Method for predicting coefficient of linear expansion of hot-extruded polyethylene reinforcing fiber composite rebar stay cable

Abstract

The present invention relates to a method for predicting the coefficient of linear expansion of a hot-extruded polyethylene reinforcing fiber composite rebar stay cable. The hot-extruded polyethylene reinforcing fiber composite rebar stay cable is a stay cable product for buildings and bridges, which stay cable product is obtained by arranging a plurality of reinforcing fiber composite rebars side by side to form a bundle, then slightly twisting same to form a rebar-twisted bundle, and hot-extruding polyethylene onto a surface layer of the twisted bundle. The reinforcing fiber composite rebar consists of a matrix (such as an epoxy resin), reinforcing fibers (such as carbon fibers) and an interface between the matrix and the reinforcing fibers, and the performance of the rebar depends on the volume ratio of the reinforcing fibers to the matrix and the performance of the components; and in the present application, the structure and constituent materials thereof are taken into consideration to provide a method for predicting the coefficient of linear expansion thereof, providing relevant basic data support for the use of a stay cable for projects.

Description

Prediction method for linear expansion coefficient of hot-extruded polyethylene fiber reinforced composite reinforcement cables Technical Field

[0001] The invention relates to a method for predicting the linear expansion coefficient of a reinforced fiber composite reinforcement material and a hot-extruded polyethylene reinforcement cable. Background Art

[0002] Hot-extruded polyethylene carbon fiber reinforced composite cables for bridges are constructed by lightly twisting multiple carbon fiber reinforced composite strands into carbon fiber bundles, then hot-extruded with high-density polyethylene to form a protective layer. The linear expansion coefficient reflects the dimensional stability of a component under high-temperature operating conditions. The smaller the linear expansion coefficient, the higher the component's dimensional stability at high temperatures, the less thermal stress generated, and the better dimensional stability of the component during temperature fluctuations. The Changtai Yangtze River Bridge, currently the world's largest multifunctional composite bridge with a main span of 1,208 meters, is characterized by its large main span, long main beams, and tall towers, which significantly increase the effects of wind loads. To mitigate these effects, longitudinal restraints are installed between the towers and beams. With these longitudinal restraints, the majority of the wind load is transferred to the towers from the longitudinal restraints at the towers and beams at the bridge deck. The load's action arm is limited to the height of the lower tower, significantly reducing the tower bending moment and beam end displacement caused by wind loads. However, the longitudinal restraints at the towers and beams limit the release of thermal deformation in the mid-span steel beams during system temperature fluctuations, generating significant thermal stress. In order to reduce temperature-added stress, Changtai Bridge used the world's first hot-extruded polyethylene carbon fiber reinforced composite reinforcement cable with a small linear expansion coefficient as the tower beam constraint horizontal cable. After super-tensioning test in the factory, it was installed on site. It has the advantages of high strength, light weight, stable structural dimensions and easy installation. The linear expansion coefficient is the key core parameter of the horizontal cable of Changtai Bridge. In order to accurately grasp this parameter, it is necessary to propose a relevant hot-extruded polyethylene carbon fiber reinforced composite reinforcement cable linear expansion coefficient prediction method to provide relevant basic data support for the application of CFRP horizontal cables in the project.

[0003] Carbon fiber reinforced composite reinforcement is an advanced composite material reinforced with carbon fibers and their structural components. Microstructurally, it is a heterogeneous material with distinct interfaces between the carbon fibers and the matrix. Carbon fiber is composed of over 90% carbon. Diamond possesses the most uniform arrangement of carbon atoms, while carbon fiber's structure is similar to graphite, though slightly less regular than diamond. It is primarily produced by solid-phase carbonization of organic fibers that have no melting point at high temperatures, removing non-carbon elements. Carbon fiber has a turbostratic or graphite structure. When heated, the carbon atoms within the graphite layers vibrate back and forth in the vertical direction, causing expansion and contraction in the horizontal direction. The higher the degree of graphitization of the carbon fiber, the smaller its linear expansion coefficient. These properties ensure that CFRP reinforcement composites have a much lower linear expansion coefficient than ordinary steel, making CFRP horizontal cables unaffected by ambient temperature during use, providing excellent dimensional stability and reducing thermal stress in related components. However, since carbon fiber itself is an axisymmetric material, not an isotropic material, its linear expansion coefficient varies in each direction, which also leads to anisotropy in the linear expansion coefficient of CFRP reinforcement composite materials. The axial linear expansion coefficient of carbon fiber composite materials is directly related to the linear expansion coefficient and elastic modulus of carbon fiber, the linear expansion coefficient and elastic modulus of the resin matrix, and the volume content of carbon fiber and resin matrix. Among them, the linear expansion coefficient, elastic modulus and volume content of carbon fiber have a greater influence on the linear expansion coefficient of CFRP reinforcement. Generally speaking, the axial linear expansion coefficient (parallel to the carbon fiber direction) of CFRP reinforcement material is small, while the transverse linear expansion coefficient (perpendicular to the carbon fiber direction) is large.

