SIST EN 17149-3:2025
(Main)Railway applications - Strength assessment of rail vehicle structures - Part 3: Fatigue strength assessment based on cumulative damage
Railway applications - Strength assessment of rail vehicle structures - Part 3: Fatigue strength assessment based on cumulative damage
This document describes a procedure for fatigue strength assessment based on cumulative damage of rail vehicle structures that are manufactured, operated and maintained in accordance with standards valid for rail system applications.
This document is applicable for variable amplitude load data with total number of cycles higher than 10 000 cycles.
An endurance limit approach is outside the scope of this document.
The assessment procedure is restricted to ferrous materials and aluminium.
This document does not define design load cases.
This document is not applicable for corrosive conditions or elevated temperature operation in the creep range.
This document is applicable to all kinds of rail vehicles; however, it does not define in which cases a fatigue strength assessment using cumulative damage is to be applied.
Bahnanwendungen - Festigkeitsnachweis von Schienenfahrzeugstrukturen - Teil 3: Betriebsfestigkeitsnachweis
Dieses Dokument beschreibt ein Verfahren für den Betriebsfestigkeitsnachweis auf Grundlage von Schadensakkumulation von Schienenfahrzeugstrukturen, welche nach Normen für Bahnanwendungen hergestellt, betrieben und instandgehalten werden.
Dieses Dokument findet Anwendung bei Lastdaten mit variabler Amplitude für Zyklenzahlen über 10 000 Zyklen.
Der Dauerfestigkeitsnachweis liegt außerhalb des Anwendungsbereichs dieses Dokumentes.
Das Nachweisverfahren beschränkt sich auf eisenhaltige Werkstoffe und Aluminium.
Dieses Dokument legt keine Bemessungslastfälle fest.
Dieses Dokument ist nicht anzuwenden für Korrosionszustände oder Betrieb bei erhöhter Temperatur im Kriechbereich.
Dieses Dokument ist für alle Arten von Schienenfahrzeugen anwendbar, es legt jedoch nicht fest, in welchen Fällen ein Betriebsfestigkeitsnachweis mittels Schadensakkumulation anzuwenden ist.
Applications ferroviaires - Évaluation de la résistance des structures de véhicule ferroviaire - Partie 3 : Évaluation de la résistance à la fatigue basée sur la méthode des dommages cumulés
Le présent document décrit une procédure d'évaluation de la limite de fatigue selon la méthode des dommages cumulés applicable aux structures de véhicules ferroviaires qui sont fabriquées, gérées et entretenues conformément aux normes valides pour les applications ferroviaires.
Le présent document est applicable pour des données de charge à amplitude variable avec un nombre total de cycles supérieur à 10 000 cycles.
La méthode d'endurance limite ne relève pas du domaine d'application du présent document.
La procédure d'évaluation se limite aux matériaux ferreux et à l'aluminium.
Le présent document ne définit pas de cas de charge de conception.
Le présent document ne s'applique pas en cas de conditions corrosives ou de conditions d'exploitation à une température élevée dans la plage de fluage.
Le présent document est applicable à tous les types de véhicules ferroviaires. Toutefois, il ne définit pas dans quels cas une évaluation de la limite de fatigue selon la méthode des dommages cumulés doit être réalisée.
Železniške naprave - Ocenjevanje odpornosti konstrukcije železniških vozil - 3. del: Ocena odpornosti proti utrujenosti na podlagi kumulativne škode
Ta dokument opisuje postopek za oceno odpornosti proti utrujenosti na podlagi kumulativne škode za konstrukcije železniških vozil, ki so izdelana, upravljana in vzdrževana v skladu s standardi za uporabo v železniških sistemih.
Ta dokument se uporablja za podatke o obremenitvi s spremenljivo amplitudo s skupnim številom ciklov, večjim od 10.000 ciklov.
Pristop z določanjem meje vzdržljivosti ne spada na področje uporabe tega dokumenta.
Postopek ocenjevanja je omejen na železne materiale in aluminij.
Ta dokument ne opredeljuje primerov konstrukcijske obremenitve.
Ta dokument se ne uporablja za korozivne pogoje ali obratovanje pri povišanih temperaturah v območju lezenja.
