Self-monitoring BFRP flexible inhaul cable and preparation method thereof

Abstract

The invention discloses a self-monitoring BFRP flexible inhaul cable and a preparation method thereof. The self-monitoring BFRP flexible inhaul cable comprises a BFRP inhaul cable body and at least one graphene modified resin sensor arranged on the BFRP inhaul cable body. The BFRP inhaul cable body is formed by arranging and combining a plurality of BFRP flexible rope strands according to a certain mode and then twisting the BFRP flexible rope strands, and the graphene modified resin sensor comprises a graphene modified resin film wrapping the surface of the BFRP inhaul cable body, two conductive silver paste layers coating the two ends of the surface of the graphene modified resin film, and a plurality of conductive silver paste layers coating the two conductive silver paste layers. The two conducting wires are bound on the two conductive silver paste layers respectively, and the two fixing pieces are fixedly arranged outside the two conductive silver paste layers in a sleeving mode respectively and used for enabling the conducting wires and the conductive silver paste layers to be in tight contact connection. The inhaul cable is good in durability, excellent in long-term use performance, long in service life and good in construction performance.

Description

Technical Field

[0001] The present invention relates to the technical field of cables, and in particular to a self-monitoring BFRP flexible cable and a preparation method thereof. Background Art

[0002] In traditional mooring systems, mooring cables mainly include steel wire ropes and synthetic fiber ropes. Steel wire ropes have the disadvantages of heavy weight, low free breaking length, and easy corrosion in marine environments. Synthetic fiber ropes have problems such as easy wear, large creep rate, and low strength conversion efficiency. Both have certain limitations. Basalt fiber reinforced polymer (BFRP) is a new type of material with excellent physical, mechanical and chemical properties such as light weight, high strength, corrosion resistance, fatigue resistance, and easy processing. It has been successfully applied in the reinforcement and transformation of civil transportation infrastructure. At present, it is increasingly being demonstrated in the mechanical properties and durability improvement of new structures. Due to the anisotropic characteristics of BFRP materials (i.e., high mechanical properties along the longitudinal direction of the fiber, weak transverse compression and shear resistance), composite cable structures are considered to be the most suitable structural form for exerting the high performance of BFRP. However, at the same time, BFRP cables have poor bending performance, the matrix is ​​easy to bend and crack, and is not suitable for repeated bending and coiling. It also has poor ductility and brittle failure. In order to solve the problems of easy cracking of the matrix and difficulty in bending and coiling, and to realize the application of BFRP in new mooring systems, it is necessary to design a BFRP flexible rope that is easy to bend and coil, and to achieve long-term real-time monitoring and timely feedback of its stress state and damage degree.

[0003] BFRP overcomes some of the defects of steel wire and synthetic fiber, can be optimized according to actual needs, and has broad application prospects in deep-sea mooring systems. Therefore, the structural characteristics of steel wire rope, synthetic fiber rope and BFRP cable can be combined to optimize the design of BFRP rope, form a safe, efficient and long-life cable system, and promote the research of new full-sea-depth, pump-free and high-capacity marine mooring system.

[0004] The existing self-monitoring cable research is mostly designed for the application of steel cables, which cannot be applied to the large deformation of BFRP flexible ropes during the construction stage. At the same time, its sensor integration method cannot be applied to cables in service and has a certain structural weakening of the cables. The point measurement of its sensing method may bring a certain degree of measurement deviation. Therefore, it is necessary to develop a new self-monitoring BFRP flexible rope. Summary of the invention

[0005] To achieve the above objectives, the present invention provides a self-monitoring BFRP flexible cable.

[0006] The technical solution adopted by the present invention is: A self-monitoring BFRP flexible cable, comprising a BFRP cable body and at least one graphene-modified resin sensor disposed on the BFRP cable body; The BFRP cable body is formed by arranging and combining a number of BFRP flexible strands in a certain manner and twisting them together. The graphene modified resin sensor includes: a graphene modified resin film coated on the surface of the BFRP cable body, two conductive silver paste layers coated on both ends of the surface of the graphene modified resin film, two wires respectively tied to the two conductive silver paste layers, and two fixing parts respectively fixedly sleeved on the outside of the two conductive silver paste layers for making the wires closely contact and connected with the conductive silver paste layers.

[0007] Furthermore, the fixing piece is an aluminum tube.

[0008] Furthermore, the graphene-modified resin film is formed by coating the graphene-modified water-based epoxy resin on the surface of the BFRP cable body and curing it at high temperature without adding a cross-linking agent.

[0009] Furthermore, 10±2wt% of a toughening agent is added to the resin matrix of the BFRP flexible strands.

[0010] Furthermore, the resin matrix is ​​ER7121 epoxy resin, and the toughening agent is QS-VA-3 Qishi toughening agent.

