CN103148785B - A kind of optical interference spectral domain phase place comparison B-scan instrument and measuring method thereof - Google Patents

Abstract

The invention discloses an optical interference spectrum domain phase contrast B scanner and a measurement method thereof, which are mainly used for perspective measurement of the out-of-plane displacement distribution inside a composite material component. Based on the principle of optical interference, the scanner uses the spatial modulation of a broadband light source to expand the interference spectrum of the internal section of the composite material component under test on the image plane of the CCD camera, and calculate the internal section of the composite material component from the phase-frequency characteristics of the spectrum. The out-of-plane displacement distribution of . The scanner can perform perspective measurement on transparent and optically turbid composite components. It is characterized by high measurement resolution of axial profile and out-of-plane displacement, and fast measurement speed. It is suitable for the study of mechanical properties of composite components and the detection and identification of small defects.

Description

An optical interference spectral domain phase contrast B-scanner and its measurement method

technical field

The invention relates to a method and an instrument for optical interferometry, in particular to a method and an instrument for measuring the three-dimensional out-of-plane displacement field distribution of composite materials and transparent or translucent multi-layer resin coatings.

technical background

With the development of aerospace industry technology, more and more composite components with different strengths, stiffnesses and materials are used. Since the complex coupling effects between various internal material components and structures bring greater challenges to the analysis and characterization of its mechanical properties, it is necessary to measure the internal mechanical quantities of composite components: three-dimensional displacement field distribution experimental apparatus and methods.

It is very practical to measure the three-dimensional displacement field distribution inside the composite member. Composite components sometimes develop internal defects due to the instability of the manufacturing process. During the entire service life, although most of the tiny defects (scale ~0.01mm) have no effect on the mechanical properties of the components, some of them will increase from small to large, and finally lead to the failure of the components. The traditional detection method is mainly through the measurement of the internal contour of the component, and it is impossible to identify the tiny defects that may cause problems in the future. However, the method of perspective measurement of the displacement field distribution inside the composite component can use the stress concentration phenomenon to directly observe and evaluate the defect. The hazard level and even the evolution process provide an effective technical means for the study of the internal mechanical properties of composite components and defect detection.

In recent years, with the continuous development of computer and component technology, several perspective methods for measuring the internal displacement field of composite components have emerged, mainly including: (1) Digital Volume Correlation (DVC): The measurement system of this method has a simple structure , the measurement accuracy is high, but the optical transparency of the measured object is required to be high, and the measurement depth is limited; (2) nuclear magnetic resonance imaging: this method has high measurement accuracy and axial resolution, but it cannot measure components containing metal inside; (3) X-ray tomography: This method has strong penetrating ability, but the disadvantage is that the system is complex, X-rays are harmful to the human body, and the absorption and reflection of resin-based materials in the X-ray band are small, and the imaging contrast is low; ( 4) Neutron diffraction: similar to the X-ray tomography method, it has stronger penetrating ability, but the disadvantage is that it is limited by the neutron element channel and the spatial resolution is low; (5) Optical wavelength interference scanning method: this method can High-precision measurement of three-dimensional displacement field distribution inside transparent, translucent or optically turbid composite components, high resolution of axial three-dimensional profile and displacement field measurement, the disadvantage is that the measurement speed is slow.

On the basis of synthesizing the existing displacement field perspective measurement methods, the present invention discloses a new instrument and method for measuring the three-dimensional out-of-plane displacement field inside the composite material, which realizes the rapid distribution of the three-dimensional out-of-plane displacement field inside the composite material component. , High-precision perspective measurement.

Contents of the invention

The invention discloses an optical interference spectrum domain phase-contrast B scanner and a measurement method thereof, which utilizes the spatial modulation of a broadband light source and the phase-frequency characteristics of the interference spectrum to measure the three-dimensional out-of-plane displacement inside a composite material component with high resolution and high speed distributed.

