Strain measuring apparatus and method for measuring mechanical strain

Abstract

The strain measurement device 100 for measuring mechanical strains in a sample 1 comprises a sample holder device 10 arranged to accommodate the sample 1 to be investigated, an indenter device 20 comprising an indenter tip 21 and an actuator stage 22 supporting the indenter tip 21, the actuator stage 22 being adapted to apply a load axis z via the indenter tip 21 in an indentation zone 2 of the sample 1 accommodated by the sample holder device 10 when the sample holder device 10 is in a load application position. 1 an indenter device 20 arranged to apply a localized mechanical load along an imaging axis z 2 a confocal Raman microscope device 30 arranged to collect at least one Raman spectrum in an indentation zone 2 of the sample 1, and a calculation device 40 arranged to calculate at least one strain parameter based on the at least one Raman spectrum, the sample holder device 10, the indenter device 20 and the confocal Raman microscope device 30 being arranged such that the confocal Raman microscope device 30 is able to collect the at least one Raman spectrum while the sample holder device 10 is in a load application position, the indenter device 20 and the confocal Raman microscope device 30 being aligned with a load axis z of the actuator stage 22. 1 and the imaging axis z of the confocal Raman microscope device 30. 2 Furthermore, a strain measurement method for measuring the mechanical strain in the sample 1 will be described.

Description

【Technical Field】 【0001】 The present invention relates to a strain measurement device configured to measure mechanical strain in a sample, particularly a laser-transparent sample. Further, the present invention relates to a strain measurement method for measuring mechanical strain in a sample. The strain measurement is based on a combination of confocal Raman spectroscopy and indentation. The applications of the present invention are available, for example, in the fields of materials science and materials research. 【Background Art】 【0002】 In this specification, references are made to the following prior arts that illustrate the technical background and related technologies of the invention. [1] A.M. Korsunsky, Chapter 8 - Residual Stress "Measurement", A Teaching Essay on Residual Stresses and Eigenstrains (edited by Korsunsky AM), Butterworth-Heinemann (2017) [2] W. Ecker et al., "Nanoscale evolution of stress concentrations and crack morphology in multilayered CrN coating during indentation, Experiment and simulation (Nanoscale changes in stress concentration and crack morphology in multilayer CrN coatings during indentation: Experiment, and simulation)", Materials & Design, Vol. 188, p. 108478 (2020) [3] AJGLunt et al., "A review of micro-scale focused ion beam milling and digital image correlation analysis for residual stress evaluation and error estimation," Surface and Coatings Technology, Vol. 283, pp. 373-388 (2015). [4] C. Gammer et al., "Measurement of local strain," MRS Bulletin Vol. 44(6), pp. 459-464 (2019). [5] J. Gim et al., "Nanoscale deformation mechanics reveal resilience in nacre of Pinna nobilis shell", Nat Commun, Vol. 10, p. 4822 (2019). [6] A. Zeilinger et al., "In-situ Observation of Cross-Sectional Microstructural Changes and Stress Distributions in Fracturing TiN Thin Film during Nanoindentation," Scientific Reports, Vol. 6, p. 22670 (2016). [7] P. Manimunda et al., "Chem.Commun.", Vol. 55, pp. 9200-9203 (2019) [8] HCLoh et al., "Commun Mater" Vol. 1, p. 77 (2020) [9] YBGerbig et al., "In-situ Raman spectroscopic measurements of the deformation region in indented glasses," JOURNAL OF NON-CRYSTALLINE SOLIDS, Vol. 530, p. 119828 (2019).

[10] WO 96 / 10737 A1

[11] RU 2 680 853 C1

[12] WO 97 / 03346 A1

[13] JP 2017 146294 A

[14] KR 101 783 541 B1 【0003】 Localized stress often influences the performance or failure of solid materials. Therefore, studying the development of localized stress is essential for understanding the mechanical response of materials. Localized stress is determined by applied stress, residual stress, and their interactions. While applied stress can be measured and controlled, residual stress is inherently difficult to detect, control, or suppress. Over the past several decades, several techniques have been developed to evaluate internal strain or stress. 【0004】 Microscale focused ion beam milling and digital image correlation analysis are destructive techniques that provide direct measurement of residual strain on a sample surface. However, these techniques are limited to the evaluation of residual strain and are not applicable to induced contact strain in the presence of external contact loads. In addition, mechanical milling ultimately destroys the region of interest. Furthermore, digital image correlation methods cannot provide volumetric information and are limited to surface areas. 【0005】 Non-destructive techniques such as transmission electron diffraction and microscopy can determine localized lattice strains with high spatial resolution down to a few nanometers (see, e.g., [4, 5]). However, transmission electron microscopy (TEM) requires relatively thin specimens, which is a drawback because the resolution must be evaluated with respect to volume so that the specimen has a given thickness and the strain value is uniform. Strain relaxation effects can be induced during specimen preparation, and free edge effects may occur during in-situ mechanical loading. In addition, the field of view of TEM is limited to a few microns, and this technique does not support 3D characterization. 【0006】 Microfocus X-ray diffraction is another known technique for real-time measurement of strain / stress with micron-sized exploration resolution [1]. However, this technique requires complex measurement techniques such as advanced synchrotron beamlines, and like electron diffraction, X-ray diffraction has its own drawbacks regarding the preparation of size-constrained samples, and the free surface of the sample may induce or relieve residual stress / strain in the sample [1, 2]. In this case as well, the applied mechanical load may result in excessive deformation at the free end of the sample. As a result, the data collected from the irradiated volume includes information from the deformation at the sample edge, inevitably leading to measurement errors. Finally, the transmission concept of X-ray diffraction measurement yields information obtained from the irradiated volume, rather than point-by-point data. Therefore, this technique cannot perform depth profiling along the irradiation axis, and only a single strain value can be obtained from the volume. 