Arrigoni, Michel

Blouin, Alain

Kruger, Sylvio E.

L\ue9vesque, Daniel

Lord, Martin

Monchalin, Jean-Pierre

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The Use of Laser-Doppler Interferometry Based on a Fabry-Perot 
Etalon for Shock Adhesion Test Applied to Adhesively Bonded 
Materials
Arrigoni, Michel; Kruger, Sylvio E.; Blouin, Alain; Lévesque, Daniel; Lord, 
Martin; Monchalin, Jean-Pierre
          1st International Symposium on Laser Ultrasonics:  
                     Science, Technology and Applications 
                     July 16-18 2008, Montreal, Canada
    
 
The Use of Laser-Doppler Interferometry Based on a Fabry-Perot 
Etalon for Shock Adhesion Test Applied to Adhesively Bonded 
Materials 
 
Michel ARRIGONI 1,2, Silvio E. KRUGER 1, Alain BLOUIN 1, Daniel LEVESQUE 1, 
Martin LORD 1, Jean-Pierre MONCHALIN 1 
 
1
 Industrial Materials Institute, National Research Council Canada, 75 de Mortagne Blvd, Boucherville 
(QC), J4B 6Y4, Canada; Phone: +1 450 641-5116, Fax: +1 450 641-5106; e-mail: 
silvio.kruger@cnrc-nrc.gc.ca, alain.blouin@cnrc-nrc.gc.ca, jean-pierre.monchalin@cnrc-nrc.gc.ca 
 
2
 Laboratoire Brestois de Mécanique et des Systèmes, Equipe d’Accueil 4325 - ENSIETA / Université de 
Brest / ENIB, 2 Rue François Verny, 29806 Brest Cedex 9 France;  
Phone: +33298348978, Fax: +33298348730, e-mail : michel.arrigoni@ensieta.fr 
 
Abstract   
Adhesively bonded assemblies satisfy several transportation industry requirements such as easiness of 
processing and lightness. These adhesively bonded assemblies also provide continuous adhesion 
compared to riveting, screwing or welding. To evaluate the bond strength between two adhesively bonded 
plates, laser shock adhesion tests have been used as a non-destructive adhesion evaluation technique. The 
method relies on a Nd-YAG pulsed laser for the shock generation. The laser power density on the surface 
is about a few GW/cm² and the irradiation is performed with a water confinement layer. An original and 
simple laser-Doppler interferometer device based on a Fabry-Perot etalon has been designed. The free 
surface velocity is thus measured with this diagnostic. Experiments were carried out on 500 µm and 410 
µm aluminium plates bonded with various adhesives. Results show that the proposed adhesion test is able 
to differentiate bond of different quality and to estimate the bond strength. 
Keywords: Shock wave, adhesion, adhesive, bond strength, Fabry-Perot interferometer, non-destructive 
technique, LASAT 
 
1. Introduction 
1.1 Adhesion techniques 
Adhesive bonding has been used for a long time as a simple method and a low-cost 
alternative to assemble very dissimilar materials [1]. However, its reliability depends on 
the quality of the adhesion. Various adhesive tests have been developed but the 
challenge of evaluating the bond strength by a non-destructive method remains. 
Adhesion strength depends on physico-chemical properties of the interface and can thus 
be affected by many factors, including the characteristics of the adhesive, the 
temperature and pressure during joining and the surface preparation. A relevant test 
consists in submitting the joint to a high stress that will destroy a weakly bonded joint 
whereas a sound joint will remain unaffected. High energy pulsed lasers are adequate 
tools for generating shock waves that result in high stresses on large structures of any 
shape. This method relies on shock physics and is inspired from techniques designed for 
bond strength measurement of coatings by shock adhesion tests for various applications 
[2-7].  
  
1.2 Shock adhesion test 
Tensile stress is generated from shock wave propagation in the target and, depending on 
the material strength, may lead to spallation [8], as described on the space-time diagram 
in Fig. 1. A shock is maintained between instant A and B on a sample. Its propagation 
(solid line in space-time diagram) towards the free surface induces a compressive stress 
(area with wavelets in Fig. 1b), followed by a release state (dashed line) corresponding 
to unloading (state after B). Once the free surface is reached, the shock is reflected as 
release waves (only the head is represented in Fig. 1b by a dashed line). When two 
release waves are crossing each other, tensile stress is generated (area with dots in Fig. 
1b). By tuning shock characteristics and sample geometry, it is possible to bring the 
tensile stress at the interface of a layered material and thus, in case of high stress, to 
delaminate the layer. The process can be exploited as an adhesion test [9]. 
 
