Composite space truss structure health monitoring method based on multi-point resistance measurement

Abstract

The application discloses a composite space truss structure health monitoring method based on multi-point resistance measurement, comprising the following steps: establishing a material failure resistance calibration curve through force-electric coupling test; abstracting the truss structure into a graph model containing rod resistance and node contact resistance, and optimizing electrode measuring points and excitation-measuring schemes through analyzing node degree and four-wire measurement data volume; performing multi-point resistance measurement based on the optimized scheme, using a sensitivity matrix and a least square method to inverse the resistance increment of each rod and contact point, and combining the calibration curve to perform damage early warning. The application takes the contact resistance as an independent variable for monitoring, solves the problem that contact failure in a welded truss structure is difficult to be identified online, reduces the wiring complexity and measurement time of an on-orbit monitoring system, and through linear and nonlinear layered solving strategies, the application takes into account both conventional monitoring and rapid response to sudden damage, and is suitable for health management of on-orbit additive manufacturing space truss structures.

Description

Technical Field

[0001] This invention belongs to the field of composite material structure health monitoring technology, and more specifically, relates to a method for health monitoring of composite material space truss structures based on multi-point resistance measurement. Background Technology

[0002] As spacecraft sizes grow to the kilometer level, the demand for large space truss structures, as ideal support platforms for ultra-large spacecraft, is becoming increasingly urgent. However, traditional ground assembly and on-orbit deployment methods are limited by the size and carrying capacity of launch vehicle fairings, making it difficult to meet the deployment requirements of ultra-large structures. On-orbit continuous manufacturing technology, by carrying raw materials and molding composite material trusses on-site in space, can overcome fairing constraints, fully leverage the advantages of lightweight and high-strength composite materials, and provide a feasible approach for the construction of ultra-large space infrastructure.

[0003] Large, in-orbit manufactured space truss structures face multiple threats during service, including alternating temperatures, vibrations, and impacts from space debris. Accumulated damage can lead to catastrophic structural failure. However, space truss structures typically consist of hundreds to thousands of members, making traditional visual inspections or equipment checks based on extravehicular activities risky and limited in scope. Damage to composite materials is even more minute, making it difficult to ensure structural health using remote video inspection technologies.

[0004] Fiber-reinforced resin matrix composites, due to their ability to achieve moderate conductivity through the fibers themselves or by adding conductive powders, exhibit significant changes in their resistive response when damage causes fiber breakage or matrix cracking. Based on this characteristic, damage self-sensing can be achieved by measuring the structural resistive response, reducing the need for additional sensor installations. In on-orbit continuous manufacturing, truss connections are typically achieved using thermal welding rather than traditional mechanical connections. This connection method introduces contact resistance between different members, increasing the complexity of the resistive network while also providing a basis for identifying contact point damage. However, applying this method to space truss structures also presents challenges. The numerous truss nodes and the large size of the members mean that placing measurement points at all nodes would lead to redundant wiring and excessive system complexity. Furthermore, the connectivity of the truss structure means that the resistance of each member is coupled into the overall network response; retrieving the independent resistance changes of each member from a limited number of node measurements is a difficult problem.

[0005] Therefore, it is urgent to establish a health monitoring method that considers the structural characteristics and nodal contact resistance of composite space trusses, to screen resistance measurement schemes and avoid the influence of the electrodes themselves, to provide criterion for monitoring damage to truss members, and to realize rapid measurement and online health monitoring of the resistance of composite space trusses. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a health monitoring method for composite material space truss structures based on multi-point resistance measurement.

[0007] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0008] A health monitoring method for composite material space truss structures based on multi-point resistance measurement includes the following steps:

[0009] Step 1: Establish a material failure resistance calibration curve through force-electric coupling test to determine the failure alarm resistance change value;

[0010] Step 2: Abstract the truss structure to be monitored into a graphical model that includes the resistance of the members and the contact resistance of the nodes. Based on the graphical model and circuit analysis, optimize the electrode measuring points and the excitation-measurement scheme.

[0011] Step 3: Perform multi-point resistance measurement based on the optimized excitation-measurement scheme, use the sensitivity matrix and least squares method to invert the resistance increment of each rod and contact point, and combine the failure alarm resistance change value to perform damage early warning.