The present invention realizes through following technical scheme:

An optical interference spectral domain phase-contrast B-scanner, as shown in Fig. 1, is suitable for the study of the mechanical properties of composite material components and the detection and identification of tiny defects, which sequentially includes a low-coherence broadband light source (1), a convex lens L ₁ (2 ), cylindrical mirror (3), beam splitter (4), polarizer (5), reference plane (6), composite component under test (7), convex lens L ₂ (8), diffraction grating (9), convex lens L ₃ (10), CCD camera (11) and computer (12).

The optical path in the main viewing direction of the instrument is shown by the dotted line in Figure 1. The principle of light transmission and imaging in the main viewing direction is: the broadband light emitted by the low-coherence broadband light source (1) is collimated by the convex lens L ₁ (2) and becomes parallel light. Because the cylindrical mirror (3) in the main viewing direction is equivalent to a plane lens, and does not change the direction of light transmission, so after passing through the beam splitter (4), the parallel light is reflected and transmitted to the measured composite material member ( 7) and the reference plane (6); the reflected light from the measured composite material component (7) and the reference plane (6) is transmitted and reflected by the beam splitter (4) again, and superimposed on each other to generate interference. Because the diffraction grating (9) is equivalent to a flat mirror in the main viewing direction, the interference light passes through the convex lenses L ₂ (8) and L ₃ (10) and irradiates in parallel on the image plane of the CCD camera (11). Rotating the polarizer (5) around its axis can make the reflected light intensity of the two arms similar, thereby ensuring the best contrast of the interference image.

The optical path of the instrument in the direction of looking down is shown by the solid line in Figure 1, and the principle of light transmission in the direction of looking down is: the broadband light emitted by the low-coherence broadband light source (1) is collimated by the convex lens L ₁ (2) and irradiates parallel to the cylindrical mirror (3 )superior. Since the cylindrical mirror (3) is equivalent to a convex lens in the direction of looking down, after being reflected and transmitted by the beam splitter (4), the broadband light is respectively focused into a light spot on the measured composite material component (7) and the reference plane (6), Combining the two dimensions of the main and top view optical paths, a light knife is formed to measure the internal axial section of the composite material component (7); the reflected light of the measured composite material component (7) and the reference plane (6) passes through the beam splitter (4) After transmission and reflection, under the collimating action of the convex lens L ₂ (8), the parallel broadband light enters the diffraction grating (9) at the same incident angle. Because the diffraction grating (9) diffracts light of different wavelengths with different diffraction angles, only light with the same wavelength can be placed at a specific y position on the image plane of the CCD camera (11) under the focusing effect of the convex lens L3 ( ₁₀ ). Imaging, after the broadband light with continuous wavelength is diffracted, it is continuously expanded in the y direction of the image plane of the CCD camera (11) according to the wavelength, forming an interference spectrum image and transmitted to the computer (12).

B-scan means that each measurement of the system can realize the measurement of the plane information of a cut surface inside the tested composite component (7).

An optical interference spectral domain phase contrast B-scan measurement method, comprising the following steps:

1), use the loading device shown in Figure 2 (b) to carry out slight pretension to the composite material member (7) to be tested, and record the interference spectrum image at this time;

2), using a loading device to apply feed or load to the tested composite material component (7), causing it to generate out-of-plane displacement, and record the interference spectrum image at this time;

3), with 1) and 2) the two interference spectrum images measured in the steps are respectively subjected to the following Fourier transform: the interference spectrum irradiated on the image plane of the CCD camera (11) is:

$\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{\mathrm{<span\; class="notranslate">\; q</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\sqrt{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&CenterDot;</span>\frac{{\mathrm{<span\; class="notranslate">\; \&Lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&Lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}}<span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; D.</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; ]</span>$

Among them, I is the interference light intensity, y is the space coordinate y of the system in Fig. 1, M is the number of surfaces participating in the interference, I _p and I _p are the reflected light intensity of the p-th and q-th surfaces respectively, and Λ _pq is the The optical path difference between the p and qth surface, φ _pq0 is the phase change produced when the light is reflected on the p and qth surface, kc is the central wavenumber of the low-coherence broadband light source (1), _C and D is a constant:

