Mechanical Properties Of Structural Materials Research Articles

Development of modifying additives for epoxy oligomers based on household waste polyethylene terephtalate

A method for synthesis of oligoester polyols (OEP) and modified resins is presented, the effect of the OEP content on the dynamic viscosity, reactivity of resins, physicochemical and mechanical properties of structural materials is studied. Materials based on epoxy-diane resin modified with glycolyzed products were obtained. It was found that the use of the developed oligomers with optimal content of epoxy-diane resin as modifier leads to an increase in some characteristics of the resulting materials: elasticity, tensile strength and elastic modulus at static bending, viability of the composition. The use of glycolysis products is advisable because it is a promising method for recycling of household waste polyethylene terephthalate. It is characterized by ease of synthesis, as well as low cost and availability of initial components, and makes it possible to increase the physical and mechanical properties of structural materials based on epoxy resins, as well as contribute to solving environmental problems.

Modeling the conditions for obtaining nanostructures during ion-plasma processing taking into account the quantum-mechanical properties of electrode material

The subject matter of the article is the thermophysical and mechanical properties of surface layers of structural materials using a quantum-mechanical approach. The aim of the article is to adjust the parameters of the heat conductivity and thermoelasticity problem, considering all possible external and internal thermal effects and the quantum-mechanical description of the material structure, for electrodes in vacuum-arc nanostructuring. The task to be solved is to perform calculations using the developed model for a copper cathode considering the energy spent on the formation of nanoparticles during ion-plasma processing with oxygen ions. The methods used are methods for solving nonlinear problems. The following results were obtained. 1. The nature of the dependencies of the maximum temperature, the expected volume of nanostructures, and the maximum depth of their formation on the energy of oxygen ions with charges z = 1 and z = 2 matches previously known dependencies obtained by the classical model, but under quantum-mechanical consideration, the maximum temperature values increase by 15%, the volume of the nanocluster increases by 50%, and the maximum depth of its occurrence increases by 1.5 times. 2. When selecting the parameters of ion-plasma processing for obtaining nanostructures with ion energies 100...500 eV, the previously proposed model with general thermophysical and mechanical properties of structural materials can be used. 3. For technologies with ion energies in the range of 103...2∙103 eV, the previously proposed model can be used but with quantum-mechanical effects of structural materials considered. 4) For technologies with ion energies above 104 eV, calculations should be performed using both approaches (the classical approach and the approach considering the quantum-mechanical properties of structural materials), and after comparison, the variant whose calculation results are closest to the experimental results should be used. Conclusions. The proposed theoretical model using the thermophysical, mechanical, and quantum-mechanical properties of structural materials can be used to adjust the technological parameters of ion-plasma processing to assess the formation of nanostructures in protective and strengthening coatings.

Research on the mechanism of thermal-mechanical coupling effects of hypersonic aircraft rudder structure

Hypersonic aircraft have achieved rapid development in the past decade, with flight speeds exceeding 5 Ma, posing a very severe aerodynamic and thermal environment for rudder structure. Especially for metal rudder wings, the extremely high temperature and temperature gradient makes the structural thermal response problem very prominent and complex. This article focuses on the study of the thermo-mechanical coupling response of the metal rudder wings of hypersonic aircraft in flight thermal environments. By simplifying the aerodynamic load and aerodynamic thermal environment under flight time sequence, a finite element model based on thermo-mechanical sequence coupling is established. The temperature, thermal stress, and deformation response curves of key parts are extracted, and the thermo-mechanical coupling response law of the rudder structure is explored. Based on the mechanical properties of structural materials at different temperatures, the corresponding relationship between stress and residual strength of key parts during flight time is obtained, and the safety factor of key parts of the structure is given.

Impact of Dilute Amounts of Fission Products on the Mechanical Behavior of Ni.

Fission products may interact with structural materials in various nuclear energy applications and cause their mechanical performance to deteriorate. Therefore, it is important to study the effects of different fission products on the mechanical properties of structural materials. In this work, nickel was chosen as a model structural material system and dilute amounts of uranium and fission product impurities X = (Tc, Te, Sb, Ce, Eu, and U) up to 4 at % were used. Density functional theory (DFT) calculations were utilized to assess the effects of these substitutional impurities on the elastic behavior of the metal. Additionally, DFT was used to investigate some aspects of plastic response by computing the generalized stacking fault energies on the {111} ⟨112⟩ slip system for all alloying elements and at varying distances away from the stacking fault plane. None of the dopants satisfied the Pugh or Pettifor criteria for embrittlement, and alloying with Tc led to a slight increase in the elasticity of nickel. The phenomenon of Suzuki segregation was observed for all alloying elements, and there was consequently a significant reduction in the intrinsic stacking fault energy. Finally, and based on the analysis of the stacking fault energies, dopants generally led to softening the nickel (except for Tc and Ce), and all of the dopants were correlated with a loss of ductility (except Eu). These findings may be useful to consider in the design of next-generation reactors and nuclear waste management systems.

