LED display screen performance simulation method based on digital twinning

Abstract

The present application relates to the technical field of performance simulation, in particular to a LED display screen performance simulation method based on digital twinning, comprising the following steps: constructing a three-dimensional geometry of the LED display screen and defining the LED lamp bead array topology structure, assigning a bidirectional reflectance distribution function to the display screen surface, and assigning a thermal expansion coefficient and an elastic modulus to the internal solder joints. Based on the defined three-dimensional geometry structure, the lamp bead array topology relationship and the material physical parameters are set, the accurate mapping between the digital model and the real device is realized, and a more actual performance response basis is provided; by introducing the real environment light distribution and the thermal cycle temperature range, the time-varying environmental load conditions are obtained, the restoration degree of the actual service conditions of the display screen is improved, and the authenticity of the performance prediction results is effectively improved; further, the stress and strain tensor data at the solder joints are extracted to form solder joint damage records, and quantitative evaluation of material damage is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of performance simulation, in particular to a LED display screen performance simulation method based on digital twinning. BACKGROUND

[0002] Performance simulation technology is a technical means for simulating and predicting the performance of equipment or system under various actual working conditions by establishing virtual environment, mathematical model and digital platform.

[0003] In the prior art, performance simulation and prediction are usually realized by a simple virtual environment, without considering the complex internal physical characteristics and material micro-behavior of actual equipment, which leads to the difficulty of reflecting the response characteristics of real equipment under actual complex environmental conditions. Therefore, improvement is needed. SUMMARY

[0004] The purpose of the present application is to solve the shortcomings in the prior art, and a LED display screen performance simulation method based on digital twinning is proposed.

[0005] In order to achieve the above purpose, the present application adopts the following technical scheme, a LED display screen performance simulation method based on digital twinning, comprising the following steps:

[0006] Constructing a three-dimensional geometry of the LED display screen and defining the LED lamp bead array topology structure, assigning a bidirectional reflection distribution function to the display screen surface, assigning a thermal expansion coefficient and an elastic modulus to the internal solder joints, and establishing a LED display screen digital twin;

[0007] Based on the LED display screen digital twin, setting the illumination parameters of the CIE standard sky and the temperature upper and lower limits of the thermal cycle, obtaining a time-varying environmental load sequence, based on the time-varying environmental load sequence, applying illumination and temperature changes to the LED display screen digital twin, and iteratively calculating the internal stress and strain distribution of the components caused by thermal expansion mismatch, generating a component stress and strain response field;

[0008] Based on the component stress and strain response field, extracting the stress tensor and strain tensor of each solder joint in each thermal cycle, obtaining a single solder joint stress and strain record, based on the single solder joint stress and strain record, obtaining a solder joint cumulative damage value;

[0009] Based on the solder joint cumulative damage value, comparing the solder joint cumulative damage value of each solder joint with a preset failure threshold, determining the light-emitting state of the corresponding pixel unit as failure, generating a pixel failure state map, based on the pixel failure state map, updating the light-emitting distribution of the LED display screen digital twin, and obtaining a simulation visual effect performance index.

[0010] Preferably, the obtaining step of the LED display screen digital twin is:

[0011] The outer contour of the LED display screen surface and the position of the internal solder joints are plotted with spatial coordinates, the three-dimensional geometry of the display screen and the internal solder joints is determined through spatial coordinate gridding, and a three-dimensional geometric model of the LED display screen is obtained;

[0012] Based on the three-dimensional geometric model of the LED display screen, the spatial position of the lamp beads on the display screen surface is set according to the regular arrangement mode of the LED lamp bead array, and the topological connection relationship between each lamp bead and the adjacent lamp beads in the lamp bead array is determined, to obtain the topological structure of the LED lamp bead array;

[0013] Based on the topological structure of the LED lamp bead array, the optical parameters of the display screen surface and the mechanical properties of the internal solder joints are respectively specified, the bidirectional reflectance distribution function of each surface element of the display screen surface is associated, and the internal solder joints are each assigned a preset thermal expansion coefficient and elastic modulus, to obtain the LED display screen digital twin.

[0014] Preferably, the obtaining step of the time-varying environmental load sequence is:

[0015] Based on the LED display screen digital twin, the sky diffuse radiation distribution in the lighting model is set, the sky brightness distribution curve of the CIE standard sky and the direct solar radiation intensity value are each mapped to each surface element on the display screen digital twin surface, to form a lighting parameter set;

[0016] Based on the lighting parameter set, the upper and lower limits of the temperature of the thermal cycle are set, the temperature variation rate and the duration in each cycle are each determined by defining the periodic variation law of the temperature upper and lower limits, and the temperature values at each time node are recorded, to form a thermal cycle temperature parameter set;

[0017] Based on the thermal cycle temperature parameter set, the sky radiation intensity at each moment in the lighting parameter set and the temperature parameter at the corresponding moment are each combined to form an environmental load change point arranged in time sequence, and all the environmental load change points are connected to form a complete time-varying environmental load sequence.

[0018] Preferably, the obtaining step of the component stress-strain response field is:

[0019] The illumination intensity value and the corresponding temperature value at each time node are extracted from the time-varying environmental load sequence in sequence, and the illumination intensity value and the temperature value are each mapped to each surface element of the LED display screen digital twin, to form a surface element per-hour environmental boundary load sequence;

[0020] Based on the time-based environment boundary load sequence of the surface element, the temperature value of each solder joint in the LED display screen digital twin at each time node is calculated, the thermal expansion coefficient value and the elastic modulus value of each solder joint are called, the thermal expansion deformation of each solder joint is calculated one by one through the product of the temperature difference and the thermal expansion coefficient value, and a solder joint thermal expansion deformation sequence is formed.

[0021] Based on the solder joint thermal expansion deformation sequence, the deformation difference between each solder joint is calculated time by time and point by point, the stress and strain value distribution caused by the deformation difference inside the solder joint connection is calculated point by point and layer by layer through the calling of the elastic modulus value and the spatial geometric topological relationship between the solder joints, and a component stress and strain response field is generated.

[0022] Preferably, the obtaining step of the single solder joint stress and strain record is:

[0023] Based on the component stress and strain response field, each time node data layer in the component stress and strain response field is traversed one by one, the stress tensor component and the strain tensor component corresponding to the position of each solder joint are extracted for each time node, and are numbered and identified according to the order of the time nodes, to obtain a solder joint time sequence stress and strain component set arranged in time sequence;

[0024] According to the time interval division mode of the thermal cycle period, all the time node data in the solder joint time sequence stress and strain component set are grouped by period, and the stress tensor component and the strain tensor component of all the time nodes of the same solder joint position in each period are aggregated and arranged, to obtain a solder joint period stress and strain component set in a thermal cycle period;

[0025] Based on the solder joint period stress and strain component set in the thermal cycle period, the period number, the stress tensor component and the strain tensor component of a single solder joint in each thermal cycle period are archived item by item, the complete stress tensor component and the strain tensor component of each solder joint in each thermal cycle period are recorded by period, and a single solder joint stress and strain record is generated.

