CN111442733A - Nondestructive testing method for rubber composite material based on terahertz time-domain spectral imaging - Google Patents
Nondestructive testing method for rubber composite material based on terahertz time-domain spectral imaging Download PDFInfo
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- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
- G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
- G01N21/3581—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation
- G01N21/3586—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation by Terahertz time domain spectroscopy [THz-TDS]
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
Abstract
The invention discloses a nondestructive testing method for a rubber composite material based on terahertz time-domain spectral imaging, which comprises the following steps: carrying out reflective imaging on a rubber material to be detected through a terahertz time-domain spectroscopy detection device to obtain a detection image; detecting the thickness of the rubber material according to the terahertz time-domain spectrum; and (4) detecting degumming and layering of the rubber material according to the terahertz time-domain spectrum. The rubber material can be subjected to nondestructive testing analysis by using terahertz time-domain spectroscopy nondestructive testing, the thickness of the rubber material is detected and analyzed through a testing image, a B-scan graph and a testing waveform, and the thickness of the rubber material is accurately calculated through the refractive index and the absorptivity of the rubber material; the layering position can be qualitatively determined by analyzing the detection gray scale image, the time domain oscillogram and the B-scan image, and the layering size can be accurately judged by calculating the refractive index.
Description
Technical Field
The invention relates to the technical field of terahertz spectrum detection, in particular to a nondestructive detection method for a rubber composite material based on terahertz time-domain spectral imaging.
Background
Rubber (Rubber) is a highly elastic polymeric material with reversible deformations. The elastic rubber is elastic at room temperature, can generate large deformation under the action of small external force, and can recover the original shape after the external force is removed. The rubber belongs to a completely amorphous polymer, and has low glass transition temperature and large molecular weight which is more than hundreds of thousands. The most used rubbers in the market at present are nitrile rubber, chloroprene rubber, ethylene propylene diene monomer rubber and the like, and the three rubbers are widely applied to medical health, commodity storage, electrical communication, civil engineering and construction and other aspects.
At present, most of rubber material detection methods are damaged, only an ultrasonic detection method is used without damage, but the absorption of ultrasonic waves to rubber materials is too large, so that only surface or subsurface defects can be detected, and the detection of the defects in rubber is incomplete; therefore, how to perform nondestructive testing on rubber materials is a problem to be solved at the present stage.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, provides a nondestructive testing method for a rubber composite material based on terahertz time-domain spectral imaging, and solves the problems that the existing testing method can damage the rubber material or detect the defects in the rubber incompletely.
The purpose of the invention is realized by the following technical scheme: a nondestructive testing method for a rubber composite material based on terahertz time-domain spectral imaging comprises the following steps:
carrying out reflective imaging on a rubber material to be detected through a terahertz time-domain spectroscopy detection device to obtain a detection image;
detecting the thickness of the rubber material according to the terahertz time-domain spectrum;
and (4) detecting degumming and layering of the rubber material according to the terahertz time-domain spectrum.
The nondestructive testing method also comprises the steps of calculating the thickness of the rubber material according to the optical parameters of the rubber material and judging the layering size.
The method for obtaining the detection image by performing reflective imaging on the rubber material to be detected through the terahertz time-domain spectroscopy detection device comprises the following steps:
placing a rubber material to be detected on a detection platform, and obtaining a gray level imaging graph of the rubber material by adopting reflective imaging through a terahertz time-domain spectroscopy detection device;
and simulating according to the flight time algorithm of the terahertz light waves in the rubber material to obtain a B-scan image of the rubber material.
The method for detecting the thickness of the rubber material according to the terahertz time-domain spectroscopy comprises the following steps:
carrying out step layering on a gray level imaging graph on the surface of the rubber material according to the color depth change;
and analyzing the thickness change of each step area according to the flight time of the terahertz spectrum in each step layer of the rubber material.
The calculation of the thickness of the rubber material according to the optical parameters of the rubber material comprises the step of calculating the thickness of each step region by analyzing the time difference of flight of the terahertz spectrum time domain and combining the refractive index and the absorption coefficient of the rubber material.
The method for detecting degumming and layering of the rubber material according to the terahertz time-domain spectroscopy comprises the following steps:
imaging each detection area of the rubber material to obtain a gray level imaging picture and a B-sacn picture;
selecting characteristic points on the gray level imaging image of each detection area;
and analyzing the time domain oscillogram and the B-scan graph of the characteristic points of each detection area.
