CN113091959A - Non-contact stress measurement method and device, electronic equipment and storage medium - Google Patents
Non-contact stress measurement method and device, electronic equipment and storage medium Download PDFInfo
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Abstract
The disclosure provides a non-contact stress measurement method and device based on image meshless, electronic equipment and a storage medium. The image-based non-grid non-contact stress measurement method comprises the following steps: acquiring speckle images I at n moments0、……、In‑1(ii) a Reading reference image I from acquired speckle image0And a time t to be measurediCorresponding image I to be measuredi(ii) a For reference image I0And an image I to be measurediPre-filtering to obtain image with reduced noise
Arranging field nodes, dispersing the current model, and constructing an overall stiffness matrix; regularizing the overall stiffness matrix and solving a discrete system equation to obtain a moment t to be measurediDistribution of the stress field. The stress field distribution is directly obtained from the speckle image, and the operation is simple; wide applicability, capability of processing complex stress and nonlinearityGeometric/physical model case; the method adopts pre-filtering and regularization processing, and has higher robustness and higher stress precision.
Description
Technical Field
The present disclosure relates to the field of stress measurement technologies, and in particular, to a non-contact stress measurement method and apparatus based on image meshless, an electronic device, and a storage medium.
Background
Stress measurement of equipment or workpieces is a vital requirement in the fields of machine manufacturing, aerospace, scientific research and the like. The stress measurement is carried out on the prepared workpiece, so that the quality of the workpiece can be evaluated, and the manufacturing process can be improved; the damage diagnosis can be realized by measuring the stress of the equipment in the service process, and the safety of important structures such as a pressure vessel, a compressor blade and the like is ensured.
Currently, the commonly used stress measurement methods can be mainly divided into contact stress measurement and non-contact stress measurement. Although the contact stress measurement methods, such as the blind hole method and the ring core method, are mature, the contact stress measurement methods can damage a to-be-tested piece, are difficult to realize full-field measurement, and limit the measurement environment; the non-contact stress measurement method can make up for the limitations, obtain full-field stress and is suitable for severe measurement environments such as high temperature and high pressure.
Stress measurement combining a digital image correlation method and a finite element method is one of the stress measurement methods widely used in the contactless method. The method is characterized in that a to-be-tested part is discretized into a finite element model, displacement field distribution is obtained through a digital image correlation method, and then finite element calculation is introduced as an essential boundary condition, so that non-contact measurement of stress is realized.
The method has high precision, can flexibly process the condition that the material property of the test piece is complex, such as a super-elastic material, an anisotropic material, a composite material and the like, but has complex measurement process and complicated pretreatment steps, and the measurement precision depends on the grid quality, thereby limiting the further popularization and application of the method.
Disclosure of Invention
Technical problem to be solved
In view of the above problems, the present disclosure provides a non-contact stress measurement method and apparatus based on image meshless, an electronic device and a storage medium.
(II) technical scheme
According to one aspect of the present disclosure, there is provided an image mesh-free non-contact stress measurement method, including:
step S1: acquiring speckle images I at n moments0、……、In-1In which I0Is a reference time t0Corresponding reference picture, In-1At a time tn-1Corresponding speckle images, wherein n is a natural number;
step S2: reading reference image I from acquired speckle image0And a time t to be measurediCorresponding image I to be measurediI is a natural number less than n;
step S3: for reference image I0And an image I to be measurediPre-filtering to obtain image with reduced noise
Step S4: arranging field nodes, dispersing the current model, and constructing an overall stiffness matrix;
step S5: regularizing the overall stiffness matrix and solving a discrete system equation to obtain a moment t to be measurediDistribution of the stress field.
According to the embodiment of the present disclosure, the pair of reference images I described in step S30And an image I to be measurediPre-filtering to obtain image with reduced noise
Adopting any one of median filtering, mean filtering, Gaussian filtering and moving average filtering to the reference image I0And an image I to be measurediPre-filtering is performed.
According to the embodiment of the disclosure, gaussian filtering is adopted in step S3 for the reference image I0And an image I to be measurediWhen pre-filtering is carried out, the Gaussian filtering is realized by adopting the following formula:
wherein, K is a Gaussian filter and represents convolution operation.
