A self-monitoring, self-repairing, constant force fastener

Abstract

The application discloses a self-monitoring, self-repairing and constant force fastener, which comprises a bolt, a nut screwed on the bolt, two conductive gaskets, an elastic corrugated gasket between the two conductive gaskets, a self-repairing sleeve, an electric resistance heating belt arranged around the circumference of the self-repairing sleeve, a control circuit and a power supply. The application has the following advantages and effects: the on-line monitoring function is realized by means of the principle that the contact surface reduction between the elastic corrugated gasket and the two conductive gaskets on the two sides leads to the increase of the resistance between the two conductive gaskets during the fastener loosening process; the constant force fastening function is realized by means of the elastic corrugated gasket providing the fastener with a continuous fastening force within the elastic deformation range of the elastic corrugated gasket; and the self-repairing function is realized by means of the self-repairing sleeve expanding and elongating along the axial direction after the electric resistance heating belt is heated, so that the loosened fastener is re-fastened.

Description

Technical Field

[0001] This invention relates to the field of fasteners, and particularly to a self-monitoring, self-repairing, constant-force fastener. Background Technology

[0002] Traditional fasteners, such as bolts, are prone to loosening when used in environments subject to periodic vibrations, such as high-speed rail, wind turbines, and bridges. The bolts on large wind turbines are often installed at high altitudes, in remote locations such as mountains and oceans, making inspection and maintenance inconvenient. Therefore, there is an urgent need to develop intelligent fasteners that integrate self-monitoring and self-repair capabilities.

[0003] Currently, some patents have proposed solutions for self-monitoring fasteners. For example, patent CN216922366U proposes using a laser displacement sensor to monitor bolt looseness; patent CN114396968A proposes using an FBG fiber optic grating to monitor bolt looseness; and patent CN215521135U proposes embedding an axial displacement sensor based on a resistive strain gauge in the center of the bolt for looseness detection. However, the above solutions (such as laser displacement sensors and fiber optic displacement sensors) either have high costs or limited functionality, and are still far from being truly intelligent fasteners. Summary of the Invention

[0004] The purpose of this invention is to provide a self-monitoring, self-repairing, constant-force fastener to solve the problems of existing fasteners being not intelligent enough, or being costly and having limited functionality.

[0005] The above-mentioned technical objective of this invention is achieved through the following technical solution: a self-monitoring, self-repairing, constant-force fastener, comprising a bolt, a nut threaded onto the bolt, two conductive washers, an elastic corrugated washer located between the two conductive washers, a self-repairing sleeve, a resistance heating band surrounding the self-repairing sleeve, a control circuit, and a power supply. When the bolt passes through two connecting parts to be connected, the entire assembly consisting of the two conductive washers and the elastic corrugated washer, and the entire assembly consisting of the self-repairing sleeve and the resistance heating band, are arbitrarily and sequentially fitted onto the bolt, and the nut is finally tightened onto the bolt; the elastic corrugated washer gradually flattens and tightly adheres to the conductive washers on both sides after being subjected to the pre-tightening force during the tightening process of the nut. The self-healing sleeve is made of a shape memory alloy with shape memory effect. The self-healing sleeve is subjected to axial pre-compression strain at the installation front and expands axially after heating. The control circuit and the two conductive pads are electrically connected via wires to monitor the resistance between the two conductive pads. The control circuit is also electrically connected to the resistance heating band and the power supply. As the fasteners loosen continuously, the contact area between the elastic corrugated washer and the two conductive pads gradually decreases, and the resistance between the two conductive pads monitored by the control circuit gradually increases. When the resistance between the two conductive pads monitored by the control circuit exceeds a set value, the control circuit controls the resistance heating band to heat the self-healing sleeve.

[0006] A further provision of the present invention is that the elastic corrugated washer is made of a high-elasticity material, which is any one of spring steel, 65 manganese steel, titanium-nickel based shape memory alloy, iron-based shape memory alloy, and copper-based shape memory alloy.

[0007] A further feature of the present invention is that the high-elasticity material used in the elastic corrugated washer is a titanium-nickel-based shape memory alloy.

[0008] A further feature of the present invention is that the inner ring of the conductive pad is coated with an insulating resin for achieving insulation between the conductive pad and the bolt.

