Effect Of Hygrothermal Aging Research Articles

The effect of hygrothermal ageing on the delamination of Carbon/epoxy laminates with Core-shell rubber nanoparticle and Micro-fibre thermoplastic veil toughening

The effect of hygrothermal ageing on the delamination of Carbon/epoxy laminates with Core-shell rubber nanoparticle and Micro-fibre thermoplastic veil toughening

An experimental investigation on the influence of environmental ageing on strength and fatigue behavior of different single lap joints

It is essential to examine the performance of CFRP and aluminum specimens after being exposed to environmental aging and to develop a technique that can predict their mechanical function. However, there is limited research on the static and fatigue strength of adhesive, mechanical, and hybrid joints (adhesive/mechanical) after environmental ageing. The study aims to examine the effect of thermal and hygrothermal ageing on the static and fatigue performance of three-point bending joints. Three groups of samples were prepared: I) unaged, II) thermally aged, and III) hygrothermally aged. The bending performance of three different types of joints (bonded, bolted, and bonded/bolted) was evaluated by conducting bending tests using three distinct types of adherends: ATA (Aluminum-to-Aluminum), CTC (Composite-to-Composite), and ATC (Aluminum-to-Composite). Also,the strength of the joints was measured and assessed for both static and fatigue (at three different levels of loading using the new fixture) loading. Static tests showed that bonded/bolted CTC specimens had the highest strength, and hygrothermal and thermal conditions significantly affected the static performance of the three types of joints and substrates. Under fatigue load, the highest fatigue life was observed in bonded, bolted, and bonded/bolted specimens for ATA, ATC, and CTC, respectively. In a bonded/bolted single lap joint, the static and fatigue strength consists of two steps: the initial step corresponds to the strength of a bonded specimen, and the next step starts when the bonded joint fails and fits the strength of a bolted joint. Finally, both ageing and static load percentage reduced the fatigue life and shifted the failure mode of the joints.

Study on the effect of hygrothermal aging on the properties of three-dimensional woven composite materials with damage

This study analyzed the hygroscopic characteristics and mechanical properties of three-dimensional woven composite materials under 70℃/85%RH conditions and with the presence of damage. First, the materials underwent hygrothermal aging tests, including analysis of mass change, moisture absorption rate, SEM microstructure, Fourier-transform infrared spectroscopy (FT-IR), dynamic mechanical analysis (DMA), and subsequent open-hole tensile and compression strength tests under different environmental conditions. Finally, macroscopic failure analysis was conducted. The results showed that as the hygrothermal aging time increased, the moisture absorption rate increased and the fiber surface became smoother, while the degree of debonding between the fiber and matrix increased. The open-hole tensile and compression strength of the composite material decreased as the aging time extended, and the environmental temperature had different effects on open-hole tensile and compression strength.

Hygrothermal aging effects on the diffusion-degradation process of GFRP composite: Experimental study and numerical simulation

The durability performance of glass fiber reinforced polymer (GFRP) has attracted wide attention, but conventional experimental methods for durability prediction are time-consuming, labor-intensive and not applicable to members with different sizes or geometries. To address this issue, a new modeling approach is developed in this study to simulate the diffusion-degradation process of GFRP composite in a moist environment. Taking a GFRP rebar as an example, the water diffusivity of composite is firstly obtained from a finite element model with the assumption of hexagonal fiber arrangement. With test results on the degradation of single coated fibers in the wet environment, and the simulated water front from the diffusion analysis, the strength retention at each location over the rebar section can be derived. The time-dependent degradation of tensile strength can hence be obtained from integration. To account for the defects (including matrix cracking, fiber erosion and fiber/matrix debonding) which can affect the water diffusivity, a refined diffusion model was also performed with increased water diffusivity (from 4.0 × 10-6 mm2/s to 4.5 × 10-6 mm2/s) and presence of interfacial crevices in the corroded region. While the refined model can lead to faster water diffusion and tensile strength degradation, the difference with the original model is within 10%. More importantly, both models are able to correctly predict the GFRP tensile strength degradation measured in the laboratory over a 12-month period. As the diffusion-degradation framework proposed in this study is applicable to any member size and geometry, it supplies engineers with an evaluation method to quickly predict the long-term tensile performance of GFRP structures.

