DE102019113120A1 - Method and device for determining a mechanical characteristic value - Google Patents

Abstract

The invention relates to a method for determining at least one mechanical material parameter of a shear-loaded bond of a test body which has a first test body element and at least one second test body element which are bonded to one another in a joining section, the method comprising the following steps: Manufacture at least one Test specimen, in which two test specimen halves are glued together to form a test specimen blank to form an adhesive layer, - the test specimen elements of the test specimen being milled out of the test specimen blank in such a way that the two test specimen elements are only connected to one another via part of the previously formed adhesive layer as a joining section, and - wherein a test weight is attached to the first test body element centric to the plane of the adhesive layer, - arranging the at least one test body produced with the second test body element on the rotor of the test centrifuge so that the centrifuge ugal force when rotating the rotor causes a shear load in the plane of the adhesive layer on the adhesive layer in the joining section between the first test body element and the second test body element.

Description

The invention relates to a method for determining at least one mechanical material parameter of a shear-loaded bond of a test body which has a first test body element and at least one second test body element which are bonded to one another in a joining section. The invention also relates to a device for this purpose.

To determine mechanical material parameters, such as the modulus of elasticity, the shear modulus, the strength limits and / or their elongation at break, material testing machines are usually used, which load a material sample (also called test specimen) supplied to it with a corresponding force until the material of the test specimen fails. In this way it can be deduced for a certain material at which force acting on it a material failure is to be expected. If the deformation of the material sample is also determined during the application of the force, which is usually continuously increased, then, in general terms, corresponding force-displacement curves can be derived, which then serve as the basis for stress and strain curves for the material used Material sample can be used.

Such material testing machines are usually complex, large systems that can only be operated by professionally qualified personnel. In each test run, which consists of clamping the sample, initializing the measurement technology and setting the software, as well as applying the corresponding test force to the test body, only one test body can be tested at a time. This has the consequence that the testing is very time-consuming and therefore very cost-intensive.

For this reason, test centrifuges have been developed in which the force on a sample body is exerted on the body by means of a centrifugal force generated by a rotor. Contact switches can be used to detect the rotational speed at which a material failure occurs. On the basis of the speed of rotation and the distance from the axis of rotation of the rotor of the test centrifuge, it is then also possible to determine the force which acted on the test specimen during the material failure. Such a test centrifuge and a method corresponding to it is, for example, from DE 10 2004 055 621 A1 as WO 2017 168 003 A1 known.

With the help of such test centrifuges it is possible to examine more than one specimen at the same time, so that several material samples can be examined at the same time in one test run. This can reduce the time required for each test specimen and the costs per test run.

From the post-published DE 10 2018 121 222.4 Furthermore, an improved test centrifuge is known in which not only the material failure can be detected with the aid of a corresponding sensor, but also stress-strain curves can be determined in order to be able to map a non-linear material behavior accordingly.

With the help of such test centrifuges, however, bonds or adhesive materials can only be examined with regard to a head tensile load in which the adhesive layer of the adhesive material to be examined is orthogonal to the plane of rotation and orthogonal to the direction of the centrifugal force. The entire adhesive layer is accordingly subjected to tensile stress in the area in that a force is exerted on the test body which is intended to pull the adhesive apart. To examine a bond with the help of a test body in such a way that the bond is subjected to shear loads is again provided and can still be implemented with currently available test bodies.

It is therefore the object of the present invention to provide an improved method and an improved device for determining a mechanical material parameter, in which the bond of the test body to be examined can be subjected to thrust by means of a test centrifuge.

The object is achieved according to the invention with the method according to claim 1 and the device according to claim 8. Advantageous embodiments of the invention can be found in the corresponding subclaims.

According to claim 1, a method is proposed for determining at least one mechanical material characteristic of a shear-loaded bond of a test body, the test body having a first test body element and at least one second test body element which are bonded to one another in a joining section. A force is to be applied to the test specimen, which loads the bond in the joining sections in shear. This is achieved in that the force acting on the bond in the joining section acts in the plane of the adhesive layer and does not act orthogonally to the plane of the adhesive layer as in the case of a head tensile load.

