High-precision material characteristic parameter identification and optimization method based on skeleton

Abstract

The invention belongs to the field of material parameter optimization, and particularly relates to a skeleton-based high-precision material characteristic parameter identification and optimization method, which comprises the following steps of S1, acquiring a parameter initial value based on a skeleton biomechanical test; s2, establishing a basic finite element model according to a bone biomechanical test, and optimizing parameters in a local level to obtain parameter optimization values; and S3, establishing an osteopathic-level finite element model, and optimizing parameters in a global level to obtain final bone material characteristic parameters. The problems that high-precision material characteristic parameter optimization of bones is low in accuracy and high in cost are solved.

Description

Technical Field

[0001] The present invention belongs to the field of material parameter optimization, and particularly relates to a high-precision material property parameter identification and optimization method based on bones. Background Art

[0002] Compared with dummy models, human body models have anatomical structures and biomaterial properties closer to those of the human body, so they have higher biological fidelity and can more accurately simulate human injuries, and have gradually become an important tool for studying injury mechanisms in industries such as automotive safety, aerospace, and medical health. Among human body models, the material constitutive parameters of bones have a crucial impact on the kinematic response and mechanical response of the models and are the key to determining the accuracy of the models.

[0003] Currently, the methods for identifying the constitutive material parameters of bones include mathematical analysis based on biomechanical tests of bones. Bones are a complex composite material, and the data obtained from limited experimental samples cannot comprehensively represent the true behavior of the entire bone system. Moreover, conducting biomechanical tests requires expensive technologies and equipment. This method has a low parameter accuracy rate and high costs. Or numerical simulation calculations are combined with specific samples, and the optimal material constitutive parameters are sought by adjusting parameters. In the process of gradually adjusting parameters, this method requires very profound prior experience and theoretical knowledge and has the risk of specificity, resulting in inaccurate parameter inverse solutions. Summary of the Invention

[0004] The present invention provides a high-precision material property parameter identification and optimization method based on bones, which solves the problems of low optimization accuracy rate and high costs of high-precision material property parameters of bones.

[0005] The basic solution provided by the present invention: A high-precision material property parameter identification and optimization method based on bones specifically includes the following steps:

[0006] S1: Obtain the initial parameter values based on bone biomechanical tests. The initial parameter values include the initial elastic modulus value, initial yield stress value, initial tangent modulus value, and initial effective plastic strain value in the elastic stage.

[0007] S2: Establish a basic finite element model according to bone biomechanical tests, and optimize the elastic modulus, yield stress, and tangent modulus with the root mean square error between the biomechanical test curve and the simulation curve as the objective function; at the same time, optimize the effective plastic strain with the displacement difference at the moment of bone fracture in the biomechanical test and the simulation as the objective function.

[0008] S3: Establish an osteopathic-level finite element model. Among them, perform statistical analysis on the elastic modulus, yield stress, tangent modulus, and effective plastic strain optimized preliminarily in S2, use the analysis results as the variable space, set the similarity score between the biomechanical test curve and the simulation curve and the displacement difference at the moment of bone fracture in the biomechanical test and simulation as the objective function, perform multi-objective parameter optimization, and output the optimized elastic modulus, yield stress, tangent modulus, and effective plastic strain as the final bone material characteristic parameters.

[0009] The principle and advantages of the present invention are as follows:

[0010] 1. The present invention optimizes the data obtained from the bone biomechanical test through the basic finite element model and the osteopathic-level finite element model respectively: optimize the bone material characteristic parameters from the local level by establishing the basic finite element model, and at the same time establish the osteopathic-level finite element model, optimize the bone material characteristic parameters at the global level according to the optimized parameters output by the basic finite element model, and perform optimization with multiple objectives, and output the finally optimized elastic modulus, yield stress, tangent modulus, and effective plastic strain as the bone material characteristic parameters. This method can achieve high-precision multi-dimensional optimization of the bone constitutive material parameters, and the obtained material constitutive parameters are highly accurate, and can reflect the true mechanical response of the bone from both the overall and local levels. Compared with the existing method of parameter optimization through mathematical analysis, the parameter accuracy is higher and the cost is lower, and relatively accurate material characteristic parameters can be obtained without expensive technologies and equipment. Compared with the existing parameter optimization method only through numerical simulation, it does not depend on prior experience, and the stability of parameter identification and optimization is higher.

