ETFE film viscoplastic shape finding and analysis evaluation method

Abstract

The invention discloses an ETFE film viscoplastic shape finding and analysis evaluation method. The method comprises the following steps that S1, the load requirement after an ETFE air pillow is formed is determined; s2, model selection is carried out on the ETFE air cushion; s3, according to the size of the ETFE air pillow, model selection is conducted on an ETFE membrane material; s4, determining a uniaxial tensile test scheme and performance parameters of the ETFE membrane material; s5, determining an ETFE viscoplastic analysis constitutive model and parameters; s6, modeling analysis is conducted on the ETFE air pillow, and shape finding parameters are determined according to forming requirements; s7, the formed ETFE air pillow is subjected to structural analysis under the load combination working condition; and S8, performing green evaluation on the air pillow. By means of the method, plane forming of the air pillow can be achieved directly through viscoplastic deformation of the film material, and the hidden carbon emission of the ETFE air pillow can be rapidly evaluated.

Description

Technical Field

[0001] This invention relates to the field of building structure technology, and more specifically to a method for finding and analyzing the viscoplasticity of ETFE membranes. Background Technology

[0002] Traditional ETFE membrane structures require form-finding and trimming analysis steps to obtain their initial shape. Form-finding analysis, which aims to obtain the initial equilibrium surface of the structure, is a crucial step in structural design. Several relatively mature research methods have been developed for form-finding in membrane structures, including dynamic relaxation, force density, and finite element methods. Based on form-finding analysis, trimming analysis and splicing are then necessary to obtain the complete membrane plane.

[0003] The curved surface obtained by planar membrane cutting and splicing is close to the ideal curved surface. This method is very suitable for fabric membrane structures with large curvature variations and complex shapes. The cut membrane sheets need to be spliced ​​together by welding to form the membrane splice line. Welding of ETFE membranes requires specialized equipment, is complex and inefficient, results in low material strength at the weld, and affects the aesthetics of the air cushion. At the same time, material waste is inevitable during cutting. Therefore, using traditional cutting and splicing methods to process ETFE air cushion structures with small individual spans is not necessarily the most efficient method.

[0004] Unlike traditional cutting and splicing methods, the ETFE air cushion surface viscoplastic forming method involves applying high internal pressure through inflation to induce significant deformation in the installed planar ETFE film via specific processing or construction steps. The internal pressure is then reduced to normal, allowing the elastic deformation to recover. This non-recoverable deformation of the ETFE film material itself forms the air cushion structure surface. This forming method not only fully utilizes the material's high elongation, leveraging its viscoplastic deformation to create the designed air cushion surface, but also significantly simplifies the manufacturing process of the ETFE air cushion film, minimizing cutting and welding steps, saving materials, and improving the continuity and aesthetics of the air cushion surface. Therefore, a viscoplastic forming and analysis evaluation method for ETFE is urgently needed to promote this technology. Summary of the Invention

[0005] In view of this, the present invention provides a method for viscoplastic shape finding and analysis evaluation of ETFE membrane, which directly shapes the air cushion plane through the viscoplastic deformation of the membrane material itself.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for viscoplasticity finding and analysis evaluation of ETFE membranes includes the following steps:

[0008] S1. Determine the load requirements after the ETFE air cushion is formed.

[0009] S2. Select the appropriate ETFE air pillow;

[0010] S3. Select the ETFE membrane material according to the ETFE air cushion size;

[0011] S4. Determine the uniaxial tensile test scheme and performance parameters for ETFE membrane material;

[0012] S5. Determine the constitutive model and parameters for ETFE viscoplasticity analysis;

[0013] S6. Model and analyze the ETFE air cushion, and determine the form-finding parameters according to the forming requirements;

[0014] S7. Perform structural analysis of the formed ETFE air cushion under combined load conditions;

[0015] S8, ETFE air cushion green assessment.

[0016] Preferably, in step S1, the loads include the structure's self-weight, internal pressure, live load, wind load, snow load, and seismic load.

[0017] Preferably, in step S2, the ETFE air cushion selection includes determining the support structure, shape, height, and number of layers of the ETFE air cushion.

[0018] Preferably, in step S3, the ETFE membrane material selection includes ETFE membrane material thickness, first yield strength, second yield strength, ultimate strength, elongation, and elastic modulus.

