Relaxation of residual stresses in surface-hardened rotating prismatic elements of structures under creep conditions

A method for solving boundary problems of relaxation of residual stresses in a rotating surface-hardened prismatic specimen under high-temperature creep conditions has been developed. The problem models the stress-strain state of a surface-hardened prismatic rod with one end fixed to an infinitely rigid disk rotating at a constant angular velocity. In the first stage, we solve the problem of reconstructing fields of residual stresses and plastic deformations after the hardening procedure, which play the role of the initial stress-strain state, is solved. In the second stage, we address  the problem of relaxation of residual stresses under creep conditions is addressed. A detailed study of the influence of angular velocity on the intensity of residual stress relaxation in different sections along the axial coordinate is carried out for a $10{\times}10{\times}150$ mm prismatic specimen made of EP742 alloy at a temperature of 650$^\circ$C, following ultrasonic mechanical hardening of one of its faces. The analysis of the calculation results revealed that for angular velocities ranging from 1500 rpm to 2500 rpm, a non-trivial effect is observed. The relaxation of residual stresses in more stressed sections experiencing axial tensile stresses due to rotation occurs less intensively than in the “tail” section, where the axial load is zero. The obtained results from this study can be useful in assessing the effectiveness of surface-hardened rotating components under high-temperature creep conditions

Derivatives of 9-phosphorylated acridine as butyrylcholinesterase inhibitors with antioxidant activity and the ability to inhibit β-amyloid self-aggregation: potential therapeutic agents for Alzheimer’s disease

We investigated the inhibitory activities of novel 9-phosphoryl-9,10-dihydroacridines and 9-phosphorylacridines against acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and carboxylesterase (CES). We also studied the abilities of the new compounds to interfere with the self-aggregation of β-amyloid (Aβ42) in the thioflavin test as well as their antioxidant activities in the ABTS and FRAP assays. We used molecular docking, molecular dynamics simulations, and quantum-chemical calculations to explain experimental results. All new compounds weakly inhibited AChE and off-target CES. Dihydroacridines with aryl substituents in the phosphoryl moiety inhibited BChE; the most active were the dibenzyloxy derivative 1d and its diphenethyl bioisostere 1e (IC50 = 2.90 ± 0.23 µM and 3.22 ± 0.25 µM, respectively). Only one acridine, 2d, an analog of dihydroacridine, 1d, was an effective BChE inhibitor (IC50 = 6.90 ± 0.55 μM), consistent with docking results. Dihydroacridines inhibited Aβ42 self-aggregation; 1d and 1e were the most active (58.9% ± 4.7% and 46.9% ± 4.2%, respectively). All dihydroacridines 1 demonstrated high ABTS•+-scavenging and iron-reducing activities comparable to Trolox, but acridines 2 were almost inactive. Observed features were well explained by quantum-chemical calculations. ADMET parameters calculated for all compounds predicted favorable intestinal absorption, good blood–brain barrier permeability, and low cardiac toxicity. Overall, the best results were obtained for two dihydroacridine derivatives 1d and 1e with dibenzyloxy and diphenethyl substituents in the phosphoryl moiety. These compounds displayed high inhibition of BChE activity and Aβ42 self-aggregation, high antioxidant activity, and favorable predicted ADMET profiles. Therefore, we consider 1d and 1e as lead compounds for further in-depth studies as potential anti-AD preparations

National records of 3000 European bee and hoverfly species: A contribution to pollinator conservation

peer reviewedPollinators play a crucial role in ecosystems globally, ensuring the seed production of most flowering plants. They are threatened by global changes and knowledge of their distribution at the national and continental levels is needed to implement efficient conservation actions, but this knowledge is still fragmented and/or difficult to access. As a step forward, we provide an updated list of around 3000 European bee and hoverfly species, reflecting their current distributional status at the national level (in the form of present, absent, regionally extinct, possibly extinct or non-native). This work was attainable by incorporating both published and unpublished data, as well as knowledge from a large set of taxonomists and ecologists in both groups. After providing the first National species lists for bees and hoverflies for many countries, we examine the current distributional patterns of these species and designate the countries with highest levels of species richness. We also show that many species are recorded in a single European country, highlighting the importance of articulating European and national conservation strategies. Finally, we discuss how the data provided here can be combined with future trait and Red List data to implement research that will further advance pollinator conservation

Mathematical modeling of creep and residual stresses relaxation in surface hardened elements of statically indefinable rod systems

