A method for diagnosing key state points of post-peak unloading of a thin-walled structure
By acquiring time-series data of thin-walled structures, calculating cumulative dissipated energy and tangential stiffness spectrum, and automatically identifying damage initiation points and unloading inflection points, the subjective and single-dimensional problems of existing diagnostic methods are solved, realizing automated, reliable diagnosis and performance evaluation of the post-peak unloading process of thin-walled structures.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NORTHWESTERN POLYTECHNICAL UNIV
- Filing Date
- 2026-03-24
- Publication Date
- 2026-05-29
AI Technical Summary
Existing technologies rely on subjective interpretation when diagnosing critical state points during the post-peak unloading process of thin-walled structures. They lack automated processes and have limited diagnostic dimensions, making it difficult to fully reveal the intrinsic relationship between damage evolution, stiffness degradation, and load-bearing capacity reduction.
By acquiring time-series data of thin-walled structures, including displacement sequences, load sequences, external work sequences, and elastic strain energy sequences, the cumulative dissipated energy, dissipated energy change rate, and tangential stiffness spectrum are calculated. Damage initiation points and unloading inflection points are automatically identified, and joint diagnosis is performed by combining macroscopic stiffness spectra with microscopic damage activity characterization quantities.
It enables automated and reliable diagnosis of critical state points after peak unloading in thin-walled structures, generates standardized performance indicators, and is suitable for rapid screening and comparison of large-scale design schemes, thus improving the comprehensiveness and reliability of the diagnosis.
Smart Images
Figure CN121901805B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of thin-walled structure performance analysis, and in particular to a diagnostic method for critical post-peak unloading state points of thin-walled structures. Background Technology
[0002] Thin-walled structures, especially fiber-reinforced composite thin-walled cylindrical shells, are widely used in lightweight load-bearing structures in aerospace and aviation due to their high specific strength and high specific stiffness. These structures are highly susceptible to buckling under axial compressive loads and subsequently enter a complex post-buckling (post-peak) stage, accompanied by significant stiffness degradation, damage accumulation, and a decrease in load-bearing capacity. Accurately diagnosing critical state points during the post-peak unloading process (such as the starting point of rapid damage development and the "inflection point" of the fastest decline in load-bearing capacity) and objectively comparing the post-peak performance of different design schemes are crucial for structural safety assessment, damage-tolerant design, and optimization.
[0003] Currently, the diagnostic methods in this field have the following main shortcomings:
[0004] Experimental methods rely on subjective interpretation: In physical experiments, damage is often monitored through acoustic emission (AE), but the definition and threshold setting of AE events depend on experience and have a weak correlation with macroscopic mechanical responses, making it difficult to form a unified and quantifiable diagnostic standard. Key points on the load-displacement curve are usually identified manually, which is inefficient and highly subjective.
[0005] Numerical simulation post-processing lacks automation: While historical data on loads, displacements, various energy components, and damage variables can be accurately obtained in finite element simulations, current analyses mostly remain at the stage of plotting curves and manual observation. There is a lack of automated algorithms capable of robustly identifying key state points from this massive amount of data without human intervention and calculating a series of standardized performance comparison indicators.
[0006] Diagnostic dimensions are limited and information utilization is insufficient: Existing methods often focus solely on the shape of the load-displacement curve or the change of a single energy component, failing to effectively integrate and analyze the macroscopic mechanical response (load, stiffness) with energy dissipation, a physical quantity that characterizes the nature of damage. This results in one-sided diagnostic information and makes it difficult to fully reveal the coupling relationship between "damage evolution - stiffness degradation - bearing capacity reduction". Summary of the Invention
[0007] The main purpose of this application is to provide a diagnostic method for key state points of peak unloading in thin-walled structures, aiming to solve the problem that the single diagnostic dimension of the key point identification method leads to low reliability of the diagnostic results.