$\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; the\; si</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\frac{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \}</span>}{{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; d</span>}\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; (</span>\frac{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}$

$\mathrm{<span\; class="notranslate">\; D.</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; sin</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; ]</span>$

d is the grating constant of the diffraction grating (9), α is the incident angle of the diffraction grating (9), β _c is the diffraction angle corresponding to k _c , and f _L3 is the focal length of the convex lens L ₃ (10). After digital sampling and windowing, the Fourier transform of the interference spectrum:

$\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; w</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; n\&Delta;y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>$

w(y) and They are the window function and the sampling function, where Δy is the sampling distance between two adjacent sampling points in the y direction of the optical knife section, and N is the maximum number of sampling points in the y direction within the field of view of the light knife section.

The amplitude-frequency characteristic after Fourier transform is:

$\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{\mathrm{<span\; class="notranslate">\; q</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\frac{\sqrt{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}}}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; \&Delta;y</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; \&PlusMinus;</span>\frac{{\mathrm{<span\; class="notranslate">\; \&Lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}{\mathrm{<span\; class="notranslate">\; \&Delta;y</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; \&PlusMinus;</span>\frac{{\mathrm{<span\; class="notranslate">\; \&Lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; )</span>}$

Using the amplitude-frequency characteristic, the optical path difference between the p-th and q-th surfaces inside the tested composite component (7) can be expressed by the peak frequency _fpq as:

Λ _pq = π·C·f _pq

Because f _pq and ∧ _pq are linearly related, f _pq can characterize the internal axial profile of the composite member (7).

After Fourier transform, the phase-frequency characteristics of the interference spectra before and after the axial out-of-plane displacement w _pq of the two surfaces of p and q are:

${{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}}}^{\mathrm{<span\; class="notranslate">\; wrap</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&Lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; D.</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}$

${{{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}}}^{\mathrm{<span\; class="notranslate">\; wrap</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&Lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; D.</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}$

The phase difference is:

Δφ _pq ^wrap (f)=φ′ _pq ^wrap (f)-φ _pq ^wrap (f)

Since the phase obtained after the Fourier transform is the winding phase from -π to π, the winding phase difference is calculated from the winding phase. After adding and subtracting an integer multiple of 2π to the jump point of the wrap phase, and performing unwrap calculation, the unwrap phase difference Δf _pq ^unwrap (f) is obtained. At this time, the axial out-of-plane displacement between the two surfaces of p and q is:

${\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; C</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; D.</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}}}^{\mathrm{<span\; class="notranslate">\; unwrap</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span>$

The above formula is the phase contrast method to calculate the out-of-plane displacement by using the phase between the p and q surfaces before and after deformation. In this method, the out-of-plane displacement of the internal section of the composite material component (7) is measured by taking interference spectrum images and signal demodulation of the internal section of the composite material component (7) before and after loading. The advantage is high sensitivity, and the measurement resolution of out-of-plane displacement is ±λ/1000.

Description of drawings

Figure 1 is the system schematic diagram of the phase contrast B-scanner in the optical interference spectral domain; the solid line and the dotted line in the figure are the top-view optical path and the front-view optical path respectively; 1 is a low-coherence broadband light source, 2 is a convex lens L ₁ , and 3 is a cylindrical mirror , 4 is a beam splitter, 5 is a polarizer, 6 is a reference plane, 7 is a composite material component to be tested, 8 is a convex lens L ₂ , 9 is a diffraction grating, 10 is a convex lens L ₃ , 11 is a CCD camera, and 12 is a computer.

Figure 2 is the internal structure and loading device of the tested composite material component; (a) the internal structure diagram of the tested composite material component; (b) the loading device; (c) the out-of-plane displacement distribution diagram of the tested composite material component after loading.

Figure 3 is the interference light intensity curve; I represents the light intensity, and k represents the wavenumber k-axis.

Figure 4 is the amplitude-frequency characteristic curve; OPD represents the optical path difference, and z represents the spatial coordinate z-axis.