First, according to the invention, a test centrifuge is provided which has a rotor on which one or more test bodies can be arranged at a certain distance from the axis of rotation of the rotor, so that by rotating the rotor a centrifugal force acting radially outward can be applied to the test body. The test centrifuge can, for example, be a table centrifuge.

The test centrifuge can have a rotor which is designed in the form of a drum rotor. In the case of a drum rotor, the test specimens are arranged on an inside of the rotor that points in the direction of the axis of rotation.

Furthermore, it is proposed according to the invention that at least one test body is produced by gluing two test body halves to one another to form a test body blank, forming an adhesive layer. Part of this adhesive layer forms the bond to be tested later in the corresponding joint section. For this purpose, the test body elements of the test body are milled out of the test body blank in such a way that the two test body elements are only connected to one another via part of the previously formed adhesive layer. This can be achieved, for example, by milling recesses from the first test body halves in the direction of the adhesive layer and then milling corresponding recesses from the second test body halves in the direction of the adhesive layer, so that two independent test body elements are then produced from the test body blank, which only have one Part of the previously formed adhesive layer are connected to one another. This part of the adhesive layer, via which the two test body elements are adhesively connected to one another, is then later to be subjected to shear loads using the test centrifuge.

In a further step, a test weight is attached to the test body with its two test body elements produced in this way on the first test body element centric to the plane of the adhesive layer in order to load the adhesive layer in the joint section between the two test body elements by turning the rotor on thrust, i.e. H. in the direction within the plane of the adhesive layer.

The test body (s) produced in this way are now arranged with their respective second test body elements on the rotor of the test centrifuge in such a way that the centrifugal force when the rotor rotates causes a shear load in the adhesive layer plane on the adhesive layer in the joint section between the first test body element and the second test body element.

The final step of the test run can then be completed by turning the rotor of the test centrifuge and thereby determining the mechanical material value of the shear-loaded bond of the adhesive layer in the joint section between the test body elements. The determination of the mechanical material parameter based on the test run by means of the test centrifuge can take place as known from the prior art.

With the aid of the method according to the invention, it is thus possible, using a test centrifuge, to determine a mechanical material characteristic of a shear-loaded bond of a test body, the test body being very simple and always reproducible to produce. In particular, the bond in the joining section between the two test body elements can be produced reliably and reproducibly due to the production of the test body from two test body halves. A test piece blank, which was glued together from two test piece halves, can be used to produce a large number of test pieces, depending on the size of the test piece halves, with each test piece having a defined bond in the joint section. The test specimen produced in this way only has one degree of freedom, namely the thickness of the adhesive layer. This can be set easily and precisely, for example, with spacer elements (also called spacer wires).

According to one embodiment it is provided that the test body is produced from two test body halves made of a fiber composite material which has a fiber material and a matrix material that embeds the fiber material. This means that bonds between two fiber composite components can be examined for shear loads. The test body halves are preferably already made from the fiber composite material.

According to a further embodiment it is provided that the test weight is glued to the first test body element by means of an adhesive material. The adhesive material used here is preferably such that it withstands higher mechanical loads than the adhesive material of the adhesive layer in the joining section, which is to be examined.

The gluing of the test weight is particularly advantageous in connection with the aforementioned fiber composite material as a material for the test specimen, since a mechanical connection (non-positive, positive) of the test weight to the test specimen can usually be excluded. In particular, no threads or other mechanical fastening means can be integrated into the fiber composite material in such a way that it can withstand the loads for the purpose of testing.

According to one embodiment, the test weight is applied centrally in relation to the plane of the adhesive layer using a centering aid glued to the first test body element by means of the adhesive material. Such a centering aid can, for example, be a test body sleeve that is often used, as will be shown later. With the help of the centering aid, the test weight is arranged centrally in relation to the plane of the adhesive layer, so that the occurrence of undesirable disruptive forces outside the desired shear load is minimized or eliminated.

