Detection method for detecting wood beam fracture crack depth based on vibration method

Abstract

The invention discloses a method for detecting the fracture crack depth of a wood beam based on a vibration method, and the method comprises the steps: starting from an Euler-Bernoulli beam model theory, obtaining an inherent frequency relational expression of each order of an intact and crack-free wood beam, constructing a vibration mechanical model of a cracked wood beam through an equivalent beam model, obtaining an inherent frequency relational expression of each order of the cracked wood beam, and obtaining the crack depth of the cracked wood beam. Through further analysis, a function relationship between the inherent frequency when the wood beam has the crack and the original change quantity of the inherent frequency when the wood beam is intact and the relative depth of the crack of the beam is obtained, so that a relationship model between the relative depth of the crack of the wood beam and the change quantity of the inherent frequency is constructed. Through the detection model, the correlation between the relative depth of the wood beam crack and the inherent frequency variation can be obtained, the relative depth of the wood beam crack can be predicted only by measuring the inherent frequency variation of the wood beam with the crack, the crack detection efficiency and accuracy are improved, the state of the wood beam can be monitored in real time, and the detection accuracy is improved. The potential crack problem is recognized in advance, so that structural damage caused by cracks is reduced, the maintenance cost can be reduced, and the service life of the wood structure is effectively prolonged.

Description

Technical Field

[0001] The invention relates to the field of wood beam crack detection, and in particular to a detection method for detecting the depth of a wood beam fracture crack based on a vibration method. Background Art

[0002] Wooden beams are widely used as load-bearing components in traditional Chinese architecture. Due to the environmental protection and renewable characteristics of wood, they have become increasingly popular in modern architecture in recent years. However, wooden beams in ancient wooden structures are prone to cracks due to long-term loads and gradually expand, which may cause the wooden beams to break and even cause the building structure to fail. This not only threatens the preservation of precious cultural relics, but also affects the safety of modern wooden structures. Therefore, monitoring the health of wooden beams has become a technical problem that needs to be solved urgently.

[0003] Crack depth has always been a key factor in the study of wood beam fracture, but in actual operation, it is still very difficult to accurately monitor the depth of fracture cracks. For example, traditional ultrasonic testing can accurately determine the location of cracks without damage, but it cannot accurately detect the depth of cracks. In addition, chemical reagents are required during the detection process, which will cause environmental pollution. Many existing fracture mechanics theories are derived from elastic mechanics, but elastic mechanics is homogeneous, and fracture cracks will change the mechanical uniformity of the material. Therefore, elastic mechanics models are difficult to directly apply to wood beams with fracture cracks. Summary of the invention

[0004] In order to solve the problems that the existing elastic mechanics model cannot be directly applied to crack propagation and the traditional ultrasonic detection cannot accurately detect the depth of fracture cracks, the present invention discloses a method for detecting the depth of fracture cracks of wooden beams. By improving the Bernoulli beam model, the vibration behavior of wooden beams with cracks can be accurately described, and the precise measurement and evaluation of the crack depth of wooden beams can be achieved, thereby reducing the risk of failure of wooden beams caused by fracture cracks.

[0005] To achieve the above purpose, the technical solution of the present invention is: a detection method for detecting the crack depth of a wooden beam based on a vibration method, comprising the following steps: S1 calculates the natural frequency of a complete and crack-free wooden beam (i.e., a crack-free beam) based on the Euler-Bernoulli beam model theory; S2 constructs an equivalent model of a cracked wooden beam; S3 constructs a vibration dynamics model of a cracked wooden beam and calculates the natural frequency of the cracked wooden beam; S4 calculates the variation of each order natural frequency of the cracked beam; S5 constructs a model for the relationship between the relative depth of each order crack and the change in natural frequency.

[0006] Furthermore, in step S1, the calculation formula for each order natural frequency of the crack-free wooden beam is: in: are the natural frequencies of the uncracked wooden beam, is the characteristic value of each order natural frequency, EI is the bending stiffness of the beam, is the density of the beam, S is the cross-sectional area of ​​the beam, r For order.

[0007] Furthermore, the step S2 is specifically as follows: S21 constructs an ideal wooden beam model; S22 simulates cracks by cutting on one side and artificially creates a crack of a certain depth in the middle of the beam; S23 simplifies the entire wooden beam into an equivalent beam consisting of two parts, one with cracks and one without cracks.

