CN109738307B - Multi-sample tension-compression creep test method - Google Patents
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Abstract
The invention provides a multi-sample tension-compression creep test method, which uses a multi-sample tension-compression creep test device to carry out a test, and arranges a sealed cavity for each sample, wherein each sealed cavity comprises two sub-cavities, and tensile or compressive stress can be provided for the corresponding sample by changing the oil pressure difference in the two sub-cavities, so that the stress magnitude and the stress time of each sample can be kept relatively independent. The invention utilizes the non-contact digital image acquisition system to measure the high-temperature deformation of the sample, avoids the problem of low measurement precision caused by different expansion coefficients of materials and external factors of the traditional indirect measurement method, and has smooth and accurate measurement data and good repeatability.
Description
Technical Field
The invention relates to a creep aging behavior detection technology of a metal material, in particular to a multi-sample tension-compression creep test method which can also be used for tension and compression relaxation aging tests.
Background
With the rapid development of aerospace industry, large-scale integral wall plate members with the advantages of high structural integrity, high strength, good sealing performance and the like are increasingly used in important structures of large civil aircrafts, military aircrafts and new generation carrier rockets. Creep age forming is a new sheet forming method developed for manufacturing large-scale integral components with high precision and high performance. The main premise of creep aging high-quality manufacturing of the large-scale component is to accurately detect the creep aging deformation and the performance evolution law of the material through a unidirectional tension or compression test. Tensile or compression tests are currently generally performed on high temperature creep machines. The creep testing machine comprises a frame, a load control system, a strain measurement system, a temperature control system and the like.
The existing tensile or compressive creep test operating procedures generally include the following procedures: 1. connecting the sample with a clamp, fixing a stretching device on convex ridges at two ends of a sample gauge length, connecting a grating displacement sensor, and measuring the strain of the sample in the test process; 2. setting technological parameters, and setting a specific temperature load path on a control computer; 3. and (4) creep aging test, wherein the creep machine keeps constant temperature and constant load for a long time to ensure the creep aging formability of the test sample.
However, the above-mentioned conventional tensile or compressive creep test has the following disadvantages: 1. because the creep aging characteristic basic test needs to systematically research the influence rules of process parameters such as different temperatures, stresses, time and the like on the creep deformation and the mechanical property of a material, a large number of tests must be carried out, and the conventional creep testing machine can only test one sample at each test, so that the test under a certain process condition (the process condition can comprise the parameters such as the temperature, the stress, the time and the like) can only be provided for the single sample at each time, but the creep aging forming formation rule of the material needs to be systematically mastered, and the tests under the process conditions such as the different temperatures, the stresses, the time and the like need to be carried out, so the creep test efficiency of the conventional single sample is very low. The rated load of the current creep machine is usually between 50 and 100KN (kilonewtons) or larger, the maximum load required by the current single sample creep test does not exceed 8KN, only a small section in front of the load stroke range of the creep testing machine is utilized, the load stroke of the creep testing machine is not fully utilized, and a larger utilization space is provided. 2. The existing creep machine mostly adopts a displacement sensor to measure the high-temperature deformation of a sample, and factors such as a clamping gap of the sample, an external environment and the like also easily cause the reading of the sensor to change, so that the system judgment error is caused, the test measurement precision is reduced, and the creep machine is specifically embodied as follows: the existing creep machine generally adopts two sets of extension rods to be respectively fixed on the upper and lower end ridges of a sample, a displacement sensor measures the deformation of the sample by measuring the relative deformation of the two sets of extension rods, wherein the extension rod part is positioned in a high-temperature box, the displacement sensor is arranged outside the high-temperature box, even if the precision of the displacement sensor is higher, the accuracy of the obtained sample deformation result is not high due to different thermal expansion coefficients of materials of the extension rods and the sample, meanwhile, the displacement sensor has high sensitivity and is exposed in the environment, and the creep machine is easily interfered by field environment factors, influences the accuracy of the experiment and even fails the experiment. 3. The conventional creep machine is heated by a resistance wire, so that the time required for heating a sample to a target temperature is long, and the test progress and efficiency are influenced.
