DE102019001226A1 - Device for vibrational excitation of a specimen - Google Patents

Abstract

The invention relates to a device (2) for vibrational excitation of a test specimen (3), comprising a sample connection unit (4) for receiving the specimen (3) and a linear guide arrangement (5) for guiding the specimen connection unit (4) parallel to an excitation direction (AR).
According to the invention, the sample connection unit (4) is arranged on a guide part (6) which is arranged at a distance therefrom by means of two spring elements (7) on a holding structure (8), wherein the spring elements (7) are designed such that the guide part (6) in the radial direction via the spring elements (7) is fixedly fixed to the support structure (8) and parallel to the excitation direction (AR) is elastically movable.

Description

The invention relates to a device for vibrational excitation of a specimen according to the features of the preamble of claim 1.

From the prior art, as in the DE 10 2014 103 299 A1 described a vibration exciter with load compensation for the dynamic excitation of specimens known. The vibration exciter with load compensation comprises a base, an actuator, a valve movable in a direction of excitation relative to the base and guided by a linear guide means parallel to the excitation armature and a weight of at least the fitting and the specimen to be excited compensating pneumatic Lastkompensationsmittel. The linear guide means comprises an air bearing, wherein the load compensation means comprises the linear guide means.

In the EP 1 577 659 B1 describe a method and a device for determining the resistance of sheet metal against bending with alternating loading direction. The device, by means of which a bending test formed from at least one sheet metal strip is fixed at both ends in clamping and deformable by relative displacement of the clamping, comprises means for detecting measured values to produce the corresponding force-displacement curve and a computer for simulating the deformation with a suitable program, so that the material parameters used can be assessed on the basis of the agreement of the measured and calculated force-displacement curve. The device further comprises a symmetrical bending test of two identical, parallel and spaced sheet metal strips whose ends are each non-rotatably clamped in rigidly interconnected and clamped only by the metal strips clamping devices, and two spaced opposite each other and longitudinally between the ends of the Sheet metal strip arranged further clamping devices, in each of which one of the sheet metal strips is clamped longitudinally and which are each rigidly connected to perpendicular to the sheet metal strip surface and relative to each other cyclically movable brackets. The application of the deformation in the four free sheet metal sections is given exclusively by axial displacement of the longitudinal center clamping relative to each other. Due to the symmetry, the bending moments in the sheet metal strips compensate each other so that the holding torques and lateral holding forces to be absorbed by the holders of the bending sample only occur due to deviations in the sample symmetry and are therefore small. The device also comprises a device for measuring the force and displacement of the sheet metal strips and their displacement for generating the force-displacement curve of the bending sample and provided independently of the bending sample computer for simulating the bending test and calculating the parameters of the force-displacement curve for only 1/8 of the bending test, which can be calibrated by the computer with the parameters of the measured force-displacement curve entered for determining improved material parameters.

The invention is based on the object to provide a comparison with the prior art improved device for vibrational excitation of a specimen.

The object is achieved by a device for vibrational excitation of a specimen with the features of claim 1.

Advantageous embodiments of the invention are the subject of the dependent claims.

A device for vibrational excitation of a test specimen comprises a specimen connection unit for receiving the specimen and a linear guide arrangement for guiding the specimen connection unit parallel to an excitation direction.

According to the sample connection unit is arranged on a guide member which is arranged by means of two spring elements on a support structure spaced therefrom, wherein the spring elements are formed such that the guide member is fixed in the radial direction via the spring elements fixed to the support structure and parallel to the excitation direction is elastically movable ,

By means of the solution according to the invention specimens can be excited purely transversally over a wide frequency and temperature range, resulting in a guided Lamb wave (antisymmetric bending wave) forms in the specimen. Advantageously, in addition, a force for determining an evaluable transfer function can be measured.

Characterized in that the guide part over the two spring elements in the longitudinal direction, d. H. parallel to the excitation direction, is suspended elastically and at the same time in all transverse directions, d. H. is fixed radially to the support structure, the guide member is only able, in the longitudinal direction, d. H. parallel to the excitation direction to swing, while transverse forces from an excitation source are absorbed by the spring elements and derived to the support structure. As a result, only the transverse excitation of the test specimen takes place, as a result of which the guided Lamb wave (antisymmetric bending wave) forms in the specimen.

