Influence Of Hygrothermal Ageing Research Articles

The influence of hygrothermal aging on the hoop tensile strength of glass fiber wound polymer composites fabricated via filament winding technique

The study investigates the impact of moisture environment treatment, on the hoop tensile strength (HTS) of glass fiber-reinforced polymer (GFRP) composites, through hygrothermal aging. GFRP cylinders were fabricated with varied parameters—volume fraction, winding angle, and stacking sequences using a filament winding machine. The fabricated samples are subjected to hygrothermal aging using seawater and tap water with oil at 80 °C for 1080 h (45 days). The HTS tests were performed on unaged and aged samples. There was a reduction in HTS for aged samples which is attributed to heat, seawater contamination, and oil. The highest and lowest HTS values recorded are 402.9 MPa and 118.3 MPa for unaged and tap water with oil-aged samples respectively. HTS in aged samples is compared with unaged samples. The study opens up avenues in identifying the best-suitable combination for retaining HTS under various aging conditions.

Hygrothermal ageing of dry gelatine adhesive films: Microstructure-property relationships

Gelatine adhesives, also known as animal glues, are collagen-based water-soluble biopolymers derived from vertebrate connective tissues. One of the various fields in which gelatine adhesives are widely used is the conservation of cultural heritage such as decorated furniture and panel paintings. It is observed that, with time, the failure in these objects often occurs along the adhesive bondlines. Given the moisture and temperature sensitivity of these adhesives, obtaining knowledge of their long-term behaviour, when exposed to climate variations, is pivotal. Here, the influence of hygrothermal ageing (exposure to a combination of elevated temperature and relative humidity (RH) cycling) on the microstructure and macroscopic properties of four different types of gelatine adhesives is investigated. These adhesives were selected from different animal origins namely bovine, rabbit, and fish with different Bloom strengths. It was observed that ageing cycles interfere with the most critical structural feature of protein chains namely triple helices. A clear decay in triple helix content at the micro-scale, determined by Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD) techniques, was observed which had implications on the macroscopic properties of these adhesives such as reduction of strain to failure and toughness (strain energy density to failure). The rate of decay in properties was revealed to be the highest in the adhesives with the lowest triple helix content. This study provides a scientific view of microstructure-property relationships in gelatinous adhesives as a function of environmental ageing, and stipulates the underlying mechanism of the degradation of mechanical properties as the loss of structural triple helices, regardless of the animal origin.

Vertical compression performance of fiber-reinforced polymer (FRP) foam sandwich composites in hygrothermal environment

The safety of utilizing composites has garnered significant attention due to their widespread application in civil engineering, aerospace, and other fields. In the present investigation, fiber-reinforced foam sandwich composites were fabricated using the vacuum-assisted resin injection (VARI) process. The constant temperature and humidity test chamber is used to carry out damp-heat aging experiments on the specimen, and the mechanical properties after damp-heat aging are studied. The present study aims to examine the vertical compression characteristics of fiber-reinforced foam sandwich composites under the influence of hygrothermal aging. This paper also elucidates the mechanism by which the hygrothermal environment affects these composites. The results indicate that the mechanical properties of the specimens decrease after damp-heat aging. The unidirectional stacked fibers exhibit better resistance to the damp-heat environment compared to the orthogonal stacked fibers. Additionally, the inclusion of drainage holes in the setup can enhance the resistance of the specimens to the damp-heat environment.

Influence of hygrothermal ageing on the novel infusible thermoplastic resin reinforced with quadriaxial non-crimp glass fabrics

Elium® is a novel liquid Methylmethacrylate thermoplastic (TP) matrix that can be cured at room temperature. Elium® resin provides the properties of TP polymer composites and is a competitive alternative to epoxy-based composites. In this work, a quadriaxial non-crimp (NC) glass fabric/Elium® based polymer composites were manufactured using vacuum assisted resin transfer moulding (VaRTM). The static mechanical properties of these composites were evaluated under the tensile and flexural loads. Further, interfacial properties like interlaminar shear strength (ILSS) and fracture toughness (Mode-I and Mode-II) were characterised. To study the influence of ageing on the mechanical properties of glass fabric/Elium® (GF/E) based composites, the test samples were aged in distilled water at a temperature of 60°C for 60 days. The obtained mechanical properties were compared between dry samples (control) and post-water immersed (aged) samples. It was found that water ageing degraded the properties of tensile, flexural strength, ILSS and Mode-II toughness by 30%, 59%, 46%, 37%, respectively. On the contrary, Mode-I fracture toughness of aged samples was 90% higher, indicating significant fibre bridging due to ageing. The microscopy and scanning electron microscopy (SEM) revealed significant failure as the degradation of fibre/matrix interface due to hygrothermal ageing. The overall performance of GF/E composites with infusible TP resin is sensitive to hygrothermal ageing.

