Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
  • G01N3/02—Details
  • G01N3/06—Special adaptations of indicating or recording means
  • G01N3/068—Special adaptations of indicating or recording means with optical indicating or recording means
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
  • G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
  • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
  • G01N21/65—Raman scattering
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
  • G01N2203/02—Details not specific for a particular testing method
  • G01N2203/06—Indicating or recording means; Sensing means
  • G01N2203/0641—Indicating or recording means; Sensing means using optical, X-ray, ultraviolet, infrared or similar detectors
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
  • G01N2203/02—Details not specific for a particular testing method
  • G01N2203/06—Indicating or recording means; Sensing means
  • G01N2203/0641—Indicating or recording means; Sensing means using optical, X-ray, ultraviolet, infrared or similar detectors
  • G01N2203/0647—Image analysis

Definitions

• the present invention relates to a device for determining the local mechanical behavior of a specimen of material.
• the material may comprise a metal, a polymer, and / or any other material that may have homogeneous or non-homogeneous finite deformations.
• Document FR 2 823 849 discloses a device making it possible to measure the real local deformations in two dimensions of a specimen of material, by means of a so-called video-traction device. This device makes it possible to film the displacement of point markers during mechanical stressing and to perform an interpolation of the displacements in order to provide the local deformation of the specimen.
• the present invention is intended to provide a device for having a better knowledge of the behavior of a material during its deformation.
• the subject of the invention is a device for determining the local mechanical behavior of a specimen of material, comprising a so-called video-traction unit, comprising:
• the device further comprising
• a Raman spectrometer comprising acquisition means and means for processing a Raman spectrum in a region for which the local deformation of the specimen is provided, and
• the interaction means of the video-traction unit and the Raman spectrometer make it possible in particular to carry out the measurements without having to stop the mechanical test or the acquisitions of the Raman spectrometer.
• the interaction means make it possible to obtain an analysis of the microstructure of the material at any time during the mechanical test, and not only at the end of a mechanical test or by momentary stops of the jaw displacement of the machine. mechanical test.
• the mechanical test is performed continuously, that is to say without stopping the movement of the jaws of the test machine, while obtaining Raman spectra during the test. This makes it possible to avoid relaxation phenomena within the material being acquired in the Raman spectrum, these relaxation phenomena interfering with the structure of the material and therefore with the quality of the Raman spectrum measurement.
• the interaction means of the video traction unit and the Raman spectrometer make it possible to control the video traction unit according to data provided by the Raman spectrometer or vice versa, to control the acquisition of Raman spectra by the spectrometer.
• Raman based on data provided by the video-pull unit. It is therefore possible to obtain mechanical data of the material as a function of the physicochemical properties of the material in a given volume of material throughout the mechanical test or vice versa.
• the interaction means make it possible to acquire a Raman spectrum when a certain displacement of the point markers is measured.
• these interaction means make it possible to control the local deformation speed of the specimen as a function of the results of the measurement obtained by means of the Raman spectrometer.
• the interpolation of the recorded displacements is a nonlinear interpolation.
• test piece of material a piece or a sample of material having a defined shape and which is used to perform a test, in this case, a mechanical test.
• a point marker is generally a task deposited on the surface of the specimen, before the start of the test, having a certain surface, and is preferably meant by "displacement of a marker" the displacement of the center of gravity of this surface.
• local deformation of the specimen is meant the actual deformation of the material in an area comprising the point markers.
• the unit of video-traction it is possible to obtain, thanks to the interpolation of the point markers, and almost instantaneously, the real deformation of the material in the zone including the point markers, which is distinguished from the macroscopic deformation of the specimen. It is therefore possible, thanks to this unit, to accurately characterize the constitutive law of the material in terms of deformations and stresses in a volume representative of the microstructural point of view with respect to the characteristic length of the deformation inhomogeneities.
• a Raman spectrometer is an analysis apparatus based on the emission of a monochromatic beam such as a laser beam on a material and to analyze the light scattered by the material. This scattered light is a proper signature of the state of the material at the time of measurement.
