JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 48

review

of the interface between the adjacent layers becomes crucial.
Since the matrix resin ensures the adhesion between plies and
is generally more susceptible to degradation by water, a greater
reduction in tensile strength is found for thicker specimens
composed of a large number of plies. As regards the influence of
the matrix nature, epoxy and vinyl ester resins are deemed to be
more resistant to the action of water. In polyester-based FRP, a
hydrolysis of the resin can take place during immersion, causing
severe damage.

Example of structural reinforcement employing CFRP stripes applied
through wet lay-up technique. (Photo kindly supplied by QuakeWrap, Inc. /
FRP Construction, LLC)

from cohesive failure, through the concrete substrate, to adhesive failure, which further supports the hypothesis of interface
degradation due to hygrothermal conditioning. An appreciable
decrease in the adhesion strength between the FRP and the
substrate can be expected when the external temperature is
close to the resin's Tg. An appreciable decrease in bond strength
was measured when the service temperature approached and
exceeded the Tg of the matrix/adhesive, for wet lay-up FRP, and
of the adhesive, for pre-cured FRP, both applied to concrete elements [Almusallam and Al-Salloum, 2006; Leone et al., 2009].
As a conclusion, due to their moderate Tg, attention must be
given to the site temperature when using cold-cured resins: the
environmental temperature under working conditions should
be some 20°C below the glass transition temperature [Hollaway,
2010].

Fibre-reinforced polymer composites
Generally speaking, the studies that analyse the effects of
weathering on the properties of FRP materials highlight the crucial role of the adhesive/matrix on the behaviour of the whole
system. Many other parameters (i.e. direction and disposition of
fibres, direction of load application) are also taken into account
when assessing the durability of FRP.
The effect of (liquid or vapour) water on composites depends
on the type of matrix resin and fibres used, on the configuration
of fabrics (number and disposition of plies) and on the direction of load application. The tensile properties of a single-ply
composite in the fibre direction are highly dependent on the
properties of the fibres. While in the case of carbon fibres, the
absorption of water has hardly any effect on its properties,
water can cause a deterioration of the mechanical properties
(stiffness and strength) of laminates manufactured with glass
fibres. When using laminates composed of several plies, the role

48 jec composites magazine / No106 July 2016

Freeze-thaw exposure generally causes a severe degradation of
FRP properties due to the stiffening and embrittlement of the
matrix resin at temperatures below its Tg, with the consequent
formation of micro-cracks. Fibre-matrix debonding and a local
loss of adhesion strength towards the substrate may occur due
to the difference in coefficients of thermal expansion as well as
to the expansion and contraction of water in the freeze-thaw
environment. A reduction in interlaminar fracture toughness
can also be observed. On the other hand, exposure to freezethaw cycling affects to a minor extent the tensile, flexural and
short beam shear strength (SBS) of the FRP. All the mentioned
effects are generally magnified by increasing the number of
freeze-thaw cycles, in the presence of a service load and when
the thaw regime is applied in saline environments; they are almost not dependent on the type of matrix resin and fibres used.
The permanence at a sub-zero temperature has only a limited
influence on the performance of an FRP material.
The durability of a composite material in saline or acid solutions
depends on the resistance of both the matrix and the reinforcing
fibres to these agents. Immersion in simulated seawater, alkaline
and acid solutions is particularly harmful for AFRP and GFRP
composites, producing damage at the fibre/resin interface for
both types of FRP and the degradation of the glass fibres for
GFRP. The tensile properties of CFRP are generally not affected
by immersion in either simulated concrete pore solutions or any
usual saline and acid solutions used to reproduce ageing. The
flexural and interlaminar characteristics of carbon fibre-based
composites appear more susceptible to exposure to alkaline and
salt solutions as compared to immersion in pure (or tap) water.
Regarding the matrix resins, epoxies have shown to be more
resistant to alkaline environments than vinyl esters and polyesters. Drying specimens over prolonged periods of time after
immersion not always results in a complete regain of the initial
performance, which indicates that such agents generally cause
irreversible changes and damages in composites.
Ultraviolet radiations mainly affect the surface and consequently degrade only the matrix of an FRP, causing a decomposition
of the resin molecules. The consequent embrittlement of the
matrix produces micro-cracks at the surface, which in the presence of other environmental agents can accelerate the degradation process by allowing easier penetration of fluids into the
laminates. In some cases, the exposure to radiations can even



Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #106 - July 2016

Cover
Edito
Point of view: Europe
Contents
COMPANY & BUSINESS
Development
Agenda of Events
APPLICATIONS
Thermoplastics
Automotive
MARKET
Aircraft engine
FEATURE AERONAUTICS
Aerostructures
Characterisation
Thermoplastics
Aero-engines
Process
CFRP
Semi-product
RESEARCH & DEVELOPMENT
Review
Core material
TECHNOLOGY & INNOVATIONS
NDT
Marine
Index
In the world
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - Ad1
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - Cover
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 2
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - Edito
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - Point of view: Europe
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 5
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - Contents
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 7
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - COMPANY & BUSINESS
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 9
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - Development
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 11
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - Agenda of Events
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 13
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - AdHEC
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - AdCro
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - Thermoplastics
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 15
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 16
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - Automotive
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - Aircraft engine
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 19
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 20
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 21
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 22
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - Aerostructures
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 24
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 25
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - Characterisation
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 27
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 28
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 29
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 30
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - Thermoplastics
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 32
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - Aero-engines
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 34
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 35
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 36
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - Process
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 38
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 39
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - CFRP
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 41
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 42
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - Semi-product
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 44
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 45
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - Review
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 47
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 48
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 49
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - Core material
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 51
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 52
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - NDT
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 54
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - Marine
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 56
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - Index
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - In the world
JEC COMPOSITES MAGAZINE - Issue #106 - July 2016 - 59
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