[0011] 2. When the present invention optimizes the bone material characteristic parameters at the local level, first identify the material parameters in the elastic stage, namely the elastic modulus, yield stress, and tangent modulus, and then identify the material parameters in the plastic stage, namely the effective plastic strain, which not only ensures the accuracy of the parameter inverse solution process, but also avoids over-fitting of the material curve.

[0012] 3. When the present invention optimizes the bone material characteristic parameters at the local level and the global level, the displacement difference at the moment of bone fracture in the biomechanical test and simulation is used as the objective function, which can ensure the accuracy of the mechanical response and failure response of the bone material at the osteopathic level.

[0013] Preferably, in step S1, the steps of obtaining the initial parameter values are as follows:

[0014] S1-1) Convert the force-displacement curves of all specimens in the biomechanical test into stress-strain curves, and determine the ultimate stress value and ultimate strain value of the material.

[0015] S1-2) Divide the stress-strain curve into curve segments according to the ultimate stress value and ultimate strain value of the material, fit each curve segment, select the curve segment with the fitting degree closest to 1, and define the slope of this curve segment as the initial value of the elastic modulus;

[0016] S1-3) Set the offset curve, and define the stress corresponding to the intersection of the offset curve and the stress-strain curve as the initial value of the yield stress, and the strain corresponding to the intersection as the initial value of the yield strain;

[0017] S1-4) Calculate the initial value of the tangent modulus and the initial value of the effective plastic strain according to the initial value of the elastic modulus.

[0018] Using mathematical models and formulas can provide initial values for the optimization process based on biomechanical tests. This helps to ensure that the subsequent parameter optimization algorithm starts searching for the optimal solution from a relatively ideal position, increases the possibility of finding the global optimal solution, and at the same time reduces unnecessary waste of computing resources; at the same time, the selection of initial values based on mathematical formulas helps to enhance the stability and reliability of the final optimization results. Reliable initial values can ensure that the obtained optimized parameters are closer to the actual situation, thereby enhancing the stability and reliability of the results.

[0019] Further preferably, in step S1-4), the calculation formula for the initial value of the tangent modulus is as follows:

[0020] ETAN initial =E initial *0.5%

[0021] In the formula, ETAN initial is the initial value of the tangent modulus, and E initial is the initial value of the elastic modulus;

[0022] The calculation formula for the initial value of the effective plastic strain is as follows:

[0023] FS initial =εmax - εy initial

[0024] In the formula, FS initial is the initial value of the effective plastic strain, εmax is the ultimate strain value, and εy initial is the initial value of the yield strain.

[0025] Calculating the initial values of parameters through a clear relational expression can simplify the entire calculation process and reduce the dependence on complex experimental data.

[0026] Preferably, step S2 includes:

[0027] S2-1) Establish a basic finite element model;

[0028] S2-2) Optimize the elastic modulus, yield stress, and tangent modulus, determine the variable space of each optimization parameter according to the initial values, and use the root mean square error between the biomechanical test curve and the simulation curve as the objective function;

[0029] S2-3) Import the elastic modulus, yield stress, and tangent modulus obtained from the bone biomechanical test into the basic finite element model in sequence until the root mean square error between the biomechanical test curve and the simulation curve meets the optimization objective, output the optimization variables that meet the optimization objective, and define them as the optimized value of the elastic modulus, the optimized value of the yield stress, and the optimized value of the tangent modulus respectively;

[0030] S2-4) Optimize the effective plastic strain, determine the variable space of the effective plastic strain according to the initial value of the effective plastic strain, and use the displacement difference at the moment of bone fracture in the biomechanical test and simulation as the objective function;

[0031] S2-5) Import the effective plastic strain obtained from the bone biomechanical test into the basic finite element model until the displacement difference at the moment of bone fracture in the biomechanical test and simulation meets the optimization objective, output the optimization variables that meet the optimization objective, and define them as the optimized value of the effective plastic strain.

[0032] When optimizing the material property parameters at the local level, the parameter optimization is completed through two stages. In the first stage, the optimization is mainly carried out for the elastic modulus, yield stress, and tangent modulus: determine their variable spaces based on the initial values of each parameter, and use the root mean square error between the biomechanical test curve and the simulation curve as the objective function. By importing the experimental data into the basic finite element model and continuously adjusting until the preset optimization objective is met, the accurate material parameters in the elastic stage (the optimized value of the elastic modulus, the optimized value of the yield stress, and the optimized value of the tangent modulus) are finally obtained. This process ensures the accuracy and reliability of the model under small deformation conditions and lays a solid foundation for subsequent analysis; The second stage focuses on identifying the key parameter in the plastic stage - the effective plastic strain: determine its variable space based on the initial value of the effective plastic strain, and optimize it with the displacement difference at the moment of bone fracture in the biomechanical test and simulation as the objective function. Through iterative adjustment until the optimization objective is reached, the optimized value of the effective plastic strain is output. This method enables the model to more accurately capture the behavior characteristics of bone materials in the large deformation or failure stage, thereby enhancing the authenticity of the overall simulation.

