Aircraft panel assembly deformation monitoring method based on smart surface

Abstract

The present invention proposes a method for monitoring the deformation of aircraft wall panel assembly based on a smart surface, which belongs to the field of aviation manufacturing engineering and aircraft assembly technology. The present invention designs a long array-shaped conductive composite material printing structure, and proposes an electrical connection method based on this array structure. It can not only accurately determine the position of deformation and monitor the change in the size of wall panel deformation, but also meet the demand for rapid response of monitoring. The present invention innovatively proposes a smart surface for monitoring the deformation of aircraft wall panel assembly. The smart surface is prepared based on 3D printing technology and can be disassembled and assembled at any time at the production site according to actual monitoring needs. It has significant advantages over traditional flexible sensing methods.

Description

Technical Field

[0001] The invention belongs to the field of aviation manufacturing engineering and aircraft assembly technology, and relates to an aircraft wall panel assembly deformation monitoring method based on an intelligent surface layer, which is used for aircraft wall panel assembly deformation monitoring. Background Art

[0002] As an important part of the aircraft's aerodynamic shape, the assembly accuracy of the wall panel directly affects the aircraft's service performance. The wall panel has the characteristics of large size and thin thickness, and the overall rigidity is weak. When the various parts are connected by bolts or rivets, deformation is inevitable in local areas, especially for composite wall panels, whose forming accuracy is difficult to accurately control, which further aggravates the degree of assembly deformation. For monitoring the deformation of wall panel assembly, the existing methods mainly include resistance strain gauges, optical fiber sensors, DIC digital correlation, intelligent flexible sensors and other methods.

[0003] The resistance strain gauge uses the resistance effect to convert the deformation of mechanical components into resistance changes, thereby achieving the purpose of measuring strain. When the optical fiber sensor is used, its own grating pitch changes, which causes the change of the reflection wavelength, and then the external strain is deduced by detecting the change of wavelength. DIC digital correlation can obtain two digital images of the specimen before and after deformation through correlation calculation, and then obtain the deformation information of the monitored area. Existing flexible sensors are mainly divided into two types: surface type and embedded type. The surface type is a conductive material and a matrix stacked and laid on the surface of the material, while the embedded type embeds the conductive material inside the measured material. Both use the significant force resistance function effect of the material, which is manifested as a change in its resistance when deformed by force. The strain information of the structure can be converted into an electrical signal for detection.

[0004] Resistance strain gauges are discrete sensors that can only measure strain at the installation point. When monitoring large-scale aircraft panels, a large number of strain gauges need to be laid, which will increase the monitoring cost. The reflection wavelength of the optical fiber sensor is relatively greatly affected by temperature, and the sensitivity coefficient will also change significantly with temperature. In addition, it uses special optical fibers and high-precision detection systems, and the monitoring cost is high. The DIC digital correlation algorithm is complex and the calculation amount for large-scale measurement is huge, which affects the calculation efficiency of the measurement results. In addition, the panel assembly cycle is long, and it is difficult to maintain the consistency and stability of the monitoring equipment and the spatial position of the panel.

[0005] Existing surface-type flexible sensors lay conductive materials on the entire surface of the location to be measured when monitoring deformation. They cannot flexibly lay conductive materials according to monitoring requirements, which not only causes a large amount of material waste, but also cannot meet the monitoring needs of special shapes of aircraft panels. When using embedded flexible sensors, conductive materials need to be embedded inside the aircraft panels. They cannot be embedded or removed at any time before and after monitoring, which will affect the original structure of the aircraft panels and their mechanical properties. Therefore, finding a new flexible sensing method for accurate and stable deformation monitoring is an urgent problem to be solved in the field of aircraft intelligent assembly.

[0006] The deformation of aircraft panel during assembly will affect its mechanical properties and service status. In order to monitor the deformation of panel assembly, the present invention mainly solves the following technical problems:

[0007] 1. The existing deformation monitoring methods have solved the problems of size limitations, high monitoring costs, strict environmental requirements, stratification during stacking, and difficulty in disassembly and assembly when embedded. A flexible sensing smart surface that can be disassembled and assembled at any time according to monitoring needs, and can flexibly print conductive composite materials and electrode arrangements is proposed.

[0008] 2. It solves the problems of waste of conductive materials and insufficient monitoring accuracy in the overall paving of the traditional intelligent surface monitoring area, and designs a long array printing structure that can accurately determine the position of wall panel deformation and monitor the size of deformation in real time.

