Young modulus measuring device and method

Abstract

The invention discloses a Young modulus measuring device and method, and belongs to the technical field of physical quantity measurement. The device comprises a fixing mechanism and a cantilever beam to be detected installed in the fixing mechanism. The length of the cantilever beam to be detected extending out of the fixing mechanism is adjustable, and an excitation mechanism is arranged at one end, far away from the fixing mechanism, of the cantilever beam to be detected; and an acquisition mechanism is arranged near the excitation mechanism and is used for acquiring a vibration sound pressure signal generated when the excitation mechanism excites the cantilever beam to be detected. Compared with an existing device for measuring the Young modulus of a metal material through an optical lever method, the measuring device is simpler and more convenient to adjust and operate, compared with other elastic modulus measuring experiments through a vibration method, a sensor does not need to be additionally arranged on an object to be measured to collect vibration signals, and non-contact measurement is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of physical quantity measurement, and in particular to a device and method for measuring Young's modulus. Background Art

[0002] The Young's modulus of solid materials, also known as the elastic modulus, is one of the most important and characteristic mechanical properties of elastic materials. Young's modulus is a physical quantity that describes the ability of solid materials to resist deformation when subjected to force within the elastic range. It is widely used in engineering design, and its determination is one of the important contents of general physical experiments.

[0003] There are two main experimental methods for measuring elastic modulus: static method and dynamic method. The optical lever amplification method in the static method is the most commonly used measurement method in physical experiments. However, this method has the disadvantages that it is more laborious to observe the image of the ruler reflected by the mirror of the optical lever when adjusting the experimental device, the shaking of the steel wire when adding and subtracting weights during the measurement of experimental data can easily cause the optical lever to shift, and the measurement steps are cumbersome and require "running back and forth" between the optical lever and the telescope. The dynamic method generally determines the elastic modulus by measuring the natural vibration frequency of the specimen, or measuring parameters such as the speed at which sound waves propagate in the specimen. However, the universal material testing machine used for measurement is expensive, cannot meet the needs of experimental teaching, and is difficult to achieve automated measurement. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and to provide a device and method for measuring Young's modulus, which can overcome the technical difficulties in the existing static and dynamic Young's modulus measurement technologies, such as complex measurement operation, high precision requirements for measuring devices and instruments, high cost, and low degree of automation.

[0005] In order to solve the above technical problems, the present invention is implemented by adopting the following technical solutions:

[0006] In one aspect, the present invention provides a device for measuring Young's modulus, comprising a fixing mechanism and a cantilever beam to be measured installed in the fixing mechanism;

[0007] The length of the cantilever beam to be measured extending out of the fixing mechanism is adjustable, and an excitation mechanism is arranged at one end of the cantilever beam to be measured away from the fixing mechanism; the excitation mechanism may be a wooden hammer.

[0008] A collection mechanism is arranged near the excitation mechanism, for collecting the vibration sound pressure signal generated by the excitation mechanism when the cantilever beam to be tested is excited.

[0009] The vibration of the cantilever beam to be measured in the present invention belongs to the vibration of a continuous elastic body. If the length of the beam is much larger than the cross-sectional dimension of the beam, only the deformation caused by bending can be considered without considering the deformation caused by shearing and the influence of its moment of inertia vibration.

[0010] Optionally, the fixing mechanism includes a base and a fixing member, and the cantilever beam to be measured is installed in the base and fixed by the fixing member. The fixing member may be a G-shaped clip.

[0011] Optionally, an axial cavity is provided in the base, and the cantilever beam to be measured is installed in the axial cavity, which is used to adjust the length of the cantilever beam to be measured extending out of the fixing mechanism.

[0012] Optionally, the thickness of the cantilever beam to be measured is much smaller than the width of the cantilever beam to be measured and the length thereof extending out of the fixing mechanism.

[0013] Optionally, the acquisition mechanism includes a microphone and a virtual oscilloscope, and the microphone is connected to the processor via the virtual oscilloscope.

[0014] Optionally, a low-pass filter is provided in the processor, and a filtering range of the low-pass filter is set according to the material and size of the cantilever beam to be measured.

[0015] On the other hand, the present invention further provides a method for measuring Young's modulus, the method using the measuring device described in the first aspect, the method comprising:

[0016] Installing the cantilever beam to be measured in the fixing mechanism to obtain the length of the cantilever beam to be measured extending out of the fixing mechanism;

[0017] Using the excitation mechanism to apply pulse excitation to the cantilever beam to be tested to generate a vibration sound pressure signal;

[0018] The vibration sound pressure signal is collected by the collection mechanism, and the vibration sound pressure signal is processed to obtain the first The first order vibration angular frequency, according to the The Young's modulus is calculated from the angular frequency of vibration.