[0012] To optimize the above technical solution, the specific measures also include:

[0013] Step 1 specifically includes:

[0014] Step 1.1: Prepare standard tensile specimens and welded joints with the same material system and additive manufacturing process as the truss structure to be monitored, and use the four-wire method to measure the initial resistivity of the material to eliminate the influence of contact resistance;

[0015] Step 1.2: Conduct axial tensile force-electric coupling tests on standard tensile specimens and welded joints, record load, strain and resistance, and establish a calibration curve between fiber breakage rate and resistance change rate;

[0016] Step 1.3: Set the failure alarm resistance change value according to the calibration curve.

[0017] The calibration curve covers the entire range of the material from the elastic stage to complete fracture, wherein the fiber breakage rate is the ratio of the number of broken fibers to the initial total number of fibers, and the rate of change of electrical resistance is... , For the real-time resistance of the material, The initial resistance of the material is given.

[0018] In step 1.2, axial tensile force-electric coupling tests were carried out at different ambient temperatures to establish calibration curves between fiber breakage rate and resistance change rate at different temperatures.

[0019] Step two specifically includes:

[0020] Step 2.1: Abstract the truss structure into a graphical model. , where the node set It includes all the intersections of the rods and the measurement points where electrodes can be placed at the ends of the rods, and the rod set. It includes all identifiable truss members. The resistance of the corresponding rod is , the set of touch points This includes all contact points at the welded joints of the members. The corresponding contact resistance is ;

[0021] Step 2.2: Based on the graphical model established in Step 2.1, construct the truss structure correlation matrix including contact resistance. , among which the former row correspondence A real rod, later The row corresponds to the virtual A contact resistance rod, element Indicator rod Starting from node , Indicator rod Termination at node ,otherwise ;

[0022] Step 2.3: Construct a diagonal resistance matrix that includes contact resistance. Based on Kirchhoff's laws, nodal admittance equations are further established. ,in , It is an incidence matrix. Let n be the nodal potential vector. Inject current vectors into nodes;

[0023] Step 2.4: Based on the graph model established in Step 2.1, determine the set of nodes that must be tested, and identify all nodes in the network with degrees of 1 and 2 that constitute the set of nodes that must be tested. The leaf node with a degree of 1 is connected to only one edge. If not measured directly, this edge is coupled to the rest of the network only through a single node, and its resistance cannot be separated and identified from the measurement response of other nodes. The node with a degree of 2 is connected to exactly two edges. If not measured directly, these two edges are in series. External measurement can only obtain its equivalent series resistance, and the independent resistance of the two edges cannot be distinguished.

[0024] Step 2.5, according to Total number of nodes included The maximum number of measurement data sets was obtained by calculating using the four-line method. If the number in this group is greater than the number of unknown resistors Then it is temporarily set. The set of nodes to be measured is defined as follows: if the set is not satisfied, additional available nodes are added to form a new set of measurement nodes. ;

[0025] Step 2.6: Each excitation requires selecting a pair of nodes to inject current. For the node set... Theoretically, at most it requires Secondary incentive, if If the maximum number of measurement data sets is much greater than the number of unknown resistors, then proceed with... This excitation is sufficient. If there exists a measurement node that is not used as an excitation node in any of the excitations, this node is selected as the global voltage reference point. The voltage difference between other nodes and this reference point is then measured. The secondary excitation-measurement constitutes the measurement scheme.

[0026] Step 2.7: Establish the potential response vector at the measurement point in the measurement scheme. Regarding the structural resistance matrix Jacobian matrix ,in It is a column vector composed of all measured voltage differences under all excitations arranged in a fixed order. Given a column vector consisting of the resistances of all members and the contact resistances, verify whether it satisfies the following conditions: If the conditions are not met, adjust the incentive node selection or increase the number of incentive cycles. or continue to proceed in sequence Add new nodes and re-evaluate through steps 2.6-2.7. The final node set is the preferred node set, and the resulting measurement scheme is the preferred measurement scheme.

[0027] Step 2.8: Calculate the sensitivity index of the resistance of each rod under the current measurement scheme. , For the k-th column of the Jacobian matrix, if there are low-sensitivity rods that cannot be avoided under the four-line measurement scheme, then add a single-sided two-line measurement for that component.

[0028] Step 2.9: Final verification of the measurement scheme, forming the final optimized electrode measurement points and excitation-measurement scheme.

