CN1800835A - Method and apparatus for extracting order value of coherent gradient sensing interference fringe - Google Patents

Abstract

The invention relates to a method to extract the coherent gradient sensitive interference fringe level number in fracture mechanics. Wherein, splitting the parallel light beam into two paths to generate coherent gradient sensitive interference fringe respectively; subtracting the background light intensity in two figures of coherent gradient sensitive interference fringe, calculating the fringe level number ml of the first figure. Wherein, the opposite device comprises: a laser, a beam expander, a convex lens, a semi-reflecting semi-transparent mirror, four gratings, two groups convex lens and diaphragms, and two cameras and computers. This invention can improve the calculation accuracy obviously without knowing the opposite load of fringe image.

Description

A kind of method and device thereof that extracts order value of coherent gradient sensing interference fringe

Technical field

The present invention relates to a kind of method and device thereof that extracts order value of coherent gradient sensing interference fringe, belong to the fracture mechanics parameter technical field of measuring.

Background technology

Coherent gradient sensing method (Coherent Gradient Sensing, hereinafter to be referred as CGS) be a kind of horizontal double grid shear interference of noncontact, whole audience optical measurement method with online spatial filtering effect, thereby it utilizes the reorganization of two parallel gratings to produce interference fringe by the distortion light beam that test piece deformation causes, and sets up relation between in-plane stress gradient or acoplanarity displacement gradient and the fringe order by the optical interference governing equation.This method can be respectively applied for the deformation information of the transparent and nontransparent object of research under transmission and reflection case, its striped distribution has directly reflected in-plane stress gradient fields under the transmission situation and the acoplanarity displacement gradient fields under the reflection case.Because this method counter stress or displacement gradient sensitivity are so be particularly suitable for studying the breakage problem with high stress concentrations phenomenon.The coherent gradient sensing method is divided into transmission-type and reflective two kinds, Figure 1 shows that typical coherent gradient sensing interference fringe picture, and black streaking is represented half progression striped in the actual photographed image, and outmost turns is 0.5 grade of striped.

The weak point of above-mentioned prior art: similar with other optical measurement method of handling bar graph, obtain fracture mechanics parameter and must extract order value of coherent gradient sensing interference fringe earlier, and will determine that order value of coherent gradient sensing interference fringe just must accurately extract stripe centerline.Interference fringe is thicker as can be seen from Figure 1, and out-of-shape, is difficult to satisfy accuracy requirement iff relying on image process method to extract stripe centerline, even can brings very big error, especially for the harmonic series striped.

Summary of the invention

The objective of the invention is to propose a kind of method and device thereof that extracts order value of coherent gradient sensing interference fringe, to improve the computational accuracy of coherent gradient sensing method.

The method of the extraction order value of coherent gradient sensing interference fringe that the present invention proposes may further comprise the steps:

(1) beam of laser is expanded bundle, obtain diverging light, planoconvex lens becomes directional light again, incides the test specimen surface;

(2) parallel beam with above-mentioned test specimen outgoing is divided into two-way light, and first via light is Δ through spacing ₁First grating and second grating, produce the coherent gradient sensing interference fringe, the second road light is Δ through spacing ₂The 3rd grating and the 4th grating, produce the coherent gradient sensing interference fringe;

(3), and take the interference fringe field to above-mentioned two interference fringe field imagings;

(4) before test specimen does not load, from the digital picture of above-mentioned two light paths shooting test specimen, the background light intensity that obtains interference fringe picture is respectively a respectively ₁, a ₂

(5) to the test specimen imposed load, take the coherent gradient sensing interference fringe picture of loading specimen respectively from above-mentioned two light paths, the light distribution of two interference fringe fields is respectively: I ₁, I ₂

(6) from two width of cloth coherent gradient sensing interference fringe pictures of the loading specimen of above-mentioned steps (5), deduct the respective background light intensity of above-mentioned steps (4), and it is carried out histogram transformation, make the amplitude of two width of cloth image striped light intensity identical, the interference fringe picture light distribution of two light paths that conversion obtains is I ₁ ^*And I ₂ ^*

(7), calculate the fringe order m of first width of cloth interference fringe picture according to above-mentioned grating space and light intensity ₁For:

$\frac{I_1^{*}}{I_2^{*}}=\frac{\cos \left({2\mathrm{\&pi;m}}_1\right)}{\cos ({2\mathrm{\&pi;<figure-callout\; id="1"\; label="m"\; filenames="A20061000136600081.png"\; state="\{\{state\}\}">m</figure-callout>}}_1{\mathrm{\&Delta;}}_2/{\mathrm{\&Delta;}}_1)}.$

The device of the extraction order value of coherent gradient sensing interference fringe that the present invention proposes comprises:

(1) is used for lasing laser instrument, is used for laser is expanded the beam expanding lens of bundle, make diverging light become the convex lens of directional light;

(2) be used for the parallel beam of test specimen outgoing is divided into the half-reflecting half mirror of two-way light, be used to produce first grating and second grating of first via coherent gradient sensing interference fringe, the spacing of first grating and second grating is a Δ ₁, being used to produce the 3rd grating and the 4th grating of the second road coherent gradient sensing interference fringe, the spacing of the 3rd grating and the 4th grating is a Δ ₂

(3) be used for first group of convex lens of above-mentioned two interference fringe field imagings and diaphragm and second group of convex lens and diaphragm, and be used to take first video camera, second video camera of interference fringe field and be used for Flame Image Process and computing machine that interference fringe progression extracts;

Above-mentioned laser instrument, beam expanding lens, convex lens, test specimen, half-reflecting half mirror, first grating, second grating, first group of convex lens and diaphragm and first video camera are on the primary optic axis successively; Above-mentioned the 3rd grating, the 4th grating, second group of convex lens and diaphragm and second video camera are on second optical axis successively, and the primary optic axis and second optical axis intersect vertically in the half-reflecting half mirror place, and computing machine is connected with second video camera with first video camera respectively.

The method and the device thereof of the extraction order value of coherent gradient sensing interference fringe that the present invention proposes, its advantage is: the fringe order that can accurately extract coherent gradient sensing interference fringe picture optional position point, experimental result shows that this method can significantly reduce because striped extracts the error of bringing, thereby improves the precision of coherent gradient sensing method.Concrete advantage is: the computational accuracy that a) can obviously improve the coherent gradient sensing method; B) do not require the load of knowing every width of cloth interference fringe image correspondence in advance, therefore be convenient in the Dynamic Fracture experiment, use.

Description of drawings

Fig. 1 is existing typical coherent gradient sensing interference fringe picture, and wherein (a) is theoretical modeling figure; (b) be the actual photographed bar graph.

Fig. 2 is the index path that produces interference fringe in the prior art.

Fig. 3 is the schematic diagram that produces interference fringe in the prior art.

Fig. 4 is the light path synoptic diagram of the extraction order value of coherent gradient sensing interference fringe that proposes of the present invention.

Fig. 5 adopts the inventive method, the crack tip reflection coherent gradient sensing interference fringe picture that on same test specimen, produces during different grating space, and wherein (a) is that grating space is a Δ ₁=50mm is that grating space is a Δ (b) ₂=100mm.

Fig. 6 is the stress intensity factor that calculates of a inventive method and prior art comparison diagram as a result, and the longitudinal axis is the relative error of experimental calculation value and theoretical value, and solid line is represented the result of calculation of prior art, and dotted line is represented the result of calculation of the inventive method.Wherein (a) is the result of calculation comparison diagram between interference fringe picture-40 °～-30 °, (b) is the result of calculation comparison diagram between interference fringe Figure 30 °～40 °.

Among Fig. 2, Fig. 3 and Fig. 4, the 1st, laser instrument, the 2nd, beam expanding lens, the 3rd, convex lens, the 4th, test specimen, 5 is first gratings, 6 is second gratings, and 7 is first filter lens, and 8 is first diaphragms, 9 is first video cameras, the 10th, and computing machine, the 11st, half-reflecting half mirror, 12 is the 3rd gratings, and 13 is the 4th gratings, and 14 is second filter lens, 15 is second diaphragms, and 16 is second video cameras.