Chinese patent 201810011860.3 discloses a high flux creep testing arrangement load loading system and compression creep equipment, including drive assembly, connect on drive assembly and be used for connecting a plurality of test sample's supporting platform and connect in the supporting platform top and can supply with the hydraulic assembly of test sample butt, drive assembly drive supporting platform reciprocates, and hydraulic assembly includes confined pneumatic cylinder and a plurality of hydraulic piston that all communicate in its pneumatic cylinder, and the diameter of each hydraulic piston is equal the same, and its hydraulic piston one end is connected in the pneumatic cylinder, the other end can supply the butt to be in test sample's top. Although the scheme can be used for simultaneously carrying out the compression creep test on a plurality of test samples, because a plurality of samples are loaded under a plurality of hydraulic pistons driven by the same hydraulic cylinder, and the plurality of samples can only be tested under the same stress condition, the multi-position synchronous test can only be realized, and compared with the creep test machine with a single sample, the creep test machine only changes the number of single tests, which can not really achieve mutual independence among the samples, therefore, the prior art still needs a scheme which can enable the plurality of samples to be independent from each other in stress, time and temperature and not to influence or be connected with each other, so as to improve the efficiency and effect of the creep test.
Disclosure of Invention
The invention aims to provide a multi-sample tension-compression creep test device to solve the problems in the background technology.
The utility model provides a many samples draw and press creep test device, includes frame, high-temperature cabinet, many sample fixing device, strain measurement device, heating device, the high-temperature cabinet sets up in the frame, many sample fixing device and heating device set up in the high-temperature cabinet, and many sample fixing device are used for the clamping sample and provide the stress that makes the sample take place to draw and press creep (tensile creep or compressive creep), heating device is used for heating or keeping warm the sample, strain measurement device is used for taking place to draw the dependent variable of pressing creep to the sample and carries out real-time measurement.
The multi-sample fixing device comprises a first supporting beam and a second supporting beam which are arranged in parallel, a plurality of (a plurality of fingers are more than or equal to 2) sealing cavities are arranged on the first supporting beam, each sealing cavity corresponds to one sample, a piston is arranged in each sealing cavity, the piston divides one sealing cavity into two sub-cavities, the piston is connected with a first tension and compression rod, one end of the first tension and compression rod, which is close to the second supporting beam, extends out of one end of the sealing cavity and is externally used for connecting the sample, a second tension and compression rod is connected to the position, which corresponds to each sealing cavity on the first supporting beam, of the second supporting beam and is used for connecting the other end of the sample, the two sub-cavities formed by separating one sealing cavity through the piston are respectively connected to two working oil ports of a hydraulic system through pipelines, and the tensile or compressive creep test.
The number of the sealing cavities (31) arranged on the first supporting beam is 4-12, and preferably 5-8.
Preferably, each component cavity body included in each sealed cavity is connected to a working oil path of the same hydraulic system.
Preferably, the sealed chamber is provided with the opening corresponding to the one end of keeping away from the sample, and the opening seals through sealed plug screw, when guaranteeing the sealed of sealed chamber, is convenient for the installation of piston and tension and compression bar one.
Furthermore, one end of the first tension and compression rod, which is used for connecting the sample, is connected with a first insulating connecting ring, and one end of the second tension and compression rod, which is used for connecting the sample, is connected with a second insulating connecting ring.
One end of the first insulating connecting ring is connected with the first tension and compression rod, the other end of the first insulating connecting ring is connected with a first sample fixing rod which is used for being directly connected with one end of a sample, one end of the second insulating connecting ring is connected with the second tension and compression rod, and the other end of the second insulating connecting ring is connected with a second sample fixing rod which is used for being directly connected with the other end of the sample.
The first sample fixing rod and the second sample fixing rod are both electric conductors, insulation gaps are reserved between the first sample fixing rod and the first tension and compression rod and between the second sample fixing rod and the second tension and compression rod, and the first sample fixing rod and the second sample fixing rod are respectively and electrically connected to the positive electrode and the negative electrode of a power supply of the heating device.
Further, the one end that a second supporting beam is connected to the second tension and compression bar is set to be a T-shaped structure, a T-shaped hole matched with the T-shaped structure of the tension and compression bar is formed in the second supporting beam, two ends of the T-shaped hole are open, one end, used for connecting a sample, of the second tension and compression bar stretches out from the opening of one end of the T-shaped hole, a nut is arranged at the opening of the other end of the T-shaped hole, and the tail end of the nut stretches into the T-shaped hole and.