We propose a method for modeling stress-strain state in surface-hardened elements of statically indefinable rod systems under creep. A method we propose is considered for a three-element asymmetric rod system. The solution consists of two steps: reconstruction of the stress-strain state after the procedure of surface plastic hardening of the cylindrical elements of the system (pneumatic blasting with micro balls) and the method for calculating the relaxation of residual stresses in the hardened elements amidst the creep state of rod system (as a whole structure). Rheological relations are determined on the basis of a model describing the first and second phases of creep. The solution of both stages and special aspects of the problem is illustrated on a model example of creep of systems with hardened elements made of ZhS6U alloy at the temperature of 650 °C. For hardening the rods of this alloy, real experimental data were used for axial and circumferential residual stresses. The technique of reconstruction of the stress-strain state after pneumatic blasting treatment is illustrated in detail. To build a rheological model, experimental data were used for the uniaxial creep curves of the ZhS6U alloy under various constant stresses at the temperature of 650 °C. The numerical values of the model parameters are given in the article. The uniaxial model is generalized to a complex stress state. The main problem is solved numerically using discretization by spatial and temporal coordinates. The stationary asymptotic stress-strain state of the rod system is investigated, which corresponds to the steady-state creep stage, which was used to estimate the convergence of the numerical method. The dependencies of the kinetics of all components of the residual stress tensor in all three strengthened elements of the system due to creep under a given external load are obtained. A comparative analysis of the residual stress relaxation rate in different rods is performed. The algorithm and software for solving the problem is developed. The main results of the work are illustrated by the residual stresses graphs over the depth of the hardened layer. Issues of applying the results obtained in the work to practical problems of assessing the reliability of hardened rod systems are discussed

Effect of anisotropy of surface plastic hardening on formation of residual stresses in cylindrical samples with semicircular notch

We study effect of anisotropy of surface plastic hardening on formation of residual stresses in solid cylindrical samples and samples with semicircular notch. Experimentally determined one and/or two components of residual stresses in a hardened layer are used as an initial information. We describe calculation method for the rest of diagonal components of residual stresses and plastic strains tensors, off-diagonal components are not considered. We propose numerical method for calculation residual stresses in semicircular notch of surface hardened cylindrical sample. This task was reduced to boundary value problem of fictitious thermoelasticity where initial (plastic) strains are modeled with temperature strains. Solution was build with the use of finite element method. We studied in detail the effect of radius of notch and anisotropy parameters of hardening on the nature and magnitude of distribution of residual stresses depending on the depth of layer in the smallest cross section of cylindrical samples of EI961 alloy steel and 45 steel. It was determined that with small radii of notch lower then thickness of hardening layer the value of axial component of residual stresses (absolute value) is higher then in the sample without a notch. Developed method was experimentally verified for samples without notches and the correspondence between calculated and experimental data was determined on distribution of axial and circumferential residual stresses depending on depth of hardening layer. For samples with notches we compare numerical solutions from this work with known solutions of other authors

To the 60th Anniversary of Professor Alexander Vladimirovich Manzhirov

On May, 24, 2017 the 60th jubilee of Prof. A.V. Manzhirov was celebrated at Ishlinsky Institute for Problems in Mechanics of the Russian Academy of Sciences. Prof. A.V. Manzhirov is known as a prominent scientist in the field of mechanics and applied mathematics. The principal directions of his academic activity are Mechanics of Growing Solids, Theory of Creep and Viscoelasticity, Biomechanics, Contact Mechanics, Tribology, Integral Equations and their numerous applications. The present dedication is devoted to the Prof. A.V. Manzhirov's scientific biography and contains the list of his selected publications

Professor Dyuis D. Ivlev. Dedication to 85th Birtday

Dyuis D. Ivlev (1930–2013) is an outstanding scientist in the fields of Continuum Mechanics (theory of Perfect Plasticity and Fracture) and Applied Mathematics. He has much contributed to the mathematical theory of plasticity, especially to study of hyperbolic three-dimensional problems of the perfect plasticity. Dyuis D. Ivlev was born in Chuvashia Republick, Russia, on September 6, 1930. In 1948 he left Chuvashia and after passing examinations entered Moscow State University. He is a Mechanical Engineering graduate (1953) of Moscow State University. In 1953 he continued his research work as a post graduate student of the same university. In 1956 he received PhD in Solid Mechanics from Moscow State University. The title of his PhD dissertation work is Approximate Solution of Elasti-Plastic Problems by the small parameter method. Three years later he was awarded DSc (Phys. & Math.) Degree from Moscow State University for his dissertation study Three-Dimensional Problem of the Theory of Perfect Plasticity. Since 1959 he has been working as head of the Department of Elasticity and Plasticity of Voronezh State University, then (1966–1970) as Prof. of Bauman State Technical University and (1971–1982) as head of the Department of Higher Mathematics of Russian Polytechnical University. In 1982 he returned to Chuvashia working in Chuvash State University (until 1993) and Chuvash State Pedagogical University (1993–2013) as head of Department of Mathematical Analysis. Prof. Dyuis D. Ivlev has been a member of National Committee on Theoretical and Applied Mechanics, Scientific Council on Problems of Solid Mechanics, Mathematics and Mechanics Expert Council of the Higher Attestation Committee. He is the author of several books on theory of perfect plasticity and its applications and nearly 250 papers on the subject

