Seawater Aging Research Articles

The effects of aging in seawater and SWSSC and strain rate on the tensile performance of GFRP/BFRP composites: A critical review

• The tensile properties of GFRP/BFRP after exposure in sea water/SWSSC are discussed. • The degradation degree increases with the exposure time, temperature and alkalinity. • The impact strength and fatigue life are reduced due to the exposure in seawater. • The dynamic performance and failure mode are obviously influenced by strain rate. • The future research needs are proposed for the FRP used in seawater/SWSSC. Replacing metallic materials (typically carbon steel bars) with fiber reinforced polymer (FRP) composites to reinforce marine concrete structures can effectively resolve the corrosion issue of carbon steel due to external chloride ions and moisture. However, the corrosion-free nature of FRP material cannot guarantee its desirable durability in the marine structures. In order to better understand the durability performance of FRP composites, this paper summarizes the quasi-static tensile properties of FRP composites after exposure in simulated seawater and seawater sea sand concrete (SWSSC) environments, and the dynamic performance of the FRP materials. It is found the degradation degree of FRP composites increases with the exposure time, temperature, stress level and alkalinity/salinity of the immersion solution. Currently, the investigations on the dynamic tensile properties of FRP composites after long-term exposure tests are quite limited. Hence this study identifies the possible research needs by summarizing the investigations on the degradation of FRP’s dynamic performance after seawater exposure and the strain rate sensitivity of glass/basalt fiber reinforced polymer (GFRP/BFRP) composites under dynamic loading. The impact strength, Young’s modulus and fatigue life will all be diminished due to exposure in seawater. And both the mechanical performance and failure mode of the FRP composites are obviously influenced by the applied strain rate. This study identifies the current knowledge gap and can serve as a valuable reference for further investigation on the long-term performance, especially the long-term dynamic tensile properties of FRP composites in seawater and SWSSC environments.

Effect of Seawater Ageing on Fracture Toughness of Stitched Glass Fiber/Epoxy Laminates for Marine Applications

Composite materials are used in various industries such as marine, aircraft, automotive, etc. In marine applications, composites are exposed to seawater, which can affect their mechanical properties due to moisture absorption. This work focuses on the durability of composite materials under the short-term effect of seawater ageing. The specimens were prepared from glass fiber/epoxy using a hand lap-up method and stitched in the z-direction with Kevlar fiber. The specimens were submerged in seawater for 24 and 35 days. A significant decrease in maximum load was found as specimen immersion time in seawater increased. The seawater ageing also affected fracture toughness with a reduction of 30% for 24 days immersion and 55% for 35 days. The ageing also caused the swelling of composites due to moisture absorption, which increased the weight of the specimens. Compared to the dry specimens, the weight of the specimen for 24 days increases to 5.2% and 7.89% for 35 days’ seawater ageing. The analysis also showed that due to seawater ageing, the de-bonding rate increased as the number of days increased.

Significantly improved shear, dynamic-mechanical, and mode II fracture performance of seawater aged basalt/epoxy composites: The impact of halloysite nanotube reinforcement

The primary concern of fiber-reinforced polymers (FRPs) subjected to seawater environment is losing their initial mechanical performance since water can diffuse into the composite and deteriorates the fiber-matrix interface. Recent studies related to aging performance in the seawater environment have shown that introducing halloysite nanotubes (HNTs) into the polymer matrix offers a combination of an efficient barrier effect and an improved fiber-matrix interface. Hereupon, the principal objective of this study was to experimentally investigate the impact of HNTs on shear and mode II fracture performances of the seawater aged basalt fiber (BF) reinforced epoxy (EP) composites. After six months of aging in seawater, the findings indicated that HNTs reinforced multi-scale composites exhibited 34 and 46% higher shear strength and mode II delamination toughness compared to the neat specimens. Moreover, according to the dynamic-mechanical analysis, higher glass transition temperatures (8%) were obtained for the multi-scale composites. The reduction in mechanical performances induced by fiber-matrix interfacial degradation was also confirmed by scanning electron microscopy analysis. Chemical deterioration of the polymer matrix was explored by Raman spectroscopy to reveal the efficiency of HNTs induced barrier effect. As a result of these investigations, HNT modified BF/EP multi-scale composites were offered for future advanced engineering applications.

