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Doctoral Thesis
DOI
https://doi.org/10.11606/T.3.2008.tde-22052009-122931
Document
Author
Full name
Miguel Angel Calle Gonzales
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2008
Supervisor
Committee
Gonçalves, Edison (President)
Driemeier, Larissa
Laier, José Elias
Ramos Júnior, Roberto
Rangel, Angelo Gil Pezzino
Title in Portuguese
Análise numérico-experimental das tensões residuais induzidas por jateamento com granalha em molas automotivas.
Keywords in Portuguese
Forjamento
Processos de fabricação
Tensão residual
Abstract in Portuguese
O jateamento com granalha (shot peening) é um processo mecânico a frio onde um jato de granalhas é impelido contra a superfície dos componentes. Cada impacto provoca deformação plástica e introduz tensões residuais de compressão na superfície, as quais aumentam a sua resistência à fadiga. Este tratamento é muito usado na indústria automotiva, particularmente no tratamento de molas automotivas devido à alta solicitação a carregamentos cíclicos. Uma variante aprimorada deste processo, exclusivo para molas automotivas planas, é o jateamento com granalha sob tensão (stress peening) onde é imposta uma pré-carga de flexão na mola que aumenta a intensidade do processo. Neste trabalho foram desenvolvidas as modelagens numéricas, usando o Método dos Elementos Finitos (MEF), do jateamento com granalha e do jateamento com granalha sob tensão, ambos aplicados a molas automotivas, para analisar o campo de tensões residuais induzido. Os modelos numéricos desenvolvidos contemplam: análise dinâmica explícita, modelagem tridimensional de múltiplos impactos de granalha numa superfície plana, avaliação da velocidade real das granalhas, atrito entre as superfícies de contato, propriedades mecânicas do aço ABNT 5160 (molas automotivas), encruamento do material e sensibilidade do material às altas taxas de deformação. A partir dos resultados da modelagem foram avaliados: o progresso da cobertura ao longo do tempo da aplicação dos múltiplos impactos de granalha, as tensões residuais, as deformações elásticas e as deformações plásticas resultantes induzidas pelo jateamento. Neste trabalho, foi realizado um programa experimental para introdução e avaliação das tensões residuais em duas molas parabólicas automotivas, uma delas submetida ao jateamento com granalha e a outra submetida ao jateamento com granalha sob tensão. A avaliação experimental das tensões residuais foi desenvolvida usando as técnicas de difração de raios-X e do furo incremental cego. Os resultados das modelagens numéricas são corroborados com as medições experimentais e com os resultados experimentais e numérico-computacionais obtidos por outros autores. Finalmente, algumas conclusões são inferidas diante da análise comparativa entre os resultados numéricos e experimentais.
Title in English
Numerical and experimental analysis of the residual stresses induced by shot peening in automotive springs.
Keywords in English
Automotive spring
Residual stress
Shot peening
Abstract in English
The shot peening is a cold-working mechanical process where a stream of tiny small balls is impelled against the surface of components. Each impact causes plastic deformation and introduces compressive residual stresses on the surface, which consequently increases their resistance to fatigue. This process is widely used in the automotive industry, particularly in the treatment of automotive springs due to high cyclic loads required. An improved variant of the shot peening process for leaf springs is the stress peening, in which a flexion pre-load is imposed to bend the spring while a conventional shot peening process is applied, resulting in an increase in the intensity of the process. In this work, numerical models of the shot peening and the stress peening process were created to be applied to automotive leaf springs. To analyze the induced residual stress field the finite elements method was used. Numerical models include: dynamic explicit formulation, three-dimensional modeling of multiple impacts of balls on a plane target, the calculation of the real shot speed, friction between the contact areas, mechanical properties of ABNT 5160 steel (for automotive leaf springs), plastic work of the material and high strain rate sensitivity of the material. The indentation coverage progress over the analyzed area, the residual stresses, the remaining elastic and plastic strains induced by the shot peening were evaluated from the modeling. In this work an experimental programme was carried out to introduce and to evaluate residual stresses in one automotive leaf spring submitted to conventional shot peening and another submitted to stress peening. The experimental evaluation of the residual stresses was done using X-ray diffraction and incremental hole drilling techniques. Results for the numerical model are compared to the experimental measurements and the experimental measurement, as well as to numerical modeling results obtained by other authors. Finally, conclusions are drawn after comparing the numerical results to experimental ones.
 
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Publishing Date
2009-08-05
 
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