1. An ultrasonic detection method for interface rigidity based on microwave network analysis is characterized by comprising the following steps:

(1) theoretical model establishment for interface rigidity detection by applying microwave network S parameters

The method comprises the following steps of representing the interface rigidity condition by detecting S parameters of a microwave network, and deducing an interface rigidity detection model by theory, wherein the formula is as follows (1):

in the formula, K is interface rigidity, rho is structural material density, c is ultrasonic longitudinal wave velocity, omega is angular frequency, and S is microwave network S parameter; from the above formula, under the condition that the materials on the two sides of the interface are not changed, the S parameter of the microwave network is detected, namely the interface rigidity value is obtained, so that the real-time monitoring of the interface contact state is realized;

(2) microwave network S parameter detection interface rigidity

Step 1, building an experiment system

The experimental system is divided into a loading part and a detecting part, wherein the loading part is responsible for providing an experimental loading load and simultaneously transmitting and receiving ultrasonic signals to a to-be-tested part, and the detecting part is responsible for detecting the microwave network S parameters in real time and recording experimental data;

1) setting up loading part of experiment system

The experimental system loading part comprises a loading device, a bearing device, a limiting block and an ultrasonic probe; attaching the two to-be-tested parts to form a contact interface; respectively placing the two ultrasonic probes into a limiting block, wherein the ultrasonic probes realize the conversion between ultrasonic signals and electromagnetic signals; the two limiting blocks are respectively arranged on the upper surface and the lower surface of the test piece and are used for fixing the ultrasonic probe and transmitting a loading load to the test piece to be tested; glycerol is used as a coupling medium at the contact part of the surface of the ultrasonic probe and the test piece; the loading device and the bearing device are respectively fixed on the limiting block, the loading device is used for applying load to the contact interface, and the bearing device is internally provided with a pressure sensor and can feed back a loading force value in real time;

2) building detection part of experiment system

The test system detection part comprises a computer system and a microwave network analyzer; the computer system is connected with the microwave network analyzer through a network cable and is responsible for recording experimental data; the microwave network analyzer is used for generating sine wave frequency sweeping signals and detecting S parameters of the microwave network in real time; the ultrasonic transmitting probe and the ultrasonic receiving probe are respectively connected with a port 1 and a port 2 of the microwave network analyzer;

step 2, searching for proper detection frequency

Loading a load to enable a contact interface of a to-be-tested piece to be in a compression state, adjusting a microwave network analyzer to display a frequency domain detection interface, selecting a frequency band according to the center frequency of an ultrasonic probe, uniformly sweeping the frequency from low to high, and recording the frequency value at the highest position of the amplitude;

step 3, searching a proper loading range

In order to ensure that two pieces to be tested still keep a contact state during unloading, a minimum loading force value is set according to the material of the pieces to be tested; gradually increasing the load, wherein the S parameter of the microwave network analyzer gradually increases along with the increase of the load, when the load increases to a certain degree, the change of the interface rigidity gradually tends to be smooth, and the increase rate of the interface rigidity gradually decreases along with the increase of the load; recording the load as the maximum loading force value at the moment, and selecting a loading force interval according to the maximum loading force value;

step 4, applying load and reading S parameter

Before the experiment, multiple loading-unloading operations are carried out on a piece to be tested in a range from the minimum loading force value to the maximum loading force value so as to eliminate the interference of the plastic deformation of the test piece on the measurement result, the frequency of the microwave network analyzer is set as the detection value in the step 3, the load of the loading device is adjusted to be the minimum loading force value, S parameters of the microwave network analyzer are read, then the load of the loading device is gradually increased, and the S parameters of the corresponding microwave network analyzer are read when the loading force value is increased once;

step 5, analyzing experimental data

Substituting S parameters measured by experiments under different load conditions into the formula (1), and calculating the interface rigidity value under the corresponding load, namely monitoring the change condition of the contact interface rigidity of the structure to be measured along with the load in real time, so as to realize indirect detection of the contact interface rigidity.

Background

The contact interface is widely existed in the engineering structure and has obvious influence on the macroscopic performance of the structure. The interface rigidity is an important parameter for representing the interface contact condition, and the reliability and the safety of an engineering structure are directly related to the detection and the evaluation of the interface rigidity.