An experimental study on low velocity impact performance of bolted composite joints-part 2: Influence of long-term seawater aging

In the first part of this two-part paper (Part 1), the low-velocity impact (LVI) response of bolted fiber-reinforced polymer joints was investigated considering with two scenarios based on the localized impact damage as the impactor hit on the top of the bolt (ToB) and the side of the washer (SoW). Moreover, the influence of halloysite nanotubes (HNTs) reinforcement of the epoxy matrix on the impact performance was also evaluated. As the second part of the research, this paper represents the effects of seawater aging on the LVI response of FRPs. For this, the composite joints were submerged in an artificial seawater environment for six months to accelerate aging. Afterward, as following the systematic experimental path exhibited in Part 1, LVI tests were conducted by dropping the impactor on ToB and SoW regions. The test results showed that the seawater aging impaired almost 30% of the composite joints' impact resistance, where HNTs reinforced multi-scale composite joints exhibited a 13% higher impact loading performance. The ToB impact scenario was considered as visually and quantitatively more detrimental than the SoW tests. The detrimental impact of seawater aging was validated by tracking the elemental evolution in the seawater environment. Based on the mechanical, morphological, and structural analyses, a novel damage mechanism was introduced to address seawater aging's progress, including the role of nanoreinforcements.

Characterization of particle-associated and free-living bacterial and archaeal communities along the water columns of the South China Sea

Abstract. There is a growing recognition of the role of particle-attached (PA) and free-living (FL) microorganisms in marine carbon cycle. However, current understanding of PA and FL microbial communities is largely focused on those in the upper photic zone, and relatively fewer studies have focused on microbial communities of the deep ocean. Moreover, archaeal populations receive even less attention. In this study, we determined bacterial and archaeal community structures of both the PA and FL assemblages at different depths, from the surface to the bathypelagic zone along two water column profiles in the South China Sea. Our results suggest that environmental parameters including depth, seawater age, salinity, particulate organic carbon (POC), dissolved organic carbon (DOC), dissolved oxygen (DO) and silicate play a role in structuring these microbial communities. Generally, the PA microbial communities had relatively low abundance and diversity compared with the FL microbial communities at most depths. Further microbial community analysis revealed that PA and FL fractions generally accommodate significantly divergent microbial compositions at each depth. The PA bacterial communities mainly comprise members of Alphaproteobacteria and Gammaproteobacteria, together with some from Planctomycetes and Deltaproteobacteria, while the FL bacterial lineages are also mostly distributed within Alphaproteobacteria and Gammaproteobacteria, along with other abundant members chiefly from Actinobacteria, Cyanobacteria, Bacteroidetes, Marinimicrobia and Deltaproteobacteria. Moreover, there was an obvious shifting in the dominant PA and FL bacterial compositions along the depth profiles from the surface to the bathypelagic deep. By contrast, both PA and FL archaeal communities dominantly consisted of euryarchaeotal Marine Group II (MGII) and thaumarchaeotal Nitrosopumilales, together with variable amounts of Marine Group III (MGIII), Methanosarcinales, Marine Benthic Group A (MBG-A) and Woesearchaeota. However, the pronounced distinction of archaeal community compositions between PA and FL fractions was observed at a finer taxonomic level. A high proportion of overlap of microbial compositions between PA and FL fractions implies that most microorganisms are potentially generalists with PA and FL dual lifestyles for versatile metabolic flexibility. In addition, microbial distribution along the depth profile indicates a potential vertical connectivity between the surface-specific microbial lineages and those in the deep ocean, likely through microbial attachment to sinking particles.