The analysis of the time domain oscillogram of each detection area comprises the following contents:
analyzing the scattering and attenuation conditions of the point of the terahertz spectrum in the time domain oscillogram according to the position of the selected feature point on the detection area;
and analyzing the peak distribution condition of the terahertz spectrum according to the time domain oscillogram of the characteristic points of the detection area.
The B-scan graph of the characteristic points comprises a row B-scan graph and a column B-scan graph of the characteristic points; the line B-scan graph is used for analyzing the layering condition of the detection area; the column B-scan is used for analyzing the detection region debonding and layering.
The B-scan graph for analyzing the characteristic points of each detection area comprises the following contents:
analyzing the change condition of the transverse grain in the B-scan image of the characteristic point row according to the selected characteristic points on the detection area, and further judging the layering change condition;
and analyzing the change condition of the longitudinal grains in the characteristic point column B-scan image according to the selected characteristic points on the detection area, and determining the degumming and layering positions.
Judging the layering size of the rubber material according to the optical parameters of the rubber material, wherein the judgment comprises the step of obtaining a flight time difference according to the change of longitudinal lines in a column B-scan graph; the delamination height was calculated from the refractive index of the rubber material.
The invention has the beneficial effects that: a nondestructive testing method for rubber composite materials based on terahertz time-domain spectral imaging can perform nondestructive testing analysis on rubber materials by using terahertz time-domain spectral nondestructive testing, the thickness of the rubber materials is detected and analyzed through a testing image, a B-scan image and a testing waveform, and the thickness of the rubber materials is accurately calculated through the refractive index and the absorptivity of the rubber materials; the layering position can be qualitatively determined by analyzing the detection gray scale image, the time domain oscillogram and the B-scan image, and the layering size can be accurately judged by calculating the refractive index.
Drawings
FIG. 1 is a flow chart of a method;
FIG. 2 is a schematic diagram of THz wave propagation in a planar bulk medium;
FIG. 3 is a schematic view of a measurement model without a sample to be measured and with a sample to be measured;
FIG. 4 is a diagram of an apparatus for pump-probe experiments;
FIG. 5 shows a terahertz signal generated by a single ZnTe crystal;
FIG. 6 shows a terahertz signal for detection realized by a single ZnTe crystal;
FIG. 7 is a diagram of a detection material;
FIG. 8 is a thickness detection gray scale imaging plot;
FIG. 9 is a thickness measurement B-scan time-of-flight plot;
FIG. 10 is a thickness detection waveform diagram;
FIG. 11 is a diagram of layered detection of objects;
FIG. 12 is a local area gray scale map;
FIG. 13 is a time domain waveform diagram of feature point 6;
FIG. 14 is a line B-scan plot of feature points 6;
fig. 15 is a column B-scan diagram of the feature point 6.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.
Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.
In the description of the present invention, it should be noted that the terms "upper", "inner", "outer", etc. indicate orientations or positional relationships based on those shown in the drawings or orientations or positional relationships that the products of the present invention conventionally use, which are merely for convenience of description and simplification of description, but do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention.
In the description of the present invention, it should also be noted that, unless otherwise explicitly specified or limited, the terms "disposed," "mounted," and "connected" are to be construed broadly, e.g., as meaning fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
The technical solutions of the present invention are further described in detail below with reference to the accompanying drawings, but the scope of the present invention is not limited to the following.
As shown in fig. 1, a nondestructive testing method for rubber composite material based on terahertz time-domain spectral imaging includes the following steps:
s1, performing reflective imaging on the rubber material to be detected through the terahertz time-domain spectroscopy detection device to obtain a detection image;
s2, detecting the thickness of the rubber material according to the terahertz time-domain spectrum;
and S3, detecting degumming and layering of the rubber material according to the terahertz time-domain spectrum.
The nondestructive testing method also comprises the steps of calculating the thickness of the rubber material according to the optical parameters of the rubber material and judging the layering size.