Furthermore, many sample fixing device still includes tensile stress sensor and compressive stress sensor, the response element setting of tensile stress sensor is between the hole shoulder in the pull and press pole two and T shape hole, the response element setting of compressive stress sensor is between pull and press pole two and the nut.
Further, when the sample is a rod-shaped sample with an external thread at the tail end, threaded holes matched with external threads at the tail end of the sample are formed in the positions, used for connecting the sample, of the first sample fixing rod and the second sample fixing rod, grooves for embedding the tail ends of the sample are formed in the positions, used for connecting the sample, of the first sample fixing rod and the second sample fixing rod, through holes for the installation pins to penetrate through are formed in the positions, corresponding to the grooves, of the first sample fixing rod and the second sample fixing rod, and the installation pins penetrate through the through holes and the installation holes at the tail ends of the sample to achieve connection of one end of the sample and the first fixing rod and connection of the other end of the sample and the second fixing rod.
Preferably, the strain measuring device adopts a Digital Image Correction (DIC) digital Image acquisition system to measure the strain of the sample, the strain measuring device comprises a mounting frame, a light source, a DIC camera and a computer connected with the DIC camera, the computer is used for performing real-time online analysis on the sample Image acquired by the DIC camera and generating a strain result of the sample, the computer can be integrated with a Personal Computer (PC) controller of the creep testing machine, the mounting frame is fixed on the rack and positioned outside the high-temperature box, the DIC camera and the light source are both arranged on the mounting frame, the irradiation directions of the lens of the DIC camera and the light source face the sample in the high-temperature box, and one side of the high-temperature box corresponding to the DIC camera is provided with a transparent window.
Preferably, the transparent window is made of transparent quartz glass.
Preferably, the number of the DIC cameras is two, and an included angle of 30-120 degrees is kept between central axes of lenses of the two DIC cameras, so that strain images of the sample can be conveniently acquired from different directions, and a computer can conveniently combine the strain images of the sample according to different positions of the sample to generate a three-dimensional strain process of the sample.
Furthermore, the heating device comprises a power supply, a thermocouple and a temperature controller, wherein the first sample fixing rod and the second sample fixing rod are both provided with a wiring terminal for connecting the anode or the cathode of the power supply, a thermoelectric sensing element of the thermocouple is attached to the surface of the sample, and the power supply and the thermocouple are both electrically controlled by the temperature controller.
The sensing element of the thermocouple is preferably attached to the side of the sample facing away from the lens of the DIC camera.
The power supply of the heating device is preferably a pulse power supply, and the frequency of the pulse power supply is 100-1000 Hz, preferably 200-500 Hz.
The invention provides a multi-sample tension-compression creep test method, which uses the multi-sample tension-compression creep test device for testing and comprises the following steps:
1) and (3) connecting the sample between the first tension and compression rod and the second tension and compression rod, specifically, connecting one end of the sample with the first tension and compression rod through the first insulation connecting ring and the first sample fixing rod, and connecting the other end of the sample with the second tension and compression rod through the second insulation connecting ring and the second sample fixing rod.
2) And starting the heating device to heat the sample to the target temperature and then starting heat preservation.
3) Starting a hydraulic system and a strain measuring device, controlling the oil pressure difference in two sub-cavities corresponding to each sample according to needs, performing a tensile or compressive creep test on the samples, and simultaneously measuring the strain of the samples by the strain measuring device in real time; the corresponding relation between the oil pressure and the oil liquid flowing direction in the two sub-cavities and the tension and compression creep test is set as follows: when the sample needs tensile stress, the oil pressure in the sub-cavity close to the sample is larger than the oil pressure in the sub-cavity far away from the sample, the sub-cavity close to the sample is fed with oil, and the sub-cavity far away from the sample is fed with oil; when the sample needs compressive stress, the oil pressure in the sub-cavity close to the sample is smaller than the oil pressure in the sub-cavity far away from the sample, the sub-cavity far away from the sample is filled with oil, and the sub-cavity close to the sample is filled with oil.
Preferably, the strain measuring device in step 3 is a DIC (digital Image correlation) Image acquisition system, and before step 1 is started, speckles are sprayed on the surface of the sample so as to facilitate Image acquisition by a DIC camera.
