GB2572866A

GB2572866A - Testing apparatus for determining tensile strength of soil and rock

Info

Publication number: GB2572866A
Application number: GB1904953.5A
Authority: GB
Inventors: Li Yanrong; Zhao Jingui; Wang Yongfeng
Original assignee: Taiyuan University of Technology
Current assignee: Taiyuan University of Technology
Priority date: 2018-04-09
Filing date: 2019-04-08
Publication date: 2019-10-16
Anticipated expiration: 2039-04-08
Also published as: CN108562479B; GB2572866B; GB201904953D0; CN108562479A

Abstract

A testing apparatus includes a control panel 138; a stationary fracturing rod 118 and an active fracturing rod 122 movable relative to the stationary rod; a sample positioning frame 144 with operating arm to position and center the sample 120 so that the two rods and center axis of the sample are aligned in the same vertical plane; a stepper driver 130 to control a stepper motor 134, the stepper motor further drives an electric cylinder 136; the electric cylinder forcibly urges the active rod towards the stationary rod to fracture the sample. A load cell 142, displacement sensor 140, and data processor are provided to collect pressure and displacement data, the processor calculates the tensile strength and generates a pressure-displacement curve for display on a display screen 112. Calculation of the tensile strength is based on a tensile strength constant, sample size correction coefficient, a maximum pressure, a mathematical constant, sample diameter and height, and a fracturing rod correction coefficient.

Description

TESTING APPARATUS FOR DETERMINING TENSILE STRENGTH OF SOIL AND

ROCK

Cross Reference of Related Applications [0001] This application claims the benefits of Chinese patent application no. 201810310994.5, filed on April 9, 2018 and entitled FRACTURING TESTING APPARATUS FOR TESTING THE TENSILE STRENGTH OF ROCK AND SOIL, which patent application is incorporated by reference herein in its entirety.

Field of the Invention [0002] The present invention relates generally to a testing apparatus for testing tensile strength of soil and rock. More so, the present invention relates to a testing apparatus for testing the tensile strength of rock and soil through use of a stationary fracturing rod and an active fracturing rod. The sample is defined in a cylindrical shape, and placed between the stationary rod and the active fracturing rod. The active fracturing rod urges the sample towards the stationary rod at a predetermined displacement rate. A sample positioning frame is provided to place the sample, in order to make sure that the center axis of the sample, the active fracturing rod and the stationary rod are in alignment within the same vertical plane. By doing so, the inaccuracies from eccentric forces and rotational torque occurred during the testing may be minimized. Therefore, the tensile strength measured by the present invention can be accurate. A control panel is provide to regulate the displacement rate of the active fracturing rod. A data processor collects and stores the pressure and displacement data generated during the testing. The collected data and the calculated results are graphically shown in real time on a display screen. The tensile strength the sample is calculated based on the following equation: ot = 2000 aFmax^dh + β, wherein ot is the tensile strength, 2000 is a tensile strength constant, a is the sample size correction coefficient, Fmax is the maximum pressure, π is mathematical constant, d is the diameter of the sample, h is the height of the sample, and β is the fracturing rod correction coefficient.

Background of the Invention [0003] The following background information may present examples of specific aspects of the prior art (e.g., without limitation, approaches, facts, or common wisdom) that, while expected to be helpful to further educate the reader as to additional aspects of the prior art, is not to be construed as limiting the present invention, or any embodiments thereof, to anything stated or implied therein or inferred thereupon.

[0004] Typically, tensile strength refers to the ultimate resistance capacity of a material for the tensile stress as generated by external loads. At present, the methods for testing the tensile strength of rock and soil are mainly the uniaxial stretching method, the Brazilian splitting method and the axial fracturing method.

