An investigation of hygrothermal aging effects on high strain rate behaviour of adhesively bonded composite joints
Introduction
Composite materials are being used progressively in a wide range of industries and applications due to their diverse advantages over traditional materials. They are used in marine, aerospace, and other industries, however, one of the most essential condition for a structural composite is its capacity to retain its loadbearing ability for longer period of time under critical environmental conditions (temperature variations, moisture, oxidation, microbiological attack …) [1,2]. In the past decades, the reinforcement and reparation of marine engineering structures utilizing GFRP laminates had attracted a large deal of attention [3]. In addition, adhesively bonded joints had been considered as premium choice for joining composite structures for many years because of their high fatigue resistance; good vibration damping properties; elimination of galvanic corrosion phenomenon and the uniform distribution of mechanical stress over the joint [4]. Therefore, it has become requisite to comprehend the dynamic behaviour of adhesively bonded composite joints under critical loads for developing constitutive models [5].
Numerous composite structures and assemblies had been applied and preferred over conventional materials such as metal, ceramic in applications which were subjected to extreme outdoor environment. Therefore, the importance of studying the effect of environmental conditions such as hygrothermal aging on mechanical properties of adhesively bonded assemblies under dynamic impact has become increasingly evident during recent years [6]. Many researchers studied the effect of seawater on polymer composites and how it led to the degradation of their performance [7]. For example, environmental exposure could result in reduction of interfacial stress transmissibility because of matrix plasticization, chemical changes and mechanical degradation. Matrix plasticization could reduce matrix modulus while chemical degradation could cause hydrolysis of bond. Mechanical degradation could be because of the strain caused by the matrix and in addition, an interfacial reaction could induce various morphological modifications in interface between the fibre and the matrix [8,9]. However, very little information was found in the literature on the study of damage mechanisms that could show diverse behaviour even in the absence of the effect of important environmental factor such as seawater on degradation of fatigue resistance. So, it was significant to better comprehend the mechanisms and extent of seawater degradation.
Various studies had reported the hygrothermal degradation of reinforced epoxy composites [10], [11], [12], [13], [14]. Schutte showed that the hygrothermal degradation of glass fibre composites included the degradation of the fibre reinforcement, polymer resin matrix, and fibre/matrix interface. However, various investigations showed that vinylester reinforced composites presented better performance in comparison with epoxy based composites because of their high durability, low cost, and resistance to thermal aging [15]. Therefore, vinylester based resins are usually chosen as the matrix material for composite structures [16,17]. Jiang et al. [18] used the experimental and numerical investigation to study the influence of moisture absorption and hygrothermal aging on glass-fibre-reinforced polymer laminates and structural adhesive. The results showed that the square and rectangular samples lost their mass below 40 °C conditions. Pillay and his colleagues [19] evaluated the effects of moisture and UV exposure on the interlaminar shear strength, flexural strength, and low-velocity impact resistance of the composite materials. Similarly, Hosur et al. [20] performed an experimental investigation on unidirectional graphite/epoxy samples under dynamic compression loading conditions at room and elevated temperatures of 51.7 °C, 121.1 °C, and 190.6 °C. The influence of temperature and fabric architecture on the dynamic properties and failure mechanisms was reported in detail.