[0019] Preferably, in step S4, the uniaxial tensile test scheme for ETFE membrane material includes determining the form and size of the uniaxial tensile specimen, the tensile testing instrument, the tensile rate, and the data processing standard.

[0020] Preferably, in step S4, the tensile specimen is in the form of a strip or dumbbell; the effective gauge length of the tensile specimen is not less than 100 mm; the tensile rate is distributed from static to 100% of the gauge length; the data processing standards include the determination of the tensile curve, the yield point and the elastic modulus.

[0021] Preferably, in step S5, the constitutive model for ETFE viscoplastic analysis is a simplified model of the Perzyna Model; the parameters of the ETFE viscoplastic analysis constitutive model include the plastic strain rate. Static yield stress σ0, strain rate parameter m, viscosity parameter γ * ; where plastic strain rate The static yield stress σ0 is determined based on the inflation rate of the ETFE air cushion, and the first yield strength obtained from the static tensile rate in S4 is also considered. The strain rate parameter m and the viscosity parameter γ are also determined. * The yield strength is determined by fitting the first yield strength with the tensile rate in step S4.

[0022] Preferably, in step S6, the modeling and analysis of the ETFE air cushion is performed using finite element software; the ETFE air cushion shape-finding parameters include the number of inflations, maximum inflation pressure, inflation speed, deflation speed, time required for each inflation, and settling time.

[0023] Preferably, in step S7, the load combination conditions include non-seismic combination conditions and seismic combination conditions, and the structural analysis is that the maximum stress on the membrane surface under the load combination conditions does not exceed the specified strength limit.

[0024] Preferably, in step S8, the implicit carbon emissions of the ETFE air cushion are determined by comprehensively considering the material consumption, energy consumption during the testing and shaping process, material transportation consumption, and the designed service life, and a green assessment of the ETFE air cushion is conducted based on this.

[0025] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a method for viscoplastic shape finding and analysis evaluation of ETFE membrane. Using the present invention, the air cushion plane can be formed directly through the viscoplastic deformation of the membrane material itself, and the implicit carbon emissions of ETFE air cushion can be quickly evaluated. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0027] Figure 1 The flowchart for the ETFE membrane viscoplasticity shape finding and analysis evaluation provided by the present invention;

[0028] Figure 2 A cross-sectional view of a long strip tensile specimen provided for the invention. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] This invention discloses a method for finding and analyzing the viscoplasticity of ETFE films, comprising the following steps:

[0031] S1. Determine the load requirements after the ETFE air cushion is formed.

[0032] The loads include the structure's self-weight, internal pressure, live load, wind load, snow load, and seismic load.

[0033] The structural self-weight includes the weight of the steel or aluminum alloy boundary structure of the membrane structure and the weight of the air cushion itself; the normal operating internal pressure is taken as 300 Pa; the live load on the non-accessible roof of the membrane structure is taken as 0.3 kN / m²; the basic snow load is taken as 0.2 kN / m² based on a 50-year return period. 2 The snow distribution coefficient on the roof is assumed to be 1.0 for an arched roof, and the standard value of the snow load is the product of the snow distribution coefficient and the basic snow pressure, which is taken as 0.2 kN / m. 2 The basic wind pressure is taken as 0.55 kN / m based on a 50-year return period. 2 The shape coefficient is taken as wind suction -1.0 and wind pressure +0.4. Assuming the air cushion roof height is 20m, the wind pressure height variation coefficient is taken as 1.23 for Class B sites, and the wind vibration coefficient is taken as 1.3. Then the standard value of wind load is -0.88 / +0.35kN / m. 2 The seismic load is taken based on the 7-degree zone. For air cushions, due to their light weight, they play a controlling role in non-seismic combination conditions in low-intensity zones.

[0034] S2. Select the appropriate ETFE air pillow;

[0035] ETFE air cushion selection includes determining the support structure, shape, height, and number of layers of the ETFE air cushion;

[0036] Assuming the supporting structure is a rigid boundary of steel or aluminum alloy, the air cushion is a square double-layer air cushion with a side length of 4m; the parameters of the ETFE membrane material are determined according to the "Technical Standard for Membrane Structures" DG / TJ 08-97-2019, with a density of 1.75g / cm3, an elastic modulus of 650N / mm2, and a Poisson's ratio of 0.42; the maximum stress on the membrane surface is determined based on calculations for different load combinations.