Preferably, the first supporting beam and the second supporting beam are in a straight rod shape which is horizontally arranged, the sealing cavities on the first supporting beam are symmetrically distributed, and when the creep stress directions of a plurality of samples which are processed at the same time are not the same, the stress states of the samples between the first supporting beam and the second supporting beam are set to be in tension-compression interval distribution, namely the creep stress directions of any two adjacent samples are opposite so as to keep the first supporting beam and the second supporting beam balanced as much as possible.
The invention has at least the following beneficial effects:
the invention provides a high-efficiency and high-precision multi-sample tension-compression creep test device and method. By arranging a sealing cavity for each sample, each sealing cavity comprises two sub-cavities, tensile stress or compressive stress can be provided for the corresponding sample by changing the oil pressure difference in the two sub-cavities, the stress and the stress time of each sample can be kept relatively independent at the same time, part of the samples can be in tension, part of the samples can be in compression, the stress time of one part of the samples can be long, the stress time of the other part of the samples can be short, and the experiment of different process conditions of a plurality of samples under the same creep machine can be realized simultaneously, and can realize the independent control of the load and time of the real sample, greatly improve the efficiency and the precision of the creep test, the invention has strong flexibility, and particularly has more outstanding advantages for the condition that single-factor test or contrast test needs to be carried out.
The invention also introduces a heating device with a pulse power supply, the temperature of each sample is independently controlled by the heating device with the power supply as pulse current, the temperatures of the samples are not influenced mutually, but the whole is concentrated in the high-temperature box. The joule heating effect and the non-heating effect of the pulse current are utilized, the thermocouple is matched for feeding back the temperature of the sample, the sample can be rapidly heated, kept warm and cooled according to the test requirement, the pulse power supply is used as an instant high-energy external field, the high-energy joule heating effect and the electromigration effect generated by the pulse power supply enable the sample to be heated to the target temperature in a short time, and the efficiency is 5-8 times that of a conventional heating method; and the electric pulse energy field has high aggregation characteristic, and the electric pulse heating system is reasonably arranged, so that the temperature coexistence of various samples in the high-temperature box can be accurately realized, the independent and accurate temperature control of the samples at different positions in the high-temperature box can be realized, and the temperatures of the samples are independent from each other and do not influence each other.
The invention utilizes the non-contact DIC digital image acquisition system to measure the high-temperature deformation of the sample, can carry out high-precision measurement on the strain of the sample, avoids the problem that the traditional indirect measurement method is easy to be interfered by different expansion coefficients of materials and external factors to cause low measurement precision, and has smoother and more accurate measurement data and good repeatability (namely, the data obtained by the measurement of the repeatability test has high consistency) because the DIC strain measurement system is non-contact.
In order to better measure the strain of a sample, two DIC cameras are arranged to form a binocular stereoscopic vision effect on the sample, the speckle images of the surface of an object are tracked, the dynamic measurement of the three-dimensional coordinates, the displacement and the strain of the surface of the sample in the deformation process is realized, and the method is more accurate and visual compared with the existing single-axis measurement adopting a displacement sensor.
By controlling the stress to be constant, the high-precision creep test device can also be used for tensile and compressive relaxation aging tests.
In addition to the objects, features and advantages described above, other objects, features and advantages of the present invention are also provided. The present invention will be described in further detail below with reference to the drawings.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1 is an overall external structural view of a multi-specimen tension-compression creep test apparatus according to a preferred embodiment of the present invention (the internal components of the high temperature box are not shown);
FIG. 2 is a front view of the multi-specimen tension-compression creep test apparatus with the high temperature box and strain measurement device removed in accordance with the preferred embodiment of the present invention;
FIG. 3 is a perspective view of a multiple sample holder according to a preferred embodiment of the present invention;
fig. 4 is a perspective view of a multi-sample holder with internal structure according to a preferred embodiment of the present invention.
