CN115077774B - A quantitative evaluation method for the residual clamping force of rapidly simulated corroded high-strength bolts - Google Patents

Abstract

The embodiment of the invention provides a quantitative evaluation method for rapidly simulating residual clamping force of a rusted high-strength bolt, which comprises the steps of firstly cutting a nut or a bolt head of the high-strength bolt test piece by adopting a wire cutting wire to simulate the corrosion shape and the corrosion size of the bolt, secondly obtaining a regression equation relation formula between the residual clamping force and the size of the high-strength bolt test piece under the condition that the nut or the bolt head of the high-strength bolt test piece is uniformly cut or trapezoid cut, and finally substituting the residual size of the nut or the bolt head of the high-strength bolt corroded in the field into the regression equation to quantitatively evaluate the residual clamping force of the corroded high-strength bolt.

Description

A quantitative evaluation method for the residual clamping force of rapidly simulated corroded high-strength bolts

Technical Field

The invention relates to the technical field of construction engineering, and in particular to a quantitative evaluation method for rapidly simulating the residual clamping force of a corroded high-strength bolt.

Background Art

At present, the residual clamping force evaluation method of corroded bolts in high-strength bolt connection nodes mainly adopts ultrasonic method and tapping method. The former has a large error in the evaluation result, and the latter relies on the experience of the staff and is difficult to achieve quantitative evaluation. After investigation and research, it was found that the shape of the nut of the corroded high-strength bolt is mainly uniform and trapezoidal. The uniform shape is that the height and thickness of the nut are reduced at the same time; the trapezoidal shape is that the corrosion thickness of the upper and lower parts of the nut is different. Generally, the nut is in a harsh corrosive environment, and it is rare for the nut and the bolt head to be in a harsh corrosive environment at the same time. In order to achieve the purpose of quantitative evaluation, researchers often use corrosive liquid to corrode the bolt. First, the duration of simulated corrosion is long; second, the simulated corrosion environment is far from the actual corrosion situation. However, the efficiency of simulating the corrosion test of high-strength bolt heads and nuts is not high, and the residual clamping force of the bolts after corrosion in the laboratory is very different from the measured results. Therefore, it is one of the problems that technicians in the field need to solve urgently to propose a quantitative evaluation method for quickly simulating the residual clamping force of corroded high-strength bolts and efficiently and accurately evaluate the residual clamping force of rusted high-strength bolts.

Summary of the invention

In view of the above-mentioned prior art, the embodiment of the present invention proposes a quantitative evaluation method for rapidly simulating the residual clamping force of a corroded high-strength bolt, and the test method is simple and fast.

Specifically, the embodiment of the present invention proposes a quantitative evaluation method for rapidly simulating the residual clamping force of a corroded high-strength bolt, comprising:

A high-strength bolt specimen is made and several percentage values of its pre-tightening force design value are selected for tensile test, and a linear relationship between the pre-tightening force and the strain value of the high-strength bolt specimen is regression analyzed to obtain a linear regression equation of the high-strength bolt specimen: ε=aN+b; wherein ε is the strain value of the high-strength bolt, and N is the pre-tightening force of the high-strength bolt;

After assembling the high-strength bolt specimen with the pressure test block, the calculated strain values corresponding to the preload design values of 50%, 100% and 110% are calculated by the linear regression equation; and the test preload is applied to the high-strength bolt specimen in stages according to the calculated strain values, and the test strain value corresponding to the test preload is read by an instrument;

The nut or bolt head of the high-strength bolt specimen is cut by wire cutting and the change of the strain value is recorded, and a regression equation of the residual clamping force of the nut or bolt head cut into different shapes and sizes and the high-strength bolt specimen is established by regression analysis;

In addition, corroded high-strength bolts are selected and the corrosion products on the nuts or bolt heads are cleaned. After measuring the remaining size of the nuts or bolt heads in the high-strength bolts, a tensile test is performed to verify the regression equation of the remaining clamping force of the high-strength bolt specimens cut into different shapes and sizes.

In some embodiments, the method for preparing the high-strength bolt specimen for tensile testing includes:

A blind hole with a diameter of 2 mm and a depth of 30-40 mm is opened in the middle of the screw rod or the bolt head of the high-strength bolt, and the blind hole is cleaned;

After the hardening slurry is poured into the blind hole, an axial temperature self-compensating strain gauge is implanted, and after hardening, the axial temperature self-compensating strain gauge is connected to a data acquisition instrument.

