Accurate computation of design sensitivities for structures under transient dynamic loads using time marching scheme

Design sensitivities for structures under transient dynamic loads with constraints on displacements and stresses are sensitive to proper space and time discretization. Accuracy within acceptable error limit is feasible when an appropriate time increment coupled with an optimal mesh is used. In this paper, we handle this problem by systematically achieving an adaptive mesh for a reasonably fine but constant time step. Design sensitivities calculated for a good number of examples demonstrate the behaviour of this integrated approach. Comparison is made in terms of total computational time between time-marching scheme and modal superposition method in the context of design sensitivity calculation. Optimal meshes are also obtained corresponding to adaptive time stepping and accurate values of design sensitivities are computed using the optimal mesh and the values of the time increment obtained adaptively. © 1998 John Wiley & Sons, Ltd.     

Recovery of valuable metals from waste printed circuit boards using organic acids synthesised by Aspergillus niveus

Organic acids such as citric acid, itaconic acid and oxalic acid synthesised by Aspergillus niveus were used for the bioleaching of metals from waste printed circuit boards. Bioleaching of valuable metals was performed in one‐step, two‐steps and spent medium approaches using A. niveus. In the absence of waste printed circuit boards (WPCBs), the dry cell weight of A. niveus was higher when compared with the presence of WPCBs. Variations in the dry cell weight were observed for the presence of different particle sizes. The increase in itaconic acid and oxalic acid synthesis was found at a reduced particle size (60–80 mesh) and reached the maximum titre of itaconic acid (22.35 ± 0.87 mM) and oxalic acid (12.75 ± 0.54 mM) in 12 days during the two‐step bioleaching. The maximum recovery of 75.66% Zn, 73.58% Ni and 80.25% Cu from WPCBs was achieved in 15 days in two‐step leaching with particle sizes of the mesh being 60–80.     

Investigation on microstructure and tensile behaviour of stir cast LM13 aluminium alloy reinforced with copper coated short steel fibers using response surface methodology

Copper coated steel fibers reinforced LM13 aluminium alloy composites have been prepared using stir casting process. Experiments have been designed using response surface methodology by varying wt% of reinforcement (0–10), stirrer speed (350–800 rpm) and pouring temperature (700–800 °C). Microstructure, tensile strength and fracture surface of composites have been investigated. Analysis of variance, significance test and confirmation tests have been performed and regressions models have been developed to predict the tensile strength of composites. Response surface plots reveal that tensile strength of composites increases with increasing wt% of copper coated steel fibers reinforcement up to 6 wt%. Further increase in wt% of steel fibers decreases the tensile strength of composites. However tensile strength of composites increases with increasing stirrer speed due to the uniform and homogeneous dispersion of steel fibers in matrix. Optimum stir cast process parameters for obtaining higher tensile strength are found to be 5.9 wt% of reinforcement, 753 °C pouring temperature and stirrer speed of 633 rpm. Fracture mechanism is dominated by steel fiber pullouts in composites with higher wt% of reinforcement and dimples are observed in the surface of composites containing lower levels of wt% of reinforcement.     

Coupled phenomenological and fracture mechanics approach to assess the fracture behaviour of TWC piping component

The present study demonstrates the numerical prediction of experimental specimen J-R curve using Gurson-Tvergaard-Needleman phenomenologically based material model. The predicted specimen J-R curve is used to determine the geometric independent initiation fracture toughness (J_SZWc) value that compares well with experimental result. Using the experimentally determined and numerically predicted J_SZWc values and specimen J-R curves, the accuracy of predicting the fracture behaviour of the cracked component is judged. Thus the present study proposed a coupled phenomenological and fracture mechanics approach to predict the crack initiation and instability stages in cracked piping components using numerically predicted specimen J-R curve obtained from tensile specimens testing data.     