[0009] 3. To solve the problems of measuring all the single-filament resistances one by one during monitoring, excessive contact resistance, and long time-consuming result output, a series-parallel hybrid output circuit was designed. This circuit reduces the number of electrodes calculated by half, allowing the array-shaped printing structure to quickly locate the single-filament with resistance changes and calculate its change amount. Summary of the invention

[0010] In order to solve the problems of size limitation, high monitoring cost, strict environmental requirements, stratification caused by stacking, and difficulty in disassembly and assembly when embedded in existing monitoring methods, the present invention proposes an aircraft wall panel assembly deformation monitoring method based on smart surface.

[0011] The technical solution of the present invention is:

[0012] A method for monitoring deformation of aircraft panel assembly based on a smart surface comprises the following steps:

[0013] 1. Preparation of conductive composite materials and substrates and analysis of piezoresistive effect

[0014] The first step is to prepare the conductive composite monofilament

[0015] The graphene and polyurethane powders are placed in an oven for drying pretreatment to remove excess moisture; the two powders are then placed in a ball mill and fully mixed in a ratio of 1:1, and a conductive composite material powder is obtained after stabilization; the mixed conductive composite material powder is then extruded using a single-screw extruder to form a single filament. This process controls the single filament diameter accuracy within the range of 1.5mm±0.1mm for subsequent smart surface 3D printing.

[0016] Step 2: Prepare the substrate

[0017] Add 10% of the total amount of acetone to the molten polyurethane for dilution, and paste a layer on the sticky plastic film at room temperature, and squeeze out the air between the polyurethane and the film by pressure curing. After forming at room temperature, put it in an oven for curing for 2 hours, and cut the cured sample into the required size of the monitoring area to obtain the matrix.

[0018] Step 3: Piezoresistive effect analysis

[0019] The positioning and measurement of wall plate deformation mainly utilizes the piezoresistance characteristics of the single wire. The piezoresistance characteristics of the single wire can be described by the following formula:

[0020] R=ρL / S

[0021] Where: ρ is the resistivity of the single wire; R is the resistance of the single wire; L is the length of the single wire; S is the cross-sectional area of ​​the single wire.

[0022] The piezoresistive effect of the single wire is also reflected in the relationship between the relative change of material strain and resistance and the strain sensitivity coefficient, so a uniaxial tensile strain load analysis is performed. The specimen used for uniaxial tension is the Type I specimen in the GB1040-92 plastic tensile performance test method. The substrate is laid on the upper layer of the parallel part in the middle of the specimen, and the single wire is printed on the upper layer of the substrate. After the single wire is cooled, a copper wire is bonded to the single wire with conductive silver glue as an electrode. The resulting specimen is as follows Figure 1 shown.

[0023] After the sample is prepared, an excitation voltage is given at both ends of the input electrode, and a uniaxial tensile test mechanical testing machine is used to provide a stable and accurate strain load for the sample. At the same time, a collector is used to collect the voltage on both sides of the output electrode, and the resistance change of the single wire during the stretching deformation process is calculated using the volt-ampere method principle, and the relationship between the strain and the relative change in resistance of the single wire is analyzed. In order to characterize the sensitivity of the mechanical resistance effect of the single wire material, the strain sensitivity coefficient is used as a measurement indicator, that is, the sensitivity of the relative change in material resistance with strain. The sensitivity coefficient K is described by the following formula:

[0024] K=ΔR / εR0

[0025] Where: K is the sensitivity coefficient; ε is the strain; ΔR is the change in single wire resistance; R0 is the single wire resistance before deformation.

[0026] 2. Deformation rapid positioning and measurement method

[0027] The size of the aircraft wall panels is large, and printing the monofilaments in the entire monitoring area of ​​the wall panels when monitoring deformation will cause material waste. Therefore, the present invention designs a printing structure in the shape of a strip array that can change the number, length and spacing of the monofilament strips according to the needs of the monitoring area, such as Figure 2As shown. Two substrates are cut according to the size required for monitoring, and long strips of monofilaments with corresponding numbers, lengths and spacings are printed in different directions of the two substrates using 3D printing technology according to the monitoring area. Conductive silver glue is used to stick copper wires on both ends of each monofilament to form electrodes, and epoxy resin is encapsulated on the surface to form a protective layer. After being completely cured, they are stacked together to form a smart surface layer.

[0028] When the above printing structure outputs each single-filament resistor one by one, a large number of measurement circuits need to be set up, which takes a long time and the monitoring response is not timely enough. In order to solve the above problems, a circuit is designed to enable the array-shaped single-filament resistor to be output quickly, such as Figure 3 This circuit connects the single wires in a series-parallel mixed form, which reduces the number of resistance change measurements by half. During monitoring, it is only necessary to collect the value changes of each parallel branch and main current to obtain the resistance change of each single wire.