[0008] To achieve the above objectives, this application provides a diagnostic method for critical post-peak unloading state points of thin-walled structures, comprising: acquiring time-series data of a composite material with a thin-walled structure during loading, wherein the time-series data includes a displacement sequence, a load sequence, an external work sequence, and an elastic strain energy sequence; determining the cumulative dissipated energy at each displacement point based on the difference between the external work sequence and the elastic strain energy sequence; determining the rate of change of dissipated energy at each displacement point based on the cumulative dissipated energy and the displacement sequence, thereby obtaining a dissipated energy rate of change sequence; determining the tangential stiffness spectrum at each displacement point based on the load sequence and the displacement sequence, thereby obtaining a tangential stiffness spectrum sequence; acquiring the displacement point corresponding to the maximum load in the load sequence as the peak load point; determining the damage initiation point in the displacement sequence based on the rate of change of dissipated energy; and determining the unloading inflection point in the displacement sequence based on the tangential stiffness spectrum sequence.
[0009] Optionally, the rate of change of dissipated energy at each displacement point is determined based on the cumulative dissipated energy and the displacement sequence, including: for each displacement point in the displacement sequence, determining the difference between the cumulative dissipated energy of the previous displacement point and the cumulative dissipated energy of the next displacement point as the first difference; the difference between the displacement of the previous displacement point and the displacement of the next displacement point as the second difference; and determining the rate of change of dissipated energy at the current displacement point based on the ratio of the first difference and the second difference.
[0010] Optionally, based on the load sequence and displacement sequence, the tangent stiffness spectrum of each displacement point is determined, including: for each displacement point in the displacement sequence, determining the difference between the load of the preceding displacement point and the load of the following displacement point as the third difference; the difference between the displacement of the preceding displacement point and the displacement of the following displacement point as the fourth difference; and determining the tangent stiffness spectrum of the current displacement point based on the ratio of the third difference and the fourth difference.
[0011] Optionally, the damage initiation point in the displacement sequence is determined based on the rate of change of dissipated energy, including: taking the displacement point in the displacement sequence where the rate of change of dissipated energy first exceeds the baseline noise threshold and is located before the peak load point as the damage initiation point; and the unloading inflection point in the displacement sequence is determined based on the tangent stiffness spectrum sequence, including: taking all displacement points after the peak load point as the post-peak stage, obtaining the tangent stiffness spectrum of the post-peak stage in the tangent stiffness spectrum sequence as the post-peak tangent stiffness spectrum sequence; and taking the displacement point corresponding to the minimum tangent stiffness spectrum in the post-peak tangent stiffness spectrum sequence as the unloading inflection point.
[0012] Optionally, the baseline noise threshold is determined based on the mean and standard deviation of the rate of change of dissipated energy within the baseline segment; before obtaining the minimum tangent stiffness spectrum in the post-peak tangent stiffness spectrum sequence, the method further includes: performing a moving average smoothing process on the post-peak tangent stiffness spectrum sequence.
[0013] Optionally, after determining the unloading inflection point in the displacement sequence, the method further includes: determining the post-peak load retention rate and the cumulative energy dissipation ratio; and evaluating the mechanical properties of the composite material with a thin-walled structure based on the post-peak load retention rate and the cumulative energy dissipation ratio.
[0014] Alternatively, the expression for the cumulative energy consumption ratio is as follows:
[0015]
[0016] In the formula, For displacement Energy dissipation during time, For the first j Load at each displacement point For the first j- Load at one displacement point For the first j Displacement of each displacement point For the first j- The displacement of one displacement point.
[0017] Optionally, after determining the unloading inflection point in the displacement sequence, the method further includes: determining the maximum dissipation intensity and the plateau segment length; and classifying the unloading mode based on the tangent stiffness spectrum, maximum dissipation intensity, and plateau segment length of the unloading inflection point.
[0018] Optionally, the maximum dissipation intensity is the maximum value in the dissipation energy change rate sequence; the plateau segment length is determined based on the length of the displacement interval of the load within the preset interval in the post-peak stage, and within the preset interval, the load fluctuation amplitude is less than or equal to the preset value; wherein, the length of the displacement interval is determined based on the difference between the maximum and minimum values in the displacement interval; the preset interval is determined based on the product of the first coefficient and the maximum load, and the product of the second coefficient and the maximum load.
