Initial Rotational Energy Research Articles

Innovative inner sleeve composite bolted connections for modular steel constructions: Experimental and numerical studies

The application scenarios of modular steel constructions (MSCs) are becoming more and more extensive due to their exceptional advantages: minimum on-site work, and higher construction speed and quality. Inter-module connections are the critical components, which can significantly affect the integrity and seismic behavior of MSCs. This study proposed an innovative inner sleeve composite bolted connection which combines blind bolts, high-strength bolts and inner sleeve to improve the constructability and seismic behavior. Experimental tests on four full-scale cruciform connections composed of hollow structural steel (HSS) columns and H-section steel beams with different configurations were carried out under cyclic load. The failure modes, moment-rotation relations, initial rotational stiffness, ductility and energy dissipation were analyzed. GB 50011–2010 was used to evaluate the seismic performance and verify the applicability for the seismic design of the proposed connection, in which the lower limit of elastic inter-story drift ratio [θe] is 0.004 rad (or 1/250) and that of elasto-plastic inter-story drift ratio [θp] is 0.02 rad (or 1/50). The yield inter-story drift ratio, [θy] = 4.00–6.75[θe], and the ultimate inter-story drift ratio, [θu] = 1.00–2.00[θp] for the test specimens under cycle load, demonstrating the satisfactory deformation capacity and ductility. Furthermore, EC3 Part 1–8 was adopted to evaluate the stiffness characteristic of the proposed connection, indicating that the proposed connection can be classified as a “semi-rigid” and partial strength connection. Finally, refined numerical models calibrated against the experimental results were established and parametric evaluation was conducted based on the numerical models. The results demonstrate that the effect of the thickness of the inner sleeve and column in the panel zone and the diameter of the blind bolt and vertical high-strength bolt is insignificant. The presented research will provide useful references for further application and popularization of MSCs.

Effects of gaps on the rotational performance of traditional straight mortise-tenon joints

Gaps are very common in the mortise-tenon (M-T) joints of traditional timber structures, and they significantly reduce the rotational performance of joints. To evaluate the effect of gaps on the rotational behavior of straight M-T joints, we fabricated four 1/3.2-scaled Chinese traditional straight M-T joint specimens using Pinus sylvestris logs, one without a gap and three with different gaps, and subjected them to cyclic loading tests strictly in accordance with the international test standard ISO-16670. The failure modes, strength, initial rotational stiffness, ductility, deformation, and energy dissipation capacity of the joints were investigated. The results indicated that the apparent slippage, the tenon pulled out, and the plastic deformation for the mortise edge were exhibited in the specimens with gaps. The bending moment, initial rotational stiffness, and energy dissipation capacity of the joints with gaps gradually decreased as the damaged degree increased. The ultimate rotation of joints with gaps reached 0.2 rad, indicating a good deformation capacity. Furthermore, the gap can aggravate the degree of stiffness degradation of the M-T joint at the same rotation. Based on the experimental results, the empirical degradation formulas related to key cyclic performance parameters, considering the gap effects, were established. Based on the degradation relationships of the key hysteretic parameters of the joint with gaps, a hysteretic model for a joint with a gap was proposed and validated. Good agreement between the model predictions and experimental results was observed.

Molecular beam scattering of a diatomic molecule from a solid surface in case of strong rotational non-equilibrium

In this work, a numerical study on molecular beam scattering of a nitrogen molecule from a graphite surface has been performed. The study was carried out using the molecular dynamics method. The focus of the study is mainly placed on investigating the scattering dynamics in the case of strong rotational non-equilibrium, defined here as a state in which rotational temperature of a molecule strongly deviates from the room temperature. To that end, the incident beam velocity and initial rotational energy of nitrogen molecules have been varied greatly in order to capture a broad range of possible initial states. The obtained results provide valuable insight into the nature of energy transfer occurring during collisions and help to quantify the intensity of rotational–translational coupling between inner kinetic modes in gas–surface collisions. Consequently, the collected data can potentially be used for more accurate characterization of the respective phenomena and improve the quality of boundary models used in rarefied gas flow simulations.