[0029] Based on the above output circuit, the measurement process is algorithm developed and data packaged to establish a deformation analysis system. The system locates the deformation position of the monitoring area according to the distribution position of the single wire with resistance change; the measurement is carried out according to the sensitive force resistance effect of the single wire material, and each resistance change value corresponds to a strain value of the single wire, thereby determining the deformation size of the area to be measured. The system input is the change in the resistance of the single wire in two directions, and the system output contains a grid model of the position and deformation of each single wire, which displays the position and size of the deformation of the wall panel to be measured in the form of a human-computer interface. At the same time, this system can also set the maximum strain threshold. If the monitored resistance change value exceeds the standard threshold, it is marked as abnormal and an alarm is issued. This method can not only accurately determine the location of the deformation and monitor the change in the size of the wall panel deformation, but also meet the rapid response of aircraft wall panel deformation monitoring.

[0030] 3. Implementation of wall panel assembly deformation monitoring

[0031] When assembling aircraft panels, stress concentration will occur around the screw holes, and the surrounding panel area will then deform by lateral stretching, denting or warping. Figure 4 As shown in the figure, a smart surface layer is laid on the surface of the deformation area around the hole, and each parallel branch and trunk are connected to the data acquisition instrument, and then the acquisition instrument is connected to the computer output terminal. A programmable digital power supply is used to give an excitation voltage to each of the two pairs of input electrodes. After the monitoring equipment is connected, a bolt connection is made in the middle of the wall panel, and the bolts are gradually tightened. By observing the output information of the deformation analysis system interface, the deformation position and size of the monitoring area can be determined, thereby realizing real-time monitoring of the wall panel assembly deformation.

[0032] Beneficial effects of the present invention: The present invention uses 3D printing to print the monofilament material onto the substrate to prepare the intelligent surface layer, avoiding the size limitation, high monitoring cost, strict environmental requirements, stratification during stacking, and difficulty in disassembly and assembly during embedded use of traditional flexible sensors. The present invention proposes a method for fast positioning and measuring deformation based on a printing structure and output circuit in the shape of a long strip array, which can accurately determine the position of the deformation and monitor the deformation size of the wallboard, improve the output efficiency, and solve the problems of long time consumption and insufficient response when outputting ordinary acquisition results. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of a uniaxial tensile specimen.

[0034] Figure 2 It is a schematic diagram of the single-filament array printing structure.

[0035] Figure 3 This is a schematic diagram of the single-wire array output circuit.

[0036] Figure 4 This is a diagram showing the connection of monitoring equipment.

[0037] In the figure: 1 clamping end; 2 input electrode; 3 output electrode; 4 substrate; 5 single wire; 6 collector; 7 digital power supply; 8 computer output end. DETAILED DESCRIPTION

[0038] The specific implementation of the present invention is further explained below in conjunction with the examples and drawings, but is not intended to limit the present invention.

[0039] A method for monitoring deformation of aircraft panel assembly based on smart surface includes three aspects: preparation of conductive composite materials and substrates and analysis of piezoresistive effect, rapid deformation positioning and measurement method, and implementation of panel assembly deformation monitoring.

[0040] 1. Preparation of conductive composite materials and substrates and analysis of piezoresistive effect

[0041] The smart surface layer of the present invention uses a mixture of graphene and polyurethane as a conductive composite material, and polyurethane itself as a matrix. The specific preparation steps are as follows:

[0042] The first step is to prepare the conductive composite monofilament

[0043] The graphene and polyurethane material powders are placed in an oven for drying pretreatment to remove excess moisture; the two powders are then placed in a ball mill and fully mixed in a ratio of 1:1, and a conductive composite material powder is obtained after stabilization; the mixed conductive composite material powder is then extruded using a single-screw extruder to form a single filament. This process controls the accuracy of the single filament diameter within the range of 1.5mm±0.1mm for subsequent smart surface 3D printing.

[0044] Step 2: Prepare the substrate

[0045] Add 10% of the total amount of acetone to the molten polyurethane for dilution, and paste a layer on the sticky plastic film at room temperature, and squeeze out the air between the polyurethane and the film by pressure curing. After forming at room temperature, put it in an oven for curing for 2 hours, and cut the cured sample into the required size of the monitoring area to obtain the matrix.

[0046] The positioning and measurement of wall plate deformation mainly utilizes the piezoresistance characteristics of the single wire. The piezoresistance characteristics of the single wire can be described by the following formula:

[0047] R=ρL / S

[0048] Where: ρ is the resistivity of the single wire; R is the resistance of the single wire; L is the length of the single wire; S is the cross-sectional area of ​​the single wire.

