Hygrothermal Aging Research Articles

Exploring the impact of void content and hygrothermal aging on the performance of carbon/epoxy composite laminates: a comprehensive study

Exploring the impact of void content and hygrothermal aging on the performance of carbon/epoxy composite laminates: a comprehensive study

Microscopic insights into the long-term ageing mechanism of asphalt in the hygrothermal environments

The humid, thermal, and oxidative environments cause the synergistic degradation of asphalt materials. To reveal the long-term ageing mechanism of asphalt in the hygrothermal environments, base asphalt (BA) and styrene-butadiene-styrene (SBS) modified asphalt (SMA) were selected to prepare the short-term, long-term, and hygrothermal-aged samples. Then the changes in micromorphology, molecular weight distribution, chemical compositions, and microstructures of each aged asphalt sample were characterized. The results indicate that the soaking duration is determined as 32 h for preparing the hygrothermal-aged asphalt sample. The moisture diffusion causes physical damage to asphalt, forming circular micro holes on the asphalt surface, which is the main reason to accelerate asphalt ageing. The ambient water and air can easily permeate into asphalt, further accelerating asphalt ageing. Additionally, the small and medium molecular components in the hygrothermal-aged BA are decreased, while the large molecular components become more. Meanwhile, the molecular weight distribution of SMA is relatively concentrated after hygrothermal ageing, and the SBS modifier is degraded from supermolecules to macromolecules. Further, no new chemical compositions are produced after hydrothermal ageing of BA and SMA. The hygrothermal ageing accelerates the oxidation of thioethers and unsaturated carbon bonds to convert into sulfoxide and carbonyl groups. Finally, the hygrothermal ageing destroys asphalt components, and the number of Catana phases on the BA surface is lowered. The Catana phases on the SMA surface were seriously damaged and almost disappeared in asphalt components. The surface elevations of BA and SMA are increased after hygrothermal ageing, but the surface roughness is decreased. This study provides the microscopic insight into the long-term ageing mechanism of asphalt in the hygrothermal environments.

Study of Hygrothermal Aging for Basalt Fiber/Epoxy Resin Composites Modified with CeCl3.

With increasing attention being paid to environmental issues, the application of natural fibers in fiber-reinforced composites has attracted more and more attention. Composite materials with basalt fibers (BFs) as reinforcement have excellent properties and are widely used in many fields. Hydrothermal aging crucially influences the durability of basalt fiber/epoxy resin composites (BF/ERCs). In this study, BFs were used as reinforcing materials, whose surfaces were modified with a rare earth modification solution (CeCl3). The density, mechanical performance, and chemical properties of BF/ERCs subjected to hygrothermal aging were analyzed by the weight method, static mechanical performance testing, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR). The effects of the modification solution with different Ce concentrations on the water absorption, tensile, bending and interlaminar shear strength (ILSS) of BF/ERCs were investigated. The test results showed that the water absorption of BF/ERCs treated with a modification solution that contained Ce 0.5 wt % as the minimum value and the retention rate of the mechanical properties of BF/ERCs reached maximum values after hygrothermal aging.

Mechanical Stability of Carbon/Ramie Fiber Hybrid Composites Under Hygrothermal Aging

Mechanical Stability of Carbon/Ramie Fiber Hybrid Composites Under Hygrothermal Aging

Effects of hygrothermal aging on the physicochemical and mechanical properties of 3D-printed PA6

Effects of hygrothermal aging on the physicochemical and mechanical properties of 3D-printed PA6

Hygrothermal Effect on GF/VE and GF/UP Composites: Durability Performance and Laboratory Assessment.

In order to investigate the durability of two kinds of fiber-reinforced composite materials, and obtain the degradation mechanism and failure model in a hygrothermal environment, E-glass- fiber-reinforced composite materials, glass fiber-reinforced epoxy vinyl ester and glass fiber-reinforced unsaturated polyester (named GF/VE and GF/UP, respectively) were chosen to suffer rigorous hygrothermal aging. Their mechanical performance was monitored during the aging process to evaluate their durability. The cause of deterioration of the composite was comprehensively analyzed. Based on the analysis results of attenuated total-reflectance-Fourier-transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA), the change mechanism of chain structure of the resin molecule was proposed. SEM (scanning electron microscopy), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were used to analyze the microstructure and degradation mechanism of the fiber and the interface between fiber and matrix. The degradation mechanism of the composite system, including the resin, the fiber and the interface, was obtained, and it was found that the deterioration of the matrix resin caused by the hygrothermal environment was the main factor leading to the decline in composites performance.

