Non-destructive and Quantitative Viscoelastic-Mapping of Cellulose Nanofibrils Using Low-Total-Force Contact Resonance Force Microscopy (LTF-CRFM)1

Low-total-force contact resonance force microscopy (LTF-CRFM), an atomic force microscopy method, is introduced as a non-destructive means to quantify the local viscoelastic loss tangent (δ) of cellulose nanofibrils (CNFs). The method limits static and dynamic forces during measurement to minimize substrate and geometry effects and to reduce the potential for stress-induced CNF damage. LTF-CRFM uses Brownian motion to achieve the thermally-limited lowest dynamic force, while approaching adhesive pull-off to achieve the low static force. LTF-CRFM measurements were shown to generate analyzable data without evidence of nonlinear artifacts and without damage to the CNF over static forces ranging from 11.6 nN to 84.6 nN. The measured δ of CNFs was 0.015 ± 0.0094, which is the first reported δ measurement of an isolated CNF. Finally, LTF-CRFM successfully mapped δ along the length of CNFs to determine that kink defects along the CNF do not impart a local viscoelastic property change at the length scale of the measurement.

Repeatability of Sheet Material Formation Results and Interchangeability of Processing Modes at Multi-Pass Laser Formation

Laser shaping of sheet materials is a flexible process and is carried out without force contact on the material, it allows forming, among other things, brittle, elastic and difficult-to-deformed materials. It is known that the main parameters of laser shaping are the beam power, the size of the focus zone and the speed of beam movement along the surface of the workpiece, however, the range of variation of these parameters is not unlimited, but due to the characteristics of a particular equipment. Therefore, it is necessary to develop an approach to selecting processing modes that can be selected from the range available on the equipment and at the same time obtain a predictable result. There is also a need to investigate a reproducibility of laser shaping results with a lot of pass-through processing. Actually, this study is aimed at solving these issues. In particular, the article formulates a provision on complex formation parameters that allow determining interchangeable modes of laser molding processing and varying parameters in ranges available on equipment. For this, the basic processing mode was chosen, formation was carried out with a fixed number of passes, after which, using complex parameters, alternative modes were determined and formation was carried out under these conditions with the same number of passes. The article also presents the methodology and results of experimental studies of checking the interchangeability of formation modes and the repeatability of formation results during processing along parallel and multi-directional trajectories. It was experimentally found that the deviation of the strain value obtained in alternative modes, compared to the base, and did not exceed 2.46% for a three-pass cycle and 5.8% - for a nine-pass cycle. And the repeatability of the formation results during laser shaping is quite high; the discrepancy in the deformation value did not exceed 5%, and, preferably, was lower.

Perturbative Treatment of Three-Nucleon Force Contact Terms in Three-Nucleon Faddeev Equations

We present a perturbative approach to solving the three-nucleon continuum Faddeev equation. This approach is particularly well suited to dealing with variable strengths of contact terms in a chiral three-nucleon force. We use examples of observables in the elastic nucleon-deuteron scattering as well as in the deuteron breakup reaction to demonstrate high precision of the proposed procedure and its capability to reproduce exact results. A significant reduction of computer time achieved by the perturbative approach in comparison to exact treatment makes this approach valuable for fine-tuning of the three-nucleon Hamiltonian parameters.

Static and Dynamic Analysis of Deformable Fractal Surface in Contact With Rigid Flat

The chapter consists of static and dynamic analyses of a fractal rough surface in contact with a rigid flat. The fractal surface is constructed using modified Weierstrass-Mandelbrot function. A rigid flat surface touches the topmost point of the rough surface, which moves towards the rough surface and deforms it. Different contact parameters (e.g., contact force, contact area, contact stress, etc. for varying fractal and material properties are obtained through finite element based static analysis. A parameter denoting the degree of nonlinearity of the contact system is extracted from the force-displacement plot of the surface. This parameter is utilized to explain the dynamic behaviour of the fractal surface which vibrates under the influence of the externally excited rigid flat surface. The dynamic analysis of the contact system is carried out by modelling the contact interface as a single degree of freedom (SDOF) spring-mass-damper system. The dynamic behavior of the system is investigated in terms of frequency response curves, time-displacement plots, and phase plots.