In the figure: 1-a frame, 11-a column I, 12-a column II, 2-a high temperature box, 21-a transparent window, 3-a support beam I, 31-a sealed cavity, 310-a cavity A, 311-a cavity B, 312-a pipeline A, 313-a pipeline B, 32-a piston, 33-a tension rod I, 34-a sealed screw plug, 35-an insulating connection ring I, 36-a sample fixing rod I, 4-a support beam II, 41-a tension rod II, 42-an insulating connection ring II, 43-a sample fixing rod II, 44-a screw cap, 45-a stress sensing element A, 46-a stress sensing element B, 5-a sample, 6-an insulating gap, 7-a connection terminal, 8-a thermoelectric sensing element, 91-a mounting rack and 92-a light source, 93-DIC camera.
Detailed Description
Embodiments of the invention will be described in detail below with reference to the drawings, but the invention can be implemented in many different ways, which are defined and covered by the claims.
Referring to fig. 1-4, the multi-sample tension-compression creep test device includes a rack 1, a high temperature box 2, a multi-sample fixing device, a strain measuring device and a heating device, the high temperature box is disposed on the rack, the multi-sample fixing device and the heating device are disposed in the high temperature box, the multi-sample fixing device is used for clamping a sample and providing stress for enabling the sample to generate tension-compression creep (tensile creep or compressive creep), the heating device is used for heating or insulating the sample, and the strain measuring device is used for measuring strain of the sample generating tension-compression creep in real time.
The multi-sample fixing device comprises a first straight-strip-shaped supporting beam 3 and a second supporting beam 4 which are arranged in parallel, the first supporting beam and the second supporting beam are fixedly connected with a rack through a first upright post 11 and a second upright post 12 which penetrate through a high-temperature box body respectively, six sealing cavities 31 which are distributed equidistantly and symmetrically are arranged on the first supporting beam, each sealing cavity corresponds to one sample 5, a piston 32 is arranged in each sealing cavity, the piston divides one sealing cavity into two sub-cavities (defined as a sub-cavity a310 and a sub-cavity b311 respectively), the piston is connected with a first tension and compression rod 33, one end of the first tension and compression rod, which is close to the second supporting beam, extends out of one end of the sealing cavity and is used for connecting the sample 5, the position of each sealing cavity on the first supporting beam corresponding to the second supporting beam is connected with a second tension and compression rod 41, the second tension and compression rod is used for connecting the other end of the sample, and the sub-cavities a and b which .
The component chambers included in each sealed chamber (a component chamber refers to a sub-chamber a310 and a sub-chamber b311 included in one sealed chamber) can be connected to the working oil path of the same hydraulic system, and the pressure difference between the two sub-chambers included in each sealed chamber can be adjusted and controlled by a set of hydraulic control valves.
Referring to fig. 4, an opening is formed in the end, which is opposite to the sample 5, of the seal cavity 31, and the opening is closed by a seal plug 34, so that the installation of the piston 32 and the first tension and compression bar 33 is facilitated while the seal of the seal cavity is ensured.
Referring to fig. 4, one end of the first tension and compression rod for connecting the sample is connected with a first insulation connection ring 35 with a cylindrical structure, and one end of the second tension and compression rod for connecting the sample is connected with a second insulation connection ring 42 with a cylindrical structure.
Two ends of the first insulating connecting ring are provided with internal threads, the internal thread at one end of the first insulating connecting ring is screwed with the external thread at the tail end of the first tension and compression rod, and the internal thread at the other end of the first insulating connecting ring is screwed with the external thread at the tail end of the first sample fixing rod 36; two ends of the second insulating connecting ring 42 are provided with internal threads, the internal thread at one end of the second insulating connecting ring is screwed with the external thread at the tail end of the second tension and compression rod 41, and the internal thread at the other end of the second insulating connecting ring is screwed with the external thread at the tail end of the second sample fixing rod 43. Referring to fig. 4, insulation gaps 6 are respectively maintained between the first sample fixing rod and the first tension and compression rod and between the second sample fixing rod and the second tension and compression rod, so that a loop is formed after current flows through the sample fixing rod and the sample, and the current is prevented from flowing into the device.
The first sample fixing rod and the second sample fixing rod are both electric conductors, the first sample fixing rod and the second sample fixing rod are both provided with a wiring terminal 7 used for connecting the positive electrode or the negative electrode of a power supply, and the first sample fixing rod and the second sample fixing rod are respectively and electrically connected to the positive electrode and the negative electrode of the power supply of a heating device (not shown in the figure) through the wiring terminal 7.