According to the embodiment of the present disclosure, the arranging field nodes, discretizing the current model, and constructing the overall stiffness matrix in step S4 includes:
the current model satisfies the virtual work principle:
∫Vσ：δεdV-∫Vq0：δudV-∫Af0：δudA＝0 (2)
where σ is the stress tensor, ∈ is the imaginary strain tensor which is work-conjugated with it, q0Is the volume force, V is the corresponding volume, f0Is the surface force, A is the corresponding surface, u is the virtual displacement; formula (2) can be rewritten as follows:
KU＝T (3)
wherein K is the overall rigidity matrix, and the rigidity matrix K of each nodeij＝∫ΩBTThe DBd Ω is assembled and the strain matrix B gives the relationship of strain and displacement:
ε＝BU (4)
the elastic matrix D gives the relationship of stress and strain:
σ＝Dε (5)
the shape function matrix phi gives the relationship between the displacement of any point and the displacement of each node in the support domain:
when the shape function is MQ radial basis functions, each element in the moment matrix R can be given by:
R＝(r2+(αd)2)β (7)
wherein r | | | x-x0And | | c, c is the radius of the tight branch domain, alpha and beta are basis function parameters, and d is the distance between field nodes.
The displacement of each node on the upper surface is recorded as UAThen it should also satisfy
f is the points on the upper surface
G is the gray value of each point on the upper surface in the image
The gray value of (1).
According to the embodiment of the disclosure, in step S5, the regularization processing is performed on the overall stiffness matrix and the discrete system equation is solved to obtain the time t to be measurediComprises:
the regularization processing of the total stiffness matrix adopts a truncated total least square method, only the degree of freedom of each node on the upper surface is regularized, and the formula (3) is further rewritten as follows:
TIb＝G-1UIb (8)
wherein U isIbFor the corresponding displacement of each node degree of freedom of the upper surface, TIbCorresponding loads of the degrees of freedom of each node on the upper surface are represented, and G is a corresponding flexibility matrix;
the truncated total least squares solution for equation (8) is given by:
wherein
Is singular value decomposition of an augmented matrix
And the dimensionalities of the right singular matrix obtained by the method are respectively as follows:
k is a regularization parameter and is taken as the rank of the amplification matrix; the time t to be measured can be obtained by combining the vertical type (9) and the formulas (4) to (7)iDistribution of the stress field.
According to the embodiment of the disclosure, the regularization processing is performed on the overall stiffness matrix and the discrete system equation is solved to obtain the time t to be measurediAfter the step of distributing the stress field, further comprising: the steps S2 to S5 are repeatedly executed, and the speckle images corresponding to the respective time instants acquired in the step S1 are processed to obtain the stress field distribution at the respective time instants.
According to the embodiment of the present disclosure, after obtaining the stress field distribution at each time, the method further includes: and storing and displaying the stress field distribution at each moment.
According to another aspect of the present disclosure, there is provided an image mesh-free non-contact stress measurement apparatus, comprising:
an image acquisition unit for acquiring speckle images I at n time instants0、……、In-1In which I0Is a reference time t0Corresponding reference picture, In-1At a time tn-1Corresponding speckle images, wherein n is a natural number;
an image reading unit for reading a reference image I from the acquired speckle image0And a time t to be measurediCorresponding image I to be measurediI is a natural number less than n;
a pre-filtering unit for pre-filtering the reference image I0And an image I to be measurediPre-filtering to obtain image with reduced noise
The overall stiffness matrix construction unit is used for arranging field nodes, dispersing the current model and constructing an overall stiffness matrix;
a stress field distribution acquisition unit for executing regularization treatment on the overall stiffness matrix and solving a discrete system equation to obtain a time t to be measurediDistribution of the stress field.
According to still another aspect of the present disclosure, there is provided an electronic device including: the device comprises a memory, a processor and a computer program stored on the memory and capable of running on the processor, wherein the processor executes the computer program to realize the image mesh-free based non-contact stress measurement method.