[0026] Preferably, the obtaining step of the single solder joint stress and strain record is:

[0027] Based on the single solder joint stress and strain record, the maximum principal strain component and the minimum principal strain component corresponding to a single solder joint in each thermal cycle period are extracted one by one, the difference between the maximum principal strain component and the minimum principal strain component is calculated and divided by two, to form the strain amplitude of the single solder joint in each thermal cycle period, and the maximum principal stress component and the minimum principal stress component corresponding to a single solder joint in each thermal cycle period are extracted synchronously, the difference between the maximum principal stress component and the minimum principal stress component is calculated and divided by two, to form the stress amplitude of the single solder joint in each thermal cycle period, and a single solder joint stress amplitude and strain amplitude sequence is obtained;

[0028] based on the single-weld stress amplitude and strain amplitude sequence, a normalized cyclic strain energy damage factor of the single-weld in each thermal cycle period is calculated;

[0029] based on the normalized cyclic strain energy damage factor of the single-weld in each thermal cycle period, all normalized cyclic strain energy damage factors are sequentially accumulated and summed according to the thermal cycle period number order to form a weld cumulative damage value of the single-weld under the current full life cycle.

[0030] Preferably, the pixel failure state map acquisition step is:

[0031] based on the weld cumulative damage value, the weld cumulative damage value corresponding to each weld is extracted one by one, and the pixel unit number associated with each weld is read at the same time, the weld cumulative damage value and the corresponding pixel unit are bound one by one to form a weld cumulative damage value mapping table;

[0032] according to the weld cumulative damage value mapping table, a failure determination factor of each weld is calculated;

[0033] based on the failure determination factor, when the failure determination factor is greater than or equal to zero, the corresponding pixel unit is marked as a failure state, and when the failure determination factor is less than zero, the corresponding pixel unit is marked as a normal state, and a pixel failure state map is generated.

[0034] Preferably, the simulation visual effect performance index acquisition step is:

[0035] based on the pixel failure state map, for each surface element, first search the pixel unit state corresponding to the element, when the pixel unit is in a failure state, set the luminous radiation brightness to zero, when the pixel unit is in a normal state, read the original luminous radiation brightness, and perform spatial mapping on the luminous radiation brightness of all elements to form a luminous distribution map;

[0036] based on the luminous distribution map, the exit point radiation brightness of the LED display screen digital twin in the target observation direction is calculated;

[0037] based on the exit point radiation brightness, all valid observation points in the LED display screen digital twin are traversed, the highest exit point radiation brightness and the lowest exit point radiation brightness in the target display area are extracted, and when the lowest exit point radiation brightness is not equal to zero, the highest exit point radiation brightness is subtracted from the lowest exit point radiation brightness and then divided by the lowest exit point radiation brightness to obtain a simulation visual effect performance index.

[0038] Compared with the prior art, the advantages and positive effects of the present application are:

[0039] The application is based on the defined three-dimensional geometric structure, sets the lamp bead array topological relationship and material physical parameters, realizes accurate mapping between the digital model and the real device, and provides a more actual performance response basis; by introducing the real environment light distribution and the thermal cycle temperature range, the time-varying environmental load conditions are obtained, the restoration degree of the actual service condition of the display screen is improved, and the authenticity of the performance prediction result is effectively improved; further, the stress and strain tensor data at the welding points are extracted to form the welding point damage record, and the quantitative evaluation of material damage is realized; based on the cumulative damage value, the failure threshold is clearly set, the actual failure state of each welding point corresponding to the pixel unit is determined, the digital light distribution map is updated, the visual performance of the display screen is accurately simulated, and the comprehensive evaluation of the visual performance is realized; the accuracy and applicability of the digital simulation performance evaluation result are effectively improved, the actual device reliability prediction ability is enhanced, and the device operation risk is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 The figure is a schematic diagram of the steps of the application. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical scheme and advantages of the application more clear, the application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the application and do not limit the application.

[0042] Please refer to Figure 1 The application provides a technical scheme, a LED display screen performance simulation method based on digital twinning, including the following steps:

[0043] Constructing the three-dimensional geometry of the LED display screen and defining the LED lamp bead array topological structure, specifying the bidirectional reflection distribution function for the display screen surface, specifying the thermal expansion coefficient and elastic modulus for the internal welding points, and establishing the LED display screen digital twin;

[0044] Based on the LED display screen digital twin, setting the light parameters of the CIE standard sky and the upper and lower limits of the temperature of the thermal cycle, obtaining the time-varying environmental load sequence, based on the time-varying environmental load sequence, applying the light and temperature changes to the LED display screen digital twin, and iteratively calculating the internal stress and strain distribution of the component caused by thermal expansion mismatch to generate the component stress and strain response field;

[0045] Based on the component stress and strain response field, the stress tensor and strain tensor of a single welding point in each thermal cycle period are extracted to obtain the single welding point stress and strain record, and based on the single welding point stress and strain record, the welding point cumulative damage value is obtained;

[0046] Based on the cumulative damage value of the welding spot, the cumulative damage value of each welding spot is compared with a preset failure threshold to determine the light-emitting state of the corresponding pixel unit as failure, a pixel failure state map is generated, and based on the pixel failure state map, the light-emitting distribution of the LED display screen digital twin is updated to obtain a simulation visual effect performance index.

[0047] The obtaining step of the LED display screen digital twin is:

[0048] The spatial coordinates of the outer contour of the LED display screen surface and the positions of the internal welding spots are drawn, the three-dimensional geometry of the display screen and the internal welding spots is determined through spatial coordinate gridding, and a three-dimensional geometric model of the LED display screen is obtained;

[0049] Based on the three-dimensional geometric model of the LED display screen, the spatial position of the lamp beads on the display screen surface is set according to the regular arrangement mode of the LED lamp bead array, and the topological connection relationship between each lamp bead and the adjacent lamp beads in the lamp bead array is determined, and the LED lamp bead array topology is obtained;

[0050] Based on the LED lamp bead array topology, the optical parameters of the display screen surface and the mechanical properties of the internal welding spots are specified respectively, the display screen surface is associated with the bidirectional reflectance distribution function, and the internal welding spots are assigned with a preset thermal expansion coefficient and elastic modulus one by one, and the LED display screen digital twin is obtained.

[0051] Specifically, first, a three-dimensional laser scanner or an industrial computed tomography device is used to scan the physical entity of the actual LED display screen to obtain point cloud data of the outer surface, the PCB board, and the key internal components, especially the welding spots. Based on the point cloud coordinates, the frame, the mask, and the outer shape of the PCB board of the display screen module are outlined, and the center three-dimensional coordinates (X, Y, Z) of each welding spot are calibrated. Subsequently, the drawn geometric contour is subjected to spatial gridding processing. For regions with gentle changes in geometric shape, such as the flat surface of the display screen, a basic grid size is set, which is determined according to the minimum outer dimension of the display screen. For example, for a 0.5-meter-long display screen, the basic grid size can be set to 1 millimeter. In key areas with complex geometric structures or stress concentration, such as the fillet transition area of the welding spot and the connection interface between the welding spot and the PCB pad, a finer grid size is used. This fine size is set according to the diameter of the welding spot, which is calculated as one-tenth of the welding spot diameter. If the welding spot diameter is 0.5 millimeters, the grid size of this area is set to 0.05 millimeters. In this way, a non-uniform finite element grid composed of tetrahedral or hexahedral elements is generated at all key positions and surfaces. The collection of these grid nodes and their connection relationships collectively constitute a three-dimensional geometric model of the LED display screen with precise geometric characteristics.

