WO2015018559A1 - A method of calibrating ultrasonic bi-wave fastener elongation measurements - Google Patents

A method of calibrating ultrasonic bi-wave fastener elongation measurements Download PDF

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Publication number
WO2015018559A1
WO2015018559A1 PCT/EP2014/063321 EP2014063321W WO2015018559A1 WO 2015018559 A1 WO2015018559 A1 WO 2015018559A1 EP 2014063321 W EP2014063321 W EP 2014063321W WO 2015018559 A1 WO2015018559 A1 WO 2015018559A1
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WO
WIPO (PCT)
Prior art keywords
fastener
tof
transversal
ultrasonic
longitudinal
Prior art date
Application number
PCT/EP2014/063321
Other languages
French (fr)
Inventor
Carl-Gustaf Carlin
Original Assignee
Atlas Copco Industrial Technique Ab
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Filing date
Publication date
Application filed by Atlas Copco Industrial Technique Ab filed Critical Atlas Copco Industrial Technique Ab
Publication of WO2015018559A1 publication Critical patent/WO2015018559A1/en

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Classifications

    • 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
    • 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
    • G01L25/00—Testing or calibrating of apparatus for measuring force, torque, work, mechanical power, or mechanical efficiency
    • G01L25/003—Testing or calibrating of apparatus for measuring force, torque, work, mechanical power, or mechanical efficiency for measuring torque
    • 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
    • G01N29/22—Details, e.g. general constructional or apparatus details
    • G01N29/30—Arrangements for calibrating or comparing, e.g. with standard objects
    • 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
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/26—Scanned objects
    • G01N2291/269—Various geometry objects
    • G01N2291/2691—Bolts, screws, heads

Definitions

  • the invention relates to a method of calibrating ultrasonic fastener elongation measurements.
  • the stress (or the elongation) of the fastener may be determined. Such a method is disclosed in US 4602511.
  • one drawback of this method is that the measurement has to be calibrated for each type of fastener in order to be able to correctly determine the stress in the fastener.
  • reference fasteners or reference calibration values needs to be kept for each batch of fastener in order to be able to perform measurements on elongation (or stress) during the lifetime of a tightened joint including such a fastener.
  • An object of the invention is to improve the method of calibrating ultrasonic bi-wave fastener elongation measurements .
  • This object is achieved by the invention according to claim 1, which relates to a method of calibrating ultrasonic fastener elongation measurements .
  • the method comprises :
  • fastener of a tightened joint, which fastener comprises a first portion with a primary deformation zone subjected to stress due to the tightening of the joint, and a second portion excluding the primary deformation zone,
  • longitudinal TOF may be determined in a portion of the fastener excluding or not comprising the primary deformation zone, and this relationship may be used as reference for an ultrasonic bi-wave measurement on the elongation of the first portion of the fastener, comprising the primary deformation zone.
  • the primary deformation zone may be defined as a portion of the fastener where the major portion of the stress is located during tightening.
  • the primary deformation zone may be localised between the head and the nut, and comprised by the elongated portion of the fastener.
  • the primary deformation zone may e.g. correspond to a waist portion on the fastener.
  • the step of defining the measured longitudinal TOF and the measured transversal TOF as reference values is to be construed broadly. It merely implies that said measured TOFs are intended for use as reference in an elongation measurement in said fastener. No particular action or calculation need to be included in said step of defining.
  • a ratio between the longitudinal TOF and the transversal TOF may be calculated as reference for an elongation measurement in said
  • the ratio may suitably be used to as reference for an ultrasonic bi-wave measurement on the elongation of the first portion of the fastener.
  • the measurement on the elongation of the first portion of the fastener subjected to stress may be performed simultaneously as the calibration of the ultrasonic bi-wave fastener elongation measurement is
  • the same ultrasonic signals may be used to both perform the calibration and the measurement of the elongation of the first portion of the fastener.
  • the second portion may comprise the head of the fastener.