[0011] Furthermore, the BFRP flexible strands are arranged in such a manner that, except for the central strand, the remaining BFRP strands are arranged layer by layer in the form of regular hexagons around the central strand.

[0012] Furthermore, the lay length of the BFRP flexible rope strands is 12 to 20 times the nominal diameter of a single BFRP flexible rope strand.

[0013] Furthermore, the nominal diameter of a single BFRP flexible strand is 1~5 mm.

[0014] The present invention also provides a method for preparing a self-monitoring BFRP flexible cable, comprising the following steps: (1) Arrange a single BFRP flexible rope strand in a regular hexagon and pass its two ends through two positioning plates; (2) The number of twisting turns is calculated according to the set lay length and the total length of the rope, and the two positioning plates are controlled to rotate in opposite directions to twist the rope to form the BFRP cable body; (3) The two ends of the BFRP cable body are wrapped with a braided fiber sheath; (4) Grind the surface of the BFRP cable body with sandpaper and then wipe it with alcohol; (5) Mixing the graphene-modified water-based resin and water in proportion, coating the mixture on the middle section of the BFRP cable body, and curing the mixture in an oven at high temperature to form a graphene-modified resin film; (6) Apply the conductive silver paste to both ends of the graphene modified resin film, ensure that the length of the free test section in the middle of the graphene modified resin film is not less than 200 mm, and use a hot air gun to quickly solidify the conductive silver paste; (7) Tie two wires to the surface of the conductive silver paste and press the aluminum tube tightly against the connection between the BFRP cable body and the wires to complete the preparation of the self-monitoring BFRP flexible cable.

[0015] Furthermore, the graphene-modified water-based resin is a water-based epoxy resin containing 10±2wt% of graphene.

[0016] Beneficial effects of the present invention: 1. The self-monitoring BFRP flexible rope of the present invention is easy to bend and can be repeatedly coiled. As a commonly used matrix material for BFRP, the three-dimensional network cross-linked structure formed by the curing reaction of epoxy resin is brittle. During the bending fatigue process, the resin matrix is ​​prone to cracking, causing the BFRP rope to produce broken wires and other damage phenomena, which is not conducive to the long-term use of the rope. Therefore, reducing the elastic modulus of the resin matrix and improving the toughness of the matrix can effectively improve the bending fatigue performance of the BFRP material. The present invention adds a toughening agent to the epoxy resin matrix. The toughening agent will automatically generate micron-sized elastic rubber balls during the curing process and is evenly distributed in the cured product to form an epoxy resin alloy with an "island structure", which can greatly improve the toughness of the epoxy resin cured product and resist crack propagation, thereby preparing a low elastic modulus and high toughness resin matrix.

[0017] 2. The self-monitoring BFRP flexible rope of the present invention has the characteristics of excellent long-term performance. Compared with traditional steel wire ropes and synthetic fiber ropes, BFRP flexible ropes have stronger tensile strength, corrosion resistance and toughness. BFRP has good durability in corrosive environments such as acid, alkali, salt, and ultraviolet rays. In the harsh marine corrosive environment, the predicted service life of the FRP structure can reach more than 100 years. In addition, the fatigue strength and fatigue load stress amplitude of BFRP are much higher than those of steel and synthetic fibers.

[0018] 3. The self-monitoring BFRP flexible rope of the present invention has the characteristics of no damage and real-time monitoring. The conductive composite film made of graphene-modified water-based epoxy resin has a good linear relationship between the resistance change rate and strain below 15000με, and the linear regression coefficient of the resistance response curve exceeds 0.999 in the design range of 0~12000με. Under the condition of normal wear degree of 10%, the change rate of the strain sensing coefficient of the composite film is linearly related to the degree of friction damage, and the linear regression coefficient is still close to 1. The composite film has good long-term performance and can meet the long-life requirements of structural design.

[0019] 4. The preparation method of the self-monitoring BFRP flexible rope of the present invention is simple and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the self-monitoring BFRP flexible cable structure of the present invention.

[0021] Figure 2 It is a schematic cross-sectional view of the self-monitoring BFRP flexible cable of the present invention.

[0022] Figure 3 The present invention is a flow chart for preparing the self-monitoring BFRP flexible cable.

[0023] Figure 4 This is a curve of the resistance change rate-fatigue cycle number of the self-monitoring BFRP flexible rope prepared in Example 1 under different fatigue stress amplitudes.