[0052] Based on the three-dimensional geometric model of the LED display screen, first, the two-dimensional surface of the effective display area of the display screen is extracted from the model, and the coordinate system origin of the area is determined, for example, the top left corner vertex is defined as (0, 0), according to the pixel spacing parameters in the design specification document of the display screen, for example, the horizontal spacing is 2.5 mm, and the vertical spacing is 2.5 mm, a virtual two-dimensional grid is generated on the surface of the display screen in a programmed manner, each intersection point of the grid is a theoretical center position of an LED lamp bead, then, the theoretical positions are mapped to the surface grid nodes of the outermost layer of the three-dimensional geometric model one by one, the grid node closest to each theoretical position in the Euclidean distance is found, and the accurate three-dimensional coordinates of the node are assigned to the corresponding LED lamp bead, the spatial position setting of all lamp beads on the display screen surface is completed, on this basis, in order to establish the topological connection relationship between the lamp beads, an eight-neighbor connection model is adopted, for each lamp bead in the array, its eight adjacent lamp beads are identified through its row and column indexes (i, j) in the two-dimensional grid, that is, the lamp beads with indexes (i-1, j-1), (i-1, j), (i-1, j+1), (i, j-1), (i, j+1), (i+1, j-1), (i+1, j), (i+1, j+1), the unique identifier of each lamp bead is associated with the identifiers of its eight adjacent lamp beads, and is stored in an adjacency list, the adjacency list records the direct adjacent relationship between all lamp beads in the entire array in detail, and thus the topological structure of the LED lamp bead array is obtained.

[0053] Based on the LED lamp bead array topology, first, the optical parameters of the display screen surface are processed, specifically, each surface grid unit, i.e. facet, in the three-dimensional geometric model of the LED display screen is traversed, and a bidirectional reflectance distribution function model is matched for it from the pre-set material optical property library according to the physical component to which the facet belongs, for example, for the epoxy resin packaging part of the LED lamp bead, the Cook-Torrance microfacet model containing the Fresnel term is selected to simulate its mirror reflection characteristics, and for the black matte plastic part of the display screen mask, the Lambertian model is selected to simulate its ideal diffuse reflection characteristics, and the parameters of the corresponding model, such as diffuse reflectivity, highlight roughness, etc., are assigned to each facet. Then, the mechanical properties of the internal solder joints are processed. According to the solder type used in the production process, such as SAC305 lead-free solder, the thermal expansion coefficient and elastic modulus of the solder at different temperatures are queried and extracted from the technical specification provided by the material supplier or the standard material mechanical property database, for example, a reference thermal expansion coefficient is assigned to SAC305 solder, and an elastic modulus is assigned. These specific mechanical parameter values are assigned to the corresponding solder joint grid units one by one. Finally, all the data including the accurate three-dimensional geometric shape, LED lamp bead array topology relationship, surface optical parameters and internal solder joint mechanical properties are integrated to form a unified, multi-physical field attribute coupled data model, and the LED display screen digital twin is obtained.

[0054] The acquisition step of the time-varying environmental load sequence is:

[0055] Based on the LED display screen digital twin, the sky diffuse radiation distribution in the lighting model is set, the sky brightness distribution curve of the CIE standard sky and the direct solar radiation intensity value are mapped to each facet on the surface of the display screen digital twin one by one to form a set of lighting parameters;

[0056] Based on the set of lighting parameters, the upper and lower limits of the temperature of the thermal cycle are set, the temperature change rate and duration in each cycle are determined one by one by defining the periodic variation law of the temperature upper and lower limits, and the temperature values at each time node are recorded to form a set of thermal cycle temperature parameters;

[0057] Based on the set of thermal cycle temperature parameters, the sky radiation intensity at each moment in the set of lighting parameters and the temperature parameter at the corresponding moment are called one by one to form time-sequentially arranged environmental load change points, and all the environmental load change points are connected to form a complete time-varying environmental load sequence.

[0058] Specifically, based on the LED display screen digital twin, first, a specific CIE standard sky model is selected, for example, a CIE standard overcast sky model is selected according to the simulated typical outdoor cloudy weather conditions, which defines the relationship between the brightness of any point on the sky dome and the zenith angle and the position of the sun, then, a specific geographic location and simulation time are set, for example, 30 degrees north latitude, midsummer noon 12 o'clock, the solar altitude angle and azimuth angle at this time are calculated, and a solar direct radiation intensity reference value is set according to the atmospheric transparency and other parameters, for example, set to 1000 watts per square meter under clear and cloudless conditions, then, the entire sky dome is discretized into hundreds of light source directions, and for each face element on the surface of the display screen digital twin, the included angle between its normal vector and each discrete light source direction, and the included angle with the direct solar radiation direction are calculated one by one, the incident radiation brightness from each sky light source direction is calculated using the brightness distribution function of the CIE standard overcast sky model, and combined with the solar direct radiation intensity value, the radiation contribution of all visible light source directions is numerically integrated, and finally the total radiation illuminance projected onto the face element is calculated, each face element and its corresponding total radiation illuminance value are stored to form a set of lighting parameters.

[0059] Based on the set of lighting parameters, first, according to the industry-accepted environmental adaptability test standard for electronic devices, the upper and lower limits of the temperature cycle are set, specifically set to a minimum temperature of minus 40 degrees Celsius and a maximum temperature of 85 degrees Celsius, then, a specific periodic temperature variation function is defined to describe the fluctuation law of the temperature between the upper and lower limits, for example, a complete sinusoidal function cycle is adopted, and the complete cycle length of each thermal cycle is set to 4 hours, which includes 1 hour of temperature rise from minus 40 degrees Celsius to 85 degrees Celsius, 1 hour of high temperature maintenance, 1 hour of temperature drop from 85 degrees Celsius to minus 40 degrees Celsius, and 1 hour of low temperature maintenance, based on this function, the average temperature change rate during the temperature rise and temperature drop stages is calculated to be about 2.08 degrees Celsius per minute, finally, a fixed time step is used, for example, every 60 seconds, the temperature variation function of the entire cycle is sampled, the temperature values at each discrete time node are recorded, and these temperature data points arranged in time sequence are collected to form a set of thermal cycle temperature parameters.

[0060] Based on the thermal cycle temperature parameter set, first determine a total simulation time span, for example, simulate continuous operation for 720 hours, and set a uniform time step, for example, 10 minutes, to discretize the entire process, then, in a time loop, traverse each time step node from 0 to 720 hours one by one, at each time node, first query or calculate the ambient temperature parameter at this time from the thermal cycle temperature parameter set by interpolation, at the same time, call the light parameter set, and dynamically adjust the position parameters of the sun, i.e. the solar elevation angle and azimuth angle, according to the position of the current time node in a day, and recalculate the sky brightness distribution and solar direct radiation intensity, to obtain the sky radiation intensity at this time mapped to each surface element of the display screen digital twin, then, combine the temperature parameter and sky radiation intensity at the current time into a data pair, which is an environmental load change point at this time node, arrange the environmental load change points calculated at all time nodes in chronological order, and finally connect all these points to form a complete time-varying environmental load sequence.

