A Method for Measuring Type II Crack Growth Rate of Composite Materials That Can Obtain S-N Curve of Crack Growth

A technology of crack growth rate and crack growth, which is used in the measurement of type II crack growth rate of composite materials and the field of composite material testing.

Inactive Publication Date: 2016-02-24
BEIHANG UNIV
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  • Description
  • Claims
  • Application Information

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Problems solved by technology

When using this method to determine the cracking threshold value, it is necessary to continuously reduce the fatigue displacement amplitude or step-by-step load reduction according to the increase of the crack growth of a single sample, and the test operation procedure is complicated; in addition, the crack interlaminar stress obtained by this method It changes with the growth of cracks and cannot meet the requirement of constant fatigue stress level in S-N curve measurement, which causes a waste of fatigue test information

Method used

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  • A Method for Measuring Type II Crack Growth Rate of Composite Materials That Can Obtain S-N Curve of Crack Growth
  • A Method for Measuring Type II Crack Growth Rate of Composite Materials That Can Obtain S-N Curve of Crack Growth
  • A Method for Measuring Type II Crack Growth Rate of Composite Materials That Can Obtain S-N Curve of Crack Growth

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Embodiment 1

[0064] S-N curve and growth rate measurement method for mode II crack growth of glass fiber composites.

[0065] 32 samples were randomly selected and numbered. The geometric dimensions are as figure 1 Shown. Perform artificial type I pre-cracking of the sample. Firstly, draw a line at a distance of 45mm from the pre-cracked end of the sample on both sides; secondly, insert a wedge-shaped blade with a straight front edge into the pre-cracked surface along the width of the test piece. And push the blade forward horizontally to expand the crack tip by about 5mm. After the cracks are prefabricated, the PTFE film is drawn out. Load the sample according to the loading method described in step 2 of the "specific implementation method" of this patent application. The test groups and the stress levels of each group are given in Table 1. The observation of cracks during the test is carried out in accordance with Step 3 in the "Specific Implementation Method" of this patent application....

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Abstract

A composite material II type crack growth rate measuring method capable of acquiring a crack growth S-N curve comprises five steps: 1, a single end-notched flexure (ENF) composite material sample is selected and formed through molding fiber cloth and resin; 2, the sample is tested through a three-point bending manner; 3, a triaxial movable high power digital measurement system is adopted to observe and measure the crack growth length, and the test load, the cycle index and the corresponding crack growth length are recorded; 4, the constant interface shear stress of a neutral surface of the composite material is worked out according to the engineering beam theory, and a three-parameter power function is adopted to fit the crack growth interface shear stress and the corresponding cycle index so as to obtain the crack growth S-N curve; 5, a dual-growth exponent function is utilized to fit the test load cycle index and the a-N curve of a corresponding crack growth length, and the crack growth rate is obtained after derivation; a Paris model and an energy release rate formula are adopted, and a crack growth rate curve is obtained through least-squares approximation.

Description

Technical field [0001] The invention provides a method for measuring the crack growth rate of a composite material with a crack growth S-N curve, which belongs to the field of composite material test methods. Background technique [0002] Compared with traditional metal materials, composite materials have higher specific strength and specific stiffness, so they are more and more widely used in structural lightweight design. However, the outstanding problem of composite material structure is the type II (in-plane) Shear) fatigue load (especially under type II in-plane shear load) is prone to interlaminar cracking. In order to ensure the safety of the composite material structure, it is necessary to determine the crack growth rate and the crack growth S-N curve of the material based on the damage tolerance design principle. The former reflects the corresponding crack growth rate under different fatigue load energies. By controlling the fatigue load energy, the design of crack arre...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): G01N3/20
Inventor 熊峻江云新尧李世秋
Owner BEIHANG UNIV
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