Figure 5 is the unwrapped phase difference curves of S ₁ S ₂ (1.57mm), S ₂ S ₃ (0.4mm) and S ₁ S ₃ (1.97mm); (a) The phase difference when 20μm feed is applied; ( b) The phase difference when 40 μm feed is applied; Pha indicates the phase, Sm indicates the tested composite component with smooth surface, and Sp indicates the tested composite component with speckle surface.

Figure 6 is the out-of-plane displacement curves of S ₂ and S ₃ surfaces before and after loading; (a) the relative out-of-plane displacement when 20 μm feed is applied; (b) the relative out-of-plane displacement when 40 μm feed is applied; RD represents the relative out-of-plane displacement displacement.

detailed description

The present invention will be further described below in conjunction with experimental examples and accompanying drawings, but the protection scope of the present invention should not be limited.

As can be seen from Fig. 1, the present invention comprises: low-coherence broadband light source (1), convex lens L ₁ (2), cylindrical mirror (3), beam splitter (4), polarizer (5), reference plane (6), by Measuring composite material member (7), convex lens L ₂ (8), diffraction grating (9), convex lens L ₃ (10), CCD camera (11) and computer (12). The dotted line and the solid line in the figure respectively represent the main view optical path and the top view optical path of the system. Since their light transmission and imaging principles are different, they will be introduced separately below.

Firstly, the system's main optical path is introduced. 1) Illumination part: low-coherence broadband light source (Superlum Diodes.Ltd SLD-371-HP1) (1) emits near-infrared light with a center wavelength of 840nm and a bandwidth of 50nm through an optical fiber, and passes through a convex lens L ₁ (2) (f _L1 = 60mm ) becomes parallel light after being collimated, because the cylindrical mirror (3) in the main optical path is equivalent to a plane lens and does not change the direction of light transmission, so after passing through the 50:50 beam splitter (4), the parallel light is reflected and transmitted to On the measured composite material member (7) and the reference plane (6) on the two arms of the interferometer. 2) Imaging part: the reflected light from the measured composite material component (7) and the reference plane (6) is transmitted and reflected by the beam splitter (4) again, and superimposed on each other to generate interference. Because the diffraction grating (THORLABS GR25-1210) (9) in the main optical path is equivalent to a flat mirror, so after the interference light passes through the convex lenses L ₂ (8) and L ₃ (10) (f _L2 = 150mm, f _L3 = 150mm) , irradiated in parallel on the image plane of a CCD camera with a pixel size of 1392×1040 (MV-VS141FM from Weishi Digital Image Technology Co., Ltd.) (11). Rotating the polarizer (5) around its axis can make the reflected light intensity of the two arms similar, thereby ensuring the best contrast of the interference image.

Next, introduce the top view optical path of the system. 1) Illumination part: the broadband light emitted by the optical fiber is collimated by the convex lens L ₁ (2) and then irradiates parallel to the cylindrical mirror (3). Since the cylindrical mirror (3) in the top view optical path is equivalent to the convex lens (f _CL = 150mm), so after being reflected and transmitted by the beam splitter (4), the broadband light is focused into a light spot on the measured composite material component (7) and the reference plane (6). Combining the two dimensions of the main and top view optical paths, a light knife is formed to measure the internal axial section of the composite material component (7). 2) Imaging part: After the reflected light of the measured composite material component (7) and the reference plane (6) is transmitted and reflected by the beam splitter (4), under the collimation of the convex lens L ₂ (8), the parallel broadband The light enters the diffraction grating (9) at the same incident angle. Because the diffraction grating (9) diffracts light of different wavelengths according to different diffraction angles, only light with the same wavelength can be placed at a specific y position on the image plane of the CCD camera (11) under the focusing effect of the convex lens L3 ( ₁₀ ). imaging. Therefore, after the broadband light with continuous wavelength is diffracted, it is continuously expanded according to the wavelength in the y direction of the image plane of the CCD camera (11) to form an interference spectrum image and transmit it to the computer (12). Figure 3 is extracted from the interference spectrum image Interference light intensity curve.