[0033] Through this staged optimization method, it is possible to accurately identify the key material parameters in different mechanical behavior stages and effectively prevent the overfitting phenomenon that may occur during the fitting process of the entire stress-strain curve. Such a strategy not only ensures the high accuracy of the parameter inverse solution process but also enhances the simplicity and generalization ability of the model, making it more suitable for practical engineering applications and scientific research.

[0034] Further preferably, the optimization objective expression in S2-3) is as follows:

[0035] RMSE ≤ 1E-6

[0036] Wherein, RMSE is the root mean square error between the biomechanical test curve and the simulation curve, and E is the elastic modulus;

[0037] The optimization objective expression in S2-5) is as follows:

[0038] Dis ≤ 1E-6

[0039] Wherein, Dis is the displacement difference at the moment of bone fracture in the biomechanical test and the simulation, and E is the elastic modulus.

[0040] Determine the optimization objective based on the biomechanical test and the simulation, combine the biomechanical test and the simulation, improve the accuracy of the prediction of the basic finite element model, and provide a solid foundation for the subsequent steps.

[0041] Further preferably, in step S2-2), when optimizing the elastic modulus, yield stress, and tangent modulus, the variable space is elastic modulus ∈ [0.5*E initial , 2*E initial , yield stress ∈ [0.5*SIGY initial , 2*SIGY initial , tangent modulus ∈ [0.5*ETAN initial , 2*ETAN initial , where E initial is the initial value of the elastic modulus, SIGY initial is the initial value of the yield stress, and ETAN initial is the initial value of the tangent modulus; in step S2-4), when optimizing the effective plastic strain, the variable space is effective plastic strain ∈ [0.1*FS initial , 10*FS initial , where FS initial is the initial value of the effective plastic strain.

[0042] Determine the variable space of the optimization variables according to the initial values of the parameters, provide a relatively reasonable and reliable optimization range for the optimization process, reduce the risk of overfitting, and an appropriate variable space setting can help avoid the model from overfitting a specific data set; it also avoids blind search in the entire possible parameter space, thus greatly improving the optimization efficiency; using their respective unique initial values to set the variable space can achieve more accurate and personalized adjustment for each sample, so as to obtain an optimization result that is more in line with the actual situation.

[0043] Further preferably, step S3 includes:

[0044] S3-1) Establish an osteopathic-level finite element model;

[0045] S3-2) Optimize the elastic modulus, yield stress, tangent modulus, and effective plastic strain. Determine the variable space of each optimization parameter based on the optimized values of the elastic modulus, yield stress, tangent modulus, and effective plastic strain. Define the similarity score between the biomechanical test curve and the simulation curve, as well as the displacement difference at the moment of bone fracture in the biomechanical test and simulation, as the objective function;

[0046] S3-3) Import the elastic modulus, yield stress, and tangent modulus obtained from the bone biomechanical test into the osteopathic-level finite element model in sequence until the optimization goal is met. Output the optimization variables that meet the optimization goal and define them as the optimal values of the elastic modulus, yield stress, tangent modulus, and effective plastic strain, respectively.

[0047] By utilizing the key parameters such as the optimized elastic modulus, yield stress, tangent modulus, and effective plastic strain in step S2, combined with biomechanical test data, a more accurate osteopathic-level finite element model is established, ensuring the accuracy and reliability of the initial state of the model; on the basis of the osteopathic-level model, comprehensive parameter optimization is carried out, aiming to improve the performance of the model at the macroscopic level. By simultaneously adjusting multiple key parameters, the mechanical response of the bone under different loading conditions can be captured more comprehensively, thereby improving the overall performance of the model; using the similarity score between the biomechanical test curve and the simulation curve, as well as the displacement difference at the moment of bone fracture in the actual and simulated tests as the dual objective function to achieve more comprehensive and accurate optimization.

[0048] More preferably, in S3-3), the optimization objective expression is as follows:

[0049]

[0050] In the formula, Cora is the similarity score between the biomechanical test curve and the simulation curve; Dis is the displacement difference at the moment of bone fracture in the biomechanical test and simulation, δ s is the failure displacement at the moment of bone fracture in the simulation, δ t is the failure displacement at the moment of bone fracture in the biomechanical test, and E is the elastic modulus.