[0008] The Euler-Bernoulli beam model is the basis of the vibration dynamics model of intact slender beams, but it is not applicable to the dynamics of cracked wooden beams. Therefore, it is necessary to construct a dynamics model of cracked wooden beams.

[0009] The cracks in the wooden beam are caused by the load borne by the wooden beam, and the moment in the middle section of the wooden beam is the largest. Therefore, in general, the cracks in the wooden beam appear in the middle position. Since the direction in which the wooden beam bears the load remains unchanged, the cracks usually appear on one side of the wooden beam, that is, a unilateral crack is usually produced. When a crack appears in the middle of the surface layer of the beam, the wooden beam is divided into a crack layer and a non-crack layer by the crack. The bending stiffness of the cracked area decreases significantly and almost no longer contributes to the overall stiffness of the beam. Therefore, the present invention regards the cracked area of ​​the wooden beam as an additional distributed mass, and the remaining non-cracked part bears most of the bending load. The entire wooden beam can be simplified into an equivalent beam consisting of a cracked and non-cracked part. The load of the wooden beam is regarded as the load of the non-cracked part, and the non-cracked part can be equivalent to a good beam with a changed thickness and unchanged other dimensions.

[0010] Furthermore, in step S3, according to the vibration dynamics model of the cracked wooden beam, the calculation formula of each order natural frequency of the cracked wooden beam is: in: The natural frequencies of cracked wooden beams. is the characteristic value of each order natural frequency, EI is the bending stiffness of the beam, is the density of the beam, S is the cross-sectional area of ​​the beam, is the relative crack depth, r For the order; The relative crack depth formula is: Where: n is the crack depth and d is the thickness of the beam.

[0011] Specifically, in step S4, the calculation formula for the change of each order natural frequency is: in: is the change of the natural frequency of the wooden beam, is the natural frequency of the beam when the crack is 0, are the natural frequencies of the cracked wooden beam, for The first derivative of .

[0012] The difference between the natural frequencies of each order when the wooden beam has cracks and the natural frequencies of each order when there is no crack is the change of each order natural frequency.

[0013] Furthermore, in step S5, the relationship model between the relative depth of each order crack and the change in the natural frequency is expressed as: in: k is the coefficient, is the change of the natural frequency of the wooden beam, is the relative depth of crack; The coefficient k is a constant: in: is the characteristic value of each order natural frequency, EI is the bending stiffness of the beam, is the density of the beam, S is the cross-sectional area of ​​the beam, r For the order, For First-order derivative.

[0014] Specifically, the relationship model between the relative depth of each order crack and the change in natural frequency is expressed as a linear relationship. Once the wooden beam is determined, its physical parameters are fixed values. The slope k is related to the order of the natural frequency. When the order of the natural frequency is fixed, the slope k can be determined. By measuring the change in each order of natural frequency, the relative depth of the crack can be inferred, and the true depth of the crack can be calculated.

[0015] Beneficial effects of the present invention: 1. Improve the accuracy of crack depth detection by constructing a linear curve model of the crack depth-natural frequency change of the wooden beam.

[0016] 2. Based on the linear curve model of the crack depth-natural frequency change of the wooden beam, the status of the wooden beam can be monitored in real time, and potential crack problems can be identified in advance, thereby reducing structural damage caused by cracks, reducing maintenance costs, and effectively extending the service life of the wooden structure.

[0017] 3. The present invention can simplify the entire monitoring process and reduce manual intervention by integrating data acquisition, signal processing and crack detection algorithms. Users only need to set monitoring parameters and the system can automatically complete monitoring, which reduces operational complexity and improves operability.

[0018] 4. Compared with traditional crack detection methods (such as ultrasonic detection), the implementation of the method of the present invention can accurately detect the depth of the fracture crack, and does not require the use of chemical reagents and other pollutants, reducing pollution to the environment and complying with the concept of sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. The drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. For those skilled in the art, other drawings can be obtained based on the drawings without paying creative work.