[0019] Optionally, the vibration sound pressure signal is processed to obtain the vibration Order vibration angular frequency, including:

[0020] Performing spectrum analysis and Fourier transform on the vibration sound pressure signal in sequence to obtain a frequency domain distribution image;

[0021] The frequency domain distribution image is subjected to filtering processing and inverse Fourier transformation in sequence to obtain a filtering waveform;

[0022] The average interval between the peak values ​​of the filtered waveform is taken as the vibration period, and the The angular frequency of vibration.

[0023] Optionally, the calculation formula of the Young's modulus is:

[0024] ;

[0025] ;

[0026] In the formula, The cantilever beam to be tested Order vibration angular frequency; The length of the cantilever beam to be measured extending out of the fixing mechanism; is the material linear density of the cantilever beam to be tested; The cantilever beam to be tested Roots of the order frequency equation; is the cross-sectional moment of inertia of the cantilever beam to be measured.

[0027] Beneficial Effects

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] Compared with the existing device for measuring the Young's modulus of metal materials by the optical lever method, the measuring device of the present invention is easier to adjust and operate. Compared with other vibration method experiments for measuring the elastic modulus, it is not necessary to install a sensor on the object to be measured to collect the vibration signal, and it is a non-contact measurement. With the help of an oscilloscope, data collection is intuitive and accurate. After the sound pressure signal is filtered out of high-order frequencies, the waveform is displayed on the oscilloscope. The waveform of the filtered signal is observed, the experimental phenomenon is intuitive, and observation and measurement are relatively convenient. It has a high degree of automation and repeatability, low cost, and is easy to promote and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The figure shows a schematic structural diagram of a device for measuring Young's modulus of the present invention in one embodiment;

[0031] Figure 2 Shown is a schematic diagram of measurement results of a method for measuring Young's modulus of the present invention in one embodiment;

[0032] In the figure: 1 - cantilever beam to be tested; 2 - microphone; 3 - virtual oscilloscope; 4 - processor; 5 - base; 6 - fixing part; 7 - excitation mechanism. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is described in detail below through the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present invention and the specific features in the embodiments are detailed descriptions of the technical solution of the present invention, rather than limitations on the technical solution of the present invention. The embodiments of the present invention and the technical features in the embodiments may be combined with each other unless there is a conflict.

[0034] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0035] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0036] The term "and / or" is only a description of the association relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " generally indicates that the related objects are in an "or" relationship.

[0037] Example 1

[0038] like Figure 1 As shown, this embodiment introduces a test device for Young's modulus, which specifically includes a cantilever beam 1 to be tested, a fixing mechanism, an excitation mechanism 7 and a collection mechanism.

[0039] The fixing mechanism includes a base 5 and a fixing member 6. An axial cavity is provided in the base 5. The cantilever beam 1 to be measured is installed in the axial cavity. The length of the cantilever beam 1 to be measured extending out of the fixing mechanism can be adjusted and fixed by the fixing member 6. The base 5 can be a rectangular metal plate, and the fixing member 6 can be a G-shaped clip.

[0040] The thickness h of the cantilever beam 1 to be measured should be much smaller than its width d and the length of the cantilever beam exposed in the axial cavity, that is, the actual vibration length L. The vibration of the cantilever beam 1 to be measured belongs to the vibration of a continuous elastic body. If the beam length is much larger than the cross-sectional size of the beam, only the deformation caused by bending can be considered, while the deformation caused by shearing and the vibration effect of its moment of inertia can be ignored.

[0041] The excitation mechanism 7 is arranged at one end of the cantilever beam 1 to be tested away from the fixing mechanism. The excitation mechanism 7 can be a wooden hammer.

[0042] The acquisition mechanism includes a microphone 2 , a virtual oscilloscope 3 and a processor 4 .

[0043] The microphone 2 is placed near the excitation mechanism 7 , and the microphone 2 is connected to the processor 4 through the virtual oscilloscope 3 .

[0044] The microphone 2 can collect the vibration sound pressure signal generated by the excitation mechanism 7 hitting the cantilever beam 1 to be measured, and the virtual oscilloscope 3 connected to the microphone 2 can store the vibration sound pressure signal collected by the microphone 2, and can display the signal waveform, and transmit it to the processor 4, in which the signal analysis and processing are performed and the Young's modulus of the cantilever beam 1 to be measured is calculated. The processor 4 is also provided with a low-pass filter, and the filtering range of the low-pass filter is designed according to the material and size of the cantilever beam 1 to be measured.

[0045] Example 2

[0046] This embodiment introduces a method for measuring Young's modulus, the method adopts the measuring device described in Embodiment 1, and the method specifically comprises the following steps:

[0047] The cantilever beam 1 to be tested is installed in the axial cavity of the base 5 and fixed by a fixing member 6 .