About the intermediate guide member with sample connection unit is a linear force transmission between an advantageously existing force sensor and / or impedance and the specimen, since a direct transfer takes place and no or only small, especially negligible, friction losses occur and attenuation is very low. In this case, losses occur due to a mass inertia of the guide part. However, these are constantly below the first resonance of the guide part. Thus, a lesser force, for example about 1/7 of the force, arrives at the test specimen than is measured at the force sensor and / or impedance sensor. However, this does not affect a measurement and evaluation process and the results.

The solution according to the invention thus makes possible, in particular, a clean, d. H. not or as little as possible affected by interference, measuring a pure uninfluenced bending vibration for accurate material characterization, which would not be evaluated by a superimposed transverse vibration. The inventive solution such superimposed transverse vibrations are avoided.

About the sample connection unit is advantageously a quick replacement of specimens possible.

Embodiments of the invention are explained in more detail below with reference to drawings.

Showing:

• 1 schematically a vibration testing device,
• 2 FIG. 2 schematically a partial sectional view of a device for vibrational excitation of a test specimen, FIG.
• 3 schematically an exploded view of the device 2 .
• 4 schematically a vibration of a connecting rod and transfer functions,
• 5 schematically a transfer function frequency coordinate system, and
• 6 schematically a diagram with memory module, loss modulus and dynamic modulus of elasticity.

Corresponding parts are provided in all figures with the same reference numerals.

1 shows a schematic representation of a vibration testing device 1 comprising a device 2 for vibration excitation of a test specimen 3 , 2 shows an embodiment of such a device 2 and 3 an exploded view of this embodiment of the device 2 ,

The device 2 for vibration excitation of the specimen 3 includes a sample attachment unit 4 for receiving the test specimen 3 and a linear guide arrangement 5 for guiding the sample connection unit 4 parallel to an excitation direction AR , The sample connection unit 4 is at a leadership part 6 , Also referred to as an intermediate part, arranged, which by means of two spring elements 7 on a support structure 8th is arranged spaced therefrom. The spring elements 7 are formed such that the guide part 6 in the radial direction over the spring elements 7 firmly on the support structure 8th is fixed and parallel to the excitation direction AR is elastically movable. The linear guide arrangement 5 is thus by this arrangement of the guide member 6 by means of the spring elements 7 at the support structure 8th educated.

The guide part 6 is thus on the two spring elements 7 in the longitudinal direction (axis direction), ie parallel to the excitation direction AR , In the example shown in the horizontal direction, elastically suspended and at the same time in all transverse directions, ie radially, firmly on the support structure 8th fixed. This is the guide part 6 only in the position, in the longitudinal direction, ie parallel to the excitation direction AR to swing while lateral forces from an in 1 shown excitation source 9 through the spring elements 7 picked up and attached to the support structure 8th be derived. As a result, only a transverse excitation of the specimen takes place 3 , resulting in a guided Lamb wave LW (antisymmetric bending wave) in the specimen 3 forms. Vibration-induced deflections of the specimen 3 are in 2 represented by dashed lines.

In the illustrated embodiment, the guide part 6 , which is formed for example as a cylinder, in particular as a metal cylinder, in a passage opening 10 the holding structure 8th from the support structure 8th arranged radially spaced. The spring elements 7 , which are each formed, for example, as a leaf spring or plate spring are in the illustrated embodiment, in each case at an opening end of the passage opening 10 on an outside of the support structure 8th arranged. Here are the spring elements 7 each in the region of a spring element outer circumference on the support structure 8th attached, for example, with the support structure 8th screwed, like out 3 visible, and in the region of a spring element inner circumference on the guide part 6 attached, for example by means of a holder 11 at the guide part 6 jammed and / or with the guide part 6 glued or otherwise with the guide part 6 connected.