Influence of Hygrothermal Aging on Mechanical Properties and Damage Mechanisms of Hemp-Reinforced Biocomposites

ABSTRACT Biocomposites are being developed for structural applications, particularly in the automotive industry. The use of plant fibers as reinforcement is a first step toward the development of eco-materials, but it is necessary to use also a more eco-friendly matrix. In this paper, woven hemp composites impregnated with two different eco-polymers are compared: hemp/Greenpoxy and hemp/Elium. Greenpoxy is a partially bio-based thermoset resin, and Elium is a recyclable thermoplastic polymer. The influence of various hygrothermal aging conditions on the mechanical properties of these composites is studied, and results are compared with the behavior of samples stored at ambient temperature and humidity. Water immersion was carried out at three different temperatures: 21°C, 60°C and 70°C. A Fick’s law was used to model the water uptake. Modulated DSC was performed to measure the evolution of the glass transition temperatures. Repeated progressive tensile loading tests were carried out and instrumented with acoustic emission monitoring. The evolution of the damage factor, the residual strains and the acoustic events was analyzed. Fracture surface analysis and microtomography observations were also performed. Damage mechanisms are discussed. Results show that mechanical properties are highly affected by the hygrothermal aging whatever the matrix, but the increase in temperature affects the two composites differently.

Chemical, mechanical and morphological investigation on the hygrothermal aging mechanism of a toughened epoxy

A systematic investigation was implemented in this work to evaluate the effect of hygrothermal aging on the chemistry, mechanics and morphology of a toughened epoxy resin exposed in a 70°C bath. This resin system reached equilibrium moisture absorption within 2530 h with a saturation water uptake of 3.6%, and the moisture diffusion displayed a non-Fick behavior, but can be illuminated well by the Langmuir model. The influence of hygrothermal aging on the glass transition temperature (Tg) was evaluated by Differential Scanning Calorimetry. Chemical changes were monitored by Fourier Transform Infrared spectroscopy, where the evidence for reversible and irreversible chemical changes was observed. The Dynamic Mechanical Analysis was employed to reveal the effect of hygrothermal aging on viscoelasticity, mainly focusing on the Prony moduli and relaxation time, where an interesting phenomenon was noted that the Prony moduli and relaxation time are not affected by hygrothermal aging. The mechanical properties involving tension, compression, and shear were studied detailedly with respect to the dry, hygrothermal, and redry samples. Finally, the fracture morphology of the epoxy under three different hygrothermal aging conditions was analyzed by using Scanning Electron Microscopy. The mechanical results show that for compression, the pre-yield and post-yield both has been strongly weakened after hygrothermal aging, but the pre-yield performance can be recovered by redry; for tension, the nonlinear behavior before final failure has been weakened; for shear, the shear ductility has been significantly enhanced. And the fracture morphology after hygrothermal aging, the representative regions are reduced to two zones: defect and smooth zone.

Influence of hygrothermal ageing on the mechanical properties of unidirectional carbon fibre reinforced powder epoxy composites

A systematic investigation was carried out in this work to evaluate the effect of seawater ageing on the mechanical properties of different composites manufactured with three types of unidirectional carbon fibres, based on a novel powder epoxy system. The flexural behaviour of the samples with and without accelerated seawater ageing was evaluated. A significant strength reduction due to seawater ageing was observed in the composites. Changes within the materials are also evaluated by interlaminar fracture toughness testing and dynamic mechanical thermal analysis . Interlaminar fracture toughness mode-I testing using the Double Cantilever Beam (DCB) test, revealed that the interfacial adhesion differences in combination with the moisture uptake could alter the fracture resistance of the composites, hence emphasising the importance of the interfacial bonding strength. A Finite Element analysis was carried out to gain insight on the important modelling parameters, for mode I dominated failure , and compared with the experimental results. Fracture surface examination by scanning electron microscopy revealed delamination , fibre debonding/bridging and plasticising of resin due to seawater effect.

Research on Hygrothermal Property of Jute Woven Fabric Reinforced Composites

Jute woven fabric reinforced composites are manufactured by means of VARI technology, hygroscopic property changes in the composites is analyzed, and the influence of hygrothermal aging on their tensile performance is investigated. The results show that moisture uptake of the composites at stage one conforms well to Fickian diffusion. Based on experimental data, the correlation between diffusion coefficient and temperature in Fickian equation is corrected. Meanwhile, the mild deviation between experiment-based moisture uptake curve and the one predicted by the modified equation validates the effectiveness of the correction. In addition, as temperature increases, the tensile strength of the composites decreases, due to the intensification of the resin dissolution.

