21 st International Conference on Composite Materials
Xi'an, 20-25th August 2017TENSILE PROPERTIES OF FRP PLY SPLICE STRUCTURES
1

1

2

Dingding Chen , Manyi Wang , Yueyao Shen and Kazuo Arakawa3
1 College of Basic Education, National University of Defense Technology, China.
Keywords: fiber reinforced composites, Ply splice, Tensile property

ABSTRACT
When the FRP structure becomes large, it is required to splice two or more plies to meet the size
requirement. In order to understand the mechanical property of the FRP ply splice structure and getstrong ply splice structures, the tensile properties of three kinds of unidirectional CFRP ply splicestructures have been tested in the previous work in [1]. In this paper, another two structures were
designed based on the S1 structure in [1], in order to improve the strength of this type of the ply splicestructure. Compared with the S1 structure, the difference of the S1-1 structure was that the spliced
point of each ply was optimized to extend the distance between the nearest spliced points. In the S1-2
structure, additional two carbon fiber fabrics were attached on each side of the S1-1 structure to
restrain the bending of the specimen under a tensile load to improve the tensile strength. The results
show that there is no big difference of the tensile strength between S1 and S1-1 structures, however,S1-2 really performs much higher tensile strength.
1

INTRODUCTION

Due to high strength and low density, fiber reinforced plastics (FRP) have been used widely, and
FRP structures with large size are required by more and more applications. When the FRP structure
becomes large, only one reinforcement ply may not large enough. In the previous work [1], the tensile
properties of three kinds of unidirectional CFRP ply splice structures were studied. The results show
that, inducing ply splices into CFRP materials, the tensile strength decreases evidently. Due to the ply
splice, stress concentrations occur, and the initial fracture happen�in the ply splice position, leading to
the final fracture on the interfaces between different plies. The interlaminar shear stress and the tensilestress in the through-thickness direction near the ply splice position are the key factors leading to theinitial failure. In this paper, some improvements were made based on one of the three ply splicestructures, expecting to get higher strength.
2 EXPERIMENTS
Two kinds of CFRP plates with ply splice structures were made through vacuum assisted resintransfer molding (VaRTM) process. As shown in Figure 1, the black line represents the unidirectional
carbon fiber fabric, TENAX STS from Saeertex GmbH . The matrix was XNR/H6815 epoxy resin
from Nagase. Four fabrics were adopted in each kind of specimens. The thickness of all the specimens
is about 2 mm. The fiber volume content is about 55%.
The S1 specimen is the structure in [1]. S1-1 was modified from S1. The splice points on the first
and the fourth ply were changed, in order to extend the distance between the splice points on the first(or the second) and the third ply (or the fourth). Based on S1-1, additional two carbon fiber fabrics
were attached on each side of it, getting S1-2 specimens.
Static tensile tests were performed to evaluate the four joints. The dimensions of the specimens areshown in Figure 2; the length was 250 mm and the width was 10 mm. Two pairs of tabs made withglass fibre-reinforced plastic (GFRP) were used for each specimen to reduce stress concentrations. The
length of the tab was 50 mm. The crosshead speed was 1 mm/min. The tensile stress was along thefibre direction. At least four samples were tested to get the average tensile strength.

21st International Conference on Composite Materials
Xi'an, 20-25 th August 2017

Initial status

80. ls

97.7s

98.6s

Figure 5. Fracture evolution of S1-1 structure

Initial status

l 02:0s

I 02.9s

Figure 6. Fracture evolution of Sl-2 structure
Compared with the S 1 structure, the difference of S1-1 structure is that the spliced point of each ply
is optimized to extend the distance between the nearest spliced points. This modification may haveobvious positive effect on reducing the fiber direction tensile stress component of the stressconcentration in the vicinity of the spliced point, however, have almost no effect on the othercomponents. The previous work has shown that the tensile stress along the fiber direction is not the
key factor deciding the final strength, coinciding with the strength of the Sl-1 structure. In the Sl-2
structure, additional two carbon fiber fabrics were attached on each side of S1-1 structure to restrain
the bending of the specimen under a tensile load to improve the tensile strength. The results show that
this modification really can make the structure stronger.
4

CONCLUSIONSIn this paper, two structures were designed based on the Sl structure in [1] in order to improve thestrength of this type of the ply splice structure. Compared with the S1 structure, the difference of S1-1
structure was that the spliced point of each ply was optimized to extend the distance between thenearest spliced points. In S1-2 structure, additional two carbon fiber fabrics were attached on each sideof S1-1 structure to restrain the bending of the specimen under a tensile load to improve the tensile
strength. The results show that there is no big difference of the tensile strength between S1 and S1-1
structures, however, S1-2 really performs much higher tensile strength, coinciding with the analysis
and conclusions in [1].

First A. Author, Second B. Author and Third C. Author

ACKNOWLEDGEMENTS

This work was supported by the Natural Science Foundation of China (NSFC) [grant numbers
51503223] and the Collaborative Research Program of the Research Institute for Applied Mechanics,
Kyushu University.
[1]

REFERENCES

D. Chen, M. Wang, K. Arakawa, S. Jiang, K. Wu and Q. Hu, Tensile properties of FRP ply
splice structures, Acta Materiae Compositae Sinica, pp. 1-6.

Bending strength of CFRP laminated adhesive joints
fabricated by vacuum-assisted resin transfer molding
Mahmoud R. Abusreaa,b , Seung-Wook Hane , Kazuo Arakawa叫 Nak-Sam Choic*a Faculty of Engineering, Cairo University, Giza 12613, Egyptb Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Fukuoka 816-8580, Japanc Department of Mechanical Engineering, Hanyang University, Ansan 426-791, South Korea
d Research Institute for Applied Mechanics, Kyushu University, Fukuoka 816-8580, Japan

Abstract
The laminated joints in this work were an adhesive joint constructed using two dry carbon fiber halves. For the joints,
some improvements were introduced to enhance the bending strength performance: Stitching ofthe two halves together
by fiber bundles, and inserting extra carbon fiber covers in the joint connection. We studied three adhesive joints:
conventional basic laminated joint and the two improved laminated joints. All joint specimens were fabricated in ourlaboratory using vacuum-assisted resin transfer molding (VARTM) process. The joint performance was evaluated witha bending test, and was compared to the bending strength ofjointless carbon fiber reinforced plastic (CFRP) laminate.
Two acoustic emission (AE) sensors were placed on a specimen to monitor the fracture progresses during the test. The
improved laminated joints, stitched joint and multiple-covers-overlapped joint, showed enhanced bending strength andjoint efficiency as well. The improvement depended significantly on the number ofcarbon fiber layers. The maximum
increase in comparison to the jointless CFRP was 24% for stitched laminated joint of 5 layer laminates and 58% formultiple-overlapped joint of 6 layer laminates, respectively. Such high joint efficiency was due to carbon fiber
reinforcement effects in the joints that many carbon fibers supported the strength in advance ofreaching the maximum
load point as indicated by AE detection analysis.
Keywords- CFRP joints, vacuum-assisted resin transfer molding, bending strength, joint efficiency

