Mechanical Engeering

The majority of design failures are attributed to a confluence of different stresses operating on the material both internally and outside. If the stress levels are controlled within the system's design parameters, early failure won't happen. The longevity of the material can be significantly shortened and failure may occur if the sum of the stresses exceeds the design capacity. The stress value utilized in the design of a structure or machine should be significantly less than the material's tensile strength to account for subpar material workmanship and potential overloading. Research has been done on improving the mechanical, electrical, and thermal properties of materials by reinforcing them with nano-or micro-particles. The stresses associated with overhead transmission lines are reviewed in this work in order to provide design and manufacturing guidelines for overhead power line conductors. It takes into account the pressures on the conductors as well as the forces that cause such stresses.

Sustainable polypropylene nanocomposites (PPNCs) were prepared by using melt blending of polypropylene (PP), and nanoclay (NC) in the presence of a compatibilizer, i.e. maleic anhydride grafted polypropylene (MAPP). The characterization of the composite samples was accomplished with tensile tester, x-ray diffractometer, scanning electron microscope, thermo gravimetric analyzer, and thermal conductivity instruments. The improved adhesion between the matrix and the reinforcement enhanced the physical, thermal and mechanical properties of the composites. The result describes how the sustainable product is a function of the process root, material composition and the micro structure. The study focused on the development of a sustainable light weight and low thermal conductive polypropylene nanocomposites for thermal insulation, which can be used in a sustainable environment that may include: alkalinity, fire, moisture, and thermal effects.

The exponential increase in the demand for energy has placed tremendous pressure on the power generation companies and the components used for the power supply. The efficiency of such supply is dependent on the operating parameters of the plants but at the expense of the useful life of the components. Turbine blade is one of the components that contribute immensely to such efficiency and it should be made of high-strength material with an exceptional ability to withstand the harsh operation environment. The properties of spark plasma sintering technique produced Inconel 738 low carbon (IN738LC) superalloy was used in finite element analysis software, Abaqus CAE/2017 to simulate the thermo-mechanical behaviour of steam turbine blade. The maximum thermomechanical stress and strain were developed on the root of the turbine blade (along the tailing edge) and the value of the maximum stress developed is far below the yield stress of the superalloy. Hence, spark plasma sintered Inconel 738LC is suitable for turbine blade production as such blade will survive several thermo-mechanical stress and strain cycles prior to failure.

The spark plasma sintering technique (SPS) was used to consolidate admixed elemental powder in order to fabricate NiCrCoAlTiW-Ta superalloy. Nickel which is the key element that formed the matrix powder particle size was varied in the range of 3-44, 45-106 and 106-150 μm. The effect of varying the starting powder particle size, on the formation of intermetallic phases was investigated. Also, important thermophysical properties in the development of superalloys for high temperature applications were investigated by using laser flash machine, in the range of 100-800 °C. The constituents of the microstructure for the sintered alloy includes, the gamma (γ) matrix phase (Ni), precipitated intermetallic gamma prime (γ’) phase Ni3(Al, Ti) and the precipitated solid solution strengthening elements (Cr and W). There was an increase in the density with decreasing powder particle size. Also, the averave grain size increased with increasing powder particle size. The thermophysical properties ob...

Environmental conservation and waste control have informed and encouraged the use of biodegradable polymeric materials over synthetic non-biodegradable materials. It has been recognized that nano-sized biodegradable materials possess relatively good properties as compared to conventional micron-sized materials. However, the strength characteristics of these materials are inferior to fossil-based non-biodegradable materials. In this study, biodegradable polylactide (PLA), reinforced with treated coconut husk particulates (CCP) for improved mechanical properties, was fabricated using an electrospinning process and representative volume element (RVE) technique, and some of the obtained mechanical properties were compared. It was observed that the electrospun CCP-PLA nanofibre composites show improved mechanical properties, and some of these mechanical properties using both techniques compared favourably well. The electrospun fibres demonstrate superior properties, mostly at 4 wt.% rein...

Flanges are vital component used in power generation plants for linking, closing and connecting of pipes to the boiler and turbine compartments. The linking of piping networks via this approach has limited the use of welding in the industry. High temperature, pressure and thermal transitions are presumed to influence the behaviour of bolted flange assemblies in service. Sadly, the behaviour of bolted steam pipeflange assembly under these conditions have not been sufficiently studied. Thus, the usage, maintenance and replacement of the steam pipe flanges are based on assumptions which can have detrimental consequences. In order to investigate this under-researched area, the thermo-mechanical behaviour of a bolted X20 (12Cr-1MoVNi) steam pipe-flange assembly subjected to a typical power generation plant operational condition was determined using finite element analysis code, Abaqus CAE/2019. The stress and strain distribution across the assembly were computed and the maximum stress in the assembly was developed on the low temperature, high compressive stress side of the bolt's shank while the maximum strain was developed on the interior surface of the pipe. Also, the value of the maximum stress (331.8 MPa) developed on the bolts is below the operational limiting stress of the assembly material, thus, indicating that the assembly is operating within the acceptable stress, but with the bolts being identified as the component most prone to failure.

The thermo-mechanical stress, strain and temperature distribution across the thickness of X20 steam pipe at region less susceptible to thermo-mechanical failure was simulated using finite element analysis software, Abaqus. The mesh convergence studies conducted showed that 10 mm mesh size was suitable for the simulation. The temperature distribution profile across the thickness of Pyrogel showed that pyrogel is an excellent insulation jacket for steam pipes. The maximum stress value obtained from the simulation shows that the pipe is operating below the yield strength of X20 steel at the region under study. Hence, the pipe's failure at this region due to thermo-mechanical stress or strain only is practically impossible over a long period of time. A deviation of 0.5% was found to exist between the analytical and simulated stress value obtained. This indicates a strong correlation between the simulated and analytical stress results.

