Monitoring device and monitoring method for fatigue damage state of crane main beam

Abstract

The invention provides a monitoring device and a monitoring method for a fatigue damage state of a crane main beam, and belongs to the field of cranes. The invention aims to solve the problem that the existing crane girder fatigue damage monitoring mostly adopts long-term monitoring in combination with indirect monitoring of a fatigue damage model instead of direct monitoring of the girder, so that the monitoring effect is poor. A bidirectional ultrasonic surface wave excitation sensor and ultrasonic surface wave receiving sensors on the two sides of the bidirectional ultrasonic surface wave excitation sensor are arranged on the side edge of a support, a graduated scale is arranged on the upper surface of the support, a magnet block is arranged on the lower surface, and temperature sensors are arranged at the two ends. The method comprises two modes, the first mode indirectly monitors the fatigue damage increase of the crane main beam in the normal working state based on the fatigue damage theory, the second mode directly monitors the fatigue damage of the crane main beam based on the ultrasonic surface wave technology, the two modes supplement each other, and the fatigue damage state of the crane main beam can be directly and indirectly monitored; and the monitoring accuracy is effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of cranes, and in particular to a monitoring device and a monitoring method for the fatigue damage state of a crane main beam. Background Art

[0002] Cranes are a common type of equipment for lifting and handling materials. Large cranes are indispensable in industries such as shipbuilding, metallurgy, and port logistics, and they play an important role in industrial production. Frequent lifting and unloading causes the crane's main beam to be subjected to alternating stress, which can easily cause fatigue damage in areas of stress concentration. The continuous accumulation of fatigue damage can easily cause the crane to fail due to fatigue under a stress state far below the strength limit. This is a very dangerous failure mode that can easily lead to major safety accidents. The crane's main beam is one of the main components of the crane. Therefore, monitoring the fatigue damage status of the crane's main beam is of great significance to reducing major safety accidents involving cranes and ensuring the normal progress of industrial production.

[0003] At present, fatigue damage monitoring of crane main beams is mainly based on fatigue damage accumulation theory. This theory regards the impact of each alternating load on the crane main beam as an accumulation of damage. The size of the damage caused is directly related to the load size. Under the action of continuous alternating loads, fatigue damage of the main beam continues to accumulate until fatigue failure. The typical monitoring process is: using a stress tester to monitor the stress of key parts of the main beam for a long time, and combining the fatigue damage model to monitor the fatigue damage state of the crane main beam. However, this method is not a direct monitoring of fatigue damage. Accidental factors such as welding defects and material defects will directly change the fatigue life of the crane main beam.

[0004] The fatigue failure process of the main beam can also be regarded as the initiation and expansion process of fatigue cracks. Fatigue cracks initiate due to stress concentration at locations such as structural mutations, welding defects and material defects. Under the action of alternating loads, fatigue cracks continue to expand, eventually leading to the failure of the main beam to fracture. Fatigue cracks generally initiate from the surface. Ultrasonic surface waves are ultrasonic waves that propagate along the surface of a medium. When passing through an open surface crack, the amplitude will be significantly attenuated. In the early stage of fatigue crack initiation, the crack is in a closed state and is not easy to be found. When the crane is lifting a load, the main beam is subjected to the bending moment, causing the fatigue cracks in the closed state to open, causing the ultrasonic surface waves passing through the fatigue cracks to be significantly attenuated. Therefore, ultrasonic surface waves are sensitive to fatigue cracks in the crane main beam. The present invention provides a monitoring device and a monitoring method for the fatigue damage state of a crane main beam based on ultrasonic surface waves. Summary of the invention

[0005] The technical problems to be solved by the present invention are: In order to solve the problem that the existing crane main beam fatigue damage monitoring mostly adopts long-term monitoring combined with indirect monitoring of fatigue damage models instead of direct monitoring of the main beam, resulting in poor monitoring effect.

