Center crack semicircular test piece for rock I-II composite fracture toughness test
By designing the central crack semicircular test piece and using uniaxial compression loading, the problems of small load and large operating error in the rock I-II composite fracture toughness test are solved, and the efficiency of rock I-II composite fracture toughness test is achieved. and precision.
Patent Information
- Application Number
- CN202420402412.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-03-04
- Publication Date
- 2024-12-17
- Estimated Expiration
- 2034-03-04
AI Technical Summary
The existing rock fracture toughness test methods have problems such as small loading, complex loading system, large operating errors, and the inability to achieve pure Type II loading, especially in I-II composite fracture toughness tests, which are difficult to obtain accurate results.
The central crack semi-circular test piece is used to achieve rock I-II composite fracture toughness test through uniaxial compression loading. The test piece is designed as a semi-circular annular plate-shaped plate with central cracks, and can be selected for straight grooves or herringbone cutting. The pure I, pure II and I-II composite fracture test is achieved by adjusting the crack inclination angle α to reduce human operation adjustment errors.
The rock I-II composite fracture toughness test can be carried out without artificially adjusting the test piece position under uniaxial compression loading, which improves the test efficiency and accuracy of results, simplifies the operation process, and reduces artificial errors.
Smart Images
Figure CN222188931U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the technical field of rock I-II composite fracture toughness testing, in particular to a central crack semicircular ring specimen used for rock I-II composite fracture toughness testing. Background Art
[0002] Rock fracture mechanics is an important branch of rock mechanics. The fracture toughness of rock is the core parameter in rock fracture mechanics, which quantifies the ability of rock materials to resist crack initiation and propagation. Therefore, accurately determining the fracture toughness of rock is not only the focus of rock fracture mechanics research, but also one of the main research tasks in this field.
[0003] The International Society of Rock Mechanics (ISRM) has successively recommended the herringbone grooved short round bar (SR specimen), herringbone grooved three-point bending round bar (CB specimen), herringbone grooved Brazilian disc specimen (CCNBD specimen) and through-hole straight grooved semi-disc bending specimen (SCB specimen) under compact tensile loading. All four specimens are further processed based on the drilled core.
[0004] Both CB and SR are "V"-shaped notch specimens, which have the advantage of not requiring pre-cracking or measuring crack length. However, its disadvantage is that the specimen requires a large number of whole rock cores in a certain direction, the load required for fracture is small, the loading system is relatively complex, the preparation of short rod specimens is cumbersome, and only type I fracture tests can be performed. The CCNBD specimen has two crack tips, and for rock-like inhomogeneous materials, there will be a problem that the two crack tips cannot crack at the same time. Before the experiment, the CCNBD specimen and the SCB specimen need to be manually adjusted to position the specimen, and manual adjustment of the specimen position often leads to operational errors.
[0005] In addition, the American Society for Testing and Materials (ASTM) also provides a variety of test specimens and test methods such as the single-edge notched beam (SENB) three-point bending test (2001) and the disk compact tension (DCT) test (1986) for material fracture toughness testing. SENB specimens with rectangular cross-sections are widely used in many industries.
[0006] SENB (Single Edge Notched Beam) specimens also face similar problems as CB (Compact Tension) specimens when conducting fracture toughness tests. That is, during the test, the load required for the material to fracture is small and pure Mode II loading cannot be achieved.
[0007] A patent document with the announcement number CN 105043849 A discloses a deep beam specimen for rock I-II composite fracture toughness test. The specimen has a simple structure and is easy to process using rock blocks. The rock I-II composite fracture toughness test is achieved by using a symmetrical three-point bending loading method. However, it is necessary to install two supports on the loading platform and a loading point on the upper end to achieve three-point bending loading. The three-point bending loading is installed with supports, and the relative position of the specimen and the support point needs to be adjusted when placing each specimen. Manual adjustment of the specimen position for alignment often leads to operational errors. For smaller specimens, the operational errors will be greater. Utility Model Content
[0008] In order to solve the above technical problems, the utility model provides a central crack semicircular ring specimen for rock I-II composite fracture toughness testing.
