DD131803B1 - MEASURING DEVICE FOR DETERMINING THE COMPLEX DYNAMIC ELASTICITY MODULE - Google Patents

Description

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Field of application of the invention;

The invention relates to a measuring device for determining the complex dynamic modulus of elasticity. The determination of the modulus of elasticity is necessary to check the elastic properties of plastics or of plastic construction elements. The modulus of elasticity is determined from the values of the resonance frequency and the bandwidth or the resonance quality.

Characteristic of the known technical solutions

The complex dynamic modulus of elasticity can not be determined in direct measurement. The determination is made indirectly, in which a sample is excited and calculated using the resonance frequency and the resonance quality of the modulus of elasticity.

It is known to determine the modulus of elasticity by means of the bending vibration measurement. For this purpose, a clamped specimen is mechanically excited so that it performs bending oscillations. These are registered by mechano-electrical converters. With frequency change of the excitation source v / ground the individual bending resonances of the specimen with the help of a level recorder recorded in terms of amount. The resonance curves of the individual vibration modes are evaluated according to resonance frequency and resonance quality. On the basis of these measurement results, the complex dynamic modulus of elasticity is calculated.

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(H. Oberst - technical description of the bending vibration measuring instrument type 3930 of Pa. Brüel and Kjaer, operating instructions Reprint October 1968)

The evaluable maximum damping of the material samples is given as approx. 0.2. This corresponds to a resonance quality of about 5 · 0 · Hit Only those materials whose mechanical properties allow bending resonance qualities above this measuring limit can be tested using the method.

If the resonance qualities in the vibration system are below 10, electronic systems use impedance measurements to determine their properties. The same procedure can be used analogously in mechanical systems.

In mechanical systems, the impedance measurement is carried out by a mechanical Srregerbeschleunigung acting on a device under test. The force acting on it is measured by means of a force gauge at the other end of the sample. The quantities "exciter acceleration" ¹ and "effective force" are recorded in terms of magnitude, and the exciter frequency and the phase difference between the exciter acceleration and the effective force through the material sample are measured.From these four measured values, the complex dynamic elastic modulus is calculated.

The accuracy of the calculation of the complex dynamic modulus of elasticity depends on the accuracy of reading or reading of each individual measurement value.

Furthermore, a thickness resonance method for the determination of the complex dynamic modulus of elasticity is known (A. Lenk.

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Electromechanical ^ Systems, Volume 1, page 55) · In this method, one-sided effects on a specimen mechanical excitation. To the opposite side of the specimen is a mass coupled. This creates a mechanical resonance system. The accelerations of the pathogen and the mass are measured. The frequency of the mechanical exciters is changed. In the vicinity of the resonant resonance of the mechanical resonance system, the transmission factor, which is formed from the amount of acceleration of the mass to the amount of acceleration of the exciter, is increased. The maximum of the overshoot is greater than or equal to 10 at the location of the resonance frequency. From the thus obtained resonance frequency and the relative 3 d B bandwidth of the resonance peak, the complex dynamic elastic modulus is calculated.

By this method, the complex dynamic elastic modulus of materials with a maximum attenuation of 0.3, which corresponds approximately to a resonance quality of up to 3, can be determined without much error. Materials with higher attenuation values can not be tested in this way.

d) Object of the invention

The invention aims to provide a measuring device for the determination of the complex dynamic modulus of elasticity, with the aid of soft elastic insulating materials, as used in electrical and building acoustical systems, regardless of their internal damping, are tested. From the measurement result, conclusions can be drawn on the material composition. The suitability of new materials can be tested easily.

e) presentation; the essence of the invention

The invention has the object of providing a measuring device for

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Determining the values for the calculation of the complex dynamic modulus of elasticity, in which these values, d. H. the resonance frequency and the resonance quality for each sample are measured.

The complex dynamic modulus of elasticity becomes formal with the equation

described.

If a resonance-capable structure is excited at its resonance frequency, then the output value is out of phase with the excitation by * f . This only applies to resonant grades larger. For smaller resonant grades the phase shift becomes smaller. For example, it is at Q, = лЩ-. By meaningful summation of the input signal with the output signal of the excited resonant structure, a signal is obtained which is always shifted by 2ZT with respect to the input signal at resonant frequency independently of the internal attenuation. This one relies on the magnitude measurement when measuring the resonant frequency nicn-c. By reading the phase shift between the excitation and the output value, the resonance frequency is measured. This phase shift is denoted by -f ". The phase shift can be formalized with the expression

: QrC tan

со

describe. Therein Q is the Rasonan2 good,

<O the set angular frequency, tog the resonance frequency.

Substituting in F 2 the expression

lO tC F 3

so you get for the phase shift

arc tone ^. F4

gl

tan

Lx.

The resolution of the equation F 3 shows that the equation F 5 at the angular frequencies

за. A _% GL ю'О una lJo β O ₁ GZ ^ o

is valid. At these frequencies the loss factor d * =

ч simply measured by measuring the phase shift. Based on this mathematical derivation, it is now possible to determine the initial values of the complex dynamic elastic modulus for each sample.