[0061] The obtaining step of the component stress-strain response field is:

[0062] From the time-varying environmental load sequence, extract the light intensity value and the corresponding temperature value of each time node in sequence, and map the light intensity value and the temperature value to each surface element of the LED display screen digital twin one by one, to form a surface element hourly environmental boundary load sequence;

[0063] Based on the surface element hourly environmental boundary load sequence, calculate the temperature value of each solder joint in the LED display screen digital twin at each time node, call the thermal expansion coefficient value and the elastic modulus value of each solder joint, and calculate the thermal expansion deformation of each solder joint by multiplying the temperature difference and the thermal expansion coefficient value one by one, to form a solder joint thermal expansion deformation sequence;

[0064] Based on the solder joint thermal expansion deformation sequence, calculate the deformation difference between each solder joint at each time point, and through the call of the elastic modulus value and the spatial geometric topological relationship between the solder joints, calculate the stress and strain value distribution caused by the deformation difference at the solder joint connection at each point and layer, to generate the component stress-strain response field.

[0065] Specifically, a time-stepping loop is initiated from the time-varying ambient load sequence, and each time node in the sequence is traversed. At each time node, the ambient temperature value at that time is first extracted, for example, at the Nth time step, the extracted temperature is 35 degrees Celsius, and a complete set of irradiance values corresponding to that time is obtained. These irradiance values are not single values but include the specific solar direct and sky diffuse irradiance fluxes projected onto each surface element of the LED display screen digital twin, for example, for the surface element facing the sun, its irradiance value is 950 watts per square meter, while for the surface element in the shade or with a large angle to the sun, its value can be as low as 150 watts per square meter. Then, these load values are applied as thermal boundary conditions to the finite element model of the digital twin. Specifically, the ambient temperature value is used to define the convective heat transfer boundary condition, and an air flow-based convective heat transfer coefficient is set, for example, in still air, it is set to 10 watts per square meter per Kelvin, and applied to all surface elements exposed to the atmosphere. At the same time, the irradiance value corresponding to each surface element is directly applied to the surface element as a heat flux density boundary condition. All the boundary conditions of all the surface elements at all time nodes are collected in time sequence to form a surface element time-varying ambient boundary load sequence.

[0066] Based on the surface element time-varying ambient boundary load sequence, a complete multi-physical field coupled transient thermal analysis is performed. This analysis solves the heat conduction equation of the entire LED display screen digital twin using the finite element method. Before the analysis begins, an initial temperature field is set, usually the reference ambient temperature at the time of assembly, for example, 25 degrees Celsius, which is also used as the zero-stress reference temperature for calculating thermal expansion. During the analysis, the software solver iteratively calculates the accurate temperature distribution of all nodes inside the entire model at the current time node based on the applied surface element time-varying ambient boundary load sequence and the pre-set thermal physical properties of each material in the digital twin, such as the thermal conductivity of the PCB board being 0.3 watts per meter per Kelvin and the thermal conductivity of the solder joint being 50 watts per meter per Kelvin. After the analysis is complete, the temperature values of all grid nodes inside each solder joint geometry at each time node are extracted from the obtained three-dimensional temperature field data. Then, the thermal expansion coefficient value assigned to each solder joint during the construction of the digital twin is called, the temperature difference of the solder joint at each time node is obtained by subtracting the zero-stress reference temperature from the temperature value, and the theoretical thermal expansion deformation of each solder joint without any external constraints is calculated by multiplying the temperature difference by the thermal expansion coefficient value. The calculation results of all solder joints at all time nodes are recorded in time sequence to form a solder joint thermal expansion deformation sequence.

[0067] Based on the complete three-dimensional temperature field obtained in the previous step, which contains the complete three-dimensional temperature field of all components at each time node, rather than just the sequence of solder thermal expansion deformation, a quasi-static thermal structure coupling analysis is performed. At each time node, the three-dimensional temperature field at that time is applied as a body load to the entire LED display screen digital twin model, and the mechanical properties defined for all components in the digital twin are called, including the elastic modulus, Poisson's ratio and thermal expansion coefficient of FR-4 substrate, electronic component package and solder. Due to the difference in thermal expansion coefficient of different materials, for example, the thermal expansion coefficient of FR-4 substrate is about 14 times 10 to the power of negative 6 per degree Celsius, and the thermal expansion coefficient of solder is 22 times 10 to the power of negative 6 per degree Celsius. Under the same temperature change, the deformation trend of each connecting component is different, resulting in internal stress at the connecting points such as solder joints. By solving the balance equation based on elastic mechanics and material constitutive relation (for solder, Anand viscoplastic constitutive model is used to describe its creep and plastic behavior), the complete stress tensor and strain tensor of each grid element in the model at the current time node are calculated. This process is repeated at all time nodes, and a four-dimensional data set containing the stress and strain state of all points in the model over the entire simulation period is finally generated, i.e. the component stress-strain response field.

[0068] The acquisition step of single solder joint stress-strain record is:

[0069] Based on the component stress-strain response field, each time node data layer in the component stress-strain response field is traversed one by one, and the stress tensor components and strain tensor components corresponding to all solder joint positions at each time node are extracted and numbered according to the order of time nodes to obtain a set of solder joint time sequence stress-strain component set arranged in time sequence;

[0070] According to the time interval division method of the thermal cycle period, all time node data in the solder joint time sequence stress-strain component set are grouped by period, and the stress tensor components and strain tensor components of all time nodes of the same solder joint position in each period are aggregated and arranged to obtain a set of solder joint period stress-strain component set in the thermal cycle period.

[0071] Based on the set of solder joint period stress-strain component set in the thermal cycle period, the period number, stress tensor component and strain tensor component of each solder joint in each thermal cycle period are archived one by one, and the complete stress tensor component and strain tensor component of each solder joint in each thermal cycle period are recorded by period to generate a single solder joint stress-strain record.

[0072] Specifically, based on the component stress-strain response field, first define a post-processing script for data extraction, the goal of the script is to traverse all time nodes in the entire four-dimensional data field, at each time node, the script will lock the finite element set marked as "weld point" in advance in the digital twin model, for all elements in a single weld point, the volume-weighted average method is used to calculate its equivalent stress and strain state, specifically, for each weld point, traverse all finite element units inside it, read the stress tensor six independent components and strain tensor six independent components of each unit, multiply each component value by the volume of the unit where it is located, then add up all the products of the units, and finally divide by the total volume of the weld point, to get an average stress tensor and an average strain tensor of the weld point at that time node, then, the integer serial number of the time node, for example, starting from 1 and increasing, is associated with the extracted average stress tensor components and average strain tensor components of all weld points. Store, this process is repeated for all time nodes to get a time-ordered weld point time series stress-strain component set.

[0073] According to the weld point time series stress-strain component set, first read the total duration of a single thermal cycle from the thermal cycle temperature parameter set, for example, 4 hours, and combine the time step used in the simulation, for example, 10 minutes, to calculate the number of time nodes contained in each thermal cycle, in this example, 24 nodes, then, for all data entries in the weld point time series stress-strain component set, group them according to their time node numbers, the grouping logic is to divide the time node number by 24, the number of nodes contained in each cycle, after subtracting 1, the quotient plus 1 is the cycle number to which the data belongs, for example, data with time node numbers ranging from 1 to 24 are classified into the first cycle, 25 to 48 into the second cycle, and so on, after completing the cycle attribution determination of all time nodes, for the data in each cycle, re-aggregate them according to the unique identifier of the weld point, reorganize the stress tensor components and strain tensor components of the same weld point in the same cycle into a sequence in the original time order, to get a thermal cycle period weld point cycle stress-strain component set.

