阅读说明：本技术 基于信号对称性的各向同性平板结构的冲击损伤识别方法 (Impact damage identification method of isotropic flat plate structure based on signal symmetry ) 是由 许龙涛 韩彦伟 辛士红 杜翠 王文胜 彭础琦 张乾 贾元青 邓微微 王玲茹 于 2021-07-26 设计创作，主要内容包括：本发明涉及一种基于信号对称性的各向同性平板结构的冲击损伤识别方法,该方法利用监测区域各个传感器信号的波达时间和信号能量来估计冲击位置,利用平板结构上下表面的传感器信号的对称性来识别冲击损伤。本发明可以有效解决冲击监测中不能同时识别冲击位置和识别损伤的问题,从而简化了系统的硬件需求,并简化了信号处理过程,能够满足结构健康监测实时监测的在线要求。(The invention relates to an impact damage identification method of an isotropic flat plate structure based on signal symmetry. The invention can effectively solve the problem that the impact position and the damage can not be identified simultaneously in the impact monitoring, thereby simplifying the hardware requirement of the system, simplifying the signal processing process and meeting the online requirement of the real-time monitoring of the structural health monitoring.)

1. The impact damage identification method of the isotropic flat plate structure based on signal symmetry is characterized by comprising the following steps of:

firstly, respectively arranging sensor arrays for monitoring impact events on the upper surface and the lower surface of an isotropic flat plate structure, wherein the sensors on the upper surface and the lower surface correspond to each other one by one, numbering the sensors on the upper surface and the lower surface, and connecting all the sensors with the same monitoring center;

step two, the position of each sensor arranged on the upper surface of the isotropic flat plate structure is respectively used as the vertex of a grid, each grid is composed of M vertices, the upper surface of the isotropic flat plate structure is provided with a plurality of grids, and M is a natural number which is greater than or equal to 3;

selecting a sensor with the earliest signal arrival time from the sensors on the upper surface of the isotropic flat plate structure when an impact event occurs, and selecting the moment when the signal of the sensor exceeds a threshold value as the starting time of sensor signal interception by taking the signal arrival time of the sensor as a reference; assume that the sensor signal intercept starts at a time ofThe end time of the interception of the sensor signal isThe signal energy of each sensor signal of the upper surface of the isotropic plate structure is calculated according to the following formula:

in the formula (I), the compound is shown in the specification,is a sensor signal;

step four, selecting the front M sensors with the strongest signal energy from the signal energy of each sensor signal calculated in the step three as impact sensors; setting the sensor signal energy of other sensors except the impact sensor in the upper surface of the isotropic flat plate structure to be zero;

step five, summing the sensor signal energy of the sensors in each grid on the upper surface of the isotropic flat plate structure, sorting the summation results according to the size, and selecting the grid with the maximum sensor signal energy as the grid where the impact point is located;

and step six, estimating the impact position according to the following formula by using the sensor signal energy and the coordinates of the sensor in the grid where the impact point is located:

，

in the formula (I), the compound is shown in the specification,andare the coordinates of the estimated impact position,andis the coordinates of the respective sensor or sensors,is the signal energy of the individual sensors;

and seventhly, arranging the sensors on the upper surface of the isotropic flat plate structure from large to small according to the signal energy of the sensors, selecting the sensors which are ranked as M, assuming that the number of the sensor is P, simultaneously selecting the corresponding sensor with the number of the lower surface of the sensor being P', carrying out correlation analysis on the sensor signals of the two selected sensors, and if the correlation of the two signals is low, determining that the isotropic flat plate structure is damaged after impact, otherwise, determining that the isotropic flat plate structure is not damaged after impact.

2. The impact damage recognition method according to claim 1, wherein the mesh is a triangular mesh, a quadrangular mesh, or a pentagonal mesh.

3. The impact damage identification method according to claim 1, wherein the data acquisition system of the monitoring center synchronously acquires signals of each sensor, and when the signals of each sensor do not exceed a signal threshold, the data acquisition system discards the acquired signals and then processes newly acquired signals; when the super-threshold signal exists in the group of collected signals, the collected signals are sent to a processing system of a monitoring center to determine the impact position and identify the damage.

Technical Field

The invention belongs to the technical field of structural health monitoring, and particularly relates to an impact damage identification method for an isotropic flat plate structure.

Background

The aluminum alloy is one of main metal materials in an aviation structure, is an isotropic material, and is widely applied to aviation structures such as skins, frames, brackets and the like. Aeronautical structures are inevitably subjected to external impacts during production, transport, use and maintenance, which cause a reduction in the strength and stability of the structure and even an abrupt breakdown of the whole structure. How to quickly estimate the impact position and determine the potential damage position is an important task for ensuring the safety of the aeronautical structure.

