Influence of the modes of operation and structural factors on the crack propagation in 12Cr–2Ni–Mo steel

We study the influence of temperature, specimen sizes, loading frequency, and the time of holding under long-term static loading on the crack growth rate in 12Cr–2Ni–Mo steel. It is shown that the influence of these factors on the crack growth rate is insignificant. A numerical-experimental model is proposed for the evaluation of the time of subcritical crack growth with regard for the duration and cyclic character of loading. Translated from Problemy Prochnosti, No. 3, pp. 66–77, May–June, 2009.     

Modeling and Optimization of Properties of Domestic Mullite–Corundum Composites

High Temperature - Mathematical modeling of spectral-kinetic, thermal, and electrophysical characteristics, which are difficult to determine experimentally, has been carried out based on the...     

Modeling the response of polymer–ionic liquid electromechanical actuators

A model is derived for the electromechanical response of a porous membrane swollen with an ionic liquid and sandwiched between two nanoscale-thin electrodes under DC current. Bending of the membrane is induced by pressure in pores arising due to diffusion of ions through a network of nanochannels. Transport of ions is governed by the applied electric field and redox reactions at the surfaces of electrodes. Constitutive equations for the mechanical response of a porous medium and diffusion of ions are derived by means of the free energy imbalance inequality under an arbitrary deformation with finite strains. Under the assumption regarding small strains, but finite changes in concentrations of ions and the electrostatic potential, an explicit expression is developed for the curvature of the membrane. A steady-state solution to the Poisson–Nernst–Planck equations is obtained by means of the method of matched asymptotic expansions. Results of numerical analysis demonstrate the ability of the constitutive equations to describe observations. In particular, the model provides an explanation for bending to the anode and to the cathode and predicts qualitatively the effects of applied voltage, concentration of ionic liquid, and thickness of a membrane on its curvature.     

Effect of mendable polymer stitch density on the toughening and healing of delamination cracks in carbon–epoxy laminates

This paper presents an investigation into the effect of stitch density on the delamination toughening and self-healing properties of carbon–epoxy laminates. The stitches provide the laminate with the synergistic combination of high mode I interlaminar fracture toughness to resist delamination cracking and healing properties to repair delamination damage. The results show that the fracture toughness of the laminate increased with stitch density, due to higher traction (crack closure) loads exerted by the stitches bridging the delamination. During the healing process these bridging stitches first melt and then flow into the delamination, leading to self-healing with full restoration of the mode I fracture toughness. Furthermore, the stitches were capable of repairing delamination cracks many times larger than the original size of the stitches. The effect of stitch density on the healing process of delamination cracks and restoration of fracture toughness was found to remain approximately the same under multiple repair operations.     

Contribution to the Improvement of the MADS–MOSAR Method for the Modeling of Domino Effects

In the literature, many studies have outlined the main existing methods and software tools used for the study and analysis of domino effects. One of these is the MADS–MOSAR model, which provides a schematic representation of the process of domino effects in the form of black boxes. The exploitation of these boxes for the deduction of short and long scenarios is based on the experience of the users of this model. Hence, the difficulty encountered by some practitioners of the model MADS–MOSAR not experienced for the modeling of domino effects. To overcome this difficulty, this paper presents a modeling of black boxes of the MADS–MOSAR model in the form of networks which allow a better exploration of the “Source-Flow-Target” triptych that intervene in the process of domino effects.     

Modeling the concentration profiles of aluminum and indium impurities in crystals of germanium–silicon solid solutions

A one-dimensional problem of the axial distribution of Al and In impurities in uniform crystals of Ge–Si solid solutions grown by double feeding of the melt method has been solved in the Pfann approximation. The mathematical modeling results suggest that the impurity concentration profile in Ge–Si crystals of constant composition can be varied in a wide range through appropriate changes in the relationship between the crystal growth rate and the rates of feeding the melt using germanium and silicon rods. We demonstrate the possibility of growing completely homogeneous Ge–Si kAl,Inl crystals, in terms of both the concentrations of their major components and the impurity concentration profile.     

Modeling thermal and stress behavior of the fuel–clad interface in monolithic fuel mini-plates

A fuel development and qualification program is in process with the objective of qualifying very high density monolithic low enriched uranium–molybdenum fuel for high-performance research reactors. The monolithic fuel foil creates differences in the mechanical and structural characteristics of the fuel plate because of the planar interface created by the fuel foil and cladding. An initial finite element analysis model has been developed to investigate worst-case scenarios for the basic monolithic fuel plate structure using typical mini-plate irradiation conditions in the Advanced Test Reactor. Initial analysis shows that the stress normal to the fuel–clad interface dominates during irradiation and that the presence of small, rounded delaminations at the interface is not of great concern. However, larger and/or fuel–clad delaminations with sharp corners can create areas of concern, as maximum principal cladding stress, strain, displacement, and peak fuel temperature are all significantly increased. Furthermore, stresses resulting from temperature gradients that cause the plate to bow or buckle in an unconstrained fuel plate configuration is greatly enhanced in a constrained fuel plate configuration. The sensitivities of the model and input parameters are discussed, along with some overlap of initial experimental observations using as-fabricated plate characterization and post-irradiation examination.     

Thermodynamic Modeling of Phase Equilibria in the U–Zr–N System

Inorganic Materials - A thermodynamic model is proposed for condensed phases in the ternary system U–Zr–N in the range 298–2800 K. The model is based on previously reported models...     

