GB2606697A - Method and system for in-field fastener preload measurement - Google Patents

Method and system for in-field fastener preload measurement Download PDF

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Publication number
GB2606697A
GB2606697A GB2105330.1A GB202105330A GB2606697A GB 2606697 A GB2606697 A GB 2606697A GB 202105330 A GB202105330 A GB 202105330A GB 2606697 A GB2606697 A GB 2606697A
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fastener
loaded fastener
loaded
length
arrangement
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GB202105330D0 (en
GB2606697B (en
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Andrews Peter
Bahlmann Quentin
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Energy Integrity Services Ltd
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Energy Integrity Services Ltd
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Priority to GB2105330.1A priority Critical patent/GB2606697B/en
Publication of GB202105330D0 publication Critical patent/GB202105330D0/en
Priority to PCT/GB2022/050922 priority patent/WO2022219328A1/en
Publication of GB2606697A publication Critical patent/GB2606697A/en
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
    • G01H5/00—Measuring propagation velocity of ultrasonic, sonic or infrasonic waves, e.g. of pressure waves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
    • F16B31/00—Screwed connections specially modified in view of tensile load; Break-bolts
    • F16B31/02—Screwed connections specially modified in view of tensile load; Break-bolts for indicating the attainment of a particular tensile load or limiting tensile load
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B17/00—Measuring arrangements characterised by the use of infrasonic, sonic or ultrasonic vibrations
    • G01B17/04—Measuring arrangements characterised by the use of infrasonic, sonic or ultrasonic vibrations for measuring the deformation in a solid, e.g. by vibrating string
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
    • G01L5/24—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for determining value of torque or twisting moment for tightening a nut or other member which is similarly stressed
    • G01L5/246—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for determining value of torque or twisting moment for tightening a nut or other member which is similarly stressed using acoustic waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/04—Analysing solids
    • G01N29/07—Analysing solids by measuring propagation velocity or propagation time of acoustic waves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
    • F16B31/00—Screwed connections specially modified in view of tensile load; Break-bolts
    • F16B31/02—Screwed connections specially modified in view of tensile load; Break-bolts for indicating the attainment of a particular tensile load or limiting tensile load
    • F16B2031/022—Screwed connections specially modified in view of tensile load; Break-bolts for indicating the attainment of a particular tensile load or limiting tensile load using an ultrasonic transducer
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/72—Wind turbines with rotation axis in wind direction

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Force Measurement Appropriate To Specific Purposes (AREA)
  • Length Measuring Devices Characterised By Use Of Acoustic Means (AREA)

Abstract

A method for determining a preload of an in-field loaded fastener, such as a stud or bolt, comprises establishing a length parameter of the loaded fastener using a measurement assembly by measuring the physical length of the loaded fastener. This may be using a datum pin, confocal instruments, high resolution digital photogrammetry, laser triangulation sensors, laser distance sensors or similar. A time parameter of an ultrasonic signal travelling through the loaded fastener using an ultrasonic transducer assembly is established by exposing an end of the fastener to an ultrasonic signal, return of the ultrasonic signal is detected and analysed to determine the time taken for ultrasonic signal to travel through the physical length of the loaded fastener. A processor is used to determine an acoustic velocity of the loaded fastener from the established length parameter and the established time parameter, and the preload of the fastener is calculated from the determined acoustic signal. The preload may be calculated by using a calibration curve or function of acoustic velocity.

Description

METHOD AND SYSTEM FOR
IN-FIELD FASTENER PRELOAD MEASUREMENT
FIELD
This relates to a method and system for determining the preload within an in-field loaded fastener, in particular a fastener for maintaining a clamping force in a joint within a wind turbine.
BACKGROUND
Structures retained by high strength friction grip joints rely on maintaining fastener preload in order to prevent prying or separation of the joint and subsequent premature fastener failure. Examples of such joints are structurally critical flanges. These may be utilised in wind turbines, oil rigs, pylons or the like. Examples of fasteners utilised in such joins are studs, bolts and the like.
In order to manage the integrity of bolted structures, such as wind turbines, it is necessary to ensure that a preload within the operational fasteners is maintained above a minimum and below a maximum acceptable level.
