A method for measuring fracture energy using a concrete wedge splitting test device

Abstract

The present invention discloses a method for measuring fracture energy by using a concrete wedge splitting test device, including: performing a splitting test on a specimen with a notch at the top by using the concrete wedge splitting test device; fixing the specimen on the support system respectively, fixing the measuring device on the specimen, placing two rectangular steel plates on the specimen and making the extended section of the serrations of the second rectangular steel plate placed in the notch at the top of the specimen; fixing the specimen on the support system respectively, fixing the measuring device on the specimen, placing two rectangular steel plates on the specimen and making the extended section of the serrations of the second rectangular steel plate placed in the notch at the top of the specimen; calculating the splitting load and splitting displacement of the specimen respectively to obtain the fracture energy of the specimen. The advantages of the present invention are: applying prestress to the specimen, reducing the number of false crack paths, increasing the ratio of the crack area to the specimen volume, and at the same time using the fracture displacement relationship at different positions to obtain the splitting displacement, simplifying the fracture energy calculation formula.

Description

Technical Field

[0001] The present invention relates to the technical field of measuring the strength of concrete materials, and in particular to a method for measuring fracture energy using a concrete wedge splitting test device. Background Art

[0002] In modern civil engineering, an accurate understanding of the properties and behaviors of building materials is crucial for the economic and safe design of structures. In recent years, increasing attention has been paid to the evaluation of the post-peak performance of structures, that is, the mechanical response when the ultimate load is reached and failure occurs.

[0003] For quasi-brittle materials, the post-peak tensile behavior is manifested as cracking. In the constitutive model of materials, the mode-I fracture energy is an important material parameter for calibrating the behavior of softening materials. Compared with Young's modulus or uniaxial compression and tensile splitting strength, the accurate experimental determination of the specific mode-I fracture energy is still a research topic, such as three-point bending test, direct tensile test, compact tension test, wedge splitting test, etc. Experiments show that as the fracture area increases, the influence of experimental scatter and material heterogeneity on the obtained results decreases, but for the economic design of experimental schemes, small-volume specimens are more preferred. Therefore, it is necessary to increase the fracture area and the ratio of the fracture area to the specimen volume. The splitting test has obvious advantages, mainly including a relatively high ratio of the fracture area to the specimen volume, being almost insensitive to the gravity effect, having small errors in the test process, and being able to conduct stable and controlled research on the post-peak state, etc.

[0004] In the prior art, in order to install the test device and determine the crack initiation position, the specimen needs to have grooves and initial notches, which greatly increases the manufacturing difficulty and reduces the applicability to brittle materials. Summary of the Invention

[0005] The object of the present invention is to provide a method for measuring fracture energy using a concrete wedge splitting test device according to the deficiencies of the above prior art. By improving the structure of the splitting loading system, the measurement of the fracture energy of the specimen can be achieved only by setting a notch on the specimen.

[0006] The object of the present invention is achieved by the following technical solutions:

[0007] A method for measuring fracture energy using a concrete wedge splitting test device, characterized in that the method comprises the following steps:

[0008] (S1) Use a concrete wedge splitting test device to conduct a splitting test on a specimen with a notch at the top. Among them, the concrete wedge splitting test device includes a wedge loading system, a splitting loading system, a prestressing system, a support system, and a measuring device. The top of the wedge loading system is connected to the testing machine, and the bottom is connected to the splitting loading system. The prestressing system is respectively connected to the splitting loading system and the support system. The splitting loading system includes two rectangular steel plates with sawteeth, namely the first rectangular steel plate and the second rectangular steel plate. The sawteeth of the two rectangular steel plates are engaged with each other. Roller wheels are respectively installed at both ends of the rectangular steel plates through rollers. An extension section is provided at the bottom of the sawteeth of the second rectangular steel plate.

[0009] (S2) Fix the specimen on the support system respectively, fix the measuring device on the specimen, place the two rectangular steel plates on the specimen, and place the extension section of the sawteeth of the second rectangular steel plate in the notch at the top of the specimen.

[0010] (S3) Start the testing machine. The testing machine drives the wedge loading system to move downward to drive the two rectangular steel plates to move in opposite directions until the specimen splits.

