Магнитно-импульсное деформирование сплава TiNi: эксперимент и расчет

Magnetic-pulse loading methods have been known since the 80s of the XX century and, as a rule, are used to determine the laws of destruction of materials under the action of pressure pulses with a duration of several microseconds. A modified scheme of a magnetic-pulse setup for high strain rate uniaxial tension is used in this work. The application of the scheme with the possibility of experimental measurement of the strain accumulation time and strain rate is shown on samples of TiNi alloy. The paper presents the results of finite element modeling and analytical description. Both approaches have demonstrated good agreement between the calculated residual strain and experimental results, even on samples of TiNi alloy with a specific stress-strain diagram. The analytical solution showed good qualitative agreement in assessing the strain accumulation time. On the basis of the analytical solution, an assessment of the capabilities of the magnetic-pulse loading method for uniaxial high strain rate tension is presented.

Investigating of Strain Effect on Cleavage Fracture for Reactor Pressure Vessel Material

Failure mechanism of 20MnMoNi55 steel in the lower self of ductile to brittle transition (DBT) region is considered as brittle fracture but it has been observed from the experimental analysis of stress-strain diagram that clear plastic deformation is shown by the material before failure. Therefore, strain correction is implemented in the cleavage fracture model proposed by different researchers in the lower self of the DBT region with the help of finite element analysis. To avoid a huge number of experiments being performed, Monte Carlo simulation is used to generate a huge number of random data at different temperatures in the lower self of the DBT region for calibration of the cleavage parameters with the help of the master curve methodology. Fracture toughness calculated after strain correction through different models are validated with experimental results for the different probability of failures.

Dynamic Effective Elasticity of Melanoma Cells under Shear and Elongational Flow Confirms Estimation from Force Spectroscopy

The detection and enrichment of circulating melanoma cells is a challenge, as the cells are very heterogeneous in terms of their biomechanical properties and surface markers. In addition, there is a lack of valid and reliable biomarkers predicting progress and therapeutic response. In this study, we analyze the elasticity of A375 melanoma cells by applying force spectroscopy and a microfluidic method. To identify and eventually separate freely circulating tumor cells, it is crucial to know their physical properties precisely. First, we use standard AFM force spectroscopy, where the elasticity of the cells is calculated from indentation with a pyramidal tip. To extend the limits of the measurements with a tip, we then use cantilevers without a tip to apply force over a larger area of the cells. The resulting Young’s moduli are slightly lower and vary less without the tip, presumably because of the spatial inhomogeneity of the cells. Finally, we implement our microfluidic method: we measure single cell elasticity by analyzing their deformation in high-speed micrographs while passing a stenosis. Combining the force field and the change in shape provides the basis for a stress–strain diagram. The results from the microfluidic deformation analysis were well in accordance with the results from force spectroscopy. The microfluidic method, however, provides advantages over conventional methods, as it is less invasive and less likely to harm the cell during the measurement. The whole cell is measured as one entity without having contact to a stiff substrate, while force spectroscopy is limited to the contact area of the tip, and in some cases dependent of the cell substrate interaction. Consequently, microfluidic deformation analysis allows us to predict the overall elastic behavior of the whole, inhomogeneous cell in three-dimensional force fields. This method may contribute to improve the detection of circulating melanoma cells in the clinical practice.

Dynamic Effective Elasticity of Melanoma Cells Under Shear and Elongational Flow Confirms Estimation From Force Spectroscopy