Conventionally, fasteners are regularly re-tightened in service to ensure preload is adequately maintained. Re-tightening is either achieved using a hydraulic tensioner with calibrated pressure control, or via torque wrenches used to apply a measured torque to the fastener. A preload is then calculated from an assumed coefficient of friction between the nut and the bolt. Alternatively, angle of turn of the nut is measured and bolt elongation is inferred through the known thread pitch or bolt elongation can be measured directly with a micrometer before and after tightening.
However, there are a number of drawbacks with conventional equipment and methodologies.
For example, conventional methods are time consuming and costly due to the nature of the activity. Moreover, they pose a safety risk due to the need for working with heavy equipment and hydraulic tightening equipment.
Preload of a Fastener can be established through measurement of fastener elongation through measurement of an initial value of the unloaded fastener which is compared to a subsequent measurement of the fastener in a loaded state. An ultrasonic transducer directs an incident ultrasonic wave to the fastener and receives the reflected ultrasonic wave from the fastener. The preload of the fastener is calculated based on a difference between the initial measured value and the subsequent measured value. Alternatively, a piezoelectric ultrasonic transducer permanently attached to the head of a fastener can be used to enable faster and more reliable ultrasonic measurements of the fastener both prior to and after tightening.
In many applications, it is not practical to take fastener measurements prior to installation. Where fasteners have already been installed, i.e. are in-field, it is therefore necessary to relax, measure and refighten the fastener in order to establish the measurement in the absence of the preload to then calculate the preload. This can be a costly and time-consuming exercise and may compromise the structural integrity of the joint whilst the fastener is relaxed or if the fastener is not retightened correctly.
Physical measurement with a traditional micrometer is extremely time consuming and introduces a high degree of uncertainty, particularly for applications such as wind turbines where large fasteners are used and hundreds or thousands of fasteners may be required to be measured for each inspection.
Comparison of elongation measurement via ultrasonic measurement is limited in that it relies upon two fixed material constants in order to determine the length of the preloaded fastener. In order to allow an ultrasonic measurement device to convert from time of flight of the ultrasonic pulse to the ultrasonic measured length of the fastener, the zero load acoustic velocity of the material and the rate at which the acoustic velocity varies with load (often referred to as the sonic stress factor) must be known. The presence of these constants can provide a significant source of error in the calculation of the elongation and subsequently the preload, and limits the use of comparison of elongation technique for applications where a high degree of accuracy is required.
SUMMARY
Aspects of the present disclosure relate to a method and system for determining a preload of an in-field loaded fastener.
According to a first aspect, there is provided a method for determining a preload of an in-field loaded fastener, the method comprising: establishing a length parameter of the loaded fastener by measuring the physical length of the loaded fastener; establishing a time parameter of an ultrasonic signal travelling through the loaded fastener by exposing an end of the loaded fastener to an ultrasonic signal, detecting the return of the ultrasonic signal and analysing the return of the ultrasonic signal to determine the time taken for the ultrasonic signal to travel through the physical length of the loaded fastener; determining an acoustic velocity of the loaded fastener from the established length parameter and the established time parameter; and determining the preload of the loaded fastener from said acoustic velocity.
Beneficially, this method allows measurements to be carried out on in-field loaded fasteners without also requiring measurement of the fastener in an unloaded condition. Accordingly, the loaded fastener can remain in situ in a joint throughout the measurement process, amongst other things mitigating the risk of joint failure and/or of the fastener being resituated and reloaded incorrectly.
Determining the preload of the loaded fastener may comprise comparing the determined acoustic velocity to reference indicia. The reference indicia may be in the form of a calibration curve or a function of acoustic velocity relative to force.
Establishing the length parameter of the loaded fastener may further include measuring the effective clamp length of the loaded fastener. Establishing the time parameter of an ultrasonic signal travelling through the loaded fastener may further comprise determining the time taken for the ultrasonic signal to travel through the effective clamp length of the loaded fastener. Beneficially, taking account of the effective clamp length of the loaded fastener increases the accuracy of the acoustic velocity determined from the length parameter and the time parameter, and therefore increases the accuracy of the determined preload for the in-field fastener.