[0020] Figure 1 This is a flow chart of a detection method for detecting fracture cracks in wooden beams based on a vibration method according to the present invention; Figure 2 Schematic diagram of the vibration dynamics model of the transverse crack of the wood beam of the present invention; Figure 3 is a graph showing the relationship between the change in natural frequency and the relative depth of cracks under different thickness specifications in an embodiment of the present invention; Figure 4 is the relationship between the variation of each order of natural frequency and the relative depth of the crack in the embodiment of the present invention; Figure 5 1 is a fitting curve of each order of relative crack depth of a specimen in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] refer to Figure 1 The embodiment of the present invention provides a test process of a method for detecting crack depth of a wood beam based on a vibration method, including construction of a linear curve model of crack depth-natural frequency variation and measurement of crack depth of the wood beam, and the specific steps are: S1 calculates the natural frequency of crack-free wooden beams based on the Euler-Bernoulli beam model theory; S2 constructs an equivalent model of a cracked wooden beam; S3 constructs a vibration dynamics model of a cracked wooden beam and calculates the natural frequency of the cracked wooden beam; S4 calculates the variation of each order natural frequency of the cracked beam; S5 constructs a model for the relationship between the relative depth of each order crack and the change in natural frequency.

[0023] The embodiment of the present invention provides a specific construction process of the relationship model between the depth of each order crack of a wood beam and the variation of the natural frequency.

[0024] Based on the Euler-Bernoulli beam model, the vibration model of the cracked beam is established, and the calculation formula (1) of the natural frequency of the uncracked beam is obtained as follows: (1) in: are the natural frequencies of the uncracked wooden beam, is the characteristic value of each order natural frequency, EI is the bending stiffness of the beam, is the density of the beam, S is the cross-sectional area of ​​the beam, r For order.

[0025] The Euler-Bernoulli beam model is the basis of the vibration dynamics model of intact slender beams, but it cannot directly describe the vibration law of beams with fracture cracks. Therefore, it is not applicable to the dynamics of cracked wooden beams. It is necessary to construct a dynamics model of cracked wooden beams.

[0026] The cracks in the wooden beam are caused by the load borne by the wooden beam, and the moment in the middle section of the wooden beam is the largest. Therefore, in general, the cracks in the wooden beam appear in the middle position. Since the reverse direction of the load borne by the wooden beam remains unchanged, the cracks usually appear on one side of the wooden beam, that is, a unilateral crack is usually produced. When a crack appears in the middle of the surface layer of the beam, the wooden beam is divided into a crack layer and a crack-free layer by the crack. The bending stiffness of the cracked area is significantly reduced and almost no longer contributes to the overall stiffness of the beam. Therefore, the present invention regards the cracked area of ​​the wooden beam as an additional distributed mass, and the remaining crack-free part bears most of the bending load. The entire wooden beam can be simplified into an equivalent beam consisting of a cracked and crack-free part. The load of the wooden beam is regarded as the load of the crack-free part. The crack-free part can be equivalent to a good beam with a changed thickness and unchanged other dimensions. The Euler-Bernoulli beam model can be used for calculation. The thickness of the cracked part becomes d-n, and the width is still w, where n is the crack depth.

[0027] Therefore, the specific method of constructing the cracked beam equivalent model is: S11 constructs an ideal wooden beam model; S12 simulates cracks by cutting on one side and artificially creates a crack of a certain depth in the middle of the beam; S13 simplifies the entire wooden beam into an equivalent beam consisting of two parts, one with cracks and one without cracks.

[0028] The length of the cracked beam is L, the width is w, and the thickness is d. In practice, cracks are generally irregular in shape. Cracks are simulated by single-sided incisions, and cracks are artificially created in the middle of the beam to simulate the fracture behavior of wooden beams under long-term loading to ensure the controllability of the experiment.

