Mechanical properties testing device and testing method of mortar under uniaxial confined compression conditions

Abstract

The present invention provides a device and method for testing the mechanical properties of mortar under uniaxial confined compression conditions, which belongs to the technical field of mortar performance measurement. The device includes a steel pressure head, a steel sleeve and a square fixed frame. The hollow steel sleeve can be spliced ​​with a solid steel pressure head with a spring to form a cylindrical tube with a completely closed bottom and top surface to simulate a high-pressure environment. The test piece is placed in the middle position of the steel sleeve and supported on the small cylinder of the steel pressure head to ensure that the test piece is in the middle part of the steel sleeve and the strain gauge is tightly attached to the outside of the steel sleeve. The relationship between the radial pressure on the inner wall of the steel sleeve and the annular strain on the outer wall is determined by numerical simulation, and the stress and strain state of the test piece is calculated, so as to evaluate the high-pressure mechanical properties of materials such as mortar. The test method is simple, easy to operate, and highly cost-effective, and can be widely promoted and used.

Description

Technical Field

[0001] The invention relates to the technical field of mortar performance measuring equipment, and in particular to a mechanical performance testing device and a testing method for mortar under uniaxial confined compression conditions. Background Art

[0002] Obtaining the mechanical properties of mortar under high hydrostatic pressure is of great engineering significance to the stability and safety of buildings. When faced with high hydrostatic pressure loads such as explosions and impacts, the material undergoes high-speed deformation at the macro level, while crystal changes also occur at the micro level, causing damage and destruction to the structural parts. At present, due to the fact that such research requires expensive special testing equipment and the operation is relatively cumbersome, the mechanism of volumetric strain and damage caused by high hydrostatic pressure to materials such as mortar is still unclear. Therefore, the strength surface equation (the relationship between hydrostatic pressure and deviatoric stress) and state equation (the relationship between volumetric strain and hydrostatic pressure) of materials such as mortar under high hydrostatic pressure are still unclear.

[0003] In order to accurately obtain the mechanical properties of mortar under high hydrostatic pressure conditions, the main methods currently adopted are: 1. Dynamic method: flying chip impact test, the size of the concrete specimen tested will be limited by the caliber of the light gas gun, so that the diameter of the test specimen generally does not exceed 50mm. This method is only suitable for testing the state equation of some fine aggregate concrete; full-scale explosion test, because the vibration generated by the explosion of explosives will affect the test accuracy of the equipment, resulting in large deviations in the measurement results; 2. Static method: The triaxial loading method is used to obtain the state equation of concrete materials with low hydrostatic pressure.

[0004] Therefore, it is necessary to seek a device and method for testing the mechanical properties of mortar that is easy to operate, low in price, and can apply high hydrostatic pressure. The existing public technology mainly focuses on the mechanical properties of materials under low hydrostatic pressure loads and the mechanical properties of materials under individual high hydrostatic pressures, and designs relevant instruments and testing methods. However, applying high hydrostatic pressure requires some special testing equipment, and such equipment is usually very expensive.

[0005] To this end, the present invention is devoted to developing a mortar mechanical property testing device and a testing method using a uniaxial confined compression test. Summary of the invention

[0006] In view of this, the device and testing method provided by the present invention make the testing operation of the uniaxial confined compression test of the mechanical properties of the mortar simple and low-cost, and ensure the accuracy of the tested mechanical properties.

[0007] The present invention provides a mechanical property testing device for mortar under uniaxial lateral confined compression conditions, characterized in that it comprises: a steel pressure head, a steel sleeve and a square fixed frame, wherein the steel pressure head and the square fixed frame are both two and symmetrically arranged; the steel pressure head is spliced ​​by a large cylinder and a small cylinder, the small cylinder is arranged at the exact center of the large cylinder, the large cylinder is fixed to the exact center of the inside of the square fixed frame by four long bolts, a spring is arranged on the outside of the small cylinder, and the spring contacts the upper and lower sides of the steel sleeve; the square fixed frame located at the lower part is provided with four symmetrical sleeves, a fixed column is inserted into each sleeve and fixed by a knob screw; a dial indicator is installed on the upper part of the fixed column, the upper part of the dial indicator contacts the lower side of the square fixed frame located at the upper part, and a cylindrical specimen is placed inside the steel sleeve; an annular strain gauge is attached to the outer wall of the steel sleeve, the steel sleeve and the steel pressure head are made of 60SiCrVA spring steel, and the inner and outer diameter ratio of the steel sleeve is 3 / 8.