 
 
 
 
 
 
Figure 1. a) Laser-material interaction and laser-induced shock wave. b) Spallation mechanisms. 
1.3 Diagnostic technique 
As shock wave propagation is a rapid phenomenon and its observation requires specific 
devices. The most accessible variable in experiments is the material velocity of the free 
surface (opposed to the impacted one). The use of laser has revolutionized shock wave 
measurement technologies. Thus, more reliable techniques based on the Doppler shift 
measurement with an optical interferometer, called Laser Doppler Interferometer (LDI), 
have been designed [10-13]. When the shock breaks out at the surface illuminated by a 
laser beam, the reflected laser light is frequency shifted by the Doppler effect from an 
incident frequency f0 to frequency f as follows: 
c
uu
f
ff )(2 0
0
0 −
=
−
     (1) 
where u is the instantaneous material velocity to be measured, u0 is the initial material 
velocity and c the speed of light. 
 
We have designed an LDI based on a solid Fabry-Perot etalon for shock measurement. 
This system allows the measurement of particle velocities ranging from less than 0.3 
m/s to 200 m/s. In this paper, we report results obtained with this device on laser-
induced shock experiments performed on Al 5754 plates adhesively bonded with 
various glues.  
  
Free surface 
0 
1 
A 
B 
Time 
Space 
Sample 
Tensile 
Compression Laser 
  
Sample 
Plasma  
  
Shock 
wave 
  
2. Fabry-Perot etalon Laser Doppler Interferometer   
Our device is based on a solid-state monolithic Fabry-Perot planar etalon [14]. This 
device is widely used in optical spectroscopy [15-17] and can be used to detect 
ultrasonic motion of material surface. Spectral information on the light source is 
obtained by selecting part of the central fringe pattern in the focal plane of a lens (Fig. 
2). When the light frequency  is swept or when the Fabry-Perot optical thickness is 
varied, resonance peaks are observed (Fig. 3). These resonance peaks are separated by 
the Free Spectral Range (FSR) of the etalon given by equation 2 where e is the thickness 
of the etalon, n its refractive index and c is the speed of light in vacuum. 
 
ne
cFSR
2
=       (2) 
 
 
 
 
 
 
 
 
Figure 2. Principle of the Fabry-Perot interferometer as used in optical spectroscopy.  
 
The full width at half maximum of the peaks, noted w, is equal to the FSR divided by 
the Fabry-Perot finesse F, which depends upon the etalon characteristics. When the 
optical frequency is stabilised at half maximum of a resonance peak of the etalon, 
modulation of the optical frequency results in modulation of the optical intensity 
transmitted through the etalon, as sketched in figure 3, with a proportionality factor 
given by the slope of the etalon frequency peak at half maximum. Since the variation of 
material velocity u induces a Doppler optical frequency shift , the etalon provides a 
direct relationship between the light intensity transmitted through the etalon I and the 
material velocity u, as summarized in equations (3). 
 
c
u∆
=
∆ 2
ν
ν
 but λ
c
v =    thus  I
k
vu ∆=∆=∆
22
λλ
.  (3) 
     
 
 
 
 
 
 
 
 
 
 
 
 
Figure 3. Resonance peaks of the Fabry-Perot etalon used in this work.  
e 
Reflective 
surfaces 
 
L
screen 
Étalon 
FSR 
w 
GHz 
Li
gh
t I
n
te
n
si
ty
 
(a.
u
.
) 
Frequency  (GHz) 
  
 
A solid etalon Fabry-Perot is used instead of one made of two parallel plates, which 
would have required a precise alignment system (usually made by 3 piezoelectric 
pushers) to make the two plates parallel. Moreover, a solid etalon does not require any 
alignment and is also weakly dependent on room temperature variations. However this 
requires in turn the detection laser source to be frequency tunable.  
3. Application to bond strength measurement 
 