【0007】 Raman spectroscopy can investigate the molecular energy properties of Raman-active materials. In addition to its ability to characterize structural materials, this technique is also used to measure mechanical strain / stress. Such strain affects the frequency of molecular vibrations, and consequently, influences the Raman spectrum through changes in peak position and width. Therefore, by measuring the position and / or width of the vibration bands in a strained sample and comparing them to the unstrained sample (reference state), information regarding the magnitude of mechanical strain / stress can be obtained. In contrast to diffraction techniques, confocal Raman spectroscopy allows for depth profiling within the penetration depth of the material. This penetration depth is a function of the laser wavelength and the absorption coefficient of the sample, and can range from a few millimeters in the case of laser-transparent materials. Therefore, depending on the thickness of the sample, the generation and propagation of strain / stress fields are possible even when there are no free ends / cut ends. 【0008】 Known protocols for investigating loaded / impacted samples include post-impact Raman spectroscopy and off-axis Raman spectroscopy under load. In post-impact Raman spectroscopy, the sample is first impacted, and then the residual trace is scanned after impact. As an example, an integrated impact setup is proposed in [7], in which a translation stage moves the sample from the impact station to another measurement station (optical position) connected to a Raman spectrometer via a fiber optic cable. However, this method does not allow for real-time measurements. Furthermore, the elastic response (induced elastic strain) recovers as soon as the load on the sample is removed, making it impossible to study the elastic response. 【0009】 On the other hand, off-axis Raman spectroscopy under load (see, e.g., [9]-

[14] ) uses Raman spectroscopy while the sample is being loaded. However, matching the incident laser off-axis while the load is applied makes it impossible to perform an in-line scan below the load application spot (i.e., measurement in the sample volume is impossible), which means that calculating the strain tensor becomes even more complex. Furthermore, in available in-situ Raman intrusion setups that include off-axis characterization of the sample, some of the induced strain field is inaccessible to the Raman microscope because it is in the shadow of the indenter. In addition, the tilt angle of the setup adds further complexity to data analysis because the intensity of the vibrational bands differs depending on the exploration direction. Off-axis Raman spectroscopy has been performed on tensile / compressed samples (not intrusion samples) [8]. However, since the strain is also dispersed when the applied load is distributed, this technique cannot be used to study the generation of strain in the loaded area (because structural materials such as bioceramics do not correlate with the microstructure of the sample, which may play an important role in the generation of concentrated stress / strain). 【0010】 In summary, conventional evaluation of localized stress under applied load has been extremely difficult because it requires the combination of two crucial aspects. First, the ability to measure the interaction between the strain / stress field generated under applied load and the possible residual strain / stress in a "time-resolved" manner. Therefore, destructive techniques cannot meet this requirement. Consequently, only non-destructive strain / stress measurement techniques, such as those based on diffraction measurements, remain as practical options. Second, the ability to explore "localized" strain / stress with submicron resolution. Therefore, synchrotron X-ray microdiffraction, transmission electron diffraction and microscopy, and confocal Raman microscopy [1, 2] remain the only techniques applicable to time-resolved measurement of localized strain / stress under contact load. However, due to physical constraints, none of these techniques have so far been able to perform three-dimensional mapping of the induced contact strain / stress field in known configurations. [Prior art documents] [Patent Documents] 【0011】 [Patent Document 1] International Publication No. 96 / 10737 [Patent Document 2] Russian Patent No. 2680853 [Patent Document 3] International Publication No. 97 / 03346 [Patent Document 4] Japanese Patent Publication No. 2017-146294 [Patent Document 5] Korean Registered Patent Publication No. 10-1783541 [Non-patent literature] 【0012】 [Non-Patent Document 1] Korsunsky,AMChapter 8-Residual Stress “Measurement”:From A Teaching Essay on Residual Stresses and Eigenstrains.2017,pp.93-107. [Non-Patent Document 2] Ecker,W.et al.Nanoscale evolution of stress concentrations and crack morphology in multilayered CrN coating during indentation:Experiment and simulation.Materials&Design.2020,vol.188.https: / / doi.org / 10.1016 / j.matdes.2020.108478 [Non-Patent Document 3] Lunt, A.J.G. et al. A review of micro-scale focused ion beam milling and digital image correlation analysis for residual stress evaluation and error estimation. Surface and Coatings Technology. 2015, vol. 283, pp. 373 - 388. [Non-Patent Document 4] Gammer, C. et al. Measurement of local strain. MRS Bulletin. 2019, vol. 44(6), pp. 459 - 464 [Non-Patent Document 5] Gim, J. et al. Nanoscale deformation mechanics reveal resilience in nacre of Pinna nobilis shell. Nature Communications. 2019, vol. 10. https: / / doi.org / 10.1038 / s41467 - 019 - 12743 - z [Non-Patent Document 6] Zeilinger, A. et al. In-situ Observation of Cross-Sectional Microstructural Changes and Stress Distributions in Fracturing TiN Thin Film during Nanoindentation. Scientific Reports. 2016, vol. 6. https: / / doi.org / 10.1038 / srep22670 [Non-Patent Document 7] Manimunda, P. et al. Probing stress induced phase transformation in aspirin polymorphs using Raman spectroscopy enabled Nanoindentation. Chemical Communications. 2019, vol. 55, pp. 9200 - 9203 【Non-Patent Document 8】 Loh, H.C. et al. Nacre toughening due to cooperative plastic deformation of stacks of co‐oriented aragonite platelets. Communnications Materials. 2020, vol.1. https: / / doi.org / 10.1038 / s43246-020-00078-y 【Non-Patent Document 9】 Gerbig, Y.B. and Michaels, C.A. In-situ Raman spectroscopic measurements of the deformation region in indented glasses. Journal of Non-Crystalline Solids. 2019, vol.530. https: / / doi.org / 10.1016 / j.jnoncrysol.2019.119828 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0013】 An object of the present invention is to provide an improved strain measuring device and / or a strain measuring method for measuring mechanical strain in a sample, which can avoid the limitations and drawbacks of conventional techniques. In particular, the strain measuring device and / or method can perform real-time three-dimensional mapping and avoid limitations caused by time offset and / or orientation offset. 【Means for Solving the Problems】 【0014】 This object is solved by a strain measuring device and / or a strain measuring method including the features of the independent claims. Advantageous embodiments and uses of the present invention are defined in the dependent claims. 