  • the second portion may be easily accessed by an ultrasonic transducer.
  • the head of the fastener is typically not subjected to high stress levels and does not include the primary deformation zone.
  • the fastener may have an extension in an axial direction, wherein the ultrasonic waves are transmitted into the head of the fastener in the axial direction. Since the head of the fastener is typically provided with a shape having a flat surface abutting with a surface of a work piece, the head is suitable for generating an acoustic reflection while avoiding the primary deformation zone and thus provide a suitable portion for calibrating the ultrasonic bi-wave fastener elongation measurement.
  • the ultrasonic bi-wave measurement on the elongation of the second portion of the fastener subjected to stress may comprise using the longitudinal and transversal ultrasonic waves transmitted into the head of the fastener in the axial direction and measuring the
  • the same ultrasonic signals may be used to both perform the calibration and the measurement of the elongation of the first portion of the fastener.
  • the fastener may have an extension in an axial direction, and wherein the ultrasonic waves are transmitted into the head of the fastener in a direction perpendicular to the axial direction of the fastener.
  • the calibration may alternatively or additionally be performed by measurements in a direction perpendicular to the axial direction to avoid cross-talk with the measurement of the elongation of the first portion of the fastener.
  • the second portion may be an unstressed threaded portion of the fastener.
  • the fastener may have an extension in an axial direction, and wherein the ultrasonic waves are transmitted into the unstressed threaded portion of the fastener in a direction perpendicular to the axial direction.
  • the unstressed threaded portion of the fastener may be formed by a portion of the fastener extending beyond a nut engaged with the thread of the fastener.
  • the second portion may be provided with a first surface for receiving generated ultrasonic waves and a second surface for reflecting the ultrasonic waves back towards the first surface.
  • the first and second surfaces may be parallel, or configured such that the second surface reflect ultrasonic waves back towards the first surface.
  • Fig. 1 shows an ultrasonic transducer in acoustic contact with the head of a treaded fastener.
  • Fig. 2 shows an ultrasonic transducer in acoustic contact with a treaded unstressed portion of a treaded fastener.
  • Fig. 3 shows steps of a method of calibrating ultrasonic fastener elongation measurements.
  • Fig. 1 shows a treaded fastener 100 comprising a screw 101 and a nut 102.
  • An ultrasonic transducer 103 is in acoustic contact with the head 104 of the screw of the fastener for measuring the elongation of the fastener.
  • the screw comprises an elongated portion comprising a threaded portion 105.
  • the nut is engaged with threads on the threaded portion.
  • a first portion 106 of the fastener is defined comprising a primary deformation zone of the fastener.
  • the primary deformation zone is defined as a portion of the fastener where the major portion of the stress is located during tightening. According to an alternative not shown, the primary deformation zone may be formed as a waist on the elongated portion.
  • the first portion of the fastener i.e. the portion of the fastener between the head of the screw and the nut, forms a clamping portion which is subjected to stress resulting in an elastic and/or plastic deformation of the primary deformation zone.
  • the distance between the head of the screw and the nut defines the clamp length L of the fastener.
  • ultrasonic wave in the fastener also referred to as a bi-wave measurement.
  • the propagation speed of a transversal wave is fairly unaffected by the stress in the material, but the propagation speed of a longitudinal wave is significantly influenced by tensional stress in the material.
  • the stress (or the elongation) of the fastener may be determined. Such a method is disclosed in US 4602511.
  • the method disclosed herein provides a method of calibrating ultrasonic bi-wave by identifying a second portion of the fastener providing a sound path avoiding the primary deformation zone.
  • the second portion of the fastener is constituted by the head 104 of the fastener.
  • the ultrasonic transducer 103 in acoustic contact with the head 104 of the fastener is therefore further configured to measure properties of the head of the fastener.
  • the level of stress in the head of the fastener is generally much lower than in the primary deformation zone of the fastener.