[0005] The uniaxial tension method is the direct application of tension at the two ends of the sample until the sample is broken. The tensile strength is calculated by the peak tension force divided by the area of the fracture section at the time of fracture. With the uniaxial tension method, in the test, the complete process towards failure of the sample can be observed, which can intuitively reflect the mechanical behavior of the sample under tension. But, the uniaxial tension process has difficulties in mounting the sample of soil and soft rock materials. At present, the uniaxial tension test often uses a clamp or a polymer glue to connect and fix the two ends of the cylindrical sample to the device. The fixing clamp is of two semi-circular jaws, and screws are used to buckle and fasten the two jaws so as to fix the two ends of the sample. Because the soil and soft rock are generally weak and brittle, the ends of the sample are easily damaged under pressure when being fixed with fixing clamp or polymer glue. Secondly, it is difficult to center the clamps at the two ends of the sample, so that eccentric force can be easily generated during the test, which affects the test result. Furthermore, the relative displacement between the clamp and the sample is easy to occur in the process of tension, so that it is difficult to measure the true value of the deformation of the sample. With the use of polymer glue to bond the ends of the sample, the internal structure of the ends of the sample is easily damaged, the sample and the device are difficult to be bonded, and it is easy for the sample and the device to get detached in the process of tension.

[0006] With the Brazilian splitting method, the cylindrical sample is put in a horizontal way, the upper and lower positions thereof are padded with splitting strips, and splitting of the sample is implemented through application of a load to the splitting strips. In the actual operation of the Brazilian splitting method, there is the problem of being difficult to manipulate padding strip placement. As required in the specification, the padding strips must be placed symmetrically on the top and bottom of the sample, and the contact line between the two padding strips and the sample should be on the vertical longitudinal section of the sample. But, because the padding strips are small in size, it is difficult for the artificial placement effect to meet the specification requirements, and eccentric pressure is likely to occur when pressure is applied, which results in erroneous test results. In addition, the splitting strips are likely to slip in the process of pressure application, which results in failure of the test.

[0007] With the axial fracturing method, a small-diameter cylindrical block is placed on the upper and lower end faces of the cylindrical sample, and a load is applied on the block to fracture the sample. In actual operation, it is difficult to center the upper and lower cylindrical blocks precisely, which results in eccentric compression of the sample. In addition, the test fracturing effects are difficult to be uniform, and the samples after fracturing failure usually do not have the conical rupture surface and a plurality of independent cracks along the radial direction as required in the specification, which affects the test results.

[0008] In addition to the aforesaid existing problems, the load in the current tensile strength test methods is generally provided by a universal testing machine, and the related parts such as clamps, padding strips and cylindrical blocks need to be manufactured and customized additionally, so that the entire test system is expensive in price, and bulky in size. The test requires multiple people to cooperate, the operation is complicated with trivial details, and the efficiency is low. The test involves many steps of manual operation, and it is difficult to achieve precise placement of parts, which affects the final results of the test.

Summary [0009] Illustrative embodiments of the disclosure are generally directed to a testing apparatus for determining tensile strength of soil and rock. The testing apparatus includes a protective housing made of multiple sidewalls and covers, in which the components reside and the testing occurs.

[0010] The testing apparatus contains a stationary fracturing rod and an active fracturing rod within the protective housing. The active fracturing rod corresponds to the stationary fracturing rod, and is driven to fracture the sample at a predetermined displacement rate. A control panel regulates the displacement rate of the active fracturing rod. A sample positioning frame aligns the active fracturing rod with the stationary fracturing rod to minimize inaccuracies from eccentric forces and rotational torque during impact. The testing apparatus has a sample positioning frame for positioning and centering the sample between the active fracturing rod and the stationary fracturing rod, so that the active fracturing rod, the stationary fracturing rod, and the center axis of the sample are aligned in the same vertical plane;

[0011] The active fracturing rod engages the sample with pressure and a displacement rate. A data processor collects and stores the pressure and displacement data, and the collected data and calculated results are displayed graphically in real time on a display screen. The data processor calculates the tensile strength of the sample according to the following equation: σι = 2000 aFmaxTrdh + β. The relevant data and final test results of the test can be exported, and subsequent data access and processing are easily accessible.

[0012] In one aspect, a testing apparatus for determining tensile strength of soil and rock, comprises:

a control panel for controlling the testing apparatus during the testing;

a stationary fracturing rod and an active fracturing rod, whereby the active fracturing rod being movable relative to the stationary fracturing rod;

a sample positioning frame having an operating arm a, the sample positioning frame being manipulated by the operating arm a for positioning and centering the sample, so that the active fracturing rod, the stationary fracturing rod, and a center axis of the sample being aligned in the same vertical plane;

a stepper driver, a stepper motor and an electric cylinder, whereby the stepper driver being able to control the stepper motor, and the stepper motor further drive the electric cylinder;