The measuring device for determining the output values for the calculation consists of a controllable and abstiminbaren electrical signal generator, which is followed by the electrical oscillations in mechanically «converting» transducer (vibrating table). On this transducer is the specimen and next to the sample a Seschleunigungsaufnehmer. On the specimen, another accelerometer is attached. The outputs cer Seschleunigungsauf participants are switched to measure the Ausgangsvverte in samples with small resonance quality erfindungsgemäS a Sufnfnierglied at an input of the phase meter. At the other input of the phase meter is directly connected to the output of the accelerometer mounted on the transducer. Furthermore, a frequency meter is connected to this output. In addition to this output, this output is fed back to the control input of the signal generator.

The measurement OCE resonant frequency is carried out by Qurchsti л.-пзп of the signal generator to the resonance frequency. The resonance case

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is indicated on the phase meter through, the phase difference s ^ of -j. The resonance frequency is now read off the frequency meter. Subsequently, the frequency is tuned to 1.62 times or 0.62 times the value of the resonance frequency. Now, the phase difference S & is read on the phase meter. БегёчиѴ ^ is equal to the loss factor. From the resonance frequency and the loss factor, the complex dynamic elastic modulus is calculated. In order to keep the vibration acceleration amplitude constant while tuning, the output of an accelerometer is fed back to the control input of the signal generator.

The meter can also be used to measure the modulus of elasticity at different temperatures. For this purpose, the transducer is housed with the sample and the accelerometers in a climate chamber and made the measurements described at different temperatures.

Furthermore, the frequency response of the complex dynamic elastic modulus can be determined, in which the natural resonance of the specimen is changed. This is done by changing the dimensions of the specimen or by changing the applied mass, d. H. Additional masses are applied in addition to the mass of the acceleration receiver.

f) Ausführunssbeispiel

The invention will be described below with reference to an exemplary embodiment. The accompanying drawing shows a block diagram of the meter.

To a controllable and tunable signal generator 1, a vibrating table 2 is connected. On the vibrating table 2 is; a specimen 3 and an accelerometer 4 attached. On

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the sample 3 is an accelerator 5 attached. To the accelerometers 4 and 5, a summer 6 is connected. The output of the summing element 6 is located at one of the inputs of a phase meter 7. The other input of the phase meter 7 is connected directly to the output of the acceleration pickup 4. At the output of the accelerometer 4, a frequency meter 8 and a feedback line 9 is also connected to the regulating input of the signal generator.

To measure the signal generator 1 is tuned. The signal emitted by it is converted in the vibrating table 2 into a proportional mechanical signal. In order to determine the frequency with which the vibrating table 2 oscillates and in order to obtain a phase reference point, the accelerometer 4 is placed on the vibrating table 2, which converts the mechanical signal back into an analogue electrical signal. On the mounted on the vibrating table 2 specimen 3 of the accelerometer 5 is placed. This accelerometer 5 converts the signal passing through the sample 3 into an analog electrical signal. In the summing 6, the output from the accelerometer 5 signal is summed with the originating from Beschleunigungsaufneamer 4 and then fed to an input of the phase meter 7. At the same time the output of the Beschleunigungsauf supers rs 4 is fed directly to the other input of the phase meter 7, so that the phase meter 7 indicates the phase shift between the signal of the accelerometer 4 and the summed signal. If this phase shift - ^ p, so the specimen 3 is in resonance with the output from the vibrating table 2 signal. The resonance frequency is read off the frequency meter 3. Now, the signal generator 1 to the frequency 1.62 u? c) and the phase shift 7 is read off the associated phase shift. By forming the tan of the phase angle thus obtained, the

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Loss factor determined. In this measurement is a prerequisite that the tuning of the signal generator 1, the amplitude of the acceleration of the vibrating table 2 remains constant. By the feedback of the output of the acceleration sensor 4 to the control input of the signal generator 1 is achieved. If the measurements are to be carried out at different temperatures, the vibrating table 2 with the test body and the accelerometers 4 and 5 is placed in a Slimakamaer. Now, the effects of temperature on the sample 3 can be examined ·

Claims (3)

93 3 8 6 Invention 1. Measuring device for the determination of the complex dynamic modulus of elasticity, in which the values "resonance frequency" and "loss factor" are measured as GrundungsgrundlaQen, where in specimens with low resonance quality, the resonance frequency by detecting the ^ f - phase shift and the loss factor by measuring the phase shift in the test specimen is determined at the l, 62fachen, or 0.62 times the resonant frequency, which consists of a controllable and tunable electrical signal generator, which is followed by the electrical signal in a mechanical transducing vibrating table, a placed on the vibrating table next to a specimen Seschleunigungsaufnehmer and on. is the specimen placed 3eschleunigungsaufnehmer, characterized in that the outputs represent accelerometer (4), (5) are brought together in a summing element (6) and via the summing element (6) at an input of the phase meter (7), and in that also at the output the other input of the phase meter (7) directly, a frequency meter (3) and a feedback line (9) are connected to the oignalgenerator (1), the accelerometer (4) mounted on the vibrating table (2), 2, measuring device according to item 1, characterized in that when measurements of the influence of temperature on the test piece (3) of the vibrating table (2) with the sample (3) and the mounted vibration sensors (4), (5) is enclosed in a climatic chamber. 3. A meter according to item l, characterized in that for determining the frequency response of the complex dynamic modulus of elasticity, the natural resonance of the specimen (3) by placing additional masses or by changing the dimensions of the specimen (3) is changed. For this 1 page drawings