Available online at www.sciencedirect.com
Available online at www.sciencedirect.com
ScienceDirect
ScienceDirect
Available
online
www.sciencedirect.com
Available
online
at at
www.sciencedirect.com
Structural Integrity Procedia 00 (2016) 000–000
Structural Integrity Procedia 00 (2016) 000–000
ScienceDirect
ScienceDirect
Procedia
Structural
2 (2016)
1561–1568
Structural
IntegrityIntegrity
Procedia
00 (2016)
000–000
www.elsevier.com/locate/procedia
www.elsevier.com/locate/procedia
www.elsevier.com/locate/procedia
21st
21st European
European Conference
Conference on
on Fracture,
Fracture, ECF21,
ECF21, 20-24
20-24 June
June 2016,
2016, Catania,
Catania, Italy
Italy
WES
WES 2808
2808 for
for Brittle
Brittle Fracture
Fracture Assessment
Assessment of
of Steel
Steel Components
Components
under
under Seismic
Seismic Conditions
Conditions –
– Part
Part I:
I: Fracture
Fracture Assessment
Assessment Procedure
Procedure
Thermo-mechanical
modeling of
turbinec blade ofc an
a
b
a a high pressure
c
Minami,
a*, Ohata, M.b, Takashima, Y.a, Shimanuki, H.c, Shimada, Y.c, Suzuki, T.c,
Minami, F.
F.
*,
Ohata,
M.
,
Takashima,
Y.
,
Shimanuki,
H.
,
Shimada,
Y. , Suzuki,g T. ,
d
d
e
e engine
f
airplane
gas
turbine
Igi,
S.
M.
T.
d, Ishii, T.d, Kinefuchi,
e, Yamaguchi,
e, Nakagomi, T.f, Hagihara, Y.g
Igi, S. , Ishii, T. , Kinefuchi, M. , Yamaguchi, T. , Nakagomi, T. , Hagihara, Y.
XV Portuguese Conference on Fracture, PCF 2016, 10-12 February 2016, Paço de Arcos, Portugal
Joining and Welding Reseach Institute, Osaka
11-1, Mihogaoka, Ibaraki, Osaka 567-0047, Japan
a University,
Joining
and Welding Reseach Institute, Osaka
University, 11-1, bMihogaoka, Ibaraki, cOsaka 567-0047, Japan
b
bMaterials and Manufacturing Science, Osaka University, 2-1, Yamadaoka, Suita, Osaka 565-0871, Japan
Materials
and Manufacturing Science, Osaka University, 2-1, Yamadaoka, Suita, Osaka 565-0871, Japan
c
cNippon Steel & Sumitomo Metal Corporation, 1-8, Fuso-cho, Amagasaki, Hyogo 660-0891, Japan
a
Nippon
Steel
Sumitomo Metal
Corporation,
1-8, Fuso-cho,
Amagasaki,
HyogoAv.
660-0891,
Japan1, 1049-001 Lisboa,
Department of
Mechanical
Engineering,
Instituto
Superior Técnico,
Universidade
de Lisboa,
Rovisco Pais,
d &
dJFE Steel Corporation, 1, Kawasaki-cho, Chuo-ku,Chiba 260-0835, Japan
JFE eSteel Corporation, 1, Kawasaki-cho,
Chuo-ku,Chiba 260-0835, Japan
Portugal
Steel, 1-5-5, Takatsukadai,Nishi-ku,Kobe 651-2271, Japan
b
eKobe
IDMEC, Department of Mechanical
Engineering,
Instituto
Superior Técnico, Universidade
deJapan
Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa,
Kobe
Steel, 1-5-5,
Takatsukadai,Nishi-ku,Kobe
651-2271,
f
Nagano, Nagano 380-0928, Japan
fShinshu University, 4-17-1, Wakasato-cho,
Portugal
Shinshu
University, 4-17-1, Wakasato-cho,
Nagano, Nagano 380-0928, Japan
g
c
University,Instituto
7-1, Kioi-cho,
Chiyoda-ku,
Tokyo 102-0094,
Japan Av. Rovisco Pais, 1, 1049-001 Lisboa,
gSophia
CeFEMA, Department of Mechanical
Engineering,
Superior
Técnico, Universidade
de Lisboa,
Sophia
University, 7-1, Kioi-cho,
Chiyoda-ku,
Tokyo 102-0094,
Japan
Portugal
a
a
P. Brandão , V. Infante , A.M. Deus *
Abstract
Abstract
Abstract
The Welding Engineering Standard, WES 2808, has been developed in the Japan Welding Engineering Society (JWES) for
TheDuring
Welding
WES 2808,
been developed
in the Japan
Welding Engineering
(JWES)
for
theirEngineering
operation, Standard,
modern aircraft
enginehascomponents
are subjected
to increasingly
demandingSociety
operating
conditions,
assessing the brittle fracture in steel components under seismic conditions. WES 2808 includes two unique ideas: 1) a reference
assessing
the the
brittle
inturbine
steel components
under
seismic
conditions.
WES parts
2808 to
includes
uniquetypes
ideas:of1)time-dependent
a reference
especially
highfracture
pressure
(HPT) blades.
Such
conditions
cause these
undergotwo
different
temperature
concept
the evaluation
the material
fracture
under cyclic
loading,
andto2)beanable
equivalent
degradation,
one offor
is creep. Aof
using the
finite toughness
element method
(FEM)and
wasdynamic
developed,
in order
to predict
temperature
concept
forwhich
the evaluation
ofmodel
the material
fracture
toughness
under cyclic
and
dynamic
loading,
and 2) an equivalent
CTOD
concept
for
the
correction
of
CTOD
toughness
for
constraint
loss
in
structural
components.
The
CTOD
design
curve
is
the creep
behaviour
of HPT blades.
Flight
data records
(FDR) loss
for ainspecific
aircraft,
provided
a commercial
aviation
CTOD
concept
for the correction
of CTOD
toughness
for constraint
structural
components.
ThebyCTOD
design curve
is
employed
for
the
assessment
of
the
crack
driving
force
of
components.
The
revision
of
WES
2808
is
in
progress
in
JWES
to
company,
used to obtain
thermal
mechanical
for threeThe
different
flight
cycles.2808
In order
create in
theJWES
3D model
employed
forwere
the assessment
of the
crack and
driving
force of data
components.
revision
of WES
is in to
progress
to
expand
thefor
range
use and
to improve
theblade
fracture
assessment
procedure.
paper describes
the keyand
contents
of WES
2808. were
needed
theof
analysis,
a HPT
scrap
was scanned,
and This
its chemical
composition
material
properties
expand
the range
ofFEM
use and
to improve
the fracture
assessment
procedure.
This
paper describes
the key contents
of WES
2808.
© 2016
The Authors.
Published