[0051] Multi-objective optimization can improve the accuracy and reliability of the model. By simultaneously optimizing objectives such as the similarity score and displacement difference, the finite element model can better reflect the behavior of real bones, thereby improving the accuracy and reliability of predictions. Description of the Drawings

[0052] Figure 1 is the flowchart of the present invention;

[0053] Figure 2 It is the flowchart of Step 2 of the present invention;

[0054] Figure 3 It is the flowchart of Step 3 of the present invention. Specific embodiments

[0055] The following is a further detailed description through specific embodiments:

[0056] The specific implementation process is as follows: Refer to Figures 1 to 3 , a high-precision material property parameter identification and optimization method based on bones, specifically including the following steps:

[0057] S1: Obtain the initial parameter values based on bone biomechanical tests. The initial parameter values include the initial elastic modulus E in the elastic stage initial , the initial yield stress SIGY initial , the initial tangent modulus ETAN initial , the initial effective plastic strain FS initial ;

[0058] In step S1, the steps to obtain the initial parameter values are as follows:

[0059] S1-1) Convert the force-displacement curves of all specimens in the biomechanical test into stress-strain curves, and determine the ultimate stress value σmax and ultimate strain value εmax of the material;

[0060] Stress conversion formula:

[0061]

[0062] In the formula, F is the loading force obtained by the force sensor in the three-point bending test, L is the distance between the two fulcrums in the three-point bending test, b is the width of the specimen, and h is the height of the specimen;

[0063] Strain conversion formula:

[0064]

[0065] In the formula, δ is the displacement of the loading point obtained by the displacement sensor in the three-point bending test, L is the distance between the two fulcrums in the three-point bending test, and h is the height of the specimen.

[0066] The highest point of the stress-strain curve is the material failure point. The stress value corresponding to this failure point is the ultimate stress value σmax, and the corresponding strain value is the ultimate strain value εmax;

[0067] In this embodiment, 573 three-point bending tests were carried out on femoral specimens with dimensions of 12 mm×2 mm×0.5 mm, and 573 test curves were obtained. The ultimate stress values and ultimate strain values of each curve were extracted respectively.

[0068] S1-2) Divide the stress-strain curve into curve segments according to the ultimate stress value and ultimate strain value of the material, fit each curve segment, select the curve segment with the fitting degree closest to 1, and define the slope of this curve segment as the initial value of the elastic modulus;

[0069] In this embodiment, with a window width of 30% of the ultimate stress value and a step size of 5% of the ultimate stress value, the stress-strain curve is divided into 15 segments; the fitlm function is used to perform a unary linear regression fit on each curve segment; the intercept and regression coefficient in the regression model are output through instructions; the goodness of fit of the model is judged by the coefficient of determination, and the curve segment with the coefficient of determination closest to 1 is selected, and the slope of this curve segment is taken as the initial value E of the elastic modulus initial ;

[0070] S1-3) Set a bias curve, and define the stress corresponding to the intersection point of the bias curve and the stress-strain curve as the initial value SIGY of the yield stress initial , and the strain corresponding to the intersection point is defined as the initial value εy of the yield strain initial ;

[0071] For the curve segment selected in S1-2), define the intersection point of this curve segment and the horizontal axis (strain axis) as the zero strain point, that is, translate the coordinate origin of the stress-strain curve to this point; offset the selected curve segment by 0.0069%, and define the offset curve as the bias curve, and define the stress corresponding to the intersection point of the bias curve and the stress-strain curve as the initial value SIGY of the yield stress initial , and the corresponding strain is defined as the initial value εy of the yield strain initial .

[0072] The expression of the bias curve is as follows:

[0073] σ = E initial *(ε - 0.0069%)

[0074] In the formula, σ is the bias curve, E initial is the initial value of the elastic modulus, and ε is the fitted curve segment.

[0075] S1-4) Calculate the initial value of the tangent modulus and the initial value of the effective plastic strain according to the initial value of the elastic modulus; in step S1-4), the calculation formula for the initial value of the tangent modulus is as follows:

[0076] ETAN initial = E initial *0.5%

[0077] In the formula, ETAN initial is the initial value of the tangent modulus, and E initial is the initial value of the elastic modulus;

[0078] The calculation formula for the initial value of the effective plastic strain is as follows:

[0079] FS inital = εmax - εy initial

[0080] In the formula, FS initial is the initial value of the effective plastic strain, εmax is the ultimate strain value, and εy initial is the initial value of the yield strain.