Rotational collisions via inductive coupling

We analyze an example of a totally inelastic interaction between two spinning objects from a didactic perspective. We first describe an interpretative model highlighting why a part of the initial rotational energy needs to be dissipated; this point can be visualized in a diagram of capacitive characteristic curves. Subsequently, we propose and discuss a concrete novel experiment, in which an inductive coupling between two spinning objects is realized. A detailed energy analysis and an introduction to dynamical modeling complete the proposed didactical approach.

Seismic behavior and design of cruciform bolted module-to-module connection with various reinforcing details

Modular steel constructions (MSC) permits rapid and economical construction and have been increasingly used for high-rise buildings with repetitive units. A new bolted connection with welded cover plate, which can better satisfy the architectural function design, was proposed in this paper. Tests on four full-scale cruciform connections made of hollow structural section (HSS) members with various configurations were conducted under combined axial compression and increasing cyclic rotations to failure. The results showed that the moment resistance capacity of the unreinforced connections was limited due to the brittle weld fracture at the end of the beam while that of the reinforced connections was enhanced considerably, either by external cover plate or triangular-shaped stiffeners, which can guarantee the desired seismic resistance. The seismic performance, including the initial rotational stiffness, moment resistance, ductility and energy dissipation were carefully evaluated. EC3 Part 1–8 was adopted to evaluate the stiffness characteristic of the proposed connection, indicating that the proposed connection can be classified as “semi-rigid” connection. Furthermore, mechanical model was developed and design recommendations were given based on the test results, which will provide useful references for the application of the proposed connection and MSC in seismic region.

A magnetar model for the hydrogen-rich super-luminous supernova iPTF14hls

Transient surveys have recently revealed the existence of H-rich super-luminous supernovae (SLSN; e.g., iPTF14hls, OGLE-SN14-073) that are characterized by an exceptionally high time-integrated bolometric luminosity, a sustained blue optical color, and Doppler-broadened HIlines at all times. Here, I investigate the effect that a magnetar (with an initial rotational energy of 4 × 1050erg and field strength of 7 × 1013G) would have on the properties of a typical Type II supernova (SN) ejecta (mass of 13.35M⊙, kinetic energy of 1.32 × 1051erg, 0.077M⊙of56Ni) produced by the terminal explosion of an H-rich blue supergiant star. I present a non-local thermodynamic equilibrium time-dependent radiative transfer simulation of the resulting photometric and spectroscopic evolution from 1 d until 600 d after explosion. With the magnetar power, the model luminosity and brightness are enhanced, the ejecta is hotter and more ionized everywhere, and the spectrum formation region is much more extended. This magnetar-powered SN ejecta reproduces most of the observed properties of SLSN iPTF14hls, including the sustained brightness of −18 mag in theRband, the blue optical color, and the broad HIlines for 600 d. The non-extreme magnetar properties, combined with the standard Type II SN ejecta properties, offer an interesting alternative to the pair-unstable super-massive star model recently proposed, which involves a highly energetic and super-massive ejecta. Hence, such Type II SLSNe may differ from standard Type II SNe exclusively through the influence of a magnetar.

Gas-Surface Interaction Study of Oxygen Molecules on Ionomer Surface in Catalyst Layer

