(19)
(11)EP 3 575 785 A1

(12)EUROPEAN PATENT APPLICATION

(43)Date of publication:
04.12.2019 Bulletin 2019/49

(21)Application number: 18175460.7

(22)Date of filing:  01.06.2018
(51)Int. Cl.: 
G01N 29/04  (2006.01)
G01N 29/44  (2006.01)
(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR
Designated Extension States:
BA ME
Designated Validation States:
KH MA MD TN

(71)Applicant: Promocion y Desarrollo de Sistemas Automaticos S.L.
20500 Arrasate (ES)

(72)Inventor:
  • ITURROSPE IREGUI, Aitzol
    20540 ESKORIATZA (ES)

(74)Representative: Igartua, Ismael et al
Galbaian S. Coop. Garaia Parke Teknologikoa Goiru Kalea 1
20500 Arrasate-Mondragón
20500 Arrasate-Mondragón (ES)

  


(54)METHOD FOR NON-DESTRUCTIVE INSPECTION OF PARTS


(57) Method for non-destructive inspection of parts for obtaining the properties and characteristics of the material of a part, comprising a step of creating a mathematical model describing the dynamic behavior of a part to be inspected, a step of exciting the part, and a step of measuring the vibratory response of the part. The method for inspection further comprises a step of optimizing surrounding conditions, a step of selecting modal shapes and a step of selecting at least one excitation point with the excitation orientation and at least one measurement point with the measurement orientation which are performed in that order after the step of creating the mathematical model.




Description

TECHNICAL FIELD



[0001] The present invention relates to methods and devices for non-destructive inspection of parts.

PRIOR ART



[0002] Methods and devices for non-destructive inspection of parts are known. Non-destructive inspection of parts can be useful, for example, to perform periodic maintenance of parts already installed in a machine, or to validate parts obtained from a manufacturing process.

[0003] US5886263A describes a method and a device for non-destructive inspection based on ultrasound. The method comprises a first step in which a finite element model of a part is created based on its geometry and the properties of its material. Next, the method predicts resonant frequencies based on said finite element model. The method subsequently adjusts the finite element model based on empirical data, thereby obtaining a validated finite element model. The method then experimentally measures the resonant frequencies of a part once it has been manufactured, and compares the experimental resonant frequencies with those obtained by means of analyzing the finite element model, storing the comparative data in a memory. The method performs the preceding inspection at maintenance intervals, comparing the data obtained in each inspection with the resonant frequencies of a well-made part, subsequently indicating if it is a well-made or poorly-made part based on the deviations between both.

DISCLOSURE OF THE INVENTION



[0004] The object of the invention is to provide a method for non-destructive inspection of parts, as defined in the claims.

[0005] The method for non-destructive inspection of the invention allows obtaining the properties and characteristics of the material of a part in the entire geometry thereof, i.e., both on the surface of the part and on the inside thereof.

[0006] The method comprises a first step of creating a mathematical model describing the dynamic behavior of a part to be inspected taking into account the geometry of the part to be inspected and the properties of the material at the different points of the part to be inspected represented by means of a set of parameters.

[0007] The method for non-destructive inspection further comprises a step of exciting the part to be inspected at at least one excitation point of the part to be inspected and with an excitation orientation, and a step of measuring the vibratory response of the part to be inspected at at least one measurement point and with a measurement orientation.

[0008] The method for non-destructive inspection of the invention is characterized in that it further comprises a step of optimizing surrounding conditions which is performed after the step of creating the mathematical model.

[0009] In the step of optimizing surrounding conditions, there are performed in an iterative manner the sub-steps of selecting surrounding conditions, then the sub-step of obtaining modal shapes and characteristic values associated with said modal shapes for the surrounding conditions previously selected in the preceding sub-step, and a last sub-step of calculating the sensitivity of the characteristic values obtained in the preceding sub-step of the same iteration to the properties and characteristics of the material of the part, for the surrounding conditions selected in the sub-step of selecting surrounding conditions of the same iteration.

[0010] The method for non-destructive inspection of the invention further comprises a step of selecting modal shapes which is performed after the step of optimizing surrounding conditions, in which the combinations of surrounding conditions and modal shapes for which the sensitivity of the characteristic values to the properties and characteristics of the material of the part is maximum are selected.

[0011] The method for non-destructive inspection of the invention comprises a step of selecting at least one excitation point with the excitation orientation and at least one measurement point with the measurement orientation depending on the modal shapes selected in the step of selecting modal shapes, the step of exciting the part then being started.