1. Introduction
The use of carbon fiber remforced plastic (CFRP) composites in engineering structures has many advantages because
oftheir high mechanical performances such as high strength-to-weight and stiffness-to-weight ratios [1]. For this reason,
they have applied to heavy duty structures in aviation, space [2, 4], automotive [3], shipbuilding [4], and wind turbine[5]. These applications generally involve large-scale manufacturing, and the parts are made from smaller components
and are joined together. In this case the mechanical performance of such CFRP structures is highly dependent on theproperties ofthe joint parts.
Since composite joints work as crucial load-carrying elements their design and analysis is a key process in the large­
scale applications to accomplish light weight, low-cost and efficient composite structure integration [6]. There areconventional mechanical fasteners such as bolts, pins, and rivets to join CFRP structures [7]. These mechanical joints
are often prefe汀ed due to the conveniences that such fastening joints can be disassembled for repair and/or recycling[8]. However, drilling holes made for parts joining may induce localized damage in the composite due to stressconcentration when the joint is loaded. In contrast, adhesively bonded joints may have mechanical advantages better
than bolted joints because the reinforcing fibers are not cut, and thus the stresses are transmitted more homogeneously[9]. Besides, bonded joints can provide good structural integrity, low weight and high strength-to-weight ratios [10-12].
Nowadays adhesive composite joints are applied widely in many composite structures for aerospace, turbine, and ship
designs [13]. These engineering struc血res are subjected to combinations of static, fatigue and impact loadings. Not
only conventional single-lap [9], double-lap [14] and stepped [15] adhesive joints, but also improved adhesive joints
have been studied to improve the mechanical performance ofadhesive composite joints. For instance, Lobel et al. [16]enhanced tensile strength by introducing z-pinning into CFRP double-lap joints. Another approach for adhesive joint
improvement was reported by Mouritz et al. [17] who placed spiked metal sheets in the bond-line to facilitate
mechanical load transfer. Furthermore, stitching was a technique for reinforcing the laminated joint. Dransfield et al.
[18] and HeB et al. [19] clarified that the stitching enhanced the fracture toughness oflaminated composites under peelloading. Kim et al. [20] made some stepped-lap joints as a function ofthe number ofsteps, joint length, and edge angle
ofthe adherends, and showed a considerable improvement in the fatigue performance by increasing the number ofsteps

1

Table 1.

Detailed information of the carbon fabric [30]

Carbon fiber
designation

Style

TRK976PQ

UD

RW

IM

No of
filaments

12,000TensileTensilestrengthmodulus

mm

MPa

GPa

％

0.33

4,900

253

1.9

WeightDensityThickness

g/m2

g/cm3

317

1.82

Elongation

The laminated joints proposed in this work are a composite adhesive joint constructed of two mating dry carbon halves
which were stacked in a pre-determined order prior to the VARTM process [10-12] schematically shown in Fig.I.
Three joint types were adopted in this work. The adhesive joint constructed of only two mating dry carbon halves
was a basic original type (see BLJ of Fig. 2a). The joint length was 40 mm in the total specimen length of 80 mm.
The fiber volume fraction measured for the joints was approximately 62%. One improvement to this joint was madeby applying a stitching technique. Fig. 2b shows a stitched laminate joint (SLJ). We conducted stitching with carbon
bundles of the same carbon fiber type, which were applied perpendicular to the plane of the laminate [18-19]. Abusrea
and Arakawa [ 11] showed a weakened stepped joint in which stitching was applied; the tensile strength of the stitchedstepped joint was 26% lower. However, it showed improved tensile strength when the stitching was applied to the dry
carbon-to-dry carbon joint state. The other improvement was made by adding carbon fiber covers of 40 mm in length
which had been prepared beforehand by sectioning the carbon fiber layers. Each carbon fiber cover was put on thecontact region between the end parts of two mating d carbon fiber layers. After finishing the VARTM process [10,11]_ry
the inserted carbon fiber covers may reinforce the mterphase layer between the two overlapping carbon halves, andmay alleviate stress concentration at the fiber ends of carbon halves. This joint type is named as a multiple-covers­
overlapped laminate joint (MCLJ) (see Fig. 2c). We applied four different numbers of carbon fiber layers for all joints.
We chose 5, 6, 7 and 10 carbon fiber layers as these numbers were common in industry use. On the other hand for thebasic type of a laminated joint, two different cases were made: a normal .BLJ and a'shifted'basic laminated joint (S­BLJ). For the normal BLJ, the six and ten carbon fiber layers were stacked'co汀ectly'at their right positions; that is,there was no gap between the fiber ends (Fig. 2a). For S-BLJ, the five and seven carbon fiber layers were a bit shiftedto form a gap between the fiber ends (Fig. 2b). Because a shifted placement of carbon fiber layer may be conductedduring mold preparation for this kind of adhesive joint fabrication, the S-BLJ was used to examine the effects of such
shifting on the final product quality in terms of thickness variation, and on the mechanical performance in terms ofbending strength.

3

�

Before molding

1

I

匹匹

After molding

(a)

□三王号

→I f ,--4;c �士0

Before molding

.5 mm

(b)

Local thinning

Figure 3. Schematic drawing before and after molding for the (a) normal basic laminated joint (BLJ) and (b) shiftedlaminated joint (S-BLJ).

2.2. Mechanical testing with AE measurement

L.N

80

ー

p

tM一

ご

―.

にし

The nominal bending strength was measured [24] to evaluate the joints'mechanical performances. The cured CFRP
joints were sectioned to form specimens for the three-point bending tests, with the geometry shown in Fig. 4. Five
specimens were prepared for each test condition. The span (L) and the width (W) of the test specimens were 50mm and12.7mm, respectively. The thickness (t) of the joints was varied according to the joint types of Fig. I, and thus measured
for the individual joint type in advance of the tests. The thickness (to) of the unjointed part of the test specimens was
also measured. During the test, each specimen was monitored with AE measurement. The bending test was carried out
at room temperature with a universal testing machine (Zwick 250, Test Xpert, version 11) with a crosshead rate of 3
mm/min. Fracture processes were examined in real time using two AE sensors (micro30, Physical Acoustic Corp.),marked as S1 and S2, which were attached to the bending specimen using vacuum grease and mechanical fixture. The
two AE sensors were put 46 mm apart, each one is 23mm distant from the specimen center. They were placed in such
positions close to the joint ends. A two-channel AE detection system (MSTRAS 2001, Physical Acoustic Corp.) wasused to record the AE data, and the AE measurement conditions were a pre-amp of 40dB, a threshold level of 40 dB,
and a sampling rate of 4 MHz. The threshold was positioned at a comparatively high level so as to filter the noisy
sounds coming from other emission sources. A band-pass filter under software control (pass range frorp 1 kHz to 1
MHz) was used for signal gain at specific frequencies. Three AE parameters were investigated: amplitude, energy, andfrequency spectrum of AE signals. AE analysis may provide a way to identify and differentiate fracture sources [24,25].
Consistent with Yoon et al. [24], we ascertained that the distance between the sensor and the crack location was closeenough to measure the AE characteristics. Considering the attenuation problems at high frequencies, we focused
primarily on frequency bands below 400 kHz for verification of the fracture mechanisms. Fractographic analysis was
also performed on damaged specimen surface and/or the fracture surface through observation by optical and scanningelectron microscopy (SEM).