  • the head comprises a first surface 107 facing away from the elongated portion of the fastener, and a second surface 108 facing the elongated portion of the fastener.
  • the first and second surfaces are substantially parallel to one another.
  • the ultrasonic transducer 103 is configured to generate both transversal (T) and a longitudinal (L) ultrasonic waves .
  • T transversal
  • L longitudinal
  • a longitudinal ultrasonic wave is generated by the transducer and transmitted into the second portion of the fastener, in this case the first surface 107 of the head 104.
  • the longitudinal ultrasonic wave is reflected by the second surface 108 of the head.
  • An echo of the longitudinal ultrasonic wave is detected by the transducer and the TOF of the longitudinal ultrasonic wave (i.e. the longitudinal TOF) along the sound path in the second portion is measured. Further to this, a transversal ultrasonic wave is generated by the transducer and transmitted into the second portion of the fastener.
  • transversal ultrasonic wave is reflected by the second surface 108 of the head.
  • An echo of the transversal ultrasonic wave is detected by the transducer and the TOF of the transversal ultrasonic wave (i.e. the transversal TOF) along the sound path in the second portion is measured .
  • the ratio of the transversal and longitudinal TOF is used as reference to correctly estimate an ultrasonic bi-wave measurement on the elongation of the first portion of the fastener.
  • Longitudinal and transversal ultrasonic measurement signals are then generated by the transducer and transmitted into the second portion of the fastener, in this case the first surface 107 of the head 104.
  • the ultrasonic measurement signals are transmitted along a sound path 110 in the fastener comprising the primary deformation zone of the first portion 106, and reflected at the end of the treaded portion 105 of the fastener. Echoes of the longitudinal and transversal ultrasonic measurement signals are thereafter detected by the ultrasonic
  • the transducer and longitudinal and a transversal TOF of the respective ultrasonic measurement signals along the sound path in the first portion are measured. Based on the longitudinal and a transversal TOF of the respective ultrasonic measurement signals, the clamp length L of the fastener and the calibration ratio determined in the second portion of the fastener, the elongation (or stress) of the fastener may be determined.
  • Fig. 2 an alternative configuration is shown where the calibration of the ultrasonic bi-wave fastener elongation measurements is
  • the fastener 200 is similar to what is described in relation to Fig. 1.
  • a sound path 209 in the fastener for the ultrasonic wave is provided, avoiding the primary deformation zone of the first portion 206.
  • measurements on the longitudinal and a transversal TOF in this portion may be used as reference to correctly estimate ultrasonic bi-wave fastener elongation measurements .
  • the measurement on the longitudinal and a transversal TOF in the second portion may be performed e.g. by proving a first and a second parallel surface at the threaded portion. These first and second surfaces may be pre-formed on the treaded portion, formed by grinding of the threaded portion, or formed by attachment of an adapter between the ultrasonic transducer 203 and the threaded portion of the nut, each together with any coupling medium.
  • a longitudinal ultrasonic wave is generated by the transducer and transmitted into the second portion of the fastener, in this case the first surface of the threaded second portion.
  • the longitudinal ultrasonic wave is reflected by the second surface of the threaded second portion.
  • An echo of the longitudinal ultrasonic wave is detected by the transducer and the TOF of the longitudinal ultrasonic wave (i.e. the longitudinal TOF) along the sound path in the second portion is measured. Further to this, a transversal ultrasonic wave is generated by the transducer and transmitted into the second portion of the fastener. The transversal ultrasonic wave is reflected by the second surface of the threaded portion. An echo of the transversal ultrasonic wave is detected by the transducer and the TOF of the transversal ultrasonic wave (i.e. the transversal TOF) along the sound path in the second portion is measured.
  • the ultrasonic waves may be transmitted by a first ultrasonic transducer into the first surface and received by a second ultrasonic transducer at the second surface of the second portion.
  • the ratio of the transversal and longitudinal TOF measured during calibration is thereafter used as basis to calculate an ultrasonic bi-wave measurement on the elongation of the first portion of the fastener.