Establishing the time parameter may comprise exposing an end of the loaded fastener to an ultrasonic signal having a frequency of 1-10 MHz.
Establishing the time parameter may be carried out using an ultrasonic transducer assembly. The ultrasonic transducer assembly may include an ultrasonic couplant. The ultrasonic couplant may reduce signal attenuation.
Establishing the length parameter may be carried out using a measurement assembly. The measurement assembly may comprise at least one non-contact measurement arrangement.
Establishing the length parameter of the loaded fastener may comprise contacting an end of the loaded fastener with a datum pin. Establishing the length parameter may further comprise positioning a non-contact measurement arrangement proximate an opposite end of the loaded fastener. The non-contact measurement arrangement may enable a displacement measurement of the physical length of the loaded fastener and/or the effective clamp length of the loaded fastener.
Establishing the length parameter of the loaded fastener may comprise positioning a first non-contact measurement arrangement proximate one end of the loaded fastener. Establishing the length parameter may comprise positioning a second non-contact measurement arrangement proximate an opposite end of the loaded fastener. The first and second non-contact measurement arrangements may enable a displacement measurement of the physical length of the loaded fastener and/or the effective clamp length of the loaded fastener.
According to a second aspect, there is provided a system for obtaining parameters to determine a preload of an in-field loaded fastener, the system comprising: an ultrasonic transducer assembly configured to establish a time parameter of an ultrasonic signal travelling through the loaded fastener, the ultrasonic transducer assembly comprising a transducer arrangement configured to expose an ultrasonic signal to an end of the loaded fastener and detect the return of the ultrasonic signal, and a processor configured to analyse the return of the ultrasonic signal to determine a time taken for the ultrasonic signal to travel through the physical length of the loaded fastener; and a measurement assembly configured to establish a length parameter of the loaded fastener, the measurement assembly comprising at least one non-contact measurement arrangement configured to determine the physical length of the loaded fastener.
Beneficially, this system is capable of being used on in-field loaded fasteners without also requiring measurement of the fastener in an unloaded condition.
Accordingly, the risk of joint failure or of fasteners being resituated and reloaded incorrectly is mitigated. Furthermore, the non-contact measurement arrangement of the apparatus provides means to increase the measurement accuracy of the physical length of the fastener, thus the accuracy of the length parameter may be increased and time taken to complete measurement of the length parameter may be reduced.
The system may further comprise a system processor configured to determine an acoustic velocity of the loaded fastener from the time parameter of an ultrasonic signal travelling through the loaded fastener and the length parameter of the loaded fastener. The system processor may be configured to determine a preload of the loaded fastener from the determined acoustic velocity. The system process may be configured to compare the calculated acoustic velocity to reference indicia. The reference indicia may be a calibration curve or a function of acoustic velocity relative to force.
The system may further comprise memory.
The reference indicia may be stored in the memory.
The memory may be configured to store at least one of the measured length, the determined time, the established time parameter, and the established length parameter.
The at least one non-contact measurement arrangement of the measurement assembly may be configured to determine the effective clamp length of the loaded fastener. The processor of the ultrasonic transducer assembly may be configured to determine a time taken for the ultrasonic signal to travel through the effective clamp length of the loaded fastener.
The ultrasonic transducer assembly may comprise an ultrasonic couplant. The ultrasonic couplant may reduce signal attenuation.
The transducer arrangement may comprise a piezoelectric transceiver. The piezoelectric transceiver may be configured to expose an ultrasonic signal to an end of the loaded fastener and to detect the return of the ultrasonic signal.
The transducer arrangement may comprise a piezoelectric transmitter. The piezoelectric transmitter may be configured to expose ultrasonic energy to an end of the loaded fastener. The transducer arrangement may comprise a piezoelectric receiver. The piezoelectric receiver may be configured to detect the return of the ultrasonic signal.