Recently, Sousa et al. [21] examined the influence of thermal cycles on adhesively bonded assemblies used in civil engineering applications. Benyahia et al. [22] studied the mechanical properties of composite pipes under different temperatures ranging from −40 to 80 °C. Experimental results showed an increase in the mechanical degradation of polymer pipes with an increase in the temperature. Jojibabu et al. [23] studied the effect of adding carbon nano-fillers on the degradation of epoxy adhesive joints subjected to hygrothermal aging. The authors concluded that the addition of nano-fillers in the adhesive joints showed higher joint strength as compared to neat epoxy joints after aging process. Akderya et al. [24] investigated the effects of thermal aging on tensile properties of adhesively bonded single lap joint of fibre/epoxy composites at three different temperatures (18 °C, 25 °C and 70 °C). It was observed from the results that thermal aging at −18 °C increased the load carrying ability of the joint while impacts applied to the joints reduced it. Moreover, decrease in tensile fracture strength of the joint was observed at the temperatures −18 °C and 70 °C. Afterward, Rafiq [25] studied the effect of nano clay on the flexural properties and water absorption resistance of glass fiber-reinforced epoxy composites at different temperatures. The results showed that the maximum water absorption was decreasing by increasing the amount of nano clay loading and it was also observed that the moisture dispersion was about 80% higher at 80 °C than that at room temperature. After the absorption process, flexural test were conducted on all the specimens and results showed that specimen with 1.5 wt % loading of nano clay showed similar behaviour as of the unexposed specimen thus, showing optimal flexural performance under exposed environment. Exposure to moisture resulted in 36% and 8% reduction in flexural strength the nano composite at 80 °C and room temperature respectively.
So, a significant amount of research had been performed previously to understand the influence of hygrothermal effect on the mechanical behaviour of polymer composites at very low strain rates. But, little or no information regarding the experimental study of the hygrothermal effect on the dynamic response of the composites and adhesively bonded composites at high strain rates could be found. On this context, the present experimental study was carried out to study the influence of hygrothermal effect on the mechanical behaviour of the adhesive bonded composite joints at high strain rates using the Split Hopkinson Pressure Bar (SHPB) machine. At first, adhesively bonded composite samples were subjected to hygrothermal aging conditions (50°C-80% RH (relative humidity)) and then in-plane dynamic compression tests were conducted at different impact pressure from 1 to 4 bar using SHPB technique. The results showed that the moisture absorption led to the degradation of dynamic compressive failure strength at high strain rates. Damage mechanisms such as micro buckling kinking and splitting of the fibres were the major failure modes observed in the specimens when subjected to in-plan dynamic compression.
Section snippets
Materials and specimen geometry
The material examined in this study was fabricated by using polyester polymer and 45 bi-axial fibre-glass mat with 0.286 mm in thickness. The polyester polymer was studied in this investigation because it could be used in marine environment as an alternative to the other polymers such as epoxy resin because of its cost effectiveness and good characteristics in a corrosive medium and under high temperatures. A NORPOL polyvinylester adhesive was used to develop an adhesive bond of 1 mm in
Moisture absorption
Various diffusion models could be used to understand the behaviour of homogeneous and heterogeneous material and one of the most famous and commonly used model is Fickian's one-dimensional isotropic model however, divergence from this model was often observed in the literature [35], Fig. 6. Langmuir-type models successfully depicted the absorption water of epoxy/fibre material [36]. When composite materials absorbed water, the local water concentration varied until equilibrium was reached.
Effects of moisture absorption on the dynamic behaviour
- a.
Mechanical behaviour
In order to ensure the reproducibility of dynamic tests, each test, for adhesively bonded composite joint specimen, was repeated three times, Fig. 8. The strain rate vs time and the Stress-Strain variation were plotted to analyse the mechanical response of the tested specimens under different impact pressures.
The moisture and the temperature could define the elastic and thermoplastic properties of a material. However, an augmentation in moisture and temperature, which could
Conclusion
In this article, adhesively bonded composite joints were aged at 50 °C temperature with 80% of the relative humidity for various periods of time intervals i.e. 0 h, 216 h, 648 h and 864 h. The stress-strain responses were determined for high strain rates ranging from 445 to 1240 s−1. The failure modes were observed by OM and SEM for each specimen. The amount of moisture absorption for adhesively bonded composite joints was observed to be 0.28% by weight at the saturation level. In all the
References (43)
- et al.
Evaluation of durability of composite materials applied to renewable marine energy: case of ducted tidal turbine
Energy Rep
(2018) - et al.
Experimental investigation on structural repair and strengthening of damaged prestressed concrete slabs utilizing externally bonded carbon laminates
Compos B Eng
(1996) - et al.