[0029] In the four-wire method measurement in step 2.5, the current excitation circuit and the voltage measurement circuit are completely independent and are not affected by the electrode contact resistance. That is, for the set of measurement points... The selected incentive pair , and the selected potential measurement point pair It should meet If there is If there are 2 test points, then after removing 2 excitation nodes, the remaining points are... A non-excited node. From this Select one node from the nodes as the global voltage reference node, and measure the remaining nodes. The voltage difference between each non-excited node and the reference node is measured, and an independent voltage value is obtained for each measurement, resulting in a total of [number missing]. Each independent voltage measurement.

[0030] The single-sided two-wire measurement method described in step 2.8 allows for the simultaneous measurement of the potential response using one of the nodes on the rod when that node is excited.

[0031] Step 3 specifically includes

[0032] Step 3.1: Arrange electrodes on the selected measurement nodes, perform current excitation and voltage measurement according to the selected excitation-measurement scheme, and select an electrode that is not used as a current injection or outflow node in all excitation schemes as the global voltage reference node.

[0033] Step 3.2: Construct the branch-node association matrix based on the structural topology. , its first The row corresponds to the first For each rod or contact resistance, take the transpose of the row vector to obtain the branch-related column vector. The overall nodal admittance matrix is ​​expressed as The admittance matrix of all measurable nodes is also expressed as... ,in Representative matrix The matrix after removing all rows and columns related to unmeasured nodes and global reference nodes. ; For the first The resistance value of a rod or contact resistor;

[0034] Step 3.3: Calculate the nominal initial conductance using the initial rod resistance and contact resistance values ​​known during the manufacturing and testing calibration processes. This value can be used to calculate the initial measurement node admittance matrix. And directly calculate the ideal measurement node voltage response under each round of excitation according to the set excitation mode. ,in The initial voltage response was calculated. It is the node injection current matrix obtained based on the excitation mode. Representing the Wheel of incentives;

[0035] Step 3.4, in and Given the information, according to the sensitivity equation Solve for and extract the components related to the actual measurement nodes, and arrange them in the measurement order to form an initial sensitivity matrix. ,

[0036] Step 3.5: When the structure first enters service, take the initial sensitivity matrix as the baseline. The initial measured node voltage is used as the baseline voltage. Then for the first The voltage increment is calculated from the corresponding baseline state in the next measurement. The increment of each conductance at the current measurement time is calculated using the following formula:

[0037]

[0038] Step 3.6: Update the conductivity and resistance of each rod and contact point:

[0039] ,

[0040] Further calculation of the resistance change The failure resistance warning value determined by the aforementioned material failure resistance calibration method is used to provide a failure warning when the resistance increment exceeds this value.

[0041] Using the first The resistance value obtained from the second measurement updates the sensitivity matrix, which is then used as a new baseline in step 3.5 for calculation.

[0042] When a sudden increase in resistance is detected, a nonlinear least squares method is used to iteratively evaluate the resistance change to prevent errors caused by the small increment assumption.

[0043] The present invention has the following beneficial effects:

[0044] 1. This invention fully leverages the structural characteristics of space trusses manufactured in orbit, where members are connected by heating and welding, resulting in non-negligible contact resistance. By incorporating this contact resistance as a virtual member into the graphical model and nodal admittance equations, it achieves simultaneous identification and monitoring of member resistance and contact resistance, providing, for the first time, online monitoring capabilities for contact failure. Simultaneously, by identifying nodes with topological degrees of 1 and 2 to form a mandatory measurement node set, and by optimizing the measurement points based on the comparison between the number of four-wire method measurement data sets and the number of unknown resistances, the solvability condition is met with the fewest measurement nodes while ensuring the synchronous identification of all unknown resistances. Furthermore, by utilizing the measurement redundancy characteristics of the four-wire method, the required number of excitations is significantly reduced from the theoretical maximum, effectively decreasing the wiring complexity, electrode quantity, and measurement time of the on-orbit monitoring system.

[0045] 2. This invention employs a small-increment assumption in the conductance increment inversion stage, using the initial sensitivity matrix as a baseline. It rapidly solves for the conductance increment using a one-step least squares method, achieving rapid inversion of structural resistance in daily monitoring. Simultaneously, a baseline dynamic update mechanism is established to update the sensitivity matrix with the latest measurement results, effectively controlling the cumulative error caused by linear approximation. When a significant abrupt change in resistance is detected, it automatically switches to a nonlinear least squares iterative solution, balancing monitoring accuracy under both conventional slow degradation and sudden damage conditions.

