International Journal of Mechanical and Materials Engineering最新文献

Structure and properties of welded joints of low-alloy thermomechanically processed (09G2FB) and quenched and tempered shipbuilding steels (10XN2MD, 08XN3MD, and 12XN3MF), welded with manual metal arc welding (MMA) and submerged arc welding (SAW), were studied.

Effects of specific energy input on the microstructure, mechanical properties, and impact energy of the heat-affected zone (HAZ) have been investigated, and probable reasons for crack formation in welded joints have been found.

It was found that welding heat input increase leads to a significant increase in grain size near the fusion boundary and the formation of martensite with high hardness. Therefore, the heat input is recommended to be limited to 2.5–3.5?kJ/mm for these specific steel grades.

The study indicates that microalloying elements can be used to limit the grain growth when the steel is subjected to high temperatures during welding thermal cycle. Carbon content and alloying level reduction tend to increase the steel ductility and lower the HAZ toughness.

This paper explores the impact of thermal radiation on boundary layer flow of dusty hyperbolic tangent fluid over a stretching sheet in the presence of magnetic field. The flow is generated by the action of two equal and opposite. A uniform magnetic field is imposed along the y-axis and the sheet being stretched with the velocity along the x-axis. The number density is assumed to be constant and volume fraction of dust particles is neglected. The fluid and dust particles motions are coupled only through drag and heat transfer between them.

The method of solution involves similarity transformation which reduces the partial differential equations into a non-linear ordinary differential equation. These non-linear ordinary differential equations have been solved by applying Runge-Kutta-Fehlberg forth-fifth order method (RKF45 Method) with help of shooting technique.

The velocity and temperature profile for each fluid and dust phase are aforethought to research the influence of assorted flow dominant parameters. The numerical values for skin friction coefficient and Nusselt number are maintained in Tables 3 and 4. The numerical results of a present investigation are compared with previous published results and located to be sensible agreement as shown in Tables 1 and 2.

It is scrutinized that, the temperature profile and corresponding boundary layer thickness was depressed by uplifting the Prandtl number. Further, an increase in the thermal boundary layer thickness and decrease in momentum boundary layer thickness was observed for the increasing values of the magnetic parameter.

Metal forming has played a significant role in manufacturing development, thus investigations in the field of metal forming to improve the quality of the forming process are necessary. In the present study, the experimental and numerical analysis of airfoil contour forming of 301 austenitic stainless steel is examined in order to reduce the spring reversible ability under preheat temperature.

Considering the stress-strain properties of the preheat temperature; the body forming is simulated in ABAQUS software according to the theory of increasing the blank holder force during forming.

The obtained results of the spring-back for simulating the austenitic stainless steel airfoil are compared and investigated with the manufactured experimental sample results using deep tensile forming.

By comparing the results it can be seen that the control of blank holder force during forming cause to minimize the spring-back effects.

Renewable energy resources are becoming more important to meet growing energy demands while reducing pollutants in the environment. In the current market, wind turbines are primarily restricted to rural use due to the large size, noise creation, and physical appearance. However, wind turbines possess the ability to run at any time of the day. Horizontal axis wind turbines remain the most widely used, but there is significant room for improvement in vertical axis wind turbines.

While vertical axis wind turbines are not reaching the same level of efficiency of horizontal axis wind turbines, there are significant benefits to researching improvements. One of the main benefits is to make use of vertical axis wind turbines in urban settings. In order to improve the efficiency of the vertical axis wind turbine, a biological approach was taken to design blades that mimic the shape of maple seeds and triplaris samara seeds. This approach was taken because due to its geometrical properties, typically extra lift is generated.

The results obtained through FEA simulations were consistent with the expected results for the application that was considered. The results obtained provide valuable insight for engineers to iterate and design optimum wind turbine blades taking advantage of biological phenomena applied to conventional airfoils.

The purpose of this paper is to provide structural analysis details into the design of a vertical axis wind turbine blades that mimic the geometry of maple and triplaris samaras seeds.

The present exploration deliberates the effect of nonlinear thermal radiation on double diffusive free convective boundary layer flow of a viscoelastic nanofluid over a stretching sheet. Fluid is assumed to be electrically conducting in the presence of applied magnetic field. In this model, the Brownian motion and thermophoresis are classified as the main mechanisms which are responsible for the enhancement of convection features of the nanofluid. Entire different concept of nonlinear thermal radiation is utilized in the heat transfer process.

Appropriate similarity transformations reduce the nonlinear partial differential system to ordinary differential system which is then solved numerically by using the Runge–Kutta–Fehlberg method with the help of shooting technique. Validation of the current method is proved by having compared with the preexisting results with limiting solution.

The effect of pertinent parameters on the velocity, temperature, solute concentration and nano particles concentration profiles are depicted graphically with some relevant discussion and tabulated result.

It is found that the effect of nanoparticle volume fraction and nonlinear thermal radiation stabilizes the thermal boundary layer growth. Also it was found that as the Brownian motion parameter increases, the local Nusselt number decreases, while the local friction factor coefficient and local Sherwood number increase.

In this study, a quasi-analytical solution for longitudinal fin and pin heat conduction problems is investigated.

