جستجوی مقالات مرتبط با کلیدواژه « Mechanical properties » در نشریات گروه « برق »

The mechanical stir casting effect on Al7075 based lightweight alloy established with Al2O3 and SiC has been studied with varied stirrer time and speed. Hybrid metal matrix improved wear resistance of composite material Al7075 (SiC+Al2O3). Experimental designs are formulated using Taguchi’s DoE. Considered 4 level 4 parameters, L16 OA is selected. Grey Relational Analysis (GRA) and Principle component analysis (PCA) coupled has been employed to calculate matrix composition. POD test (Pin-on-Disc) was used to measure the wear resistance of the casted pins. Further, mechanical characterization tests like tensile, hardness, impact, density and porosity were also accomplished. Optimum parameters are found, SiC of 6%, Al2O3 of 4%, Stirrer time of 15 min and stirrer speed of 600rpm, which gives low wear loss of 0.0034g, superior micro hardness 154.22 BHN, the tensile strength of 443.61 Mpa and Impact energy is 3J. From the ANOVA results, Stirrer speed is the most influential parameter with 49.40%. SEM-EDX analysis characterized the worn surfaces.

Miniaturization of bulk crystals in any direction down to nanometer dimensions leads to the emergence of quantum confinement phenomenon, which is technologically favorable. Transition Metal Dichalcogenides (TMDs) are important mechanical materials that have a layered structure. In addition, ach layer consists of three atomic layers. TMD Nano Tubes (TMDNTs) can be created by rolling such a layer. This study investigates structural, mechanical, and bonding properties of TMDNTs. In particular, two important quantities, Young’s modulus and Poisson’s ratio, are calculated for 6 zigzag MX2 (M=Zr, Hf; X=S, Se, Te) nanotubes and the results are compared with those of other known nanotubes. The computed value of Young’s modulus is greater than that of blue Phosphorus and, in some cases, higher than those of WS2 nanotubes (which are experimentally synthesized). Given the increase in the bond length between M and X atoms, the ratio of Young’s modulus to Poisson’s increases as the atomic number X is reduced. However, there is no significant difference in the aforementioned quantity for ZrX2 and HfX2 nanotubes due to the close bond lengths of Zr-X and Hf-X. The band gap confirms this finding. A Mulliken charge analysis was conducted to investigate the amount of charge transfer between M and X atoms to observe the strength of bond lengths.

Nowadays, the use of lattice structure designs in metallic parts to produce lightweight systems has gained importance owing to advances in additive manufacturing technology. On the other hand, vehicle manufacturers are constantly looking for new ways to reduce weight due to the depletion of fossil fuels, the demand for vehicles having higher performance, global warming and increasingly stringent emission standards. In this study, in order to reduce the weight of the internal combustion engine, different lattice designs were made in the connecting rods. Four different 2.5D lattice designs, hexagonal, octagonal, square and triangular, were created in reference connecting rod body. The dimension of the lattice designs was 10x10x12 mm with the wall thickness of 1.5 mm. The fatigue behaviors of the connecting rods as well as mechanical properties under static conditions were analyzed using finite element approach. Three different materials were used in the analyzes: AISI 4140, Inconel 718 and Ti6Al4V. As a result, it was seen that weight reduction of up to 15.75% was possible in the connecting rod thanks to the lattice designs and the maximum stresses were below the yield stresses of the materials. Moreover, connecting rods with lattice design had satisfactory safety factor values.

In this study, Mg-Sn alloys were produced through the powder metallurgy (P/M) method by adding Sn in different ratios into Mg powder. A new mixing technique has been used in production to prevent the disadvantages of high reactivity that the Mg powders have. The prepared powder mixtures were turned into components by processing through hot pressing. The produced components were characterized by density measurements, microstructure examinations and mechanical tests. The density measurements were made according to the Archimedes principle. The microstructural characterization was performed by X-ray diffraction (XRD) analysis, scanning electron microscope (SEM) investigations and energy dispersive spectrometry (EDS) analyses. The hardness measurements and the tensile tests were used for the determination of mechanical properties. Densities close to the theoretical density were obtained in the produced parts. XRD and SEM investigations have shown that the components produced are composed of α-Mg and Mg2Sn phases of the microstructure consisting of coaxial grains. The rising Sn content increased the amount of discrete Mg2Sn precipitates at the grain boundaries, thereby ensuring higher hardness and strength values.