[0081] In this embodiment, a total of 573 tests were conducted. Statistical analysis was performed on the initial values obtained from each test, and the average value of the initial elastic modulus of the whole was 14.4 Gpa, the average value of the initial yield stress was 92.67 Mpa, the average value of the initial tangent modulus was 0.72 Gpa, and the average value of the initial effective plastic strain was 1.71%.

[0082] S2: Establish a basic finite element model based on the bone biomechanical test. Using the root mean square error between the biomechanical test curve and the simulation curve as the objective function, optimize the elastic modulus, yield stress, and tangent modulus; at the same time, using the displacement difference at the moment of bone fracture in the biomechanical test and the simulation as the objective function, optimize the effective plastic strain;

[0083] S2-1) Establish a basic finite element model;

[0084] Measure the widths (b1, b2, b3) and thicknesses (h1, h2, h3) at the middle and both ends of each specimen, as well as the length (L) of the specimen. Determine the positions of the middle four nodes based on the width and thickness at the middle of the specimen, and similarly determine the positions of the eight nodes at both ends according to the width and thickness at both ends of the specimen. Divide the specimen into two equal left and right parts from the middle of the specimen. Taking the right side as an example. The dimensional changes between h1 and h2 and between b1 and b2 are interpolated through a linear function to achieve a linear smooth transition of the mesh, realizing a mesh element division with 9 nodes in the thickness direction, 17 nodes in the width direction, and 97 nodes in the length direction. The construction of the left specimen is the same, and finally a 20-sided polyhedron model similar to the actual size and shape of the corresponding specimen is formed. The specimen adopts the *MAT_PIECEWISE_LINEAR_PLASTICITYA bilinear elastoplastic material constitutive model. The support shafts at both ends of the specimen and the middle impact head are both simulated by rigid walls, and the contact with the specimen is defined, with the friction coefficient set to 0.05. Apply acceleration to the impact head to simulate the actual loading. Output the time history curves of the displacement of the impact head and the contact force between it and the specimen at the same sampling frequency as the experiment, and then obtain the force-displacement curve of the numerical simulation to ensure that the boundary conditions and output results of the finite element model are consistent with the experiment.

[0085] S2-2) Optimize the elastic modulus, yield stress, and tangent modulus. Determine the variable space of each optimization parameter according to the initial values, and take the root mean square error between the biomechanical test curve and the simulation curve as the objective function;

[0086] In step S2-2), when optimizing the elastic modulus, yield stress, and tangent modulus, the variable space is elastic modulus ∈ [0.5*E initial , 2*E initial , yield stress ∈ [0.5*SIGY initial , 2*SIGY initial , tangent modulus ∈ [0.5*ETAN initial , 2*ETAN initial , where E initial is the initial value of the elastic modulus, SIGY initial is the initial value of the yield stress, ETAN initial is the initial value of the tangent modulus. In this step, the material failure range is not set, that is, the effective plastic strain is not defined;

[0087] The objective function expression in S2-2) is as follows:

[0088]

[0089] In the formula, RMSE is the root mean square error between the biomechanical test curve and the simulation curve, and σ s (ε i) The numerical value of the sampling point in the stress-strain curve during simulation, σ t (ε i ) is the numerical value of the sampling point in the stress-strain curve during the biomechanical test, and n is the number of sampling points.

[0090] S2-3) Import the elastic modulus, yield stress, and tangent modulus obtained from the bone biomechanical test into the basic finite element model in sequence until the root mean square error between the biomechanical test curve and the simulation curve meets the optimization goal, and output the optimization variables that meet the optimization goal, and define them as the optimized value of the elastic modulus, the optimized value of the yield stress, and the optimized value of the tangent modulus respectively;

[0091] The optimization goal expression in S2-3) is as follows:

[0092] RMSE ≤ 1E-6

[0093] In the formula, RMSE is the root mean square error between the biomechanical test curve and the simulation curve, and E is the elastic modulus;

[0094] Specifically, as Figure 2 shown, import the i-th elastic modulus E, the i-th yield stress SIGY, and the i-th tangent modulus ETAN into the basic finite element model, and perform simulation through the DYNA main program; when the optimization goal RMSE ≤ 1E-6 is met, output the optimized value E of the elastic modulus opt , the optimized value SIGY of the yield stress opt and the optimized value ETAN of the tangent modulus opt , if not satisfied, then i = i + 1, import new parameters until the parameters within the traversed space range are exhausted.