by Elsevier
B.V.
obtained.
The
data
that
was
gathered
was
fed
into
the
FEM
model
and
different
simulations
were
run,
first
with
a
simplified
3D
©
2016
The Authors.
Published
byIntegrity)
ElsevierHosting
B.V. by Elsevier Ltd. All rights reserved.
©
2016,
PROSTR
(Procedia
Structural
Peer-review
of the
Scientific
Committee
of ECF21.
rectangularunder
blockresponsibility
shape, in order
to better
establish
the model,
and then with the real 3D mesh obtained from the blade scrap. The
Peer-review
under
responsibility
of
the
Scientific
Committee
of
ECF21.
Peer-review under responsibility of the Scientific Committee of PCF 2016.
overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade. Therefore such a
Keywords:
brittle
assessment;
steel
components;
pre-strain;
loading;
strain;
constraint loss; Weibull stress; ISO 27306
model can
befracture
useful in
the goal of
predicting
turbine
bladedynamic
life, given
a setlocal
of FDR
data.
Keywords:
brittle
fracture
assessment;
steel
components;
pre-strain;
dynamic
loading;
local
strain;
constraint loss; Weibull stress; ISO 27306
© 2016 The Authors. Published by Elsevier B.V.
1.
Introduction
under responsibility of the Scientific Committee of PCF 2016.
1. Peer-review
Introduction
The
great
earthquake,
happened
in
caused
aa considerable
damage
Keywords:
High
Pressure
Turbine Blade;
Creep; Finite
Element
Method;
3D Model; Simulation.
The Kobe
Kobe
great
earthquake,
happened
in 1995,
1995,
caused
considerable
damage to
to steel
steel frame
frame structures.
structures. Beam-toBeam-tocolumn
connections
failed
in
a
brittle
manner
as
reported
by
Toyoda
(1995).
During
the
earthquake,
column connections failed in a brittle manner as reported by Toyoda (1995). During the earthquake, structures
structures
* Corresponding author. Tel.: +81-6-6879-4373; Fax: +81-6-6879-4373.
* Corresponding author. Tel.: +81-6-6879-4373; Fax: +81-6-6879-4373.
E-mail address: minami@jwri.osaka-u.ac.jp
E-mail address: minami@jwri.osaka-u.ac.jp
2452-3216 © 2016 The Authors. Published by Elsevier B.V.
2452-3216 © 2016 The Authors. Published by Elsevier B.V.
* Corresponding
Tel.: +351of218419991.
Peer-review
underauthor.
responsibility
the Scientific Committee of ECF21.
Peer-review under responsibility of the Scientific Committee of ECF21.
E-mail address: amd@tecnico.ulisboa.pt
2452-3216 © 2016 The Authors. Published by Elsevier B.V.
Peer-review under responsibility of the Scientific Committee of PCF 2016.
2452-3216 © 2016, PROSTR (Procedia Structural Integrity) Hosting by Elsevier Ltd. All rights reserved.
Peer review under responsibility of the Scientific Committee of PCF 2016.
10.1016/j.prostr.2016.06.198
F. Minami et al. / Procedia Structural Integrity 2 (2016) 1561–1568
Minami, F., et al./ Structural Integrity Procedia 00 (2016) 000–000
1562
2
sustain a large cyclic and dynamic straining, which decreases the resistance to brittle fracture. According to the postKobe earthquake investigation by Hashida et al. (1998) and APD Committee in JWES (Japan Welding Engineering
Society), residual strains of 15% to 20% and strain rates of 10% to 20% per second were estimated in the beam-tocolumn connection area. The brittle fracture due to pre-strain and dynamic loading is out of the scope of the existing
standards such as BS7910, API 579-1/ASME FFS-1.
A new fracture assessment procedure, WES 2808, was published in 2003 for assessing brittle fracture of steel
structures subjected to cyclic and dynamic loading. Two unique ideas are implemented in WES 2808: 1) a reference
temperature concept for the fracture toughness evaluation under seismic conditions, and 2) an equivalent CTOD
concept for the CTOD toughness correction for constraint loss in structural components..
The revision of WES 2808 is in progress in JWES to include structural steels of 400 MPa to 780 MPa strength
class and welded joints, and to improve the fracture assessment procedure based on the reference temperature
concept and the equivalent CTOD concept. This paper describes the key contents underlying WES 2808.
2. Conditions for use
WES 2808 is applied under the following conditions:
- Steel components with a center surface crack, edge surface crack or edge through-thickness crack are assessed;
- Structural steels covered are rolled plates and wide-flange beam steels of 400 MPa to 780 MPa strength class with
the plate thickness of 12.5 mm to 50 mm;
- The crack size, c (length) and a (depth), and the plate thickness, t, covered by this standard are as follows:
Center surface crack: 2c ≥ 16 mm, 0.04 ≤ a/t ≤ 0.24, 12.5 ≤ t ≤ 50 mm
Edge surface crack: 2c ≥ 24 mm, 0.04 ≤ a/t ≤ 0.24, 12.5 ≤ t ≤ 50 mm
Edge through-thickness crack: 5 ≤ 2a ≤ 30 mm
- The local strain, e local, local strain rate, e local, and the local pre-strain, ε pre, local, defined in this standard, are in the
range, 0 < e local ≤ 10 %, 0 < e local ≤ 100 %/s and 0 < ε pre, local < uniform elongation of the steel, respectively;
- The strength mismatch, Sr = σ TW/σ TB, in welds is in the range, 0.9 < Sr < 1.5, where σ TW and σ TΒ are the tensile
strengths of the weld metal and base metal, respectively.
3. Key contents
3.1. CTOD design curve
WES 2808 employs the CTOD design curve, Eq. (1), specified in WES 2805 for assessing the fracture driving
force of a crack in the strain concentration area:
 struc (π / 2)(elocal /  Y ) 2