This study aims to examine how friction stir welding parameters, such as welding speed and rotational rate, affect the microstructure, defects, and mechanical properties of AA7075-T651 aluminum alloy joints. It also assesses the relation of the defects and microstructure to the mechanical properties. Microstructural investigations using optical microscopy (OM) and scanning electron microscopy (SEM) indicated remarkable grain structure variations among the different welding zones. Especially, it was found out that the interface between welding nugget zone (WNZ) and thermo-mechanically affected zone (TMAZ) is a dominant determinant of the mechanical properties of joints. The importance of the interface comes from the fact that it is the most prone region to cracks, micro-cavities and tunneling defects. WNZ and TMAZ interfaces as well as their grain structures can be influenced by the heat generated from the friction between rotating tool and workpiece material. Therefore, coarser grain structures observed at the WNZ-TMAZ interfaces of the samples welded at higher rotational rates or lower welding speeds is due to the greater heat generated in such cases. Besides, microstructural variations in the weld zone affect the hardness and mechanical properties of weld joints. Thus, samples with coarse-grained structures display lower values of yield stress and microhardness.

Oil and its derivatives such as gasoline, motor oil and gasoil are using in various industrial and non-industrial sectors as the main energy sources all over the world. However, within the process of exploration, transportation and storage they may spill or leaking into the soil. Among them the gasoil which is more widely used in different parts and machineries has the largest contribution in contaminating lands. Purgation of these areas is not always feasible or possible. Instead, they can be used in many engineering practices if the level of contamination is not high. In such cases knowing the geotechnical properties of these areas are of great necessity and importance. In this study, extensive laboratory tests were performed on remolded clayey samples mixed with gasoil to evaluate their geotechnical properties. The Response Surface Methodology (RSM) was used to analyze the data and find behavioral equations. According to testing results and RSM outputs a decrease in Atterberg limits, and increase in maximum dry density happen by increasing contamination. Also their shear strength parameters (c and f) both exhibit a turning change point at 8% gasoil content, while their variations trends are quite in opposite directions

The environmental effects of production of Portland cement (PC) have provoked to examine the growth of concrete with 100% replacement of cement with industrial byproducts containing high amount of Si and Al, which are activated by alkali solutions termed as geopolymer concrete. Concrete made with PC can be durable under mild exposure condition when properly designed whereas undergo deterioration under severe exposure condition. Since very few works have been performed on the ambient cured alkali activated slag concrete (AASC) under aggressive environmental condition, this work was intended to study the effect of binder content and sodium hydroxide concentration on AASC subjected to aggressive environment. In this regard, an experimental investigation was carried out to study the influence of AASC under chloride, acid and sulphate environment on its physical and mechanical properties. The results infer that the AASC mixes perform well under aggressive environment condition.

The microstructure formation and mechanical properties of coiled tube CT80 grade steel was investigated with different heat treatments. Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) were used to evaluate the microstructure. Acicular ferrite, polygonal and quasi-polygonal ferrite, granular bainite, martensite, pearlite, and small Martensite-Austenite (MA) islands with the banding structure were revealed in original and heat treated samples. In order to assess the effect of grain size and microstructure, mechanical properties were evaluated by hardness, charpy impact, tensile, and fatigue life tests. The best mechanical properties by tensile and fatigue test is obtained from the normalized specimen with the grain size of ASTM 13.

SU8 is an epoxy-Novolac resin, which is used as photo initiator in micro- and nano- fabrication techniques. From literature, graphene has been proved that results in significant improvement in the properties of the composites. However, due to nanometer size of the graphene layers there is no any experimental tool to obtain insight of the fillers inside the resin especially when the materials are under mechanical deformations where simulation techniques work well. Therefore, SU8 and SU8-graphene nanocomposites as the model compounds were taken to be investigated from atomistic molecular dynamic approach to demonstrate the effect of graphene layers. This leads to mechanical property enhancement such as Young’s, bulk and shear modules being affected by the aspect ratio of the graphene layers high aspect ratio graphene in SU8 leads to an 81% improvement in Young’s, 100% in bulk and 83% in shear moduli in addition to higher density and less graphene wrinkling.