• the analysis method, implemented by this device, is a non-destructive method for characterizing in particular the chemical composition, the structure of a material or the amorphous or crystalline state of a material.
• the lens used to focus the light makes it possible to adapt to the type of measurement and the desired accuracy. Indeed, it is possible to vary the focal length of the lens from a few millimeters to several tens of centimeters, which makes it possible to obtain spatial resolutions ranging from a few tenths of a micrometer to a few tens, or even hundreds of micrometers.
• the acquisition time of the spectrum is of the order of one second.
• the acquisition time may vary depending on the material and the quality of the spectrum that is desired.
• the acquisition time is two seconds, plus advantageously, the acquisition time is less than one second. It is understood that the longer the acquisition time, the better the quality of the Raman spectrum obtained.
• a device according to the invention may further comprise one or more of the following additional features, taken alone or in combination:
• the mechanical biasing means comprise means for moving gripping means of the test piece, such as jaws of the traction, compression or shearing machine and means for controlling the speed of movement of the gripping means as a function of the displacement of point markers.
• the interaction means comprise communication means between the Raman spectrum processing means and the mechanical stressing means of the specimen.
• the mechanical stress of the specimen can be controlled from data obtained by the treatment of the Raman spectrum.
• the specimen comprises a polymeric material
• the data obtained by the treatment of the Raman spectrum that can be taken into account by the mechanical biasing means can also be chosen from the evolution of the damage of the material, the evolution of the internal stresses of the material or the evolution of the crystalline phases in the test tube.
• the interaction means comprise means of communication between the interpolation means and the acquisition means of the Raman spectrum.
• the acquisition of the Raman spectrum can be controlled from data obtained by the interpolation means of the deformations recorded by the video recording means. It is possible, for example, to trigger the acquisition of the Raman spectrum according to the actual local deformations of the specimen.
• the Raman spectrometer comprises a light beam emission axis and the video recording means of the video traction unit comprise an axis called video axis, the video axis being parallel, antiparallel or perpendicular to the video axis; axis of the Raman spectrometer.
• video axis is meant the axis of view of the video recording means.
• parallel is meant the case in which the two axes are parallel and have the same orientation; by “antiparallel”, the a case in which the two axes are parallel and an opposite orientation; and by perpendicular, the case in which the two axes are perpendicular.
• the parallel configuration has the advantage of avoiding any interference between the laser beam emitted by the Raman spectrometer and the video-traction unit, which is particularly interesting when the specimen is a thin film of material.
• the antiparallel configuration has the advantage of making it possible to acquire the Raman spectrum in the same region as the video recording, but on the opposite face of the specimen, which is particularly interesting when the specimen is opaque to the light used. .
• the configuration in which the axes are perpendicular allows in particular to determine the deformation of the specimen in a third direction by simply measuring the lateral displacement of the spectrometer.
• this measurement of the thickness of the specimen, and therefore of the deformation can be performed by moving the focussing point of the spectrometer over the entire thickness of the sample.
• the video traction unit comprises means for emitting light having a wavelength preferably greater than 500 nm, for example 785 nm. It may be advantageous not to work in UV light for video recording of the displacement of point markers. Indeed, this light can disturb the acquisition of the Raman spectrum, in particular by the appearance of parasitic radiation.
• 785 nm it is also possible to overcome problems due to luminescence effects when the specimen comprises polymeric materials.
• the invention also relates to a method for determining the local mechanical behavior of a specimen of material comprising the following steps:
• a video recording is made of the displacement of a plurality of point markers placed on the specimen in order to provide the local deformation of the specimen undergoing mechanical stress
• the method according to the invention may further comprise one or more of the following additional steps:
• the mechanical stress of the specimen is modified according to the results Raman spectrum, for example by changing the rate of deformation as a function of the orientation of molecular chains provided by the Raman spectrum. For example, one can increase or decrease the rate of deformation as a function of the ratio between the intensity of the same peak in two successive Raman spectra.