 Y a  (π / 8)[9 (elocal /  Y )  5]
(elocal   Y )
(elocal   Y )
(1)
where δstruc is the CTOD of a crack in the structural component, e local is a local strain defined as an average strain in
the assumed crack area, ε Y is the yield strain of the material and a is a half length of the equivalent throughthickness crack. Any crack in the component shall be converted to the through-thickness crack in an infinite plate
with the equivalent stress intensity factor. It was confirmed by the numerical analysis that Eq. (1) is applicable to
beam-to-column connections to the strain level of e local /ε Y = 50.
3.2. Active strain and pre-strain in cyclic loading
Structural components sustain damage by cyclic loading at the earthquake. WES 2808 defines the active strain
and the pre-strain in cyclic loading as follows:
Let us assume that a structural component fails at the Nth load cycle (fracture load cycle). The active strain, e, is
defined by the strain created in a positive load range of the Nth load cycle. The strain rate, e , at the fracture load
F. Minami et al. / Procedia Structural Integrity 2 (2016) 1561–1568
Minami, F., et al./ Structural Integrity Procedia 00 (2016) 000–000
1563
3
cycle is given by the average strain rate of the active strain. The pre-strain, ε pre, is evaluated on the basis of the
skeleton strain concept proposed by Nakagomi et al. (1995). The skeleton strain is an accumulation of the plastic
strain in each load cycle, where the load range exceeding the prior peak load is taken, as shown in Fig. 1. The
skeleton strains are counted on both tension and compression load sides to (N -1)th load cycle, and the larger of their
absolute values is defined as the pre-strain, ε pre, imposed by cyclic loading.
The local pre-strain, ε pre, local, and the local strain rate (active strain rate), e local, in the target area are estimated
with the strain concentration factor, Kε, in the form
 pre, local 
K   pre , elocal 
K  e
(2)
Fig. 2 shows the typical Kε-values for beam-to-column connections.
Surface crack at access hole
bottom (Conventional type)
Surface crack at access hole
bottom (JASS6 new type)
Strain concentration factor, K
10
5
1
Fig. 1. Definition of active strain and pre-strain in cyclic loading.
connections.
Surface crack
at weld start/end
Through-thickness crack
at weld start/end
1
2
3
Assumed crack depth a (mm)
Fig. 2. Strain concentration factors for beam-to-column
3.3. Reference temperature concept
During the earthquake, structural components are subjected to pre-straining and dynamic loading simultaneously,
both of which decrease the material fracture toughness. Thus, the fracture toughness under pre-strained and high
strain rate conditions is needed for the assessment of seismic performance of structures. However, such fracture
toughness is not generally available.
In WES 2808, the fracture toughness under seismic conditions is replaced by the static toughness without prestrain at a reference temperature of T – ΔTPD, as shown in Fig. 3, where T and ΔTPD are the service temperature of
the component and a temperature shift of the fracture toughness caused by pre-strain and dynamic loading. In a
technical committee in JWES, the temperature shift, ΔTPD, was investigated by a series of CTOD toughness tests of
structural steels of 490 MPa to 780 MPa strength class at loading rates (crosshead speed) of 0.01 mm/s (static) to
300 mm/s with pre-strains of 0 % to 10 %, as reported by Minami and Arimochi (2001), Minami et al. (2008) and
Igi et al. (2016). Fig. 4 shows the relationship between ΔTPD and the flow stress elevation, Δσ f PD = (Δσ Y +Δσ T) /2,
by pre-strain and dynamic loading, where ΔTPD at CTOD toughness levels of 0.05 mm to 0.1 mm was focused and
Δσ Y and Δσ T are the increase in the yield strength and that in the tensile strength, respectively.
In WES 2808, the temperature shift, ΔTPD, is specified as:
PD
(0   f PD  100 MPa)
0.4 f
TPD (C) 