[0019] To achieve the above objectives, this application also provides a diagnostic device for critical state points of post-peak unloading in thin-walled structures, comprising: a data acquisition module for acquiring time-series data of composite materials with thin-walled structures during loading, wherein the time-series data includes displacement sequence, load sequence, external work sequence, and elastic strain energy sequence; an energy calculation module for determining the cumulative dissipated energy at each displacement point based on the difference between the external work sequence and the elastic strain energy sequence; determining the rate of change of dissipated energy at each displacement point based on the cumulative dissipated energy and the displacement sequence, thereby obtaining a dissipated energy rate of change sequence; a stiffness calculation module for determining the tangential stiffness spectrum at each displacement point based on the load sequence and the displacement sequence, thereby obtaining a tangential stiffness spectrum sequence; and a critical point identification module for acquiring the displacement point corresponding to the maximum load in the load sequence as the peak load point; determining the damage initiation point in the displacement sequence based on the rate of change of dissipated energy; and determining the unloading inflection point in the displacement sequence based on the tangential stiffness spectrum sequence.
[0020] Compared with the prior art, the beneficial effects of this application are as follows:
[0021] By automatically identifying key points and calculating indicators from time-series data, this method completely replaces inefficient and subjective manual curve interpretation, making it particularly suitable for rapid screening and comparison of large-scale design schemes. It determines the tangent stiffness spectrum sequence based on load and displacement sequences, and then identifies the unloading inflection point based on the tangent stiffness spectrum sequence. Furthermore, it determines the cumulative dissipated energy based on the external work sequence and elastic strain energy sequence. Finally, it determines the rate of change of dissipated energy based on the cumulative dissipated energy and displacement sequence, and then identifies the damage initiation point based on the rate of change of dissipated energy. By combining the macroscopic tangent stiffness spectrum with the microscopic damage activity characterization quantity "rate of change of dissipated energy" for joint diagnosis, it can more comprehensively and profoundly reveal the intrinsic relationship between "damage evolution - stiffness decay - bearing capacity reduction" than single-dimensional analysis, resulting in more reliable diagnostic conclusions. The method is based on general load, displacement, and energy data and does not rely on specific software or damage models. Attached Figure Description
[0022] Figure 1 This is a flowchart illustrating a diagnostic method for critical state points of post-peak unloading in a thin-walled structure according to this application.
[0023] Figure 2 This is a schematic diagram of the diagnostic device for critical state points of post-peak unloading in a thin-walled structure according to this application.
[0024] Figure 3 This is a graph showing the evolution of energy components and the rate of change of dissipated energy obtained in Example 1 of this application;
[0025] Figure 4 This is a schematic diagram of key state point fusion recognition obtained in Embodiment 1 of this application;
[0026] Figure 5 This is a classification result diagram of Embodiment 1 of this application.
[0027] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation
[0028] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0029] The first embodiment of the present invention provides a diagnostic method for critical post-peak unloading state points of thin-walled structures, such as... Figure 1Specifically, it includes the following steps:
[0030] Step S1: Obtain time-series data of the composite material with thin-walled structure during the loading process, wherein the time-series data includes displacement sequences. Load sequence External power sequence and elastic strain energy sequence ,in , This represents the total number of data points.
[0031] In this embodiment, the thin-walled structure can be a thin-walled cylindrical shell, a thin-walled profile, or other structures, such as a thin-walled cylindrical shell made of fiber-reinforced composite material. Specifically, time-series data of a complete loading process is obtained from the result files of finite element software (such as Abaqus or ANSYS) or from the experimental data acquisition system.
[0032] Before identifying key points based on the aforementioned time-series data, preprocessing is required, including sign unification (compression direction is positive), data smoothing filtering, and monotonicity checking and resampling of the displacement sequence. The specific process of monotonicity checking and resampling of the displacement sequence is as follows: if non-monotonic points are detected in the displacement sequence (such as numerical oscillations or arc-length bounces), the displacement sequence is rearranged in ascending order according to the magnitude of the displacement, and multiple sets of data within the same displacement neighborhood are aggregated or resampled. The aggregation or resampling process involves interpolating the average or median of the rearranged displacement sequence into a specified monotonic grid to generate a strictly monotonically increasing displacement sequence and corresponding load and energy sequences.