• the Raman spectrum is triggered according to the results of an interpolation of the displacements of the point markers, for example periodically, the period being defined by a deformation or stress value provided by the results of the interpolation of the movements of point markers.
• At least one dimension of the test piece is measured by means of the spectrometer
• Raman for example the thickness of the specimen.
• the invention also relates to a computer program comprising program code instructions for executing the steps of the method defined above when said program is executed on a computer.
• FIG. 1 is a schematic view illustrating a device for determining the local mechanical behavior of a specimen of material according to one embodiment
• FIG. 2 is a schematic view illustrating a first variant configuration of the device of FIG. 1,
• FIG. 3 is a schematic view illustrating a second variant of configuration of the device of FIG.
• FIG. 1 shows a device 11 for determining the local mechanical behavior of a specimen of material comprising a video traction unit 10, a Raman spectrometer 12 and means 13 for interaction between the video unit traction 10 and the Raman spectrometer 12. It should be noted that this representation is particularly schematic and does not take into account in particular the proportions of the elements relative to each other.
• the video traction unit 10 comprises a mechanical testing machine which is briefly described.
• the mechanical testing machine comprises in particular a frame 14 and gripping means comprising two jaws 16 in which there is placed a test piece 18 of the material whose mechanical behavior is to be characterized.
• Each jaw 16 is secured to a cross member 20 and these crosspieces 20 are movably mounted, translation, one with respect to the other.
• the video-traction unit 10 also comprises video recording means 23 comprising a camera 24 and means 22 for processing or storing the images provided by the camera 24, the means 22 being housed in a computer 26. It is understood that so that the computer 26 includes a part of the video recording means 23, another part being the camera 24.
• the video recording means 23 communicate with interpolation means 28 also included in the computer 26.
• the video traction unit 10 also comprises mechanical biasing means 29 comprising, in particular, control means 30, the jaws 16, the crosspieces 20 as well as hydraulic cylinders 32 and force cells 34.
• the control means 30 make it possible in particular to control the movement of the crosspieces 20, therefore of the jaws 16.
• the device 11 also comprises a Raman spectrometer 12 comprising means for acquiring a Raman spectrum which comprise a detector 38 and means for processing the Raman spectrum communicating with the acquisition means 36. means for emitting a light beam.
• the detector 38 is disposed on the frame 14 while the remainder of the acquisition means 36 and the Raman spectrum processing means 40 are included in the computer 26.
• the computer 26 further comprises means 42 for interaction between the video traction unit 10 and the Raman spectrometer 12.
• the interaction means 42 comprise in particular means of communication between the means 40 for processing the Raman spectrum and the mechanical biasing means 29 of the specimen 18 and / or the means of communication between the interpolation means 28 and the acquisition means Raman spectrum 12.
• the interaction means 42 it is possible to use, to regulate the speed of movement of the crosspieces 20 relative to one another, therefore the jaws 16, or the data obtained by the video-traction unit 10, the data obtained using the Raman spectrometer.
• the transmission axis 41 of the incident light beam of the detector 38 is parallel and has the same orientation as the video axis 43 of the camera 24.
• Figure 2 shows another alternative configuration in which the video axis
• FIG. 3 represents another alternative configuration of the device in which the video axis 43 and the transmission axis 41 are antiparallel, that is to say that the two axes 41, 43 are parallel and have an opposite orientation.
• the Raman spectrum is obtained in the region for which the local deformation of the specimen 18 is provided. It is therefore possible, simultaneously with the deformation and the mechanical characteristics of the specimen 18, to obtain physicochemical characteristics of the material subjected to deformation.
• the video axis 43 and the transmission axis 41 can take, relative to each other, all positions between 0 ° and 180 °.
• the three configurations shown in the figures are special cases in which: when the two axes are in parallel configuration, the angle between the two axes is 0 °;
• the angle between the two axes is 180 °.
• a specimen 18 made in the material to be characterized is used.