(100   f PD  300 MPa)
40
(3)
F. Minami et al. / Procedia Structural Integrity 2 (2016) 1561–1568
Minami, F., et al./ Structural Integrity Procedia 00 (2016) 000–000
1564
4
Temperature shift TPD (°C)
which is drawn in the bilinear form in Fig. 4. The upper bound of 40 °C is assigned from an engineering judgment
of a temperature rise due to adiabatic plastic deformation during the earthquake in the assumed crack area in the
structural component. Miki et al. (2001) measured the temperature rises of 40 °C to 60 °C in the beam-to-column
connection zone at the cyclic dynamic loading test of full-scale subassemblies.
SM490A, SN490B
60
5% pre (static)
10% pre (static)
10mm/s (pre = 0)
300mm/s (pre = 0)
50
40
5% pre + 10mm/s
10% pre + 10mm/s
5% pre + 300mm/s
30
20
10
0
10% pre + 300mm/s
WES 2808
Critical CTOD
= 0.05 ~ 0.10 mm
0 50 100 150 200 250 300
Flow stress elevation fPD (MPa)
Fig. 3. Reference temperature concept for fracture toughness
evaluation under seismic conditions.
HT780
2.5% pre (static)
6% pre (static)
300mm/s (pre = 0)
2.5% pre + 300mm/s
6% pre + 300mm/s
Fig. 4. Temperature shift of CTOD toughness, ΔTPD, by pre-strain and
dynamic loading as a function of flow stress elevation, ΔσfPD.
3.4. Estimation of flow stress elevation under seismic conditions
Extended works in a technical committee in JWES devised formulae, Eq. (4) to Eq. (9), for the estimation of the
yield and tensile strengths of structural steels and welds under pre-strained and dynamic loading conditions, as
presented by Minami and Ohata (2007), Kubo et al. (2007) and Shimada et al. (2016). These equations were derived
by a regression analysis of round-bar tension test results of structural steels of 400 MPa to 780 MPa strength class, a
weld metal of 590 MPa strength class and a simulated CGHAZ (coarse-grained heat affected zone) of 490 MPa
strength class steel. The pre-strain was ranged from 0 % to 20 %, but less than the uniform elongation of each steel,
and the strain rate from 10-4 /s (static) to 102 /s.
For structural steels and welds of 400 MPa to 590 MPa strength class, the yield strength σ Y and tensile strength σ T
at the strain rate e and temperature T [K] with pre-strain ε pre are estimated by
1.5