[0009] A further feature of the present invention is that the shape memory alloy used in the self-healing sleeve is any one of titanium-nickel shape memory alloy, titanium-nickel-niobium shape memory alloy, or iron-manganese-silicon shape memory alloy.

[0010] A further feature of the present invention is that the shape memory alloy used in the self-healing sleeve is a titanium-nickel-niobium shape memory alloy.

[0011] A further provision of the present invention is that the method of using the fastener includes the following steps: S1: A pre-compression strain is applied axially to the self-healing sleeve before installation. After the bolt passes through the two connected components, the entire assembly consisting of two conductive washers and an elastic corrugated washer, and the entire assembly consisting of the self-healing sleeve and the resistance heating strip are placed on the bolt in any order. Then, the nut is tightened to provide pre-tightening force and to gradually flatten the elastic corrugated washer and make it tightly fit with the conductive washers on both sides; S2: As the fastener continues to loosen, the elastic corrugated washer gradually resets and fits tightly with the conductive washers on both sides. The reduced contact area between the gaskets causes the resistance between the two conductive gaskets monitored by the control circuit to gradually increase. The degree of looseness of the fastener is judged by the magnitude of the resistance, realizing the self-detection function. Furthermore, the elastic corrugated washer provides a continuous tightening force to the fastener within its elastic deformation range, realizing the constant force tightening function. S3: When the control circuit detects that the resistance between the two conductive gaskets is greater than the set value, the control circuit controls the resistor heating band to heat the self-repairing sleeve. After heating, the self-repairing sleeve expands and elongates along the axis, causing the loose fastener to be tightened again, thus achieving the self-repair function.

[0012] In summary, the present invention has the following beneficial effects: It achieves online monitoring by utilizing the principle that the contact area between the elastic corrugated washer and the conductive pads on both sides decreases during the loosening of the fastener, leading to an increase in resistance between the two conductive pads; it also utilizes the elastic corrugated washer to provide continuous tightening force to the fastener within its elastic deformation range, achieving a constant force tightening function; simultaneously, it utilizes the self-healing sleeve to expand and elongate axially after being heated by the resistance heating band, allowing the loose fastener to be re-tightened, thus achieving a self-healing function; and this method has the following beneficial effects:

[0013] (1) Two conductive pads and an elastic corrugated washer between the two conductive pads are installed on the bolt. The self-monitoring of fastener loosening is achieved by monitoring the resistance between the two conductive pads. Compared with laser displacement sensor and fiber optic displacement sensor, this method has the advantage of low cost. Compared with adhesive strain gauge, it has the advantages of easy installation, not easy to fall off, and good weather resistance.

[0014] (2) The elastic corrugated washer provides a continuous fastener within the elastic strain range of the fastener, which has the advantage of large interference and realizes the constant force fastening function.

[0015] (3) The elastic corrugated gasket is made of a high elastic material. The high elastic material is any one of spring steel, 65 manganese steel, titanium nickel-based shape memory alloy, iron-based shape memory alloy, and copper-based shape memory alloy. It has the advantage of large elastic strain. Taking titanium nickel-based shape memory alloy as an example, its superelastic recoverable strain can reach more than 8%, which is much higher than the elastic strain of ordinary spring steel material.

[0016] (4) The self-repairing sleeve is installed. Before installation, the self-repairing sleeve is pre-compressed and strained. After the fastener is detected to be loose, the self-repairing sleeve is heated so that it can expand and elongate along the axis, thereby realizing the self-repairing function.

[0017] (5) It integrates multiple advantages such as self-monitoring, self-repair and large interference (constant force fastening), making it more intelligent and lower in maintenance cost than traditional fasteners. It has broad application prospects in places where manual maintenance is inconvenient, such as large wind turbines and offshore platforms. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of Example 1 (the elastic corrugated gasket is in an uncompressed state);

[0019] Figure 2 This is a schematic diagram of the elastic corrugated washer structure in Example 1;

[0020] Figure 3 This is a diagram demonstrating the usage process of Example 1;

[0021] Reference numerals: 1. Bolt; 2. Nut; 3. Conductive washer; 4. Elastic corrugated washer; 5. Self-healing sleeve; 6. Resistance heating band; 7. Control circuit; 8. Power supply; 9. Connector. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the accompanying drawings.