Proton exchange membrane fuel cells (PEMFCs) are well known as the promising energy conversion system. The high current density operation is required for the automotive use. However, as the current density increases, the cell performance drops due to the restriction of mass transport in the cell. In particular, oxygen transport in a catalyst layer (CL) of cathode side is the main cause of the power losses. In CLs, oxygen transport involves the transport in porous media and the permeation through ionomer thin film. Although many researchers have investigated the oxygen permeability through ionomer, the former effect remains unclear. In CLs, Knudsen number of oxygen flows, which is defined as the ratio of the mean free path of gas molecules to the characteristic pore size, becomes of the order of 0.1‒1. It indicates that the oxygen gas transport mechanism falls in the transition regime of the Knudsen diffusion and the molecular diffusion. In this case, the collision between a gas molecule and a surface should be taken into account for the gas transport analysis because gas molecules collide with pore walls much more frequently than with other oxygen molecules. Therefore, the gas–surface interaction between ionomer surface and oxygen molecules plays a critical role for the accurate analysis of gas transport. In previous studies, Kinefuchi et al. investigated the oxygen diffusion resistance in microporous layers (MPLs) and CLs using the direct simulation Monte Carlo (DSMC) method. They reported that the numerical simulations accurately reproduce the pressure dependence of diffusion resistance originating from the coexistence of the Knudsen and molecular diffusion mechanisms in MPLs. However, the overall oxygen diffusion resistance was underestimated in CLs. This discrepancy is attributable to the scattering model of oxygen molecules on the ionomer surface. Although the scattering model on the surface determines the gas flow in Knudsen diffusion regime, the diffuse reflection model, which is the most widely used model, is used in spite of different surface structure in MPLs and CLs. The construction of the scattering model of oxygen molecules on ionomer surface is of great importance to analyze accurately the oxygen diffusion resistance in CLs. In this study, molecular dynamics (MD) simulations have been performed for the analysis of oxygen scattering and surface diffusion phenomena on the ionomer surface. The solid surface in CLs was modeled as an ionomer film on a graphite surface. The ionomer film consists of polymer chains and solvent molecules, which are water molecules and hydronium ions. In all simulations, Nafion chain, which has the chemical structure with EW=1100, has been employed. Four polymer chains and 40 hydronium ions were placed on the graphite surface to ensure charge neutrality. The annealing process was applied in order to equilibrate the system. The initial position of oxygen molecules and the orientation to the ionomer surface were given randomly. 25 oxygen molecules were directed to the ionomer surface at the same time to obtain sufficient statistics. Trajectory calculations of oxygen molecules on the ionomer surface was carried out. The intermolecular interactions between oxygen molecules were not calculated to make the scattering phenomena of these molecules independent of each other. Oxygen molecules were given the incident temperature and incident angle as the initial condition. The incident temperature ranged every 150 K from 150 K to 600 K. The initial translational and rotational energies were determined according to the energy equipartition law. The bond length between the oxygen atoms in each molecule was fixed at the equilibrium length by the RATTLE method. The incident angle was set at 0°, 30° and 60° with respect to the surface normal. The trajectory calculations of 2000 molecules were performed until the scattered molecules moved away more than the cutoff length (12 Å) from the ionomer surface. Two different scattering processes, which are the inelastic scattering (IS) and trapping desorption (TD) processes, were observed. It was found that the translational energy of reflected oxygen molecules in the IS process depends on the incident temperature, indicating that oxygen molecules were reflected retaining the effect of the incident energy. On the other hand, the translational energy distributions of the TD process are independent of the incident temperature and different from the Maxwell–Boltzmann distribution of the surface temperature. These scattering processes depend on the incident temperature and the water content. The dependence on the incident temperature suggests that oxygen molecules are more likely to reflect directly as the incident energy increases. Moreover, the TD process is likely to occur when oxygen molecules collide with solvent molecules in the ionomer surface.

Constraints on millisecond magnetars as the engines of prompt emission in gamma-ray bursts

We examine millisecond magnetars as central engines of Gamma Ray Bursts' (GRB) prompt emission. Using the proto-magnetar wind model of Metzger et al. 2011, we estimate the temporal evolution of the magnetization and power injection at the base of the GRB jet and apply these to different prompt emission models to make predictions for the GRB energetics, spectra and lightcurves. We investigate both shock and magnetic reconnection models for the particle acceleration, as well as the effects of energy dissipation across optically thick and thin regions of the jet. The magnetization at the base of the jet, $\sigma_0$, is the main parameter driving the GRB evolution in the magnetar model and the emission is typically released for $100\lesssim \sigma_0 \lesssim 3000$. Given the rapid increase in $\sigma_0$ as the proto-magnetar cools and its neutrino-driven mass loss subsides, the GRB duration is typically limited to $\lesssim 100$ s. This low baryon loading at late times challenges magnetar models for ultra-long GRBs, though black hole models likely run into similar difficulties without substantial entrainment from the jet walls. The maximum radiated gamma-ray energy is $\lesssim 5 \times 10^{51}$erg, significantly less than the magnetar's total initial rotational energy and in strong tension with the high end of the observed GRB energy distribution. However, the gradual magnetic dissipation model (Beniamini & Giannios 2017) applied to a magnetar central engine, naturally explains several key observables of typical GRBs, including energetics, durations, stable peak energies, spectral slopes and a hard to soft evolution during the burst.