[0029] like Figure 2 As shown in the figure, the vibration dynamics model of the cracked wooden beam is constructed by the equivalent model of the cracked wooden beam, that is, the relationship between the natural frequencies of each order of the cracked wooden beam and the physical parameters. The calculation formula (2) of the natural frequencies of each order of the cracked wooden beam is expressed as: (2) in: The natural frequencies of cracked wooden beams. is the characteristic value of each order natural frequency, EI is the bending stiffness of the beam, is the density of the beam, S is the cross-sectional area of ​​the beam, r For the order; The relative depth is expressed as: in: is the relative depth of the crack, n is the crack depth, d is the thickness of the beam, and is substituted into formula (2) to obtain formula (3): (3) in: The natural frequencies of cracked wooden beams. is the characteristic value of each order natural frequency, EI is the bending stiffness of the beam, E is the bending elastic modulus, I is the section moment of inertia, is the density of the beam, S is the cross-sectional area of ​​the beam, is the relative crack depth, r For the order; From formula (1) and formula (3), we can see that there is a functional relationship between the natural frequency of the wood beam when cracks appear and the natural frequency when there is no cracks, as well as the relative depth of the cracks.

[0030] Once the beams are determined, is a constant, and is expanded using Taylor expansion as follows: in: is the natural frequency of the wood beam without cracks, for The first derivative of is the second-order derivative, is the Lagrangian remainder, The value range is , is the relative crack depth, The value range is ,when When it is relatively small, it can be expressed as:

[0031] Therefore, the change in the natural frequency of the cracked wood beam can be expressed as formula (4): (4)

[0032] Formula (4) can reflect the functional relationship between the change in the natural frequency of a cracked beam and the natural frequency when it was originally intact and the relative depth of the crack in the beam.

[0033] Set a constant k to represent: (5) Then, the relationship model between the relative crack depth of the wood beam and the change in natural frequency can be expressed as formula (6): (6) in: k is the coefficient, is the change of the natural frequency of the wooden beam, is the relative depth of crack.

[0034] From formula (6), it can be seen that there is a linear relationship between the relative crack depth of the wood beam and the change in the natural frequency. Once the wood beam is determined, its physical parameters are fixed values. The coefficient k is related to the order of the natural frequency. When the order of the natural frequency is fixed, the coefficient k can be determined. By measuring the change in the natural frequency of each order of the wood beam, the relative crack depth can be inferred and the true crack depth can be calculated.

[0035] The present invention provides an embodiment for verifying the accuracy of a model for the relationship between a crack depth of a wood beam and a change in the natural frequency.

[0036] First, a cracked beam model was constructed according to the above steps, the physical parameters of the wood beam specimen were measured, and the natural frequency of the uncracked beam was measured using the stress hammer method. The specific steps are as follows: Measure the size and weight parameters of the wood beam specimens, and obtain the density and bending modulus data of the specimens according to the density formula and the national standard GB / T1927.13 "Test methods for physical and mechanical properties of small defect-free wood specimens"; Hang the wooden beam specimen, fix the sensor on the specimen, and connect the sensor to the processor; The stress hammer continuously strikes the same position of the specimen; The sensor collects the vibration signal and transmits it to the processor for data calculation to obtain the natural frequencies of each order.

[0037] After testing the natural frequencies of the crack-free beams, the samples were processed into wooden beams with five relative crack depths of 10%, 20%, 30%, 40%, and 50%, and the natural frequencies of the cracked wooden beams were measured using the stress hammer tapping method mentioned above.

[0038] By measuring the first to fifth order natural frequencies of specimens with five different thicknesses under different crack depths, the change values ​​between the natural frequencies of each order and the natural frequencies of the crack-free beam under five relative crack depths of 10%, 20%, 30%, 40% and 50% were calculated, and linear fitting was performed to obtain the slope, intercept, correlation coefficient and residual sum of squares.

[0039] In this embodiment, the consistency between the linear curve model of crack depth of each order of wood beam and the measured data is verified by comparing the calculated results of the linear curve model of crack depth of each order of wood beam and the measured data.

[0040] like Figure 3 As shown in the figure, the relationship curve between the change of natural frequency and the relative depth of crack under five different thickness specifications detected by the experiment. For the same thickness of wood beams, with the increase of order, the slope of the curve decreases significantly, and the change amplitude of natural frequency increases significantly. The high-order natural frequency is more sensitive to the relative depth of crack, and the change of natural frequency caused by crack is more obvious. With the increase of the order of natural frequency, the eigenvalue Gradually increases, at this time, the model slope It gradually decreases, indicating that the experimental results are consistent with the model calculation.

