JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 52

health monitoring

Strain measurements and damage detection
by fibre optics sensors in large structures
By means of a novel and robust automated technique based on strain field pattern recognition, a
defect detectability study was performed for two
13.5-metre-long wind turbine blade prototypes
under different load scenarios. Fibre optic sensors
(FOS) were embedded into the blades (fully made
of composite materials) during the manufacturing
process, which consisted in an experimental RTM
light procedure. Two different FOS technologies
were used: fibre Bragg gratings (FBGs) and distributed sensing by means of an optical backscatter
reflectometer (OBR). Some challenges associated with the integration of the sensor within the
structure had to be faced in order to guarantee
the appropriate operation of the sensors network
during the service life of the blades (in this case,
during the experiments). Several static tests were
conducted, including a test campaign in a wind turbine test laboratory with known artificial damages
induced into the structure, and the sensitivity of
the technique was evaluated. The results showed
that each damage could be detected using both
sensing techniques.

T

he integrity and reliability of structures are extremely important in many engineering fields like aeronautics, space,
civil engineering, architecture and energy, among others.
They are controlled through adequate knowledge of existing
damages. Typically, achieving the level of knowledge necessary
to characterize structural integrity involves the usage of nondestructive testing techniques (NDT), which are often expensive
and time consuming.

Need for health monitoring
As the complexity of structures increases, so do the physical and/
or mathematical models that describe such structures as well as
the techniques used to ensure their structural integrity during
their service life. Nowadays, several structural health monitoring (SHM) techniques for determining at an early stage whether
a structure is damaged are being developed by diverse research
groups around the world. One of the proposed "philosophies"
consists in building models based on information (experimental
data). This current has been called data-driven models (DDM)
and employs experimental data instead of deterministic models
(such as the stiffness matrix, modal parameters, etc.). Experimental data are used for "training" or "learning" of different types of
algorithms. The technique has been called "pattern recognition".
Thanks to their high strength-to-weight ratios, corrosion
resistance, fatigue performance, high stiffness and many other
advantages over conventional metallic materials, composite
materials are increasingly used in aerospace structures. However,
composite materials present some uncertainties and limitations
from the reliability perspective and, therefore, the development
of techniques which allow replacing the current schedule-based
maintenance of damage-tolerant composite structures by condition-based maintenance would allow improving the durability
and safety of structures.
In recent years, several authors have been working on the development of SHM techniques in order to predict the onset of damage in complex structures made of composite materials.

By

Strain measurement methodology
Dr. Julián Sierra-Pérez
aSSociate ProfeSSor
aeroSPace engineering reSearch grouP
univerSiDaD Pontificia Bolivariana

52 jec composites magazine / No96 April 2015

A novel methodology for damage detection in structures is
proposed. The methodology is based on strain measurements
and consists in the development of strain field pattern recognition techniques. The changes in the local strain field may be very



JEC COMPOSITES MAGAZINE - Issue #96 - April 2015

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #96 - April 2015

Cover
Edito
Point of view : composites integration
Contents
COMPANY & BUSINESS
China
In brief
JEC Americas
Agenda of Events
APPLICATIONS
Catamaran
RIB
Trimaran
MARKET
Carbon fibre
FEATURE AERONAUTICS
Simulation
Cost-effectiveness
Low cost manufacturing
Thin-ply
High temperature
LFT
Thermoplastics
Laser projection
Release agent
Manufacturing
RESEARCH & DEVELOPMENT
Health Monitoring
Health monitoring techique for large composite structures
TECHNOLOGY & INNOVATIONS
IOT
Braiding
Resin
Vacuum infusion
Machining center
PBT
Index
In the world
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Cover
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 2
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Edito
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Point of view : composites integration
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 5
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Contents
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 7
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - China
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - In brief
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - JEC Americas
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 11
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 12
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 13
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Agenda of Events
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 15
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Catamaran
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 17
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - RIB
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Trimaran
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 20
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Carbon fibre
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 22
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 23
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 24
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 25
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Simulation
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 27
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Cost-effectiveness
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 29
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Low cost manufacturing
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 31
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 32
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Thin-ply
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 34
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 35
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - High temperature
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 37
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - LFT
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 39
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 40
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Thermoplastics
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 42
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 43
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 44
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Laser projection
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 46
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Release agent
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Manufacturing
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 49
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 50
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 51
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Health Monitoring
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 53
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 54
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 55
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Health monitoring techique for large composite structures
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 57
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 58
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 59
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - IOT
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 61
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Braiding
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 63
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 64
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Resin
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 66
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Vacuum infusion
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 68
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Machining center
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 70
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 71
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - PBT
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - Index
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - In the world
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 75
JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 76
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