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Testing method of steel fiber reinforced concrete fracture test crack initiation load

A technology of steel fiber concrete and crack initiation load, which is applied in the direction of testing the strength of materials by applying a stable bending force, which can solve the problems of complex test process, insufficient sensitivity, and difficulty in accurate determination, and achieve simple analysis and processing methods, and test equipment The effect of simplicity and low test cost

Active Publication Date: 2014-04-30
YELLOW RIVER INST OF HYDRAULIC RES YELLOW RIVER CONSERVANCY COMMISSION
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Problems solved by technology

[0015] Using these methods to determine the crack initiation load has high requirements for test technology and test equipment. For components and structures with small strains, the sensitivity is not enough, the test process is more complicated, and the processing and analysis of test results are also required. Ordinary test conditions It is difficult to determine a more accurate cracking load under
[0016] Steel fiber reinforced concrete is a new type of multiphase composite material formed by mixing short steel fibers randomly distributed in ordinary concrete. These randomly distributed steel fibers can effectively prevent the expansion of micro-cracks and macro-cracks in concrete. The formation of concrete significantly improves the tensile, bending, impact and fatigue properties of concrete, and has good ductility; the crack propagation of steel fiber reinforced concrete is retarded by steel fibers. Unlike concrete, the stress-strain field at the tip of the crack changes It is more complicated than concrete. When the crack starts, the steel fiber will bridge the crack surface, resulting in the closure of the crack surface. Especially when the strain is small, it is difficult to accurately determine it with existing technical means, and the process is more complicated.

Method used

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  • Testing method of steel fiber reinforced concrete fracture test crack initiation load
  • Testing method of steel fiber reinforced concrete fracture test crack initiation load
  • Testing method of steel fiber reinforced concrete fracture test crack initiation load

Examples

Experimental program
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Effect test

Embodiment 1

[0063] see Figure 1-4 , using the notched beam three-point bending test to test the crack opening displacement, the notched beam size is l×b×h=515 mm×100 mm×100 mm, the prefabricated initial crack length a 0 = 40 mm, the steel fiber concrete is MF05, that is, the steel fiber volume ratio is 0.5%, and the comparison specimen MF05-0 does not add steel fibers. The results of the concrete fracture toughness test are shown in Table 1.

[0064] The specific steps are:

[0065] (1) Arrange one group of knife edges symmetrically on both sides of the bottom notch of the concrete notched beam, and another group of knife edges symmetrically arranged on both sides of the tip of the initial crack in the beam prefabrication, and clamp the knife edge fixed on the notched beam by the clip-type extensometer cutting groove;

[0066] (2) Continuously load the notched beam, and use the computer data acquisition system to realize automatic data collection, and stop loading until the maximum load...

Embodiment 2

[0070] The test method of this example is the same as that of Example 1, with some differences: the steel fiber concrete is MF15, that is, the steel fiber volume ratio is 1.5%, the comparison test piece MF15-0 does not add steel fibers, and the crack initiation load of the concrete fracture test is P c The results are shown in Table 1.

[0071] Test method verification of the present invention

[0072] According to the analysis of the test results according to the theory of fracture mechanics, it can be known that the closing force σ of steel fiber reinforced concrete and the opening displacement δ of the crack tip t Satisfies formula ⑨ relation:

[0073] ⑨

[0074] In the formula: a 1 、a 2 、a 3 is a constant.

[0075] When σ is zero, that is, the steel fiber has no crack resistance effect, corresponding to the cracking time of the specimen, the theoretical value of the stress intensity factor in the crack front area reaches the fracture toughness of concrete. ...

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Abstract

The invention relates to a testing method of steel fiber reinforced concrete fracture test crack initiation load, and belongs to the technical field of concrete cracking parameter testing. The testing method provided by the invention is characterized in that when a steel fiber reinforced concrete coped beam specimen cracks, a stress intensity factor of a prefabrication crack front edge achieves concrete fracture toughness, and the steel fibre blocking action is not exerted; the stress intensity factor generated by external load and concrete cracking toughness(i)K( / i) IC are equal, the external load value which is corresponding to a numerical value (i)K( / i)IC of the stress intensity factor generated by the external load can be used for determining the crack initiation load according to the curve relation graph of the external load and the stress intensity factor (i)K generated by the external load (img file='2014100081259100004dest_path_image002.TIF'wi='8'he='21' / )( / i)-(i)P( / i) curve relational graph. The testing method provided by the invenytion has the advantages that the required equipment, analyzing and processing method are simple, the cost is low, and the precision is high.

Description

technical field [0001] The invention belongs to the technical field of concrete fracture parameter testing, and in particular relates to a testing method for measuring the crack initiation load of steel fiber concrete by using a notched beam three-point bending test. Background technique [0002] According to the double K fracture criterion, the crack propagation in the concrete fracture process can be divided into three stages, that is, the crack initiation, the stable crack growth and the crack instability growth. The critical stress intensity factor of the instability growth is the fracture toughness K IC , the fracture toughness reflects the ability of concrete materials to resist crack propagation, and is an important fracture parameter for crack control of engineering structures and for judging the stability of crack propagation. [0003] The method of determining the crack initiation fracture toughness of concrete is generally to determine the crack initiation load f...

Claims

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Application Information

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IPC IPC(8): G01N3/20
Inventor 张廷毅郑光和宋万增张凯王萍宋海亭邵菁魏民周永海蔡怀森谢义兵刘慧王玮屏伍艳赵志忠
Owner YELLOW RIVER INST OF HYDRAULIC RES YELLOW RIVER CONSERVANCY COMMISSION
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