Hardening Type Research Articles

Effects of curing temperature and hardener type on the mechanical properties of bisphenol F-type epoxy resin concrete

This study investigated the effects of curing temperature and hardener type on the compressive strength, flexural strength, and modulus of elasticity of concrete made with bisphenol F-type epoxy resin as a binder. The results showed that a higher curing temperature resulted in faster strength development at an early age, and the strength was greatest for the mixture with meta-xylenediamine (MXDA), followed by modified cycloaliphatic amine (MCAA) and isophorone diamine (IPDA). The higher curing temperature resulted in a greater modulus of elasticity and ultimate strain, as well as strength, and the effect of hardener type was in the same order as was observed for strength development. Also, an equation to predict the modulus of elasticity based on compressive strength was presented for each hardener type. It can be concluded that the compressive strength, flexural strength, and modulus of elasticity of bisphenol F-type epoxy resin concrete was affected by both curing temperature and hardener type.

Nonlinear primary resonance of a rigid-flexible space symmetric antenna

This paper studies the nonlinear response of a T-shape space antenna structure composed of two rigid arms jointed by a spring and two uniform beams made by isotropic material. Based on the Lagrange equation and the assumed modes method, the nonlinear dynamic equations of in-plane motion of the rigid-flexible coupled antenna are established, with four degrees of freedom. In order to reveal the dynamic characteristics of the nonlinear system, the method of multiple scales expressed in matrix form is used to solve the primary resonance responses of third-order approximation. Analyzing the frequency-amplitude response gives the jumping phenomenon in the primary resonance response. With increase of the excitation amplitude, the frequency-amplitude response curve would have a conversion between the hardening and softening types. Under small excitation amplitude, the frequency-response curve exhibits the hardening-type behavior, whereas the softening-type behavior would appear once the excitation amplitude is out to a critical value. In the case of softening-type behavior, the resonance frequencies decrease with increase of the excitation amplitudes.

Prediction of early-age compressive strength of epoxy resin concrete using the maturity method

This study is investigated with the prediction of the compressive strength of early-age bisphenol F-type epoxy resin concrete when using the maturity method. When testing the compressive strength of epoxy resin concrete, the strength development started from an age of 20h at a curing temperature of 0°C, and the difference between the compressive strengths at the ages of 6h and 168h was markedly reduced at a higher curing temperature. Thus, it appeared that the bisphenol F-type epoxy resin concrete was heavily affected by curing temperature. In addition, there were significant differences in strength development based on the hardener type. When calculating the maturity index, it was appropriate to use data up to the age of 72h, and it appeared that the appropriate value of the constant n is 0.4 in the equation proposed by Ohama, et al. The maturity index was more heavily affected by curing temperature than curing age, and there was a significant difference depending on the hardener type. This study reviewed three prediction models, and when using the dose-response curve model, the coefficient of determination (R2) was the largest, so this is the model that should be used. Although it is possible to apply this model differently based on the hardener type, it was determined that there would be no problem even if a prediction model combining all the test data on the three hardeners was used. In conclusion, when using the prediction model deduced in the study, it was possible to easily predict the early-age compressive strength of bisphenol F-type epoxy resin concrete, and to prove that the maturity method is a non-destructive test useful for cast-in-place applications.

The correlation between adhesion durability and viscoelastic creep-recovery behavior in epoxy coatings

Abstract The durability of the adhesion between coating and substrate is of utmost importance in organic coatings. In the present study, we endeavor to find a correlation between adhesion durability (loss of adhesion and adhesion recovery) after wet conditions and viscoelastic properties of coatings. To that end, an epoxy resin was cured with four types of hardeners. Furthermore, Polyamine-based hardener, Polyamido amine-based hardener, Polyether polyamine-based hardener, and Cycloaliphatic Polyamine-based hardener, were employed in order to prepare the coatings with different viscoelastic properties. The storage modulus increased as H active of hardeners and crosslink density decreased. After applying these coatings to mild steel, the samples were placed in humidity chamber for 2000 h. Adhesion loss and recovery of adhesion were measured in wet and dry conditions during the time by pull-off test. We found that the higher the elastic module, the more the adhesion loss. Recovery of adhesion after wet and dry cycles correlated with glass transition temperature and elastic element of creep and recovery data. Polyether polyamine based sample and polyamine based samples indicated good adhesion durability through cycles. Moreover, creep recovery of these samples (response of polymer to constant load and its effect on removal of that load) demonstrated a more reversible behavior compared to polyamido amine and cycloaliphatic polyamine based sample. The microscopic delaminated areas of coatings were analyzed by breakpoint frequency method (another useful parameter to describe the extent of coating detachment from the substrate when exposed to humidity) using electrochemical impedance spectroscopy measurement. Finally, EIS measurements approved the adhesion data.