Embodiment

The method of the extraction order value of coherent gradient sensing interference fringe that the present invention proposes at first expands bundle to beam of laser, obtains diverging light, and planoconvex lens becomes directional light again, incides the test specimen surface; The parallel beam of test specimen outgoing is divided into two-way light, and first via light is Δ through spacing ₁First grating and second grating, produce the coherent gradient sensing interference fringe, the second road light is Δ through spacing ₂The 3rd grating and the 4th grating, produce the coherent gradient sensing interference fringe; To two interference fringe field imagings, and take the interference fringe field; Before test specimen does not load, take the digital picture of test specimen respectively from two light paths, the background light intensity that obtains interference fringe picture is respectively a ₁, a ₂To this test specimen imposed load, take the coherent gradient sensing interference fringe picture of loading specimen respectively from two light paths, the light distribution of two interference fringe fields is respectively: I ₁, I ₂Deduct the respective background light intensity from two width of cloth coherent gradient sensing interference fringe pictures of loading specimen, and it is carried out histogram transformation, make the amplitude of striped light intensity of two width of cloth images identical, the interference fringe picture light distribution of two light paths that conversion obtains is I ₁ ^*And I ₂ ^*According to grating space and light intensity, calculate the fringe order m of first width of cloth interference fringe picture ₁For: $\frac{{\mathrm{<figure-callout\; id="1"\; label="I"\; filenames="A20061000136600081.png"\; state="\{\{state\}\}">I</figure-callout>}}_1^{*}}{I_2^{*}}=\frac{\cos \left({2\mathrm{\&pi;m}}_1\right)}{\cos ({2\mathrm{\&pi;<figure-callout\; id="1"\; label="m"\; filenames="A20061000136600081.png"\; state="\{\{state\}\}">m</figure-callout>}}_1{\mathrm{\&Delta;}}_2/{\mathrm{\&Delta;}}_1)}.$

The device of the extraction order value of coherent gradient sensing interference fringe that the present invention proposes as shown in Figure 4, comprising:

(1) is used for lasing laser instrument 1, is used for laser is expanded the beam expanding lens 2 of bundle, make diverging light become the convex lens 3 of directional light;

(2) be used for the parallel beam of test specimen 4 outgoing is divided into the half-reflecting half mirror 11 of two-way light, be used to produce first grating 5 of first via coherent gradient sensing interference fringe and the spacing of second grating, 6, the first gratings 5 and second grating 6 is a Δ ₁, be used to produce the 3rd grating 12 of the second road coherent gradient sensing interference fringe and the spacing of the 4th grating 13, the three gratings 12 and the 4th grating 13 is a Δ ₂, the light distribution of two interference fringe fields is respectively: I ₁, I ₂

(3) be used for first group of convex lens 7 of above-mentioned two interference fringe field imagings and diaphragm 8 and second group of convex lens 14 and diaphragm 15, and be used to take first video camera 9, second video camera 16 of interference fringe field and be used for Flame Image Process and computing machine 10 that interference fringe progression extracts;

Above-mentioned laser instrument 1, beam expanding lens 2, convex lens 3, test specimen 4, half-reflecting half mirror 11, first grating 5, second grating 6, first group of convex lens 7 and diaphragm 8, first video camera 9 are on the primary optic axis successively; Above-mentioned the 3rd grating 12, the 4th grating 13, second group of convex lens 14 and diaphragm 15, second video camera 16 are on second optical axis successively, the primary optic axis and second optical axis intersect vertically in half-reflecting half mirror 11 places, and computing machine 10 is connected with second video camera 16 with first video camera 9 respectively.

Below in conjunction with accompanying drawing, introduce content of the present invention in detail:

Existing coherent gradient sensing method light path is as shown in Figure 2: a branch of coherent laser beam forms directional light by optical lens after through the beam expanding lens that has the filtering hole, parallel beam is vertically by being with the test specimen of crackle, be subjected to the influence of test piece deformation and stress field, the direction of parallel beam and phase place will change.Though the light beam by the test specimen outgoing no longer is a parallel beam, because deviation in driction is very little, for simplicity, the light beam that still will have test piece deformation information is considered as parallel beam.By (x, y) (x, y), similarly the light by (x, y+ ε) some outgoing on the test specimen has optical path difference δ S (x, y+ ε) owing to test piece deformation to the light of some outgoing because test piece deformation has optical path difference δ S on the test specimen.As shown in Figure 3, the high density Ronchi grating (pitch is all p mutually) that these parallel beams are parallel to each other through two after the test specimen outgoing, spacing is Δ, produce diffraction, if behind diaphragm, place video camera, can photograph the interference fringe that causes optical path difference to cause owing to test piece deformation, and by computing machine striped be handled and to be extracted relevant mechanics parameter.

