Dynamic behavior analysis of drill-threading process when machining AISI Al-Si-Cu(4) alloy

Conventional threading operations involve two distinct machining processes: drilling and threading. Therefore, it is time consuming for the tools must be changed and the workpiece has to be moved to another machine. This paper presents an analysis of the combined process (drilling followed by threading) using a single tool for both operations: the tap-milling tool. Before presenting the methodology used to evaluate this hybrid tool, the ODS (operating deflection shapes) basics is shortly described. ODS and finite element modeling (FEM) were used during this research to optimize the process aiming to achieve higher stable machining conditions and increasing the tool life. Both methods allowed the determination of the natural frequencies and displacements of the machining center and optimize the workpiece fixture system. The results showed that there is an excellent correlation between the dynamic stability of the machining center-tool holder and the tool life, avoiding a tool premature catastrophic failure. Nevertheless, evidence showed that the tool is very sensitive to work conditions. Undoubtedly, the use of ODS and FEM eliminate empiric decisions concerning the optimization of machining conditions and increase drastically the tool life. After the ODS and FEM studies, it was possible to optimize the process and work material fixture system and machine more than 30,000 threaded holes without reaching the tool life limit and catastrophic fail.

A Fault-Tolerant Manipulator Robot Based on H(2), H(infinity), and Mixed H(2)/H(infinity) Markovian Controls

This paper develops a Markovian jump model to describe the fault occurrence in a manipulator robot of three joints. This model includes the changes of operation points and the probability that a fault occurs in an actuator. After a fault, the robot works as a manipulator with free joints. Based on the developed model, a comparative study among three Markovian controllers, H(2), H(infinity), and mixed H(2)/H(infinity) is presented, applied in an actual manipulator robot subject to one and two consecutive faults.

Neural network-based H(infinity) control for fully actuated and underactuated cooperative manipulators

This paper develops H(infinity) control designs based on neural networks for fully actuated and underactuated cooperative manipulators. The neural networks proposed in this paper only adapt the uncertain dynamics of the robot manipulators. They work as a complement of the nominal model. The H(infinity) performance index includes the position errors as well the squeeze force errors between the manipulator end-effectors and the object, which represents a complete disturbance rejection scenario. For the underactuated case, the squeeze force control problem is more difficult to solve due to the loss of some degrees of manipulator actuation. Results obtained from an actual cooperative manipulator, which is able to work as a fully actuated and an underactuated manipulator, are presented. (C) 2008 Elsevier Ltd. All rights reserved.

Reliability-based evaluation of design code provisions for circular concrete-filled steel columns

This paper presents an investigation of design code provisions for steel-concrete composite columns. The study covers the national building codes of United States, Canada and Brazil, and the transnational EUROCODE. The study is based on experimental results of 93 axially loaded concrete-filled tubular steel columns. This includes 36 unpublished, full scale experimental results by the authors and 57 results from the literature. The error of resistance models is determined by comparing experimental results for ultimate loads with code-predicted column resistances. Regression analysis is used to describe the variation of model error with column slenderness and to describe model uncertainty. The paper shows that Canadian and European codes are able to predict mean column resistance, since resistance models of these codes present detailed formulations for concrete confinement by a steel tube. ANSI/AISC and Brazilian codes have limited allowance for concrete confinement, and become very conservative for short columns. Reliability analysis is used to evaluate the safety level of code provisions. Reliability analysis includes model error and other random problem parameters like steel and concrete strengths, and dead and live loads. Design code provisions are evaluated in terms of sufficient and uniform reliability criteria. Results show that the four design codes studied provide uniform reliability, with the Canadian code being best in achieving this goal. This is a result of a well balanced code, both in terms of load combinations and resistance model. The European code is less successful in providing uniform reliability, a consequence of the partial factors used in load combinations. The paper also shows that reliability indexes of columns designed according to European code can be as low as 2.2, which is quite below target reliability levels of EUROCODE. (C) 2009 Elsevier Ltd. All rights reserved.

Eucalyptus pulp fibres as alternative reinforcement to engineered cement-based composites

This paper evaluates the advantages of using hardwood short fibre pulp (eucalyptus) as alternative to softwood long fibre pulp (pinus) and polymer fibres, traditionally used in reinforcement of cement-based materials. The effects of cellulose fibre length on microstructure and on mechanical performance of fibre-cement composites were evaluated before and after accelerated ageing cycles. Hardwood pulp fibres were better dispersed in the cement matrix and provided higher number of fibres per unitary weight or volume, in relation to softwood long fibre pulp. The short reinforcing elements lead to an effective crack bridging of the fragile matrix, which contributes to the improvement of the mechanical performance of the composite after ageing. These promising results show the potential of eucalyptus short fibres for reducing costs by both the partial replacement of expensive synthetic fibres in air curing process and the energy savings during pulp refining. (C) 2009 Elsevier B.V. All rights reserved.

