Clamped-end effect on static detection signals of DNA-microcantilever

Boundary constraint induced inhomogeneous effects are important for mechanical responses of nano/micro-devices. For microcantilever sensors, the clamped-end constraint induced inhomogeneous effect of static deformation, so called the clamped-end effect, has great influence on the detection signals. This paper is devoted to developing an alternative mechanical model to characterize the clamped-end effect on the static detection signals of the DNA-microcantilever. Different from the previous concentrated load models, the DNA adsorption is taken as an equivalent uniformly distributed tangential load on the substrate upper surface, which exactly satisfies the zero force boundary condition at the free-end. Thereout, a variable coefficient differential governing equation describing the non-uniform deformation of the DNA-microcantilever induced by the clamped-end constraint is established by using the principle of minimum potential energy. By reducing the order of the governing equation, the analytical solutions of the curvature distribution and static bending deflection are obtained. By comparing with the previous approximate surface stress models, the clamped-end effect on the static deflection signals is discussed, and the importance of the neutral axis shift effect is also illustrated for the asymmetric laminated microcantilever.

Development of a laboratory and experimental installation for checking the reliability of a mathematical model and an information and technical method for preventing emergencies at landfills of solid household waste with technological liquidation energy-intensive equipment

The paper presents a developed laboratory setup that allows experimental studies of the influence of indicators of the physical state of landfill soil on the stability of slopes to shear, to check the reliability of the mathematical model and the information and technical method developed on its basis for preventing emergencies of the cascade type of propagation due to the displacement of landfill soil on a solid landfill household waste with technological liquidation energy-intensive equipment. The main elements of the developed installation are a rectangular experimental box with swivel and fixed parts, swivel and locking mechanisms, tabletop plates, a sprayer, and a tangential load system. As the main requirements for the installation, the possibility of conducting a series of experiments based on the use of landslide experimental blocks with a change in their humidity, density, temperature and angle of inclination of the base of the sliding surface, as well as mechanical characteristics - the angle of internal friction, specific adhesion of landfill soil. Carrying out research using a laboratory setup is based on the assumption that the transition of a landslide experimental block of landfill soil into a dynamic state is considered the onset of an emergency at the object level of distribution. In the course of the work, a technique was developed for conducting experimental studies and processing observation results. The methodology includes the following procedures: establishment of initial and boundary conditions; preparation of a laboratory installation; conducting a series of experiments to determine the mechanical parameters and the shear angle of the experimental blocks, and a series of experiments to determine the indicators of moisture, temperature and density of landfill soil on the fact of the shift, taking into account the gradual increase in moisture; statistical processing to obtain a statistical sample of the values of the effective indicators of the physical state of landfill soil included in the confidence interval according to the classical statistical method - Student's t-test.

MODELING THE PROCESS OF DISINTEGRATION OF SOLID MATERIALS BY ASYMMETRIC LOADING IN CRUSHING MACHINES IN ORDER TO FIND WAYS TO REDUCE ENERGY COSTS

Subject of study. the processes of cracking and destruction of rocks under the action of the working bodies of machines for disintegration. Methodology. A complex method of generalizing the laws of the theory of elasticity and plasticity was used; theoretical and experimental confirmation of the regularities of the distribution of contact normal and tangential stresses, equations of the limiting state of materials based on the Coulomb strength criterion; slip line theory; comparison of theoretical results with experimental diagrams "normal stresslongitudinal deformation" of samples; facts and phenomena of destruction of rocks; generalization of the theoretical regularities arising from the power contact of the tool with the rock in crushers. Purpose. Reducing energy consumption and increasing the efficiency of rock disintegration by controlling its stress-strain state in crushers on the basis of mathematical modeling and using the established regularities of stresses and deformations in rocks when interacting with a working tool. Output. In the contact area, with an increase in the tangential load, the zone of uniform compression of the material decreases, the depth of the most stressed point approaches the contact surface. There is a significant zone of shear deformations, which are the decisive factor in crack initiation. The development of the crack in depth and complete destruction occurs along the shear lines. Such conditions of rock loading are observed in jaw crushers with complex jaw movement, in cone crushers, in roller crushers with different roll rotation speeds and correspond to the model of the most effective sliding compression. The creation of asymmetric loading conditions using the forces of contact friction, frictional and strength characteristics of the destroyed material can reduce the energy consumption of disintegration.

Revisited the Critical Load Assessment of Huang et al. on Willems Tested Beck Column

Dynamic stability of elastic structures is a fascinating topic. Many researchers have examined the problem theoretically considering a cantilever column under a tip-concentrated tangential load, the so-called Beck column. Experimental verification is demanded since the critical load of Beck column is found to be approximately eight times to that of the classical Euler column. Different types of testing procedures are being adopted to create the follower force. Among them, notable Willems experimentation provides the critical load close to that of Beck column. Investigations made by other researchers indicate the controversy associated with modeling and testing of Willems on Beck column. Such an intriguing problem of structures loaded by non-conservative forces is revisited here through a simple mathematical formulation. This paper confirms the adequacy of Willems approach on Beck column and the wrong critical load assessment of others. It indicates the possibility on the practical realization of follower forces

Application of the refined asymptotic model for describing of the transient extensional edge wave exited by a tangential load applied to the edge

Изучается возможность применения уточненной асимптотической модели планарной краевой волны в задаче о действии нестационарной касательной нагрузки, приложенной на торце. При построении уточненной модели используется асимптотическая двумерная теория растяжения пластин высшего порядка точности. Приводятся результаты сравнения с решением по трехмерной теории упругости для различных законов распределения нагрузки. Показано, что уточненная модель позволяет достаточно точно описать влияние дисперсии краевой волны, не учитываемое в первом приближении. The possibility of application of the refined explicit model for extensional edge wave in the problem of transient waves excitation by an edge tangential load is investigated. The refined model is based on the higher order theory of plate extension. The results of comparison with the 3D solution for various distributions of the load are presented. It is shown that the refined model allows correct describing of dispersion effects which are not taken into account in the leading approximation.