[0006] The present invention adopts the following technical solutions to solve the above technical problems: The present invention provides a monitoring device for the fatigue damage state of a crane main beam, comprising a long plate-shaped bracket, a bidirectional ultrasonic surface wave excitation sensor is arranged at the center of the side of the bracket, an ultrasonic surface wave receiving sensor is arranged on both sides of the bidirectional ultrasonic surface wave excitation sensor, and each ultrasonic surface wave receiving sensor has the same spacing as the bidirectional ultrasonic surface wave excitation sensor, a scale is arranged on the upper surface of the bracket close to the ultrasonic surface wave receiving sensor and one side of the bidirectional ultrasonic surface wave excitation sensor, at least two magnet blocks are fixed on the bracket, and a temperature sensor is arranged at each end of the bracket, and each temperature sensor has the same spacing as the bidirectional ultrasonic surface wave excitation sensor.

[0007] Furthermore, each temperature sensor is arranged on the bracket via a telescopic rod.

[0008] A monitoring method of a monitoring device for a fatigue damage state of a crane main beam comprises the following steps: S100, select the key monitoring parts of crane main beam fatigue damage; S200, installing the monitoring device at the key monitoring location; S300, the bidirectional ultrasonic surface wave excitation sensor excites a group of signals, which are received by two ultrasonic surface wave receiving sensors, and the time when the signals are received is recorded as t1 and t2. According to the scale on the bracket, the distance between the two ultrasonic surface wave receiving sensors and the bidirectional ultrasonic surface wave excitation sensor is recorded as L1 and L2 respectively; the velocity of the ultrasonic surface wave is calculated according to v=L / t respectively. and ,Pick ; When the crane main beam is loaded, the relationship between the velocity and stress of the ultrasonic surface wave is as follows: (1) in, and are the principal stresses on the surface, is the velocity of the ultrasonic surface wave in the absence of stress, is along the principal stress The velocity of ultrasonic surface waves propagating in the direction of and are the material-related acoustoelastic constants; Since the crane main beam is subjected to force along the length direction, formula (1) becomes: (2) S400, the speed of the ultrasonic surface wave is related to the temperature, and the average temperature of the two temperature sensors is recorded as the temperature of the main beam surface; when the crane main beam is without a load, the speed v0 of the ultrasonic surface wave under all integer temperature conditions within the working temperature range T1-T2 is recorded according to v=L / t, where T1 and T2 represent the minimum temperature and maximum temperature of the crane main beam surface during the crane operation process, respectively; S500, when the crane is fully loaded, formula (2) becomes: (3) According to v=L / t, the velocity v1 of the ultrasonic surface wave in the working temperature range T1-T2 is recorded: According to formula (3), the velocity v1 of the ultrasonic surface wave in the working temperature range T1-T2 is calculated ; S600, let the speed of ultrasonic surface wave of crane main beam under any load be v2, (4) (5) (6) in, is the measured working stress; The stress state of the main beam is monitored by monitoring the velocity v2 of the ultrasonic surface wave under any load within the working temperature range T1-T2 ; According to Miner's theory, under a single constant amplitude load, the damage D Defined as: (7) In the formula, is the number of cycles of constant amplitude load; is the stress value The corresponding fatigue life; Assume stress amplitude effect The number of cycles for the material to fail at this stress level is , then the fatigue damage caused by this part of the stress cycle to the structure is , total damage D is the damage sum of stress amplitudes at each level, that is: (8) Based on measured working stress values , the fatigue damage state of the crane main beam is recorded using Miner's linear cumulative damage theory.

