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This paper presents research on variable curing temperature of commercially available epoxy adhesives used for structural strengthening with externally bonded and near surface mounted fiber reinforced polymer laminates, strips and bars. An innovative technique for anchorage of prestressed FRP laminates called “gradient anchorage” based on accelerat...
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... Adhesives should be cured under optimal conditions, such as at the appropriate temperature and time (Kotynia et al. 2017). The curing behavior of the DAS-PA 6N adhesive was analyzed by dynamic thermodynamic analysis (DMA) and differential scanning calorimetry (DSC), and the results are shown in Fig. 6. ...
Manufacturing green and sustainable bio-based adhesives is an effective strategy to alleviate both serious energy and environmental issues. Herein, based on the aldehyde–amine covalent reaction between dialdehyde starch (DAS) and polyamine (PA6N), a hyperbranched crosslinked starch-based adhesive was prepared, which overcomes the disadvantage of poor water resistance of conventional starch-based adhesive. The imine groups (C = N) and aminal groups (N–C–N) produced by the reaction of dialdehyde starch and polyamines stably “weld” the molecular chains of dialdehyde starch and polyamine. In addition, the dense cross-linking network formed by the molecular chains stacking and entanglement also plays a crucial role in enhancing the water resistance of the adhesives. The FTIR, XPS, and ¹³C NMR indicated that the imine and aminal covalent bonds were formed between the starch molecular chain and the polyamine. The dry bonding strength of the modified starch adhesive reached 2.12 MPa, which was increased by 162% compared to the natural starch adhesive. The wet strength of the adhesive after 63 °C of hot/boiling water soaking for 3 h broke from 0 to 1.92/1.34 MPa. The proposed DAS-PA6N starch-based adhesive has the advantages of low cost, high performance, and green sustainability, suggesting broad application prospects in aldehyde-free bio-based wood adhesives.
... On the one hand, intrinsic adhesive properties (in particular strength and stiffness) are significantly changed depending on material type and composition of admixed particles [158,166] . On the other hand, particles may influence adhesion performance on the considered substrate [167] , which additionally depends on adhesive type [168] , joint geometry [169] , surface pre-treatment of the substrate [170] , the curing conditions [171] as well as the type of applied load [172] . ...
The present thesis summarises my research on accelerated curing of adhesives, and adhesively bonded connections, using inductively heated Curie-particles (CP). Induction heating is used as a rapid and versatile heating technique. Curie particles have been considered because of their property to generate heat up to their corresponding Curie temperature, if subjected to an electromagnetic field (EMF), but not beyond. The combination of induction heating and CP aimed at resulting in an accelerated curing process completely freed of the constraints of process control as usual for adhesively bonded joints. In the first part of my thesis, I describe the conceptual and technical background necessary to understand the core issues of my research, and detail its scientific objectives. The second part includes all necessary information regarding the materials used and methods applied for the accelerated curing experiments. In the third part, my eight peer-reviewed accepted publications that constitute the core of my thesis are summarised. In the next, fourth, part, the achievements of the scientif work were assessed, a summary and an outlook conclude the thesis. Finally, the fifth part includes my curriculum vitæ and other personal information. During the research, I maintained a coherence between the individual chapters represented by the individual publications by systematically using the same adhesives and CP so to incrementally increase the level of investigation complexity based upon a solid background. The investigations started on the level of curing kinetics of the considered two-component (2K) structural adhesives in order to highlight influences of the process thereof. Afterwards, experimental investigations were scaled up to the level of bulk adhesive properties (most importantly strength and stiffness), over small-scale joints up to large bonded applications. In addition, two publications focus on the development and application of a numerical model to predict heating- and curing-related aspects of the technique to design more predictable and practitioneer-friendly CP-curing processes. Finally, CP were also considered to cure adhesives starting from low temperatures, in which the polymerisation would not occur at all, thus paving the way for additional application fields for adhesively bonded joints.
... Previous research suggests that the adhesive is the critical element in glued-in rod connections when exposed to elevated temperatures since its capacity decreases drastically when the glass transition temperature (Tg) is exceeded [4][5][6][7]. The latter is defined as the temperature where permanent modifications occur in the molecular structure of the polymer, leading to a transition of a solid to rubberlike state of the adhesive [8][9][10][11]. At temperatures above the Tg, this results in a considerable loss of adhesion and cohesion in the adhesive layer, translating to a poor performance of the connection with an undesirable brittle failure mode [7,[12][13][14][15]. ...
... Hence, the adhesive used to strengthen engineering structures should be easy to operate, and able to cure in simple conditions. Some cold curing structural epoxy adhesives could cure at a low temperature and perform well, but their glass transition temperature is as low as 70℃ [33][34][35]. ...
his paper firstly explores the hydrothermal aging performance of a new room temperature cured structural adhesive at four different levels of relative humidity through dynamic mechanical analysis (DMA). The results show that the strengthening effect of post-curing was stronger than weakening effect of humidity. Then, the Arrhenius equation was introduced to calculate the ratio of the apparent activation energy of this adhesive at the glass transition temperature before and after hydrothermal aging. The little change of the ratio suggests that the adhesive boasts a strong resistance to hydrothermal aging. In addition, the adhesive was tested on concrete structures at room temperature to observe its repairing effect of concrete cracks. The observations reveal that the compressive strength of the cracked concrete block repaired by the adhesive was as high as 90.5% of that of the intact concrete block. Furthermore, the adhesive was used to bond rebars to concrete under three different constant tensile speeds. The results demonstrate that the bonding effect was better under slow constant loading.