Identifiability of Tyre Force Contact Prediction from Deformation Measurements

The possibility of accurately inferring the external forces applied to a vehicle can directly contribute to better safety systems and thus lowers the chance of injury or loss of life. These external forces are applied to a vehicle through the tyres and are challenging to measure directly. Still, it is possible to measure acceleration, deformation, or strain on the inner surface of a tyre. These measurements are theorized to be strongly linked to the forces produced by the tyre. However, it is still unknown whether or not one can always identify external forces from internal measurements in this way. Research has mainly focused on obtaining estimates of tyre forces rather than establishing to what extent these tyre forces are identifiable. This paper investigates this by conducting a virtual experiment that simulates known external forces applied to the tyre and computes the strains and displacements inside the tyre. A virtual inverse simulation then recovers the external forces from either the deformation or strain computed on the inside of the tyre. The identifiability of the forces recovered by the virtual inverse simulation is investigated by adding artificial measurement noise and initial guess perturbations to quantify the variance in the identified forces.

The Applied model of grinding a spherical solid particle with a direct impact on a non-deformable flat surface

A grinding process using a free impact breakage mechanism is used in industries. In order to make calculations, predict grinding results, and evaluate mills functioning, it is necessary to assess the parameters of the grinding process and interrelations between the process parameters, mills parameters and materials properties, i.e. it is necessary to use an adequate mechanical-mathematical model of the process. However it is difficult to model due to some phenomena occurring in this process. Nowadays, various researchers have established the basis for the structure of the grinding process, but the application of the existing hypotheses and methods to evaluate the grinding process is quite difficult. This paper solves the problem of a spherical shape particle impacting an absolutely rigid half-space. It proposes a refined mechanical and mathematical model describing the process of destruction of the particle using the free direct impact breakage mechanism on an absolutely rigid, stationary, and flat surface. By using the Hertz-Staerman's classical analytical dependencies on the force contact interaction of the spherical bodies and the technical theory of the longitudinal waves’ propagation in the elastic continuous medium, we obtained a new refined solution of the applied dynamic problem related to a direct impact of a ball simulating a particle of a feeding material (an absolutely rigid surface simulating the working body of the mill) taking into account local physically linear deformations, the time parameter and radial particle size. The improved theoretical model of the spherical particle destruction was brought to applicable analytical calculations, tested and illustrated by a numerical example. It made it possible to describe the fracture of the material particles, predict the result and calculate the grinding process depending on its parameters providing the required quality of grinding by regulating and selecting characteristics, designing and selecting the grinding equipment, and modeling the grinding process using the free impact breakage mechanism.

Method for studying the parameters of the surface hardening of parts with a protective coating

Поверхностные покрытия деталей получили широкое распространение в технике, в том числе для судовых энергетических установок, а также вспомогательных судовых механизмов и устройств. Для экспериментального исследования работоспособности деталей на контактные силовые воздействия используются как цельные образцы, разделяемые после силового воздействия в месте его приложения, так и составные образцы, силовое воздействие на которые производится в месте стыка отдельных элементов. В последнем случае деформирующее разделение образца и получение нежелательных дополнительных пластических деформаций в ходе разделения исключаются. При обеспечении равной точности результата этих методов второй является более надёжным, не требующим контроля побочных деформаций для анализа зоны деформации получаемой от планового силового контактного воздействия. Нанесение поверхностного слоя осложняет использование составных образцов при исследовании зон пластической деформации Процедура их получения и испытания может быть усовершенствована. Предлагаются варианты формирования образцов, а также способы их получения и использования. Делается заключение об упрощении процедуры экспериментальных исследований при использовании предлагаемых образцов и получении более достоверных результатов. Обращается внимание на возможность одновременного ведения испытания для разных материалов деталей, что предполагает сокращение расхода наносимого материала покрытия и трудоёмкости работ. Surface coatings of parts are widely used in engineering, including for ship power plants, as well as auxiliary ship mechanisms and devices. For experimental study of the performance of parts for contact force effects, both whole samples that are share separated after the force action at the place of its application, and composite samples that are subjected to force action at the junction of individual elements are used. In the latter case, deforming separation of the sample and unwanted additional plastic deformations during separation are excluded. While ensuring equal accuracy of the results of these methods, the second method is more reliable and does not require control of side deformations for analyzing the deformation zone affected by the planned force contact action. The application of a surface layer complicates the use of composite samples in the study of plastic deformation zones. Procedure for obtaining and testing them can be improved. Options for forming samples, as well as ways to obtain and use them are offered. The conclusion is made about simplification of the experimental research procedure when using the proposed samples and obtaining more reliable results. Attention is drawn to the possibility of simultaneous testing for different materials of parts, which implies a reduction in the consumption of the coating material applied and the complexity of work.