Curing and seawater aging effects on mechanical and physical properties of glass/epoxy filament wound cylinders

Polymer composites in marine structures that operate under seawater environment may be seriously affected, reducing durability estimates. This work aims at evaluating the effect of seawater exposure at 80 °C for 7–28 days on filament-wound glass fiber/epoxy composite cylinders partially cured by passing saturated steam through them just after winding seeking a faster curing route. The winding angle is varied (±55, ±65 and ± 75) and some of the cylinders are later post-cured for comparison. The unaged partially cured specimens do not reach complete curing, with a glass transition temperature (Tg) of 132 °C, below the Tg for the other samples (154–159 °C). Fully cured cylinders present mechanical properties slightly higher than partially cured ones. Moreover, aging in seawater for 7 days enhances the cross-linking degree of epoxy, with a positive effect on both hoop tensile strength and stiffness. Aging is, however, not critical for the radial compressive properties.

Influence of Seawater Ageing on Fracture of Carbon Fiber Reinforced Epoxy Composites for Ocean Engineering

Carbon fiber reinforced composite materials are finding new applications in highly loaded marine structures such as tidal turbine blades and marine propellers. Such applications require long-term damage resistance while being subjected to continuous seawater immersion. However, few data exist on which to base material selection and design. This paper provides a set of results from interlaminar fracture tests on specimens before and after seawater ageing. The focus is on delamination as this is the main failure mechanism for laminated composites under out-of-plane loading. Results show that there are two contributions to changes in fracture toughness during an accelerated wet ageing program: effects due to water and effects due to physical ageing. These are identified and it is shown that this composite retains over 70% of its initial fracture properties even for the worst case examined.

Cement Composites’ Biostability

The studies to establish the species composition of micro-mycetes inhabiting the surface of cement composites after aging in sea water have been carried out. Cement stone made on the basis of Portland cement clinker, a mineral additive and a fungicidal preparation was considered as the studied material. To determine the materials’ fouling by microorganisms, their species composition, imprints and sampling methods were used. A change in the species composition of mycobiota isolated from the cement composites’ surface modified with sodium sulfate and sodium fluoride depending on the amount of active filler, gypsum, and biocidal additives was experimentally revealed. The effectiveness of using the biocidal cement composites with an active mineral additive has been confirmed. It was found that the composites on the developed compositions showed higher resistance compared to the materials on ordinary cement. The compositions modified with biocidal additives showed a fungicidal effect.

Seawater effects on interlaminar fracture toughness of glass fiber/epoxy laminates modified with multiwall carbon nanotubes

In this work, the effect of seawater ageing on mode I and mode II interlaminar fracture toughness ([Formula: see text] and [Formula: see text]) of prepreg-based woven glass fiber/epoxy laminates with and without multiwall carbon nanotubes (MWCNTs) has been investigated. The first part of the investigation reports the moisture absorption behavior of multiscale composite laminates exposed to seawater ageing for ∼3912 h at 70 °C. Then, the results of mode I and mode II fracture tests are presented and a comparison of [Formula: see text] and [Formula: see text] for each type of material group and condition is made. Experimental results showed the significant effect of seawater ageing on [Formula: see text] of multiscale composite laminates due to matrix plasticization and fiber bridging. The improvement in [Formula: see text] of the wet glass fiber/epoxy laminate was about 50% higher than that of the neat laminate (without MWCNTs) under dry condition. It was also found that the presence of MWCNTs into composite laminates promotes a moderate increase (8%) in their [Formula: see text] as a result of the additional toughening mechanisms induced by CNTs during the delamination process. Scanning electron microscopy analysis conducted on fracture surface of specimens reveals the transition from brittle (smooth surface) to ductile (rough surface) in the morphology of composite laminates due to the influence of seawater ageing on the polymeric matrix and fiber/matrix interface.