  • a method 300 of calibrating ultrasonic fastener elongation measurements comprising
  • fastener of a tightened joint, which fastener comprises a first portion with a primary deformation zone subjected to stress due to the tightening of the joint, and a second portion providing a sound path avoiding the primary deformation zone,
  • transversal TOF as reference values for an elongation measurement in said fastener.
  • an elongation measurement is performed over the first portion with the primary deformation zone.
  • the elongation measurement is compared to the reference values in order correctly estimate the elongation of the fastener .

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  • General Health & Medical Sciences (AREA)
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Abstract

The invention relates to a method (300) of calibrating ultrasonic bi- wave fastener elongation measurements comprising - providing (301) a fastener (100, 200) of a tightened joint comprising a first portion(106, 206) with a primary deformation zone and a second portion (104, 205) excluding the primary deformation zone, - generating (302, 304) a longitudinal and a transversal ultrasonic wave and transmitting them into the second portion of the fastener, - detecting (303, 305) echoes of the longitudinal and transversal ultrasonic waves and measuring a longitudinal and a transversal TOF of the respective ultrasonic wave along a sound path in the second portion, and - defining(306) the measured longitudinal TOF and the measured transversal TOF as reference values for an elongation measurement in said fastener.

Description

A method of calibrating ultrasonic bi-wave fastener elongation measurements
The invention relates to a method of calibrating ultrasonic fastener elongation measurements.
Background
In order to be able to measure or control the tightening of fasteners, e.g. threaded fasteners such as screws, without having to loosen the fasteners it is known to measure the TOF (time of flight) of a transversal (T) and a longitudinal (L) ultrasonic wave in the
fastener. This is known as a bi-wave measurement. The propagation speed of a transversal wave is fairly unaffected by the stress in the material, but the propagation speed of a longitudinal wave is
significantly influenced by the stress (tensional or compressional ) in the material. Thus, by measuring the TOF of the T-wave and the TOF of the L-wave in the same fastener, the stress (or the elongation) of the fastener may be determined. Such a method is disclosed in US 4602511.
However, one drawback of this method is that the measurement has to be calibrated for each type of fastener in order to be able to correctly determine the stress in the fastener. Thus, in practice, reference fasteners or reference calibration values needs to be kept for each batch of fastener in order to be able to perform measurements on elongation (or stress) during the lifetime of a tightened joint including such a fastener.
This is a cumbersome procedure, and hence, there is a need for an improved method of calibrating ultrasonic fastener elongation
measurements .
Summary of the invention
An object of the invention is to improve the method of calibrating ultrasonic bi-wave fastener elongation measurements . This object is achieved by the invention according to claim 1, which relates to a method of calibrating ultrasonic fastener elongation measurements . The method comprises :
- providing a fastener of a tightened joint, which fastener comprises a first portion with a primary deformation zone subjected to stress due to the tightening of the joint, and a second portion excluding the primary deformation zone,
- generating a longitudinal ultrasonic wave and transmitting it into the second portion of the fastener,
- detecting an echo of the longitudinal ultrasonic wave and measuring a longitudinal TOF of the longitudinal ultrasonic wave along a sound path in the second portion,
- generating a transversal ultrasonic wave and transmitting it into the second portion of the fastener,
- detecting an echo of the transversal ultrasonic wave and measuring a transversal TOF of the transversal ultrasonic wave along the sound path in the second portion,
- defining the measured longitudinal TOF and the measured transversal TOF as reference values for an elongation measurement in said
fastener .
Thereby the relationship between the transversal TOF and the
longitudinal TOF may be determined in a portion of the fastener excluding or not comprising the primary deformation zone, and this relationship may be used as reference for an ultrasonic bi-wave measurement on the elongation of the first portion of the fastener, comprising the primary deformation zone.
