METHOD AND DEVICE FOR PREPARING A TENSILE TEST

Abstract

The invention relates to a method for preparing a tensile test on an elongate, more particularly fibrous, specimen, for example on a collagen fibril, comprising the steps of: -providing the elongate specimen; - attaching a handling particle to the elongate specimen; - providing a force sensor, on which a retainer for the handling particle on the elongate specimen is disposed; - connecting a handling apparatus to the handling particle on the elongate specimen; and - connecting the handling particle on the elongate specimen to the retainer on the force sensor by means of the handling apparatus. The invention also relates to a method and a device for performing a tensile test on an elongate specimen.

Claims

1. A method for preparing a tensile test on an elongated specimen, with the steps of: providing the elongated specimen, attaching a manipulating particle to the elongated specimen, providing a force sensor on which a retainer for the manipulating particle on the elongated specimen is arranged, manipulating the manipulating particle on the elongated specimen by means of a manipulating device and connecting the manipulating particle on the elongated specimen to the retainer on the force sensor with the aid of the manipulating device.

2. The method as claimed in claim 1, wherein the attachment of the manipulating particle to the elongated specimen comprises adhesion.

3. The method as claimed in claim 1, wherein the manipulating particle is guided by means of a magnetic force between the manipulating device and the manipulating particle.

4. The method as claimed in claim 3, wherein the manipulating device is a pair of magnetic tweezers, wherein the manipulating particle has a magnetisable material.

5. The method as claimed in claim 1, wherein a spherical element is provided as the manipulating particle.

6. The method as claimed in claim 1, wherein the force sensor has a cantilever on which the retainer for the manipulating particle on the elongated specimen is provided.

7. The method as claimed in claim 1, wherein the retainer has two prong elements with a recess between them, wherein the manipulating particle is placed on the prong elements and the specimen is guided through the recess between the prong elements.

8. The method as claimed in claim 7, wherein when it is in the state in which it is connected to the retainer, the manipulating particle is secured against slipping out of the retainer by means of prominences, in at free ends of the prong elements.

9. The method as claimed in claim 1, wherein a nanofibre or microfiber is provided as the specimen.

10. The method as claimed in claim 8, wherein the specimen is located in a liquid in the state in which the specimen is connected to the retainer.

11. A method for carrying out a tensile test on an elongated specimen, with the steps of: preparing the tensile test with the method as claimed in claim 1, carrying out the tensile test with the force sensor, wherein the specimen is stretched.

12. The method as claimed in claim 11, comprising recording a force-displacement diagram or force-time diagram when carrying out the tensile test with the force sensor.

13. The method as claimed in claim 11, wherein after carrying out the tensile test, the specimen is removed from the retainer on the force sensor with the aid of the manipulating device, wherein the specimen is fibrous.

14. A device for carrying out a tensile test on an elongated specimen, comprising: a force sensor with a retainer for connection to a manipulating particle on the elongated specimen.

15. The device as claimed in claim 14, wherein the manipulating particle on the elongated specimen is connected to the retainer of the force sensor.

16. The device as claimed in claim 14, wherein the retainer comprises two prong elements with a recess between them.

17. The device as claimed in claim 14 to 16, wherein the force sensor comprises a cantilever, wherein, an interferometer is provided for the detection of a bending state of the cantilever.

Description

[0043] The invention will now be described in more detail with the aid of a preferred exemplary embodiment which is illustrated in the drawings.

[0044] FIG. 1 shows a device in accordance with the invention for carrying out a tensile test on a fibrous specimen.

[0045] FIGS. 2 to 7 show the sequence for the tensile test.

[0046] FIG. 8 shows a top view and FIG. 9 shows a front view of a detail of the device of FIG. 1.

[0047] FIGS. 10 to 13 diagrammatically show the preparation of the fibrous specimen for the tensile test in accordance with FIGS. 2 to 7.

[0048] FIG. 14 shows a force-time diagram which was recorded during a tensile test on a bundle of collagen fibrils.

[0049] FIG. 15 shows a section of the force-time diagram of FIG. 14.

[0050] FIG. 1 diagrammatically shows a device 1 for carrying out a tensile test on a fibrous specimen 2, which is preferably a nanofibre or microfibre, in particular a fibril, for example a collagen fibril.