The differential transform method, which is based on the Taylor series expansion, is adapted for the development of the solution. The proposed differential transform solution uses a set of mathematical operations to transform the heat conduction equation together with the fin profile in order to yield a closeform series of homogeneous extended surface heat diffusion equation.

The application of the proposed differential transform method solution to longitudinal fins of rectangular and triangular profiles and pins of cylindrical and conical profiles heat conduction problems showed an excellent agreement on both fin temperature and efficiencies when compared to exact results. Therefore, the proposed differential transform method can be useful for optimal design of practical extended surfaces with suitable profile for temperature response.

The gouging torch process using air carbon arc cutting (CAC) device is a standard maintenance procedure carrying out in high-tonne equipment used in the minery industry. The application of this process could locally affect the mechanical properties and the microstructure in the thermally affect zone (HAZ). The changes involve variation in the local carbon concentration and a tempering effect. In commonly used steels in the manufacture of buckets (SAE 5130) and shovel handles (ASTM 514 grade S), the processes influence negatively the work lifetime and the future maintenance works on the device.

Hardness, metallographic analysis trhough optical (OM) and scanning electron microscopy (SEM) were used to evaluate the affected zone.

An increasing carbon content up to 2 wt% C was observed in the affected area of the sample, on the slag adhered to it. Presumably, the rest of carbon is lost by evaporation during the process.

The hardness measured on the surface of the cut zone shows an increased value for ASTM A 514 grade S, which does not present a notable change for SAE 5130. However, both steels showed a tempering effect. Micro-cracks of 20 to 40 μm appear, and in a few opportunities, a larger crack was found, reaching a total length of 1480 μm.

Membranes often feature in dynamic structures. The design of such structures generally includes the evaluation of their dynamic characteristics, such as natural frequecies and mode shapes.

The quasi-statics ad dyamic responses of thin rubber sheeting were investigated through non-contact experimental techniques. The rubber sheeting was modelled as a membrane structure and the material was assumed to be hyper-elastic, isotopic and incompressible. Two hyper-elastic material models were considered, namely the Mooney-Rivlin model and the Neo-Hookean model. The natural frequencies and mode shapes of the hyprt-elastic membrane were anatically and numerically calculated by assuming small linear vibrations and an equi-bi-axial stress state in the membrane. To validate the mathematical analyses, experimental modal analysis was performed where the vibration response was measured with a laser Doppler vibrometer.

The analytical model, shows that the natural frequencies of the membrane depend on the initial stretch. Mathematical and experimental results agree well at the lower modes. However, measurement resolution is found to be a vital factor which limits the extraction of closely spaced modes due to difficulties with the accurate identification of nodal line in a purely experimental approach.

Vanadium alloy is one of the potential candidate material for structural applications in a commercial fusion reactor. Extended survival of a structural material has a direct consequence on the net energy produced in a fusion reaction, it is important to develop ultra-functional materials with tailored microstructures, to meet the harsh fusion environments. Microstructure of material, indeed depend upon the thermodynamics and kinetics of material processing.

Aiming to meet the harsh fusion conditions, we have developed oxide dispersion strengthened V-4Cr-4Ti alloys by high energy ball milling and field assisted sintering technique. Possible microstructural, morphological aftermaths observed in ball milled yttria dispersed V-4Cr-4Ti powders is explored.

Electron microscopy and laser particle analysis acknowledge that yttria addition aids powder agglomeration during ball milling. Ball milled powder was then consolidated (to a relative density of ~100%) using field assisted sintering technique, under optimal sintering conditions. Densification profile has implied that heterogeneous powder characteristic (apparent particle size and shape of powder) tends to impede the direct-current conductivity across the powder particle during various stages of field assisted sintering. In order to understand the kinetics of the field assisted sintering process on the starting powders, a new method was developed to compute the activation energy required for the direct-current conductivity across the individual powder particles. Relatively higher activation energy (for direct-current conductivity) is required for sintering yttria dispersed V-4Cr-4Ti powder than its V-4Cr-4Ti counterpart.

Quantitative dynamic sintering kinetics analysis of FAST processed vanadium alloys

One of the current problems in studying the mechanical properties and behavior of structurally inhomogeneous media with cracks is the characterization of acoustic wave propagation. This is especially important in Geomechanics and prognosis of earthquakes.

In this work, the authors propose an approach that could simplify characterization of wave propagation in medium with cracks. It is based on homogenization procedure performed at a set of equations characterizing acoustic wave propagation in media weakened by fractures under condition of external distributed loading. Such kind of loading in most cases is close to the real one in case of consideration of Geomechanics problems.

On the basis of the proposed homogenization technique, we performed characterization of elastic properties and plane acoustic waves propagation in a pre-loaded linear elastic medium weakened by a large amount of cracks. We have investigated two special cases of loading: uniaxial compression and complex compression. We have also studied how the wavespeeds depend on averaged concentration and distribution of craks.

Effective elastic properties were theoretically characterized for fractured media under external loading. The results revealed high dependency of the longitudinal wave propagation speed on the relation between stresses reasoned by an external loading.