wherein the electric cylinder forcibly urging the active fracturing rod towards the stationary fracturing rod to fracture the sample at a displacement rate, whereby the displacement rate being set by the control panel;

a load cell, a displacement sensor and a data processor, whereby the load cell being able to detect pressure from the active fracturing rod, to send the pressure data to the data processor for processing, whereby the displacement sensor being able to detect displacement of the active fracturing rod, to send the displacement data to the data processor for processing;

wherein the data processor receiving pressure data from the load cell, receiving the displacement data from the displacement sensor, calculating the tensile strength of the sample based on the following factor: a tensile strength constant, a sample size correction coefficient, a maximum pressure, a mathematical constant, a diameter of the sample, a height of the sample, and a fracturing rod correction coefficient.

wherein the data processor generating a pressure-displacement curve diagram based on the pressure force and the displacement; and a display screen graphically displaying the pressure force, the displacement, and the pressure-displacement curve diagram generated by the data processor in real time.

[0013] In another aspect, the apparatus further comprising a protective housing, wherein the protective housing comprises a front cover, a motor cover, and a frame platform.

[0014] In another aspect, wherein the operating arm a extending outside of the protective housing, so that when being operated, the operating arm a driving the sample positioning frame to a position where the center axis of the sample, the active fracturing rod and the stationary fracturing rod being aligned in the sample vertical plane.

[0015] In another aspect, wherein the stationary fracturing rod being fixed on the frame platform, and the sample being positioned between the stationary fracturing rod and the active fracturing rod, by means of moving and adjusting the sample positioning frame via the operating arm a.

[0016] In another aspect, the apparatus further comprising a nylon backing plate, wherein the frame platform is disposed adjacently to a nylon backing plate at an upper side of the frame platform and multiple foot pads at a bottom side of the frame platform.

[0017] In another aspect, the apparatus further comprising an adapter plate, wherein the active fracturing rod is operatively connected to the load cell through the adapter plate.

[0018] In another aspect, the apparatus further comprising a power module for supplying and manipulating power supply to the testing apparatus.

[0019] In another aspect, the apparatus further comprising a power switch, wherein the power switch being operatively connected to the power module.

[0020] In another aspect, the stepper motor and the stepper driver being operatively connected, so that the stepper driver being able to control the stepper motor.

[0021] In another aspect, the apparatus further comprising a mounting plate, wherein the mounting plate being disposed on the frame platform and adjacently to the stepper motor.

[0022] In another aspect, the electric cylinder operatively connects to the stepper motor, and the stepper motor being able to drive the electric cylinder.

[0023] In another aspect, the active fracturing rod being driven by the electric cylinder to move towards the stationary fracturing rod to fracture the sample during the testing, and mover away from the stationary fracturing rod when the testing being completed.

[0024] In another aspect, the data processor calculates the tensile strength value of the sample based on the following equation: σι = «Fmax/ndh + β, wherein σι is the tensile strength, is a tensile strength constant, a is the sample size correction coefficient, Fmax is the maximum pressure, π is mathematical constant, d is the diameter of the sample, h is the height of the sample, and β is the fracturing rod correction coefficient.

[0025] One objective of the present invention is to accurately test the tensile strength of soil and rock.

[0026] Another objective is to align the active fracturing rod with the stationary fracturing rod through a sample positioning frame, such that the sample positioning frame minimizes eccentric forces and rotational torque during the testing.

[0027] Another objective is to combine the mechanical structure that fractures the sample with the computer program that determines the tensile strength.

[0028] Yet another objective is to provide a mechanical structure that is light and simple in structure, easy to carry.

[0029] Yet another objective is to simplify the experimental operation and improves the experimental efficiency.

[0030] Other systems, testing apparatus, methods, features, and advantages will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims and drawings.

Brief Description of the Drawings [0031] The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

[0032] FIG. 1 illustrates a perspective view of an exemplary tensile strength testing apparatus, in accordance with an embodiment of the present invention;

[0033] FIG. 2 illustrates a perspective view of the inside of the housing of the tensile strength testing apparatus, shown in FIG. 1, in accordance with an embodiment of the present invention;

[0034] FIG. 3 illustrates the right side view of FIG. 2, in accordance with an embodiment of the present invention;

[0035] FIG. 4 illustrates the top view of FIG. 2, in accordance with an embodiment of the present invention;

[0036] FIGs. 5A-5D illustrate schematic views of the fracturing rods, in accordance with an embodiment of the present invention;

[0037] Like reference numerals refer to like parts throughout the various views of the drawings.