The method for obtaining the detection image by performing reflective imaging on the rubber material to be detected through the terahertz time-domain spectroscopy detection device comprises the following steps:
placing a rubber material to be detected on a detection platform, and obtaining a gray level imaging picture of the rubber material by adopting reflective imaging through a terahertz time-domain spectroscopy detection device, wherein the detection step distance is 0.5 mm;
and simulating according to the flight time algorithm of the terahertz light waves in the rubber material to obtain a B-scan image of the rubber material.
The method for detecting the thickness of the rubber material according to the terahertz time-domain spectroscopy comprises the following steps:
carrying out step layering on a gray level imaging graph on the surface of the rubber material according to the color depth change;
and analyzing the thickness change of each step area according to the flight time of the terahertz spectrum in each step layer of the rubber material.
The calculation of the thickness of the rubber material according to the optical parameters of the rubber material comprises the step of calculating the thickness of each step region by analyzing the time difference of flight of the terahertz spectrum time domain and combining the refractive index and the absorption coefficient of the rubber material.
Furthermore, the terahertz pulse has the characteristic of low single photon energy, and cannot generate ionization on biological tissues, so that the terahertz time-domain spectroscopy technology is a good nondestructive detection method. And because the absorption peaks corresponding to vibration and rotation of many biological molecules and chemical substances just fall in the terahertz range, people pay attention to the application of the terahertz time-domain spectroscopy technology in the fields of biology, chemistry and medicine. Furthermore, the coherent characteristics of terahertz pulses can simultaneously acquire the electric fieldAmplitude and phase information are convenient for extracting optical information of the sample. In recent years, the work of measuring fingerprint absorption spectra of various substances by using a terahertz transmission type time domain spectroscopy system for substance identification is much. The substances absorb the terahertz waves very weakly, and the terahertz waves still have good terahertz time-domain waveforms after penetrating through the substances; in addition, an algorithm for extracting substance optical parameters from the transmission-type terahertz spectrum is mature, so that the application of the terahertz transmission-type time-domain spectrum technology in various fields is very wide. However, there are many substances that absorb terahertz waves strongly, and if the terahertz transmission time-domain spectroscopy system is still used for measurement, a very thin sample needs to be prepared, which brings great difficulty to sample processing, so the terahertz reflection time-domain spectroscopy system is necessary for accurately measuring the optical parameters of the substances. In recent years, the work of measuring a sample using a terahertz reflective system has increased, but an algorithm for extracting optical parameters of the sample has not yet been developed. According to a model for extracting optical parameters of a material by adopting a terahertz reflection type time-domain spectroscopy technology, the frequency spectrums of a sample signal and a reference signal are compared to obtain the transfer function of the sample to terahertz waves, wherein the transfer function contains the complex refractive index information of the sample, and the complex refractive index of the sample is solved
The refractive index and absorption coefficient of the sample were obtained.
As shown in FIGS. 2 and 3, the A-model diagram (measurement model diagram without sample to be measured) in FIG. 3 is a measurement model without sample to be measured placed above a petri dish, wherein the thickness of the petri dish is L, and the complex refractive index is
Refractive index of air is n a1 is ═ 1; model B (model diagram for measuring sample to be measured) is a model for measuring sample to be measured placed on the top of the culture dish, and the complex refractive index of the liquid is set as
Suppose terahertz wave is at an incident angle θ1Incident on the bottom of the dish, transmission and reflection occur between the upper and lower surfaces of the bottom of the dish. Given by the Fresnel formula, the equation1Is an incident angle, in theta2The complex refractive indexes of the incident medium and the emergent medium are respectively set as
And
the formula of the interface transmission coefficient and the reflection coefficient is as follows:
considering again the propagation factor of the propagation distance d in the medium 2
An expression of terahertz electric field intensity corresponding to the three reflection signals can be obtained:
Ea(ω)＝E0rasPa(ω,ΔL)，Eb(ω)＝E0tasPs(ω,d)rsaPs(ω,d)tsa，Ec(ω)＝E0tasPs(ω,d)rs1Ps(ω,d)tsa；