[0012] The method for non-destructive inspection of the invention allows determining the properties and characteristics of the material both on its surface and at any point of its internal geometry by means of using a mathematical model. In a preferred embodiment of the method for inspection of the invention, the mathematical method is a linear mathematical method.

[0013] The method allows precisely determining the presence or absence of a fault in any region of the geometry of the part, and characterizing the material in the region in which the fault has occurred, identifying the properties and characteristics of the material in said region. The method allows graphically representing the properties and characteristics of the material in three dimensions, preferably by means of tomographies.

[0014] The method for non-destructive inspection of the invention allows obtaining the properties and characteristics of the material of the part in the entire geometry thereof in a shorter time than the methods for non-destructive inspection known in the prior art because, in the method, surrounding conditions are selected, a set of modal shapes is selected based on the mathematical model and on the previously selected surrounding conditions, and the excitation point, the excitation orientation, the measurement point, and the measurement orientation in which the non-destructive inspection of the part will be carried out are also selected.

[0015] These and other advantages and features of the invention will become evident in view of the drawings and detailed description of the invention.

DESCRIPTION OF THE DRAWINGS



[0016] Figure 1 shows a flow chart of the steps of an embodiment of the method for non-destructive inspection of the invention.

DETAILED DISCLOSURE OF THE INVENTION



[0017] Figure 1 shows in a flow chart the steps of the method for non-destructive inspection of parts for obtaining the properties of the material of a part in the entire geometry thereof of the invention.

[0018] The method for non-destructive inspection of parts of the invention comprises a first step of creating a mathematical model describing the dynamic behavior of a part to be inspected taking into account the geometry of the part to be inspected and the properties of the material at the different points of the part to be inspected represented by means of a set of parameters, as shown in blocks 1 and 2 of Figure 1.

[0019] The method for non-destructive inspection further comprises a step of exciting the part to be inspected at at least one excitation point of the part to be inspected and with an excitation orientation, as shown in block 8 of Figure 1. The method for non-destructive inspection then comprises a step of measuring the vibratory response of the part to be inspected at at least one measurement point and with a measurement orientation, as shown in block 9 of Figure 1.

[0020] The method for non-destructive inspection of the invention is characterized in that it further comprises a step of optimizing surrounding conditions which is performed after the step of creating the mathematical model, as shown in block 5 of Figure 1.

[0021] In the step of optimizing surrounding conditions, there are performed in an iterative manner the sub-steps of selecting surrounding conditions, then the sub-step of obtaining modal shapes and characteristic values associated with said modal shapes for the surrounding conditions previously selected in the preceding sub-step of the same iteration, and then a last sub-step of calculating the sensitivity of the characteristic values obtained in the preceding sub-step of the same iteration to the properties and characteristics of the material in the entire geometry of the part or in a portion of the part, for the surrounding conditions selected in the sub-step of selecting surrounding conditions of the same iteration, as shown in blocks 51, 52, and 53 of Figure 1.

[0022] In a preferred embodiment of the method for inspection of the invention, calculating the sensitivity of the characteristic values associated with the modal shapes will result in a vector of sensitivity for each characteristic value, in which each element of the vector is the partial derivative of the characteristic value associated with the modal shape with respect to a local property of the material or to a local characteristic of the material of the part, such as the internal stresses of that material. A local property of the material of the part is considered to be the property of the material at a specific point of the part. Similarly, a local characteristic of the material of the part is considered to be the characteristic of the material at a specific point of the part.

[0023] The method of the invention allows focusing the inspection on one or more specific regions or volumes of interest of the geometry of the part. Depending on the regions or volumes to be considered in the inspection, in each iteration, in the sub-step of selecting surrounding conditions, the method selects the surrounding conditions most suitable for the identification of the properties and characteristics of the material of the part in said regions. Once the surrounding conditions are selected, the modal shapes, their natural frequencies, and the characteristic values associated with said modal shapes for the surrounding conditions selected in the preceding sub-step of said iteration will be obtained from the mathematical model. Finally, for the selected surrounding conditions and for each of the modal shapes obtained in the preceding sub-steps of said iteration, the sensitivity of the obtained characteristic values to the properties and characteristics of the material in the entire part or in the regions or volumes to be considered in the inspection, for the previously selected surrounding conditions, will be calculated.

[0024] In the first performance of the sub-steps of the step of optimizing surrounding conditions of the method of the invention, the method will select first surrounding conditions, subsequently obtaining the modal shapes associated with the first surrounding conditions, and finally calculating the sensitivity of the characteristic values associated with said modal shapes to the properties and characteristics of the material. In a second performance of the sub-steps of the step of optimizing surrounding conditions of the method, the method will select second surrounding conditions, subsequently obtaining the modal shapes associated with the second surrounding conditions, and finally calculating the sensitivity of the characteristic values associated with the modal shapes associated with the second surrounding conditions to the properties and characteristics of the material. The iterative performance of the preceding sub-steps will be carried out as many times as necessary in order to obtain optimum surrounding conditions and modal shapes for the inspection.

