Apparatus and Method for Determining a Material Property of a Test Specimen in a Test Specimen Region Near the Surface

Abstract

The invention relates to an apparatus (1; 1a; 1b; 1c) and a method for determining a material property of a test specimen (5; 5a; 5b; 5c) in a test specimen region (6; 6a; 6b; 6c) near the surface, said apparatus comprising at least one electromagnetic radiation source (2; 2a; 2b; 2c) for irradiating at least one surface region (4; 4a; 4b; 4c) of the test specimen, and a detection device (8; 8a; 8b; 8c) for detecting thermal radiation (9; 9a; 9b) emitted by the surface region and/or for detecting radiation (31) reflected from the surface region (4; 4a; 4b; 4c) of the test specimen. An evaluation device (13; 13a; 13b; 13c) for ascertaining the material property to be determined on the basis of the emitted thermal radiation (9: 9a: 9b) and/or the reflected radiation (31) is expediently provided. Advantageously, it is possible for the material property to be determined particularly reliably and nondestructively.

Claims

1. Apparatus for determining a material property of a test specimen in a test specimen region near the surface, said apparatus comprising at least one electromagnetic radiation source for irradiating at least one surface region of the test specimen, and a detection device for detecting thermal radiation omitted by the surface region and/or for detecting radiation reflected from the surface region of the test specimen, characterized in that an evaluation device for ascertaining the material property to be determined on the basis of the emitted thermal radiation and/or the reflected radiation is provided.

2. The apparatus according to claim 1, characterized in that the radiation source for irradiating the at least one surface region can be controlled in such way that its radiation can be frequency-modulated and/or intensity-modulated and is preferably configured for heating the at least one surface region.

3. The apparatus according to claim 1, characterized in that a means for spatial and/or temporal intensity modulation of radiation generated by the radiation source is provided, said means preferably comprises a controllable liquid crystal display and/or a diffractive optical element.

4. The apparatus according to claim 1, characterized in that the detection device has a matrix-shaped sensor field which is configured for a point-by-point detection of thermal radiation omitted by the at least one surface region and/or is configured for a point-by-point detection of radiation reflected from the at least one surface region.

5. The apparatus according to claim 1, characterized in that each sensor of a matrix-shaped sensor field of the detection device is designed as a bolometric detector, as a thermocouple, as a semiconductor-based detector or as a pyroelectric sensor.

6. The apparatus according to claim 1, characterized in that the evaluation device comprises a means for amplifying a measurement signal detected by the detection device, preferably at least a lock-in amplifier.

7. The apparatus according to claim 6, characterized in that the amplification means is configured to amplify the measurement signal of each sensor of a matrix-shaped sensor field of the detection device.

8. The apparatus according to claim 1, characterized in that the apparatus is configured for determining thermophysical properties in the test specimen region near the surface, a layer thickness, a roughness of a layer, in particular a coating layer, thicknesses of single layers of a multilayer coating, a material hardness of the material forming the test specimen in the test specimen region near the surface, a hardening depth in the test specimen region near the surface and/or for determining and localizing defects in the test specimen region near the surface.

9. The apparatus according to claim 1, characterized in that the radiation source, the detection device and/or the evaluation device is or are arranged in a stationary manner or is or are movable relative to the test specimen.

10. Method for determining material properties of a test specimen in a test specimen region near the surface, in which at least one surface region of the test specimen is irradiated with an electromagnetic radiation source and thermal radiation emitted from the at least one surface region and/or radiation reflected from the at least one surface region is detected by a detection device characterized in that the emitted thermal radiation and/or the reflected radiation is used for ascertaining the material property to be determined in the region near the surface.

11. The method according to claim 10, characterized in that the at least one surface region is irradiated, preferably heated, with frequency-modulated and/or intensity-modulated radiation.

12. The method according to claim 10, characterized in that the test specimen, the radiation source and/or the detection device is/are moved or are moved relative to one another.

13. The method according to claim 10, characterized in that an amplitude (I.sub.D) and a phase shift (d) of a measurement signal are determined, preferably by a cross-correlation.

14. The method according claim 10, characterized in that an intensity and/or phase distribution of the thermal radiation emitted by the at least one surface region or of the radiation reflected from the at least one surface region of the test specimen is graphically displayed.

15. The method according to claim 10, characterized in that a frequency at which the at least one surface region is irradiated by the radiation source, preferably heated, to determine properties of single layers of a multilayer coating changes in time or is a superposition of several discrete frequencies.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Embodiments of the invention are to be explained in more detail below on the basis of examples with reference to the non-limiting figures. It is shown:

[0047] FIG. 1 an embodiment of an apparatus according to the invention,

[0048] FIG. 2 a further embodiment of an apparatus according to the invention,

[0049] FIG. 3A a third embodiment of an apparatus according to the invention,

[0050] FIG. 3B a control signal (15b) is generated from superposition of four frequencies f1 to f4,

[0051] FIG. 3C a phase shift d can be determined as a function of frequency,

[0052] FIG. 4 a fourth embodiment of an apparatus according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] An apparatus (1) shown schematically in FIG. 1a comprises a controllable radiation source (2) having light-emitting diodes for irradiating (3) a surface region (4) of a test specimen (5) which comprises a substrate (7) covered with a layer (6), a bolometer camera (8) for detecting thermal radiation (9) emitted by the surface region (4), a multi-channel lock-in amplifier (10) for amplifying a measurement signal (12) detected by the bolometer camera (8) in each pixel (11), and an evaluation device (13) which is configured to determine a layer thickness distribution in the surface region (4) and to display it graphically.