  Y0pre (T0 ) 


1
1
pre
4




 Y ( pre , e, T ) =  Y0 (T0 )  exp 8  10  T0  


8
8




E




ln(10
/
)
ln(10
/
)
T
e
T
e

0
0 





(4)
1.5

  T0pre (T0 ) 


1
1

4


(T0 )  exp 8  10  T0  


9
9



E
 T  ln(10 / e) T0  ln(10 / e0 ) 





(5)
 T ( pre , e, T ) =  T0
pre
where σY0pre(T0) and σT0pre(T0) are the static yield strength and tensile strength, respectively, at the room temperature
T0 (= 293 K) with pre-strain ε pre, E is Young’s modulus (= 206 GPa) and e 0 is the static strain rate (= 10-4 /s).
The elevation of the yield strength, Δσ Y, and that of the tensile strength, ΔσT, by pre-strain and dynamic loading
are given by Δσ Y = σ Y(εpre, e , T ) – σ Y0(T ) and Δσ T = σ T(εpre, e , T ) – σ T0(T ), respectively, where σ Y0(T ) and σ T0(T )
are the static yield strength and tensile strength at the temperature T without pre-strain. The σ Y0(T ) and σ T0(T ) are
provided by replacing σY0pre(T0) and e in Eq. (4) with σY0(T0) and e 0, and by replacing σT0pre(T0) and e in Eq. (5)
with σT0(T0) and e 0, respectively, where σY0(T0) and σT0 (T0) are the static yield strength and tensile strength at the
room temperature T0 without pre-strain.
F. Minami et al. / Procedia Structural Integrity 2 (2016) 1561–1568
Minami, F., et al./ Structural Integrity Procedia 00 (2016) 000–000
1565
5
For structural steels of 780 MPa strength class, the yield strength σ Y and tensile strength σ T at the strain rate e
and temperature T [K] with pre-strain ε pre are estimated by
 Y ( pre , e, T ) =

(6)
1.1

  T0pre (T0 ) 


1
1
2


(T0 )  exp 1 10  T0  
 

9
9




E




ln(10
/
)
ln(10
/
)
T
e
T
e


0
0 





(7)


 T ( pre , e, T ) =  T0
pre
1.1

1
1

 



8
8

 T  ln(10 / e) T0  ln(10 / e0 ) 
 Y0pre (T0 )  exp 1 102
  pre (T0 ) 
 T0   Y0



E


The rate-temperature parameter R proposed by Bennett and Sinclair (1966) is implemented into Eq. (4) to Eq. (7):
the strain rate e and temperature T are equivalent in the form of R = T•ln (A/ e ), where A is a material constant.
Empirical formulae are given by Shimada et al. (2016) for estimating the static yield strength σY0pre(T0) and
tensile strength σT0pre(T0) at the room temperature T0 with pre-strain ε pre:
1/4
 Y0pre (T
0)