[0074] Based on the set of stress and strain components of the solder joint in each thermal cycle, all unique solder joint identifiers are traversed, and for each solder joint, all thermal cycle numbers are traversed, for example, from the first cycle to the last simulation cycle. In each cycle, an independent structured data record is created, which contains three core fields. The first field is the unique identifier of the single solder joint being processed, the second field is the number of the current thermal cycle, and the third field is an array or list that contains the complete stress tensor components and strain tensor components of each time node of the solder joint in the thermal cycle in chronological order. This process formats and itemizes the previously aggregated data, ensuring that the stress and strain history of each solder joint in each cycle is an independent and complete unit. All such structured data records of all solder joints and all cycles are collected to generate a single solder joint stress and strain record.

[0075] The acquisition step of the cumulative damage value of the solder joint is:

[0076] Based on the single solder joint stress and strain record, the maximum principal strain component and the minimum principal strain component of the single solder joint in each thermal cycle are extracted one by one. The difference between the maximum principal strain component and the minimum principal strain component is calculated and divided by two to form the strain amplitude of the single solder joint in each thermal cycle. At the same time, the maximum principal stress component and the minimum principal stress component of the single solder joint in each thermal cycle are extracted synchronously. The difference between the maximum principal stress component and the minimum principal stress component is calculated and divided by two to form the stress amplitude of the single solder joint in each thermal cycle. The stress amplitude and strain amplitude sequences of the single solder joint are obtained;

[0077] Based on the single solder joint stress amplitude and strain amplitude sequence, the normalized cyclic strain energy damage factor of the single solder joint in each thermal cycle is calculated, and the calculation formula is:

[0078] ;

[0079] wherein, is the normalized cyclic strain energy damage factor of the single solder joint in the i-th thermal cycle, is the stress amplitude of the single solder joint in the i-th thermal cycle, is the strain amplitude of the single solder joint in the i-th thermal cycle, is the fatigue strength coefficient of the single solder joint material, is the fatigue ductility coefficient of the single solder joint material, is the energy damage conversion index;

[0080] ​​​Based on the normalized cyclic strain energy damage factor of each hot cycle period of a single weld point, all normalized cyclic strain energy damage factors are sequentially accumulated and summed in order of hot cycle period number to form the weld point cumulative damage value of the single weld point under the current full life cycle.

[0081] Specifically, based on the stress-strain record of a single weld point, the record of each weld point in each hot cycle period is processed. First, for a specific hot cycle period, such as the 5th cycle, the stress tensor and strain tensor sequence recorded at all time nodes in the cycle are extracted. The stress tensor of each time node in the sequence is subjected to eigenvalue decomposition to obtain three principal stress components at that time. At the same time, the corresponding strain tensor is subjected to the same eigenvalue decomposition to obtain three principal strain components. All principal stress components calculated at all time nodes in the cycle are collected, and the global maximum and global minimum are found. For example, in a cycle, the maximum value of all principal stress components is 30 MPa, and the minimum value is -15 MPa. The stress amplitude of the cycle is calculated by subtracting the minimum value from the maximum value and dividing by two, which is 22.5 MPa. The same processing procedure is used to find the global maximum and global minimum of all principal strain components in the cycle. For example, the maximum value is 0.005, and the minimum value is -0.002. The strain amplitude of the cycle is calculated to be 0.0035. This calculation process is performed independently for each weld point and each hot cycle period. Finally, the stress amplitude and strain amplitude of each weld point in each cycle are recorded in pairs to form a sequence of single weld point stress amplitude and strain amplitude.

[0082] Formula: The formula has the advantage that it uses a cyclic strain energy-based damage model, which can more accurately reflect the energy dissipation and damage accumulation process of materials under complex loading conditions by using the product of stress amplitude and strain amplitude as the core damage parameter. This is especially true for materials such as weld points that exhibit significant elastic-plastic and creep behavior, which can better capture their fatigue mechanism. At the same time, the formula normalizes the damage factor through the fatigue strength coefficient and the fatigue ductility coefficient, making the calculation results have a clear physical meaning, i.e., the fatigue life fraction consumed by a single cycle. The presence of the exponential term provides flexibility for the model to fit the fatigue behavior of different materials.

[0083] for the stress amplitude of the single weld point in the th hot cycle period. This parameter is directly obtained from the single weld point stress amplitude and strain amplitude sequence generated in the previous step, according to the weld point number and cycle number being processed The extracted value reflects half of the maximum stress variation range experienced by the solder joint in a complete temperature cycle, representing the intensity level of the cyclic loading. For example, for solder joint number 158, the stress amplitude extracted from the sequence in the 200th thermal cycle is 28 MPa.

[0084] For the first The strain amplitude of a single weld point within a thermal cycle is obtained in the same way as the stress amplitude, directly extracted from the stress amplitude and strain amplitude sequence of a single weld point. It represents half of the maximum strain change range experienced by the weld point in the same cycle, reflecting the degree of deformation under cyclic loading. For example, for weld point number 158, the extracted strain amplitude is 0.004 in the 200th thermal cycle.

[0085] The fatigue strength coefficient is the fatigue performance index of a single solder joint material. This parameter is an inherent fatigue performance index of the material and is determined by performing standardized uniaxial strain-controlled fatigue tests (according to ASTM E606 standard) on the solder used (e.g., SAC305). In the test, the number of cycles at which the material fails is recorded under different strain amplitudes, and the relationship curve between stress amplitude and failure reversal number is plotted on a double logarithmic coordinate system. The intercept of this curve is the fatigue strength coefficient. For SAC305 solder, a typical value of its fatigue strength coefficient is 78 MPa, obtained by consulting public material property databases or test reports provided by suppliers.

[0086] The fatigue ductility coefficient of a single solder joint material is also an inherent fatigue property of the material. It is determined through the same tests used to obtain the fatigue strength coefficient. The curve showing the relationship between the plastic strain amplitude and the number of failure reversals is plotted in a double logarithmic coordinate system. The intercept of this curve is the fatigue ductility coefficient, which characterizes the plastic deformation capacity of the material during the fatigue process. For SAC305 solder, a typical value of 0.42 is obtained from the same material property data source.

[0087] The energy damage conversion index is an empirical fitting constant used to correlate cyclic strain energy with fatigue life. Its value is determined by the fatigue test data of the material. By performing a double log-linear regression analysis on the strain energy (the product of stress amplitude and strain amplitude) of each cycle in the test and the corresponding failure cycle number, the slope of the resulting straight line is the reciprocal of the index. This index reflects the sensitivity of the material to energy damage. For solders such as SAC305, the value of the energy damage conversion index is set to 1.75.

[0088] Calculation process:

[0089] For the weld No. 158, the normalized cyclic strain energy damage factor at the 200th thermal cycle is calculated as ,

[0090] First, the acquired parameters are substituted into the formula:

[0091] MPa;

[0092] ;

[0093] MPa;

[0094] ;

[0095] ;

[0096] The cyclic strain energy item is calculated as

[0097] ;

[0098] The normalized energy item is calculated as

[0099] ;

[0100] The damage factor is calculated as

[0101] ;

[0102] ;

[0103] ;

[0104] The result shows that the damage amount of the weld No. 158 at the 200th thermal cycle is about .