[0048] The excitation mechanism 7 is arranged at the end of the cantilever beam 1 to be measured away from the base 5 .

[0049] The microphone 2 and the virtual oscilloscope 3 are placed near the excitation mechanism 7 to collect the vibration sound pressure signal generated by the excitation mechanism 7 striking the cantilever beam 1 to be tested. The excitation mechanism 7 quickly strikes the cantilever beam 1 to be tested to apply pulse excitation.

[0050] The vibration sound pressure signal is transmitted to the processor 4, and the signal is analyzed and processed in the processor 4 to calculate the Young's modulus of the cantilever beam 1 to be measured, specifically:

[0051] The vibration sound pressure signal is subjected to spectrum analysis and Fourier transformation in sequence to obtain a frequency domain distribution image.

[0052] The frequency domain distribution image is subjected to filtering processing and inverse Fourier transformation in sequence to obtain a filtering waveform.

[0053] The average interval between the peak values ​​of the filtered waveform is taken as the vibration period, and the Order vibration angular frequency .

[0054] According to the said The Young's modulus is calculated from the order vibration angular frequency .

[0055] In this embodiment, the thickness h of the cantilever beam 1 to be measured should be much smaller than its width d and the length of the cantilever beam exposed from the axial cavity, that is, the actual vibration length L. The vibration of the cantilever beam 1 to be measured belongs to the vibration of a continuous elastic body. If the beam length is much larger than the cross-sectional size of the beam, only the deformation caused by bending can be considered without considering the deformation caused by shearing and the vibration effect of its moment of inertia. The Euler-Bernoulli beam theory is applicable, and its vibration differential equation is:

[0056] ;

[0057] Among them, the arm length direction of the cantilever beam 1 to be measured is taken as the positive direction of the coordinate axis x-axis, and y is the longitudinal displacement of the axis; is Young's modulus; is the cross-sectional inertia moment of the cantilever beam 1 to be measured, ; is the material linear density of the cantilever beam 1 to be tested, , is the mass of the cantilever beam 1 to be measured, is the length of the cantilever beam 1 to be measured; t is time. According to the above vibration differential equation, the expression of the longitudinal displacement y of the cantilever beam 1 to be measured along the axis with time t can be written in the form of superposition of vibration modes of each order, such as the formula:

[0058] ;

[0059] in, is a constant; is the order; is the vibration mode function, which is related to the boundary conditions of the cantilever beam 1 to be measured; For the Order vibration angular frequency; is the phase difference related to the initial condition.

[0060] According to the above formula, the boundary condition that the left end of the cantilever beam 1 to be measured is fixed and the right end is free, the vibration frequency equation of the cantilever beam 1 to be measured can be obtained as:

[0061] ;

[0062] in, For the cantilever beam to be tested, The roots of the order frequency equation ( , , .......), and the cantilever beam to be tested is Order vibration angular frequency for:

[0063] .

[0064] Then, Young's modulus is established and the vibration angular frequency corresponding to any order of main vibration mode, the Young's modulus The calculation formula is:

[0065] ;

[0066] In this embodiment, if the first-order vibration angular frequency in the sound pressure signal of the cantilever beam 1 to be measured is retained , the Young's modulus The calculation formula is:

[0067] .

[0068] That is, if we choose to retain the second-order vibration angular frequency in the sound pressure signal of the cantilever beam 1 to be measured , the Young's modulus The calculation formula is:

[0069] .

[0070] And so on.

[0071] Example 3

[0072] This embodiment introduces an experimental design of a method for measuring Young's modulus, which includes the following steps:

[0073] Before setting up the instrument, first measure the mass of the cantilever beam 1 to be tested. ,length , width d and thickness h, calculate the linear density of the cantilever beam 1 to be tested and the cross-sectional moment of inertia .

[0074] In this embodiment, cantilever beam specimens processed from aluminum are selected for testing in three sizes, and the sizes are 400×25×1.5 mm, 400×38×1.0 mm, and 400×38×1.5 mm, respectively.

[0075] The cantilever beam 1 to be tested is placed in the axial cavity of the base 5 and clamped by the fixing member 6 , and the actual vibration length L of the cantilever beam target part clamped by the fixing member 6 and the base 5 and exposed in the cavity is recorded.

[0076] The excitation mechanism 7 is used to quickly tap the cantilever beam 1 to be tested, and the sound pressure signal generated by the vibration after pulse excitation is applied. The microphone 2 is fixed at the same sample height as a sound pressure collection mechanism, 1 cm horizontally away from the tapping position, and the virtual oscilloscope 3 connected to the microphone 2 collects and displays the vibration waveform.