[0023] Example 1: A self-monitoring, self-repairing, constant-force fastener, such as... Figure 1 and Figure 2 As shown, the assembly includes a bolt 1, a nut 2 threaded onto the bolt 1, two conductive washers 3, an elastic corrugated washer 4 located between the two conductive washers 3, a self-healing sleeve 5, a resistance heating band 6 surrounding the self-healing sleeve 5, a control circuit 7, and a power supply 8. When the bolt 1 passes through the two connecting parts 9 to be connected, the entire assembly consisting of the two conductive washers 3 and the elastic corrugated washer 4, and the entire assembly consisting of the self-healing sleeve 5 and the resistance heating band 6 are either placed on the bolt 1 in any order, and the nut 2 is finally tightened onto the bolt 1. In this embodiment, the entire assembly consisting of the two conductive washers 3 and the elastic corrugated washer 4 is first placed on the bolt 1, and then the entire assembly consisting of the self-healing sleeve 5 and the resistance heating band 6 is placed on the bolt 1.

[0024] like Figure 1 As shown Figure 2As shown, the conductive pad 3 is made of a copper alloy with good conductivity. When used in corrosive environments, it can also be made of stainless steel with good corrosion resistance and conductivity. To prevent conductivity between the conductive pad 3 and the bolt 1, an insulating resin (not shown in the figure) is applied to the inner ring of the conductive pad 3. A wire is used to electrically connect the two conductive pads 3 to the resistance test port of the control circuit 7.

[0025] like Figure 1 As shown, the elastic corrugated washer 4 is made of a highly elastic material. The highly elastic material can be any one of spring steel, 65 manganese steel, titanium-nickel based shape memory alloy, iron-based shape memory alloy, or copper-based shape memory alloy. In this embodiment, titanium-nickel-cobalt shape memory alloy is used. The martensitic transformation initiation temperature Ms of titanium-nickel-cobalt shape memory alloy is -40°C, and its superelastic recoverable strain can reach more than 8%, which is much higher than the elastic strain of ordinary spring steel.

[0026] like Figure 1 As shown, the self-healing sleeve 5 is made of a shape memory alloy with shape memory effect. The shape memory alloy can be any one of titanium-nickel shape memory alloy, titanium-nickel-niobium shape memory alloy, or iron-manganese-silicon shape memory alloy. In this embodiment, a titanium-nickel-niobium shape memory alloy with wide hysteresis is used. The austenite transformation start temperature As of the titanium-nickel-niobium alloy is 80°C, and the martensitic transformation start temperature Ms is -20°C. A compressive strain of 9% is applied along the axial direction to the self-healing sleeve 5, and then unloaded. At this point, the self-healing sleeve 5 elastically recovers 1%, and the remaining compressive strain is 8%.

[0027] like Figure 1 As shown, during installation, the resistance heating strip 6 is wrapped and adhered to the periphery of the self-healing sleeve 5, and electrically connected to the heating output port of the control circuit 7 using wires. The substrate of the resistance heating element is made of a polymer-based material; in this embodiment, polyimide material is used, with nickel-chromium resistance material composited within the polyimide substrate. The potential for detachment due to the expansion and elongation of the self-healing sleeve 5 has minimal impact, and the number of times the self-healing sleeve 5 needs to be repaired by heating is limited, generally requiring only one repair.

[0028] like Figure 1 and Figure 3As shown, the elastic corrugated washer 4 gradually flattens and fits tightly against the conductive pads 3 on both sides after being pre-tightened by the nut 2 during tightening. The self-healing sleeve 5 is subjected to axial pre-compression strain at the installation front and expands axially after heating. The control circuit 7 is electrically connected to the two conductive pads 3 via wires to monitor the resistance between the two conductive pads 3. The control circuit 7 is also electrically connected to the resistance heating band 6 and the power supply 8. As the fasteners loosen continuously, the contact area between the elastic corrugated washer 4 and the two conductive pads 3 gradually decreases, and the resistance between the two conductive pads 3 monitored by the control circuit 7 gradually increases. When the resistance between the two conductive pads 3 monitored by the control circuit 7 is greater than the set value, the control circuit 7 controls the resistance heating band 6 to heat the self-healing sleeve 5.