Ta dokument se uporablja za vse vrste železniških vozil, pri čemer ne določa, v katerih primerih je treba uporabiti oceno odpornosti proti utrujenosti na podlagi kumulativne škode.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-marec-2025
Železniške naprave - Ocenjevanje odpornosti konstrukcije železniških vozil - 3.
del: Ocena odpornosti proti utrujenosti na podlagi kumulativne škode
Railway applications - Strength assessment of rail vehicle structures - Part 3: Fatigue
strength assessment based on cumulative damage
Bahnanwendungen - Festigkeitsnachweis von Schienenfahrzeugstrukturen - Teil 3:
Betriebsfestigkeitsnachweis
Applications ferroviaires - Évaluation de la résistance des structures de véhicule
ferroviaire - Partie 3 : Évaluation de la résistance à la fatigue basée sur la méthode des
dommages cumulés
Ta slovenski standard je istoveten z: EN 17149-3:2025
ICS:
45.060.01 Železniška vozila na splošno Railway rolling stock in
general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EN 17149-3
EUROPEAN STANDARD
NORME EUROPÉENNE
January 2025
EUROPÄISCHE NORM
ICS 45.060.01
English Version
Railway applications - Strength assessment of rail vehicle
structures - Part 3: Fatigue strength assessment based on
cumulative damage
Applications ferroviaires - Évaluation de la résistance Bahnanwendungen - Festigkeitsnachweis von
des structures de véhicule ferroviaire - Partie 3 : Schienenfahrzeugstrukturen - Teil 3:
Évaluation de la résistance à la fatigue basée sur la Betriebsfestigkeitsnachweis
méthode des dommages cumulés
This European Standard was approved by CEN on 27 October 2024.
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, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye 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
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 17149-3:2025 E
worldwide for CEN national Members.
Contents Page
European foreword . 6
Introduction . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 8
4 Stress determination . 8
4.1 General. 8
4.2 Parent material . 9
4.3 Welded joints . 9
4.3.1 Modified nominal stresses . 9
4.3.2 Structural stresses and notch stresses . 9
5 Fatigue strength . 9
5.1 Parent material . 9
5.1.1 General. 9
5.1.2 Component fatigue strength Δσ and Δτ . 10
R R
5.1.3 Material properties . 10
5.1.4 Design Parameters . 11
5.1.5 Fatigue strength factors for direct stresses f and for shear stresses f . 13
R,σ R,τ
5.1.6 Correction factor for casting f . 14
R,C
5.1.7 S-N curves and methods of cumulative damage rule . 15
5.2 Welded joints . 17
5.2.1 General. 17
5.2.2 Fatigue classes Δσ and Δτ . 17
C C
5.2.3 Component fatigue strength Δσ and Δτ . 18
R R
5.2.4 Influence of thickness f and bending . 18
thick
5.2.5 Residual stress factors f and f . 19
res,σ res,τ
5.2.6 Enhancement factor for post-weld improvement f . 19
post
5.2.7 Quality level factor f . 20
QL
5.2.8 Enhancement factor for the weld inspection class f . 21
CT
5.2.9 S-N curves and methods of cumulative damage rule . 21
5.3 Determination of the fatigue strength of parent material and welded joints by
laboratory tests . 23
6 Partial factors covering uncertainties . 24
6.1 General. 24
6.2 Partial factor for loads γ . 24
L
6.3 Partial factor for the component fatigue strength γ . 25
M
6.3.1 General. 25
6.3.2 Partial factor for the consequence of failure γ . 26
M,S
6.3.3 Partial factor for the inspection during maintenance γ . 26
M,I
6.3.4 Partial factor for the degree of the validation process γ . 27
M,V
7 Procedure of the fatigue strength assessment based on cumulative damage
calculation . 28
7.1 General . 28
7.2 Stress determination . 29
7.3 Determination of the design stress spectrum . 29
7.3.1 Conditioning . 29
7.3.2 Stress history adjustment . 29
7.3.3 Counting . 29
7.3.4 Mean stress adjustment . 30
7.3.5 Omission . 30
7.4 Damage calculation for each single stress component . 31
7.4.1 General . 31
7.4.2 Determination of stress spectrum shape factor A . 32
eq
7.4.3 Determination of admissible damage sum D . 32
m
7.4.4 Determination of the utilization for a single stress component U . 32
c
7.5 Assessment of fatigue strength . 34
7.6 Critical plane approach . 35
Annex A (informative) Procedure for determination of mean stress factors for parent
material and welded joints . 36
A.1 General . 36
A.2 Mean stress sensitivity . 36
A.2.1 Parent material . 36
A.2.2 Welded joints . 37
A.3 Determination of mean stress factors . 37
Annex B (informative) Specification example for permissible volumetric defects in steel,
iron and aluminium castings . 41