According to one embodiment, the test body is arranged on the rotor of the test centrifuge by arranging the second test body element on a second end of a test body sleeve and the test body sleeve with an opposite first end on the rotor. The test weight is usually received in an interior of the test body sleeve. Due to the test body sleeve, the test body is arranged at a distance from the inner wall of the drum rotor in the direction of the rotor axis, particularly in the case of a drum rotor, so that the test weight is aligned in the direction of the drum rotor.

It is particularly advantageous if on one side of the second test body element of the test body, which is defined orthogonally to the plane of the adhesive layer and orthogonally to the direction of the centrifugal force, a recess (annular groove) is milled into the second test body element, in which the test body sleeve is used positively. A part of the first test body element including the test weight arranged on the first test body element preferably protrudes into the interior of the test body sleeve and thus represents a defined distance from the rotor. The milled recess is in particular aligned centrally with the adhesive layer in the joining section, so that the test body sleeve also is arranged correspondingly centrally to the adhesive layer in the joining section on the second test body element.

In this context, it is particularly advantageous if the second end of the test body sleeve is positively inserted into the recess and the test weight is pushed from the first end into the test body sleeve, the first test body element being glued to the test weight in the test body sleeve. In this way it can be ensured, even for untrained personnel, that the test weight is always attached to the first test body element centrally to the adhesive layer in the joining section and with a predetermined adhesive layer thickness. This is because the centric alignment of the test body sleeve with respect to the adhesive layer in the joint section of the test body and the precisely fitting insertion of the test weight into the test body sleeve ensure that the test weight is always attached centrally to the first test body element.

• - eine Prüfzentrifuge mit einem Rotor, an dem ein oder mehrere Prüfkörper in einem gewissen Abstand zu der Rotationsachse des Rotors angeordnet sind, so dass durch Drehen des Rotors eine radial nach außen wirkende Zentrifugalkraft auf den Prüfkörper aufbringbar ist,
• - mindestens einen Prüfkörper, der hergestellt ist, indem zwei Prüfkörperhälften unter Bildung einer Klebschicht zu einem Prüfkörperrohling miteinander verklebt werden und anschließend die Prüfkörperelemente des Prüfkörpers aus dem Prüfkörperrohling derart herausgefräst werden, dass die beiden Prüfkörperelemente lediglich über die einen Teil der zuvor gebildeten Klebschicht als Fügeabschnitt miteinander verbunden sind,
• - wobei ein Prüfgewicht an dem ersten Prüfkörperelement zentrisch zu der Ebene der Klebschicht befestigt ist, und
• - wobei der Prüfkörper mit dem zweiten Prüfkörperelement an dem Rotor der Prüfzentrifuge so angeordnet ist, dass die Zentrifugalkraft beim Drehen der Prüfzentrifuge eine Schubbelastung in der Klebschichtebene auf die Klebschicht im Fügeabschnitt zwischen dem ersten Prüfkörperelement und dem zweiten Prüfkörperelement bewirkt.

The object is also achieved according to the invention with the device for determining at least one mechanical material characteristic value of a shear-loaded bond according to claim 8, the device having:

• - a test centrifuge with a rotor on which one or more test bodies are arranged at a certain distance from the axis of rotation of the rotor so that a centrifugal force acting radially outward can be applied to the test body by rotating the rotor,
• - At least one test body which is produced by gluing two test body halves together to form a test body blank to form an adhesive layer and then the test body elements of the test body are milled out of the test body blank in such a way that the two test body elements are only a part of the previously formed adhesive layer as a joining section are connected to each other,
• - wherein a test weight is attached to the first test body element centrally to the plane of the adhesive layer, and
• - The test body with the second test body element on the rotor of the test centrifuge is arranged in such a way that the centrifugal force when the test centrifuge rotates causes a shear load in the plane of the adhesive layer on the adhesive layer in the joint section between the first test body element and the second test body element.