The geometrical increase in the demand for electrical energy has posed serious pressure on the power generation components such as the steam pipes due to the consequential increase in the operating parameters such as temperature and pressure. This increment in operating parameters tends to limit the useful life of these pipes. Thus, high creep resistant materials such as X20 CrMoV12-1 and P91 (9Cr-1Mo) are used to manufacture steam pipes. In this paper, the creep behaviour of X20 CrMoV12-1 and P91 (9Cr-1Mo) steam piping network subjected to typical operating condition was determined via a finite element analysis code, Abaqus CAE/2017 alongside fe-safe/Turbolife software, and their results were compared. The maximum creep stress, strain rate, creep damage and worst creep life in both piping materials were developed on the intrados of the elbow, with P91 steam pipe having higher useful creep life. Furthermore, a good correlation was achieved between the result of the analytically calculated and numerically simulated creep rate at the straight section of the piping networks.

Creep behaviour of X20 (12Cr-1MoVNi) steam piping subjected to a typical operating pressure of 18 MPa and temperature of 550°C have been investigated using finite element analysis code, Abaqus and fe-safe/ Turbolife software. User subroutine script for the modified hyperbolic sine creep model used was developed in Fortran and implemented in Abaqus. The maximum creep stress and strain were developed on the intrados of the elbows in the piping network. The maximum creep stress and minimum creep rate were obtained after an hour of operation and the stress was observed to relax with increase in operational time while the creep strain increases with time. Under the specified operating conditions, the steam pipe is expected to survive a useful creep life of 15.3 and 16.9 years with corresponding maximum creep damage of 7:479 Â 10 À6 and 7:479 Â 10 À6 for machine-finished and fine machine-finished steam pipe surfaces respectively. Lastly, strong correlation exists between the numerically simulated and analytically computed creep strain rate at the straight region of the piping.

The accurate prediction of the thermomechanical properties of newly developed polymer composites is important in the determination of their possible areas of application. In this study, a 3D model of representative volume element (RVE) with different wood flour weight ratios (5, 10, 15, 20, 25 and 30 %) was used to develop wood flour polymer composites. Micromechanical material modelling software (Digimat) was used in conjunction with finite element analysis software (Abaqus) to develop the polymer composites and to determine their thermomechanical properties (modulus of elasticity, Poisson’s ratio, thermal conductivity, density, and hardness). The hardness, tensile strength and modulus of elasticity increase with an increase in the wt.% of wood flour, while the Poisson ratio, thermal conductivity and density decrease with an increase in the wt.% of wood flour. Also, the predicted thermomechanical properties using the micromechanical material modelling software (RVE) follow the same...

The introduction of computational modelling during alloy development has significantly reduced the cost of production and the prolonged time spent by researchers doing trials and errors in the laboratory. In this study, computational software (JMat Pro) was used to simulate the effect of the addition of Zr and Co, on the material properties of NiAl-Mo(Cr) alloy such as the elastic modulus, hardness, thermal conductivity, bulk modulus and specific heat capacity. A significant improvement in the mechanical properties was observed in the developed alloys as compared to those without Zr and Co. Also, the addition of as low as 0.5 at. % Zr and 1.0 at. % Co to NiAl-Cr(Mo) resulted in improved compressive strength and plasticity of the alloy.

The influences of sintering temperature on the microstructure and giant dielectric properties of a new co-doped TiO 2 system, i.e., V and Ta co-doped TiO 2 , were investigated. The grain size of (V 1/2 Ta 1/ 2) 0.01 Ti 0.99 O 2 ceramics was enlarged with increasing sintering temperature. Dense microstructure and homogeneous dispersion of dopants were achieved in the ceramics sintered at 1400e1500 C for 5 h. The dielectric permittivity in the frequency range 40e10 6 Hz of the (V 1/2 Ta 1/2) 0.01 Ti 0.99 O 2 ceramics significantly increased with the mean grain size, while the dielectric loss tangent was reduced to 0.033 at 10 2 Hz. Furthermore, the high-temperature stability of the dielectric permittivity was improved with increasing mean grain size. The electrically heterogeneous microstructure consisting of semiconducting grains and insulating grain boundaries and/or surface layers was confirmed using impedance spectroscopy. The conduction inside the semiconducting grains was attributed to electron hopping between Ti 4þ and Ti 3þ , which was confirmed by X-ray photoelectron spectroscopy. Very high resistivity with a large conduction activation energy of the insulating parts was suggested as the primary cause of the giant dielectric permittivity with low loss tangent.

Kopiereg: © 2020. Authors. Licensee: Die SuidAfrikaanse Akademie vir Wetenskap en Kuns. Hierdie werk is onder die Creative Commons Attribution License gelisensieer. Die konstruksie van oorhoofse kraglyne, en veral dié wat as “ekstra hoë spanning” gekategoriseer word, is ’n duur besigheid. Met die oprigting van torings wat die geleiers ondersteun het mobiele hyskrane ’n dominante stuk toerusting geword. Alhoewel hierdie metode relatief vinnig is, kom dit teen ’n baie hoë prys. Daarom sal alternatiewe, goedkoper konstruksiemetodes verseker baie meer aantreklik lyk vir die kontrakteurs wie verantwoordelik dit is vir sodanige konstruksie. Hierdie artikel ondersoek alternatiewe opsies om oorhoofse kraglyntorings op te rig. Klem word gelê op die gebruik van nutspale (‘gin poles’) en wen-asse (‘winches’) vir die oprigting van die tipe 520B kabelgesteunde V-toring sodat mobiele hyskrane heeltemal uitgeskakel kan word. Die werk wat hier aangebied word, stel ook voor dat ’n lugkussing as ’n o...