According to yet another aspect of the present disclosure, a computer-readable storage medium is provided, on which a computer program is stored, which, when being executed by a processor, carries out the method for image mesh-less based contactless stress measurement.
(III) advantageous effects
Compared with the prior art, the non-contact stress measurement method, the non-contact stress measurement device, the non-contact stress measurement electronic equipment and the storage medium based on the image non-grid have at least one of the following beneficial effects:
1. the image non-grid-based non-contact stress measurement method, the image non-grid-based non-contact stress measurement device, the electronic equipment and the storage medium directly obtain the stress field distribution at a certain moment from the speckle image at the moment, are simple to operate and wide in applicability, and can process the conditions of complex stress and nonlinear geometric/physical models.
2. The image non-grid-based non-contact stress measurement method and device, the electronic equipment and the storage medium comprise pre-filtering and regularization processing, and have higher robustness.
3. According to the image non-grid-based non-contact stress measurement method and device, the electronic equipment and the storage medium, the global high-order continuity of the displacement field is ensured by using the high-order continuous shape function, and the obtained stress precision is high.
Drawings
The invention is further illustrated with reference to the following figures and examples.
Fig. 1 schematically illustrates a flow chart of an image gridless noncontact stress measurement method according to an embodiment of the present disclosure.
Fig. 2 schematically shows a schematic diagram of a physical model of a device under test according to an embodiment of the present disclosure.
FIG. 3 shows the top surface stress component τ of the physical model of the device under test of FIG. 2zxDistribution of theoretical values of (a).
FIG. 4A illustrates a reference time t obtained according to an embodiment of the disclosure0Corresponding reference picture I0。
FIG. 4B shows time t obtained according to an embodiment of the disclosure1Corresponding speckle image I1。
FIG. 5A illustrates a method of employing the invention in accordance with an embodiment of the disclosureCalculating the upper surface stress component tau of the physical model of the device to be tested shown in FIG. 2zxAnd (4) distribution.
FIG. 5B shows the top surface stress component τ of the physical model of the DUT shown in FIG. 2 calculated by the conventional method according to the embodiment of the disclosurezxAnd (4) distribution.
Fig. 6 schematically illustrates a schematic diagram of an image gridless noncontact stress measurement device according to an embodiment of the present disclosure.
Fig. 7 schematically shows a block diagram of an electronic device according to an embodiment of the disclosure.
Detailed Description
For the purpose of promoting a better understanding of the objects, aspects and advantages of the present disclosure, reference is made to the following detailed description taken in conjunction with the accompanying drawings.
Certain embodiments of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the disclosure are shown. Indeed, various embodiments of the disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements.
Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be understood that the description is illustrative only and is not intended to limit the scope of the present disclosure. In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the disclosure. It may be evident, however, that one or more embodiments may be practiced without these specific details. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present disclosure.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The terms "comprises," "comprising," and the like, as used herein, specify the presence of stated features, steps, operations, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, or components.
All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art unless otherwise defined. It is noted that the terms used herein should be interpreted as having a meaning that is consistent with the context of this specification and should not be interpreted in an idealized or overly formal sense.
In one exemplary embodiment of the present disclosure, an image mesh-less non-contact stress measurement method is provided. As shown in fig. 1, fig. 1 schematically shows a flow chart of an image mesh-free based non-contact stress measurement method according to an embodiment of the present disclosure, the method comprising:
step S1: acquiring speckle images I at n moments0、……、In-1In which I0Is a reference time t0Corresponding reference picture, In-1At a time tn-1Corresponding speckle images, wherein n is a natural number;
step S2: reading reference image I from acquired speckle image0And a time t to be measurediCorresponding image I to be measurediI is a natural number less than n;
step S3: for reference image I0And an image I to be measurediPre-filtering to obtain image with reduced noise
Step S4: arranging field nodes, dispersing the current model, and constructing an overall stiffness matrix;
step S5: regularizing the overall stiffness matrix and solving a discrete system equation to obtain a moment t to be measurediDistribution of the stress field.