Effects of hygrothermal aging on the tensile and bonding performance of consolidated 3D printed polyamide-6 composites reinforced with short and multidirectional continuous carbon fibers

Effects of hygrothermal aging on the tensile and bonding performance of consolidated 3D printed polyamide-6 composites reinforced with short and multidirectional continuous carbon fibers

Tensile behaviour of unaged and hygrothermally aged discontinuous Bouligand structured CFRP composites

AbstractThe aim of this article is to determine the effects of hygrothermal ageing on the tensile behaviour of asymmetric discontinuous helicoidally stacked (Bouligand structured) carbon fibre reinforced plastic (CFRP) composites. Eight different discontinuous Bouligand stacking sequences were manufactured using both major and minor pitch angles. The major pitch angles used were 90° and 120° while minor pitch angles at 5°, 10°, 15° and 25° were stacked from each of the major pitch angles. The composites were tested in tension as either dry unaged specimens or following hygrothermal ageing in seawater at the constant temperatures of 40°C and 60°C for over 2000 h. Both tensile modulus and tensile strength are found to be detrimentally affected by hygrothermal ageing and the extent to which ageing affects these properties is shown to be a function of the inter-ply pitch angle. All discontinuous Bouligand structured composites that were hygrothermally aged at the higher temperature of 60°C were less stiff and weaker than those aged at 40°C and those that were unaged. This is a result of increased heat exacerbating the ingress of water and consequently damaging fibre-matrix interfaces and plasticizing the matrix. The results showed that the minor pitch angles had clear effects on the strength and stiffness of the composites. Composites with 120° major pitch angles exhibited superior elastic modulus and strength values compared with composites with 90° major pitch angles. The Hashin damage model is shown to be accurate in predicting failure in discontinuous Bouligand structured CFRP composites, as evidenced by comparison to fracture paths observed after mechanical testing.

The effect of hygrothermal aging on the adhesion performance of nanomaterial reinforced aluminium adhesive joints

Adhesive joints are subjected to various environmental factors such as humidity and temperature, depending on their use in industrial applications. It is important to examine and improve the performance of adhesive joints formed with polymeric adhesives, which are known to be sensitive to humidity and temperature parameters, under these conditions. For this reason, in this study, FPL-etched AA7075-T6 aluminium adherends bonded with nonreinforced and BNNP (boron nitride nanopowder), ANP (alumina nanopowder) and MWCNT (multiwalled carbon nanotubes) reinforced epoxy adhesive as a single lap adhesive joint. Thereafter, performance of the adhesive joints that exposed hygrothermal aging conditions of 1, 2, 4 and 6 weeks at 100% relative humidity (RH) and 60 °C were investigated. Glass transition temperature (Tg) values of nonreinforced and reinforced epoxy adhesives before and after hygrothermal aging were determined by DSC (Differential Scanning Calorimeter) analyses. Depending on the nanomaterial types, the tendency of the adhesive joints to water uptake was determined and compared with nonreinforced adhesive joints. When the shear strength findings were investigated, it was defined that the adhesive joints reached almost saturation after 2 weeks of hygrothermal aging. In addition, the most effective nanomaterial type against hygrothermal aging was determined as MWCNT. After 2 weeks hygrothermal aged, the shear strength decreases of MWCNT reinforced adhesive joints were 21.77% and 16.97% less than BNNP and ANP reinforced adhesive joints, respectively. Although the adhesive deteriorates chemically after hygrothermal aging, its adhesion performance improved with the physical benefits of nanomaterials. However, ANP, which is cheaper in terms of price/shear strength performance in long-term aging times, showed similar results with MWCNT. In addition, fracture mechanisms were examined in more detail with SEM (Scanning Electron Microscope) analyses before and after aging, and the effects of hygrothermal aging on the adhesive joints were determined.

Effects of hygrothermal ageing and temperature on the mechanical behavior of aluminum-CFRP hybrid (riveted/bonded) joints

Hygrothermal ageing and temperature significantly affect the mechanical properties of joints, but the research on their coupling effect in hybrid joints is insufficient. In this work, the combined effects of the long-term factor of hygrothermal ageing and the short-term factor of temperature on the mechanical properties of Al/CFRP hybrid (riveted/bonded) joints (HJs) are investigated by quasi-static tensile experiments and an advanced simulation method. The mechanical properties of HJs with four kinds of ageing degrees are tested at four temperatures (−40 °C, 20 °C, 50 °C, and 80 °C). Experimental results show that the joint strength is mainly affected by temperature, while the breaking elongation is sensitive to the degree of ageing. Although the joint stiffness and strength decrease significantly under the combined action of the increase in temperature and the deepening of the ageing degree, the three-stage characteristics of failure (first, the adhesive bond and the rivet share the load; and then the adhesive bond gradually fractures and loses its load-bearing capacity; finally, the rivet bears the load alone) do not change. Furthermore, by integrating the change information of moisture absorption and Fourier transform infrared spectrum into the material model, the simulation shows new light on the failure mechanisms of the HJs on the coupling effect of temperature and hygrothermal ageing. In conclusion, this research helps deepen the understanding of the changing laws of mechanical behavior of Al/CFRP hybrid joints under actual service conditions.

