Applied Mechanics and Materials Vols. 541-542

Abstract: The photoluminescence from III-V wide band-gap semiconductors as InGaN is characterized by localized large intensity fluctuations, known as blinking, that, despite decades of research, is not yet completely understood. In structures where there is a three-dimensional confinement, as for example semiconductors nanocrystals, the phenomena is supposed to be related to temporary quenching due to highly efficient non-radiative recombination processes (for example, Auger). Nevertheless, in typical InGaN devices, the band structure is an infinitely wide quantum well, so the understanding of the blinking phenomenon remains elusive. We present experimental data and a model that suggests that the discussed optical fluctuations are a general phenomena caused by the slow beating between THz thermal vibrations of the Quantum Well. These minuscule displacements are occurring naturally all over the device, the displacements along the growth direction induce a modulation of the matrix elements that drives the optical emission process; this have measurable effect on the device photo-luminescence. In presence of impurities or gradient of concentration, the vibrations have locally slight frequency differences on adjacent domains, this give rise to a band of beats, and we observe the lower frequency tail of this band.

Abstract: The optimization of dry sliding wear process parameters of in-situ aluminium based metal matrix composites to obtain multiple objectives to minimize wear rate, specific wear rate, co-efficient of friction and maximize wear resistance was attempted by Taguchi Grey Relational Analysis. Moreover to identify the significance of the parameters, a statistical analysis was performed using analysis of variance. Based on the analysis, the sliding speed was identified as the major contributor with 71.41% followed by percentage of reinforcement with 8.13% and other parameters load and sliding distance are found to be insignificant. The optimum parameters identified by the Grey Relational Analysis are verified through experimental confirmation test.

Abstract: The AA7075-4%TiC metal matrix composite produced through in-situ casting technique was hot extruded and subjected to annealing at 415°C for 150 minutes. Another set of hot extruded AA7075-4%TiC metal matrix composite was heat treated to T6 condition. Dry sliding wear test was conducted with different sliding speeds and loads for both annealed and T6 conditioned composites to compare their wear behaviour. It was observed that irrespective of the heat treatment conditions, the depth of wear, decreases with increasing sliding velocity for all the loads tested and increases with increasing load for all the sliding velocities.

Abstract: For enhance the heating efficiency and the formability of the magnesium alloy and aluminium matrix composite sheets, pulse current is adopted to the gas bulging and stamping processes. During the bulging process of magnesium alloy sheet, the effects of dynamic pulse current on the formed sheet combine both thermoelectricity and electro-plasticity. The effect and the applicability of the pulse current heating have been evaluated. The deformation properties, microstructure characteristics, and dislocation movement of the AZ31 alloy sheet during bulging process by the resistance heating are investigated. And the resistance heating has been adopted to improve the formability of SiC_p/2024Al composites in stamping process. The pulse current density achieved 21.7A/mm² and temperature of SiC_p/2024Al composite correspondingly reached to around 400°C in the 50s. The results showed that stainless steel inserts between sheet and copper electrodes successfully prevented the heat dissipation and promote temperature uniformity over the sheet during electrifying. In addition, workpiece formed by the pulse current deep drawing shows better shape retention, surface quality and high geometry dimensional accuracy.

Abstract: The effects of two admixtures content i.e. water reducer, cellulose ether and water-cement ratio on mechanical strength and dry density of cement-based lightweight thermal insulation board are studied. The result indicates that the water-cement ratio is the important influential factor, which is easier to get good workability. And based on the mechanical strength and dry density, the best range of water reducer content and cellulose ether content are 0.3%-0.6% and 0.4%-0.6% respectively.

Abstract: This paper proposes a more accurate springback prediction method of ageing forming for 2124 aluminum alloy. In age forming of panels, pre-bending radius, aging time and wall thickness of panels are selected as three parameters, make use of uniform design to arrange experiment and obtain springback radius using ABAQUS simulation. By means of regression analysis, the data is processed to get the influence caused by parameters on springback radius. Regression and BP neural network forecasting method are used respectively to predict springback radius and maximum prediction error is less than 31%. Combination method based on BP neural network is adopted and this method gets the satisfying prediction results that prediction error is within 5%. So conclusion can be drawn that prediction accuracy of combination method is much better than that of regression and BP neural network forecasting.

Abstract: We studied the strengthening performance of prestressed laterally bonded carbon fiber sheets (CFS) to two-span continuous beams in this paper, which included one unstrengthened beam, two non-prestressed laterally bonded CFS strengthening beams, and four prestressed laterally bonded CFS strengthening beams, and all of them were sticked with CFS on different styles on tension part of lateral beam. We discussed the stress and deformation of laterally bonded CFS strengthened continuous beams under different initial load cases and different prestressed impact, and studied the influence of initial load and prestressing to reinforcement effect. The results showed that the size of initial load and prestressing would affect the reinforcement effect of laterally bonded CFS to continuous beams; The smaller initial load, the better reinforcement effect; The reinforcement effect to continuous beams of prestressed laterally bonded CFS was better than the non-prestressed laterally bonded CFS. Corresponding to latter, the former also owned better deformation performance, less cracks number and width.

Abstract: The mechanical and thermal properties of B30/iPP, B30/sPS and sPS/iPP/B30 blends were investigated by unnotched izod impact tester, DSC and tensile strength tester. The results showed that the mechanical properties of B30/iPP, B30/sPS and sPS/iPP/B30 blends were better than that of homopolymer B30 and sPS. The blend of sPS/B30 with the ratio of 80/20, unnotched izod impact strength was 41.2 KJ/m², tensile strength 32.5 MPa. The blend of B30/iPP with the ratio of 90 to 10, the unnotched izod impact strength was 46.2 KJ/m² and the tensile strength 27.2 MPa; and the blend of sPS/iPP/B30 with the ratio of 90/10/10, the unnotched izod impact strength was 42.3 KJ/m², and the tensile strength 33.7 MPa. DSC result showed that in the blend system of B30/iPP and sPS/iPP/B30 the iPP-Tg region shifted toward the sPS-Tg. However, the sPS-Tg shifted inward slightly.

Abstract: This paper presented characterization of spray velocity and angle of spray nozzle systems for cosmetic products. Diameter and length of nozzle orifice were chosen as shape factors of the spray system. Combinations of the factors were determined by using Central Composite Design. Fluid analysis was conducted by using Fluent to obtain spray angle and velocity. RSM (Response Surface Method) was used to approximate the relationship between these 2 factors and spray characteristics. To evaluate the proposed method, experimental work with existing was conducted and good agreement between simulation and experimental results.

Abstract: The reinforced shin shell structures are widely used in many fields such as mechanical, architecture, aerospace and shipbuilding, etc. The leaf can be seen as shin plate structures with stiffener (vein) and the venation distributions are closed related to the external environment load. Leaf venation growing algorithm is the abstract description of vein growing process and reflects an ideological of learning from nature. This article concerns the mechanical analysis for thin-walled stiffened plates, which consist of static mechanical behavior and dynamic performance. Numerical method is used to analyze three types of plants: non-stiffened plate, traditional stiffened plate and stiffened plate optimized by leaf venations growth algorithm (VGA) method. The calculation results proved that the VGA stiffened plate has better mechanical performances than traditional method and illustrated the effectiveness of the bionic venations layout method for stiffened structures.