[0077] The processor 4 is used to perform spectrum analysis and Fourier transformation on the measured vibration time response sound pressure signal in sequence to obtain a frequency domain distribution image.

[0078] A low-pass filter is used to filter out high-order vibration modes and perform filtering processing to retain the waveform corresponding to the fundamental frequency of vibration. The upper frequency limit of the low-pass filter used is set to 100 Hz, and this frequency can be adjusted according to the frequency domain distribution image.

[0079] Then perform inverse Fourier transform to obtain the filtered waveform, calculate the average interval of the peak value of the filtered waveform as the vibration period T, and thus obtain the first-order vibration angular frequency after the excitation mechanism 7 applies pulse excitation to the cantilever beam 1 to be tested. The first-order vibration angular frequency It can be obtained directly through measurement in actual experiments.

[0080] Calculate the Young's modulus The calculation formula is:

[0081] .

[0082] like Figure 2 The test results of Young's modulus are shown in Table 1. In this embodiment, the cantilever beam 1 to be tested is an aluminum beam. The natural frequency and Young's modulus (theoretical value is 70 GPa) are shown in Table 1, which are the calculated data of Young's modulus.

[0083] Table 1 Natural frequency and Young's modulus of aluminum beam (theoretical value is 70Gpa)

[0084]

[0085] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the enlightenment of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present invention and the claims, which all fall within the protection of the present invention.

Claims

1. A device for measuring Young's modulus, characterized in that: It comprises a fixing mechanism and a cantilever beam (1) to be tested installed in the fixing mechanism; The length of the cantilever beam (1) to be measured extending out of the fixing mechanism is adjustable, and an excitation mechanism (7) is provided at one end of the cantilever beam (1) to be measured away from the fixing mechanism; A collection mechanism is provided near the excitation mechanism (7) for collecting the vibration sound pressure signal generated by the excitation mechanism (7) when the cantilever beam (1) to be tested is excited.

2. The device for measuring Young's modulus according to claim 1, characterized in that: The fixing mechanism comprises a base (5) and a fixing member (6); the cantilever beam (1) to be measured is mounted in the base (5) and fixed by the fixing member (6).

3. The measuring device of Young's modulus according to claim 2, characterized in that: An axial cavity is provided in the base (5), and the cantilever beam (1) to be measured is installed in the axial cavity, so as to adjust the length of the cantilever beam (1) to be measured extending out of the fixing mechanism.

4. The testing device for Young's modulus according to claim 1, characterized in that: The thickness of the cantilever beam (1) to be measured is much smaller than the width of the cantilever beam (1) to be measured and the length thereof extending out of the fixing mechanism.

5. The device for measuring Young's modulus according to claim 1, characterized in that: The acquisition mechanism comprises a microphone (2) and a virtual oscilloscope (3), and the microphone (2) is connected to a processor (4) via the virtual oscilloscope (3).

6. The device for measuring Young's modulus according to claim 5, characterized in that: The processor (4) is provided with a low-pass filter, and the filtering range of the low-pass filter is set according to the material and size of the cantilever beam (1) to be tested.

7. A method for measuring Young's modulus, characterized in that: The method adopts the measuring device according to any one of claims 1 to 6, and the method comprises: The cantilever beam (1) to be measured is installed in the fixing mechanism, and the length of the cantilever beam (1) to be measured extending out of the fixing mechanism is obtained; Using the excitation mechanism (7) to apply pulse excitation to the cantilever beam (1) to be tested, thereby generating a vibration sound pressure signal; The vibration sound pressure signal is collected by the collection mechanism, and the vibration sound pressure signal is processed to obtain the first The first order vibration angular frequency, according to the The Young's modulus is calculated from the angular frequency of vibration.

8. The method for measuring Young's modulus according to claim 7, characterized in that: The vibration sound pressure signal is processed to obtain the Order vibration angular frequency, including: Performing spectrum analysis and Fourier transform on the vibration sound pressure signal in sequence to obtain a frequency domain distribution image; The frequency domain distribution image is subjected to filtering processing and inverse Fourier transformation in sequence to obtain a filtering waveform; The average interval between the peak values ​​of the filtered waveform is taken as the vibration period, and the The angular frequency of vibration.

9. The method for measuring Young's modulus according to claim 7, characterized in that: The calculation formula of the Young's modulus is: ； ； In the formula, For the cantilever beam to be tested (1) Order vibration angular frequency; is the length of the cantilever beam (1) to be measured extending out of the fixing mechanism; is the material linear density of the cantilever beam (1) to be tested; For the cantilever beam to be tested (1) Roots of the order frequency equation; is the cross-sectional moment of inertia of the cantilever beam (1) to be measured.

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