[0009] Furthermore, in step S200, it includes: S210, installing a magnet block on the bracket, and using the magnet block to adsorb the monitoring device on the surface of the main beam at the key monitoring location; S220, adjusting the position of the bidirectional ultrasonic surface wave excitation sensor so that it fits the center of the side of the bracket and fits it to the surface of the main beam; S230. Adjust the positions of the two ultrasonic surface wave receiving sensors so that they fit on the side of the bracket on one side of the bidirectional ultrasonic surface wave excitation sensor. According to the scale ruler, make the two ultrasonic surface wave receiving sensors symmetrically distributed with the bidirectional ultrasonic surface wave excitation sensor as the center, and fit the two ultrasonic surface wave receiving sensors to the surface of the main beam.

[0010] Furthermore, the key monitoring areas include structural transition areas where stress concentration occurs, weld areas where stress concentration occurs, or areas subject to impact loads.

[0011] A monitoring method of a monitoring device for a fatigue damage state of a crane main beam comprises the following steps: S100, select the key monitoring parts of crane main beam fatigue damage; S200, installing the monitoring device at the key monitoring location; S300, respectively record the amplitudes of the two ultrasonic surface wave receiving sensors at different temperatures within the working temperature range T1-T2 when the crane is in an unloaded state and a fully loaded state; let the amplitudes of the left ultrasonic surface wave receiving sensor in an unloaded state and a fully loaded state be recorded as A1(T) and A2(T), respectively; let the amplitudes of the right ultrasonic surface wave receiving sensor in an unloaded state and a fully loaded state be recorded as B1(T) and B2(T), respectively; S400, the amplitude of the ultrasonic surface wave receiving sensor on the left side under any load is A(T), and the amplitude of the ultrasonic surface wave receiving sensor on the right side is B(T). When the crane main beam is in a normal working state, The ratio is constant; set up If the crane is working, If the ratio of is significantly different from m, stop the machine immediately for inspection; if The ratio is greater than p*m, where p>1, and the p value is set by the user according to the internal crane management system of the enterprise, then abnormal fatigue damage occurs in the area between the bidirectional ultrasonic surface wave excitation sensor and the right ultrasonic surface wave receiving sensor; if If the ratio is less than m / p, abnormal fatigue damage occurs in the area between the bidirectional ultrasonic surface wave excitation sensor and the left ultrasonic surface wave receiving sensor (2); S500, monitoring the stress of the main beam during crane operation The stress at full load is ; According to the following formula, the real-time monitoring amplitude Calculate and set up monitoring indicators : (9) (10) S600, set fatigue warning value ;During the operation of the crane, When the value of gradually approaches k; if The value of gradually approaches k, then the fatigue damage in the area between the bidirectional ultrasonic surface wave excitation sensor and the left ultrasonic surface wave receiving sensor has reached the warning value; if When the value of gradually approaches k, the fatigue damage in the area between the bidirectional ultrasonic surface wave excitation sensor and the right ultrasonic surface wave receiving sensor has reached the warning value.

[0012] Furthermore, in step S200, it includes: S210, installing a magnet block on the bracket, and using the magnet block to adsorb the monitoring device on the surface of the main beam at the key monitoring location; S220, adjusting the position of the bidirectional ultrasonic surface wave excitation sensor so that it fits the center of the side of the bracket and fits it to the surface of the main beam; S230. Adjust the positions of the two ultrasonic surface wave receiving sensors so that they fit on the side of the bracket on one side of the bidirectional ultrasonic surface wave excitation sensor. According to the scale ruler, make the two ultrasonic surface wave receiving sensors symmetrically distributed with the bidirectional ultrasonic surface wave excitation sensor as the center, and fit the two ultrasonic surface wave receiving sensors to the surface of the main beam.

