Effects of Temperature and Loading Rate on the Mechanical Properties of a High Temperature Epoxy Adhesive (original) (raw)
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Mechanical characterization of a high temperature epoxy adhesive
It is well known that, in order to properly design a joint the adhesive behaviour has to be characterized. Thus, to determine the stresses and strains in adhesive joints in a variety of configurations, it is necessary to know the adhesive mechanical properties. In this work, the performance of a high temperature epoxy adhesive has been studied through bulk specimens and adhesive joint tests. In order to obtain a tensile strength profile of the adhesive, bulk specimens of cured adhesive were produced and tested in tension at RT and high temperatures (100ºC, 125ºC, 150ºC and 200ºC). The thick adherend shear test (TAST) was performed in order to measure the shear properties. In addition, single lap joints (SLJs) were fabricated and tested to assess the adhesives performance in a joint. The results showed that the failure loads of both the bulk test and joint test specimens vary with temperature and this needs to be considered in any design procedure. KEY WORDS: Epoxy adhesive, high tem...
Journal of Adhesion Science and Technology, 2012
There has been a growing requirement in the last years, particularly in the aerospace industry, for adhesives to withstand high temperatures. The most important factor to consider when studying the effect of temperature on adhesively-bonded joints is the variation of adhesive mechanical properties with temperature such as the stress-strain curve and the toughness. Adhesive strength and strain show temperature dependence, especially near the glass transition temperature (T g ) of the adhesive. Similarly, the fracture toughness is expected to show temperature dependence.
Influence of temperature and strain rate on cohesive properties of a structural epoxy adhesive
International Journal of Fracture, 2009
Effects of temperature and strain rate on the cohesive relation for an engineering epoxy adhesive are studied experimentally. Two parameters of the cohesive laws are given special attention: the fracture energy and the peak stress. Temperature experiments are performed in peel mode using the double cantilever beam specimen. The temperature varies from-40°C to +80ºC. The temperature experiments show monotonically decreasing peak stress with increasing temperature from about 50 MPa at-40ºC to about 10 MPa at +80ºC. The fracture energy is shown to be relatively insensitive to the variation in temperature. Strain rate experiments are performed in peel mode using the double cantilever beam specimen and in shear mode, using the end notch flexure specimen. The strain rates vary; for peel loading from about 10-4 s-1 to 10 s-1 and for shear loading from 10-3 s-1 to 1 s-1. In the peel mode, the fracture energy increases slightly with increasing strain rate; in shear mode, the fracture energy decreases. The peak stresses in the peel and shear mode both increase with increasing strain rate. In peel mode, only minor effects of plasticity are expected while in shear mode, the adhesive experiences large dissipation through plasticity. Rate dependent plasticity, may explain the differences in influence of strain rate on fracture energy between the peel mode and the shear mode.
Procedia Engineering, 2017
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 accelerated curing of the epoxy adhesive was invented at EMPA in order to avoid the mechanical fastening systems. The main importance of the "gradient anchorage" is selection of the most appropriate conditions for curing of the epoxy resin in terms of different curing and cooling times and temperatures. In order to specify the best curing conditions the research on two commercially available adhesives was performed. The test program consisted of eight series of adhesive specimens prepared in accordance with the producer and stoichiometric composition defined in the simultaneous chemical research. Both compositions were differed in a temperature and a crosslinking time. The following temperature and time of the epoxy adhesive curing were investigated in the shear test joints: 80°C for 25 minutes (4 series), 80°C for 35 minutes (4 series). The shear strength of the epoxy joints was tested after 10, 20 and 30 minutes of the adhesive curing in a high temperature. Analysis of variable curing and cooling time enabled to define the best curing conditions to obtain the highest shear strength of the adhesive joints. Simultaneously with the mechanical test, the glass transition temperature of the epoxy adhesive was determined by the Differential Scanning Calorimetry method.
Journal of Materials Science, 1991
Adhesive joints are subjected during their service life to different combinations of dynamic and static stresses. While the behaviour of the adhesives in relatively simple states of stress is well characterized, their response to superimposed stresses of different types acting in different directions has scarcely been investigated. In the study presented in this paper, single lap joints made with different formulations of epoxy adhesives were subjected to combined shear creep stresses and torsional oscillations applied simultaneously and along perpendicular axes of the specimen. The main conclusion based on the results of this investigation is that such a simple combination of stresses affects considerably the mechanical behaviour of the joint. A significant increase of the shear strength of the joint was recorded for specimens subjected to superimposed stresses at temperatures lower than the Tg of the adhesive. Application of similar combinations of stresses at temperatures close to or higher than the Tg led to a decrease of the shear strength of the joint. The fracture morphology of the joints made with the investigated epoxy resins was qualitatively correlated with changes induced by the superimposed loading in the Tg of the adhesive. The fatigue fracture surface of adhesives is characterized by striations and furrows, similar to bulk specimens that failed in the same fashion.