A Monte Carlo Approach to Magnetar-powered Transients. I. Hydrogen-deficient Superluminous Supernovae

Abstract In this paper we collect 19 hydrogen-deficient superluminous supernovae (SLSNe) and fit their light curves, temperature evolution, and velocity evolution based on the magnetar-powered model. To obtain the best-fitting parameters, we incorporate the Markov chain Monte Carlo approach. We get rather good fits for seven events (χ 2/dof = 0.24–0.96) and good fits for another seven events (χ 2/dof = 1.37–3.13). We find that the initial periods (P 0) and magnetic strength (B p ) of the magnetars that supposedly power these SLSNe are in the range of ∼1.2–8.3 ms and G, respectively; the inferred masses of the ejecta of these SLSNe are between 1 and , and the values of the gamma-ray opacity are between 0.01 and 0.82 cm2 g−1. We also calculate the fraction of the initial rotational energy of the magnetars harbored in the centers of the remnants of these SLSNe that is converted to the kinetic energy of the ejecta and find that the fraction is ∼19%–97% for different values of P 0 and B p , indicating that the acceleration effect cannot be neglected. Moreover, we find that the initial kinetic energies of most of these SLSNe are so small ( erg) that they can be easily explained by the neutrino-driven mechanism. These results can help clarify some important issues related to the energy-source mechanisms and explosion mechanisms and reveal the nature of SLSNe.

Seismic strengthening of weak bolted end plate connections using welded haunches

Bolted steel connections have been frequently used after Northridge earthquake. Among the concerns regarding the poor performance of weak connections is the ability to effectively and economically rehabilitate steel moment connections in existing buildings. Strengthening of these connections without the need for changing or replacing their components is a problem that has been recently considered by engineers. This study develops and experimentally validates an innovative technique for enhancing the seismic performance of steel beam to column moment connections. The use of haunch as a way to rehabilitate end plate bolted connections with weak end plate or bolts is studied constructing 6 experimental specimens of corner connections under SAC (Structural Engineers Association of California) cyclic loading protocol. The results of the study show that this strengthening method improves the cyclic behavior of the weak connections. Besides, it provides specimens with better performance than that of the reference connection designed according to AISC. The moment capacity, initial rotational stiffness and energy dissipation of the rehabilitated connections are averagely higher than those of the reference connection by 25, 10 and 12 percent respectively. Moreover, the failure potential in the connection is reduced because the plastic hinge is kept away from connection region and is transferred to the haunch end. It should be noted that this strengthening method is more efficient for cyclic behavior of a bolted connections with weak end-plate than a bolted connection with weak bolts, since the moment capacity is more increased.

ПАРАМЕТРЫ, ОПРЕДЕЛЯЮЩИЕ ОТСУТСТВИЕ ДИССИПАТИВНЫХ ПОТЕРЬ ВО ВРАЩАЮЩЕМСЯ КОЛЬЦЕ ЖИДКОСТИ

The article covers the problem of studying thermal processes in rotating by inertia in the absence of gravity capillary viscous fluid ring with free boundaries that are acted by pressure of gas medium. Thus there is no heat exchange with the environment at the boundaries of the ring. System under consideration depending on the initial angular velocity, initial radial perturbation and geometry is able to be in different move modes such as infinite expansion, collapse, periodic oscillations. In a series of numerical experiments where only one parameter that determine the character of motion changed and the rest remaining unchanged the effect of minimization dissipative losses was detected at certain critical values of the parameters (viscosity, size, pressure in the cavity). That is, a new mode of ring motion was detected; mode in which regardless of the initial radial perturbations it has minimum dissipative losses. That means that the distribution of the tangential component of the velocity vector is close to a linear function of ring radius. Such kind of dependence inherent to a rigid body motion. That distribution causes liquid layers do not move relative to each other and therefore there are no friction effects, no heat losses of the ring and no loses of initial rotational energy. Analysis of the mathematical model of the motion of liquid ring yielded analytical formulas for calculating the critical values of dynamic viscosity, surface tension, the difference of the gas pressures in the cavities of the ring, the ring sizes. Critical parameters, calculated according to the formulas and found in the course of the numerical experiment coincide with good accuracy. Received 11.12.20 16; accepted 0 2.02.20 1 7