[0013] Furthermore, the key monitoring areas include structural transition areas where stress concentration occurs, weld areas where stress concentration occurs, or areas subject to impact loads.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a monitoring device and a monitoring method for the fatigue damage state of a crane main beam. A bidirectional ultrasonic surface wave excitation sensor and ultrasonic surface wave receiving sensors on both sides of the sensor are arranged at the center of the side of a bracket. A scale ruler is arranged on the upper surface of the bracket. At least two magnet blocks are fixed to the bracket by screws. A temperature sensor which can be adjusted up and down is respectively arranged at both ends of the bracket. The structure is simple and can realize the installation and removal of different crane main beams and different monitoring parts of the same crane main beam. The monitoring method includes two modes. Mode 1 indirectly monitors the increase of fatigue damage of the crane main beam under normal working conditions based on fatigue damage theory. Mode 2 directly monitors the fatigue damage of the crane main beam based on ultrasonic surface wave technology and can monitor the increase of fatigue damage under accidental factors such as weld cracks, internal defects of materials and impact loads. Mode 1 and Mode 2 complement each other and can directly and indirectly monitor the fatigue damage state of the crane main beam, thereby effectively improving the accuracy of monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The present invention is a schematic structural diagram of a monitoring device for fatigue damage status of a crane main beam according to an embodiment of the present invention.

[0016] Description of reference numerals: 1. Bidirectional ultrasonic surface wave excitation sensor; 2. Ultrasonic surface wave receiving sensor; 3. Magnet block; 4. Screw; 5. Bracket; 6. Scale ruler; 7. Temperature sensor. DETAILED DESCRIPTION

[0017] In the description of the present invention, it should be noted that the terminology nouns in the various embodiments, such as "up", "down", "front", "back", "left", "right", etc., which indicate directions, are only for simplifying the description of the positional relationship based on the drawings in the specification, and do not mean that the referred elements and devices must be operated according to the specific directions and defined operations and methods and structures in the specification. Such directional nouns do not constitute a limitation on the present invention.

[0018] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0019] Specific implementation plan 1: Combine Figure 1As shown, the present invention provides a monitoring device for fatigue damage state of crane main beam, comprising a long plate-shaped bracket 5, a bidirectional ultrasonic surface wave excitation sensor 1 is provided at the center of the side of the bracket 5, an ultrasonic surface wave receiving sensor 2 is respectively provided on both sides of the bidirectional ultrasonic surface wave excitation sensor 1, and each ultrasonic surface wave receiving sensor 2 is at the same distance from the bidirectional ultrasonic surface wave excitation sensor 1, a scale ruler 6 is provided on the upper surface of the bracket 5 close to the ultrasonic surface wave receiving sensor 2 and the bidirectional ultrasonic surface wave excitation sensor 1, at least two magnet blocks 3 are fixed to the bracket 5 by a screw 4, and a temperature sensor 7 that can be adjusted up and down is respectively provided at both ends of the bracket 5, and the temperature sensor 7 can be fixed to the bracket 5 by a telescopic rod, the temperature sensor 7 is adjusted downward in working state to directly contact with the main beam, and measures the temperature of the main beam instead of the ambient temperature, and the temperature sensor 7 is adjusted upward in non-working state to avoid damaging the sensitive element of the temperature sensor 7, and each temperature sensor 7 is at the same distance from the bidirectional ultrasonic surface wave excitation sensor 1.