[0004] On the other hand, the hot-extruded polyethylene carbon fiber reinforced composite reinforcement cable is made of multiple carbon fiber reinforced composite reinforcements twisted together, and the linear expansion coefficient and elastic modulus of each reinforcement are also different. At the same time, after the reinforcements are twisted into bundles, a double-layer high-density polyethylene sheath is hot-extruded on the outside. It is a parallel hybrid structure composed of carbon fiber reinforced composite reinforcement bundles with different linear expansion coefficients and elastic moduli and high-density polyethylene sheaths, and the linear expansion coefficient is relatively complex.

[0005] In order to solve the above problems, the present invention proposes a method for predicting the linear expansion coefficient of a reinforced fiber composite reinforcement material and a hot-extruded polyethylene cable thereof.

[0006] Summary of the Invention

[0007] The inventors of the present application have provided a method for predicting the linear expansion coefficient of fiber reinforced composite materials, taking into account the composition of reinforcement products such as fiber reinforced composite materials and the structure of hot-extruded polyethylene cables.

[0008] Hot-extruded polyethylene reinforced fiber composite reinforcement cable (hereinafter referred to as cable) is a cable product for construction and bridges obtained by arranging multiple reinforced fiber composite reinforcements (hereinafter referred to as reinforcements) into bundles, then lightly twisting them at about 3 degrees to form a reinforcement twisted bundle, and hot-extruding polyethylene on the surface of the twisted bundle.

[0009] Fiber-reinforced composite reinforcements are composed of a matrix (e.g., epoxy resin), reinforcing fibers (e.g., carbon fibers), and the interface between the two. The reinforcement performance depends on the volume ratio of the reinforcing fibers to the matrix, as well as the properties of the components. The matrix is ​​the continuous phase in the composite material, binding the reinforcing fibers together and giving the composite a certain shape, transmitting external forces, and protecting the reinforcement from environmental erosion. Reinforcing fibers are components in composite materials that can improve the mechanical properties of the matrix material. They are an important component of composite materials and play a role in improving the strength, toughness, and heat resistance of the composite material. The interface is a tiny area between the matrix and the reinforcing fibers where the chemical composition changes significantly, forming a bond between each other and capable of transferring loads, etc.

[0010] The technical solution of the present invention includes two parts: a method for predicting the linear expansion coefficient of reinforcement and a method for predicting the linear expansion coefficient of cable, which are as follows:

[0011] A method for predicting the linear expansion coefficient of a reinforced fiber composite reinforcement material, comprising:

[0012] Step 1: Calculation of the theoretical value of the axial linear expansion coefficient of the reinforcement

[0013] The reinforcement material includes reinforcing fibers, matrix and their interface. The matrix is ​​bonded to the reinforcing fibers. The reinforcing fibers are continuous fibers. Ignoring the influence of the interface, the theoretical value of the linear expansion coefficient of the reinforcement material is α a The approximate calculation formula is:

[0014] Where:

[0015] α a —Theoretical value of the linear expansion coefficient of the reinforcement material in the axial direction, i.e. parallel to the direction of the reinforcing fibers;

[0016] α f1 —Axial linear expansion coefficient of the reinforcing fiber tow;

[0017] α e —Linear expansion coefficient of the matrix;

[0018] E f1 —Axial tensile modulus of elasticity of the reinforcing fiber;

[0019] E e — tensile elastic modulus of the matrix;

[0020] V f—Volume proportion of reinforcing fibers;

[0021] In the above-mentioned reinforced fiber composite reinforcement structure, the matching of the linear expansion coefficients of the carbon fiber bundles must be considered. That is, the linear expansion coefficients of the fiber bundles in the carbon fiber reinforced composite reinforcement should be as consistent as possible to prevent the carbon fibers from being cut due to thermal expansion and contraction. In addition, due to the anisotropic linear expansion coefficient of carbon fiber composite materials, in order to obtain a stable composite structure, all carbon fibers must be distributed symmetrically with respect to their central plane.