[0049] The piezoresistive effect of the single wire is also reflected in the relationship between the relative change of material strain and resistance and the strain sensitivity coefficient, so a uniaxial tensile strain load analysis is performed. The specimen used for uniaxial tension is a type I specimen in the GB1040-92 plastic tensile performance test method. The substrate 4 is laid on the upper layer of the parallel part in the middle of the specimen, and the single wire 5 is printed on the upper layer of the substrate 4. After the single wire is cooled, a copper wire is bonded to the single wire 5 with conductive silver glue as an electrode. The resulting specimen is as follows: Figure 1 shown.

[0050] After the sample is prepared, an excitation voltage is given at both ends of the input electrode 4, and a uniaxial tensile test mechanical testing machine is used to provide a stable and accurate strain load for the sample. At the same time, a collector is used to collect the voltage on both sides of the output electrode 3, and the resistance change of the single wire during the stretching deformation process is calculated using the volt-ampere method principle, and the relationship between the strain and the relative change in resistance of the single wire is analyzed. In order to characterize the sensitivity of the mechanical resistance effect of the single wire material, the strain sensitivity coefficient is used as a measurement indicator, that is, the sensitivity of the relative change in material resistance with strain. The sensitivity coefficient K is described by the following formula:

[0051] K=ΔR / εR0

[0052] Where: K is the sensitivity coefficient; ε is the strain; ΔR is the change in single wire resistance; R0 is the single wire resistance before deformation.

[0053] 2. Deformation rapid positioning and measurement method

[0054] The size of the aircraft wall panels is large, and printing the monofilaments in the entire monitoring area of ​​the wall panels when monitoring deformation will cause material waste. Therefore, the present invention designs a printing structure in the shape of a strip array that can change the number, length and spacing of the monofilament strips according to the needs of the monitoring area, such as Figure 2As shown. Two substrates are cut according to the size required for monitoring, and the monofilaments of the above shape are printed in different directions of the two substrates using 3D printing technology. The copper wires are pasted on both ends of each monofilament as shown in the figure using conductive silver glue to form electrodes, and the surface is encapsulated with epoxy resin to form a protective layer. After being completely cured, they are stacked together to form a smart surface layer.

[0055] When the above printing structure outputs each single-filament resistor one by one, a large number of measurement circuits need to be set up, which takes a long time and the monitoring response is not timely enough. In order to solve the above problems, a circuit is designed to enable the array-shaped single-filament resistor to be output quickly, such as Figure 3 This circuit connects the single wires in a series-parallel mixed form, reducing the number of resistance change measurements by half. During monitoring, it is only necessary to collect the numerical changes of each parallel branch A1, A2, A3, A4, A5, ..., An / 2 and the trunk current A0 to obtain the resistance change of each single wire.

[0056] Based on the above output circuit, the measurement process is algorithm developed and data packaged to establish a deformation analysis system. The system locates the deformation position of the monitoring area according to the distribution position of the single wire with resistance change; the measurement is carried out according to the sensitive force resistance effect of the single wire material, and each resistance change value corresponds to a strain value of the single wire, thereby determining the deformation size of the area to be measured. The system input is the change in the resistance of the single wire in two directions, and the system output contains a grid model of the position and deformation of each single wire, which displays the position and size of the deformation of the wall panel to be measured in the form of a human-computer interface. At the same time, this system can also set the maximum strain threshold. If the monitored resistance change value exceeds the standard threshold, it is marked as abnormal and an alarm is issued. This method can not only accurately determine the location of the deformation and monitor the change in the size of the wall panel deformation, but also meet the rapid response of aircraft wall panel deformation monitoring.

[0057] 3. Implementation of wall panel assembly deformation monitoring

[0058] When assembling aircraft panels, stress concentration will occur around the screw holes, and the surrounding panel area will then deform by lateral stretching, denting or warping. Figure 4 As shown, the smart surface layer is laid on the surface of the deformation area around the hole, and each parallel branch and the main line are connected to the data acquisition instrument 6, and then the acquisition instrument 6 is connected to the computer output terminal 8, and a programmable digital power supply 7 is used to give an excitation voltage to each of the two pairs of input electrodes. After the monitoring equipment is connected, a bolt connection is made in the middle of the wall panel, and the bolts are gradually tightened. By observing the output information of the deformation analysis system interface, the deformation position and size of the monitoring area can be determined, thereby realizing real-time monitoring of the wall panel assembly deformation.

