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.     

Influence of multi-walled carbon nanotubes on creep behavior of adhesively bonded joints subjected to elevated temperatures

Polymeric materials are prone to creep loading. This paper is aimed to study the effect of multi-walled carbon nanotubes (MWCNTs) on creep behavior of adhesively bonded joints. Neat and MWCNTs-reinforced adhesively bonded joints were manufactured and tested under creep loading at elevated temperatures. Two MWCNT weight percentages of 0.1 and 0.3 were used for reinforcing the single lap joints (SLJs) and the joints were tested at different temperature and load levels. The results showed that 0.1 wt% of MWCNTs resulted maximum improvements in creep behavior of adhesive joints. Adding 0.1 wt% of MWCNTs into the adhesive layer caused maximum reductions of 57%, 60% and 47% in the steady-state creep rates of the joints tested at 30, 40 and 50°C, respectively. Furthermore, 0.1 wt% of MWCNTs resulted maximum reductions of 29%, 33% and 37% in the creep strains corresponding to a specific creep loading time and maximum reductions of 23%, 45% and 49% in the elastic strains corresponding to the time at which creep loading started.     

基于十字交叉法的陶瓷胶粘剂剪切蠕变性能研究

本研究设计了“十字交叉法”陶瓷胶粘剂剪切蠕变试验装置,选取刚性环氧树脂及柔性硅酮结构胶进行剪切蠕变试验,研究了环境温度、剪切应力、粘结面积等因素对胶粘剂剪切蠕变的影响,通过模型拟合对胶粘剂的剪切蠕变行为进行了分析和预测,探究了两种胶粘剂的蠕变破坏模式。结果表明:采用十字交叉法能够准确便捷地测试陶瓷胶粘剂的蠕变性能。增大胶粘层柔性、提高环境温度、增大剪切应力都会加速蠕变的发展,但粘结面积对蠕变速率无明显影响。刚性环氧树脂胶粘剂试样的蠕变失效形式为粘结层内聚破坏及界面脱粘,符合时间硬化模型;柔性硅酮结构胶试样失效形式为粘结层内聚破坏,符合Burgers模型。     

Creep Resistance of Pressure Sensitive Mounting Tapes

The first part of the paper deals with an approach towards a systematic testing procedure to evaluate the creep behavior of single lap shear specimens bonded with PSA mounting tapes under the influence of temperature and humidity. The study includes commercial tapes as well as self-formulated pressure sensitive adhesives based on styrene block copolymers. The second part of the paper relates the obtained data, consisting of the time-dependent sample deformation and time-to-failure, to the observed failure modes. The results show that the creep behavior of a pressure sensitive adhesive is not only dependent on the environmental, conditions but also on the substrate material and its surface composition. The results for the self-formulated adhesives reveal the possibility of enhancing creep resistance of PSA's by adding fillers to the formulation. The paper closes with a modification of the Burgers model that is suitable for describing the creep/creep recovery behavior of tested lap shear specimens. The effect of nonlinear behavior in cyclic loading experiments is described and a thesis for the relation of nonlinear creep behavior to damaging processes in the adhesive bond is presented.     

Improving the mechanical behavior of the adhesively bonded joints using RGO additive

In this research, Araldite 2011 has been reinforced using different weight fractions of Reduced Graphene Oxide (RGO). Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analyses were conducted and it has been shown that introduction of the RGO greatly changes the film morphology of the neat adhesive. Uni-axial tests were carried out to obtain the mechanical characteristics of the adhesive-RGO composites. It has been observed that introducing 0.5 wt% RGO enhances the ultimate tensile strength of the composites by 30%. In addition, single lap joints using neat adhesive and adhesive-RGO composites were fabricated to investigate the effect of the added RGO on the lap shear strength of the joints. Results show that the joints with added 0.5 wt RGO exhibited 27% higher lap shear strength compared to the joints bonded with neat adhesive. Finally, Finite Element (FE) numerical solutions using Cohesive Zone Modeling (CZM) have been carried out to simulate the failure behavior of the joints, and it has been shown that the FE models can predict the joint’s failure load.     