A study on effects of viscoelastic properties on protective performance of epoxy coatings using EIS

Abstract Organic coatings are the single most widely applied materials to protect metallic substrates against corrosion. Therefore it is important to understand how a coating can guarantee the protective performance during service life. In this study it is tried to find how viscoelastic properties can affect the protective performance of a coating. An epoxy resin (Araldite GY 783) was cured with a mixture of two types of hardeners (a polyether polyamine and a cycloaliphatic polyamine) in four different mixing ratios (i.e. 20–80, 50–50, 70–30, 90–10) to achieve various adhesion behaviors, water permeability and viscoelastic properties. Samples were exposed to humidity in testing chamber for 300 days and adhesion was measured at wet and dry conditions over time. After drying, adhesion loss and recovery were evaluated by pull-off test. Electrochemical behavior of coatings was studied by electrochemical impedance spectroscopy (EIS). A series of impedance spectra of coatings during exposure to humidity were recorded and their protective properties were compared. The results showed a correlation between protective properties and viscoelastic behavior of coatings. It was found that a sample with higher percentage of cycloaliphatic hardener has higher elastic modulus (1275 MPa) and a sample with higher percentage of polyether poly amine hardener has the lower elastic modulus (465 MPa). Additionally It was found that a sample with excellent initial protective properties (|Z| = 10 10 Ω cm 2 ), higher elastic modulus and low initial water permeability (0.308 g/m 2 hr) may quickly fail because of the adhesion failure after wet cycles.

Slip versus twinning in low and very low stacking-fault energy Cu-Al alloy single crystals

The effect of stacking fault energy on slip to twin shear changeover in soft oriented single crystals of single phase Cu-Al alloys loaded in tension, was investigated. The single crystals of stacking fault energy between 4 mJ/m2 and 7.5 mJ/m2, or alternatively of a solute content between 11.5 at.%Al and 7.5 at.%Al, were able to twin during room temperature tensile deformation performed at a strain rate of 10−4s−1. For other stacking fault energy values, lower than 4 mJ/m2 and higher than 7.5 mJ/m2, the crystal lattice shear was produced by slip. It was also found, that as the stacking fault energy decreases from 7 mJ/m2 to 4 mJ/m2, the twinning stress increases from 90 MPa to 110 MPa and for the lower values approaching 3 mJ/m2 is expected to exceed 160 MPa. To rationalize the existence of the stacking fault energy window and the inversely proportional dependence of twinning stress, a conversion of mutual work hardening rates of twin and slip systems was found via latent hardening type experiments. It is postulated, that the conversion results from the stacking fault energy controlled transformation of forest dislocations from un-extended into extended dislocation configurations. Additionally, a dual role of material stacking fault energy on the activation of twinning and twinning stress of face-centered cubic materials is emphasized.

Study on postbuckling of axial compressed elastoplastic functionally graded cylindrical shells

ABSTRACTPostbuckling of plates and shells is an important and cumbersome problem in the structural stability field. Presently, postbuckling behaviors of elastoplastic functionally graded cylindrical shells are investigated by a numerical simulation. The elastoplastic material properties are assumed to be of a multilinear hardening type, according to the constituent distributions, and are modeled using the laminate method. The Riks algorithm is used to obtain the equilibrium path. The postbuckling deformation and stain history of elastoplastic functionally graded cylindrical shells are investigated and various effects of the shell thickness and the constituent distributions are discussed. The results show material unloading effects in the postbuckling state.

Effects of Hardener Type on Cure Behavior and Physical Properties of TMP Modified UF Resin and Its Composites with Bamboo Powder

In this study, effects of mixed hardeners (ammonium chloride mixed with ammonium persulfate, oxalate and phosphoric acid) on the properties of 2,4,6-trimethylolphenate modified UF resin (TMPUF) were studied, and the potlife, gel time and curing temperature of TMPUF/hardeners were characterized. The results indicated that the hardeners used have critical influence on the pH value of TMPUF and some proton donor can be used to lower the pH value of TMPUF with low formaldehyde content. Besides, bamboo particleboards were made with TMPUF/hardeners, and tensile properties, water absorption ratio and the swelling ratio of bamboo particleboards were characterized. The study demonstrated that the tensile strength of bamboo particleboards increased when partial ammonium chloride was replaced by ammonium persulfate to cure the TMPUF adhesives in our experiment.