Advantageous configurations of the device can be found in the corresponding subclaims.

• 1 perspektivische Darstellung des Prüfkörpers mit Prüfgewicht;
• 2 Seitenansicht des Prüfkörpers mit Prüfgewicht;
• 3 Darstellung des Prüfkörpers in einer Draufsicht;
• 4 Darstellung des Prüfkörpers in einer Frontansicht;
• 5 Darstellung des Prüfkörpers in einer Ansicht von unten.

The invention is explained in greater detail using the attached figures. Show it:

• 1 perspective view of the test body with test weight;
• 2 Side view of the test body with test weight;
• 3 Representation of the test body in a top view;
• 4th Representation of the test body in a front view;
• 5 Representation of the test body in a view from below.

1 and 2 show the test specimen according to the invention 10 on which the test weight 20th and the test body sleeve 30th are arranged accordingly. The test specimen according to the invention 10 is produced by gluing two test body halves (not shown) and then machining them. The one when gluing the adhesive layer formed on both test body halves 13 is on the entire test body 10 recognizable.

After the two test body halves have been glued together, the two test body elements become 11 and 12 milled out, as shown later. The two test body elements 11 and 12 are then only through the part of the adhesive layer 13 connected to the joining section 14th between the first test body element 11 and the second test body element 12 forms. Only over this joint section 14th is the first specimen element 11 with the second test body element 12 Cohesively or adhesively connected via the adhesive layer.

This joining section 14th and its part of the adhesive layer 13 is to be loaded with the help of a test centrifuge (not shown) on thrust, ie with a force within the plane of the adhesive layer 13 .

This is done on one face 15th of the first test body element 11 a screw adapter via an adhesive connection 17th glued, the adhesive bond 17th withstands higher loads, in particular tensile loads, than the adhesive layer to be tested 13 in the joining section 14th .

To this screw adapter 16 , the one at the front 15th of the first test body element 11 with an adhesive connection 17th is glued on, the test weight is now 20th screwed to the test weight 20th with the first test body element 11 of the test body 10 to be able to connect firmly.

A test body sleeve is also used as a spacer element and centering aid 30th used that in the manner of a snug fit in a recess 18th of the second test body element 12 is used. This depression 18th is when the first test body element is milled out 11 and the second test body element 12 produced from the glued test body halves. The depression 18th is centered around the adhesive layer 13 produced so that the test body sleeve 30th also centric to the adhesive layer 13 can be used.

When joining test weights 20th and test specimen 10 is now the test body sleeve 30th into the recess 18th used, due to the central production of the recess 18th also the test body sleeve 30th centric to the adhesive layer 13 is arranged. The test body sleeve 30th is therefore based on a second end 32 on the second test body element 12 and is form-fitting in the recess 18th recorded.

Then from the opposite first end 31 the test body sleeve 30th the test weight 20th including the screw adapter already screwed in 16 and an applied adhesive material in the test body sleeve 30th towards the second end 32 pushed in until the applied adhesive material hits the front 15th of the first test body element 11 contacted.

In this way it can be ensured, even for inexperienced personnel, that the test weight 20th always centric to the adhesive layer 13 is arranged because the test body sleeve 30th also represents a centering aid. Incorrect test runs due to incorrect arrangement of the test weight 20th can thus be avoided.

The test body 10 with the test weight 20th the test body sleeve 30th is now used in a test centrifuge, not shown, by the test body sleeve 30th with their first end 31 is used in a recording of a rotor of the test centrifuge.

Such a rotor, also called a drum rotor, is for example from the US 2014 371 047 A1 known. A receptacle for such a drum rotor is for example in the DE 10 2004 055 621 A1 shown. The test body sleeve 30th is attached to the inside of the drum rotor with its first end 31 inserted so that over the test body sleeve 30th the second test body element 12 is connected to the rotor.