[0033] Step S2: Determine the cumulative dissipated energy at each displacement point based on the difference between the external work sequence and the elastic strain energy sequence; determine the rate of change of dissipated energy at each displacement point based on the cumulative dissipated energy and the displacement sequence, and obtain the dissipated energy rate of change sequence.
[0034] Step S21, dissipated energy is defined as the difference between external work and recoverable elastic strain energy, expressed as:
[0035]
[0036] In the formula, For the first i Energy dissipation at each displacement point For the first i Elastic strain energy at each displacement point For the first i The cumulative external work at each displacement point, where 0 represents the physical lower limit of energy dissipation, ensuring that numerical noise at the initial stage of the calculation does not cause energy loss. At that time, the dissipated energy does not exhibit a negative value that violates the physical meaning.
[0037] In this embodiment, the maximum value of the difference between the external work and the recoverable elastic strain energy is taken as the dissipated energy. This serves several purposes: it ensures the purity of the physical logic; even with minor numerical errors, It is also possible to produce a negative value. Once a negative dissipation energy occurs, the subsequent calculated rate of change of dissipation energy may produce a false negative peak, which is not only difficult to interpret, but also seriously interferes with the determination of the damage initiation point.
[0038] As a "numerical filter," max(..., 0) effectively acts as a lower limit cutoff, directly reducing tiny negative values that violate physical meaning due to numerical noise to zero. This is equivalent to adding an "insurance" layer at the very beginning of data processing, a key feature preventing noise contamination of subsequent steps. It also avoids singularities in subsequent derivative calculations: without processing negative values, fluctuations caused by negative values might be amplified when calculating the rate of change of dissipated energy, leading to oscillations in the initial stage of the dissipated energy rate curve that do not conform to physical laws.
[0039] Step S22: For each displacement point in the displacement sequence, determine the difference between the cumulative dissipated energy of the preceding displacement point and the cumulative dissipated energy of the following displacement point, as the first difference; the difference between the displacement of the preceding displacement point and the displacement of the following displacement point, as the second difference; determine the rate of change of dissipated energy at the current displacement point based on the ratio of the first difference and the second difference. i Rate of change of dissipated energy at each displacement point The expression is as follows:
[0040]
[0041] In the formula, For the first i+ Energy dissipation at one displacement point For the first i- Energy dissipation at one displacement point;
[0042] Step S3: Based on the load sequence and displacement sequence, determine the tangent stiffness spectrum at each displacement point to obtain the tangent stiffness spectrum sequence; the tangent stiffness spectrum is used to characterize the change in instantaneous bearing stiffness of the structure during loading.
[0043] Specifically, for each displacement point in the displacement sequence, the difference between the load of the preceding displacement point and the load of the following displacement point is determined as the third difference; the difference between the displacement of the preceding displacement point and the displacement of the following displacement point is determined as the fourth difference; based on the ratio of the third difference and the fourth difference, the tangent stiffness spectrum of the current displacement point is determined. i Tangent stiffness spectrum at each displacement point The expression is:
[0044]
[0045] In the formula, For the first i+ Load at one displacement point.
[0046] Step S4: Obtain the displacement point corresponding to the maximum load in the load sequence, as the peak load point; peak load point The displacement point is determined by the load sequence. :
[0047]
[0048] Step S5: Determine the damage initiation point in the displacement sequence based on the rate of change of dissipated energy;
[0049] Specifically, the displacement point in the displacement sequence where the rate of change of dissipated energy first exceeds the baseline noise threshold and is located before the peak load point is taken as the damage initiation point. :
[0050]
[0051] in, The rate of change of dissipated energy, the baseline noise threshold. The baseline segment is determined based on the mean and standard deviation of the rate of change of dissipated energy within the baseline segment. The baseline segment is the linear segment during the initial loading phase, and the baseline segment is determined based on... Confirmed, among which This is a configurable parameter (e.g., 0.3). ,in and These represent the mean and standard deviation of the rate of change of dissipated energy within the baseline segment, respectively. This is a configurable parameter (e.g., 6).
[0052] Step S6: Determine the unloading inflection point in the displacement sequence based on the tangent stiffness spectrum sequence.