In some embodiments, the pressure test block is a cylindrical steel block with an inner hole in the middle; the diameter of the inner hole is adapted to the screw rod of the high-strength bolt test piece; and the outer diameter of the pressure test block is 3-4 times that of the screw rod of the high-strength bolt test piece.

In some embodiments, the tensile test method includes: selecting 20%, 40%, 60%, 80%, 100%, and 110% of the design value of the high-strength bolt preload force to stretch the high-strength bolt, and reading the strain value under the current preload force.

In some embodiments, the method of wire cutting the nut or bolt head of the high-strength bolt specimen includes uniform cutting or trapezoidal cutting; wherein the uniform cutting cuts the height and thickness of the nut or bolt head, and the thickness of the cut on each side is the same; the trapezoidal cutting cuts the thickness of the nut or bolt head and the cutting thickness in the height direction of the nut is different.

In some embodiments, the nut or bolt head of the high-strength bolt specimen is cut by wire cutting, and the relationship equation between the thickness of the nut and the residual clamping force of the high-strength bolt specimen after cutting along different diameters is:

The relationship equation between the residual clamping force of the high-strength bolt specimen after cutting the bolt head thickness along different diameters is:

The relationship equation of the residual clamping force between the nut or the bolt head and the high-strength bolt specimen after uniform cutting is:

The relationship equation of the residual clamping force between the nut or the bolt head and the high-strength bolt specimen after trapezoidal cutting is:

P＝1.3232+0.1454x ₂ +0.1711y ₂ ;

Where P is the percentage of clamping force loss, _x1 is the thickness loss ratio, _y1 is the height loss ratio; _x2 is the thickness loss ratio of the lower surface of the trapezoid, and _y2 is the thickness loss ratio of the upper surface of the trapezoid;

in

Where _y1 is the height loss ratio, h′ is the remaining height of the nut after corrosion, and h is the height of the uncorroded nut.

Where _x1 is the thickness loss ratio, b′ is the remaining thickness of the nut after corrosion, b is the thickness of the uncorroded nut, and r is the inner diameter of the uncorroded nut.

Where p is the percentage of clamping force loss, F′ is the axial force of the bolt after corrosion, and F is the axial force of the uncorroded bolt.

In some embodiments, the assembly method of the high-strength bolt specimen and the pressure test block is: passing the screw of the high-strength bolt specimen through the inner hole of the pressure test block, wherein the screw length of the high-strength bolt specimen is greater than the height of the pressure test block; then tightly fitting the nut of the high-strength bolt specimen with the screw thread, wherein gaskets are arranged between the bolt head and the pressure test block, and between the nut and the pressure test block.

In some embodiments, after the corroded high-strength bolts are cleaned of corrosion products, the corrosion shape is determined, and the remaining size of the nut or bolt head in the high-strength bolt is measured based on uniform corrosion or trapezoidal corrosion; wherein the remaining size of the nut or bolt head in the high-strength bolt is calculated by taking the average height and average thickness of the nut or bolt head.

Compared with the prior art, the beneficial effects of the present invention are:

In this embodiment, firstly, the nut or bolt head of the high-strength bolt specimen is cut by wire cutting to simulate the corrosion shape and corrosion size of the bolt. Secondly, the linear regression method is used to obtain the regression equation relationship formula between the residual clamping force and the size of the high-strength bolt specimen when the nut or bolt head of the high-strength bolt specimen is uniformly cut or trapezoidally cut. Finally, the residual size of the nut or bolt head of the high-strength bolt corroded on site is measured and substituted into the regression equation to quantitatively evaluate the residual clamping force of the corroded high-strength bolt.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

FIG1 is a schematic diagram of the structure of a bolt head punching and nut uniform cutting in an embodiment of the present invention;

FIG2 is a schematic diagram of a bolt head punching nut trapezoidal cutting structure according to an embodiment of the present invention;

FIG3 is a schematic diagram of the structure of uniform cutting of nut punching and bolt heads in an embodiment of the present invention;

FIG4 is a schematic structural diagram of a nut punching bolt head with a trapezoidal cut according to an embodiment of the present invention;

FIG5 is a flow chart of a bolt test in an embodiment of the present invention;

FIG6 is a graph showing the relationship between the corrosion thickness, height and residual clamping force of the nut according to an embodiment of the present invention;

7 is a graph showing the relationship between the corrosion upper surface thickness, the lower surface thickness and the residual clamping force of the nut according to an embodiment of the present invention;

FIG8 is a diagram showing the relationship between the tensile axial force and the strain of the bolt in an embodiment of the present invention;

FIG9 is a linear relationship diagram of the thickness corrosion and the residual clamping force of bolt heads with different diameters according to an embodiment of the present invention;

FIG10 is a linear relationship diagram between thickness corrosion and residual clamping force of nuts with different diameters according to an embodiment of the present invention;

FIG. 11 is a general diagram of the linear relationship between the nut and bolt head thickness corrosion and the residual clamping force in an embodiment of the present invention.