When the measured object (7) and the reference plane (6) have a total of M surface reflected light for interference, the expression of the interference spectrum is:

$\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{\mathrm{<span\; class="notranslate">\; q</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\sqrt{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{{\mathrm{<span\; class="notranslate">\; \&Lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&Lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; D.</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; ,</span>$

Among them, I is the interference light intensity, y is the space coordinate y of the system in Fig. 1, I _p and I _p are the reflected light intensity of the pth and qth surface respectively, ∧ _pq is the distance between the pth and the qth surface Optical path difference; φ _pq0 is the phase change produced when light is reflected on the p-th and q-th surfaces, k _c =7.48×10 ⁶ /m ^-1 is the central wavenumber of the low-coherence broadband light source (1), C and D are constants:

$\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; the\; si</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\frac{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \}</span>}{{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; d</span>}\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; (</span>\frac{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; ,</span>$

$\mathrm{<span\; class="notranslate">\; D.</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; sin</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; ,</span>$

d=1200 lines/mm is the grating constant of the diffraction grating (9), α=80° is the incident angle of the diffraction grating (9), β _c =-1.75° is the corresponding diffraction angle of k _c , f _L3 =150mm is the convex lens The focal length of L ₃ (10). After digital sampling and windowing, the Fourier transform of the interference spectrum:

$\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; w</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; n\&Delta;y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>$

w(y) and They are the window function and the sampling function, where Δy is the sampling distance between two adjacent sampling points in the y direction of the optical knife section, and N is the maximum number of sampling points in the y direction within the field of view of the light knife section.

The amplitude-frequency characteristic after Fourier transform is:

$\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{\mathrm{<span\; class="notranslate">\; q</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\frac{\sqrt{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}}}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&Delta;y</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; \&PlusMinus;</span>\frac{{\mathrm{<span\; class="notranslate">\; \&Lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}}}{\mathrm{<span\; class="notranslate">\; C\&pi;</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}{\mathrm{<span\; class="notranslate">\; \&Delta;y</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; \&PlusMinus;</span>\frac{{\mathrm{<span\; class="notranslate">\; \&Lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; )</span>}$

Using the amplitude-frequency characteristic, the optical path difference between the p-th and q-th surfaces inside the tested composite component (7) can be expressed by the peak frequency _fpq as:

Λ _pq = π·C·f _pq

Because f _pq and ∧ _pq are in a linear relationship, f _pq can characterize the internal axial profile of the composite material member (7). Fig. 4 shows the amplitude-frequency characteristic curve of the interference signal in Fig. 3 after Fourier transform. In Fig. 4, the abscissas of the three interference peak signals from left to right respectively represent the optical paths between the two surfaces of the section S ₂ S ₃ , S ₁ S ₂ and S ₁ S ₃ of the tested composite material member (7) Difference. Because the air-gap layer S ₂ S ₃ of the composite material component (7) is a standard thickness separated by a precision gasket (KOOCZ00515-20) of 0.4mm, so its corresponding abscissa value is used as the optical path difference reference standard, The other two peaks S ₁ S ₂ and S ₁ S ₃ are calculated to correspond to the optical path difference between the two groups of surfaces: 1.57mm and 1.97mm, which are the same as the previous test results for each layer of material.

The maximum measurement depth of the optical interference spectral domain phase contrast B-scanner is:

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; \&Lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&Delta;k</span>}}$

The measurement resolution of the axial profile is:

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; \&Lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; \&Delta;k</span>}}$

After bringing in the data, it is calculated that the single maximum axial measurement depth and axial profile measurement resolution of this method are 2.66mm and ±26.6μm, respectively. In order to meet the requirement of measuring the deeper area inside the composite material component (7), the position of the reference plane (6) can be adjusted to change the depth range of measurement.

