CN-122021095-A - Virtual field inversion method for determining rigidity coefficient of glass fiber reinforced composite material

Abstract

The invention discloses a virtual field inversion method for determining a rigidity coefficient of a glass fiber reinforced composite material, which is characterized by comprising the following steps of: s1: balancing the magnitude of shear strain and positive strain in two main directions before applying a virtual field method; s2: optimizing the shape of the sample by using commercial finite element software; s3: setting a special virtual field method of iterative initial value application optimization; s4: calculating the relative error of the identification result of each stiffness coefficient, and determining the optimal design parameter on the condition that the sum of absolute values of the stiffness coefficients is minimum; s5: the invention provides a virtual field inversion method for determining a rigidity coefficient of a glass fiber reinforced composite material, which is characterized in that a virtual field method is used for combining a virtual field method and a finite element to optimally design the shape and the position of a V-shaped notch of a tensile sample, a calculated result is substituted into the virtual field method to invert and identify the rigidity coefficient, an inversion error is calculated by comparing an inversion result with a finite element input parameter, and the geometric shape corresponding to the minimum error is used as an optimized result of a test piece.

Inventors

• JIANG HAO
• ZHU RONGXIN
• GUO ZHENFEI

Assignees

• 东北林业大学

Dates

Publication Date

20260512

Application Date

20251107

Claims (5)

1. 1. The virtual field inversion method for determining the rigidity coefficient of the glass fiber reinforced composite material is characterized by comprising the following steps of: S1, balancing the magnitude of shear strain and positive strain of two main directions before applying a virtual field method; S2, optimizing the shape of the sample through commercial finite element software ABAQUS, traversing and modeling in a design variable value range, substituting ideal strain field data of a simulation test into a virtual field method for inversion calculation, calculating inversion result errors by comparing material parameters input by finite elements, and determining optimal design parameters under the condition of minimum errors; S3, setting a special virtual field method of iterative initial value application optimization, wherein the quality of the initial value directly determines the convergence speed due to the influence of various errors and noise in actual strain data, and under the condition that material parameters are unknown, self-defining four groups of initial virtual fields to calculate the initial value; S4, calculating the relative error of the identification result of each stiffness coefficient, and determining the optimal design parameter on the condition that the sum of absolute values of the relative errors is minimum; and S5, performing data processing of a strain field, encrypting data points by reducing grid intervals, reducing the size of sub-regions, expanding the calculation range of a boundary region as much as possible by reducing the effectiveness of a boundary, calculating by using an optimized finite element grid, taking the average value of all data points in a unit as the unit strain, determining the coordinates of the central point of each unit and the unit area according to the coordinates of the grid nodes, and calculating the corresponding virtual field by using the coordinates of the central point of the unit.
2. 2. The virtual field inversion method for determining the rigidity coefficient of a glass fiber reinforced composite material according to claim 1, wherein in the step S1, three geometric parameters of a central symmetry V-shaped notch sample of 90 degrees, namely a notch position x1, an opening size x2 and a notch chamfer r are selected as design variables, the width of the sample is fixed to 25mm according to a uniaxial tensile test standard, meanwhile, the length of an effective area is taken as another design variable, and the geometric shape and the design variables of the sample and the value range of each parameter are determined.
3. 3. A virtual field inversion method for determining rigidity coefficient of glass fiber reinforced composite material according to claim 1, wherein said modeling in step S2 uses shell elements, and typical rigidity coefficient of glass fiber reinforced composite material is used as simulation test parameter, and comprises Q66=4gpa, setting a displacement loading of 0.5mm, simulating a three-node triangular linear unit with a side length of 2mm.
4. 4. The virtual field inversion method for determining stiffness coefficient of glass fiber reinforced composite material of claim 1, wherein the step S4 is performed by: Wherein, the Is the result of the inversion of the virtual field method, Is the stiffness coefficient of the finite element input.
5. 5. The virtual field inversion method for determining stiffness coefficient of glass fiber reinforced composite material according to claim 4, wherein said satisfying formula is characterized in that, considering more design variables and abundant samples, ten samples with the smallest relative error are selected for comprehensive evaluation, the sample is too long to facilitate focusing of CCD camera, and the whole ten sizes are easier to memorize, the geometric shape is more standard, the sample is easier to process, so that the finally determined geometric parameters of the sample are And (3) each time the four geometric parameters are changed, fixing the other three geometric parameters to calculate the identification error of each stiffness coefficient, and observing the sensitivity of the identification result to each geometric parameter.

