Formation kinetics of austenite in pearlitic ductile iron

This work evaluated the isothermal transformation of austenite in unalloyed pearlitic ductile iron and drew the isothermal phase diagram of austenitization in the ductile iron. Austenite forms at grain boundaries and then grows up to graphite regions during austenitiza-tion. The formation kinetics of austenite complies with the Avrami equation, in which the parameter (n) ranges from 4.71 to 4.99. The start time and finish time of transformation can be calculated at each temperature using the Avrami equation.     

Intelligent Cooperative Control Architecture: A Framework for Performance Improvement Using Safe Learning

Planning for multi-agent systems such as task assignment for teams of limited-fuel unmanned aerial vehicles (UAVs) is challenging due to uncertainties in the assumed models and the very large size of the planning space. Researchers have developed fast cooperative planners based on simple models (e.g., linear and deterministic dynamics), yet inaccuracies in assumed models will impact the resulting performance. Learning techniques are capable of adapting the model and providing better policies asymptotically compared to cooperative planners, yet they often violate the safety conditions of the system due to their exploratory nature. Moreover they frequently require an impractically large number of interactions to perform well. This paper introduces the intelligent Cooperative Control Architecture (iCCA) as a framework for combining cooperative planners and reinforcement learning techniques. iCCA improves the policy of the cooperative planner, while reduces the risk and sample complexity of the learner. Empirical results in gridworld and task assignment for fuel-limited UAV domains with problem sizes up to 9 billion state-action pairs verify the advantage of iCCA over pure learning and planning strategies.     

Biocompatible/bioabsorbable silver nanocomposite coatings

A novel biomass‐mediated method to synthesize cellulose‐stabilized silver nanoparticles (SNPs) and incorporate them into biocompatible/bioabsorbable poly‐L ‐lactic acid (PLLA) for producing SNP–PLLA nanocomposite thin films was developed and the antimicrobial efficacy and biocompatibility of the SNP–PLLA films were studied. The formation and coating morphology of SNPs were characterized with UV–visible spectrophotometry and transmission electron microscopy (TEM), and the release rate of silver ion from the SNP–PLLA films was determined by inductively coupled plasma‐optical emission spectrometry. Antimicrobial testing of the SNP–PLLA films performed with Staphylococcus aureus and Escherichia coli according to ISO 22196 standards demonstrated that the SNP–PLLA nanocomposite films with a SNP concentration of 700 ppm reduced colonies forming unit (CFU) counts by 99.8 and 99.99%, respectively. Despite the significant antimicrobial activity, the nanocomposite films with the same SNP concentration had little effect on the viability of human HeLa cells. This strategy that has been developed for the synthesis of nanoparticles and the formation of composite films demonstrates promise for reducing perioperative surgical site infections associated with indwelling devices. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

A new methodology for identifying location errors in 5-axis machine tools using a single ballbar set-up

Ballbar testing of rotary axes in 5-axis machine tools can be time-consuming and requires high levels of operator expertise; especially in the set-up process. Faster tests reduce down-time and encourage frequent updates to compensation parameters to reflect the current state of the machine. A virtual machine tool (VMT) is developed to emulate the machine tool, its geometric errors and the testing procedures. This was used to develop a new single set-up testing method to identify all rotary axis locations errors, whilst remaining robust in the presence of set-up error and linear axis squareness errors. New testing and data processing techniques remove the requirement for fine-adjustment of the tool-cup and permit full automation of necessary toolpaths, including transitions. Using the VMT, error identification residuals were found to be 2.7 % or less. Experiments and statistical analysis then showed that all errors can be measured using a single set-up, and values are sufficiently close to the values measured using conventional multi-set-up procedures to be used in error compensation. This method will significantly reduce set-up durations and removes the need for any modified testing hardware.     

Comparative investigation on using cryogenic machining in CNC milling of Ti-6Al-4V titanium alloy

Ti-6Al-4V titanium alloy is one of the most important materials in industry, 80% of which is used in aerospace industry. Titanium alloys are also notoriously difficult-to-machine materials owing to their unique material properties imposing a major bottleneck in manufacturing systems. Cryogenic cooling has been acknowledged as an alternative technique in machining to improve the machinability of different materials. Although milling is considered to be the major machining operation for the manufacture of titanium components in aerospace industries, studies in cryogenic machining of titanium alloys are predominantly concentrated on turning operations. To address this gap, this article provides an investigation on the viability of cryogenic cooling in CNC end-milling of aerospace-grade Ti-6Al-4V alloy using liquid nitrogen in comparison with traditional machining environments. A series of machining experiments were conducted and surface roughness, tool life, power consumption, and specific machining energy were investigated for cryogenic milling as opposed to conventional dry and flood cooling. Analysis revealed that cryogenic machining using liquid nitrogen has the potential to significantly improve the machinability of Ti-6Al-4V alloy in CNC end-milling using solid carbide cutting tools and result in a paradigm shift in machining of titanium products. The analysis demonstrated that cryogenic cooling has resulted in almost three times increased tool life and the surface roughness was reduced by 40% in comparison with flood cooling.     

Semi-analytical approach for free vibration analysis of cracked beams resting on two-parameter elastic foundation with elastically restrained ends

In present study, free vibration of cracked beams resting on two-parameter elastic foundation with elastically restrained ends is considered. Euler-Bernoulli beam hypothesis has been applied and translational and rotational elastic springs in each end considered as support. The crack is modeled as a mass-less rotational spring which divides beam into two segments. After governing the equations of motion, the differential transform method (DTM) has been served to determine dimensionless frequencies and normalized mode shapes. DTM is a semi-analytical approach based on Taylor expansion series that converts differential equations to recursive algebraic equations. The DTM results for the natural frequencies in special cases are in very good agreement with results reported by well-known references. Also, the DTM procedure yields rapid convergence beside high accuracy without any frequency missing. Comprehensive studies to analyze the effects of crack location, crack severity, parameters of elastic foundation and boundary conditions on dimensionless frequencies as well as effects of elastic boundary conditions on cracked beams mode shapes are carried out and some problems handled for first time in this paper. Since this paper deals with general problem, the derived formulation has capability for analyzing free vibration of cracked beam with every boundary condition.     

Explicit formulation for natural frequencies of double-beam system with arbitrary boundary conditions

In this paper, free transverse vibration of two parallel beams connected through Winkler type elastic layer is investigated. Euler-Bernoulli beam hypothesis has been applied and it is assumed that boundary conditions of upper and lower beams are similar while arbitrary without any limitation even for non-ideal boundary conditions. Material properties and cross-section geometry of beams could be different from each other. The motion of the system is described by a homogeneous set of two partial differential equations, which is solved by using the classical Bernoulli-Fourier method. Explicit expressions are derived for the natural frequencies. In order to verify accuracy of results, the problem once again solved using modified Adomian decomposition method. Comparison between results indicates excellent accuracy of proposed formulation for any arbitrary boundary conditions. Derived explicit formulation is simplest method to determine natural frequencies of double-beam systems with high level of accuracy in comparison with other methods in literature.