Detailed Description of the Invention [0038] The following detailed description is merely exemplary in nature and is not intended to limit the described embodiments or the application and uses of the described embodiments. As used herein, the word “exemplary” or “illustrative” means “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” or “illustrative” is not necessarily to be construed as preferred or advantageous over other implementations. All of the implementations described below are exemplary implementations provided to enable persons skilled in the art to make or use the embodiments of the disclosure and are not intended to limit the scope of the disclosure, which is defined by the claims. For purposes of description herein, the terms “upper,” “lower,” “left,” “rear,” “right,” “front,” “vertical,” “horizontal,” and derivatives thereof shall relate to the invention as oriented in FIG. 1. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. It is also to be understood that the specific testing systems and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments of the inventive concepts defined in the appended claims. Specific dimensions and other physical characteristics relating to the embodiments disclosed herein are therefore not to be considered as limiting, unless the claims expressly state otherwise.

[0039] A testing apparatus 100 for determining tensile strength of soil and rock is referenced in FIGs. 1-5. The testing apparatus 100 is configured to test the tensile strength of soil and rock. The testing apparatus 100 is light and compact in structure; no additional parts are needed for testing with minimal systematic errors; it is convenient to position the sample and simple in operation with high efficiency for the testing.

[0040] In some embodiments, the testing apparatus 100 may include a protective housing 102 made of multiple sidewalls and covers, in which the components reside and the testing occurs. The housing 102 contains a stationary fracturing rod 118 that works together with an active fracturing rod 122 to fracture a sample 120. The active fracturing rod 122 corresponds to the stationary fracturing rod 118, and that fracture the sample 120 at a predetermined displacement rate. A control panel 138 regulates the displacement rate of the active fracturing rod 122. A sample positioning frame 144 aligns the active fracturing rod 122 with the stationary fracturing rod 118 to minimize inaccuracies from eccentric forces and rotational torque during impact.

[0041] The active fracturing rod 122 engages the sample 120 with pressure and displacement. A data processor 126 includes data acquisition module, data analysis module. The data acquisition module collects and stores the pressure and displacement data, which can be displayed graphically in real time on a display screen 112. The data analysis module calculates the tensile strength value of the sample 120 according to the following equation: σι = 2000 «Fmax/ndh + β. The relevant data and final test results of the test can be exported, and subsequent data access and processing are easily accessible.

[0042] As referenced in FIG. 2, the testing apparatus 100 comprises a housing 102 that provides a protective component for the electrical and mechanical structures contained therein. In some embodiments, the housing 102 comprises a front cover 104, a motor cover 106, and a frame platform 146. The frame platform 146 is disposed adjacently to a nylon backing plate 108 at an upper side of the frame platform 146 and multiple foot pads 110 at a bottom side of the frame platform 146 (FIG. 3).

[0043] As FIG. 4 shows, the testing apparatus 100 further includes a stationary fracturing rod 118 being operable to work together with the active fracturing rod for fracturing a sample 120, the sample 120 being defined by a cylindrical shape. The sample 120 is mounted vertically, and is stable without slip, the sample positioning frame 144 is used to standardize the position of sample 120, which prevents the generation of deviatory stress and guarantees unification of sample damage effects, so that the test result is accurate and reliable.

[0044] During the testing process, the sample 120 is placed vertically, the center axis of the sample 120 in cylindrical shape is vertical to surface of the frame platform 146, and the two flat surfaces of the sample 120 in cylindrical shape are horizontal to the surface of the frame platform 146. The fracturing rods apply pressure to the sample 120 in the horizontal direction to ensure that the sample 120 is always in a stable state during the test without slip, which avoids the problem of instability resulting from horizontal placement of the sample 120 in the Brazilian splitting method and from putting a small block at the lower end of the sample 120 in the axial fracturing method.