【0015】 According to a first general aspect of the present invention, the above object is solved by a strain measuring device configured to measure mechanical strain in a sample, the strain measuring device comprising: a sample holder device arranged to accommodate a sample to be investigated; an indenter device including an indenter tip and an actuator stage supporting the indenter tip, wherein the actuator stage is arranged to apply a localized mechanical load along the load axis via the indenter tip in the indentation zone of the sample accommodated by the sample holder device when the sample holder device is in a load application position; a confocal Raman microscope device (preferably a confocal Raman microscope) having an imaging axis and arranged to collect at least one Raman spectrum in the indentation zone of the sample; and a calculation device arranged to calculate at least one strain parameter based on at least one Raman spectrum. 【0016】 According to the apparatus of the present invention, the sample holder device, the indenter device, and the confocal Raman microscope device are arranged such that the confocal Raman microscope device can collect at least one Raman spectrum while the sample holder device is in the load application position. Furthermore, according to the present invention, the indenter device and the confocal Raman microscope device are arranged such that the load axis (press-in direction) of the actuator stage coincides with the imaging axis of the confocal Raman microscope device. 【0017】 According to a second general aspect of the present invention, the above objective is solved by a strain measurement method for measuring mechanical strain in a sample, the method comprising the steps of: placing the sample to be investigated on a sample holder device; applying a localized mechanical load to the sample using an indenter device including an indenter tip and an actuator stage supporting the indenter tip, wherein the mechanical load is applied in the indentation zone of the sample via the indenter tip along the load axis using the actuator stage when the sample holder device is in the load application position; collecting at least one Raman spectrum in the indentation zone of the sample using a confocal Raman microscope device having an imaging axis; and calculating at least one strain parameter based on the at least one Raman spectrum. 【0018】 According to the method of the present invention, at least one Raman spectrum is collected while the sample holder device is in the load application position. Furthermore, according to the present invention, the indenter device and the confocal Raman microscope device are positioned such that the load axis of the actuator stage coincides with the imaging axis of the confocal Raman microscope device. Preferably, the strain measurement method according to the second general embodiment or embodiment thereof of the present invention is performed using the strain measurement apparatus according to the first general embodiment or embodiment thereof of the present invention. 【0019】 The term "strain measurement" refers to the determination of strain, which is a measure of the deformation of a material under the influence of force, particularly external force. Deformation results in a change in the molecular vibration frequency of the material. In elastic deformation, induced strain and stress are correlated. Therefore, the strain measuring apparatus and method of the present invention can also be considered a stress measuring apparatus and method for measuring mechanical stress in a sample, in which case at least one stress parameter is obtained by correlation with changes in peak width and / or position of the collected Raman spectrum. 【0020】 Providing the sample holder device at the load application position involves arranging the sample holder device and the indenter device such that the indenter tip can contact and press against the sample on the sample holder device by the indenter tip's indentation. Preferably, the sample holder device and the indenter device have fixed positions relative to each other so that the sample holder device remains at the load application position throughout the strain measurement. The sample holder device preferably comprises a support platform with a surface on which the sample is placed. The support platform has sufficient mechanical stability to withstand any forces resulting from the application of localized mechanical load to the sample by the indenter tip. The support platform is preferably configured to allow probe light to pass through for collecting at least one Raman spectrum, either through holes (windows) in the platform to directly expose a self-supporting (thick) transmissive sample, or by using a transmissive backplate to support a thin sample (<1 mm). Particularly preferably, the sample holder, and in particular its support platform, has concentric windows mounted upside down beneath the confocal Raman microscope device. 【0021】 The actuator stage of the indenter device is preferably fixedly positioned relative to the sample holder device and configured to shift the indenter tip relative to the sample holder device, and more particularly relative to the sample housed by the sample holder device, preferably along a linear shift axis perpendicular to the surface of the support platform. Particularly preferably, the actuator stage comprises a piezoelectric actuator and transducer, which have advantages with respect to the amount and time control of the applied load. Advantageously, the actuator stage may be configured to indent the indenter tip with a resolution step size of a minimum of 5 nm. The indenter tip is made of a non-deformable material, such as a hard ceramic such as diamond. 【0022】 By shifting the indenter tip toward the sample holder device, particularly its support platform, the indenter tip contacts and presses against the sample, resulting in the application of a mechanical load to the sample. By shifting in the opposite direction, the load can be reduced to zero (release of the sample). Due to the tip shape of the indenter tip, the direct application of the load is localized to a point-shaped contact section between the indenter tip and the sample. This contact section provides the indentation zone, and the load axis (the axis through which force is applied to the sample) is the shift axis of the indenter tip. 【0023】 A confocal Raman microscope device generally comprises a light source device, such as a laser light source, for generating excitation light; an imaging optical system for directing the excitation light onto a sample, focusing the excitation light at a selectable sample depth, and collecting Raman scattered light from the sample; and a spectral resolution detector device, such as a spectrometer, for detecting the Raman scattered light. The imaging optical system may be configured to relay the excitation light in free space and / or in an optical guide. 【0024】 The imaging axis (surveillance direction) is set according to the direction in which the imaging optical system illuminates the sample. The imaging axis coincides with the load axis; that is, both axes are preferably identical or parallel at a distance from each other at the point where the load is applied, so that the effect of this distance on the obtained measurement results is negligible. The coincident axis can be provided by adjusting at least one of the imaging optical system and the actuator stage. Preferably, the imaging axis is perpendicular to the surface of the support platform, and in particular perpendicular to the surface of the sample placed on the support platform. 