In the embodiment of the present disclosure, acquiring speckle images I at n time instants as described in step S10、……、In-1The speckle pattern can be obtained by painting or spot-coating, and can be realized by image acquisition device such as CCD camera, CMOS camera, electronic Computed Tomography (CT) device or microscopic imaging equipmentThe collected speckle images may be two-dimensional or three-dimensional.
In the embodiment of the present disclosure, reading the reference image I from the acquired speckle image as described in step S20And a time t to be measurediCorresponding image I to be measurediA processor may be used to read from the acquired speckle images.
In the embodiment of the present disclosure, the pair of reference images I in step S30And an image I to be measurediPre-filtering to obtain image with reduced noise
Adopting any one of median filtering, mean filtering, Gaussian filtering and moving average filtering to the reference image I0And an image I to be measurediPre-filtering is performed.
In the embodiment of the present disclosure, the regularization is performed on the overall stiffness matrix and the discrete system equation is solved to obtain the time t to be measurediAfter the step of distributing the stress field, further comprising: the steps S2 to S5 are repeatedly executed, and the speckle images corresponding to the respective time instants acquired in the step S1 are processed to obtain the stress field distribution at the respective time instants.
In an embodiment of the present disclosure, after obtaining the stress field distribution at each time, the method further includes: the stress field distribution of each moment is stored and displayed, and can be transmitted to a display for displaying and stored in a computer readable storage medium, so that a user can check and analyze the result.
The image-grid-free non-contact stress measurement method provided by the present disclosure is further described in detail below with reference to a specific simulation example.
As shown in fig. 2, fig. 2 schematically shows a schematic diagram of a physical model of a device under test according to an embodiment of the present disclosure. The physical model of the device to be tested is an isotropic linear elastic material with the size of 30m multiplied by 10m, the Young modulus E is 1000Pa, and the Poisson ratio v is 0.3. The bottom surface is fixedly restrained, the side surface is hinged, and two circular domains with the radius of 3m act on the upper surfaceWith uniform surface forces f in the x-direction of equal and opposite magnitude0The center of the first circular field is 10m and 15m, and the center of the second circular field is 20m and 15 m. By the Cauchy's basic theorem, the upper surface stress component τzxShould be equal to the applied external load, the stress component is mainly calculated and compared in this embodiment. FIG. 3 shows the top surface stress component τ of the physical model of the device under test of FIG. 2zxDistribution of theoretical values of (a).
The invention realizes the surface stress component tau on the physical model of the equipment to be testedzxThe specific steps for performing the measurement are as follows:
the first step is as follows: acquiring speckle images I of the surface at 2 time points by using an image acquisition device0And I1In which I0The speckle image corresponding to the reference moment is the speckle image, and the physical model of the device to be tested is under the no-load condition, as shown in fig. 4A; i is1Is a target time t1Corresponding speckle images, the physical model of the device under test is loaded with the load as described above, fig. 4B; the image size is 1200 × 1200 pixels (pixels) with a signal-to-noise ratio of 30 dB.
The second step is that: reading the speckle image obtained by the processor and calculating the stress field distribution by using a computer program in a computer readable storage medium, wherein the computer program executes the following specific steps:
2.1 reading speckle image I0And I1Here, the image is obtained by pre-filtering using gaussian filtering
Where denotes convolution operation, K is a gaussian filter, and the mean μ is 0 and the variance S is 1.5.
2.2, arranging field nodes, dispersing a physical model of the current equipment to be tested, and constructing an overall rigidity matrix, wherein the specific method comprises the following steps:
the physical model of the equipment to be tested satisfies the virtual power principle:
∫Vσ：δεdV-∫Vq0：δudV-∫Af0：δudA＝0 (2)
where σ is the stress tensor, ∈ is the imaginary strain tensor which is work-conjugated with it, q0Is the volume force, V is the corresponding volume, f0The surface force means the corresponding surface, and u is the virtual displacement. This formula (2) can be rewritten as follows:
KU＝T (3)
wherein K is the overall rigidity matrix, and the rigidity matrix K of each nodeij＝∫ΩBTThe DBd Ω is assembled and the strain matrix B gives the relationship of strain and displacement:
ε＝BU (4)
the elastic matrix D gives the relationship of stress and strain:
σ＝Dε (5)
the shape function matrix phi gives the relationship between the displacement of any point and the displacement of each node in the support domain:
taking the shape function as MQ radial basis function as an example, each element in the moment matrix R can be given by:
R＝(r2+(αd)2)β (7)
wherein r | | | x-x0I/c, c is the radius of the tight branch region, α and β are basis function parameters, d is the field node spacing, where α is 0.1, β is 1.6, d is 1, and c is 2.3.
