Method for analyzing a scratch test
A method for analyzing a scratch from a scratch test includes (a) locating the beginning of the scratch relative to a reference position, (b) making the scratch on a bulk with an indenter while recording the applied force and at least one measurement parameter, as a function of the displacement of the indenter relative to the reference position, (c) acquiring and recording images of the scratch relative to the reference position, (d) synchronizing the recorded images, the applied force and the measurement parameter, as a function of the displacement of the indenter, (e) displaying curves of the applied force and of the measurement parameter as a function of the displacement of the indenter, and (f) displaying in a synchronized way an image of the scratch reconstructed from the recorded images.
1. A method for analyzing a scratch from a scratch test, implementing a digital image acquisition device provided with a high magnification objective able to shoot only a part of the scratch, a bulk and an indenter for applying a force on the bulk, said method comprising the following steps:
determining the position of the beginning of the scratch relatively to a reference position,
making the scratch on the bulk by means of the indenter by recording the applied force and at least one measurement parameter, as a function of the displacement of the indenter on the bulk relatively to the reference position,
acquiring and recording a set of images of the whole of the significant portion of the scratch, each image corresponding to a magnified zone of the scratch, the position on the scratch of each recorded images being determined relatively to the reference position,
synchronization of the recorded images, of the applied force and of the measurement parameter, as a function of the displacement of the indenter, and
displaying the curves of the applied force and of the measurement parameter as a function of the displacement of the indenter, and displaying in a synchronized way with the applied force and with the measurement parameter a panoramic image of the significant portion of the scratch, reconstructed from the recorded images.
2. The method according to claim 1 , wherein it begins with a calibration step comprising a step for determining the size of a pixel, with which a correspondence between a pixel of the digital image acquisition device and its corresponding actual dimension at the bulk may be established.
3. The method according to claim 2 , wherein the calibration step also comprises a step for determining the field of the image acquisition device.
4. The method according to claim 3 , wherein after each shot, the objective and the scratch are displaced with reference to each other, by a fraction of the field of said image acquisition device, two consecutive images being positioned with reference to each other by intercorrelation.
5. The method according to claim 2 , wherein the image acquisition device comprises several objectives, the calibration step being applied to each of the objectives.
6. The method according to claim 1 , wherein it comprises, consecutively to the step for determining the position of the beginning of the scratch and before making the scratch, a step for measuring and recording the altitude of the bulk carried out by moving the image acquisition device with reference to the area of the bulk where the scratch will be made.
7. The method according to claim 6 , wherein the recorded altitude of the bulk is used during the step for acquiring images of the scratch in order to optimize the adjustment of the image acquisition device.
8. The method according to claim 7 wherein the acquisition device comprises an objective, wherein during the step for acquiring and recording images, the bulk is placed at a distance d of the objective, d being defined as follows: d=d 0 +hi+pi
wherein d 0 is the optimum initial distance between the bulk and the objective, hi is the altitude of the bulk in a given position, and pi is the depth of the scratch in a given position, defined by the vertical position of the indenter.
9. The method according to claim 8 , wherein, for a given position of the scratch, said device is controlled in order to take a series of images, at variable distances between the bulk and the objective, as long as d>d 0 +hi, the images of the series being processed so as to reconstruct a final image of the scratch at said given position.
10. The method according to claim 9 , wherein after each shot, the objective and the scratch are displaced with reference to each other, by a fraction of the field of said image acquisition device, two consecutive images being positioned with reference to each other by intercorrelation.
11. The method according to claim 8 , wherein after each shot, the objective and the scratch are displaced with reference to each other, by a fraction of the field of said image acquisition device, two consecutive images being positioned with reference to each other by intercorrelation.
12. The method according to claim 7 , wherein after each shot, the objective and the scratch are displaced with reference to each other, by a fraction of the field of said image acquisition device, two consecutive images being positioned with reference to each other by intercorrelation.
13. The method according to claim 6 , wherein after each shot, the objective and the scratch are displaced with reference to each other, by a fraction of the field of said image acquisition device, two consecutive images being positioned with reference to each other by intercorrelation.
14. The method according to claim 1 , wherein the reference position is the beginning of the scratch.