The ultrasonic transducer assembly may further comprise a temperature sensor. The temperature sensor may be configured to measure the temperature of the loaded fastener. The processor of the ultrasonic transducer assembly may be configured to compensate for the sensed temperature of the loaded fastener when determining the time taken for the ultrasonic signal to travel through the physical length of the loaded fastener.
The system may further comprise at least one power source, e.g. portable power source.
The system may further comprise a locating arrangement. The locating arrangement may be configured to retain the transducer arrangement in a selected position in contact with an end of the loaded fastener. The locating arrangement may be configured to retain the at least one non-contact measurement arrangement in a selected position proximate at least one end of the loaded fastener.
The locating arrangement may be adjustable to locate the at least one non-contact measurement arrangement and/or the transducer arrangement in the selected position for loaded fasteners of different sizes.
The locating arrangement may comprise at least one support member.
The locating arrangement may comprise at least one cap member. The at least one end cap may be mounted on an end of the at least one support member. The at least one cap member may be locatable on at least one end of the loaded fastener.
The transducer arrangement may be mounted on the at least one cap member. The transducer arrangement may be mounted on one end of the at least one support member.
The at least one non-contact measurement arrangement may be mounted on an end of the at least one support member.
The at least one non-contact measurement arrangement may comprise one non-contact measurement arrangement. The non-contact measurement arrangement may be mounted on an end of a support member opposite an end of the support member upon which a cap member is mounted. The measurement assembly may further comprise a datum pin. The datum pin may be configured to provide a reference point from which length is determined by the measurement assembly. The locating arrangement may be configured to retain the datum pin in a selected position in contact with an end of the loaded fastener. The datum pin may be mounted on the support member. The datum pin may be mounted on an end of the support member opposite the end of the support member upon which the non-contact measurement arrangement is mounted.
The at least one non-contact measurement arrangement may comprise two non-contact measurement arrangements. Each non-contact measurement arrangement may be mounted on opposite ends of a support member. The locating arrangement is configured to locate the non-contact measurement arrangements at selected positions proximate either end of the fastener.
The locating arrangement may comprise one support member. The transducer arrangement may be mounted on one end of the support member. The measurement assembly may comprise one non-contact measurement arrangement. The non-contact measurement arrangement may be located on an opposite end of the support member from the end of the support member upon which the transducer arrangement is mounted. The transducer arrangement may be configured to provide a reference point from which length is measured by the measurement assembly.
The measurement assembly may comprise a setting standard or a collection of setting standards configured to provide a reference length or lengths.
The non-contact measurement arrangement may comprise a remote 3D measurement apparatus. The non-contact measurement arrangement may comprise a high resolution digital photogrammetry apparatus or a laser tracking device. The remote 3D measurement apparatus may be a high resolution digital photogrammetry apparatus or a laser tracking device. The non-contact measurement arrangement may comprise a proximate displacement measurement apparatus. The non-contact measurement arrangement may comprise a confocal instrument or a laser triangulation sensor. The proximate displacement measurement apparatus may comprise a confocal instrument or a laser triangulation sensor.
It should be understood that features defined above in accordance with any aspect of the present disclosure or below relating to any specific embodiment of the disclosure may be utilised, either alone or in combination with any other defined feature, in any other aspect or embodiment or to form a further aspect or embodiment of the disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a flow chart showing a method for determining a preload of an infield loaded fastener; Figure 2 is a schematic view of a measurement assembly of a system for establishing parameters to determine a preload of an in-field fastener; Figure 3 is a schematic view of a measurement assembly of a system for establishing parameters to determine a preload of an in-field fastener; Figure 4 is a schematic view of a measurement assembly of a system for establishing parameters to determine a preload of an in-field fastener; Figure 5 is a schematic view of an ultrasonic transducer assembly of a system for establishing parameters to determine a preload of an in-field fastener; Figure 6 is a schematic view of a system for establishing parameters to determine a preload of an in-field fastener; and Figure 7 is a reference indicia of acoustic velocity relative to load.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring first to Figure 1 of the accompanying drawings, there is shown a method for determining the preload of an in-field loaded fastener B. As shown in Figure 1, a time parameter of an ultrasonic signal travelling through the loaded fastener B and a length parameter of the loaded fastener B are established. An acoustic velocity of the in-field loaded fastener B is then determined from the established time parameter and the established length parameter. The preload of the loaded fastener B is then determined from the determined acoustic velocity. The preload is determined by comparing the determined acoustic velocity with a calibration curve or a function of acoustic velocity relative to force.
