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Method for determining fracture toughness and strength by using double-cut small-sized specimens

A technology of fracture toughness and small size, which is applied in the direction of using stable tension/pressure to test the strength of materials, etc., can solve the problem that small-size specimens cannot be directly used for evaluation, and achieves easy judgment of the rationality of the results, test operation, good stability

Active Publication Date: 2017-09-01
NORTH CHINA UNIV OF WATER RESOURCES & ELECTRIC POWER
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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 by using double-cut small-sized specimens
  • Method for determining fracture toughness and strength by using double-cut small-sized specimens
  • Method for determining fracture toughness and strength by using double-cut small-sized specimens

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0049] 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 0.20mm. 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.

[0050] 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.

[0051] see image 3 , determine the fracture toughness K and y...

Embodiment 2

[0055] 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.

[0056] 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.

[0057] 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.

[0058] Table 2 embodiment 2 determines fracture toughness and tensile strength of cement mortar

[0059] Δ / mm K / MPa·m 1 / 2

[0060] It can be seen that...

Embodiment 3

[0062] 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.

[0063] Based on formula (2) and formula (3), the nominal strength σ of each specimen can be calculated from the measured peak load F, combined with A, brought into formula (1) for regression analysis, the concrete material can be obtained at the same time fracture toughness and tensile strength.

[0064] 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.

[0065] Table 3 embodiment 3 determines the fracture toughness and tensile strength of concrete

[0066] Δ / mm K / MPa·m 1 / 2

[0067] It can be seen that the fracture toughness and tensile strength of ...

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Abstract

The invention discloses a method for determining fracture toughness and strength by using double-cut small-sized specimens. The method comprises the following steps: pouring the specimens, cutting out cracks, loading a static force, recording the peak loads, calculating the nominal strengths sigman, calculating geometric parameters A of the specimens, and finally performing regression analysis to obtain the fracture toughness K and the tensile strength f of a material without a size effect. Based on an idea of progressive extrapolation as well as theoretical analysis in elastoplastic fracture mechanics, material parameters of infinitely large slab specimens (the material parameters of the infinitely large slabs have no size effect) are extrapolated from experimental data of finite-size specimens, so that the fracture toughness and the strength of the material without the size effect can be determined only according to the key loads F of the small-sized specimens; strict current domestic and foreign specifications on the sizes and the types of the specimens, loading conditions and the like are not required to be met, and the stability of the double-sided tensile specimens is better than that of the single-sided tensile specimens, so that operation is easier.

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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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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