Theoretical and experimental investigation of tyre dynamics

The lateral vibration of towed wheels - also called shimmy - is related to the elasticity of the suspension system or to the elasticity of the wheel. The second case is studied here since the majority of the vehicles has pneumatic tyres. A one degree-of-freedom wheel model is considered with perfect rolling and elastic tyre. To verify the theoretical stability charts, an experimental rig is built and one of the stability boundaries is identified. Close to a double Hopf bifurcation point quasiperiodic vibrations are observed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Theoretical and experimental investigation of anisotropic damage in textile-reinforced composite structures

In the present work, a phenomenological plane-stress damage-mechanics-based model for textile-reinforced composites is presented and its predictive capability is evaluated by carrying out a series of experimental tests. Damage variables are introduced to describe the evolution of the damage state and, as a subsequence, the degradation of material stiffness. For calculating the nonlinear stress and strain distribution of complexly loaded composites with a textile reinforcement, a special emphasis has to be placed on the interaction between the fiber failure due to the stress in the fiber direction and the matrix failure due to the transverse and shear stresses. This demands the formulation of realistic failure criteria taking into account the microstructural material behavior and different fracture modes. The new failure criteria, like the fracture mode concepts, consider these fracture modes, as well as further fracture types, in the reinforcement plane. The failure criteria are based on equations for failure surfaces in the stress space and damage thresholds in determining the stiffness degradation of the composite. The model proposed was used to characterize the strength and the failure behavior of carbon-fiber-reinforced composites. For this purpose, several unidirectional and bidirectional tests were performed to determine the specific properties of the material. The specimens were investigated by using acoustic emission techniques and strain-controlled tension and torsion tests.Russian translated published in Mekhanika Kompozitnykh Materialov, Vol. 40, No. 6, pp. 791–810, November–December, 2004.     

An experimental study of the effect of fracture and operative intervention on acoustical properties of human tibial bone

Conclusions 1. The differences between the ultrasonic parameters c and determined for the right and left tibial bones as well as between values obtained directly on the bone and through the skin are statistically insignificant (p>0.1).2. Experimental fracture of the tibia leads to a significant decrease in the ultrasound speed (p<0.001) and increase in the ultrasound damping coefficient (p<0.001).3. Operative intervention, as a whole, and any of the surgical manipulations, in particular, significantly alter the initial acoustic parameters of the tibia with fracture or after osteotomy relative to fracture or osteotomy without osteosynthesis. These groups of patients should have different criteria for the degree of fracture repair.4. Weakening of the stability of the fixation of a fracture by screwing in or loosening screws attaching a splint plate to the bone cause an increase in the damping coefficient. This sign is rather sensitive for use in clinical practice to diagnose weakening of the rigidity of fixation.5. The ultrasound parameters c and depend on the magnitude of the cross-sectional defect of the diaphysis and in conjunction may be used for diagnosis of the degree of adhesion of a fracture or operation site after corrective osteotomy.6. The values for c and found for undamaged bone may be used to evaluate their values for a diaphysis used for preparing bone samples.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Riga Scientific Research Institute of Traumatology and Orthopedics. Translated from Mekhanika Polimerov, No. 1, pp. 88–96, January–February, 1978.     

Theoretical and experimental investigation of cartilage replacement material for medical applications

Soft tissues are commonly applied in surgery to replace the injured articular cartilage. Many biological researches were carried out through mechanical and histological experiments. They focus on the function, degeneration and regeneration of the articular cartilage and fibrocartilage. The aim of the presented work is to develop a method to characterize the mechanical properties of different kinds of soft tissues and to trace the evolution of elastic properties in implants during the remodeling process. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Theoretical and experimental investigation of the state of stress of a cantilevered plate with low shear stiffness

A general solution is obtained for the problem of a cantilevered, transversely isotropic plate in the form of an infinite strip with a clamped edge bent by a concentrated load applied at the free edge. The investigation relies on the equations of the generalized theory of plates [21–23] with allowance for interlaminar shears. In contrast with the Papkovich solution [1], the maximum theoretical bending moment at the clamped edge depends on the relative width of the strip and on the properties of the material. The classical result is asymptotically exact as h 0 or G_Z . The experimental results confirm the principal conclusions based on the theoretical solution.Kamenetsk-Podol'sk General Engineering Department, Khmel'nitskii Technological Institute. L'vov Physicomechanical Institute, Academy of Sciences of the Ukrainian SSR. Translated from Mekhanika Polimerov, No. 3, pp. 476–481, May–June, 1971.     

Modeling,analysis and simulation of the human femur: prosthesis of femur head

We report the results obtained when carrying out the analysis of the strengths and strains that take place when prosthesis of femur head are implanted in the human femur. The modeling is made with tools provided by Computer Aided Geometry Design, using Non Uniform Rational B-Splines representations (NURBS). In the analysis of the strengths and strains, produced in the bone-cement-prosthesis interaction, partial differential equations of the coupled system are obtained for the displacements and deformations, that allow to analyze cases of physical and biological loads, under which will be work the implants during their useful life, which also is estimated; because of the frequent phenomenon of bony absorption and the consequent relaxation and loss of the replacement surgery. The obtained equations are solved by finite element method, with the corresponding estimation of the obtained errors. The simulations will be performed using high level software able to show realistic visualizations of the observed phenomena in real time. The fracture of the femur neck is a frequently observed trauma and has taken to the authors to make the present work. The obtained results will allow to make the modeling, analysis and simulation of other bony structures and the implants of the corresponding prosthesis. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Theoretical investigation of the flow in a stenosis