[0053] Specifically, the displacement point located after the peak load point is considered as the post-peak stage. ), obtain the tangent stiffness spectrum of each displacement point in the post-peak stage of the tangent stiffness spectrum sequence. This forms a post-peak tangent stiffness spectrum sequence. The minimum tangent stiffness spectrum in this sequence is obtained, and its corresponding displacement point is used as the unloading inflection point. To improve robustness, a moving average smoothing process is applied to the post-peak tangent stiffness spectrum sequence before obtaining the minimum tangent stiffness spectrum, resulting in a smoothed tangent stiffness spectrum sequence. The displacement point is The expression is:
[0054]
[0055] Based on the peak load point, damage initiation point, and unloading inflection point identified above, and combined with time series data, corresponding curves can be obtained. Through the peak load point, damage initiation point, unloading inflection point, and curves, the comprehensive mechanical properties and damage evolution patterns of thin-walled composite materials can be evaluated and classified in a standardized and quantitative manner, as follows.
[0056] Step S7: Determine the post-peak load retention rate and cumulative energy dissipation ratio; evaluate the mechanical properties of the composite material with thin-walled structure based on the post-peak load retention rate and cumulative energy dissipation ratio.
[0057] Among them, the post-peak load retention rate is used to evaluate the remaining load-bearing capacity at a specific displacement, and its expression is:
[0058]
[0059] In the formula, Displacement in the post-peak stage Peak load retention rate The load at the peak load point, i.e., the maximum load; for example, it can be taken as... , This is a configurable parameter (e.g., 0.2). This represents the displacement at the peak load point. This represents the maximum displacement during the post-peak phase.
[0060] Cumulative energy consumption ratio Used to assess displacement The proportion of irreversible dissipated energy to the total input mechanical work is given. The total input mechanical work can be obtained through numerical integration, and the numerical integration method includes at least the rectangular method or the trapezoidal method. Its expression is as follows:
[0061]
[0062] In the formula, For displacement Energy dissipation during time, For the first j Load at each displacement point For the first j- Load at one displacement point. satisfy The summation term in the denominator represents the total input work approximated by the trapezoidal rule.
[0063] Step S8: Determine the maximum dissipation intensity and the plateau segment length; classify the unloading modes based on the tangent stiffness spectrum at the unloading inflection point (minimum tangent stiffness spectrum in the post-peak stage), the maximum dissipation intensity, and the plateau segment length.
[0064] Among them, the maximum dissipation intensity This represents the maximum value in the dissipation energy change rate sequence, reflecting the intensity of the most severe damage activity. The expression is:
[0065]
[0066] Platform segment length This reflects the residual load-bearing stability of a thin-walled structure after damage, based on the condition that the load in the post-peak stage is within a preset range and the fluctuation amplitude is less than or equal to a preset value. The length of the displacement interval is determined; the length of the displacement interval is determined based on the difference between the maximum and minimum values within the displacement interval; the preset interval is determined based on the first coefficient. The product of the maximum load and the second coefficient The product of the maximum load and the maximum load is determined, i.e. , For configurable parameters (e.g.) ).
[0067] Unloading modes include drop-rate and stable platform types, and the specific classification rules are as follows:
[0068] Sharp Drop: The minimum tangent stiffness spectrum in the post-peak stage. (For example The load (N / mm) decreases rapidly after the peak, failing to maintain a stable load-bearing platform. This mode corresponds to brittle fracture or severe instability and damage to the structure.
[0069] Stable Plateau: When And the platform segment length Exceeding the critical value (e.g.) This model corresponds to a structure with good toughness and energy absorption capacity.
[0070] Example: If the calculation yields If N / mm is much less than the threshold, it is automatically classified as "rapid drop type".
