Structural approach to enhance the fracture resistance of high-strength metallic materials

The paper proposes an approach to form (by special heat treatment) a structure and phase composition of martensitic steel that would enhance its ductility in the high-strength state. A correlation is experimentally established between the stability of fracture resistance and ductility in linear and plane stress states. The behavior of the scatterband of the ultimate strength with increase in the degree of ductility is analyzed. The possibility of predicting the ultimate strength from the lower edge of its scatterband is demonstrated with an example of a circular cylindrical shell __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 8, pp. 68–78, August 2006.     

Axial compression and energy absorption characteristics of high-strength thin-walled cylinders under impact load

Non-linear finite element software LS-DYNA is used to analyze the axial compression behavior and energy absorption of a high-strength thin-walled member under an impact load. To elucidate the effect of dynamic impact on the strain rate, the Cowper-Symonds equation is applied to analyze the plastic state of stress and the onset of dynamic yielding under different strain rates, such that the modeled deformation behavior of the member is consistent with the actual situation. Results for the thin-walled members made of mild steel and dual phase steel are compared. Assuming two different materials with equal sectional areas, an analysis confirms that the energy absorption of high-strength steel thin-walled component is better than the mild steel thin-walled component. Hence, thin-walled tubes made of high-strength steel are investigated using a series of analysis. The relationships between displacement and load, average load and energy absorption properties are obtained.     

A multigrid finite difference approach to steady flow between eccentric rotating cylinders

A simple finite difference scheme over a non‐uniform grid is proposed to solve the two‐dimensional, steady Navier–Stokes equations. Instead of the Newton method, a more straightforward line search algorithm is used to solve the resultant system of non‐linear equations. By adopting the multigrid methodology, a fast convergence is achieved, at least for low‐Reynolds number flow. This scheme is applied, in particular, to flow between eccentric rotating cylinders. The computed results are shown in good agreement with some analytic findings. Copyright © 2000 John Wiley & Sons, Ltd.     

New analytical solutions to water wave radiation by vertical truncated cylinders through multi-term Galerkin method

New analytical solutions to water wave radiation by vertical truncated circular cylinders are developed based on linear potential flow theory. Two typical cylinder configurations of a surface-piercing cylinder and a submerged floating cylinder are considered. The multi-term Galerkin method is employed in the solution procedure, in which the fluid velocity on the interface between different regions is expanded into a set of basis function involving the Gegenbauer polynomials, and the cube-root singularity of fluid velocity at the side edges of the truncated cylinders is correctly modeled. The present solutions have the merits of very rapid convergence. The results with six-figure accuracy for added mass and radiation damping can be obtained using a few truncated numbers in the basis function for three motions (surge, heave and roll). The calculated results of the present solutions agree well with that by a higher-order boundary element method solution. Calculation examples are presented to investigate the influence of the motion frequency on the added mass and the radiation damping of the truncated cylinders with different geometric parameters. The present solutions can be used as a reliable benchmark for numerical solutions to water wave radiation by complicated structures.

     

Analysis of the vibrational behavior of the composite cylinders reinforced with non-uniform distributed carbon nanotubes using micro-mechanical approach

Nanocomposites are a promising new class of structural materials for the aerospace structural components. This paper presents a detailed theoretical investigation of dynamic characteristics of cylinders made of carbon nanotube-reinforced composites. The cylinders are modeled as a cylindrical shell consisting of an isotropic matrix reinforced with transversely isotropic carbon nanotubes. Two different types of carbon nanotube reinforcements are considered: single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs). The effects of carbon nanotube aspect ratio, dispersion, alignment and volume fraction on the elastic modulus are analyzed using the Eshelby–Mori–Tanaka theory. Mass and stiffness matrices are obtained via Ritz method and natural frequencies of the structure are derived through solving the eigenvalue problem. Finally, the effects of the CNT distribution on mode shapes and natural frequencies are discussed.     

Service-simulation tests to determine the fatigue life of outside-diameter-notched thick-wall cylinders

Simulation specimens were used to model the fatigue behavior of outside-diameter-notched internally pressurized cylinders of alloy steel. Results from continuum mechanics and finite-element analyses are described for use in selection of simulation-test conditions. The effects of notch depth and residual stress on fatigue life are determined from the simulation tests.     