B.1 General . 41
Annex C (informative) Material factors for parent material . 42
Annex D (normative) Fatigue classes Δσ and Δτ for welded joints based on the nominal
C C
stress approach . 44
D.1 Explanation of the tables for fatigue classes . 44
D.1.1 General . 44
D.1.2 Number and marking in accordance with EN 15085-3:2022+A1:2023, Table B.1 . 44
D.1.3 Sketch of the joint . 44
D.1.4 Joint specific requirements . 45
D.1.5 Potential crack initiation point . 45
D.1.6 Feasibility for inspection . 45
D.1.7 Relevant thickness for the assessment of a welded joint . 45
D.1.8 Material . 45
D.1.9 Fatigue classes Δσ and Δτ . 46
C C
D.1.10 Exponent m and number of cycles at the knee point of the S-N curve N . 46
D
D.1.11 Thickness correction exponents n n and n . 46
σ,┴, σ,|| τ
D.1.12 Lower limit of the plate thickness for the thickness correction t . 46
min
D.1.13 Parameter α used for the determination of f . 46
bend bend
D.2 Tables of fatigue classes for welded joints . 47
D.3 Determination of fatigue strength based on comparative notch case models . 82
Annex E (informative) Thickness and bending influence on nominal and structural stress
approaches for welded joints . 83
E.1 General. 83
E.2 Influence quantities . 84
E.2.1 Thickness correction factor f . 84
thick
E.2.2 Enhancement factor for bending f . 85
bend
E.3 Methods for application of f in the assessment process . 86
bend
E.3.1 General. 86
E.3.2 General ratio method . 87
E.3.3 Constant ratio method . 87
E.3.4 Comparative notch case model method. 87
Annex F (informative) Stress adjustment due to joint geometry for welded joints for nominal
stress approach . 88
F.1 General. 88
F.2 Methods for stress adjustment . 88
F.2.1 General. 88
F.2.2 Modelling techniques for welded joints . 89
F.2.3 Adjustment in the stress evaluation . 90
Annex G (informative) Application of structural stress approach for welded joints of steel
and aluminium . 95
G.1 General for fatigue stress determination on weld toe . 95
G.2 Fatigue stress determination with Finite Element method . 96
G.2.1 Fatigue stress determination at the weld toe . 96
G.2.2 Fatigue stress determination at the root . 97
G.3 Fatigue strength assessment with structural stresses . 97
Annex H (informative) Application of notch stress approach for welded joints of steel and
aluminium . 99
H.1 General. 99
H.2 Calculation of notch stresses . 99
H.2.1 General. 99
H.2.2 Reference notch radius r for modelling of weld notches . 100
ref
H.2.3 Modelling of nominal weld cross-sections . 100
H.2.4 Methods for notch stress calculation . 103
H.3 S-N curves . 104
H.3.1 Direct stress transverse to the weld . 104
H.3.2 Direct stress longitudinal to the weld . 105
H.3.3 Shear stress . 105
H.3.4 Characteristic values dependent on thickness effect . 105
Annex I (informative) Example for fatigue strength assessment . 106
I.1 Description . 106
I.2 Task . 107
I.3 Assessment . 107
Annex J (informative) Flow chart diagrams of the fatigue strength assessment procedure
................................................................................................................................................................ 113
Bibliography . 119
European foreword
This document (EN 17149-3:2025) has been prepared by Technical Committee CEN/TC 256 “Railway
applications”, the secretariat of which is held by DIN.
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 July 2025, and conflicting national standards shall be
withdrawn at the latest by July 2025.
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.
This document is part of the EN 17149 series, Railway applications — Strength assessment of railway
vehicle structures, which consists of the following parts:
— Part 1: General;
— Part 2: Static strength assessment;
— Part 3: Fatigue strength assessment based on cumulative damage.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia,
Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland,
Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of North
Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the United
Kingdom.
Introduction
If a fatigue strength assessment is necessary for rail vehicle structures, this assessment may be made with
an endurance limit approach or a cumulative damage approach.
An endurance limit approach is based on the assessment of the stress ranges (e.g. derived from the design
load cases or from measurements) against an admissible endurance limit. Such an approach is applicable
in combination with the loads given in the EN 12663 series or EN 13749.