[0011] (S4) Calculate the splitting load and splitting displacement of the specimen respectively to obtain the fracture energy of the specimen.

[0012] Arc-shaped cuts are provided on the sawteeth of the two rectangular steel plates. Among them, the arc-shaped cut on the sawteeth of the first rectangular steel plate is close to the notch of the specimen, and the arc-shaped cut on the sawteeth of the second rectangular steel plate contacts the top edge of the notch of the specimen and is far from the arc-shaped cut on the sawteeth of the first rectangular steel plate.

[0013] The wedge loading system includes a horizontal beam and two wedge blocks. The top of the wedge block is connected to the end of the horizontal beam, and the bottom is installed in the middle of the roller wheels on the same side of the two rectangular steel plates.

[0014] The prestressing system includes a steel cable and a tension control device. The two ends of the steel cable are respectively connected to the same ends of the rollers of the two rectangular steel plates, and the steel cable is wound around the support system. The tension control device is installed on the steel cable.

[0015] The support system includes a base and a central linear support. The central linear support is installed in the base, and the top and both ends of the central linear support extend outside the base.

[0016] The measuring device is a linear displacement sensor or an extensometer.

[0017] Calculate the splitting load of the specimen Where F mMeasure the maximum pressure for the test machine, and φ is the included angle between the wedge and the roller.

[0018] Calculate the splitting displacement of the test piece In the formula, δ sc1 and δ sc2 are the displacements of the test piece measured by the measuring device at distances l1 and l2 from the bottom of the test piece respectively, and a is the distance from the roller shaft to the bottom of the test piece.

[0019] Obtain the fracture energy of the test piece In the formula, A f is the fracture area of the test piece.

[0020] The advantages of the present invention are as follows: When conducting a splitting test, grooves do not need to be provided in the test piece; prestress is applied to the test piece, reducing the number of incorrect crack paths, increasing the ratio of the crack area to the volume of the test piece, and at the same time, using the fracture displacement relationship at different positions to calculate the splitting displacement, simplifying the fracture energy calculation formula; better studying the crack propagation behavior of quasi-brittle materials. Description of the Drawings

[0021] Figure 1 is the overall structure diagram of the device of the present invention;

[0022] Figure 2 is the top view of the rectangular steel plate of the present invention;

[0023] Figure 3 is the front view of the rectangular steel plate of the present invention;

[0024] Figure 4 is the structure diagram of the test piece under the prior art. Detailed Embodiments

[0025] The features of the present invention and other related features are further described in detail below through embodiments with reference to the drawings for the understanding of those skilled in the same industry:

[0026] As Figures 1-4 shown, the marks in the figure are respectively represented as: wedge-shaped loading system 1, horizontal beam 1-1, wedge 1-2, splitting loading system 2, rectangular steel plate 2-1, arc-shaped notch 2-2, roller shaft 2-3, roller 2-4, prestress system 3, steel cable 3-1, tension control device 3-2, test piece 4, notch 4-1, groove 4-2, support system 5, central linear support 5-1, base 5-2, measuring device 6, F m is the maximum pressure measured by the test machine, δ sc1 and δ sc2 are the displacements of the test piece measured by the measuring device at distances l1 and l2 from the bottom of the test piece respectively, a is the distance from the roller shaft to the bottom of the test piece, the splitting load F of the test piece sp , the splitting displacement δ of the test piecesp 。

[0027] As Figure 4 shown, under the existing technology, the test piece 4 is successively provided with a communicating groove 4-2 and a notch 4-1 from top to bottom. The groove 4-2 is for placing the splitting device and has a large size, while the notch 4-1 is for facilitating the determination of the crack position and has a small size. However, setting the groove 4-2 will increase the number of false crack paths, thereby reducing the measurement accuracy of the fracture energy of the test piece.