Effects of Catalyst Content, Anhydride Blending, and Nanofiller Addition on Anhydride-Cured Epoxidized Linseed Oil-Based Thermosets

A series of formulations based on epoxidized linseed oil, ELO cured with various anhydride hardeners, were investigated to assess the potential for enhanced elastic properties and thermal transitions through variations in catalyst concentration (1,8-diazabicyclo[5.4.0]undec-7-ene, DBU), hardener type (nadic methyl anhydride, NMA, methyltetrahydrophthalic anhydride, MTHPA, and their blends with phthalic anhydride, PA), and nanofiller (organically modified hydrotalcite, Perkalite F100S) content. To facilitate rapid screening, Shore D hardness was used as a proxy for Young’s modulus, and the limits of this approach were tested via comparisons with modulus measurements made via dynamic mechanical analysis (DMA). ELO cured with MTHPA at a 1:1 epoxy/anhydride molar ratio with 4.5 phr DBU gave a particularly attractive combination of rigidity, homogeneity, and alpha transition temperature rarely seen in thermosets composed of a 100% biobased epoxy component. Nanocomposite formation provided a modest increase in ...

Influence of the Hardener Type on the Hardening Process Kinetics of the Selected Self-setting Sands

Abstract Measurements of the hardening process of the selected self-setting sands are presented in the hereby paper. Moulding sands were prepared on the matrix of „Szczakowa” sand of the Sibelco Company. Two resins: phenol-formaldehyde-furfuryl (FF/AF) and urea-formaldehydefurfuryl (MF/AF) were used for making moulding sands. - Methylbenzene-sulphonic acid was applied as a hardener for the moulding sand on FF/AF resin, while paratoluene-sulphonic acid for the moulding sand on MF/AF resin. Both hardeners were used in two concentrations: low - the so-called ‘slow’ hardener and high - ‘fast’ hardener. During investigations, the courses of the hardening process were determined, more accurately changes of the velocity of the ultrasound wave passage through the moulding sand cL = f(t) and changes of the moulding sand hardening degree versus time, Sx = f(t). In addition, the kinetics of the hardening process was determined. Measurements were performed on the research stand for ultrasound investigations.

Experimental and theoretical study on large amplitude vibrations of clamped rubber plates

In this paper, the large amplitude forced vibrations of thin rectangular plates made of different types of rubbers are investigated both experimentally and theoretically. The excitation is provided by a concentrated transversal harmonic load. Clamped boundary conditions at the edges are considered, while rotary inertia, geometric imperfections and shear deformation are neglected since they are negligible for the studied cases. The von Kármán nonlinear strain-displacement relationships are used in the theoretical study; the viscoelastic behaviour of the material is modelled using the Kelvin-Voigt model, which introduces nonlinear damping. An equivalent viscous damping model has also been created for comparison. In-plane pre-loads applied during the assembly of the plate to the frame are taken into account. In the experimental study, two rubber plates with different material and thicknesses have been considered; a silicone plate and a neoprene plate. The plates have been fixed to a heavy rectangular metal frame with an initial stretching. The large amplitude vibrations of the plates in the spectral neighbourhood of the first resonance have been measured at various harmonic force levels. A laser Doppler vibrometer has been used to measure the plate response. Maximum vibration amplitude larger than three times the thickness of the plate has been achieved, corresponding to a hardening type nonlinear response. Experimental frequency-response curves have been very satisfactorily compared to numerical results. Results show that the identified retardation time increases when the excitation level is increased, similar to the equivalent viscous damping but to a lesser extent due to its nonlinear nature. The nonlinearity introduced by the Kelvin-Voigt viscoelasticity model is found to be not sufficient to capture the dissipation present in the rubber plates during large amplitude vibrations.

A Statistical Analysis of Epoxy Polymer Reinforced with Micro Ceramic Particles

A significant amount of research has been focused on the use of ceramic nano/micro particles to enhance the strength and stiffness of polymeric matrices. This work evaluates the effect of Portland cement or crystalline silica (quartz) particle inclusions into epoxy polymer. Two experiments were conducted based on a full factorial design analysis. Experiment I investigated the effect of Portland cement amount (ASTM III), two types of hardeners (HY 951 and 956) and two curing times (7 and 28 days) on the compressive behaviour and density of particulate composites. Experiment II evaluated the incorporation of quartz or cement particles by mixing different mass fraction levels, considering 28 days of curing time and HY 951 hardener. The samples were prepared in a randomized manufacturing process and tested in compression. The mechanical properties were significantly affected by the type of hardener used. Both particles can enhance the compressive strength and stiffness of the composites.