The primary deformation zone may be defined as a portion of the fastener where the major portion of the stress is located during tightening. For a threaded fastener comprising a head, an elongated portion comprising a threaded portion, and a nut engaged with the threaded portion, the primary deformation zone may be localised between the head and the nut, and comprised by the elongated portion of the fastener. The primary deformation zone may e.g. correspond to a waist portion on the fastener.
The step of defining the measured longitudinal TOF and the measured transversal TOF as reference values is to be construed broadly. It merely implies that said measured TOFs are intended for use as reference in an elongation measurement in said fastener. No particular action or calculation need to be included in said step of defining.
A ratio between the longitudinal TOF and the transversal TOF may be calculated as reference for an elongation measurement in said
fastener .
Since the ratio of the longitudinal and transversal TOF is
dimensionless and independent of the length of the sound path in the fastener, the ratio may suitably be used to as reference for an ultrasonic bi-wave measurement on the elongation of the first portion of the fastener.
The measurement on the elongation of the first portion of the fastener subjected to stress may be performed simultaneously as the calibration of the ultrasonic bi-wave fastener elongation measurement is
performed. Thus, the same ultrasonic signals may be used to both perform the calibration and the measurement of the elongation of the first portion of the fastener.
The second portion may comprise the head of the fastener. Thus the second portion may be easily accessed by an ultrasonic transducer. The head of the fastener is typically not subjected to high stress levels and does not include the primary deformation zone.
The fastener may have an extension in an axial direction, wherein the ultrasonic waves are transmitted into the head of the fastener in the axial direction. Since the head of the fastener is typically provided with a shape having a flat surface abutting with a surface of a work piece, the head is suitable for generating an acoustic reflection while avoiding the primary deformation zone and thus provide a suitable portion for calibrating the ultrasonic bi-wave fastener elongation measurement.
The ultrasonic bi-wave measurement on the elongation of the second portion of the fastener subjected to stress may comprise using the longitudinal and transversal ultrasonic waves transmitted into the head of the fastener in the axial direction and measuring the
respective TOF of these waves in the first portion of the fastener. Thus, the same ultrasonic signals may be used to both perform the calibration and the measurement of the elongation of the first portion of the fastener.
The fastener may have an extension in an axial direction, and wherein the ultrasonic waves are transmitted into the head of the fastener in a direction perpendicular to the axial direction of the fastener.
Thus, the calibration may alternatively or additionally be performed by measurements in a direction perpendicular to the axial direction to avoid cross-talk with the measurement of the elongation of the first portion of the fastener.
The second portion may be an unstressed threaded portion of the fastener. The fastener may have an extension in an axial direction, and wherein the ultrasonic waves are transmitted into the unstressed threaded portion of the fastener in a direction perpendicular to the axial direction. The unstressed threaded portion of the fastener may be formed by a portion of the fastener extending beyond a nut engaged with the thread of the fastener.
The second portion may be provided with a first surface for receiving generated ultrasonic waves and a second surface for reflecting the ultrasonic waves back towards the first surface. The first and second surfaces may be parallel, or configured such that the second surface reflect ultrasonic waves back towards the first surface. Other features and advantages of the invention will be apparent from the figures and from the detailed description of the shown
embodiment (s ) .
Short description of the drawings In the following detailed description reference is made to the accompanying drawings, of which:
Fig. 1 shows an ultrasonic transducer in acoustic contact with the head of a treaded fastener.
Fig. 2 shows an ultrasonic transducer in acoustic contact with a treaded unstressed portion of a treaded fastener.
Fig. 3 shows steps of a method of calibrating ultrasonic fastener elongation measurements.
Detailed description of the shown embodiment of the invention
Fig. 1 shows a treaded fastener 100 comprising a screw 101 and a nut 102. An ultrasonic transducer 103 is in acoustic contact with the head 104 of the screw of the fastener for measuring the elongation of the fastener. The screw comprises an elongated portion comprising a threaded portion 105. The nut is engaged with threads on the threaded portion. Part of the elongated portion, between the nut 102 and the head 104, a first portion 106 of the fastener is defined comprising a primary deformation zone of the fastener. The primary deformation zone is defined as a portion of the fastener where the major portion of the stress is located during tightening. According to an alternative not shown, the primary deformation zone may be formed as a waist on the elongated portion.