Effect of hygrothermal aging on moisture diffusion and tensile behavior of CFRP composite laminates

Carbon Fiber Reinforced Polymer (CFRP) composites are widely used in aircraft structures, because of their superior mechanical and lightweight properties. CFRP composites are often exposed to hygrothermal environments in service. Temperature and moisture can affect the material properties of composites. In order to make clear the moisture diffusion behavior and the properties degradation of composites, the TG800/E207 composite laminates with four stacking sequences [0]16, [90]16, [±45]4s, and [(+45/0/0/–45)s]s are designed and manufactured. Moisture absorption tests are carried out at 80 ℃, 90 %RH. It is shown that the moisture absorption curves of composite laminates present a three-stage. A modified Fickian model was proposed to capture the diffusion behavior of TG800/E207 composite laminates. The relationships among the non-Fickian parameters, the environmental parameters and the stacking sequences of CFRP were correlated and compared. Results showed that the modified Fickian curve is sensitive to the diffusivity of Stage I and Stage II. Compared with unaged specimens, the maximum tensile stress for [0]16, [90]16, [±45]4s, and [(+45/0/0/–45)s]s decreased by 14.94 %, 28.15 %, 11.96 %, and 26.36 %, respectively. The strains at failure for [0]16, [90]16, [±45]4s, and [(+45/0/0/–45)s]s decreased by 55.38 %, 62.65 %, 46.41 %, and 31.71 %, respectively. The elastic modulus for [0]16, [90]16, [±45]4s, and [(+45/0/0/–45)s]s increased by 90.93 %, 94.57 %, 49.22 %, and 8.22 %, respectively. [90]16 sample has the minimum saturated moisture content and the maximum strength degeneration.

Effects of Hygrothermal Aging and Cyclic Compressive Loading on the Mechanical and Electrical Properties of Conductive Composites.

Conductive polymers and their composites have been widely applied in different applications, including sensing applications. Herein, we constructed a conductive composite of polypropylene, carbon black, and multi-walled carbon nanotubes (PP/CB/MWCNTs) to experimentally study its sensing behaviors in a humid thermal environment. The as-synthesized PP/CB/MWCNT composite polymer was immersed in simulated sweat in deionized water at 67 °C. Regarding their electrical and mechanical properties, different experimental parameters, such as cyclic loading and hygrothermal aging, were investigated by recording the mass changes, carrying out strain sensing experiments, and performing dynamic mechanical analyses before and after the immersion test. The results reveal that the filler content improved the rate of water absorption but decreased at higher concentrations of the solution. The sensitivity of the material decreased by up to 53% after the hygrothermal ageing and cyclic loading. Moreover, the sensitivity under cyclic compression loading decreased with an increasing immersion time, qualitatively illustrated by an effective quantum tunneling effect and conducting path model. Finally, hygrothermal aging reduced the composite's glass transition temperature. This reduction was the most significant for specimens immersed in deionized water, ascribed to the moisture absorption, reducing the molecular chain activity.

Moisture Content Prediction in Polymer Composites Using Machine Learning Techniques.

The principal objective of this study is to employ non-destructive broadband dielectric spectroscopy/impedance spectroscopy and machine learning techniques to estimate the moisture content in FRP composites under hygrothermal aging. Here, classification and regression machine learning models that can accurately predict the current moisture saturation state are developed using the frequency domain dielectric response of the composite, in conjunction with the time domain hygrothermal aging effect. First, to categorize the composites based on the present state of the absorbed moisture supervised classification learning models (i.e., quadratic discriminant analysis (QDA), support vector machine (SVM), and artificial neural network-based multilayer perceptron (MLP) classifier) have been developed. Later, to accurately estimate the relative moisture absorption from the dielectric data, supervised regression models (i.e., multiple linear regression (MLR), decision tree regression (DTR), and multi-layer perceptron (MLP) regression) have been developed, which can effectively estimate the relative moisture absorption from the dielectric response of the material with an R¬2 value greater than 0.95. The physics behind the hygrothermal aging of the composites has then been interpreted by comparing the model attributes to see which characteristics most strongly influence the predictions.