If transmission coherent gradient sensing method, optical path difference δ S (x, y) specimen thickness that causes of test specimen variations in refractive index that is mainly caused by stress changes and poisson effect changes two factors and produces, so the photodynamics governing equation of transmission coherent gradient sensing method is:

$\mathrm{cd}\frac{\&PartialD;({\widetilde{\mathrm{\&sigma;}}}_x+{\widetilde{\mathrm{\&sigma;}}}_y)}{\&PartialD;x}=\frac{\mathrm{mp}}{\mathrm{\&Delta;}}---\left(1\right)$

Wherein m is a fringe order, and p is a raster pitch, and Δ is two spacings between the grating, and c is the optical constant of material, and d is a specimen thickness,

With Represent the mean stress component on the specimen thickness direction.

Photodynamics governing equation (1) shows when grating principal direction is parallel to the x axle, and the physical significance of coherent gradient sensing striped representative is a test specimen principle stress and to the isoline of x direction gradient under the transmission situation.

For reflection coherent gradient sensing method, optical path difference δ S (x, y) specimen thickness that is only caused by poisson effect changes generation, so the photodynamics governing equation of reflection coherent gradient sensing method is:

$\frac{\&PartialD;w}{\&PartialD;x}=\frac{\mathrm{mp}}{2\mathrm{\&Delta;}}---\left(2\right)$

Wherein m is a fringe order, and p is a raster pitch, and Δ is two spacings between the grating, and w represents the acoplanarity displacement of test specimen.

Photodynamics governing equation (2) shows that when grating principal direction is parallel to the x axle physical significance of coherent gradient sensing interference fringe representative is the isoline of test specimen acoplanarity displacement to the x direction gradient under reflection case.

The light path of the inventive method utilizes half-reflecting half mirror that the parallel beam of test specimen 4 outgoing is divided into two-way light as shown in Figure 4, and each road light all produces the coherent gradient sensing interference fringe through two gratings, and the light distribution of these two interference fringe fields is respectively:

I ₁＝a ₁+b ₁cos2πm ₁ (3)

I ₂＝a ₂+b ₂cos2πm ₂ (4)

Wherein a represents the background light intensity, and bar graph changes according to cosine rule bcos2 π m.Owing to be the interference fringe field that different light paths forms, so their background light intensity a is different mutually with striped light intensity b.For the ease of subsequent treatment, light distribution is transformed to following form:

I ₁-a ₁＝b ₁cos2πm ₁ (5)

I ₂-a ₂＝b ₂cos2πm ₂ (6)

Background light intensity a wherein ₁, a ₂Two light path shot digital images do not obtain when loading by test specimen.After the influence of coherent gradient sensing interference fringe picture subtracting background light intensity, handle by digital picture being carried out histogram transformation, can change the striped light intensity b of two width of cloth images ₁, b ₂Make them be all b mutually, but fringe order m does not change.The interference fringe picture light distribution of handling with latter two light path through the digital picture method is I ₁ ^*And I ₂ ^*:

I ₁ ^*＝bcos2πm ₁ (7)

I ₂ ^*＝bcos2πm ₂ (8)

According to the photodynamics governing equation (1) and (2) formula of coherent gradient sensing method, the separation delta of two parallel gratings is directly proportional with interference fringe progression m:

$\frac{{\mathrm{\&Delta;}}_1}{{\mathrm{\&Delta;}}_2}=\frac{m_1}{m_2}---\left(9\right)$

If adopt Fig. 4 light path to take two width of cloth coherent gradient sensing interference fringe pictures of same test specimen under different grating spaces, the interference fringe light intensity I after convolution (7), (8) can obtain two grating space Δs and handle through the digital picture method with (9) ^*With fringe order m ₁Between relation:

$\frac{I_1^{*}}{I_2^{*}}\frac{\cos \left({2\mathrm{\&pi;m}}_1\right)}{\cos ({2\mathrm{\&pi;<figure-callout\; id="1"\; label="m"\; filenames="A20061000136600081.png"\; state="\{\{state\}\}">m</figure-callout>}}_1{\mathrm{\&Delta;}}_2/{\mathrm{\&Delta;}}_1)}---\left(10\right)$

The light distribution I of the interference fringe picture after grating space Δ during according to shooting two width of cloth bar graphs and two width of cloth digital picture methods are handled ^*, (10) formula of utilization just can obtain the accurate fringe order m of any point on first width of cloth bar graph ₁

With the experiment of reflection coherent gradient sensing method is that the effect that example is extracted fringe order to the grating space method is tested.Figure 5 shows that two width of cloth coherent gradient sensing interference fringe pictures that same test specimen adopts Fig. 4 light path to take, grating space is respectively a Δ ₁=50mm and Δ ₂=100mm, get according to (10) formula this moment:

$\frac{{\mathrm{<figure-callout\; id="1"\; label="I"\; filenames="A20061000136600081.png"\; state="\{\{state\}\}">I</figure-callout>}}_1^{*}}{I_2^{*}}=\frac{\cos \left({2\mathrm{\&pi;m}}_1\right)}{\cos \left({4\mathrm{\&pi;m}}_1\right)}---\left(11\right)$

Two width of cloth interference fringe images among Fig. 5 are carried out Flame Image Process, and the influence of subtracting background light intensity and make their striped light intensity identical is calculated according to (11) formula then and is obtained Δ ₁The fringe order of any arbitrarily in the bar graph that=50mm light path is taken.For the result with direct employing Flame Image Process extraction stripe centerline compares, Fig. 6 has shown the error condition that adopts grating space method front and back.Can see by Fig. 6, compare the grating space method with direct method and obviously reduced the error that the striped extraction brings by Flame Image Process extraction stripe centerline, improved the computational accuracy of coherent gradient sensing method, and the grating space method is obvious for the harmonic series stripe effect.

Claims (1)

1, a kind of method of extracting order value of coherent gradient sensing interference fringe is characterized in that this method may further comprise the steps:

(1) beam of laser is expanded bundle, obtain diverging light, planoconvex lens becomes directional light again, incides the test specimen surface;

(2) parallel beam with above-mentioned test specimen outgoing is divided into two-way light, and first via light is Δ through spacing ₁First grating and second grating, produce the coherent gradient sensing interference fringe, the second road light is Δ through spacing ₂The 3rd grating and the 4th grating, produce the coherent gradient sensing interference fringe;

(3), and take the interference fringe field to above-mentioned two interference fringe field imagings;

(4) before test specimen does not load, from the digital picture of above-mentioned two light paths shooting test specimen, the background light intensity that obtains interference fringe picture is respectively a respectively ₁, a ₂

(5) to the test specimen imposed load, take the coherent gradient sensing interference fringe picture of loading specimen respectively from above-mentioned two light paths, the light distribution of two interference fringe fields is respectively: I ₁, I ₂

(6) from two width of cloth coherent gradient sensing interference fringe pictures of the loading specimen of above-mentioned steps (5), deduct the respective background light intensity of above-mentioned steps (4), and it is carried out histogram transformation, make the amplitude of two width of cloth image striped light intensity identical, the interference fringe picture light distribution of two light paths that conversion obtains is I ₁ ^*And I ₂ ^*

(7), calculate the fringe order m of first width of cloth interference fringe picture according to above-mentioned grating space and light intensity ₁For:

$\frac{I_1^{*}}{I_2^{*}}=\frac{\cos \left(2\mathrm{\&pi;}{m}_1\right)}{\cos (2\mathrm{\&pi;}{m}_1{\mathrm{\&Delta;}}_2/{\mathrm{\&Delta;}}_1)}.$

The device of the extraction order value of coherent gradient sensing interference fringe that the present invention proposes comprises:

(1) is used for lasing laser instrument, is used for laser is expanded the beam expanding lens of bundle, make diverging light become the convex lens of directional light;

(2) be used for the parallel beam of test specimen outgoing is divided into the half-reflecting half mirror of two-way light, be used to produce first grating and second grating of first via coherent gradient sensing interference fringe, the spacing of first grating and second grating is a Δ ₁, being used to produce the 3rd grating and the 4th grating of the second road coherent gradient sensing interference fringe, the spacing of the 3rd grating and the 4th grating is a Δ ₂

(3) be used for first group of convex lens of above-mentioned two interference fringe field imagings and diaphragm and second group of convex lens and diaphragm, and be used to take first video camera, second video camera of interference fringe field and be used for Flame Image Process and computing machine that interference fringe progression extracts;

Above-mentioned laser instrument, beam expanding lens, convex lens, test specimen, half-reflecting half mirror, first grating, second grating, first group of convex lens and diaphragm and first video camera are on the primary optic axis successively; Above-mentioned the 3rd grating, the 4th grating, second group of convex lens and diaphragm and second video camera are on second optical axis successively, and the primary optic axis and second optical axis intersect vertically in the half-reflecting half mirror place, and computing machine is connected with second video camera with first video camera respectively.

Images