[0008] Preferably, the edge of the square fixed frame is solid, the fixed column is solid, and the spring is detachable.

[0009] Preferably, the inner wall diameter of the steel sleeve is 30.2mm, the outer wall diameter is 80mm, and the height is 80mm; the large cylindrical bottom surface diameter of the steel pressure head is 80mm, the height is 30mm, the small cylindrical bottom surface diameter is 30mm, and the height is 40mm; the square fixed frame has a side length of 14.5cm, a wall thickness of 15mm, an outer diameter of the connected outer ring is 40mm, and an inner diameter is 24mm; the fixed column has a height of 18.5cm and a diameter of 12mm; the range of the dial indicator is 20mm.

[0010] The present invention also provides a method for testing the mechanical properties of mortar under uniaxial confined compression conditions, the method using the above-mentioned testing device, comprising the following steps:

[0011] S1. The steel sleeve, the steel pressure head and the basic tensile mechanical properties test pieces made from the same batch of steel materials are heat treated until the inner wall of the steel sleeve can withstand a uniform pressure of about 700 MPa. The tensile mechanical properties of the steel are tested using the basic tensile mechanical properties test pieces. The relationship between the radial pressure on the inner wall of the steel sleeve and the circumferential strain on the outer wall is obtained by numerical simulation using a method of applying uniform pressure to the inner wall of the steel sleeve.

[0012] S2. Prepare a mortar cylindrical specimen with the same diameter as the small cylinder of the steel pressure head and a height of 40 to 60 mm, and apply vaseline on the inner wall surface of the inner cylinder of the steel sleeve, the small cylinder surface of the steel pressure head, and the surface of the cylindrical specimen;

[0013] S3. Attach 12 circumferential strain gauges to the outer wall of the steel sleeve. Divide the steel sleeve vertically into three parts: upper, middle and lower. A strain gauge is attached to the upper and lower parts every 120°, and a strain gauge is attached to the middle part every 60°. The strain gauges in the upper, middle and lower parts are aligned in the longitudinal position to measure the circumferential strain of the outer wall of the steel sleeve.

[0014] S4. A steel pressure head with a spring is tightly buckled inside the square fixed frame at the bottom, fixed and tightened with long bolts, a steel sleeve with a strain gauge is tightly buckled on the spring of the steel pressure head, a cylindrical specimen is placed in the inner tube of the steel sleeve, another steel pressure head with a spring is turned over, the spring is aligned with the center of the cylindrical specimen, the steel pressure head is tightly buckled inside the square fixed frame at the top, fixed and tightened with long bolts; 4 dial indicators are installed on the upper part of the fixed column, so that the upper part of the dial indicator contacts the lower side of the square fixed frame at the top, to measure the vertical displacement of the cylindrical specimen;

[0015] S5. Place the assembled test device horizontally on the platform of the universal testing machine, and connect the strain gauge and dial indicator tightly to the connection port of the loading instrument through connecting wires;

[0016] S6. The cylindrical specimen is loaded uniaxially at a quasi-static loading speed of 5 mm / min using a uniaxial confined compression test. The stress on the steel sleeve and the steel indenter is controlled not to exceed 1700 MPa during loading, otherwise plastic yielding will occur. The maximum load applied to the test device during the test is controlled not to exceed 1000 kN.

[0017] S7. Calculate the Mises strength and state equation of the cylindrical specimen, organize the stress and strain data in the experiment, and draw the hydrostatic pressure-equivalent stress and hydrostatic pressure-volume strain relationship curves of the cylindrical specimen.

[0018] Preferably, the relationship between the circumferential strain at the middle position of the outer wall of the steel sleeve in S1 and the pressure applied by the inner wall is y=1.61x, wherein y is the pressure applied by the inner wall, and x is the circumferential strain at the middle position of the outer wall.

[0019] Preferably, the vertical displacement (l a ) minus the vertical displacement of the upper and lower steel pressure heads (1) to obtain the vertical displacement (l s ):

[0020] l s = l a -2*l p *F axial / E

[0021] Among them l a is the average value of the four percentage indicators, lp is the height of the steel pressure head, F axial is the axial force, and E is the elastic modulus of the steel indenter.