Heating device includes power, thermocouple and temperature controller, 8 subsides of thermoelectric induction element of thermocouple are established on the sample surface, and induction element preferably pastes and establishes the one side that deviates from DIC camera lens at the sample to be located sample length direction's intermediate position, power and thermocouple all by temperature controller electricity connection control, the temperature controller starts or closes the power according to the sample real-time temperature of thermocouple feedback, when not reaching the sample creep test temperature of settlement, the power is opened and the sample is heated to the power, when reaching the sample creep test temperature of settlement, the accessible reduces the electric current size and the frequency of power and keeps warm to the sample, in this embodiment, the fast pulse power supply of rate of heating is selected for use to heating device's power.
Referring to fig. 4, one end of the tension and compression rod II, which is connected with the support beam II, is set to be a T-shaped structure, a T-shaped hole matched with the tension and compression rod T-shaped structure is formed in the support beam II, two ends of the T-shaped hole are both opened, one end of the tension and compression rod II, which is used for connecting a sample, extends out from an opening at one end of the T-shaped hole, a nut 44 is arranged at an opening at the other end of the T-shaped hole, and the tail end of the nut extends into.
In this embodiment, the multi-sample fixing device further comprises a tensile stress sensor and a compressive stress sensor, wherein the stress sensing element a45 of the tensile stress sensor is arranged between the second tensile rod and the hole shoulder of the T-shaped hole, and the stress sensing element b46 of the compressive stress sensor is arranged between the second tensile rod and the nut. When a compression creep test is carried out, namely a sample is under compressive stress, the stress sensing element b46 of the compressive stress sensor is under compression, and the stress sensing element a45 of the tensile stress sensor does not work; in the case of a tensile creep test, i.e. when the sample is under tensile stress, the stress-sensitive element a45 of the tensile stress sensor is under compression, and the stress-sensitive element b46 of the compressive stress sensor is not operated.
The stress sensing element a45 of the tensile stress sensor and the stress sensing element b46 of the compressive stress sensor are respectively used for measuring the stress borne by the sample in real time when the sample is under the tensile stress and the compressive stress, and the stress value borne by the sample is fed back to a control terminal of the hydraulic system, so that the control terminal can adjust the pressure difference between the sub-cavity a and the sub-cavity b in time to form a closed-loop control system.
In this embodiment, the sample is a rod-shaped sample with an external thread at the end, and the first sample fixing rod and the second sample fixing rod are provided with threaded holes matched with the external thread at the end of the sample at positions for connecting the samples.
Referring to fig. 1, the strain measuring apparatus of this embodiment adopts a DIC (digital Image correction) digital Image acquisition system to measure the strain of the sample, and the strain measuring apparatus includes a mounting bracket 91, a light source 92, a DIC camera 93 and a computer (not shown in the figure) connected with the DIC camera, the mounting bracket is fixed on the rack and located outside the high temperature box, the DIC camera and the light source are both arranged on the mounting bracket, the lens of the DIC camera and the irradiation direction of the light source both face the sample in the quasi-high temperature box, one side of the high temperature box corresponding to the DIC camera is provided with a transparent window 21, and the transparent window is made of transparent quartz glass.
In this embodiment, the number of the DIC cameras is two, and an included angle of 45 ° is maintained between central axes of lenses of the two DIC cameras, so as to collect strain images of the sample from different directions, and facilitate a computer to combine the strain images at different positions of the sample to generate a three-dimensional strain process of the sample.
A multi-sample tension-compression creep test method is used for testing by using the multi-sample tension-compression creep test device, and comprises the following steps:
1) and (3) connecting the sample between the first tension and compression rod and the second tension and compression rod, specifically, connecting one end of the sample with the first tension and compression rod through the first insulation connecting ring and the first sample fixing rod, and connecting the other end of the sample with the second tension and compression rod through the second insulation connecting ring and the second sample fixing rod.
2) Connecting and starting the heating device to heat the sample to the target temperature and then starting heat preservation.