The common impact positioning method generally only identifies the impact position, does not evaluate whether the structure is damaged or not, and cannot meet the requirements of an aviation impact monitoring system.

The existing impact damage monitoring system is generally divided into two systems, namely a passive impact monitoring system and an active damage monitoring system. The passive impact monitoring system is used for impact position monitoring, and the active damage monitoring system is used for damage monitoring. An active damage monitoring system has high requirements for hardware, and needs to actively excite signals in a structure and perform signal processing on damage scattering signals of multiple paths, so that damage identification is obtained.

Disclosure of Invention

The invention aims to provide a method for identifying impact damage of an isotropic flat plate structure based on signal symmetry, which can effectively solve the problem that impact position and damage cannot be identified simultaneously in impact monitoring and can quickly identify and monitor the impact position and the impact damage of a monitored area.

In order to achieve the purpose, the invention adopts the technical scheme that: the impact damage identification method of the isotropic flat plate structure based on signal symmetry comprises the following steps:

firstly, respectively arranging sensor arrays for monitoring impact events on the upper surface and the lower surface of an isotropic flat plate structure, wherein the sensors on the upper surface and the lower surface correspond to each other one by one, numbering the sensors on the upper surface and the lower surface, and connecting all the sensors with the same monitoring center;

step two, the position of each sensor arranged on the upper surface of the isotropic flat plate structure is respectively used as the vertex of a grid, each grid is composed of M vertices, the upper surface of the isotropic flat plate structure is provided with a plurality of grids, and M is a natural number which is greater than or equal to 3;

selecting a sensor with the earliest signal arrival time from the sensors on the upper surface of the isotropic flat plate structure when an impact event occurs, and selecting the moment when the signal of the sensor exceeds a threshold value as the starting time of sensor signal interception by taking the signal arrival time of the sensor as a reference; assume that the sensor signal intercept starts at a time ofThe end time of the interception of the sensor signal isThe signal energy of each sensor signal of the upper surface of the isotropic plate structure is calculated according to the following formula:

in the formula (I), the compound is shown in the specification,is a sensor signal;

step four, selecting the front M sensors with the strongest signal energy from the signal energy of each sensor signal calculated in the step three as impact sensors; setting the sensor signal energy of other sensors except the impact sensor in the upper surface of the isotropic flat plate structure to be zero;

step five, summing the sensor signal energy of the sensors in each grid on the upper surface of the isotropic flat plate structure, sorting the summation results according to the size, and selecting the grid with the maximum sensor signal energy as the grid where the impact point is located;

and step six, estimating the impact position according to the following formula by using the sensor signal energy and the coordinates of the sensor in the grid where the impact point is located:

，

in the formula (I), the compound is shown in the specification,andare the coordinates of the estimated impact position,andis the coordinates of the respective sensor or sensors,is the signal energy of the individual sensors;

and seventhly, arranging the sensors on the upper surface of the isotropic flat plate structure from large to small according to the signal energy of the sensors, selecting the sensors which are ranked as M, assuming that the number of the sensor is P, simultaneously selecting the corresponding sensor with the number of the lower surface of the sensor being P', carrying out correlation analysis on the sensor signals of the two selected sensors, and if the correlation of the two signals is low, determining that the isotropic flat plate structure is damaged after impact, otherwise, determining that the isotropic flat plate structure is not damaged after impact.

The meshes are triangular meshes, quadrilateral meshes or pentagonal meshes.

The data acquisition system of the monitoring center synchronously acquires signals of all the sensors, and when the signals of all the sensors do not exceed the signal threshold, the data acquisition system discards the acquired signals and processes newly acquired signals; when the super-threshold signal exists in the group of collected signals, the collected signals are sent to a processing system of a monitoring center to determine the impact position and identify the damage.

The basic idea of the invention is that the earlier the arrival time of the sensor signal is, the stronger the signal energy of the sensor signal is according to the closer the sensor signal is to the impact point; when the structure is damaged by impact, the symmetry of the sensor signals on the upper and lower surfaces of the flat plate structure is broken. According to the invention, the impact position is estimated by using the arrival time and the signal energy of each sensor signal in the monitoring area, the impact damage is identified by using the symmetry of the sensor signals on the upper surface and the lower surface of the flat plate structure, and the problem that the impact damage is monitored by using a traditional passive monitoring system and an active monitoring system is unified into the passive monitoring system to monitor the impact position and whether the impact damage occurs or not, so that the hardware requirement of the system is simplified, the signal processing process is simplified, and the online requirement of the real-time monitoring of the structural health monitoring can be met.