[0095] In this embodiment, according to the initial values obtained in step S1, perform simulation and comparison and optimization of the test curves for 573 tests in sequence to obtain the optimized values of the material parameters corresponding to each test curve. Perform statistical analysis on the optimized values of each test obtained in step S2, and the statistical average of the optimized value of the elastic modulus is 12.06 pa, the statistical average of the optimized value of the yield stress is 78.13 Mpa, the statistical average of the optimized value of the effective plastic strain is 1.99%, and the statistical average of the optimized value of the tangent modulus is 0.59 Gpa.

[0096] S2-4) Optimize the effective plastic strain, determine the variable space of the effective plastic strain according to the initial value of the effective plastic strain, and determine the displacement difference at the moment of bone fracture in the biomechanical test and simulation as the objective function;

[0097] In step S2-4), when optimizing the effective plastic strain, the variable space is the effective plastic strain ∈ [0.1*FS initial , 10*FS initial , where FSinitial is the initial value of the effective plastic strain; during the optimization process of the effective plastic strain, the elastic modulus, yield stress, and tangent modulus are respectively the optimized values of the elastic modulus E output in step S2-3) opt , the optimized value of the yield stress SIGY opt and the optimized value of the tangent modulus ETAN opt That is, the elastic modulus E = E opt , the yield stress SIGY = SIGY opt , the tangent modulus ETAN = ETAN opt ;

[0098] The objective function expression in S2-4) is as follows:

[0099] Dis = |δ s -δ t |

[0100] In the formula, Dis is the displacement difference at the moment of bone fracture in the biomechanical experiment and simulation, and δ s is the failure displacement at the moment of bone fracture in the simulation, and δ t is the failure displacement at the moment of bone fracture in the biomechanical experiment.

[0101] S2-5) Import the effective plastic strain obtained from the bone biomechanical experiment into the basic finite element model until the displacement difference at the moment of bone fracture in the biomechanical experiment and simulation meets the optimization goal, and output the optimization variables that meet the optimization goal, which are defined as the optimized value of the effective plastic strain.

[0102] The optimization goal expression in S2-5) is as follows:

[0103] Dis ≤ 1E-6

[0104] In the formula, Dis is the displacement difference at the moment of bone fracture in the biomechanical experiment and simulation, and E is the elastic modulus.

[0105] Specifically, as Figure 2 shown, import the jth effective plastic strain FS into the basic finite element model, and perform simulation through the DYNA main program. When Dis ≤ 1E-6, output the effective plastic strain that meets the optimization goal as the optimized value of the effective plastic strain FS opt , if not satisfied, then j = j + 1, import new parameters until all parameters within the spatial range are traversed.

[0106] S3: Establish an osteopathic-level finite element model. Among them, perform statistical analysis on the elastic modulus, yield stress, tangent modulus, and effective plastic strain preliminarily optimized in S2, use the analysis results as the variable space, set the similarity score between the biomechanical test curve and the simulation curve and the displacement difference at the moment of bone fracture in the biomechanical test and the simulation as the objective function, perform multi-objective parameter optimization, and output the optimized elastic modulus, yield stress, tangent modulus, and effective plastic strain as the final bone material characteristic parameters.

[0107] Step S3 includes:

[0108] S3-1) Establish an osteopathic-level finite element model;

[0109] The bone is given a bilinear elastoplastic material constitutive of *MAT_PIECEWISE_LINEAR_PLASTICITYA. The support axes at both ends of the bone and the middle impactor are both simulated by rigid walls, and the contact with the specimen is defined, with the friction coefficient set to 0.1. Restrict the displacements at both ends of the bone through *BOUNDAR_SPC, and set the loading speed of the impactor to be consistent with the osteopathic test through *BOUNDARY_PRESCRIBED_MOTION_RIGID(Vel). Output the time history curves of the displacement of the impact head and the contact force between it and the specimen at the same sampling frequency as the test, and then obtain the force-displacement curve of the numerical simulation.

[0110] S3-2) Optimize the elastic modulus, yield stress, tangent modulus, and effective plastic strain. Determine the variable space of each optimization parameter according to the optimized values of the elastic modulus, yield stress, tangent modulus, and effective plastic strain, and determine the similarity score between the biomechanical test curve and the simulation curve and the displacement difference at the moment of bone fracture in the biomechanical test and the simulation as the objective function;

[0111] When defining the variable space, perform statistical analysis according to the biomechanical test and the material constitutive parameters obtained from the simulation in step S2, obtain the mean value and the standard deviation, and define the mean value ± the standard deviation as the variable space, variable space = [mean - standard deviation, mean + standard deviation].