[0020] Specific implementation plan 2: Combination Figure 1 As shown, the present invention provides a monitoring method for a monitoring device of fatigue damage state of a crane main beam. The method is based on damage accumulation theory to monitor fatigue state of the main beam, and comprises the following steps: S100. Select key monitoring locations for fatigue damage of crane main beams, such as structural transition areas prone to stress concentration, weld areas prone to stress concentration, or areas susceptible to impact loads; S200, install monitoring devices at key monitoring locations, including: S210, installing the magnet block 3 on the bracket 5 through the screw rod 4, and using the magnet block 3 to adsorb the monitoring device on the main beam surface of the key monitoring position; S220, adjusting the position of the bidirectional ultrasonic surface wave excitation sensor 1 so that it fits the center of the side of the bracket 5, and fits it to the surface of the main beam; S230, adjust the positions of the two ultrasonic surface wave receiving sensors 2 so that they are attached to the side of the bracket 5 located on one side of the bidirectional ultrasonic surface wave excitation sensor 1, and according to the scale ruler 6, the two ultrasonic surface wave receiving sensors 2 are symmetrically distributed with the bidirectional ultrasonic surface wave excitation sensor 1 as the center, and the two ultrasonic surface wave receiving sensors 2 are attached to the surface of the main beam; S300, the bidirectional ultrasonic surface wave excitation sensor 1 excites a group of signals, which are received by the two ultrasonic surface wave receiving sensors 2, and the time when the signals are received is recorded as t1 and t2. According to the scale 6 on the bracket 5, the distances between the two ultrasonic surface wave receiving sensors 2 and the bidirectional ultrasonic surface wave excitation sensor 1 are accurately recorded as L1 and L2; the speed of the ultrasonic surface wave is calculated according to v=L / t. and ,Pick ; When the crane main beam is loaded, the relationship between the velocity and stress of the ultrasonic surface wave is as follows: (1) in, and They are the principal stresses on the surface (the crane main beam is subjected to bidirectional forces in orthogonal directions), is the velocity of the ultrasonic surface wave in the absence of stress, is along the principal stress The velocity of ultrasonic surface waves propagating in the direction of and are the acoustic elastic constants related to the material (if the material is anisotropic, k1 and k2 are different); Since the crane main beam is mainly subjected to force along the length direction, formula (1) can be changed to: (2) When the crane girder is under load, the speed of the ultrasonic surface wave will change; S400, the speed of the ultrasonic surface wave is related to the temperature. The readings of the two temperature sensors 7 should be very close. If the temperature difference is large, it means that the temperature sensor is faulty and should be repaired or replaced. If the temperature difference is less than 1°C, the average temperature of the two temperature sensors 7 is recorded as the temperature of the main beam surface. When the crane main beam is not hoisted, the speed v0 of the ultrasonic surface wave under all integer temperature conditions within the working temperature range T1-T2 is recorded according to v=L / t. T1 and T2 respectively represent the minimum temperature and maximum temperature on the crane main beam surface during the crane operation process. S500, when the crane is fully loaded, equation (2) becomes: (3) According to v=L / t, the velocity v1 of the ultrasonic surface wave in the working temperature range T1-T2 can be calculated according to formula (3): ; S600, assuming that the speed of the ultrasonic surface wave of the crane main beam under any load is v2,

[0021] (5) (6) in, is the measured working stress; Therefore, the stress state of the main beam can be monitored by monitoring the velocity v2 of the ultrasonic surface wave under any load within the working temperature range T1-T2. ; The most typical fatigue damage accumulation theory is Miner's linear accumulation damage theory. According to Miner's theory, under a single constant amplitude load, the damage D Defined as: (7) In the formula, is the number of cycles of constant amplitude load; is the stress value The corresponding fatigue life; Miner theory holds that the fatigue damage of materials at each stress amplitude is independent and the total damage can be accumulated linearly; assuming that the stress amplitude effect The number of cycles for the material to fail at this stress level is , then the fatigue damage caused by this part of the stress cycle to the structure is , total damage D is the damage sum of stress amplitudes at each level, that is: (8) Based on the measured working stress state , the fatigue damage state of the crane main beam can be recorded using Miner's linear cumulative damage theory.

[0022] The other combinations and connection relationships of this embodiment are the same as those of the first embodiment.

