Hardening Type Research Articles

Experimental study on the thixotropic strength of the marine soft clay from the Yangtze River estuary

Soft clay in the offshore area of the Yangtze River estuary has been investigated considering its basic physical properties. Forty-five unconfined compressive strength tests were conducted on the remolded marine soft clay to investigate the impacts of curing time T, water content w, plasticity index IP, and clay particle content ρc on the thixotropic static shear strength ratio As of the marine soft clay from the Yangtze River estuary. Results show that the stress–strain curves were primarily strain hardening and strain softening curve types. Unconfined compressive strength qu increased with an increase in T. All specimens with different basic physical properties were capable of thixotropic strength recovery. When T = 0–28 days, As increased rapidly, while for T > 28 days, As of most specimens increased slightly or tended to stabilize. The impacts of w, IP and ρc on As do not follow a consistent pattern, but there is a strong correlation between As and w/wL (wL is the liquid-limit water content). For w/wL < 0.75, As increased with increasing w/wL, whereas for w/wL ≥0.75, As decreased with increasing w/wL. We proposed a simple and widely applicable power function prediction model for the As of the soft clay from the Yangtze River estuary.

In English

Biopolymer matrices has been synthesized on the basis of ED-20 epoxy resin and soybean oil (SbO) bearing cyclocarbonate and epoxy groups. Mono(cyanoethyl)diethylenetriamine (UP) and tris(2-hydroxyethyl)amine (TEA) were used as hardeners. Chemical structure, mechanical properties, thermo-oxidative resistance of the samples and their changes after contact with distilled water, alkaline or acidic environment were studied. By means of ATR-FTIR the possible formation of H-NIPU (hybrid non-isocyanate polyurethane) fragments between cyclocarbonate groups of SbO and amino groups of the hardener was demonstrated. Influence of the curing mode and the type of hardener on water absorption, chemical and thermal oxidation resistance of the developed biopolymer matrices was thoroughly investigated. UP-based biopolymer matrices showed water and alkali resistance similar to the ones of neat epoxy polymers, while TEA-based biopolymer matrices showed better resistance to the acidic medium. The thermo-oxidative stability of the chosen samples was revealed by the TGA method in an air atmosphere. It was demonstrated that epoxy polymer cured with TEA hardener were more stable than the one cured with UP hardener. The similar dependence is observed for biopolymer matrices based on TEA hardener. At the same time, the curing mode has almost no effect on ultimate tensile strength value of the samples with ED-20/UP composition. However, the addition of functionalized SbO to the epoxy matrix cured with both TEA and UP hardeners increases the ultimate tensile strength values regardless of the type of oil functionalization. As expected, all biopolymer matrices exhibited higher ultimate tensile strength compared with unmodified epoxy polymers, which provides the possibility of their further application to obtain multi-layered bioplastics.

Ductile rupture under cyclic loadings at high triaxiality: The influence of strain hardening and elasticity

Previous works (Devaux et al., 1997; Cheng et al., 2017) have emphasized the effects of strain hardening and elasticity upon ductile rupture of metals under cyclic loading conditions. This work pursues the study and modelling of these two effects by distinct theoretical methods, each coupled with micromechanical finite element simulations of the behaviour of some “representative cell”. For the effect of strain hardening, we employ Morin et al. (2017)’s approach, based on the theory of sequential limit-analysis (Yang, 1993; Leu, 2007; Leblond et al., 2018). This approach is applied to various types of hardening of the metallic matrix: isotropic, linear kinematic, nonlinear kinematic with one or two kinematic variables (Armstrong and Frederick, 2007) , and even a simplified version of Chaboche (1991)’s model accounting for complex cyclic effects. Numerical micromechanical simulations of a hollow sphere made of elastic–plastic materials obeying the various hardening laws considered, and subjected to cyclic loadings at high triaxiality, fully confirm the predictions of the model developed, provided elasticity is made negligible by using an artificially high value of Young’s modulus. When a realistic value is employed, however, the agreement between theoretical predictions and numerical results is degraded, thus emphasizing again the importance of the effect of elasticity in cyclic ductile rupture. To deal with this effect we derive, apparently for the first time, an evolution equation of the porosity accounting for (compressible) elasticity. However, numerical micromechanical simulations reveal that simply using this new evolution law, while keeping all other aspects of the model unchanged, remains insufficient to get a good match of theoretical and numerical results. Such a match is achieved by introducing the ad hoc hypothesis that the yield criterion and flow rule derived from sequential analysis still apply in the presence of elasticity, but with some “effective porosity” slightly differing from the true one through some heuristic, adjustable factor.