As described further below, a calibration exercise is completed in order to generate the calibration curve and the function that can be used to determine the preload of the fastener B from the parameters established in the field. Beneficially, the same system can be used to carry out the calibration exercise as to establish
parameters in the field.
Calibration Exercise The system S comprises a measurement assembly M. The physical length (lo) of an unloaded fastener B, representative of the in-field fasteners B to be inspected, is measured with the measurement assembly M such as those shown and described below with reference to Figures 2, 3, 4 and 6.
The system S further comprises an ultrasonic transducer assembly U. An ultrasonic signal is introduced to the unloaded fastener B and the time of flight (to) of return of the ultrasonic signal is recorded using the ultrasonic transducer assembly U such as those shown and described below with reference to Figures 5 and 6.
In Figure 2, a measurement assembly M is shown, oriented by a locating arrangement L of the system S to provide a measurement of the axial length of a fastener B. The measurement assembly M comprises a datum pin 1 in contact with one end of the fastener B. The locating arrangement L comprises a support member 2. The locating arrangement L can be adjusted to allow the measurement assembly M to be used with fasteners B of different lengths and/or to accommodate different connection geometries. The measurement assembly M comprises a non-contact measurement arrangement 3. The non-contact measurement arrangement 3 is a proximate displacement measurement apparatus, for example a confocal instrument, a laser triangulation sensor, a laser distance sensor or similar. The non-contact measurement arrangement 3 is connected to a processor 4 to record a displacement measurement and establish the length parameter. A power source 5 is utilised to provide power to the non-contact measurement arrangement 3. The power source 5 is a portable power source. Alternatively, the power source may be a fixed power supply. A setting standard 6 of the measurement assembly M is used to provide a reference length. The setting standard 6 allows the measurement assembly M to be zeroed to a known length. The measurement assembly M may comprise a collection of setting standards of different lengths for use with fasteners of different lengths. The locating arrangement L further comprises a cap members 7, 8 to locate the datum pin 1 consistently in the same position in contact with one end of the fastener B, and to locate the non-contact measurement arrangement 3 consistently in a position proximate the opposite end of the fastener B to provide a scanning zone for the non-contact measurement arrangement 3.
Figure 3 of the accompanying drawings shows an alternative measurement assembly M with a non-contact measurement arrangement 103 at each end of the support member 102 so that each non-contact measurement arrangement 103 is positioned proximate opposite ends of the fastener B. The non-contact measurement arrangements are proximate displacement measurement apparatus, for example confocal instruments, laser triangulation sensors, laser distance sensors or similar. The non-contact measurement arrangements 103 are connected to a processor 104 to record a displacement measurement and establish the length parameter. A power source 105 is utilised to provide power to the non-contact measurement arrangements 103.
Figure 4 of the accompanying drawings shows an alternative measurement assembly M comprising a non-contact measurement arrangement 203 remote from the fastener B. The non-contact measurement arrangement 203 is supported by a locating arrangement L, in the form of a stand 202. The non-contact measurement arrangement 203 is a remote 3D measurement apparatus, for example a high resolution digital photogrammetry apparatus, a laser tracking device or similar. The non-contact measurement arrangement 203 is connected to a processor 204 to establish the length parameter of the fastener B. Figure 5 of the accompanying drawings shows an ultrasonic transducer assembly U. The ultrasonic transducer assembly U comprises a transducer arrangement 309 connected to a processor 304 which is used to initiate a pulse of ultrasonic energy in the transducer 309 by providing a source of electrical stimulation, and to compute the time of flight for an ultrasonic signal to pass axially through the fastener B. The transducer 309 is attached to one end of the fastener B via a locating arrangement L. The locating arrangement L comprises a cap member 307 for accurately locating the transducer 309 repeatedly in the same position and same orientation on one end of the fastener B. The ultrasonic transducer assembly U further comprises a temperature probe 310. The temperature probe 310 may or may not be used to measure the temperature of the fastener B and to enable temperature compensation in the time of flight calculated by the processor 304.