[0023] Specific implementation plan three: Combined Figure 1 As shown, the present invention provides a monitoring method for a monitoring device of fatigue damage state of a crane main beam. The method is based on monitoring the fatigue state of the main beam attenuated by ultrasonic surface waves at fatigue cracks, and comprises the following steps: S100. Select key monitoring locations for fatigue damage of crane main beams, such as structural transition areas prone to stress concentration, weld areas prone to stress concentration, or areas susceptible to impact loads; S200, install monitoring devices at key monitoring locations, including: S210, installing the magnet block 3 on the bracket 5 through the screw rod 4, and using the magnet block 3 to adsorb the monitoring device on the main beam surface of the key monitoring position; S220, adjusting the position of the bidirectional ultrasonic surface wave excitation sensor 1 so that it fits the center of the side of the bracket 5, and fits it to the surface of the main beam; S230, adjust the positions of the two ultrasonic surface wave receiving sensors 2 so that they are attached to the side of the bracket 5 located on one side of the bidirectional ultrasonic surface wave excitation sensor 1, and according to the scale ruler 6, the two ultrasonic surface wave receiving sensors 2 are symmetrically distributed with the bidirectional ultrasonic surface wave excitation sensor 1 as the center, and the two ultrasonic surface wave receiving sensors 2 are attached to the surface of the main beam; S300, respectively record the amplitudes of the two ultrasonic surface wave receiving sensors 2 at different temperatures within the working temperature range T1-T2 when the crane is in an unloaded state and a fully loaded state; assume that the amplitudes of the left ultrasonic surface wave receiving sensor 2 in an unloaded state and a fully loaded state are recorded as A1(T) and A2(T), respectively (the amplitude changes with the temperature T); the amplitudes of the right ultrasonic surface wave receiving sensor 2 in an unloaded state and a fully loaded state are recorded as B1(T) and B2(T), respectively; S400, under any load, the amplitude of the left ultrasonic surface wave receiving sensor 2 is A(T), and the amplitude of the right ultrasonic surface wave receiving sensor 2 is B(T). Since the two ultrasonic surface wave receiving sensors 2 receive signals from the same bidirectional ultrasonic surface wave excitation sensor 1, and the propagation distances L1 and L2 of the ultrasonic surface waves are substantially the same, therefore, when the crane main beam is in a normal working state, The ratio is basically constant; Assumptions If the crane is working, If the ratio of is significantly different from m, the machine should be stopped for inspection immediately; if If the ratio is greater than p*m (p>1, the p value is set by the user according to the internal crane management system of the enterprise), it means that abnormal fatigue damage has occurred in the area between the bidirectional ultrasonic surface wave excitation sensor 1 and the right ultrasonic surface wave receiving sensor 2; if The ratio is less than m / p, indicating that abnormal fatigue damage occurs in the area between the bidirectional ultrasonic surface wave excitation sensor 1 and the left ultrasonic surface wave receiving sensor 2; S500, monitoring the stress of the main beam during crane operation The stress at full load is ; According to the following formula, the real-time monitoring amplitude Calculate and set up monitoring indicators : (9) (10) S600, set fatigue warning value ( The value of k is determined by the crane user's management requirements for the crane. When the crane is in operation, When the value of gradually approaches k; if The value of is gradually approaching k, indicating that the fatigue damage in the area between the bidirectional ultrasonic surface wave excitation sensor 1 and the left ultrasonic surface wave receiving sensor 2 has reached the warning value; the value of k is based on the management requirements of the crane user unit for the crane, and the tolerance for equipment fatigue is low. The larger value between the two; high tolerance for equipment fatigue, If The value of gradually approaches k, indicating that the fatigue damage in the area between the bidirectional ultrasonic surface wave excitation sensor 1 and the right ultrasonic surface wave receiving sensor 2 has reached the warning value.

[0024] The other combinations and connection relationships of this embodiment are the same as those of the first embodiment.

[0025] Although the present invention is disclosed as above, the protection scope of the present invention is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A monitoring device for fatigue damage status of crane main beam, characterized in that: The invention comprises a long plate-shaped bracket (5), wherein a bidirectional ultrasonic surface wave excitation sensor (1) is provided at the center of a side of the bracket (5), an ultrasonic surface wave receiving sensor (2) is provided on each side of the bidirectional ultrasonic surface wave excitation sensor (1), and each ultrasonic surface wave receiving sensor (2) is at the same distance from the bidirectional ultrasonic surface wave excitation sensor (1), and a scale (6) is provided on the upper surface of the bracket (5) close to the ultrasonic surface wave receiving sensor (2) and the bidirectional ultrasonic surface wave excitation sensor (1), at least two magnet blocks (3) are fixed on the bracket (5), and a temperature sensor (7) is provided at each end of the bracket (5), and each temperature sensor (7) is at the same distance from the bidirectional ultrasonic surface wave excitation sensor (1).