Roles of texture and latent hardening on plastic anisotropy of face-centered-cubic materials during multi-axial loading

This study investigates the joint impact of preferred texture and latent hardening on the plastic anisotropy of face centered cubic (FCC) materials. The main result is that both aspects have significant impact on the anisotropy, but the two can either counteract each other or synergistically reinforce each other to maximize anisotropy. Preferred texture results in significant anisotropy in plastic yielding. However, the latent hardening significantly alters the texture-induced anisotropy. In addition, one latent hardening type can cancel out the anisotropy of another type. Consequently, if all dislocation-based latent hardening types are included at the same level as the self-hardening, the result might not reveal the complexity of plastic anisotropy. The present study of the synergistic influence of detailed latent hardening and texture presented helps provide new insights into the complex anisotropic behavior of FCC materials during multi-axial forming.

Adjustable Nonlinear Mechanism System for Wideband Energy Harvesting in Rotational Circumstances

Nonlinear energy harvesters have already been exhibited to draw energy from ambient vibration owing to their particular dynamic characteristics, and are feasible to desirable responses for broadband excitations of bistable and monostable systems. This study proposes an energy harvester for rotational applications, in which a cantilever beam pasted piezoelectric film and magnets with the same polarity are comprised as a nonlinear vibrating system. As the rotationally angular velocity gradually increases, the tensile stress to the cantilever beam is also self-adjusted with the increscent centrifugal force, causing the potential barriers of bistable type become shallow, so that the cantilever beam has the ability to maintain the high energy orbit motion from bistable hardening type to monostable hardening behavior. From the implemented results, the valid bandwidth of angular frequency can be improved from 26 rad/s - 132 rad/s to 15 rad/s - 215 rad/s, under the case of the effect of centrifugal force on nonlinear vibrating behavior. It demonstrates that the centrifugal force can significantly promote the performance of nonlinear energy harvesters.

Effect of ozone pretreatment on the physical and mechanical properties of particleboard panels made from bagasse

Abstract The main objective of this study was to investigate the applied properties of particleboard panels made from bagasse, which were either treated or not treated with gaseous ozone (O 3 ). Variable parameters were ozone exposure time (1–3 min) at 9 ppm and storage period (1–5 months). Other parameters such as resin content (12 wt%), hardener content (1 wt%), type of hardener (NH 4 Cl), press closing time (5 mm/s), board density (0.70 g/cm 3 ), and press pressure (30 kg/m 2 ) were held constant. The experimental panels were tested for their mechanical properties including modulus of elasticity (MOE), modulus of rupture (MOR); and internal bonding strength (IBS) and physical properties in terms of water absorption (WA) and thickness swelling (TS) according to the procedures defined by EN standards. Overall results showed that all panels made from treated bagasse exceeded the EN standards for MOE, MOR, and IBS. However, WA and TS values decreased after ozone pretreatment compared to the un-treated (control) panels. Application of Duncan’s Multiple Range Test for the mean values of the results showed that the effects of both variables, except their interactions, on the mechanical and physical properties were highly significant ( p ⩽ 0.01%). All the mechanical properties of the panels decreased when the treatment duration increased from 1 to 5 months.

Ecological Consequences of Shoreline Hardening: A Meta-Analysis.

Protecting coastal communities has become increasingly important as their populations grow, resulting in increased demand for engineered shore protection and hardening of over 50% of many urban shorelines. Shoreline hardening is recognized to reduce ecosystem services that coastal populations rely on, but the amount of hardened coastline continues to grow in many ecologically important coastal regions. Therefore, to inform future management decisions, we conducted a meta-analysis of studies comparing the ecosystem services of biodiversity (richness or diversity) and habitat provisioning (organism abundance) along shorelines with versus without engineered-shore structures. Seawalls supported 23% lower biodiversity and 45% fewer organisms than natural shorelines. In contrast, biodiversity and abundance supported by riprap or breakwater shorelines were not different from natural shorelines; however, effect sizes were highly heterogeneous across organism groups and studies. As coastal development increases, the type and location of shoreline hardening could greatly affect the habitat value and functioning of nearshore ecosystems.