[0045] As FIG. 1 shows, the testing apparatus 100 also provides an active fracturing rod 122 corresponding to the stationary fracturing rod 118. The active fracturing rod 122 is movable in an axial path which is parallel to the surface of the frame platform 146 and vertical to the center axis of the sample 120, at a displacement rate to forcibly urge the sample 120 towards the stationary fracturing rod 118. The active fracturing rod 122 is pushed forward in the horizontal direction to complete the fracturing of the sample 120.

[0046] FIGs. 5A-5D illustrate schematic views of various types of the tip of the fracturing rods. FIG. 5A shows a fracturing rod 500 with a 10 mm diameter and frustoconical shape having a 2mm nose. FIG. 5B shows a fracturing rod 502 with a 10 mm diameter and frustoconical shape having a 1mm nose. FIG. 5C shows a fracturing rod 504 with a 10 mm diameter and round nose. FIG. 5D shows a fracturing rod 506 with a semicircular shape. In one non-limiting embodiment, the stationary fracturing rod 118 and active fracturing rod 122 are the same in structure, and the cross sections are trapezoidal, semicircular in shape or of an isosceles triangle in shape with the vertex angle as a round angle.

[0047] The test object of the present invention is a cylindrical soil or soft rock sample. The testing apparatus 100 simplifies the test operation, the test efficiency is high, and the sample 120 only needs to be placed in the test area without the need for clamps, glue or other additional parts to fix the sample 120, so that damage to the structure of the sample 120 is avoided. The testing apparatus 100 uses a sample positioning frame 144 to standardize the position of the sample 120, which ensures that the two fracturing rods are on the same center plane of the sample 120, thus avoiding the problem of eccentric force that easily occurs in the direct stretching method, the Brazilian splitting method and the axial fracturing method, so that the accuracy of the test result is guaranteed. The fracture plane is fitted to the center plane, the damage effect of the sample 120 is uniform, and the test result is reliable.

[0048] Referring to FIGs. 1 and 4, the sample positioning frame 144 has an operating arm 144a which extends outside the protective housing 102, so that the operator can hold the operating arm 144a to move the sample positioning frame 144. By hold the operating arm 144a and adjusting the sample positioning frame 144, the sample 120 can be accurately positioned between the active fracturing rod 122 and the stationary fracturing rod 118. Actually the sample 120 is positioned in a position where the center axis of the sample 120, the stationary fracturing rod 118 and the active fracturing rod 122 are in axial alignment within a single vertical plane. The stationary fracturing rod 118 and the active fracturing rod 122 are mirrored relative to the center axis of the sample 120.

[0049] In order to create an efficient and accurate tensile strength value, the testing apparatus 100 include the sample positioning frame 144 aligning the active fracturing rod 122 with the stationary fracturing rod 118, whereby the sample positioning frame 144 minimizes eccentric forces and rotational torque during impact from the active fracturing rod 122. The sample 120 is positioned between the stationary fracturing rod 118 and active fracturing rod 122, and through adjusting a sample positioning frame 144, the sample 120 is centered and fitted into the accurate testing position.

[0050] In some embodiments, the testing apparatus 100 further includes an electric cylinder 136 forcibly urging the active fracturing rod 122 towards the stationary fracturing rod 118 for fracturing the sample 120 at a displacement rate. In this manner, the active fracturing rod 122 engages the sample 120 with pressure and a displacement rate.

[0051] In some embodiments, the testing apparatus 100 further includes a control panel 138 operatively connected to the electric cylinder 136, the control panel 138 regulating the displacement rate of the active fracturing rod 122. In one possible embodiment, the control panel 138 includes the display screen 112, a control button, and an adjustment button. In some embodiments, the testing apparatus 100 may also include a power module 128, such as a battery or power outlet. A power switch 114 operatively connects to the power module 128 to power on and power off the testing apparatus 100.

[0052] In some embodiments, the testing apparatus 100 further includes a stepper motor 134 being operatively connected to the electric cylinder 136. Furthermore, the testing apparatus 100 includes a stepper driver 130 that is operatively connected to the stepper motor 134. In some embodiments, the testing apparatus 100 further includes a load cell 142 that is configured to detect pressure from the active fracturing rod 122. In some embodiments, the active fracturing rod 122 is operatively connected to the load cell 142 through an adapter plate 124. In some embodiments, the testing apparatus 100 further includes a displacement sensor 140 detecting displacement from the active fracturing rod 122.