wherein, Delta L is 2L sin theta1tanθ2Is the optical path difference of two reflected signals on the front and back surfaces of the culture dish in the air, and d is 2L/cos theta2The terahertz time-domain spectroscopy system can provide two methods for calculating light of a sample to be measured for people, namely, the terahertz time-domain spectroscopy system is characterized in that the terahertz wave travels in a plastic culture dish with the thickness of L, two main peaks appear in front and at back in a measured terahertz time-domain spectroscopy due to two reflections on the upper surface and the lower surface of the bottom of the plastic culture dish, the first main peak is reflected on the lower surface of the bottom of the culture dish, the second main peak is reflected on the upper surface of the bottom of the culture dish, namely, reflected on the surface contacted with liquid to be measured, the delay time between the two main peaks is mainly determined by the optical path difference of the terahertz wave transmitted in the culture dishA method for learning a parameter. The method is to use a B model diagram in FIG. 3 to obtain a reflected signal of the lower surface of the bottom of the culture dish, namely a first main terahertz peak Ea(ω) is a reference signal; the upper surface of the bottom of the culture dish contacting with the sample to be measured, i.e. the second main peak EcAnd (omega) is a sample signal, and the optical parameters of the sample to be measured are obtained through calculation. The method can obtain the reference signal and the sample signal only by one-time measurement, thereby shortening the experimental time, reducing the experimental operation steps and improving the experimental efficiency. Second method uses the second main peak of the A and B model diagrams of FIG. 3 as reference signal Eb(omega) and sample signal EcAnd (omega), and obtaining the optical parameters of the liquid sample through an algorithm. This method requires separate measurements for obtaining the reference and sample signals, and is more complicated than the former method in experimental operation, but the algorithm procedure is simpler than the former method.
Method of use-selection of Ea(ω) as reference signal, with Ec(ω) as sample signal. Handle type
And formula
And the expression of the propagation factor is substituted into formula Ea(ω)＝E0rasPa(ω, Δ L) and formula Ec(ω)＝E0tasPs(ω,d)rs1Ps(ω,d)tsaThe expression of the available transfer function:
by modifying the above formula, r can bes1The expression is written as:
the complex refractive index of the sample is then:
wherein r issa，tsaAnd tasAll can be obtained by the Fresnel formula,
is the complex refractive index of the culture dish. In the calculation, HTheory(ω) from the experimental value HMeasure(ω) instead. Complex refractive index through liquid to be measured
The real part and the imaginary part of the optical fiber can obtain that the refractive index, the extinction coefficient and the absorption coefficient are respectively:
THz-TDS becomes an important technical means in the field of THz science, and has a great application prospect in the fields of physical, material, chemical and biological compound sample analysis and identification, biomedicine, safety detection and the like. At present, a THz time domain spectrum system generally used in experiments mainly comprises a femtosecond laser, a THz emitter, a THz detector, a time delay control system and other four main parts. The terahertz pulse laser has the basic principle that a femtosecond laser pulse emitted by a femtosecond laser device is divided into two beams after passing through a beam splitter, one beam of laser pulse (generated pulse) is incident on a terahertz emitter after passing through a time delay system to generate terahertz radiation, the other beam of laser pulse (detection pulse) and the terahertz pulse are incident on a terahertz detector together, and the whole waveform of the terahertz pulse can be obtained by adjusting the time delay between the detection pulse and the terahertz pulse.
The pump-detection technology is the basis of other THz time-domain spectroscopy technology experimental systems and is mainly used for measuring the time resolution spectrum of the change of an excited state of a material along with time under the excitation of femtosecond laser pulses. The basic principle of pump-detection is to obtain the delay of the beam in time by a spatial delay. The pump-probe system can be used for researching the ultra-fast power of a semiconductor carrierIn science, the terahertz time-domain spectrum of the same sample which serves as both the THz generator and the THz detector can be researched. The experimental optical path is shown in fig. 4, and is suitable for detecting the situation that the THz reflector and the detector are on the same sample. Wherein the thick solid line represents pump (pump) light and the thin solid line represents probe (probe) light (general I)pump/Iprobe> 10: 1). Laser pulse emitted by a laser is divided into two beams by a Beam Splitter (BS), transmitted strong pulse is used as pump light, the pump light passes through a chopper and a one-dimensional electric translation table controlled by a computer, and is focused to the same point of a sample with reflected weak detection light by a lens, the pump light is blocked by a light screen after passing through the sample, and the reflected detection light enters a detector (a) connected with a phase-locked amplifier and an electro-optical sampling system (b). The signals are amplified by phase lock and recorded by a computer data acquisition system, averaged and digitized, and finally recorded by a computer.