*All d1mens1ons 1n mm

Figure 14. Illustration of an adhesive joint specimen under the three-point bending test with acoustic emission (AE)monitoring.

5

2.3. Data reduction of the adhesive joints under the bending test
The maximum load taken during the bending test of Fig.4 is used to evaluate the mechanical performance of thecomposite adhesive joints. It is reasonable that the joint performance should be compared with the bending strength ofjointless original composite laminates. In this respect, the'nominal'bending strength cr1 for every joint type can becalculated using(1)

CJJ = 3PL/2Wt訊，

where P is the maximum load value obtained from the load-deflection curve of the respective joint types , L the span
length, W the specimen width, and to the thickness of the unjointed ligament part. The nominal bending strength
assumes that the adhesive joint has a thickness equal to the unjointed ligament part. However, the thicknesses of thecomposite adhesive joints are varied according to the adhesive joint types, and can bring about a large variety of actual
bending strength.

Thus a joint efficiency (TJ) for the various joint types is evaluated with reference to the bending

strength (era) of the jointless original composite laminate and can be determined by a simple equation
1}。

= (Jj/0:(2)

For S-BLJ, the nominal bending stress (cr2) on the surface at the thinned section of a joint specimen is given byび2 = 3Pb/Wtc2,(3)where b is the distance between the support roller and the thinned section, and tc the thickness of the thinned part.

3. Results and discussion
3.1. Thickness profile behaviors of the joint specimens

Table 2 shows thickness measurement data obtained for the normal BLJ. The average thicknesses were 1.83 and 3.04
mm for 6 and 10 layers, respectively. The minimum thickness and the maximum deviation were also measured forevaluating the product quality. The thickness deviation ranged to 2.8% for 6 layers and to 3.5% for 10 layers. For the
S-BLJ, the average thicknesses for 5 and 7 and layers were 1.46 and 2.02 mm, respectively as shown in Table 3.
The thickness deviation was as high as 23%. The low minimum thickness and the large deviation indicate a bad
quality that may lead to a weaker strength for the thinned part of the S-BLJ specimens. Several previous papers
mentioned that the thickness variation was one of the geometrical parameters that exerted a bad influence on theperformance of the adhesively bonded joints [41]. For example, a local thinning due to the thickness variation could
affect the stress concentration, the strain inhomogeneity as well as the crack initiation. Ribeiro et al. [42] calculated
the stress distributions along single lap adhesive joint to show a rapid increase in stress gradients around the overlap
edges.
Jensen et al. [43] showed a strain inhomogeneity reaching nearly 20% of the mean strain value incomposite laminates under a transverse load.
Figure 5 compares the specimen thickness profiles along the specimen lengthwise direction for the three kind of
joints ( normal BLJ, stitched BLJ and MCLJ) with the same 6 fabric layers, and also for an'ideal'6-layer jointless
CFRP. The stitched joints showed higher thickness deviation especially at the stitched sites. The thickness deviation
was about士0.45 mm. Much greater thickness increase at the joint part was observed for the MCLJ. The thickness at
the joint part along the joint length of 40 mm was measured to be 3.3 mm on average, which was almost twice thethickness of the jointless CFRP.

This was because the number of carbon fiber covers made additional thickness

exceeding the initial thickness of the adherend constructed of the original number of carbon fiber layers. This big
variation in the thickness appeared along the upper surface profile of the joint part because all carbon fiber layers
including the additional covers were placed on a rigid flat surface of the mold as illustrated in Figure 1c.

61000�� 800■ SCLJ■ NCLJ

i

ビ 600
ぢ

i=

』

且

400

頁 2

00

゜

Figure 6.

5 layers

6 layers

7 layers

10 layers

Bending strength results for normal basic laminated joint (BLJ) and shifted BLJ specimens

Such bending strength behaviors may be clarified on the basis of AE analysis in combination with microscopic
fractography. Figure 7 shows a typical bending stress curve versus time for normal BLJ specimen of 6 layers which
was recorded together with accompanying AE amplitudes. With increasing displacement the load began to increase
and then dropped down largely just after reaching the peak, and finally decreased very slowly. Low amplitude emission
occurred from the low level of load, whereas big amplitude emission began to be generated around 65% of the peakload, and then appeared intermittently until the peak load. High amplitudes may correspond to fiber breakages while
low amplitudes may arise from crackings in the resin and/or interface between fiber and matrix, as ascertained in ref.
[ 24,25]. In this sense it was confirmed that for normal BLJ some amount of reinforcing fibers were broken before
reaching the bending strength. However only low amplitudes arose with the rapid load drop just after the peak. After
finishing the large load drop, very high amplitudes were generated again, following a mild AE behavior.
Typical bending stress behavior for 5 layers S-BLJ specimens with accompanying AE amplitudes is shown in Fig.8.
Clear differences from the normal BLJ appeared in this figure. The peak load level for S-BLJ was a bit lower, andthe load drop proceeded in several steps and times. �ig amplitude emissions began to occur at quite high level of 90%
peak load prior to the peak, and sustained for a considerably long time with a slow decrease of load after the peak load.
This behavior shows that around the peak load the reinforcing fibers were broken in a very different process from thenormal BLJ. After passing such strong emission period, the load dropped down to around 50% of the peak load

8

1400
1200

Amplitude

90

1000

m dm yHP'apn:

puaa
s�u!
g#
oo
oo
w oo
尽I

―

100

―Bending stress

80

800
70
600
60

400

50

200

゜゜

Figure 7.

40

20

80

60

100

40

Time, sTypical bending stress curve versus time with accompanying AE amplitudes for normal BLJ specimen

constructed of6 fiber layers.

―

1200

Bending stress90―Amplitude

gp'apnindm v
0
0
0
6
7
8

!PUa9
S� ll
J
S IK ぶ Sa.l

1000

100

800
600
400
200

゜゜

50

20

40

60

80

100

120

140

160

40

Time, sFigure 8. Typical bending stress-time curve with accompanying AE amplitude for a S-BLJ specimenof 5 fiber layers.