Investigation on interlayer debonding behavior of unidirectional composite laminates under cyclical hygrothermal aging duration effects

AbstractThe composite interlamination is the key part of load transfer and plays a decisive role in the overall mechanical performance of composite structures. The interlaminar property is predominantly influenced by the matrix resin which is easily affected by the hygrothermal environment. This paper delved into the effect of hygrothermal aging duration on the interlayer debonding behavior of unidirectional (UD) laminates. The pre‐cracked specimens were treated by hygrothermal aging with a period of 0, 15, 30, 60, 90, and 120 days. The double cantilever beam (DCB) tests were employed to evaluate the interlaminar property. The effect of hygrothermal aging on load–displacement responses, R‐curves, crack growth speed, and fracture surface topography was analyzed. The results revealed that the load‐bearing capacity of aged specimens presented a reduction of 18.6%–29.0% compared with unaged ones. The interlaminar fracture toughness of specimens subjected to 15 days of treatment decreased significantly compared with that of unaged specimens due to the increase of water absorption caused by hygrothermal aging. With the increase in hygrothermal aging time, the interlaminar fracture toughness peaked at 60 days because of the post‐curing effect, followed by a declining trend influenced by the dominant hygrothermal aging effect. The fiber bridging of aged samples was increasingly obvious, became the most prominent at 60 days, and then gradually reduced. The fiber bridging diminished the crack propagation speed, hindered interlaminar debonding, and contributed to the interlaminar toughening.Highlights The samples underwent hygrothermal aging for 0, 15, 30, 60, 90, and 120 days. Load ability of aged samples was at least 18.6% lower than that of unaged ones. R‐curves rose before the crack length of 79 mm and then tended to stabilize. Fracture toughness first decreased, then increased and reduced with aging time. Fiber bridging could hinder crack growth and improve the interlayer property.

Degradation of Mechanical Properties of Flax/PLA Composites in Hygrothermal Aging Conditions.

The main advantage of green composites is their biodegradability, but this biodegradability can also be considered a drawback if the degradation appears during the service life of the component. Therefore, the study of the mechanical behavior of green composites after hygrothermal aging tests is necessary to analyze their degradation process. This study aims to comprehensively analyze the hygrothermal aging behavior and aging mechanism of flax-fiber-reinforced polylactic acid (PLA) biocomposites. The fully biodegradable composites are manufactured by compression molding. In addition, the influence of atmospheric-pressure plasma treatment on the mechanical properties of the biocomposite is studied. Specimens are exposed to water vapor and 40 °C environmental conditions in a stove for up to 42 days. Several specimens of each type are taken out at regular intervals and tested to examine the water absorption, mechanical properties, and thermal characterization. The results show that the stiffness was significantly reduced after 24 h due to matrix degradation, while the strength was reduced only after three weeks.

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.

On crashworthiness and energy-absorbing mechanisms of hygrothermal-aged CFRP structures subjected to quasi-static loads

Understanding the gradual performance degradation of carbon fiber reinforced polymers (CFRP) is critical for the design of engineering structures that are expected to be affected by hygrothermal environments. This study aims to investigate the effects of hygrothermal aging on the degradation mechanisms of the mechanical properties and energy absorption of CFRP structures. An experimental database comprising tensile, compressive, and shear tests for CFRP composite laminates (in this study) and axial crushing tests for energy-absorbing structures (from the literature) was constructed, in which all CFRP samples were immersed in deionized water to achieve a saturated water-absorption state. A material constitutive model considering the effects of water absorption and temperature was developed and implemented via the user subroutine VUMAT of the ABAQUS software. The simulated results correlated well with the experimental measurements. Simulation results of axial crushing indicated that the degradation of the inter-layer properties tends to worsen the mismatch between the intra-layer and inter-layer properties, thus significantly degrading the load-carrying capability. Owing to degradation in compressive fracture toughness, the simulated results showed reduced post-crushing integrity, thus indicating a favorable effect on the load-carrying capability.