[0041] like Figure 4 As shown in the figure, the relationship curve between the change in natural frequency and the relative depth of crack under the conditions of the first to fifth order natural frequencies tested in the experiment shows that as the thickness of the wood beam increases, the change in natural frequency also increases accordingly, that is, the slope of the curve becomes smaller accordingly.

[0042] In formula (1), the moment of inertia of the section is , it can be known from the derivation and calculation of the model that when the order is fixed, the model slope can be expressed as , where I is the moment of inertia of the section, w is the width of the beam, and d is the thickness of the beam. At this time, the slope is only related to the thickness d of the wooden beam. The larger the thickness d, the smaller the slope k and the larger the range of the natural frequency change, which further shows that the model calculation is highly consistent with the experimental test results.

[0043] The natural frequency characteristic values ​​of the first to fifth orders are shown in Table 1: Table 1 Eigenvalues ​​of natural frequencies from the first to the fifth order Order 1 2 3 4 5 Eigenvalue 4.730 7.853 10.995 14.137 17.279 In the table, the orders 1, 2, 3, 4, and 5 correspond to the eigenvalue symbols respectively. , , , , .

[0044] like Figure 5 As shown in the figure, the slope, intercept, correlation coefficient and residual sum of squares of the sample curve are processed by the mean, and the fitting curves of each order of all samples in the experiment meet the linear properties, and the data points are evenly distributed on both sides of the fitting curve or on the line, which further indicates that the model calculation is consistent with the experimental results.

[0045] The test calculated the residual sum of squares and correlation coefficient between the curve and the actual test value based on the model obtained by curve fitting. The residual sum of squares data obtained from 10 samples of five different thickness specifications were averaged as shown in Table 2: Table 2 Residual analysis

[0046] In Table 2, A, B, C, D, and E correspond to the wood beam specimens with relative crack depths of 10%, 20%, 30%, 40%, and 50%, respectively; 1, 2, 3, 4, and 5 correspond to the first to fifth natural frequency orders, respectively.

[0047] As can be seen from the table, the mean of the residual sum of squares is below 0.03, which indicates that the model has high accuracy. At the same time, the standard deviation of the residual sum of squares is also lower than 0.03, indicating that the model is highly reliable and has good consistency. With the increase of the natural frequency order and thickness, the mean and standard deviation of the residual sum of squares show a gradual downward trend, and decrease to below 0.01 at the fifth order. This shows that the higher the natural frequency order, the higher the accuracy of the model fitting, the smaller the error, and the more concentrated the data, especially at the fourth and fifth orders, the model fitting effect is significantly improved.

[0048] The average values ​​of the correlation coefficients R obtained from the five samples are shown in Table 3: Table 3 Correlation coefficient R analyze

[0049] In Table 3, A, B, C, D, and E correspond to the wood beam specimens with relative crack depths of 10%, 20%, 30%, 40%, and 50%, respectively; 1, 2, 3, 4, and 5 correspond to the first to fifth natural frequency orders, respectively.

[0050] It can be seen from the table that most of the correlation coefficients R are higher than 0.9 (the closer the correlation coefficient is to 1, the more consistent the data is), indicating that the model has good linear fitting properties. At the same time, the standard deviation of the correlation coefficient is below 0.08 (the closer the standard deviation is to 0, the more consistent the data is), indicating that the model data set is concentrated and shows good regularity. With the increase of the natural frequency order and thickness, the mean of the correlation coefficient generally increases, and the value is close to or exceeds 0.99, which can be regarded as a linear property. At the same time, the standard deviation of the correlation coefficient gradually decreases, which means that the model prediction is more accurate.

[0051] This embodiment describes the accuracy of a detection method for detecting the crack depth of a broken wooden beam based on a vibration method. By establishing a vibration model of the Euler-Bernoulli beam model and making the cracked beam equivalent, the relative crack depth of the cracked beam is linearly related to the change in the natural frequency of the cracked beam. Therefore, as long as the change in the natural frequency of the cracked beam is measured, the crack depth of the wooden beam at this time can be calculated based on physical parameters such as the size, density, and elastic modulus of the wooden beam.