Анализ основных направлений снижения интенсивности массовых потоков рабочего тела через неплотности рабочей камеры поршневой длинноходовой тихоходной компрессорной ступени

The working processes and integral characteristics of piston long-stroke low-speed compressor stages are considered. Well-known technologies for increasing the feed rate are considered as objects of comparison: selection of the main dimensions and parameters of the stage; changing the size and design of valves, using elastomeric structural materials; change in the design of the cylinder-piston seal; changing the layout of the suction valve in the working chamber. Indicator efficiency, supply coefficient and tightness coefficient, as well as discharge temperature are considered as integral indicators. The following independent parameters are considered: parameters of the state of the working fluid at suction, discharge pressure, main dimensions and parameters of the stage, distance from the suction valve to the top dead center, seat diameters of the suction and discharge valves, as well as physical and mechanical properties of structural materials. A comparative analysis of the efficiency of the working process of the stage under consideration is carried out using various technologies for reducing the intensity of mass transfer through leaks in the working chamber of a low-speed, long-stroke piston stage. An assessment is made of the achievable value of the feed coefficient with the combined use of various technologies. The features of the working processes of the object under consideration and the relationship between the intensity of mass flows of working gas through leaks in the working chamber of the stage and the technologies used have been studied. The presented results of the theoretical analysis reflect the nature of the change in the integral characteristics of the stage depending on the technologies used to reduce the intensity of mass transfer through leaks in the working chamber of the stage under consideration.

High-throughput determination of grain size distributions by EBSD with low-discrepancy sampling.

Because microstructure plays an important role in the mechanical properties of structural materials, developing the capability to quantify microstructures rapidly is important to enabling high-throughput screening of structural materials. Electron backscatter diffraction (EBSD) is a common method for studying microstructures and extracting information such as grain size distributions (GSDs), but is not particularly fast and thus could be a bottleneck in high-throughput systems. One approach to accelerating EBSD is to reduce the number of points that must be scanned. In this work, we describe an iterative method for reducing the number of scan points needed to measure GSDs using incremental low-discrepancy sampling, including on-the-fly grain size calculations and a convergence test for the resulting GSD based on the Kolmogorov-Smirnov test. We demonstrate this method on five real EBSD maps collected from magnesium AZ31B specimens and compare the effectiveness of sampling according to two different low discrepancy sequences, the Sobol and R2 sequences, and random sampling. We find that R2 sampling is able to produce GSDs that are statistically very similar to the GSDs of the full density grids using, on average, only 52% of the total scan points. For EBSD maps that contained monodisperse GSDs and over 1000 grains, R2 sampling only required an average of 39% of the total EBSDpoints.

Effects of reducing impurity addition on corrosion and mechanical properties of structural materials in molten LiF-NaF-KF

A proposed method for preventing corrosion in molten fluoride salts is adding certain reducing impurities that can control the oxidizing impurities. The effectiveness of many potential reducing impurities in preventing corrosion and their effects on mechanical properties of structural materials have not been studied. This work studies the effectiveness of six different reducing impurities on preventing corrosion of Hastelloy N and SS316H in molten LiF-NaF-KF (FLiNaK) at 700 °C. Our results indicate that addition of reducing metals can be effective in controlling the corrosion of alloys depending on the testing conditions but may affect the mechanical behavior of SS316H.

Dynamic mechanical performance of FeNiCoAl-based high-entropy alloy: Enhancement via microbands and martensitic transformation

The non-equiatomic FeNiCoAlTaB high-entropy alloy exhibits outstanding quasi-static mechanical properties. Here, we investigate the microstructural evolution and mechanical response of this alloy subjected to dynamic loading, which has not been done before. A novel strategy combining extensive microbanding and martensitic transformation improves the resistance to the plastic instability by deterring the formation of adiabatic shear bands, that only occur beyond a critical shear strain larger than 4. The aged alloy, with grain sizes up to 400 μm, exhibits a dynamic yield stress over 1300 MPa with good deformability in this regime. This investigation sheds light on potential strategies for the enhancement of dynamic mechanical properties of structural materials through the use of a stress-induced martensitic transformation.