Hardening of gear teeth depending on the concentration of abrasive particles in the transmission oil

The article deals with the issues of determining the life and limiting concentration of abrasive particles in the oil of transmission units, depending on the type of hardening of gear teeth. Resource was determined after volume hardening, hardening by current of high frequency and cementation by hardness of gears materials, on the friction machine on the samples which have been made of gears material, working in oil with abrasive particles, considering coefficient of acceleration at test. Maximum allowable concentration of abrasive particles in machine oil, were estimated on the basis of expression for calculation of wear rate, providing the set life, maximum allowable wear depending on modulus of gearing, hardness of gearing material, size of abrasive particles, geometrical and kinematic parameters of gearing.

Manufacturing and Characteristics of Hardness Controllable Epoxy for Restoration of Earthenware

Fatty acids, tall-oil, reaction products with tetraethylenepentamine and 1-(2-aminoethyl) piperazine-based epoxy resin were mixed to manufacture 2 types of hardener to enable hardness control for restoration of earthenware. The mixed epoxy resin was manufactured in 2-solution reaction hardening type to control the hardness in the range of approximately 40∼65 Hs, and tensile strength in the range of 27∼121 kgf/mm<sup>2</sup> and hardening type of 20∼30 min were secured. Moreover, it has wear rate that has been enhanced by 2 folds compared to the existing restoration material, which can be controlled in accordance with the mixing ratio, and was manufactured to enable mixing of diversified fillers later on. These results indicate that this is a restoration material that can solve the problems pointed out for the earthenware restoration materials such as processability and workability that occurred due to high level of hardness, tensile force and adhesion strength, etc., and increase in the level of fatigue due to tension with earthenware surface, etc. Accordingly, it is deemed that it is a material that can be used in actual restoration.

On exploiting the transition of nonlinear characteristics of a broadband piezoelectric energy harvester for tuning it to low and high-frequency applications

In this work, the applicability of nonlinear piezoelectric energy harvesters is demonstrated for high and low-frequency applications. An axially loaded piezoelectric patched beam model is derived considering in-plane stretching. The harvester setup is developed in the laboratory, and the energy-based numerical model is validated with experimental results. Optimum dimensions of the harvester are obtained. The broadband nature of the harvester is explored, considering nonlinear effects and axial loads on the harvester’s performance. The applicability of the proposed harvester is demonstrated meaningfully by exploiting bifurcation between hardening and softening types of non-linearity by adjusting axial loads with the help of a simple tunable harvester setup.

Investigation of Novel Flax Fiber/Epoxy Composites with Increased Biobased Content.

Currently, biobased epoxy resins derived from plant oils and natural fibers are available on the market and are a promising substitute for fossil-based products. The purpose of this work is to investigate novel lightweight thermoset fiber-reinforced composites with extremely high biobased content. Paying attention to the biobased content, following a cascade pathway, many trials were carried out with different types of resins and hardeners to select the best ones. The most promising formulations were then used to produce flax fiber reinforced composites by vacuum bagging process. The main biocomposite properties such as tensile, bending, and impact properties as well as the individuation of their glass transition temperatures (by DSC) were assessed. Three biocomposite systems were investigated with biobased content ranging from 60 to 91%, obtaining an elastic modulus that varied from 2.7 to 6.3 GPa, a flexural strength from 23 to 108.5 MPa, and Charpy impact strength from 11.9 to 12.2 kJ/m2. The properties reached by the new biocomposites are very encouraging; in fact, their stiffness vs. lightweight (calculated by the E/ρ3 ratio) is comparable to some typical epoxy-glass composites.