Mathematical modeling of deformation of reinforced femur during prolonged static loads

A two-layer mathematical model of a human femur neck reinforced implants of different design for modeling stress-strain state which occurs during a surgical procedure to prevent femur neck fractures by the forced introduction of metallic implants is proposed. Engineered implant designs are provided. Methods and software for geometric modeling of femur embedded with the implants are developed. New boundary value problems to evaluate kinetics in creep conditions of the stress-strain state of reinforced and non-reinforced femoral neck during prolonged static loads corresponding to human foot traffic are formulated. Effective elastic properties of cortical and cancellous bone, power and kinematic boundary value problems. A phenomenological creep model for compact bone tissue is constructed. The technique of identifying the parameters is developed. A check of its adequacy to experimental data is carried out. Based on the finite element method the numerical method for solving the provided boundary value problems at macro level of continuum mechanics is developed. A lot of variative calculations allowed developing recommendations for the rational positioning of the implant in order to minimize stress concentrations. The performed analysis showed that there is a significant relaxation of stresses in the most loaded areas due to creep. Relaxation is more intense in reinforced femoral neck than in the unreinforced. Thus the tension in the most loaded femoral neck area due to creep is reduced by 49 % with respect to the intensity of the initial time of loading for femur which is reinforced by the spoke-spoke-type implant when loading duration is 1 year under natural loads corresponding to human foot traffic. It was found that the time component (long-term fixed load) does not impair the positive effect of reducing the stress concentration due to a femoral neck reinforcement which is a positive fact from the medical practice point of view

The method of solution of the elastic-plastic boundary value problem of tension of strip with stress raisers with allowance for local domains of softening plasticity of material

The way of solution of the coupled boundary value problem of solid body deformation for the case of a plastically softening material is offered. The strain and stress fields obtained by the simulated undamaged construction behavior modeling under the action of fictitious forces are used as basic data for calculation. The equivalence of simulated undamaged medium strains and real medium strains is supposed. At each point of construction the damage parameter $\omega$ is calculated by means of constitutive relations of the endochronic plasticity theory. This damage parameter associates the components of the true stress tensor $\sigma_{ij}$ of simulated undamaged medium and the engineering stress tensor $\sigma^0_{ij}$ of real medium by $\sigma^0_{ij}=\sigma_{ij}/(1+\omega)$. Using the tensor $\sigma^0_{ij}$ we can calculate the generalized forces of real construction. The problems of tension of the plates weakened with centric circular hole and semicircular notches are solved and the necessary experiments are conducted. The strain and true stress fields are obtained by numerical calculation at the finite element analysis software and are used for the engineering stress of real construction computation according to the foregoing expression. Softening plasticity domains are plotted. It is found that at the moment before failure the stage of post critical deformation is implementing in the region of stress concentration, although the curve “total displacement – axial force” corresponds to the stage of plastic hardening

To the 70th Anniversary of Professor Alexander Pavlovich Soldatov

The paper is devoted to Alexander Pavlovich Soldatov, the well known mathematician, and his contribution to the development of scientific theories and applications. Alexander Pavlovich has turned 70 years on the January, 18th, so we give a short biographical background to his anniversary. Alexander Pavlovich Soldatov was a student of Novosibirsk State University, and graduated from with honours. He continued his education, defended a thesis in the famous V. A. Steklov Mathematical Institute of the USSR Academy of Sciences, became a Candidate of Physical and Mathematical Sciences and then Doctor habilitated of Physical and Mathematical Sciences (in Moscow State University). Today he is a professor, the Leading Researcher of Dorodnicyn Computing Centre in Federal Research Center “Computer Science and Control” of RAS, and has a title of Honored Scientist of Russia. The studies of Alexander Pavlovich in partial differential equations are well known to the specialists. He is an author of more then 170 scientific articles and four monographies. Here we give a list (not complete) of A. P. Soldatov publications for the last five years, that should help readers to see the modern interests of scientist. Alexander Pavlovich Soldatov is an excellent teacher, also he works as reviewer for mathematical journals, develops the mathematical competitions for school and university students and organizes mathematical conferences including international. In the paper we introduce the contribution of Alexander Pavlovich to the mathematics and education science, and give a short compilation of his remarkable scientific results