[0028] Example: As Figures 1-3 shown, this embodiment relates to a method for measuring fracture energy using a concrete wedge splitting test device, and the method includes the following steps:

[0029] (S1) Using a concrete wedge splitting test device to perform a splitting test on the test piece 4 with a notch 4-1 at the top. Among them, the concrete wedge splitting test device includes a wedge loading system 1, a splitting loading system 2, a prestressing system 3, a support system 5, and a measuring device 6. The top of the wedge loading system 1 is connected to the testing machine, and the bottom is connected to the splitting loading system 2. The prestressing system 3 is respectively connected to the splitting loading system 2 and the support system 5. The test piece 4 can be fixed on the support system 5, and the measuring device 6 can be fixed on the test piece 4. The splitting loading system 2 includes two rectangular steel plates 2-1 with sawteeth, namely the first rectangular steel plate and the second rectangular steel plate. The sawteeth of the two rectangular steel plates 2-1 are engaged with each other. At both ends of the rectangular steel plate 2-1, a roller 2-4 is installed through a roller shaft 2-3. The two rectangular steel plates 2-1 are both placed on the test piece 4, and the sawteeth of the second rectangular steel plate extend downward into the notch 4-1 at the top of the test piece 4. The testing machine drives the wedge loading system 1 to move downward to drive the two rectangular steel plates 2-1 to move in opposite directions to achieve the splitting of the test piece 4.

[0030] Specifically, arc-shaped cuts 2-2 are provided on the sawteeth of the two rectangular steel plates 2-1. Among them, the arc-shaped cut 2-2 on the sawteeth of the first rectangular steel plate is close to the notch of the test piece 4, which is convenient for the installation and positioning of the first rectangular steel plate. The arc-shaped cut 2-2 on the sawteeth of the second rectangular steel plate contacts the top edge of the notch 4-1 of the test piece 4 and is far from the arc-shaped cut 2-2 on the sawteeth of the first rectangular steel plate, which can avoid local damage of the end concrete when the second rectangular steel plate is stressed and moves to the right. In this embodiment, the size of the arc-shaped cut 2-2 on the sawteeth of the first rectangular steel plate is 1 / 4 circle, and the size of the arc-shaped cut 2-2 on the sawteeth of the second rectangular steel plate is 3 / 4 circle.

[0031] Specifically, the wedge loading system 1 includes a horizontal beam 1-1 and two wedges 1-2. The size of the wedges 1-2 gradually decreases from top to bottom. The two ends of the horizontal beam 1-1 are respectively connected to the tops of the two wedges 1-2. The bottoms of the wedges 1-2 are installed in the middle of the rollers 2-4 on the same side of two rectangular steel plates 2-1, and the rollers 2-4 can rotate. The testing machine drives the two wedges 1-2 to move downward. The wedges 1-2 act on the rollers 2-4 to apply a horizontal load to the rollers 2-4 and the rectangular steel plates 2-1, so as to drive the two rectangular steel plates 2-1 to move in opposite directions.

[0032] Specifically, the prestressing system 3 includes a steel cable 3-1 and a tension control device 3-2. The two ends of the steel cable 3-1 are respectively connected to the ends of the rollers 2-3 of the two rectangular steel plates 2-1, and the steel cable 3-1 is wound around the support system 5 (the end of the central linear support 5-1). The tension control device 3-2 is installed on the steel cable 3-1. The magnitude of the tension of the steel cable 3-1 is controlled by the tension control device 3-2 to ensure that cracks appear at the bottom of the notch 4-1 and develop downward.

[0033] Specifically, the support system 5 includes a base 5-2 and a central linear support 5-1. The central linear support 5-1 is installed in the base 5-2. The top and both ends of the central linear support 5-1 extend outside the base 5-2. In addition to fixing the specimen 4, the support system 5 can also provide a winding point for the steel cable 3-1 to ensure the normal operation of the steel cable 3-1.

[0034] In this embodiment, the measuring device 6 is a linear displacement sensor or an extensometer, which is used to measure the splitting displacement of the specimen.

[0035] (S2) Fix the specimen 4 on the support system 5 respectively, fix the measuring device 6 on the specimen 4, place the two rectangular steel plates 2-1 on the specimen 4, and place the extended section of the saw teeth of the second rectangular steel plate in the notch 4-1 at the top of the specimen 4.

[0036] (S3) Start the testing machine. The testing machine drives the wedges 1-2 of the wedge loading system 1 to move downward to drive the two rectangular steel plates 2-1 to move in opposite directions until the specimen 4 splits.

