JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 61

In summary, this work aims to address questions related to
the composite/sensor interaction in long-term use, while
strengthening the use of micro-CT technology for non-destructive inspections of composite materials.

Materials and method
A carbon fibre epoxy prepreg (M55J-M18 from Hexcel)-based
cross-ply laminate with a [902,02]2s lay-up was manufactured
by autoclave, using a 2-hour curing temperature of 180°C, a
vacuum level of -80 kPa and an external pressure of 7 bar. In
the mid-layer of the laminate, optical fibre sensors (OFS) with
different diameters were embedded in alignment with the
reinforcing fibres (0° layers). A total of 5 rectangular samples
were cut from the laminate (dimensions t x w x l = 2 mm x 10
mm x 250 mm) and were tested under fatigue. Samples 1 and
2 had a 60/96 μm cladding/coating diameter optical fibre,
Sample 5 an 80/116 μm cladding/coating diameter optical
fibre, and Sample 8 an 80/190 μm cladding/coating diameter
optical fibre. Sample 9 had a 125/195 μm cladding/coating
diameter. All the fibres were coated with Ormocer (organic
modified ceramic material) through a continuous process, best
known as draw tower grating (DTG®) (see: www.fbgs.com).
The samples were loaded for fatigue testing for a predefined
number of cycles. The fatigue test setup is depicted in Figure
1 (left). A tension-tension sinusoidal load cycle with a load
ratio (R) of approximately 0.1 was chosen in order to avoid
compression. To define the load limits, a preliminary set of
tensile static tests was performed on 3 reference specimens,
which were cut from the manufactured plate according to the
dimensions provided in the ASTM D3039 standard. The average ultimate tensile stress (UTS) of the material was measured
(830±40 MPa). The applied cyclic load was aligned with the
fibre optic direction. The cycling frequency was set to 5 Hz.
The stress varied sinusoidally between 50 and 450 MPa (~50%
of the UTS) for 1,000 cycles. The sample was subsequently
dismounted from the test bench and moved to the micro-CT
facility for the scan.
The cycle was then resumed at the same stress level till
1,000,000 cycles. Since no evident damage was found after
this last stage, the load amplitude was increased to 600 MPa
(~70% of the expected UTS) and cycled for another 1,000 cycles, resulting in a total of 1,001,000 cycles. The following load
cycles were continued at the same stress level till 2,000,000
cycles and, finally, till 4,000,000 cycles. Before and after each
load cycle, a static test was performed to evaluate the stiffness
degradation related to the damage state. The axial deformation
of the sample during these tensile tests was measured in the
central gauge length region using an extensometer.
To evaluate damage evolution inside the samples in the OFS
surroundings, micro-CT scans were performed after each cycle sequence. The central zone circled in red in Figure 1 (right)
represents the location where a micro-CT scan was taken.

Fig. 2: Micro-computed tomography (micro-CT) scanner used for the nondestructive inspections

Aluminium tape stripes were used as a boundary to define the
scanning region and were kept as a reference (to ensure the
same region was scanned each time) on the samples during
fatigue testing.
Micro-CT setup
The scans were obtained using a modular 900-nm CT scanner [4]. A high-resolution micro-CT scanner optimized for
research purposes is presented in Figure 2 as an example.
The sample was placed on a high-precision piezo-positioning
manipulator and rotated, in order to obtain projections at
different orientations. The X-ray tube, with medium (160
keV-150 W) to high energy (240 keV-280 W), directed its
X-rays towards the sample at a minimum focal spot size of 2-4
μm. The size and energy of the X-ray beam were crucial for
reaching high-resolution CT quality. Far behind the sample, a
flat detector panel acquired the outcoming rays on a relatively
large area (20 x 25 cm2). The scanner was equipped with up to
9 motorized axes, which allowed a large degree of freedom and
the possibility of using large, bulky samples. After a first set
of trials, the X-ray source was selected at 100 kV and 3 watts
of target power, resulting in a voxel pitch of 2 μm (resolution
of the cross-section images). In total, 1500 projections were
recorded over 360° and the radiographs were reconstructed
with the in-house developed Octopus software package. The
reconstructed pictures were post-processed with MATLAB®
and analysed, while 3D renderings were made with VGStudio
Max® from the original reconstructed images.

Experimental results
Initial state after curing
The scans presented in this section were taken after laminate
production and sample preparation, while no mechanical
load was applied yet. Figure 3 (top) shows the result of a slice
(cross-section) of the laminate, which was reconstructed
from the radiographs taken at different orientations. The area
corresponds approximately to a region of 4 x 2 mm2. One can
distinguish between the 0° and the 90° oriented layers; every
layer is composed of two plies about 100 μm thick. The mid
No97 May - June 2015 /

jec composites magazine 61


http://www.fbgs.com

JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015

Cover
Edito
Point of view : Excellence as a motto
Contents
COMPANY & BUSINESS
In brief
Equipment
Agenda of Events
APPLICATIONS
Marine
Watch
MARKET
USA
SPECIAL JEC AMERICAS
Conferences
Awards
Brazil, country guest of honor
Natural fibes
Manufacturing
Oil & Gas / overview
Oil & Gas / manufacturing
Oil & Gas / testing
Oil & Gas / Coating
RESEARCH & DEVELOPMENT
CFRP
Health monitoring
TECHNOLOGY & INNOVATIONS
Pultrusion
AFP
Prepreg
Repairing
Index
In the world
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Cover
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 2
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Edito
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Point of view : Excellence as a motto
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 5
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Contents
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 7
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - In brief
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Equipment
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 10
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 11
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Agenda of Events
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 13
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Ad1
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Ad2
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Marine
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 15
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Watch
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 17
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - USA
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 19
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 20
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 21
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 22
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Conferences
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 24
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 25
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Awards
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 27
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 28
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 29
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 30
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 31
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Brazil, country guest of honor
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 33
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Natural fibes
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 35
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 36
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 37
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 38
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Manufacturing
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 40
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 41
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 42
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 43
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 44
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Oil & Gas / overview
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 46
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 47
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Oil & Gas / manufacturing
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 49
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 50
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Oil & Gas / testing
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 52
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 53
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Oil & Gas / Coating
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 55
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - CFRP
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 57
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 58
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 59
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Health monitoring
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 61
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 62
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 63
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Pultrusion
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 65
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - AFP
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 67
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 68
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Prepreg
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 70
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Repairing
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 72
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Ad3
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Ad4
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - Index
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - In the world
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 75
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 76
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