A SUPRAMASSIVE MAGNETAR CENTRAL ENGINE FOR GRB 130603B

We show that the peculiar early optical and in particular X-ray afterglow emission of the short duration burst GRB 130603B can be explained by continuous energy injection into the blastwave from a supra-massive magnetar central engine. The observed energetics and temporal/spectral properties of the late infrared bump (i.e., the "kilonova") are also found consistent with emission from the ejecta launched during an NS-NS merger and powered by a magnetar central engine. The isotropic-equivalent kinetic energies of both the GRB blastwave and the kilonova are about $E_{\rm k}\sim 10^{51}$ erg, consistent with being powered by a near-isotropic magnetar wind. However, this relatively small value demands that most of the initial rotational energy of the magnetar $(\sim {\rm a~ few \times 10^{52}~ erg})$ is carried away by gravitational wave radiation. Our results suggest that (i) the progenitor of GRB 130603B would be a NS-NS binary system, whose merger product would be a supra-massive neutron star that lasted for about $\sim 1000$ seconds; (ii) the equation-of-state of nuclear matter would be stiff enough to allow survival of a long-lived supra-massive neutron star, so that it is promising to detect bright electromagnetic counterparts of gravitational wave triggers without short GRB associations in the upcoming Advanced LIGO/Virgo era.

Properties of young pulsar wind nebulae: TeV detectability and pulsar properties

Among dozens young pulsar wind nebulae, some have been detected in TeV \gamma-rays (TeV PWNe), while others have not (non-TeV PWNe). The TeV emission detectability is not correlated either with the spin-down power or with the characteristic age of their central pulsars, and it is an open problem what determines the detectability. To study this problem, we investigate spectral evolution of five young non-TeV PWNe, 3C58, G310.6-1.6, G292.0+1.8, G11.2-0.3 and SNR B0540-69.3. We use a spectral evolution model which has been developed to be applied to young TeV PWNe in our previous works. TeV \gamma-ray flux upper limits of non-TeV PWNe give upper or lower limits on parameters, such as the age of the PWN and the fraction of the spin-down power going to the magnetic energy injection (the fraction parameter). Combined with other independent observational and theoretical studies, we can guess a plausible value of the parameters for each object. For 3C58, we prefer the parameters with an age of 2.5 kyr old and the fraction parameter of 3.0x10^{-3}, although the spectral modeling alone does not rule out a shorter age and a higher fraction parameter. The fraction parameter of 3.0x10^{-3} is also consistent for other non-TeV PWNe and then the value is regarded as common to young PWNe including TeV PWNe. Moreover, we find that the intrinsic properties of the central pulsars are similar, 10^{48-50}erg for the initial rotational energy and 10^{42-44}erg for the magnetic energy (2x10^{12} - 3x10^{13}G for the dipole magnetic field strength at their surfaces). The TeV detectability is correlated with the total injected energy and the energy density of the interstellar radiation field around PWNe. Except for G292.0+1.8, a broken power-law injection of the particles well reproduces the broadband emission from non-TeV PWNe.

Ultrafast Librational Relaxation of H2O in Liquid Water

The ultrafast librational (hindered rotational) relaxation of a rotationally excited H2O molecule in pure liquid water is investigated by means of classical nonequilibrium molecular dynamics simulations and a power and work analysis. This analysis allows the mechanism of the energy transfer from the excited H2O to its water neighbors, which occurs on a sub-100 fs time scale, to be followed in molecular detail, i.e., to determine which water molecules receive the energy and in which degrees of freedom. It is found that the dominant energy flow is to the four hydrogen-bonded water partners in the first hydration shell, dominated by those partners' rotational motion, in a fairly symmetric fashion over the hydration shell. The minority component of the energy transfer, to these neighboring waters' translational motion, exhibits an asymmetry in energy reception between hydrogen-bond-donating and -accepting water molecules. The variation of the energy flow characteristics with rotational axis, initial rotational energy excitation magnitude, method of excitation, and temperature is discussed. Finally, the relation of the nonequilibrium results to equilibrium time correlations is investigated.