Fractographs taken for the normal BLJ and S-BLJ were analyzed as shown in Figure 9. For the normal BLJ
specimen, a tensile bending fracture occurred along the center line ofthe specimen 20mm distant from the joint ends,
and it induced many fiber breakages as revealed in SEM observation (see Fig.9a). It is to be noted that the tensile
bending stress at the joint end ofthis specimen calculated by equation (3) approached only about 80% ofthe peak stressat the middle ofthe specimen. Shorter the distance ofthe joint end from the specimen center, larger the tensile stressarising at the joint end should be. Thus short joints can cause a fracture at the joint end because the joint ends have aweaker strength by lack ofreinforcing fibers, which may lead to a lower joint strength than the long joints used in thisstudy. In contrast, the S-BLJ showed a different failure behavior as confirmed by optical microscopic observation

(see Fig. 9b). A resin crack initiated at the joint end where the local thinning had been formed as exhibited in Table 3,
and proceeded in the loading period without observed fiber breakages along the laminate interface. This phenomenon
was also confirmed in accordance with the low amplitude distribution until about 90% the peak load as shown in Fig.8.
The S-BLJ can arouse a peak tensile stress at the bottom of the concaved part where the local thinned section was
located. For this stress analysis, a stress concentration effect should be considered on the basis of the measured notch
length a and the measured notch tip radius Pt by the equation:

Stress concentration factor (Kt)
= ;:9::i::l s;;;;; (���= [ 1 + 2
s

*長］

(4)

The values ofK1 for S-BLJ specimens of5 and 7 layers may be estimated as 1.34 and 1.45, respectively. The high stressvalues beyond the stress at the center of the joint specimen must have caused such crack initiation at the local thinned
position leading to a low bending strength of S-BLJ specimens. However many fiber breakages seemed to occur justaround the peak load in the process .of macroscopic delamination in the joint part, as indicated by the strong amplitude
emissions shown in Fig.8. It is thought that the collapse mechanism of S-BLJ specimens was significantly associatedwith not only the resin cracking and delamination in the loading stage but also the fractures of reinforcing fibers in the
joint.
Fracture mode detection using AE frequency analysis was performed in the entire loading stage. We classified the AEfeatures according to the fracture mode on the basis of the previous study results in which low spectral features below
160 kHz corresponded to the resin fractures, intermediate spectral features in the range of 160-240 kHz corresponded
to the matrix-fiber mixed fractures, while high spectral features above 240 kHz were associated with the fiber fractures[24,25].
Figures 10 shows percentage data of AE energy accumulated until just after the peak load point according to the above
mentioned frequency bands for all specimens. Different fracture behaviors were identified for the normal BLJ and S­
BLJ. It was found that for the normal BLJ the AE energy spectra occurred very mostly (85 ~ 90%) in the highfrequency band (f > 240 kHz). Thus, the dominant fracture mode was obviously the fiber breakages. On the other
hand, the S-BLJ showed that the resin crackings were in a considerable majority in the overall loading stage, because
a high fraction (50 ~ 65%) of the AE energy spectrum occurred in the low frequency band (f<160 kHz). A significant
portion (20~30%) of the fiber breakages was also shown in this joint, which should have arisen through thedelamination process in the joint part as confirmed with the strong emissions in Fig.8.

10

L.
N

一

80

―- �―�-'- ー＿—-三
•: y

国目

．---- =

(a)(b)

Figure 9. Typical optical microscopy and SEM micro graphs for the fracture of (a) normal BLJ with 6 layers and (b)S-BLJ with 5 layers

113.4. Bending strength and fracture processes of multiple-covers laminated joints
MCLJ achieved much higher nominal bending strength than the basic laminated joint. As shown in Fig.13 the MCLJ
with 6 layers had a bending strength of2.33 GPa, which represented the maximum bending performance among all thetested MCLJ types. The strength value indicated a drastic increase by 321% than the normal BLJ and a considerable
increase by 66% than the stitched BLJ. The other MCLJ with 10 layers showed a decreasing value of 1.29 MPa, stilllarger than the stitched BLJ. The increase in the bending strength for the MCLJ can be explained by simple stressanalysis: The insertion of seven extra carbon fiber covers as illustrated in Fig.2c made a thick laminated joint which
could work as a multiple-bonded double lap joint (DLJ). Because the MCLJ specimen was manufactured with the
VARTM method, the joint part smoothly changed to the thin ligament adherend by filling the resin to the comer
between the thick joint part and the thin adherend. The thickness ofthe joint part was almost twice as large as that of
the adherend. In this case the tensile stress at the bottom surface of the joint part is calculated to be one-fourth of thatfor the corresponding BLJ according to equation (1) under the same bending load. The macroscopic fracture shownin Fig.14 proceeded at the center line ofthe joint part, which was similarly observed also for the normal BLJ specimen(Fig.9). When the same material strength is assumed for both the BLJ and MCLJ, bending strength ofMCLJ should
be four times as large as that for BLJ, which agreed well with the above bending strength result about 4.21 times larger
than the BLJ. The small mismatch of the bending strength data between measurement and calculation might beconsidered due to the fluctuated deviation in the thickness ofthe joint part (see Fig.5).
On the other hand,the thickness change from the adherend to the joint part was measured as shown in Fig.5, whichshould induce a peak stress concentrated at the local site just where the joint began from the adherend. However all thefracture events only occurred in the middle ofthe joint part, which indicates that the peak stress at the boundary site of
the joint part did not reach the tensile strength of the MCLJ specimens. The peak stress site and the fracture initiation
might occur probably at the end ofthe joint part with decreasing the length ofMCLJ part in comparison to the test span.
In this case the bending strength mechanisms should be different on account ofthe fracture process arising at the joint
ends.
The macroscopic fracture along the center line ofthe joint part was similar for all the MCLJ specimens with various
layers adopted in this study. The MCLJs with 5, 7 and 10 layers showed lower bending strengths than the MCLJ with
6 layers. The low bending strength for the 5 layers joint might be predicted with the simple stress theory of equation(1) stated above for the 6 layers joint, in that the 5 layers joint had an average thickness larger by about 10% than that
expected from the normal layup thickness. The rather thicker 5 layers joint was due to the more resin infiltration in the
VARTM process than the 6 layers joint. However the decreasing bending strength of MCLJs with 7 and 10 layers
could not be clarified with the simple stress theory, but be attributed to a large defect formation in the thick layup joints.
For the 7 and 10 layers joint, extra fiber covers were inserted between the layers causing much thicker joint part which
could contain bigger voids during the VARTM process. The existence of critical large voids might induce an easy
fracture of the thick MCLJ. Figure 15 shows typical percentages of AE energy in the three frequency bands for
MCLJs with 5, 6, 7 and 10 layers. Most MCLJ specimens emitted a high percentage (60~ 98%) of AE energy in thehigh frequency band (>240 kHz). This represents that fiber breakages were very dominant in the fracture processuntil the peak load as confirmed again in the SEM observation of Fig.I 4. The bending strength behaviors of Fig.13
which largely depended on the thicknesses of MCLJs are considered to have been associated mainly with a fracture
procedure ofthe carbon fabric during the loading stage.
Joint efficiencies for all the types oflaminated adhesive joints were calculated using equation (2) in comparison
to the jointless CFRP laminates as summarized in Fig.16. The average bending strength of the jointless CFRP wasmeasured to be around !1500 MPc1;[Cl]. For normal BLJ, joints efficiencies were distributed in the range of 24% ~58%. For stitched LJ, the joint efficiency was the largest (124%) at the 5 layers joint, however the increasing layers
over 5 layers reduced significantly. Excellent joint efficiency exceeding 100% was also shown for the MCLJs with 5 ~7 layers. The best efficiency among all the joint types was obtained at the 6 layers MCLJ.