[0029] like Figure 3 As shown, the method of using the fastener includes the following steps: (1) Apply a pre-compression strain axially to the self-healing sleeve 5 before installation. After the bolt 1 passes through the two connected connectors 9, first, put the whole consisting of the two conductive washers 3 and the elastic corrugated washer 4, and the whole consisting of the self-healing sleeve 5 and the resistance heating band 6 onto the bolt 1 in any order. Then, tighten the nut 2 to provide pre-tightening force and make the elastic corrugated washer 4 gradually flatten and fit tightly with the conductive washers 3 on both sides. At this time, the fastener is as follows: Figure 3 As shown in the first state; (2) as the fasteners continue to loosen, the contact area between the elastic corrugated washer 4 and the conductive pads 3 on both sides gradually decreases during the resetting process, causing the resistance between the two conductive pads 3 monitored by the control circuit 7 to gradually increase. The degree of loosening of the fasteners is judged by the magnitude of the resistance, thus realizing the self-detection function; and the elastic corrugated washer 4 provides a continuous tightening force to the fasteners within its elastic deformation range to realize the constant force tightening function. At this time, the fasteners are like Figure 3 The second state is shown; (3) When the control circuit 7 detects that the resistance between the two conductive pads 3 is greater than the set value, the control circuit 7 controls the heating band 6 to heat up and conduct heat to the self-healing sleeve 5 in contact with it. When the temperature rises above the austenite transformation start temperature As, the self-healing sleeve 5 will expand and elongate along the length direction (from L1 to L2) and compress the elastic corrugated washer 4, so that the loose fastener is tightened again, which plays a self-healing function. At this time, the fastener is like Figure 3 The third state is shown.

[0030] Example 2: A self-monitoring, self-repairing, constant-force fastener, differing from Example 1 in that the elastic corrugated washer 4 in Example 1 is made of titanium-nickel-cobalt shape memory alloy, and the self-repairing sleeve 5 is made of titanium-nickel-niobium shape memory alloy with wide hysteresis; in this example, the elastic corrugated washer 4 is made of spring steel 65, and the self-repairing sleeve 5 is made of Fe-28Mn-6Si-5Cr (mass percentage) shape memory alloy, wherein the spring steel 65 and the Fe-28Mn-6Si-5Cr (mass percentage) shape memory alloy are made from lower-cost raw materials.

[0031] As shown in Embodiments 1 and 2 above, the present invention has the following beneficial effects: by utilizing the principle that the contact area between the elastic corrugated washer 4 and the conductive pads 3 on both sides decreases during the loosening of the fastener, resulting in an increase in the resistance between the two conductive pads 3, an online monitoring function is achieved; and by utilizing the elastic corrugated washer 4 to provide a continuous tightening force to the fastener within its elastic deformation range, a constant force tightening function is achieved; at the same time, by utilizing the self-healing sleeve 5 to expand and elongate axially after being heated by the resistance heating band 6, the loose fastener is re-tightened, thus achieving a self-healing function.

[0032] Furthermore, this method has the following beneficial effects: (1) Two conductive washers 3 and an elastic corrugated washer 4 between the two conductive washers 3 are installed on the bolt 1. By monitoring the resistance between the two conductive washers 3, the loosening of the fastener is self-monitored. Compared with laser displacement sensors and fiber optic displacement sensors, this method has the advantage of low cost. Compared with adhesive strain gauges, it has the advantages of easy installation, not easy to fall off, and good weather resistance; (2) The elastic corrugated washer 4 provides continuous fastening to the fastener within the elastic strain range. It has the advantage of large interference and realizes constant force fastening function; (3) The elastic corrugated washer 4 is made of high elastic material. The high elastic material is elastic Any one of spring steel, 65 manganese steel, titanium nickel-based shape memory alloy, iron-based shape memory alloy, and copper-based shape memory alloy has the advantage of large elastic strain; (4) It is equipped with a self-repairing sleeve 5. Before installation, the self-repairing sleeve 5 is subjected to pre-compression strain treatment. After the fastener is detected to be loose, the self-repairing sleeve 5 is heated so that the self-repairing sleeve 5 can expand and elongate along the axis, thereby realizing the self-repairing function; (5) It integrates the advantages of self-monitoring, self-repairing and large interference (constant force fastening), etc. It is more intelligent than traditional fasteners, has lower maintenance costs, and has broad application prospects in large wind turbines, offshore platforms and other occasions where manual maintenance is inconvenient.