Description of reference numerals:

1. Bolt head; 2. Polyester ethylene copper wire; 3. Lower gasket; 4. Blind hole; 5. Axial strain gauge; 6. Pressure test block; 7. Upper gasket; 8. Nut; 9. Screw; 10. Cut off the nut; 11. Cut off the bolt head.

DETAILED DESCRIPTION

Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

The following describes a quantitative evaluation method for rapidly simulating the residual clamping force of a corroded high-strength bolt according to an embodiment of the present invention with reference to Figures 1 to 5, which can efficiently and accurately evaluate the residual clamping force of a corroded high-strength bolt. In order to achieve the above purpose, the method of the embodiment of the present invention adopts the technical solution as shown in Figure 5:

S1: Make a high-strength bolt specimen and select several percentage values of its pre-tightening force design value for tensile test, and perform regression analysis on the linear relationship between the pre-tightening force and the strain value of the high-strength bolt specimen to obtain the linear regression equation of the high-strength bolt specimen: ε=aN+b; where ε is the strain value of the high-strength bolt, and N is the pre-tightening force of the high-strength bolt;

S2: After assembling the high-strength bolt specimen with the pressure test block 6, the calculated strain values corresponding to the preload design values of 50%, 100% and 110% are calculated by a linear regression equation; and the test preload is graded and applied to the high-strength bolt specimen according to the calculated strain value, and the test strain value corresponding to the test preload is read by an instrument;

S3: cutting the nut 8 or bolt head 1 of the high-strength bolt specimen by wire cutting and recording the change of its strain value, and establishing a regression equation of the residual clamping force of the nut 8 or bolt head 1 cut according to different shapes and sizes and the high-strength bolt specimen by regression analysis;

S4: Select another corroded high-strength bolt and clean the corrosion products on its nut 8 or bolt head 1, measure the remaining size of the nut 8 or bolt head 1 in the high-strength bolt, and then perform a tensile test to verify the regression equation of the residual clamping force of the high-strength bolt specimens cut into different shapes and sizes.

The wire cutting method proposed for the first time in the embodiment of the present invention simulates the rust of the nut 8 or bolt head 1 of the high-strength bolt, and the wire cutting machine does not generate heat or additional force during the cutting process, and the cutting is fast and the size is accurate, which has no effect on the collection of the residual clamping force of the bolt. In addition, the regression equation between the residual clamping force and the size of the high-strength bolt specimen under uniform cutting or trapezoidal cutting shape of the nut 8 or bolt head 1 of the high-strength bolt specimen can quantitatively evaluate the residual clamping force of the high-strength bolt after rust, and the residual size of the high-strength bolt nut 8 or bolt head 1 after rust can be simply measured on-site by the staff to evaluate the residual clamping force of the high-strength bolt, and the evaluation method is efficient, accurate and convenient.

Specifically, the method for making high-strength bolt specimens in S1 is:

Step 1: Select a high-strength bolt, and use a 1.9mm alloy drill bit to drill a blind hole 4 with a diameter of 2mm and a depth of 30-40mm at its screw 9 or bolt head 1, and use alcohol to wipe the surface of the bolt head 1 or screw 9 of the high-strength bolt, and wrap the drill bit with a single layer of medical cotton cloth to slowly wipe the blind hole 4 until it is clean, as shown in Figures 1 and 2;

Step 2: Pour room temperature hardening or heat hardening glue into the blind hole 4, quickly implant the axial strain gauge 5 with the polyester ethylene copper wire 2, and wait for hardening;

Step 3: After hardening, the wire is connected to the polyester vinyl copper wire 2 on the axial strain gauge 5 by welding, and the other end of the wire is connected to the static data acquisition instrument;

Step 4: Place the finished high-strength bolt specimen into the high-strength bolt tensile test fixture and wait for the universal testing machine to tension the bolt;

Step 5: Perform tensile tests at 20%, 40%, 60%, 80%, 100%, and 110% of the preload design value of the high-strength bolt specimen. After stretching to each load level, the force is maintained for 15 to 25 seconds. When the strain value of the high-strength bolt specimen collected by the static strain collector is stable, read the strain value under the current load until all tensile tests are completed. The linear regression method is used to regress and analyze the linear relationship between the axial force (preload) and the strain value of the high-strength bolt specimen, and the linear regression equation of the high-strength bolt specimen is obtained. ε = aN + b; where ε is the strain value of the high-strength bolt, and N is the preload of the high-strength bolt. Repeat steps 1-5 to complete the tensile test of multiple high-strength bolt specimens, and select 10 bolt specimen test data to draw a linear relationship diagram, as shown in Figure 8.