... There is also a sense of urgency in conceptualizing and developing materials that are derived from natural resources, are reusable, recyclable and biodegradable. In this context, natural fibers have proven their potential as a feasible alternative to the synthetic fibers in polymer matrix composites (Kotynia et al. 2017;Thomas, Dick, and Feng 2014;Zhou et al. 2017). Sisal and jute woven mat reinforced epoxy composites belong to the family of partially biodegradable natural fiber-based polymer composites (Fiore et al. 2015;Salleh et al. 2013). ...
The natural fiber-based polymeric composites are being used extensively in various engineering applications, especially in the non-structural parts and components. Although, a large number of primary processing techniques, such as hand-layup and compression molding are available for fabrication of parts, still the secondary processing in terms of joining and machining is inevitable. The joining of composite parts becomes necessary in case of complicated and intricate product designs. Adhesive joining is one of the most commonly used processes for polymer-based composite materials. It is a cheap, easy, and smooth bonding process and does not necessitate the drilling of holes for the purpose of mechanical fastening. In the present experimental investigation, the joint strength of woven fiber mat (sisal, jute, and hybrid) reinforced epoxy composites has been investigated using different joint configurations, namely, single lap, double-strap butt, and scarf joint. The effect of adhesives has also been explored by joining composites with two types of epoxy resins and corresponding hardener. It was observed that the hybrid composites recorded better joining performance for both types of adhesives. Moreover, the Field Emission Scanning Electron Microscopy (FE-SEM) has been used to understand the failure mechanisms during tensile testing of adhesively bonded natural fiber-reinforced composite laminates. The three-dimensional assembly models of adherend specimens were created using the SOLIDWORK V.16 modeling software. ANSYS-V.18.2 WORKBENCH was employed for the analysis of the joint performance. The maximum shear stress and the total deformation results were determined. The finite element analysis (FEA) results were compared with experimental findings and were found to be in good agreement.
... A lot of efforts (Frigione et al. 2006a,b;Vietri et al. 2014;Silva et al. 2016;Prolongoa et al. 2006) were devoted to modifying epoxy resin, for example, by adding fibers, one can improve the strength and stiffness to a certain extent. However, the adhesives must be in some certain conditions for curing, such as certain temperature and certain time, or the properties of the adhesives cannot reach the expectation (Kotyniaa et al. 2017). In terms of practical applications of these developed adhesives in the field of civil engineering, most of them are outside, even in some remote places without any external heating source. ...
To evaluate the performance and reliability of a new type of epoxy resin adhesive, the dynamic mechanical analysis (DMA) testing was performed at different levels of temperature and frequency after hydrothermal aging. The results of the DMA and the thermodynamic analysis that the performance of the adhesive has little change after hydrothermal aging for 30 days meant that the resistance to hydrothermal aging of this adhesive was excellent. In addition, the time-temperature equivalence principle and time-aging time equivalence principle were proposed here to offer additional insights into the dynamic mechanical performance of the newly developed adhesive. Moreover, an effective method by which the generalized curve of definite aging time in certain conditions of definite temperature and humidity can be obtained was introduced.
Graphical abstract
... They found that T g and mechanical properties behaved similarly by changing curing conditions. Another experimental study about influence of curing conditions on T g and shear strength of epoxy-based adhesives was conducted by Kotynia et al. [24] For both types of adhesives they used, there was no important effect of variations in curing time (25 to 35 minutes) on T g . Cassidy et al. [25] conducted a study to determine the link between T g and adhesive strength and as a consequence of this work they stated that T g could be used as a tool to predict the strength of the adhesive at the working temperature. ...
... Studies have shown that, T g of epoxy-based adhesives is in a relationship with their shear strength, modulus and mechanical properties and T g of the adhesives is directly proportional to the mechanical properties. [22][23][24][25] Thus, it is expected that the SLJs showing decreases in their shear strength will show a decrease in their T g values and the SLJs showing an increase in their shear strength will also increase in their T g values. According to [63], the decrease in T g values with thermal ageing effect is related to the chain scissions caused by thermal degradation and thermo-oxidative mechanisms. ...
A comprehensive and comparative experimental study was conducted to determine how the thermal ageing process, applied at different temperatures for different exposure durations, affects the mechanical properties and mechanical performance of the single lap composite joints bonded by adhesives with different properties. Initially, the glass fibre/epoxy composite joints were divided into seven different groups and each group was subjected to thermal ageing at -10 to 120 °C. Subsequently, specimens aged for 24 to 1440 hours were subjected to single lap shear tests to determine the change in their mechanical properties. As a result of this study, it is deduced that the maximum load carrying capacity generally decreases as the thermal ageing duration increases and take its lowest value at 120 °C, however, surprisingly the capacity of joints bonded with a ductile characteristic adhesive (DP 460) and aged at 80 °C shows an increasing trend as the ageing duration is prolonged.