The displacement of each node on the upper surface is recorded as UAThen it should also satisfy
f is the points on the upper surface
G is the gray value of each point on the upper surface in the image
The gray value of (1).
2.3 add regularization to the global stiffness matrix and solve the discrete system equation: taking the truncated total least square as an example, in order to improve the calculation efficiency, only the degree of freedom of each node on the upper surface is regularized, and the formula (3) is further rewritten as follows:
TIb＝G-1UIb (8)
wherein U isIbFor the corresponding displacement of each node degree of freedom of the upper surface, TIbAnd G is a corresponding flexibility matrix.
The truncated total least squares solution for this equation is given by:
wherein
Is singular value decomposition of an augmented matrix
And the dimensionalities of the right singular matrix obtained by the method are respectively as follows:
k is a regularization parameter, typically taken as the rank of the augmented matrix. In the present embodiment, k is equal to n. The formula is combined with the formulas (4) to (7), so that the time t to be measured can be obtained1The corresponding stress field.
2.4 in the present example only one time step is involved, i.e. only the time t is obtained1Corresponding speckle image I1Only the time t has to be measured1Corresponding stress field distribution, thus finishing the calculation; if stress field distribution at multiple moments needs to be measured, the stress field distribution needs to be further measuredSteps 2.1-2.3 are repeated and all acquired images are processed to give a stress distribution at each moment.
The third step: the results are transmitted to a display and saved to a computer readable storage medium.
The stress field tau of the upper surface obtained by the measurement of the inventionzxAs shown in fig. 5A, as a comparison, the upper surface stress field τ obtained using the conventional digital image correlation method and the hexahedral cell-based finite cell methodzxAs shown in fig. 5B, the distribution of nodes involved in both calculations remains the same. The feasibility and the beneficial effect of the invention can be seen through the process and the result.
It can be seen from the above embodiments that, the image non-grid-based non-contact stress measurement method provided by the present disclosure directly obtains the stress field distribution at a certain moment from the speckle image at the moment, is simple to operate, has wide applicability, and can handle complex stress and nonlinear geometric/physical model conditions. And pre-filtering and regularization processing are adopted, so that higher robustness is achieved. By using the high-order continuous shape function, global high-order continuity of the displacement field is ensured, and the obtained stress precision is high.
Based on the image gridless noncontact stress measurement method according to the embodiment of the present disclosure shown in fig. 1 to 5B, fig. 6 schematically shows a schematic diagram of an image gridless noncontact stress measurement device 600 according to an embodiment of the present disclosure.
As shown in fig. 6, an image mesh-free non-contact stress measurement apparatus 600 provided by the embodiment of the present disclosure includes an image acquisition unit 601, an image reading unit 602, a pre-filtering processing unit 603, an overall stiffness matrix construction unit 604, and a stress field distribution acquisition unit 605, where: an image acquisition unit 601 for acquiring speckle images I at n time instants0、……、In-1In which I0Is a reference time t0Corresponding reference picture, In-1At a time tn-1Corresponding speckle images, wherein n is a natural number; an image reading unit 602 for reading a reference image I from the acquired speckle image0And a time t to be measurediCorresponding image I to be measurediI is a natural number less than n; a pre-filtering unit 603 for pre-filtering the reference image I0And an image I to be measurediPre-filtering to obtain image with reduced noise
A total stiffness matrix constructing unit 604, configured to arrange field nodes, discretize a current model, and construct a total stiffness matrix; a stress field distribution obtaining unit 605, configured to perform regularization on the overall stiffness matrix and solve a discrete system equation to obtain a time t to be measurediDistribution of the stress field.