The specific steps in S2 in this embodiment are as follows:

Step 6: The high-strength steel plate is machined and a cylindrical steel block with an inner hole in the middle is obtained according to the steel structure design specification. The inner hole diameter is slightly larger than the screw rod 9 diameter of the high-strength bolt specimen, and the outer diameter of the ring of the cylindrical steel block is 3 to 4 times the screw rod 9 diameter of the high-strength bolt specimen;

Step 7: The high-strength bolt specimen is assembled with the pressure test block 6, and the method is: the screw rod 9 of the high-strength bolt specimen is passed through the inner hole of the pressure test block 6, wherein the length of the screw rod 9 of the high-strength bolt specimen is greater than the height of the pressure test block 6; then the nut 8 of the high-strength bolt specimen is tightly matched with the screw rod 9 thread, wherein an upper gasket 7 is arranged between the bolt head 1 and the pressure test block 6, and a lower gasket 3 is arranged between the nut 8 and the pressure test block 6, as shown in Figures 1 to 4.

Among them, e is the outer diameter of the bolt head 1 or the nut 8 of the high-strength bolt; s is the outer diameter of the bolt head 1 or the nut 8 in the high-strength bolt after cutting; k is the height of the bolt head 1; d is the diameter of the nominal diameter of the screw 9; m is the diameter of the blind hole 4; h is the height of the cylindrical steel block; H is the height of the nut 8; n is the height of the upper gasket 7 or the lower gasket 3; k′ is the height of the bolt head 1 cut; e′ is the thickness of the bolt head 1 cut; H′ is the height of the nut 8 cut.

Step 8: According to the linear regression equation obtained in step 5, the linear regression equation ε＝aN+b; where ε is the strain value of the high-strength bolt, and N is the preload force of the high-strength bolt, the strain values corresponding to the preload force design values of 50%, 100% and 110% are calculated. Calculate the strain value; and apply the test preload force manually in stages using an extended wrench according to the calculated strain value, and use a static strain acquisition instrument to read the test strain value corresponding to the test preload force applied in stages. Considering that the prestress loss is about 10% within 48 hours, this embodiment increases the preload force design value by 10%, that is, the final tightening value is 110% of the preload force design value.

The specific steps in S3 in this embodiment are as follows:

Step 9: Use a wire-cutting machine to cut the thickness of the nut 8 in the high-strength bolt along different diameters to cut off the nut 10 as shown in Figures 1-2, wherein the uniform corrosion of the nut 8 is simulated by cutting the height and thickness of the nut 8 in sequence as shown in Figure 1; the trapezoidal corrosion is simulated by cutting obliquely along the thickness of the nut 8, as shown in Figure 2; similarly, use a wire-cutting machine to cut the thickness of the bolt head 1 in the high-strength bolt along different diameters, and cut off the bolt head 11 as shown in Figures 3-4, wherein the uniform corrosion of the bolt head 1 is simulated by cutting the height and thickness of the bolt head 1 in sequence as shown in Figure 3; the trapezoidal corrosion is simulated by cutting obliquely along the thickness of the bolt head 1, as shown in Figure 4. This embodiment uses a wire-cutting machine to cut the thickness of the nut 8 or bolt head 1 in the high-strength bolt along different diameters and records the shape, size and strain value of the cut nut 8 or bolt head 1 and the corresponding strain value of the test bolt.

The relationship between the actual and theoretical residual clamping force values of the nut 8 due to trapezoidal corrosion is shown in Table 1, and the relationship between the actual and theoretical residual clamping force values of the nut 8 due to uniform corrosion is shown in Table 2.