Effect of silicon carbide nanoparticles on the adhesion strength of steel–epoxy composite joints bonded with acrylic adhesives

This paper reports a study on the effect of silicon carbide nanoparticles on the adhesion strength of steel–glass/epoxy composite joints bonded with two-part structural acrylic adhesives. The introduction of nanosilicon carbide in the two-part acrylic adhesive led to a remarkable enhancement in the shear and tensile strength of the composite joints. The shear and tensile strengths of the adhesive joints increased with adding the filler content up to 1.5?wt%, after which decreased with adding more filler content. Also, addition of nanoparticles caused a reduction in the peel strength of the joints. DSC analysis revealed that Tg values of the adhesives rose with increase in the nanofiller content. The equilibrium water contact angle was decreased for adhesives containing nanoparticles. SEM micrographs revealed that addition of nanoparticles altered the fracture morphology from smooth to rough fracture surfaces.     

EVALUATION OF THE LONG-TERM DURABILITY OF HIGH-PERFORMANCE POLYIMIDE ADHESIVES FOR BONDING TITANIUM

This study was conducted to investigate the performance of the Ti-6Al-4V/FM-5 adhesive bonded system for potential applications on high-speed aircraft. The long-term environmental aging effects on Ti-6Al-4V/FM-5 bonded joints and neat FM-5 and PETI-5 resin specimens were investigated. Dynamic mechanical analysis (DMA) and uniaxial tensile testing using dogbone samples were performed on neat FM-5 and PETI-5 resin specimens before and after high-temperature aging in both ambient and reduced pressure environments. Mode I fracture testing was also performed on beam specimens fabricated with mat-scrim-cloth-supported films of FM-5 adhesive bonding titanium adherends prior to and after environmental aging. Experimental results revealed that both physical aging, which is reversible, and irreversible chemical aging took place simultaneously in the adhesive systems, and both types of aging could contribute to loss in adhesive bond performance. Furthermore, the properties of several different Ti-6Al-4V/FM-5 systems, prepared using different surface pretreatment methods and different supportive matrices of FM-5 resin, were compared in this study, and the effect of mode-mixity on the fracture toughness of the adhesive-bonded systems was also evaluated by conducting double cantilever beam (DCB), end-notched flexure (ENF), and mixed-mode flexure (MMF) tests. The creep behavior of the Ti/FM-5 bonded joint was also investigated by performing thick adherend shear tests.     

EVALUATION OF THE LONG-TERM DURABILITY OF HIGH-PERFORMANCE POLYIMIDE ADHESIVES FOR BONDING TITANIUM

This study was conducted to investigate the performance of the Ti-6Al-4V/FM-5 adhesive bonded system for potential applications on high-speed aircraft. The long-term environmental aging effects on Ti-6Al-4V/FM-5 bonded joints and neat FM-5 and PETI-5 resin specimens were investigated. Dynamic mechanical analysis (DMA) and uniaxial tensile testing using dogbone samples were performed on neat FM-5 and PETI-5 resin specimens before and after high-temperature aging in both ambient and reduced pressure environments. Mode I fracture testing was also performed on beam specimens fabricated with mat-scrim-cloth-supported films of FM-5 adhesive bonding titanium adherends prior to and after environmental aging. Experimental results revealed that both physical aging, which is reversible, and irreversible chemical aging took place simultaneously in the adhesive systems, and both types of aging could contribute to loss in adhesive bond performance. Furthermore, the properties of several different Ti–6Al-4V/FM-5 systems, prepared using different surface pretreatment methods and different supportive matrices of FM-5 resin, were compared in this study, and the effect of mode-mixity on the fracture toughness of the adhesive-bonded systems was also evaluated by conducting double cantilever beam (DCB), end-notched flexure (ENF), and mixed-mode flexure (MMF) tests. The creep behavior of the Ti/FM-5 bonded joint was also investigated by performing thick adherend shear tests.     

Characterization and modeling of creep behavior of a thermoset nanocomposite

In this article, we report creep and recovery behavior of nanocomposites based on a high‐temperature‐resistant thermosetting matrix. Nanocomposites with up to 2 wt% of organically modified clay were prepared. The creep and recovery behavior was investigated under various stress levels and at various temperatures. Creep behavior was modeled by a modified Burgers model by introducing a stretched exponential function. This stretched Burgers model satisfactorily describes the creep behavior of the matrix and nanocomposites. The role of filler on the system dynamics has been also discussed and an interesting finding discovered from the stretched Burgers model results. The model results suggest that the dynamics of the filled system is independent of the filler, which is scientifically quite interesting in the field of nanocomposites. The multiple cycle creep and recovery behavior of the matrix were also investigated and the Boltzmann superposition principle was applied to describe the multistep loading creep response. POLYM. COMPOS., 36:322–329, 2015. © 2014 Society of Plastics Engineers     