In a tightened condition, the first portion of the fastener, i.e. the portion of the fastener between the head of the screw and the nut, forms a clamping portion which is subjected to stress resulting in an elastic and/or plastic deformation of the primary deformation zone. The distance between the head of the screw and the nut defines the clamp length L of the fastener.
As described initially, in order to be able to measure or control the tightening of fasteners, e.g. threaded fasteners such as screws, without having to loosen the fasteners it is known to measure the TOF (time of flight) of a transversal (T) and a longitudinal (L)
ultrasonic wave in the fastener, also referred to as a bi-wave measurement. The propagation speed of a transversal wave is fairly unaffected by the stress in the material, but the propagation speed of a longitudinal wave is significantly influenced by tensional stress in the material. Thus, by measuring the TOF of the T-wave and the TOF of the L-wave in the same fastener, the stress (or the elongation) of the fastener may be determined. Such a method is disclosed in US 4602511.
In order to perform such measurements, the method disclosed herein provides a method of calibrating ultrasonic bi-wave by identifying a second portion of the fastener providing a sound path avoiding the primary deformation zone.
In the example shown in Fig. 1, the second portion of the fastener is constituted by the head 104 of the fastener. The ultrasonic transducer 103 in acoustic contact with the head 104 of the fastener is therefore further configured to measure properties of the head of the fastener. The level of stress in the head of the fastener is generally much lower than in the primary deformation zone of the fastener. The head comprises a first surface 107 facing away from the elongated portion of the fastener, and a second surface 108 facing the elongated portion of the fastener. The first and second surfaces are substantially parallel to one another. Thus, an ultrasonic wave transmitted by the ultrasonic transducer into the first surface of the head of the fastener will be reflected by the second surface of the head of the fastener. Thus the head will provide a sound path 109 in the fastener for the ultrasonic wave, avoiding the primary deformation zone of the first portion 106. The ultrasonic transducer 103 is configured to generate both transversal (T) and a longitudinal (L) ultrasonic waves . During the calibration a longitudinal ultrasonic wave is generated by the transducer and transmitted into the second portion of the fastener, in this case the first surface 107 of the head 104. The longitudinal ultrasonic wave is reflected by the second surface 108 of the head. An echo of the longitudinal ultrasonic wave is detected by the transducer and the TOF of the longitudinal ultrasonic wave (i.e. the longitudinal TOF) along the sound path in the second portion is measured. Further to this, a transversal ultrasonic wave is generated by the transducer and transmitted into the second portion of the fastener. The
transversal ultrasonic wave is reflected by the second surface 108 of the head. An echo of the transversal ultrasonic wave is detected by the transducer and the TOF of the transversal ultrasonic wave (i.e. the transversal TOF) along the sound path in the second portion is measured .
The ratio of the transversal and longitudinal TOF is used as reference to correctly estimate an ultrasonic bi-wave measurement on the elongation of the first portion of the fastener. Longitudinal and transversal ultrasonic measurement signals are then generated by the transducer and transmitted into the second portion of the fastener, in this case the first surface 107 of the head 104. The ultrasonic measurement signals are transmitted along a sound path 110 in the fastener comprising the primary deformation zone of the first portion 106, and reflected at the end of the treaded portion 105 of the fastener. Echoes of the longitudinal and transversal ultrasonic measurement signals are thereafter detected by the ultrasonic
transducer and longitudinal and a transversal TOF of the respective ultrasonic measurement signals along the sound path in the first portion are measured. Based on the longitudinal and a transversal TOF of the respective ultrasonic measurement signals, the clamp length L of the fastener and the calibration ratio determined in the second portion of the fastener, the elongation (or stress) of the fastener may be determined.