Tensile Strength Alteration of GFRP Composite Pipes Under Seawater-Dominated Conditions

Glass fiber-reinforced epoxy composite pipes are used in submarine applications, natural gas, and oil transportation lines, transfer of chemical liquids. Especially in the transport of pressurized fluids, changes in the strength of the pipes are important. The corrosive effect of seawater has an important impact on the mechanical properties of the composite material. In particular, the alteration in hoop tensile strength is one of the issues to be investigated. In this experimental study, glass fiber-reinforced epoxy resin composite pipes were exposed to the seawater aging process for different time periods (1, 2 and 3 months) in order to determine the effects of seawater absorption behavior on hoop tensile strength. Hoop tensile strength test was realized in accordance with ASTM D2290 Procedure A. As a result of this work, the average tensile strength values of the composite pipes decreased as the waiting times in seawater increased.

Halloysite nanotube reinforcement endows ameliorated fracture resistance of seawater aged basalt/epoxy composites

Seawater aging-dominated delamination failure is a critical design parameter for marine composites. Modification of matrix with nanosized reinforcements of fiber-reinforced polymer composites comes forward as an effective way to improve the delamination resistance of marine composites. In this study, we aimed to investigate experimentally the effect of halloysite nanotube nanoreinforcements on the fracture performance of artificial seawater aged basalt–epoxy composites. For this, we introduced various amounts of halloysite nanotubes into the epoxy and the halloysite nanotube–epoxy mixtures were used to impregnate to basalt fabrics via vacuum-assisted resin transfer molding, subsequently. Fracture performances of the halloysite nanotubes modified epoxy and basalt/epoxy composite laminated were evaluated separately. Single edge notched tensile tests were conducted on halloysite nanotube modified epoxy nanocomposites and the average stress intensity factor (KIC) was increased from 1.65 to 2.36 MPa.m1/2 (by 43%) with the incorporation of 2 wt % halloysite nanotubes. The interlaminar shear strength and Mode-I interlaminar fracture toughness (GIC) of basalt–epoxy hybrid composites were enhanced from 36.1 to 42.9 MPa and from 1.22 to 1.44 kJ/m2, respectively. Moreover, the hybrid composites exhibited improved seawater aging performance by almost 52% and 34% in interlaminar shear strength and GIC values compared to the neat basalt-epoxy composites after conditioning in seawater for six months, respectively. We proposed a model to represent fracture behavior of the seawater aged hybrid composite based on scanning electron microscopy and infrared spectroscopy analyses.

Low‐velocity impact behavior of glass fiber‐MWCNT/polymer laminates exposed to seawater and distilled water aging

AbstractThe influence of seawater (SW) and distilled water (DW) aging on low‐velocity impact behavior of glass fiber/polymer laminates with and without multiwalled carbon nanotubes (MWCNTs) is experimentally investigated. To this aim, unidirectional glass fiber fabrics were coated with 0.75 wt% MWCNTs by airbrushing, infused with resin (epoxy or vinylester), and cured. Then, composite laminates with and without MWCNTs were cut into specimens for low‐velocity impact testing and exposed to hydrothermal aging by immersing them to SW and DW at 60°C for ~2000 h. After that time of conditioning, dry and wet specimens were tested using a drop‐weight tower with an impact energy of 15 J. Results showed that the moisture absorption content of composite laminates exposed to SW and DW aging is considerably higher on epoxy‐based specimens with respect to vinylester ones. The impact tests revealed that the measured impact peak force and absorbed energy in wet specimens are significantly lower compared to dry specimens due to plasticizing effect of the matrix. With the incorporation of MWCNTs into the laminates, the absorbed energy is increased due to additional damage mechanisms induced at CNT‐rich regions during the impact loading. It was also found that the damage area of the laminates after impact tends to be more prominent for laminates fabricated using vinylester resin than for those using epoxy resin as a result of its brittle behavior during impact loading. Post impact damage analyses by ultrasonic C‐scan imaging and scanning electron microscopy showed that matrix cracking, fiber breakage, fiber/matrix debonding, and delamination are the main damage mechanisms induced in the dry and wet specimens during impact.