[0054] The apparatus (1) further comprises an AC voltage source (14) provided for intensity-modulated control (15) of the radiation source (2) and for supplying a reference signal (16) to the lock-in amplifier (10). In this embodiment, the reference signal (16) and the control signal (15) are identical and sinusoidal. Furthermore, the reference signal is the same for each pixel (11) of the bolometer camera (8) because the surface region (3) is uniformly irradiated by the radiation source (2).

[0055] Visible light (3) emitted from the radiation source (2) and intensity-modulated by the AC voltage source (14) passes through a lens (17) onto a beam splitter (18) and is directed toward the surface region (4) of the test specimen (5), heating the surface region (4) and emitting thermal radiation (9). The thermal radiation passes through the beam splitter (18) and a lens (19) and is detected by the bolometer camera (8), which in this embodiment has 1920×1080 pixels (11) arranged in a matrix. Each pixel is designed as a bolometric detector and is connected to an input channel of the multi-channel lock-in amplifier (10).

[0056] In each pixel (11) of the bolometer camera (8), a measurement signal (12) is generated, said measurement signal is correlated with the reference signal by the multi-channel lock-in amplifier (10) to determine both an amplitude I.sub.D of the measurement signal and its phase shift d with respect to the reference signal for each pixel (11).

[0057] A determination of an amplitude I.sub.D as well as the phase shift d by a Fourier transformation is conceivable.

[0058] The evaluation device (13) outputs a two-dimensional amplitude distribution I.sub.D (x,y) (20) and a spatial distribution of the phase shift d (x,y) (21) as a false-color or grayscale representation on a display screen not shown in FIG. 1.

[0059] If a thickness of the layer (6) is for example homogeneous in the surface region (3), a phase shift d (x,y) is the same for each pixel (11).

[0060] Although not shown in FIG. 1, it is conceivable that a coating thickness distribution is graphically displayed on a display screen. For its determination, reference values for the amplitude I.sub.D of the measurement signal and its phase shift d are stored in the evaluation device.

[0061] It is also conceivable that the surface region (4) is intensity- and frequency-modulated excited, i.e. irradiated.

[0062] Reference is now made to FIG. 2, where identical or equal-acting parts are designated by the same reference number as in FIG. 1, and the letter a is added to the respective reference number.

[0063] An apparatus (1a) schematically shown in FIG. 2 for determining a paint layer thickness distribution on a motor vehicle body (5a) differs from that shown in FIG. 1 in that a controllable radiation source (2a) emits light (3a) which is modulated by a diffractive optical element (22) designed as a spatial light modulator (SLM) in such way that a surface region (4a) of the motor vehicle body (5a) is irradiated with adjacent, discrete lines (4b) and emitted thermal radiation (9a) is detected by a stationarily arranged bolometer camera (8a). A lock-in amplifier (10a) and an evaluation device (13a) are part of a computer (24) and are designed as software in this embodiment.

[0064] It is understood that a reference signal required for the lock-in amplifier (10a) is dependent on the control of the diffractive optical element (22).

[0065] The radiation source (2a) and the diffractive optical element (22) are attached to an industrial robot (25) and are movable in the direction of a double arrow (26). The motor vehicle body (5a) is also movable so that the stationarily arranged bolometer camera (8a) can detect a plurality of surface regions (4a) at different locations on the body (5a). It is conceivable that a frequency-, intensity- or spatially modulated irradiation (3a) is not performed by controlling a radiation source (2a), but by controlling the liquid crystal display (LCD). The radiation source (2a) can emit radiation continuously. Advantageously, inert radiation sources (2a) whose response time is longer than a required control time can be used.

[0066] A reference signal required for a lock-in amplifier (10a) in this case would be a control signal used to control the liquid crystal display.

[0067] Reference is now made to FIG. 3, where identical or equal-acting parts are designated by the same reference number as in FIGS. 1 and 2, and the letter b is added to the respective reference number.

[0068] An apparatus (1b) schematically shown in FIG. 3A is designed for determining a thickness of single layers (27-30) of a four-layer coating (6b) applied to a substrate (7b).

[0069] A radiation source (2b) is controlled by a multi-frequency method in which a control signal (15b) shown as an example in FIG. 3B is generated from superposition of four frequencies f1 to f4, where f1<f2<f3<f4.

[0070] By means of an evaluation device not shown in FIG. 3, a phase shift d shown in FIG. 3C can be determined as a function of frequency. By assigning a phase shift to one of the frequencies f1 to f4, the thickness of each of the layers (27-30) can be ascertained on the basis of reference curves.

[0071] Advantageously, the apparatus according to the invention and the method according to the invention enable a determination of thicknesses of individual layers of a multilayer coating with only one single measurement and a single apparatus.

[0072] Reference is now made to FIG. 4, where identical or equal-acting parts are designated by the same reference number as in FIGS. 1 to 3, and the letter b is added to the respective reference number.

[0073] An apparatus (1c) shown schematically in FIG. 4 differs from that shown in FIG. 2 in that radiation (31) reflected from a surface region (4c) is used to determine air inclusions in a paint layer (6c) of a painted motor vehicle body (5c).

[0074] It is understood that all combinations of features of the embodiments shown in FIGS. 1 to 4 are conceivable.