M1-M7 mirror, BS is beam splitter, L1 is lens, QWP is lambda/4 wave plate, WP is Wollaston prism (a) is detector, and (b) is electro-optical sampling system when the device of FIG. 4 is used, the detector detects the change of the intensity of probe light with time, and the device is suitable for detecting THz signal obtained by nonlinear frequency up-conversion.
6H-SiC and N-doped 6H-SiC were studied by optical pumping with a central wavelength of 400nm and optical probing with a central wavelength of 800 nm: the carrier ultra-fast dynamic process of N, in addition this system is also suitable for detecting the THz signal that utilizes nonlinear frequency up-conversion to get. If (a) is replaced by (b), the balanced photodetector detects a change in the polarization state of the detected light. The device is suitable for detecting terahertz signals obtained by free space electro-optic sampling. Fig. 5 shows the time-domain spectrum results of terahertz electro-optical sampling done using a single ZnTe crystal, with the inset portion being the amplified signal of the terahertz oscillating portion. Fig. 6 is a frequency domain spectrum obtained by fourier transforming the terahertz oscillation partial spectrum in fig. 5.
The experiment requires that the pump light pulse and the detection light pulse are strictly overlapped in time and space, and the overlapping in space is realized by adopting a method of cutting light spots by a blade. The vertically crossed blades are placed on a sample rack, and the sample platform is adjusted forwards and backwards to enable the two light spots to disappear and appear simultaneously, so that the blades are just positioned on the focal point of the lens. Then the sample stage is acted and moved up and down, the direction of a reflector (M4), namely the pumping light, is adjusted, so that the two beams of light disappear and appear simultaneously, and the spatial coincidence of the pumping light and the detection light is realized. The time coincidence of the pump light and the probe light can be realized by changing the optical paths of the pump light and the probe light by moving the delay line. A signal is detected when the pump light pulses and the probe light pulses overlap both temporally and spatially. The pumping-detection optical path can detect terahertz signals of frequency up-conversion and electro-optical sampling, and has a very important function of finding equal optical path points, and the characteristic lays an experimental foundation for building THz-TDS with a terahertz emitter and a detector separated from each other.
In a reflection detection mode, the focal length of a lens is 7.62cm (3inch), a copper plate is placed at the focus of a detector to collect a reference signal, and then a sample is placed for sample signal detection. According to the characteristics of the tested object, two detection modes of horizontal and vertical can be set.
The reflection imaging mode is different from the transmission mode, in the scanning detection process, a detected sample is fixed, the sample is placed on a metal flat plate which has stronger terahertz wave reflection generally serving as a reference reflector in a horizontal mode, and the upper surface of the metal flat plate is a reflection focusing position. The two-dimensional moving platform controls the reflection receiving device to move, so that terahertz pulse reflection signals of each point on the sample are obtained. The vertical mode selects whether to use a reference reflector according to the property of the sample to be detected, and if the sample to be detected reflects the terahertz signal strongly, a metal plate is not required to be added during imaging, and the metal plate is only used as a reference signal for extraction.
As shown in fig. 7 and 8, the color is divided into 5 levels from dark to light, the surface of the material is basically 4 step layers, and the thickness of the region 1 is thinner due to the surface damage of the first step layer region; by analyzing the area color, the difference of the material thickness can be qualitatively analyzed.
As shown in fig. 9, it can be seen that the time of flight of terahertz in the rubber material changes in a step-like manner, which is consistent with the form in fig. 4. The thickness variation of each region can be analyzed, and the thickness of each region of the rubber material can be calculated through the refractive index and the absorptivity according to the flight time diagram.
As shown in fig. 10, the left to right in the figure corresponds to the 4 stepped layers of the rubber material from the left guide part in fig. 4, i.e. the left to right corresponds to the first stepped layer, the second stepped layer, the third stepped layer and the fourth stepped layer, respectively; as the thickness of the rubber increases, the flight time increases while the energy decreases; the time delay of each step area is respectively as follows: the first step layer 251.5ps-40.7 ps-210.8 ps, the second step layer 240.7ps-63 ps-177.7 ps, the third step layer 206.6ps-101.9 ps-104.7 ps, and the fourth step layer 188.7ps-117.4 ps-71.3 ps; the refractive index of the rubber material was about 1.2214, and the thicknesses of the first to fourth stepped layers were calculated to be 16.2mm, 13.6mm, 8mm and 5.4mm, respectively.