[0025] The method for non-destructive inspection of the invention further comprises a step of selecting modal shapes which is performed after the step of optimizing surrounding conditions, as shown in block 6 of Figure 1. In the step of selecting modal shapes, the combinations of surrounding conditions and modal shapes for which the sensitivity of the characteristic values to the properties and characteristics of the material of the part is maximum are selected, the characteristic values for which the sensitivity is calculated corresponding to each combination of surrounding conditions and modal shapes.

[0026] In a preferred embodiment of the method for inspection of the invention, the method for inspection minimizes the number of modes necessary to reach the required spatial resolution, preferably by means of a principal component analysis. A mode is considered to be the combination of a modal shape with its associated characteristic value. Selection is performed among all the combinations of surrounding conditions and modal shapes obtained in the step of optimizing surrounding conditions, as shown in block 6 of Figure 1.

[0027] The method for non-destructive inspection of the invention comprises a step of selecting at least one excitation point with the excitation orientation and at least one measurement point with the measurement orientation, as shown in block 7 of Figure 1, the step of exciting the part then being started. The selection of at least one excitation point with the excitation orientation and at least one measurement point with the measurement orientation is performed depending on the modal shapes selected in the step of selecting modal shapes.

[0028] In a preferred embodiment, the CAD of the part to be inspected will be used to provide the mathematical model with information concerning the geometry of the part to be inspected.

[0029] In a preferred embodiment of the method for non-destructive inspection of the invention, the mathematical model will be a finite element model (FEM). The mathematical model will describe, by means of a plurality of mathematical equations, the dynamic behavior of the part to be inspected. In said equations, the mathematical model will use a plurality of parameter value matrices, such that each parameter value matrix will represent one of the properties of the material in the geometry of the part. The properties of the material represented by means of each of said parameters comprise, among others, the mass, stiffness, and damping at the different points of the part. The characteristics of the material, though not obtained directly from the parameters of the mathematical model, are indeed derived from said parameters. The characteristics of the material comprise the internal stresses of the material in different directions at the different points of the part.

[0030] The internal stresses of the material of the part to be inspected can be determined by means of the method for inspection of the invention, entailing an advantage with respect to methods for non-destructive inspection known in the prior art.

[0031] In a preferred embodiment, the excitation will be a frequency sweep which mechanically excites the part in the acoustic range and/or in the ultrasound range, although in other embodiments, the excitation could be an impact or a white noise. The frequency sweep will comprise the natural frequencies associated with the modal shapes selected in the step of selecting modal shapes of the method of the invention. In another embodiment of the method for inspection of the invention, the excitation could be any type of excitation with a sufficient bandwidth comprising the natural frequencies of interest.

[0032] In block 10 of Figure 1, the method for non-destructive inspection of the invention comprises, after the step of measuring, a step of resolving the parameters of the mathematical model in which the properties and characteristics of the material of the part in the entire geometry thereof are obtained depending on the differences between the vibratory response of the part obtained in the step of measuring and the response provided by the mathematical model with the same excitation points and excitation orientations, and the same measurement points and measurement orientations, and with the same surrounding conditions. The values of the parameter value matrices of the mathematical model are obtained in the step of resolving the parameters of the mathematical model, therefore determining the properties of the material in the geometry of the part. The characteristics of the material in the geometry of the part are derived from the parameters of the mathematical model.

[0033] In a preferred embodiment of the method for inspection of the invention, a system of linear equations linking the variation of the characteristic values to the change in the local properties or characteristics of the part is obtained for a linear model. In said system of equations, the unknown parameters are the values of the local properties and characteristics of the material in the geometry of the part.

[0034] In another embodiment of the method for inspection, the system of equations is indeterminate. In this embodiment, the unknown parameters of the system of equations are optimized using constrained optimization methods, preferably compressive testing methods.

[0035] In a preferred embodiment of the method of the invention, the parameters of the mathematical model represent the mass, stiffness, damping, and/or internal stresses of the material of the part.

[0036] In a preferred embodiment of the method for non-destructive inspection of the invention, the surrounding conditions comprise holding the part in a portion of its geometry.

[0037] In another embodiment of the method for non-destructive inspection of the invention, the surrounding conditions comprise the application of a force on one or more points of the geometry of the part.