[0022] Step 2: Consider the influence of the interface and calculate the interface correction coefficient K of the axial linear expansion coefficient of the reinforcement

[0023] The interface is a new phase - the interface phase (or interface layer) - with a certain thickness (above nanometers), a structure that varies with the matrix and reinforcing fibers, and is significantly different from the matrix. When the reinforcing fibers and the matrix come into contact with each other, under certain conditions, chemical reactions or physical and chemical reactions may occur, such as mutual diffusion and dissolution of elements between the two phases, thereby producing a new phase different from the original two phases. Even if no reaction, diffusion, or dissolution occurs, the internal stress generated by the solidification and solidification of the matrix, or the inductive effect of the organizational structure, will cause the matrix close to the reinforcement to undergo structural changes or changes in packing density, resulting in the performance of this local matrix being different from the bulk performance of the matrix, forming an interface phase. The above-mentioned interface's influence on the performance of carbon fiber reinforced composite reinforcement cannot be directly calculated, but the interface correction coefficient can be proposed by comparing the approximate calculation results of the axial linear expansion coefficient of carbon fiber composite reinforcement with the measured results.

[0024] The present invention is based on the theoretical value of the axial linear expansion coefficient of the reinforcement material α calculated according to formula (1-1) a Compared with the actual measured value α b Compare and obtain the interface correction coefficient K, K = α b / α a ;

[0025] Step 3: Calculation of the actual value of the axial linear expansion coefficient of the reinforcement

[0026] Where:

[0027] α h —actual value of the axial linear expansion coefficient of the reinforcement;

[0028] K—Interface correction coefficient.

[0029] Preferably, the reinforcing fiber is carbon fiber, the matrix is ​​epoxy resin, and the axial linear expansion coefficient α of the carbon fiber tow is f1 (-0.1~-1.0)×10 -6 / ℃, below 200℃; the linear expansion coefficient of epoxy resin is 30~80×10 -6 / ℃; the axial tensile elastic modulus of the carbon fiber filament is 160-290GPa, the tensile elastic modulus of the epoxy resin is 1.5-4.5GPa, and the volume proportion of the carbon fiber is 60%-80%.

[0030] Preferably, in step 2, the interface correction coefficient K of the reinforcement axial linear expansion coefficient is obtained as follows:

[0031] Step 2.1: Measure the axial linear expansion coefficient and tensile elastic modulus of the reinforcing fiber tow

[0032] When the reinforcing fiber is a carbon fiber tow, the axial linear expansion coefficient test is conducted in accordance with T / CSTM 00251-2020- "Test method for axial average linear expansion coefficient of carbon fiber - mandrel differential method"; the axial tensile elastic modulus is conducted in accordance with GB T3362-2017 "Test method for tensile properties of carbon fiber multifilaments." Because carbon fiber is a bundle of filaments, each bundle consists of thousands of individual filaments. The axial linear expansion coefficient and tensile elastic modulus of a single filament are not very meaningful. Therefore, a bundle of carbon fibers is tested as a whole. The number of fiber bundles used for the test is consistent with the number of bundles in the actual reinforcement material. The axial linear expansion coefficient and axial tensile elastic modulus of the carbon fiber tow are obtained.

[0033] Step 2.2: Measure the linear expansion coefficient and tensile elastic modulus of the substrate

[0034] The linear expansion coefficient of the matrix is ​​tested in accordance with ASTM E831-14 "Test method for linear thermal expansion of solid materials by thermomechanical analysis"; the tensile elastic modulus of the matrix is ​​tested in accordance with GB / T 2567-2008 "Test method for properties of resin castings";

[0035] Step 2.3: Calculate the volume ratio of the reinforcing fibers in the reinforcement material. Since the reinforcing fibers have the same length, the volume ratio is the ratio of the cross-sectional area of ​​the reinforcing fibers to the cross-sectional area of ​​the reinforcement material. The calculation process is as follows:

[0036] Reinforcement fiber cross-sectional area ratio = (cross-sectional area of ​​a single reinforcing fiber * number of fibers in each bundle * number of bundles) / cross-sectional area of ​​the reinforcement material;