Table 1 Relationship between actual and theoretical residual clamping force values of nut 8 trapezoidal corrosion

Table 2 Relationship between actual and theoretical residual clamping force values of uniform corrosion of nut 8

Among them, a linear relationship diagram is drawn according to the test data of the nut 8 or the bolt head 1, as shown in Figures 9 and 10. Through the linear relationship, it can be obtained that when the corrosion degree is the same, the residual clamping force of nuts 8 or bolt heads 1 of different diameters is basically the same; as shown in Figure 11, by comparing the linear relationship between the corrosion thickness and the residual clamping force of the nut 8 and the bolt head 1, when the diameter and the corrosion degree are the same, the residual clamping force of the bolt head 1 and the nut 8 is basically the same; as shown in Figures 6 and 7, the relationship diagrams of the corrosion thickness and height of the nut 8 and the residual clamping force and the relationship diagrams of the corrosion upper surface thickness and lower surface thickness of the nut 8 and the residual clamping force are simulated.

It should be noted that uniform cutting is the cutting of both the height and thickness of the nut 8 or bolt head 1. Taking the common regular hexagonal nut 8 or bolt head 1 as an example, the thickness of the hexagonal cutting is the same, and the height of the nut 8 or bolt head 1 is cut first and then the thickness is cut; trapezoidal cutting only cuts the thickness of the nut 8 or bolt head 1 and the cutting thickness in the height direction of the nut 8 is different, wherein the height direction of the nut 8 is consistent with the up and down direction, that is, the thickness of the upper and lower surfaces of the nut 8 or bolt head 1 after cutting in the trapezoidal cutting is different.

Step 10: Use regression analysis to establish different regression relationship equations;

The equation for the residual clamping force of the high-strength bolt specimen after cutting the nut 8 thickness along different diameters is:

The relationship equation between the residual clamping force of the high-strength bolt specimen after cutting the bolt head 1 thickness along different diameters is:

The relationship equation of the residual clamping force between the nut 8 or bolt head 1 and the high-strength bolt specimen after uniform cutting is:

The relationship equation of the residual clamping force between the nut 8 or bolt head 1 and the high-strength bolt specimen after trapezoidal cutting is:

P＝1.3232+0.1454x ₂ +0.1711y ₂ ;

Where P is the percentage of clamping force loss, _x1 is the thickness loss ratio, _y1 is the height loss ratio; _x2 is the thickness loss ratio of the lower surface of the trapezoid, and _y2 is the thickness loss ratio of the upper surface of the trapezoid;

in

Where _y1 is the height loss ratio, h′ is the remaining height of the nut after corrosion, in mm, and h is the height of the uncorroded nut, in mm;

Where _x1 is the thickness loss ratio, b ^′ is the remaining thickness of the nut after corrosion, in mm, b is the thickness of the uncorroded nut, in mm, and r is the inner diameter of the uncorroded nut, in mm;

Where p is the percentage of clamping force loss, F ^′ is the axial force of the bolt after corrosion, in N, and F is the axial force of the uncorroded bolt, in N.

Specifically, the regression equation method for the residual clamping force of the high-strength bolt specimens cut into different shapes and sizes after the corroded bolts in S4 are verified is:

Step 11: Select the corroded high-strength bolts on the node plate, clean the corrosion products of the nut 8 or bolt head 1, determine the corrosion shape (uniform corrosion or trapezoidal corrosion), and measure the remaining size of the corroded high-strength bolt nut 8 or bolt head 1 (measure the six-sided height and the thickness of the three pairs of sides in the case of uniform corrosion of the nut 8 or bolt head 1 and calculate their average values respectively; measure the thickness of the upper and lower three pairs of sides in the case of trapezoidal corrosion and calculate their average values respectively); perform the test according to steps 1, 2, and 3, remove the corroded bolt to be tested, and record the bolt strain change value after the strain is stable. Perform the tensile test according to steps 4 and 5, and find out the load value corresponding to the strain change value of the bolt after the bolt is removed, which is the residual clamping force of the bolt.

In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims (7)

1. A quantitative evaluation method for rapidly simulating residual clamping force of a rusted high-strength bolt is characterized by comprising the following steps:

Manufacturing a high-strength bolt test piece, selecting a plurality of percentage values of the pretightening force design values of the high-strength bolt test piece to carry out a tensile test, and carrying out regression analysis on the linear relation between the pretightening force and the strain value of the high-strength bolt test piece to obtain a linear regression equation of the high-strength bolt test piece: ; wherein, The strain value of the high-strength bolt is obtained, and N is the pretightening force of the high-strength bolt;

After the high-strength bolt test piece and the pressure-bearing test piece are assembled, calculating calculated strain values corresponding to the pretightening force design values of 50%, 100% and 110% through the linear regression equation; the test pre-tightening force is applied to the high-strength bolt test piece in a grading manner according to the calculated strain value, and an instrument is adopted to read the test strain value corresponding to the test pre-tightening force;

