EN 4859:2019

SLOVENSKI STANDARD
01-junij-2019
Aeronavtika - Uporaba senzorjev za ugotavljanje obremenitve objemke/vijaki z
veliko natezno trdnostjo - Tehnična specifikacija
Aerospace series - Sensor based clamp load determination / high tensile bolts -
Technical specification
Luft- und Raumfahrt - Sensor basierende Vorspannkraftmessung / hochfeste Schrauben
- Technische Lieferbedingungen
Série aérospatiale - Détermination de la tension de serrage avec capteur / Boulons
fortement contraints - Spécification technique
Ta slovenski standard je istoveten z: EN 4859:2019
ICS:
49.030.20 Sorniki, vijaki, stebelni vijaki Bolts, screws, studs
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 4859
EUROPEAN STANDARD
NORME EUROPÉENNE
February 2019
EUROPÄISCHE NORM
ICS 49.030.20
English Version
Aerospace series - Sensor based clamp load determination
/ high tensile bolts - Technical specification
Série aérospatiale - Détermination de la tension de Luft- und Raumfahrt - Sensorbasierte
serrage avec capteur / Boulons fortement contraints - Vorspannkraftmessung/hochfeste Schrauben -
Spécification technique Technische Lieferbedingungen
This European Standard was approved by CEN on 6 August 2018.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 4859:2019 E
worldwide for CEN national Members.

Contents
Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Clamp load measurements on bolts . 5
4.1 Configuration of thin film transducer based sensor bolts. 5
4.2 Determination of the clamp load on thin film transducer based sensor bolts . 7
4.3 Basic components of an ultrasonic measurement system . 8
4.4 Geometrical requirements on sensor bolts . 9
5 Certification and quality assurance for thin film transducer based sensor bolts . 11
5.1 Qualification . 11
5.1.1 Purpose . 11
5.1.2 Conditions . 11
5.1.3 Product Qualification . 12
5.1.4 Manufacturer's approval . 12
5.2 Acceptance . 12
5.2.1 Purpose . 12
5.2.2 Conditions . 12
5.3 Quality system certification . 12
5.3.1 Purpose . 12
5.3.2 Requirements and procedure . 12
5.4 Inspection and test report . 12
5.5 Environmental durability . 12
6 Application restriction . 13
7 Technical requirements and test methods . 13
Bibliography . 20

European foreword
This document (EN 4859:2019) has been prepared by the Aerospace and Defence Industries
Association of Europe - Standardization (ASD-STAN).
After enquiries and votes carried out in accordance with the rules of this Association, this Standard has
received the approval of the National Associations and the Official Services of the member countries of
ASD, prior to its presentation to CEN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by August 2019, and conflicting national standards shall
be withdrawn at the latest by August 2019.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Introduction
Aerospace and Defence Standardisation (ASD-STAN) draws attention to the fact that it is claimed that
compliance with this document may involve the use of a patent concerning “Connector component with
temperature-resistant sensor element” EP 2010883 B1, US 8,177,464 B2.
ASD-STAN takes no position concerning the evidence, validity and scope of this patent right.
The holder of this patent right has assured ASD-STAN that he/she is willing to negotiate licenses under
reasonable and non-discriminatory terms and conditions with applicants throughout the world. In this
respect, the statement of the holder of this patent right is registered with ASD-STAN. Information may
be obtained from:
Intellifast GmbH
Siemensstrasse 18
67346 Speyer
Germany
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights other than those identified above. ASD-STAN shall not be held responsible for identifying
any or all such patent rights.
1 Scope
This European standard specifies the technical, qualification and quality assurance requirements for
sensor based clamp load measurement systems for high tensile bolts and other clamp load sensitive
elements. Primarily for aerospace applications, it is applicable to such products when referenced on the
product standard or drawing.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
EN 2424, Aerospace series — Marking of aerospace products
EN 10204:2014, Metallic products — Types of inspection documents
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
thin film ultrasonic transducer
this kind of transducer applied to one of the two a bolt ends converts an electrical pulse in an ultrasonic
wave travelling through the bolt body and transforms the reflected ultrasonic wave back into an
electrical echo signal; the thereby used physical principles are the piezoelectric effect and its reversion
3.2
sputtering
PVD (physical vapour deposition) process to apply thin films onto a substrate; under vacuum and by
means of physical methods the base material becomes transformed into the gas phase; the condensing
particles form the target layer on the substrate; sputtering is used to apply thin film ultrasonic
transducer on bolts
3.3
clamp load
needed axial force in a bolt to secure a save operation in a bolted joint
4 Clamp load measurements on bolts
4.1 Configuration of thin film transducer based sensor bolts
Three layers coated onto the top of the bolt (a) form an ultrasonic thin film transducer. Applied in a
vacuum process the transducer becomes a permanent part of the bolt (see Figure 1). The transducer
consists of a piezoelectric thin film (b), followed by a protection layer (c) and an electrode
metallization (d). Figure 2 shows different sensor bolts equipped with a thin film transducer.
Key
(a) top of the bolt
(b) piezoelectric thin film
(c) protection layer
(d) electrode metallization
Figure 1 — Thin film transducer configuration