[0046] 3. This invention forms a complete technical closed loop from obtaining intrinsic material properties to quantitative assessment of structural damage by sequentially executing three core steps: material failure calibration, optimization of measurement points and schemes, and conductivity increment inversion based on the sensitivity matrix. This method is not dependent on a specific truss topology and is universally applicable to the number of members, node distribution, and welding processes, providing a systematic methodological reference for on-orbit health monitoring of composite material space truss structures. Attached Figure Description

[0047] Figure 1 This is a flowchart of the overall method of the present invention;

[0048] Figure 2 The diagram shows the results of the axial force-electric coupling tensile test and calibration of the specimen used.

[0049] Figure 3 This is a schematic diagram of the truss structure to be tested.

[0050] Figure 4 This is a topology diagram of a truss structure considering contact resistance, where red represents nodes with a degree of 1, yellow represents nodes with a degree of 2, and green represents nodes with a degree of 3.

[0051] Figure 5 This is a schematic diagram of the preferred measurement nodes and excitation modes, where green represents mandatory measurement nodes, red represents supplementary nodes, and gray represents non-measured nodes;

[0052] Figure 6 This is the effect of introducing 0.1% Gaussian white noise and performing a 4% incremental inversion on resistor R7. Detailed Implementation

[0053] The present invention will be further described in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following embodiments. Any equivalent substitutions or modifications made by those skilled in the art based on the disclosure of the present invention without departing from the concept of the present invention should fall within the scope of protection of the present invention.

[0054] Step 1, as follows Figure 1As shown, this invention first proposes a method for calibrating the failure resistance of a material, obtaining the calibration curve of the material, and establishing a failure alarm value:

[0055] Step 1.1: Prepare standard tensile specimens with the same material system and additive manufacturing process as the truss structure to be monitored. In this embodiment, the material is carbon fiber reinforced PEEK unidirectional tape. Electrodes and adhesive insulating reinforcing sheets are fabricated on its surface. The initial resistance of the material is measured using the two-wire method and the four-wire method, respectively. The resistance of the four-wire method is significantly smaller than that of the two-wire method. It is considered that the electrode contact resistance introduced by the two-wire method is too large. The four-wire method is used for subsequent tests.

[0056] Step 1.2: Conduct three sets of axial tensile force-electric coupling tests on the tensile specimens on a tensile testing machine, and record the specimen load, strain, and resistance; calculate the fiber breakage rate using the stiffness change rate, and establish the relationship between fiber breakage rate and resistance as the damage-resistance calibration curve for this process and material. The test results and calibration results are as follows: Figure 2 As shown;

[0057] Step 1.3: Based on the requirements, determine the failure alarm resistance change value according to the calibration curve. In this embodiment, the fiber resistance growth rate of 4% is used as the failure warning value.

[0058] Furthermore, the calibration curve should cover the entire range from the elastic stage to complete fracture, with the fiber breakage rate being the ratio of the number of broken fibers to the initial total number of fibers, and the rate of change in electrical resistance being... , For the real-time resistance of the material, The initial resistance of the material is given.

[0059] Furthermore, based on the actual on-orbit service environment temperature, high and low temperature environmental chambers can be used to conduct electromechanical coupling tests under different environmental temperatures, and material damage-resistance calibration curves can be established at different temperatures.

[0060] Furthermore, welded joint samples with the same material system and additive manufacturing process as the truss structure to be monitored can be used to establish a welded joint damage degree-resistance calibration curve and alarm value using the above process.

[0061] Step 2, as follows Figure 1 As shown, this invention further proposes a method for optimizing electrode measuring points and measurement schemes, establishing a method for... Figure 3 Measurement scheme for the truss structure shown:

[0062] Step 2.1: Abstract the additive manufacturing composite truss structure to be monitored into a graphical model. , where the node set The rod set includes all the junctions of the rods and the measurement points at the ends of the rods where electrodes can be placed. Includes all identifiable truss members. The resistance of the corresponding rod is , the set of touch points Includes all contact points at the welded joints of the rods. The corresponding contact resistance is The constructed graph structure is as follows Figure 4 As shown;