Cutting nuts or bolt heads of the high-strength bolt test piece by adopting a wire cutting line, recording the change of strain values of the nuts or bolt heads, and establishing a regression equation of residual clamping force between the nuts or the bolt heads and the high-strength bolt test piece after cutting according to different shapes and sizes by regression analysis;

the method comprises the steps of cutting nuts or bolt heads of the high-strength bolt test piece by a wire, cutting the thicknesses of the nuts along different diameters, and then carrying out relation equation between the nuts and the residual clamping force of the high-strength bolt test piece: p= 0.8177-0.0663 -0.0146；

Cutting the thickness of the bolt head along different diameters, and then carrying out a relation equation of the residual clamping force of the high-strength bolt test piece: p=0.5664+0.0036-0.0154；

And after uniform cutting, the relation equation of the residual clamping force of the nut or the bolt head and the high-strength bolt test piece is as follows: p= -3.81-1.3224+0.1707-0.0775-0.0125；

And after trapezoid cutting, the relation equation of the residual clamping force of the nut or the bolt head and the high-strength bolt test piece is as follows: p=1.3232+0.1454+0.1711；

Is a thickness loss ratio,Is the height loss ratio; Is a trapezoid lower surface thickness loss ratio, The thickness loss ratio of the upper surface of the trapezoid is;

Wherein the method comprises the steps of *100％，

In the middle ofIs a height loss ratio,Is the residual height of the nut after corrosion,To the height of the unetched nut

*100％，

In the middle ofIs a thickness loss ratio,Is the residual thickness of the nut after corrosion,Is the thickness of a non-corroded nut,Is the inner diameter of a non-corroded nut

*100％，

In the middle ofAs a percentage of clamping force loss,Is the axial force of the bolt after corrosion,Is the non-corroded bolt shaft force;

and (3) selecting a corroded high-strength bolt, cleaning corrosives of the nut or the bolt head, measuring the residual size of the nut or the bolt head in the high-strength bolt, and then carrying out a tensile test to verify a regression equation of the residual clamping force of the high-strength bolt test piece after cutting according to different shapes and sizes.

2. The method according to claim 1, wherein the method for preparing the high-strength bolt test piece for tensile test comprises:

a blind hole with the diameter of 2mm and the depth of 30-40mm is formed in the middle of a screw rod or a bolt head of the high-strength bolt, and the blind hole is cleaned;

And implanting a shaft-shaped temperature self-compensating strain gauge after pouring hardening slurry into the blind hole, and connecting the shaft-shaped temperature self-compensating strain gauge with a data acquisition instrument after hardening.

3. The method according to claim 1, wherein the pressure-bearing test block is a cylindrical steel block with an inner hole in the middle; the diameter of the inner hole is matched with the screw rod of the high-strength bolt test piece; the outer diameter of the pressure-bearing test block is 3-4 times of that of the screw rod of the high-strength bolt test piece.

4. A method according to claim 3, wherein the method of tensile testing comprises: and respectively selecting 20%, 40%, 60%, 80%, 100% and 110% of the design value of the pretightening force of the high-strength bolt, stretching the high-strength bolt, and reading the strain value under the current pretightening force.

5. A method according to claim 3, wherein the method of wire cutting the nut or bolt head of the high strength bolt specimen comprises a uniform cut or a trapezoidal cut; wherein the uniform cutting cuts the height and thickness of the nut or bolt head, wherein the thickness cut on each side is the same; the trapezoid cutting cuts the thickness of the nut or bolt head and the cutting thickness in the height direction of the nut is different.

6. The method of claim 3, wherein the method of assembling the high strength bolt test piece and the pressure-bearing test piece comprises: the screw rod of the high-strength bolt test piece passes through the inner hole of the pressure-bearing test block, wherein the length of the screw rod of the high-strength bolt test piece is larger than the height of the pressure-bearing test block; and then tightly matching the nut of the high-strength bolt test piece with the screw thread of the screw rod, wherein gaskets are arranged between the bolt head and the pressure-bearing test block and between the nut and the pressure-bearing test block.

7. The method according to claim 1, wherein after the corroded high-strength bolt is cleaned of corrosions, the corrosion shape is judged, and the residual size of the nut or the bolt head in the high-strength bolt is measured according to uniform corrosion or trapezoid corrosion; the method for calculating the size of the nut or the bolt head of the residual size in the high-strength bolt is to take the average value of the height and the average value of the thickness of the nut or the bolt head.