.3: and (3) after standing the heated coal samples to normal temperature, respectively pasting CFRP strips with different layers on the outer surfaces of each group of coal samples for reinforcement.
In the embodiment, glue is uniformly smeared on two sides of the CFRP strip by using a hairbrush, and the CFRP strip is compacted and wrapped on the whole side face of the coal sample, wherein the lap joint length of the CFRP is 50mm.
Step 2: taking a coal sample with the same CFRP layer number from each group, applying pressure to the coal sample longitudinally until the coal sample is destroyed, actually measuring to obtain a stress-strain curve of each group of coal samples and obtaining peak intensity sigma on the curve p ；
In this example, one coal sample from all groups was taken and pressed on a universal tester at 0.2mm/s until destroyed. The stress-strain curve of the test piece shown in FIG. 6 is obtained by actual measurement and the peak strength sigma is obtained p 。
Step 3: to simulate the conditions of different stages, three values less than the peak strength sigma are chosen on the stress-strain curve p Is denoted as stress intensity sigma A 、σ B Sum sigma C As shown in fig. 6;
in the present embodiment, σ A ＝50％σ p ，σ B ＝70％σ p ，σ C ＝90％σ p And correspondingly converting the selected stress magnitude and creep stress magnitude of each stage with the weight of the weight. The conversion is determined by the following formula:
mg＝σ×πr 2
wherein m is the weight mass corresponding to the loading stress, sigma is the loading stress, pi is 3.14, the radius r is 0.025m, and g is 9.8m/s 2 。
Step 4: attaching strain gauge to coal sample and placing the strain gauge on load sensor of creep-impact coupling test system, and obtaining stress intensity sigma in step 3 A And carrying out a step-by-step loading creep test, simultaneously applying n times of cyclic impact disturbance with the frequency f at the constant-speed creep stage of each corresponding creep stage until the coal sample is subjected to instability damage after a plurality of creep stages, and recording the creep-impact disturbance strength applied when the coal sample is subjected to instability damage, wherein the process is as follows:
step 4.1: a plurality of strain gauges are vertically and circumferentially stuck outside a CFRP strip of a coal sample, the coal sample is placed on a load sensor, and the coal sample is lifted to the bottom of a light-touch balance weight through a hydraulic jack, so that the condition that the coal sample is subjected to load to generate fine damage before a test is avoided;
in the embodiment, 12 strain gages are arranged on each coal sample in total, 3 strain gages are uniformly arranged on the periphery of the side face of each coal sample in the height direction, the annular strain gages are used for detecting CFRP restraint force and horizontal fracture positions, and axial stress and axial fracture positions are detected vertically. The strain gauge is evenly distributed around the side face of the coal sample, the center position of the strain gauge in the middle is at half of the height of the coal sample, the center height difference of each strain gauge is 30mm, and the specific arrangement of the strain gauge is shown in fig. 4 and 5.
Step 4.2: the weights on the weight tray are reduced, so that the balance weight pressurizes the coal sample, the load collector controls the load sensor to collect the load born by the coal sample, load data are transmitted to the computer, and meanwhile, the number of the weights is adjusted to control the loading value on the coal sample at the stress sigma A ；
Step 4.3: the strain acquisition instrument controls the strain gauge to acquire strain data of the coal sample in real time, the data is transmitted to the computer, and the computer analyzes the strain data;
step 4.4: when the strain meets the constant-speed creep condition, a computer sends a control instruction to a winch, and the winch drives a heavy hammer to apply n times of cyclic impact disturbance with the frequency f to the balance hammer;
the constant-speed creep meeting condition is that dε/dt=Ω, ε is a strain value, t is time, dε/dt is a strain value in unit time, Ω is a constant;
step 4.5: loading continues after each stage of creep is completed, and n times of cyclic impact disturbance with frequency f are applied in the constant-speed creep stage after the same time passes after each stage of loading, as shown in fig. 8.
In this embodiment, each stage is performed for a time t 2 At the same time, a winch is used for lifting the bottom of the heavy hammer to be 0.5m away from the bottom of the groove of the counter weight, and t is the corresponding creep stage of each stage 1 N times of cyclic impact disturbance with the frequency f are applied at the moment until the coal sample is subjected to destabilization and damage through about 4 to 5 creep stages.