[0063] Step 2.2: Based on the graphical model established in Step 2.1, construct the truss structure correlation matrix including contact resistance. , among which the former row correspondence A real rod, later The row corresponds to the virtual A contact resistance rod, element Indicator rod Starting from node , Indicator rod Termination at node ,otherwise ;

[0064] Step 2.3: Construct a diagonal resistance matrix that includes contact resistance. Based on Kirchhoff's laws, nodal admittance equations can be further established. ,in Here is the nodal admittance matrix. Let n be the nodal potential vector. Inject current vectors into nodes;

[0065] Step 2.4: Based on the graph model established in Step 2.1, determine the set of nodes that must be tested, and identify all nodes in the network with degrees of 1 and 2 that constitute the set of nodes that must be tested. The node contains nodes {1,2,3,4,9,10,11,12}. A leaf node with a degree of 1 is connected to only one edge. If not directly measured, this edge is coupled to the rest of the network only through a single node, and its resistance cannot be separated and identified from the measurement response of other nodes. A node with a degree of 2 is connected to exactly two edges. If not directly measured, these two edges are in series. External measurement can only obtain its equivalent series resistance, and the independent resistance of the two edges cannot be distinguished.

[0066] Step 2.5, first according to Total number of nodes included The calculation shows that the maximum number of measurement data sets that can be obtained using the four-line method is [number]. If the number in this group is greater than the number of unknown resistors tentative The set of nodes to be measured;

[0067] Step 2.6, at this point, it is possible The maximum number of measurement data sets is much larger than the number of unknown resistors, so it is unnecessary to perform all of them. Group incentives only require... This excitation is sufficient. Node 4 is selected as the global voltage reference point, and the voltage difference between other nodes with respect to this reference point is measured. The selected... The secondary excitation-measurement constitutes the measurement scheme;

[0068] Step 2.7: However, there may be correlations among these measurement data, making it impossible to solve. Further steps are needed to establish the potential response vector at the measurement point within the measurement scheme. Regarding the structural resistance matrix Jacobian matrix ,in It is a column vector composed of all measured voltage differences under all excitations arranged in a fixed order. Given a column vector consisting of the resistances of all members and the contact resistances, verify whether it satisfies the following conditions: If the conditions are not met, more measurement nodes are added. In this embodiment, it has been verified that even if all nodes are selected for measurement, the maximum rank of the Jacobian matrix is ​​8, and there are 4 unidentifiable links. The single-sided two-line method must be introduced as a supplement. The other 8 links can be completely identified by the four-line method. Therefore, this step only verifies the 8 measurable resistors. It has been verified that the measurable resistors can be identified by the nodes of the mandatory set under 3 excitations.

[0069] Step 2.8: In this embodiment, there is a resistor. The corresponding rods cannot be measured under the four-line measurement scheme. Therefore, two-line measurement on one side is added separately for these four components. Thus, it is necessary to add measuring points 6 and 7.

[0070] Step 2.9: Final verification of the measurement plan, resulting in the final measurement plan. (For example...) Figure 5 As shown, in this embodiment, the final measurement points are selected as {1,2,3,4,6,7,9,10,11,12}, and the four-wire excitation scheme is as follows: 10-11 :11-12、 :11-9, at this time the rank of the Jacobian matrix is ​​8, satisfying except To meet the external resistance identification requirements and add a new single-sided two-wire measurement scheme. 3-7、 12-7、 11-6、 :2-6, allows the voltage of nodes 2,3,11,12 to be measured during excitation, at which time the Jacobian matrix is ​​full rank.

[0071] Furthermore, since the weld joint consists of two rods welded together, two different electrodes can be arranged on the surfaces of the two rods, and the contact point can be considered as a virtual rod. Therefore, the node set... At the intersection of members, there are two measuring points, both of which should be included in the node set.

[0072] Furthermore, in step 7, new nodes are added to the node set. Priority inclusion If a node increases the rank but decreases the condition number of the matrix, try another candidate node, unless no other node can increase the rank.

[0073] Furthermore, in the four-wire measurement scheme in step 2.5, the current excitation circuit and the voltage measurement circuit are completely independent and unaffected by the electrode contact resistance. That is, for the set of measurement points... The selected incentive pair , and the selected potential measurement point pair It should meet If there is If there are 10 measurement points, then at 10 ... Select one of the non-excitation measurement points as the reference voltage node, and measure the remaining... The voltage difference between each node and the reference node is obtained. Each independent voltage measurement.

