Temperature and stress distribution in ultrasonic metal welding—An FEA-based study

In ultrasonic welding, high frequency vibrations are combined with pressure to join two materials together quickly and securely, without producing significant amount of heat. During ultrasonic welding of sheet metal, normal and shear forces act on the parts to be welded and the weld interface. These forces are the result of ultrasonic vibrations of the tool, pressed onto the parts to be welded. In this study a model for the temperature distribution during welding and stress distribution in the horn and welded joints are presented. With the knowledge of the forces that act at the interface it is possible to control weld strength and avoid sonotrode welding (sticking of the sonotrode to the parts). The presented finite element model is capable of predicting the interface temperature and stress distribution during welding and their influences in the work piece, sonotrode and anvil. The study also included the effect of clamping forces, material thickness and coefficient of friction during heat generation at the weld interface.     

Microstructure and properties of squeeze cast Cu-carbon fibre metal matrix composite

There have been reported attempts of producing Cu based MMCs employing solid phase routes. In this work, copper was reinforced with short carbon fibres by pressure infiltration (squeeze casting) of molten metal through dry-separated carbon fibres. The resulting MMC's microstructure revealed uniform distribution of fibres with minimum amount of clustering. Hardness values are considerably higher than that for the unreinforced matrix. Addition of carbon fibres has brought in strain in the crystal lattice of the matrix, resulting in higher microhardness of MMCs and improved wear resistance. Tensile strength values of MMCs at elevated temperatures are considerably higher than that of the unreinforced matrix processed under identical conditions.     

Analysis of temperature dependence of CMOS transistors' threshold voltage

In this paper an investigation of influence of the metal-semiconductor work function difference on the threshold voltage of high-temperature (up to 473 K) operating CMOS transistors, which is often neglected in the literature, is presented. Expressions for temperature dependence of the threshold voltage of both Al-gate and Si-gate CMOS transistors, which take into account the influence of the metal-semiconductor work function difference, are derived starting from the standard expression for the MOS transistor threshold voltage. The temperature coefficient of the threshold voltage is considered in more detail, to provide a simple approximate model for the temperature dependence of the threshold voltage. It is shown that neglecting the temperature dependence of the metal-semiconductor work function difference significantly affects accuracy in prediction of the threshold voltage temperature behavior.     

Studies on High Density Polyethylene in the Far-field Region in Ultrasonic Welding of Plastics

Polyethylene (PE) is an extremely versatile plastic and has the largest sales turnover than other plastics. With new uses for PE, researchers continue to find innovative technologies to process and join the material. Ultrasonic welding is one such process that is rapidly emerging as a major joining process for thermoplastics because of its reliability, ease of operation, fastness, and economic feasibility. Amorphous polymers are ideal materials for ultrasonic welding, but semicrystalline polymers are difficult to weld in the far-field region. This paper deals with the far field welding of semicrystalline polymer/high-density polyethylene (HDPE). The temperature distribution has been modeled for varying lengths of the specimen using Ansys to predict the temperature spikes, which can be related to the performance of the joints achieved. Experimental work studied the temperature at the joint interface and the variation in tensile strength for different lengths of the specimen.     

Sustained impact of publications of C.V. Raman

C.V. Raman is being acknowledged by worldwide physics community for his classic works. The present study has made an effort to analyze how much impact in number of citation receiving for his publications. Of course, there was a lack of tools for such a study some years back. The study has limited to the database Science Citation Index for the period 1982–2005. The noteworthy results are: One third of his research papers have been cited at least once; The research papers published during 1918–1940 could make remarkable impact; Three of his papers have shown an upward growth in number of citations receiving; The total citations to papers of age 46 and 54 as on the year 1982 accounted for more than 50 per cent of the total citations received; Research works in the ‘Acoustics’ area have been cited more than any other area of his works; Eponymal citations are to be explored and analysed to understand the real impact of his works.     

Structure–property relationship of different types of polyester industrial yarns

Four major types of polyester industrial yarns (1000 Denier) which are used commercially were studied for their key structural parameters. An attempt has been made to establish a relationship between morphology and properties of these yarns. High tenacity (HT) polyester yarn has the highest birefringence, amorphous orientation, and long period but is relatively less crystalline. High shrinkage characteristic of HT polyester yarn can be accounted for its higher amorphous orientation. High modulus low shrinkage (HMLS) polyester yarn has higher crystallinity and crystal size compared to HT yarn. Fraction of tie molecules of these yarns has been calculated and found that low shrinkage (LS) and super low shrinkage (SLS) yarns have lesser tie molecules. These LS and SLS yarns are tailor-made to achieve lower shrinkage and at the same time maintaining a good level of tenacity. This is achieved with lower amorphous orientation in the final drawn yarn structure. Amorphous orientation was found to have stronger influence than any other structural parameter on the key yarn properties like modulus, tenacity, elongation, and shrinkage.     

Optimization of ultrasonic welding parameters for copper to copper joints using design of experiments

In this paper, a laser surface micromachining process planning system is presented. In this system, based on a regression model approach, the empirical coefficients, which provide the material removal rate, are automatically generated by a specific software according to the different materials that have to be processed. Numerical models generally present some limits due to the elevated calculation time requested to simulate the laser micromachining of industrial features, especially when transient solutions are considered, and, for this reason, to carry out a useful industrial tool for the evaluation of the material removal rate, the regression model represents the best solution. The presented statistical method, avoiding physical considerations, correlates the material removal rate with the process parameters in a very short calculation time. The automatic procedure for the generation of the coefficients of the regression polynomial permits to easily extend the regression model to any working material and system configuration allowing us to determine the best process parameters in a very short period of time. The results of this work have been patented.     

Organic extract mediated synthesis of stable methylammonium lead bromide nanoparticles

Journal of Materials Science: Materials in Electronics - The growth of methylammonium lead bromide (CH3NH3PbBr3) nanoparticles using ligand-assisted Re-precipitation technique expending extract...