Bulk ultrafine grained microstructures with high thermal stability via intragranular precipitation of coherent particles

Producing ultrafine-grained (UFG) microstructures with enhanced thermal stability is an important yet challenging route to further improve mechanical properties of structural materials. Here, a high-performance bulk UFG copper that can stabilize even at temperatures up to 750 °C (∼ 0.75Tm, Tm is the melting point) was fabricated by manipulating its recrystallization behavior via low alloying of Co. Addition of 1 wt.%–1.5 wt.% of Co can trigger quick and copious intragranular clustering of Co atoms, which offers high Zener pinning pressure and pins the grain boundaries (GBs) of freshly recrystallized ultrafine grains. Due to the fact that the subsequent growth of the coherent Co-enriched nanoclusters was slow, sufficient particles adjacent to GBs remained to inhibit the migration of GBs, giving rise to the UFG microstructure with prominently high thermal stability. This work manifests that the strategy for producing UFGs with coherent precipitates can be applied in many alloy systems such as Fe- and Cu-based, which paves the pathway for designing advanced strain-hardenable UFGs with plain compositions.

Influence of strengthening interventions on the structural performance of a Maillart‐type arch bridge: the case of “Ciolo Bridge” in the South of Italy

AbstractRecent collapses of existing bridges occurred worldwide demonstrated the need of risk mitigation strategies. The failure of existing bridges can be attributed to many reasons: unexpected external actions due to both natural and anthropogenic catastrophes, materials degradation, increased traffic loads, inadequate original design or construction, lack of maintenance. In this context, it is remarkable that a significant percentage of the existing infrastructures has reached its nominal service life, requiring the allocation of relevant resources for their assessment, repair and upgrading. This study investigates the structural performance of a Maillart bridge built in 1960s in the South‐East of Italy. Due to its exposure close to the sea, the bridge has been subjected to a significant degradation, which asked strengthening interventions over the years. A detailed survey and tests were performed to investigate the mechanical properties of structural materials and detailing. A structural analysis was led by considering the original configuration and the retrofitted one. The results of the numerical analyses are shown and discussed in the paper, also by assessing the safety levels of the bridge and the effectiveness of the strengthening interventions occurred during the service life.

Criterion of damageability of structural materials

The work considers the quantitative assessment of the accumulation of scattered damage as a multi-scale and multi-stage phenomenon under elastic-plastic loading, which leads to the degradation of the physical and mechanical properties of structural materials, which is expressed in the change of the modulus of elasticity G and E. The paper proposes a criterion of damage, containing the effect of damage on the service life of the structure under an external complex load. The physics of the process of kinetics of damage accumulation suggests a factor of structural changes as a result of loosening of the material under load for separation and shearing of the representative element in the most loaded section.

In-situ TEM investigation of dislocation loop evolution in HR3 steel during Fe+ ion irradiation

The evolution and characteristics of dislocation loops, which are affected by the value of temperature play a crucial role in the mechanical properties of structural materials. This study explores the evolution processes of the dislocation loops with the increasing values of the temperature, and the effect of precipitate on the dislocation loop. In-situ TEM experimental observations are performed using HR3 steel, which is commonly used as a structural material in nuclear reactors, during 400 keV Fe+ irradiation at room temperature (RT), 300 °C, 400 °C and 500 °C. The evolution of the dislocation loop at different values of the temperature is characterized in detail. The average size and density of dislocation loops as a function of displacement per atom (dpa) and values of temperature were constructed and analyzed comparatively. Irradiated samples at higher temperatures have a larger average size and a lower density of dislocation loops. The pre-existing dislocation lines have a profound effect on the density and Burgers vector of dislocation loops. Our present results provide a fundamental insight into the evolution and characteristics of dislocation loops in HR3 steel in a gradually changing of temperature environment.