Thermodynamic Modeling of Mechanical Alloying in the Fe–Sn System

X-ray diffraction analysis and thermodynamic calculations in the Miedema model are used to study the sequence of solid-state reactions during mechanical alloying in the Fe–Sn system. The results indicate that the formation of FeSn₂ in the initial stages of the process is a quasi-equilibrium process reducing the volume contribution to the free energy. A simple model, considering a random distribution of particles, is used to obtain an expression for the total free energy, comprising the volume and interface contributions, as a function of particle size. It is shown that the formation of a supersaturated solid solution is thermodynamically possible over a wide composition range if the particle size is reduced to a few nanometers and surface Sn segregation occurs. The limit of the supersaturated solid solution obtained by mechanical alloying is determined by the relationship between the limit of size reduction and the particle size which ensures stabilization of the solid solution. In the Fe–Sn system, the limit of the supersaturated fcc solid solution is found to be 20 at. % Sn.     

Modeling the solar absorption performance of Copper@Carbon core–shell nanoparticles

Journal of Materials Science - The working fluid is a critical component in direct absorption solar collectors. Nanoparticle (NP) suspensions can be used as efficient solar absorption media. In...     

Role of microstructure on initiation and propagation of fatigue cracks in precipitate strengthened Cu–Ni–Si alloy

Fatigue tests were conducted on round-bar specimens to understand the fatigue behavior of precipitate-strengthened Cu–6Ni–1.5Si alloy. Aging at 500 °C for 0.5 h produced δ-Ni₂Si precipitates in the matrix, homogeneously and heterogeneously precipitated δ-Ni₂Si particles, and a precipitate-free zone around the grain boundaries. The cracks were initiated at the grain boundaries, followed by growth along the crystallographic slip planes in the adjacent grains. Crack propagation from the crack origin along the grain boundaries was occasionally observed. The physical background of fatigue damage is discussed in light of the role of microstructure on the behavior of fatigue cracks.     

Modeling and Simulation of the Microstructure Evolution of the Gas-atomized Alloy Droplets during Spray Forming

In order to understand the solidification process of an atomized droplet and predict the fraction solidification of droplets with flight distance during spray forming, a numerical model based on thepopulation dynamics approach is developed to describe the microstructure evolution under the common action of the nucleation and growth of grains.The model is coupled with droplets heat transfer controlling equations and solved for Al-4.5 wt pct Cu alloy. It is demonstrated that the numerical results describe the solidification process well.     

Modeling the Process of Liquid Flow in the System “Formation–Pipeline”

Journal of Engineering Physics and Thermophysics - A model of the process of nonstationary motion of a liquid in the conjugate system “formation–pipeline” has been constructed,...     

Modeling of the solid–liquid bubble interface in partial nucleate boiling

Several models of heat transfer in partial nucleate boiling are identified in order to determine the relationship between the dominant physical parameters. The correlations are different for different models, so the main goal of this analysis is to determine the validity of each model and to identify the most dominant physical phenomenon in the nucleate boiling heat transfer. This is done by comparing the results of different models with a vast range of reliable experimental data. The comparison shows that the Sakashita and Kumada model gives the best results in the nucleate boiling heat transfer. It is also shown that the most dominating phenomenon in isolated partial bubbles zones is the transient conduction taking place mainly under the bubbles. This is in contradiction with a majority of the models that consider convection as the most important mode in the nucleate boiling heat transfer. The selected model can also be extrapolated and used in the case of fully developed bubbles zones.     

Modeling and Investigation of Nonstationary Pressure and Temperature Fields in a Deformable Formation During the Filtration of a Gas–Condensate Mixture

Journal of Engineering Physics and Thermophysics - A procedure and an algorithm have been proposed that allow modeling the problem of identification of parameters of a deformable formation during...     

Modeling the response of physical and mechanical properties of Cr–Mo prealloyed sintered steels to key manufacturing parameters

In this study an experimental investigation using response surface methodology has been undertaken in order to model and evaluate the physical and mechanical properties of Cr–Mo prealloyed sintered steels with respect to the variation of powder metallurgy process parameters such as compacting pressure, sintering temperature and Cr content of the prealloyed steel powder. Mathematical models were developed at 95% confidence level to predict the physical properties such as sintered density and electrical resistivity and mechanical properties such as transverse rupture strength, apparent (=macro-)hardness, and impact energy. Analysis of variance was used to validate the adequacy of the developed models. The obtained mathematical models are useful not only for predicting the physical and mechanical properties with higher accuracy but also for selecting optimum manufacturing parameters to achieve the desired properties.     

Modeling of initial crystallization in the alloys Al–10Ni and Al–5Ni–2.7Y at high undercoolings

Formation and growth of crystallization centers of aluminum in amorphous alloys Al–10Ni and Al–5Ni–2.7Y have been studied by a method of the molecular dynamics. Local radial pair distribution functions were calculated for studying of structure. Growth kinetics of the comparatively large aluminum crystals in the binary system is studied. Latencies of appearance of the first crystallization centre are found. The energies of interatomic interaction averaged locally and also in the bulk of the amorphous phase are determined. It is researched how the size of the crystallization centre influences its structure and the local interaction energy. Formation of icosahedrons and their lifetimes are in consideration.