In-situ heat dissipation monitoring in adhesively bonded composite joints under dynamic compression loading using SHPB
Compos B Eng
(2018) - et al.
Effect of seawater immersion on the explosive blast response of a carbon fibre-polymer laminate
Compos Appl Sci Manuf
(2018) Thermal shock on interfacial adhesion of thermally conditioned glass fiber/epoxy composites
Mater Lett
(2004)Effects of crosshead velocity and sub-zero temperature on mechanical behavior of hygrothermally conditioned glass fiber reinforced epoxy composites
Mater Sci Eng
(2004)- et al.
Higher performance carbon fiber reinforced thermoplastic composites from thermoplastic prepreg technique: heat and moisture effect
Compos B Eng
(2018) - et al.
The comparison of effects of hygrothermal conditioning on mechanical properties of fibre metal laminates and fibre reinforced polymers
Compos B Eng
(2018) - et al.
Initiation of stress-corrosion cracking in unidirectional glass/polymer composite materials
Compos Sci Technol
(2001) - et al.
Effects of hygrothermal aging on glass-fibre reinforced polymer laminates and adhesive of FRP composite bridge: moisture diffusion characteristics
Compos Appl Sci Manuf
(2014)
Effects of moisture and UV exposure on liquid molded carbon fabric reinforced nylon 6 composite laminates
Compos Sci Technol
Mechanical properties of offshoring polymer composite pipes at various temperatures
Compos B Eng
Effect of carbon nano-filler addition on the degradation of epoxy adhesive joints subjected to hygrothermal aging
Polym Degrad Stabil
Effects of thermal ageing and impact loading on tensile properties of adhesively bonded fibre/epoxy composite joints
Compos B Eng
An investigation of in-plane dynamic behavior of adhesively-bonded composite joints under dynamic compression at high strain rate
Compos Struct
Investigation of water absorption characteristics of nano-gelcoat for marine application
Prog Org Coating
On the use of SHPB techniques to determine the dynamic behavior of materials in the range of small strains
Int J Solids Struct
A review on split Hopkinson bar experiments on the dynamic characterisation of concrete
Constr Build Mater
Factors governing water absorption by composite matrices
Compos Sci Technol
Hygrothermal history dependence of equilibrium moisture sorption in epoxy resins
Polymer
Damage detection versus heat dissipation in E-glass/Epoxy laminated composites under dynamic compression at high strain rate
Compos Struct
Cited by (52)
Analytical investigation of hygrothermal effects on failure mechanisms of adhesively bonded corrugated sandwich structures under three-point bending
2024, International Journal of Adhesion and AdhesivesComparative experimental study on mechanical properties of CFRP subjected to seawater and hydrostatic pressure
2023, Composites Science and TechnologyMechanical degradation and corrosion characterization of riveted joints for CFRP/Al stacks in simulated marine environments
2022, Engineering Failure AnalysisCitation Excerpt :Since the water absorbed by carbon fibers was generally insignificant and the resin matrix was constituted of hydrophilic functional groups, the matrix was the principal one in moisture absorption in CFRP materials [29]. This suggested that only the matrix was prone to lose its mechanical properties and swelling, resulting in residual stresses between fibers and resin, as well as loss of fibers/matrix interface adhesion, consequently causing CFRP degradation [30]. Besides, the corroded rivet head in region 6 was evident with the formation of some pits and presented superficial asperities, which was related to severe corrosion subjected to the salt spray and wet environment.
Salt spray aging effects on dynamic responses and failure characteristics of hybrid bonded-riveted CFRP/Al joints under high speed loading
2021, Journal of Manufacturing ProcessesCitation Excerpt :The adhesive layer fracture occurred before the catastrophic failure of joint. Nevertheless, with the presence of steel rivet, the joint was still capable of resisting higher load until the final failure, which could be attributed to the composites strength dependency on high loading speed [9]. At the rivet fracture stage (III), the load progressively decreased to zero and the rivet was sheared.