[0053] Referring to FIGs. 2 and 3, the displacement sensor 140 is configured inside the protective housing 102. The displacement sensor 140 is configured under the surface of the frame platform 146. Because the displacement sensor 140 is set inside the protective housing 102 and under the frame platform 146, it cannot be seen from the FIGs. 2 and 3.

[0054] Looking back at FIG. 1, the data processor 126 of the testing apparatus 100 includes a data acquisition module collecting and storing the pressure from the load cell 142 and the displacement rate from the displacement sensor 140. In some embodiments, the data processor 126 of the testing apparatus 100 further includes a display screen 112 graphically displaying the pressure and the displacement in real time. After the testing is finished, the data analysis module of the data processor 126 calculates the tensile strength value. The data analysis module calculates the tensile strength value of the sample 120 based on the following factors: a tensile strength constant, the sample size correction coefficient, the maximum pressure, a mathematical constant, the diameter of the sample, the height of the sample, and the fracturing rod correction coefficient.

[0055] In one non-limiting embodiment, the data analysis module calculates the tensile strength value of the sample 120 based on the following equation: σι = 2000 «Fmax/ndh + β. In this equation: 2000 is a tensile strength constant, a is the sample size correction coefficient, Fmax is the maximum pressure, π is mathematical constant, d is the diameter of the sample, h is the height of the sample, and β is the fracturing rod correction coefficient. In one non-limiting embodiment, the height and diameters are calculated in millimeters.

[0056] In one non-limiting embodiment, the data acquisition module generates a pressuredisplacement curve diagram based on the pressure and the displacement. The pressuredisplacement curve diagram is displayed on the display screen 112.

[0057] In one non-limiting embodiment, the data processor 126 is used to collect and manipulate data about the pressure and displacement of the active fracturing rod 122. The data processor 126 includes at least one of the following: the display screen 112, an indicator light, a control button, a debugging button, and a USB jack.

[0058] The beneficial effects of the present invention are as follows: (1) the testing apparatus 100 as provided in the present invention has a compact structure, integrates the mechanical structure with the data processing module, and requires no additional parts for testing. (2) The testing apparatus 100 is provided with four different sets of fracturing rods of different structures, and provides calculation correction factors for different fracturing rods to meet the testing requirements of samples since the sample could contain materials of different hardness. (3) The testing apparatus 100 is simple for sample placement and sample replacement operations, uses a sample positioning frame 144 to standardize and accurately position the sample, and makes the fracturing rods at the two ends right on the same center plane along the center axis of the sample, which ensures that eccentric force does not occur during the test, so that the accuracy of the test result is guaranteed.

[0059] Some additional benefits include (4) In the process of fracturing, the sample is always upright without the phenomenon of tilted sliding, so that the test result is true and reliable. The testing apparatus 100 collects and stores the pressure and displacement through the acquisition module of the data processor 126, and displays it on the display screen 112 in real time. (5) After the test is finished, the data analysis module of the data processor 126 automatically calculates the tensile strength value of the sample, and displays it on the display screen. And (6) the relevant data and final test results of the test process can be exported and transplanted, and subsequent data access and further processing are convenient and quick.

[0060] In another possible embodiment of the present invention, the testing apparatus 100 comprises a data processor 126, a power module 128, a stepper driver 130, a stepper motor 134, an electric cylinder 136, a power switch 114, a control panel 138, a displacement sensor 140 and a load cell 142, a mounting plate 132 is set on top of the stepper motor 134, the mounting plate 132 is a fixation platform for fixing other parts through bolts or snaps; the mounting plate 132 is set with the power module 128 and the stepper driver 130, the stepper driver 130 is connected with the stepper motor 134; the electric cylinder 136 is connected with the stepper motor 134, the stepper motor 134 provides displacement power for the electric cylinder 136; a control panel is set at the junction of the front cover 104 and the motor cover 106, the control panel is set with the data processor 126, the control panel 138 and the power switch 114; the control panel 138 is connected with the stepper driver 130, the control panel 138 is used to send a control signal to the stepper driver 130 to control the steering, speed and travel of the stepper motor 134; one end of the displacement sensor 140 is fixed to the bottom surface of the frame platform 146, the other end is in contact with the active fracturing rod 122, and the displacement sensor 140 is connected with the data processor 126 by wire; the control panel 138 is used to input the displacement rate of the test, the control panel 138 is connected with the stepper driver 130, so as to control the rotation speed of the stepper motor 134, and to further control the displacement rate of the active fracturing rod 122.