KARAKTERSTIK SERAPAN SUARA KOMPOSIT POLYESTER BERPENGUAT SERAT TAPIS KELAPA

The purpose of this study is to investigate of sound absorption of coconut filter fiber composites. The research material made with coconut filter fiber as reinforcement and matrix resin unsaturated polyester (UPRs) type Yukalac BQTN 157 with 1% hardener types MEKPO (Methyl Ethyl Ketone Peroxide) and fiber treatment by 0,5% KMnO4. Production methods is poltrusion and the variations of fiber volume fraction are 20, 25 and 30% and fiber length are 5, 10 and 15 mm. Testing of sound absorption frequency are 250, 500, 1000, 2000 and 4000 Hz. The results of research show that the highest value of sound absorption coefficient is on the composites with composition of 10 mm fiber length and 30% fiber volume fraction, that is 0.550828. The values are included in the class “Sound Absorption Coefficient Class D (Extremely absorbing)” with the range 0.40 – 0.60 based on ISO standard 11654:1997.

The use of colemanite and ulexite as novel fillers in epoxy composites: Influences on thermal and physico-mechanical properties

Abstract Boron compounds such as colemanite, tincal and ulexite are of interest in many application areas due to their great properties. Colemanite and ulexite was used individually as fillers to prepare epoxy composites in this study. The influences of amount of filler, type of hardener and plasticizer addition on the properties of the novel composites were investigated with instrumental analyses and tests. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses showed good dispersion of filler in the epoxy matrix. Improvement in tensile properties was obtained up to 5 wt% filler content in the composites. Water sorption reduced dramatically with increasing amount of filler compared to neat epoxy. Excellent corrosion resistance and strong adhesion properties were observed in all composites. Thermogravimetric analyses (TGA) and vicat softening temperature (VST) tests indicated that colemanite had better synergistic effect on the thermal properties of the neat epoxy than ulexite. Resistance to cold environment of the composites was quite high. It was thought that the composites can be evaluated successfully with the mentioned advantages in many industrial fields such as construction, coating, flooring, and so on.

Nonlinear Breathing Vibrations and Chaos of a Circular Truss Antenna with 1:2 Internal Resonance

This paper investigates the nonlinear breathing vibrations and chaos of a circular truss antenna under changing thermal environment with 1:2 internal resonance for the first time. A continuum circular cylindrical shell clamped by one beam along its axial direction on one side is proposed to replace the circular truss antenna composed of the repetitive beam-like lattice by the principle of equivalent effect. The effective stiffness coefficients of the equivalent circular cylindrical shell are obtained. Based on the first-order shear deformation shell theory and the Hamilton’s principle, the nonlinear governing equations of motion are derived for the equivalent circular cylindrical shell. The Galerkin approach is utilized to discretize the nonlinear partial governing differential equation of motion to the ordinary differential equation for the equivalent circular cylindrical shell. The case of the 1:2 internal resonance, primary parametric resonance and 1/2 subharmonic resonance is taken into account. The method of multiple scales is used to obtain the four-dimensional averaged equation. The frequency-response curves and force-response curves are obtained when considering the strongly coupled of two modes. The numerical results indicate that there are the hardening type and softening type nonlinearities for the circular truss antenna. Numerical simulation is used to investigate the influences of the thermal excitation on the nonlinear breathing vibrations of the circular truss antenna. It is demonstrated from the numerical results that there exist the bifurcation and chaotic motions of the circular truss antenna.

Optimization mechanical properties of polyurethane/Sio2 nanocomposite on Polypropylene substrate for automotive clear coating by Taguchi method

The effect of different parameters including: nano silica content, curing temperature, type of hardener, and flash-off time on mechanical and optical properties of polyurethane PU based clearcoat was investigated via standard Taguchi L9 method. Dispersion of nano silica in the resultant nanocomposites was explored by scanning electron microscopy SEM. SEM images showed a fine dispersion through the nanocomposites at different loadings. All PU nanocomposites showed gloss in the range of 91-94 which confirms the presence of nano silica did not have an adverse impact on optical properties. Moreover, the most significant factor contributed in the hardness of samples was the nano silica content. It was shown that using high amount of nano silica 5 wt reduced hardness of clearcoats due to interrupting curing process. The clearcoats performance after carwash test indeed showed that sample containing 2 nano silica cured at 85oC with a mixture of hardener 50 biuret, 50 trimer after flash-off time of 5 min had the optimum physical and optical properties.