Vibration and buckling characteristics of cracked natural fiber reinforced composite plates with corner point-supports

This paper is concerned with the accurate free vibration and buckling analysis of a partially or internally cracked natural fiber reinforced composite (NFRC) plate with corner point-supports by symplectic elasticity method. Mechanical degradation of NFRC plate during the hygrothermal ageing is described by using a theoretical damage model. Crack effects on the plate derived by using the line spring model (LSM) are considered in the governing equation of motion in the form of crack compliance coefficients. In the framework of symplectic elasticity, free vibration and buckling eigenvalue problems for three types of boundary conditions can be reduced into a set of algebraic equations by a superposition of boundaries. Highly accurate critical buckling loads, fundamental frequencies and corresponding mode shapes are solved simultaneously. A comparison of the new proposed model with finite element method is presented to validate the accuracy and effectiveness of the present method. Subsequently, the influence of hygrothermal ageing and crack parameters on the free vibration and buckling behaviors of cracked NFRC plates is rigorously presented. The research results conclude that both length and crack location are important factors that affect the hygrothermal ageing of NFRC plates.

Influence of hygrothermal ageing on the mechanical properties of CFRP-concrete joints and of their components

Externally bonded (EB) fiber reinforced polymer (FRP) composites have been effectively employed to strengthen existing reinforced concrete (RC) structures. However, relatively limited information is available regarding the long-term behavior of FRP-concrete joints. In this paper, different experimental tests are employed to investigate the effect of hygrothermal ageing on the bond behavior of a carbon FRP composite applied to a concrete substrate and on the mechanical properties of the epoxy resin and FRP composite considered. The experimental campaign includes tensile tests of epoxy resin, carbon FRP (CFRP) coupon, pull-off tests of the CFRP bonded to the concrete substrate, and single-lap direct-shear tests of CFRP-concrete joints. Specimens were conditioned in warm water (38 ± 2 °C) for 500, 1000, and 1500 h to accelerate the possible degradation induced by a simulated high-moisture exposure environment. The parameters studied were the tensile properties of epoxy resin and CFRP coupons and the fracture energy of the CFRP-concrete interface, which was computed from the CFRP strain measured in the single-lap direct-shear tests using the digital image correlation (DIC) method. Results indicate that both the mechanical properties of the epoxy resin and the CFRP-concrete interface fracture energy were slightly affected by the exposure conditions.

Influence of hygrothermal aging on the quasi-static and impact behavior of single lap joints using CFRP and aluminum substrates

The use of adhesive to bond composites in vehicles continues to increase. Due to hygrothermal conditions, both adhesive and composite properties can be altered, making the mechanical behavior of a joint unpredictable. The novelty of this work is the assessment of the behavior of joints manufactured using composite and aluminum substrates tested under quasi-static and impact conditions in the following states: unaged, hygrothermally aged, and dried after hygrothermal aging. A significant reduction of failure load was registered for composite joints (quasi-static and impact) after hygrothermal aging. Joints dried after aging achieved a recovery in the failure load of quasi-static tests.

Detection of Ageing Effect in Polyesterimide by Terahertz Time-Domain Spectroscopy

The ageing and degradation of polyesterimide (PESI) may threat the safe operation of the electrical equipment. Due to the lack of effective experimental methods, the ageing mechanism is still under debate. In this article, we employ differential scanning calorimetry and terahertz time-domain spectroscopy (THz-TDS) at variable temperatures to investigate the glass transition temperature and molecular dynamics of PESI. Ageing sample with a duration of 30 days was prepared to study the influence of hygrothermal ageing. Three peaks emerge in both absorption spectra and dielectric spectrum of ageing sample at the range of 0.2–2.25 THz. We investigate the temperature dependence of dielectric loss for both samples. Four temperature regimes and three crossover temperatures are extracted according to the slope of fitting curves. We find that the ageing treatment has different effect on the molecular dynamics in each temperature range. This indicates the evolution of ageing at various space scales. We believe that THz-TDS has immediate application potential in the detection of ageing degree and service-life evaluation.