Linear relationship of normal and tangential contact stiffness with load

Measurements with digital image correlation of normal and tangential contact stiffness for ground Ti-6Al-4V interfaces suggest a linear relationship between normal contact stiffness and normal load and a linear relationship between tangential contact stiffness and tangential load. The normal contact stiffness is observed approximately to be inversely proportional to an equivalent surface roughness parameter, defined for two surfaces in contact. The ratio of the tangential contact stiffness to the normal contact stiffness at the start of tangential loading is seen to be given approximately by the Mindlin ratio. A simple empirical model is proposed to estimate both the normal and tangential contact stiffness at different loads for a ground Ti-6Al-4V interface, on the basis of the equivalent surface roughness and the coefficient of friction.

Design and analysis of a strain gauge based eight-shaped elliptical ring dynamometer for milling force measurement

This study describes the design, analysis, and development of a strain gauge-based dynamometer for measuring the cutting force during the milling process. The objective is to increase the deformation of the ring with an applied load so that it can be measured more easily. Based on the analysis and test results, the eight-shaped (ES) rings with an elliptical hole were finalized. It was shown that the ring has a higher deformation of 0.02822 mm for a normal load and 0.2136 mm for a tangential load. Also, the induced von Mises stress is 39.63 MPa for axial and 194.8 MPa for tangential load, each of which is less than half of the yield strength. Hence, for the finalized design the metallic ring was fabricated, and sensors were bonded. Then, the calibration and metrological characterization was performed. Overall, the designed dynamometer is found as suitable for measuring the cutting force in the milling process.

The onset of friction for rubber across an ice bead

Purpose The exploration of the polar regions is of immeasurable potential. It brings great challenges to tribology in the extreme environment. Moreover, the static friction force is an essential index of the braking performance. The purpose of this paper is the static friction force between the rubber of marine pipe tensioner and the ice bead. Design/methodology/approach The frictional phenomena were studied for rubber-ice bead at different contact positions (front edge, front part and end part) by means of image processing and measuring. Also, the image sequences of the contact were combined with friction force and displacement data. Findings As rubber across the ice bead, the forces of rubber and ice bead at different contact positions determined the order of static friction force (front edge > front part > end part). Meanwhile, there were two different contact states in this process. In addition, under the low tangential load growth rate, the higher temperature can increase the static friction force by increasing the viscoelasticity and contact area of rubber. Originality/value The research on the static friction of rubber-ice bead leads to more controlled and higher friction levels during marine pipeline laying. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-12-2019-0526/

On the Degree of Irreversibility of Friction in Sheared Soft Adhesive Contacts

A number of authors have experimentally assessed the influence of friction on adhesive contacts, and generally the contact area has been found to decrease due to tangential shear stresses at the interface. The decrease is however generally much smaller than that predicted already by the Savkoor and Briggs 1977 classical theory using “brittle” fracture mechanics mixed mode model extending the JKR (Griffith like) solution to the contact problem. The Savkoor and Briggs theory has two strong assumptions, namely that (i) shear tractions are also singular at the interface, whereas they have been found to follow a rather constant distribution, and that (ii) no dissipation occurs in the contact. While assumption (ii) has been extensively discussed in the Literature the role of assumption (i) remained unclear. We show that assuming entirely reversible slip at the interface with a constant shear stress fracture mechanics model leads to results almost indistinguishable from the Savkoor and Briggs model (and further in disagreement with experiments), hence it is assumption (ii) that critically affects the results. We analyze a large set of experimental data from Literature and show that the degree of irreversibility of friction can vary by orders of magnitude, despite similar materials and geometries, depending on the velocity at which the tangential load is applied.

Recording microindentation and adhesion tests to analyse the depth-dependent mechanical and adhesive properties of multilayer polymer films as shown for gelatine-coated polyethylene terephthalate and polyethylene films

Further developed methods based on an indenter penetration into a material allow generalised quantitative statements on the composition, the depth-dependent mechanical properties and the delamination behaviour of multilayer polymer films, which is demonstrated on gelatine-coated polyethylene terephthalate and polyethylene films. These highly sensitive polymer testing methods, include the recording microindentation test and the recording adhesion test, describe the material behaviour multi-parametrically and are fast (raw data acquisition within several minutes) and relatively simple, requiring a minimum 1 gram sample depending on the film thickness. Based on the Vickers hardness under load approach, the hardness–depth diagrams calculated from the recording microindentation test provide information about the structure, the thickness and the coating hardness and the substrates. The tangential load vs. tangential path length diagrams from recording adhesion test can detect different scratch processes such as continuous scratching or non-continuous stick-slip layer delamination. Furthermore, they form the basis to quantitatively analyze adhesion, i.e. to determine the critical tangential load and the critical tangential delamination work. Both are highly dependent on the substrate type and treatment.