The detection and enrichment of circulating melanoma cells is a challenge as the cells are very heterogeneous in terms of their biomechanical properties and surface markers. In addition, there is a lack of valid and reliable biomarkers that predict progress and therapeutic response. We here analyzed the elasticity of A375 melanoma cells applying force spectroscopy and a microfluidic method. To identify and eventually separate circulating tumor cells, it is crucial to precisely know their physical properties. First, we used standard AFM force spectroscopy, where the elasticity of the cells is calculated from indentation with a pyramidal tip. To extend the limits of measurement with a tip, we then used cantilevers without a tip to press on the cells over a large area. The resulting Young’s moduli are slightly lower and vary less without tip presumably because of the inhomogeneity of the cells. Finally, we implemented our microfluidic method. We measured single cell elasticity by analyzing its deformation in high-speed micrographs while passing a stenosis. Combining the force field and the change in shape provides the basis for a stress strain diagram. The results from microfluidic deformation analysis were in accordance with the results from force spectroscopy. The microfluidic method provides advantages over conventional methods, since it is less invasive and less likely to harm the cell during the measurement, and the whole cell is measured as one entity without contact to a stiff substrate, while force spectroscopy is limited to the contact area of the tip, and in some cases dependent of the cell substrate interaction. Consequently, microfluidic deformation analysis allows to predict the overall elastic behavior of the whole inhomogeneous cell in three-dimensional force fields. This method may contribute to improve the detection of circulation melanoma cells in the clinical practice.

Numerical and Experimental Investigations of Fracture Behaviour of Welded Joints with Multiple Defects

Current standards related to welded joint defects (EN ISO 5817) only consider individual cases (i.e., single defect in a welded joint). The question remains about the behaviour of a welded joint in the simultaneous presence of several different types of defects, so-called multiple defects, which is the topic of this research. The main focus is on defects most commonly encountered in practice, such as linear misalignments, undercuts, incomplete root penetration, and excess weld metal. The welding procedure used in this case was metal active gas welding, a common technique when it comes to welding low-alloy low-carbon steels, including those used for pressure equipment. Different combinations of these defects were deliberately made in welded plates and tested in a standard way on a tensile machine, along with numerical simulations using the finite element method (FEM), based on real geometries. The goal was to predict the behaviour in terms of stress concentrations caused by geometry and affected by multiple defects and material heterogeneity. Numerical and experimental results were in good agreement, but only after some modifications of numerical models. The obtained stress values in the models ranged from noticeably lower than the yield stress of the used materials to slightly higher than it, suggesting that some defect combinations resulted in plastic strain, whereas other models remained in the elastic area. The stress–strain diagram obtained for the first group (misalignment, undercut, and excess root penetration) shows significantly less plasticity. Its yield stress is very close to its ultimate tensile strength, which in turn is noticeably lower compared with the other three groups. This suggests that welded joints with misalignment and incomplete root penetration are indeed the weakest of the four groups either due to the combination of the present defects or perhaps because of an additional unseen internal defect. From the other three diagrams, it can be concluded that the test specimens show very similar behaviour with nearly identical ultimate tensile strengths and considerable plasticity. The diagrams shows the most prominent yielding, with an easily distinguishable difference between the elastic and plastic regions. The diagrams are the most similar, having the same strain of around 9% and with a less obvious yield stress limit.

Determination of the Actual Stress–Strain Diagram for Undermatching Welded Joint Using DIC and FEM

This paper presents new methodology for determining the actual stress–strain diagram based on analytical equations, in combination with numerical and experimental data. The first step was to use the 3D digital image correlation (DIC) to estimate true stress–strain diagram by replacing common analytical expression for contraction with measured values. Next step was to estimate the stress concentration by using a new methodology, based on recently introduced analytical expressions and numerical verification by the finite element method (FEM), to obtain actual stress–strain diagrams, as named in this paper. The essence of new methodology is to introduce stress concentration factor into the procedure of actual stress evaluation. New methodology is then applied to determine actual stress–strain diagrams for two undermatched welded joints with different rectangular cross-section and groove shapes, made of martensitic steels X10 CrMoVNb 9-1 and Armox 500T. Results indicated that new methodology is a general one, since it is not dependent on welded joint material and geometry.

