Novel synthesis of calix[n]arene amidoazobenzene derivatives

Article abstract of DOI:10.1179/174329306X77894

A series of calix[n]arenas and calix[4]resorciarenes containing azo chromophores on the lower rim were synthesised with two routes. The first direct route involved alkylating calixarenes with 4-chloroacetoaminoazobenzene. The second indirect route was by acylating 4-aminoazobenzene with calix[n]arylacetyl chloride. Their extracting abilities for transition metal ions were tested.

Full text of DOI:10.1179/174329306X77894

Effect of dynamic loading on ductile crack
initiation behaviour of notched specimen with
strength mismatch
G.-B. An*1, M. Ohata2, J.-U. Park3 and M. Toyoda2
The present study focuses on the effects of a geometrical discontinuity, strength mismatching,
which can increase plastic constraint due to heterogeneous plastic straining, and the loading rate
on the critical condition for ductile fracture initiation using a two-parameter criterion based on
equivalent plastic strain and stress triaxiality. Fracture initiation testing was conducted under
dynamic loading using circumferentially notched bend specimens. In order to evaluate the
condition for the ductile crack initiation state in the specimens, a thermal elastic/plastic dynamic
finite element analysis considering the temperature increase due to plastic deformation was
performed. The two-parameter criterion was shown to be applicable to ductile cracking from the
surface of the prenotched root in the strength mismatched specimen under dynamic bend loading.
Keywords: Ductile crack initiation, Dynamic loading, Plastic constraint, Strength mismatch, Stress triaxiality
strength mismatch leads to more plastic constraints in
the lower strength regions,5–7 it can be assumed that the
ductile fracture initiation behaviour is also influenced by
Introduction
Brittle failure of high toughness steel structures tends to
occur after ductile crack initiation/propagation. An
strength mismatch. In addition, it has been reported that
example is the damage to steel structures in the
Hanshin Great Earthquake in Japan.1–3 Several brittle
dynamic loading,8 and the strain rate effect on mechan-
the mechanical properties of steels change under
failures were observed in the beam-to-column connec-
tion zones, which have geometrical discontinuity. In
some of these zones, brittle fractures occurred after large
ical properties also depends on the strength level of
steel.9
The present study focuses on fundamentally clarifying
scale plastic deformation associated with ductile crack
the effect of the loading rate on the critical conditions
initiation and extension from stress–strain concentra-
for initiating ductile fracture from the notch root with
tors. This earthquake, in particular, led to brittle
strength mismatch. The behaviour of ductile crack
failures of steel structures under high speed ground
initiation from the prenotched root of Charpy type
motion (104 cm s21) and significantly large ground
specimens with the strength mismatch effect of dynamic
displacement (27 cm).
loading was investigated by bending tests. Moreover, in
The integrity of steel framed structures under earth-
order to evaluate the ductile crack initiation behaviour
quake induced large scale deformation and a high speed
in the specimens under dynamic loading, thermal elastic/
loading rate can be evaluated by estimating ductile crack
plastic dynamic finite element (FE) analyses, considering
initiation and propagation, followed by brittle fracture.
the temperature rise due to adiabatic plastic deforma-
Based on ductile crack initiation behaviour, the ductile
tion, were carried out. Finally, it is shown that the
cracking controlling mechanical parameters can be
condition for ductile crack initiation using the two
expressed in terms of two parameters, i.e. equivalent
parameters of equivalent plastic strain and stress
ꢀ
plastic strain ep and stress triaxiality sm=sꢀ (sm5mean
triaxiality can be
evaluation of ductile crack initiation from the surface
of a prenotched root.
a transferable criterion for the
stress, sꢀ 5Von Mises equivalent stress).4 Ductile crack
initiation has been shown in experiments using circum-
ferentially notched bend specimens. A welded joint in a
steel structure exhibits not only geometrical heterogene-
ity, but also strength mismatching. As the existence of
Criterion for ductile crack initiation from
prenotched root surfaces and the effect
of strength mismatching and dynamic
loading
1Institute of Industrial Technology, Welding Research Part, Geoje
Shipyard, Samsung Heavy Industries Co., Ltd., 530, Jangpyung-Ri,
Sinhyun-Up, Geoje, Gyeongsangnam-Do 656-710, Korea
2Department of Manufacturing Science, Graduate School of Engineering,
Osaka University, 2-1, Yamada-oka, Suita, Osaka 565-0871, Japan
3Department of Civil Engineering, Chosun University, 375, Seosek-dong,
Dong-Gu, Gwangju, 501-759, Korea
The critical condition for the formation of ductile cracks
from the surface of a prenotched root was estimated by
using Charpy type bend specimens with a sharp V-type
notch under dynamic loading. Also, the effect of
*Corresponding author, email gyubaek.an@samsung.com
ß 2006 Institute of Materials, Minerals and Mining
Published by Maney on behalf of the Institute
Received 25 February 2005; accepted 15 September 2005
DOI 10.1179/174329306X77894
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An et el. Effect of dynamic loading on ductile crack initiation behaviour
1
Vickers hardness distribution of welded joint
strength mismatching near the prenotched root on
ductile crack initiation was investigated.
mismatch were investigated using a Charpy type bend
specimen. Figure 2 presents the configurations of two
types of three-point bend test specimens used. One is a
strength mismatched specimen in which a notch tip is
located at the fusion line of a welded joint, while the
other is a homogeneous specimen with a notch in the
centre of the weld metal.