[0037] S3. Select the ETFE membrane material according to the ETFE air cushion size;

[0038] ETFE membrane material selection includes ETFE membrane thickness, first yield strength, second yield strength, ultimate strength, elongation, and elastic modulus.

[0039] The thickness of the ETFE membrane is determined based on the maximum stress on the membrane surface in step S2; the commonly used thickness of ETFE membrane is 0.15–0.3 mm. Other parameters of the ETFE membrane, such as the first yield strength, second yield strength, ultimate strength, elongation, and modulus of elasticity, are determined and verified through experiments.

[0040] S4. Determine the uniaxial tensile test scheme and performance parameters for ETFE membrane material;

[0041] The uniaxial tensile test protocol for ETFE membrane materials includes determining the form and size of the uniaxial tensile specimen, the tensile testing instrument, the tensile rate, and the data processing standards.

[0042] The tensile specimens are in the form of strips or dumbbells; the effective gauge length of the tensile specimens is not less than 100 mm; the tensile rate is distributed from static to 100% of the gauge length; the data processing standards include the determination of the tensile curve, the yield point and the elastic modulus.

[0043] In this embodiment, the tensile specimen can be either elongated or dumbbell-shaped; the dimensions are determined based on the testing equipment, and an effective gauge length of not less than 100 mm is recommended. The elongated specimen can be prepared as follows: Figure 2 As shown, the sample width is 15mm, the total length is 150mm, and the initial distance between the fixtures is 100mm. Mark the sample according to the dimensions shown in the diagram to control the gauge length. Care should be taken not to affect the sample during the marking process.

[0044] The tensile rate is distributed from static to 100% gauge length. Figure 2 Taking the specimen as an example, the tensile rate can be selected as 3 mm / min, 6 mm / min, 9 mm / min, 50 mm / min, or 100 mm / min. The tensile curve obtained at a tensile rate of 3 mm / min is used as the static tensile curve.

[0045] Data processing standards include determining the tensile curve, yield point, and elastic modulus. The tensile curve needs to be converted from the engineering stress-strain curve to the true stress-strain curve based on the test results. The yield strength and elastic modulus can be determined based on the rigid inflection point of the curve.

[0046] S5. Determine the constitutive model and parameters for ETFE viscoplasticity analysis;

[0047] The constitutive model for ETFE viscoplastic analysis is a simplified version of the Perzyna Model; the parameters of the ETFE viscoplastic analysis constitutive model include plastic strain rate. Static yield stress σ0, strain rate parameter m, viscosity parameter γ * ;

[0048] The constitutive model for ETFE viscoplastic analysis is a simplified version of the Perzyna Model, expressed as follows:

[0049]

[0050] In the formula, σ0 is the plastic strain rate, σ0 is the static yield stress, m is the strain rate parameter, and γ is the strain rate parameter. * Here, is the viscous parameter; where, plastic strain rate The static yield stress σ0 is determined based on the inflation rate of the ETFE air cushion, and the first yield strength obtained at a tensile rate of 3 mm / min in step S4 is also determined. The strain rate parameter m and the viscosity parameter γ are also considered. * The first yield strength and tensile rate in step S4 are determined by least squares fitting.

[0051] S6. Model and analyze the ETFE air cushion, and determine the form-finding parameters according to the forming requirements;

[0052] The modeling and analysis of ETFE air cushions are performed using finite element software, such as ANSYS and ABAQUS.

[0053] Depending on the size and forming height of the air cushion, the parameters that need to be determined during the plastic forming process include the number of inflations, maximum inflation pressure, inflation speed, deflation speed, time required for each inflation, and settling time. The number of inflations can be one or multiple times; when inflation is performed in one molding cycle, multi-stage molding can be used, with speed controlled in stages.

[0054] S7. Perform structural analysis of the formed ETFE air cushion under combined load conditions;

[0055] The load combination conditions include non-seismic combination conditions and seismic combination conditions; the air cushion is checked under both non-seismic and seismic combination conditions, and the maximum stress on the membrane surface is required to not exceed the specified strength limit.