[0024] Figure 5 Resistance change rate-time curve of the self-monitoring BFRP flexible rope prepared in Example 1 after holding load for 500 hours Among them: 1. BFRP cable body; 2. Braided fiber sheath; 3. Graphene modified resin film; 4. Conductive silver paste layer; 5. Aluminum tube fixings; 6. Strain gauge; 7. Wire. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the present invention more clear, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and a preferred implementation manner. Example

[0026] See also Figure 1-Figure 4 , this embodiment provides a self-monitoring BFRP flexible cable, comprising a BFRP cable body 1 and at least one graphene modified resin sensor disposed on the BFRP cable body; The BFRP cable body 1 is formed by twisting a plurality of BFRP flexible strands arranged and combined in a hexagonal manner. The BFRP flexible strands are made of basalt fibers with a linear density of 1200 tex, and the resin matrix is ​​made of ER7121 epoxy resin, to which 10±2 wt% of QS-VA-3 toughening agent is added. The preparation method of the BFRP flexible strands is a common method in the art.

[0027] In this embodiment, the BFRP cable body 1 is twisted from 7 BFRP flexible strands, and the diameter of a single BFRP flexible strand is 5 mm. Among the 7 BFRP flexible strands, the center strand is arranged in a straight line, and the other 6 strands are arranged in a regular hexagon around the center strand. In other embodiments, the diameter of a single BFRP flexible strand can also be selected within the range of 1-5 mm, the center strand is arranged in a straight line, and the remaining strands are increased layer by layer from the inside to the outside. For example, with the center strand as the first layer, the number of strands in the 2nd layer is 7, the number of strands in the 3rd layer is 19, the number of strands in the 4th layer is 37, and the number of strands in the Nth layer is 3. n 2 -3 n +1, n is a natural number. The method for twisting the BFRP cable body 1 is the prior art, such as step (1) and step (2) in Example 2, and the twist pitch is preferably 12 to 20 times the nominal diameter of a single BFRP flexible rope strand.

[0028] The graphene modified resin sensor comprises: a graphene modified resin film 3 coated on the surface of a BFRP cable body 1, two conductive silver paste layers 4 coated on both ends of the surface of the graphene modified resin film, two conductive wires 7 respectively tied to the two conductive silver paste layers, and two aluminum tube fixings 5 ​​respectively fixedly sleeved on the outside of the two conductive silver paste layers for making the conductive wires closely contact and connected with the conductive silver paste layers. Example

[0029] The preparation method of the self-monitoring BFRP flexible cable described in Example 1 is as follows: (1) Arrange the seven BFRP flexible rope strands in a regular hexagon and pass them through two positioning plates, with the two positioning plates 50 mm away from each end of the rope strand; (2) Select a lay length of 12 times the rope diameter, calculate the number of twisting turns based on the full length of the rope, and rotate the two positioning plates in opposite directions to twist the rope; (3) Both ends of the rope are wrapped with a braided fiber sheath 2; (4) Use sandpaper to polish the surface of the BFRP rope to remove the residual release agent during the preparation process of the BFRP rope strands, and wipe the surface of the BFRP rope with alcohol; (5) The graphene-modified water-based resin and water were fully mixed in a ratio of 1:1 and coated on the middle section of the BFRP rope, and then placed in an oven for high-temperature curing at 120°C for 3 hours to form a graphene-modified resin film 2; (6) Apply the conductive silver paste 3 to the edges of the graphene modified resin film 2 at both ends at a length of 10 mm, ensuring that the free test section in the middle of the graphene modified resin film is 140 mm, and use a hot air gun to quickly solidify the conductive silver paste; (7) The wire 6 is tied to the conductive silver paste 3, and the aluminum tube 5 is tightly pressed on the connection between the BFRP rib 1 and the wire 6 to form a graphene-modified resin sensor; thus, the preparation of the self-monitoring BFRP flexible cable is completed.

[0030] The test method is: Fatigue test: Loading was performed using force control. First, the specimen was loaded at a constant speed of 0.08 kN / s to an average fatigue stress of 0.5 (σ min +σ max ), and then the fatigue load cycle is set in the form of a sine wave, and the fatigue load frequency is selected as 5 Hz. During the fatigue test loading process, the load and resistance changes in the static tensile stage are collected until the fatigue cycle ends. The test results are shown in Figure 4 .

[0031] Load-holding test: A tensioning frame with a main body of 300 mm in length is used. There is an opening of 35 mm in diameter at each end of the tensioning frame. The BFRP flexible cable passes through the middle and is tensioned by turning the loading screw. A 20 mm thick steel plate is placed at the junction of each component to increase its load-bearing area. Two steel half rings with an inner diameter of 8 mm and a thickness of 10 mm are fixed on the inner side of the loading end of the steel pipe to avoid bending damage of the anchor end caused by uneven loading end surface of the steel pipe or incorrect position of the flexible rope strands in the steel pipe. A load sensor is set on the tensioning frame. The load sensor is used to measure the axial load on the BFRP flexible cable during the loading stage. Its range is 50 kN and the height is 52 mm. The test results are shown in Figure 5 .

