IN SITU ACOUSTIC IMAGING TO REVEAL GLAZE DELAMINATIONS, IN THE EARLY STAGES, IN PORTUGUESE AZULEJOS

Paola CalicchiaJoão Manuel Mimoso

Dória Maria Rodrigues Costa

13 April 2011NON DESTRUCTIVE TESTING

NDT12

13 April 2011, NDT12 P. Calicchia

manufacturing defects

a mismatch between the coefficients of thermal expansion of

the glaze and the ceramic body brings toshivering

a planar compression is induced on the glaze, and may cause glaze delamination

Moreover, a weak bond between the ceramic body and the glaze may cause glaze delamination

a thin cavity of airis formed

at the interface

moisture absorption In the ceramic bodysalts crystallization

in the cavity

the glaze breaks and/or is pushed out until it falls off

P. Calicchia

from J. M. Mimoso, A.S. Silva, S. X. Coentro, Studying the cracking system in 17-18th century Portuguese Azulejos with SEMSEM2010, London

A specific IR thermographic procedure, still in the early phases of experimenting for heritage azulejos , applied locally;

Investigation based on Ultrasonic Testing;

no defined protocol including instrumental diagnosis to reveal glaze delamination,

in particular in the early stagesbefore lacunas become visible.

a possible solution to the localization of delaminations is investigated:in situ ND acoustic technique

ACoustic Energy Absorption Diagnostic Device ACEADD

employed to azulejo panels for the first time

13 April 2011, NDT12

G. B. Cannelli, P. CalicchiaEU Patent EP1190243B1 (2006)

US Patent US 6728661 (2004)IT Patent N. RM 99 A000410 (1999)

P. Calicchia

provides

acoustic absorption maps

identifies anomalous acoustic absorption

processes in a multilayer

heterogeneous structure

automatically scans an area,radiating towards the surface

an acoustic wave with audible frequency content

it records the reflected wave

reveals

sub-surface cavitiesby measuring

the acoustic absorption coefficient

d

c

M

kf

S

air

00

0 22

1

mass - air spring systemMass => surface glazed layer

Spring => air volume rigidity kair

13 April 2011, NDT12

M

Dkair

F

THE METHOD

THE DEVICE

0 = air density ; 0 = glaze surf density; d = air cavity thickness

P. Calicchia

SourceS

ReceiverM

TRANSCEIVER UNIT& TRANSDUCER CIRCUITRY

SCAN UNIT

DATA ACQUISITION, DATA PROCESSING,MOTION CONTROL UNIT

13 April 2011, NDT12

back reflection geometry

coaxial configuration

standard HW components

custom SW component

p(t) = pd(t) + pr(t) = pd(t) + kr pd(t) h(t-)

DIR Extrh(t-) |H(f)|2 = r(f)

|H(f)|2 = r(f) INV Extr

E = ∫dt |h(t-)|2 = ∫df |H(f)|2

P. Calicchia13 April 2011, NDT12

C(t) = Cdir(t)+ kr h(t-) + h.o.t.

Cepstrum algorithm

P. Calicchia

The selected site is locatedin the renaissance cloister of the building,a part of the exhibition space of the museum

Madre de Deus Convent, in Lisbon, which houses nowadays the Portuguese National Tile Museum - MNAz

The azulejo panels, all around the cloister, are greatly affected by glaze delamination with high percentage of glaze loss

13 April 2011, NDT12

P. Calicchia

ACEADD PROTOCOL & OPERATING PROCEDURETESTS FUNCTION UNDER TESTSYSTEM FUNCTIONALITY:IN SITU

Scan unitAcoustic source and transmission lineMicrophone and receiving line

PRELIMINARY TEST:IN SITU

Microphone calibrationAcoustic source Frequency Response at working distance

Environmental NOISE characterizationDirect signal spectral analysisCepstral background evaluation (Free-Field condition) Identification of the area of analysisSystem alignment & Reference PointsRepeatability test

ACEADD MEASUREMENT:IN SITU

SCANs

ACOUSTIC IMAGEs

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P. Calicchia

Point (i):[xi; yi; i; Ei; hi (t-); |Hi (f)|2; (f)]

NMA4

[20L x 39PTs][0,19m x 0,38m]10mm step780 PTs

NMA5

[17L x 21PTs][0,16m x 0,20m]

10mm step357 PTsDispersion of values of indicator E:

Analysis of the degree of homogeneity

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0,08 0,10 0,12 0,14 0,16 0,18 0,20 0,22 0,24 0,260

20

40

60

80

Total reflected energy

N o

f po

ints

NMA4 (780pts)

0,08 0,10 0,12 0,14 0,16 0,18 0,20 0,22 0,24 0,260

5

10

15

20

25

30

35

40

N o

f p

oin

tsTotal reflected energy

NMA5 (357pts)

from repeatability teststhe max interval of valuesrelative to the same point

wrt = 0,054

wmap = 0,045 wmap = 0,060

P. Calicchia

30% 40% 50%

13 April 2011, NDT12

MINIMUM ABSORPTION

MAXIMUMABSORPTION

THRESHOLDS DELIMITINGMOST ABSORBING AREAS

P. Calicchia, J. M. Mimoso“Investigation on the presence of detachments of glazed ceramic tile panels by means of non destructive acoustic mapping”LNEC Report 134/2010 (2010)

REFERENCE POINT PT(14, 8)

[xi; yi; (ERP-Ei)/ERP]

P. Calicchia

30% 40% 50%

13 April 2011, NDT12

MINIMUM ABSORPTION

MAXIMUMABSORPTION

THRESHOLDS DELIMITINGMOST ABSORBING AREAS

P. Calicchia, J. M. Mimoso“Investigation on the presence of detachments of glazed ceramic tile panels by means of non destructive acoustic mapping”LNEC Report 134/2010 (2010)

REFERENCE POINT PT(4, 6)

[xi; yi; (ERP-Ei)/ERP]

fabs = 11,3kHzd = 13m

P. Calicchia

ACKNOWLEDGEMENTS This work was possible thanks to the efforts of many special people. Thanks to the team of the Stone & Ceramics Division of the Department of Materials of LNEC; thanks to the colleagues of the Institute of Acoustics and Sensor of CNR.A special thank to the Director and the staff of the Portuguese National Tile Museum (Museu Nacional do Azulejo).

13 April 2011, NDT12

Insight into the glaze delamination process, for preventive conservation actions; Definition of a reliable diagnostic protocol, integrating different and complementary methods, such as the IR thermography and the acoustic method, aiming at the detection of subsurface cavities in the early stages , before glaze loss occur; Insight into the acoustic response of ceramics, through lab test and comparison with IR thermography; Technological development of ND acoustic diagnostic device ; Definition of a proper operating procedure, assessment of the method reliability on different artefacts (frescoes, ceramics, mosaics) and in different operating conditions.