It should be understood that the image acquisition unit 601, the image reading unit 602, the pre-filtering processing unit 603, the overall stiffness matrix construction unit 604, and the stress field distribution acquisition unit 605 may be combined and implemented in one module, or any one of them may be split into a plurality of modules. Alternatively, at least part of the functionality of one or more of these modules may be combined with at least part of the functionality of the other modules and implemented in one module.
According to an embodiment of the present disclosure, at least one of the image acquisition unit 601, the image reading unit 602, the pre-filtering processing unit 603, the overall stiffness matrix construction unit 604, and the stress field distribution acquisition unit 605 may be at least partially implemented as a hardware circuit, such as a Field Programmable Gate Array (FPGA), a Programmable Logic Array (PLA), a system on a chip, a system on a substrate, a system on a package, an Application Specific Integrated Circuit (ASIC), or may be implemented in hardware or firmware in any other reasonable manner of integrating or packaging a circuit, or in a suitable combination of three implementations of software, hardware, and firmware. Alternatively, at least one of the image acquisition unit 601, the image reading unit 602, the pre-filtering processing unit 603, the overall stiffness matrix construction unit 604, and the stress field distribution acquisition unit 605 may be at least partially implemented as a computer program module, which when executed by a computer, may perform the functions of the respective modules.
The present disclosure also provides an electronic device, as shown in fig. 7, fig. 7 schematically shows a block diagram of an electronic device 700 according to an embodiment of the present disclosure. The electronic device 700 includes a processor 710 and a memory 720. The electronic device 700 may perform an image gridless non-contact stress measurement method according to an embodiment of the present disclosure shown in fig. 1.
In particular, processor 710 may comprise, for example, a general purpose microprocessor, an instruction set processor and/or associated chipset, and/or a special purpose microprocessor (e.g., an Application Specific Integrated Circuit (ASIC)), and/or the like. The processor 710 may also include on-board memory for caching purposes. Processor 710 may be a single processing unit or a plurality of processing units for performing the different actions of the method flows according to embodiments of the present disclosure.
The memory 720 may include a computer program 721, which computer program 721 may include code/computer executable instructions that, when executed by the processor 710, cause the processor 710 to perform a method according to an embodiment of the disclosure or any variant thereof.
The computer program 721 may be configured with, for example, computer program code comprising computer program modules. For example, in an example embodiment, code in computer program 721 may include at least one program module, including, for example, module 721A, module 721B, … …. It should be noted that the division and number of modules are not fixed, and those skilled in the art may use suitable program modules or program module combinations according to actual situations, so that the processor 710 may execute the method according to the embodiment of the present disclosure or any variation thereof when the program modules are executed by the processor 710.
The present disclosure also provides a computer-readable medium, which may be embodied in the apparatus/device/system described in the above embodiments; or may exist separately and not be assembled into the device/apparatus/system. The computer readable medium carries one or more programs which, when executed, implement an image mesh-less based non-contact stress measurement method according to an embodiment of the disclosure.
According to embodiments of the present disclosure, a computer readable medium may be a computer readable signal medium or a computer readable storage medium or any combination of the two. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination of the foregoing. More specific examples of the computer readable storage medium may include, but are not limited to: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the present disclosure, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. In contrast, in the present disclosure, a computer-readable signal medium may include a propagated data signal with computer-readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated data signal may take many forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer readable signal medium may also be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device. Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to: wireless, wired, optical fiber cable, radio frequency signals, etc., or any suitable combination of the foregoing.
The present disclosure also provides a computer program comprising: computer-executable instructions that when executed are for implementing an image gridless non-contact stress measurement method in accordance with an embodiment of the present disclosure.
The present disclosure has been described in detail so far with reference to the accompanying drawings. From the above description, those skilled in the art should clearly recognize the present disclosure.