14

4. Conclusions
The laminated adhesive joints were made using VARTM process. Three types of laminated joints were studied:conventional basic laminated joint (BLJ), stitched laminated joint (S�J), and multiple-covers overlapped laminatedjoint (MCLJ). All joint specimens were tested under the three-pomts bending load to evaluate their strength
performances in terms of the nominal bending strength. For normal BLJ, increasing layers improved the bending
strength while a shifted layup formed a concave notch where larger number of layers caused weaker bending strength.
Acoustic emission analysis and fractographic observation confirmed that the fracture mode for the normal BLJ was
mainly fiber breakages prior to the maximum load point which dominated the bending strength mechanisms of normal
BLJ. The shifted layup in the joint caused the fracture initiation mode to be the resin cracking at the notch site. On
the other hand, stitched laminated joints (SLJs) showed much improved bending strength compared to the BLJ. The
SLJ with 5 layers showed excellent joint efficiency around 124%. The MCLJ achieved superior bending strength inwhich the joint efficiency for 5 ~ 7 layers joints exceeded 120%. The best efficiency among all the joint types was
obtained at the 6 layers MCLJ. It was confirmed by combined AE and microscopic analysis that fiber breakages werevery dominant, i.e. fiber reinforcement caused the superior bending strength for the two joint types of SLJ and MCLJ.
Consequently, stitching and multiple covers insertion reinforced clearly the adhesive joints, in which some optimal
layup thickness and surface profile perfectness formed by the VAR TM were required to show the be·st bending strength.

ACKNOWLEDGMENT
This work was partly supported by a research grant from the Japan Society for Promotion of Science(#JP26630496), and by the Collaborative Research Program of Research Institute for Applied Mechanics,
Kyushu University.

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[1].
[2].
[3].
[4].

[5].

[6].

[7].
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[30]. Mitsubishi Rayon CO.,LTD.,Profile Department, www.mrc.co.jp[31]. Zhao, T.,Palardy,G.,Villegas,I. F.,Rans,C.,Martinez,M.,& Benedictus,R. (2017). Mechanical behaviour ofthermoplastic composites spot-welded and mechanically fastened joints: A preliminary comparison. Composites Part
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Compos Mater, 38,2004; pp. 243—257

19Collaboration report
Frederic Mercier
SIMAP, France
My research is focused on the thin film fabrication with a special emphasis on
the development .of chemical vapor deposition-based techniques of nitrides. My work is
aimed at understanding the fundamental mechanisms that control the materials
deposition processes and the final properties. Development of oriented and epitaxial
thin films serve as a basis for fundamental understanding and for improved functional
properties.
Within this context, this research project is focused on Aluminium nitride(AlN), which is of technological importance for energy applications (UV-LED, laser
diodes and high power and temperature electronic device, energy harvesters). Despite
its strong potential, the scientific and technological difficulties hinder the developmentof this material. For example, the performance of white and UV-based AlN diodes islimited by the density of crystalline defects in the active layers of the devices. Such thedefects are generated during the material fabrication in a poorly controlled process.
The aim of the report is to understand the link between the process conditions
and the occurrence of defects (nucleation and multiplication) during the chemical vapor
deposition of AlN. Toward this objective, a first step has been reached by The Crystal
Growth Dynamics Section lab, who developed very recently a model that describes
defects generation in crystalline materials. Originally developed on silicon, then on GaN
at RIAM, I successfully extended it to AlN in order to understand the evolution of theplastic deformation during its crystal growth.

The aim of the proposal is to understand the link between the process

conditions and the occu汀ence of defects (nucleation and multiplication) during thechemical vapor deposition of AlN. Toward this objective, one step has been reached by

the SIMAP lab who developed a multiscale model of AlN deposition by CVD whichallows the quantification of local values like supersaturation. Another step has beenreached by the Crystal Growth Dynamics Section lab who developed very recently amodel that describes defects generation in crystalline materials, originally developed on
silicon, then on GaN. The aim of this project is to unify this two modeling approaches inorder to understand the evolution of the plastic deformation of AlN crystalline thin films

in the CVD process. We could discuss the details of growth mechanism by thecollaboration.

真空紫外光の高原に必須なAINの結晶成長に関する共同研究を行った。応
用力学研究所で従来開発されてきたシリコンや GaN の計算コ ー ドを用いてAlNの結晶成長を記述できるコ ー ド開発を共同で行った。その結果、AINの結晶成長の解析が可能となった。さらに、このコ ー ドをCVDに拡張するべく、今後とも共同研究を継続していく。

国際化推進共同研究概要

No.16
タイトル：

Computational and experimental analysis for marine renewable energy development.

研究代表者：

WAN, Decheng

所内世話人：

胡長洪

概要： 今年度の国際化推進共同研究「Computational and experimental analysis for marine renewableenergy development」に関して、共同研究・研究集会とも予定通り実施した。共同研究成果について、2編の国際学会論文を投稿し採択された。研究集会について、世話人が担当した特定研究の研究集会と共同開
催で、外国から9名、日本から約30名の参加者があり、海洋再生可能エネルギー開発に関する有意義な
国際研究集会となった。

Report for 2017 RIAM International Joint Research ProjectComputational and experimental analysis for marine renewableenergy development
PurposeMarine renewable energy devices are usually installed in a sea area where severe environmental conditions

have to be considered. On the other hand, cost control is strictly required for those devices in order to passeconomic evaluations. Therefore for successful design of those devices, accurate numerical methods as wellas efficient experimental methods are required to evaluate the hydro- and aerodynamic performance of thesedevices. This joint research project aims to provide an opportunity for researchers, especially younger

researchers in SJTU and RIAM, to exchange their knowhow on development of computational andexperimental tools for the purpose.

Research Plan
(1) Carry out collaborative research between SJTU and RIAM, in the area of advanced modeling of
unsteady hydrodynamic and aerodynamic forces interacting on offshore floating wind turbine, toprovide a benchmark for validation and comparison of various analytical, simulation and experimental
models on the study of the floating offshore wind turbine problem.