By rotating the drum rotor, a centrifugal force is now applied in the direction of the arrow Fz shown on the test weight and the first test body element that has been glued on 11 exercised, creating the adhesive layer 13 in the joining section 14th is loaded on thrust.

The 3 to 5 show a representation of the test body 10 in a top view ( 3 ), in a front view ( 4th ) and in a view from below ( 5 ). The orientation results from the representation in 1 and 2 .

3 shows the test specimen 10 in a top view. To make the test body from the two glued test body halves 10 with his first test body element 11 and its second test body element 12 Milling out must be from the first half of the specimen in the direction of the adhesive layer 13 as well as from the second test body half in the direction of the adhesive layer 13 Channels or gaps or free spaces are milled in to ensure that the first test body element 11 with the second test body element 12 only over the adhesive layer 13 in the joining section 14th connected is.

In top view in 3 therefore becomes a channel 40 Milled into the upper half of the specimen around the first specimen element 11 from the second test body element 12 to separate. In relation to the first and upper half of the test body are the two test body elements 11 and 12 now no longer connected except via the joining section 14th . The same applies to the second half of the test specimen ( 5 ), in which also up to the adhesive layer 13 a channel 41 is milled, so does this connection of the first test body element 11 and the second test body element 12 to separate. After the channels 40 and 41 are milled into it is the first specimen element 11 and the second specimen element 12 only over the adhesive layer 13 in the joining section 14th connected to each other so that by a tensile load in the plane of the adhesive layer 13 just just the adhesive layer 13 in the joining section 14th is loaded on thrust. The remaining parts of the adhesive layer 13 are now part of the respective test body element 11 and 12 and are not subjected to thrust.

As in 4th shown is a depression 18th into the second test body element 12 centric to the adhesive layer 13 milled in so that the test body sleeve can be positively received. Because the recess 18th both in the first test body half and the second test body half of the second test body element 12 has been milled into it, the test body sleeve is supported 30th with their second end 32 at the bottom of the depression 18th also on both halves of the test specimen, so that the adhesive layer 13 between the first test body half and the second test body half of the second test body element 12 is not loaded on thrust.

Furthermore, the face is 15th of the first test body element 11 formed both by the first test body half and the second test body half, so that the test weight 20th on both the first half of the test body and the second half of the test body on the end face 15th is glued. This also creates the adhesive layer 13 of the first test body element 11 not loaded on thrust.

This arrangement only leaves the adhesive layer 13 in the joining section 14th , which is loaded in the direction shown by thrust with a corresponding centrifugal force Fz.

List of reference symbols

10

Test specimen

11

first test body element

12

second test body element

13th

Adhesive layer

14th

Joining section

15th

Front side of the first test body element

16

Screw adapter

17th

Adhesive connection

18th

Recess (receiving the test body sleeve)

20th

Test weight

30th

Test body sleeve

31

first end of the test body sleeve

32

second end of the test body sleeve

40

Milling channel

41

Milling channel

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102004055621 A1 [0004, 0038]
• WO 2017168003 A1 [0004]
• DE 102018121222 [0006]
• US 2014371047 A1 [0038]

Claims (13)