[0009] The utility model is realized by the following technical solutions:
[0010] A central crack semicircular ring specimen for rock I-II composite fracture toughness testing comprises a specimen body, wherein the specimen body is in the shape of a semicircular ring plate and has a central crack.
[0011] Optionally, the central crack is a straight cut groove that opens along the thickness direction of the inner circular surface of the specimen body, extends toward the inside of the specimen body, and passes through the front and rear end surfaces of the specimen body in the thickness direction.
[0012] Optionally, the angle between the central crack and the vertical plane in the specimen body is α, and α≥0°.
[0013] Optionally, the inner circular surface and the outer circular surface of the specimen body are coaxial.
[0014] Optionally, the central crack is a herringbone groove that opens along the thickness direction of the inner circular surface of the specimen body, extends toward the inside of the specimen body, and passes through the front and rear end surfaces of the specimen body in the thickness direction.
[0015] Optionally, the central crack opens along the center line of the inner circular surface of the specimen body in the thickness direction.
[0016] Optionally, a platform is processed in the middle of the outer circumferential surface of the specimen body, and the platform is perpendicular to the mid-vertical plane of the specimen body.
[0017] Among them, the radius of the inner circle of the specimen body is r, the radius of the outer circle is R, the thickness of the specimen body is B, and the length of the central crack is L;
[0018] Optionally, r / R is 0.3-0.6.
[0019] Optionally, B>0.8R.
[0020] Optionally, L / Rr is 0.2-0.5.
[0021] Compared with the prior art, this application has at least the following beneficial effects:
[0022] The central crack semicircular ring specimen can be directly placed on the uniaxial compression test bench for loading. There is no need to manually adjust the specimen position and align the loading point, which can greatly reduce the error of manual operation adjustment and make the rock I-II composite fracture toughness test results more accurate. At the same time, pure type I, pure type II and I-II composite fracture toughness tests of rocks can be achieved through simple uniaxial loading, which is conducive to improving efficiency. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] In order to more clearly illustrate the technical solutions of the embodiments of the utility model, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the utility model and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying creative work.
[0024] Figure 1 It is a three-dimensional stereogram of the central crack semicircular ring specimen used for the rock I-II composite fracture toughness test in Example 1;
[0025] Figure 2 This is a front view of the center crack semicircular ring specimen used for rock I-II composite fracture toughness test in Example 1;
[0026] Figure 3 It is a side view of the central crack semicircular ring specimen used for rock I-II composite fracture toughness test in Example 1;
[0027] Figure 4 This is a schematic diagram of the test piece in Example 1 when in use;
[0028] Figure 5 It is a three-dimensional stereogram of the central crack semicircular ring specimen used for rock I-II composite fracture toughness test in Example 2;
[0029] Figure 6 It is a longitudinal cross-sectional view of the specimen body at the central crack in Example 2;
[0030] Figure 7 This is a schematic diagram of the test piece in Example 2 when in use;
[0031] Figure 8 This is the front view of the center crack semicircular ring specimen used for rock I-II composite fracture toughness test in Example 3. DETAILED DESCRIPTION
[0032] In order to make the purpose, technical scheme and advantages of the embodiments of the utility model clearer, the technical scheme in the embodiments of the utility model will be clearly and completely described below in conjunction with the drawings in the embodiments of the utility model. Obviously, the described embodiments are part of the embodiments of the utility model, not all of the embodiments. Generally, the components of the embodiments of the utility model described and shown in the drawings here can be arranged and designed in various different configurations.
[0033] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. It should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the various embodiments can be referred to each other.
[0034] In the description of the present utility model, it should be noted that the terms "upper", "lower", "inner", "outer", etc. indicate the orientation or position relationship based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the utility model product is usually placed when in use, or the orientation or position relationship commonly understood by those skilled in the art, which is only for the convenience of describing the present utility model and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present utility model. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.
[0035] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.
[0036] Example 1
[0037] like Figure 1 , Figure 2 As shown, the central crack semicircular ring specimen for rock I-II composite fracture toughness test disclosed in this embodiment includes a specimen body 1, which is in the shape of a semicircular plate and has a central crack 2.