[0112] S3-3) Import the elastic modulus, yield stress, and tangent modulus obtained from the bone biomechanical test into the osteopathic-level finite element model in turn until the optimization goal is met. Output the optimization variables that meet the optimization goal and define them as the optimal value of the elastic modulus, the optimal value of the yield stress, the optimal value of the tangent modulus, and the optimal value of the effective plastic strain respectively.

[0113] In S3-3), the optimization goal expression is as follows:

[0114]

[0115] In the formula, Cora is the similarity score between the biomechanical test curve and the simulation curve; Dis is the displacement difference at the moment of bone fracture in the biomechanical test and the simulation, δ s is the failure displacement at the moment of bone fracture in the simulation, δ t is the failure displacement at the moment of bone fracture in the biomechanical test, and E is the elastic modulus;

[0116] Specifically, as Figure 3 shown, the k-th elastic modulus E, the k-th yield stress SIGY, the k-th tangent modulus ETAN, and the k-th effective plastic strain FS are imported into the osteopathic-level finite element model, and the simulation is carried out through the DYNA main program. If the optimization goal in S3-3) is satisfied, the optimized elastic modulus E, yield stress SIGY, tangent modulus ETAN, and effective plastic strain are output as the final value E of the elastic modulus last , the final value SIGY of the yield stress last , the final value ETAN of the tangent modulus last and the final value FS of the effective plastic strain last . If not, k = k + 1, and other parameter values in the input variable space are input until the parameters in the variable space are traversed.

[0117] In this embodiment, the final value E of the elastic modulus last is 17.3 GPa, the final value SIGY of the yield stress last is 89.6 Mpa, the final value ETAN of the tangent modulus last is 1.22 GPa, and the final value FS of the effective plastic strain last is 1.4%.

[0118] The above are only the embodiments of the present invention. The specific structures and characteristics and other common knowledge in the solution are not described in detail here. Those of ordinary skill in the art know all the common technical knowledge in the technical field to which the invention belongs before the application date or the priority date, can know all the existing technologies in this field, and have the ability to apply the conventional experimental means before this date. Those of ordinary skill in the art can, under the inspiration given in this application, complete and implement this solution in combination with their own abilities. Some typical well-known structures or well-known methods should not become obstacles for those of ordinary skill in the art to implement this application. It should be noted that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can be made, and these should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent. The protection scope required by this application should be subject to the content of its claims, and the specific implementation manners and the like recorded in the specification can be used to explain the content of the claims.

Claims

1. A high-precision material characteristic parameter identification and optimization method based on bones, characterized in that: The specific steps include: S1: obtaining initial values ​​of parameters based on bone biomechanics tests, wherein the initial values ​​of parameters include an initial value of elastic modulus, an initial value of yield stress, an initial value of tangent modulus, and an initial value of effective plastic strain in an elastic stage; S2: A basic finite element model is established based on the bone biomechanical test. The root mean square error between the biomechanical test curve and the simulation curve is used as the objective function to optimize the elastic modulus, yield stress, and tangent modulus. At the same time, the displacement difference at the moment of bone fracture in the biomechanical test and simulation is used as the objective function to optimize the effective plastic strain. S3: Establish a whole-bone finite element model, in which the elastic modulus, yield stress, tangent modulus, and effective plastic strain that were initially optimized in S2 are statistically analyzed. The analysis results are used as the variable space, and the similarity score between the biomechanical test curve and the simulation curve and the displacement difference at the moment of bone fracture in the biomechanical test and simulation are set as the objective function. Multi-objective parameter optimization is performed, and the optimized elastic modulus, yield stress, tangent modulus, and effective plastic strain are output as the final bone material characteristic parameters.

2. The method for identifying and optimizing high-precision material characteristic parameters based on bones according to claim 1, characterized in that: In step S1, the steps for obtaining the initial value of the parameter are as follows: S1-1) converting the force-displacement curves of all types of biomechanical tests into stress-strain curves, and determining the ultimate stress value and ultimate strain value of the material; S1-2) dividing the stress-strain curve into curve segments according to the ultimate stress value and the ultimate strain value of the material, fitting each curve segment, selecting the curve segment with the fitting degree closest to 1, and defining the slope of the curve segment as the initial value of the elastic modulus; S1-3) setting a bias curve, defining the stress corresponding to the intersection of the bias curve and the stress-strain curve as the initial value of the yield stress, and defining the strain corresponding to the intersection as the initial value of the yield strain; S1-4) Calculate the initial value of the tangent modulus and the initial value of the effective plastic strain based on the initial value of the elastic modulus.