Monolithic titanium, Ti–1 wt% B4C, Ti–2.5 wt% TiB2 were spark plasma sintered at 1050 ºC for 5 min under 50 MPa. The effect of B4C and TiB2 additions on densification process, microstructural development and mechanical properties of titanium was investigated. The results revealed that relative density of undoped, B4C- and TiB2-doped Ti samples reached ~98-99%. X-ray diffraction patterns, thermodynamic assessments, and microstructural investigations verified the in-situ formation of TiB whiskers in both composite samples as well as appearance of TiC spheres in Ti–B4C composite. However, trace unreacted TiB2 and B4C additives were remained in the composites as a result of incomplete chemical reactions due to short-time SPS process. Compared to undoped Ti sample, grain growth was hindered when the sample was doped by B4C or TiB2. Elongation, ultimate tensile strength and Vickers hardness of B4C- or TiB2-doped samples were higher than those of monolithic titanium but bending strength of ceramic-doped samples significantly lower, compared to undoped titanium. These outcomes were discussed in detail and related to presence/formation of several ceramic phases with different morphologies in Ti matrix.

Particle size effects in metal matrix composites are studied within the continuum theory of mechanism-based strain gradient (CMSG) plasticity. This theory has been quite successful in predicting the size dependent plastic behavior in a wide variety of problems. Two-dimensional (plane-strain) analyses which are carried out on the composite unit cell models with multi-particles of circular shape show that the flow stress of the composites increases by decreasing particle size with a high sensitivity to small particle size. The numerical results are in good agreement with experimental data. Subsequently, the effects of particle shape, orientation and size distribution on the behavior of composites are investigated. Analyses are carried out on the composites containing squared, rectangular and elliptical (with aspect ratio of four) particles of various orientations with respect to the loading direction (i.e. vertical, horizontal and 45 degree inclined directions). The stress inhomogeneity in the matrix, the overall stress-strain curve and the maximum principle stress in the particles of composites with non-circular particles are investigated and compared with those obtained for the composites containing circular particles. The effects of particle size distribution on the behavior of composites are also addressed.

In this study, workability and mechanical properties of fiber reinforced self-compacting lightweight concretes (FRSCLC) were investigated. Concrete samples were produced with steel fiber include low and high carbon were added. Fluidity of FRSCLC has been conducted by two categories of flow ability property and viscosity of fresh concrete. Mechanical performance of the concrete mixes was determined with short and long-term tests, which include compressive and flexural strength at 3, 7, 28 and 365 days. The test results showed that adding fibers to self-compacting lightweight concrete mixtures decreased workability. On the other hand, compressive strength was lower enhanced compare to the results of flexural strength. As a result, compressive and flexure strengths of SCLWC’s increased up to 30% and 43% adding fiber at 28 days, respectively.

Silica fume as new supplementary cements have several effects on initial mechanical characteristics and long term improvement. In this paper, the impact resistance and mechanical properties of concrete mixed with silica fume are statistically investigated with selecting 288 specimens in three mix designs. Zero,7% and 14% of Portland cement by weight was replaced by silica fume in silica-fume mixtures. Twenty 100×100×100mm cubic specimens, twenty100×200mm cylindrical specimens, twenty 60×80×320mm specimens and thirty-six 150×64-mm discs were cast from each batch to prepare specimens for different test purposes. Cubic and cylindrical specimens were used to determine the compressive strength and prismatic specimens were tested to obtain rupturing tensile. Also, cylindrical cutting specimens were subjected to the drop-weight test following the ACI committee 544 to determine impact strength of mixed concretes. Experimental data on the mechanical properties of the different mixes indicated that silica fume improves mechanical properties and impact resistance while statistical analysis done based on these experimental tests showed the reduction the coefficient of variation values. In other words, adding silica fume improves statistical dispersion of data.

Renewable resources such as natural fillers in reinforced materials with their new range of applications represent an important basis of fulfilling the ecological objective of creating environmental friendly materials. Study on composites using breadfruit seed hull ash particles (BFSHAp) as a reinforcing material and recycled low-density polyethylene (RLDPE) as a novel matrix has been made. The composites were produced by varying the breadfruit seed hull ash particles from 5-25wt% and the properties studied using mechanical tests and microstructural analysis. The results show that there was a uniform distribution of the breadfruit seed hull ash particles in the microstructure of RLDPE composites which is the major factor responsible for the improvement in the mechanical properties.

A comparison between the elastic modulus of carbon nanotube (CNT) polymer nano composites predicted by classical micromechanics theories, based on continuum mechanics and experimental data, was made and the results revealed a great di erence. To improve the accuracy of these models, a new two-step semi-analytical method was developed, which allowed consideration of the e ect of the interphase, in addition to CNT and matrix, in the modeling of nanocomposites. Based on this developed method, the in fluence of microstructural parameters, such as CNT volume fraction, CNT aspect ratio, partial and complete agglomerations of CNTs, and overlap and exfoliation of CNTs, on the overall elastic modulus of nanocomposites was investigated.