(2) Evaluate the system's responses of 6DOF motions, which are excited by both wave and wind undervarious conditions as well as the rotation of blades.

(3) Organize an international symposium in the end of each fiscal year, in which relative researchers will
present and discuss their research results

The members involved in this collaborative research are shown in the following table.
Researcher's NameLu ZouYang Huang
Makoto Sueyoshi

Name of University
or Institute
SJTU

Present Status or Grade(graduate students)
Professor

Representative person (CFD )SJTU

Lecturer

Co-researcher (CFD)

SJTU

SJTU

PhD student

RIAM

Cheng Liu

Assistant professor

RIAM

Changhong Hu

PosdocRIAM

Professor

Researcher role

Co-researcher (CFD)Summary of Collaboration Research
In 2017, one of the most critical factors in wind farm, the inter-turbine spacing has been studied by CFD
simulations. This parameter has a great influence on aerodynamic power output, wind speed deficit, lifetime, andwake vortex structure. Considering the uniform inflow conditions, the effects of inter-turbine spacing changing
from three to nine times of rotor diameter on aerodynamics for wind farms containing two NREL SMW baseline
wind turbines in tandem layout are analyzed using actuator line model and CFD method. The RANS equation
withk⑩ SST血bulence model was solved in the simulations conducted in the OpenFOAM. From the study, it isconcluded that the inter-turbine spacing has significant effects on the aerodynamic power and wake characteristics.
The aerodynamic power output of the downstream wind turbine exits sharp fluctuation before power output of thedownstream wind turbine is becoming steady. Furthermore, periodic oscillation whose period is about the
one-third of rotor rotating period can be also concluded from the study. Moreover,there is strong wake interaction
which will impact the aerodynamics for wind farms seriously.
Two international conference papers related to this joint research project in 2017are listed as follows.
1) Yong Ai, Decheng Wan, Changhong Hu, Effects of Inter-Turbines Spacing on Aerodynamics for Wind
Farms Based on Actuator Line Model,Proceedings of the Twenty-seven (2017) International Ocean andPolar Engineering Conference San Francisco, California,USA,June 25-30, 2017, pp. 3 86-394
2 ) Yang Huang, Decheng Wan, Changhong Hu, Coupled Aero-hydrodynamic Analysis on a Floating
Offshore Wind Turbine under Extreme Sea Conditions, Proceeqings of the Twenty-seven (2017)
International Ocean and Polar Engineering Conference San Francisco, California, USA, June 25-30,
2017, pp. 395-402
As a main event of this international joint research project,'International RlAM Symposium on Ocean
Renewable Energy Technologies and Related Computational and Experimental Researches'was held on
January 22-23, 2018. On the symposium, overseas scholars are invited to present their recent researches on
ocean renewable energy development.
The research budget provided for this international joint research has been used to support part of thetravel expenses of the following 5 scholars to attend the symposium.
1.

Decheng Wan, Professor, Shanghai Jiao Tong University, China

2.

Shiu-Wu Chau, Professor, National Taiwan University, Taiwan, R.O.C.

3.

Di Deng, PhD Student, Shanghai Jiao Tong University, China

4.

Yang Huang, PhD Student, Shanghai Jiao Tong University, China

5.

Xiao Wen, PhD Student, Shanghai Jiao Tong University, China

The program of the symposium is as follows.

PROGRAM
Date: January 22-23, 2018

Place: Meeting Room at 2nd Floor, RlAM, Kyushu University
22 January (Monday)
13:00 - 13:10

I Opening Address

Changhong Hu

Session 1
13:10 - 14:00

Yonghwan Kim (Seoul National University, Korea)
Invited Lecture
Statistical Probability Modeling of Deck Slamming on Offshore Structures

14:00 - 14:30

Xiao Wen, Decheng Wan (Shanghai Jiao Tong University, China)
Numerical Simulations of Sloshing Flows in an Elastic Tank by MPSFEM-SJTU Solver

14:30 - 15:00

Jin Huang, Bin Teng (Dalian University of Technology, China)
Numerical Simulation of Wave Slamming of Two-Dimensional Bodies

15:00 - 15:30

Coffee break

Session 2
15:30 - 16:00

Taiga Asaumi, Masashi Kashiwagi (Osaka University)
Cloaking of a Vertical Cylinder using Variable Bathymetry

16:00 - 16:30

D. Ohno, Y. Higo, H. Iwashita (Hiroshima University)
Hydrodynamics and Motions of a FOWT in the Low-Speed Current

16:30 - 17:00

lsshiki Hiroshi (Institute of Numerical Analysis)
Generation of Curvilinear Coordinates for Numerical Analysis

17:00 - 17:30

Patxi Garcia Novo, Yusaku Kyozuka (Nagasaki University)
Estimation of Tidal Peak Velocity by an Empirical Approach

18:00 - 20:00

Dinner Party

23 Januarv (Tuesdav)
Session 3
9:20 - 10:00

Shiu-Wu Chau (National Taiwan University, Taiwan, R.O.C.)
Invited Lecture
Wake Modeling of Wind Turbine Array in an Offshore Wind Farm

10:00 - 10:30

Yang Huang, Decheng Wan (Shanghai Jiao Tong University, China)
FOWT -UALM-SJTU Solver for Coupled Aero-hydrodynamic Interactions of OC3 Floating

Offshore Wind Turbine
10:30 - 11:00

Yi Zhang, Bin T eng (Dalian University of T echnology, China)
High-Frequency Wave Loads and Ringing of Offshore Structures

11:00 - 11:30

Dief Tarek (Kyushu University)
System Identification and Control Design for Kite Power System

11:30 - 12:00

Di Deng, Decheng Wan (Shanghai Jiao Tong University, China)
Numerical Study of Vortex-Induced Motions of a Semi-Submersible Platform in Different
Reduced Velocities and Current Headings

12:00 - 12:30.....................

Hongzhong Zhu (Kyushu University)
細

・疇'

-

Modelling and Attitude Control of a Shrouded Floating Offshore Wind Turbine with Hinged

Structure
12:30 - 12:40

Closing Address

Changhong Hu

国際化推進共同研究概要
No.17

タイトル：

Step dynamics on surfaces/interfaces of a crystal: atomic and mesoscopic scales

研究代表者： Theodore L. Einstein(Department of Physics, University of Maryland, USA)

所内世話人： 寒川義裕
実施期間：2017 年 10 月 19日""11 月 2日

デバイス品質の半導体薄膜を得るにはエピタキシャル成長表面における成長素過程、 特に
ステップダイナミクスを理解することが重要である。 本研究課題では、 先ず、 最近の研究成果およびこの研究分野の世界動向をセミナー 形式で発表し議論を行った。 セミナー 発表の内
容を次頁に記す。 次に、 共同研究者を含めて集中的な議論を行った。 ステップダイナミクス
に関する知識を深めるとともに、 引き続き共同研究を継続していくことを確認した。
Controlling step dynamics is an important ingredient to fabricate nano-scale structures on a substrate
to develop new types of devices to solve energy problems. We study the step dynamics associatedwith the step meandering and the macrostep formation connected to dynamic phenomena on a crystal
surface at the atomic scale. It is shown that the spatial periodicity of the step meandering depends on
the strength of the next-nearest-neighbor (NNN) interaction between unit constituents. The attractive
step-step interaction between NNN sites is shown to cause self-assembly of macrosteps at low
temperatures. The origin of these NNN interactions is also studied by first-principles calculations at
the atomic scale.