[0051] The device 1 comprises a force sensor 3 with a cantilever 4. A bending state, in this case a deflection, of the cantilever 4 can be detected with the aid of an interferometer 5. The force sensor 3 is connected to a positioning device 6 with which the force sensor 3 can be moved in all three directions in space, namely x, y, z. The positioning device serves for coarse positioning of the force sensor 3. Furthermore, an adjusting element 7, preferably a piezo element, for example a piezoelectric lever-amplified actuator, is provided, with which the force sensor is adjusted in order to carry out the tensile test, in this case backwards and forwards in the z direction. An output signal 8, in particular a force-displacement diagram or a force-time diagram, is generated from the signal from the adjusting element 7 and the interferometer 5. The tensile test is controlled via an input signal 9. In the embodiment shown, a control element 10 is additionally provided which forms a control signal 12 for the adjusting element 7 out of the input signal 9 and a feedback signal 11. In the embodiment shown, the force sensor 3 comprises a retainer 13 which — as will be described in detail below — is connected to the fibrous specimen 2 which is located in a liquid cell 15 filled with a liquid 14.

[0052] FIGS. 2 to 7 show the individual steps of the tensile test.

[0053] As can be seen in FIG. 2, the fibrous specimen 2 is arranged on an object holder 16 in the liquid cell 15. One end of the fibrous specimen 2 is fixed to the object holder 16 by means of an adhesive mass 17. The other end of the fibrous specimen 2 is provided with a manipulating particle 18 which is formed by a spherical element in the embodiment shown.

[0054] In the next step — FIG. 3 — a manipulating device 19 is connected to the manipulating particle 18 on the fibrous specimen 2. In the embodiment shown, the manipulating device 19 and the manipulating particle 18 are coupled together magnetically. To this end, the manipulating device 19 may be a pair of magnetic tweezers which, when switched on, (see the symbolic magnetic field lines 20 in FIG. 2), attracts a magnetisable material, in particular a neodymium alloy, of the manipulating particle 18.

[0055] In the next step — FIG. 4 — the manipulating particle 18 on the fibrous specimen 2 is connected to the retainer 13 of the force sensor 3 by moving the manipulating device 19.

[0056] In the next step — FIG. 5 — the manipulating device 19 can be removed and the tensile test can be carried out. To this end, the adjusting element 7 can move the force sensor 3 with the cantilever 4 in accordance with the input signal 9. Because the manipulating particle 18 on the fibrous specimen 2 is connected to the retainer 13 of the force sensor 3, the fibrous specimen 2 is stretched by the movement of the force sensor 3, so that a force is exerted on the cantilever 4 of the force sensor 3. As described above, the deflection of the cantilever 4 is detected by interferometry in order to determine the force and stretching behaviour of the fibrous specimen 2.

[0057] As indicated in FIG. 6, the tensile test may be terminated by tearing failure of the fibrous specimen 2.

[0058] In the last step — FIG. 7 — the manipulating particle 18 with a portion of the fibrous specimen 2 can be removed from the retainer 13 of the force sensor 3 with the aid of the manipulating device 19. Thus, the device 1 is ready for the next tensile test.

[0059] FIGS. 8 and 9 show in detail the connection of the manipulating particle 18 on the fibrous specimen 2 to the retainer 13 of the force sensor 3. Accordingly, the retainer 13 comprises two prong elements 21 between which a recess 22 is formed. The manipulating particle 18 is placed on the prong elements 21, whereas the fibrous specimen 2 is guided through the recess 22 between the prong elements. Prominences 23 are formed on the free ends of the prong elements 21, these prominences 23 secure the manipulating particle 18 against slipping out of the retainer 13.

[0060] FIGS. 10 to 13 illustrate the preparation of the fibrous specimen for the tensile test in accordance with FIGS. 2 to 7. In this regard, a manipulating particle 18 from a reservoir of manipulating particles 18 is provided with adhesive 17, in particular epoxy adhesive (FIG. 10), picked up with the manipulating device 19 (FIG. 11) and adhered to one end of the fibrous specimen 2 (FIG. 12), whereas the other end of the fibrous specimen 2 is disposed on the object holder 16 with adhesive 17. After the adhesive has cured, the end of the fibrous specimen which is adhered to the manipulating particle 18 is preferably released from the object holder with a fine needle-shaped tip. Finally, the fibrous specimen 2 with the manipulating particle 18 is ready for the tensile test (FIG. 13).

[0061] FIG. 14 shows a force-time diagram which was recorded with the device 1 described above during the tensile test on a collagen fibril bundle. According to this, the force due to the stretching of the collagen fibrils on the retainer 13 of the force sensor 3 is measured as the force sensor 3 is moved over the specified distances with the aid of the adjusting element 7. In the example shown, the collagen fibril bundle is stretched multiple times by different distances. On the far right, tearing of the collagen fibril during the final stretching is shown. FIG. 15 shows a section of the force-time diagram. It can be seen from the curves that the mechanical behaviour of the collagen fibrils deviate from elastic deformation which obeys Hook’s Law. Both viscoelastic and viscoplastic behaviour can be detected with the present test device.