The invention has the beneficial effects that: according to the invention, the impact position is identified through the arrival time and the signal energy of the sensor signal, and the damage is identified by utilizing the symmetry of the sensor signals on the upper surface and the lower surface of the flat plate structure, so that the problems that the impact position cannot be identified and the damage cannot be identified simultaneously in impact monitoring can be effectively solved; the algorithm of the invention is novel, the algorithm speed is fast, and the requirements on software and hardware are low. The invention can meet the requirement of large-area online real-time impact monitoring of an isotropic structure and can promote the application and development of the structure health monitoring technology of our country.

Drawings

Fig. 1 is a schematic flow chart of the impact damage identification method of the present invention.

Fig. 2 is a schematic diagram of the signal intercept time of the sensor signal.

FIG. 3 is a graph of impact point and sensor position for an impact test.

Fig. 4 is a graph of the signal energy of each sensor.

FIG. 5 shows the similarity coefficient of the sensor signals of the upper and lower surfaces of the flat plate structure at different impact velocities.

FIG. 6 is a signal diagram of the top surface sensor and the bottom surface sensor when the plate structure is not damaged.

FIG. 7 is a graph of signals from the top surface sensor and the bottom surface sensor when the plate structure is damaged.

Detailed Description

The present invention will be described in further detail with reference to the following drawings and examples, but the invention is not limited thereto.

The impact damage identification method of the isotropic flat plate structure based on the signal symmetry is carried out according to the flow shown in figure 1, and comprises the following detailed steps:

the method comprises the following steps that firstly, two groups of sensor arrays are distributed on an isotropic flat plate structure, one group of sensor arrays are distributed on the upper surface of a flat plate, the other group of sensor arrays are distributed on the lower surface of the flat plate, and the sensors are in one-to-one correspondence up and down; each sensor in the two groups of sensor arrays is connected with a data acquisition system of a monitoring center, and the monitoring center synchronously acquires a sensor signal of each sensor;

dividing a monitoring area of the isotropic flat plate structure into a plurality of non-overlapping grids serving as monitoring sub-areas by using the distribution of the sensors, wherein the sensors in any grid serve as vertexes of the grid; the mesh can be flexibly selected according to the actual distribution of the sensors, for example, triangular mesh, quadrilateral mesh, pentagonal mesh and the like can be used, when the quadrilateral mesh is adopted for division, every 4 adjacent sensors are used as the vertex of a mesh unit, the mesh unit is a monitoring subarea, similarly, when the pentagonal mesh is used, each mesh has 5 sensors as the vertices;

step three, (1) when an impact event occurs, the signal of the sensor on the flat plate exceeds a threshold value, each sensor receives a response signal of the flat plate structure, and the data acquisition system stores the acquired signal into the system for analysis and use by an impact damage identification method; if the signals of all the sensors do not exceed the signal threshold, the data acquisition system discards the acquired signals and processes the newly acquired signals;

(2) selecting a sensor with the earliest signal arrival time from sensors on the upper surface of the isotropic flat plate structure, and selecting the moment when the signal of the sensor exceeds a threshold value as the starting time of intercepting the signal of the sensor by taking the signal arrival time of the sensor as a reference; assume that the sensor signal intercept starts at a time ofThe end time of the interception of the sensor signal isThe signal energy of each sensor signal of the upper surface of the isotropic plate structure is calculated according to the following formula:

in the formula (I), the compound is shown in the specification,is a sensor signal;

step four, selecting the front M sensors with the strongest signal energy from the signal energy of each sensor signal calculated in the step three as impact sensors; setting the sensor signal energy of other sensors except the impact sensor in the upper surface of the isotropic flat plate structure to be zero; wherein M is the number of vertices in the divided single mesh, for example, M may be 4, that is, four sensors surround one monitoring sub-region;

step five, summing the sensor signal energy of the sensors in each grid on the upper surface of the isotropic flat plate structure, sorting the summation results according to the size, and selecting the grid with the maximum sensor signal energy as the grid where the impact point is located;

and step six, estimating the impact position by using the sensor signal energy and the coordinates of the sensor in the grid where the impact point is located and a gravity center method according to the following formula:

，

in the formula (I), the compound is shown in the specification,andare the coordinates of the estimated impact position,andis the coordinates of the respective sensor or sensors,is the signal energy of the individual sensors;

and seventhly, arranging the sensors on the upper surface of the isotropic flat plate structure from large to small according to the signal energy of the sensors, selecting the sensors which are ranked as M, assuming that the number of the sensor is P, simultaneously selecting the corresponding sensor with the number of the lower surface of the sensor being P', carrying out correlation analysis on the sensor signals of the two selected sensors, and if the correlation of the two signals is low, determining that the isotropic flat plate structure is damaged after impact, otherwise, determining that the isotropic flat plate structure is not damaged after impact.

