Damage Identification of the Sandwich Plate Having Core from Rice

Husk-Epoxy for Ship Deck Structure

Abdi Ismail

, Achmad Zubaydi

, Agung Budipriyanto

and Yudiono

Department of Naval Architecture, Faculty of Marine Technology, Institut Teknologi Sepuluh Nopember (ITS), Jl. Arief

Rahman Hakim, Surabaya, Indonesia

Department of Civil Infrastructure Engineering, Faculty of Vocational Studies, Institut Teknologi Sepuluh Nopember (ITS),

Jl. Menur 127, Surabaya, Indonesia

Keywords: Ships Structure, Sandwich Plate, Damage Identification, Natural Frequency, Ramping Ratio.

Abstract: This paper discusses vibration-based damage identification applied on sandwich plate for ship structure using

Finite Element Analysis Method (FEM) and Experimental Modal Analysis (EMA). The sandwich plate had

6mm-thick steel faceplates and 15mm-thick core. The core was made from epoxy and rice husk powder with

two compositions, i.e., 10% and 15% rice husk powder by weight. The thickness of the faceplates and the

core was designed for the main deck of a coal barge ship. Damage was introduced in the core. Then natural

frequency and damping were measured before and after the damage was introduced. It was observed that for

the sandwich plate with core made from 10% rice husk, the natural frequency deviations due to damage

obtained by EMA and FEM is 0.39% and 0.81% respectively. Natural frequency deviations obtained by EMA

and FEM for the sandwich with the core of 15% rice husk is 5.39% and 5.00% respectively. The damping

ratios deviations due to damage for sandwich with core of 10% and 15% rice husk powder differed by 0.16%

and 0.13% respectively. Thus, natural frequency and damping ratio could be used as damage identification

parameters. Nevertheless, sensitivity analysis of the damage size is required for future development.

1 INTRODUCTION

The use of sandwich plate in ship structures has

several advantages. The weight of the structure using

sandwich plate is lighter than the that of conventional

stiffened plate structure. It was reported that the

weight reduction was more than 10% (Momčilović &

Motok, 2009). Another advantage is better

construction design and easier fabrication process

(Ramakrishnan & Kumar, 2016).

The sandwich plate can be fast constructed. It has

high stiffness-weight ratio, high fatigue strength,

good acoustic and thermal insulation (Reis &

Rizkalla, 2008). The sandwich plate consists of two

parts, the faceplates and the core. The faceplate is

made of material that has high strength and stiffness

while the core layer is made of materials that has

lower strength, stiffness and material density

(Borsellino, et al., 2004). The combination of the two

parts will provide a very efficient strength-weight

ratio, which is a key requirement for lightweight

structures such as those used in the shipping industry.

The use of sandwich plate on the ship's structure

would reduce the overall weight of the ship so that it

could increase the payload.

Several studies of sandwich plate applications on

ships have been carried out. Research on the design

and testing of T-joint sandwich for ships has been

carried out (Toftegaard & Lystrup, 2005). Sandwich

made of faceplate steel and concrete cores have been

researched for ship hull applications (Dai & Liew,

2006). In the maritime field, sandwich plate have

potential applications in bridge decks, anti-collision

structures, ship hulls and offshore structures (Liew &

Sohel, 2009). Sandwich Plate System (SPS) has been

applied to ship repair using an overlay process

(Momčilović & Motok, 2009). Research on the peak

strength of L-joint sandwich for ship structures was

carried out (Shen, et al., 2017).

Ships structure needs the Structural Health

Monitoring (SHM) and damage identification to

prevent catastrophic structural failure. SHM will be

developed based on the damage identification

method. Local damage-identification methods are

difficult to do on large structures, complex structures,

or structures that are difficult to access (Yan, et al.,

112

Ismail, A., Zubaydi, A., Budipriyanto, A. and Yudiono, .

Damage Identiﬁcation of the Sandwich Plate Having Core from Rice Husk-Epoxy for Ship Deck Structure.

DOI: 10.5220/0008543301120118

In Proceedings of the 3rd International Conference on Marine Technology (SENTA 2018), pages 112-118

ISBN: 978-989-758-436-7

2007), as in ship structures. Global damage-

identification such as vibration method is an effective

and appropriate way to detect damage in large and

complex ship structures.