3. The method for identifying and optimizing high-precision material characteristic parameters based on bones according to claim 2, characterized in that: In step S1-4), the calculation formula of the initial value of the tangent modulus is as follows: ON initial =E initial *0.5% Where, ETAN initial is the initial value of the tangent modulus, E initial is the initial value of elastic modulus; The calculation formula of the initial value of effective plastic strain is as follows: FS initial =εmax-εy initial Where, FS initial is the initial value of effective plastic strain, εmax is the limit strain value, εy initial is the initial value of yield strain.

4. The method for identifying and optimizing high-precision material characteristic parameters based on bones according to claim 1, characterized in that: Step S2 includes: S2-1) Establishing a basic finite element model; S2-2) optimizing the elastic modulus, yield stress, and tangent modulus, determining the variable space of each optimization parameter according to the initial value, and determining the root mean square error between the biomechanical test curve and the simulation curve as the objective function; S2-3) The elastic modulus, yield stress, and tangent modulus obtained from the bone biomechanical test are sequentially imported into the basic finite element model until the root mean square error between the biomechanical test curve and the simulation curve meets the optimization target, and the optimization variables that meet the optimization target are output and defined as the elastic modulus optimization value, yield stress optimization value, and tangent modulus optimization value, respectively; S2-4) optimizing the effective plastic strain, determining the variable space of the effective plastic strain according to the initial value of the effective plastic strain, and determining the displacement difference at the moment of bone fracture in the biomechanical test and the simulation as the objective function; S2-5) The effective plastic strain obtained from the bone biomechanical test is imported into the basic finite element model until the displacement difference at the moment of bone fracture in the biomechanical test and the simulation meets the optimization target, and the optimization variable that meets the optimization target is output and defined as the effective plastic strain optimization value.

5. The method for identifying and optimizing high-precision material characteristic parameters based on bones according to claim 4, characterized in that: The optimization objective expression in S2-3) is as follows: RMSE≤1E-6 Where RMSE is the root mean square error between the biomechanical test curve and the simulation curve, and E is the elastic modulus; The optimization objective expression in S2-5) is as follows: Dis≤1E-6 Where Dis is the displacement difference at the moment of bone fracture in biomechanical test and simulation, and E is the elastic modulus.

6. The method for identifying and optimizing high-precision material characteristic parameters based on bones according to claim 4, characterized in that: In step S2-2), when optimizing the elastic modulus, yield stress, and tangent modulus, the variable space is elastic modulus∈[0.5*E initial ,2*E initial ], yield stress∈[0.5*SIGY initial ,2*SIGY initial ], tangent modulus ∈[0.5*ETAN initial ,2*ETAN initial ], where E initial is the initial value of elastic modulus, SIGY initial is the initial value of yield stress, ETAN initial is the initial value of the tangent modulus; in step S2-4), when optimizing the effective plastic strain, the variable space is the effective plastic strain ∈ [0.1*FS initial ,10*FS initial ], where FS initial is the initial value of effective plastic strain.

7. The method for identifying and optimizing high-precision material characteristic parameters based on bones according to claim 4, characterized in that: Step S3 includes: S3-1) Establishing a bone-level finite element model; S3-2) optimizing the elastic modulus, yield stress, tangent modulus, and effective plastic strain, determining the variable space of each optimization parameter according to the optimized value of the elastic modulus, the optimized value of the yield stress, the optimized value of the tangent modulus, and the optimized value of the effective plastic strain, and determining the similarity score between the biomechanical test curve and the simulation curve and the displacement difference at the moment of bone fracture in the biomechanical test and the simulation as the objective function; S3-3) The elastic modulus, yield stress, and tangent modulus obtained from the bone biomechanical test are sequentially imported into the whole bone-level finite element model until the optimization target is met. The optimization variables that meet the optimization target are output and defined as the optimal value of the elastic modulus, the optimal value of the yield stress, the optimal value of the tangent modulus, and the optimal value of the effective plastic strain, respectively.

8. The method for identifying and optimizing high-precision material characteristic parameters based on bones according to claim 7, characterized in that: In S3-3), the optimization objective expression is as follows: Where Cora is the similarity score between the biomechanical test curve and the simulation curve; Dis is the displacement difference at the moment of bone fracture in the biomechanical test and simulation, δ s is the failure displacement when the bone breaks in the simulation, δ t is the failure displacement when the bone breaks in the biomechanical test, and E is the elastic modulus.

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