[0037] For example, a 7mm carbon fiber reinforcement is made of 31 carbon fiber bundles, each of which contains 24,000 carbon fiber filaments with a diameter of 7 microns. Then, the volume ratio = cross-sectional area ratio = area of ​​a single carbon fiber filament * number of filaments in each bundle * number of bundles = 0.007 * 0.007 * 24,000 * 31 / 49 = 74.4%;

[0038] Step 2.4: Calculate the theoretical value of the reinforcement axial linear expansion coefficient according to formula 1-1;

[0039] Step 2.5: Conduct trial production of the reinforcement material. The trial production adopts the pultrusion process: the reinforcing fiber impregnated with the matrix is ​​passed through a shaping die, and after heating and curing, a sample with the same composition and specifications as the actual reinforcement material is obtained;

[0040] Step 2.6: Take several steel samples obtained in step 2.5 and test the linear expansion coefficient. The measured axial linear expansion coefficient is α b The test is carried out in accordance with GB / T2572-2005 "Test method for average linear expansion coefficient of fiber reinforced plastics"; the average linear expansion coefficient refers to the average value of the relative change in sample length corresponding to a temperature change of 1°C between temperatures T1 and T2. The test method is to use a linear expansion coefficient tester with a mandrel differential method to uniformly heat the sample, control the sample temperature rise rate, accurately measure the sample temperature and the corresponding sample length change, draw an expansion curve that changes with temperature, and calculate the average linear expansion coefficient of the straight part of the curve or calculate the average linear expansion coefficient within a certain temperature range as required.

[0041] Step 2.7: Interface correction coefficient K is α b / α a .

[0042] Table 1 Calculation and test results of linear expansion coefficient of carbon fiber reinforced composite reinforcement under typical material parameters

[0043] A method for predicting the linear expansion coefficient of a hot-extruded polyethylene reinforced fiber composite cable. The cable is made by arranging multiple strands of steel into a bundle, twisting them together, and then sheathing them with hot-extruded polyethylene. The linear expansion coefficient of the cable is predicted as follows:

[0044] Step 1: Calculate the axial linear expansion coefficient of the reinforcement bundle without considering twist

[0045] Step 1.1: Determine the volume ratio of the reinforcement in the cable. Since each reinforcement has the same diameter, its volume is the average. In a cable composed of n carbon fiber reinforced composite reinforcements, the volume ratio of a single carbon fiber reinforced composite reinforcement is 1 / n.

[0046] Step 2.2: Measure the axial linear expansion coefficient and tensile elastic modulus of n bars, in order of α1 and E1, α2 and E3, until α n and E n ;

[0047] Step 2.3 does not consider the axial linear expansion coefficient α of the twisted reinforcement h Calculation

[0048] Where:

[0049] αk is the linear expansion coefficient of each reinforcement;

[0050] E k is the axial elastic modulus of each reinforcement;

[0051] Step 2: Calculate the radial expansion coefficient of the twisted reinforcement bundle

[0052] The theoretical calculation formula for the transverse linear expansion coefficient of the reinforcement bundle is as follows:

[0053] Where:

[0054] ν f is the Poisson's ratio of the reinforcing fiber;

[0055] ν e is the Poisson's ratio of the matrix material;

[0056] α f2 is the radial linear expansion coefficient of the reinforcing fiber;

[0057] E f2 is the radial tensile elastic modulus of the reinforcing fiber;

[0058] V f is the volume fraction of reinforcing fibers;

[0059] Step 3: Calculate the axial linear expansion coefficient α of the reinforcement bundle considering twisting c

[0060] α c =α h cosθ+α v sinθ, θ is the twist angle;

[0061] Step 4: Calculate the axial linear expansion coefficient α of the cable considering hot-extruded polyethylene k

[0062] in:

[0063] α k is the axial linear expansion coefficient of the cable;

[0064] α c is the axial linear expansion coefficient of the reinforcement bundle considering the twist angle;

[0065] E c is the axial average elastic modulus of the reinforcement;

[0066] V c is the volume ratio of the carbon fiber reinforced composite reinforcement bundle to the carbon fiber reinforced composite reinforcement cable body;

[0067] α Pis the axial linear expansion coefficient of the polyethylene sheath, which is measured in accordance with GB / T1036 “Determination of linear expansion coefficient of plastics”;

[0068] Ep is the axial tensile elastic modulus of the polyethylene sheath, which is determined in accordance with GB / T-1040.1 “Determination of tensile properties of plastics”.