Global damage-identification using vibration

method has been conducted by many researchers. All

structures can be expressed as dynamic systems with

certain structural parameters, such as stiffness, mass,

and damping constants. If the structure gets damaged,

the structural parameters will also change (Yan, et al.,

2007). Thus, changes in these structural parameters

can be detected through vibration signals that indicate

the existence of damage in a structural system (Shi, et

al., 2000; Gawronski & Sawicki, 2000; Kawiecki,

2001; Shi, et al., 2002; Abdo & Hori, 2002; Sampaio,

et al., 2003; Fan & Qiao, 2011). Vibration method

detects the existence of damage in certain objects by

observing changes in natural frequency (Liang, et al.,

1991; Chinchalkar, 2001; Al-Waily, 2013; Yang, et

al., 2016; Zhao, et al., 2016) and damping (Panteliou,

et al., 2001; Kyriazoglou, et al., 2004; Huang, et al.,

2016; Cao, et al., 2017).

Damage identification research is needed on the

sandwich ships-structure to prevent severe structural

failure. Laboratory testing was conducted to get data

which could be used as reference before being applied

to larger ship structures.

In this research, vibration-based damage

identification was conducted on sandwich plate

which designed for the main deck of a coal barge ship

using Finite Element (FEM) and Experimental Modal

Analysis (EMA) methods. Natural frequency and

damping ratio were used as a damage identification

parameter to distinguish the dynamic characteristics

of the intact (no damage) and damaged core in

sandwich plate structure.

2 METHOD

This research discusses the damage identification of

sandwich plate that was designed for the main deck

of a coal barge ship. The sandwich plate had 6 mm

thick steel faceplates and 15 mm thick core which was

fabricated from epoxy and rice husk powder. The

thickness of the faceplates and the core were designed

for the main deck of a coal barge ship (Thomson,

1981).

Core with the composition of 10% rice husk

powder and 15% rice husk powder was chosen to be

developed into a sandwich plate. These compositions

were selected because these cores met the Lloyd

The natural frequency of the r-mode was

computed based on the highest value of the amplitude

on the frequency around the mode, as in equation (1)

where

is the amplitude in the r-mode and

is the

natural frequency estimation in r-mode.

%&#'

()*

+%#

+ #

,-).

(1)

Damping ratio was estimated using equation (2).

The ω1 and ω2 values were determined by procedure

depicted in Figure 1.

is the frequency at point 1

corresponding to the amplitude of (

1 234

the frequency at point 2 and.

is the damping ratio.

:%/

(2)

Figure 1: Damping ratio estimation.

Damage identification was used by detecting the

natural frequency and damping ratio of intact and

damaged sandwich plate having core made from rice-

hush powder. The dynamic characteristics of the two

sandwiches ware used as a reference to determine the

existence of a damage in a similar sandwich type.

Natural frequencies of the sandwich plate were

obtained by using Finite Element Method (FEM) and

Experimental Modal Analysis (EMA) method.

Damping ratio was obtained by EMA results. The

natural frequency and damping ratio of intact

sandwich and damaged sandwich could be compared.

Sandwich specimens had dimensions of 240 mm

x 60 mm x 27 mm. Damage was introduced to the

sandwich plate core. It was similar to the damage that

occurred in flexure tests, that was a damage with a

length of 15 mm and a depth of 35 mm (Yudiono, et

al., 2018).

2.1 FEM Set-up

Sandwich plate with core made from 10% rice husk

(S10RH) and sandwich plate with core made from

Damage Identiﬁcation of the Sandwich Plate Having Core from Rice Husk-Epoxy for Ship Deck Structure

113

15% rice husk (S15RH) were analyzed using FEM to

estimate the value of natural frequency. The vibration

analysis used the first mode. The boundary condition

was a fix condition on both ends of the sandwich

model. The meshing process has been conducted on

the intact sandwich model and the damaged sandwich

model. The size of the meshing was 0.005 m.

2.2 EMA Set-up

Finite element analysis results were validated using

experiment. The sandwich plate specimen was placed

on a clamp that was strongly attached to the fraise

machine. The clamp served to fasten both ends of the

specimen. Experimental set-up of the specimen test

can be seen in Figure 2.

Figure 2: Experimental set-up of sandwich plate specimen

in EMA.

Data retrieval of dynamic characteristics from

specimen of sandwich plate used the instrument

arrangement as shown in Figure 3. The accelerometer

type is piezoelectric. The most widely used

Accelerometer type is piezoelectric (He & Fu, 2001).

The hammer was used as a source of vibration

(impact input). The accelerometer was used to

capture the vibration response from the sandwich

plate.

Figure 3: Instrument set-up of EMA.

To get the appropriate vibration response, it was

necessary to determine the proper configurations of

the hammer and the accelerometer. The

configurations of the hammer and accelerometer can

be seen in Figure 4. The raw data from the instrument

has been converted from the time domain to the

frequency domain using the Fourier Transform.