【0025】 A calculation device for calculating at least one strain parameter comprises a computer circuit and is optionally included in the control device of the strain measuring device. 【0026】 The arrangement of the sample holder device, indenter device, and confocal Raman microscope device according to the present invention includes setting the sample holder device and / or indenter device such that the sample holder device is in a load-applied position, i.e., such that the advancing indenter tip can strike the sample. Simultaneously, the arrangement of the sample holder device, indenter device, and confocal Raman microscope device according to the present invention includes setting the sample holder device and / or confocal Raman microscope device such that the imaging optical system can direct excitation light towards the sample on the support platform, in particular towards the sample indentation zone, and collect Raman scattered light from the sample, in particular the sample indentation zone. Advantageously, at least one Raman spectrum can be collected when the sample holder device is in a load-applied position, in particular when the sample resting on the sample holder device can be subjected to a localized mechanical load, e.g., a static load or a dynamically changing load. 【0027】 In contrast to conventional techniques (e.g., [7]), the technique of the present invention aligns the indentation direction (load axis) with the Raman microscope (imaging axis on the same straight line), colocalizing the load application spot and contact zone, thereby enabling the determination of the amount (single value) of induced contact strain / stress under elastic-inelastic deformation, and optionally its 1D, 2D, or 3D distribution. Changes in molecular vibrational bands in the indentation zone of the sample are measured by improved Raman spectroscopy. In particular, the present invention allows for real-time loading and measurement of the induced contact strain / stress field with submicron spatial resolution in Raman-active materials, preferably laser-transparent and / or sufficiently thin materials. Advantageously, the arrangement of the indenter device and confocal Raman microscope device in the present invention, where the load axis and imaging axis coincide, eliminates the limitations of off-axis techniques (e.g., [8]). Furthermore, the arrangement of the confocal Raman microscope device according to the present invention allows for the collection of at least one Raman spectrum during and / or after load application without moving the sample, resulting in accurate strain measurement in the press-fit zone. In particular, it allows for the measurement of sample recovery during load reduction. 【0028】 According to a preferred embodiment of the present invention, the sample holder device, the indenter device, and the confocal Raman microscope device are arranged such that the confocal Raman microscope device can collect at least one Raman spectrum simultaneously with the application of a localized mechanical load. With respect to this method, at least one Raman spectrum is preferably collected simultaneously with the step of applying the localized mechanical load, i.e., during the application of the load. Advantageously, at least one strain parameter is estimated without being affected by the relaxation process after the application of the load. Alternatively, or in addition, at least one Raman spectrum may be collected before and / or after the application of the localized mechanical load. 【0029】 According to a particularly preferred embodiment of the present invention, the indenter device, in particular at least its indenter tip, and the confocal Raman microscope device, in particular at least a portion of its imaging optical system, are positioned opposite the sample holder device, particularly opposite the support platform of the sample holder device, so that a localized mechanical load can be applied at a load application spot on the first side of the sample, and at least one Raman spectrum can be collected in the indentation zone, in particular at a load application spot from the second side opposite the sample. With respect to this method, the localized mechanical load is preferably applied at a load application spot on the first side of the sample, and at least one Raman spectrum is collected in the indentation zone, in particular at a load application spot from the second side opposite the sample. Advantageously, sufficient space is obtained by positioning the indenter and the confocal Raman microscope device (or its components) opposite each other. 【0030】 Applying a load and collecting Raman scattered light from the opposite side preferably includes providing a vertical orientation of the load axis and the imaging axis, applying the load from above along the direction of gravity, and collecting at least one Raman spectrum from below the support platform. Alternatively, it may be provided that the load is applied from below parallel to the direction of gravity, and at least one Raman spectrum is collected from above the support platform. 【0031】 According to a more preferred embodiment of the present invention, the sample holder device is provided with a translation stage positioned to adjust the x and y positions of the sample holder device in a plane perpendicular to the imaging axis of the confocal Raman microscope device. With respect to this method, it is preferable that the x and y positions of the sample holder device are adjusted in a plane perpendicular to the imaging axis. Advantageously, the translation stage facilitates the adjustment of the sample with respect to the load axis and the imaging axis, and therefore, by operating the translation stage, two-dimensional (in a plane parallel to the surface of the support platform) or three-dimensional scan measurements can be performed. 【0032】 Another particular advantage of the present invention arises when the confocal Raman microscope device is configured to collect multiple Raman spectra in time resolution, enabling, for example, the investigation of the relaxation characteristics of the sample. Alternatively, or in addition, mapping of the sample within a range including the intrusion zone may be provided. Advantageously, this mapping function provides additional reference information about the sample in areas of low strain or even no strain. To map the sample, an optical scanner device may be provided, positioned to continuously focus excitation light at different locations within and / or outside the intrusion zone. 【0033】 According to a more advantageous embodiment of the present invention, the indenter device comprises a load cell connected to an actuator stage, the load cell being arranged to measure a mechanical load applied to a sample. With respect to this method, the mechanical load applied to the sample can be measured using a load cell connected to an actuator stage. Advantageously, the load cell can determine the correlation between at least one Raman spectrum and / or at least one strain parameter collected and the amount of load applied to the sample. Furthermore, the load cell can be used for load control, and / or the load can be applied according to a predetermined time function, so that at least one strain parameter can be calculated according to a given test protocol. 