Step 5: repeating the step 4 to obtain the coal samples with the same CFRP layer number in different groups, namely under different heat damages, at the stress intensity sigma A 、σ B Sum sigma C The stress-strain diagram below and the creep-impact disturbance strength applied when the instability is broken;
step 6: repeating the steps 2 to 5 until obtaining stress-strain images of the coal samples in the same group, namely under the same heat damage degree and different CFRP layer numbers, and creep-impact disturbance strength applied when the coal samples are unstable and damaged;
as shown in FIG. 7, the coal sample is subjected to a total of three forces, σ 1 Is the ground stress, sigma Side of the vehicle Circumferential restraining force, σ, provided for CFRP layer d Is an impact load. The impact energy of the drop of the weight is calculated as follows:
E＝m 1 gh
wherein the weight mass m 1 10kg and h of 0.5m.
Step 7: and comparing the stress-strain diagram of the coal samples with different CFRP layers and the creep-impact disturbance intensity applied during the destabilization damage under the same heat damage degree and the same loading stress in the same group, obtaining the CFRP wrapping layer number with optimal creep-impact disturbance resistance according to the increment of the strength improvement of the test piece by different reinforcing layers, and analyzing the influence of the heat damage on the mechanical property of the coal samples for resisting the creep-impact disturbance.

Claims (1)

1. A method for researching the mechanical properties of CFRP-like constrained heat damage coal samples is characterized in that,
a creep-impact coupling test system is adopted to realize a method for researching the mechanical properties of CFRP-like constrained heat damage coal samples;
the system comprises: the device comprises a top plate, a balance weight, a heavy hammer, a weight tray, a supporting steel column, a hydraulic jack, a load sensor, a load collector, a bottom plate, a winch, a strain gauge, a strain collector and a computer;
the support steel column is provided with a chute, three ends of the counter weight are provided with sliding blocks, and the sliding blocks on the counter weight are in sliding connection with the chute on the support steel column;
the heavy hammer is connected with the winch through a central pulley fixed on the top plate and a steel rope; the weight tray and the balance weight are connected through three small pulleys and a large pulley which are fixed on the top plate by steel ropes, and the balance weight is controlled to apply pressure to the test piece by increasing or decreasing the number of the weights on the weight tray;
the three small pulleys are distributed around the central pulley in a regular triangle shape, correspond to the three end parts of the balance weight, and are fixed at positions on the top plate, corresponding to the weight plates; the large pulley and the winch are arranged at the opposite side of the central pulley, and the central pulley, one small pulley of the three small pulleys and the large pulley are sequentially arranged at a straight line position; in order to avoid the intersection between the wires, the connecting wire between the winch and the central pulley on the plane does not pass through the small pulley;
the strain acquisition instrument controls the strain gauge to acquire strain data in real time and transmits the data to the computer; the computer sends a control instruction to the winch by analyzing the strain data, and the winch drives the heavy hammer to apply impact disturbance to the balance hammer;
the middle part of the balance weight is provided with a hemispherical groove, so that a test piece is convenient to be impacted uniformly;
the load sensor is arranged at the upper part of the hydraulic jack, and a test piece to be detected is placed on the load sensor; the load collector controls the load sensor to collect the load of the test piece, and transmits load data to the computer for simulating working conditions at different stages;
the method comprises the following steps:
step 1: collecting and manufacturing coal samples under different heat injuries, and carrying out reinforcing treatment on the coal samples under different heat injuries to different degrees, wherein the process of the step 1 is as follows:
step 1.1: collecting coal blocks from a deep mine, firstly polishing the coal blocks to a standard coal sample, wherein the coal sample is required to be polished smoothly, and the clean and pollution-free surface is ensured, and the standard coal sample is a standard cuboid with the length-to-width ratio of 1:1:2;