Cellulose modified fibres in cement based composites

The objective of the present work is to evaluate the effect of surface modification of cellulose pulp fibres on the mechanical and microstructure of fibre-cement composites. Surface modification of the cellulose pulps was performed with Methacryloxypropyltri-methoxysilane (MPTS) and Aminopropyltri-ethoxysilane (APTS) in an attempt to improve their durability into fibre-cement composites. The surface modification showed significant influence on the microstructure of the composites on the fibre-matrix interface and in the mineralization of the fibre lumen as seen by scanning electron microscopy (SEM) with back-scattered electron (BSE) detector. Accelerated ageing cycles decreased modulus of rupture (MOR) and toughness (TE) of the composites. Composites reinforced with MPTS-modified fibres presented fibres free from cement hydration products, while APTS-modified fibres presented accelerated mineralization. Higher mineralization of the fibres led to higher embrittlement of the composite after accelerated ageing cycles. These observations are therefore very useful for understanding the mechanisms of degradation of fibre-cement composites. (C) 2009 Elsevier Ltd. All rights reserved.

A FEM procedure based on positions and unconstrained vectors applied to non-linear dynamic of 3D frames

This study presents an alternative three-dimensional geometric non-linear frame formulation based on generalized unconstrained vector and positions to solve structures and mechanisms subjected to dynamic loading. The formulation is classified as total Lagrangian with exact kinematics description. The resulting element presents warping and non-constant transverse strain modes, which guarantees locking-free behavior for the adopted three-dimensional constitutive relation, Saint-Venant-Kirchhoff, for instance. The application of generalized vectors is an alternative to the use of finite rotations and rigid triad`s formulae. Spherical and revolute joints are considered and selected dynamic and static examples are presented to demonstrate the accuracy and generality of the proposed technique. (C) 2010 Elsevier B.V. All rights reserved.

Determination of in situ uniaxial compressive strength of coal seams based on geophysical data

The central issue for pillar design in underground coal mining is the in situ uniaxial compressive strength (sigma (cm)). The paper proposes a new method for estimating in situ uniaxial compressive strength in coal seams based on laboratory strength and P wave propagation velocity. It describes the collection of samples in the Bonito coal seam, Fontanella Mine, southern Brazil, the techniques used for the structural mapping of the coal seam and determination of seismic wave propagation velocity as well as the laboratory procedures used to determine the strength and ultrasonic wave velocity. The results obtained using the new methodology are compared with those from seven other techniques for estimating in situ rock mass uniaxial compressive strength.

Estimation of Mass Transfer Velocity Based on Measured Turbulence Parameters

The aim of this study is to quantify the mass transfer velocity using turbulence parameters from simultaneous measurements of oxygen concentration fields and velocity fields. The surface divergence model was considered in more detail, using data obtained for the lower range of beta (surface divergence). It is shown that the existing models that use the divergence concept furnish good predictions for the transfer velocity also for low values of beta, in the range of this study. Additionally, traditional conceptual models, such as the film model, the penetration-renewal model, and the large eddy model, were tested using the simultaneous information of concentration and velocity fields. It is shown that the film and the surface divergence models predicted the mass transfer velocity for all the range of the equipment Reynolds number used here. The velocity measurements showed viscosity effects close to the surface, which indicates that the surface was contaminated with some surfactant. Considering the results, this contamination can be considered slight for the mass transfer predictions. (C) 2009 American Institute of Chemical Engineers AIChE J, 56: 2005-2017; 2010

Atmospheric impacts of the life cycle emissions of fuel ethanol in Brazil: based on chemical exergy

An assessment is made of the atmospheric emissions from the life cycle of fuel ethanol coupled with the cogeneration of electricity from sugarcane in Brazil. The total exergy loss from the most quantitative relevant atmospheric emission substances produced by the life cycle of fuel ethanol is 3.26E+05 kJ/t of C(2)H(5)OH, Compared with the chemical exergy of 1 t of ethanol (calculated as 34.56E + 06 kJ). the exergy loss from the life cycle`s atmospheric emission represents 1.11% of the product`s exergy. The activity that most contributes to atmospheric emission chemical exergy losses is the harvesting of sugarcane through the methane emitted in burning. Suggestions for improved environmental quality and greater efficiency of the life cycle of fuel ethanol with cogenerated energy are: harvesting the sugarcane without burning, renewable fuels should be used in tractors, trucks and buses instead of fossil fuel and the transportation of products and input should be logistically optimized. (C) 2009 Elsevier Ltd. All rights reserved.