【0034】 Advantageously, various features of the indenter tip are available to improve strain measurement. Preferably, the indenter tip has a distal contact section that is exposed to contact the sample and has dimensions of less than 1 μm. Alternatively, larger dimensions are possible, e.g., in the range of 1 μm to 1 mm, or up to 3 mm, or even up to 5 mm. The smaller dimensions of the contact section allow for advantageous improvement of the application of high external pressure and position-resolved measurements. Alternatively, or in addition, the indenter tip may be interchangeable. Thus, it may be easier to adapt the measurement setup to a particular sample. Alternatively, or in addition, the indenter tip may be a diamond tip. Because diamond has high hardness, it is possible to measure almost all materials of interest. Furthermore, the indenter tip material may include, for example, zirconia, sapphire, ruby, or tungsten carbide. Alternatively, or in addition, the indenter tip may be a conical spherical tip. A conical spherical shape offers advantages in homogeneous load application and strain generation in the sample. Alternatively, the indenter tip may have a tip shape with cube corners or a Berkovich shape to further localize stress concentration or to partially deform the sample in an inelastic manner. Furthermore, the tip shape may include, for example, a Vickers shape or a flat punch shape. 【0035】 The tip can be modified to accommodate one of several different tip shapes and / or materials. The tip dimensions and contact radius can also be varied. In practice, the tip is selected according to the measurement conditions, e.g., sample size, sample hardness, or sample structure. For example, a conical tip may have a radius in the range of 300 nm to several mm, while a cube corner may have a tip dimension of about 70 to 100 nm, and a Berkovich tip may have a tip dimension of about 120 nm. 【0036】 Features disclosed in the context of strain measuring devices and embodiments thereof also represent preferred features of strain measuring methods and embodiments thereof of the present invention. The aforementioned embodiments and preferred features of the present invention, in particular the configuration of the devices and features relating to the dimensions and configuration of individual components described in connection with the devices, also apply to the methods. The above preferred embodiments, variations, and features of the present invention can be combined with each other as needed. 【0037】 Further advantages and details of the present invention are described below with reference to the accompanying drawings, and are outlined below. [Brief explanation of the drawing] 【0038】 [Figure 1] The features of a strain measuring device according to a preferred embodiment of the present invention are shown. [Figure 2] Further features of the strain measuring device shown in Figure 1 are shown. [Figure 3] Further features of the strain measuring device shown in Figure 1 are shown. [Figure 4] A scan configuration using a strain measurement method according to a preferred embodiment of the present invention is shown. [Figure 5] The results of an in-situ Raman impregnation survey conducted in point measurement mode while gradually increasing the load are shown. [Figure 6] This shows the experimental results of in-situ Raman impregnation studies conducted in 3D mapping mode. [Figure 7]The results of an in-situ Raman impregnation survey conducted in 2D mode while gradually increasing the load at the same location are shown. [Modes for carrying out the invention] 【0039】 Embodiments of the present invention will be described below with particular reference to the arrangement and operation of the sample holder device, indenter device, and confocal Raman microscope device of the in-situ strain measuring apparatus. The present invention is preferably carried out using, for example, a known confocal Raman microscope for strain measurement. Therefore, details of the confocal Raman microscope, its available control methods, and available methods for acquiring the Raman signal will not be described insofar as they are known from the prior art. 【0040】 Calculating at least one strain parameter is preferably performed based on at least one collected Raman spectrum and at least one measured load amount, as is done in conventionally known Raman-based strain measurements. In particular, this involves signal evaluation of at least one Raman spectrum, correlating features of at least one Raman spectrum, such as band peak positions and / or bandwidths and / or their variations, with the amount of deformation, e.g., indentation of the indenter tip, and analytically or numerically calculating at least one stress or strain parameter from the load amount and the amount of deformation. Calculating at least one stress or strain parameter may include calculating a single stress or strain parameter as a single value, such as localized strain, or calculating multiple stress or strain parameters as a map and / or function of time. 【0041】 Generally, the samples include solid Raman-active materials such as ceramics or plastics. In exemplary forms, plate-shaped samples are referenced, and plate-shaped samples are preferably transparent in the wavelength range of the confocal Raman microscope, particularly in the probe light wavelength of its light source and in the Raman scattered light wavelength. The wavelength range of the confocal Raman microscope is, for example, about 400 nm to 1.5 μm. Transparent samples have thicknesses ranging from, for example, 10 μm (supported by a laser-transparent backplate such as quartz) to 5 mm (freestanding). It should be noted that optical transparency is not an essential feature of the sample. If there is no optical transparency, strain measurements may be limited to thin samples (e.g., tooth enamel) with thicknesses ranging from, for example, 10 μm to 100 μm. 【0042】 Figure 1 schematically shows a side view of one embodiment of a strain measuring device 100 for measuring mechanical strain in a sample 1. This strain measuring device 100 comprises a sample holder device 10, an indenter device 20 having an indenter tip 21 and an actuator stage 22, a confocal Raman microscope 30, and a calculation device 40 included in a control device 50, such as a control computer. The load axis z1 of the indenter device 20, particularly its indenter tip 21, and the imaging axis z2 of the confocal Raman microscope 30 both extend along the vertical z-axis. The sample holder device 10 is adapted to position the sample in a plane perpendicular to the load axis and the imaging axis, particularly in the horizontal xy plane. Figure 2 also shows a preferred translation stage 60 for adjusting the positions of the sample holder device 10 and the indenter device 20 relative to the confocal Raman microscope device 30 and / or for scanning the sample for sample map measurement (see Figure 4). Details of the sample holder device 10 are shown in the top view of Figure 3. 