Bolt extension axial force calibration device

Abstract

The invention provides a bolt extension axial force calibration device. The bolt extension axial force calibration device comprises an ultrasonic probe, a supporting gasket, a force sensor, a calibration adjusting block, a part, a protection gasket and a calibration bolt. The force sensor and the calibration adjusting block are sequentially arranged above the part from top to bottom, and a protective gasket is arranged between the force sensor and the calibration adjusting block; the calibration bolt penetrates through the force sensor and the calibration adjusting block to be in threaded connection with the part; the top of the calibration bolt is provided with an ultrasonic probe. Real parts are used for calibration, the influence of thread friction is considered, the method is particularly suitable for a blind hole screw connection structure, and the thread screwing depth and the design requirement are kept consistent during calibration. The calibration cushion block is used for adjusting the clamping length during calibration, and accurate evaluation of the bolt axial force after the bolt axial force exceeds the yield point is guaranteed.

Description

Technical Field

[0001] The present invention belongs to the field of axial force calibration, and particularly relates to a bolt elongation axial force calibration device. Background Art

[0002] At present, there are mainly the following several methods for measuring the bolt axial force, and the characteristics are as follows: a. Strain gauges are pasted on the bolt surface, with high precision, but the pasting is difficult, easy to damage, greatly affected by the operation process, and may require damaging the structure; b. Special strain gauges are installed by drilling holes in the bolt, with high precision, long cycle, high cost, easy to damage, and greatly affected by the operation process; c. Ultrasonic measurement, with high precision, fast and efficient, simple operation, non-destructive measurement, suitable for batch measurement; The ultrasonic measurement method utilizes the acoustoelastic principle. By transmitting and receiving ultrasonic pulse signals, the time difference between the transmitted and echo signals is measured and calculated to measure the bolt elongation, which has the characteristics of non-destructive measurement, simple operation, and fast and efficient, and is particularly suitable for carrying out batch bolt axial force measurements; Bolt elongation axial force calibration is the preparatory work before ultrasonic bolt axial force measurement. Only by obtaining the corresponding relationship between bolt elongation and axial force can the bolt elongation obtained in the subsequent measurement be converted into bolt axial force.

[0003] Currently, the conventional bolt elongation axial force calibration generally uses a tensile testing machine; this calibration method is simple to operate, but the bolt only bears the tensile load and does not consider the influence of torsional stress during the bolt installation process, and is suitable for the calibration of bolts used in the elastic section. However, with the increasing application of high-strength bolts beyond the yield point, this calibration method cannot accurately obtain the yield point and the maximum load point that the bolt can withstand, which is not conducive to the bolt installation specification and reliability assessment. Summary of the Invention

[0004] In view of this, the present invention aims to provide a bolt elongation axial force calibration device, which uses real parts for calibration, considers the influence of thread friction, is particularly suitable for blind hole screw connection structures, and the thread screwing depth during calibration is consistent with the design requirements. The calibration pad is used to adjust the clamping length during calibration to ensure the accurate assessment of the bolt axial force after exceeding the yield point.

[0005] To achieve the above object, the technical solution of the present invention is realized as follows: A bolt elongation axial force calibration device includes an ultrasonic probe, a support gasket, a force sensor, a calibration adjustment block, a part, a protection gasket, and a calibration bolt; The force sensor and the calibration adjustment block are sequentially arranged above the part from top to bottom, and a protection gasket is provided between the force sensor and the calibration adjustment block; The calibration bolt passes through the force sensor and the calibration adjustment block and is threadedly connected to the part; An ultrasonic probe is provided at the top of the calibration bolt.

[0006] Furthermore, a support gasket is also provided between the calibration bolt and the force sensor.

[0007] Furthermore, the calibration adjustment block is used to ensure that the length of the calibration bolt screwed into the part is the same as the actual installation state.

[0008] Furthermore, the number of the calibration bolts is not less than 3.

[0009] Furthermore, the calibration steps are as follows; S1. Test and record the initial length of each calibration bolt; S2. Gradually tighten the calibration bolts for calibration, and record the axial force and elongation of the bolts at each step; S3. Stop calibration when the calibration axial force exceeds the maximum load point that the bolt can bear, that is, when the axial force shows an obvious decline; S4. Loosen the bolts after calibration and record the residual elongation of the bolts; S5. Perform average fitting processing on all calibration data to obtain an elongation-axial force calibration curve as the calibration data for axial force measurement.