Description

Virtual field inversion method for determining rigidity coefficient of glass fiber reinforced composite material Technical Field The invention relates to the field of rigidity coefficients of composite materials, in particular to a virtual field inversion method for determining rigidity coefficients of glass fiber reinforced composite materials. Background The fiber reinforced composite material has the advantages of high specific modulus, high specific strength, strong designability of material performance and the like, and is widely applied to the fields of aerospace, vehicle engineering, wind power generation and the like. Before the material is applied to engineering practice, a great amount of finite element structure simulation analysis is often required to be carried out by a designer, and the accuracy of a simulation result is highly dependent on the accuracy of the intrinsic parameters of the material. Unidirectional fiber reinforced composites can be considered orthotropic materials, and have four independent in-plane stiffness coefficientsRespectively corresponding to Cheng Danxing constantsWith existing standards, these parameters require three tests to be measured in total. Two tensile tests according to ASTM D3039 standard were used to determine the modulus of elasticity in the direction of the fibersModulus of elasticity perpendicular to the fiber directionAnd main poisson ratio In addition, shear modulusIs difficult to measure, and two types of schemes can be referred to. The test piece is characterized in that two ends of the test piece are enabled to move in parallel along opposite directions, and direct shearing actions, such as a slide rail shearing test, a Iosipescu test and a V-shaped notch sample slide rail shearing test, are generated. The direct shear test requires a special fixture and has low success rate. The other type is an off-axis tensile test, such as a + -45 DEG symmetrical ply sample tensile test, a 10 DEG off-axis test, a 45 DEG off-axis test, etc., but a pure shearing state cannot be generated due to interlayer stress and coupling effect, andThe curve is significantly nonlinear and therefore the off-axis tensile test results are not particularly accurate. The method is based on the assumption of uniform strain, the deformation state of the designated position on the surface of the test piece is recorded through a strain gauge or an extensometer, and the constitutive parameters are calculated according to the stress-strain relation, and the method belongs to a direct measurement method. In practice, the identification of the constitutive parameters of the material can be realized by some inversion methods, and the rapid development of full-field deformation measurement technologies such as a digital image correlation method, a grid method and the like makes the inversion methods applicable to engineering practice possible. The basic idea of the finite element updating method is to construct a cost function according to the difference between the numerical calculation result and the actual experimental measurement result, and update the material property parameter to iterate finite element calculation until the convergence criterion is met. Molimard, lecompte, cugnoni et al have conducted an inversion identification study of the elastic constant of orthotropic materials based on this. Notably, the virtual field method directly extracts constitutive parameters from the material full-field deformation data by solving a virtual work equation, and avoids repeated iteration finite element calculation, so that the calculation efficiency can be greatly improved. As with the finite element update method, to reverse the 4 stiffness coefficients of the orthotropic material at one time using the virtual field method, it is necessary to optimize the shape of the test piece to generate a complex strain field, thereby reflecting the contributions of all parameters. For this purpose, a number of nonstandard tests such as T-shaped specimen tensile test, short beam shear or bending test, arcan test, open cell specimen tensile test, etc. were developed successively. The appropriate virtual field is a necessary condition for the VFM to solve the constitutive parameters of the material, so it directly affects inversion accuracy. Initially, the virtual field is directly defined by a mathematical function, and the method is simple and direct, and has high calculation speed, but the most suitable virtual field configuration is difficult to find, so that the result is accurately inverted. The special virtual field method solves the problem, and can automatically construct a virtual field and directly calculate the parameters from the virtual work of external force, but the special virtual field is often endless and difficult to be selected and removed. Avril et al put forward the special virtual field method of optimization with the recognition result least sensitive to random noise as constraint