• the test piece 18, depending on the type of material, may be a solid test specimen or a film.
• a plurality of point markers 46 are applied whose number, in this case seven (FIGS. 2 and 3), and the relative position of one relative to the others are adapted in particular to the geometry of the specimen 18 before deformation. As can be seen in FIGS. 2 and 3, these markers approximately form a cross along a transverse axis X and a longitudinal axis Y of the test piece 18. It will be noted that the point markers 46 are not necessarily aligned. It may be advantageous for these point markers 46 to be slightly offset relative to each other with respect to the X and Y axes.
• the point markers 46 make it possible to determine the actual deformation of the specimen 18 in the region where they were applied.
• Point markers 46 are generally made of an adhesive substance, deformable, and of contrasting color relative to the material of specimen 18.
• the specimen 18 is placed and fixed in the jaws 16 of the test machine so that the camera 24 is arranged perpendicular to the face 44 carrying the point markers 46 and so that it can record the displacement of these point markers 46 during the mechanical test.
• the mechanical test is here to exert traction on the test piece 18. However, a similar test in shear or in compression could be considered.
• the axis 41 of emission of the light beam of the Raman spectrometer and the video axis 43 of the camera 24 are parallel and have the same orientation, thereafter, it will simply be said that they are parallel.
• the instructions are defined by means of a computer program executed on the computer 26.
• the instructions for controlling the mechanical stressing means of the specimen the instructions for controlling the acquisition and processing of the Raman spectra.
• the interaction means 42 make it possible to modify the mechanical stress of the specimen 18 as a function of the results of the Raman spectrum and / or to trigger the obtaining of a Raman spectrum according to the results of the interpolation of the displacements of the point markers. 46.
• the video recording means 23 record the deformations experienced by the specimen 18.
• the images are processed by the interpolation means 28 which make it possible to provide the local deformation of the specimen in real time by following the procedure described in FIG. displacement of the centroids of the point markers 46, by nonlinear interpolation. It is advantageous to illuminate the test piece 18, to record the displacement of the point markers 46 by using a light source having a wavelength close to 785 nm in order to to avoid phenomena of luminescence of the polymer material.
• the interpolation means 28, making it possible to follow the displacement of the barycenters of the point markers 46, communicate, via the interaction means 42, with the means 36 for acquiring a Raman spectrum in order to obtain a Raman spectrum at a given interval of actual local deformation of the specimen 18; this actual local deformation being provided by the interpolation means 28.
• the mechanical test can therefore be controlled according to mechanical parameters or as a function of physicochemical parameters.
• the mechanical parameters may for example be the actual local strain rate or the stress level in the test piece 18; the physico-chemical parameters may for example be the molecular chain alignment rate in a polymer or the evolution of the crystallinity of the material.
• the video axis 43 is perpendicular to the transmission axis 41 of the Raman spectrometer, it is possible to determine the variation in thickness of the specimen 18 by moving the beam of light emitted in a horizontal plane and parallel to the face of the specimen. the specimen to which the detector 38 is directed. In all three configurations, when the beam does not reach the specimen, the detector 38 does not receive light scattered by the material of the specimen 18, it is thus possible to determine the dimension along the Z axis of the specimen 18.
• FIG. 1 there is shown a single computer 26.
• the device can of course include several computers connected to each other so as to interact with each other. It is also conceivable that the device comprises two cameras 24 whose video axes are, for example, perpendicular. Moreover, a very schematic and functional representation of the computer 26 has been described here. It will be understood that the computer 26 is a calculation unit comprising program code instructions for executing the steps of the behavior determination method. local mechanics of the specimen 18.

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• Investigating, Analyzing Materials By Fluorescence Or Luminescence (AREA)

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• 2011
  • 2011-10-14 FR FR1159297A patent/FR2981452B1/fr active Active
• 2012
  • 2012-10-12 WO PCT/FR2012/052333 patent/WO2013054062A1/fr active Application Filing
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