[0069] Preferably, in step 2, the radial tensile elastic modulus of the reinforcing fiber is 6% of the axial tensile elastic modulus.

[0070] Preferably, the axial average elastic modulus E of the reinforcement is c : Take a group of 5 steel bars whose reinforcing fibers are carbon fibers. Measure their axial tensile elastic modulus according to T3362-2017 "Test Method for Tensile Properties of Carbon Fiber Multifilaments" and then take the average value. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] FIG1 is a cross-sectional view of a hot-extruded polyethylene carbon fiber reinforced composite reinforcement cable according to the present invention;

[0072] FIG2 is a cross-sectional view of a carbon fiber reinforced composite bar according to the present invention;

[0073] FIG3 is a cross-sectional view of a carbon fiber reinforced composite reinforcement bundle of the present invention;

[0074] FIG4 is a schematic diagram showing the calculation of the axial thermal expansion coefficient of the reinforcement bundle considering twisting;

[0075] In the figure, 1 is carbon fiber reinforced composite reinforcement, 2 is outer polyethylene sheath, 2' is inner polyethylene sheath, 101 is carbon fiber tow, and 102 is epoxy resin. DETAILED DESCRIPTION

[0076] The present invention is further described in detail below with reference to the examples. The examples are illustrative and intended to explain the present invention, but are not to be construed as limiting the present invention.

[0077] Taking the Ø7mm-127mm hot-extruded polyethylene carbon fiber reinforced composite reinforcement cable as an example, the linear expansion coefficient prediction process is as follows:

[0078] Step 1: The calculation process for predicting the axial linear expansion coefficient of each carbon fiber reinforced composite bar is as follows:

[0079] The calculation process and results of the linear expansion coefficient of each carbon fiber reinforcement that makes up the cable are shown in the following table:

[0080] Step 2: Calculate the axial linear expansion coefficient of the carbon fiber reinforced composite reinforcement bundle without considering the twist angle according to the following formula:

[0081] Calculate the axial linear expansion coefficient of carbon fiber reinforced composite reinforcement bundles without considering the twist angle

[0082] α h =0.23×10 -6 / ℃

[0083] Step 3: Calculate the radial linear expansion coefficient of the carbon fiber reinforced composite reinforcement bundle

[0084] Since carbon fiber has a very low linear expansion coefficient in the axial direction, but its radial linear expansion coefficient is relatively large, generally positive, which leads to a large transverse linear expansion coefficient of carbon fiber reinforced composite reinforcement. The theoretical calculation formula is as follows:

[0085] in:

[0086] ν f is the Poisson's ratio of carbon fiber material, generally between 0.1 and 0.3;

[0087] ν e is the Poisson's ratio of epoxy resin material, generally between 0.2 and 0.4;

[0088] α f2 is the radial linear expansion coefficient of carbon fiber, generally around 5.5×10 －6 / ℃ to 8.4×10 －6 / ℃;

[0089] E f2 It is the radial tensile elastic modulus of carbon fiber, which is generally about 6% of the axial tensile elastic modulus, generally between 12 and 20 GPa;

[0090] V f is the carbon fiber volume fraction;

[0091] According to the above theoretical calculation, the axial linear expansion coefficient α of the carbon fiber reinforced composite reinforcement bundle without considering the twist angle is v =2.65×10 -6 / ℃

[0092] Step 4: Axial linear expansion coefficient of carbon fiber reinforced composite reinforcement bundle after considering twist angle

[0093] After considering the above twist angles, the calculation results of the axial linear expansion coefficient of the carbon fiber reinforced composite reinforcement bundle after considering the twist angle are as follows:

[0094] α c =αh cosθ+α v sinθ=0.36×10 -6 / ℃

[0095] Where θ is the twist angle of the hot-extruded polyethylene carbon fiber reinforced composite reinforcement cable, which is 3 degrees.

[0096] Step 5: After considering the influence of high-density polyethylene sheath, calculate the axial linear expansion coefficient of the hot-extruded polyethylene carbon fiber reinforced composite reinforcement cable as follows:

[0097] in:

[0098] α k The finished product coefficient of hot-extruded polyethylene carbon fiber reinforced composite reinforcement cable

[0099] α c is the axial linear expansion coefficient of the carbon fiber reinforced composite reinforcement bundle after considering the twist angle;

[0100] E c The axial average elastic modulus of the carbon fiber reinforced composite reinforcement is measured by taking a group of 5 carbon fiber reinforced composite reinforcements according to T3362-2017 "Test Method for Tensile Properties of Carbon Fiber Multifilaments" and then taking the average value.