[0022] The initial length (l0) of the cylindrical specimen (8) minus the vertical displacement (l s ) to obtain the length (l) of the cylindrical specimen (8) after the test:

[0023] l=l0-l s

[0024] Due to the uneven axial deformation, the deformation of the cylindrical specimen is simplified by the equivalent diameter method to obtain the volume strain. According to the relationship between the annular strain of the outer wall and the annular strain of the inner wall of the steel sleeve, the radial strains of the upper, middle and lower parts of the cylindrical specimen are obtained as follows:

[0025] ε1=4.84g u ,

[0026] ε2=4.92g m ,

[0027] ε3=4.84g l ,

[0028] where g u , g m and g l are the average values ​​of the strain gauge data of the upper, middle and lower parts of the outer wall of the steel sleeve respectively; ε1 is the average radial strain of the upper part of the cylindrical specimen; ε2 is the average radial strain of the middle part of the cylindrical specimen; ε3 is the average radial strain of the lower part of the cylindrical specimen;

[0029] Equivalent radial strain ε of the cylindrical specimen in the test d for

[0030] ε d =(ε1+2ε2+ε3) / 4,

[0031] The equivalent diameter of the cylindrical specimen in the test is

[0032] d=d0(ε d +1),

[0033] Where d0 is the initial diameter of the cylindrical specimen,

[0034] The volume of the cylindrical specimen after the test is

[0035] v=πld 2 / 4,

[0036] The volume strain of the cylindrical specimen in the test is

[0037] ε v=(v0-v) / v0,

[0038] Where v0 is the initial volume of the cylindrical specimen, that is, v0 = πl0d0 2 / 4;

[0039] The vertical stress of the cylindrical specimen can be obtained by dividing the axial force by the equivalent cross-sectional area of ​​the cylindrical specimen during loading.

[0040] σ z =4Faxial / (πd 2 ),

[0041] Since the circumferential strain at the middle of the outer wall of the steel sleeve is linearly related to the pressure on the inner wall of the steel sleeve, and the pressure on the inner wall of the steel sleeve and the pressure on the cylindrical specimen are mutually acting and reacting, the radial confining pressure of the cylindrical specimen is:

[0042] σ r =1.61×g m ,

[0043] The hydrostatic pressure on the cylindrical specimen is

[0044] p=(σ z +2σ r ) / 3,

[0045] The Misess stress of the cylindrical specimen is:

[0046] σ deviatoric =|σ z -σ r |.

[0047] The beneficial effects are as follows:

[0048] 1. The test device and method provided by the present invention, the hollow steel sleeve can be spliced ​​with the solid steel pressure head with a spring to form a cylindrical tube with the bottom and the top completely closed, simulating a high-pressure environment. The overall structure is mainly composed of a steel sleeve, a steel pressure head with a spring and a square fixed frame, etc. The structure is simple, the steel sleeve and the steel pressure head are connected by a fixed bracket, the test piece is placed in the middle position of the steel sleeve and supported by a small cylinder of the steel pressure head, ensuring that the test piece is in the middle part of the steel sleeve; the strain gauge is tightly attached to the outside of the steel pipe, ensuring the accuracy of the strain on the outside of the steel pipe; the dial indicator is fixed on the fixed column to ensure the measurement of the axial strain of the steel pressure head and the test piece, thereby ensuring the accuracy of the measurement result.

[0049] 2. The present invention determines the relationship between the radial pressure on the inner wall of the steel sleeve and the annular strain on the outer wall through numerical simulation, which can be used to study the high-pressure mechanical properties of materials such as mortar. It is simple to operate, has a very high cost-effectiveness, and can be widely promoted and used. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 A schematic structural diagram of a mechanical property testing device showing a cylindrical specimen according to an embodiment of the present invention is shown;

[0051] Figure 2 A schematic diagram of a mechanical property testing device according to an embodiment of the present invention from a first viewing angle is shown;

[0052] Figure 3 A schematic diagram of a mechanical property testing device according to an embodiment of the present invention from a second viewing angle is shown;

[0053] Figure 4 A schematic diagram of the mechanical properties testing device according to an embodiment of the present invention from a third viewing angle is shown;

[0054] Figure 5 A schematic diagram of the installation of long bolts and fixed columns according to an embodiment of the present invention is shown;