[0074] Furthermore, the single-sided two-wire method in step 2.8 is used for measurement. That is, for one of the nodes on the rod, it is allowed to use the node to measure the potential response at the same time when the node is excited. However, it will inevitably introduce the contact resistance of the node electrode, so it is used as a supplementary means.

[0075] Step 3, as follows Figure 1 The present invention further proposes a damage early warning method based on resistance increment:

[0076] Step 3.1: Arrange electrodes at the measurement nodes determined by the preferred electrode measurement points and measurement scheme. Perform current excitation and voltage measurement according to the preferred and verified excitation-measurement scheme. Select node 4 as the global voltage reference node. The final number of measurement points determined by the selected scheme is as follows. The number of excitations in the four-line method is If the single-sided two-line method requires 4 excitation cycles, then this measurement method provides... Group voltage response;

[0077] Step 3.2: Construct the branch-node association matrix based on the structural topology. , its first The row corresponds to the first For each rod or contact resistance, take the transpose of the row vector to obtain the branch-related column vector. The overall nodal admittance matrix can be expressed as The admittance matrix of all measurable nodes can also be expressed as: ,in Representative matrix The matrix after removing all rows and columns related to unmeasured nodes and global reference nodes. ;

[0078] Step 3.3: Calculate the nominal initial conductance using the initial rod resistance and contact resistance values ​​known during the manufacturing and testing calibration processes. This value can be used to calculate the initial measurement node admittance matrix. And directly calculate the ideal measurement node voltage response under each round of excitation according to the set excitation mode. ,in The initial voltage response was calculated. It is the node injection current matrix obtained based on the excitation mode. Representing the In this embodiment, the initial resistance of the rod is 0.8 ohms and the initial contact resistance is 2 ohms.

[0079] Step 3.4, in and Given the information already obtained, further analysis is conducted based on the sensitivity equation. Solve for and extract the components related to the actual measurement nodes, and arrange them in the measurement order to form an initial sensitivity matrix. ,

[0080] Step 3.5: When the structure first enters service, take the initial sensitivity matrix as the baseline. The initial measured node voltage is used as the baseline voltage. Then for the first The voltage increment is calculated from the corresponding baseline state in the next measurement. The increment of each conductance at the current measurement time is calculated using the following formula:

[0081]

[0082] Step 3.6: Update the conductivity and resistance of each rod and contact point:

[0083] ,

[0084] Further calculation of the resistance change A failure resistance warning value is determined by a material failure resistance calibration method, and a failure warning is provided when the resistance increment exceeds this value.

[0085] Furthermore, the initial nodal admittance matrix can be estimated based on the material electrical parameters obtained during the calibration process, or it can be comprehensively calibrated for the first time after manufacturing to reduce the deviation from the true value.

[0086] Furthermore, the third can be utilized as needed. The resistance of each rod obtained from the second measurement is used to calculate a new sensitivity matrix, which is then used as a new baseline and recalculated in step 5.

[0087] Furthermore, if a sudden increase in the resistance of a rod is found in a certain measurement, it may correspond to sudden damage such as an impact from an external object. In this case, the nonlinear least squares method can be used to iteratively and accurately evaluate the resistance change, preventing errors caused by small increment assumptions.

[0088] To further verify the actual effect of the present invention, such as... Figure 6 As shown, this embodiment uses an electrode measuring point and measurement scheme optimization method to obtain an optimized measurement scheme. Then, a damage early warning method based on resistance increment is used to inversely calculate the resistance increase caused by rod damage. When the resistance increases by 4% while other resistances remain unchanged, and 0.1% Gaussian noise is introduced to simulate the measurement error, the results show that this method can still accurately identify the resistance increase caused by rod damage.

[0089] It should be noted that the types of nanofluid working fluids, microstructure forms, abrasive layer types, connection methods, frequency ranges, and filling rates in the above embodiments are merely preferred embodiments and are not intended to limit the scope of protection of this invention. Any technical solution that, based on the technical concept of this invention, introduces nanofluid working fluids into the interior of a heat pipe grinding head and utilizes ultrasonic vibration to enhance its dispersion stability, thereby improving grinding heat dissipation and processing performance, falls within the scope of protection of this invention.