DEUTSCHE EDELSTAHLWERKE CRYODUR 2721

Abstract Deutsche Edelstahlwerke Cryodur 2721 is a medium-carbon, nickel-chromium alloy cold-work tool steel. This oil hardening type cold work tool steel offers a combination of high hardness, good wear resistance, high toughness, and good machinability. This datasheet provides information on composition, physical properties, microstructure, hardness, and elasticity. It also includes information on forming and heat treating. Filing Code: TS-839. Producer or source: Deutsche Edelstahlwerke Specialty Steel.

DEUTSCHE EDELSTAHLWERKE CRYODUR 2510

Abstract Deutsche Edelstahlwerke Cryodur 2510 is a high-carbon, manganese-chromium-tungsten-vanadium alloy cold-work tool steel. This oil hardening type cold work tool steel offers a combination of high hardness, good wear resistance, and good cutting edge retention. This datasheet provides information on composition, physical properties, microstructure, and hardness. It also includes information on heat treating. Filing Code: TS-838. Producer or source: Deutsche Edelstahlwerke Specialty Steel.

Cohesion and Adhesion Performance of Tannin-Glyoxal Adhesives at Different Formulations and Hardener Types for Bonding Particleboard Made of Areca (Areca catechu) Leaf Sheath.

The use of alternative raw materials, such as agricultural biomass and by-products, in particleboard (PB) production is a viable approach to address the growing global demand for sustainable wood-based materials. The purpose of this study was to investigate the effect of the type of hardener and tannin-glyoxal (TG) adhesive formulation on the cohesion and adhesion performance of TG adhesives for areca-based PB. Two types of hardeners were used, NH4Cl and NaOH, and three adhesive formulations with tannin:glyoxal ratios (i.e., F1 (1:2), F2 (1:1), and F3 (2:1)) were applied to improve the cohesion performance and adhesion for areca-based TG adhesive for PB. The basic, chemical, and mechanical properties of the TG adhesive were investigated using a Fourier transform infrared spectrometer, rotational rheometer, dynamic mechanical analyzer (DMA), and X-ray diffractometer. The results show that a high glyoxal percentage increases the percentage of crystallinity in the adhesive. This shows that the increase in glyoxal is able to form better polymer bonds. DMA analysis shows that the adhesive is elastic and the use of NH4Cl hardener has better mechanical properties in thermodynamic changes than the adhesive using NaOH hardener. Finally, the adhesion performance of the TG adhesives on various types of hardeners and adhesive formulations was evaluated on areca-based PB panels. Regardless of the type of hardener, the TG adhesive made with F1 had better cohesion and adhesion properties compared to F2 and F3. Combining F1 with NH4Cl produced areca-based PB panels with better physical and mechanical qualities than the adhesive formulations F2 and F3, and complied with Type 8 particleboard according to SNI 03-2105-2006 standard.