A fatigue strength assessment based on cumulative damage takes into consideration stress spectra with
variable amplitudes and numbers of cycles or stress time histories. This document provides the basic
procedure and criteria for a pragmatic method to be applied for fatigue strength assessments based on
the cumulative damage approach.
This document does not provide any procedures or criteria for an endurance limit approach. However,
the fatigue strength data included in this document can also be applicable for an endurance limit
approach.
The main body of the document is based on the nominal stress approach, but the consideration of variable
amplitudes and number of cycles using methods described in this standard may equally be applied with
the structural stress and the notch stress approach (additional information for these assessment methods
is included as informative annexes).
Within this document, the term fatigue strength assessment is always related to the cumulative damage
approach unless otherwise noted.
1 Scope
This document describes a procedure for fatigue strength assessment based on cumulative damage of
rail vehicle structures that are manufactured, operated and maintained in accordance with standards
valid for rail system applications.
This document is applicable for variable amplitude load data with total number of cycles higher than
10 000 cycles.
An endurance limit approach is outside the scope of this document.
The assessment procedure is restricted to ferrous materials and aluminium.
This document does not define design load cases.
This document is not applicable for corrosive conditions or elevated temperature operation in the creep
range.
This document is applicable to all kinds of rail vehicles; however, it does not define in which cases a
fatigue strength assessment using cumulative damage is to be applied.
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 15085-3:2022+A1:2023, Railway applications — Welding of railway vehicles and components —
Part 3: Design requirements
EN 17149-1:2024, Railway applications — Strength assessment of rail vehicle structures — Part 1: General
ISO/TR 25901-1:2016, Welding and allied processes — Vocabulary — Part 1: General terms
3 Terms and definitions
For the purposes of this document, the terms, definitions, symbols and abbreviations given in
ISO/TR 25901-1:2016 and EN 17149-1:2024 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org
4 Stress determination
4.1 General
Fatigue loads acting on a component cause fatigue stresses that can be expressed as a stress spectrum.
The stress spectrum used to perform the fatigue strength assessment based on cumulative damage
approach shall be expressed in terms of stress ranges, mean stresses and number of cycles to represent
the design life.
The design stress spectrum shall incorporate any necessary allowance to account for uncertainties in
their values (see 6.2).
NOTE The EN 12663 series, EN 15827 and EN 13749 contain information on how to determine design loads
for cumulative damage assessment of rail vehicles.
The combination of the individual stress components direct stress and shear stress is considered in 7.5.
4.2 Parent material
The stresses for the parent material shall be determined as described in EN 17149-1:2024, 5.1 and 5.2.
4.3 Welded joints
4.3.1 Modified nominal stresses
The modified nominal stresses for welded joints shall be determined in accordance with
EN 17149-1:2024, 5.1 and 5.3.
4.3.2 Structural stresses and notch stresses
For the fatigue strength assessment of welded joints, the structural stress approach and the notch stress
approach may be applied. For the application of these approaches, the requirements for the calculation
of the relevant stresses and fatigue strength are described in the following informative annexes:
— Annex G for the structural stress approach and
— Annex H for the notch stress approach.
5 Fatigue strength
5.1 Parent material
5.1.1 General
This clause describes the method to derive the fatigue strength of parent material under the following
conditions:
— materials used such as construction steel, weldable cast steel, cast iron (GJS and ADI), steel (rolled or
forged), cast aluminium, and wrought aluminium;
— application temperature up to 100 °C for aluminium and up to 200 °C for steel;
— plane stress tensor on the components surface (no significant stress component perpendicular to the
surface as would occur e.g. with a press fit connection).
The restrictions specified above are met with most applications of parent material for rail vehicles, in
which case a simplified assessment method is appropriate. If the scope of the application is exceeded, an
assessment method shall be chosen which accounts for the specific application (e.g. high temperatures
or 3-dimensional stress states).
Annex C gives an overview of the applicable material factors.
5.1.2 Component fatigue strength Δσ and Δτ
R R
The fatigue strength is specified by S-N curves, which specify the values of the component fatigue strength
expressed as stress range Δσ and Δτ (in N/mm , unless stated otherwise) related to:
R R
— ,
N = 10
C
— stress ratio RR= =−1 ,
στ
— survival probability of P = 97,5 %,
s
— membrane stresses.