[0052] In practical applications, the initial physical parameters of wooden beams can be tested before they leave the factory, including: size, weight, density, bending stiffness, elastic modulus, characteristic values ​​of each order of natural frequency, and each order of natural frequency, and they can be numbered so that each wooden beam used in the factory has a unique code and corresponding initial physical parameter test data, that is, the wooden beam-number-physical parameter corresponds one to one, or the initial physical parameter detection of the wooden beam can be carried out before the use of the wooden beam, providing a basis for subsequent design, use, maintenance and monitoring.

[0053] When cracks appear in a wooden beam, by measuring the natural frequencies of the cracked wooden beam at each order, the difference between the natural frequency of the cracked wooden beam and the natural frequency of the initial crack-free state, that is, the change in natural frequency, can be used to obtain the relative depth of the crack through the crack relative depth-natural frequency change relationship model, and the true depth of the crack can be obtained through the crack relative depth formula.

[0054] When the wooden beam is confirmed at the factory, its inherent physical parameters have been determined, that is, the linear curve of the crack depth-natural frequency change of the wooden beam has been determined. Therefore, it can be connected to a signal detection device and a signal processing device to automatically monitor the natural frequency of the wooden beam through integrated data acquisition, signal processing and crack detection algorithms, and the status of the wooden beam can be monitored in real time according to the linear curve model.

[0055] You can also set up an early warning program to sound an alarm when the depth of cracks in the wooden beams reaches the early warning value, thereby reducing the risks caused by the cracks.

[0056] Although the preferred implementation cases of the present invention have been described above in conjunction with the accompanying drawings, 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 guidance of the present invention, ordinary technicians in this field can also make many forms of specific changes without departing from the scope of protection of the invention spirit and claims, which all fall within the scope of protection of the present invention.

Claims

1. A method for detecting the crack depth of a wood beam based on a vibration method, characterized in that: The following steps are involved: S1 calculates the natural frequency of a sound wooden beam without cracks based on the Euler-Bernoulli beam model theory; S2 constructs an equivalent model of a cracked wooden beam; S3 constructs a vibration dynamics model of a cracked wooden beam and calculates the natural frequency of the cracked wooden beam; S4 calculates the variation of each order natural frequency of the cracked beam; S5 constructs a model for the relationship between the relative depth of each order crack and the change in natural frequency.

2. The method for detecting fracture cracks of wooden beams based on the vibration method according to claim 1 is characterized in that: In step S1, the calculation formula for each order of natural frequency of a complete and crack-free wooden beam is: in: are the natural frequencies of the uncracked wooden beam, is the characteristic value of each order natural frequency, EI is the bending stiffness of the beam, is the density of the beam, S is the cross-sectional area of ​​the beam, r For order.

3. The method for detecting fracture cracks of wooden beams based on vibration method according to claim 1, characterized in that: The step S2 is specifically as follows: S21 constructs an ideal wooden beam model; S22 simulates cracks by cutting on one side and artificially creates a crack of a certain depth in the middle of the beam; S23 simplifies the entire wooden beam into an equivalent beam consisting of two parts, one with cracks and one without cracks.

4. The method for detecting fracture cracks of wooden beams based on vibration method according to claim 1, characterized in that: In step S3, the calculation formula for each order natural frequency of the cracked wooden beam is: in: The natural frequencies of cracked wooden beams. is the characteristic value of each order natural frequency, EI is the bending stiffness of the beam, is the density of the beam, S is the cross-sectional area of ​​the beam, is the relative crack depth, r For the order; The relative crack depth formula is: Where: n is the crack depth and d is the thickness of the beam.

5. The method for detecting fracture cracks of wooden beams based on vibration method according to claim 1, characterized in that: In step S4, the calculation formula for the change of each order natural frequency is: in: is the change of the natural frequency of the wooden beam, is the natural frequency of the wood beam when the crack is 0, are the natural frequencies of the cracked wooden beam, for The first derivative of .

6. The method for detecting fracture cracks of wooden beams based on vibration method according to claim 1, characterized in that: In step S5, the relationship model between the relative depth of each order crack and the change in natural frequency is: in: k is the coefficient, is the change of the natural frequency of the wooden beam, is the relative depth of crack; The coefficient k is a constant: in: is the characteristic value of each order natural frequency, EI is the bending stiffness of the beam, is the density of the beam, S is the cross-sectional area of ​​the beam, r For the order, For First-order derivative.

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