2. The monitoring device for fatigue damage state of crane main beam according to claim 1 is characterized in that: Each temperature sensor (7) is arranged on the bracket via a telescopic rod.

3. A monitoring method for the monitoring device of the fatigue damage state of the crane main beam according to claim 1 or 2, characterized in that: The following steps are involved: S100, select the key monitoring parts of crane main beam fatigue damage; S200, installing the monitoring device at the key monitoring location; S300, the bidirectional ultrasonic surface wave excitation sensor (1) excites a group of signals, which are received by the two ultrasonic surface wave receiving sensors (2), and the time when the signals are received is recorded as t1 and t2. The distances between the two ultrasonic surface wave receiving sensors (2) and the bidirectional ultrasonic surface wave excitation sensor (1) are recorded as L1 and L2 according to the scale ruler (6) on the bracket; the speed of the ultrasonic surface wave is calculated according to v=L / t. and ,Pick ; When the crane main beam is loaded, the relationship between the velocity and stress of the ultrasonic surface wave is as follows: （1） in, and are the principal stresses on the surface, is the velocity of the ultrasonic surface wave in the absence of stress, is along the principal stress The velocity of ultrasonic surface waves propagating in the direction of and are the material-related acoustoelastic constants; Since the crane main beam is subjected to force along the length direction, formula (1) becomes: （2） S400, the speed of the ultrasonic surface wave is related to the temperature, and the average temperature of the two temperature sensors (7) is recorded as the temperature of the main beam surface; when the crane main beam is unloaded, the speed v0 of the ultrasonic surface wave under all integer temperature conditions within the working temperature range T1-T2 is recorded according to v=L / t, where T1 and T2 represent the minimum temperature and maximum temperature of the crane main beam surface during the crane operation process, respectively; S500, when the crane is fully loaded, formula (2) becomes: （3） According to v=L / t, the velocity v1 of the ultrasonic surface wave in the working temperature range T1-T2 is recorded: According to formula (3), the velocity v1 of the ultrasonic surface wave in the working temperature range T1-T2 is calculated ; S600, let the speed of ultrasonic surface wave of crane main beam under any load be v2, （4） （5） （6） in, is the measured working stress; The stress state of the main beam is monitored by monitoring the velocity v2 of the ultrasonic surface wave under any load within the working temperature range T1-T2 ; According to Miner's theory, under a single constant amplitude load, the damage D Defined as: (7) In the formula, is the number of cycles of constant amplitude load; is the stress value The corresponding fatigue life; Assume stress amplitude effect The number of cycles for the material to fail at this stress level is , then the fatigue damage caused by this part of the stress cycle to the structure is , total damage D is the damage sum of stress amplitudes at each level, that is: (8) Based on measured working stress values , the fatigue damage state of the crane main beam is recorded using Miner's linear cumulative damage theory.

4. The monitoring method of a crane main beam fatigue damage state monitoring device according to claim 3 is characterized in that: In step S200, it includes: S210, installing the magnet block (3) on the bracket (5), and using the magnet block (3) to adsorb the monitoring device on the surface of the main beam at the key monitoring location; S220, adjusting the position of the bidirectional ultrasonic surface wave excitation sensor (1) so that it fits the center of the side of the bracket (5) and fits it to the surface of the main beam; S230, adjusting the positions of the two ultrasonic surface wave receiving sensors (2) so that they are attached to the side of the bracket located on one side of the bidirectional ultrasonic surface wave excitation sensor (1), and symmetrically distributing the two ultrasonic surface wave receiving sensors (2) with the bidirectional ultrasonic surface wave excitation sensor (1) as the center according to the scale ruler (6), and attaching the two ultrasonic surface wave receiving sensors (2) to the surface of the main beam.

