Dynamic fracture toughness testing device based on endb specimen and installation method thereof

Abstract

The application discloses a kind of based on ENDB sample dynamic fracture toughness testing device, including test auxiliary device and Hopkinson bar experimental device, Hopkinson bar experimental device includes incident bar and transmission rod, test auxiliary device includes load transmission structure, dial, support seat component, sample fixing assembly and auxiliary fixing assembly, dial, sample fixing assembly and support seat are fixed by distance adjusting component of three through three connections.This application can accurately adjust the included angle α between loading rod and prefabricated crack, so that the dynamic fracture toughness test of a variety of different angles III and I, III mixed type can be realized, the dynamic fracture toughness test experiment of a variety of diameter sizes ENDB sample can be satisfied, and a certain fracture failure play space is reserved between dial and sample, to improve sample damage effect and the accuracy of experimental results.The whole device has no direct or indirect contact with the outside world, reduces the loss of energy, improves the accuracy of experimental results.

Description

Technical Field

[0001] This invention relates to the field of indoor rock mechanics testing technology, and in particular to a dynamic fracture toughness testing device based on ENDB specimens and its installation method. Background Technology

[0002] Fracture mechanics classifies cracks into three main types based on their stress characteristics: opening cracks (Type I), slip cracks (Type II), and tearing cracks (Type III). With the increasing frequency of impact disturbances in underground rock engineering projects, leading to a gradual increase in disasters, pure Type III fractures and mixed Type I and III fracture failures under the dynamic action of rock materials have gradually become research hotspots.

[0003] The ENDB (Edge Notched Disc Bend) specimen is a disc with edge cracks generated along the diameter of one side of the specimen. By simply changing the angle α between the loading support and the pre-existing crack, it is possible to obtain pure Type I, pure Type III, and a complete mixture of both.

[0004] First, Type III fracture requires a specific angle. Current three-point bending dynamic fracture toughness testing devices cannot alter or accurately determine the angle α between the pre-existing crack and the loading bar in the ENDB specimen, making it impossible to complete pure Type III or mixed Type I / III dynamic fracture toughness tests. Some methods involve first sketching the loading bar's placement using a protractor and then gluing it to the specimen. This method is not only cumbersome but also results in weak adhesion. Because the loading bar and specimen are only in linear contact, instantaneous impacts can occur during the test, causing the loading bar to shift or even fall off.

[0005] Secondly, the uniqueness of the diameter of the Hopkinson bar, a traditional dynamic testing instrument, directly limits the dimensional flexibility of the ENDB method for dynamic fracture toughness testing, making it impossible to complete dynamic tests that take into account the effect of the specimen diameter.

[0006] Furthermore, the existing three-point bending dynamic fracture toughness testing device is separated from the Hopkinson bar, resulting in a partial loss of energy of the incident bar during the experiment, thus the accuracy of the experimental mechanical test results cannot be guaranteed. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a dynamic fracture toughness testing device and its installation method based on ENDB specimens, which aims to meet the needs of Type III and Type I / III mixed dynamic fracture toughness testing of ENDB specimens with various diameters and improve the convenience and accuracy of Type III and Type I / III mixed dynamic fracture toughness testing.

[0008] The technical solution of the present invention is as follows: a dynamic fracture toughness testing device based on ENDB specimens, including a testing auxiliary device and a Hopkinson bar experimental device, wherein the Hopkinson bar experimental device includes an incident bar and a transmission bar, characterized in that the testing auxiliary device includes: a load transmission structure, a scale, a support base assembly, a specimen fixing assembly, and an auxiliary fixing assembly.

[0009] The centers of the incident rod, the ENDB sample, and the transmission rod are located on the same axis.

[0010] The specimen fixing assembly is clamped on the outside of the cylindrical surface of the ENDB specimen, and the end face of the ENDB specimen is placed between the dial and the support assembly.

[0011] The load transmission structure includes a loading rod and a cylindrical rod perpendicular to the loading rod, with the outer side of the cylindrical rod in close contact with the incident rod.

[0012] The end face of the dial is provided with angle scales and concentric circle scales, and the loading rod protrudes and is installed on the scale surface of the dial.

[0013] The support assembly includes: a support base and two adjustable support rods connected to the support base;

[0014] The auxiliary fixing component is located on the back of the support base assembly and is used to fix the transmission rod;

[0015] The dial, sample fixing assembly, and support base are connected and fixed by an adjusting assembly that runs through them, and the three components can be moved and adjusted on the adjusting assembly.