Digital Image Correlation Technique to Aid Monotonic and Cyclic Testing in a Noisy Environment during In Situ Electrochemical Hydrogen Charging

Hydrogen is receiving growing interest as an energy carrier to facilitate the shift to a green economy. However, hydrogen may cause the significant degradation of mechanical properties of structural materials, premature strain localisation, crack nucleation, and catastrophic fracture. Therefore, mechanical testing in hydrogenating conditions plays a vital role in material integrity assessment. Digital image correlation (DIC) is a versatile optical technique that is ideally suited for studying local deformation distribution under external stimuli. However, during mechanical testing with in situ electrochemical hydrogen charging, gas bubbles inherent to hydrogen recombination are created at the sample surface, causing significant errors in the DIC measurements, and posing significant challenges to researchers and practitioners utilising this technique for testing in harsh environments. A postprocessing technique for the digital removal of gas bubbles is presented and validated for severe charging conditions (−1400 mV vs. Ag/AgCl) under monotonic and cyclic loading conditions. Displacement fields and strain measurements are produced from the filtered images. An example application for measuring the crack tip opening displacement during a slow strain rate tensile test is presented. The limitations of the technique and a comparison to other bubble mitigation techniques are briefly discussed. It was concluded that the proposed filtering technique is highly effective in the digital removal of gas bubbles during in situ electrochemical hydrogen charging, enabling the use of DIC when the sample surface is almost completely obscured by gas bubbles.

ЦІЛЬОВІ РІВНЯННЯ РКЛА НА ЕТАПІ РОЗРОБКИ ЕСКІЗНОГО ПРОЕКТУ

The development of each new rocket and spacecraft (RS) must correspond to the target design function, which most often selects the minimum starting mass m0, or the minimum cost of the c0 project. When designing the RS of the minimum starting mass, mass equations of zero, first and second approximations are used. At the stage of development of the terms of reference, a mass equation is drawn up in which the value of the relative dry mass is set on the basis of statistical data from the previous kind of modification of the aircraft of this type and is an approximation of the zero order. After calculating the main flight and technical parameters of the designed RS, the value of the relative dry mass is specified by using the target given mass equations, in which the mass of the main compartments, systems and structures is determined through the basic flight and technical parameters, design parameters and statistical relative mass coefficients. The mass values of the individual components of the RS obtained in this way make it possible to calculate the flight and technical characteristics in the first approximation. After the design calculations of the first approximation, it becomes possible to clarify the values of the static coefficients of the reduced dry weight through the functional and operational parameters affecting the specific design, the physical and mechanical properties of structural materials, and other factors affecting the mass of the structure. The equations obtained in this way are called the detailed mass equations of the second approximation. 
 The presented sequence of compilation and use of target mass equations in the design of the minimum mass RS can also be used in the development of the RS project of minimum cost.

Toward tunable microstructure and mechanical properties in additively manufactured CoCrFeMnNi high entropy alloy

Tailoring microstructure and mechanical properties of structural materials to meet application requirements is a long-standing challenge in materials science. Here we have studied the effects of laser energy density (LED) on the microstructure and mechanical properties of single-track CoCrFeMnNi high entropy alloy (HEA) samples fabricated by laser directed energy deposition (LDED). The results indicate that the molten pool size of the single-track HEA samples gradually increases with increasing LED. All of the samples possess a single face-centered cubic (FCC) solid solution structure. The microstructures of the single-track HEA samples are mainly composed of columnar and equiaxed grains, and as the LED increases, their grain size increases while the micro-hardness decreases. Additionally, the relationship among the processing parameters, cooling rate and grain size was investigated via combining the numerical simulation and experimental observations. This work provides mechanistic insights into establishing the processing-structure-property relationships in the additively manufactured HEAs and contributes to achieve LDED of tunable HEA parts with desired microstructure and mechanical performance.

Using lifetime of point defects for dislocation bias in bcc Fe

The interaction between dislocations and point defects is key to deformation processes and microstructural evolution of structural materials. In this work, we compute the lifetime of point defects to describe their interaction with dislocations. This approach can accurately account for the effects of the dislocation core and anisotropic defect dynamics to accumulatively determine the capture efficiency, sink strength, and dislocation bias at different temperatures and dislocation densities. Particularly, the absorption of point defects by straight screw and edge dislocations in a model bcc iron system is studied. The maximum swelling rates based on the obtained bias factors are in close agreement with a variety of experimental measurements, including both neutron and ion-irradiation data, especially when considering the survival fraction for point defects from displacement cascades. This approach applies to many other processes and sinks, such as dislocation loops and interfaces, providing a powerful means to develop fundamental insights critical for improving radiation resistance and mechanical properties of structural materials through controlling defect interaction and evolution.