The influence of hygrothermal ageing on creep behavior of nanocomposite adhesive joints containing multi-walled carbon nanotubes and graphene oxide nanoplatelets

The effect of hygrothermal ageing on the creep behavior of multi-walled carbon nanotube (MWCNT) and graphene oxide nanoplatelet (GONP)-reinforced adhesive joints was investigated. The neat, MWCNT and GONP-reinforced adhesive single lap joints were manufactured and immersed in hot deionized water with three different temperatures for 24 h and then tested under creep loading. The results showed that the elastic and creep shear strain values of the neat adhesive joints increased by 14% and 25%, respectively, when the water temperature was increased from 30 to 50 °C. It was found out that 0.1 wt% MWCNTs had the maximum reinforcing effect against the creep behavior of adhesive joints pre-aged in hot water by 56% and 33% reductions in the elastic and creep strain values of the nanocomposite adhesive joints compared to the neat adhesive joints. Whereas, GONPs caused the maximum reductions of 45% and 20% in the elastic and creep strains of the nanocomposite adhesive joints compared to the neat joints. Furthermore, the Burgers rheological model was employed for simulating the creep response of adhesive joints. Semi-empirical models were proposed for the elastic and creep strains and the Burgers model parameters as functions of the water temperature and MWCNT/GONP weight percentage using the response surface methodology.

Damage of Hygrothermally Conditioned Carbon Epoxy Composites under High-Velocity Impact.

The influence of hygrothermal aging on high-velocity impact damage of carbon fiber-reinforced polymer (CFRP) laminates is investigated. Composite laminate specimens were preconditioned in water at 70 °C. The laminates were subsequently impacted by flat-, sphere-, and cone- ended projectiles with velocities of 45, 68, and 86 m/s. The incident and residual velocities were collected during the impact test. The impact-induced damages were measured by ultrasonic C-scan, a digital microscope system, and a scanning electron microscope. The results show that the hygrothermally conditioned laminates offer a higher energy absorption during high-velocity impact. Due to the weakening of the interlaminar properties, the hygrothermally conditioned laminates are more susceptible to delamination failure, and shear-induced debonding dominates. The projected delamination area increases with the increment of impact velocity. The damaged region becomes close to a circular shape after hydrothermal conditioning, and close to a rhomboidal shape for the dry specimens.

Influence of hygrothermal aging on the durability and interfacial performance of pultruded glass fiber-reinforced polymer composites

The influence of the fiber/matrix interface of pultruded glass fiber-reinforced polymer (GFRP) composites exposed to hygrothermal environments, including deionized water immersion and saltwater immersion at 20 ± 5 °C, 30 ± 1 °C, and 60 ± 1 °C for 180 days, was investigated. The effect of moisture absorption on tensile properties was discussed. After 180 days of immersion in deionized water, tensile strength and modulus of specimens decreased 25.7% and 26%, whereas the equivalent respective losses were 2.1% and 18.2% for specimens immersed in saltwater. The short-beam-shear test and the single-fiber fragmentation test were selected to reflect the degradation of macro- and micro-interfacial properties, respectively. After 180-day immersion in deionized water and saltwater at 60 ± 1 °C, the inter-laminar shear strength of specimens decreased 28.8% and 18.5%, respectively, and the corresponding interfacial shear strength decreased 53.2% and 23.5%, indicating that the diffusion rate of micro-interface was higher than that of macro-interface in the fiber direction. Immersion in all media leads to pronounced degradation in tensile strength, modulus, and inter-laminar shear strength. Furthermore, based on the change of interfacial strength and Weibull distribution, a prediction model was proposed to describe the degradation trends and temperature effects on ultimate bearing capacity of pultruded GFRP composites in hygrothermal environments.

The influence of hygrothermal ageing on the mechanical properties and thermal degradation kinetics of long glass fibre reinforced polyamide 6 composites filled with sepiolite

In this article, the influence of relatively long hygrothermal ageing on long glass fibre reinforced polyamide 6 (LGF/PA6) composites filled with sepiolite (Sep) are analyzed.

Influence of hygrothermal aging on dimensional stability of thin injection‐molded short glass fiber reinforced PA6 materials

ABSTRACTThe hygrothermal aging of short glass fiber reinforced polyamide 6 materials (PA6/GF) is a major problem for thin‐walled components used in the automotive sector. In this work, the thickness and glass fiber content of PA6/GF materials were varied and exposed to hygrothermal aging. The temperature and relative humidity were chosen to range from −40 to 85°C and 10% RH to 85% RH respectively, according to automotive requirements for components in the passenger compartment. For the absorption of moisture, the diffusion behavior could not be generally described by Fick's law. However, the results indicate that the diffusion behavior is dependent on the relative humidity and thickness of the PA6/GF material. The morphology of the test specimen, which is influenced by injection molding, was also found to affect the diffusion behavior. The states of equilibrium for moisture absorption are strongly dependent on the relative humidity during hygrothermal aging and less dependent on the temperature. The maximum absorbed humidity was found at a temperature of 65°C and 85% RH, which was higher than at 85°C and 85% RH because of reduced contrary aging processes, such as postcrystallization. In certain climatic conditions and test specimen thicknesses, there was a characteristic overshoot in the mass change. This behavior could be attributed to a different degree of crystallization and lower glass fiber content. Both moisture absorption and an overshoot of the mass affected the dimensional stability of the test specimens. This effect on dimensional stability could be correlated with the glass fiber orientation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42245.