【0043】 The sample holder device 10 comprises a support platform 11 extending in the horizontal xy plane for housing the sample 1. The support platform 11 is attached to a support plate 13 via four support columns 12 (see Figures 1 and 3). Preferably, the support platform 11 comprises an adjustable sample holder frame 14 with a central laser exploration window 15 for transmitting probe light and collecting at least one Raman spectrum. The sample 1 can be fixed to the surface of the sample holder frame 14. The position of the sample holder frame 14 in the xy plane can be adjusted via a sample adjustment knob 16. When the sample 1 is placed on the sample holder frame 14, the sample holder device 10 is in a load-applied position, and the clamped sample 1 is in contact with the indenter tip (from below) and exposed to light / laser (from above). The sample adjustment knob 16 is provided for positioning the sample 1 relative to the load axis z1 and the imaging axis z2. The scanning operation of the sample in the xy plane may be provided by the translation stage 60. Thus, the contact zone / area in the sample 1 can be scanned through the optical / laser exploration window 15 by operating the translation stage 60 in the xy plane, and the measurement depth in the sample 1 can be scanned by operating the translation stage 60 in the z direction and / or shifting the focus of the confocal Raman microscope device 30 along the z axis. 【0044】 The indenter device 20 comprises an indenter tip 21, an actuator stage 22, and a load cell 23. The indenter tip 21 has, for example, a conical rigid tip section 21A made of diamond (see Figure 4) and a tip support body section 21B. This setup allows for the exchange of different indenter tips having different sizes and shapes, adapted to form and apply different stress fields. The actuator stage 22 is supported by a support plate 13 and / or a translation stage 60 and is a piezoelectric actuator capable of applying indentation with, for example, a minimum step size of 5 nm and a maximum applied load of, for example, 20 N. The load cell 23 is positioned between the actuator stage 22 and the tip support body section 21B to measure the load applied to the sample 1. In particular, the load cell 23 may have, for example, a reading resolution of 0.01 N and a maximum load of, for example, 20 N, and the load cell 23 is connected to the shank of the piezoelectric actuator. The load cell 23 is connected to a control device 50 for analyzing the load cell output and for optionally providing loop control of the actuator stage 22 according to the load cell output. 【0045】 The confocal Raman microscope 30 preferably comprises a microscope body 34 (Schematically shown in Figure 2) equipped with, for example, a granite damped vibration microscope baseplate 35, which includes a light source device 31, an imaging optical system 32, and a detector device 33. The light source device 31 is, for example, a laser (λ=488nm, 532nm, 633nm, or 785nm). The detector device 33 is connected to a calculation device 40. The confocal Raman microscope 30 is, for example, a confocal Raman microscope (e.g., WITec Alpha 300R from B-TECH, Germany). Preferably, the confocal Raman microscope 30 is provided with a conventional confocal imaging section that enables microscopic imaging for visual monitoring of the sample. 【0046】 The translation stage 60 is fixedly positioned on the microscope base plate 35 to support the sample holder device 10, to adjust the position of the sample holder device 10 in the xy plane, and to adjust the load axis z1 of the indenter tip 21. Furthermore, the translation stage 60 is configured to adjust the position of the sample holder device 10 along the z direction, i.e., to adjust the focal position of the confocal Raman microscope 30 on the sample 1 along the z direction. This adjustment can be performed by an electric actor and / or a manually driven micrometer screw gauge 61. 【0047】 The indenter device 20 is mounted upside down beneath the confocal Raman microscope 30 with the sample 1 in between to apply a given load to the sample 1 (applied by the indenter tip 21 sinking into the sample) (see Figure 1). The load induces a change in the vibrational band of the Raman signal, particularly in at least one Raman spectrum of the sample collected by the confocal Raman microscope 30. This change is filtered and mapped so that the induced elastic strain / stress of the sample 1 can be evaluated by the calculation device 40. Because the indenter device 20 and the confocal Raman microscope 30 are positioned so that the load axis z1 and the imaging axis z2 coincide, the confocal Raman microscope device 30 can collect at least one interference-free Raman spectrum while the sample holder device 10 is in the load application position, and even during load application. 【0048】 As an alternative to the illustrated embodiment, the confocal Raman microscope 30 can be mounted upside down beneath the indenter device 20 with the sample 1 in between, thereby reversing the arrangement of the indenter device 20 and the confocal Raman microscope 30, or the coincident load axis and imaging axis can be tilted relative to the vertical z-axis. 【0049】 In the strain measurement according to the present invention, the strain measuring device 100 preferably operates as follows: Prior to strain measurement, the x and y positions of the indenter tip 21 can be adjusted using the micrometer screw gauge 61 of the translation stage 60 (see Figure 2). After mounting the sample 1 on the support platform 11 of the sample holder device 10, the region of interest (ROI) can be selected using the sample adjustment knob 16 while monitoring the sample 1 with the microscopic imaging section of the confocal Raman microscope device 30. The sample can then be fixed in place using the sample holder grip screw 17 (see Figure 3). As a preliminary reference measurement, the vibrational bands of the molecular structure of the sample in an unloaded state can be obtained using the confocal Raman microscope 30 before indentation. The characteristics of the vibrational bands can be used as a reference for subsequent strain measurements. 【0050】 Strain measurement includes the step of applying a localized mechanical load to the sample 1 using the indenter tip 21 of the indenter device 20. The indenter tip 21 is pressed in until contact with the sample 1 is achieved and an indentation zone 2 is formed (see Figure 4). Further indentation of the indenter tip 21 applies a load to the sample 1, resulting in elastic and / or inelastic deformation being induced in the indentation zone 2, i.e., the direct contact zone and adjacent areas of the sample 1. 