Combined effects of seawater ageing and fatigue loading on the bearing performance and failure mechanism of CFRP/CFRP single-lap bolted joints

The aim of this paper is to investigate the combined effects of seawater ageing and fatigue loading on the bearing performance and failure mechanism of CFRP/CFRP single-lap bolted joints. The bolted joints with an interference fit size of 1.15% were prepared and then immersed in artificial seawater (50 °C-3.5% NaCl solution) for 7 months. After that, fatigue loads were further applied to the unaged and aged joints. Finally, single-lap bearing tests were carried out to evaluate the bearing performance of seawater aged and fatigue load treated joints. Scanning electron microscope (SEM) was used to analyze bearing failure morphology. The experimental results showed that the ultimate bearing load of joints suffered the single effect of seawater ageing decreased exponentially with the increase of ageing time, while the joints suffered the combined effect of seawater ageing and fatigue loading decreased linearly. Moreover, compared with the single effect joints, the bearing capacity of combined effect joints showed a significant improvement. Furthermore, the failure mechanism of single effect joints was mainly the shearing fracture in bearing zones, and such shear angle increased with ageing time. However, the failure mechanism of combined effect joints was changed to be delamination in bearing zones.

Mechanical Behaviour of Composites Reinforced by Bamboo Strips, Influence of Seawater Aging

Mechanical Behaviour of Composites Reinforced by Bamboo Strips, Influence of Seawater Aging

Effects of acid, alkaline, and seawater aging on the mechanical and thermomechanical properties of glass fiber/epoxy composites filled with carbon nanofibers

ABSTRACTOwing to the superior corrosion resistance, fiber‐reinforced polymer (FRP) composites are the prime choice of structural materials for various marine and chemical industries, where there is a long‐term direct contact of the components takes place with corrosive fluids. In this present work, glass fiber/epoxy (GE) composites have been fabricated with and without carbon nanofibers (CNFs), and aging has been carried out in acidic (pH = 1), seawater (pH = 8.2), and alkaline (pH = 13) solutions for 150 days. The resistance of CNF‐filled GE composites toward the corrosive fluids has been evaluated in terms of alteration in the mechanical (flexural), microstructural (fractography analysis by field emission scanning electron microscope), and thermomechanical (dynamic mechanical analysis) behavior of the materials. It is revealed that as the immersion time increases, there is a continuous decrement in flexural strength and modulus, and glass‐transition temperature (Tg) of all the materials in all these solutions. Compared to the 1% CNF‐filled GE composite, control GE composite showed more degradation in the case of alkaline aging and seawater aging. Maximum reduction (56%) in the strength of GE composite was observed due to 150 days of alkaline aging. However, the control GE composite showed better resistance to the acidic solution than that of CNF‐filled GE composite. Possible failure modes, changes in the chemistry of the material due to aging have been studied by fractography analysis. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48434.

Influence of seawater aging on mechanical properties of nano-Al2O3 embedded glass fiber reinforced polymer nanocomposites

Retention of mechanical and thermal properties of nano-Al2O3 embedded glass fiber reinforced polymer (GFRP) composites in marine environment is necessary and need to be evaluated to realize the full potential of the nanocomposites. The plain and nanocomposites were seawater aged in a temperature controlled seawater bath at 70 °C for a duration of 40 days. The results revealed that seawater aged plain and nanocomposites deteriorate their flexural strength, interlaminar shear strength and glass transition temperature. However, with the addition of 0.1 wt% of nano-Al2O3 particles into the plain GFRP composite, the flexural strength increased by 12%, interlaminar shear strength by 11% in dry condition and seawater diffusion coefficient was reduced by 17% as compared to plain GFRP composites. Nevertheless, the glass transition temperature of the nanocomposites was not improved in dry and seawater aged conditions significantly. The fractured surfaces of tested samples were investigated through FESEM to support the new findings.