[0056] S8, ETFE air cushion green assessment.

[0057] The implicit carbon emissions of ETFE air pillows are determined by considering the comprehensive material consumption, energy consumption during testing and shaping, material transportation consumption, and design service life. Based on this, a green assessment of ETFE air pillows is conducted.

[0058] The implied carbon emissions of ETFE air pillows are from the "cradle to factory" stage, excluding carbon emissions during the repair, maintenance, and recycling stages.

[0059] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0060] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for finding and analyzing the viscoplasticity of ETFE films, characterized in that, Includes the following steps: S1. Determine the load requirements after the ETFE air cushion is formed. S2. Select the appropriate ETFE air pillow; S3. Select the ETFE membrane material according to the ETFE air cushion size; S4. Determine the uniaxial tensile test scheme and performance parameters for ETFE membrane material; S5. Determine the constitutive model and parameters for ETFE viscoplasticity analysis; S6. Model and analyze the ETFE air cushion, and determine the form-finding parameters according to the forming requirements; S7. Perform structural analysis of the formed ETFE air cushion under combined load conditions; S8, ETFE air cushion green assessment.

2. The method for finding and analyzing the viscoplasticity of ETFE films according to claim 1, characterized in that, In step S1, the loads include the structure's self-weight, internal pressure, live load, wind load, snow load, and seismic load.

3. The method for finding and analyzing the viscoplasticity of ETFE membranes according to claim 2, characterized in that, In step S2, the ETFE air cushion selection includes determining the support structure, shape, height, and number of layers of the ETFE air cushion.

4. The method for finding and analyzing the viscoplasticity of ETFE films according to claim 3, characterized in that, In step S3, the selection of ETFE membrane material includes ETFE membrane material thickness, first yield strength, second yield strength, ultimate strength, elongation and elastic modulus.

5. The method for finding and analyzing the viscoplasticity of ETFE films according to claim 4, characterized in that, In step S4, the uniaxial tensile test procedure for ETFE membrane material includes determining the form and size of the uniaxial tensile specimen, the tensile testing instrument, the tensile rate, and the data processing standard.

6. The method for finding and analyzing the viscoplasticity of ETFE films according to claim 5, characterized in that, In step S4, the tensile specimen is in the form of a strip or dumbbell; the effective gauge length of the tensile specimen is not less than 100 mm; the tensile rate is distributed from static to 100% of the gauge length; the data processing standards include the determination of the tensile curve, the yield point and the elastic modulus.

7. The method for finding and analyzing the viscoplasticity of ETFE films according to claim 5, characterized in that, In step S5, the constitutive model for ETFE viscoplastic analysis is a simplified version of the Perzyna Model; the parameters of the ETFE viscoplastic analysis constitutive model include the plastic strain rate. Static yield stress σ0, strain rate parameter m, viscosity parameter γ * Among them, plastic strain rate The static yield stress σ0 is determined based on the inflation rate of the ETFE air cushion, and the first yield strength obtained from the static tensile rate in step S4 is also considered. The strain rate parameter m and the viscosity parameter γ are also determined. * The yield strength is determined by fitting the first yield strength with the tensile rate in step S4.

8. The method for finding and analyzing the viscoplasticity of ETFE films according to claim 7, characterized in that, In step S6, the modeling and analysis of the ETFE air cushion is performed using finite element software; the ETFE air cushion shape-finding parameters include the number of inflations, maximum inflation pressure, inflation speed, deflation speed, time required for each inflation, and settling time.

9. The method for finding and analyzing the viscoplasticity of ETFE films according to claim 8, characterized in that, In step S7, the load combination conditions include non-seismic combination conditions and seismic combination conditions; the structural analysis ensures that the maximum stress on the membrane surface under the load combination conditions does not exceed the specified strength limit.

10. The method for finding and analyzing the viscoplasticity of ETFE films according to claim 9, characterized in that, In step S8, the implicit carbon emissions of the ETFE air pillow are determined by comprehensively considering the material consumption, energy consumption during the testing and shaping process, material transportation consumption, and the designed service life. Based on this, a green assessment of the ETFE air pillow is conducted.

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