【0051】 Furthermore, the strain measurement includes the step of collecting at least one Raman spectrum in the press-fit zone 2 using a confocal Raman microscope device 30. Simultaneously with the application of the load, at least one Raman spectrum is collected using the confocal Raman microscope device 30. Calculating at least one strain parameter from at least one Raman spectrum includes, for example, filtering the collected at least one Raman spectrum of the explored zone for a selected peak position and / or bandwidth, and correlating it with press-fit data (load, indentation, and / or contact shape) using a calculation device 40. The correlation between the features of at least one Raman spectrum and the induced strain / stress results in at least one strain parameter to be obtained. 【0052】 By collecting and evaluating a single spectrum, a zero-dimensional map of the sample is obtained, yielding a single strain value (see Figure 4A). Preferably, multiple Raman spectra are collected while operating the translation stage 60 to scan the intrusion zone 2, thereby obtaining vibrational bands of the molecular structure of the sample 1 in and / or around the intrusion zone 2 with local resolution. Thus, one-dimensional, two-dimensional, or three-dimensional maps of the sample can be obtained, as schematically illustrated in the line scan, area scan, and volume scan in Figures 4B–4D. The line scan in Figure 4B preferably provides depth-direction analysis of strain in the sample. Alternatively, other directions of the line scan can be set. In addition, the mappings shown in Figures 4A–4D can be performed with temporal resolution, for example, by repeated collection and evaluation of Raman spectra. 【0053】 In summary, performing time-resolved 3D mapping of localized strain / stress using the confocal Raman microscope 30 requires the combination of two key elements. First, a pointed micro-indenter or nano-indenter (indenter tip 21) with controllable indentation or load forms a localized contact stress field. This task cannot be achieved with conventional micro-tensile or bending testers because the applied stress field is not localized and / or the laser for scanning the stress / strain zone is not fully accessible. Second, the confocal Raman microscope 30 and calculation device 40 provide at least one strain parameter, preferably with spatial resolution for mapping the indentation area. Combining the Raman microscope device 30 with a translation stage 60 advantageously provides submicron scanning resolution in the x, y, and z directions. 【0054】 The spatial resolution of the imaging optical system 32 can be improved by selectively choosing an objective lens with a larger numerical aperture (NA) and a laser with a shorter wavelength (λ). For example, by using a 532 nm laser and an objective lens with NA=0.9 in the light source device 31, the spatial resolution (0.61*λ / NA) can be reduced to 360 nm. In addition, to detect changes in the vibration band of the sample 1 exposed to an external force, the detector device 33 of the confocal Raman microscope 30 preferably has a Raman shift (≤1 cm²). -1 A spectrometer with high resolution of ) shall be provided. This resolution can be adjusted, for example, by selecting a high grating number (>1800 g / mm) and a large focal length (>300 mm) accessible with an available confocal Raman microscope. 【0055】 As an example, by applying and controlling the indentation of the indenter tip 21 using a piezoelectric actuator of the actuator stage 22 via a diamond tip having a known shape, and recording the resulting load using a load cell 23, the applied Hertz contact stress σ and indentation strain ε at the contact point can be obtained from the following equations. 【number】 In the formula, P is the load, a is the contact radius, R is the radius of the indenter tip 21, and h is the applied contact depth (penetration into the sample 1). By collecting a Raman spectrum from the loaded sample 1 and comparing it with the spectrum under unloaded conditions, any change in the vibration band can be achieved, and this change can be used to correlate the induced peak shift with the applied contact stress. In particular, the contact stress can be calculated using the above formula based on the measured load, the known radius, and the contact depth derived from the induced peak shift. 【0056】 The applications of the present invention are not limited to the determination of Hertzian contact stress as a strain parameter. Instead, any correlation between the applied force or pressure and the change in the vibration band of a Raman-activated material can be calculated, in particular, in real time and / or time-resolved manner. 【0057】 The inventors investigated induced strain / stress and Raman peak shift in a series of point measurements, area scans, and 3D mappings (stacks of area scans to obtain volumetric data) of a geological fluorapatite sample (1 mm thick) under different contact loads using the strain measuring device 100 and method of the present invention in field tests. As an example, Figure 5 illustrates the results of an in-situ Raman intrusion test performed in point measurement mode while gradually increasing the load (0 to 170 g). As shown in Figure 5A, the extracted Raman peak of the ν1 vibration band of the phosphate group of fluorapatite at the contact point of the intrusion zone shows changes in peak position and width. Figure 5B shows the measured load depending on the applied intrusion of the indenter tip 21. The linear behavior of the extracted load-intrusion curve indicates the elastic response of the sample. Thus, the correlation between the Raman peak change (induced peak shift) and the applied intrusion (contact depth) can be obtained as shown in Figure 5C. This correlation is used to calculate the strain parameter (Hertz contact stress). 【0058】 Further tests, as shown in Figure 6, allowed for the characterization of stress distribution around the indentation zone and / or at different depths in the fluorine apatite sample by in-situ Raman indentation in mapping (3D) mode under a constant load of 1 N or 1.45 N. Figures 6A and 6B show the spatial distribution of indentation stress and strain in the sample under the action of an indenter tip with a radius of 125 μm, while Figure 6C shows a cross-sectional view of the sample in plane i. 【0059】 Furthermore, by using the in-situ function of this method and performing load scan cycles, changes in mechanical strain in calcite samples were revealed (Figure 7). In this study, a series of images were processed at the same location on the xy plane (2D scan) at defined applied contact loads P=84mN, P=147mN, and P=0 (scan after removing the 147mN load), representing the elastic (1), elastic-inelastic (2), and residual strain (3) states, respectively. 【0060】 The features of the invention disclosed in the above description, drawings, and claims may be important individually, in combination, or in partial combination in the realization of the invention in various embodiments. The invention is not limited to the preferred embodiments described above. Rather, multiple modifications and derivatives that use the concept of the invention are also possible and fall within the scope of protection. In addition, the invention also claims protection for the subject matter and features of dependent claims, independently of the features and claims referenced by those dependent claims.

