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Method for testing composite fracture toughness of rock based on asymmetric three-point bending loading of ndb specimens

A three-point bending and composite fracture technology, which is used in the application of stable bending force to test the strength of materials and the preparation of samples for testing, etc. question

Active Publication Date: 2021-04-20
SICHUAN UNIV
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

However, previous studies have pointed out that it is difficult to process disc-type specimens when carrying out fracture toughness testing of large-scale specimens.
Chinese patent ZL201510397736.1 proposes a unilateral notched deep beam specimen (NDB) with inclined cracks and symmetrical loading to achieve simple specimen configuration and convenient I / II composite fracture toughness test loading, but the composite fracture toughness Inclined cracks are required in the test of fracture toughness and fracture toughness of type II, and it is difficult to prefabricate cracks with large dip angles
However, in order to achieve composite loading, samples with traditional SENB, NDB and other configurations need to use complex loading or prefabricated inclined cracks, which have high requirements on the processing level of samples and loading devices

Method used

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  • Method for testing composite fracture toughness of rock based on asymmetric three-point bending loading of ndb specimens
  • Method for testing composite fracture toughness of rock based on asymmetric three-point bending loading of ndb specimens
  • Method for testing composite fracture toughness of rock based on asymmetric three-point bending loading of ndb specimens

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Experimental program
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Embodiment 1

[0070] The deep beam specimen that is used for rock fracture toughness test described in this embodiment, see Figure 1~4 , the test material is sandstone, the test piece body 1 is a cuboid shape, and the body is provided with a center line opening along the thickness B direction of the lower end surface of the body, extending to the inside of the body, and running through the front and rear end faces of the body thickness direction. The length L is 200mm, the width W is 100mm, and the thickness B is 80mm; the groove length a is 50mm (a / W ratio is 0.5), and the crack inclination β is 90°. The operation of rock fracture test with the above specimens is as follows:

[0071] 1) Adjust the distance S between the left support and the center line according to the scale of the three-point bending fixture 1 and the distance between the right support and the center line S 2 , such that S 1 60mm, S 2 is 6.5mm, and the difference between the front-end distance and the rear-end distan...

Embodiment 2

[0079] The deep beam specimen that is used for rock fracture toughness test described in this embodiment, see Figure 1~4 , the test material is sandstone, the test piece body 1 is a cuboid shape, and the body is provided with a centerline opening along the thickness B direction of the lower end surface of the body, extending to the inside of the body, and running through the front and rear end faces of the body thickness direction. The length L is 200mm, the width W is 100mm, and the thickness B is 80mm; the groove length a is 50mm (a / W ratio is 0.5), and the crack inclination β is 90°. The operation of rock fracture test with the above specimens is as follows:

[0080] 1) Adjust the distance S between the left support and the center line according to the scale of the three-point bending fixture 1 and the distance between the right support and the center line S 2 , such that S 1 60mm, S 2 The distance between the front end and the rear end of the two supports after adjust...

Embodiment 3

[0089] The deep beam specimen that is used for rock fracture toughness test described in this embodiment, see Figure 1~4 , the test material is sandstone, the test piece body 1 is a cuboid shape, and the body is provided with a center line opening along the thickness B direction of the lower end surface of the body, extending to the inside of the body, and running through the front and rear end faces of the body thickness direction. The length L is 200mm, the width W is 100mm, and the thickness B is 80mm; the groove length a is 50mm (a / W ratio is 0.5), and the crack inclination β is 90°. The operation of rock fracture test with the above specimens is as follows:

[0090] 1) Adjust the distance S between the left support and the center line according to the scale of the three-point bending fixture 1 and the distance S between the right support and the center line 2 , such that S 1 60mm, S 2 is 40mm, and the difference between the front-end distance and the rear-end distanc...

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Abstract

The invention provides a method for testing rock composite fracture toughness based on asymmetric three-point bending loading of NDB samples. The notch with a height of a extends in the thickness direction of the body and runs through the front and rear surfaces of the body thickness direction; the length L of the specimen body is twice the width W of the specimen body, and the thickness B is not less than 0.8W. Based on this NDB sample, the present invention provides a method for testing pure type I, pure type II and I‑II composite fracture toughness of rocks by using asymmetric three-point bending loading. Tension and shearing are realized by asymmetric loading Application of shear loads. The NDB sample used in the invention has a simple structure and is easy to be processed by using rock blocks; the fixture used for loading is an ordinary three-point bending fixture, which only needs to be arranged asymmetrically. I‑II Composite Fracture Toughness Testing in the Composite Loading Interval.

Description

technical field [0001] The invention belongs to the field of rock fracture toughness testing, in particular to a rock composite fracture toughness testing method. [0002] technical background [0003] Rock fracture mechanics is an important branch of rock mechanics. The fracture toughness of rock characterizes the ability of rock materials to resist crack initiation and expansion. It is the core parameter for solving rock engineering problems by using fracture mechanics. Degree is one of the main research work of rock fracture mechanics at present. [0004] The International Society of Rock Mechanics (ISRM) has successively suggested 4 kinds of specimens and corresponding test methods for rock I mode static fracture toughness testing, including: herringbone notched short round rod (SR) specimen under compact tensile loading (1977), chevron-notched three-point bending round bar (CB) specimen (1988), radially loaded chevron-notched Brazilian disc (CCNBD) specimen (1995) and s...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): G01N3/20G01N1/28
Inventor 刘洋艾婷张朝鹏张茹任利
Owner SICHUAN UNIV
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