[0038] In a preferred embodiment, the method for non-destructive inspection of the invention comprises a step of adjusting the mathematical model based on empirical data obtained from measurements performed on valid parts, obtaining a validated mathematical model, which is performed after the step of creating the mathematical model, as shown in blocks 3 and 4 of Figure 1.

[0039] A valid part is considered to be that part the material of which has the expected properties and characteristics, i.e., those corresponding to a part manufactured without errors. However, a non-valid, erroneous, or faulty part is considered to be that part the material of which has properties or characteristics which are unexpected, in either the entire volume of the part or in a specific region of the part, or on the surface or the inside thereof.

[0040] When the inspection is not performed as validation of the part following its manufacture, but rather as part of its maintenance, a valid part is considered to be that part the material of which does not have modified properties and characteristics due to use. However, a non-valid, erroneous, or faulty part is considered to be that part the material of which does have modified properties and characteristics due to use, either in the entire volume of the part or in a specific region of the part, or on the surface or the inside thereof.

[0041] Before performing measurements on valid parts of block 3 of Figure 1, it must be verified that said parts have both the geometry and the precise properties and characteristics of the material corresponding to a valid part. Subsequently, in block 4 of Figure 1, the measurements obtained in block 3 of Figure 1 are compared with the estimations provided by the mathematical model, reconciling both and thereby obtaining a validated mathematical model. The obtained measurements and the estimations provided by the mathematical model to be compared must be done with the same surrounding conditions, for an excitation caused at the same excitation point and in the same direction, and measured at the same measurement point and with the same direction.

[0042] In a preferred embodiment of the method for inspection of the invention, the properties and characteristics of the material of the inspected part are graphically represented by means of tomography. By means of tomography, the method of the invention identifies, locates, and characterizes the fault or faults in the inspected part, indicating where they are and their magnitude, based on deviations in the measured frequency response with respect to the response provided by the validated mathematical model.

[0043] In a preferred embodiment of the method of the invention, a tool which allows holding the part in a portion of its geometry, and/or the application of a force on one or more points of the geometry of the part, will be used. The tool will make it easier exciting the part at at least one excitation point with an excitation orientation and the measurement of the vibratory response of the part at at least one measurement point and with a measurement orientation. The tool can be an adaptive and automated tool. In a preferred embodiment, automation would be performed by means of using orientable robot arms.

[0044] In a preferred embodiment of the method for non-destructive inspection of the invention, the mathematical model only resolves the value of one or more of the parameters of the validated mathematical model, considering the value of the rest of the parameters of the validated mathematical model as known. At times, it is of interest to only obtain the value of one or more of the properties or characteristics of the material of the part, i.e., it is of interest to only obtain the value of one or more of the parameters of the mathematical model, given that the process of manufacturing the part produces parts in which certain properties and characteristics of the material of the part are correct, and the possible faults are concentrated on certain other properties and/or characteristics of the part. Other times, it is the use of the part which causes certain properties and/or characteristics of the material of the part to not be altered, only some of the properties and/or characteristics of that part being altered. Knowing the value of some of the parameters of the validated mathematical model allows shortening the time of performing the method, given that only the value of part of the parameters of the validated mathematical model must be obtained.

[0045] In a preferred embodiment of the method for non-destructive inspection of the invention, the surrounding conditions are dynamic conditions. In the presence of an excitation caused at one and the same excitation point and excitation direction, one and the same measurement point and measurement direction, the vibratory response of the part changes under dynamic surrounding conditions. The use of different surrounding conditions allows performing several measurements with an excitation caused at one and the same excitation point and excitation direction, one and the same measurement point and measurement direction, providing the method with more information when resolving the value of the parameter value matrices in the system of equations of the mathematical model, which allows a shorter time for performing the method and a higher precision of the values obtained for the parameters of the mathematical model.

[0046] In a preferred embodiment of the method of the invention, the mathematical model is linear. In the preferred embodiment of the method of the invention, the mathematical model is a finite element model.

[0047] In a preferred embodiment of the method of the invention, the mathematical model describes, by means of a plurality of mathematical equations, the dynamic behavior of the part to be inspected, the mathematical model using a plurality of parameter value matrices, and each parameter value matrix representing one of the properties of the material in the geometry of the part.

[0048] In a preferred embodiment of the method of the invention, the excitation used in the step of exciting the part is a frequency sweep which mechanically excites the part in the acoustic range and/or in the ultrasound range.