To the swinging of the spring elements 7 and thus the leadership part 6 in the direction of excitation AR to allow, is only the area of the spring element outer circumference of the spring element 7 , with which the respective spring element 7 at the support structure 8th is attached to the support structure 8th on and the other areas of the respective spring element 7 , in particular the area of the spring element inner circumference, are from the outside of the holding structure 8th spaced. To achieve this, has the support structure 8th at its opposite and for fastening the spring elements 7 provided outer sides, for example, an inner recess and / or at least one outer edge side elevation 12 on, in the example according to 3 three outside edge elevations 12 on which the respective spring element 7 rests with its region of the spring element outer circumference and on the support structure 8th is attached.

The sample connection unit 4 is at one, in particular end-side, end of the guide part 6 arranged, for example, jammed. This is in 2 shown schematically simplified. In 3 this is shown in more detail. Here it can be seen that the sample connection unit 4 in the holder 11 is trapped and on this formed as an intermediate piece guide part 6 is arranged. The entire elastically mounted oscillating structure thus consists of the holder 11 for the sample connection unit 4 and the leadership part 6 and is advantageously a separate overall part. The test piece 3 is at the sample connection unit 4 , in particular radially to the excitation direction AR aligned, fastened, in particular glued, in the illustrated embodiment already attached thereto, in particular glued. About the sample connection unit 4 , in particular by the jamming of the sample connection unit 4 at the guide part 6 , is thus a quick replacement of specimens 3 possible.

One from the sample connection unit 4 opposite end of the guide part 6 is with the excitation source 9 connected to vibrational excitation. In the illustrated embodiment, this is done via a connecting rod 13 Also known as Stinger. The excitation source 9 , also referred to as shaker, is expediently an actuator.

Between that of the sample connection unit 4 opposite end of the guide part 6 and the connecting rod 13 is advantageously a force sensor and / or impedance sensor 14 arranged so that the sample connection unit 4 opposite end of the guide part 6 via the force sensor and / or impedance sensor 14 with the excitation source 9 is connected to vibrational excitation.

About the intermediary guide part 6 with sample connection unit 4 Thus, a linear force transmission between the force sensor and / or impedance sensor 14 and the specimen 3 , Since a direct transfer takes place and no or only small, in particular only negligible, friction losses occur and a damping is very low.

The solution described thus makes possible in particular a clean, d. H. not or as little as possible affected by interference, measuring a pure uninfluenced bending vibration for accurate material characterization, which would not be evaluated by a superimposed transverse vibration. By the described solution such superimposed transverse vibrations are avoided.

In this device 2 for vibration excitation of the specimen 3 thus becomes a stimulating force of the excitation source 9 over the connecting rod 13 to the force sensor and / or impedance sensor 14 passed. This metrologically detects a vibration-inducing force in the guide part 6 is initiated. The guide part 6 gives the initiated force on the example on the guide part 6 clamped sample connection unit 4 at the arranged thereon, for example, glued, specimen 3 and puts this in a pure bending vibration in the normal direction of the specimen 3 , The spring elements 7 in which the guide part 6 in the holding structure 8th is stored, prevent it from becoming an in 2 by crossed out arrows P shown bending of the guide part 6 from a natural vibration of the connecting rod 13 comes. Otherwise, the specimen would 3 no longer purely in the normal direction are excited and an evaluation of material data would be due to poor transfer functions UF not possible anymore.

4 shows in the upper part schematically in the device 2 for vibration excitation of the specimen 3 occurring vibration of the connecting rod 13 , The natural vibration of the connecting rod 13 becomes in the device described here 2 by means of the spring elements 7 compensated. In the middle range of 4 is a vibration diagram with an amplitude axis AA and a frequency axis FA shown, which has a bad transfer function UF shows, which results from the fact that the natural vibration of the connecting rod 13 is not compensated. In the lower part of 4 is shown in comparison to a vibration diagram which the through the device 2 achieved good transfer function UF shows, to achieve this good transfer function UF in addition, the connecting rod 13 was dampened.

3 shows a detailed embodiment of the embodiment of the device 2 for vibration excitation of the specimen 3 in exploded view. As already described, the device comprises 2 the holding structure 8th with the lead-through opening 10 as well as the leadership part 6 , The holding structure 8th is for example by means of a connecting element 15 , which by means of screw elements 16 for which there are appropriate screw holes 17 having, with the support structure 8th can be screwed, connected to a base, not shown here.

The spring elements 7 are in the example shown, each with the support structure 8th to screw. For this purpose are screw elements 16 and washers 18 intended.