Figure 2 — Samples of sensor bolts with thin film transducer
In addition to the thin film transducer method, there are other systems to measure the clamp load in
bolts. Examples are strain gages, electromagnetic acoustic transducers (EMAT) or conventional
piezoelectric transducers (glued on transducer, hand held transducer).
This standard describes the requirements, test procedures etc. for thin film transducer based sensor
bolts.
4.2 Determination of the clamp load on thin film transducer based sensor bolts
The ultrasonic clamp load determination in sensor bolts is based on the pulse echo method. This
technique works similar to systems like sonar or ultrasonic based material testing.
The thin film transducer placed at one of the bolt ends receives an alternating current (AC) pulse. The
transducer follows the change of the electrical voltage by changing its length. The coupling of the
transducer with the bolts surface leads to an ultrasonic wave travelling through the bolt. The ultrasonic
waves are reflected by the opposite side of the bolt and travel back in direction of the transducer (see
Figure 3). There, an echo signal can be detected. The transducer works as both, as sender and receiver.
∆t is the time period between pulse sending and receiving the echo.

Figure 3 — Determination of the clamp load in a bolt using a thin film ultrasonic transducer
The time-of-flight (TOF) of an ultrasonic pulse travelling along the bolt axis shows a marked
dependence on the applied tensile stress. In addition to the strain approximately given by Hook’s law,
there is a decrease in sound velocity, the latter of which remarkably accounts for ≈ 75 % (for steel) of
the total TOF increase. Fortunately, both effects act in the same direction and are sufficiently linear so
that the changes in TOF between an unloaded and a loaded state can be used as a direct measure of the
applied load.
The TOF dependence on load can be described with low (first or second) order polynomials:
𝐹𝐹 =𝑘𝑘 ⋅∆𝑇𝑇𝑇𝑇𝐹𝐹 =𝑘𝑘 ⋅ (𝐹𝐹𝑇𝑇𝑇𝑇𝐹𝐹−𝐵𝐵𝑇𝑇𝑇𝑇𝐹𝐹)
1 1
𝐹𝐹 =𝑘𝑘 ⋅∆𝑇𝑇𝑇𝑇𝐹𝐹 +𝑘𝑘 ⋅∆𝑇𝑇𝑇𝑇𝐹𝐹
1 2
where
F is the load in kN;
∆TOF is the measured TOF difference in ns;
BTOF is the measured TOF under no-load conditions in ns;
FTOF is the measured TOF under load conditions in ns;
k , k is the material and bolt- dependent linear and quadratic load scale factors.
1 2
The desired scale factors k and k can be obtained by using a load cell or a tensile testing machine as
1 2
reference for the applied loads and an ultrasonic measurement system to determine the TOF value for
the different load steps.
Temperature variations affect ultrasonic TOF measurements by changing the length of the inspected
material according to the thermal expansion law. To eliminate this influence, all TOF values determined
and stored in the measuring device must be compensated for the current temperature. One way to do
the temperature compensation is to refer all measured TOF values to 0 °C.
The dependence of the TOF on temperature can be described by a low order polynomial with sufficient
accuracy. For short bolts, for materials with a highly linear thermal expansion and for small
temperature ranges during TOF measurements, the TOF correction to 0 °C using a first order
polynomial (straight line) is recommended. See the following formula:
𝑇𝑇𝑇𝑇𝐹𝐹
𝑇𝑇𝑇𝑇𝐹𝐹 =
𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘
( )
1 +𝐶𝐶 ⋅𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇
For long bolts, for materials with non-linear thermal expansion behaviour, and for large temperature
ranges during TOF measurements, correction to 0° C using a second order polynomial (parabola) is
recommended. The following formula can be used:
𝑇𝑇𝑇𝑇𝐹𝐹
𝑇𝑇𝑇𝑇𝐹𝐹 =
𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘
(1 +𝐶𝐶 ⋅𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇 +𝐶𝐶 ⋅𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇 )
1 2
where
TOF is the measured TOF in ns;
TOF is the TOF corrected to 0° C in ns;
korr
Temp is the material temperature during TOF measurement in °C;
C , C is the material and bolt- dependent temperature calibration factors.
1 2
The specific material and bolt- dependent temperature calibration factors (C , C in the formulae above)
1 2
can be determined by measuring the raw (uncorrected) TOFs while stepping through the desired
temperature range in 10 K steps.
The temperature stepping requires a programmable climate chamber which allows specific (constant)
temperatures to be realized for sufficiently long time spans so that the bolt definitely reaches thermal
equilibrium at the given temperatures while the TOFs are measured with the ultrasonic measurement
system. Evidence for thermal equilibrium can be gained from the constancy of the TOF values once the
temperature level has been reached.
4.3 Basic components of an ultrasonic measurement system
The minimal configuration for an ultrasonic measurement system (see Figure 4) consists of an
ultrasonic unit (1) that generates the ultrasonic pulses and receives the echoes. This unit is coaxially (3)
connected with the bolt to be measured (2) and communicates with the processing unit (4). The
processing unit (4) controls the ultrasonic unit (1), displays the load values, and is the interface for the
user. A temperature probe (5) sitting on the joint measures the current bolt temperature. The
ultrasonic unit (1) and the processing unit (4) are often combined into one device. This minimal
configuration allows the permanent monitoring of one test joint.
In case that more than one bolt
...