E 
 Y0 (T0 )  34 

  (T ) 
 Y0 0 
 ln(1  34 pre )
(8)
pre
 T0
(T0 )  T0 (T0 )  750 pre
(9)
Fig. 5 compares the yield strengths measured and estimated by the above formulae for the structural steels of 400
MPa to 780 MPa strength class, the weld metal of 590 MPa strength class and the simulated CGHAZ. A good
accuracy of these formulae can be recognized.
Fig. 5. Comparison between tensile properties measured and estimated
under pre-strained and dynamic loading conditions.
Fig. 6. Equivalent CTOD ratio, β, for toughness correction
for constraint loss in structural component.
3.5. Equivalent CTOD ratio, β
Most components in steel frame structures are subjected to tension, which leads to a constraint loss in a crack
region. By contrast, fracture toughness specimens are in bend mode, holding highly constrained state near the crack
F. Minami et al. / Procedia Structural Integrity 2 (2016) 1561–1568
Minami, F., et al./ Structural Integrity Procedia 00 (2016) 000–000
1566
6
tip. In order to correct the CTOD toughness for constraint loss, an equivalent CTOD concept was proposed by
Minami et al. (1999) on the basis of the Beremin model (1983). The equivalent CTOD ratio, β, is defined as
   /  struc
(10)
where δ and δstruc are CTODs of the standard fracture toughness specimen and the structural component,
respectively, at the same level of the Weibull stress (Fig. 6). The structural component at a CTOD level of δstruc and
the fracture toughness specimen at the CTOD level of β•δstruc are equivalent in terms of the Weibull stress. When the
CTOD fracture toughness, δcr, of the material is given, the constraint-corrected toughness for the component is
assigned as δcr, struc = δcr / β. Note that β is in the range, 0 < β < 1. Minami et al (2006) has standardized β in ISO
27306 for CSCP (center surface crack panel), CTCP (center surface crack panel), ESCP (edge surface crack panel)
and ETCP (edge through-thickness crack panel) subjected to tension.
The equivalent CTOD ratio, β, depends on the yield-to-tensile ratio RY = σ Y/σ T (σ Y: yield strength, σ T: tensile
strength) and the Weibull shape parameter m of the material; decreasing with increasing RY and m. WES 2808
specifies β with RY = 0.6 and m = 20 for steel components under seismic conditions. The low RY-value is selected in
consideration of the Baushinger effect during cyclic loading at the earthquake. The m = 20 is a lower-bound m-value
for structural steels with a moderate CTOD toughness of δcr > 0.05 mm. The use of a low RY-value along with a low
m-value leads to a conservative fracture assessment of the structural component. It is shown by Ohata et al. (2016)
that the beam-to-column component develops almost the same Weibull stress as the tension wide plate. Thereby
WES 2808 employs the equivalent CTOD ratios, β, for CSCP, ESCP and ETCP with RY = 0.6 and m = 20, which
are formulated by Eq. (11), Eq. (12) and Eq. (13), respectively.
 0.11 25 / t  (2c / 40)0.393