3) And starting the hydraulic system and the strain measuring device, controlling the oil pressure difference in the two sub-cavities corresponding to each sample as required, performing a tensile or compressive creep test on the sample, and simultaneously measuring the strain of the sample by the strain measuring device in real time. The corresponding relation between the oil pressure and the oil liquid flowing direction in the two sub-cavities and the tension and compression creep test is set as follows: when a sample needs tensile stress, the oil pressure in the sub-cavity close to the sample (namely sub-cavity a) is larger than the oil pressure in the sub-cavity far away from the sample (namely sub-cavity b), the sub-cavity close to the sample is fed with oil, and the sub-cavity far away from the sample is fed with oil; when the sample needs compressive stress, the oil pressure in the sub-cavity close to the sample is smaller than the oil pressure in the sub-cavity far away from the sample, the sub-cavity far away from the sample is filled with oil, and the sub-cavity close to the sample is filled with oil.
In this embodiment, the strain measuring device in step 3 adopts a DIC (digital image correlation) image acquisition system, and before step 1 starts, the sample surface is coated with the speckles by using the matte white paint, so as to facilitate image acquisition by the DIC camera.
In this embodiment, the first supporting beam and the second supporting beam are in the shape of a straight rod which is horizontally placed, the sealing cavities on the first supporting beam are symmetrically distributed, and when the creep stress directions of a plurality of samples which are processed at the same time are not the same, the stress states of the samples between the first supporting beam and the second supporting beam are set to be in tension-compression interval distribution as much as possible, that is, the creep stress directions of any two adjacent samples are opposite, so that the first supporting beam and the second supporting beam are kept in stress balance as much as possible.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (9)
1. The multi-sample tension-compression creep test method is characterized by comprising the steps of carrying out a test by using a multi-sample tension-compression creep test device, wherein the multi-sample tension-compression creep test device comprises a rack (1), a high-temperature box (2), a multi-sample fixing device, a strain measuring device and a heating device, the high-temperature box is arranged on the rack, the multi-sample fixing device is arranged in the high-temperature box and used for clamping a sample and providing stress for enabling the sample to generate tension-compression creep, the heating device is used for heating or insulating the sample, and the strain measuring device is used for measuring the strain quantity of the sample generating the tension-compression creep in real time;
the multi-sample fixing device comprises a first supporting beam (3) and a second supporting beam (4) which are arranged in parallel, a plurality of sealing cavities (31) are formed in the first supporting beam, each sealing cavity corresponds to a sample (5), a piston (32) is arranged in each sealing cavity, each sealing cavity is divided into two sub-cavities by the piston, the piston is connected with a first tension and compression rod (33), one end, close to the second supporting beam, of each first tension and compression rod extends out of the sealing cavity and is used for connecting one end of the sample, a second tension and compression rod (41) is connected to the position, corresponding to each sealing cavity, of the first supporting beam, the second tension and compression rod is used for connecting the other end of the sample, and the two sub-cavities formed by dividing one sealing cavity by the piston are;
the first supporting beam and the second supporting beam are in a straight rod shape which is horizontally arranged, the sealing cavities on the first supporting beam are symmetrically distributed, and when the creep stress directions of a plurality of samples which are processed at the same time are not the same, the stress states of the samples between the first supporting beam and the second supporting beam are set to be in tension-compression interval distribution, namely the creep stress directions of any two adjacent samples are opposite;
the multi-sample tension-compression creep test method specifically comprises the following steps:
1) the method comprises the following steps of installing and connecting a sample between a first tension and compression rod and a second tension and compression rod, specifically, connecting one end of the sample with the first tension and compression rod through a first insulating connecting ring and a first sample fixing rod, and connecting the other end of the sample with the second tension and compression rod through a second insulating connecting ring and a second sample fixing rod;
2) starting a heating device to heat the sample to a target temperature and then starting heat preservation;
3) starting a hydraulic system and a strain measuring device, controlling the oil pressure difference in two sub-cavities corresponding to each sample according to needs, performing a tensile or compressive creep test on the samples, and simultaneously measuring the strain of the samples by the strain measuring device in real time; the corresponding relation between the oil pressure and the oil liquid flowing direction in the two sub-cavities and the tension and compression creep test is set as follows: when the sample needs tensile stress, the oil pressure in the sub-cavity close to the sample is larger than the oil pressure in the sub-cavity far away from the sample, the sub-cavity close to the sample is fed with oil, and the sub-cavity far away from the sample is fed with oil; when the sample needs compressive stress, the oil pressure in the sub-cavity close to the sample is smaller than the oil pressure in the sub-cavity far away from the sample, the sub-cavity far away from the sample is filled with oil, and the sub-cavity close to the sample is filled with oil.