step 1.2: dividing coal samples into a plurality of groups, heating the coal samples of different groups in a mode of increasing temperature, wherein the coal samples of different groups are selected to be grouped, a high-temperature reinforcing group, a high-temperature non-reinforcing group, a normal-temperature reinforcing group and a normal-temperature non-reinforcing group are arranged, a plurality of high-temperature reinforcing groups and high-temperature non-reinforcing groups are arranged according to temperature, a high-temperature reinforcing group and a normal-temperature reinforcing group are arranged according to the number of layers of strips, at least 7 coal samples in each group are heated, the coal samples in the high-temperature reinforcing group and the high-temperature non-reinforcing group are taken for heating treatment, a test piece is heated by adopting a resistance furnace, a power supply is started after the coal samples are placed into the furnace according to the temperature groups, the temperature is regulated to be controlled to a corresponding temperature value, the temperature is kept constant for 4 hours after the temperature is increased to the set temperature, the furnace is naturally cooled to the room temperature, and the heating temperature range is 100-500 ℃;
step 1.3: standing the heated coal samples to normal temperature, and respectively pasting CFRP strips with different layers on the outer surfaces of each group of coal samples for reinforcement;
step 2: taking a coal sample with the same CFRP layer number from each group, applying pressure to the coal sample longitudinally until the coal sample is destroyed, actually measuring to obtain a stress-strain curve of each group of coal samples and obtaining peak intensity sigma on the curve p ；
Step 3: to simulate the conditions of different stages, three values less than the peak strength sigma are chosen on the stress-strain curve p Is denoted as stress intensity sigma A 、σ B Sum sigma C Wherein σ is A ＝50％σ p ，σ B ＝70％σ p ，σ C ＝90％σ p For selected stress magnitude and eachThe level creep stress and the weight are correspondingly converted, and the conversion is determined by the following formula:
mg＝σ×πr 2
wherein m is the weight mass corresponding to the loading stress, sigma is the loading stress, pi is 3.14, the radius r is 0.025m, and g is 9.8m/s 2 ；
Step 4: attaching strain gauge to coal sample and placing the strain gauge on load sensor of creep-impact coupling test system, and obtaining stress intensity sigma in step 3 A Step-by-step loading creep test is carried out, n times of cyclic impact disturbance with the frequency f are applied at the constant-speed creep stage of each corresponding creep stage until the coal sample is subjected to instability damage after a plurality of creep stages, and the creep-impact disturbance strength applied when the coal sample is subjected to instability damage is recorded;
the process of the step 4 is as follows:
step 4.1: a plurality of strain gauges are vertically and circumferentially stuck outside a CFRP strip of a coal sample, the coal sample is placed on a load sensor, and the coal sample is lifted to the bottom of a light-touch balance weight through a hydraulic jack, so that the condition that the coal sample is subjected to load to generate fine damage before a test is avoided;
step 4.2: the weights on the weight tray are reduced, so that the balance weight pressurizes the coal sample, the load collector controls the load sensor to collect the load born by the coal sample, load data are transmitted to the computer, and meanwhile, the number of the weights is adjusted to control the loading value on the coal sample at the stress sigma A ；
Step 4.3: the strain acquisition instrument controls the strain gauge to acquire strain data of the coal sample in real time, the data is transmitted to the computer, and the computer analyzes the strain data;
step 4.4: when the strain meets the constant-speed creep condition, a computer sends a control instruction to a winch, and the winch drives a heavy hammer to apply n times of cyclic impact disturbance with the frequency f to the balance hammer, wherein the constant-speed creep condition is met, dε/dt=Ω, ε is a strain value, t is time, dε/dt is a strain value in unit time, Ω is a constant;
step 4.5: continuously loading after each stage of creep is completed, applying n times of cyclic impact disturbance with the frequency f at the constant-speed creep stage after the same time is passed after each stage of creep is loaded;
step 5: repeating the step 4 to obtain the coal samples with the same CFRP layer number in different groups, namely under different heat damages, at the stress intensity sigma A 、σ B Sum sigma C The stress-strain diagram below and the creep-impact disturbance strength applied when the instability is broken;
step 6: repeating the steps 2 to 5 until obtaining stress-strain images of the coal samples in the same group, namely under the same heat damage degree and different CFRP layer numbers, and creep-impact disturbance strength applied when the coal samples are unstable and damaged;
step 7: and comparing the stress-strain diagram of the coal samples with different CFRP layers and the creep-impact disturbance intensity applied during the destabilization damage under the same heat damage degree and the same loading stress in the same group, obtaining the CFRP wrapping layer number with optimal creep-impact disturbance resistance according to the increment of the strength improvement of the test piece by different reinforcing layers, and analyzing the influence of the heat damage on the mechanical property of the coal samples for resisting the creep-impact disturbance.
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