5. The monitoring method of the crane main beam fatigue damage state monitoring device according to claim 4 is characterized by: The key monitoring locations include structural transition areas where stress concentration occurs, weld areas where stress concentration occurs, or areas subject to impact loads.

6. A monitoring method for the monitoring device of the fatigue damage state of the crane main beam according to claim 1 or 2, characterized in that: The following steps are involved: S100, select the key monitoring parts of crane main beam fatigue damage; S200, installing the monitoring device at the key monitoring location; S300, respectively recording the amplitudes of the two ultrasonic surface wave receiving sensors (2) at different temperatures within the working temperature range T1-T2 when the crane is in an unloaded state and a fully loaded state; assuming that the amplitudes of the left ultrasonic surface wave receiving sensor (2) in an unloaded state and a fully loaded state are recorded as A1(T) and A2(T) respectively; and the amplitudes of the right ultrasonic surface wave receiving sensor (2) in an unloaded state and a fully loaded state are recorded as B1(T) and B2(T) respectively; S400, the amplitude of the left ultrasonic surface wave receiving sensor (2) under any load is A(T), and the amplitude of the right ultrasonic surface wave receiving sensor (2) is B(T). When the crane main beam is in a normal working state, The ratio is constant; set up If the crane is working, and If the ratio of is significantly different from m, stop the machine immediately for inspection; if The ratio of is greater than p*m, where p>1, and the p value is set by the user unit according to the internal crane management system of the enterprise, then abnormal fatigue damage occurs in the area between the bidirectional ultrasonic surface wave excitation sensor (1) and the right ultrasonic surface wave receiving sensor (2); if If the ratio is less than m / p, abnormal fatigue damage occurs in the area between the bidirectional ultrasonic surface wave excitation sensor (1) and the left ultrasonic surface wave receiving sensor (2); S500, monitoring the stress of the main beam during crane operation The stress at full load is ; According to the following formula, the real-time monitoring amplitude Calculate and set up monitoring indicators : (9) (10) S600, set fatigue warning value ;During the operation of the crane, When the value of gradually approaches k; if The value of gradually approaches k, then the fatigue damage in the area between the bidirectional ultrasonic surface wave excitation sensor (1) and the left ultrasonic surface wave receiving sensor (2) has reached the warning value; if When the value of gradually approaches k, the fatigue damage in the area between the bidirectional ultrasonic surface wave excitation sensor (1) and the right ultrasonic surface wave receiving sensor (2) has reached the warning value.

7. The monitoring method of a crane main beam fatigue damage state monitoring device according to claim 6 is characterized in that: In step S200, it includes: S210, installing the magnet block (3) on the bracket (5), and using the magnet block (3) to adsorb the monitoring device on the surface of the main beam at the key monitoring location; S220, adjusting the position of the bidirectional ultrasonic surface wave excitation sensor (1) so that it fits the center of the side of the bracket (5) and fits it to the surface of the main beam; S230, adjusting the positions of the two ultrasonic surface wave receiving sensors (2) so that they are attached to the side of the bracket (5) located on one side of the bidirectional ultrasonic surface wave excitation sensor (1), and symmetrically distributing the two ultrasonic surface wave receiving sensors (2) with the bidirectional ultrasonic surface wave excitation sensor (1) as the center according to the scale ruler, and attaching the two ultrasonic surface wave receiving sensors (2) to the surface of the main beam.

8. The monitoring method of the crane main beam fatigue damage state monitoring device according to claim 7 is characterized by: The key monitoring locations include structural transition areas where stress concentration occurs, weld areas where stress concentration occurs, or areas subject to impact loads.

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