[0016] Furthermore, the end face of the dial is provided with an embedded groove along the diameter direction for accommodating the loading rod.

[0017] Furthermore, the inner groove of the dial is provided with a crescent-shaped wedge that fits into the inner groove and the loading rod.

[0018] Furthermore, the support base is provided with a graduated sliding groove, on which two bases are slidably mounted, and two support rods are respectively installed on the two bases.

[0019] Furthermore, the sample fixing assembly is a notched support ring with threaded holes evenly distributed on its cylindrical surface, through which bolts pass and abut against the ENDB sample.

[0020] Furthermore, the auxiliary fixing component is a cylindrical tube groove, and the cylindrical surface of the cylindrical tube groove is evenly distributed with threaded holes.

[0021] Furthermore, the adjustment assembly includes a screw that passes through the dial, the sample fixing assembly, and the support base, as well as nuts that fix the three components onto the screw.

[0022] The present invention also provides a method for installing the testing device as described above, comprising the following steps:

[0023] S1. Adjusting the support assembly: Determine and adjust the distance between the two support rods based on parameters such as the diameter D and thickness H of the ENDB specimen and the angle α between the loading rod and the pre-fabricated crack required by the fracture mode.

[0024] S2. Assemble the load transmission structure and the dial, and then press the incident rod tightly against the load transmission structure.

[0025] S3. Place the sample: Place the ENDB sample at the center of the dial of the assembly in step S2 according to the required angle α between the loading bar and the precast crack.

[0026] S4. Determine the sample position: Adjust and fix the clamping position of the sample fixing assembly on the ENDB sample;

[0027] S5. Adjust and fix the relative positions of the dial, sample fixing assembly and support base;

[0028] S6. After the ENDB sample is completely fixed by the loading rod and the two support rods in step S5, release the clamping of the ENDB sample by the sample fixing assembly.

[0029] S7. Coupling transmission rod: Place the transmission rod inside the auxiliary fixing assembly and fix it. Then install the auxiliary fixing assembly on the back of the support base and ensure that the center of the incident rod, the ENDB sample, and the transmission rod are on the same axis.

[0030] Furthermore, before proceeding to step S5, adjust the dial to allow for a certain amount of space for fracture failure to occur between it and the ENDB sample.

[0031] Further, in step S3, the incident rod end of the assembly from step S2 is vertically downward so that the scale surface of the dial is horizontally upward. Then, the pre-crack surface of the ENDB sample is facing upward, and it is placed horizontally on the dial according to the required angle α between the loading rod and the pre-crack.

[0032] By adopting the above solution, the present invention has the following beneficial effects:

[0033] (1) It can precisely adjust the angle α between the loading rod and the precast crack, thereby enabling dynamic fracture toughness testing of various types III and mixed types I and III with different angles;

[0034] (2) It can meet the dynamic fracture toughness test of ENDB specimens with various diameters, and a certain space for fracture failure is reserved between the dial and the specimen to improve the failure effect of the specimen and the accuracy of the test results.

[0035] (3) The entire device has no direct or indirect contact with the outside world, which reduces energy loss and improves the accuracy of experimental results. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the overall structure of the testing device of the present invention.

[0037] Figure 2 This is the fixed structure of the testing device of the present invention.

[0038] Figure 3 This is a schematic diagram of the scale of the present invention.

[0039] Figure 4 This is a schematic diagram of the support base assembly of the present invention.

[0040] Figure 5 This is a schematic diagram of the sample fixing assembly of the present invention.

[0041] Figure 6 This is a front view of the crescent-shaped wedge of the present invention.

[0042] Figure 7 This is a side view of the crescent-shaped wedge of the present invention. Detailed Implementation

[0043] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0044] Please see Figure 1 The dynamic fracture toughness testing device based on ENDB specimens disclosed in this embodiment includes a testing auxiliary device and a Hopkinson bar experimental device. The Hopkinson bar experimental device includes an incident bar 1 and a transmission bar 2. The testing auxiliary device includes a load transmission structure 3, a scale 4, a specimen fixing assembly 5, a support base assembly 6, and an auxiliary fixing assembly 7.

