Influence of the temperature on the fracture energy of a methacrylate adhesive for mining applications
© Moller et al. 2015
Received: 19 August 2015
Accepted: 22 September 2015
Published: 16 October 2015
The effects of the increase in temperature are of great importance when evaluating the strength of an adhesive. Some processes in mining, such as copper electro-wining, produce thermal changes that modify the working conditions of equipment and structures; these elements are exposed to temperatures that can reach up to 80 °C. The study presented here aims to determine the behavior, under fracture of mode I type, of a two-component adhesive regularly used to join pieces in acid mist extraction systems. For this purpose, specimens for a double cantilever beam test were produced and tested in an Instron tensile machine, which includes an environmental chamber to control the test temperature; each lot of specimens was tested at 20, 50 and 80 °C respectively, at a speed of 1 mm/min. From the results obtained, it is possible to appreciate that the adhesive at 50 °C decreased its strength by 14 % with respect to those at the reference temperature of 20 °C. The same tendency was observed in the specimens tested at 80 °C, in which there was a pronounced reduction in strength quantified by 26 %. Moreover, deformation in the adhesive grew with the increase in temperature, acquiring greater plasticity and modifying its cohesive properties.
KeywordsDouble cantilever beam (DCB) Adhesive joint Experimental testing
The addition of new material technologies in mining, energy, construction and aerospace industry, among others, have requested the concentration of several researches to guide and enhance the implementation of the same. Due to the development of these new materials, a number of researches have been developed to improve the materials adhesion, which traditionally use bolted or riveted joints, whose solutions may bring some disadvantages such as stress concentration. Structural adhesives are an alternative that seeks to avoid these problems. Adhesive joints have strength and stiffness properties superior to mechanically-fastened joints since they evenly distribute the resulting load avoiding stress concentrations [1, 2]. These joints also provide other benefits, such as high fatigue strength, the possibility of maintaining the integrity of the substrates, no corrosion and minimum difference due to thermal expansion of the adhesive .
The knowledge of mechanical properties and fracture modes of an adhesive allows us to define failure mechanisms that may occur in specific load conditions and environmental degradation. Experimental tests and numerical models provide us the information needed to optimize the selection and use of adhesives, and provides the foundation to implement possible improvements on their joint properties and/or configurations. In this sense, many researchers have studied the mechanical characterization of adhesives through Double Cantilever Beam (DCB) test, End Notched Flexure (ENF) test, Impact test, Single Lap Joint test (SLJ), among others. Saldanha et al. has mechanically characterized an adhesive that combines the properties of an epoxy and polyurethane adhesive. Experimental tests were performed to measure the stress properties, shear properties, fracture and thermal properties .
Regarding the Critical fracture toughness in mode I (G Ic ), double cantilever beam test is the most appropriate to calculate this parameter . Estimating critical fracture energy is based on Linear-Elastic Fracture Mechanics (LEFM), requiring for its calculation a continuous measurement of the crack length in the DCB test. In order to calculate the G Ic , several methods have been developed. The Compliance Calibration Methods (CCM), based on the Irwin-Kies equation , requiring the calculation of the compliance (C) relative to the crack length during crack growth. The Corrected Beam Theory (CBT), that includes the effects of crack tip rotation and deflection . Finally, in the Compliance-Based Beam Method (CBBM), is not necessary to measure the crack length, since using the crack equivalent concept this measurement is irrelevant depending only on the specimen’s compliance during the test [8, 9]. In this sense, Campilho et al., using the CBBM method, has found an increasing linear trend of the critical fracture energy as thickness increases . Similar studies conducted by Banea et al. and Marzi et al. determined the same trend, concluding that the fracture energy increases by the increase of thickness, because the adhesive has the ability to generate increased plastic flow areas before the fracture [11, 12]. Campilho et al. studied the influence of adherend thickness on the measured value of G Ic of a ductile adhesive through DCB tests. Regardless of the data reduction methods, a growing trend of GIC regarding the thickness has been found, suggesting that the G Ic is not a material parameter, but it is a parameter dependent on the geometry used . Moreover, in thin-layer adhesive joints, cracks are forced to follow the defined path through the middle area, since in general the adhesive is weaker and more adaptable than the substrates, which usually causes a cohesive failure of the adhesive .
The effects of the increasing temperature are very important when evaluating the strength of an adhesive. Some processes in the mining industry, such as electro-winning process, produce thermal changes that modify the working conditions of equipment and structures. Such variations are related to the shrinkage, thermal expansion coefficients and the mechanical properties modification of the adhesives used .