Claims

1. A method for monitoring deformation of aircraft panel assembly based on smart surface, characterized in that: The method comprises the following steps:

1. Preparation of Conductive Composite Materials and Substrates and Analysis of Piezoresistive Effect The first step is to prepare the conductive composite monofilament The graphene and polyurethane powders are placed in an oven for drying pretreatment to remove excess moisture; the two powders are then placed in a ball mill and fully mixed in a ratio of 1:1 to obtain conductive composite material powder after stabilization; the mixed conductive composite material powder is then extruded using a single-screw extruder to form a monofilament for subsequent smart surface 3D printing; Step 2: Prepare the substrate Add 10% of the total amount of acetone to the molten polyurethane for dilution, paste a layer on the sticky plastic film at room temperature, and squeeze out the air between the polyurethane and the film by pressure curing; after forming at room temperature, put it in an oven for curing for 2 hours, and cut the cured sample according to the required size of the monitoring area to obtain the matrix; Step 3: Piezoresistive effect analysis The positioning and measurement of wall plate deformation mainly utilizes the piezoresistance characteristics of the single wire; the piezoresistance characteristics of the single wire are described by the following formula: R=ρL / S Where: ρ is the resistivity of the single wire; R is the resistance of the single wire; L is the length of the single wire; S is the cross-sectional area of ​​the single wire; The piezoresistive effect of a single wire is also manifested in the relationship between the relative change in material strain and resistance and the strain sensitivity coefficient. Therefore, a uniaxial tensile strain load analysis is performed. In order to characterize the sensitivity of the piezoresistive effect of the single wire material, the strain sensitivity coefficient is used as a measurement index, that is, the sensitivity of the relative change in material resistance to the change in strain. The sensitivity coefficient K is described by the following formula: K=ΔR / εR0 Where: K is the sensitivity coefficient; ε is the strain; ΔR is the change in single-filament resistance; R0 is the single-filament resistance before deformation; 2. Deformation rapid positioning and measurement method Design a printing structure of a strip array shape that changes the number, length and spacing of the single filament strips according to the needs of the monitoring area, i.e., a smart surface layer; In order to quickly output the resistance of arrayed single wires, a circuit is designed. The single wires are connected in series-parallel hybrid form, which reduces the number of resistance change measurements by half. During monitoring, only the value changes of the currents of each parallel branch and the main line need to be collected to obtain the resistance change of each single wire. Based on the above output circuit, the measurement process is algorithm developed and data packaged to establish a deformation analysis system; the system locates the deformation position of the monitoring area according to the distribution position of the single wire with resistance change; the measurement is carried out according to the sensitive force resistance effect of the single wire material, and each resistance change value corresponds to a strain value of the single wire, thereby determining the deformation size of the area to be measured; the system input is the change in the resistance of the single wire in two directions, and the system output includes a grid model of the position and deformation of each single wire, and displays the position and size of the deformation of the wall panel area to be measured in the form of a human-computer interface; 3. Implementation of wall panel assembly deformation monitoring An intelligent surface layer is laid on the surface of the deformation area around the hole, and each parallel branch and the main line are connected to a data acquisition instrument, which is then connected to the computer output terminal. A programmable digital power supply is used to give an excitation voltage to each of the two pairs of input electrodes. After the monitoring equipment is connected, a bolt connection is made in the middle of the wall panel, and the bolts are gradually tightened. The output information of the deformation analysis system interface is observed to determine the deformation position and size of the monitoring area, thereby realizing real-time monitoring of the wall panel assembly deformation.

2. The method for monitoring deformation of aircraft panel assembly based on smart surface according to claim 1, characterized in that: In the second step, the method for designing the smart surface is as follows: two substrates are cut according to the size required for monitoring, and long strips of monofilaments with corresponding numbers, lengths and spacings are printed in different directions of the two substrates using 3D printing technology according to the needs of the monitoring area. Copper wires are pasted on both ends of each monofilament using conductive silver glue to form electrodes, and epoxy resin is encapsulated on the surface to form a protective layer. After complete curing, they are stacked together to form a smart surface.

3. The method for monitoring aircraft panel assembly deformation based on smart surface according to claim 1 or 2, characterized in that: The deformation analysis system can set a maximum strain threshold. If the monitored resistance change value exceeds the standard threshold, it is marked as abnormal and an alarm is issued.

4. The method for monitoring deformation of aircraft panel assembly based on smart surface according to claim 1 or 2, characterized in that: In the first step, the accuracy of the monofilament diameter is controlled within the range of 1.5 mm ± 0.1 mm.

5. The method for monitoring deformation of aircraft panel assembly based on smart surface according to claim 3 is characterized in that: In the first step, the accuracy of the monofilament diameter is controlled within the range of 1.5 mm ± 0.1 mm.

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