爆炸自紧残余应力及对构件疲劳强度的影响

用贴腻子炸药法和动液压法两种爆轰工艺对不同类型厚壁构件实施了爆炸自增强处理,并对爆炸处理形成的残余应力进行了实验测定。对内壁有缺口和裂缝的厚壁圆环以及带缺口的超高压圆筒和四通构件进行了爆炸自紧处理并进行了疲劳实验检验,结果是:在高周疲劳阶段,经爆炸处理的构件缺口根部疲劳裂纹萌生寿命可提高5倍,内压疲劳开裂寿命可提高8~10倍。在低周塑性疲劳阶段构件的疲劳开裂寿命仍可提高1倍左右。由于用贴腻子炸药方法可使构件表面硬度增加从而获得更高的残余压应力,故其自增强效果优于动液压法。     

Inelastic behavior of thick-walled cylinders subjected to nonproportionate loading

Inelastic behavior of thick-walled cylinders subjected to nonproportionate loading was studied by the testing of specimens made of C1045 steel and of annealed copper. Several theories were reviewed. A closed-form solution proposed by Mendelson¹² was used to predict external strains for open-end and closed-end thick-walled cylinders. An incremental theory proposed by Chu¹³ was used to provide incremental solutions for open-end thick-walled cylinders, and for cylinders subjected to nonproportionate loading. Test data for open-end and closed-end thick-walled cylinders made of C1045 steel and of annealed copper were in excellent agreement with the incremental theory. Larger values were predicted by use of the closed-form solution for circumferential strains than actual test data for open-end thick-walled cylinders at large depth of yielding. For cylinders subjected to nonproportionate loading, excellent agreement was indicated between the incremental theory and the experiments for the plot of axial load vs. circumferential strain for specimens made of both metals. Agreement between the incremental theory prediction of axial strains for the specimens made of annealed copper and test data is quite satisfactory. Larger values were predicted by the incremental theory for axial strain than experimental data for specimens made of C1045 steel. The error was conservative.     

New approach to the evaluation of the effort state of steel based on magneto-mechanical effects

The current innovative technical approach has involved the use of advanced computer-assisted design and structure optimization systems. Widely developed computer modelling has accounted for complex loads in facilities and economic and ecological issues, and it has been focused on minimizing the factors that could harm the environment in the course of the construction of a technical facility. The approach fails to guarantee sufficient safety, which is demonstrated by the continuing occurrence of unpredicted failures and catastrophes. There are also many examples of catastrophic events in sea and rail transportation that could seriously affect not only people directly connected with the transportation system but also the surrounding environment. The optimal means of failure/damage risk assessment can be estimated on the basis of the current technical condition of the analysed object. This possibility is offered by the research presented in this paper, which clearly leads to the development of a diagnostic model for a passive magnetic method to determine the state of stress and effort of a structure. Many materials that could cause a real threat of catastrophe due to fatigue wear, exceeded stress limits or the emergence of plastic deformation has magnetic properties that could affect the local magnetic field. This paper addresses the problems of mathematical modelling and analytical/computational modelling of phenomena for the needs of the diagnosis and detection of diagnostic information regarding the passive magnetic method. Numerical modelling along with laboratory experiments and processing, which agree with Bayesian updating, will be indispensable to optimize the method of detecting diagnostic information for a real-life technical object. The results prove that by introducing dynamics into the system, there exist parameters that must be considered when analysing the changes of the magnetic field of the examined object in the function of its effort and when analysing the global effort of the structure. With the help of a hysteresis model, changes that could be connected with the technical state of the research object can be observed and identified. The proposed diagnostics can be used for any dynamic system in which one can observe magneto-mechanical effects.     

On the theory of uniformly loaded cylinders

A characterization of the Almansi-Michell solution to the relaxed Almansi-Michell problem is established. This result leads to a simple derivation of the Almansi-Michell solution.     

On the theory of loaded inhomogeneous cylinders

This article is concerned with the relaxed Saint-Venant’s problem in the case when the body forces and surface tractions on the lateral surface are polynomials in the axial coordinate. A new method of solving this problem is presented. The method is applied to study the problem of a uniformly loaded cylinder.     

Heat transfer between gas-liquid spray stream flowing perpendicularly to the row of the cylinders

Experimental investigation and analysis of heat transfer process between a gas-liquid spray flow and the row of smooth cylinders placed in the surface perpendicular to the flow has been performed. Among others, there was taken into account in the analysis the phenomenon of droplets bouncing and omitting the cylinder as well as the phenomenon of the evaporation process from the liquid film surface.In the experiments test cylinders were used, which were placed between two other cylinders standing in the row.From the experiments and the analysis the conclusion can be drawn that the heat transfer coefficients values for a row of the cylinders are higher than for a single cylinder placed in the gasliquid spray flow.

