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Method for Determining Fracture Toughness and Strength from Small-Sized Specimens with Double Side Notches

A technology of fracture toughness and small size, applied in the direction of applying stable tension/pressure to test the strength of materials, etc., can solve the problem that small-sized test pieces cannot be directly used for evaluation, and achieve easy judgment of the rationality of the results, test operation, The simple effect of the method form

Active Publication Date: 2019-09-24
NORTH CHINA UNIV OF WATER RESOURCES & ELECTRIC POWER
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

Therefore, the test results of small-sized specimens cannot be directly used to evaluate its real material properties

Method used

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  • Method for Determining Fracture Toughness and Strength from Small-Sized Specimens with Double Side Notches
  • Method for Determining Fracture Toughness and Strength from Small-Sized Specimens with Double Side Notches
  • Method for Determining Fracture Toughness and Strength from Small-Sized Specimens with Double Side Notches

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0048] Hot-rolled carbon steel is used to make double-sided slit tensile specimens, and the specific shape of the specimens can be found in figure 2 , the sample height is 2D=40mm, B=6mm, L=60mm, the height of the sample arc section is 20mm, and the size of the rectangular clamping end is: 70mm×80mm. The obtained samples were cut into cracks by wire cutting process, and the crack width was less than 0.20 mm. The slit height ratio of the fabricated sample a 0 / D = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 5 samples were made for each group of seam height ratio, a total of 7 groups of 35 samples.

[0049] The test was carried out at a constant speed according to the rate specified in the "Metallic Materials Tensile Test Part 1: Room Temperature Test Method" (GB / T 228.1-2010) and other specifications, and the load was continued until the specimen was broken. The yield load of each specimen was recorded during the test.

[0050] see image 3 , determine the fracture toughness K and ...

Embodiment 2

[0054] In this example, cement mortar specimens are used in the test, and the specimen sizes D×B×W are three types, which are 51×19×19mm, 102×19×38mm, 153×19×76mm, and the initial joint height ratio α= a 0 / D=0.3.

[0055] Based on formula (2) and formula (3), the nominal strength σ of each specimen can be calculated from the measured peak load F n , combined with A, brought into formula (1) for regression analysis, the tensile strength and fracture toughness of the cement mortar material can be obtained at the same time.

[0056] For the fracture toughness and tensile strength results of the cement mortar material determined by the regression of the test data of embodiment 2, see Figure 4 , the fracture toughness and tensile strength data of the determined cement mortar materials are shown in Table 2 below.

[0057] Table 2 embodiment 2 determines fracture toughness and tensile strength of cement mortar

[0058] Δ / mm K / MPa·m 1 / 2

[0059] It can be seen that...

Embodiment 3

[0061] In this example, concrete specimens are used in the test, and the specimens have three dimensions D×B×W, which are 51×19×19mm, 102×19×38mm, 153×19×76mm, and the initial joint height ratio α=a 0 / W=0.3.

[0062] Based on formula (2) and formula (3), the nominal strength σ of each specimen can be calculated from the measured peak load F n , combined with A, into formula (1) for regression analysis, the fracture toughness and tensile strength of concrete materials can be obtained at the same time.

[0063] The fracture toughness and tensile strength results of the concrete material determined by embodiment 3 test data regression can be found in Figure 5 . The fracture toughness and tensile strength data of the determined concrete are shown in Table 3 below.

[0064] Table 3 embodiment 3 determines the fracture toughness and tensile strength of concrete

[0065] Δ / mm K / MPa·m 1 / 2

[0066] It can be seen that the fracture toughness and tensile strength of t...

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Abstract

The invention discloses a method for determining the crack initiation toughness of concrete without size effect from a small-sized test piece, including pouring the test piece, cutting out cracks, static loading and recording peak load, and calculating nominal strength σ n , Calculate the geometric parameters of the test piece A and other steps, and finally the fracture toughness of the material without size effect is obtained through regression analysis K and tensile strength f . The present invention is based on the idea of ​​gradual extrapolation and the theoretical analysis of elastic-plastic fracture mechanics, and extrapolates the material parameters of the infinite plate test piece from the test data of the finite size test piece (the material parameter of the infinite plate has no size effect). Therefore, the fracture toughness and strength of materials without size effect can be determined only by the critical load F of small-sized specimens. It does not need to meet the strict requirements of the current domestic and foreign standards on the size, type, and loading conditions of the test specimen, and the stability of the bilateral tensile specimen during the test is better than that of the unilateral tensile specimen, which is easier to operate.

Description

technical field [0001] The invention belongs to the technical field of material properties of civil engineering and water conservancy engineering, and in particular relates to a method for determining fracture toughness and strength of a small-sized test piece with double-sided slits. Background technique [0002] The fracture toughness and tensile strength of construction materials such as cement mortar, concrete, and metal are important performance material parameters for engineering design and scientific research. However, a large number of studies have shown that there is an obvious size effect on the tensile strength and fracture toughness of materials. To obtain real material parameters that are independent of the size of the specimen, larger specimens must be used. Therefore, the test results of small-sized specimens cannot be directly used to evaluate their real material properties. How to use small-sized specimens under elastic-plastic fracture damage conditions t...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): G01N3/08
Inventor 管俊峰胡晓智白卫峰姚贤华郝颖姜斌陈记豪程远兵李长永李晓克赵顺波谢超鹏钱国双杨振
Owner NORTH CHINA UNIV OF WATER RESOURCES & ELECTRIC POWER
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