The three-point bending test was carried out by using
the servohydraulic high loading rate bending test
machine on the homogeneous and mismatched Charpy
Three-point bending test
The strength mismatch welded joint was made by
electrogas welding using a welding wire for 500 MPa
class steel and a 22 mm thick HT80 steel plate as the
base metal. The chemical compositions of the base metal
and mechanical properties of the weld metal and base
metal are shown in Tables 1 and 2, respectively. This
welded joint is a strength mismatch joint with strength
ratio of yield stress (Sr(Y)) and tensile strength (Sr(T))
type specimens with
a sharp V-type notch (R5
.
0 25 mm). The bending tests were carried out at a
crosshead displacement speed of 10 mm s–1. To clarify
the load levels of ductile crack initiation from the surface
of the prenotched root, unloading tests were carried out
at various loading levels before failure. After loading,
each specimen was cut longitudinally through its centre.
One side of the specimen was used for observing crack
.
.
of approximately 1 7 and 1 3, respectively. A micro-
graph of the joint and the Vickers hardness distribution
near the welded joint in the thick central part of the plate
are shown in Fig. 1.
The characteristics of ductile crack initiation from the
surface of a prenotched root and the effects of strength
Table 1 Chemical composition of base metal (HT80 steel) used
Steel
C
Si
Mn
P
S
Cu
Cr
Mo
V
Ti
Nb
Al
Ni
B
Ceq
Pcm
.
.
.
.
.
.
.
.
.
.
HT80 0 10 0 26 0 85 0 004 0 002 0 23 0 49 0 47 0 037 0 016 0 011 0 046 1 16 0 0012 0 50 0 25
.
.
.
.
.
.
Ceq5CzMn/6z(CrzMozV)/5z(CuzN)/15
Pcm5CzSi/30zMn/20zCu/20zNi/60zCr/20zMo/15zV/10z5B
Table 2 Mechanical properties of weld metal and base metal used
Material
sY, MPa
sT, MPa
YR
Sr (Y)
Sr (T)
eT, %
EL, %
.
.
.
.
Base metal (BM)
Weld metal (WM)
846
509
887
672
96
76
1 67
1 31
6 0
30 8
.
1 67
.
1 31
.
11 4
.
32 0
sY5lower yield stress, sT5tensile strength, YR5yield-to-tensile ratio (sY/sT), eT5uniform elongation, EL5elongation (gage length5
WM
12 mm, diameter56 mm), Sr(Y)5sYBM/sYWM, Sr(T)5sTBM/sT
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An et el. Effect of dynamic loading on ductile crack initiation behaviour
2
Geometry and size of a three-point bend specimen
initiation behaviour, while the other side was subjected
to brittle fracture using liquid nitrogen, to compare the
ductile fracture surface characteristics according to
ductile crack initiation.
Influence of the strength mismatching on
ductile crack initiation behaviour under dynamic
loading
Figures 3 and 4 show the relationship between load P
and displacement of crosshead Dy, and the SEM
observation results near the prenotched root tip at the
middle section of homogeneous and mismatched speci-
mens under dynamic loading. Ductile crack initiation
behaviour, i.e. initiation from the prenotched root
surface along the shear band in the weld metal, was
the same as that for the static load.10 In addition, Fig. 5
shows the comparison of the ductile crack initiation at
level 1 in Fig. 3 with the fracture surface, which showed
brittle fracture resulting from the use of liquid nitrogen
after unloading level 1. The dimple was observed near
the prenotched root in the fracture surface. Also, these
results are very similar to those of homogeneous
specimens under dynamic loading. No significant
difference is observed in the ductile crack initiation
behaviour between homogeneous and mismatched speci-
mens under dynamic loading.
(a)
Applicability of two-parameter criterion
effect of dynamic loading with strength
mismatched specimens
b
c
The dependence of triaxial stress state on ductile crack
initiation in materials has been widely expressed by
using two parameters, equivalent plastic strain and stress
triaxiality.4
a P–D curves; b at level 1; c at level 2
Ductile crack initiation behaviour of mismatched speci-
mens under dynamic loading
3
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An et el. Effect of dynamic loading on ductile crack initiation behaviour
Numerical analysis
The coupled heat conduction and elastic/plastic dynamic
FE analyses were used for analysing the stress–strain
behaviours of homogeneous and mismatched specimens.