Glass formation of alloys selected by lambda and electronegativity criteria in the Ti-Zr-Fe-Co system

This work evaluates the glass formation of selected alloys based on the Ti-Zr-Fe-Co system, assuming the synergy of two distinct criteria: minimum topological instability and average electronegativity plots. Combining the minimum topological instability and the average electronegativity values result in a plot in which the most probable good glass former compositions are identified Ti-Zr rich alloys with Fe and Co additions were produced, compared against the final plot, and the best glass forming alloy composition was found to be very close the theoretically predicted ones on the Ti-Zr rich side, for both Ti-Zr-Fe and Ti-Zr-Co systems. (C) 2009 Elsevier B V All rights reserved

Fatigue behaviour of friction stir welded AA2024-T3 alloy: longitudinal and transverse crack growth

The fatigue crack growth properties of friction stir welded joints of 2024-T3 aluminium alloy have been studied under constant load amplitude (increasing-Delta K), with special emphasis on the residual stress (inverse weight function) effects on longitudinal and transverse crack growth rate predictions (Glinka`s method). In general, welded joints were more resistant to longitudinally growing fatigue cracks than the parent material at threshold Delta K values, when beneficial thermal residual stresses decelerated crack growth rate, while the opposite behaviour was observed next to K-C instability, basically due to monotonic fracture modes intercepting fatigue crack growth in weld microstructures. As a result, fatigue crack growth rate (FCGR) predictions were conservative at lower propagation rates and non-conservative for faster cracks. Regarding transverse cracks, intense compressive residual stresses rendered welded plates more fatigue resistant than neat parent plate. However, once the crack tip entered the more brittle weld region substantial acceleration of FCGR occurred due to operative monotonic tensile modes of fracture, leading to non-conservative crack growth rate predictions next to K-C instability. At threshold Delta K values non-conservative predictions values resulted from residual stress relaxation. Improvements on predicted FCGR values were strongly dependent on how the progressive plastic relaxation of the residual stress field was considered.

Thixocasting of an A356 alloy: Fluidity, porosity distribution and thermomechanical fatigue behavior

An extensive set of experiments was performed on a semi-solid A356 alloy in order to assess its flow behavior, mechanical properties, microstructural evolution and porosity level. Three different microstructural conditioning techniques (raw material preparation) were employed: deformation recrystallization, magnetohydrodynamic stirring and low temperature pouring. Measurement of microstructural parameters such as Al-alpha particle size, shape factor, contiguity and entrapped liquid showed a relative equivalency among the various conditioning techniques. It was found that the strongest influence on semi-solid slurry fluidity is exerted by the mould temperature. Tensile properties and porosity levels were measured on a demonstration part produced with different slurry ingate velocities. Results showed similar strength levels among all thixocast samples, a strong correlation between elongation and pore volume fraction and porosity levels much lower than the typical figure for permanent mould or die cast Al-Si alloys. Finally, thermomechanical fatigue tests results were much more favorable to the semi-solid material when compared with the conventionally cast alloy, a result attributed to lower porosity, spheroidal shape of the Al-alpha phase, and refined Si eutectic particles. alpha 2007 Elsevier B.V. All rights reserved.

Topological instability and electronegativity effects on the glass-forming ability of metallic alloys

The glass-forming ability (GFA) of metallic alloys is associated with a topological instability criterion combined with a new parameter based on the average electronegativity difference of an element and its surrounding neighbours. In this model, we assume that during solidification the glassy phase competes directly with the supersaturated solid solution having the lowest topological instability factor for a given composition. This criterion is combined with the average electronegativity difference among the elements in the alloy, which reflects the strength of the liquid. The GFA is successfully correlated with this combined criterion in several binary glass-forming systems.

Reducing Urban Transport Energy Dependence: A New Urban Development Framework and GIS-Based Tool

High urban transport energy consumption is directly influenced by transport energy dependence. Dramatic reductions in urban transport energy dependence or consumption are not yet being widely observed despite the variety of urban planning tools currently available. A new urban development framework is presented to tackle this issue that makes use of a recently developed and successfully trialed GIS-based tool, the Transport Energy Specification (TES). The TES was simulated on a neighborhood in Sao Carlos, Brazil. In the simulation, energy dependence was reduced by a factor of 8 through activity location or infrastructure modifications to the built environment.