Effect of service temperature and hygrothermal aging coupling on mechanical properties of adhesively bonded BFRP-Aluminum alloy joints

To study the coupled effect of hygrothermal aging and service temperature on the mechanical properties of adhesively bonded basalt FRP-aluminum alloy joints (BFRP-Al joints), the mechanical properties and failure mechanism of BFRP-Al joints at different temperatures before and after aging were analyzed in this paper. The accelerated aging test of the adhesively bonded joint was performed under the hygrothermal condition (80 °C&95% relative humidity), and the hygroscopic property of the joint were analyzed by the water absorption test. Then, the mechanical properties of the aged joints were measured at 80 °C, room temperature (RT 25 °C), and −40 °C. The failure mechanism of the joints under the coupling effect of hygrothermal aging and service temperature was analyzed based on the Differential Scanning Calorimetry (DSC) results. The results reveal that the BFRP-AL joint reaches moisture saturation after exposure to hygrothermal environment for 200 h, and the moisture absorption behavior complies with Fick's law. Due to the decrease of material Tg caused by hygrothermal aging, the mechanical properties of the joint at 80℃ decrease more obviously after aging. Moreover, the failure modes of joint are altered as a result of hygrothermal aging and temperature coupling. A methodology for predicting the performance of bonded joints was established based on the variation laws in Tg and failure load, taking into consideration the effects of hygrothermal aging and service temperature which can provide guidance for the lifetime design of the hygrothermal aged adhesive structures within the entire service temperature range.

Mesoscale analysis of aging mechanical behaviors of 3D woven composites

3D orthogonal woven composites (3DOWCs) are inevitably subjected to the severe cyclic hygrothermal aging environment in the application of supersonic aircraft structures and their durability should be proven. However, most current works relating to the hygrothermal aging of 3DOWCs rely on the experimental methods which are of high cost. To address this issue, a matrix-yarn mesoscale model of 3DOWCs was established to investigate the cyclic hygrothermal aging mechanical behaviors in this paper. High-fidelity mesoscale representative volume element (RVE) was constructed with realistic geometric configuration of the reinforcement. Only the aging properties of pure resin were needed in the mesoscale model. The aging properties of fiber yarns were calculated with Chamis formulas accounting for resin aging. Tension-compression asymmetry behavior of resin matrix was accounted in the constitutive model. The damage initiation and propagation of resin matrix, yarn and cohesive interface were modeled by the progressive 3D damage model. The mechanical properties of 3DOWCs before and after aging were predicted by the mesoscale model and validated with experiment. This work can provide effective tool for the design of 3DOWCs applied in harsh environments.

Investigation on moisture absorption behavior on GFRP and neat epoxy systems in hygrothermal salt fog aging

This work investigates the moisture absorption behavior in epoxy matrix composites reinforced with glass fibers, used in repairs of offshore topside metal pipelines exposed to aging in saline environment. The materials used were a bicomponent DGEBA epoxy and a woven bidirectional E-glass fabric. In order to simulate the harsh environment, the composites were exposed to accelerated hygrothermal aging tests in three independent salt spray chambers at temperatures of 35, 55 and 70 °C and the materials had their mass gain monitored. The moisture absorption of the neat epoxy resin was also investigated and correlated with that of the composites. Thermal analyses by Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Thermal Analysis (DMTA) were performed to evaluate the curing state of the polymeric materials tested and the effects of temperature on the material's post-curing. Fourier-Transform Infrared (FTIR) analyses were performed to investigate the occurrence of post-curing, hydrolysis and thermo-oxidation processes during aging. As expected, it was seen that temperature increased diffusivity for both the composite and the unreinforced epoxy matrix. The neat epoxy resin presented a decrease in moisture absorbed with temperature, evidencing the effect of post-curing on moisture absorption. Furthermore, from the thermal analyses, it was observed the presence of an interphase between matrix and fibers with a Tg higher than the bulk matrix. Non-Fickian models confirmed structural changes caused by temperature and moisture in the materials. A modification of the Berens-Hopfenberg (BH) non-Fickian model was proposed to account for post-curing effects on moisture absorption.

Comparison of the effect of thermal and hygrothermal sub-Tg aging on the durability and appearance of multilayered filament wound composite structure

The study conducts an experimental investigation to compare the effect of accelerated aging on a glass fiber/vinylester matrix filament wound composite. Two static aging conditions, thermal and hygrothermal, were chosen. Samples were aged at temperatures below the glass transition temperature (Tg) of vinylester for 224 days. Mechanical test – ILSS and flexure testing and physicochemical assessments – DMA, FTIR and colorimetry were conducted to gauge the aging effects on long-term durability and appearance. Results are presented as retained property values over aging durations and environments. Notably, coupons aged below 60 °C under both conditions exhibited residual curing, enhancing mechanical properties. Time-temperature coupling influenced behavior, with higher temperatures and longer durations leading to degradation. Hygrothermal aging at 80 °C prompted earlier degradation than thermal aging, highlighting moisture's impact. DMA revealed interfacial degradation for hygrothermally aged coupons, verified by fractography. Conversely, damping factor analysis indicated residual curing for thermally aged coupons. Results were confirmed through color change and FTIR, showcasing evolving chemical patterns with aging.