During the loading experiment, the internal structure and loading device of the tested composite component (7) are shown in Fig. 2 . The object to be tested is a variable strength and variable rigidity composite material member (7) composed of three flat plates consisting of a glass layer, an air gap layer and a resin layer. The loading device of the composite material component (7) to be tested is composed of two φ10mm fixed columns with an interval of 60mm and a ball screw micrometer, which can precisely load the component in steps of 0.01mm per step.

After Fourier transform, the phase-frequency characteristics of the interference spectra before and after the axial out-of-plane displacement w _pq of the two surfaces of p and q are:

${{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}}}^{\mathrm{<span\; class="notranslate">\; wrap</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&Lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; D.</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}$

${{{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}}}^{\mathrm{<span\; class="notranslate">\; wrap</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&Lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; D.</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}$

The phase difference is:

Δφ _pq ^wrap (f)=φ′ _pq ^wrap (f)-φ _pq ^wrap (f)

Since the phase obtained after the Fourier transform is the winding phase from -π to π, the winding phase difference is calculated from the winding phase. After adding and subtracting an integer multiple of 2π to the jump point of the wrapping phase, and performing the unwrapping calculation, the unwrapping phase difference Δf _pq ^unwrqp (f) is obtained, as shown in FIG. 5 . At this time, the axial out-of-plane displacement between the two surfaces of p and q is:

${\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; C</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; D.</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; pq</span>}}}^{\mathrm{<span\; class="notranslate">\; unwrap</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span>$

The above formula is the phase contrast method to calculate the out-of-plane displacement by using the phase between the p and q surfaces before and after deformation. In this method, the out-of-plane displacement of the internal section of the composite material component (7) is measured by taking interference spectrum images and signal demodulation of the internal section of the composite material component (7) before and after loading. The advantage is high sensitivity, and the measurement resolution of out-of-plane displacement is ±λ/1000.

After low-pass filtering the unwound phase difference curves of different loads in Fig. 5, multiply by the proportional coefficient C/2(k _c CD) to obtain the out-of-plane displacement and refractive index of S ₁ S ₂ and S ₁ S ₃ The product curve, since the refractive index of air is 1 and the refractive index of glass is 1.45, the out-of-plane displacement curves of S ₁ S ₂ and S ₁ S ₃ are obtained. The out-of-plane displacement inside the tested composite member (7) is shown in Figure 2(c). From the structure of the composite member (7) and the loading method of the _three -point support, it can be known that when the resin layer S3 is compressed and deformed, , due to the blocking effect of the air gap layer on the force transmission, the load will be directly transmitted to the support cylinder on the other side of the glass layer along the two sides of the resin layer and the glass layer, so the surface of S ₃ produces a large out-of-plane displacement, S ₂ undergoes a slight translation, i.e. a slight compression, and S ₁ remains stationary. Since the reference surface S ₁ has no displacement before and after loading, the out-of-plane displacement of S ₁ S ₂ is the out-of-plane displacement of S ₂ , the out-of-plane displacement of S ₁ S ₃ is the out-of-plane displacement of S ₃ , and the out-of-plane displacement of S ₂ and S ₃ The out-of-plane displacement curve of is shown in Fig. 6.

It is worth noting that the position where the feed is applied is z=-5mm, and the detection area is z=0mm～3.5mm, so the place where the maximum displacement from the plane occurs in the detection area is at z=0mm closest to z=-5mm . According to Fig. ₆ , when the surface of S3 was subjected to a loading feed of 20 μm, an out-of-plane displacement of 7 μm occurred at z = 0 mm; when the surface was subjected to a loading feed of 40 μm, an out-of-plane displacement of 13.2 μm occurred at z = 0 mm. The linear relationship between the loading feed and the out-of-plane displacement variation verifies the conclusion of the phase contrast algorithm.

As shown in Figure 6, due to the scattering of light by the speckle surface, the smoothness of the unwound curve of the speckle surface composite member (7) is not as smooth as that of the smooth surface composite member (7), but under the same load The measured speckle surface and the smooth surface have similar out-of-plane displacement, which proves that the B-scanner with phase contrast in the optical interference spectral domain and its measurement method can be used for perspective measurement of the internal section of transparent and optically turbid composite components (7) Off-plane displacement with good repeatability.