2. The multi-specimen tension-compression creep test method according to claim 1, characterized in that in step 3), the strain measurement device is a DIC image acquisition system, and before step 1), speckles are sprayed on the surface of the specimen to facilitate image acquisition by a DIC camera.
3. The method for testing the multi-specimen tension-compression creep of claim 1, wherein the component chamber bodies included in each sealed chamber are connected to the working oil line of the same hydraulic system, and the pressure difference between the two component chamber bodies included in each sealed chamber is adjusted and controlled by a set of hydraulic control valves.
4. The multi-specimen tension-compression creep test method according to claim 1, characterized in that the end of the sealed cavity (31) corresponding to the end far away from the specimen is provided with an opening, and the opening is closed by a sealing plug screw (34);
one end of the first tension and compression rod, which is used for connecting a sample, is connected with a first insulating connecting ring (35), and one end of the second tension and compression rod, which is used for connecting the sample, is connected with a second insulating connecting ring (42);
one end of the first insulating connecting ring is connected with the first tension and compression rod, and the other end of the first insulating connecting ring is connected with a first sample fixing rod (36) which is used for directly connecting one end of a sample; an internal thread at one end of the insulating connecting ring II is connected with a tension-compression rod II, and the other end of the insulating connecting ring II is connected with a sample fixing rod II (43) which is used for directly connecting the other end of the sample;
insulation gaps (6) are respectively reserved between the first sample fixing rod and the first tension and compression rod and between the second sample fixing rod and the second tension and compression rod; the first sample fixing rod and the second sample fixing rod are both electric conductors, the first sample fixing rod and the second sample fixing rod are both provided with a wiring terminal (7) used for being connected with the positive pole or the negative pole of a power supply, and the first sample fixing rod and the second sample fixing rod are respectively and electrically connected to the positive pole and the negative pole of the power supply of the heating device through the wiring terminals.
5. The multi-sample tension-compression creep test method according to claim 2, characterized in that the heating device comprises a power supply, a thermocouple and a temperature controller, wherein a thermoelectric sensing element (8) of the thermocouple is attached to the surface of the sample, the thermoelectric sensing element is attached to the surface of the sample, which is away from the lens of the DIC camera, and is located at the middle position in the length direction of the sample, both the power supply and the thermocouple are electrically connected and controlled by the temperature controller, and the power supply of the heating device is a pulse power supply.
6. The multi-sample tension-compression creep test method according to any one of claims 1 to 5, characterized in that one end of the tension-compression rod II connected with the support beam II is set to be a T-shaped structure, the support beam II is provided with a T-shaped hole matched with the tension-compression rod T-shaped structure, both ends of the T-shaped hole are open, one end of the tension-compression rod II used for connecting the sample extends out from the opening at one end of the T-shaped hole, the opening at the other end of the T-shaped hole is provided with a nut (44), and the tail end of the nut extends into the T-shaped hole to abut against the tension-compression rod II (41.
7. The multi-specimen tension-compression creep test method according to claim 6, wherein the multi-specimen fixture further comprises a tension stress sensor and a compression stress sensor, the stress sensing element a (45) of the tension stress sensor is arranged between the second tension-compression rod and the hole shoulder of the T-shaped hole, and the stress sensing element b (46) of the compression stress sensor is arranged between the second tension-compression rod and the nut.
8. The multi-sample tension-compression creep test method according to any one of claims 1 to 5, characterized in that the strain measuring device measures the strain of the sample by using a DIC digital image acquisition system, the strain measuring device comprises a mounting frame (91), a light source (92), a DIC camera (93) and a computer connected with the DIC camera, the mounting frame is fixed on the rack and located outside the high temperature box, the DIC camera and the light source are both arranged on the mounting frame, the lens of the DIC camera and the irradiation direction of the light source both face the sample in the quasi high temperature box, one side of the high temperature box corresponding to the DIC camera is provided with a transparent window (21), and the transparent window is made of transparent quartz glass.
9. The multi-sample tension-compression creep test method according to claim 8, wherein the number of the DIC cameras is two, and the central axes of the lenses of the two DIC cameras are kept at an included angle of 30-120 °.
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