The values of the component fatigue strength are determined with Formula (1) and Formula (2):
∆σ N =10 , R =−1 = Rf⋅⋅ f ⋅ f (1)
( )
R C σ m R,σσSR,,R C
∆τ N 10 , R −1 = Rf⋅ ⋅⋅f f ⋅ f (2)
( )
R C τ m RR,,τσ SRR,,τ C
5.1.3 Material properties
5.1.3.1 Tensile strength in accordance with material standards R
m,N
R is the nominal tensile strength in accordance with the material standards considering the actual
m,N
sheet thickness. For machined components, the thickness of the semi-finished product before machining
shall be considered.
For rolled sheets and extrusions an anisotropy factor f shall be considered in the direction transverse to
A
the main direction of rolling in accordance with Table 1, unless this is already considered or explicitly
excluded in the material standard or component specification. For other material applications f = 10, .
A
(3)
R = fR⋅
m A mN,
Table 1 — Anisotropy factor f for steel and aluminium
A
Material R f
m,N A
[N/mm ]
Rolled Steel ≤ 600 0,9
> 600 0,86
≤ 900
Rolled sheets and extrusions of aluminium ≤ 200 1,0
> 200 0,95
≤ 400
> 400 0,9
≤ 600
All other material applications Any value 1,0
Heat-affected zone Any value 1,0
==
For heat-affected zones in the vicinity of welded joints the nominal tensile strength for the heat-affected
zone R shall be used instead of R . The value for R shall be derived from technical literature.
m,HAZ m m,HAZ
NOTE Examples for such technical literature are [2], [5], [57], [58].
5.1.3.2 Tensile strength specified by drawing or specification R
m,S
As an alternative to a material standard, the mechanical properties may be specified by the drawing or
specification.
R is the tensile strength in accordance with a drawing or component specification. If higher values than
m,S
those specified in the material standards are specified for R and the values are checked only by random
m,S
testing, then the specified values are not sufficiently reliable and therefore would be non-conservative to
use for the purposes of a fatigue strength assessment. To perform a fatigue strength assessment with a
survival probability of P = 97,5 % the tensile strength R specified by the drawing or component
S m,S
specification shall be reduced in accordance with Formula (4):
(4)
Rf= ⋅ R
m RmS,,mS
If the strength value is checked by three random tests (e.g. hardness test or tensile test) a value of
f = 0,94 is applicable. For other numbers of tests, this value shall be adjusted in accordance with
Rm,S
technical literature (e.g. [2]).
If a validated P = 97,5 % value within the component is available, f may be set to 1,0.
S Rm,S
NOTE Strength values verified with 3.1 certificate in accordance with EN 10204 are examples for such
validated values.
The R values specified in material standards for a given wall thickness may be used for the purposes
m,N
of fatigue strength assessment with a survival probability of P = 97,5 %.
S
5.1.3.3 Influence of technological size
The assessment method described in this standard does not make any adjustment for the wall thickness
of the component. The strength properties used shall consider the appropriate wall thickness.
For components made from semi-finished products the strength properties shall consider the wall
thickness of the semi-finished product before machining.
5.1.3.4 Influence of application temperature
If the component operating temperature remains within the scope of applicability specified by this
standard, no further adjustment to account for the application temperature is required for the fatigue
strength assessment.
5.1.4 Design Parameters
5.1.4.1 Surface roughness factor f
SR
The surface roughness factor f depends on the material, the nominal tensile strength R , the surface
SR m
roughness R and the manufacturing process and is specified by Formula (5) and Formula (6).
Z
RR2
Z m
ff ⋅−1 a⋅ log ⋅ log (5)
SR,,σσSR edge R,
b
µm
R
=
RR2
Z m
f f ⋅−1 f⋅ a⋅ log ⋅ log
(6)
SR,τ SR,edge R,,τσR
b
µm
R
a and b are given in Table 2, f and R are given in Table 3 and f is given in Table 4.
R,σ R SR, edge Z R,τ
Table 2 — Factors a and b for steel and aluminium
Rσ R
Material a b
R,σ R
[N/mm ]
Steel (rolled or forged) 0,22 400
Steel castings 0,20 400
Spheroidal graphite cast iron (GJS) 0,16 400
Ausferritic spheroidal graphite cast iron (ADI) 0,16 400
Wrought aluminium 0,22 133
Cast aluminium 0,20 133
Typical values of the surface roughness R correlating to the average surface roughness R are given in
Z a
Table 3. The factor f accounts for the effect of thermal cut edges of steel.