Figure 6 shows a system S comprising an ultrasonic transducer assembly U and a measurement assembly M. The system S further comprises a locating arrangement L. The datum pin 1 of Figure 2 is replaced with a transducer arrangement 409 of the ultrasonic transducer assembly U to enable concurrent measurement of the physical length of the fastener B and the time taken for ultrasonic energy to travel through the physical length of the fastener B. The system S further comprises a system processor 440 configured to receive inputs from the ultrasonic transducer assembly U and the measurement assembly M, and to determine acoustic velocity of the fastener B. The processor 404 comprises a display which can output the acoustic velocity of the fastener B. The system S further comprises a power source 405 that can provide power to the measurement assembly M, the ultrasonic transducer assembly U and the system processor 404.
Once the time and length parameters for the unloaded fastener B are established, a known force is applied to the fastener B in increments through the use of a tensile test machine or other similar device. For each incremental load applied, the physical length (11) of the fastener B, the length of the stressed portion of the fastener B (the effective length) (lc), and the time of flight (ti) for the ultrasonic energy pulse are measured and recorded using the system S. These measurements are combined as below in order to calculate the acoustic velocity (Vc) within the effective length of the fastener B or each applied force (F).
The acoustic velocity (Ve) in the effective length of a loaded fastener can be calculated thus: Ve is the acoustic velocity in the effective clamp length of the loaded fastener. IC Vc = -t, lc is the effective clamp length of the loaded fastener, which is measured using the measurement assembly of the system.
tc is the time of flight of the ultrasonic signal through the effective clamp length of the loaded fastener. -Ic tc =
ti is the time of flight of the ultrasonic signal through the physical length of the loaded fastener, which is determined by the ultrasonic transducer assembly.
Ii is the physical length of the loaded fastener, which is measured using the measurement assembly of the system.
Vo is the acoustic velocity of the unloaded fastener to 1/0 = -to lo is the physical length of the unloaded fastener, which is measured using the measurement assembly of the system.
to is the time of flight of the ultrasonic signal through the unloaded fastener, which is determined by the ultrasonic transducer assembly.
For each loading increment, the acoustic velocity is recorded against the known applied force. The acoustic velocity and force are plotted and a line of best fit is established to create a calibration curve for the fastener, as shown in Figure 6.
Multiple different fasteners can be used to create a calibration curve, in which case the results are combined and a best fit approximation calculation is used to represent the data set.
The calibration curve will result in a function of the form: F = (17c)
Determining In-Field Loaded Fastener Preload
For inspection of in-field loaded fasteners, an ultrasonic transducer assembly U as shown in Figure 5 and 6 is used to measure the time of flight for each loaded fastener to be inspected. A measurement assembly M as shown in Figure 2, 3, 4 or 6 is used to measure the physical length of the loaded fastener B and to measure the effective clamp length of the loaded fastener B. As shown in Figure 5 and 6, a transducer arrangement 309, 409 is placed on one end of the loaded fastener B. As shown in Figure 5, the transducer arrangement 309 can be located in contact with the end of the loaded fastener B by a cap member 307 of the locating arrangement L. The transducer arrangement 309 is located such that the ultrasonic signal exposed to the loaded fastener B travels along the axis of the loaded fastener B. Alternatively, as in Figure 6, the transducer arrangement 409 is magnetic to locate the transducer 409 in the correct orientation.
The processor of the ultrasonic transducer assembly U is used to measure and record the time taken for a pulse of ultrasonic energy to travel axially through the physical length of the loaded fastener B, reflect from the opposite end of the loaded fastener B and be measured at a receiver of the ultrasonic transducer assembly U. A measurement assembly M shown in Figure 2, 3, 4 or 6 can be used to individually measure the physical length of each loaded fastener B to be inspected, and also to measure the effective clamp length of each loaded fastener B. The measurement assembly M comprises a non-contact measurement arrangement 3, 103, 203 which is either a proximate displacement measurement apparatus as in Figures 2 and 3, or a remote 3D measurement apparatus as in Figure 4.