Hygrothermal aging effect on the water diffusion in glass fiber reinforced polymer (GFRP) composite: Experimental study and numerical simulation

Understanding the water diffusion process in glass fiber reinforced polymer (GFRP) is critical to bridging the gap between the long-term degradation performance of GFRP composite and the retained strength of glass fibers under water attack. In this study, the water diffusion in GFRP with consideration of defects is systematically investigated through experimental and simulation methods. The water diffusivity of GFRP decreased from 6.60 × 10−7 to 2.05 × 10−7 mm2/s as glass fiber volume fraction increased from 0 to 50.21%. In addition, the diffusivity increases slightly with the presence of voids, and significantly with matrix cracking, debonding and fiber erosion, while it is insensitive to fiber size. Furthermore, the square or hexagonal fiber arrangement models produce similar results to random fiber arrangements in the actual situation. GFRP water absorption curves are found to be underestimated and overestimated respectively for models without and with defects taken into consideration. Finally, the simplified and refined FE models are supposed to be employed to rapidly estimate the water absorption of GFRP composite.

Hygrothermal aging effects on tribological and mechanical behaviors of mollusc shell-reinforcement UHMWPE biocomposites

The effect of hygrothermal aging on the tribological and mechanical behaviors of UHMWPE biocomposites reinforced with different weight fractions of mollusc shell (MS) particles was investigated. The developed MS-UHMWPE biocomposites samples were subjected to accelerated hygrothermal aging in Ringer’s solution at 80°C. The results showed that hygrothermal aging increases the tribological behavior of these biocomposites. The effect of hygrothermal aging on the wear resistance depends on the reinforcement rate of the MS particles. The mechanical properties of the MS-UHMWPE biocomposite were affected by hygrothermal aging as well as by the weight content of the added MS particles. The modulus of elasticity increased with increasing MS particle content for all tested materials. A scenario of the wear mechanism of aged biocomposites will be proposed.

Characterization and rapid prediction of the effect of hygrothermal ageing on the interlaminar shear strength of CFRP at a high temperature

Characterization and rapid prediction of the effect of hygrothermal ageing on the interlaminar shear strength of CFRP at a high temperature

Contributions of atmospheric plasma treatment on a hygrothermal aged carbon/epoxy 3D woven composite material

In this paper, the effects of hygrothermal ageing and atmospheric plasma surface treatment on a 3D carbon/epoxy-amine woven composite material are studied. The goal is to study the surface evolution of the materials in terms of chemical composition and morphology. Plasma treatment is applied on new and hygrothermally aged samples in order to analyse its contribution to the surface modifications and degradations. It appears that hygrothermal ageing has irreversible absorption behaviour causing hydrolysis, oxidation and particle losses, which modifies the surface chemistry and topology. On the other hand, the atmospheric plasma causes oxidation of the matrix. Indeed, when a repair is necessary, the damaged part could evolve due to moisture absorption related to ageing. As the fibres are exposed, the topology and surface chemistry are modified. Nevertheless, it allows to desorb the humidity adsorbed on the surface and reach an oxidation level similar to unaged treated samples.

The Tensile Behaviour of Unaged and Hygrothermally Aged Asymmetric Helicoidally Stacked CFRP Composites