Claims

1. A method for health monitoring of composite material space truss structures based on multi-point resistance measurement, characterized in that, Includes the following steps: Step 1: Establish a material failure resistance calibration curve through force-electric coupling test to determine the failure alarm resistance change value; Step 2: Abstract the truss structure to be monitored into a graphical model that includes the resistance of the members and the contact resistance of the nodes. Based on the graphical model and circuit analysis, optimize the electrode measuring points and the excitation-measurement scheme. Step 3: Perform multi-point resistance measurement based on the optimized excitation-measurement scheme, use the sensitivity matrix and least squares method to invert the resistance increment of each rod and contact point, and combine the failure alarm resistance change value to perform damage early warning.

2. The method for health monitoring of composite material space truss structures based on multi-point resistance measurement according to claim 1, characterized in that, Step 1 specifically includes: Step 1.1: Prepare standard tensile specimens and welded joints with the same material system and additive manufacturing process as the truss structure to be monitored, and use the four-wire method to measure the initial resistivity of the material to eliminate the influence of contact resistance; Step 1.2: Conduct axial tensile force-electric coupling tests on standard tensile specimens and welded joints, record load, strain and resistance, and establish a calibration curve between fiber breakage rate and resistance change rate; Step 1.3: Set the failure alarm resistance change value according to the calibration curve.

3. The method for health monitoring of composite material space truss structures based on multi-point resistance measurement according to claim 2, characterized in that, The calibration curve covers the entire range of the material from the elastic stage to complete fracture. The fiber breakage rate is the ratio of the number of broken fibers to the initial total number of fibers, and the rate of change in electrical resistance is... , For the real-time resistance of the material, The initial resistance of the material is given.

4. The method for health monitoring of composite material space truss structures based on multi-point resistance measurement according to claim 2, characterized in that, In step 1.2, axial tensile force-electric coupling tests were carried out at different ambient temperatures to establish calibration curves between fiber breakage rate and resistance change rate at different temperatures.

5. The method for health monitoring of composite material space truss structures based on multi-point resistance measurement according to claim 1, characterized in that, Step two specifically includes: Step 2.1: Abstract the truss structure into a graphical model. , where the node set It includes all the intersections of the rods and the measurement points where electrodes can be placed at the ends of the rods, and the rod set. It includes all identifiable truss members. The resistance of the corresponding rod is , the set of touch points This includes all contact points at the welded joints of the members. The corresponding contact resistance is ; Step 2.2: Based on the graphical model established in Step 2.1, construct the truss structure correlation matrix including contact resistance. , among which the former row correspondence A real rod, later The row corresponds to the virtual A contact resistance rod, element Indicator rod Starting from node , Indicator rod Termination at node ,otherwise ; Step 2.3: Construct a diagonal resistance matrix that includes contact resistance. Based on Kirchhoff's laws, nodal admittance equations are further established. ,in , It is an incidence matrix. Let n be the nodal potential vector. Inject current vectors into nodes; Step 2.4: Based on the graph model established in Step 2.1, determine the set of nodes that must be tested, and identify all nodes in the network with degrees of 1 and 2 that constitute the set of nodes that must be tested. The leaf node with a degree of 1 is connected to only one edge. If not measured directly, this edge is coupled to the rest of the network only through a single node, and its resistance cannot be separated and identified from the measurement response of other nodes. The node with a degree of 2 is connected to exactly two edges. If not measured directly, these two edges are in series. External measurement can only obtain its equivalent series resistance, and the independent resistance of the two edges cannot be distinguished. Step 2.5, according to Total number of nodes included The maximum number of measurement data sets was obtained by calculating using the four-line method. If the number in this group is greater than the number of unknown resistors Then it is temporarily set. The set of nodes to be measured is defined as follows: if the set is not satisfied, additional available nodes are added to form a new set of measurement nodes. ; Step 2.6: Each excitation requires selecting a pair of nodes to inject current. For the node set... Theoretically, at most it requires Secondary incentive, if If the maximum number of measurement data sets is much greater than the number of unknown resistors, then proceed with... This excitation is sufficient. If there exists a measurement node that is not used as an excitation node in any of the excitations, this node is selected as the global voltage reference point. The voltage difference between other nodes and this reference point is then measured. The secondary excitation-measurement constitutes the measurement scheme. Step 2.7: Establish the potential response vector at the measurement point in the measurement scheme. Regarding the structural resistance matrix Jacobian matrix ,in It is a column vector composed of all measured voltage differences under all excitations arranged in a fixed order. Given a column vector consisting of the resistances of all members and the contact resistances, verify whether it satisfies the following conditions: If the conditions are not met, adjust the incentive node selection or increase the number of incentive cycles. or continue to proceed in sequence Add new nodes and re-evaluate through steps 2.6-2.