At present, the rigidity detection method of the pressure-bearing interface is mainly divided into a direct detection method and an ultrasonic detection method. The direct detection method is to detect the interface rigidity directly from the definition by detecting the interface stress and the interface displacement, and although the definition method is simple and easy to use, the situation of the contact interface displacement is difficult to measure directly due to the complexity of the actual engineering structure; the ultrasonic detection method is characterized in that the interface rigidity is represented by detecting the reflection/transmission coefficient of the ultrasonic wave transmitted to the contact interface, the interface pressure and displacement do not need to be directly measured, and the ultrasonic detection method is widely applied to engineering practice at present.

However, the existing ultrasonic detection technology needs to detect incident waves and transmitted waves respectively, the experimental procedure is complex, and the experimental error is large; and the numerical value of the ultrasonic detection result of the interface rigidity is obviously higher than that of the direct measurement value of the interface rigidity. Accordingly, there is a need for improved methods of ultrasound detection.

The microwave network technology is a key test technology necessary for modern electronic equipment, and the technology is used for measuring the impedance characteristic and the transmission characteristic of a network to be tested through a time domain or a frequency domain, is similar to ultrasonic detection of reflection/transmission coefficients, and can represent the transmission characteristic of a tested element through detecting the relation between incident wave voltage and reflection/transmission wave voltage of a microwave network.

Disclosure of Invention

The invention provides an interface rigidity detection method based on a microwave network S parameter, aiming at the problems of complex experimental steps, large detection result error and the like of the existing interface rigidity detection method.

The technical scheme of the invention is as follows:

an ultrasonic detection method for interface rigidity based on microwave network analysis comprises the following steps:

1. establishing an interface rigidity detection theoretical model by using microwave network S parameters:

the interface rigidity condition is represented by detecting the S parameter of the microwave network (the S parameter can be directly read by a microwave network analyzer). An interface rigidity detection model is derived through theory, and is expressed as formula (1):

in the formula, K is interface rigidity, rho is structural material density, c is ultrasonic longitudinal wave velocity, omega is angular frequency, and S is microwave network S parameter. According to the formula, under the condition that materials on two sides of the interface are not changed, the interface rigidity value can be obtained by detecting the S parameter of the microwave network, and therefore the real-time monitoring of the interface contact state is achieved.

2. The technical scheme for detecting the interface rigidity by using the microwave network S parameters comprises the following steps:

step 1, building an experiment system

The experiment system is divided into a loading part and a detecting part, wherein the loading part is responsible for providing an experiment loading load and simultaneously transmitting and receiving ultrasonic signals to a to-be-tested part, and the detecting part is responsible for detecting the microwave network S parameters in real time and recording experiment data.

(1) Building an experimental system loading part

The experimental system loading part comprises a loading device, a bearing device, a limiting block and an ultrasonic probe; attaching the two to-be-tested parts to form a contact interface; respectively placing the two ultrasonic probes into a limiting block, wherein the ultrasonic probes realize the conversion between ultrasonic signals and electromagnetic signals; the two limiting blocks are respectively arranged on the upper surface and the lower surface of the test piece and are used for fixing the ultrasonic probe and transmitting a loading load to the test piece to be tested; glycerol is used as a coupling medium at the contact part of the surface of the ultrasonic probe and the test piece; the loading device and the bearing device are respectively fixed on the limiting block, the loading device is used for applying load to the contact interface, and the bearing device is internally provided with a pressure sensor and can feed back a loading force value in real time;

(2) building an experimental system detection part

The test system detection part comprises a computer system and a microwave network analyzer; the computer system is connected with the microwave network analyzer through a network cable and is responsible for recording experimental data; the microwave network analyzer is used for generating sine wave frequency sweeping signals and detecting S parameters of the microwave network in real time; the ultrasonic transmitting probe and the ultrasonic receiving probe are respectively connected with a port 1 and a port 2 of the microwave network analyzer;

step 2, searching for proper detection frequency

And (3) properly loading the load to enable the contact interface of the to-be-tested piece to be in a compression state, adjusting the microwave network analyzer to display a frequency domain detection interface, selecting a proper frequency band according to the central frequency of the ultrasonic probe, uniformly sweeping the frequency from low to high, and recording the frequency value at the highest position of the amplitude.

Step 3, searching a proper loading range

In order to ensure that two pieces to be tested still keep a contact state during unloading, a minimum loading force value is set according to the material of the pieces to be tested; the load is gradually increased, S parameters of the microwave network analyzer are gradually increased along with the increase of the load, when the load is increased to a certain degree, the change of the interface rigidity gradually tends to be smooth, and the increase rate of the interface rigidity is gradually reduced along with the increase of the load. And recording the load as the maximum loading force value at the moment, and selecting a proper loading force interval according to the maximum loading force value.

