CN104316390B - Method for measuring brittle fracture impact remission of descending branch of brittle test piece - Google Patents

Abstract

A brittle test piece descending section measurement and brittle impact mitigation method, when it is detected that the test piece enters the critical state of brittle fracture in the descending section, reverse loading immediately, so that the loading chamber originally connected to the high-pressure oil inlet pipe is switched to the low-pressure oil return pipe, allowing the pressure Rapid attenuation; at the same time, the original oil return chamber becomes a loading chamber. On the one hand, the oil in the chamber drags the piston to prevent its inertia from sliding down; And the recovery of the elastic deformation of the loading equipment is also offset by the reverse recovery of the piston rod until the pressure of the original loading chamber is less than the bearing capacity of the specimen to regain balance and restore normal control; this cycle until the test specimen is met to stop the test. The invention does not need to increase mechanical structure and control system hardware, thus saving cost. No additional damping force is superimposed on the bearing capacity of the specimen, which does not affect the measurement accuracy and the difficulty of data processing. Real-time moderate response to brittle fractures of any tonnage.

Description

Measurement of the descending section of brittle specimens and brittle fracture impact relief method

technical field

The invention relates to a method for measuring the descending section of a brittle test piece and brittle fracture impact mitigation, and belongs to the technical field of large-scale civil engineering structure tests.

Background technique

In the field of large-scale civil engineering structural test technology, the measurement of the descending section of brittle specimens such as plain concrete columns is a difficult problem in the academic circle, and the impact damage caused by the instantaneous energy release during slowing down of brittle failure is also a difficult problem in the academic circle.

The control system and control algorithm currently used cannot predict the state of the test piece. When the brittle test piece enters the descending section, due to the extremely fast damage of the test piece, the system has not responded to the bearing capacity that has dropped at the previous moment. bearing capacity has become lower. Because the unloading speed of the system to the load is less than the decline speed of the bearing capacity, the unloading control adjustment is later than the bearing capacity decline, and the unloading adjustment of the system always lags behind the change of the bearing capacity state of the specimen. Coupled with the superimposed effect of the instantaneous release of elastic energy stored in the loading device, the specimen collapsed instantly.

One of the commonly used solutions at present is to increase the flow rate and shorten the system delay, but this requires more powerful motors and oil pumps, thicker oil pipes, more sophisticated components and higher costs.

Another method is to connect the damping device in parallel with the test piece, which firstly increases the installation, measurement work and cost; secondly, due to the different tonnage of the brittle break point of different test pieces, the damping device can only play a protective role within the range of its own bearing capacity ; Due to a certain degree of nonlinearity in the damper, the difficulty of data processing is increased, and the accuracy of measurement results is also reduced.

Contents of the invention

The object of the present invention is to provide a brittle test piece descending section measurement and brittle fracture impact mitigation method, the method and device not only overcome the limitations of traditional measurement methods, but also reduce the difficulty of later data processing.

In order to achieve the above object, the technical solution adopted in the present invention is a method for measuring the descending section of a brittle test piece and a brittle fracture impact mitigation method. The state of the brittle test piece is monitored in real time by a force sensor and a displacement sensor, and the test piece is arranged on the sensor and between the ground.

When it is detected that the test piece enters the critical state of brittle fracture in the descending section, that is, under the condition of displacement control, the bearing capacity of the test piece decreases, the displacement deformation increases and the displacement control precision is out of tolerance, at this time, reverse the load immediately, so that the original connection of the high-pressure oil inlet pipe The loading chamber is switched to the low-pressure oil return pipe, so that the pressure quickly decays; at the same time, the original oil return chamber becomes a loading chamber, and the oil in the chamber on the one hand drags the piston to prevent its inertia from sliding down, and on the other hand accelerates the unloading of the original loading chamber. At the same time, the release of the elastic energy stored in the loading device and the recovery of the elastic deformation of the loading device are also offset by the reverse recovery of the piston rod until the pressure of the original loading chamber is less than the bearing capacity of the test piece and regains balance and restores normal control; so Cycle until the test piece meets the test stop condition: that is, the bearing capacity F ₂ is less than the preset test stop force threshold P _F or the specimen deformation is greater than the preset test stop displacement threshold _PL .

The basis of the invention for detecting the brittle fracture critical state of the test piece entering the descending section is: when the position control command is constant, the bearing capacity of the test piece decreases, the displacement deformation of the test piece increases, and the error between the target displacement and the displacement command exceeds the allowable error of the control accuracy.

Compared with the prior art, the present invention has the following beneficial effects.

1. There is no need to increase the mechanical structure and control system hardware, saving costs.

2. No additional damping force is superimposed on the bearing capacity of the specimen, which does not affect the measurement accuracy and the difficulty of data processing.

3. Real-time and moderate response to brittle fracture of any tonnage.

Description of drawings

Fig. 1 is a flow chart of the method of the present invention.

Fig. 2 is the loading diagram of the embodiment of the device.

Fig. 3 is the unloading diagram of the embodiment of the device.