0.393
 CSCP(2c, t ) 
0.15 25 / t  (2c / 40)

0.393
0.20 25 / t  (2c / 40)
0.077 25 / t  (2c / 30)0.44

0.44
 ESCP(2c, t ) 
 0.11 25 / t  (2c / 30)

0.44
0.18 25 / t  (2c / 30)
 ETCP(2
0.2  (2a /11)0.745
a)
for a / t 
0.04
for a / t 
0.12
(11)
for a / t 
0.24
for a / t 
0.04
for a / t 
0.12
(12)
for a / t 
0.24
(13)
Note that Eq. (11) and Eq. (12) hold under a given crack depth ratio, a/t, where t is the plate thickness.
Eq. (12) and Eq. (13) give β for double-edge surface crack of length 2 × c and double-edge surface crack of depth
2 × a. In cases of single-edge surface crack (crack length c) and single-edge through-thickness crack (crack depth a),
the equivalent CTOD ratios are given in the form:
 ESCP(c, t ) (1/ 2)0.44   ESCP(2c, t ) 0.737  ESCP(2c, t )
(14)
 ETCP(a )   ETCP(2a ) / 2
(15)
Eq. (14) and Eq. (15) are based on the volumetric effect in the Weibull stress.
Fig. 7 shows the crack size dependence of β for CSCP, ESCP and ETCP provided by Eq. (11) to Eq. (13) with
the plate thickness of t = 25 mm. The β-value increases with the crack size, which is more significant for ETCP.
Minami et al. (2013) indicate that the β-solutions are applicable to components with a crack in welds. The strength
mismatch in welds may exert an influence on β. But the numerical results show that the strength mismatch effect on
β is marginal in the range, 0.9 < Sr = σ TW/σ TB < 1.5, where σ TW and σ TΒ are the tensile strengths of the weld metal
and base metal.
F. Minami et al. / Procedia Structural Integrity 2 (2016) 1561–1568
Minami, F., et al./ Structural Integrity Procedia 00 (2016) 000–000
0.5
 =  / WP
0.3
0.2
0.1
0
(a) CSCP (center surface crack) and ESCP (double-edge surface crack)
m = 20, RY = 0.6
ETCP
0.4
1567
7
0
5
10
15
20
25
30
Crack depth, 2a (mm)
35
(b) ETCP (double-edge through-thickness crack)
Fig. 7. Crack size dependence of the equivalent CTOD ratio, β.
3.6. Correlation between CTOD fracture toughness and Charpy absorbed energy
In those cases where the CTOD fracture toughness data are not available, the CTOD toughness may be estimated
from the Charpy impact energy. WES 2805 presents the correlation between the CTOD fracture toughness, δcr [mm],
and the Charpy energy, vE [J], in the form:
)
 cr (T 
1
vE (T  T ), T 87  0.10 Y0 (T0 )  6 t
250
(16)
where vE (T + ΔT ) is the Charpy energy [J] at the temperature of T + ΔT, σY0(T0) is the yield strength [MPa] at the
room temperature T0 and t is the plate thickness [mm] (= thickness of CTOD toughness specimen). Eq. (16) is
applicable to structural steels with tensile strengths of 400 MPa to 780 MPa. Extended work by Yamaguchi et al.
(2016) confirms that Eq. (16) is applicable also to the heat-affected zone of the structural steel. Hence, WES 2808
adopts Eq. (16) for the estimation of the CTOD fracture toughness.
4. Fracture assessment procedure
The procedure in WES 2808 for the fracture assessment of steel components under seismic conditions is given as
follows:
1) Input the pre-strain εpre defined in Fig. 1 and the strain rate e in the target area of the component.
2) Estimate the local pre-strain, ε pre, local, and the local strain rate, e local, by Eq. (2).
3) Estimate the flow stress elevation, Δσ f PD = (Δσ Y +Δσ T) /2, by the local pre-strain, ε pre, local, and local strain rate,
e local, at the service temperature T of the component. The increases in the yield and tensile strengths, Δσ Y and
Δσ T, are given as Δσ Y = σ Y(εpre, local, e local, T ) – σ Y0(T ) and Δσ T = σ T(εpre, local, e local, T ) – σ T0(T ), respectively,
with Eq. (4) to Eq. (9), depending on the strength class of the steel.
4) Determine the temperature shift, ΔTPD, by Eq. (3) from the flow stress elevation, Δσ f PD.
5) Employ the CTOD fracture toughness, δcr (T–ΔTPD), at the reference temperature of T–ΔTPD.
6) Determine the equivalent CTOD ratio, β, for the component with Eq. (11) to Eq. (15), depending on the crack
type.
7) Correct the CTOD fracture toughness for constraint loss to lead to δcr, struc (T ) = δcr (T–ΔTPD) / β.
8) Get the local strain, ef, local, at fracture of the component by substituting δcr struc (T ) into Eq. (1).
9) Convert the fracture local strain, ef, local, to the fracture global strain, ef, of the component: ef = ef, local / Kε.
1568
8
F. Minami et al. / Procedia Structural Integrity 2 (2016) 1561–1568
Minami, F., et al./ Structural Integrity Procedia 00 (2016) 000–000
5. Summary
The fracture assessment standard, WES 2808, was developed in JWES for assessing brittle fracture of steel frame
structures subjected to large cyclic and dynamic loading at the earthquake. WES 2808 is characterized by two
unique ideas: 1) a reference temperature concept for the fracture toughness evaluation under seismic conditions and
2) the equivalent CTOD ratio, β, for correction of the CTOD toughness for constraint loss in structural components.
Shimada et al. (2016), Igi et al. (2016), Yamaguchi et al. (2016) and Ohata et al. (2016) describe the details of the