As can be seen from the analysis, the waveform variation trend of each layer is basically the same. Since the material composition is not uniform, the material surface is rough and damaged, and thus the thickness of the material cannot be accurately determined. If the thickness of the material needs to be analyzed accurately and quantitatively, the thickness can be detected and judged by manufacturing a standard sample block and taking the detection result as data reference.
The method for detecting degumming and layering of the rubber material according to the terahertz time-domain spectroscopy comprises the following steps:
imaging each detection area of the rubber material to obtain a gray level imaging picture and a B-sacn picture;
selecting characteristic points on the gray level imaging image of each detection area;
and analyzing the time domain oscillogram and the B-scan graph of the characteristic points of each detection area.
The analysis of the time domain oscillogram of each detection area comprises the following contents:
analyzing the scattering and attenuation conditions of the point of the terahertz spectrum in the time domain oscillogram according to the position of the selected feature point on the detection area;
and analyzing the peak distribution condition of the terahertz spectrum according to the time domain oscillogram of the characteristic points of the detection area.
The B-scan graph of the characteristic points comprises a row B-scan graph and a column B-scan graph of the characteristic points; the line B-scan graph is used for analyzing the layering condition of the detection area; the column B-scan is used for analyzing the detection region debonding and layering.
The B-scan graph for analyzing the characteristic points of each detection area comprises the following contents:
analyzing the change condition of the transverse grain in the B-scan image of the characteristic point row according to the selected characteristic points on the detection area, and further judging the layering change condition;
and analyzing the change condition of the longitudinal grains in the characteristic point column B-scan image according to the selected characteristic points on the detection area, and determining the degumming and layering positions.
Judging the layering size of the rubber material according to the optical parameters of the rubber material, wherein the judgment comprises the step of obtaining a flight time difference according to the change of longitudinal lines in a column B-scan graph; the delamination height was calculated from the refractive index of the rubber material.
As shown in fig. 11 and 12, when the B-scan diagram is analyzed according to the gray scale diagram, the transverse direction is the Y-axis direction, and the longitudinal direction is the X-axis direction, and the corresponding position of the physical diagram is enlarged, it can be seen that the delamination of the adhesive layer at the first step layer is obvious, and the delamination appears at the position 3mm away from the upper surface after the measurement; and a layering state also appears in the third step layer, a material layering region can be seen through analyzing and comparing corresponding waveforms, and the layering region of the rubber can be judged through an abnormal region in a B-scan graph. The layering detection analyzes the specific layering condition of the cross section of different characteristic points by selecting different characteristic points on the gray-scale image and using the time domain oscillogram and the B-scan image.
The different places of the materials are selected for testing, so that the characteristic points 1-6 in the figure 9 have layering phenomena, the characteristic point 6 is selected as an object to be analyzed, and the analysis of other points is similar to the characteristic point 6.
As shown in fig. 13, it can be known from the time domain waveform diagram that Good is a normal waveform, another waveform is a waveform of a characteristic 6 point, and a waveform of the characteristic 6 point can be seen in a circle in the diagram to have an echo signal, which indicates that there is an interface boundary, and then the layering phenomenon at this point can be analyzed.
As shown in FIG. 14 and FIG. 15, the layered state can be clearly seen in the figure, the difference from the normal area can be seen through the Bscan diagram of the rows and columns of the characteristic 6 points, and the internal defect size can be calculated through the pixel points of the boundary in the Bscan diagram of the characteristic 6 points, the refractive index of the rubber is 3.48 through detection because the detection step distance is 0.5mm, the boundary defect values are selected through the Bscan image, and the layered sizes of the characteristics 1 to 6 points are respectively (the length is ×, the width is ×, the height is 5.33 × 010.10 × 13.10.10 mm, 10.24 × 218.21 × 35.32.32 mm, 9.25 × 11.42 × 3.21.21 mm, 17.80 × 21.88.88 21.88 × 4.86.86 mm, 19.48 × 23.57.57 23.57 × 6.44.44 mm, 18.95 × 21.12.12 21.12 × 3.21.21 mm).