[0045] The load transmission structure 3 includes a loading rod 31 and a cylindrical rod 32 perpendicular to the loading rod 31. The outer side of the cylindrical rod 32 is in close contact with the incident rod 1, and the inner side of the load transmission structure 3 is in close contact with the dial 4.

[0046] Please see Figure 3The end face of the dial 4 is arranged with angle scales and equidistant concentric circle scales. Since the angle between the pre-fabricated crack 110 and the linear loading is strictly required during Type III dynamic fracture toughness testing, the angle scale greatly facilitates the placement of the ENDB specimen 100 and enables experiments on mixed Type I and Type III dynamic fracture modes with various included angles. The concentric circle scales are mainly to help place the specimen as close to the center as possible. In this embodiment, the accuracy of the angle scale is 0.5°, and the accuracy of the concentric circle scale is 2mm. The end face of the dial 4 has an embedded groove 41 along the diameter direction to accommodate the loading rod 31. This embedded groove 41 is a cylindrical groove, mainly used to hold the loading rod 31, facilitating specimen placement and angle measurement.

[0047] The loading rod 31 protrudes from the surface of the dial 4. Considering that the sample being in close contact with the dial scale surface will affect the experimental fracture failure effect, an appropriate space is left in the inner groove 41 to insert a crescent-shaped wedge 8. The wedge 8 fits the shape of the loading rod 31, and the loading rod 31 is embedded in the notch of the wedge 8. This allows for a certain amount of fracture failure space to be reserved between the ENDB sample 100 and the dial scale surface of the dial 4, so as to improve the sample failure effect and the accuracy of the experimental results.

[0048] Please see Figure 4 The support assembly 6 includes a support base 61 and two adjustable support rods 62 connected to the support base 61. Specifically, the support base 61 has a graduated sliding groove 62 with a graduation measurement accuracy of 0.5 mm. Two bases 63 are slidably mounted on the sliding groove 62. The bases 63 can automatically slide and be fixed within the sliding groove 62. The bases 63 are fixed to the support base 61 by base bolts 64 and sliding groove washers 67. The two support rods 62 are respectively mounted on the two bases 63. The two ends of the support rods 62 are connected to the bases 63 by steel plates 65. The support rods 62 and steel plates 65, and the steel plates 65 and bases 63 are fixed by bolts 66, facilitating the assembly and disassembly of the support rods 62.

[0049] Please see Figure 5 The specimen fixing assembly 5 is clamped on the outer side of the cylindrical surface of the ENDB specimen 100. It includes a movable metal support ring 51 and three long bolts 52 for fixing the specimen. The center of the support ring 51 has a sufficiently large through hole to accommodate specimens of different diameters. The cylindrical surface of the support ring 51 is evenly distributed with threaded holes. The long bolts 52 pass through the threaded holes to fix the specimen. The three sufficiently long bolts can be adjusted to hold ENDB specimens 100 of various diameters, thereby realizing the dynamic fracture toughness test of ENDB specimens that takes into account the effects of multiple diameter sizes. The metal support ring 51 has a 1 / 4 notch to facilitate the high-speed camera to capture the fracture path of the specimen.

[0050] Please see Figure 1and Figure 2 The auxiliary fixing assembly 7 is used to fix the transmission rod 2. It includes a cylindrical tube groove 71, in which the transmission rod 2 is embedded. The centers of the incident rod 1, the ENDB sample 100, and the transmission rod 2 are located on the same axis. The cylindrical surface of the cylindrical tube groove 71 has four threaded holes evenly distributed. Four device fixing bolts 72 are locked in the threaded holes and abut against the transmission rod 2 to fix the transmission rod 2.

[0051] The ENDB sample 100 is placed between the loading rod 31 inside the dial 4 and the two support rods 62 inside the support base assembly 6. The dial 4, sample fixing assembly 5, and support base 61 are connected and fixed by an adjusting assembly 9 that passes through them. The three components can be moved and adjusted on the adjusting assembly 9 to adjust their respective distances. Specifically, the adjusting assembly 9 includes a screw 91 that passes through the dial 4, sample fixing assembly 5, and support base 61, and nuts 92 that fix the three components to the screw 91. The distance between the three components is adjusted by rotating the screw 91, and then the nuts 92 are used to fix the three components to the screw 91. In this embodiment, three long screws 91 are evenly distributed along the circumference, and each screw 91 is provided with six nuts 92. The dial 4, sample fixing assembly 5, and support base assembly 6 each correspond to two nuts 92 on one screw 91.