[0105] Based on the normalized cyclic strain energy damage factor of each thermal cycle of a single weld, the damage accumulation calculation is performed for each independent weld. This process follows the linear damage accumulation rule. Specifically, first, an accumulated damage value variable is initialized for each weld and set to zero. Then, starting from the first cycle, the normalized cyclic strain energy damage factor calculated for each cycle of the weld is read in sequence, and the value is added to the corresponding accumulated damage value variable. For example, for a certain weld, the damage factor at the 1st cycle is , and the damage factor at the 2nd cycle is , then after two cycles, the accumulated damage value of the weld is ​The accumulation process continues until all simulated thermal cycle periods are traversed, and the final value of the final cumulative damage value variable of each solder joint is the solder joint cumulative damage value of the solder joint under the current full life cycle.

[0106] The obtaining step of the pixel failure state map is:

[0107] Based on the solder joint cumulative damage value, the solder joint cumulative damage value corresponding to each solder joint is extracted one by one, and the pixel unit number associated with each solder joint is read at the same time. The solder joint cumulative damage value is bound to the corresponding pixel unit one by one to form a solder joint cumulative damage value mapping table.

[0108] According to the solder joint cumulative damage value mapping table, the failure determination factor of each solder joint is calculated, and the calculation formula is:

[0109] ;

[0110] Among them, is the failure determination factor of the i th solder joint, is the solder joint cumulative damage value of the i th solder joint, is the failure threshold value. Based on the failure determination factor, when the failure determination factor is greater than or equal to zero, the corresponding pixel unit is marked as a failure state, and when the failure determination factor is less than zero, the corresponding pixel unit is marked as a normal state, and a pixel failure state map is generated.

[0111] Specifically, based on the solder joint cumulative damage value, first, traverse all the unique identifiers of the solder joints in the entire LED display screen digital twin. For each solder joint identifier, extract its corresponding solder joint cumulative damage value from the final result calculated in the previous step. At the same time, query the unique number of the pixel unit associated with the solder joint identifier from the topological structure information established when the digital twin is constructed. Usually, a pixel unit is composed of three sub-pixel lamp beads of red, green and blue, and each lamp bead has at least two solder joints. Therefore, it is necessary to clarify which pin of which pixel unit each solder joint belongs to. The extracted solder joint cumulative damage value and the queried pixel unit number are constructed into a key-value pair, where the key is the solder joint identifier, and the value is a composite structure containing the solder joint cumulative damage value and the pixel unit number. All solder joint key-value pairs are stored to form a solder joint cumulative damage value mapping table.

[0112] The formula is:

[0113] Among them,

[0114] is the failure determination factor of the i th solder joint, ​​cumulative damage value of the weld point, which is the final output of all previous calculation steps, is directly generated from the cumulative damage value of the last key step according to the weld point number being processed extracted, which comprehensively reflects the total fatigue damage of the weld point under the repeated thermal expansion and contraction throughout the entire simulated service period, and is a dimensionless value, for example, for the weld point numbered 305, after 50000 simulated thermal cycle periods, the calculated cumulative damage value of the weld point is 1.25.

[0115] is the failure threshold, which is a key engineering judgment reference, and its setting directly determines the degree of conservatism or aggressiveness of the simulation results. When the cumulative damage value reaches 1, the material fails in fatigue. In actual engineering applications, in order to introduce a certain safety margin and take into account factors such as model uncertainty and material performance dispersion, a value less than 1 will be selected. The determination of this value is based on a comparison and analysis of a large amount of accelerated life test data and actual product failure statistical data. For example, a batch of LED display screens are tested under high temperature and high humidity cycles for a long time, and the average cycle number at which the first pixel fails is recorded, and the cumulative damage value of the key weld point at this time is calculated. Through statistical analysis of multiple sets of such test data, it is found that when the cumulative damage value reaches 0.8, the product failure probability increases significantly. Therefore, the failure threshold is set to 0.8.

[0116] Calculation process:

[0117] For the weld point numbered 305 (i.e. ), the failure determination factor ,

[0118] First, substitute the obtained parameters into the formula:

[0119] ;

[0120] ;

[0121] Calculate the failure determination factor:

[0122] ;

[0123] ;

[0124] The result shows that the failure determination factor of the weld point numbered 305 is 0.45. Since the value is greater than zero, according to the determination rule, the weld point is determined to have failed. The size of this positive value can reflect the degree of overshoot to some extent, i.e. the amount of cumulative damage exceeding the failure threshold. This calculation provides a direct basis for generating the pixel failure state diagram subsequently.

[0125] Based on the failure determination factor, a state marking program is started, which traverses all the failure determination factors of the welding points. For each welding point, the value of its failure determination factor is first read, and a conditional judgment is performed. The judgment logic is that if the value of the failure determination factor is greater than or equal to zero, for example, the calculated value is 0.45, the state of the pixel unit associated with the welding point is marked as “failure”. If there are multiple welding points in a pixel unit, as long as the failure determination factor of any one of the welding points is greater than or equal to zero, the pixel unit is marked as failure. If the failure determination factor of a welding point is less than zero, for example, the calculated value is -0.2, the corresponding pixel unit remains in the “normal” state. The program sets the initial state of all pixel units on the display screen to “normal”, and then updates them one by one according to the above logic. Finally, all pixel units and their final states (“normal” or “failure”) are organized and stored in the form of a two-dimensional matrix. The row and column indices of the matrix correspond to the physical positions of the pixel units on the display screen, and the values of the matrix elements are the states of the pixel units, thereby generating a pixel failure state map.

[0126] The acquisition steps of the simulation visual effect performance index are:

[0127] Based on the pixel failure state map, for each surface patch, first retrieve the state of the pixel unit corresponding to the patch. When the pixel unit is in a failure state, set the luminous radiation brightness to zero. When the pixel unit is in a normal state, read the original luminous radiation brightness. Map the luminous radiation brightness of all patches in space to form a luminous distribution map.

[0128] Based on the luminous distribution map, calculate the exit point radiation brightness of the LED display screen digital twin in the target observation direction. The calculation formula is:

[0129] ;

[0130] Where, is the exit radiation brightness of point along the observation direction , is the self-luminous radiation brightness of point along the observation direction , is the hemispherical integral domain representing all incident directions, is the bidirectional reflectance distribution function of point in the incident direction and the exit direction , is the incident radiation brightness of point along the incident direction , is the incident direction vector dot product with surface normal vector , representing the angle modifier in Lambert's cosine law;

[0131] Based on the exit point radiance, traverse all the valid observation points in the LED display screen digital twin, extract the highest exit point radiance and the lowest exit point radiance in the target display area, and when the lowest exit point radiance is not equal to zero, use the highest exit point radiance minus the lowest exit point radiance divided by the lowest exit point radiance to obtain the simulation visual effect performance index.

[0132] Specifically, based on the pixel failure state map, first, an original luminous radiance reference needs to be defined, which represents the luminous condition of the display screen when displaying a specific picture in an ideal state, for example, in order to evaluate the visual impact in the worst case, set the display picture to full white field, and according to the product specification of the display screen, set the original luminous radiance of each pixel unit to 1200 watts per square meter per steradian, then start a luminance update program, which traverses each surface element constituting the light-emitting surface in the LED display screen digital twin model, for each surface element, first query its pixel unit number through its geometric position index, then use the pixel unit number to search in the pixel failure state map to obtain the state of the pixel unit, if the searched state is "failure", the program will forcibly set the luminous radiance value of the current surface element to zero, if the state is "normal", the program will read the original luminous radiance value from the previously set reference, i.e. 1200 watts per square meter per steradian, and assign it to the current surface element, after this process is performed for all surface elements associated with the pixel unit, a dataset containing the latest luminous radiance values of all surface elements is generated, this dataset is the luminous distribution map.