[0032] Depend on Figure 4 It can be seen that in the early stage of the fatigue test, the resistance change rate of the specimen increases rapidly with the number of fatigue cycles. After exceeding this limit, the growth rate of the resistance change rate gradually slows down, and the resistance change rate and the number of fatigue cycles show a certain linear relationship. Before macroscopic fatigue failure occurs, the resistance change rate does not exceed 7.29%. It can be concluded that the resistance measurement value change of the graphene-modified composite film coated on the BFRP flexible rope is within an acceptable range under no-load conditions before the rope body undergoes macroscopic failure.

[0033] Depend on Figure 5It can be seen that the degradation of the sensing performance of the self-monitoring BFRP flexible cable under long-term load conditions is detected through a 500-h load-holding test. Under long-term load conditions, the resistance increases rapidly with time in the first 60-80 hours, and then the resistance gradually tends to be stable. The resistance change rate in 500 hours does not exceed 2.2%.

[0034] It can be seen from the above tests that the self-monitoring BFRP flexible cable proposed in the present invention has stable sensing performance, large measuring range, excellent fatigue performance, can meet the requirements of integration, and does not affect the internal structure of the component itself.

[0035] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications are also within the protection scope of the present invention.

Claims

1. A self-monitoring BFRP flexible cable, characterized in that: It includes a BFRP cable body and at least one graphene-modified resin sensor disposed on the BFRP cable body; The BFRP cable body is formed by arranging and combining a number of BFRP flexible strands in a certain manner and twisting them together. The graphene modified resin sensor includes: a graphene modified resin film coated on the surface of the BFRP cable body, two conductive silver paste layers coated on both ends of the surface of the graphene modified resin film, two wires respectively tied to the two conductive silver paste layers, and two fixing parts respectively fixedly sleeved on the outside of the two conductive silver paste layers for making the wires closely contact and connected with the conductive silver paste layers.

2. A self-monitoring BFRP flexible cable according to claim 1, characterized in that: The fixing piece is an aluminum tube.

3. A self-monitoring BFRP flexible cable according to claim 1, characterized in that: The graphene-modified resin film is formed by coating the graphene-modified water-based epoxy resin on the surface of the BFRP cable body and curing it at high temperature without adding a cross-linking agent.

4. A self-monitoring BFRP flexible cable according to claim 1, characterized in that: 10±2wt% of toughening agent is added to the resin matrix of the BFRP flexible strands.

5. A self-monitoring BFRP flexible cable according to claim 4, characterized in that: The resin matrix is ​​ER7121 epoxy resin, and the toughening agent is QS-VA-3 Qishi toughening agent.

6. A self-monitoring BFRP flexible cable according to claim 1, characterized in that: The BFRP flexible strands are arranged in such a manner that, except for the central strand, the remaining BFRP strands are arranged layer by layer in the form of regular hexagons around the central strand.

7. A self-monitoring BFRP flexible cable according to claim 1, characterized in that: The lay length of the BFRP flexible rope strands is 12 to 20 times the nominal diameter of a single BFRP flexible rope strand.

8. A self-monitoring BFRP flexible cable according to claim 7, characterized in that: The nominal diameter of a single BFRP flexible rope strand is 1~5 mm.

9. The method for preparing the self-monitoring BFRP flexible cable according to any one of claims 1 to 8, characterized in that: The following steps are involved: (1) Arrange a single BFRP flexible rope strand in a regular hexagon and pass its two ends through two positioning plates; (2) The number of twisting turns is calculated according to the set lay length and the total length of the rope, and the two positioning plates are controlled to rotate in opposite directions to twist the rope to form the BFRP cable body; (3) The two ends of the BFRP cable body are wrapped with a braided fiber sheath; (4) Grind the surface of the BFRP cable body with sandpaper and then wipe it with alcohol; (5) Mixing the graphene-modified water-based resin and water in proportion, coating the mixture on the middle section of the BFRP cable body, and curing the mixture in an oven at high temperature to form a graphene-modified resin film; (6) Apply the conductive silver paste to both ends of the graphene modified resin film, ensure that the length of the free test section in the middle of the graphene modified resin film is not less than 200 mm, and use a hot air gun to quickly solidify the conductive silver paste; (7) Tie two wires to the surface of the conductive silver paste and press the aluminum tube tightly against the connection between the BFRP cable body and the wires to complete the preparation of the self-monitoring BFRP flexible cable.

10. The preparation method according to claim 9, characterized in that: The graphene-modified water-based resin is a water-based epoxy resin containing 10±2wt% of graphene.

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