Figure 4: Configurations of hammer and accelerometer on

sandwich plate.

3 RESULT AND DISCUSSION

3.1 FEM Results

FEM was conducted to get the natural frequency from

the intact sandwich model and damaged sandwich

model in S10RH and S15RH. The material properties

of sandwich plate for FEM input was reported in

(Yudiono, et al., 2018).

Figure 5 (a) shows the intact sandwich model,

while Figure 5 (b) shows the damaged sandwich

model. The boundary condition was a fix condition

on both ends of the sandwich model, as shown in

Figure 6.

(a)

(b)

Figure 5: (a) Intact sandwich model (b) damaged sandwich

model.

SENTA 2018 - The 3rd International Conference on Marine Technology

114

Figure 6: Boundary conditions of the model.

The vibration analysis used was the first mode. The

mode shape of the sandwich model is shown in Figure

7. The natural frequency of intact S10RH and S15RH

were 635.13 Hz and 589.71 Hz respectively while the

natural frequency of damaged S10RH and S15RH

were 640.26 Hz and 560.22 Hz respectively.

Figure 7: Mode shapes of vibration analysis.

3.2 EMA Results

The original vibration data from EMA was in time

domain. The data were converted to frequency

domain using Fourier Transform so the value of

natural frequency of each sandwich plate has been

obtained. Figure 8 and Figure 9 show the spectrum of

vibration response in frequency domain. Figure 8

shows the vibration response spectrum of intact

sandwich plate and Figure 9 shows the vibration

response spectrum of damaged sandwich plate.

(a)

(b)

Figure 8: Vibration response spectrum of intact sandwich

with core made from (a) 10% (b) 15% rice husk powder.

(a)

(b)

Figure 9: Vibration response spectrum of damaged

sandwich with core made from (a) 10% and (b) 15% rice

husk powder.

The peak of the curve was the value of natural

frequency. The natural frequency of intact S10RH

and S15RH were 625.5 Hz and 575 Hz respectively.

The natural frequency of damaged sandwiches

S10RH and S15RH ware 623 Hz and 544 Hz

respectively.

3.3 Damage Identification of Sandwich

Plate using FEM and EMA

Damage identification of the sandwich plate having

core from rice husk-epoxy was conducted by using

FEM and EMA by identifying the natural frequency

deviation and the damping ratio deviation. The results

of numerical studies needed to be validated using the

results of the experimental study. In this research, the

Damage Identiﬁcation of the Sandwich Plate Having Core from Rice Husk-Epoxy for Ship Deck Structure

115

results of FEM needed to be validated using the

results from EMA.

Table 1: Difference in the sandwich plate’s natural

frequency obtained using FEM and EMA in intact

condition.

Intact

sandwich

Natural Frequency

(Hz)

Differenc

(%)

FEM

EMA

10%

635.13

625.5

1.54

15%

589.71

575

2.56

Table 2: Difference in the sandwich plate’s natural

frequency obtained using FEM and EMA in damaged

condition.

Damaged

sandwich

Natural Frequency (Hz)

Difference

(%)

FEM

EMA

10%

640.26

623

2.77

15%

560.22

544

2.98

Table 1 shows the difference between FEM and

EMA in intact sandwich plate. While Table 2 shows

the difference between FEM and EMA in damaged

rice husk sandwich plate. FEM models of intact

S10RH and S15RH have FEM-EMA difference of

1.54% and 2.56%, respectively. FEM models of

damaged S10RH and S15RH have FEM-EMA

difference of 2.77% and 2.98%, respectively. FEM

model of intact S10RH has the lowest FEM-EMA

difference in first mode analysis.

The increased composition of the rice husk causes

an increase in the FEM-EMA difference because the

composite becomes increasingly non-homogeneous.

Composite characteristics that are not homogeneous,

can be modelled using orthotropic models. In

addition, natural frequency of the model should be

analyzed using other mode shape analysis.

Table 3: Natural frequency deviation in sandwich plate with

core made from 10% rice husk using FEM and EMA for

intact and damage conditions.

Method

Natural Frequency (Hz)

Natural

frequency

deviation

(%)

intact

sandwich

Damaged

sandwich

FEM

635.13

640.26

0.81

EMA

625.5

623

0.39

Table 4: Natural frequency deviation in sandwich plate with

core made from 15% rice husk using FEM and EMA for

intact and damage conditions.