7. The final node set is the preferred node set, and the resulting measurement scheme is the preferred measurement scheme. Step 2.8: Calculate the sensitivity index of the resistance of each rod under the current measurement scheme. , For the k-th column of the Jacobian matrix, if there are low-sensitivity rods that cannot be avoided under the four-line measurement scheme, then add a single-sided two-line measurement for that component. Step 2.9: Final verification of the measurement scheme, forming the final optimized electrode measurement points and excitation-measurement scheme.

6. The method for health monitoring of composite material space truss structures based on multi-point resistance measurement according to claim 5, characterized in that, In the four-wire method measurement in step 2.5, the current excitation circuit and the voltage measurement circuit are completely independent and are not affected by the electrode contact resistance. That is, for the set of measurement points... The selected incentive pair , and the selected potential measurement point pair It should meet If there is If there are 2 test points, then after removing 2 excitation nodes, the remaining points are... A non-excited node. From this Select one node from the nodes as the global voltage reference node, and measure the remaining nodes. The voltage difference between each non-excited node and the reference node is measured, and an independent voltage value is obtained for each measurement, resulting in a total of [number missing]. Each independent voltage measurement.

7. The method for health monitoring of composite material space truss structures based on multi-point resistance measurement according to claim 5, characterized in that, The single-sided two-wire measurement method described in step 2.8 allows for the simultaneous measurement of the potential response using one of the nodes on the rod when that node is excited.

8. The method for health monitoring of composite material space truss structures based on multi-point resistance measurement according to claim 1, characterized in that, Step 3 specifically includes Step 3.1: Arrange electrodes on the selected measurement nodes, perform current excitation and voltage measurement according to the selected excitation-measurement scheme, and select an electrode that is not used as a current injection or outflow node in all excitation schemes as the global voltage reference node. Step 3.2: Construct the branch-node association matrix based on the structural topology. , its first The row corresponds to the first For each rod or contact resistance, take the transpose of the row vector to obtain the branch-related column vector. The overall nodal admittance matrix is ​​expressed as The admittance matrix of all measurable nodes is also expressed as... ,in Representative matrix The matrix after removing all rows and columns related to unmeasured nodes and global reference nodes. ; For the first The resistance value of a rod or contact resistor; Step 3.3: Calculate the nominal initial conductance using the initial rod resistance and contact resistance values ​​known during the manufacturing and testing calibration processes. This value can be used to calculate the initial measurement node admittance matrix. And directly calculate the ideal measurement node voltage response under each round of excitation according to the set excitation mode. ,in The initial voltage response was calculated. It is the node injection current matrix obtained based on the excitation mode. Representing the Wheel of incentives; Step 3.4, in and Given the information, according to the sensitivity equation Solve for and extract the components related to the actual measurement nodes, and arrange them in the measurement order to form an initial sensitivity matrix. , Step 3.5: When the structure first enters service, take the initial sensitivity matrix as the baseline. The initial measured node voltage is used as the baseline voltage. Then for the first The voltage increment is calculated from the corresponding baseline state in the next measurement. The increment of each conductance at the current measurement time is calculated using the following formula: Step 3.6: Update the conductivity and resistance of each rod and contact point: ， Further calculation of the change in resistance The failure resistance warning value determined by the aforementioned material failure resistance calibration method is used to provide a failure warning when the resistance increment exceeds this value.

9. The method for health monitoring of composite material space truss structures based on multi-point resistance measurement according to claim 8, characterized in that, Using the first The resistance value obtained from the second measurement updates the sensitivity matrix, which is then used as a new baseline in step 3.5 for calculation.

10. The method for health monitoring of composite material space truss structures based on multi-point resistance measurement according to claim 8, characterized in that, When a sudden increase in resistance is detected, a nonlinear least squares method is used to iteratively evaluate the resistance change to prevent errors caused by the small increment assumption.

Images