[0038] In this embodiment, the central crack 2 is a straight cut groove that opens along the thickness direction of the inner circular surface of the specimen body 1, extends toward the inside of the specimen body 1, and passes through the front and rear end surfaces of the specimen body 1 in the thickness direction.
[0039] like Figure 3 , Figure 4 As shown, the radius of the inner circular surface of the specimen body 1 is r, the radius of the outer circular surface is R, the thickness of the specimen body 1 is B, and the length of the central crack 2 is L. The thickness B is greater than 0.4 times the outer diameter 2R of the semi-circular disk; the ratio of the crack length L to the width of the ring (Rr) is 0.2 to 0.5; the ratio of the inner diameter to the outer diameter of the disk r / R is 0.3-0.6.
[0040] The angle between the central crack 2 and the vertical plane in the specimen body 1 is α, and α≥0°.
[0041] In a possible design, the inner circumferential surface and the outer circumferential surface of the specimen body 1 are coaxial. Optionally, the central crack 2 extends radially toward the inside of the specimen body 1 .
[0042] like Figure 4 As shown, when in use, the specimen body 1 is placed directly on the loading platform, and the planes at the left and right ends of the specimen body 1 can be used as two supporting surfaces; the middle of the outer cylindrical surface of the specimen body 1 is located at the highest point, which can be automatically used as the upper loading point. There is no need to manually adjust the specimen position to align with the loading point. Direct uniaxial compression loading can achieve composite fracture toughness testing, which can greatly reduce manual operation adjustment errors and improve efficiency.
[0043] It is worth noting that during uniaxial compression loading, the friction between the two contact surfaces at the bottom of the specimen body 1 and the loading platform cannot be ignored. The tangential friction coefficient f between the specimen and the loading platform can be considered in finite element modeling, and the friction coefficient f can be obtained through relevant common test methods.
[0044] The present application can be used to perform pure type I, pure type II and type I-II composite fracture toughness tests on rocks using uniaxial compression loading, by adjusting the crack inclination angle α until pure type II loading is achieved.
[0045] Optionally, before the rock fracture toughness test, the dimensionless stress intensity factor Y at the crack tip of the specimen is fully calibrated using the finite element numerical software ABAQUS I , Y II and the dimensionless nonsingular stress T * .
[0046] After the model was established using finite element software, the “binary method” was used in the calculation to continuously adjust the value of the crack inclination angle α until pure type II loading was achieved, as shown in Table 1.
[0047]
[0048] Optional, the specific steps are as follows:
[0049] (1) Using finite element numerical calculation software, a two-dimensional geometric model including the specimen body, the upper indenter and the lower loading platform is established. The rock material is assumed to be a linear elastic material and the elastic parameters of the specimen are assigned. Then, the grid is divided, the horizontal displacement of the indenter is constrained, and the vertical and horizontal displacements of the loading platform are constrained. A vertical reference load P is applied to the indenter loading point. Under the action of load P, the dimensionless stress intensity factors Y of the specimen type I and type II are I , Y II and the dimensionless nonsingular stress T * It can be expressed as:
[0050]
[0051]
[0052]
[0053] In the above formula, r is the radius of the inner surface of the specimen body 1, R is the radius of the outer surface of the specimen body 1, B is the thickness of the specimen body 1, L is the length of the central crack 2, α is the inclination angle of the central crack 2, P is the vertical reference load, and K is I and K II The mode I and mode II stress intensity factors at the crack tip are calculated and output for the finite element numerical calculation software.
[0054] Based on the numerical calibration model of step (1), the "binary method" is used in the calculation to continuously adjust the value of the crack inclination angle α; the absolute value of the ratio of the type I stress intensity factor to the type II stress intensity factor is less than 1 / 10000, which is considered to have reached a pure type II fracture.
[0055] Example 2
[0056] like Figure 5 , Figure 6 , Figure 7 As shown, the central crack semicircular ring specimen for rock I-II composite fracture toughness test disclosed in this embodiment includes a specimen body 1, which is in the shape of a semicircular plate and has a central crack 2.