Method

Natural Frequency (Hz)

Natural

frequency

deviation

(%)

Intact

sandwich

Damaged

sandwich

FEM

589.71

560.22

5.00

EMA

575

544

5.39

Table 3 shows the natural frequency deviation in

sandwich plate with core made from 10% rice husk

and Table 4 shows the natural frequency deviation in

sandwich plate with core made from 15% rice husk

by using FEM and EMA. Natural frequency deviation

due to damage from the S10RH rice husk is 0.39% by

EMA and 0.81 by FEM. Natural frequency deviation

due to damage from the sandwich 15% rice husk is

5.39% by EMA and 5.00 by FEM.

The natural frequency deviation data can be used

as damage identification parameter for sandwich

plate with core made from 10% and 15% rice husk.

Although S10RH and S15RH have the same damage

size, the sandwiches have different natural frequency

deviations. The value of natural frequency deviations

applies specifically to a sandwich plate. Different

sandwich plate has different natural frequency

deviations.

Table 5: Damping ratio of the sandwich plates for in intact

and damaged conditions.

Type of sandwich and rice husk

contents

Damping

ratio (%)

Intact - (10% rice husk powder)

0.96

Damaged - (10% rice husk powder)

0.8

Intact - (15% rice husk powder)

0.96

Damaged - (15% rice husk powder)

0.83

Damping ratio could also be used as a damage

identification parameter. Based on Table 5, intact

sandwich has a damping ratio 0.96%. For the

composition of 10% rice husk, damage causes a

deviation in the sandwich damping ratio by 0.16%.

For the composition of 15% rice husk, damage causes

a deviation in the sandwich damping ratio by 0.13%.

The natural frequency and damping ratio

deviation could be used as the damage identification

parameters for sandwich plate with core made from

10% and 15% rice husk. Nevertheless, sensitivity

analysis is still needed by varying the size of the

damage.

SENTA 2018 - The 3rd International Conference on Marine Technology

116

4 CONCLUSIONS

Sandwich plate has advantages and potential

applications to replace conventional steel stiffened

plate on ships structure. To ensure the structure’s

health and prevent sudden structural failure, it is

important to develop a damage identification method

for sandwich ships structure. In this research,

laboratory testing on sandwich plate was conducted

before testing on larger ship structures could be

performed

The experiment results showed that damage

caused decrease in the natural frequency of sandwich

with core made from 10% and 15% rice husk powder

by 0.39% and 5.39% respectively. The damping ratio

was changed due to damage; there were 0.16% and

0.13% changes observed for sandwich having core

made form 10% and 15% rice husk powder

respectively. Therefore, natural frequency and

damping ratio can be used as damage identification

parameters.

Sensitivity analysis in the size of damage needs to

be performed. In addition, better FEM model is

needed so the model can simulate damage in the core

and response of sandwich plate due to damage. The

identification of the damage location will be the main

concern for the next step of our research.

ACKNOWLEDGMENTS

This research was funded by Directorate of Research

and Community Services, Ministry of Research,

Technology and Higher Education, Republic of

Indonesia through PUPTN research scheme. Abdi

Ismail, the first author, gratefully thanks for the

support given by the Ministry through The Master’s

Degree Program Leading to Doctoral Degree for

Excellent Bachelor Graduates (PMDSU) fund.

REFERENCES

Abdo, M. A. B. & Hori, M., 2002. A Numerical Study of

Structural Damage Detection Using Changes in the

Rotation of Mode Shapes. Journal of Sound and

Vibration, Volume 2, no. 251, p. 227–239.

Al-Waily, M., 2013. Experimental and Numerical

Vibration Study of Woven Reinforcement Composite

Laminated Plate with Delamination Effect.

International Journal of Mechanical Engineering,

Volume 2, no. 5, pp. 1-18.

Borsellino, C., Calabrese, L. & Valenza, A., 2004.

Experimental and Numerical Evaluation of Sandwich

Composite Structures. Composites Science and

Technology, Volume 64 No. 64, pp. 1709-1715.

Cao, M. S., Sha, G. G., Gao, Y. F. & Ostachowic, W., 2017.

Structural Damage Identification Using Damping: a

Compendium of Uses and Features. Smart Materials

and Structures, Volume 26, no. 043001.

Chinchalkar, S., 2001. Determination of Crack Location in

Beams Using Natural Frequencies. Journal of Sound

and Vibration, Volume 247, no. 3, p. 417–429.

Dai, X. X. & Liew, J. Y. R., 2006. Steel-Concrete-Steel

Sandwich System for Ship Hull Construction. s.l.,

International Colloquium on Stability and Ductility of

Steel Structures, pp. 877-884.

Fan, W. & Qiao, P., 2011. Vibration-based Damage

Identification Methods: A Review and Comparative

Study. Structural Health Monitoring, Volume 10, no

83.