A method for determining at least one mechanical material parameter of a shear-loaded bond of a test body (10) which has a first test body element (11) and at least one second test body element (12) which are glued to one another in a joining section (14), the method being the includes the following steps: - Provision of a test centrifuge with a rotor on which one or more test bodies (10) can be arranged at a certain distance from the axis of rotation of the rotor so that a centrifugal force acting radially outward can be applied to the test body (10) by rotating the rotor , - Production of at least one test body (10) by gluing two test body halves together to form a test body blank, forming an adhesive layer (13), - The test body elements (11, 12) of the test body (10) being milled out of the test body blank in such a way that the two test body elements (11, 12) are connected to one another as a joining section (14) only via part of the previously formed adhesive layer (13), and - wherein a test weight (20) is attached to the first test body element (11) centrally to the plane of the adhesive layer (13), - Arranging the at least one test body (10) produced with the second test body element (12) on the rotor of the test centrifuge so that the centrifugal force when the rotor rotates creates a shear load in the adhesive layer plane on the adhesive layer (13) in the joining section (14) between the first Test body element (11) and the second test body element (12) causes, and - Rotating the rotor of the test centrifuge and determining the mechanical material characteristic of the shear-loaded bond of the adhesive layer (13) in the joining section (14) between the test body elements (11, 12). Procedure according to Claim 1 , characterized in that the test body (10) is made from two test body halves made of a fiber composite material which has a fiber material and a matrix material embedding the fiber material. Method according to one of the Claims 1 or 2 , characterized in that the test weight (20) is glued to the first test body element (11) by means of an adhesive material. Procedure according to Claim 3 , characterized in that, using a centering aid, the test weight (20) is glued centrally in relation to the plane of the adhesive layer (13) to the first test body element (11) by means of the adhesive material. Method according to one of the preceding claims, characterized in that the test body (10) is arranged on the rotor of the test centrifuge by the second test body element (12) at a second end (32) of a test body sleeve (30) and the test body sleeve (30) with an opposite first end (31) is arranged on the rotor. Procedure according to Claim 5 , characterized in that on one side of the second test body element (12) which is defined orthogonally to the plane of the adhesive layer (13) and the direction of the centrifugal force, a recess (18) is milled into the second test body element (12) into which the test body sleeve (30) is inserted positively. Procedure according to the Claims 3 to 6th , characterized in that the test body sleeve (30) is inserted with the second end (32) into the recess (18) with a positive fit and the test weight (20) is pushed from the first end (31) into the test body sleeve (30), in the test body sleeve (30), the first test body element (11) is glued to the test weight (20). Device for determining at least one mechanical material parameter of a shear-loaded bond of at least one test body (10) which has a first test body element (11) and at least one second test body element (12) which are glued together in a joining section (14), the device having: - a test centrifuge with a rotor on which one or more test bodies (10) are arranged at a certain distance from the axis of rotation of the rotor, so that a centrifugal force acting radially outward can be applied to the test body (10) by rotating the rotor, - At least one test body (10) which is produced by two test body halves being glued together to form a test body blank to form an adhesive layer (13) and then the test body elements (11, 12) of the test body (10) are milled out of the test body blank in such a way that the two test body elements (11, 12) are only connected to one another via part of the previously formed adhesive layer (13) as a joining section (14), - wherein a test weight (20) is attached to the first test body element (11) centrally to the plane of the adhesive layer (13), and - The test body (10) with the second test body element (12) being arranged on the rotor of the test centrifuge in such a way that the centrifugal force when the test centrifuge rotates creates a shear load in the adhesive layer plane on the adhesive layer (13) in the joining section (14) between the first test body element (11) and the second test body element (12) causes. Device according to Claim 8 , characterized in that the test body (10) is made from two test body halves made of a fiber composite material which has a fiber material and a matrix material which embeds the fiber material. Device according to Claim 8 or 9 , characterized in that the test weight (20) is glued to the first test body element (11) by means of an adhesive material. Device according to one of the Claims 8 to 10 , characterized in that a test body sleeve (30) is provided, which is arranged with a first end (31) on the rotor and with an opposite second end (32) on the second test body element (12) of the test body (10). Device according to Claim 11 , characterized in that on one side of the second test body element (12) which is defined orthogonally to the plane of the adhesive layer (13) and the direction of the centrifugal force, a recess (18) is provided in the second test body element (12) into which the test body sleeve (30) is inserted positively. Device according to Claim 11 or 12 , characterized in that the first test body element (11) is at least partially and / or the test weight (20) is at least partially received in the interior of the test body sleeve (30).

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