This paper concerns the effects of hygrothermal ageing on the tensile behaviour of assymetric helicoidally stacked carbon fibre reinforced plastic (CFRP) composites. MR70 12P carbon fibre epoxy prepreg sheets were manufactured into laminated composites comprising constant inter-ply pitch angles ranging from 0° to 30°. The composites were tested in tension (according to BS ISO 527-5:2009) as either dry unaged specimens or following hygrothermal ageing in seawater at the constant temperatures of 40 °C and 60 °C for 2000 h. Both tensile modulus and tensile strength are found to be detrimentally affected by hygrothermal ageing, and the extent to which ageing affects these properties is a function of the inter-ply pitch angle. Higher hygrothermal ageing temperatures are found to decrease the tensile modulus and strength ratios of asymmetric helicoidally stacked composites when compared against UD composites subjected to the same conditions and the strength and stiffness ratios of all composites when compared against unaged equivalents. Significantly, therefore, we show that the degradation of helicoidal composite properties under hygrothermal conditions, in general, occurs more rapidly than it does in UD composites, and thus the long-term use of helicoidal composites in immersed environments should take into account these differences. A second order relationship is observed for the mechanical properties of the composites when plotted against their inter-ply helicoidal pitch angles. As such, a mixtures model was modified to incorporate the observed effects of laminate inter-ply pitch angle and used to predict the tensile modulus of unaged composites. The predictions are within one standard deviation of the experimental arithmetic mean; however, the model can only be used for dry helicoidal composites, as ageing alters the microstructures in an irregular manner between the different sample sets. The development of this mixture model is useful as it provides a justifiably simple route to predicting the properties of dry helicoidal structures, albeit within the bounds of specific interply-pitch angles. Finite element analyses (Hashin failure) elucidate the plies that are most likely responsible for composite failure. The validity of these numerical predictions is evidenced by observing primary fracture paths in the composites. Finally, hygrothermal ageing is found to enable greater in-plane (mode III) twisting of individual laminates under loading, with certain laminate angles being more prone to twisting than others.

Experimental study of quasi-static and dynamic tensile behavior of epoxy resin under cyclic hygrothermal aging

Fiber-reinforced polymer (FRP) structures used in aviation are typically exposed to cyclic hygrothermal environments in which they may be subjected to impact loads that threaten flight safety. Although the effects of hygrothermal aging on the mechanical behavior of FRPs have been extensively explored, few authors have discussed the impact-induced behavior of composites after long-term hygrothermal aging, and hardly any study has examined the effect of the strain rate of neat epoxy resin after hygrothermal aging. This study examines the quasi-static and dynamic tensile properties of TDE86 epoxy resin under cyclic hygrothermal aging for the first time. The resin specimens were aged for 0, 1, 7, 14, 28, 56, 70, and 140 days, representing specimens that were unaged, and had been in service for one month, six months, one year, two years, four years, five years, and 10 years respectively. The strain rate at which they were tested ranged from 7.5 × 10−6 s−1 to 1000 s−1. This yielded the hygroscopic law, the process of evolution of crack-induced damage, and the viscoelastic behavior of the specimens, including the hygrothermal effect and the effect of the strain rate of the epoxy resin. This information can be used to predict the hygrothermal behavior of FRPs based on the micromechanics method.

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.

Effect of hygrothermal ageing on the shear creep behaviour of eco-friendly sandwich cores

The development of sustainable sandwich materials is needed in the transportation sector to address environmental concerns related to the production and operation of vehicles. In addition to biobased composite skins, alternatives to classic synthetic core materials must be found to reduce the ecological footprint of whole sandwich-structured composites. This study focused on three eco-friendly lightweight core materials: balsa wood, paper honeycomb, and recycled PET foam. The effect of the hygrothermal ageing on their shear creep/recovery behaviour has been here investigated. Two different environmental conditions were tested: 23 °C-50% RH and 70 °C-65% RH. The results indicate that the maximum shear strain , the time-delayed strain and the residual strain increase for the three core materials with the severity of the hygrothermal conditions. This was attributed to the softening of the constitutive polymeric materials of the cell walls at temperatures close to 70 °C. The balsa wood exhibits the best creep resistance under the two environmental conditions. The identification of the viscoelastic properties highlights that the release times and the shear viscous parameters of the balsa wood and the PET foam depend on the stress level and the hygrothermal conditions.

Investigation of effect of hygrothermal ageing on physical properties of graphene oxide / epoxy nano-composites

The present article investigates the effect of hygrothermal ageing on the physical and mechanical properties of graphene oxide reinforced epoxy/glass composites. Both neat and graphene reinforced composite laminate structures were immersed in hot artificial seawater with different temperatures namely 50 °C and 60 °C for 72 h and then tested for different physical and mechanical properties. Langmuir's model was employed for simulating the physical properties. Fick’s law was proposed for the diffusion coefficient and parameters as a function of temperature and graphene content. The results showed that diffusion coefficient, permeability and moisture absorption decrease with the addition of graphene oxide, but glass transition temperature and hardness increase with graphene. The water uptake of graphene oxide reinforced laminates has significantly decreased due to graphene oxide acting as a water barrier in laminates. The improvement in microhardness of graphene oxide reinforced laminates due to strengthened interface bonding and enhanced epoxy stability.