Journal of Applied Mechanics and Technical Physics最新文献

In this study, the effect of patient’s physical activity in terms of the heart rate on the growth of the thoracic aortic aneurysm (TAA) is studied. Using medical images of the patient, a patient-specific geometry model is constructed. Then the hemodynamic parameters of the blood flow are numerically analyzed for different heart rate conditions. The simulation results show that the maximum wall shear stress, the maximum velocity, and the maximum pressure during a cardiac cycle increase by 19.1, 12.7, and 50%, respectively, as the heart rate increases from 60 to 174 beats per minute. Results also indicate that an increase in the heart rate leads to reduction of the time-averaged wall shear stress and simultaneously to an increase in the wall shear stress oscillations. According to the literature, these hemodynamic conditions are undesirable and can increase the likelihood of aneurysm development and aortic rupture.

Results of studying interaction of two colliding axisymmetric laminar microjets of hydrogen in the course of their diffusion combustion are reported. Gas exhaustion occurs with identical velocities through pairs of micronozzles, which are thin-walled cylindrical tubes with an inner diameter of 200 (mu)m. The transverse positions of the tubes with respect to each other are changed during the experiment. Specific features of flame formation from two interacting microjets are found for different transverse positions of the tubes, and the results are compared with flames of single microjets with the same exhaustion velocity.

This paper presents the results of a study of the effect of molding pressure on the characteristics of radioprotective composites based on polyethylene and boron carbide (B₄C). Software simulation is applied to select a temperature range for heating a press mold of a given size. Experiments are performed to determine the required holding time of the composite and identify defects arising from various deviations from the optimal temperature parameters. The strength of samples under various molding pressure conditions is tested, and the optimal pressure is determined. A composite with the following mechanical characteristics under optimal molding conditions is obtained: density ((1.09 pm 0.01)) g/cm³, bending strength ((5.72 pm 0.18)) MPa, and sound velocity in the composite ((2050.00pm 0.01)) m/s.

This study is aimed at understanding some characteristics of the shock wave generated by a novel composite charge consisting of an inner high explosive, a medium non-detonating layer, and an outer aluminized explosive. The influence of the shell restraints and initiation modes on the peak overpressure and impulse of the charge is investigated. Numerical models are developed based on the mapping function of AUTODYN for determining the spatial distribution of the shock wave overpressure. By means of validation experiments, the accuracy of the developed model is verified. It is found that the peak overpressure and impulse obtained from experiments and simulations are in good agreement, with a deviation of less than 16.9%. The difference in the overpressures at various azimuths decreases with increasing distance, and the shock wave profile eventually evolves into a spherical shape. The radial overpressure of the shelled composite charge is initially greater than that in the axial direction and decays rapidly with increasing distance. The azimuth corresponding to the maximum peak overpressure is shifted from 75° for the bare charge to 110° for the shelled charge. It is found that the energy utilization of the composite charge under inner initiation is apparently smaller than that under simultaneous initiation.

It is proposed to use the relations of the endochronic theory of thermoplasticity to describe the nonlinear deformation of isotropic materials under non-isothermal loading. A version of the constitutive relations in integral and differential form is given for the general loading case. Based on the results of uniaxial tension (torsion) tests, analytical relations are determined for a number of material parameters of the model. A numerical algorithm based on the Euler method with inner iteration carried out by the Seidel method is proposed to analyze the constitutive relations. An example of numerical calculation of the uniaxial tension of a rod under complex thermal force loading. It is shown that the calculation results are in satisfactory agreement with the results obtained using the flow theory of plasticity with isotropic hardening.

Salmonella typhimurium and Listeria monocytogenes bacteria, which are two important bacteria used for bacterial therapy purposes in order to limit tumor growth, are studied. Mechanical specifications of the bacteria obtained applying nanoindentation with the use of atomic force microscopy (AFM) are reported. The results show that Salmonella typhimurium bacteria have a greater elastic modulus, but smaller adhesion than Listeria monocytogenes bacteria. The elastic modulus of the AFM extension stroke is larger than that of the retraction stroke. The resonant frequencies and amplitudes of the frequency response function of the AFM beam’s vertical movements with two bacteria as samples are investigated using the finite element method. The results show that an increase in the elastic modulus of the sample raises the resonant frequency; therefore, the resonant frequency of Salmonella typhimurium bacteria is greater than that of Listeria monocytogenes bacteria. The results obtained by the finite element method and experimental techniques are found to be in good agreement.

This paper presents an analysis of the effectiveness of using one-dimensional network models for virtual assessment of the hemodynamic indices widely used in clinical practice to choose a treatment strategy for coronary heart disease with stenotic coronary arteries. It is shown that existing approaches make it is possible to assess hemodynamic indices based on clinical data collected without intervention into the body with an accuracy comparable to the accuracy of the input data and direct measurements. It is also important to take into account the state of the myocardial microvasculature and its influence on the interpretation of modeling results and direct clinical measurements.

In this paper, we present a brief review of experimental approaches to the study of the sliding tribology of various bodies on snow or ice and propose a model and a digital twin of a tribological system. The distribution of the deformation of a tank filled with snow rotating at a specific speed was obtained by numerical simulation, and the work done by the friction force per sliding cycle was determined by testing the motion of a ski sample on a flat snow surface. The proposed system can be used to evaluate the sliding performance on snow at given temperature, snow structure, humidity, and the roughness of the ski surface sliding on snow.

A two-dimensional exact analytical solution of the thermal field developed during the submerged arc welding process with visualization of the thermal surface contour for analyzing the heat flow in the domain with the hybrid application of Duhamel’s theorem and finite integral transform approach is obtained. The thermal field arising in submerged arc welding of thick EH36 steel plates is studied. An ellipsoidal heat source model is assumed. The developed thermal field is investigated with variations of several process parameters, such as the heat source velocity, heat input, and lag time of movement of the heat source involved in the welding process.

A two-layer rod with a box section twisted by angle (theta) under the action of shear stresses is considered. It is assumed that the rod deformations are elastic and its lateral surface is stress-free. The layers have different elastic properties and different thicknesses. The contact line between the layers is assumed to be rigid, i.e., the stresses on it are the same. An exact solution describing the stress state of this structure is constructed using conservation laws. The stress state is determined at each point of the cross section using outer contour integrals.