In the figure: 1. High-pressure oil inlet pipe, 2. Electro-hydraulic servo valve, 3. Upper chamber oil pipe, 4. Oil cylinder, 5. Upper chamber, 6. Piston, 7. Piston rod, 8. Lower chamber, 9. Force sensor, 10. Displacement sensor, 11. Lower cavity oil pipe, 12. Low pressure oil return pipe, 13. Controller, 14. Test piece.

ΔL _L is the displacement loading (piston, piston rod descending) increase;

ΔU _L is the displacement unloading (piston, piston rod descending) increase;

PF is the preset test stop condition _force threshold;

P _L is the displacement threshold of the preset test stop condition;

δ _L is the system control precision.

detailed description

The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments.

As shown in Figure 1-2, a method for measuring the falling section of a brittle test piece and brittle fracture impact mitigation, the state of the brittle test piece is monitored in real time by a force sensor 9 and a displacement sensor 10, and the test piece 14 is arranged on the sensor 9 and the ground.

When it is detected that the test piece 14 enters the critical state of brittle fracture in the descending section, that is, under the condition of displacement control, the bearing capacity of the test piece decreases, the displacement deformation increases, and the displacement control precision is out of tolerance, at this time, the reverse load is applied immediately, so that the original connection high pressure enters the critical state. The loading chamber of the oil pipe 1 is switched to the low-pressure oil return pipe 12, so that the pressure quickly decays; at the same time, the original oil return chamber becomes a loading chamber, and the oil in the chamber holds the piston 6 on the one hand to prevent its inertia from sliding down, and on the other hand accelerates the original oil return chamber. The pressure relief of the loading chamber, the release of the elastic energy stored in the loading device and the recovery of the elastic deformation of the loading device are also offset by the reverse recovery of the piston rod 7, until the pressure in the original loading chamber is lower than the bearing capacity of the test piece 14 to achieve balance And return to normal control; so cycle until the test piece meets the test stop condition: that is, the bearing capacity _{F 2} is less than the preset test stop force threshold PF or the deformation of the test piece is greater than the preset test stop displacement threshold _PL .

The basis of the invention for detecting the brittle fracture critical state of the test piece entering the descending section is: when the position control command is constant, the bearing capacity of the test piece decreases, the displacement deformation of the test piece increases, and the error between the target displacement and the displacement command exceeds the allowable error of the control accuracy.

In Fig. 2-3, the controller 13 collects the data of the displacement sensor 10 and the force sensor 9 in real time in the position control mode, and judges the brittle fracture state of the specimen according to the decrease of the bearing capacity, the increase of the displacement deformation and the deviation of the displacement control precision. Once the controller 13 determines that the test piece is currently in a brittle fracture state, it controls the electro-hydraulic servo valve 2 to perform a reversing operation, connects the high-pressure oil inlet pipe 1 to the lower chamber oil pipe 11, injects high-pressure oil into the lower chamber 8 of the oil cylinder 4, and simultaneously The low-pressure oil return pipe 12 is connected to the upper chamber oil pipe 3, so that the oil in the upper chamber 5 of the oil cylinder 4 is relieved and flowed back, so that the piston 6 drives the piston rod 7 to move in reverse to unload the test piece and release the elastic energy stored in the equipment until After the specimen is out of the brittle fracture state, it continues to be loaded normally.

ΔL _L is the artificially set increment of each displacement loading command, that is, the displacement increment of the oil cylinder moving downward, that is to say, the displacement command increases ΔL _L on the original basis each time.

ΔU _L is the increment of each displacement unloading command artificially set, that is, the displacement increment of the oil cylinder moving upwards, that is to say, the displacement command is reduced by ΔU _L on the original basis each time.

_PL is the displacement threshold of the preset test stop condition set artificially, that is to say, when the deformation of the specimen is greater than _PL , the deformation of the specimen meets the test requirements.

δ _L is the artificially set system control precision, and it is also the error band of the control system. When the absolute value of the difference between the two measured values is greater than δ _L , it means that the system is currently out of control.

S1 first measures the bearing capacity F of the current specimen and assigns it to F ₁ , measures the displacement L and assigns it to L ₁ ;

S2 reads the current displacement control loading command (hereinafter referred to as the displacement command) C _L , and C _L is the operating value carried by the controller specimen to currently control the action of the electro-hydraulic servo valve;

S3 measures the current force F and assigns it to F ₂ , measures the displacement L and assigns it to L ₂ ;

The current force or displacement meets the stop condition, that is, the _force drops below the threshold PF or the deformation reaches above the threshold _PL , and the test ends;

S4 Otherwise, it is judged whether the specimen is in a critical state of brittle fracture;

S5.1 If yes, assign the current force and displacement to F ₁ and L ₁ respectively, and then subtract the displacement unloading increment from the current displacement command, that is, lift the piston and piston rod in the opposite direction based on the current position. At this time, the controller controls the servo valve to change direction, the original loading chamber (upper chamber) is switched from the high-pressure oil inlet pipe to the low-pressure oil return pipe, and at the same time, the original unloading chamber (lower chamber) is changed from the loading chamber to the high-pressure oil inlet pipe to realize the upper chamber Rapid unloading and release of elastic energy;

S5.2 If it is not in the critical state of brittle fracture, assign the current force and displacement to F ₁ and L ₁ respectively, then increase the displacement loading increment on the basis of the original command, and continue the test;

S6 measures the current force F, assigns it to F ₂ , measures the displacement L, assigns it to L ₂ , and continues this cycle;

S7 until the end of the test.