МЕТОДЫ ОЦЕНКИ МЕХАНОАКТИВИРОВАННОГО МИНЕРАЛЬНОГО СЫРЬЯ ДЛЯ КОМПОЗИЦИОННЫХ ВЯЖУЩИХ

In the conditions of constantly increasing construction volumes, there is a necessity to transfer to environmentally efficient technologies for the production of building materials in order to reduce industrial pressure on the ecosphere and ensure rational subsoil use. One of the solutions is to reduce cement consumption by using composite binders with a reduced proportion of the clinker component. Improving the quality of composite binders is possible due to the preliminary activation of the surface of raw components. One of the most effective methods of activating raw materials is mechanical activation. A reasonable choice of its method and mode is possible only on the basis of the results of comprehensive studies in the system "the object of mechanical activation – the instrument of mechanical activation – the indicator of mechanical activation – the product of improvement by methods of mechanical activation". A comprehensive determination of the activity of mechanoactivated mineral raw materials as an indicator of the effectiveness of mechanoactivation includes the use of various research methods and evaluation of: the area of the interface boundary, granulometric composition, morphostructural features, sorption capacity, donor-acceptor surface centers, the energy state of the system and other parameters. The paper proposes a decomposition of the methodology for evaluating mineral raw materials from the position of mechanical activation in the production of composite binders. The use of this methodology will make it possible to rank mineral raw materials of natural and technogenic origin, optimize the process of mechanical activation from the point of view of choosing a rational method and develop generalized recommendations for the selection of technological modes of milling, taking into account the genesis of raw materials for obtaining active mineral components of composite binders of various composition, type of hardening and functional purpose. The development and implementation of the principles of rational selection of mineral raw materials components, based on the example of their application in composite binders, will ensure the specified functional properties and implement a predictive assessment of the performance characteristics of building composites as a whole.

Influence of Curing Agents Molecular Structures on Interfacial Characteristics of Graphene/Epoxy Nanocomposites: A Molecular Dynamics Framework

AbstractThis paper presents a comprehensive molecular dynamics study on the effects of the stoichiometric ratio of epoxy:hardener, hardener's linear and cyclic structure, and number of aromatic rings on the interfacial characteristics of graphene/epoxy nanocomposite. The van der Waals gap and polymer peak density as a function of the type of the hardener is calculated by analyzing the local mass density profile. Additionally, steered molecular dynamics are used to conduct normal pull‐out of graphene to study the effect of the mentioned features of hardeners on the interfacial mechanical properties of nanocomposites, including traction force, separation distance, and distribution quality of reacted epoxide rings in the epoxy. Influence of the hardeners on the damage mechanism and its initiation point are also studied by analyzing the evolution of local mass density profile during the normal pull‐out simulation. It is seen that stoichiometric ratio and geometrical structure of the hardeners affect the interfacial strength. It is also revealed that the hardener type can change the epoxy damage initiation point. The damage occurs in the interphase region for a higher stoichiometric ratio or cyclic structure of hardener. In comparison, for hardener's lower stoichiometric ratio and non‐cyclic structure, failure begins in the epoxy near graphene layers.

Boron Nitride Nanotubes: Force Field Parameterization, Epoxy Interactions, and Comparison with Carbon Nanotubes for High-Performance Composite Materials

Boron nitride nanotubes (BNNTs) are a very promising reinforcement for future high-performance composites because of their excellent thermo-mechanical properties. To take full advantage of BNNTs in composite materials, it is necessary to have a comprehensive understanding of the wetting characteristics of various high-performance resins. Molecular dynamics (MD) simulations provide an accurate and efficient approach to establish the contact angle values of engineering polymers on reinforcement surfaces, which offers a measure for the interaction between the polymer and reinforcement. In this research, MD simulations and experiments are used to determine the wettability of various epoxy systems on BNNT surfaces. The reactive interface force field (IFF-R) is parameterized and utilized in the simulations to accurately describe the interaction of the epoxy monomers with the BNNT surface. The effect of the epoxy monomer type, hardener type, local atomic charges, and temperature on the contact angle is established. The results show that contact angles decrease with increases in temperature for all the epoxy/hardener systems. The bisphenol-A-based epoxy system demonstrates better wettability with the BNNT surface than the bisphenol-F based epoxy system. Furthermore, the MD predictions demonstrate that these observations are validated with experimental results, wherein the same contact angle trends are observed for macroscopic epoxy drops on nonwoven nanotube papers. As wetting properties drive the resin infusion in the reinforcement materials, these results are important for the future manufacturing of high-quality BNNT/epoxy nanocomposites for high-performance applications such as aerospace and aeronautical vehicles.

Experimental Study of Stress and Deformation of Reclaimed Asphalt Concrete at Different Temperatures.