Influence of hygrothermal aging on carbon nanofiber enhanced polyester material systems

Four polyester composites (neat polyester, polyester reinforced with glass fibers, polyester reinforced with carbon nanofibers, and polyester reinforced with both glass fibers and carbon nanofibers) were prepared with the Vacuum Assisted Resin Transfer Molding (VARTM) process. These material systems were exposed to 60 °C/60% RH for 3600 h. Diffusivity was determined using moisture uptake curves. And, it was discovered that the addition of glass fibers (GFs) increased diffusivity, while the addition of carbon nanofibers (CNF) decreased diffusivity. Optical analysis was performed on the manually delaminated glass fiber reinforced polymer (GFRP) and nano-enhanced GFRP. This analysis indicated that the addition of CNF retarded the degradation of the matrix after exposure to elevated heat and humidity. Thermo-mechanical analysis was performed across material systems during various stages of the environmental preconditioning to determine alterations in properties such as storage modulus (SM) and glass transition temperature (Tg). The addition of GF to the system initially increased the maximum storage modulus, it also increased degradation from elevated heat and humidity exposure In contrast with GF, the addition of CNF retarded SM degradation and increased thermal stability. Upon re-drying, the nano-enhanced material systems recouped more than 90% of the maximum SM and maintained a Tg between the baseline and saturated hygrothermal treatments. This indicated both a reversible plasticization and an irreversible retarded degradation which could be potentially attributed to the addition of CNF.

Influence of hygrothermal aging on the gas and water transport properties of Nafion® membranes

The membrane durability is a critical issue for proton exchange membrane fuel cell development. Nafion® is usually considered as a reference membrane due to its high chemical stability. However, a condensation mechanism of the sulfonic groups to form anhydrides was evidenced when Nafion® membranes were stored at 80°C under humid atmospheres. In the present work, Nafion® 112 membranes and chemically stabilized Nafion® NRE212CS membranes commercialized to replace Nafion® 112 were studied under hygrothermal aging performed at 80°C for two relative humidity conditions: 80% and 95%. The impact of the aging conditions was investigated on membrane water and gas transport properties over the whole range of water activity. For both membrane types, a progressive decrease of the water uptakes was observed as a function of aging time. The hygrothermal aging process was faster for Nafion® 112 membranes than for the chemically stabilized Nafion® membranes. It became slower as the relative humidity of the aging atmosphere decreased from 95% to 80%. A water transport mechanism based on sorption and permeation data was proposed for the aged membranes taking account of the water/polymer interactions and of the progressive crosslinking of the Nafion® hydrophilic phase. The gas transport properties were studied for H2, O2 and CO2 at different water activities. The decrease of the gas permeability coefficients observed for the aged membranes in comparison with the neat membranes confirmed the presence of gas diffusion pathways within the Nafion® hydrophilic phase. The role of these diffusion paths was discussed as a function of the membrane hydration state, as a function of the aging conditions and of the polarity and size of the diffusing gas molecules.

Co-Cured Structural Steel-Composite Joints for Deck to Superstructure Connections

Through experimental and numerical analyses this paper proposes to improve the confidence in the use of steel-composite joints through understanding of their performance for application as the attachment of a composite superstructure to a steel hull envelope. This is achieved through investigation of the static and fatigue performance of a typical connection, the influence of hygrothermal ageing, the numerical prediction of the failure path within the connection subject to static loading and the optimisation of the connection to increase performance. The results show that the strength and durability of the proposed joint is sufficient to withstand the expected applied loads to the superstructure and that the exposure to moisture does not influence the performance even after 2 years of accelerated ageing. The numerical method proposed accurately predicted the path of failure within the joint and also predicted the response of the joint during failure using a novel approach of modelling the failure of the adhesive material. The use of genetic algorithms provided an efficient way of searching the steel-composite design space to minimise the main design driver, weight. This research provides significant confidence in the performance of the steel-composite connection and its application to structures such as helicopter hangars on naval and commercial vessels.