The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes performed by the present specification and drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (10)
1. A nondestructive testing method for rubber composite materials based on terahertz time-domain spectral imaging is characterized by comprising the following steps: the nondestructive testing method comprises the following steps:
carrying out reflective imaging on a rubber material to be detected through a terahertz time-domain spectroscopy detection device to obtain a detection image;
detecting the thickness of the rubber material according to the terahertz time-domain spectrum;
and (4) detecting degumming and layering of the rubber material according to the terahertz time-domain spectrum.
2. The nondestructive testing method for the rubber composite material based on terahertz time-domain spectral imaging according to claim 1, characterized in that: the nondestructive testing method also comprises the steps of calculating the thickness of the rubber material according to the optical parameters of the rubber material and judging the layering size.
3. The nondestructive testing method for the rubber composite material based on terahertz time-domain spectral imaging according to claim 2, characterized in that: the method for obtaining the detection image by performing reflective imaging on the rubber material to be detected through the terahertz time-domain spectroscopy detection device comprises the following steps:
placing a rubber material to be detected on a detection platform, and obtaining a gray level imaging graph of the rubber material by adopting reflective imaging through a terahertz time-domain spectroscopy detection device;
and simulating according to the flight time algorithm of the terahertz light waves in the rubber material to obtain a B-scan image of the rubber material.
4. The nondestructive testing method for the rubber composite material based on terahertz time-domain spectral imaging according to claim 3, characterized in that: the method for detecting the thickness of the rubber material according to the terahertz time-domain spectroscopy comprises the following steps:
carrying out step layering on a gray level imaging graph on the surface of the rubber material according to the color depth change;
and analyzing the thickness change of each step area according to the flight time of the terahertz spectrum in each step layer of the rubber material.
5. The nondestructive testing method for the rubber composite material based on terahertz time-domain spectral imaging according to claim 4, characterized in that: the calculation of the thickness of the rubber material according to the optical parameters of the rubber material comprises the step of calculating the thickness of each step region by analyzing the time difference of flight of the terahertz spectrum time domain and combining the refractive index and the absorption coefficient of the rubber material.
6. The nondestructive testing method for the rubber composite material based on terahertz time-domain spectral imaging according to claim 3, characterized in that: the method for detecting degumming and layering of the rubber material according to the terahertz time-domain spectroscopy comprises the following steps:
imaging each detection area of the rubber material to obtain a gray level imaging picture and a B-sacn picture;
selecting characteristic points on the gray level imaging image of each detection area;
and analyzing the time domain oscillogram and the B-scan graph of the characteristic points of each detection area.
7. The nondestructive testing method for the rubber composite material based on terahertz time-domain spectral imaging according to claim 6, characterized in that: the analysis of the time domain oscillogram of each detection area comprises the following contents:
analyzing the scattering and attenuation conditions of the point of the terahertz spectrum in the time domain oscillogram according to the position of the selected feature point on the detection area;
and analyzing the peak distribution condition of the terahertz spectrum according to the time domain oscillogram of the characteristic points of the detection area.
8. The nondestructive testing method for the rubber composite material based on terahertz time-domain spectral imaging according to claim 6, characterized in that: the B-scan graph of the characteristic points comprises a row B-scan graph and a column B-scan graph of the characteristic points; the line B-scan graph is used for analyzing the layering condition of the detection area; the column B-scan is used for analyzing the detection region debonding and layering.
9. The nondestructive testing method for the rubber composite material based on terahertz time-domain spectral imaging according to claim 8, characterized in that: the B-scan graph for analyzing the characteristic points of each detection area comprises the following contents:
analyzing the change condition of the transverse grain in the B-scan image of the characteristic point row according to the selected characteristic points on the detection area, and further judging the layering change condition;
and analyzing the change condition of the longitudinal grains in the characteristic point column B-scan image according to the selected characteristic points on the detection area, and determining the degumming and layering positions.
10. The nondestructive testing method for the rubber composite material based on terahertz time-domain spectral imaging according to claim 9, characterized in that: judging the layering size of the rubber material according to the optical parameters of the rubber material, wherein the judgment comprises the step of obtaining a flight time difference according to the change of longitudinal lines in a column B-scan graph; the delamination height was calculated from the refractive index of the rubber material.
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