Asphalt concrete has been used as a material for dam core walls because of its impermeability, durability and reliability. Firstly, asphalt is a temperature-sensitive material, and many of its characteristics are related to temperature. Secondly, because of the increasing construction height of the dam, the pressure on the asphalt concrete core wall is also great. Finally, for the purpose of resource utilization, it is necessary to verify whether the reclaimed asphalt concrete can be used in dam construction. Therefore, it is necessary to study the stress and deformation characteristics of recycled asphalt concrete under different temperatures and confining pressures. In this study, three groups of triaxial tests of reclaimed asphalt concrete were carried out for the first time in a new temperature-controlled room. Duncan Zhang's E-v model was used to fit the test results. The results show that the stress-strain curves of reclaimed asphalt concrete show softening characteristics at low temperatures and low confining pressure. It evolves to a hardening type with the increase in temperature and confining pressure. The bulk curve is first contracts but is followed by dilatancy. The dilatancy characteristics become more obvious at low temperatures and low confining pressure. With the increase in temperature and confining pressure, the dilatancy characteristics will weaken. Duncan Zhang's E-v model has a good fitting effect on the stress-strain relationship but a poor fitting effect on the volumetric curve. The research of this paper can better combine the utilization of waste resources with engineering and achieve the aim of resource-saving and waste utilization under the premise of ensuring the safety of the engineering.

Modeling of the elastoplastic deformation process of single crystal superalloys

The aim of the research is the development and verification of a micromechanically motivated model of elastoplastic deformation of two-phase single-crystal nickel-based alloys, predicting behavior under high-temperature thermomechanical actionswith taking into account the presence of γ and γ' phases. The model is relevant for computations of the stress-strain state of cooled single crystal blades of gas turbine units. The constitutive equations for each of the phases took into account the anisotropy of elastic and plastic properties, the presence of octahedral slip systems, features of the cubic system, and various hardening mechanisms, including kinematic, isotropic and latent ones. The identification of the elastic and plastic constants of the material for the γ and γ 'phases was carried out on the basis of the known stress-strain curves for each phase. The determination of the effective properties and deformation diagrams of a two-phase single-crystal alloy, taking into account the presence of γ-γ'phases, was carried out both on the basis of finite element homogenization for the representative volume element, and using the simplest rheological (structural) models of the material, considering serial and parallel connection of phases. The dependences of the elastoplastic properties of two-phase single-crystal nickel-based alloys on the volume fraction of the γ'phase are determined by computational experiments and analytical estimates. In order to determine the optimal strategy for solving the class of problems under consideration, multivariant computational experiments were carried out for various types of boundary conditions of the homogenization problem, the number of periodicity cells, forms of inclusion of the γ'phase, volume fractions of the γ' phase, types of hardening, variants of rheological models and appropriate recommendations were given. The simulation results using the proposed two-level microstructural model of the material demonstrate a good agreement with the experimental data for the single-crystal superalloy CMSX-4.

Structure and Properties of Epoxy Polysulfone Systems Modified with an Active Diluent

An epoxy resin modified with polysulfone (PSU) and active diluent furfuryl glycidyl ether (FGE) was studied. Triethanolaminotitanate (TEAT) and iso-methyltetrahydrophthalic anhydride (iso-MTHPA) were used as curing agents. It is shown that during the curing of initially homogeneous mixtures, heterogeneous structures are formed. The type of these structures depends on the concentration of active diluent and the type of hardener. The physico-mechanical properties of the hybrid matrices are determined by the structure formed. The maximum resistance to a growing crack is provided by structures with a thermoplastic-enriched matrix-interpenetrating structures. The main mechanism for increasing the energy of crack propagation is associated with the implementation of microplasticity of extended phases enriched in polysulfone and their involvement in the fracture process.