In order to better explain the technical scheme of the invention, impact damage monitoring is carried out on an isotropic aluminum plate, and sensor arrays are uniformly distributed on the upper surface and the lower surface of the aluminum plate, so as to sequentially explain the specific implementation process of the method.

As shown in FIG. 3, the isotropic aluminum plate has a size ofAnd 16 sensors are respectively arranged on the upper surface and the lower surface of the isotropic aluminum plate, the sensors on the upper surface are marked as No. 1 to No. 16 sensors, and the sensors on the lower surface are marked as No. 1 'to No. 16' sensors. As shown in fig. 3, 16 sensors, 4 sensors are grouped, the monitoring area is divided into 9 monitoring sub-areas, and the monitoring sub-areas are numbered from left to right and from top to bottom as sub-areas No. 1 to 9. The lower surface of the flat plate structure is also provided with 16 sensors, the distribution of the sensors is the same as that of the sensors on the upper surface of the flat plate, the sensors on the lower surface also divide the monitoring area into 9 monitoring sub-areas, and the numbering mode of the sub-areas is the same as that of the sub-areas on the upper surface of the flat plate.

In the case of impact at the center of the flat plate structure, the complete monitoring process is as follows:

(1) and arranging the sensors and dividing the monitoring sub-regions according to the mode.

(2) When an impact event occurs, the flat plate structure generates stress waves at an impact point, the stress waves are transmitted to the structure, the monitoring system adopts synchronous acquisition, the sensor array on the flat plate structure receives stress wave signals, and each sensor acquires 600 data points.

(3) The arrival time of the sensor signal on the upper surface of the flat plate structure is extracted, the sensor signal with the earliest arrival time is selected, the arrival time of the sensor is taken as the starting time of signal interception, and the signal length is determined by the distance and wave speed of the sensor, as shown in fig. 2.

(4) The signal energy of each sensor on the upper surface of the flat structure is calculated, the 4 sensors with the strongest signal energy are selected, and then the signal energy of the other sensors is set to 0. As shown in fig. 4, the first four sensors with the strongest signal energy are numbers 6, 7, 10, 11.

(5) The sum of the signal energies of the sensors in each monitoring subarea is calculated, the subarea with the largest sum of the signal energies is selected as the area where the impact position is located, and the monitoring subarea surrounded by the sensors No. 6, 7, 10 and 11 can be determined as the area where the impact position is located from the distribution of the signal energies of the sensors in FIG. 4.

(6) The impact position is further estimated by using the barycentric method, using the sensor signal energy and the coordinates of the sensors in the grid where the impact is located. The impact position is (-0.0077 cm, -0.0119 cm) and the real position is (0 cm ), and the estimated position is close to the real position.

(7) The mth sensor is selected according to the ranking of the sensor signal energy from large to small, where M is 4, and it can be known from fig. 4 that the sensor with sensor number 7 is selected. The symmetry of the sensor signals on the upper and lower surfaces of the flat plate at the sensor position whose analysis number is 7 can be analyzed for correlation, and a correlation coefficient can be obtained.

(8) As shown in fig. 5, as the impact velocity increases, the flat plate structure changes from intact to damaged, and the symmetry of the sensor signals on the upper and lower surfaces of the flat plate structure decreases. When there is damage, the symmetry of the structure is broken, and therefore, the symmetry can be used to identify whether the structure is damaged.

(9) As shown in fig. 6, when the impact velocity is 5m/s, the flat plate structure is not damaged, the signals on the upper and lower surfaces of the flat plate structure have good symmetry, and the waveforms of the signals almost coincide. As shown in fig. 7, when the impact velocity is 20m/s, the flat plate structure is damaged, the symmetry of the signals on the upper and lower surfaces of the flat plate structure is deteriorated, and the waveforms of the signals are significantly different.

Therefore, when an impact event occurs, the symmetry of the sensor signals on the upper surface and the lower surface of the flat plate structure is analyzed through the similarity coefficient of the signals, and whether the structure is damaged or not is identified.

The above embodiments are only intended to illustrate the technical solution of the present invention and not to limit the same, and it should be understood by those of ordinary skill in the art that the specific embodiments of the present invention can be modified or substituted with equivalents with reference to the above embodiments, and any modifications or equivalents without departing from the spirit and scope of the present invention are within the scope of the claims to be appended.