Water mass modification in the Japan Sea and East Asian marginal seas
Hong-Ryeol Shin (Kongju National University)
Tomoharu Senjyu (RIAM, Kyushu University)
Introduction
Water mass modification associated with global warming and climate change has beenreported from the East Asian marginal seas, such as the Okhotsk Sea, the Japan/East Sea, the East
China Sea, and the Yellow Sea. In this study, we studied the Japan/East Sea as a typical East Asian
marginal sea showing long-term trends of warming and decreasing concentration of dissolved oxygenin the abyssal layer. The warming of deep waters indicates a structural change of the Japan/East Sea.

However, relationship between the observed changes in the water mass structure and flow conditionin the deep layer is unknown. Therefore, we carried out deep flow observations and hydrographic
observations in the southern part of the Japan/East Sea.

Observations
The direct current observations using moored aco,ustic current meters of RIAM, Kyushu
University were carried out at the southern edge of the Yamato Basin, the southeastern Japan/East
Sea (Fig. 1). The mooring operations were conducted by TN Nagasaki Maru of Nagasaki University
in May and October, 2016. Hydrographic observations with CTD were also carried out in the samecruise. These current meters were recovered on May 10, 2017 using T/V Nagasaki Maru.

Results and Discussion
The stick diagrams of flows at Sta. Y (37 ° 21'N, 135° 40'E) are shown in Fig. 2. In addition
to the mooring observation in this study, two times deep flow observations were carried out at thisstation in the depth range of 1800-1900 m: during the periods from May 2009 to May 2010 and fromMay 2010 to May 2011. Although, unfortunately, the record of current meter in this study was stopped

in January 2017 due to instrument trouble, our current meter successfully captured general featuresin the flow field, for example, prevailing eastward flow along the isobaths and several-days
fluctuation in flow speed and direction.
We here focus on the mean flows over the observation periods to investigate the long-term
variation in the deep flow field. The direction and speed of mean flows are ENE (100-1 l 0° T) andabout 5.6 cm s-1, respectively, in the all observations (Table 1). Furthermore, standard deviations ineach flow component are almost the same among the observations. This indicates that the conditionof mean flows in this area is near! y same between the periods of 2009-2011 and 2016-2017, though
the warming of deep water in the Yamato Basin is confirmed by some hydrographic observations.

In the eastern Japan Basin, the northern Jap血East Sea, a significant change in the mean
flow is reported (Senjyu, personal communication). To clarify the relationship between the long-termchanges in flow field and oceanic structure, we need more detailed observations.

37 30'

R16

3T20'

37 10'
135'10'135'40'135"30'135'20'Fig. 1 Map of observation site in 201615

10手Y09 (1800 m)

゜

5

-5

10

ー
ー

15

ー 15
5 10
--‘― `

MAY JUN JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY

I

2009

2010

>- 5

I- 0
(.) -5
0 -10
_J

u」-15

>

MAY JUN JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY

1510 J Y16 (1890 m)

I

2010

2011

゜

5

-5

-10
-15

MAY JUN JUL AUG SEP OCT NOV DEC I JAN FEB MAR APR MAY

2017

2016

Fig. 2 Stick diagrams of flows at Sta. Y.

Table 1 Direction and speed of mean flows and standard deviations of each component
PeriodY09 (1800m)
YlO (1900 m)
Y16 (1890 m)

Mean (cm s- 1 )Dir. ( 0 T)

Speed

E-W

110.9

5.65
5.62

5.52

106.4
102.2

5.63

5.40

5.25

―

N-S

-1.59
-1.20
-2.01

SD (cm s 1 )
N-S
E-W
3.55
4.44

4.39

2.55

2.45

3.45

国際化推進共同研究概要
No.19
タイトル：

ModeI inter-comparison study of I ong-range chemicaItransport modeI to have a better understanding of M
P 2.5
issue over East Asia

研究代表者：

Zifa WANG

所内世話人：

鵜野

実施期間：

2017年11月3日-11月8日、2018年3月13日-3月14日、

伊津志

概要：
2015年3月末から4月初めに北京市内で観測された黄砂と大気汚染粒子の混合状態の観測結果と、同期間を対象としたモデル解析結果をNatureScientific
Reportに論文として発表した。
中国華北平原から北京にかけて観測される高濃度のPM2.5汚染とその越境影
響について、野外観測結果の解析と複数の化学輸送モデルを用いた 相互比較実験の取りまとめを進め、2018年3月13日-3月 14日にアジア大気汚染研究センタ ー （新潟市）と共同で、日本 ・ 中国 ・ 韓国 ・ アメリカ合衆国・ベトナム ・タイなどからの約5 0名の研究者が参加するMICS - Asiaモデル相互比較国際
ワ ー クショップを九州大学筑紫キャンパスで開催する。

国際化推進共同研究概要

No.21
タイトル：

Dynamical mechanisms of stratospheric control on the tropical troposphere and ocean研究代表者：

Ueyama, Rei

所内世話人：

江口 菜穂

概要：

1990年代後半から現在における熱帯の大循環場の変化を気象デ ー タ（人工衛星、客観解析等）を用いて解析を行った。特にここ30年間で北半球夏季に南東太平洋の水温の低下がみられ、それは赤道をまたぐ南西風の強化、すなわち対流圏内の南北循環場(Hadley循環；HD循環）が北側ヘシフトしたことに起因することがわかった。さらにHD循環の強化が、近年の温室効果気体の増加による成層圏の寒冷化によって変詞をきたした成層圏の南北循環場(Brewer-Dobson循環）と関係することが示唆された。