[0055] Figure 6 A schematic diagram showing the installation effect of the upper and lower steel pressure heads according to an embodiment of the present invention is shown;

[0056] Figure 7 A schematic diagram showing the relative positions of a steel sleeve and a steel pressing head with a spring according to an embodiment of the present invention is shown;

[0057] Figure 8 A schematic diagram of a steel pressing head with a spring according to an embodiment of the present invention is shown;

[0058] Fig. 9 A schematic diagram showing the pasting position of the strain gauge according to an embodiment of the present invention is shown;

[0059] Reference numerals list

[0060] 1. Steel pressure head; 2. Steel sleeve; 3. Spring; 4. Square fixing frame; 5. Long bolts; 6. Dial indicator; 7. Fixed column; 8. Cylindrical specimen; 9. Knob screw. DETAILED DESCRIPTION

[0061] In order to make the purpose, scheme and advantages of the technical solution of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of specific embodiments of the present invention.

[0062] Embodiment 1:

[0063] Please refer to the instruction manual Figures 1 to 9 :

[0064] The present invention provides a mechanical property testing device for mortar under uniaxial lateral confined compression conditions, comprising: a steel pressure head 1, a steel sleeve 2 and a square fixed frame 4, wherein the steel pressure head 1 and the square fixed frame 4 are both two in number and symmetrically arranged, and the edge of the square fixed frame 4 is solid; the steel pressure head 1 is formed by splicing a large cylinder and a small cylinder, wherein the small cylinder is arranged at the exact center of the large cylinder, and the large cylinder is fixed at the exact center of the inside of the square fixed frame 4 by four long bolts 5, and the long bolts 5 penetrate the side of the square fixed frame 4 and are fixed on the large cylinder, and a spring 3 is arranged on the outside of the small cylinder, and the spring 3 is detachable, and the spring 3 is connected to the upper and lower sides of the steel sleeve 2 touch; the square fixed frame 4 located at the bottom is provided with four symmetrical sleeves, the sleeves are arranged on the adjacent sides of the square fixed frame 4 located below which are penetrated by the long bolts 5, a fixed column 7 is inserted into each sleeve and fixed by the knob screw 9, and the fixed column 7 is solid; the upper part of the fixed column 7 is installed with a dial indicator 6, the upper part of the dial indicator 6 is in contact with the lower side of the square fixed frame 4 located at the top, and a cylindrical specimen 8 is placed inside the steel sleeve 2; the outer wall of the steel sleeve 2 is affixed with annular strain gauges, the steel sleeve 2 and the steel pressure head 1 are made of 60SiCrVA spring steel, and the inner and outer diameter ratio of the steel sleeve 2 is 3 / 8.

[0065] The hollow steel sleeve 2 can be spliced ​​with the solid steel pressure head 1 with spring 3 to form a cylindrical tube with completely closed bottom and top surfaces to simulate a high pressure environment. The cylindrical specimen 8 is placed in the middle position of the steel sleeve 2. The steel pressure head 1 with spring 3 is tightly buckled on the top and bottom of the steel sleeve 2 by splicing to complete the fixation and test link of the cylindrical specimen 8, ensuring that the cylindrical specimen 8 is in the middle part of the steel sleeve 2. The strain gauge is tightly attached to the outside of the steel sleeve 2 to ensure the accuracy of the strain on the outside of the steel sleeve 2. The dial indicator 6 is fixed on the fixed column 7 to ensure the measurement of the axial displacement of the steel pressure head 1 and the cylindrical specimen 8, thereby ensuring the accuracy of the measurement result, and realizing the measurement of the vertical strain and pressure of the cylindrical specimen 8 and the circumferential strain of the outer wall of the steel sleeve 2 under axial compression, so as to obtain the deviatoric stress and volume strain of the cylindrical specimen 8 under different pressure levels, and further obtain the strength surface equation and state equation of materials such as mortar. The operation is simple, the cost performance is extremely high, and it can be widely promoted and used.

[0066] Embodiment 2:

[0067] Based on Example 1, this embodiment provides a preferred device size, wherein the inner wall diameter of the steel sleeve 2 is 30.2 mm, the outer wall diameter is 80 mm, and the height is 80 mm; the large cylindrical bottom diameter of the steel pressure head 1 is 80 mm, the height is 30 mm, the small cylindrical bottom diameter is 30 mm, and the height is 40 mm; the square fixed frame 4 has a side length of 14.5 cm and a wall thickness of 15 mm; the fixed column 7 has a height of 18.5 cm and a diameter of 12 mm; the range of the dial indicator 6 is 20 mm; the diameter of the cylindrical specimen 8 is selected to be 30 mm, and the height is 40 to 60 mm.