[0033] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A self-monitoring, self-repairing, constant-force fastener, comprising a bolt (1) and a nut (2) threaded onto the bolt (1), characterized in that: It also includes two conductive pads (3), an elastic corrugated washer (4) located between the two conductive pads (3), a self-healing sleeve (5), a resistance heating band (6) surrounding the self-healing sleeve (5), a control circuit (7) and a power supply (8). When the bolt (1) passes through the two connectors (9) to be connected, the whole consisting of the two conductive pads (3) and the elastic corrugated washer (4) and the whole consisting of the self-healing sleeve (5) and the resistance heating band (6) are arbitrarily and sequentially fitted onto the bolt (1), and the nut (2) is finally tightened onto the bolt (1). The elastic corrugated washer (4) is gradually flattened and tightly fitted with the conductive pads (3) on both sides after being subjected to the pre-tightening force during the tightening process of the nut (2). The self-healing sleeve (5) is made of a shape memory alloy with shape memory effect. The self-healing sleeve (5) is subjected to axial pre-compression strain at the front of installation and expands and elongates along the axial direction after heating. The control circuit (7) and the two conductive pads (3) are electrically connected by wires to monitor the resistance between the two conductive pads (3). The control circuit (7) is electrically connected to the resistance heating band (6) and the power supply (8). As the fasteners loosen continuously, the contact area between the elastic corrugated washer (4) and the two conductive pads (3) gradually shrinks and the resistance between the two conductive pads (3) monitored by the control circuit (7) gradually increases. When the control circuit (7) monitors that the resistance between the two conductive pads (3) is greater than the set value, the control circuit (7) controls the resistance heating band (6) to heat the self-healing sleeve (5).

2. The self-monitoring, self-repairing, constant-force fastener according to claim 1, characterized in that: The elastic corrugated washer (4) is made of a high elastic material, which is any one of spring steel, 65 manganese steel, titanium-nickel based shape memory alloy, iron-based shape memory alloy, and copper-based shape memory alloy.

3. The self-monitoring, self-repairing, constant-force fastener according to claim 2, characterized in that: The elastic corrugated gasket (4) is made of a titanium-nickel-based shape memory alloy.

4. The self-monitoring, self-repairing, constant-force fastener according to claim 1, characterized in that: The inner ring of the conductive pad (3) is coated with insulating resin to achieve insulation between the conductive pad (3) and the bolt (1).

5. A self-monitoring, self-repairing, constant-force fastener according to claim 1, characterized in that: The shape memory alloy used in the self-healing sleeve (5) is any one of titanium-nickel shape memory alloy, titanium-nickel-niobium shape memory alloy, or iron-manganese-silicon shape memory alloy.

6. A self-monitoring, self-repairing, constant-force fastener according to claim 5, characterized in that: The shape memory alloy used in the self-healing sleeve (5) is a titanium-nickel-niobium shape memory alloy.

7. A self-monitoring, self-repairing, constant-force fastener according to claim 1, characterized in that: The method of using fasteners includes the following steps: S1: A pre-compression strain is applied axially to the self-healing sleeve (5) at the front edge of installation. After the bolt (1) passes through the two connected connectors (9), the whole consisting of the two conductive pads (3) and the elastic corrugated washer (4), and the whole consisting of the self-healing sleeve (5) and the resistance heating strip (6) are put on the bolt (1) in any order. Then the nut (2) is tightened to provide pre-tightening force and make the elastic corrugated washer (4) gradually flattened and tightly fit with the conductive pads (3) on both sides. S2: As the fasteners continue to loosen, the contact area between the elastic corrugated washer (4) and the conductive pads (3) on both sides gradually decreases during the resetting process, causing the resistance between the two conductive pads (3) monitored by the control circuit (7) to gradually increase. The degree of loosening of the fasteners is judged by the magnitude of the resistance, thus realizing the self-detection function; and the elastic corrugated washer (4) provides a continuous fastening force to the fasteners within its elastic deformation range to realize the constant force fastening function. S3: When the control circuit (7) detects that the resistance between the two conductive pads (3) is greater than the set value, the control circuit (7) controls the resistance heating band (6) to heat the self-repairing sleeve (5). After heating, the self-repairing sleeve (5) expands and elongates along the axis, so that the loose fasteners are tightened again, thus playing a self-repairing function.

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