Investigation of the effect of ion implantation on tribotechnical characteristics of cast iron

The article presents studies of the tribotechnical characteristics of cast iron after various types of hardening. Samples (chemical composition of the obtained cast iron: C - 3.06%; Cu - 2.38%; Si - 2.2%; Mn - 0.75%; Cr - 0.32%; P - 0.18%; Ni - 0.1%; S - 0.05%, and Brinell hardness - 1.97-2.07 GPa) for wear tests were previously implanted with N+, B+, C+ ions, as well as TiN sputtering and carbonitration. The research was carried out on a friction machine making reciprocating motion along the counterbody. In the course of the work, the main tribotechnical characteristics of cast iron samples were analyzed in the initial state, after implantation, carbonitration and deposition of TiN. The surface morphology of cast iron samples was also studied using a scanning electron microscope in the initial state and after the above types of processing.

Comparative evaluation of the yield strength of ferrite-pearlite steels by structure parameters

The influence of different hardening mechanisms on the yield strength of carbon and low-alloy steels is studied. It is established that for Ст.5пс hot-rolled steel, the greatest influence on the yield strength is exerted by solid-solution and grain-boundary hardening, and for 16Г2АФ low-alloyed steel, in addition to these types of hardening, it is also dispersion type. It is shown that thermomechanical treatment of Ст.5пс steel increases dislocation hardening as a result of a decrease in the increase in the density of dislocations and their preservation during accelerated cooling of hot-worked austenite in rolled products. Keywords: hardening, yield strength, thermomechanical treatment, accelerated cooling, phase components, grain size. aman-kanaev2012@yandex.ru, remshev@mail.ru, mash-kalugin@yande.ru, aliya-981@mail.ru

Effect of Water Content on Strength of Alluvial Silt in The Lower Yellow River

In order to study the strength characteristics of alluvial silt in the lower Yellow River Channel at Luokou, Jinan, by varying the moisture content five times, direct shear tests were conducted and soil–water characteristics curves were obtained to explore the relationships between moisture content and matric suction as well as the bishop coefficient and shear strength. The soil–water characteristics curve test shows that the water retention curve of silt samples in the lower Yellow River can be fitted by the VG (Van Genuchten) model with the appropriate fitting coefficients. The direct shear test reveals that the relationship between shear stress and shear displacement alters from the shear softening type to the hardening type with the increase in moisture content and normal stress. The cohesion has a nonlinear inverse relationship with moisture content while a small variation is reported in the internal friction angle. Finally, a simple shear strength equation for silt in the lower Yellow River is proposed in relation to moisture content, to define the relationship between the effective stress parameter and the matric suction for future engineering purposes.

Effect of Hardener Type on the Photochemical and Antifungal Performance of Epoxy and Oligophosphonate S-IPNs.

Due to their highly reactive character and multiple crosslinking capacity, epoxy resins are one of the worldwide market-dominating classes of thermosetting polymers and are present in a wide range of technical applications, including structural adhesives, coatings and polymer matrices for composite materials. Despite their excellent features, epoxy resins are known to be highly flammable and possess low thermal stability and a brittle character and crack easily under impact forces. An efficient approach towards eliminating such drawbacks resides in obtaining epoxy-based semi-interpenetrating polymer networks, which possess excellent control over the morphology. The article describes the comparative effect of three hardeners (aromatic, cycloaliphatic and aliphatic) in the presence of an oligophosphonate (–R–O–PO(C6H5)–O–) (2 wt.% phosphorus) on the photochemical, fire and antifungal performance of bisphenol A diglycidyl ether semi-interpenetrating polymer networks. The networks are designed as future potential outdoor protective coatings for different substrates. The fire resistance capacity of the networks was undertaken with microscale combustion calorimetry before and after photochemical aging. Structural changes during photoirradiation were monitored via color modification studies, Fourier-transform infrared spectroscopy, differential scanning calorimetry, morphological assessment through scanning electron microscopy and mass loss measurements in order to propose the action mode of the hardeners and the oligophosphonate on the material properties. Microbiological testing was also undertaken with the aid of three specific wood decaying fungi as a first substrate.