Mechanics of Materials, 2020
Adhesively bonded joints using epoxy resin are nowadays often replacing welding in offshore applications for safety reasons. During its lifetime, the bonded joint epoxy is submitted to severe environmental and loading conditions, such as humidity, water uptake, thermal aging, and complex loading conditions affecting its mechanical performance. We investigate here the dynamic mechanical behavior of an epoxy resin at large strain over a wide range of temperatures. Analysis of the elastic modulus, yield strain, yield stress and plastic flow as a function of the temperature and strain rate is carried out. Unlike the elastic modulus and the yield stress showing strong sensitivities to the temperature and the strain rate, the plastic flow appears to have a limited sensitivity to the temperature and the strain rate. Numerical modeling is used to determine the yield stress and elastic modulus variations over the glass transition temperature and good agreement is observed between numerical predictions and experimental results.
International Journal of Non-Linear Mechanics, 2019
Nowadays, adhesively bonded structures have received exhaustive attention mainly because, contrary to mechanical joints, they are able to avoid stress concentration. When a material is externally bonded to another structural member to improve the strength or stiffness of the latter, the adhesive joint is supposed to perform well for a long time, independently of the type of loading the bonded joint will be subjected to. However, studies dedicated to this topic are scarce when it comes to the influence of thermal action. The influence of temperature variations on bonded joints is not yet well understood, so more studies are needed to improve the current level of knowledge. The present study aims to develop an analytical solution capable of simulating the interfacial bond behaviour between two structural materials subjected to thermal loading. The complete debonding processes of such adhesively bonded joints are estimated based on a bi-linear bond-slip relationship. The proposed analytical model is validated by the numerical simulation of several examples, where some parameters previously identified as potentially affecting the bond behaviour are investigated. A commercial software based on the Finite Element Method (FEM) is used to support those examples in which either the analytical or the numerical simulations agreed very well. Some authors [15,16] have identified epoxy resins with different constitutive behaviours (linear and non-linear until rupture) that, when used to bond an FRP composite to a concrete or steel substrate, lead to different local behaviours with subsequent impact on the global performance of the joint. Temperature is another aspect that concerns everyone who is working on bonded structures because it changes the resin behaviour significantly (e.g. [24,25]). When temperature increases, resins begin to change from a glassy state to a rubbery, viscous state and lose their initial mechanical properties, which compromises the bond transfer efficiency between materials. The temperature beyond which the resins lose their mechanical properties is called the glass transition temperature () and for regular resins this value may range between 55 o C and 120 o C [26], but there are commercial epoxy resins with high available on the market for which, according to the supplier, this value may go up to 190-240 o C [27-30] once a pre-heat curing process is carried out to fully cure the resin. This explains why some authors [31,32] have proposed models that take into account this aspect of the temperature-dependency reflected on the interfacial behaviour between two materials. The main principle
With the aim of characterising a commercially available epoxy adhesive used for fibre-reinforced 12 polymers strengthening applications, when submitted to different environmental conditions, mainly thermal 13 (TC), freeze-thaw (FT), and wet-dry (WD) cycles and immersion in pure (PW) and water with chlorides (CW) 14 for periods of exposure that lasted up to 16 months, an experimental program was carried out. Several 15 methodologies were used in its characterization, mainly the scanning electron microscope (SEM), dynamic 16 mechanical analysis (DMA), standard tensile tests (STT) coupled with digital image correlation (DIC). In 17 general the results revealed that the chemical composition was not affected by the environmental conditions. 18
High temperature adhesives for aerospace applications
Adhesives used in structural high temperature space and aerospace applications must operate in extreme environments. They need to exhibit high-temperature capabilities in order to maintain their mechanical properties and their structural integrity at the intended service temperature. One of the main problems caused by the high temperature conditions is the fact that the adhesives have different mechanical properties with temperature, such as the stress-strain curve and toughness. The objective of this work was to investigate the mechanical behaviour of two different types of high-temperature adhesives, one for strength at high temperatures and one for strength at low temperatures, which will be subsequently used to design a mixed-adhesive joint suitable for use from low to high temperatures. An epoxy adhesive with a high strength at high temperatures but most likely very brittle at low temperatures would be combined with a silicone adhesive which is tough at low temperatures and does not degrade at the high temperatures even being very ductile and creep.
The Journal of Adhesion, 2018
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.