Step 4, applying load and reading S parameter

Before the experiment, multiple loading-unloading operations are carried out on a piece to be tested in a range from the minimum loading force value to the maximum loading force value so as to eliminate the interference of the plastic deformation of the test piece on the measurement result, the frequency of the microwave network analyzer is set as the detection value in the step 3, the load of the loading device is adjusted to be the minimum loading force value, S parameters of the microwave network analyzer are read, then the load of the loading device is gradually increased, and the S parameters of the corresponding microwave network analyzer are read when the loading force value is increased once.

Step 5, analyzing experimental data

And substituting S parameters measured by experiments under different load conditions into the interface rigidity detection model, and calculating the interface rigidity value under the corresponding load, so that the change condition of the contact interface rigidity of the structure to be detected along with the load can be monitored in real time, and the indirect detection of the contact interface rigidity is realized.

The invention has the beneficial effects that: the method only needs to detect the ultrasonic signal once, does not need to respectively detect the incident wave and the transmitted wave twice, and effectively simplifies the experimental process; and the detection experiment result of the microwave network analysis method is more in line with the actual interface contact condition, thereby providing a novel microwave network analysis detection method for the contact interface rigidity detection.

Drawings

Fig. 1 is a schematic diagram of an ultrasonic detection device for interface rigidity by applying microwave network analysis.

Fig. 2 is a diagram of the assembly positions of the limiting block and the ultrasonic probe.

FIG. 3 is a flow chart of ultrasonic detection of interface stiffness using microwave network analysis.

FIG. 4 is a graph showing the results of the interfacial stiffness measurements in the experimental examples.

In the figure: 1 a computer system; 2, a microwave network analyzer; 3, a loading device; 4, a limiting block; 5, testing the piece to be tested; 6, an ultrasonic probe; 7 carrying the device.

Detailed Description

The following further describes a specific embodiment of the present invention by taking a 45-steel square test piece of a certain type as an example.

Step 1, building an experiment system

An ultrasonic receiving probe is matched with a limiting block and is arranged on the surface of a bearing device, as shown in figure 2, the wiring of the ultrasonic receiving probe is connected with a port 2 of a microwave network analyzer, a to-be-tested part is matched to form a contact interface and is integrally arranged on the limiting block, an ultrasonic transmitting probe is matched with the limiting block and is arranged on the upper surface of the to-be-tested part integrally, the wiring of the ultrasonic transmitting probe is connected with a port 1 of the microwave network analyzer, and the network analyzer is connected with a computer system through a network cable.

Step 2, searching for proper detection frequency

Applying 100N load to a test piece to be tested to enable a contact interface of the test piece to be in a compressed state, adjusting a network analyzer to display a frequency domain detection interface, setting the factory center frequency of an ultrasonic probe to be 5MHz, setting the network analyzer to carry out frequency sweep of a 2-8MHz frequency band, and recording the highest frequency of 6.2MHz in a frequency domain graph as a detection frequency.

Step 3, searching a proper loading range

The material of the to-be-tested piece is 45 steel, the estimated structural rigidity is large, the minimum loading load is set to be 1kN, the load is gradually increased, the S parameter of the microwave network analyzer is increased along with the increase of the load, when the load is increased to a certain degree, the S parameter tends to be stable, the interface rigidity at the moment can be reflected to reach the limit, and the loading load at the moment is recorded to be 10 kN.

Step 4, carrying out experiment and obtaining the detection result of the interface rigidity

Before the experiment, a test piece to be tested is subjected to multiple loading-unloading operations in a force value range of 1kN to 10kN, the interference of plastic deformation on a detection result is eliminated, the frequency of a microwave network analyzer is set to be 6.2MHz, the loading load is adjusted to be 1kN, S parameters of the microwave network analyzer are read, then the loading load is gradually increased, the corresponding S parameters are read when the loading load and the S parameters are increased by 1kN, the loads and the S parameters are collected through a computer, the S parameters are substituted into a formula 1, the interface rigidity under the corresponding load condition can be obtained through calculation, the calculation result is shown in a table 1, and the curve diagram of the detection result of the interface rigidity of the test piece to be.

Table 1 shows S parameters measured by experiments under corresponding loads and interface rigidity data obtained by calculation