[0133] Formula: The advantage of the formula is that it can simulate the complex interaction of light and display screen surface, decompose the visual performance of the display screen into two parts of self-luminous and ambient light reflection, take the self-luminous distribution calculated in the previous step, which contains aging failure information, as input, and combine the bidirectional reflectance distribution function of the display screen surface with the real ambient light , to generate simulation images with high physical reality, not only showing the bad points themselves, but also showing the visual impact of the bad points under different light and observation angles due to the reflection characteristics of the surface material, such as "bright" bad points under dark screen or "dark" bad points under bright screen;

[0134] dot product with surface normal vector along the observation direction ​​the spontaneous luminous intensity of the pixel at the current point , which reflects the actual luminous capability of the pixel after considering fatigue failure, for example, if the point is located on a pixel unit that is judged to be normal and is simulating a full white screen, its value is the original luminous intensity of the pixel, which is set to 1200 watts per square meter per steradian, if the point is located on a pixel unit that has failed, its value is 0.

[0135] is the bidirectional reflectance distribution function of the point in the incident direction and the outgoing direction , which is specified according to the material type at the location of the point when constructing the digital twin of the LED display screen, for example, if the point is located on the epoxy resin packaging surface of the LED lamp bead, the Cook-Torrance model is selected, and its parameters are set according to optical measurement experimental data, if the point is located on the black mask between the lamp beads, the Lambertian model is selected, and its diffuse reflectivity is obtained by measuring the sample with a spectrophotometer, for example, the diffuse reflectivity of the mask material is measured to be 0.05, and the value of its bidirectional reflectance distribution function is , that is, .

[0136] is the incident radiation intensity of the point in the incident direction , which is determined by the set environmental lighting model, that is, the lighting parameters from the time-varying environmental load sequence, when performing visual simulation, a specific environmental condition is selected, for example, CIE standard overcast day, and the total horizontal illuminance is set to 20000 lux, the radiation intensity value in any direction on the sky dome is calculated through the sky brightness distribution model, for example, the incident radiation intensity from the zenith direction is 20 watts per square meter per steradian.

[0137] is the dot product of the incident direction vector and the surface normal vector , which is obtained by querying the normal vector data of the point in the digital twin geometric model and performing dot product operation with the given incident direction vector, which describes the angle relationship between the incident light and the surface, for example, when the light is vertically incident, the value is 1.

[0138] Calculation process:

[0139] The Monte Carlo path tracing method is used for numerical solution. The exit radiance of normal pixel point and failure pixel point under uniform diffuse ambient light is calculated. The ambient light is set as uniform Lambertian light source, and its radiance is 20 W per square meter per steradian in all directions,

[0140] The exit radiance of failure pixel point (point ) is calculated. The point is located on the black mask,

[0141] ;

[0142] The bidirectional reflectance distribution function of the point is Lambertian model, ;

[0143] The integral term represents the total irradiance received by point . For isotropic incident radiance , the irradiance ;

[0144] W per square meter;

[0145] The radiance of the reflected part is W per square meter per steradian;

[0146] W per square meter per steradian.

[0147] The exit radiance of normal pixel point (point ) is calculated. The point is located on the light emitting lamp core;

[0148] W per square meter per steradian;

[0149] The lamp core surface also has reflection, and its diffuse reflectivity is set to 0.2. Its ,

[0150] The irradiance it receives is the same as that of the failure point, W per square meter,

[0151] The radiance of the reflected part is W per square meter per steradian,

[0152] W per square meter per steradian.

[0153] The results show that, under the given ambient light, a failed point has an exit radiance of 1 watt per square meter per steradian due to the reflection of ambient light, while a normally lit point has a total exit radiance of 1204 watts per square meter per steradian, which is the sum of its own light and the reflected light. These calculated exit point radiance values are the basis for generating the final simulation image.

[0154] Based on the exit point radiance, first define a target display area for evaluation, for example, exclude 5% of the pixels at the edges of the screen and only consider the central 90% area to avoid the influence of edge optical distortion, then in the target display area, sample points at a certain sampling density, for example, every other pixel, traverse all the sampling points and read the exit point radiance value calculated in the previous step for each point. During the traversal, set two variables, one to record the highest exit point radiance encountered so far and the other to record the lowest exit point radiance, and constantly update them. After the traversal is complete, the highest exit point radiance in the region, for example, 1204 watts per square meter per steradian, and the lowest exit point radiance, for example, 1 watt per square meter per steradian, are obtained. Subsequently, the program checks whether the value of the lowest exit point radiance is zero. In this example, due to the presence of ambient light reflection, the value is 1, not zero, so the calculation continues. Subtract the lowest value from the highest value and divide the difference by the lowest value, i.e. (1204-1) / 1=1203. This calculation result is a quantitative contrast index. The simulation visual performance index provides an objective and quantitative evaluation standard for the visual quality degradation of LED display screens after long-term service. It not only predicts the physical failure of individual pixels, but also deeply couples the reliability problem at the physical level with the visual effect at the application level by establishing a complete simulation link from micro solder stress damage to macro visual performance. This index can comprehensively reflect the appearance of failed pixels (black spots) caused by solder fatigue cumulative damage and the visual interference caused by the surface reflection characteristics of these failed points under complex environmental lighting, thereby quantitatively predicting common aging phenomena such as "flower screen" and "mottling" on display screens. Using this simulation visual performance index, designers can quickly perform virtual testing and comparative evaluation of different structural designs, material selection (e.g. using PCB substrates with different thermal expansion coefficients or solders with different fatigue characteristics), and heat dissipation schemes in the early stages of product development. By comparing the simulation visual performance index decay curves of different design schemes under simulated full life cycle, the solution with the slowest visual performance decay and the highest reliability within the expected service life can be iteratively optimized at extremely low cost and extremely short cycle.

[0155] The above merely describes the preferred embodiments of the present application, and is not intended to limit the present application in other forms. Any skilled person in the art can modify or change the disclosed technical content into equivalent embodiments with equivalent changes, and apply them to other fields. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application, without departing from the technical solution content of the present application, still falls within the protection scope of the present application.

Claims

1. A method for performance simulation of an LED display based on digital twinning, characterized in that, The method comprises the following steps: constructing a three-dimensional geometry of the LED display screen and defining a LED lamp bead array topology, assigning a bidirectional reflectance distribution function to the surface of the display screen, assigning a thermal expansion coefficient and an elastic modulus to the internal solder joints, and establishing a digital twin of the LED display screen; based on the digital twin of the LED display screen, setting the illumination parameters of the CIE standard sky and the temperature upper and lower limits of the thermal cycle, obtaining a time-varying environmental load sequence, based on the time-varying environmental load sequence, applying illumination and temperature changes to the digital twin of the LED display screen, and iteratively calculating the internal stress and strain distribution of the component caused by thermal expansion mismatch to generate a component stress and strain response field; based on the component stress and strain response field, extracting the stress tensor and strain tensor of each solder joint in each thermal cycle to obtain a single solder joint stress and strain record, and based on the single solder joint stress and strain record, obtaining a solder joint cumulative damage value; based on the solder joint cumulative damage value, comparing the solder joint cumulative damage value of each solder joint with a preset failure threshold to determine the light-emitting state of the corresponding pixel unit as failed, generating a pixel failure state map, and based on the pixel failure state map, updating the light-emitting distribution of the digital twin of the LED display screen to obtain a simulation visual effect performance indicator.

