Set cement tensile strength testing device and method

Abstract

The invention relates to a set cement tensile strength testing device and method, set cement is prepared through a plurality of overlapped dies (1), the set cement connects a plurality of overlapped dies (1) into a die assembly (6), and a fixing clamp (18) and a stress sleeve (15) are respectively connected with two adjacent dies (1) on the die assembly (6) during a tensile test. Due to the fact that the fixing clamp (18) and the stress sleeve (15) both act on the die (1), the die (1) evenly acts on set cement, and a problem of stress concentration of the set cement in the tensile test is avoided.

Description

technical field [0001] The invention relates to the technical field of tensile strength testing, in particular to a cement stone tensile strength testing device and method. Background technique [0002] Tensile strength refers to the resistance of the material to the tensile stress generated by the load. For cement stone materials, the tensile strength is much smaller than the compressive strength, and the damage of cement stone is mostly tensile failure, so the tensile strength is cement stone an important mechanical index. At present, the testing methods for the tensile strength of cement stone mainly include uniaxial tensile method, Brazilian splitting method and axial fracturing method. [0003] The uniaxial tensile method is to apply tensile stress at both ends of the sample, and the tensile strength is calculated by the area of ​​the fracture surface and the tensile stress at the time of fracture. The uniaxial tensile method can directly measure the tensile strength o...

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Problems solved by technology

However, there are problems such as stress concentration and eccentric force in the uniaxial tensile method. If the two ends of the sample are not aligned with the pull rod, a large eccentric force will be generated and a stress concentration point will be generated, which will affect the test results.

The Brazilian splitting method lays the cylindrical sample flat, places pads above and below the sample, and applies compressive stress to the pad to fracture the sample; however, in operation, the pad placement requires high requirements, and the pad must be symmetrical to the sample Placement, the plane where the upper and lower pads are located should be tangent to the cylindrical sample, and ensure that the compressive stress runs through the central axis of the sample; however, due to the small size of the pad, it is difficult to place it stably on the side of the cylindrical sample, and artificial placement is very difficult. Difficult to meet the specification requirements, resulting in eccentric compressive stress easily generated when the sample is under pressure, causing errors in the test results. In addition, the pads are prone to slip on the side of the cylinder, resulting in test failure

The axial fracturing method is to place small cylindrical pads on the upper and lower surfaces of the cylindrical sample, and apply compressive stress on the upper and lower two small pads, the compressive stress runs through the central axis of the cylindrical sample, and the sample is fractured at the center; However, in the process of axial fracturing, it is difficult to ensure that the small pads on the upper and lower surfaces are centered and penetrate the central axis of the sample. If the small pads are not centered, the sample will be eccentrically compressed; moreover, the axial fracturing method is very difficult It is difficult to ensure that the compressive stress is always kept in the axial direction, and it is easy to have multiple independent cracks along the radial direction, causing errors in the results

[0004] At present, there are certain deficiencies in domestic testing methods and experimental devices for testing the tensile strength of rocks and cement stones: Su Zhandong’s rock tensile strength testing system (patent publication number: CN107389441A), a Brazilian company that quickly fixes and improves stability The splitting method can accurately and conveniently measure the tensile strength, but it still has the problems of the above-mentioned Brazilian splitting method; Chen Denghong's rock tensile strength testing device and test method (patent publication number: CN108693035A) through a new type of axial tension The stretching method avoids the problem that the stretching is easy to eccentric in the stretching process, but there are the following problems: it is easy to produce stress concentration at the contact position through the clamping method, which makes the result error; Li Yanrong's soft rock and soil The direct stretch tensile strength testing device and method of the body (patent publication number: CN108844817A) directly installs and fixes the sample on the pull rod device by the direct stretch method to ensure that the tensile stress is along the same straight line, avoiding the problem of eccentric force, but by Tensile stress is applied to the central point of the hollow cylindrical sample, which is easy to generate stress concentration at the central point of the sample. It is difficult to keep the direction of the tensile force constant during the stretching process, and it is easy to generate multiple cracks in other directions, which will cause errors in the results.

There are certain deficiencies in the above methods, no matter whether they measure the tensile strength of cement stone by splitting method or uniaxial tension method.

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