Gawronski, W. & Sawicki, J. T., 2000. Structural Damage

Detection using Modal Norms. Journal of Sound and

Vibration, Volume 229, no. 1, p. 194–198.

He, J. & Fu, Z. F., 2001. Modal Analysis. Butterworth

Heinemann. Great Britain.

Huang, X., Dyke, S., Sun, Z. & Xu , Z., 2016. Simultaneous

Identification of Stiffness, Mass, and Damping Using

an On‐line Model Updating Approach. Structural

Control Health Monitoring, Volume 24, no. 4.

Kawiecki, G., 2001. Modal Damping Measurement for

Damage Detection. Smart Materials and Structures,

Volume 10, no. 3, p. 466–471.

Kyriazoglou, C., Le Page, B. H. & Guild, F. J., 2004.

Vibration Damping for Crack Detection in Composite

Laminates. Composites Part A—Applied Science and

Manufacturing, Volume 35, p. 945–953.

Liang, R. Y., Choy, F. K. & Hu, J., 1991. Detection of

Cracks in Beam Structures Using Measurements of

Natural Frequencies. Engineering and Applied

Mathematics, Volume 328, p. 505–518.

Liew, J. Y. R. & Sohel, K. M. A., 2009. Lightweght steel-

Concrete-Steel Sandwich System with J-hook

Connectors. Engineering Structures, Volume 31, pp.

1166-1178.

Momčilović, N. & Motok, M., 2009. Estimation of Ship

Lightweight Reduction by Means of Application of

Sandwich Plate System. FME Transactions, Volume

37, pp. 123-128.

Panteliou, S. D., Chondros, T. G., Argyrakis, V. C. &

Dimarogonas, A. D., 2001. Damping Factor as an

Indicator of Crack Severity. Journal of Sound and

Vibration, Volume 241, p. 235–245.

Ramakrishnan, K. V. & Kumar, P. G. S., 2016.

Applications of Sandwich Plate System for Ship

Structures. Journal of Mechanical and Civil

Engineering, pp. 83-90.

Reis, E. M. & Rizkalla, S. H., 2008. Material

Characteristics of 3-D FRP Sandwich Panels. Journal

of Construction and Building Materials, Volume 22, p.

1009–1018.

Sampaio, R. P. C., Maia, N. M. M. & Silva, J. M. M., 2003.

The Frequency Domain Assurance Criterion as a Tool

Damage Identiﬁcation of the Sandwich Plate Having Core from Rice Husk-Epoxy for Ship Deck Structure

117

for Damage Detection. Damage Assessment of

Structures, Volume 245, no. 2, p. 69–76.

Shen, W. et al., 2017. Ultimate Strength Analysis of

Composite Typical Joints for Ship Structures.

Composite Structures, Volume 171, pp. 32-42.

Shi, Z. Y., Law, S. S. & Zhang, L. M., 2000. Structural

Damage Detection from Modal Strain Energy Change.

Journal of Engineering Mechanics-ASCE, Volume 126,

no. 12, p. 1216–1223.

Shi, Z. Y., Law, S. S. & Zhang, L. M., 2002. Improved

Damage Quantification from Elemental Modal Strain

Energy Change. Journal of Engineering Mechanics-

ASCE, Volume 128, no. 5, p. 521–529.

Thomson, W. T., 1981. Theory of Vibration with

Applications. Prentice-Hall. New Jersey.

Toftegaard, H. & Lystrup, A., 2005. Design and Test of

Lightweight Sandwich T-joint for Naval Ships.

Composites, Volume 36, pp. 1055-1065.

Yang, C., Hou, X. B., Wang, L. & Zhang, X. H., 2016.

Applications of Different Criteria in Structural Damage

Identification Based on Natural Frequency and Static

Displacement. Science China Technological Sciences,

Volume 59, no. 11, p. 1746–1758.

Yan, Y. J., Cheng, L., Wu, Z. Y. & Yam, L. H., 2007.

Development in Vibration-based Structural Damage

Detection Technique. Mechanical Systems and Signal

Processing, Volume 21, p. 2198–2211.

Yudiono, Zubaydi, A. & Budipriyanto, A., 2018. Static and

Dynamic Analyses of Sandwich Panel with Core

Material From Rice Husk for Ship Deck Structure,

Department of Naval Architecture, Institut Teknologi

Sepuluh Nopember. Surabaya.

Zhao, B. et al., 2016. Structural Damage Detection by

Using Single Natural Frequency and the Corresponding

Mode Shape. Shock and Vibration, Volume 2016, no.

8194549.

SENTA 2018 - The 3rd International Conference on Marine Technology

118