Synthesis and hygrothermal aging of polycarbonates containing a bisphenol fluorene moiety.

This study aims to synthesize a specific type of polycarbonate with high refractive index, low birefringence, and resistance to hygrothermal aging by copolymerizing 2,2'-bis(2-hydroxyethoxy)-1,1'-binaphthyl (BNE) with 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene (BPEF). Comparative analysis revealed that the copolymer synthesized from BNE and BPEF demonstrated superior hydrolytic stability relative to the bisphenol A-based polycarbonate. This augmented stability can be attributed to the monomers' higher pKa values, rendering acidic substances less capable of dissociating and thereby mitigating ester hydrolysis under hygrothermal conditions. Furthermore, the investigation probed into the phenomenon of physical aging in copolymerized polycarbonate when exposed to hygrothermal environments. It was discerned that the enthalpy loss, observable under both dry and hygrothermal conditions, could be linearly correlated with the difference between the aging temperature and the glass transition temperature (Tg), signifying a close correlation between the magnitude of physical aging and Tg. A lower Tg in the copolymerized polycarbonate led to more pronounced physical aging within the same timeframe, resulting in an augmentation of tensile strength and modulus, while higher Tg effectively mitigated the physical aging phenomenon.

Assessment of Structural Integrity and Interfacial Debonding in Carbon Fiber/Epoxy Composites Undergoing Hygrothermal Aging

Assessment of Structural Integrity and Interfacial Debonding in Carbon Fiber/Epoxy Composites Undergoing Hygrothermal Aging

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.

Mechanical behavior of polyamide-6 after combined photo-oxidative and hygrothermal aging

Mechanical behavior of polyamide-6 after combined photo-oxidative and hygrothermal aging

Hygrothermal effects on fatigue delamination behavior in composite laminates

Fatigue delamination growth (FDG) is an important failure in composite structures during their long-term operations. Hygrothermal aging can have significant effects on interlaminar resistance. It is therefore really necessary to explore FDG behavior in composite laminates with hygrothermal aging. Dynamic mechanical thermal analysis (DMTA), mode I FDG experiments and fractographic examinations were conducted to fully investigate hygrothermal aging effects and the corresponding mechanisms on FDG behavior. The DMTA results indicated that environmental aging can induce obvious Tg decrease. Mode I experimental fatigue data interpreted via different Paris-type correlations demonstrated that: Bridging has obvious retardation effects on FDG behavior via the Paris interpretations; The modified Paris relation can well characterize the intrinsic FDG behavior around the crack front; The use of the two-parameter Paris-type relation can appropriately account for R-ratio effects, contributing to a master resistance curve in determining mode I FDG behavior. According to these interpretations, it can be concluded that hygrothermal aging can have adverse effects on mode I FDG behavior. SEM examinations demonstrated that moisture absorption can cause fibre/matrix debonding and resin matrix pores/voids in the composite. However, no obvious difference in damage mechanisms was identified in mode I fatigue delamination for composite with/without environmental conditioning. Both fibre/matrix debonding and matrix brittle fracture were identified on fatigue fracture surfaces. Accordingly, it was concluded that fibre/matrix interface and matrix degradation induced by water absorption were the main reasons for a faster mode I fatigue crack growth in environmental aged composite.

Effect of hygrothermal aging on compression behavior of CFRP material with different layups

This study investigates the mechanical degradation mechanism and statistical analysis of residual compressive strength of three lay-up laminates under more than one-year seawater environment. Fick and Langmuir model were used to describe the moisture absorption process with a maximum moisture equilibrium content of 3.78% and various characterization methods were used to reveal the microstructural evolution of CFRP during aging. Experimental results demonstrate that the multiple fiber directions in the MD specimens provide additional moisture absorption channels, leading to a stronger wicking effect and a higher equilibrium moisture content. The layups can significantly affect the compression failure mode after long-term aging. The compressive strength of the cross-ply and multidirectional laminates decreased by 50% while that of unidirectional laminates decreased by 28%, and surface cracking is easily observed in the aged specimens. An empirical prediction model based on the Langmuir model and experimental data was proposed and verified by the data from the literature, with at least a 10% improvement in prediction accuracy. Meanwhile the three-parameter Weibull distribution was used to describe the residual compressive strength after hygrothermal aging and tested by Kolmogorov-Smirnov test. It is expected to provide insight for the application of CFRP in seawater environment.