The Fabry-Perot etalon interferometer was used for measuring the free surface velocity 
(surface opposed to the impacted one) of adhesively bonded aluminium plates. Each 
sample is made of two 70 mm x 60 mm plates of aluminium alloy AA 5754 of 410 µm 
and 500 µm thickness that were adhesively bonded with different adhesives. Table I 
shows a summary of the tested samples. 
Table 1. Aluminium plates assembled with four kinds of adhesives 
Sample Thickness plate 1 
± 5 µm 
Nominal adhesive 
thickness (µm) 
Thickness plate 2 
± 5 µm 
Al / ESP 310 / Al 410 130 500 
Al / FM1000 / Al 410 400 500 
Al / L414 / Al 410 50 500 
Al / E5min / Al 410 60 500 
 
The experimental configuration consists of a shock generation on the top side of the 
sample and surface velocity measurement on the bottom side (Fig. 4a). Shock 
generation is performed with a Nd-YAG high energy pulsed laser which provides 10 ns 
duration gaussian pulses of up to 2.4 J at a wavelength of 1.064 µm and at a repetition 
rate of 10 Hz. Laser irradiation is performed under water confinement regime, which 
allows increasing the shock pressure and its duration [18]. The laser beam is focused on 
the 3-layer sample to a spot of about 2 mm diameter. Energy loss due to the light 
absorption in the 3 mm thick water layer [19] and spurious reflections on optical 
components is about 0.5 J. In such conditions, Berthe [20] showed that the shock 
pressure could reach up to 5 GPa at a power density of 9 GW/cm². Shock detection is 
performed with a long pulse Nd-YAG laser, which delivers 400 µs duration pulses of 
about 500 W peak power. The detection laser beam is focused to a 400 µm spot 
diameter on the sample bottom surface. The detection laser light collected from the 
sample surface is sent to the Fabry-Perot etalon by a large core optical fibre. Generation 
and detection lasers are synchronised by a clock control unit. Because of the water 
confinement regime, we used a shot by shot measurement procedure, which allows 
wiping optical components sprinkled by the confining water during the laser impact. 
The signal acquisition is trigged with an avalanche photodiode detecting the laser light 
at the shock generation.  
Signals of free surface velocity are compared for several shots involving different power 
densities ranging from less than 1 GW/cm² up to near 6 GW/cm² for the four kinds of 
adhesives. The analysis of velocity peaks gives information on wave propagation and 
allows the rupture diagnostics. However, with multilayered samples, multiple wave 
rebounds make interpretation more complex. In order to facilitate the interfacial rupture 
diagnostics, the fast Fourier transformation (FFT) of velocity signals is performed for 
each shot. The periodicity of the wave rebounds are then viewed as peaks at given 
  
frequencies. An example is shown in figure 5 showing free surface velocities (fig. 5a) 
and their corresponding FFT (fig. 5b) for shots performed at 2.47 GW/cm² (without 
delamination) and at 4.69 GW/cm² (delamination) on aluminium plates bonded with 
Loctite® 414 adhesive. Figure 4b shows the delamination threshold for each adhesive, 
where the empty symbols indicate delamination in the sample. 
 
 
Figure 4. (a) Experimental set-up diagram and (b) adhesion thresholds in GW/cm² for tested samples, 
with empty marks when delaminated. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 5. Example of free surface velocity (a) and FFT analysis (b) for shots on aluminium plates 
adhesively bonded with Loctite® 414. 
4. Conclusions 
 
We have designed and tested a simple laser Doppler velocimeter based on a solid state 
monolithic Fabry-Perot etalon coupled to a single-frequency tunable detection laser. 
The technique was tested for evaluation of bonded aluminium plates with four kinds of 
adhesives. The technique can be applied for real-time diagnostics of bonds, can be 
automated and remains non-destructive as long as the laser power is below the known 
rupture threshold. The FFT analysis consolidates the delamination diagnostics. Also, the 
developed interferometer appears as an alternative to the well-known VISAR (Velocity 
Interferometer System for Any Reflectors). 
Water 
confinement 
Laser 
 = 1.06 µm 
2 J, 10 ns  
O-ring 
 