[0052] This embodiment also provides an installation method for the testing device as described above, including the following steps:

[0053] S1. Adjusting the support assembly 6: Determine the distance L between the two support rods 62 of the support assembly 6 according to the diameter D and thickness H of the ENDB sample 100 and the angle α between the loading rod and the precast crack 110 required by the fracture mode, and adjust the position of the two support rod bases 63. Finally, tighten the bolt 64 to adjust the tightness between the sliding groove shim 67 and the base 63 to fix the two bases 63.

[0054] S2. Assemble the load transmission structure 3 and the dial 4, and then press the incident rod 1 against the outside of the load transmission structure 3.

[0055] S3. Specimen Placement: The loading method is primarily a three-point bending linear loading method. A specific angle α between the linear loading and the pre-existing crack 110 on the specimen is crucial for both pure Type III and mixed Type I / III dynamic fracture failure. Position the incident rod 1 vertically downwards so that the scale surface of the dial 4 is horizontally upwards. Place the pre-existing crack 110 of the ENDB specimen 100 upwards on the dial 4 of the assembly from step S2, according to the required angle α between the loading rod 31 and the pre-existing crack. Position the ENDB specimen 100 as close to the center of the dial 4 as possible to ensure that the centers of the incident rod 1, the ENDB specimen 100, and the transmission rod 2 are on the same axis during the experiment.

[0056] S4. Determine the sample position: After the sample is placed horizontally, adjust and fix the clamping position of the sample fixing component 5 on the ENDB sample 100. First, determine the appropriate relative position between the support ring 51 and the ENDB sample 100 by adjusting the screw 91 and the nut 92. Then, tighten the three long bolts 52 for fixing the sample to clamp the ENDB sample 100.

[0057] S5. Fracture space reservation: Considering that the close contact between the sample and the scale surface of the dial will affect the experimental fracture failure effect, the nut 92 is tightened again to adjust the position of the metal support ring 51 containing the sample, leaving an appropriate space in the inner groove 41 of the dial and inserting the crescent-shaped wedge 8, so as to reserve a certain fracture failure space between the ENDB sample 100 and the scale surface of the dial 4, so as to improve the accuracy of the sample failure results and experimental results.

[0058] S6. Adjust and fix the relative positions of the dial 4, the sample fixing assembly 5, and the support base 61. Adjust the appropriate positions of the dial 4, the sample fixing assembly 5, and the support base 61 by turning the nut 92. The purpose is to properly clamp the ENDB sample 100 with the loading rod 31 and the two support rods 62 to ensure that the sample does not slip during the experiment.

[0059] In steps S7 and S6, after the ENDB sample 100 is completely fixed by the loading rod 31 and the two support rods 62, the clamping of the sample fixing assembly 5 on the ENDB sample 100 is released to avoid the long bolt 52 fixing the sample affecting the sample failure results and experimental data during the dynamic experiment.

[0060] S8. Coupling transmission rod 2: For the device with the sample fixed, first loosen the four device fixing bolts 72, then place the transmission rod 2 into the tube groove 71 of the auxiliary fixing assembly and fix it (note that the transmission rod 2 should be placed at the bottom of the tube groove 71), and then tighten the four device fixing bolts 72 to fix the transmission rod 2. Then install the auxiliary fixing assembly 5 on the back of the support 61, and ensure that the centers of the incident rod 2, the ENDB sample 100, and the transmission rod 2 are on the same axis. This measure avoids direct or indirect contact between the entire device and the outside world during the experiment, reduces energy loss, and improves the accuracy of the experimental results.

[0061] After the entire apparatus is installed, the dynamic experiment begins. The loading method is mainly a three-point bending linear loading method. The angle α between the linear loading and the pre-existing crack in the specimen determines the dynamic fracture failure mode. Before the experiment, the incident rod 1 is placed close to the load transmission structure 3, and the relevant equipment is adjusted before the experiment can begin. When conducting the next specimen experiment, simply remove the apparatus that has completed the experiment (i.e., the central dial 4, specimen fixing assembly 5, and support assembly 6), and replace it with the apparatus that has fixed the new specimen on the transmission rod 2. To improve experimental efficiency and ensure experimental accuracy, 2-3 of these apparatuses can be prepared simultaneously for alternating experiments and specimen installation.