Atomistic structure and thermal stability of dislocation loops, stacking fault tetrahedra, and voids in face-centered cubic Fe

Irradiation-induced hardening and changes to mechanical properties can often lead to material degradation and can limit the operation of reactor components. In addition, changes to mechanical properties can be a precursor to other material environmental degradation. Dislocation loops, stacking fault tetrahedra (SFT), and voids are major irradiation-induced lattice defects that occur in structural materials and are often observed post-irradiation. However, these defects are often considered only as obstacles to dislocation motion, with hardening assumed to be dependent on the habit plane and Burgers vector of the defect. The stability and nature of dislocation loops and SFTs with temperature are often overlooked, and this may play a crucial role in the mechanical properties of structural materials. We combine high-resolution transmission electron microscopy (HR-TEM) and atomistic simulations to determine the atomistic configurations and thermal stability of dislocation loops and SFTs. Dislocation dissociations are observed in both vacancy and interstitial-type perfect dislocation loops as well as in vacancy-type Frank loops, whereas interstitial-type Frank loops remain stable and are the least influenced by temperature. Triangle-shaped intrinsic stacking faults are formed at the edges of Frank vacancy loops, and a direct transformation from triangle-shaped Frank vacancy loops to SFTs is observed in atomistic simulations. SFTs are energetically more stable than Frank vacancy loops based on formation energy calculations in pure face-centered cubic Fe, which may explain why vacancy-type Frank loops are infrequently observed experimentally. The motivation for this study is to develop a framework for the stability and nature of irradiation defects as a function of temperature, which will be subsequently used for more complex (alloy) systems.

Topology design and equivalent mechanical properties of a three-dimensional star-shaped auxetic structure

Topology design is the most important method of obtaining optimal material distribution that is directly related to the mechanical properties of structural materials. Aimed at improving the accuracy and efficiency of topology design, this paper explores an innovative topological technique that integrates a sigmoid-rational approximation of material properties approach, with a modified optimality criteria algorithm. Furthermore, a three-dimensional (3D) star-shaped auxetic structure, based on the sigmoid-rational approximation of material properties approach and a modified optimality criteria technique is proposed. The unit cell structural parameters are extracted, and the mechanical properties of the 3D star-shaped structure, including the relative density, equivalent elastic modulus, and equivalent Poisson's ratio, are investigated using mechanical derivation, numerical, and experimental methods. The subsequent results demonstrate that the sigmoid-rational approximation of material properties approach and a modified optimality criteria technique provides a feasible novel idea for multicellular structure development and that the advantageous 3D star-shaped auxetic structure has great potential within the field of structural safety.

Investigation into creep‐to‐rupture of SIMP steel in stagnant LBE at 300–450°C

AbstractFerritic/martensitic steel was chosen as a primary candidate structural material for China Initiative Accelerator Driven System (CiADS) which started in 2015. A new kind of tempered martensitic steel, Steel of Institute of Modern Physics (SIMP), was designed to meet the requirements of the special operating environment. Structural materials suffer from liquid Pb‐Bi corrosion and liquid metal wetting at 450°C. Liquid metal wetting can seriously affect the mechanical properties of structural materials due to the decrease in surface energy and transition from martensitic laths to ferritic grains. Creep‐to‐rupture of SIMP steel was explored in stagnant liquid Pb‐Bi eutectic at 450°C. The possible reasons for creep‐to‐rupture are discussed. The results of the present study provide a new insight into challenges related to the application of SIMP steel in CiADS.

Unique atomic structure of metals at the moment of fracture induced by laser shock

To effectively control the mechanical properties of structural materials and design their safety margins, understanding the properties of metal fracture is essential. However, it is difficult to experimentally investigate the atomic structures at the moment of fracture; therefore, the detailed fracture mechanism remains an active area of research. In this study, we in situ examined how the atomic structure of copper changes during the fracture process on the nanosecond scale using X-ray absorption spectroscopy and X-ray diffraction. The fracture was triggered by a shock wave induced by an optical laser and was examined with a single 100-ps synchrotron X-ray pulse with a delay time of 0–200 ns. This novel experimental approach provides insights into how the short- and long-range order of an atomic structure change on the nanosecond scale. The results showed that there was an irreversible change in the deformation state on the nanosecond scale. The initial elastic deformation state (0–20 ns) was superseded by a plastic deformation state (20–50 ns). Then, at the moment of fracture (50–320 ns), the plastic deformation state transformed into a state in which the heterogeneous atomic structures exhibited short-range disorder while maintaining long-range order (a “short-range-disorder-only” state). This unique “short-range-disorder-only” state, which has never been reported using conventional ex situ analytical techniques, triggered metal fracture; therefore, controlling the occurrence of this state could suppress fracture and allow the design of reasonable metal safety margins to avoid overengineering.