Where the measurement assembly M comprises a proximate displacement measurement apparatus, the setting standard of the measurement assembly M is placed axially within the measurement range of the non-contact measurement arrangement, abutting the datum pin 1 of the measurement assembly M in the case of Figure 2, or the ultrasonic transducer assembly U in the case of Figure 5. The processor 4, 104, 404 is used to measure and record the readings from the non-contact measurement arrangement to the end of the setting standard. The non-contact measurement arrangement is then placed proximate an end of the loaded fastener B to measure the physical length of the loaded fastener B. In Figure 2, the location of the non-contact measurement arrangement 3 is controlled by the cap members 7, 8 of the locating arrangement L. The processor 4, 104, 404 is used to measure and record a number of displacement readings from the non-contact measurement arrangement to the end of the loaded fastener B. The processor 4, 104, 404 then establishes the minimum measured displacement distance, which is added to the known length of the setting standard in order to establish the physical length of the loaded fastener B and the effective clamp length of the loaded fastener B. Where the measurement assembly M comprises a remote 3D measurement apparatus, the physical length of the loaded fasteners B and the effective clamp length of the loaded fasteners B can be measured. These lengths can be measured either collectively or individually using photogrammetry.
Once the physical length (I1), effective clamp length (la) and time of flight (ti) are known for each in-field loaded fastener B, this data can be combined with the non-load acoustic velocity (V0) from the calibration exercise, and the loaded acoustic velocity (Vc) can be determined using the equation given above.
The calibration curve or the function of acoustic velocity relative to force generated from the calibration exercise is then used to determine the preload within the in-field loaded fastener B according to acoustic velocity determined from the length and time parameters.

Claims (24)

  1. CLAIMS1. A method for determining a preload of an in-field loaded fastener, the method comprising: establishing a length parameter of the loaded fastener by measuring the physical length of the loaded fastener, establishing a time parameter of an ultrasonic signal travelling through the loaded fastener by exposing an end of the fastener to an ultrasonic signal, detecting return of the ultrasonic signal and analysing the return of the ultrasonic signal to determine the time taken for the ultrasonic signal to travel through the physical length of the loaded fastener, determining an acoustic velocity of the loaded fastener from the established length parameter and the established time parameter, determining the preload of the loaded fastener from said acoustic velocity.
  2. 2. The method of claim 1, wherein determining the preload of the loaded fastener comprises comparing the determined acoustic velocity to reference indicia.
  3. 3. The method of claim 2, wherein the reference indicia are in the form of a calibration curve or a function of acoustic velocity relative to force.
  4. 4. The method of any preceding claim, wherein establishing the length parameter further includes measuring the effective clamp length of the loaded fastener, and wherein establishing the time parameter further comprises calculating the time taken for the ultrasonic signal to travel through the effective clamp length of the loaded fastener.
  5. 5. The method of any preceding claim, wherein the end of the loaded fastener is exposed to an ultrasonic signal having a frequency of 1-10 MHz. 30
  6. 6. The method of any preceding claim, wherein establishing the length parameter of the loaded fastener comprises contacting an end of the loaded fastener with a datum pin and positioning a non-contact measurement arrangement proximate an opposite end of the loaded fastener to enable a displacement measurement of the physical length of the loaded fastener.
  7. 7. The method of any of claims 1 to 5, wherein establishing the length parameter of the loaded fastener comprises positioning a first non-contact measurement arrangement proximate an end of the loaded fastener and positioning a second non-contact measurement arrangement proximate an opposite end of the loaded fastener to enable a displacement measurement of the physical length of the loaded fastener.
  8. 8. A system for obtaining parameters to determine a preload of an in-field loaded fastener, the system comprising: an ultrasonic transducer assembly configured to establish a time parameter of an ultrasonic signal travelling through the loaded fastener, the ultrasonic transducer assembly comprising a transducer arrangement configured to expose an ultrasonic signal to an end of the loaded fastener and detect return of the ultrasonic signal, and a processor configured to analyse the return of the ultrasonic signal to determine a time taken for the ultrasonic signal to travel through the physical length of the loaded fastener; and a measurement assembly configured to establish a length parameter of the loaded fastener, the measurement assembly comprising at least one non-contact measurement arrangement configured to determine the physical length of the loaded fastener.
