JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 59

Non-destructive evaluation of the mechanical strength of a TA6V4/composite bond using LASAT

Fig. 1: Schematic view of the generation of a laser-induced shockwave in a
confined geometry

Fig. 2: Laser adhesion test configuration

ergy (E) pulsed laser beam is focused on some mm² of focal spot (S)
on the front face of a given target for a time period (τ) of several nanoseconds. The laser pulse can therefore be characterized by its intensity
(Equation 1).

proof test since the use of a calibrated laser pulse should discriminate
weak bonds from healthy ones. The main challenge for industrial applications is to demonstrate the non-destructive side of LASAT. This
work brings some serious results assessing the NDT capacity of the
technique.

Experiments
Due to collisional absorption and inverse Bremsstrahlung phenomena [3], the matter is quickly heated up to the vapour and plasma state.
According to Newton's third law, the ejection of matter from the front
face towards the laser beam creates a reaction force in the opposite direction, i.e. towards the sample.
The use of a confining dielectric layer, such as water, has long been
identified as an optimization technique to generate shocks with smaller laser intensities [4] (Figure 1). This type of geometry prevents plasma expansion and hence maximizes both the shock amplitude and duration. Nevertheless, it must be kept in mind that a water breakdown
plasma occurs at intensities around 10 GW/cm², depending on the
laser pulse duration and wavelength [5]. This phenomenon limits to
a few GPa the maximum ablation pressure that can be applied to the
target.

Materials
The samples investigated are made of a TA6V titanium alloy/3D woven
composite bonded together with a typical aeronautic epoxy glue. The
thickness of the titanium, glue and composite is 0.4 mm, 0.150 mm and
3.8 mm, respectively, for the considered samples. The side dimensions
of the bonding are 240x40 mm².
Two different mechanical grades of bonding quality were achieved
varying the glue reticulation during the curing step. The mechanical properties of the resulting bond quality were investigated using
typical static mechanical testing methods. The results are shown in
Table 1.
Tab. 1: Mechanical strength of the samples

Healthy bond

Weak bond

Shear mechanical strength

35 MPa

15 MPa

Longitudinal mechanical strength

39 MPa

10 MPa

The amplitude (a few GPa) and duration (a few nanoseconds) of the
resulting loading, named the ablation pressure (Pabl), imply strong
temporal and spatial discontinuities, typical of a shock wave. The maximum ablation pressure can be estimated using well-known analytical
laws [6] or even validated laser-matter interaction codes [7].

As expected, the healthy bond has a higher failure resistance than the
weak bond. Weak-to- healthy properties were expected to be about
50%. The results differ significantly depending on the mechanical
stress.

The shock wave generated in the front face then propagates through
the thickness of the sample. According to acoustic impedance transmission-reflection laws, tensile stress zones can be generated due to the
recombination of release waves. If the applied tensile stress is higher
than the dynamic mechanical resistance of the bond, then a cohesive
or adhesive fracture of the bond is observed. However, the use of conventional NDT techniques for the post-shock evaluation is necessary
to determine which laser shots lead to disbonding. The LASAT technique coupled with a disbonding diagnostic can therefore be seen as a

Laser facility
LASAT experiments were performed in the Hephaistos facility at
the ENSAM-Paris PIMM (Procédés et Ingénierie en Mécanique et
Matériaux) laboratory. This installation can produce 7-ns FWHM
Gaussian pulses in the visible wavelength spectrum (532 nm). This
Thales Gaia HP laser can generate up to 14 J that can be deposited on
the target in a single pulse.
In the experiments, the Hephaistos laser beam was focused on the
front face of the material, either the TA6V4 or the 3D composite face
N°116 October 2017

/ jec composites magazine

59



Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #116 - October 2017

Cover
Edito
Opinion: Renewable energy
Contents
NEWS
In brief
JEC Asia
Agenda
BUSINESS
Strategy - Airbus strengthens its position in China
Database - The new technical database for composites
MANUFACTURING
NDT - New flexibility in 3D digitalisation and defect detection for batch composite production
Thermoplastics - Development of a carbonthermoplastic hub for the H160 helicopter
Feature Wind energy - An increasingly efficient sector
Market news - TPI Composites agreements with Gamesa and Vestas Wind Systems
Overview - Double digit growth again for the wind energy
Focus - lnside lndia’s wind turbine industry
Testimony - Strong growth in wind energy worldwide
Process - Perfect composite parts, thanks to the «direct infusion» process and resin conditioning
Technologies - Evolution of technologies and materials used in wind turbine blade manufacturing
Resin - New products for longer blades help to cut cost
SOLUTIONS
Aeronautics - lnnovative thermoplastic composite wing rib
Bike - Taking the lead with composites
Motorbike - lnnovative SLS front air inlet made with high-performance materials
Solar energy - Ultra-light photovoltaic panel based on polyamide honeycomb technology
TECHNOLOGY
NDT - Non-destructive evaluation of the mechanical strength of a TA6V4/composite bond using LASAT
Efficiency - Cost-efficient preforming using tailored textiles
Index
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JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 68
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Cover
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 2
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Edito
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Opinion: Renewable energy
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 5
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Contents
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 7
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - In brief
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 9
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - JEC Asia
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 11
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 12
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 13
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 14
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 15
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Agenda
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 17
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 18
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Ad1
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Ad2
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Strategy - Airbus strengthens its position in China
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 20
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 21
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Database - The new technical database for composites
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 23
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 24
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - NDT - New flexibility in 3D digitalisation and defect detection for batch composite production
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 26
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 27
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Thermoplastics - Development of a carbonthermoplastic hub for the H160 helicopter
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 29
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 30
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 31
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 32
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 33
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 34
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Market news - TPI Composites agreements with Gamesa and Vestas Wind Systems
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 36
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 37
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Overview - Double digit growth again for the wind energy
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 39
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Focus - lnside lndia’s wind turbine industry
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 41
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Testimony - Strong growth in wind energy worldwide
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 43
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Process - Perfect composite parts, thanks to the «direct infusion» process and resin conditioning
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Technologies - Evolution of technologies and materials used in wind turbine blade manufacturing
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 46
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 47
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Resin - New products for longer blades help to cut cost
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 49
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 50
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Aeronautics - lnnovative thermoplastic composite wing rib
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Bike - Taking the lead with composites
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 53
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Motorbike - lnnovative SLS front air inlet made with high-performance materials
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 55
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 56
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Solar energy - Ultra-light photovoltaic panel based on polyamide honeycomb technology
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - NDT - Non-destructive evaluation of the mechanical strength of a TA6V4/composite bond using LASAT
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 59
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 60
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 61
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 62
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Efficiency - Cost-efficient preforming using tailored textiles
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 64
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 65
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - Advertisers
JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 67
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