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Fracture toughness measurement method based on optics

A fracture toughness and measurement method technology, applied in the field of mechanical measurement, can solve problems such as errors and increase the complexity of experiments

Inactive Publication Date: 2010-02-10
XI AN JIAOTONG UNIV
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

The traditional method has the following disadvantages: 1. The external force and displacement value loaded by the testing machine are required to derive the fracture toughness. The experiment must be carried out on a testing machine with a suitable range and high precision. If the testing machine range is much higher than the load required for specimen fracture, A large error will be introduced. Second, all standards can only give a limited number of measurement methods for experimental configurations. With the emergence of new materials in recent years, traditional methods can no longer meet the needs. Third, when using flexible Extensometers are used when measuring the crack length by the degree method, which increases the complexity of the experiment and requires contact measurement

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  • Fracture toughness measurement method based on optics
  • Fracture toughness measurement method based on optics
  • Fracture toughness measurement method based on optics

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0100] Embodiment 1: The test piece is a steel piece

[0101] The first step: measure the Young's modulus E of the specimen, and the thickness direction v z and the in-plane Poisson's ratio v xy , the thickness of the specimen is B, the Young's modulus E is 213GPa, and the Poisson's ratio in the thickness direction and in-plane is both 0.3, namely v xy =v z =0.3, the thickness B of the specimen is 7.51mm,

[0102] In the second step, the specimen is fixed according to the required experimental configuration, and the photographing device of the optical strain gauge is used to prepare to photograph the area near the crack tip,

[0103] Step 3: Turn on the soft light and camera to start the experiment. The fatigue crack is preset with a load of 3000N, and the specimen stiffness is measured by measuring the displacement change of the specimen notch during the loading and unloading process using an optical method: the specimen stiffness is 94201 / mm measured before the fatigue t...

Embodiment 2

[0122] Embodiment 2: The test piece is a steel piece

[0123] The first step is to measure the Young's modulus E of the steel part as 213GPa, and the Poisson's ratio in the thickness direction and in-plane is 0.3, v xy =v z =0.3, the thickness B of the specimen is 11.39mm,

[0124] In the second step, the specimen is fixed according to the required experimental configuration, and the photographing device of the optical strain gauge is used to prepare to photograph the area near the crack tip,

[0125] The third step is to turn on the soft light and the camera to start the measurement. The fatigue crack is preset with a load of 4000N. The optical method is used to measure the displacement change of the specimen notch during the loading and unloading process, and then the stiffness of the specimen is measured. Before the fatigue test The measured stiffness of the test piece is 131410N / mm, and the fatigue pre-crack is carried out. When the stiffness is reduced to 107670N / mm, th...

Embodiment 3

[0138] Embodiment three: the test piece is sintered stainless steel fiber felt

[0139] The first step: measure the Young's modulus E of the sintered stainless steel fiber felt to be 9.667GPa, and the in-plane Poisson's ratio v xy is 0.2, Poisson's ratio v in the thickness direction z is 0, it is a transversely isotropic material, and the thickness B of the specimen is 10.91mm,

[0140] In the second step, the specimen is fixed according to the required experimental configuration, and the photographing device of the optical strain gauge is used to prepare to photograph the area near the crack tip,

[0141] Step 3: Turn on the soft light and the camera to start the experiment. Since the porous material cannot use the traditional method for fatigue crack preset, according to the experimental results of Fleck, N.A in 2004, as long as the diameter of the crack tip is smaller than the unit cell size of the porous material, that is It can be considered that the crack is sharp enou...

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Abstract

The invention relates to a fracture toughness measurement method based on optics. By measuring the Young's modulus E, the thickness direction Poisson ratio vz, the internal Poisson ratio vxy and the thickness B of a test piece, a shooting device of an optical strain measurement instrument is used for shooting an area near a crack tip, fatigue crack prefabrication and loading are carried out on thetest piece until the fracture of the test piece is stopped, and then numerical value operation is carried out to obtain a J surface: further KIC reflecting brittle fracture or a ductile fracture toughness value is obtained. The method can be suitable for various strength materials and has the advantages of more convenient measurement, more accurate data and contact-free measurement in measurementunder various working conditions; experiments prove that the method can measure cracks as long as shooting the cracks; and when an experiment configuration which is not related or can not be measuredby the traditional method yet needs to be used, the method can play an important role.

Description

technical field [0001] The invention relates to the technical field of mechanical measurement, in particular to an optical-based fracture toughness measurement method. Background technique [0002] With the development of optical measurement instruments and computer technology, optical measurement methods are widely used in mechanical experiments due to their large range and non-contact advantages. However, there is no systematic optical fracture toughness measurement method at present. Fracture resistance is an important indicator to measure materials, especially brittle materials. China State Bureau of Technical Supervision, American Society of Mechanical Engineering and other relevant organizations in various countries have promulgated standards for fracture toughness measurement, such as GB 2038, GB 4461, ASTME813, ASTM E1820 , ASTM E1823, but these standards are calculated based on the force and displacement load during the loading process of the experimental machine, a...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G01N3/00G01B11/16
Inventor 陈常青金明钊赵天飞
Owner XI AN JIAOTONG UNIV