[0061] The load cell 142 is set at the rear end of the active fracturing rod 122 and is connected with the data processor 126 by wire to record the pressure data as transmitted by the active fracturing rod 122 during the testing.

[0062] The power module 128 is connected with the power supply interface for the power switch 114, the data processor 126, the control panel 138 and the stepper driver 130 to supply power to the entire set of the testing apparatus 100.

[0063] The electric cylinder 136 is mainly used to drive the active fracturing rod 122 to move forward, and the electric cylinder 136 converts the rotation of the stepper motor 134 into a forward displacement, which thus drives the active fracturing rod 122 to move forward. It produces effects on the load cell 142 and the displacement sensor 140 while moving forward, and generates the displacement and pressure data.

[0064] Furthermore, the frame platform 146 is set with a nylon backing plate 108 at the upper side and with foot pads 110 at the bottom. The stationary fracturing rod 118 is mounted on the frame platform 146 through the stationary fracturing rod fixing seat 116 of the stationary fracturing rod 118.

[0065] Furthermore, the sample positioning frame 144 is set between the stationary fracturing rod 118 and the active fracturing rod 122, the sample positioning frame 144 is embedded on the frame platform 146, the sample positioning frame 144 is composed of two guiding blocks, the two guiding blocks are respectively set on the two sides of the sample 120, and can move back and forth along the guiding hole. The guiding hole is configured under the frame platform 146, so it cannot been seen from the drawings; however, the operating arm 144a extends through the guiding hole towards outside of the protective housing 102 (FIGs 1 and 4).

[0066] Furthermore, the active fracturing rod 122 is connected with the load cell 142 through the adapter plate 124, and a threaded interface is set at each end of the adapter plate 124 to be respectively connected to the active fracturing rod 122 and the load cell 142.

[0067] The stationary fracturing rod and the active fracturing rod are the same in structure, and the fracturing rods are of a truncated cone in shape, hemispherical in shape or of an isosceles triangle in shape with the vertex angle as a round angle. The different types of the tips of the fracturing rod are shown in FIG. 5, and the cross sections of the fracturing rods with different serial numbers are different in shape. For the data of the formula, the correction coefficient values a and β are obtained by using the remolded loss samples of different sizes, and by correcting the tensile strength values as measured by the testing machine through the tensile strength as measured by the direct stretching method, see Table 1 and Table 2 below:

Table 1 Sample size correction coefficient a according to samples of the same diameter but different heights

Sample parameters	a
Diameter 50 mm, height 30 mm	1.075
Diameter 50 mm, height 50 mm	1.054
Diameter 50 mm, height 80 mm	1.000
Diameter 50 mm, height 100 mm	0.941

Table 2 Fracturing rod correction coefficient β according to different fracturing rods as shown in FIG. 5

Fracturing rod number	β
NO. A	0.118
NO. B	0.024
NO. C	-0.094
NO. D	-0.116

[0068] In conclusion, the testing apparatus 100 is configured to complete fracturing failure of the rock and soil samples by way of providing power through a stepper motor (134), pushing the active fracturing rod 122 to move through an electric cylinder 136, and controlling the fracturing rate through a control panel 138 and a stepper driver 130. During the test, the data acquisition module of the data processor 126 collects and stores the pressure and displacement, displays it on the display screen 112 of the data processor 126 in real time, and generates the pressuredisplacement curve diagram. After the test is finished, the data analysis module of the data processor 126 calculates the tensile strength value of the sample 120.

[0069] These and other advantages of the invention will be further understood and appreciated by those skilled in the art by reference to the following written specification, claims and appended drawings.

[0070] Because many modifications, variations, and changes in detail can be made to the described preferred embodiments of the invention, it is intended that all matters in the foregoing description and shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense. Thus, the scope of the invention should be determined by the appended claims and their legal equivalence.