  9. 9. The system of claim 8, further comprising a system processor configured to determine an acoustic velocity of the loaded fastener from the time parameter and the length parameter.
  10. 10. The system of claim 9, wherein the system processor is further configured to compare the calculated acoustic velocity of the loaded fastener to reference indicia to determine the preload of the loaded fastener.
  11. 11. The system of any of claims 8 to 10, wherein the transducer arrangement comprises a piezoelectric transceiver configured to expose ultrasonic energy to one end of the loaded fastener and to detect the return signal.
  12. 12. The system of any of claims 8 to 10, wherein the transducer arrangement comprises a piezoelectric transmitter configured to expose ultrasonic energy to one end of the loaded fastener, and a piezoelectric receiver configured to detect the return of the ultrasonic signal.
  13. 13. The system of any of claims 8 to 12, wherein the ultrasonic transducer assembly further comprises a temperature sensor configured to measure the temperature of the loaded fastener.
  14. 14. The system of claim 13, when dependent on claim 9, wherein the processor is configured to compensate for the sensed temperature of the loaded fastener when determining the time taken for ultrasonic energy to travel through the physical length of the loaded fastener.
  15. 15. The system of any of claims 8 to 14, further comprising at least one portable power source 15
  16. 16. The system of any of claims 8 to 15, further comprising a locating arrangement configured to retain the transducer arrangement in a selected position in contact with one end of the loaded fastener and configured to retain the at least one non-contact measurement arrangement in a selected position proximate at least one end of the loaded fastener.
  17. 17. The system of claim 16, wherein the locating arrangement comprises at least one support member and/or at least one cap member.
  18. 18. The system of claim 16 or 17, wherein the locating arrangement is adjustable to retain the transducer arrangement and the at least one non-contact measurement arrangement in the selected positions for loaded fasteners of different sizes.
  19. 19. The system of any of claims 8 to 18, wherein the measurement assembly comprises a datum pin configured to provide a reference point from which the physical length of the loaded fastener is determined.
  20. 20. The system of claim 19, when dependent on claim 16, wherein the datum pin is mounted on the locating arrangement and the locating arrangement is configured to retain the datum pin in a selected position in contact with one end of the loaded fastener.
  21. 21. The system of any of claims 8 to 20, further comprising memory configured to store at least one of the measured length, the determined time, the established time parameter, and the established length parameter.
  22. 22. The system of any of claims 8 to 21, wherein the measurement assembly comprises a setting standard configured to provide a reference length.
  23. 23. The system of any of claims 8 to 22, wherein the non-contact measurement arrangement comprises a remote 3D measurement apparatus.
  24. 24. The system of any of claims 8 to 22, wherein the non-contact measurement arrangement comprises a proximate displacement measurement apparatus.
GB2105330.1A 2021-04-14 2021-04-14 Method and system for in-field fastener preload measurement Active GB2606697B (en)

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Citations (2)

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US20060137463A1 (en) * 2004-12-23 2006-06-29 Sayed Nassar Ultrasonic control of bolt tightening
WO2017108051A1 (en) * 2015-12-21 2017-06-29 Kk Wind Solutions A/S Ultrasonic bolt monitoring

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US5970798A (en) * 1997-09-25 1999-10-26 The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration Ultrasonic bolt gage
US11885703B2 (en) * 2018-04-30 2024-01-30 University Of Houston System Monitoring bolt tightness using percussion and machine learning
DK180269B1 (en) * 2018-12-18 2020-09-22 R&D Eng A/S Bolt tension measuring device and method

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20060137463A1 (en) * 2004-12-23 2006-06-29 Sayed Nassar Ultrasonic control of bolt tightening
WO2017108051A1 (en) * 2015-12-21 2017-06-29 Kk Wind Solutions A/S Ultrasonic bolt monitoring

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WO2022219328A1 (en) 2022-10-20
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