[0101] V c is the volume ratio of the carbon fiber reinforced composite reinforcement bundle to the carbon fiber reinforced composite reinforcement cable body;

[0102] α P The axial linear expansion coefficient of the high-density polyethylene sheath is determined according to GB / T1036 "Measurement method for linear expansion coefficient of plastics". －6 / ℃;

[0103] E p It is the axial tensile elastic modulus of the high-density polyethylene sheath. The axial elastic modulus is tested in accordance with GB / T-1040.1 "Determination of tensile properties of plastics", and is generally 0.5GPa.

[0104] Comprehensively considering the factors, the calculation results of the axial linear expansion coefficient of the hot-extruded polyethylene carbon fiber reinforced composite reinforcement cable with high-density polyethylene sheath are as follows:

[0105] α k k = 0.55 × 10 -6 / ℃.

Claims

1. A method for predicting the linear expansion coefficient of a fiber reinforced composite reinforcement, characterized by: include: Step 1: Calculation of the theoretical value of the axial linear expansion coefficient of the reinforcement The reinforcement material includes reinforcing fibers, matrix and their interface. The matrix is ​​bonded to the reinforcing fibers. The reinforcing fibers are continuous fibers. Ignoring the influence of the interface, the theoretical value of the linear expansion coefficient of the reinforcement material is α a The approximate calculation formula is: Where: α a —Theoretical value of the linear expansion coefficient of the reinforcement material in the axial direction, i.e. parallel to the direction of the reinforcing fibers; α f1 —Axial linear expansion coefficient of the reinforcing fiber tow; α e —Linear expansion coefficient of the matrix; E f1 —Axial tensile modulus of elasticity of the reinforcing fiber; E e — tensile elastic modulus of the matrix; V f —Volume proportion of reinforcing fibers; Step 2: Consider the influence of the interface and calculate the interface correction coefficient K of the axial linear expansion coefficient of the reinforcement The theoretical value of the axial linear expansion coefficient of the reinforcement α calculated according to formula (1-1) a Compared with the actual measured value α b Compare and obtain the interface correction coefficient K, K = α b / α a ; Step 3: Calculation of the actual value of the axial linear expansion coefficient of the reinforcement Where: α h —actual value of the axial linear expansion coefficient of the reinforcement; K—Interface correction coefficient.

2. The method for predicting the linear expansion coefficient of a reinforced fiber composite reinforcement according to claim 1, wherein: The reinforcing fiber is carbon fiber, the matrix is ​​epoxy resin, and the axial linear expansion coefficient of the carbon fiber tow is α f1 (-0.1~-1.0)×10 -6 / ℃, below 200℃; the linear expansion coefficient of epoxy resin is 30~80×10 -6 / ℃; the axial tensile elastic modulus of the carbon fiber filament is 160-290GPa, the tensile elastic modulus of the epoxy resin is 1.5-4.5GPa, and the volume proportion of the carbon fiber is 60%-80%.

3. The method for predicting the linear expansion coefficient of a reinforced fiber composite reinforcement according to claim 1, wherein: In step 2, the interface correction coefficient K of the reinforcement axial linear expansion coefficient is obtained as follows: Step 2.1: Measure the axial linear expansion coefficient and tensile elastic modulus of the reinforcing fiber tow When the reinforcing fiber is a carbon fiber tow, the axial linear expansion coefficient test is conducted in accordance with T / CSTM 00251-2020-"Test method for axial average linear expansion coefficient of carbon fiber - mandrel differential method"; the axial tensile elastic modulus is conducted in accordance with GB T3362-2017 "Test method for tensile properties of carbon fiber multifilament". A bundle of carbon fibers is tested as a whole. The number of fiber bundles used for the test is consistent with the number of bundles in the actual reinforcement material. The axial linear expansion coefficient and axial tensile elastic modulus of the carbon fiber tow are obtained. Step 2.2: Measure the linear expansion coefficient and tensile elastic modulus of the substrate The linear expansion coefficient of the matrix is ​​tested in accordance with ASTM E831-14 "Test method for linear thermal expansion of solid materials by thermomechanical analysis"; the tensile elastic modulus of the matrix is ​​tested in accordance with GB / T 2567-2008 "Test method for properties of resin castings"; Step 2.3: Calculate the volume ratio of the reinforcing fibers in the reinforcement material. Since the reinforcing fibers have the same length, the volume ratio is the ratio of the cross-sectional area of ​​the reinforcing fibers to the cross-sectional area of ​​the reinforcement material. The calculation process is as follows: Reinforcement fiber cross-sectional area ratio = (cross-sectional area of ​​a single reinforcing fiber * number of fibers in each bundle * number of bundles) / cross-sectional area of ​​the reinforcement material; Step 2.4: Calculate the theoretical value of the reinforcement axial linear expansion coefficient according to formula 1-1; Step 2.5: Conduct trial production of the reinforcement material. The trial production adopts the pultrusion process: the reinforcing fiber impregnated with the matrix is ​​passed through a shaping die, and after heating and curing, a sample with the same composition and specifications as the actual reinforcement material is obtained; Step 2.6: Take several steel samples obtained in step 2.5 and test the linear expansion coefficient. The measured axial linear expansion coefficient is α b The test is carried out in accordance with GB / T2572-2005 "Test method for average linear expansion coefficient of fiber reinforced plastics"; Step 2.7: Interface correction coefficient K is α b / α a .