[0068] Embodiment 3:

[0069] The present invention provides a method for testing the mechanical properties of mortar under uniaxial confined compression conditions. The method uses the testing device described in Example 1 or 2 and comprises the following steps:

[0070] S1. The steel sleeve 2, the steel pressure head 1 and the basic tensile mechanical properties test piece made of the same batch of steel materials are heat treated until the inner wall of the steel sleeve can withstand a uniform pressure of about 700 MPa. The tensile mechanical properties of the steel are tested using the basic tensile mechanical properties test piece. The relationship between the inner wall and the outer wall of the steel sleeve 2 under the action of hydrostatic pressure and the relationship between the radial pressure on the inner wall of the steel sleeve 2 and the circumferential strain on the outer wall are obtained by numerical simulation of applying uniform pressure to the inner wall of the steel sleeve 2. The inner wall of the steel sleeve 2 and the cylindrical test piece 8 act on each other as forces and reaction forces of the same magnitude. The force on the inner wall of the steel sleeve 2 reflects the force on the cylindrical test piece 8.

[0071] The tensile mechanical properties specimens treated under the same conditions were loaded at a speed of 5 mm / min, and the transverse and vertical stress-strain curves of the steel were measured using a clamp extensometer and a strain gauge. The yield strength of 60SiCrVA steel was further calculated to be 2200 MPa, the ultimate elastic strength was 1700 MPa, the elastic modulus was 209 GPa, and the Poisson's ratio was 0.3.

[0072] The relationship between the radial stress on the inner wall of the steel sleeve 2 and the hoop strain on the outer wall of the steel sleeve 2 is obtained by applying uniform pressure to the inner wall of the steel sleeve 2 through numerical simulation. The finite element analysis results show that the relationship between the hoop strain at the middle position of the outer wall of the steel sleeve 2 and the pressure applied on the inner wall is y=1.61x, where y is the pressure applied on the inner wall and x is the hoop strain at the middle position of the outer wall.

[0073] S2. Prepare a mortar cylindrical specimen 8 with the same diameter as the small cylinder of the steel pressure head 1 and a height of 40 to 60 mm, and apply vaseline on the inner wall surface of the inner cylinder of the steel sleeve 2, the small cylinder surface of the steel pressure head 1, and the surface of the cylindrical specimen 8;

[0074] S3, 12 circumferential strain gauges are attached to the outer wall of the steel sleeve 2, and the steel sleeve 2 is vertically divided into three parts: upper, middle and lower. The distance between the position where the strain gauges are attached to the upper and lower parts and the position where the strain gauges are attached to the middle part is preferably 3 / 8H, and H refers to the height of the steel sleeve 2. A strain gauge is attached to the upper and lower parts at every 120° interval, and a strain gauge is attached to the middle part at every 60° interval. The longitudinal positions of the strain gauges in the upper, middle and lower parts are aligned to measure the circumferential strain of the outer wall of the steel sleeve 2;

[0075] S4. A steel pressure head 1 with a spring 3 is tightly buckled inside the square fixed frame 4 located at the bottom, fixed and tightened with a long bolt 5, a steel sleeve 2 with a strain gauge attached is tightly buckled on the spring 3 of the steel pressure head 1, a cylindrical specimen 8 is placed in the inner tube of the steel sleeve 2, another steel pressure head 1 with a spring 3 is turned over, the spring 3 is aligned with the center of the cylindrical specimen 8, the steel pressure head 1 is tightly buckled inside the square fixed frame 4 located at the top, fixed and tightened with a long bolt 5; four dial indicators 6 are installed on the upper part of the fixed column 7, the upper part of the dial indicators 6 is in contact with the lower side of the square fixed frame 4 located at the top, for measuring the vertical displacement of the cylindrical specimen 8;

[0076] S5. Place the assembled test device horizontally on the platform of the universal testing machine, and tightly connect the strain gauge and dial indicator 6 to the connection port of the loading instrument through connecting wires;

[0077] S6. The cylindrical specimen is subjected to uniaxial loading at a quasi-static loading speed of 5 mm / min using a uniaxial confined compression test. The stress on the steel sleeve 2 and the steel pressure head 1 is controlled not to exceed 1700 MPa during loading, otherwise plastic yielding will occur. The maximum load applied to the test device during the test is controlled not to exceed 1000 kN.