[0010] Compared with the prior art, the bolt elongation axial force calibration device of the present invention has the following advantages: The bolt elongation axial force calibration device of the present invention uses real parts for calibration, considers the influence of thread friction, and is especially suitable for blind hole screw connection structures. When calibrating, the threaded insertion depth is consistent with the design requirements. The calibration cushion block is used to adjust the clamping length during calibration to ensure accurate evaluation of the bolt axial force after exceeding the yield point. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings: Figure 1 It is a schematic diagram of a bolt elongation axial force calibration device according to an embodiment of the present invention.

[0012] Description of the reference numerals: 1. Ultrasonic probe; 2. Support gasket; 3. Force sensor; 4. Calibration adjustment block; 5. Actual part; 6. Gasket; 7. Calibration bolt. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0013] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0014] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "plurality" is two or more.

[0015] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific circumstances.

[0016] The present invention will be described in detail below with reference to the drawings and in conjunction with embodiments.

[0017] A bolt elongation axial force calibration device, as Figure 1 shown, includes an ultrasonic probe, a support gasket, a force sensor, a calibration adjustment block, a part, a protection gasket, and a calibration bolt; The force sensor and the calibration adjustment block are sequentially arranged above the part from top to bottom, and a protection gasket is provided between the force sensor and the calibration adjustment block; The calibration bolt passes through the force sensor and the calibration adjustment block and is threadedly connected to the part; An ultrasonic probe is provided at the top of the calibration bolt.

[0018] Preferably, a support gasket is further provided between the calibration bolt and the force sensor.

[0019] Preferably, the calibration adjustment block is used to ensure that the length of the calibration bolt screwed into the part is consistent with the actual installation state.

[0020] Preferably, the number of the calibration bolts is not less than 3.

[0021] Preferably, the calibration steps are as follows; S1. Measure and record the initial length of each calibration bolt; S2. Calibrate by tightening the calibration bolts step by step, and record the axial force and elongation of the bolts at each step; S3. Stop calibration when the calibrated axial force exceeds the maximum load point that the bolt can withstand, that is, when the axial force shows a significant decrease; S4. Loosen the bolts after calibration and record the residual elongation of the bolts; S5. Perform average fitting processing on all calibration data to obtain the elongation-axial force calibration curve as the calibration data for axial force measurement.

[0022] The point where the axial force is zero must be included during fitting.

[0023] Example: The calculation formula for the yield point of a bolt considering torsional effects is as follows. The thread friction coefficient directly affects the evaluation of the actual yield point of the bolt; Formula 1: ; : Thread friction coefficient; : Thread stress cross-sectional area; d2: Pitch diameter of the thread; d0: Minor diameter of the thread; P: Pitch; : Non-proportional extension 0.2% stress; Use an ultrasonic measuring instrument to collect the bolt elongation signal at a frequency of 10 kHz, and synchronously read the data of the force sensor; Record data at every 5% preset torque interval until the bolt breaks or the elongation changes suddenly; Tighten the bolt step by step, and record the readings of the force sensor and the elongation of the ultrasonic probe corresponding to each torque value; Correct the actual axial force according to Formula 1; Establish a calibration curve; When fitting the curve, the data in the initial state and the overload stage must be included to ensure the accuracy of the demarcation point between the linear section and the non-linear section.

[0024] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A bolt elongation axial force calibration device, characterized in that: It includes an ultrasonic probe, a support gasket, a force sensor, a calibration adjustment block, a part, a protection gasket, and a calibration bolt; The force sensor and the calibration adjustment block are sequentially arranged above the part from top to bottom, and a protection gasket is arranged between the force sensor and the calibration adjustment block; The calibration bolt passes through the force sensor and the calibration adjustment block and is threadedly connected to the part; An ultrasonic probe is arranged at the top of the calibration bolt.

2. The bolt elongation axial force calibration device according to claim 1, characterized in that: A support gasket is also arranged between the calibration bolt and the force sensor.

3. A bolt elongation axial force calibration device according to claim 1, characterized in that: The calibration adjustment block is used to ensure that the length of the calibration bolt screwed into the part is consistent with the actual installation state.

4. A bolt elongation axial force calibration device according to claim 1, characterized in that: The number of the calibration bolts is not less than 3.

5. A bolt elongation axial force calibration device according to claim 1, characterized in that: The calibration steps are as follows; S1. Test and record the initial length of each calibration bolt; S2. Tighten the calibration bolts step by step for calibration, and record the axial force and elongation of the bolts at each step; S3. Stop calibration when the calibration axial force exceeds the maximum load point that the bolt can bear, that is, when the axial force shows an obvious decline; S4. Loosen the bolts after calibration and record the residual elongation of the bolts; S5. Perform average fitting processing on all calibration data to obtain an elongation-axial force calibration curve as the calibration data for axial force measurement.

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