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Made available in DSpace on 2014-06-11T19:29:53Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-02-25Bitstream added on 2014-06-13T19:18:31Z : No. of bitstreams: 1 bartoli_i_me_guara.pdf: 2975428 bytes, checksum: a76f4d7230755abec71b3ba036e4cbf0 (MD5) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Processos contínuos que utilizam o sistema de produção sob encomenda, como o caso do processo siderúrgico, tem sido pouco abordados como exemplos de implantação da manufatura enxuta por sua pequena similaridade com processos discretos que utilizam o sistema de produção para estoque. Por meio da utilização de práticas e ferramentas enxutas em uma companhia siderúrgica que utiliza o sistema de produção sob encomenda, da análise de seus resultados e de uma pesquisa de campo realizada com gestores de dessa companhia com o objetivo de levantar suas impressões e os resultados alcançados e sobre a eficácia dessas práticas e ferramentas, o trabalho demonstra que a Manufatura Enxuta é aplicável em indústrias siderúrgicas que utilizam sistemas de produção sob encomenda Continuous processes that use the make-to-order (MTO) system, as the case of the make steel process, has been little attention as examples of implementation of lean manufacturing for its similarity to small discrete processes that use the production system of make-to-stock (MTS). Through the use of lean tools and practices in a MTS steel company, of the analysis of their results and a field research with managers of that company in order to raise their views and achievements and the effectiveness of these practices and tools, the work demonstrates that Lean Manufacturing is applicable in steel industries that use MTO production system

Guided ultrasonic waves provide a highly efficient method for the non-destructive evaluation (NDE) and the structural health monitoring (SHM) of solids with finite cross-sectional dimensions (waveguides). Compared to the widely used ultrasonic bulk waves, guided waves provide larger monitoring ranges and the complete coverage of the waveguide cross-section. Compared to global vibrations, guided waves offer increased sensitivity to smaller defects due to the smaller wavelengths involved. These advantages can be fully exploited only once the complexities of guided wave propagation (multimode, dispersion, frequency-dependent attenuation) are unveiled and managed for the given test structure. This doctoral dissertation is aimed at developing a Semi-Analytical Finite Element (SAFE) method for modeling wave propagation in waveguides of arbitrary cross-section. The method requires the finite element discretization of the cross- section of the waveguide, and assumes harmonic motion along the wave propagation direction. The general SAFE technique was extended to account for viscoelastic material damping by allowing for complex stiffness matrices for the material. The dispersive solutions are obtained in terms of phase velocity, group velocity (for undamped media), energy velocity (for damped media), attenuation, and cross-sectional mode shapes. Once the dispersive properties are computed, the wave motion can be interpreted and the forced response can be predicted. The proposed SAFE formulation was applied to enhance the use of ultrasonic guided waves in a number of applications and to interpret the corresponding experimental results. The following three applications were considered : defect detection in adhesively-bonded joints found in the wing skin-to-spar assemblies of Unmanned Aerial Vehicles; defect detection in railroad tracks; load monitoring and defect detection in seven-wire steel strands used in cables and prestressed concrete structures

This paper reports on the status of ongoing collaborative studies between UCSD, University of Bologna and University of Pittsburgh aimed at developing a monitoring system for prestressing strands in post-tensioned structures based on guided ultrasonic waves (GUWs) and built-in sensors. A Semi-Analytical Finite Element (SAFE) method was first used to compute dispersion curves of a pretwisted waveguide representing a seven-wire strand. The strand embedded in grout and surrounded by a concrete media was subsequently modeled as an axisymmetric waveguide. The SAFE method allows to account for the material damping and can be used to discriminate low loss guided modes. Experimental tests targeted at the defect detection and prestress level monitoring were performed. Notch like defects, machined in a seven wire strand, were successfully detected using a reflection-based Damage Index (D.I.) vector. The D.I. vector was extracted from GUWs measurements which were processed using Discrete Wavelet Transform (DWT). A four dimensional Outlier analysis was performed to discriminate indications of flaws. In a parallel study, transmission measurements were collected to identify wave features sensitive to prestress level in strands embedded in post-tensioned concrete blocks. The most sensitive features are being investigated further to assess their reliability in a monitoring system whit sensors embedded in a real post-tensioned concrete structure.

This paper deals with a semi-analytical finite element (SAFE) method for modeling wave propagation in waveguides of arbitrary cross-section. The method simply requires the finite element discretization of the cross-section of the waveguide, and assumes harmonic motion along the wave propagation direction. The general SAFE technique is extended to account for viscoelastic material damping by allowing for complex stiffness matrices for the material. The dispersive solutions are obtained in terms of phase velocity, group velocity (for undamped media), energy velocity (for damped media), attenuation, and cross-sectional mode shapes. Knowledge of these properties is important in any structural health monitoring attempt that uses ultrasonic guided waves. The proposed SAFE formulation is applied to several examples, including anisotropic viscoelastic layered plates, composite-to-composite adhesive joints and railroad tracks.