[0062] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A dynamic fracture toughness testing device based on ENDB specimen, comprising a testing auxiliary device and a Hopkinson bar experimental device, the Hopkinson bar experimental device comprising an incident bar and a transmission bar, characterized in that, The test auxiliary device comprises a load transmission structure, a scale disc, a support seat assembly, a sample fixing assembly and an auxiliary fixing assembly; Centers of the incident rod, the ENDB sample and the transmission rod are located on the same axis; The sample fixing assembly is clamped on the outside of the cylindrical surface of the ENDB sample, and the end surface of the ENDB sample is arranged between the scale disc and the support seat assembly; The load transmission structure comprises a loading rod and a cylindrical rod perpendicular to the loading rod, and the outside of the cylindrical rod is close to the incident rod; An end surface of the scale disc is provided with an angle scale and a concentric circle scale, and the loading rod is protrudingly installed on the scale surface of the scale disc; The support seat assembly comprises a support seat and two adjustable distance support rods connected to the support seat; The auxiliary fixing assembly is arranged on the back of the support seat assembly and is used for fixing the transmission rod; The scale disc, the sample fixing assembly and the support seat are connected and fixed through an adjustable distance assembly penetrating through the three, and the three can be moved and adjusted in position on the adjustable distance assembly.

2. The apparatus for dynamic fracture toughness testing of ENDB specimens according to claim 1, wherein An embedded slot for accommodating the loading rod is formed in the end surface of the scale disc in the diameter direction.

3. The apparatus for dynamic fracture toughness testing of ENDB specimens according to claim 2, wherein A crescent-shaped clamping wedge that fits the embedded slot and the loading rod is arranged in the embedded slot of the scale disc.

4. The apparatus for dynamic fracture toughness testing of ENDB specimens according to claim 1, wherein A sliding groove with a scale is arranged on the support seat, and two bases are slidingly arranged on the sliding groove, and the two support rods are respectively installed on the two bases.

5. The apparatus for dynamic fracture toughness testing of ENDB specimens of claim 1, wherein, The sample fixing assembly is a notched retainer ring, and the cylindrical surface of the retainer ring is uniformly provided with threaded holes, and a bolt penetrates through the threaded holes and abuts against the ENDB sample.

6. The apparatus for dynamic fracture toughness testing of ENDB specimens of claim 1, wherein, The auxiliary fixing assembly is a cylindrical pipe groove, and the cylindrical surface of the cylindrical pipe groove is uniformly provided with threaded holes.

7. The apparatus for dynamic fracture toughness testing of ENDB specimens of claim 1, wherein, The adjustable distance assembly comprises a screw penetrating through the scale disc, the sample fixing assembly and the support seat, and nuts respectively fixing the three on the screw.

8. The method of installing a test device according to any one of claims 1-7, wherein, The method comprises the following steps: S1, adjusting the support seat assembly: according to the diameter D and thickness H of the ENDB sample and the angle α between the loading rod and the prefabricated crack required by the fracture mode, the distance between the two support rods is determined and adjusted; S2, assembling the load transmission structure and the scale disc, and then arranging the incident rod close to the load transmission structure; S3, placing the sample: placing the ENDB sample at the center position of the scale disc of the assembly assembled in step S2 according to the required angle α between the loading rod and the prefabricated crack; S4, determining the position of the sample: adjusting the clamping position of the sample fixing assembly on the ENDB sample and fixing it; S5, adjusting the relative positions of the scale disc, the sample fixing assembly and the support seat and fixing them; S6, after the ENDB sample is completely fixed by the loading rod and the two support rods in step S5, the clamping of the sample fixing assembly on the ENDB sample is released; S7, coupling the transmission rod: arranging the transmission rod in the auxiliary fixing assembly and fixing it, then installing the auxiliary fixing assembly on the back of the support seat, and ensuring that the centers of the incident rod, the ENDB sample and the transmission rod are located on the same axis.

9. The method of mounting according to claim 8, wherein, Before step S5, a certain space for fracture failure is reserved between the scale disc and the ENDB sample.

10. The method of installing of claim 8, wherein, In step S3, the incident bar end of the assembly of step S2 is oriented vertically downward so that the scale face of the dial is oriented horizontally upward, and the precrack face of the ENDB specimen is then placed horizontally on the dial according to the desired loading bar to precrack angle a requirement.

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