The holding structure 8th has corresponding screw holes 17 on, which here in the area of the elevations 12 are formed, and the spring elements 7 have appropriate holes 19 for performing the screw elements 16 on.

The connection of the spring elements 7 with the guide part 6 takes place in the example shown by means of the corresponding holder 11 by jamming on the guide part 6 , The holder 11 on the sample connection unit 4 facing side of the guide part 6 also has a clamp for receiving and clamping the sample connection unit 4 on. To clamp the clamp is a screw 16 provided, which in corresponding screw holes 17 the clamp is inserted with a washer between the clamp and the screw head 18 is provided. The two holders 11 are not identical, because in the holder 11 on the sample connection unit 4 facing side of the guide part 6 the sample connection unit 4 is trapped and attached to the other holder 11 , which on the other, ie from the sample connection unit 4 facing away, side of the guide part 6 is arranged, the force sensor and / or impedance sensor 14 is connected. These two holders 11 thus differ fundamentally.

The vibration tester 1 which the device 2 for vibration excitation of the specimen 3 , including the excitation source 9 , Conveniently, further comprises a measuring and control computer 20 and a signal generator 21 , which with the measuring and control computer 20 and the excitation source 9 connected is.

Furthermore, the vibration testing device comprises 1 a climatic chamber 22 in which the linear guide arrangement 5 ie the holding structure 8th with the two spring elements 7 and the leadership part 6 , as well as the sample connection unit 4 with the sample already arranged thereon 3 , which is designed, for example, as a test bar, and the force sensor and / or impedance sensor 14 are arranged. The excitation source 9 is in the example shown outside the climate chamber 22 arranged so that the connecting rod 13 in the climatic chamber 22 protrudes.

The climate chamber 22 has an anti-reflective disc 23 on, ie a window opening, which with the transparent anti-reflective disc 23 is closed. Outside the climatic chamber 22 is a scanning laser vibrometer 24 also called a laser scanning vibrometer, ie a scanning laser vibrometer 24 , for detecting vibrations of the specimen 3 arranged and with the measuring and control computer 20 connected. It's in front of the anti-reflective disc 23 positioned to the vibrations of the specimen 3 through this anti-reflective disc 23 through and to the measuring and control computer 20 forward.

5 shows in an amplitude A-frequency f-diagram the transfer function UF ie the quotient of resulting acceleration and stimulating force. Shown is the first natural frequency. Here, f _{0, n is} the frequency position of the n-th resonance maximum of the test specimen 3 ie resonant frequency at the nth resonance and Δf _n is the half width in the nth resonance, ie the width at which the resonance peak has dropped by 3dB on both sides (corresponds to a halving of the vibration energy).

The test piece 3 resonates here.

The material data is determined analogously to DIN EN ISO 6721-3 :
Loss factor: $$\text{tan}\left(\delta \right)=\frac{\Delta f_n}{f_{0n}}$$

Where:
δ the loss angle
Memory module: $$e_n^{\text{'}}=\frac{4{\mathrm{<figure-callout\; id="2"\; label="\pi "\; filenames="DE102019001226A1\_0006.png,DE102019001226A1\_0007.png"\; state="\{\{state\}\}">\pi </figure-callout>}}^2\rho A{L}^2}{I}\frac{f_{0n}^2}{{\left({\gamma }_{n}L\right)}^4}$$

• $E_n^{\text{'}}$
  
  das Speichermodul an der Stelle der n-ten Resonanzfrequenz p die Werkstoffdichte
• A der Querschnitt des Probekörpers 3 (quaderförmig: Breite*Höhe)
• L die frei schwingende Länge des Probekörpers 3
• / das Flächenträgheitsmoment des Querschnitts (Quader: = Breite*Höhe³/12, Höhe= Dicke des Probekörpers 3
• γ_nL Lösung der charakteristischen Gleichung aus Resonanzordnung n und Lagerungsbedingung, z. B. fest-frei: I+cos(γL)*cosh(γL)=0

Where:

• $e_n^{\text{'}}$
  
  the memory module at the location of the n-th resonant frequency p the material density
• A is the cross section of the test specimen 3 (cuboid: width * height)
• L is the freely oscillating length of the test specimen 3
• / The area moment of inertia of the cross section (square: = width * height ^3/12, height = thickness of the test specimen 3
• γ _n L solution of the characteristic equation of resonance order n and storage condition, eg. Fixed-free: I + cos (γL) * cosh (γL) = 0

Other formula contexts, in particular also shown in 6 : $$\text{tan}\left(\delta \right)=\frac{e\text{'}\text{'}}{e\text{'}}$$

• E" Verlustmodul = Imaginärteil des komplexen Elastizitätsmoduls und charakterisiert den viskosen (gedämpften) Schwingungsanteil
• E' Speichermodul = Realteil des komplexen Elastizitätsmoduls und charakterisiert den elastischen Schwingungsanteil
• komplexer Elastizitätsmodul: E*=E'+i*E"
• dynamischer Elastizitätsmodul = Betrag des komplexen Elastizitätsmoduls: $$E_{dyn}=\sqrt{E^{\text{'}2}+E^{\text{'}\text{'}2}}$$
  

Where:

• E "loss modulus = imaginary part of the complex modulus of elasticity and characterizes the viscous (damped) vibrational component
• E 'storage modulus = real part of the complex modulus of elasticity and characterizes the elastic vibration component
• complex elastic modulus: E * = E '+ i * E "
• dynamic modulus of elasticity = amount of the complex modulus of elasticity: $$e_{dyn}=\sqrt{e^{\text{'}2}+e^{\text{'}\text{'}2}}$$
  

LIST OF REFERENCE NUMBERS

1

Vibration test device

2

device

3

specimens

4

Samples connection unit

5

Linear guide arrangement

6

guide part

7

spring element

8th

holding structure

9

excitation source

10

Through opening

11

holder

12

increase

13

connecting rod

14

Force sensor and / or impedance sensor

15

connecting element

16

screw elements

17

screw opening

18

washer

19

hole

20

Measuring and control computer

21

signal generator

22

climatic chamber

23

disc

24

Laservibrometer

A

amplitude

AA

amplitude axis

AR

excitation direction

f

frequency

FA

frequency axis

LW

Lamb wave

P

arrow

UF

transfer function

e '

memory module

e "

loss modulus

e *

dynamic modulus of elasticity

i

imaginary axis

j

real axis

δ

loss angle

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited patent literature

• DE 102014103299 A1 [0002]
• EP 1577659 B1 [0003]

Cited non-patent literature

• DIN EN ISO 6721-3 [0038]

Claims (7)

Device (2) for vibrational excitation of a test specimen (3), comprising a sample connection unit (4) for receiving the specimen (3) and a linear guide arrangement (5) for guiding the specimen connection unit (4) parallel to an excitation direction (AR), characterized in that the sample connection unit (4) is arranged on a guide part (6), which is arranged at a distance to it by means of two spring elements (7) on a holding structure (8), wherein the spring elements (7) are designed such that the guide part (6) in Radially on the spring elements (7) fixed to the support structure (8) is fixed and parallel to the excitation direction (AR) is elastically movable. Device (2) according to Claim 1 , characterized in that the guide part (6) in a passage opening (10) of the support structure (8) of the support structure (8) is arranged radially spaced. Device (2) according to Claim 2 , characterized in that the spring elements (7) are arranged at an opening end of the passage opening (10) on an outer side of the support structure (8), wherein the spring elements (7) are each attached to the support structure (8) in the region of a spring element outer circumference and in the region of a spring element inner circumference on the guide part (6) are attached. Device (2) according to one of the preceding claims, characterized in that the respective spring element (7) is designed as a plate spring or leaf spring. Device (2) according to one of the preceding claims, characterized in that the specimen (3) on the sample connection unit (4) can be fixed radially aligned with the excitation direction (AR), in particular adhesively bonded. Device (2) according to one of the preceding claims, characterized in that one of the sample connection unit (4) facing away from the end of the guide member (6) is connected to an excitation source (9) for vibration excitation. Device (2) according to Claim 6 , characterized in that the sample connection unit (4) facing away from the end of the guide part (6) via a force sensor and / or impedance sensor (14) with the excitation source (9) is connected to the vibration excitation.

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