Mechanical properties of adhesively single lap-bonded joints reinforced with multi-‌‌‌walled carbon nanotubes and silica nanoparticles

This paper aims to investigate the effect of adding nanoparticles to the adhesive layer on the shear strength and elongation at failure of adhesively bonded single lap joints (SLJs). Two different toughening particles including the silica nanoparticles (SNPs) and the multi-walled carbon nanotubes (MWCNTs) were considered for reinforcing the adhesive joints. The experimental results showed that the highest improvements in the SLJ shear strength and elongation at failure were obtained for 0.2 and 0.8 wt% of MWCNTs and SNPs, respectively. The fractography results indicated that adding nanoparticles improved the failure mode from adhesive to dominant cohesive representing improved adhesion between the adhesive and adherends. Moreover, different damage mechanisms were observed for the adhesives reinforced with different toughening particles. Several mechanisms including crack growth deviation, shear yielding, plastic deformation, and pull out phenomena were observed from scanning electron microscope (SEM) fractography of the fracture surfaces of the joints reinforced by MWCNTs. While in the case of reinforcing by SNPs, the shear yielding, the particle debonding, and subsequent void growth were found as the effective energy absorbing mechanisms.     

Numerical study of the effect of carbon fiber/epoxy resin adhesive thickness on the creep behaviour of carbon steel plate joints

Nowadays, the use of adhesive and adhesively bonded joints have been considerably appreciated in the industry due to the dramatic reduction in bonding strength, reduced stress concentration, rust prevention, uniform bonding of the bonding surface and a significant reduction in costs compared to other types of permanent joints such as welding. In this study, the effect of adhesive thickness on creep behaviour of a single lap adhesive joint with the aid of Abaqus FEM software is investigated. It should be noted that the two-layer and two-dimensional models are considered, in which their adhesive layer is made of a reinforced epoxy resin with 0.5% carbon fiber and the adherend layers are made of carbon steel plates, which is affected by tensile forces. Since the main purpose of this paper is to study the effect of adhesive thickness on the adhesive joints behaviour, the effects of the distribution of shear stress, effective stress and creep strain were studied in different thicknesses of the adhesive layer. The results show that by increasing the thickness, the stress and the creep strain decrease, and over time, the stress decreases and the creep behaviour of adhesives increases.     

Analysis of the nonlinear creep behavior of concrete/FRP-bonded assemblies

This paper investigates the creep behavior of adhesively bonded concrete/fiber-reinforced polymer (FRP) joints, through experimental and modeling approaches. The first part proposes a methodology for predicting the long-term creep response of the bulk epoxy adhesive; such a procedure consists of (1) performing short-term tensile creep experiments at various temperatures and stress levels, (2) building the creep compliance master curves according to the time–temperature superposition principle in order to assess the long-term evolution for each stress level, and (3) developing a rheological model whose parameters are identified by fitting the previous master curves. In our case, it was found that master curves (and, consequently, parameters of the rheological model) are dependent on the applied stress level, highlighting the nonlinear creep behavior of the bulk epoxy adhesive. Therefore, evolution laws of the model parameters were established to account for this stress dependence. The second part focuses on the creep response of the concrete/FRP assembly in the framework of a double lap joint shear test configuration. Experiments showed that creep of the adhesive layer leads to a progressive evolution of the strain profile along the lap joint, after only one month of sustained load at 30% of the ultimate strength. Besides, a finite element approach involving the abovementioned rheological model was used to predict the nonlinear creep behavior of the bonded assembly. It confirmed that creep modifies the stress distribution along the lap joint, especially the stress value at the loaded end, and leads to a slight increase in the effective load transfer length. This result is of paramount interest since the transfer length is a key parameter in the design of FRP-bonded strengthening systems. Moreover, instantaneous and long-term calculated strain profiles were found in fair agreement with experimental data, validating the modeling approach.     