[0049] The method of the invention can be implemented with a device for non-destructive inspection comprising information processing means, information storage media, and information input and output interfaces. The mathematical model is created and the steps of the method are performed by the processing means. To that end, the processing means use the information stored in the information storage media, or the information provided through the input interfaces. The information provided by the method for inspection is stored in the storage means, and is graphically represented by means of the output interfaces.

[0050] The measurements of the vibratory response of the part obtained in the step of measuring can be sent directly to the device for non-destructive inspection in the case in which the frequency signal receiver is directly connected to said device, or through a communications network, which allows the inspection of the part to be performed in a location remote from the location in which the processing of said measurements is performed.

[0051] Similarly, the information required for graphically representing the properties and characteristics of the material of the inspected part can be sent directly to an output interface, or to an interface remotely located, through a data communication network.

[0052] The graphical representation can be done by means of tomography or by means of another type of representation known in the prior art which allows locating, quantifying, and characterizing, in the geometry of the part, the fault or faults existing therein.


Claims

1. Method for non-destructive inspection of parts for obtaining the properties and characteristics of the material of a part, comprising the following steps:

- step of creating a mathematical model describing the dynamic behavior of a part to be inspected taking into account the geometry of the part to be inspected and the properties of the material at the different points of the part to be inspected represented by means of a set of parameters,

- step of exciting the part to be inspected at at least one excitation point of the part to be inspected and with an excitation orientation, and

- step of measuring the vibratory response of the part to be inspected at at least one measurement point and with a measurement orientation,

characterised in that the method for inspection further comprises:

- a step of optimizing surrounding conditions which is performed after the step of creating the mathematical model, in which the following sub-steps are performed in an iterative manner:

∘ sub-step of selecting surrounding conditions,

∘ sub-step of obtaining the modal shapes and associated characteristic values for the surrounding conditions selected in the preceding sub-step, and

∘ sub-step of calculating the sensitivity of the characteristic values obtained in the preceding sub-step of the same iteration to the properties and characteristics of the material of the part, for the surrounding conditions selected in the sub-step of selecting surrounding conditions of the same iteration,

- a step of selecting modal shapes which is performed after the step of optimizing surrounding conditions in which the combinations of surrounding conditions and modal shapes for which the sensitivity of the characteristic values to the properties and characteristics of the material of the part is maximum are selected, and then

- a step of selecting at least one excitation point with the excitation orientation and at least one measurement point with the measurement orientation depending on the modal shapes selected in the preceding step, the step of exciting the part then being started.


 
2. Method for non-destructive inspection of parts according to claim 1, comprising, after the step of measuring, a step of resolving the parameters of the mathematical model in which the properties and characteristics of the material of the part in the entire geometry thereof are obtained depending on the differences between the vibratory response of the part obtained in the step of measuring and the response provided by the validated mathematical model with the same excitation points and excitation orientations, the same measurement points and measurement orientations, and with the same surrounding conditions.
 
3. Method for non-destructive inspection according to claim 2, wherein the parameters of the mathematical model represent the mass, stiffness, damping, and/or internal stresses of the material of the part.
 
4. Method for non-destructive inspection according to any of the preceding claims, wherein the surrounding conditions comprise holding the part in a portion of its geometry.
 
5. Method for non-destructive inspection according to any of the preceding claims, wherein the surrounding conditions comprise the application of a force on one or more points of the geometry of the part.
 
6. Method for non-destructive inspection according to any of claims 2 to 5, wherein the mathematical model only resolves the value of one or more of the parameters of the validated mathematical model, considering the value of the rest of the parameters of the validated mathematical model known.
 
7. Method for non-destructive inspection according to any of the preceding claims, comprising, after the step of creating the mathematical model and before the step of optimizing surrounding conditions, a step of adjusting the mathematical model based on empirical data obtained from measurements performed on valid parts, obtaining a validated mathematical model.
 
8. Method for non-destructive inspection according to any of the preceding claims, wherein the surrounding conditions are dynamic conditions.
 
9. Method for non-destructive inspection according to any of the preceding claims, wherein the mathematical model is linear.
 
10. Method for non-destructive inspection according to claim 9, wherein the mathematical model is a finite element model.
 
11. Method for non-destructive inspection according to claim 9 or 10, wherein the mathematical model describes, by means of a plurality of mathematical equations, the dynamic behavior of the part to be inspected, the mathematical model using a plurality of parameter value matrices, and each parameter value matrix representing one of the properties of the material in the geometry of the part.
 
12. Method for non-destructive inspection according to any of the preceding claims, wherein the excitation used in the step of exciting the part is a frequency sweep which mechanically excites the part in the acoustic range and/or in the ultrasound range.
 




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REFERENCES CITED IN THE DESCRIPTION



This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description