2. The digital-twin-based LED display screen performance simulation method according to claim 1, characterized in that, The obtaining step of the digital twin of the LED display screen is: spatial coordinate drawing is performed on the outer contour of the LED display screen surface and the position of the internal solder joints, the three-dimensional geometry of the display screen and the internal solder joints is determined through spatial coordinate gridding, and a three-dimensional geometric model of the LED display screen is obtained; based on the three-dimensional geometric model of the LED display screen, the spatial position of the lamp beads on the display screen surface is set according to the regular arrangement mode of the LED lamp bead array, and the topological connection relationship between each lamp bead and the adjacent lamp beads in the lamp bead array is determined, and a LED lamp bead array topology is obtained; based on the LED lamp bead array topology, the optical parameters of the display screen surface and the mechanical properties of the internal solder joints are specified respectively, the bidirectional reflectance distribution function is associated with each surface element of the display screen surface, the internal solder joints are sequentially assigned with a preset thermal expansion coefficient and elastic modulus, and a digital twin of the LED display screen is obtained. 3.The digital-twin-based LED display screen performance simulation method according to claim 1, wherein, The obtaining step of the time-varying environmental load sequence is: based on the digital twin of the LED display screen, the sky diffuse radiation distribution in the illumination model is set, the sky brightness distribution curve of the CIE standard sky and the solar direct radiation intensity value are mapped to each surface element on the surface of the display screen digital twin one by one to form a set of illumination parameters; based on the set of illumination parameters, the temperature upper and lower limits of the thermal cycle are set, the temperature change rate and duration in each cycle are determined one by one by defining the periodic variation law of the temperature upper and lower limits, and the temperature values at each time node are recorded to form a set of thermal cycle temperature parameters; based on the set of thermal cycle temperature parameters, the sky radiation intensity at each moment in the set of illumination parameters and the temperature parameters at the corresponding moment are called one by one to form a time-sequential arrangement of environmental load change points, and all the environmental load change points are connected to form a complete time-varying environmental load sequence.

4. The digital-twin-based LED display screen performance simulation method according to claim 1, characterized in that, The obtaining step of the component stress and strain response field is: The illumination intensity value and the corresponding temperature value of each time node are extracted from the time-varying environmental load sequence in sequence, and the illumination intensity value and the temperature value are mapped to each surface element of the LED display screen digital twin one by one, forming a surface element time-varying environmental boundary load sequence; Based on the surface element time-varying environmental boundary load sequence, the temperature value of each solder joint in the LED display screen digital twin at each time node is calculated, the thermal expansion coefficient value and the elastic modulus value of each solder joint are called, and the thermal expansion deformation amount of each solder joint is calculated by multiplying the temperature difference and the thermal expansion coefficient value one by one, forming a solder joint thermal expansion deformation amount sequence; Based on the solder joint thermal expansion deformation amount sequence, the deformation amount difference between each solder joint is calculated at each time point, and the stress and strain value distribution caused by the deformation difference inside the solder joint connection is calculated point by point and layer by layer by calling the elastic modulus value and the spatial geometric topological relationship between the solder joints, to generate a component stress and strain response field.

5. The digital-twin-based LED display screen performance simulation method according to claim 1, characterized in that, The obtaining step of the single solder joint stress and strain record is: Based on the component stress and strain response field, each data layer of each time node in the component stress and strain response field is traversed one by one, and the stress tensor component and the strain tensor component corresponding to the position of each solder joint are extracted for each time node, and are numbered and identified according to the order of the time nodes, to obtain a solder joint time sequence stress and strain component set arranged in time sequence; According to the solder joint time sequence stress and strain component set, all time node data in the solder joint time sequence stress and strain component set are grouped in cycles according to the time interval division method of the thermal cycle period, and the stress tensor component and the strain tensor component of all time nodes at the same solder joint position in each cycle are aggregated and arranged, to obtain a solder joint cycle stress and strain component set in a thermal cycle period; Based on the solder joint cycle stress and strain component set in the thermal cycle period, the cycle number, the stress tensor component and the strain tensor component of each single solder joint in each thermal cycle period are itemized and archived, and the complete stress tensor component and the strain tensor component of each solder joint in each thermal cycle period are recorded cycle by cycle, to generate a single solder joint stress and strain record.

6. The digital-twin-based LED display screen performance simulation method according to claim 1, characterized in that, The obtaining step of the solder joint cumulative damage value is: Based on the single solder joint stress and strain record, the maximum principal strain component and the minimum principal strain component corresponding to each thermal cycle period of each single solder joint are extracted one by one, the difference between the maximum principal strain component and the minimum principal strain component is calculated and divided by two, to form a strain amplitude of each thermal cycle period of each single solder joint, and the maximum principal stress component and the minimum principal stress component corresponding to each thermal cycle period of each single solder joint are extracted synchronously, the difference between the maximum principal stress component and the minimum principal stress component is calculated and divided by two, to form a stress amplitude of each thermal cycle period of each single solder joint, to obtain a single solder joint stress amplitude and strain amplitude sequence; Based on the single solder joint stress amplitude and strain amplitude sequence, a normalized cyclic strain energy damage factor of each thermal cycle period of each single solder joint is calculated. Based on the normalized cyclic strain energy damage factor of each thermal cycle period of a single weld point, all normalized cyclic strain energy damage factors are sequentially accumulated and summed in order of thermal cycle period number to form a weld point cumulative damage value of the single weld point under the current full life cycle.

7. The digital-twin-based LED display screen performance simulation method according to claim 1, characterized in that, The pixel failure state map acquisition step is: Based on the weld point cumulative damage value, the weld point cumulative damage value corresponding to each weld point is extracted one by one, and the pixel unit number associated with each weld point is read at the same time, the weld point cumulative damage value and the corresponding pixel unit are bound one by one to form a weld point cumulative damage value mapping table; According to the weld point cumulative damage value mapping table, the failure determination factor of each weld point is calculated; Based on the failure determination factor, when the failure determination factor is greater than or equal to zero, the corresponding pixel unit is marked as a failure state, and when the failure determination factor is less than zero, the corresponding pixel unit is marked as a normal state, and a pixel failure state map is generated. 8.The digital-twin-based LED display screen performance simulation method according to claim 1, wherein, The acquisition step of the simulation visual effect performance index is: Based on the pixel failure state map, for each surface element, first search the pixel unit state corresponding to the element, when the pixel unit is in a failure state, set the luminous radiation brightness to zero, when the pixel unit is in a normal state, read the original luminous radiation brightness, and perform spatial mapping on the luminous radiation brightness of all elements to form a luminous distribution map; Based on the luminous distribution map, the exit point radiation brightness of the LED display screen digital twin in the target observation direction is calculated; Based on the exit point radiation brightness, all valid observation points in the LED display screen digital twin are traversed, the highest exit point radiation brightness and the lowest exit point radiation brightness in the target display area are extracted, and when the lowest exit point radiation brightness is not equal to zero, the highest exit point radiation brightness is subtracted from the lowest exit point radiation brightness and then divided by the lowest exit point radiation brightness to obtain the simulation visual effect performance index.

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