Magnetic fields during the early stages of massive star formation - II. A generalized outflow criterion

Numerical simulations of outflows formed during the collapse of 100-M⊙ cloud cores are presented. We derive a generalized criterion from magnetohydrodynamical wind theory to analyse the launching mechanism of these outflows. The criterion is successfully applied to the whole outflow structure and cases with sub-Keplerian disc rotation. It allows us to decide whether an outflow is driven centrifugally or by the toroidal magnetic pressure. We show that quantities such as the magnetic field line inclination or the ratio of the toroidal to poloidal magnetic field alone are insufficient to determine the driving mechanism of outflows. By performing 12 simulations with variable initial rotational and magnetic energies, we are able to study the influence of the initial conditions on the properties of outflows and jets around massive protostars in detail. Our simulations reveal a strong effect of the magnetic field strength on the morphology of outflows. In runs with weak fields or high rotational energies, well-collimated, fast jets are observed, whereas for strong fields poorly collimated, low-velocity outflows are found. We show that the occurrence of a fast jet is coupled to the existence of a Keplerian protostellar disc. Despite the very different morphologies, all outflows are launched from the discs by centrifugal acceleration with the toroidal magnetic field increasingly contributing to the gas acceleration further away from the discs. The poor collimation of the outflows in runs with strong magnetic fields is a consequence of the weak hoop stresses. This in turn is caused by the slow build-up of a toroidal magnetic field due to strongly sub-Keplerian disc rotation. The mass and momentum outflow rates are of the order of 10−4 M⊙ yr−1 and 10−4 M⊙ km s−1 yr−1, respectively. The mass ejection/accretion ratios scatter around a mean of 0.3 in accordance with observational and analytical results. Based on our results, we suggest an evolutionary scenario for the earliest stage of massive star formation in which initially poorly collimated outflows develop, which successively get better collimated during their evolution due to the generation of fast jets.

Coulomb reorientation in near-barrier fusion of deformed+spherical systems in classical dynamical approach

A classical rigid-body dynamics model which takes into account all the translational and the rotational degrees of freedom is developed to study Coulomb reorientation of deformed nuclei in heavy-ion collisions. Various aspects of the collision dynamics in the case of near-barrier fusion of 24Mg + 208Pb system due to the Coulomb reorientation are studied; the dependence of the extent of reorientation of the symmetry axis of the deformed nucleus, isotropy of the initial orientations, barrier parameters, and rotational excitation energy are discussed in detail. It is found that the barrier parameters not only depend on the initial orientations of the deformed nucleus but also on the collision energy; with maximum reorientation effect at near- and below-barrier energies. Even small amount of the rotational excitation energy gained by the deformed nucleus at large separation distances is crucial in determining the conditions at the barrier. Study of 154Sm + 16O and 238U + 16O systems involving heavier deformed nuclei shows that the extent of reorientation also depends on the moment of inertia of the deformed nucleus.

Magnetic fields during the early stages of massive star formation - I. Accretion and disc evolution

We present simulations of collapsing 100 M_\sun mass cores in the context of massive star formation. The effect of variable initial rotational and magnetic energies on the formation of massive stars is studied in detail. We focus on accretion rates and on the question under which conditions massive Keplerian disks can form in the very early evolutionary stage of massive protostars. For this purpose, we perform 12 simulations with different initial conditions extending over a wide range in parameter space. The equations of magnetohydrodynamics (MHD) are solved under the assumption of ideal MHD. We find that the formation of Keplerian disks in the very early stages is suppressed for a mass-to-flux ratio normalised to the critical value \mu below 10, in agreement with a series of low-mass star formation simulations. This is caused by very efficient magnetic braking resulting in a nearly instantaneous removal of angular momentum from the disk. For weak magnetic fields, corresponding to \mu > 10, large-scale, centrifugally supported disks build up with radii exceeding 100 AU. A stability analysis reveals that the disks are supported against gravitationally induced perturbations by the magnetic field and tend to form single stars rather than multiple objects. We find protostellar accretion rates of the order of a few 10^-4 M_\sun yr^-1 which, considering the large range covered by the initial conditions, vary only by a factor of ~ 3 between the different simulations. We attribute this fact to two competing effects of magnetic fields. On the one hand, magnetic braking enhances accretion by removing angular momentum from the disk thus lowering the centrifugal support against gravity. On the other hand, the combined effect of magnetic pressure and magnetic tension counteracts gravity by exerting an outward directed force on the gas in the disk thus reducing the accretion onto the protostars.