[0078] S7. Calculate the Mises strength and state equation of the cylindrical specimen 8, organize the stress and strain data in the experiment, and draw the hydrostatic pressure-equivalent stress and hydrostatic pressure-volume strain relationship curves of the cylindrical specimen 8. Specifically, the vertical displacement and pressure of the cylindrical specimen 8 and the circumferential strain of the outer wall of the steel sleeve 2 are measured under axial compression, so as to obtain the hydrostatic pressure, deviatoric stress and volume strain of the cylindrical specimen 8 at different pressure levels, and further obtain the strength surface equation and state equation.

[0079] The vertical displacement of the test device in S7 (l a ) minus the vertical displacement of the upper and lower steel pressure heads (1) to obtain the vertical displacement (l s ):

[0080] l s = l a -2*l p *F axial / E

[0081] Among them l a is the average value of the four percentage indicators, l p is the height of the steel pressure head, F axial is the axial force, and E is the elastic modulus of the steel indenter.

[0082] The initial length (l0) of the cylindrical specimen 8 minus the vertical displacement (l s ) to obtain the length (l) of the cylindrical specimen 8 after the test:

[0083] l=l0-l s

[0084] Due to the uneven axial deformation, the deformation of the cylindrical specimen 8 is simplified by the equivalent diameter method to obtain the volume strain. According to the relationship between the annular strain of the outer wall and the annular strain of the inner wall of the steel sleeve 2, the radial strains of the upper, middle and lower parts of the cylindrical specimen 8 are obtained as follows:

[0085] ε1=4.84g u ,

[0086] ε2=4.92g m ,

[0087] ε3=4.84g l ,

[0088] where g u , g m and g l are the average values ​​of the strain gauge data of the upper, middle and lower parts of the outer wall of the steel sleeve 2; ε1 is the average radial strain of the upper part of the cylindrical specimen 8; ε2 is the average radial strain of the middle part of the cylindrical specimen 8; ε3 is the average radial strain of the lower part of the cylindrical specimen 8;

[0089] The equivalent radial strain ε of the cylindrical specimen 8 in the test d for

[0090] ε d =(ε1+2ε2+ε3) / 4,

[0091] The equivalent diameter of the cylindrical specimen 8 in the test is

[0092] d=d0(ε d +1),

[0093] Where d0 is the initial diameter of the cylindrical specimen 8,

[0094] The volume of the cylindrical specimen 8 after the test is

[0095] v=πld 2 / 4,

[0096] The volume strain of the cylindrical specimen 8 in the test is

[0097] ε v =(v0-v) / v0,

[0098] Where v0 is the initial volume of the cylindrical specimen 8, that is, v0 = πl0d0 2 / 4;

[0099] The vertical stress of the cylindrical specimen 8 can be obtained by dividing the axial force by the equivalent cross-sectional area of ​​the cylindrical specimen 8 during loading.

[0100] σ z =4F axial / (πd2),

[0101] Since the circumferential strain at the middle of the outer wall of the steel sleeve 2 is linearly related to the pressure on the inner wall of the steel sleeve 2, and the pressure on the inner wall of the steel sleeve 2 and the pressure on the cylindrical specimen 8 are mutually acting and reacting forces, the radial confining pressure of the cylindrical specimen 8 is

[0102] σ r =1.61×g m ,

[0103] The hydrostatic pressure on the cylindrical specimen 8 is

[0104] p=(σ z +2σ r ) / 3,

[0105] The Misess stress of cylindrical specimen 8 is

[0106] σ deviatoric =|σ z -σ r |.

[0107] Embodiment 4:

[0108] On the basis of Example 3, the same method can also be used to carry out performance testing of concrete, such as using a core sampling machine to drill core samples of test blocks cured under standard curing conditions. The inner diameter of the sampling head of the core sampling machine is 30 mm, so the diameter of the taken concrete sample is 30 mm. The sample is cut into a cylindrical sample with a height of 40 to 60 mm and a diameter of 30 mm. Then, the taken sample is polished with sandpaper to remove unevenness and burrs, and a layer of vaseline is evenly applied on the surface of the polished sample to form a cylindrical specimen 8.