Research of the Mechanical Properties of the Filament from the Percentage of Filling when Prototyping Machine Parts

The article contains the analysis of thermoplastics used in prototyping machine parts. We used several types of experimental samples with different filling percentages. The equipment on which the experimental studies were carried out is shown. During the experiment, a specialized tensile testing machine was used. The experimental samples were installed in the developed centering device. Normal conditions were observed during the tests. The results of an experimental tensile study of PLA-plastic specimens are presented. The typical stress-strain diagram of an experimental sample is described, which describes the dependence of stress on relative deformation. An equation of the linear dependence of the tensile strength on the percentage of filament filling has been compiled, which makes it possible to determine the tensile strength of the product at any percentage of the filling of the plastic filament. The assessment is adequately verified by Fisher's criterion. Recommendations for filament filling in prototyping machine parts are given.

Application of Cluster Analysis for Polymer Classification According to Mechanical Properties

The selection of the appropriate polymer material represents one phase in the product design, both, in terms of data on the different properties of the material and for detailed assessments and selection of the best material for the selected product. In the material selection phase, it is necessary to define criteria related to the mechanical properties of the material (strength, stiffness, toughness). Another important item is certainly the stress-strain diagram by which the materials can be classified into certain groups, based on their mechanical properties. The paper presents a study of materials classification according to the following groups: Hard and brittle, Hard and strong, Hard and tough and Soft and tough materials, using the cluster analysis (k-means algorithm).

Study of Nonlinear Stress-Strain Diagram of Concrete Based on Local Raw Materials in Central Yakutia

This paper presents the study results of the nonlinear stress-strain diagrams of concrete based on the local materials of Central Yakutia. The results of comparing the obtained data with the requirements of normative documents of the Russian Federation, European countries, India and China are presented. The calculation results for bending bearing elements with concrete nonlinear deformation taken into account obtained using the Ansys software are given. The reliability of the calculated data was verified using the proposed diagrams, using the example of the results of a survey of characteristic failures of bending concrete and reinforced concrete elements in the Republic of Sakha (Yakutia).

To the design of the deflections of flexural concrete members reinforced with fiber-reinforced polymer bars

Introduction. Fiber-reinforced polymers (FRP) reinforcement has a relatively low modulus of elasticity compared to steel. In this connection, the bent members with such reinforcement have a higher deformability. The stress-strain diagram for FRP under short-term loading is almost straight and does not have a yield line, as in steel reinforcement. At the same time, modern methods of calculating structures with for FRP reinforcement are based on existing approaches for reinforced concrete structures. In this regard, the current direction for study is to assess the reliability and improve the existing methods for calculating members with FRP reinforcement for the serviceability limit states. Materials and methods. Experimental studies were carried with regard for and in compliance with the provisions of National State Standard 8829-94. Tested samples represented concrete beams that were 1,810 mm long and had a cross section of 120 × 220 mm. Their tensile side was reinforced with two bars. Steel, glass fiber-reinforced polymer (GFRP) and basalt fiber-reinforced polymer (BFRP) bars were used to reinforce the beams. The value of the reinforcement ratio varied. Deflections calculation methods, applied according to Construction rules and regulations 295.1325800.2017 (Russia) and ACI 440.1R-06 (USA) were analyzed. Results. The results of the theoretical and experimental studies of the deformability of flexural members having FRP reinforcement are obtained. The inaccurate determination of the cracking moment Mcrc has a negative impact on the results of the deflection calculation. The deviation of the theoretical values of the cracking moment according to the method of Construction rules and regulations 295.1325800.2017 from the experimental ones is 26.2–59.1 %, in the method of ACI 440.1 R-06 — 20.1–57.1 %. For the ACI 440.1 R-06 method, the calculation is more accurate, in which the short-term deflection was multiplied by the factor λ = 0,6ξ = 0,6 · 2 = 1,2, for the Construction rules and regulations 295.1325800.2017 method — when using ψf = 1 – 0,8Mcrc / M. Conclusions. The results obtained showed the need to improve the considered calculation methods. To increase the accuracy of the calculation of deflections according to the method of SP 295.1325800.2017, at the first stage, it is possible to approximate the theoretical values of the cracking moment to the experimental data by introducing correction factor in the equation according to the calculation of Mcrc: for beams with a GFRP high-bond bars — 0.7, for BFRP with a sanded surface — 0.5.