SR,edge
Table 3 — Typical values for R , R and f
Z a SR,edge
R R f Example
Z a SR,edge
[µm] [µm]
a a
1,0 Plate surface or machined edge of steel
b b
1,0 Shot blasted rolled sheet surface;
80 25
Rolled sheet and extrusions of aluminium
b b
1,0 Rolled sheet surface of steel, not shot blasted;
200 50
Forged steel; Cast surface
b b
0,81 Thermal flame cutting of steel, shot blasted
50 12,5
b b
0,81 Thermal flame cutting of steel, not shot blasted
200 50
b b
0,94 Plasma or laser cut plate edges of steel, shot blasted
25 6,3
b b
0,94 Plasma or laser cut plate edges of steel, not shot blasted
200 50
200 50 1,0 Plasma or laser cut plate edges of aluminium, not shot
blasted. (An improvement in the surface roughness
factor is only applicable if the affected material
(typically 2 mm) is completely removed by machining
after cutting.)
a
The values in accordance with the drawing or component specification shall be used. When applied to
castings the benefit of machined surfaces is only applicable if the machined surface is free from surface
breaking defects.
b
If explicit values for surface roughness are specified in the drawing or component specification those values
shall be used for the fatigue strength assessment. When applied to castings the benefit of machined surfaces
is only applicable if the machined surface is free from surface breaking defects.
=
For plate edges of rolled sheets the following requirements shall be applied:
— Sharp corners and surface rolling flaws shall be removed by longitudinal grinding or during
subsequent manufacturing processes, for example shot blasting;
— cracks or visible gouges are not permitted;
— weld repairs shall be treated as welded joints;
— notch effects due to shape of edges shall be considered;
— minimum corner radius or chamfer 1 mm;
— all burrs shall be removed.
For plate edges of steel manufactured by plasma and laser cut the surface roughness factor for cut edges
f shall be applied in accordance with Table 3.
SR,edge
For plate edges of aluminium, manufactured by plasma or laser cut a surface roughness of R = 200 μm
z
shall be applied independent of the actual surface roughness to account for the local metallurgical effects.
An improvement in the surface roughness factor is only applicable if the affected material (typically
2 mm) is completely removed by machining after cutting.
The values are valid for nominal stress without the consideration of any stress gradients perpendicular
to the surface. In the case of a stress gradient perpendicular to the surface (e.g. stress concentration) the
influence of the surface roughness may be reduced in accordance with technical literature, e.g. [2].
5.1.4.2 Influence of stress gradient
In the assessment method described in this standard the benefit for the fatigue strength associated with
the stress gradient perpendicular to the surface (e.g. due to stress concentration or bending stress) is not
included in the fatigue strength values.
The beneficial effects of stress gradients may be considered in accordance with technical literature,
e.g. [2].
5.1.4.3 Influence of surface treatment
As a conservative approach in this simplified assessment method the benefit for the fatigue strength
associated with the surface treatment (e.g. peening) is not included.
The beneficial effects of the surface treatment may be considered in accordance with technical literature,
e.g. [2].
5.1.5 Fatigue strength factors for direct stresses f and for shear stresses f
R,σ R,τ
For the determination of the component fatigue strength (stress range) for parent material the fatigue
strength factors given in Table 4 shall be used. These fatigue strength factors are related to N = 10
C
cycles and a stress ratio of R = −1 and correspond to a survival probability of P = 97,5 %.
S
Table 4 — Fatigue strength factors for direct stresses and shear stresses related to N = 10
C
cycles
a
Material f
f
R,σ
R,τ
Steel (rolled or forged) 0,75 0,577
Steel castings 0,57 0,577
Spheroidal graphite cast iron 0,65
117 N /²mm
0, 42+
(GJS)
R
m
Ausferritic spheroidal graphite 0,7
492 N /²mm
cast iron (ADI)
R
m
Wrought aluminium 0,6 0,577
Cast aluminium 0,6 0,75
a
Ratio between the fatigue strength of shear stress and the one of direct stress.
NOTE For steel castings and spheroidal graphite cast iron, the fatigue strength factors f given in Table 4 are
R,σ
). The fatigue strength
derived in accordance with [2] (fatigue strength factor for alternating direct stresses f
w,σ
factors represent the fatigue strength ratio with respect to stress range, these factors include a margin of 1,2 as
given in [2] to cover uncertainties. For aluminium, the fatigue strength factors given in Table 4 are determined in
accordance with test results.
