JEC COMPOSITES MAGAZINE - Issue #129 - July/August 2019 - 57

Effects of ageing on the mechanical and structural properties of glass/epoxy composite pipes in seawater

used composite materials such as carbon/polyester, glass/polyester,
carbon/vinyl ester and glass/vinyl ester. They found that the resin matrix and the fibre/matrix interface suffered from chemical degradation.
Pegoretti and Migliaresi [4] studied the long-term consequences of
water ageing on the mechanical and physical properties of a composite
dental prosthetic fabric at two testing temperatures. More specifically, the researchers discovered that flexural strength strongly decreases
throughout hydrothermal ageing. Mercier et al. [5] also concentrated
on the damage to glass fibre-epoxy composites caused by immersion.
They studied the effects of mechanical loading and diffusion on the
material stiffness during ageing and then produced a model for the estimation of material properties. Deniz et al. [6] determined the effects
of seawater on the behaviour of cross-wise impacted composite pipes
with different diameters. They discovered that the impact performance
and breakdown of composite pipes were strongly affected by seawater
penetration. The effects of moisture combined with temperature on
glass/epoxy composites considering the presence of salt in seawater
were reported by various workers. According to the research work conducted by A.P. Chakraverty et al. [7], cracking, swelling, chemical loss,
hydrolysis, debonding, oxidation and leakage are caused by moisture
absorption when the specimen is placed in seawater for a prolonged
period of time. The rupture at the interface is initiated by hydrolysis,
which is enhanced at elevated temperature and tends to disintegrate the
chemical bonds at the edge of the specimen, causing the separation of
the matrix and fibre. At room temperature, hydrolysis can cause an enlargement of the matrix that will start to improve mechanical bonding
between the matrix and fibre, with plasticization outcomes in sustaining the modulus and increasing the matrix ductility [8]. Gellert, E.P. et
al. [9] calculated the time period for the exposure of glass/polyester and
glass/vinyl ester composites to seawater at 32°C that resulted in a loss of
elastic strength and modulus of rigidity. In this study, the temperature
played an important role in controlling the properties of the specimens.
The absorption of seawater and distilled water in glass/epoxy composites was shown to initiate a variation in the mechanical, thermo-physical
and chemical properties of the epoxy and matrix through plasticization
and hydrolysis. As absorption increased, the structural and mechanical
properties of the matrix and epoxy tended to change, the method implemented by the researchers being hydrolysis and plasticization. The
research conducted by Vigier et al. [11] indicated that the degradation
of the composite is due to physical ageing or plastification resulting
from the dispersal of water in the polymer matrix at the fibre/matrix
interface [12]. Pritchard et al. [13] detected a separation of the fibre/
resin interface of glass composites immersed in water up to 1500 hours
in the temperature range from 35 to 80°C, even without applying an
external load. Gaur et al. [14] showed by means of a microbond pull-out
method that the bond strength of E-glass and epoxy micro-composites
was reduced by almost 40% following one hour of ageing in water at
88°C. This method was tested but following the work of other researchers, the ageing time was improved at a given temperature according to
the studies. Carlsson et al. [15] testified that the strength and transverse
modulus of E-glass/epoxy were brought down to less than 50% of their
dry values following 4800 hours of immersion in water at 35°C. The
test results were also used to calculate the transverse modulus/strength
plot of E-glass/epoxy immersed in the medium at a certain tempera-

ture. Metcalfe and Schmitz [16] also reported past work illustrating
the same consequences on E-glass filaments aged in water with 100%
comparative humidity. Their work demonstrated that the level of humidity depends on the temperature of the water and the environmental
conditions. The work conducted by Appicella et al. [17] suggested that
there is a useful effect between matrix plasticization as an outcome of
water absorption and stiffness growth due to the shortfall of low-molecular-weight substances so that both water absorption and the specimen stiffness increase. Since the epoxy matrix resin has an organic
nature, an extended immersion in seawater can change its physical and
chemical properties [18]. In their work, McKague E.L. and Weitsman
Y.J. et al. [19, 20] concluded that the main physical consequences of
water absorption on polymer structures are due to the plasticization
and swelling of the composite when it is placed under water for a prolonged period of time. These plasticization and swelling properties can
even affect the resin and matrix interface bonding, which can lead to
microcracks and delamination of the bond. Kolat et al. [21] found out
the causes of fracture toughness of a composite sandwich subjected to
seawater conditions. The composite's toughness was determined in various temperature and humidity conditions to determine the fracture intensity. When composites take in water and are then dehydrated, water
acceptance and loss can produce stresses and micro-cracks, which tend
to result in even greater water absorption [22]. Several works showed
that the flexural strength and interlaminar shear strength are reduced
when the level of water absorption is increased [23-25]. Zhang et al. [26]
examined the failure of a composite pipe made of a corrosion-resistant plastic alloy and analysed it after several years of usage. Ellyin and
Maser [27] studied the effects of distilled water ingress on the mechanical properties of glass/epoxy composite pipes at high temperatures and
discovered that the pipes' strength weakened as the temperature and
moisture absorption increased. The pipes' strength also diminished
when increasing the immersion period due to the loss of the fibre-matrix connection. The study conducted by Farshad and Necola [28] focused on the effects of immersion in distillate water on glass/epoxy
composite pipes, including their creep behaviour. Buehler and Seferis
[29] found a decrease of the mechanical properties of epoxy/glass composites upon water absorption. The researchers conducted the analysis
in two modes to predict the damage in different intervals of time.
Ageing process of glass/epoxy
composite pipes in seawater
Ageing is defined in industry as the reduction in performance of a component as a function of the applied conditions. Generally, when fibre/
epoxy reinforced composite pipes are used in underwater applications,
it is important that the composites retain their mechanical properties
and are not damaged when submerged in seawater for a long period of
time. When glass/epoxy composite pipes are submerged in seawater
for extended periods of time, they undergo damage due to the diffusion of hydrogen and hydroxyl ions into the fibre fabric, and the ions are
slowly replaced by the sodium ions that originally exist in the seawater.
The eccentric strain resulting from the substitution of ions can initiate
cracks in the fibre overlays. Liquid solutions can hydrolyse the siloxane
groups of the glass fabric and increase the growth of the flaw. A breakdown also occurs in the interfacial area owing to the chemical reactions

N°129 July - August 2019

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JEC COMPOSITES MAGAZINE - Issue #129 - July/August 2019

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