4. A method for predicting the linear expansion coefficient of a hot-extruded polyethylene reinforced fiber composite reinforcement cable, characterized by: The cable is made of multiple steel bars arranged side by side into a bundle, which is then twisted to form a twisted bundle of steel bars. The surface of the twisted bundle is hot-extruded with polyethylene as a sheath. The linear expansion coefficient of the cable is predicted as follows: Step 1: Calculate the axial linear expansion coefficient of the reinforcement bundle without considering twist Step 1.1: Determine the volume ratio of the reinforcement in the cable. Since each reinforcement has the same diameter, its volume is the average. In a cable composed of n carbon fiber reinforced composite reinforcements, the volume ratio of a single carbon fiber reinforced composite reinforcement is 1 / n. Step 2.2: Measure the axial linear expansion coefficient and tensile elastic modulus of n bars, in order of α1 and E1, α2 and E3, until α n and E n ; Step 2.3 does not consider the axial linear expansion coefficient α of the twisted reinforcement h Calculation Where: α k is the linear expansion coefficient of each reinforcement; E k is the axial elastic modulus of each reinforcement; Step 2: Calculate the radial expansion coefficient of the twisted reinforcement bundle The theoretical calculation formula for the transverse linear expansion coefficient of the reinforcement bundle is as follows: Where: ν f is the Poisson's ratio of the reinforcing fiber; ν e is the Poisson's ratio of the matrix material; α f2 is the radial linear expansion coefficient of the reinforcing fiber; E f2 is the radial tensile elastic modulus of the reinforcing fiber; V f is the volume fraction of reinforcing fibers; Step 3: Calculate the axial linear expansion coefficient α of the reinforcement bundle considering twisting c ɑ c =ɑ h cosθ+ɑ v sinθ, θ is the twist angle; Step 4: Calculate the axial linear expansion coefficient α of the cable considering hot-extruded polyethylene k Among them: a v a h α k is the axial linear expansion coefficient of the cable; α c is the axial linear expansion coefficient of the reinforcement bundle considering the twist angle; E c is the axial average elastic modulus of the reinforcement; V c is the volume ratio of the carbon fiber reinforced composite reinforcement bundle to the carbon fiber reinforced composite reinforcement cable body; α P is the axial linear expansion coefficient of the polyethylene sheath, which is measured in accordance with GB / T1036 “Determination of linear expansion coefficient of plastics”; Ep is the axial tensile elastic modulus of the polyethylene sheath, which is determined in accordance with GB / T-1040.1 “Determination of tensile properties of plastics”.

5. The method for predicting the linear expansion coefficient of hot-extruded polyethylene reinforced fiber composite reinforcement cable according to claim 4, characterized in that: In step 2, the radial tensile elastic modulus of the reinforcing fiber is 6% of the axial tensile elastic modulus.

6. The method for predicting the linear expansion coefficient of the hot-extruded polyethylene reinforced fiber composite reinforcement cable according to claim 4, characterized in that: Axial average elastic modulus E of the reinforcement c : Take a group of 5 steel bars whose reinforcing fibers are carbon fibers. Measure their axial tensile elastic modulus according to T3362-2017 "Test Method for Tensile Properties of Carbon Fiber Multifilaments" and then take the average value.

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