[0037] (S4) Calculate the splitting load of the specimen In the formula, F m is the maximum pressure measured by the testing machine, and φ is the angle between the wedge and the roller. Calculate the splitting displacement of the specimen In the formula, δ sc1 and δ sc2 are the displacements of the specimen measured at distances l1 and l2 from the bottom of the specimen through the measuring device respectively. a is the distance from the roller to the bottom of the specimen. Using the fracture displacement relationship at different positions, the splitting displacement is obtained, which simplifies the fracture energy calculation formula. Obtain the fracture energy of the specimen Where A f is the fracture area of the test piece.

[0038] The beneficial technical effects of this embodiment are as follows: When performing the splitting test, grooves do not need to be provided in the test piece; prestress is applied to the test piece, reducing the number of false crack paths, increasing the ratio of the crack area to the volume of the test piece, and at the same time, using the fracture displacement relationship at different positions to obtain the splitting displacement, simplifying the fracture energy calculation formula; better studying the crack propagation behavior of quasi-brittle materials.

[0039] Although the above embodiments have described in detail the concept and implementation of the object of the present invention with reference to the drawings, those of ordinary skill in the art can recognize that various improvements and transformations can still be made to the present invention without departing from the scope defined by the claims, so they will not be elaborated here one by one.

Claims

1. A method for measuring fracture energy using a concrete wedge splitting test device, characterized in that, The method includes the following steps: (S1) Performing a splitting test on a specimen with a notch at the top using a concrete wedge splitting test device. The concrete wedge splitting test device includes a wedge loading system, a splitting loading system, a prestressing system, a support system, and a measuring device. The top of the wedge loading system is connected to a testing machine, and the bottom is connected to the splitting loading system. The prestressing system is connected to the splitting loading system and the support system respectively. The splitting loading system includes two rectangular steel plates with serrations, namely a first rectangular steel plate and a second rectangular steel plate. The serrations of the two rectangular steel plates are engaged with each other. A roller is installed at each end of the rectangular steel plate through a roller shaft. An extension section is provided at the bottom of the serrations of the second rectangular steel plate; (S2) Fixing the specimen on the support system respectively, fixing the measuring device on the specimen, placing the two rectangular steel plates on the specimen, and placing the extension section of the serrations of the second rectangular steel plate in the notch at the top of the specimen; (S3) Starting the testing machine, and the testing machine drives the wedge loading system to move downward to drive the two rectangular steel plates to move in opposite directions until the specimen splits; (S4) Calculating the splitting load and splitting displacement of the specimen respectively to obtain the fracture energy of the specimen; Arc-shaped notches are provided on the serrations of the two rectangular steel plates. Among them, the arc-shaped notch on the serrations of the first rectangular steel plate is close to the notch of the specimen, and the arc-shaped notch on the serrations of the second rectangular steel plate contacts the top edge of the notch of the specimen and is away from the arc-shaped notch on the serrations of the first rectangular steel plate; The wedge loading system includes a horizontal beam and two wedges. The top of the wedge is connected to the end of the horizontal beam, and the bottom is installed in the middle of the rollers on the same side of the two rectangular steel plates; The prestressing system includes a steel cable and a tension control device. The two ends of the steel cable are respectively connected to the same ends of the roller shafts of the two rectangular steel plates, and the steel cable is wound around the support system. The tension control device is installed on the steel cable; The support system includes a base and a central linear support. The central linear support is installed in the base, and the top and both ends of the central linear support extend outside the base.

2. A method for measuring fracture energy using a concrete wedge splitting test device as described in claim 1, characterized in that, The measuring device is a linear displacement sensor or an extensometer.

3. A method for measuring fracture energy using a concrete wedge splitting test device according to claim 1, characterized in that, Calculate the splitting load of the test piece , where F m is the maximum pressure measured by the testing machine, is the included angle between the wedge block and the roller.

4. A method for measuring fracture energy using a concrete wedge splitting test device as claimed in claim 3, characterized in that, Calculate the splitting displacement of the test piece , where and are the displacements of the test piece measured by the measuring device at distances of l 1 and l 2 from the bottom of the test piece respectively, and is the distance from the roller to the bottom of the test piece.

5. A method for measuring fracture energy using a concrete wedge splitting test device as described in claim 4, characterized in that, Obtain the fracture energy of the test piece , where A f is the fracture area of the test piece.

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