Claims (5)

1. an optical interference spectral domain phase place comparison B-scan instrument, it is characterised in that: before the light beam of Low coherence wideband light source (1) The side's of entering upstream sequence places convex lens L₁(2), cylindrical mirror (3), spectroscope (4), light beam is divided into reference arm light path by spectroscope (4) With sample arm light path；The light of reference arm focuses in reference plane (6) after polaroid (5)；The light of sample arm directly focuses on On tested composite element (7)；The outfan order of spectroscope (4) places convex lens L₂(8), diffraction grating (9), convex lens Mirror L₃(10), CCD camera (11) and computer (12)；Wherein B-scan refers to measure each time and is obtained in that tested composite The plane information of the internal tangent plane of component (7).

A kind of optical interference spectral domain phase place comparison B-scan instrument the most according to claim 1, it is characterised in that: use bandwidth The Low coherence wideband light source (1) of more than 10nm.

3. an optical interference spectral domain phase place comparison B-scan measuring method, it is characterised in that comprise the following steps:

1) slight pretension, record Interferogram now, to tested composite element (7) are carried out；

2), tested composite element (7) is loaded so that it is produce acoplanarity displacement, record Interferogram now；

3), by 1) and 2) step measures two Interferograms obtained carry out Fourier transformation respectively, take phase-frequency characteristic and make Difference, calculates the three-dimensional acoplanarity displacement field distribution of tested composite element (7)；

Wherein B-scan refers to measure the plane information being obtained in that the internal tangent plane of tested composite element (7) each time.

A kind of optical interference spectral domain phase place comparison B-scan measuring method the most according to claim 3, it is characterised in that: profit Calculate the internal three-D profile of tested composite element (7) with the crest frequency of interference spectrum amplitude-frequency characteristic to be distributed:

Optical path difference between the internal pth of tested composite element (7) and q-th surface can be by corresponding amplitude-frequency characteristic superiors Value frequency f_pqObtain

Λ_pq=π C f_pq

Wherein C is constant:

$C=\frac{-2\mathrm{\&pi;}\&CenterDot;f_{L3}\{1+tan{\&lsqb;{\sin }^{-1}(\frac{-2\mathrm{\&pi;}}{k_{c}d}+\sin \mathrm{\&alpha;})+{\mathrm{\&beta;}}_c\&rsqb;}^2\}}{{k_c}^{2}d\sqrt{1-{(\frac{-2\mathrm{\&pi;}}{k_{c}d}+\sin \mathrm{\&alpha;})}^2}}$

f_L3For convex lens L₃(10) focal length, k_cFor the center wave number of Low coherence wideband light source (1), d is the light of diffraction grating (9) Grid constant, α is the angle of incidence of diffraction grating (9), β_cFor k_cThe corresponding angle of diffraction.

A kind of optical interference spectral domain phase place comparison B-scan measuring method the most according to claim 3, it is characterised in that: profit Winding phase by tested composite element (7) internal p, the q before and after loading two interference spectrum phase-frequency characteristic before and after the stress of surface Potential difference Δ φ_pq ^wrapF (), after carrying out solving winding calculating to 2 π of the jump plus-minus integral multiple of winding phase place, is solved Winding phase difference φ_pq ^unwrap(f)；Unwrapped phase difference is used to calculate the acoplanarity displacement that tested composite element (7) is internal Distribution:

$w_{pq}=\frac{C}{2(k_c\&CenterDot;C-D)}\&CenterDot;{{\mathrm{\&Delta;\&phi;}}_{pq}}^{unwrap}\left(f\right)$

Wherein C and D is constant:

$D=f_{L3}\&CenterDot;tan\&lsqb;{\sin }^{-1}(\frac{2\mathrm{\&pi;}}{k_{c}d}-\sin \mathrm{\&alpha;})-{\mathrm{\&beta;}}_c\&rsqb;.$