The theoretical investigation of the flow in stenosis is presented. We use a new formulation of the incompressible Navier–Stokes equation in terms of an auxiliary field that differs from the velocity by a gauge transformation [1]. The gauge freedom allows us to formulate simple boundary conditions for the auxiliary field and the gauge field as well. The gauge field eliminates the pressure distribution in the Navier–Stokes equation. The numerical investigation of the creeping flow, depending on the geometrical parameters of the system, is performed. The influence of the pressure drop has been taken into account. An excellent agreement with the analytical results in frames of the film theory was observed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Theoretical background and experimental measurements of human brain noise intensity in perception of ambiguous images

We propose a theoretical approach associated with an experimental technique to quantitatively characterize cognitive brain activity in the perception of ambiguous images. Based on the developed theoretical background and the obtained experimental data, we introduce the concept of effective noise intensity characterizing cognitive brain activity and propose the experimental technique for its measurement. The developed theory, using the methods of statistical physics, provides a solid experimentally approved basis for further understanding of brain functionality. The rather simple way to measure the proposed quantitative characteristic of the brain activity related to the interpretation of ambiguous images will hopefully become a powerful tool for physicists, physiologists and medics. Our theoretical and experimental findings are in excellent agreement with each other.     

Determination of the elastic and damping properties of the human femur in bending

The results of an experimental investigation of the deflection of the human femur subjected to a bending moment are presented. The existence of two principal bending planes is established. The equivalent flexural rigidity of the dry bone is calculated for both static and dynamic loading. It is found that the human femur has a nonlinear elastic characteristic. The stiffness and damping properties obtained in static and dynamic testing are compared.Paper presented at the First All-Union Conference on Engineering and Medical Biomechanics, Riga, October, 1975.Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 642–646, July–August, 1975.     

Electron-fractographic investigation of the brittle fracture of polyethylene

The results are presented of an electron-microscope investigation of the brittle fracture of linear polyethylene at the temperature of liquid nitrogen. It is shown that the physical nature of the structural details of the microrelief of the fracture surface is conditioned by local plastic deformation of the stratified lamellar structures in a thin layer adjacent to the fracture surface preceding and accompanying fracture. The possibility of local self-heating is discussed and a possible mechanism of plastic deformation of the crystal platelets at low temperatures is proposed.Mekhanika Polimerov, Vol. 3, No. 2, pp. 286–290, 1967     

Elastomeric materials: Theoretical investigation and experiments

In this contribution we investigate an incompressible carbon–filled rubber experimentally and theoretically. On the experimental side we perform uniaxial tension tests and theoretically we use two different constitutive models, the Arruda–Boyce–Model and the Yeoh–Model, to describe the experimental observed behaviour. The model parameters are identified by a comercial fitting tool Origin Pro from National Instruments. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Theoretical and experimental researches of size effect in micro-indentation test

Micro-indentation tests at scales on the order of sub-micron have shown that the measured hardness increases strongly with the indent depth or indent size decreasing, which is frequently referred to as the size effect. However, the trend is at odds with the size-independence implied by conventional elastic-plastic theory. In this paper, strain gradient plasticity theory is used to model the size effect for materials undergoing the micro-indenting. Meanwhile, the micro-indentation experiments for single crystal copper and single crystal aluminum are carried out. By the comparison of the theoretical predictions with experimental measurements, the micro-scale parameter of strain gradient plasticity theory is predicted, which is fallen into the region of 0.8–1.5 micron for the conventional metals such as copper (Cu), aluminum (Al) and silver (Ag). Moreover, the phenomena of the pile-up and sink-in near micro-indent boundary are investigated and analyzed in detail.     

Theoretical investigation of electro-osmotic flows and chaotic stirring in rectangular cavities

Two-dimensional, time-independent and time-dependent electro-osmotic flows driven by a uniform electric field in a closed rectangular cavity with uniform and non-uniform zeta potential distributions along the cavity’s walls are investigated theoretically. First, we derive an expression for the one-dimensional velocity and pressure profiles for a flow in a slender cavity with uniform (albeit possibly different) zeta potentials at its top and bottom walls. Subsequently, using the method of superposition, we compute the flow in a finite length cavity whose upper and lower walls are subjected to non-uniform zeta potentials. Although the solutions are in the form of infinite series, with appropriate modifications, the series converge rapidly, allowing one to compute the flow fields accurately while maintaining only a few terms in the series. Finally, we demonstrate that by time-wise periodic modulation of the zeta potential, one can induce chaotic advection in the cavity. Such chaotic flows can be used to stir and mix fluids. Since devices operating on this principle do not require any moving parts, they may be particularly suitable for microfluidic devices.     

Electron-microscope investigation of the type of fracture of filled polymers

An electron microscope was used to study the type of fracture of filled compositions based on SKN-40, SKMS-30, and SKS-85 polymers with TeG-10 thermal-decomposition black, DG-100 channel black, and chalk fillers. It is shown that in all the cases investigated the filled systems fracture along the polymer-filler interphase boundary.Mekhanika Polimerov, Vol. 3, No. 2, pp. 291–295, 1967     

Theoretical and numerical investigation of the D-gap function for box constrained variational inequalities

The D-gap function, recently introduced by Peng and further studied by Yamashita et al., allows a smooth unconstrained minimization reformulation of the general variational inequality problem. This paper is concerned with the D-gap function for variational inequality problems over a box or, equivalently, mixed complementarity problems. The purpose of this paper is twofold. First we investigate theoretical properties in depth of the D-gap function, such as the optimality of stationary points, bounded level sets, global error bounds and generalized Hessians. Next we present a nonsmooth Gauss-Newton type algorithm for minimizing the D-gap function, and report extensive numerical results for the whole set of problems in the MCPLIB test problem collection. The work of this author was supported in part by the Scientific Research Grant-in-Aid from the Ministry of Education, Science, Sports and Culture, Japan.