[0057] In this embodiment, the central crack 2 is a herringbone groove that opens along the thickness direction of the inner circular surface of the specimen body 1 , extends toward the inside of the specimen body 1 , and passes through the front and rear end surfaces of the specimen body 1 in the thickness direction.
[0058] like Figure 3 , Figure 4 As shown, the radius of the inner circular surface of the specimen body 1 is r, the radius of the outer circular surface is R, the thickness of the specimen body 1 is B, the length of the central crack 2 is L, and the inclination angle of the central crack 2 is 0°.
[0059] In a possible design, the central crack 2 opens along the center line of the inner circular surface of the specimen body 1 in the thickness direction.
[0060] The central herringbone grooved semicircular ring specimen of the present embodiment has a simple structure. The herringbone groove has a sharp point where stress is concentrated, and can automatically form a crack with no thickness during the loading process, avoiding the influence of artificial cutting thickness. The rock fracture toughness test can be achieved through simple uniaxial loading. The operation method is simple and can effectively control the human operation error during the experiment.
[0061] Example 3
[0062] like Figure 8 As shown, the difference between this embodiment and embodiment 1 or embodiment 2 is that: in this embodiment, a platform 3 is processed in the middle of the outer cylindrical surface of the specimen body 1, and the platform 3 is perpendicular to the mid-vertical plane of the specimen body 1. The platform can improve the stress concentration problem of the upper pressure head and the specimen point contact during the loading process.
[0063] The center crack semicircular ring specimen of the present application has a simple structure and can realize rock I-II composite fracture toughness test through simple uniaxial loading. The operation method is simple and there is no need to manually position and align the specimen. The human operation error in the experimental process can be effectively controlled, making the rock I-II composite fracture toughness test results more accurate.
[0064] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may be subject to various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.
Claims
1. A center crack semicircular ring specimen for rock I-II composite fracture toughness testing, comprising a specimen body (1), characterized in that: The specimen body (1) is in the shape of a semicircular plate, and the specimen body (1) has a central crack (2).
2. The center crack semicircular ring specimen for rock I-II composite fracture toughness test according to claim 1, characterized in that: The central crack (2) is a straight cut groove that opens along the thickness direction of the inner circular surface of the specimen body (1), extends toward the inside of the specimen body (1), and penetrates the front and rear end surfaces of the specimen body (1) in the thickness direction.
3. The center crack semicircular ring specimen for rock I-II composite fracture toughness test according to claim 2, characterized in that: The included angle between the central crack (2) and the vertical plane of the specimen body (1) is α, and α≥0°.
4. The center crack semicircular ring specimen for rock I-II composite fracture toughness test according to claim 1, characterized in that: The inner circumferential surface and the outer circumferential surface of the test piece body (1) are coaxial.
5. The center crack semicircular ring specimen for rock I-II composite fracture toughness test according to claim 1, 2 or 4, characterized in that: The central crack (2) is a herringbone groove that opens along the thickness direction of the inner circular surface of the specimen body (1), extends toward the inside of the specimen body (1), and penetrates the front and rear end surfaces of the specimen body (1) in the thickness direction.
6. The center crack semicircular ring specimen for rock I-II composite fracture toughness test according to claim 5, characterized in that: The central crack (2) opens along the center line of the inner circular surface of the specimen body (1) in the thickness direction.
7. The center crack semicircular ring specimen for rock I-II composite fracture toughness test according to any one of claims 1 to 4 and 6, characterized in that: A platform (3) is processed in the middle of the outer cylindrical surface of the specimen body (1), and the platform (3) is perpendicular to the mid-vertical plane of the specimen body (1).
8. The center crack semicircular ring specimen for rock I-II composite fracture toughness test according to any one of claims 1 to 4 and 6, characterized in that: The radius of the inner circular surface of the test piece body (1) is r, the radius of the outer circular surface is R, and r / R is 0.3-0.
6.
9. The center crack semicircular ring specimen for rock I-II composite fracture toughness test according to claim 8, characterized in that: The thickness of the specimen body (1) is B, and B>0.8R.
10. The center crack semicircular ring specimen for rock I-II composite fracture toughness test according to claim 8, characterized in that: The length of the central crack (2) is L, and L / Rr is 0.2-0.5.