Comparative Analysis Carried Out on Modern Indentation Techniques for the Measurement of Mechanical Properties: A Review

Nowadays many indentation techniques are being commonly employed for determining some mechanical properties (harness, elastic modulus, toughness, etc.) using simple method of measuring the indentation depth. On the basis of measurement of depth of penetration, indentation technique has be classified into major categories i.e. microindentation and nanoindentation. Nanoindentation technique uses indirect method of determining the contact area as the depth of penetration is measured in nanometers, while in conventional indentation the area in contact is measured by elementary measurement of the residual area after the indenter is removed from the specimen. Dynamic hardness is the best result of dynamic indentation which can be expressed as the ratio of energy consumed during a rapid indentation to the volume of indentation. The parameter which are taken into consideration are indentation depth, contact force, contact area, mean contact pressure.

Simulating the Behaviour of a Rail String Segment under Dynamic Impac

The paper presents a mathematical model for behaviour of a rail string segment bound by several railway sleepers. The model makes it possible to account for prestressing due to joining rail sections into a string, for anisotropic properties of the rail-and-sleeper assembly, and effects caused by the rolling stock for various initial loading conditions. We considered eleven functions describing wheel--rail contact. These functions enable us to select the most accurate model to describe the effects that vehicles have on railway segments that may differ in design specifics, mechanical properties of materials used, operation modes, and the presence of flaws on the rail tread and wheelset tread. The wave equations used to describe the behaviour of a rail string segment can simulate the process of elastic wave propagation after wheelset contact takes place, which is considerable in the case of high vehicle velocities. The investigation conducted allowed us to plot the wheel--rail interaction force for various contact models. The functions specified make it possible to select the optimum force ratio, taking into account the following: geometrical, mechanical and design parameters of the railway segment; operation modes; and the functions sought for in terms of obtaining the desired maximum contact force, contact duration, and loading and relief times

Adhesive Contact Between Cylindrical (Ebola) and Spherical (SARS-CoV-2) Viral Particles and a Cell Membrane

A critical event during the process of cell infection by a viral particle is attachment, which is driven by adhesive interactions and resisted by bending and tension. The biophysics of this process has been studied extensively but the additional role of externally applied force or displacement has generally been neglected. In this work we study the adhesive force-displacement response of viral particles against a cell membrane. We have built two models: one in which the viral particle is cylindrical (say, representative of filamentous virus such as Ebola) and another in which it is spherical (such as SARS-CoV-2 and Zika). Our interest is in initial adhesion, in which case deformations are small and the mathematical model for the system can be simplified considerably. The parameters that characterize the process combine into two dimensionless groups that represent normalized membrane bending stiffness and tension. In the limit where bending dominates, for sufficiently large values of normalized bending stiffness, there is no adhesion between viral particles and the cell membrane without applied force. (The zero-external-force contact width and pull-off force are both zero.) For large values of normalized membrane tension, the adhesion between virus and cell membrane is weak but stable. (The contact width at zero external force has a small value.) Our results for pull-off force and zero force contact width help to quantify conditions that could aid the development of therapies based on denying the virus entry into the cell by blocking its initial adhesion.