Dynamical Mechanisms of Stratospheric Control on the Tropical Troposphere and Ocean
Rei Ueyama (NASA Ames Research Center)
I. Abstract
The cause of recent (from the mid to late 1990s) decadal variations in tropicalcirculation is studied by making use of a meteorological reanalysis dataset. Cooling of theequatorial southeastern Pacific Ocean occurred in association with enhanced cross­equatorial southerlies, which resulted from a strengthening and poleward shift of the risingbranch of the boreal summer Hadley circulation connected to the stratospheric Brewer­
Dobson circulation. From boreal summer to winter, the anomalous convective activity
center moves southward following the seasonal march to the equatorial Indian Ocean­
Maritime Continent region, which strengthens the surface easterlies over the equatorial
central Pacific. Accordingly, ocean surface cooling extends over the equatorial central
Pacific. We hypothesize that the fundamental factor causing the recent decadal change inthe tropical troposphere and the ocean is a poleward shift of the rising branch of thesummertime Hadley cell, which can result from a strengthening of extreme deep convection
penetrating into the tropical tropopause layer (TTL), in particular over the continents ofAfrica and Asia, and adjacent oceans. We conjecture that this effect is produced by a
combination of land surface warming due to increased CO2 and a reduction of static stability
in the tropical tropopause layer due to tropical stratospheric cooling.
II. Introduction
Large changes in tropical circulation occurred from the mid to late 1990s. These
include (i) a slowdown, or hiatus, of global warming in association with a decrease in thetropical eastern Pacific sea surface temperature (SST), UO the advancement of the onset of
the Asian summer monsoon, and (iiO an increase in precipitation in western Africa over the
Sahel and in southern Africa during the austral summer. Besides the large-scale circulation
changes, mesoscale phenomena such as an increase in the cyclone frequency and intensity
over the Arabian Sea were also reported. Wang et al. (2012) argued that these phenomena
are related to the early onset of the Asian summer monsoon. Several studies have also
shown a relationship between changes in the TTL and the tropical troposphere, namely
tropical cyclone activity in the Atlantic (Emanuel et al嘗， 2013) and the intensity of tropicalstorms and SSTs (Ramsay, 2013; Wang et al., 2014).
III. Method/Data
Datasets used in this study include JRASS reanalysis, JRASS-AMIP (which uses thesame model and boundary conditions as JRASS, but without assimilation of observational
data in the atmosphere), outgoing longwave radiation derived from High Resolution
Infrared Radiation Sounder, Global Precipitation Climatology Project precipitation, andCOBE-1 gridded SST.
IV. Results
Since the mid 1990s, equatorial ocean in the southern hemisphere has cooled inassociation with a strengthening of cross-equatorial southerlies near the surface. This was
induced by a northward shift of convective activity connected to the rising branch of the
Hadley circulation and the stratospheric Brewer-Dobson circulation. Water vapor
transport by the enhanced cross-equatorial southerlies further amplified the convective
activity in the northern hemisphere. An increase in the vertical velocity was most apparent

in the TTL,which may have been driven by the decreased stability in the TTL from the
combined effects of lower stratospheric cooling and upper tropospheric warming.
V. Discussion/Summary
We hypothesize that recent tropical circulation changes originate primarily from astrengthening of deep convective activity over the continents and their vicinity in thesummer hemisphere,particularly over the African-Asian sector. This working hypothesis
applies well during boreal summer and where a large land mass is located off the equator.
Further investigation is needed to determine whether the stratosphere is merely passively
responding to the tropospheric warming or playing an active role in the troposphericcirculation change.
To better understand the details of the stratosphere-troposphere coupling process,we will conduct case studies on the northward shift of convective activity similar to thatassociated with the recent trend,but associated with a sudden cooling of the tropicalstratosphere during a boreal sum,mer monsoon. The coupling process as depicted inconvective overshooting and cloud top data will be the topic of future work.
VI. List of Publications
Kodera, K., Eguchi, N.,Ueyama,R.,Kuroda,Y.,and Kobayashi,C.: Impact of tropical lower
stratospheric cooling on deep convective activity: (I) Recent trends in tropical circulation,
Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2018-128,in review,2018.
VII. Research workshops and seminar
Joint SPARC Dynamics & Observations Workshop: QBOi,FISAPS & SATIO-TCS
October 9-14,2017; Kyoto University, Kyoto,Japan
Program of the workshop,list of participants,and proceedings can be found at:
http://www-mete.kugi.kyoto-u.ac.jp/SPARCjws2017 /VIII. References
Emanuel, K,Solomon,S.,Folini,D.,Davis,S.,and Cagnazzo, C.: Influence of tropical
tropopause layer cooling on Atlantic hurricane activity,J. Clim.,26,2288-2301,
https://doi.org/10.1175/JCLI-D-12-00242.1,2013.
Ramsay,H.: The effects of imposed stratospheric cooling on the maximum intensity oftropical cyclones in axisymmetric radiative-convective equilibrium,J. Clim.,26,9977-9985,
doi: 10.1175/JCLI-D-13-00195.1書，2013.
Wang,B.,Xu,S.,and Wu,L.: Intensified Arabian Sea tropical storms,Nature 489,E1-E2,
doi:10.1038/nature11470,2012.
Wang,S喜， Camargo,S.J.,Sobel,A.H.,and Polvani,LM.: Impact of the tropopause temperatureon the intensity of tropical cyclones—an idealized study using a mesoscale mode,J. Atmos.
Sci.,71,4333-4348,2014.
IX. Member
Rei Ueyama
Nawo Eguchi
Kunihiko Kodera

NASA Ames Research Center
RIAM,Kyushu University
ISEE,Nagoya University

Quant. Spectrosc. Radiat. Transfer v. 113, 1728, 2012; 2) Opt. Express v. 20, 16763, 2012; 3) J.
Quant. Spectrosc. Radiat. Transfer v. 129, 169, 2013; 4) Opt. Express v. 22, 23620, 2014]. The
second method is called the invariant imbedding T-matrix method (II-TM), it is described in thepapers [J. Quant. Spectrosc. Radiat. Transfer v. 116, 169, 2013] H [J. Quant. Spectrosc. Radiat.
Transfer v. 138, 17, 2014].
Simulations in 2017
We used the physical-optics method for calculating the backscatter Mueller matrix and thebackscatter ratios for the following input parameters:
crystal shapes: hexagonal plates, hexagonal solid and hollow columns, solid columns with
distorted shape, bullet-rosettes and droxtals;
wavelengths: 0.355, 0.532 and 1.064 micrometers;
crystal sizes: from 10 up to 1000 micrometers;
crystal orientations: quasi-horizontal orientation with arbitrary effective crystal tilts up to therandom orientation;
lidar tilts: 0, 3 and 5 degrees about the vertical direction.
Results:
We concluded that the backscatter ratios (lidar, depolarization and color ratios) reveal strong
dependence on shape and size of the crystals.
Joint publications:
1. Konoshonkin A.V., Borovoi A.G., Kustova N.V., Okamoto H., Ishimoto H., Grynko Y.,
閻rstner J. Light scattering by ice crystals of cirrus clouds: from exact numerical methods tophysical-optics approximation // Journal of Quantitative Spectroscopy and Radiative Transfer.
2017. V. 195. P. 132-140. doi: 10.1016/j.jqsrt.2016.12.024
2. Kustova N.V., Konoshonkin A.V., Borovoi A.G., Okamoto H., Sato K., Katagiri S. Powerlaws for the backscattering matrices in the case of lidar sensing of cirrus clouds // Proceedings of
SPIE, V. 10466. [10466-116]. 2017