In Fig. 2 an alternative configuration is shown where the calibration of the ultrasonic bi-wave fastener elongation measurements is
performed by an ultrasonic transducer 203 in acoustic contact with the treaded portion of the screw of the fastener. Thus the treaded portion extending beyond the nut 202 constitutes a second portion of the fastener, which is substantially unaffected by the fastener's
elongation. The fastener 200 is similar to what is described in relation to Fig. 1. In the treaded portion extending beyond the nut, a sound path 209 in the fastener for the ultrasonic wave is provided, avoiding the primary deformation zone of the first portion 206. Thus measurements on the longitudinal and a transversal TOF in this portion may be used as reference to correctly estimate ultrasonic bi-wave fastener elongation measurements .
The measurement on the longitudinal and a transversal TOF in the second portion may be performed e.g. by proving a first and a second parallel surface at the threaded portion. These first and second surfaces may be pre-formed on the treaded portion, formed by grinding of the threaded portion, or formed by attachment of an adapter between the ultrasonic transducer 203 and the threaded portion of the nut, each together with any coupling medium. As described in relation to Fig. 1, during the calibration a longitudinal ultrasonic wave is generated by the transducer and transmitted into the second portion of the fastener, in this case the first surface of the threaded second portion. The longitudinal ultrasonic wave is reflected by the second surface of the threaded second portion. An echo of the longitudinal ultrasonic wave is detected by the transducer and the TOF of the longitudinal ultrasonic wave (i.e. the longitudinal TOF) along the sound path in the second portion is measured. Further to this, a transversal ultrasonic wave is generated by the transducer and transmitted into the second portion of the fastener. The transversal ultrasonic wave is reflected by the second surface of the threaded portion. An echo of the transversal ultrasonic wave is detected by the transducer and the TOF of the transversal ultrasonic wave (i.e. the transversal TOF) along the sound path in the second portion is measured. Alternatively, the ultrasonic waves may be transmitted by a first ultrasonic transducer into the first surface and received by a second ultrasonic transducer at the second surface of the second portion. The ratio of the transversal and longitudinal TOF measured during calibration is thereafter used as basis to calculate an ultrasonic bi-wave measurement on the elongation of the first portion of the fastener.
In Fig. 3, a method 300 of calibrating ultrasonic fastener elongation measurements is illustrated comprising
- providing 301 a fastener of a tightened joint, which fastener comprises a first portion with a primary deformation zone subjected to stress due to the tightening of the joint, and a second portion providing a sound path avoiding the primary deformation zone,
- generating 302, 304 a longitudinal and a transversal ultrasonic wave and transmitting them into the second portion of the fastener,
- detecting 303, 305 echoes of the longitudinal and transversal ultrasonic waves and measuring a longitudinal and a transversal TOF of the respective ultrasonic wave along the sound path in the second portion, and
- defining 306 the measured longitudinal TOF and the measured
transversal TOF as reference values for an elongation measurement in said fastener.
In another step, which may be performed before after or simultaneously as the steps above, and which does not form part of the invention, an elongation measurement is performed over the first portion with the primary deformation zone. The elongation measurement is compared to the reference values in order correctly estimate the elongation of the fastener . As is obvious for a skilled person, a number of other implementations modifications, variations and/or additions can be made to the above described exemplary embodiments . It is to be understood that the invention includes all such other implementations, modifications, variations and/or additions which fall within the scope of the claims

Claims

A method (300) of calibrating ultrasonic bi-wave fastener elongation measurements comprising
- providing (301) a fastener (100, 200) of a tightened joint, which fastener comprises a first portion (106, 206) with a primary deformation zone subjected to stress due to the
tightening of the joint, and a second portion (104, 205) excluding the primary deformation zone,
- generating (302) a longitudinal ultrasonic wave and
transmitting it into the second portion of the fastener,
- detecting (303) an echo of the longitudinal ultrasonic wave and measuring a longitudinal TOF of the longitudinal ultrasonic wave along a sound path in the second portion,
- generating (304) a transversal ultrasonic wave and transmitting it into the second portion of the fastener,
- detecting (305) an echo of the transversal ultrasonic wave and measuring a transversal TOF of the transversal ultrasonic wave along the sound path in the second portion,
- defining (306) the measured longitudinal TOF and the measured transversal TOF as reference values for an elongation measurement in said fastener.