[0071] In this embodiment, by automatically identifying key points and calculating indicators from time-series data, the inefficient and subjective manual curve interpretation is completely replaced, making it particularly suitable for rapid screening and comparison of large batches of design schemes. The tangent stiffness spectrum sequence is determined based on the load and displacement sequences, and the unloading inflection point is determined based on the tangent stiffness spectrum sequence. The cumulative dissipated energy is determined based on the external work and elastic strain energy sequences. The rate of change of dissipated energy is determined based on the cumulative dissipated energy and displacement sequences, and the damage initiation point is determined based on the rate of change of dissipated energy. Combining the macroscopic tangent stiffness spectrum with the microscopic damage activity characterization quantity "rate of change of dissipated energy" for joint diagnosis reveals the intrinsic relationship between "damage evolution - stiffness decay - bearing capacity reduction" more comprehensively and profoundly than single-dimensional analysis, resulting in more reliable diagnostic conclusions. The generated indicators (such as...) It possesses clear physical meaning and good normalization characteristics, providing a unified "performance benchmark" for structural schemes with different geometric dimensions, ply designs, and defect types, greatly facilitating horizontal comparison and design decisions; it has strong engineering applicability and robustness: the method is based on general load, displacement, and energy data, and does not depend on specific software or damage models; the built-in automatic threshold calculation, data smoothing, resampling, and robust key point identification mechanisms ensure the method's adaptability to different data sources (simulation / experiment) and different data qualities (step size, noise), and has strong robustness.
[0072] A second embodiment of the present invention provides a diagnostic device for critical post-peak unloading state points of a thin-walled structure, such as... Figure 2 As shown, it includes:
[0073] The data acquisition module is used to acquire time-series data of composite materials with thin-walled structures during the loading process. The time-series data includes displacement sequence, load sequence, external work sequence and elastic strain energy sequence.
[0074] The energy calculation module is used to determine the cumulative dissipated energy at each displacement point based on the difference between the external work sequence and the elastic strain energy sequence; and to determine the rate of change of dissipated energy at each displacement point based on the cumulative dissipated energy and the displacement sequence, thereby obtaining the dissipated energy change rate sequence.
[0075] The stiffness calculation module is used to determine the tangent stiffness spectrum at each displacement point based on the load sequence and displacement sequence, and obtain the tangent stiffness spectrum sequence.
[0076] The key point identification module is used to obtain the displacement point corresponding to the maximum load in the load sequence as the peak load point; determine the damage initiation point in the displacement sequence based on the rate of change of dissipated energy; and determine the unloading inflection point in the displacement sequence based on the tangent stiffness spectrum sequence.
[0077] Example 1: Independent Post-Processing Diagnostic Program Based on Common CSV Data Files
[0078] This embodiment demonstrates an implementation of a standalone, batch-running post-processing program. This program can perform diagnostics directly based on data derived from existing simulations or experiments.
[0079] Input data: The program accepts a standard format CSV file as input. This file should contain at least four columns of data: Displacement (displacement) ), Load (load) External_Work Strain_Energy (elastic strain energy) ).
[0080] The program executes steps S2 to S6 sequentially. Based on the four input columns of data, it obtains the energy component evolution and dissipation energy change rate diagram, including curves for displacement-external work, displacement-elastic energy, displacement-dissipation energy, and displacement-dissipation energy change rate. See [link to relevant documentation]. Figure 3 The program performs the following parameter settings and calculations based on the four columns of data: the program defaults to setting the displacement from 0 to... The interval is defined as the baseline segment. In this embodiment, the peak displacement is identified. mm, retrieve configuration parameters The baseline segment is then the interval with a displacement of [0, 0.2840] mm. The program calculates the statistical characteristics of the dissipation efficiency within this segment: mean... N, standard deviation N. Automatically set damage initiation threshold (Pick ), calculated 456.42 N. A continuous method was used to identify the damage initiation point. Criteria for each point exceeding a threshold automatically locates the damage initiation displacement. mm. This point is located before the peak load (approximately 48%). (At this point), it aligns with the physical fact of early microcrack initiation in the composite matrix. To robustly identify the unloading inflection point, the program performs post-peak stage analysis. The sequence is smoothed using a moving average to find the global minimum point and locate the unloading inflection point. mm, the tangent stiffness spectrum reaches a minimum here. N / mm indicates the most severe loss of structural load-bearing capacity.