선박 디젤 엔진용 피스톤 로드의 마찰용접 공정해석 용접부 기계적 특성

The two objectives of this study were, first, to determine the optimal friction welding process parameters using finite element simulations and, second, to evaluate the mechanical properties of the friction welded zone for large piston rods in marine diesel engines. Since the diameters of the rod and its connecting part are very different, the manufacturing costs using friction welding are reduced compared to those using the forging process of a single piece. Modeling is a generally accepted method to significantly reduce the number of experimental trials needed when determining the optimal parameters. Therefore, because friction welding depends on many process parameters such as axial force, initial rotational speed and energy, amount of upset and working time, finite element simulations were performed. Then, friction welding experiments were carried out with the optimal process parameter conditions resulting from the simulations. The base material used in this investigation was AISI 4140 with a rod outer diameter of 280 mm and an inner diameter of 160 mm. In this study, various investigation methods, including microstructure characterization, hardness measurements and tensile and fatigue testing, were conducted in order to evaluate the mechanical properties of the friction welded zone.

A Molecular Dynamics Study of the Effect of the Incidence Angle on the Dissociation Probability of H2 on Pt(111)

Dissociative adsorption processes of hydrogen molecules on a platinum surface were simulated by a molecular dynamics (MD) method. The effect of the incidence angle of the impinging gas molecules on the dissociation probability was analyzed. The embedded atom method (EAM) was used to construct an interaction potential between the gas molecule and the Pt(111) surface. Initially, the effect of the motions of atoms or molecules (dynamic effects) on the dissociation probability was studied. It showed that dynamic effects on the dissociation phenomena are very large for adsorption at the top site. A number of MD simulations of H2 or D2 molecules impinging on a Pt(111) surface were also carried out, with varying initial orientations and rotational energy of the molecule, and differing collision locations on the surface. The results were averaged and the effects of the isotopic nature, incident angle, and translational energy of the adsorbate were analyzed. The results were also compared to those obtained from molecular beam experiments to check the validity of the simulations. This comparison showed that the dependences of the dissociation probability on translational energy and incident angle roughly agree with experiments.

Rotational effects in complex-forming bimolecular substitution reactions: A quantum-mechanical approach

The quantum dynamics of the complex-forming S(N)2 reaction Cl(-)+CH(3)Br-->ClCH(3)+Br(-) is studied with emphasis on rotational effects. The pseudotriatomic system Cl-Me-Br is treated with a corresponding three-dimensional (3D) potential energy surface as a function of the two scattering coordinates and the enclosed angle where the geometry of the methyl group Me is optimized at each point. The 3D space is divided into three different parts, the interaction region, an intermediate region, and the asymptotic region. In line with simple classical-mechanical arguments and previous classical trajectory calculations, initial rotational motion of CH(3)Br seemingly decreases the reaction probability. However, the dynamical inclusion of the rotational degree of freedom and the presence of the many rovibrational product states overall lead to a large increase in reactivity compared to our previous collinear study on this reaction. If the reactant is rotationally excited, the higher vibrational product states are depleted in favor of lower-lying levels. Starting the reaction with rotationless reactants may end up in significant rotational excitation in the product molecules (translation-to-rotation energy transfer). On the other hand, initial rotational energy in rotationally highly excited reactants is to a large amount converted into translational and vibrational energy. The average amount of rotational energy in the products shows a twofold vibrational excitation-independent saturation (i.e., memorylessness), with respect to both initial rotational excitation and translational energy. Since only about one-half of all reactant states end in rotationless products, the reaction probability should be increased by a factor of 2; the actually larger reactivity points to other dynamical effects that play an important role in the reaction.