5.1.6 Correction factor for casting f
R,C
The NDT-level and the corresponding casting quality level applied for castings have an influence on the
fatigue strength values for the cast component. The correction factor for casting f accounts for the
R,C
effects of any remaining defects on the fatigue strength within the casting component. For all non-cast
components f = 1,0.
R,C
In the case of structural castings, it is necessary to specify the quality requirements with respect to the
permitted volumetric and surface defect levels to guarantee the mechanical properties to be achieved in
regions subjected to high stresses. The relevant mechanical properties and quality requirements shall be
verified in accordance with the component specification.
The correction factor for casting f shall be chosen in accordance with the casting quality achieved in
R,C
the cast component. The values given in Table 5 may be used for castings depending on the NDT-level
during production and the verified quality level in accordance with Annex B.
Table 5 — Correction factor for casting f
R,C
Volumetric inspection by NDT Inspection of surface conditions Correction factor for
castings
Relevant Quality level in
Relevant Quality class
f
R,C
Standard accordance with standard
ASTM
The
Level 3 EN 1369 LM3, AM3, SM4 0,8
EN 12680
EN 1370 4S1/5S2, VC3
series
(UT)
EN 1371-1 LP3, AP3
The
SP3/CP3
EN 12681
series
Level 2 EN 1369 LM2, AM2 0,9
(RT)
SM2
EN 1370 3S1/3S2, VC2
EN 1371-1 LP2, AP2
SP2/CP2
The specification of castings needs to ensure appropriate cast quality to maintain the applicability of the
assessment method specified in this document. Informative Annex B gives an example for the casting
specification requirements related to volumetric quality levels.
An enhancement of the correction factor f up to 1,0 is applicable, if the fatigue strength values within
R,C
the component are proven by corresponding tests using test specimens extracted from these regions of
the component and corresponding quality assurance measures for the manufacturing process.
A strength assessment method that does not consider the internal casting defects (e.g. voids) in
components during the stress determination (e.g. a FEA model representing nominal geometry) should
be restricted to castings of quality level 3 or better. For components or parts of components that are not
stressed significantly inferior quality levels may also be applied.
For an assessment of such castings, it should be considered that bigger defects can affect significantly the
actual stress distributions (e.g. due to locally reduced sections). Therefore, these effects should either be
considered for the determination of the stress distribution or the correction factor for castings f should
R,C
be reduced accordingly.
5.1.7 S-N curves and methods of cumulative damage rule
For S-N curves of parent material all relevant information is given in Table 6 and Table 7.
Table 6 — Parameters for S-N curves
Cumulative Exponent beyond Cut-off Damage sum limit
damage rule knee point N limit D
D m,min
Δσ
L
a
Modified version 0,5 Δσ 1,0 for spheroidal graphite cast iron, (GJS, ADI),
2m-1
D
of Miner’s rule 0,3 for all other materials
Consistent version m for austenitic - 1,0 for spheroidal graphite cast iron, (GJS, ADI),
of Miner’s rule 0,3 for all other materials
steel and aluminium
a
No specific symbol is assigned to the exponent beyond the knee point N , the slope is specified only by the
D
formula above.
In Figure 1, the principal representation of S-N curves is given for parent material for direct stress. For S-
N-curves of shear stresses the symbol σ is replaced by symbol τ.
Figure 1 — S-N curves for parent material for direct stresses: a) Miner modified; b) Miner
consistent for ferritic steel, steel castings and spheroidal graphite cast iron; c) Miner consistent
for austenitic steel and aluminium
For parent material, the knee point position N is at 10 cycles.
D
Since N = N Formula (7) and Formula (8) apply:
D C
(7)
∆σ R=−=1 ∆σ
( )
DR
(8)
∆τ R=−=1 ∆τ
( )
D R
For parent materials austenitic steel and aluminium, the exponent beyond the knee point until a second
knee point at N = 10 cycles is given in Table 7. This is only necessary for application of the consistent
D,2
version of Miner’s rule.
Table 7 — Material-related values for S-N curve parameters
Material Stress type Exponent Exponent of S-N Second knee point
of S-N curve curve N for consistent
D,2
version of Miner's
m m for consistent
rule
version of Miner's
rule
Ferri
...
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