[0109] The other operation steps are the same and will not be described in detail. After the test is completed, the pressure head of the press is adjusted to take out the cylindrical test piece 8, and the steps of applying vaseline to the device and the new test piece are repeated after cleaning, and the next test can be carried out.

Claims

1. A method for testing the mechanical properties of mortar under uniaxial confined compression conditions, characterized in that: The test method adopts a mechanical property test device for mortar under uniaxial lateral confinement compression conditions, and the test device comprises: a steel pressure head (1), a steel sleeve (2) and a square fixed frame (4), wherein the steel pressure head (1) and the square fixed frame (4) are both two and symmetrically arranged; the steel pressure head (1) is formed by splicing a large cylinder and a small cylinder, wherein the small cylinder is arranged at the exact center of the large cylinder, and the large cylinder is fixed at the exact center of the square fixed frame (4) by four long bolts (5); a spring (3) is arranged on the outside of the small cylinder, and the spring (3) contacts the upper and lower sides of the steel sleeve (2). ; The square fixed frame (4) at the bottom is provided with four symmetrical sleeves, each sleeve is inserted with a fixed column (7) and fixed by a knob screw (9); the upper part of the fixed column (7) is installed with a dial indicator (6), the upper part of the dial indicator (6) is in contact with the lower side of the square fixed frame (4) at the top, and a cylindrical specimen (8) is placed inside the steel sleeve (2); the outer wall of the steel sleeve (2) is affixed with an annular strain gauge, and the steel sleeve (2) and the steel pressure head (1) are made of 60SiCrVA spring steel, wherein the inner and outer diameter ratio of the steel sleeve (2) is 3 / 8; The test method is as follows: S1. The steel sleeve (2), the steel pressure head (1) and the basic tensile mechanical properties test piece made from the same batch of steel materials are heat treated until the inner wall of the steel sleeve (2) can withstand a uniform pressure of about 700 MPa. The tensile mechanical properties of the steel are tested using the basic tensile mechanical properties test piece. A numerical simulation method is used to apply a uniform pressure to the inner wall of the steel sleeve (2) to obtain the relationship between the radial pressure on the inner wall of the steel sleeve (2) and the circumferential strain on the outer wall; S2. Prepare a mortar cylindrical specimen (8) with the same diameter as the small cylinder of the steel pressure head (1) and a height of 40 to 60 mm, and apply vaseline on the inner wall surface of the inner cylinder of the steel sleeve (2), the surface of the small cylinder of the steel pressure head (1), and the surface of the cylindrical specimen (8); S3. 12 circumferential strain gauges are attached to the outer wall of the steel sleeve (2). The steel sleeve (2) is vertically divided into three parts: upper, middle and lower. A strain gauge is attached to the upper and lower parts at intervals of 120°, and a strain gauge is attached to the middle part at intervals of 60°. The strain gauges in the upper, middle and lower parts are aligned in the longitudinal direction to measure the circumferential strain of the outer wall of the steel sleeve (2). S4. A steel pressure head (1) with a spring (3) is tightly buckled inside the square fixed frame (4) located at the bottom, fixed and tightened with a long bolt (5), a steel sleeve (2) with a strain gauge attached is tightly buckled on the spring (3) of the steel pressure head (1), a cylindrical specimen (8) is placed in the inner tube of the steel sleeve (2), another steel pressure head (1) with a spring (3) is turned over, the spring (3) is aligned with the center of the cylindrical specimen (8), the steel pressure head (1) is tightly buckled inside the square fixed frame (4) located at the top, fixed and tightened with a long bolt (5); four dial indicators (6) are installed on the upper part of the fixed column (7), the upper part of the dial indicators (6) is in contact with the lower side of the square fixed frame (4) located at the top, for measuring the vertical displacement of the cylindrical specimen (8); S5. Place the assembled test device horizontally on the platform of the universal testing machine, and tightly connect the strain gauge and the dial indicator (6) to the connection port of the loading instrument through the connecting wire; S6. A uniaxial confined compression test is performed to load the cylindrical specimen uniaxially at a quasi-static loading speed of 5 mm / min. During loading, the stress on the steel sleeve (2) and the steel pressure head (1) is controlled not to exceed 1700 MPa, otherwise plastic yielding will occur. During the test, the maximum load applied to the test device is controlled not to exceed 1000 kN. S7. Calculate the Mises strength of the cylindrical specimen (8), organize the stress and strain data in the experiment, and draw the hydrostatic pressure-equivalent stress and hydrostatic pressure-volume strain relationship curves of the cylindrical specimen (8).