fracture assessment procedure. Takashima et al. (2016) demonstrates a good agreement between the fracture strains
of beam-to-column subassemblies measured and estimated by WES 2808.
References
APD Committee, The Japan Welding Engineering Society: Strength and Fracture Toughness of Weld Connections in Steel Framed Structures,
Seminar on Seismic Damage to Steel Framed Structures 1997, JWES-IS-9701, 47-192 (in Japanese).
Bennett, P. E., Sinclair, G. M., 1966. Parameter Representation of Low-Temperature Yield Behavior of Body-Centered Cubic Transition Metals.
Journal of Basic Engineering 88, 518-524.
Beremin, F. M., 1983. A Local Criterion for Cleavage Fracture of a Nuclear Pressure Vessel Steel. Metallurgical Transactions 14A, 2277-2287.
Hashida, T., Fujihira, S., Morikawa, J., Minami, F., Toyoda, M., 1998. Fracture Toughness and Mechanical Properties of Beam-to-Column
Connections of Steel Framed Structures Damaged in Hyogoken-Nambu Earthquake. International Conference on Welded Constructions in
Seismic Areas. Maui, Hawaii, USA, 212-225.
Igi, S., Shimada, H., Kinefuchi, M., Minami, F., 2016. WES 2808 for Brittle Fracture Assessment of Steel Components under Seismic Conditions
– Part III: Change in CTOD Fracture Toughness of Structural Steels by Pre-Strain and Dynamic Loading. Structural Integrity Procedia, to be
published.
Kubo, T., Igi, S., Handa, T., Suzuki, N., Toyoda, M., Ohata, M., Minami, F., 2007. Application of WES 2808 to Brittle Fracture Assessment for
High Strength Gas Pipelines. 26th International Conference on Offshore Mechanics and Arctic Engineering. San Diego, California, USA,
paper OMAE2007-29246.
Miki, T., Sato, Y., Nakashima, M., Sugaya, M., Suita, K., Hokoi, S., Harada, K., 2001. Full-Scale Dynamic Loading Test on Plastic Deformation,
Thermal Energy and Temperature Rise of Welded Steel Beam-to-Column Connections. Summaries of Technical Papers of Annual Meeting,
Architectural Institute of Japan, C-1, Structures III, Timber Structures, Steel Structures, Steel Reinforced Concrete Structures, 887-892. (in
Japanese)
Minami, F., Katou, T., Nakamutra, T., Arimochi, K., 1999. Evaluation of Fracture Toughness Results and Transferability to Fracture Assessment
of Welded Joints. 18th International Conference on Offshore Mechanics and Arctic Engineering. St. John’s, Newfoundland, Canada, paper
OMAE/MAT-2130.
Minami. F., Arimochi, K., 2001. Evaluation of Pre-Straining and Dynamic Loading Effects on the Fracture Toughness of Structural Steels by the
Local Approach. Journal of Pressure Vessel Technology 123, 362-372.
Minami, F., Ohata, M., Shimanuki, H., Handa, T., Igi, S., Kurihara, M., Kawabata, T., Yamashita, Y., Tagawa,T., Hagihara, Y., 2006. Method of
Constraint Correction of CTOD Fracture Toughness for Fracture Assessment of Steel Components. Engineering Fracture Mechanics 73,
1996-2020.
Minami, F., Ohata, M., 2007. Fracture Mechanics Assessment of Beam-to-Column Joints Subjected to Cyclic and Dynamic Loading. Welding in
the World 51, 22-33.
Minami, F., Ohata, M., Watanabe, D., 2008. Fracture Assessment Procedure for Structural Components under Cyclic and Dynamic Loading.
International Journal of Offshore and Polar Engineering 18, 196-203.
Minami, F., Takashima, Y., Ohata, M., Yamashita, Y., 2013. Constraint-Based Assessment of Fracture in Welded Components. Welding in the
World 57, 707-718.
Nakagomi, T., Yamada, T., Hisada, S., Okabayashi, I., 1995. Experimental Study on the Fracture Behavior under Cyclic Plastic Strain and the
Worsen Properties of SM 490A. Journal of Construction Steel 3, 387-394 (in Japanese).
Newman, Jr. J. C., Raju I.S., 1984. Stress Intensity Equations for Cracks in Three-Dimensional Finite Bodies Subjected to Tension and Bending
Loads, NASA Technical Memorandum 85793.
Ohata, M., Takashima, Y., Minami, F., 2016. WES 2808 for Brittle Fracture Assessment of Steel Components under Seismic Conditions – Part V:
Equivalent CTOD Ratio for Correction of Constraint Loss in Beam-to Column Connections. Structural Integrity Procedia, to be published.
Shimada, H., Shimanuki, H., Igi, S., Minami, F., 2016. WES 2808 for Brittle Fracture Assessment of Steel Components under Seismic
Conditions – Part II: Change in Mechanical Properties of Structural Steels by Pre-Strain and Dynamic Loading. Structural Integrity Procedia,
to be published.
Takashima, Y., Ohata, M., Ishii, T., Hagihara, Y., Minami, F., 2016. WES 2808 for Brittle Fracture Assessment of Steel Components under
Seismic Conditions – Part VI: Application of WES 2808 to Beam-to-Column Connections. Structural Integrity Procedia, to be published.
Toyoda, M., 1995. How Structures Fared in Japan’s Great Earthquake. Welding Journal 74, 31-42.
Yamaguchi, T., Kinefuchi, M., Igi, S., Shimada, H., Takashima, Y., Minami, F., 2016. WES 2808 for Brittle Fracture Assessment of Steel
Components under Seismic Conditions – Part IV: Change in Mechanical Properties and Fracture Toughness of Steel Weld HAZ by Pre-Strain.
Structural Integrity Procedia, to be published.