In situ synthesis of novel biomass lignin/silica based epoxy resin adhesive from renewable resources at different pHs

Novel biomass lignin/silica composites were prepared and isolated from rice husk renewable resources at different pHs. Selective precipitation was achieved by decreasing the solution pH from 9.5 to 1.5. When pH reached 3.5, the ratio of lignin and silica mostly achieved the maximum of 1:1. We selected lignin/silica composites as reactants to replace 20?wt% bisphenol A in preparing epoxy resin. The cured novel biomass function lignin/silica-based epoxy resin adhesive showed the highest adhesive strength up to 2.68?MPa, which displayed 123% of neat epoxy resin adhesive. In addition, lignin/silica composites were depolymerized through the hydrothermal method by NaOH as a catalyst, which was used as reactants to replace 35?wt% bisphenol A in the process of in situ synthesis of epoxy resin adhesive. At this point, the high epoxy value (1.42?wt%) and large adhesive strength (3.98?MPa) of lignin/silica-based epoxy resin adhesive were obtained, which adhesive strength was 183% of neat epoxy resin adhesive. The results demonstrated that depolymerized lignin/silica-based epoxy resin adhesive showed the higher epoxy value and the adhesive strength compared with neat epoxy resin adhesive and lignin/silica-based epoxy resin adhesive. Their function in epoxy matrix resulted in better processability.     

Use of master curves based on time-temperature superposition to predict creep failure of aluminium-glass adhesive joints

Advancements in materials technology and the use of innovative designs have led to extensive application of adhesive bonding techniques in the electric appliance industry. While the static strength of such joints is sufficient for the intended applications, long term durability remains a major concern, mainly due to creep effects. Conventional creep testing can be performed at the service temperature but it is a long test that can take decades, although it can be accelerated using high temperatures. In this work, glass-aluminium joints were studied under static and creep loads. Glass-aluminium specimens were subjected to creep testing at various temperatures. Using the time temperature superposition principle, the results of these individual creep tests were combined in a master curve that approximates the creep behaviour of the adhesive joint in a long time period. These master curves were used to guarantee a minimum service life of the joint.     

Enhanced mechanical,thermal and adhesion properties of polysilsesquioxane spheres reinforced epoxy nanocomposite adhesives

ABSTRACT

Epoxy-based systems serve as excellent adhesives to join a wide range of substrates such as metal, ceramics, plastics, etc. The mechanical properties of such systems can be improved considerably by the addition of filler to the epoxy matrix. Herein, polymethylsilsesquioxane (PMS) and poly(methyl/vinyl)silsesquioxane (PMVS) nanosphere were synthesised by hydrolytic condensation of oraganosilane as a precursor in aqueous phase. The epoxy nanocomposite adhesives were prepared by adding different weight percentages (1–4 wt%) of the PS nanospheres. Tensile and compressive strength of the adhesive formulations were studied using the universal testing machine (UTM) and it was observed that the mechanical properties of the composites showed an increasing trend on increasing the filler loading. Adhesive strength of the epoxy composites on mild steel substrate was studied by conducting the lap shear test and EPV-4 exhibited a 31% increase in adhesive strength on the mild steel compared to the neat epoxy. Surface morphology of the epoxy composites were visualised from the SEM images and the composites also showed enhanced thermal conductivity. Higher mechanical and adhesive strength indicates the potential of the prepared nanocomposites to be used as an effective formulation in adhesive-based systems.     

Effect of creep on the mode II residual fracture energy of adhesives

Viscous flow that often occurs in adhesive materials leads to a permanent deformation when adhesives are subjected to creep loading. Creep loading has a significant influence on the strength of bonded structures. Due to the viscous behavior, the fracture energy also may change with time for joints that experience creep loading in service. In this work the effects of two creep parameters (creep load and time) on the residual mode II fracture energy of an adhesive was investigated using end notched flexure (ENF) specimens. To achieve this, ENF samples were subjected to different creep loading levels at different creep times followed by quasi static tests to obtain the residual shear fracture energy of the adhesive. Experimental results showed that pre-creep loading of the bonded structures can significantly improve the fracture energy and the static strength of the joints.     