Figure 6 shows the mesh division used in these analyses.
The geometry and dimensions of the bend models are
the same as those used in the bend test.
The most important aspect in analysis is employing
the proper material constitutive equation, especially for
a dynamic loaded specimen which produces a tempera-
ture rise during the loading. The authors have suggested
a simple and correct method for analysing the stress–
strain state at a local area in the specimen at current
temperature and strain rate during dynamic loading.11
This method is based on using the so-called strain rate–
temperature parameter R,12,13 which was originally
proposed for the characterisation of the effect of strain
rate and test temperature on yield stress sY.14 The tensile
strength sT is also characterised by using the modified R
parameter, taking into account the temperature rise DT,
which is generated by adiabatic plastic strain up to the
applied stress sT, since the stress sT obtained with tensile
testing under dynamic loading cannot be the stress at the
initial specimen temperature.15 The modified R para-
meter used is defined as follows
(a)
R~(TzDT) ln (A=e)
(1)
where e is strain rate, T is test temperature (initial
specimen temperature), DT is temperature rise, and A is
material constant. The FE analysis taking into account
heat generation and conduction was carried out using
the finite element code ABAQUS version 5.8.16 In this
coupled thermal elastic/plastic FE analysis, 90% of the
plastic work generated was assumed to be converted into
heat, causing a temperature rise.17–19 The physical
properties shown in Table 3 were used for heat
conduction and thermal stress analysis.
b
c
a P–D curves; b at level 1; c at level 2
4
Ductile crack initiation behaviour of homogeneous
specimens under dynamic loading
5
Fractography near the ductile crack initiation region and brittle fracture region in mismatch specimen under dynamic
loading
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An et el. Effect of dynamic loading on ductile crack initiation behaviour
6
Mesh division of a three-point bend specimen used for FE analysis
initiation for the surface of the prenotched root as the
maximum strain element for homogeneous and strength
mismatched specimens under dynamic bend loading.
Strength mismatching did not affect the history of the
ꢀ
ep{sm=sꢀ relation. In addition, the critical value of the
strength mismatched specimen was also slightly lower
than that of the homogeneous specimen. However, the
criterion was expressed as the critical value of a
homogeneous round bar tensile specimen. Conse-
quently, by conducting the coupled heat conduction
and elastic/plastic FE analyses, the two-parameter crite-
rion can be shown to be applicable to the ductile crack-
ing initiation from the surface of a prenotched root in
the strength mismatched specimen under dynamic
loading. The results would be in accordance with the
constant plastic strain condition of a surface cracking
type of specimen.
Discussion
The strength mismatch cannot affect the change of
failure mode but only the change of plastic constraint,
which leads to different stress triaxiality when the
loading mode is single bend. This result enables us to
estimate the ductile crack initiation for strength mis-
match specimens by using the two parameter criterion. It
was found that the dynamic loading in single bend which
produces the change of local strain rate also gave the
same ductile crack criterion.
7
Condition for ductile crack initiation using the two
parameters equivalent plastic strain and stress
e
¯
p
triaxiality s /s, for homogeneous and mismatched spe-
¯
m
cimens under dynamic loading
Effect of dynamic loading on the critical
conditions for ductile crack initiation of
specimen with strength mismatch
The effect of dynamic loading on the critical condition
for ductile crack initiation of mismatch specimens was
investigated by carrying out FE analyses.
Figure 7 shows the history of the equivalent plastic
strain and stress triaxiality relationship at ductile crack
Conclusions
The transferability of local mechanical conditions for
ductile cracking was examined in this study by investigat-
ing two parameters, i.e. equivalent plastic strain and
Table 3 Material constants used for coupled thermal elastic/plastic FE analysis
Material
E, MPa
n
c, J kg–1 K21
r, kg mm23
k, m2 s21
b, K21
Base metal (BM)
Weld metal (WM)
2
26
25
25
.
0 3
.
.
.
.
206
4 8610
8 0610
2 17610
1 2610
E5Young’s modulus, n5Poisson’s ratio, c5specific heat, r5density, k5heat conductivity, b5coefficient of heat.
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An et el. Effect of dynamic loading on ductile crack initiation behaviour
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with a prenotched root and under dynamic loading. The
two parameter criterion was shown to be applicable to
ductile cracking from the surface of the prenotched root
in the strength mismatched specimen under dynamic
bend loading based on the results obtained from
conducting coupled heat conduction and elastic/plastic
FE analyses considering the temperature rise. The results
were in accordance with the constant plastic strain
condition of surface cracking type specimens.
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