Kinetics, mechanism, isotherm and thermodynamic analysis of adsorption of cadmium ions by surface-modified Strychnos potatorum seeds

The surface-modified Strychnos potatorum seeds (SMSP) were used as an effective low-cost adsorbent for the removal of cadmium ions from aqueous solution. SMSP was characterized by Fourier transform infrared spectroscopy and scanning electron microscopic analyses. The effect of operating variables such as solution pH, adsorbent dose, contact time, initial cadmium ions concentration and temperature on the removal of cadmium ions were studied in a batch mode adsorption operation. The optimum conditions for the adsorption of cadmium ions onto the SMSP were found to be: pH of 5.0, SMSP dose of 2 g/L, contact time of 30min, temperature of 30 °C for an initial cadmium ions concentration of 100 mg/L. Kinetic data were analyzed using the pseudo-first order and pseudo-second order kinetic equations, intraparticle diffusion model, Boyd kinetic model and shrinking core model. The characteristic parameters for each model have been estimated. Adsorption of cadmium ions onto the SMSP follows the pseudo-second order kinetic model. The rate-limiting steps in the adsorption process were found to be external and internal diffusion. Equilibrium data were well described by the Langmuir isotherm model than the Freundlich isotherm model, which yields a maximum monolayer adsorption capacity of 200 mg/g. Thermodynamic parameters such as standard free energy change, enthalpy change and entropy change were also estimated. The results show that the removal of cadmium ions by the SMSP was found to be spontaneous and exothermic.     

Effect of blend proportion on moisture management characteristics of bamboo/cotton knitted fabrics

This study reports an investigation of the effect of the blend-ratio of bamboo and cotton fibres on the moisture management properties of single jersey knitted fabrics composed of them. The moisture management properties of the fabrics were measured in SDL-ATLAS moisture management tester. The liquid transport properties of textiles, such as wetting time, maximum moisture absorption rate, maximum wetted radii, spreading speeds, cumulative one-way transport capacity and overall moisture management capacity (OMMC), have been considered and correlated to the blend ratio of bamboo/cotton yarn single jersey knitted fabrics. It was observed that as the bamboo content increased, the wetting time decreased, maximum wetted radius decreased, rate of absorption increased, spreading speed decreased and OMMC decreased.     

Influence of blend ratio and linear density on liquid spreading characteristics of bamboo/cotton-blended yarn knitted fabrics measured by liquid spread tester

In this study, a new liquid spread tester, designed and developed in an earlier work by the authors, has been used for the study and analysis of the transverse wicking characteristics of single jersey-knitted fabric produced from bamboo/cotton-blended yarn. The most significant liquid spreading characteristic, namely the liquid spreading rate, has been measured and analysed for two sets of the knitted fabric composed of bamboo/cotton yarn, one of linear density Ne 20s and the other of Ne 40s yarn. The yarn blend composition was varied in a similar manner for both sets of fabric. It was observed that liquid spreading rate decreased with increase in bamboo content for all the blend proportions investigated. It was also found that this property is higher in the wale-way direction than the course-way direction.     

Room temperature amorphous to nanocrystalline transformation in ultra-thin films under tensile stress: an in situ TEM study

The amorphous to crystalline phase transformation process is typically known to take place at very high temperatures and facilitated by very high compressive stresses. In this study, we demonstrate crystallization of amorphous ultra-thin platinum films at room temperature under tensile stresses. Using a micro-electro-mechanical device, we applied up to 3% uniaxial tensile strain in 3-5 nm thick focused ion beam deposited platinum films supported by another 3-5 nm thick amorphous carbon film. The experiments were performed in situ inside a transmission electron microscope to acquire the bright field and selected area diffraction patterns. The platinum films were observed to crystallize irreversibly from an amorphous phase to face-centered cubic nanocrystals with average grain size of about 10 nm. Measurement of crystal spacing from electron diffraction patterns confirms large tensile residual stress in the platinum specimens. We propose that addition of the externally applied stress provides the activation energy needed to nucleate crystallization, while subsequent grain growth takes place through enhanced atomic and vacancy diffusion as an energetically favorable route towards stress relaxation at the nanoscale.     

Metal hydride batteries research using nanostructured additives

We describe here, our recent research efforts to improve the capacity of metal hydride batteries using nanostructured additives. Nanostructured additives of palladium, copper and nickel were incorporated separately into the negative electrode of the metal hydride batteries. The nanomaterials were synthesized by template-based methods and characterized by scanning electron microscopy. These nanomaterials were incorporated in the negative electrode of the metal hydride battery and the electrochemical performance at 2 C rate was studied. The nanomaterial-incorporated negative electrodes all showed increased cell voltage and negative electrode potential compared to that of a pristine cell. The increase in discharge capacity for a cut-off voltage of 1 V depends on the nanomaterial incorporated and a comparative analysis of the performance of the different batteries is presented.