Effect of seawater ageing with different temperatures and concentrations on static/dynamic mechanical properties of carbon fiber reinforced polymer composites

The aim of this paper was to investigate the static/dynamic mechanical properties and failure mechanism of carbon fiber reinforced polymer composites (CFRP) in seawater environments. The prepared specimens were immersed in artificial seawater with different temperatures and NaCl concentrations for 7 months. Quasi-static tensile and dynamic mechanical analysis (DMA) tests were carried out to evaluate the tensile and damping properties. Ageing damage and fracture morphology were observed by using scanning electron microscope (SEM) technology. The results show that tensile strength was sensitive to ageing time and environmental temperature but non-sensitive to NaCl concentration. In addition, the failure mode was changed.

Aging of packaging films in the marine environment

The present article examines the aging behavior in the marine environment of some representative flexible plastic packaging films including supermarket plastic bags made of low‐density polyethylene (LDPE), polyethylene terephthalate (PET) films, polyamide–polyethylene (PAPE) films and films made of a material under the commercial name Mater‐Bi®. The effect of aging was studied by Fourier transform infrared spectroscopy, differential scanning calorimetry, and tension including creep‐recovery tests. The polyethylene films were not hydrolytically degraded during aging in seawater, and the polyethylene chains did not undergo any substantial chain scission. The PET films after exposure for 8 months in seawater did not suffer any substantial degradation, and the PET chains were plasticized by the absorbed water. After prolonged exposure to seawater (12 months), the PET films started to degrade. The PAPE film underwent extensive chemical and structural changes during aging in seawater as result of plasticization and hydrolysis of the polyamide (PA) component in combination with an eventual loosening of the tie layer. Mater‐Bi® film underwent a severe deterioration during aging in seawater due to the hydrolysis of the starch and polycaprolactone components. All films exhibited a marked degradation of their tensile properties after exposure to accelerating aging conditions under UV radiation. POLYM. ENG. SCI., 59:E432–E441, 2019. © 2019 Society of Plastics Engineers

Impact of hydrolytic degradation on mechanical properties of PET - Towards an understanding of microplastics formation

Ocean pollution by microplastics, i.e. small pieces of plastic of less than 5 mm, is one of the major concerns for the future of our planet. Secondary microplastics formation is due to fragmentation of macroplastic waste. This fragmentation can be attributed to environmental loadings such as waves, winds and tides, coupled with a change in mechanical properties of polymers induced by UV and seawater ageing. This study aims to characterize and understand changes in the mechanical behaviour of Polyethylene Terephthalate (PET) induced by hydrolysis, especially for high degradation levels. Thin films (200 μm) of PET were aged in water at temperatures from 110 °C to 80 °C for up to 150 days. Embrittlement occurs with chain scission during hydrolysis when molar mass of the polymer falls below 17 kg/mol. When the polymer is brittle, i.e. for high levels of degradation, the stress at break decreases linearly with the molar mass, and can be described by a simple mathematical expression.

Flexural and Specific Wear Rate of Seawater Aged Bamboo, Jute and Glass Fiber Reinforced Polymer Hybrid Composites

Abstract Natural fiber reinforced polymer composites have been used in different industries because of its high specific strength, modulus, cheaper and biodegradability. However, natural fiber reinforced polymer composites have lower mechanical properties and degrades its mechanical properties through seawater aging or moisture absorption than the composites having synthetic fiber. Therefore, the hybridization of natural fiber with synthetic fiber is needed to improve its mechanical properties in seawater aged condition. In this present investigation jute, bamboo and glass fiber is taken as the reinforcement medium for the preparation of the polymer hybrid composites. Three variety of hybrid composites such as [GJB]s,[GBJ]s,[JBG]s were considered for this investigation. The specimens were aged in seawater for 30days. It is found that [GBJ]s hybrid composite absorb more amount of seawater than the other two hybrid composites followed by degradation of its flexural strength by 42% and modulus by 33%. The [GBJ]s type hybrid composites shows lowest specific wear rate than the other two hybrid composites in dry condition and for seawater aged condition [JBG]s type hybrid composites shows minimum specific wear rate as compared to other hybrid composites