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Wärmeübergang an eine senkrecht anf eine Zylinderreihe auftreffende Gas-Flüssigkeits-Sprüh-Strömung

Zusammenfassung Es wurden Messungen und theoretische Analysen des Wärmeübergangs zwischen einer Gas-FlüssigkeitsSprüh-Strömung und den glatten Oberflächen einer Zylinderreihe durchgeführt, die senkrecht zum Sprühstrahl angeordnet waren. Dabei wurde in der Analyse unter anderem das Phänomen betrachtet, daß die Tropfen die Zylinderwand treffen und verfehlen können und daß sich ein Verdampfungsprozeß aus dem flüssigen Film an der Zylinderoberfläche einstellt.Gemessen wurde an einem zwischen zwei Randzylindern befindlichen Zylinder.Die Experimente und die Analyse gestatten die Schlußfolgerung, daß der Wärmeübergangskoeffizient für eine Zylinderreihe höher ist als für einen einzelnen Zylinder in der Sprühströmung.

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Nomenclature a distance between axes of cylinders, m - c _l specific heat capacity of liquid, J/kg K - c _g specific heat capacity of gas, J/kg K - D cylinder diameter, m - g _l mass velocity of liquid, kg/m²s - ¯k average volume ratio of liquid entering film to amount of liquid directed at the cylinder in gas-liquid spray flow, dimensionless - k() local volume ratio of liquid entering film to amount of liquid directed at the cylinder in gas-liquid spray flow, dimensionless - L specific latent heat of vaporisation, J/kg - m mass fraction of water in gas-liquid spray flow, dimensionless - M constant in Eq. (9) - p pressure, Pa - p _g statical pressure of gas, Pa - p _w pressure of gas on the cylinder surface, Pa - p external pressure on the liquid film surface, Pa - r cylindrical coordinate, m - R radius of cylinder, m - T temperature, K, °C - T _l, t_l liquid temperature in the gas-liquid spray, K, °C - T _w,t_w temperature of cylinder surface, K, °C - T temperature of gas-liquid film interface, K - U liquid film velocity, m/s - w gas velocity on cylinder surface, m/s - w _g gas velocity in free stream, m/s - W _l liquid vapour mass ratio in free stream, dimensionless - W liquid vapour mass ratio at the edge of a liquid film, dimensionless - x coordinate, m - y coordinate, m - z complex variable, dimensionless - average heat transfer coefficient, W/m²K - local heat transfer coefficient, W/m² K - average heat transfer coefficient between cylinder surface and gas, W/m² K - _g, local heat transfer coefficient between cylinder surface and gas, W/m² K - mass transfer coefficient, kg/m²s - liquid film thickness, m - _lg dynamic diffusion coefficient of liquid vapour in gas, kg/m s - pressure distribution function on a cylinder surface - function defined by Eq. (3) - _l liquid dynamic viscosity, kg/m s - _g gas dynamic viscosity, kg/m s - cylindrical coordinate, rad, deg - _l thermal conductivity of liquid, W/m K - _g thermal conductivity of gas, W/m K - mass transfer driving force, dimensionless - _l density of liquid, kg/m³ - _g density of gas, kg/m³ - _w shear stress on the cylinder surface, N/m² - _w shear stress exerted by gas at the liquid film surface, N/m² - air relative humidity, dimensionless - T -T _w - _w =T _wT_l Dimensionless parameters I= enhancement factor of heat transfer - m ^*=M _l/M_g molar mass of liquid to the molar mass of gas ratio - Nu _g= D/ _g gas Nusselt number - Pr _g=c _{g g}/_g gas Prandtl number - Pr _l=c_lll liquid Prandtl number - ¯r=(r–R)/ dimensionless coordinate - Re _g=w_gD _g/_g gas Reynolds number - Re _g,max=w_g,max D _g/_g gas Reynolds number calculated for the maximal gas velocity between the cylinders - Sc=m ^* _g/_l–g Schmidt number =/R dimensionless film thickness     

Natural convection to water from arrays of short wall-attached cylinders

Experiments of natural convection from arrays of one, two, and three horizontal cylinders attached vertically one above the other to a heated, vertical flat plate in water have shown that the lowest cylinder is essentially unaffected by cylinders above it and has a heat transfer rate less than that of an infinitely long cylinder. The effect on the heat transfer from cylinders in the wake of the lowest cylinder is primarily a function of the spacing between the cylinders, with the increase being larger for greater spacing. For these wake cylinders, increases are sufficient to cause the heat transfer to equal that of an infinite cylinder.