[0081] Output: The program automatically generates a diagnostic report, which includes:
[0082] (a) Key curves: merged display (Load-Displacement) (Stiffness (i.e., tangent stiffness spectrum) - displacement) and The three curves (rate of change of dissipated energy - displacement) are shown below. Figure 4 .like Figure 4 As shown in (c), place, The curve (green) breaks through the threshold for the first time. (Dashed line) marks the point where the damage begins; e.g. Figure 4 As shown in (a), then in The load reaches its peak value. That is, the peak load point, such as Figure 4 As shown in (b), ultimately in place, The curve (blue) reaches a deep valley (minimum value), marking the unloading inflection point.
[0083] (b) Key Indicator Table: Determine the coordinates of key points: , , , Performance index value: Post-peak load retention rate (That is, the remaining load-bearing capacity is approximately 53.6% of the peak capacity), and the cumulative energy consumption ratio (Approximately 40.4% of the input work is converted into irreversible dissipation), maximum dissipation intensity .
[0084] (c) Unloading mode classification conclusion: such as Figure 5 As shown, the system calculates the minimum tangent stiffness spectrum after the peak. According to the preset rule (threshold - 5000 N / mm), this value is much smaller than the threshold, and Because it is relatively short (only about 0.107 mm), the system automatically outputs the conclusion as "Sharp Drop" and warns in the report that the structure has the risk of brittle failure.
[0085] Example 2: Automated Post-Processing Script (Batch Processing Tool) Integrated into Abaqus This example demonstrates how the method of the present invention can be encapsulated into a Python post-processing script that runs within the Abaqus simulation environment to achieve automated diagnosis.
[0086] Implementation: Implemented as an Abaqus Python script, it can run in the Abaqus / CAE command line or in batch processing mode without a graphical interface, and supports batch processing of multiple .odb result files.
[0087] Workflow:
[0088] Automatic data extraction: The script automatically reads historical output data from a preset reference point in a specified .odb file via the Abaqus Python API: displacement (U), reaction force (RF), total external work (ALLWK), and total elastic strain energy (ALLSE).
[0089] Data conversion and processing: The script organizes the data into the CSV format required in Example 1, and then calls the diagnostic algorithm of Example 1 (or a function with the same embedded logic).
[0090] Output results: The script will automatically save the calculated summary table of indicators and classification conclusions to the user-specified directory. The format is shown in Table 1.
[0091] Table 1 Automated Diagnostic Indicator Report
[0092]
[0093] Therefore, this embodiment realizes a "one-click" automated closed loop from simulation calculation to diagnostic report, seamlessly integrates into the existing analysis process, and significantly improves post-processing efficiency.
[0094] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.
Claims
1. A diagnostic method for critical post-peak unloading state points in a thin-walled structure, characterized in that, include: Acquire time-series data of composite materials with thin-walled structures during loading, including displacement sequence, load sequence, external work sequence, and elastic strain energy sequence; The cumulative dissipated energy at each displacement point is determined based on the difference between the external work sequence and the elastic strain energy sequence. Based on the cumulative dissipated energy and displacement sequence, the rate of change of dissipated energy at each displacement point is determined, and the dissipated energy change rate sequence is obtained. Based on the load sequence and displacement sequence, the tangent stiffness spectrum of each displacement point is determined, and the tangent stiffness spectrum sequence is obtained. Obtain the displacement point corresponding to the maximum load in the load sequence as the peak load point; The damage initiation point in the displacement sequence is determined based on the rate of change of dissipated energy. Based on the tangent stiffness spectrum sequence, determine the unloading inflection point in the displacement sequence.
2. The diagnostic method for critical post-peak unloading state points of thin-walled structures according to claim 1, characterized in that, Based on the cumulative dissipated energy and displacement sequence, determine the rate of change of dissipated energy at each displacement point, including: For each displacement point in the displacement sequence, the difference between the cumulative dissipated energy of the previous displacement point and the cumulative dissipated energy of the next displacement point is determined as the first difference; the difference between the displacement of the previous displacement point and the displacement of the next displacement point is determined as the second difference; the rate of change of dissipated energy at the current displacement point is determined based on the ratio of the first difference and the second difference.
3. The diagnostic method for post-peak unloading critical state points of thin-walled structures according to claim 1, characterized in that, Based on the load sequence and displacement sequence, determine the tangent stiffness spectrum at each displacement point, including: For each displacement point in the displacement sequence, determine the difference between the load of the previous displacement point and the load of the next displacement point as the third difference; the difference between the displacement of the previous displacement point and the displacement of the next displacement point as the fourth difference; and determine the tangent stiffness spectrum of the current displacement point based on the ratio of the third difference and the fourth difference.