Claims (3)

1. a brittle test piece descending section measurement and brittle fracture impact mitigation method, is characterized in that: the state of described brittle test piece is carried out real-time monitoring by force sensor (9), displacement sensor (10), and test piece (14) is set between the force sensor (9) and the ground; When it is detected that the test piece (14) enters the critical state of brittle fracture in the descending section, that is, under the condition of displacement control, the bearing capacity of the test piece decreases, the displacement deformation increases and the displacement control accuracy is out of tolerance, at this time, the reverse load is applied immediately to make the original connection The loading chamber of the high-pressure oil inlet pipe (1) is switched to the low-pressure oil return pipe (12), so that the pressure quickly decays; at the same time, the original oil return chamber becomes a loading chamber, and the oil in the chamber drags the piston (6) on the one hand to prevent its Inertial slide, on the other hand, speeds up the pressure relief of the original loading chamber. At the same time, the elastic energy stored in the loading device is released and the recovery of the elastic deformation of the loading device is also offset by the reverse recovery of the piston rod (7), until the pressure of the original loading chamber The bearing capacity less than the test piece (14) regains balance and restores normal control; this cycle until the test stop condition is met, that is, the test piece bearing capacity F is less _than the preset test stop force threshold P _F or the deformation of the test piece is greater than the preset test stop displacement threshold _PL ; The basis for detecting the brittle fracture critical state of the test piece entering the descending section is that when the position control command is constant, the bearing capacity of the test piece (14) decreases, the displacement deformation of the test piece increases, and the error between the target displacement and the displacement command exceeds the allowable error of the control accuracy. 2. A kind of brittle test piece descending section measurement and brittle fracture impact mitigation method according to claim 1, is characterized in that: controller (13) collects displacement sensor (10) and force sensor (9) in real time under position control mode ) data, and judge the brittle fracture state of the specimen according to the decrease of the bearing capacity, the increase of the displacement deformation and the deviation of the displacement control precision. Once the controller (13) determines that the current specimen is in the brittle fracture state, it controls the electro-hydraulic servo valve ( 2) Execute the reversing operation, connect the high-pressure oil inlet pipe (1) to the lower chamber oil pipe (11), inject high-pressure oil into the lower chamber (8) of the oil cylinder (4), and connect the low-pressure oil return pipe (12) to the upper chamber The oil pipe (3) allows the oil in the upper chamber (5) of the oil cylinder (4) to release pressure and flow back, so that the piston (6) drives the piston rod (7) to move in reverse to unload the test piece and release the elastic energy stored in the equipment , and continue to load normally until the specimen is out of the brittle fracture state; ΔL _L is the artificially set increment of each displacement loading command, that is, the displacement increment of the oil cylinder moving downward, that is to say, the displacement command increases ΔL _L on the original basis each time; ΔU _L is the increment of each displacement unloading command artificially set, that is, the displacement increment of the oil cylinder moving upwards, that is to say, the displacement command reduces ΔU _L on the original basis each time; _PL is the artificially set preset test stop displacement threshold, that is to say, when the deformation of the specimen is greater than _PL , the deformation of the specimen meets the test requirements; δ _L is the artificially set system control precision, and it is also the error band of the control system. When the absolute value of the difference between the two measured values is greater than δ _L , it means that the system is currently out of control. 3. a kind of brittle test piece descending section measurement and brittle fracture impact mitigation method according to claim 1, is characterized in that: the implementation process of this method is as follows, S1 first measures the bearing capacity F of the current specimen and assigns it to F ₁ , measures the displacement L and assigns it to L ₁ ; S2 reads the current displacement control loading command C _L , where C _L is the operating value carried by the controller specimen to control the action of the electro-hydraulic servo valve; S3 measures the current force F and assigns it to F ₂ , measures the displacement L and assigns it to L ₂ ; The current force or displacement meets the stop condition, that is, the _force drops below the threshold PF or the deformation reaches above the threshold _PL , and the test ends; S4 Otherwise, it is judged whether the specimen is in a critical state of brittle fracture; S5.1 If yes, assign the current force and displacement to F ₁ and L ₁ respectively, and then subtract the displacement unloading increment from the current displacement command, that is, lift the piston and piston rod in the opposite direction based on the current position; at this time , the controller controls the reversing of the servo valve, the original loading chamber is switched from the high-pressure oil inlet pipe to the low-pressure oil return pipe, and at the same time the original unloading chamber is changed from the loading chamber to the high-pressure oil inlet pipe, realizing the rapid unloading of the upper chamber and the release of elastic energy; S5.2 If it is not in the critical state of brittle fracture, assign the current force and displacement to F ₁ and L ₁ respectively, then increase the displacement loading increment on the basis of the original command, and continue the test; S6 measures the current force F, assigns it to F ₂ , measures the displacement L, assigns it to L ₂ , and continues this cycle; S7 until the end of the test.