It is to be noted that, in the attached drawings or in the description, the implementation modes not shown or described are all the modes known by the ordinary skilled person in the field of technology, and are not described in detail. In addition, the above definitions of the respective elements are not limited to the specific structures, shapes or modes mentioned in the embodiments, and those skilled in the art may easily modify or replace them.
Of course, the present disclosure may also include other parts according to actual needs, and since the parts are not related to the innovation of the present disclosure, the details are not described herein.
Unless otherwise indicated, the numerical parameters set forth in the specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the present disclosure. Generally, the expression is meant to encompass variations of ± 10% in some embodiments, 5% in some embodiments, 1% in some embodiments, 0.5% in some embodiments by the specified amount.
In addition, unless steps are specifically described or must occur in sequence, the order of the steps is not limited to that listed above and may be changed or rearranged as desired by the desired design. The embodiments described above may be mixed and matched with each other or with other embodiments based on design and reliability considerations, i.e., technical features in different embodiments may be freely combined to form further embodiments.
Similarly, it should be appreciated that in the foregoing description of exemplary embodiments of the disclosure, various features of the disclosure are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various disclosed aspects. However, the disclosed method should not be interpreted as reflecting an intention that: that is, the claimed disclosure requires more features than are expressly recited in each claim. Rather, as the following claims reflect, disclosed aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this disclosure.
In addition, in the drawings or the description, technical features in the embodiments illustrated in the description can be freely combined to form a new scheme without conflict, in addition, each claim can be taken as an embodiment alone or technical features in each claim can be combined to form a new embodiment, and in the drawings, the shape or thickness of the embodiment can be expanded, and is indicated in a simplified or convenient manner. Further, elements or implementations not shown or described in the drawings are of a form known to those of ordinary skill in the art. Additionally, while exemplifications of parameters including particular values may be provided herein, it is to be understood that the parameters need not be exactly equal to the respective values, but may be approximated to the respective values within acceptable error margins or design constraints.
Unless a technical obstacle or contradiction exists, the above-described various embodiments of the present disclosure may be freely combined to form further embodiments, which are all within the scope of protection of the present disclosure.
While the present disclosure has been described in connection with the accompanying drawings, the embodiments disclosed in the drawings are intended to be illustrative of the preferred embodiments of the disclosure, and should not be construed as limiting the disclosure. The dimensional proportions in the drawings are merely schematic and are not to be understood as limiting the disclosure.
Although a few embodiments of the present general inventive concept have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the claims and their equivalents.
The above-mentioned embodiments are intended to illustrate the objects, aspects and advantages of the present disclosure in further detail, and it should be understood that the above-mentioned embodiments are only illustrative of the present disclosure and are not intended to limit the present disclosure, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present disclosure should be included in the scope of the present disclosure.
Claims (10)
1. A non-contact stress measurement method based on image meshless is characterized by comprising the following steps:
step S1: acquiring speckle images I at n moments0、……、In-1In which I0Is a reference time t0Corresponding reference picture, In-1At a time tn-1Corresponding speckle images, wherein n is a natural number;
step S2: reading reference image I from acquired speckle image0And a time t to be measurediCorresponding image I to be measurediI is a natural number less than n;
step S3: for reference image I0And an image I to be measurediPre-filtering to obtain image with reduced noise
Step S4: arranging field nodes, dispersing the current model, and constructing an overall stiffness matrix;
step S5: regularizing the overall stiffness matrix and solving a discrete system equation to obtain a moment t to be measurediDistribution of the stress field.
2. The image gridless noncontact stress-measuring method of claim 1, wherein said pair of reference images I in step S30And an image I to be measurediPre-filtering to obtain image with reduced noise
Adopting any one of median filtering, mean filtering, Gaussian filtering and moving average filtering to the reference image I0And an image I to be measurediPre-filtering is performed.
3. The image gridless noncontact stress measurement method of claim 2, wherein said step S3 is implemented by using gaussian filtering for said reference image I0And an image I to be measurediWhen pre-filtering is carried out, the Gaussian filtering is realized by adopting the following formula:
wherein, K is a Gaussian filter and represents convolution operation.