Kinetics of Adhesion Interaction of Polyolefins with Metals Under Conditions of Contact Thermooxidation

The formation of gradients of macromolecular transformations at contact oxidation in the adhesive layer during formation of adhesive joints of pure and peroxide-containing polyolefins with steel was studied. Indirect methods were used, such as measurement of fluidity in adhesive samples, measurement of shear creep and shear modulus of a polymer melt layer for different adhesive thickness, and some others. Effective viscosity, μ, was calculated from the experimental shear creep curves as a function of the thickness, b, of a cross-linking PE melt layer for several levels of contact time. The experimentally-measured values of viscosity were regarded as the complex average values of a certain viscosity gradient. It was found that in the case of catalytically-inactive substrate (Cellophane), there was no gradient. The dependence of the shear modulus on the layer thickness was determined. The measurements of fluidity of adhesive samples scraped at different distances from the interface for various contact times confirmed that the gradient of macromolecular transformations also originated when steel was in adhesion contact with polyethylene and ethylene-vinylacetate copolymer which did not contain peroxide. In the adhesive layers near the adhesive-steel interface, the catalyzed oxidative cross-linking prevailed. Within the adhesive layers located far enough from the interface, the oxidative destruction was dominant. For a catalytically-inert substrate (Teflon), the oxidative destruction prevailed over the whole thickness of the polymer layer.     

Kinetics of Adhesion Interaction of Polyolefins with Metals Under Conditions of Contact Thermooxidation

The formation of gradients of macromolecular transformations at contact oxidation in the adhesive layer during formation of adhesive joints of pure and peroxide-containing polyolefins with steel was studied. Indirect methods were used, such as measurement of fluidity in adhesive samples, measurement of shear creep and shear modulus of a polymer melt layer for different adhesive thickness, and some others. Effective viscosity, μ, was calculated from the experimental shear creep curves as a function of the thickness, b, of a cross-linking PE melt layer for several levels of contact time. The experimentally-measured values of viscosity were regarded as the complex average values of a certain viscosity gradient. It was found that in the case of catalytically-inactive substrate (Cellophane), there was no gradient. The dependence of the shear modulus on the layer thickness was determined. The measurements of fluidity of adhesive samples scraped at different distances from the interface for various contact times confirmed that the gradient of macromolecular transformations also originated when steel was in adhesion contact with polyethylene and ethylene-vinylacetate copolymer which did not contain peroxide. In the adhesive layers near the adhesive-steel interface, the catalyzed oxidative cross-linking prevailed. Within the adhesive layers located far enough from the interface, the oxidative destruction was dominant. For a catalytically-inert substrate (Teflon), the oxidative destruction prevailed over the whole thickness of the polymer layer.     

Effect of multi-walled carbon nanotubes and silicon carbide nanoparticles on the deleterious influence of water absorption in adhesively bonded joints

In this study, the deleterious influence of hot deionized water on adhesively bonded joints was reduced with silicon carbide (SiC) nanoparticles and multi-walled carbon nanotubes (MWCNTs). A gravimetric method was used to study the kinetics of water ingress into the neat and nanocomposite epoxy adhesives. Then, joints were manufactured using the same neat and nanocomposite adhesives and aged for different periods according to the results obtained from the bulk sample tests and finite element modeling. The results showed that the reinforcing effect of nanofillers on the strength was about three times higher for the wet epoxy adhesive compared to the dry one. Moreover, it was found out that introducing 4.4 wt% of SiCs or 0.52 wt% of MWCNTs to the adhesive can compensate the degrading influence of aging under near-saturated condition. Furthermore, the scanning electron microscope (SEM) fractography was used to assess the fracture surfaces of the neat and reinforced samples.     

Time-dependent properties of graphene nanoplatelets reinforced high-density polyethylene

The deformation of polymers at constant applied stress is one of their major drawbacks, limiting their use in advanced applications. The study of this property using classical techniques requires extensive testing over long periods of time. It is well known that reinforced polymers show improved behavior over time compared to their neat counterparts. In this study, the effect of adding different amounts of graphene nanoplatelets (GNPs) on the time-dependent properties of high-density polyethylene (HDPE) is investigated using short-term creep tests and load/unload recovery tests. The results are discussed in terms of the test profile and the influence of loading history. Viscoplasticity/viscoelasticity analysis is performed using Zapas model and by comparing creep, creep compliance and pure viscoelasticity curves. The results show that the reinforcement of 15 wt% GNP have the most significant effect on the time-dependent behavior, reducing the strain by more than 50%. The creep compliance curves show that nano-reinforced HDPE behaves nonlinearly viscoelastically even at very low stresses. In addition to demonstrating the effect of nano-reinforcement, the discussion of the results concludes that the influence of loading history can be quite significant and should not be neglected in the design and evaluation of material behavior.