The method according to claim 1 wherein a ratio between the measured longitudinal TOF and the measured transversal TOF is calculated as reference for an elongation measurement in said fastener .
The method according to claim 1 or 2 wherein an elongation measurement on the elongation of the first portion of the fastener subjected to stress is performed simultaneously with the calibration of the ultrasonic bi-wave fastener elongation measurement .
The method according to any one of claims 1-3, wherein the second portion comprises the head (104) of the fastener, the measured longitudinal TOF and the measured transversal TOF being generated and measured in said second portion.
The method according to claim 4 wherein the fastener has an extension in an axial direction, and wherein the ultrasonic waves are transmitted into the head of the fastener in the axial direction .
The method according to claim 5 wherein the ultrasonic bi-wave measurement on the elongation of the first portion of the fastener comprises transmitting longitudinal and transversal ultrasonic waves into the head of the fastener in the axial direction, measuring the respective TOF of these waves in the first portion of the fastener to measure the elongation of the first portion, and calibrating the measurement on the elongation of the first portion based on the longitudinal TOF and the transversal TOF measured in the second portion.
The method according to claim 4 wherein the fastener has an extension in an axial direction, and wherein the ultrasonic waves are transmitted into the head of the fastener in a direction perpendicular to the axial direction of the fastener.
The method according to any one of claims 1-3 wherein the second portion is an unstressed threaded portion (205) of the fastener, in which the measured longitudinal TOF and the measured
transversal TOF are generated and measured.
The method according to claim 8 wherein the fastener has an extension in an axial direction, and wherein the ultrasonic waves are transmitted into the unstressed threaded portion of the fastener in a direction perpendicular to the axial direction.
The method according to any one of the preceding claims wherein the second portion is provided with a first surface for receiving generated ultrasonic waves and a second surface for reflecting the ultrasonic waves back towards the first surface.
PCT/EP2014/063321 2013-08-07 2014-06-25 A method of calibrating ultrasonic bi-wave fastener elongation measurements WO2015018559A1 (en)

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JP2017015707A (en) * 2015-07-06 2017-01-19 非破壊検査株式会社 Axial force measuring apparatus, axial force measuring method, ultrasonic inspection apparatus, ultrasonic inspection method and vertical probe fixture used for the same
US20190203599A1 (en) * 2016-08-16 2019-07-04 National Research Council Of Canada Methods and systems for ultrasonic rock bolt condition monitoring
US11619132B2 (en) * 2016-08-16 2023-04-04 National Research Council Of Canada Methods and systems for ultrasonic rock bolt condition monitoring
CN108151947A (en) * 2017-12-26 2018-06-12 北京理工大学 The caliberating device and scaling method of a kind of pretightning force and elongation
WO2020055261A1 (en) * 2018-09-12 2020-03-19 Sintef Tto As Assembly and method for measuring strain in a washer
US11867582B2 (en) 2018-09-12 2024-01-09 Sintef Tto As Assembly and method for measuring strain in a washer
GB2593743A (en) * 2020-03-31 2021-10-06 Tribosonics Ltd Bolt transducer
WO2021198367A1 (en) * 2020-03-31 2021-10-07 Tribosonics Limited Bolt transducer
WO2022041398A1 (en) * 2020-08-25 2022-03-03 苏州博昇科技有限公司 Method for quick calibration and measurement of axial forces of high-strength bolts by transverse and longitudinal ultrasonic waves

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