4. The image mesh-free non-contact stress measurement method according to claim 3, wherein the step S4 of arranging the field nodes, discretizing the current model, and constructing the overall stiffness matrix comprises:
the current model satisfies the virtual work principle:
∫Vσ：δεdV-∫Vq0：δudV-∫Af0：δudA＝0 (2)
where σ is the stress tensor, ∈ is the imaginary strain tensor which is work-conjugated with it, q0Is the volume force, V is the corresponding volume, f0Is the surface force, A is the corresponding surface, u is the virtual displacement; formula (2) can be rewritten as follows:
KU＝T (3)
wherein K is the overall rigidity matrix, and the rigidity matrix K of each nodeij＝∫ΩBTThe DBd Ω is assembled and the strain matrix B gives the relationship of strain and displacement:
ε＝BU (4)
the elastic matrix D gives the relationship of stress and strain:
σ＝Dε (5)
the shape function matrix phi gives the relationship between the displacement of any point and the displacement of each node in the support domain:
when the shape function is MQ radial basis functions, each element in the moment matrix R can be given by:
R＝(r2+(αd)2)β (7)
wherein r | | | x-x0I/c, c is the radius of the tight branch domain, alpha and beta are basis function parameters, and d is the distance between field nodes;
the displacement of each node on the upper surface is recorded as UAThen it should also satisfy
f is the points on the upper surface
G is the gray value of each point on the upper surface in the image
The gray value of (1).
5. The image meshless-based non-contact stress measurement method according to claim 4, wherein the regularization processing is performed on the overall stiffness matrix and the discrete system equation is solved in step S5 to obtain the time t to be measurediComprises:
the regularization processing of the total stiffness matrix adopts a truncated total least square method, only the degree of freedom of each node on the upper surface is regularized, and the formula (3) is further rewritten as follows:
TIb＝G-1UIb (8)
wherein U isIbFor the corresponding displacement of each node degree of freedom of the upper surface, TIbCorresponding loads of the degrees of freedom of each node on the upper surface are represented, and G is a corresponding flexibility matrix;
the truncated total least squares solution for equation (8) is given by:
wherein
Is singular value decomposition of an augmented matrix
And the dimensionalities of the right singular matrix obtained by the method are respectively as follows:
k is a regularization parameter and is taken as the rank of the amplification matrix; the time t to be measured can be obtained by combining the vertical type (9) and the formulas (4) to (7)iDistribution of the stress field.
6. The image gridless non-contact stress measurement method according to claim 5, wherein the regularization is performed on the overall stiffness matrix and a discrete system equation is solved to obtain a time t to be measurediAfter the step of distributing the stress field, further comprising:
the steps S2 to S5 are repeatedly executed, and the speckle images corresponding to the respective time instants acquired in the step S1 are processed to obtain the stress field distribution at the respective time instants.
7. The image gridless non-contact stress measurement method according to claim 6, wherein after obtaining the stress field distribution at each time, the method further comprises:
and storing and displaying the stress field distribution at each moment.
8. An image gridless noncontact stress measurement device, comprising:
an image acquisition unit for acquiring speckle images I at n time instants0、……、In-1In which I0Is a reference time t0Corresponding reference picture, In-1At a time tn-1Corresponding speckle images, wherein n is a natural number;
an image reading unit for reading a reference image I from the acquired speckle image0And a time t to be measurediCorresponding image I to be measurediI is a natural number less than n;
a pre-filtering unit for pre-filtering the reference image I0And an image I to be measurediPre-filtering to obtain image with reduced noise
The overall stiffness matrix construction unit is used for arranging field nodes, dispersing the current model and constructing an overall stiffness matrix;
a stress field distribution acquisition unit for executing regularization treatment on the overall stiffness matrix and solving a discrete system equation to obtain a time t to be measurediDistribution of the stress field.
9. An electronic device, comprising: memory, processor and computer program stored on the memory and executable on the processor, characterized in that the processor, when executing the computer program, implements the image mesh-less based contactless stress measurement method according to any of claims 1 to 7.
10. A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out the image mesh-less based contactless stress-measuring method of any one of claims 1 to 7.
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