Composite material II type crack growth rate measuring method capable of acquiring crack growth S-N curve

A crack growth rate and crack growth technology, which is applied in the measurement of type II crack growth rate of composite materials and in the field of composite material testing, can solve the problems of waste of fatigue test information, failure to meet the requirement of constant fatigue stress level, and complicated test operation procedures, etc.

Inactive Publication Date: 2013-12-11
BEIHANG UNIV
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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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  • Composite material II type crack growth rate measuring method capable of acquiring crack growth S-N curve
  • Composite material II type crack growth rate measuring method capable of acquiring crack growth S-N curve
  • Composite material II type crack growth rate measuring method capable of acquiring crack growth S-N curve

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Embodiment 1

[0064] Type II crack growth S-N curve of glass fiber composites and determination method of growth rate.

[0065] 32 samples are randomly selected and numbered, the geometric dimensions are as follows figure 1 shown. Artificial Type I pre-cracking is performed on the sample. First, draw a line at 45mm from the pre-crack end on both sides of the sample; secondly, insert a wedge-shaped blade with a straight front edge into the pre-crack surface along the width direction of the test piece, slowly And push the blade forward horizontally to expand the crack tip by about 5mm. Pull out the PTFE film after crack prefabrication. Load the sample according to the loading method described in step 2 in 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 according to step 3 in the "specific implementation method" of this patent application. The...

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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 type II crack growth rate of a composite material capable of obtaining a crack growth S-N curve, belonging 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 structures is that in Type II (in-plane Shear) fatigue loads (especially under type II in-plane shear loads) are prone to interlaminar cracking. In order to ensure the structural safety of composite materials, it is necessary to measure the crack growth rate and crack growth S-N curve of the material based on the principle of damage tolerance design. The former reflects the corresponding crack growth rate under different fatigue load energies. By controlling the fatigue load energ...

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Application Information

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