Regarding to researches concerning the determination of toughness of stress fracture in adhesive thin-layers, these are concentrated in experiments at room temperature. However, some studies focus on the analysis of structural adhesives subjected to high and low temperatures. Banea et al. evaluated the effect of high temperature in mode I of an epoxy adhesive through DCB tests. To define the adhesive performance and predict the P-δ curve of the adhesive depending on the temperature; a Cohesive Zone Model (CZM) was used expressing damage propagation by the bilinear traction–separation law . Furthermore, Banea et al. has studied the fracture toughness in mode I for RTV silicone adhesives at high temperature (200 °C), showing that the fracture toughness and the traction–separation law exhibit a temperature dependence . Melcher at al. identified a significant reduction on fracture toughness at −196 °C using carbon fiber adherents and an epoxy adhesive (AF-191M) . Carlberger et al. has identified that the fracture energy in the epoxy adhesive XW1044-3 is affected significantly at temperatures between −40 and 80 °C . Furthermore, the combined effect of test speed and temperature on the tensile properties of a high-temperature epoxy adhesive have been studied  Tensile tests were performed at three different speeds and various temperatures (Room Temperature (RT), 100, 125 and 150 °C), noting that with increasing temperature, the adhesive becomes ductile, resulting in a higher deformation to breakage; the maximum tensile stress decreased linearly with temperature, while increasing logarithmically with the speed test. Recently, Banea et al. investigated the performance of a polyurethane adhesive structurally modified with Thermally Expandable Particles (TEP) at different temperature ranges, performing tensile tests to get the tensile properties of the modified and unmodified adhesive, as well as DCB tests to evaluate strength to mode I crack propagation .
In this work, the double cantilever beam test is analyzed in order to evaluate the influence of the temperature on the adhesive bicomponent Methacrylate Plexus MA310, about mode I fracture toughness.
The methacrylate Plexus MA310 adhesive (ITW Plexus, Chicago, USA) has been selected to develop the study, since it is one of the most widely used adhesives in the manufacture of equipment for the extraction of acid mist produced by the copper cathode electro-winning process. Plexus MA310 is a two-part methacrylate adhesive designed for structural bonding of thermoplastic, metal and composite assemblies. Combined at a 1:1 ratio, MA310 has a working time of 15 min and achieves approximately 75 % of ultimate strength in 35 min at room temperature (23 °C). The operating temperature of the adhesive is between −55 and 121 °C and the gap filling are established between 0.6 and 4 mm .
A key parameter in the study of the joints is the glass transition temperature (Tg) of the adhesive. To determine the glass transition temperature of the adhesive Plexus MA310 an equipment whose functioning is based on the method proposed by Zhang et al.  was used. A Tg was determined for each sample (three specimens were tested), thereby achieving an average value of Tg equal to 125 °C for the adhesive Plexus MA310.
SAE 1045 steel mechanical properties
Young’s modulus, E [GPa]
Yield strength, σ [MPa]
Ultimate tensile strength [MPa]
Shear modulus, G [MPa]
Poisson coefficient, ν
Bulk tensile test
For the mechanical characterization of the adhesive, an adhesive plate of 300 × 300 × 3 mm thick has been manufactured, using two hard plates impregnated with a release agent and spacers calibrated to get uniform adhesive thickness. The adhesive plate cured for 24 h. The geometry of the specimens required for tensile test was machined on a CNC machine, according to the specifications of ASTM D-638 standard.
Plexus MA310 mechanical properties at room temperature
Young’s modulus, E [MPa]
Ultimate tensile strength [MPa]
Shear modulus, G [MPa]a
Poisson coefficient, ν
Double cantilever beam test
After positioning the separators, the adhesive was applied through an injection gun with a mix nozzle to make a homogeneous mixture of components. The cure of the specimens was conducted at a room temperature of 20 °C for 24 h. After that period, the spacers sheets were removed before testing each sample.
DCB test procedure
DCB data analysis
DCB FE simulation
Cohesive zone modelling
At 80 °C, a marked increase in G Ic of approximately 30 % can be observed. This can be explained by the fact that, as the temperature increases, near to the adhesive Tg, the strength decreases but the ductility increases giving an additional plastic deformation at the crack tip, hence an increase in toughness.
The gradual temperature increase in the adhesive causes a decrease of the maximum load, while displacement increases progressively.
Considering fracture energy with respect to the aep, at RT, it can be seen that after the failure is produced, there is an area in which the G Ic is kept constant.
Regarding the G Ic , it is seen a slight decrease at 50° regarding the RT; however, by increasing the temperature to 80 °C, there is a significantly increase of the G Ic , which may be explained due to increased ductility given by an additional plastic deformation at the crack tip.
The effect generated by the change in the thermal conditions caused the adhesive to modify its cohesive properties, directly influencing the strength under peel loads.
Regarding to the DCB simulation, the cohesive zone model have been used to determine the behavior and predict the P-δ curve. The simulation results shows that the stress levels are inside to the range of steel and adhesive properties and also shows a good stress symmetry. The difference between the experimental and numerical P-δ curves it is produced by a gap in the displacement of the experimental P-δ curve. This gap occurs due to the adjustment of the jaws during the test execution. Respect to this gap, the application of a pre-load previous to the DCB test, minimize the excessive displacement produced by the jaws during the experimental test.
JM carried out some parts of the draft preparation and in the analysis data. RH carried out the draft and the experimental results. JMM participated in the specimen preparation of the single lap joint and the mechanical tensile test. AV participated in the draft manuscript and in the critical analysis of the experimental data. JP participated in the analysis of the experimental and statistical analysis. LS participated in the analysis data and helped to the draft manuscript. All authors have read and approval the final manuscript .
The authors acknowledge the funding of projects FONDECYT 1131058 and DIUFRO DI08-0030 for the development of this work.
The authors declare that they have no competing interests.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
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