4. The diagnostic method for critical post-peak unloading state points of thin-walled structures according to claim 1, characterized in that, The damage initiation point in the displacement sequence is determined based on the rate of change of dissipated energy, including: The displacement point in the displacement sequence that is the first point in which the rate of change of dissipated energy exceeds the baseline noise threshold and is located before the peak load point is taken as the damage initiation point. Based on the tangent stiffness spectrum sequence, determine the unloading inflection point in the displacement sequence, including: All displacement points located after the peak load point are taken as the post-peak stage, and the tangent stiffness spectrum of the post-peak stage in the tangent stiffness spectrum sequence is obtained as the post-peak tangent stiffness spectrum sequence. The displacement point corresponding to the minimum tangent stiffness spectrum in the post-peak tangent stiffness spectrum sequence is taken as the unloading inflection point.
5. The diagnostic method for critical post-peak unloading state points of thin-walled structures according to claim 4, characterized in that, The baseline noise threshold is determined based on the mean and standard deviation of the rate of change of dissipated energy within the baseline segment; Before obtaining the minimum tangent stiffness spectrum in the post-peak tangent stiffness spectrum sequence, the method also includes: The post-peak tangent stiffness spectrum sequence was smoothed using a moving average.
6. The diagnostic method for post-peak unloading critical state points of thin-walled structures according to claim 1, characterized in that, After determining the unloading inflection point in the displacement sequence, the method also includes: Determine the post-peak load retention rate and cumulative energy consumption ratio; The mechanical properties of composite materials with thin-walled structures are evaluated based on the post-peak load retention rate and cumulative energy dissipation ratio.
7. The diagnostic method for critical post-peak unloading state points of thin-walled structures according to claim 6, characterized in that, The expression for the cumulative energy consumption ratio is as follows: In the formula, For displacement Energy dissipation during time, For the first j Load at each displacement point For the first j- Load at one displacement point For the first j Displacement of each displacement point For the first j- The displacement of one displacement point.
8. The diagnostic method for post-peak unloading critical state points of thin-walled structures according to claim 1, characterized in that, After determining the unloading inflection point in the displacement sequence, the method also includes: Determine the maximum dissipation intensity and the length of the platform segment; The unloading modes are classified based on the tangent stiffness spectrum, maximum dissipation intensity, and platform segment length at the unloading inflection point.
9. The diagnostic method for critical post-peak unloading state points of thin-walled structures according to claim 8, characterized in that, The maximum dissipation intensity is the maximum value in the sequence of dissipation energy change rates; The length of the platform segment is determined based on the length of the displacement interval of the load within the preset range during the post-peak stage, and within this preset range, the fluctuation amplitude of the load is less than or equal to the preset value. The length of the displacement interval is determined by the difference between the maximum and minimum values within the displacement interval. The preset interval is determined based on the product of the first coefficient and the maximum load, and the product of the second coefficient and the maximum load.
10. A diagnostic device for critical state points of post-peak unloading in a thin-walled structure, characterized in that, include: The data acquisition module is used to acquire time-series data of composite materials with thin-walled structures during the loading process. The time-series data includes displacement sequence, load sequence, external work sequence and elastic strain energy sequence. The energy calculation module is used to determine the cumulative dissipated energy at each displacement point based on the difference between the external work sequence and the elastic strain energy sequence; and to determine the rate of change of dissipated energy at each displacement point based on the cumulative dissipated energy and the displacement sequence, thereby obtaining the dissipated energy change rate sequence. The stiffness calculation module is used to determine the tangent stiffness spectrum at each displacement point based on the load sequence and displacement sequence, and obtain the tangent stiffness spectrum sequence. The key point identification module is used to obtain the displacement point corresponding to the maximum load in the load sequence as the peak load point; determine the damage initiation point in the displacement sequence based on the rate of change of dissipated energy; and determine the unloading inflection point in the displacement sequence based on the tangent stiffness spectrum sequence.