Claims

[Claim 1] A strain measuring device (100) configured to measure the mechanical strain in a sample (1), A sample holder device (10) is provided, comprising a support platform (11) for accommodating the sample (1) and positioned to accommodate the sample (1) to be investigated. An indenter device (20) including an indenter tip (21) and an actuator stage (22) supporting the indenter tip (21), wherein the actuator stage (22) is configured such that, when the sample holder device (10) is in a load application position, the load axis (z) is transmitted through the indenter tip (21) in the indentation zone (2) of the sample (1) housed by the sample holder device (10). １ An indenter device (20) is positioned to apply a localized mechanical load along the ) Image axis (z ２ A confocal Raman microscope device (30) having ) and arranged to collect at least one Raman spectrum in the intrusion zone (2) of the sample (1), The system comprises a calculation device (40) arranged to calculate at least one strain parameter based on the at least one Raman spectrum, The sample holder device (10), the indenter device (20), and the confocal Raman microscope device (30) are arranged such that the confocal Raman microscope device (30) can collect the at least one Raman spectrum while the sample holder device (10) is in the load application position. The sample holder device (10), the indenter device (20), and the confocal Raman microscope device (30) are arranged such that the confocal Raman microscope device (30) can collect at least one Raman spectrum simultaneously with the application of the localized mechanical load. The indenter device (20) and the confocal Raman microscope device (30) are located on the load axis (z) of the actuator stage (22). １ ) and the imaging axis (z) of the confocal Raman microscope device (30) ２ They are positioned so that they match, The indenter device (20) and the confocal Raman microscope device (30) are positioned opposite the sample holder device (10) such that the localized mechanical load can be applied at the load application spot on the first side of the sample (1), and at least one Raman spectrum can be collected in the indentation zone (2). The actuator stage (22) comprises a piezoelectric actuator and a transducer, and is fixedly positioned relative to the sample holder device (10). The strain measuring device (100) is configured to apply a load from below parallel to the direction of gravity and to collect the at least one Raman spectrum from above the support platform (11). [Claim 2] The strain measuring apparatus according to claim 1, wherein the indenter device (20) and the confocal Raman microscope device (30) are arranged on opposing sides of the sample holder device (10) such that the localized mechanical load can be applied at a load application spot on a first side of the sample (1), and at least one Raman spectrum can be collected at the load application spot from a second side opposite the sample (1). [Claim 3] The sample holder device (10) has the imaging axis (z) of the confocal Raman microscope device (30). ２ The strain measuring apparatus according to claim 1, further comprising a translation stage (60) positioned to adjust the x-y position of the sample holder device (10) in a plane perpendicular to the sample holder device (10). [Claim 4] The strain measuring apparatus according to claim 1, wherein the confocal Raman microscope device (30) is configured to perform at least one of the following: time-resolved collection of a plurality of Raman spectra and mapping the sample (1) within a range including the intrusion zone (2). [Claim 5] The indenter tip (21) is characterized by having a distal contact section that is exposed to contact the sample (1), The indenter tip (21) is replaceable, The indenter tip (21) is characterized by being a diamond tip, a sapphire tip, or a ruby ​​tip. The indenter tip (21) is characterized by being a conical spherical tip, and The strain measuring device according to claim 1, wherein the indenter tip (21) has at least one of the following characteristics: a tip shape including a cube corner, a Berkovich shape, a Vickers shape, or a flat punch shape. [Claim 6] The indenter device (20) is characterized by comprising a load cell (23) connected to the actuator stage (22), the load cell (23) being arranged to measure the mechanical load applied to the sample (1), and A strain measuring apparatus according to any one of claims 1 to 5, comprising at least one of the following features: the sample holder device (10) has a concentric window that is mounted upside down below the confocal Raman microscope device (30). [Claim 7] A strain measurement method for measuring the mechanical strain in a sample (1), The steps include: placing the sample (1) to be investigated on a sample holder device (10) equipped with a support platform (11) for housing the sample (1); A step of applying a localized mechanical load to the sample (1) using an indenter device (20) including an indenter tip (21) and an actuator stage (22) supporting the indenter tip (21), wherein the mechanical load is applied in the indentation zone (2) of the sample (1) using the actuator stage (22) via the indenter tip (21) at the load application position when the sample holder device (10) is in the load application position, １ Steps applied along the lines of, In the press-fitting zone (2) of the sample (1), the imaging axis (z ２ The steps include: collecting at least one Raman spectrum using a confocal Raman microscope device (30) having the following: The process includes the step of calculating at least one strain parameter based on the at least one Raman spectrum, The at least one Raman spectrum is collected while the sample holder device (10) is in the load application position. The at least one Raman spectrum is collected simultaneously with the step of applying the localized mechanical load, The piezoelectric device (20) and the confocal Raman microscope device (30) are such that the load axis (z １ ) of the actuator stage (22) and the imaging axis (z ２ ) of the confocal Raman microscope device (30) are arranged to coincide with each other. The localized mechanical load is applied at the load application spot on the first side of the sample (1), and the at least one Raman spectrum is collected in the press-fit zone (2). The actuator stage (22) comprises a piezoelectric actuator and a transducer, and is fixedly positioned relative to the sample holder device (10). The strain measurement method includes the steps of applying a load from below parallel to the direction of gravity and collecting the at least one Raman spectrum from above the support platform (11). [Claim 8] The strain measurement method according to claim 7, wherein the localized mechanical load is applied at a load application spot on the first side of the sample (1), and the at least one Raman spectrum is collected at the load application spot from the second side opposite the sample (1). [Claim 9] The strain measurement method according to claim 7, comprising adjusting the x-y position of the sample holder device (10) in a plane perpendicular to the imaging axis of the confocal Raman microscope device (30). [Claim 10] Time-resolved collection of multiple Raman spectra, and A strain measurement method according to claim 7, comprising at least one of the following: mapping the sample (1) within a range including the press-fit zone (2). [Claim 11] Time-resolved collection of multiple Raman spectra, and A strain measurement method according to claim 10, comprising at least one of the following: three-dimensional mapping of the sample (1) within the range including the press-fit zone (2). [Claim 12] A strain measurement method according to any one of claims 7 to 11, further comprising measuring the mechanical load applied to the sample (1) using a load cell (23) connected to the actuator stage (22).

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