Claims

1. A testing apparatus (100) for determining tensile strength of soil and rock, the apparatus comprising:

a control panel (138) for controlling the testing apparatus (100) during the testing;

a stationary fracturing rod (118) and an active fracturing rod (122), whereby the active fracturing rod (122) being movable relative to the stationary fracturing rod (118);

a sample positioning frame (144) having an operating arm (144a), the sample positioning frame (144) being manipulated by the operating arm (144a) for positioning and centering the sample (120), so that the active fracturing rod (122), the stationary fracturing rod (118), and a center axis of the sample (120) being aligned in the same vertical plane;

a stepper driver (130), a stepper motor (134) and an electric cylinder (136), whereby the stepper driver (130) being able to control the stepper motor (134), and the stepper motor (134) further drive the electric cylinder (136);

wherein the electric cylinder (136) forcibly urging the active fracturing rod (122) towards the stationary fracturing rod (118) to fracture the sample (120) at a displacement rate, whereby the displacement rate being set by the control panel (138);

a load cell (142), a displacement sensor (140) and a data processor (126), whereby the load cell (142) being able to detect pressure from the active fracturing rod (122), to send the pressure data to the data processor (138) for processing, whereby the displacement sensor (140) being able to detect displacement of the active fracturing rod (122), to send the displacement data to the data processor (138) for processing;

wherein the data processor (126) receiving pressure data from the load cell (142), receiving the displacement data from the displacement sensor (140), calculating the tensile strength of the sample (120) based on the following factor: a tensile strength constant, a sample size correction coefficient, a maximum pressure, a mathematical constant, a diameter of the sample (120), a height of the sample (120), and a fracturing rod correction coefficient. wherein the data processor (126) generating a pressure-displacement curve diagram based on the pressure force and the displacement; and a display screen (112) graphically displaying the pressure force, the displacement, and the pressure-displacement curve diagram generated by the data processor (126) in real time.

2. The apparatus of claim 1, further comprising a protective housing (102), wherein the protective housing (102) comprises a front cover (104), a motor cover (106), and a frame platform (146).

3. The apparatus of claim 2, wherein the operating arm (144a) extending outside of the protective housing (102), so that when being operated, the operating arm (144a) driving the sample positioning frame (144) to a position where the center axis of the sample (120), the active fracturing rod (122) and the stationary fracturing rod (118) being aligned in the sample vertical plane.

4. The apparatus of claim 3, wherein the stationary fracturing rod (118) being fixed on the frame platform (146), and the sample (120) being positioned between the stationary fracturing rod (118) and the active fracturing rod (122), by means of moving and adjusting the sample positioning frame (144) via the operating arm (114a).

5. The apparatus of claim 2, further comprising a nylon backing plate (108), wherein the frame platform (146) is disposed adjacently to a nylon backing plate (108) at an upper side of the frame platform (146) and multiple foot pads (110) at a bottom side of the frame platform (146).

6. The apparatus of claim 1, further comprising an adapter plate (124), wherein the active fracturing rod (122) is operatively connected to the load cell (142) through the adapter plate (124).

7. The apparatus of claim 1, further comprising a power module (128) for supplying and manipulating power supply to the testing apparatus (100).

8. The apparatus of claim 7, further comprising a power switch (114), wherein the power switch (114) being operatively connected to the power module (128).

9. The apparatus of claim 1, wherein the stepper motor (134) and the stepper driver (130) being operatively connected, so that the stepper driver (134) being able to control the stepper motor (134).

10. The apparatus of claim 2, further comprising a mounting plate (13 2), wherein the mounting plate (132) being disposed on the frame platform (146) and adjacently to the stepper motor (134).

11. The apparatus of claim 9, wherein the electric cylinder (136) operatively connects to the stepper motor (134), and the stepper motor (134) being able to drive the electric cylinder (136).

12. The apparatus of claim 11, wherein the active fracturing rod (122) being driven by the electric cylinder(136) to move towards the stationary fracturing rod (118) to fracture the sample (120) during the testing, and mover away from the stationary fracturing rod (118) when the testing being completed.

13. The apparatus of claim 1, wherein the data processor (126) calculates the tensile strength value of the sample (120) based on the following equation: ot = 2000 «F,liaxTrdh + β, wherein ot is the tensile strength, 2000 is a tensile strength constant, a is the sample size correction coefficient, Fmax is the maximum pressure, π is mathematical constant, d is the diameter of the sample, h is the height of the sample, and β is the fracturing rod correction coefficient.

14. An apparatus substantially as hereinbefore described with reference to any one of the embodiments or to any one of the accompanying drawings.