Maks Oblak

Application of the european SINTAP procedure to the failure analysis of a broken forklift

Abstract The recently developed European flaw assessment procedure SINTAP was applied to the failure analysis of a broken fork of a forklift. Based on the service load at failure critical crack sizes were determined at different analysis levels of the procedure. It was shown in the present case study that the reason of the failure was defective design.

Thermal Conductivity, Viscosity, and Thermal Diffusivity Calculation for Binary and Ternary Mixtures

A mathematical model is presented for computing viscosity, thermal conductivity, and thermal diffusivity in the liquid and gas domains for pure components and mixtures. To calculate the transport properties of a real fluid, models based on Lennard-Jones intermolecular potential were applied. The new mathematical model is used for the calculation of transport properties for binary and ternary mixtures. The model is based on a new theory for mixtures. The results obtained by statistical thermodynamics are compared with the REFPROP model and show relatively good agreement.

Effect of Strength of Mismatch Interface on Crack Driving Force

Abstract. A welded joint is a critical part of a welded structure with respect to defects, pores, geometry, misalignments, and mechanical anisotropy. Differences in the mechanical properties appear between weld metals, heat affected zone, and base metal. Crack growth resistance curves, e.g., determined in terms of crack tip opening displacement (CTOD), exhibit variations in the crack growth resistance of the welded joint as a consequence of the local variations in the material properties. Theoretical investigations have shown that also the local near-tip crack driving force (CDF) may deviate strongly from the far-field CDF, if the material properties vary locally. The reason is that the material inhomogeneity induces an additional CDF-term, called the material inhomogeneity term, Cinh, which leads to a shielding or anti-shielding of the crack tip. A model developed by Simha et al. is applied to evaluate the magnitude of Cinh in a welded joint with a strength mis-match interface. Both a stationary and a propagating crack are considered.

Valve Gear Refinement

This paper describes a new type of valve gear cam-MULTICAM-which consists of seven curves and allows an optimum cam profile design. In order to calculate the cinematic and dynamic values and to assess the minimum oil film thickness in the valve gear the mathematical model of an ideal valve gear was used. In addition, the comparison of the results between the polysine cam and the new MULTICAM cam design was made. By means of the new cam design the Hertz pressures were reduced at the point of contact between the cam and the cam follower and the lubrication properties at the top of the cam improved.

The Calculation of Thermal Conductivity for Nanofluids on the Basis of Statistical Nano-Mechanics

The paper features the mathematical model of calculation of thermal conductivity for nanofluids on the basis of statistical nano-mechanics. Calculation of transport properties for nanofluids for real substances is possible by the classical and statistical mechanics. Classical mechanics has no insight into the microstructure of the substance. Statistical mechanics, on the other hand, calculates the properties of state on the basis of molecular motions in a space, and on the basis of the intermolecular interactions. The equations obtained by means of classical thermomechanics are empirical and apply only in the region under observation. The main drawback of classical thermomechanics is that it lacks the insight into the substance of microstructure. Contrary to classical mechanics, statistical mechanics calculates the thermomechanic properties of state on the basis of intermolecular and intramolecular interactions between particles in the same system of molecules. It deals with the systems composed of a very large number of particles. The results of the analysis are compared with experimental data and show a relatively good agreement. The analytical results obtained by statistical mechanics are compared with the experimental data and show relatively good agreement.

The Calculation of Thermal Conductivity for Metals

The calculation of transport properties of solids is of vital importance in the engineering practice. This paper is focused on the development of a mathematical model for the calculation of the thermal conductivity for simple solids with the help of statistical mechanics. Contrary to classical mechanics, the use of statistical theories provides an insight into the world of atoms and molecules (a microscopic description of phenomena). The observation of the phenomena of molecules and atoms enables us to calculate all thermomechanical properties of state of the macroscopic world. The Eliashberg coupling function was used for the calculation of electronic contribution. New constants for some metals were obtained with the presented model. The analytical results obtained by statistical mechanics are compared with the experimental data and show a relatively good agreement.

Analytical Calculation of Diffusion Coefficients and Other Transport Properties in Binary Mixtures

Nomenclature D12 = binary diffusion coefficient, m2/s Fc = secondand third-order correction factor of viscosity k = Boltzmann constant, J/K kt = thermal diffusion ratio M = molecular mass, kg/kmol N = number of molecules in system Rm = universal gas constant, J/kmol K T = temperature, K T ∗ = reduced temperature αt = thermal diffusion factor e = Lennard–Jones parameter, J η = dynamic viscosity, Pas σ = Lennard–Jones parameter, m ψi = molar fraction of component I = collision integral, m3/s ∗ = reduced collision integral

Self-excited Oscillations and Fuel Control of a Combustion Process in a Rijke Tube

Abstract This paper treats the control of nonstationary oscillations of the pressure which arise in the combustion process of a Rijke tube. The low order model of a nonstationary combustion process in a Rijke tube with multiplicative feedback control function is considered, which is investigated by means of two-DOF coupled van der Pol oscillator. The self-excited oscillations in the combustion process are analysed by means of the Extended Lindstedt-Poincare (EL-P) method with multiple time scales. By applying the EL-P method, it is ascertained, that nonstationary oscillations are almost periodic with amplitude and phase, which are functions of the slow time scale. Without control of the fuel influx, the self excited oscillations can approach limit cycles. By applying the fuel control, the influence of control parameters on the quenching of the self excited oscillations is investigated in a phenomenon of competitive quenching and mutual synchronization with close frequencies and multiple harmonics, respectively.

The Calculation of Thermodynamic and Transport Properties for Nanofluids on the Basis of Statistical Nano-Mechanics

The paper features the mathematical model of calculation of thermophysical properties for nanofluids on the basis of statistical nano-mechanics. Calculation of properties for nanofluids for real substances is possible by the classical and statistical mechanics. Classical mechanics has no insight into the microstructure of the substance. Statistical mechanics, on the other hand, calculates the properties of state on the basis of molecular motions in a space, and on the basis of the intermolecular interactions. The equations obtained by means of classical thermomechanics are empirical and apply only in the region under observation. The main drawback of classical thermomechanics is that it lacks the insight into the substance of microstructure. Contrary to classical mechanics, statistical mechanics calculates the thermomechanic properties of state on the basis of intermolecular and intramolecular interactions between particles in the same system of molecules. It deals with the systems composed of a very large number of particles. The results of the analysis are compared with experimental data and show a relatively good agreement. The analytical results obtained by statistical mechanics are compared with the experimental data and show relatively good agreement.

Nonstationary Vibration and Transition through Fundamental Resonance of Electromechanical Systems Forced by a Nonideal Energy Source

This paper presents the Extended Lindstedt-Poincare (EL-P) method with multiple time scales to treat nonstationary vibrations of the electromechanical system, which are forced by a nonideal energy source. The subject of research are two electromechanical systems consisting from rotor system with rotating disc mounted on an elastic shaft and a system with a rotating eccentric mass coupled by a nonlinear shock absorber, which are driven by a D.C. motor as a nonideal energy source. By using extended Hamilton principle, governing nonlinear differential equations of the system are derived. By using multiple time scales, which correspond to the nonlinear frequencies of the system in addition to the slow time scale, which corresponds to the slowly varying parameter, the system of partial differential equations is obtained, which is successively solved by using the proposed EL-P method. The results of computation of the nonstationary vibrations in the passage through fundamental resonance in both systems are presented.