Al 410 µm 
Surface velocity 
measurement 
Al 500 µm 
adhesive 
delaminated 
not delaminated 
Time µs 
Fr
ee
 
su
rfa
ce
 
v
el
o
ci
ty
 
m
/s 
Frequency (MHz) 
in
te
n
sit
y 
a) b) 
FM1000 
ESP310 
E5min 
L414 
(a) (b) 
  
Acknowledgements 
Authors are grateful to the National Research Council Canada for its support through 
the Natural Sciences and Engineering Research Council of Canada. Authors would like 
to thanks B. Arsenault and Jean-François Alarie from IMI-CNRC for the adhesive 
assembly, the useful information and advises they kindly provided, and Laurent Berthe 
and Michel Boustie from the CNRS France for their helpful remarks. 
 
References 
 
1. M. Regert, Journal of separation science 27, 244-254, 2004. 
2. W.E. Snowden, I.A. Aksay, Material Science Res. 14, pp. 651-660, 1981. 
3. I.G. Epishin, V.V. Suslov, and V.A. Yanushkevich, “Determination of adhesion 
strengh of film structures of components in electronic devices using laser shock 
waves”, Fizika i Khimiya Obrabovki Materialov, 22, pp. 80-84, 1988. 
4. V. Gupta. And A.S. Argon., Materials Science and Engineering, AL26, pp. 105-
117, 1990. 
5. E. Auroux, "Etude de l’adhérence de couches minces sur des substrats soumis à 
un choc laser", Thèse de l’Université de Poitiers, 1999.  
6. R. Bossi, K. Housen. and C. Walters, NTIAC (Nondestructive Testing 
Information Analysis Center) Newsletter, Vol. 30, 2005. 
7. S. S. V. Kandula, C. D. Hartfield, P. H. Geubelle, N. R. Sottos, Thin Solid Films 
(2008). 
8. T. Antoun, L. Seaman, D.R. Curran, G.I. Kanel, S.V. Razorenov, A.V. Utkin, 
“Spall fracture”, Springer, 2003. 
9. C. Bolis, L. Berthe, M. Boustie, M. Arrigoni, S. Barradas and M. Jeandin J. 
Phys. D: Appl. Phys. 40, pp. 3155–3163, 2007. 
10. Mc Millan, Goosman, Parker et al., Rev. Sci. Instrum. 59, 1988. 
11. J.-P. Monchalin “Optical detection of ultrasound”, IEEE Transactions on 
ultrasonics, ferroelectrics and frequency control, UFFC-33, 1986. 
12. R. J. Dewhurst and Q. Shan, Meas. Sci. Technol. 10, R139–R168, 1999. 
13. L.M. Barker and R.E. Hollenbach, “Laser interferometry for measuring high 
velocities for any reflecting surface”, Journal of Applied Physics 43, pp. 4669–
4675, 1972. 
14. M. Arrigoni, J.-P. Monchalin, A. Blouin, S. E. Kruger, M. Lord, “Laser Doppler 
Interferometer based on a solid Fabry-Perot Etalon for measurement of surface 
velocity in shock experiments”, submitted to Meas. Sci. and Technol., 2008. 
15. C.B. Scruby, L. E. Drain, “Laser ultrasonics, techniques and applications”, 
Adam Hilger, 1990. 
16. G. Hernandez, “Fabry-Perot interferometers”, Cambridge University Press, 
1988. 
17. J. M. Vaughan, “The Fabry-Perot interferometer, History, theory, practice and 
applications”, Adam Hilger, 1989. 
18. R. Fabbro, P. Ballard, J. Fournier, D. Devaux, J. Virmont,  J. of Appl. Phys., vol. 
68 (2), p. 775-784, 1990. 
19. K. Kanayama et al., Heat transfert Japanese research – 26, 1997. 
20. L. Berthe, R. Fabbro, P. Peyre, L. Tollier, and E. Bartnicki, J. Appl. Phys. 82, p. 
15, 1997. 
 


The Use of Laser-Doppler Interferometry Based on a Fabry-Perot Etalon for Shock Adhesion Test Applied to Adhesively Bonded Materials

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