2. The method for testing the mechanical properties of mortar under uniaxial confined compression conditions according to claim 1, characterized in that: The edge of the square fixed frame (4) is solid, the fixed column (7) is solid, and the spring (3) is detachable.

3. The method for testing the mechanical properties of mortar under uniaxial confined compression conditions according to claim 1, characterized in that: The inner wall diameter of the steel sleeve (2) is 30.2 mm, the outer wall diameter is 80 mm, and the height is 80 mm; the large cylindrical bottom surface diameter of the steel pressure head (1) is 80 mm, the height is 30 mm, and the small cylindrical bottom surface diameter is 30 mm, and the height is 40 mm; the side length of the square fixed frame (4) is 14.5 cm, and the wall thickness is 15 mm; the height of the fixed column (7) is 18.5 cm, and the diameter is 12 mm; the range of the dial indicator (6) is 20 mm.

4. The method for testing the mechanical properties of mortar under uniaxial confined compression conditions according to claim 1, characterized in that: The relationship between the circumferential strain at the middle position of the outer wall of the steel sleeve (2) in S1 and the pressure applied by the inner wall is y = 1.61x ， Where y is the pressure applied by the inner wall and x is the hoop strain at the middle of the outer wall.

5. The method for testing the mechanical properties of mortar under uniaxial confined compression conditions according to claim 4, characterized in that: The vertical displacement l of the test device in S7 a Subtract the vertical displacement of the upper and lower steel pressure heads (1) to obtain the vertical displacement l of the cylindrical specimen (8). s : l s =l a -2*l p *F axial / E Among them l a is the average value of the four percentage indicators, l p is the height of the steel pressure head, F axial is the axial force, E is the elastic modulus of the steel indenter; The initial length l0 of the cylindrical specimen (8) minus the vertical displacement l of the cylindrical specimen (8) is calculated as follows: s The length l of the cylindrical specimen (8) after the test is obtained: l＝l0-l s Due to the uneven axial deformation, the deformation of the cylindrical specimen (8) is simplified by the equivalent diameter method to obtain the volume strain. According to the relationship between the annular strain of the outer wall and the annular strain of the inner wall of the steel sleeve (2), the radial strains of the upper, middle and lower parts of the cylindrical specimen (8) are obtained as follows: ε1=4.84g u , ε2=4.92g m , ε3=4.84g l , where g u , g m and g l are the average values ​​of the strain gauge data of the upper, middle and lower parts of the outer wall of the steel sleeve (2); ε1 is the average radial strain of the upper part of the cylindrical specimen (8); ε2 is the average radial strain of the middle part of the cylindrical specimen (8); ε3 is the average radial strain of the lower part of the cylindrical specimen (8); The equivalent radial strain ε of the cylindrical specimen (8) during the test d for e d =(ε1+2ε2+ε3) / 4, The equivalent diameter d of the cylindrical specimen (8) in the test is d=d0(ε d +1), Where d0 is the initial diameter of the cylindrical specimen (8), The volume v of the cylindrical specimen (8) after the test is v=πld 2 / 4, The volume strain ε of the cylindrical specimen (8) during the test v for ε v =(v0-v) / v0, Where v0 is the initial volume of the cylindrical specimen (8), that is, v0 = πl0d0 2 / 4; Vertical stress σ of cylindrical specimen (8) z It is obtained by dividing the axial force by the equivalent cross-sectional area of ​​the cylindrical specimen (8) during loading. s z =4F axial / (πd 2 ), Since the circumferential strain at the middle of the outer wall of the steel sleeve (2) is linearly related to the pressure on the inner wall of the steel sleeve (2), and the pressure on the inner wall of the steel sleeve (2) and the pressure on the cylindrical specimen (8) are mutually acting and reacting, the radial confining pressure σ of the cylindrical specimen (8) is r for s r =1.61×g m , The hydrostatic pressure p on the cylindrical specimen (8) is p=(σ z +2s r ) / 3, Misess stress σ of cylindrical specimen (8) deviatoric for s deviatoric =|s z -s r |。

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