Este trabalho foi estruturado visando apresentar os efeitos causados pelo shot peening (jateamento por esferas) em componentes mecânicos. Este processo introduz tensões residuais compressivas na superfície do material, o que retarda a nucleação de trincas de fadiga, promovendo aumento na vida em fadiga. O material utilizado foi o aço SAE 1060, laminado, com um perfil de 15 por 5mm. Para o jateamento foram selecionados dois tamanhos de esferas de aço: S110 e S280. Para cada tamanho foram realizadas três condições de cobertura superficial no material: 80%, 100% e 500%. Foram realizados metalografia, ensaio de tração, análise de tensões residuais, curvas de fadiga, rugosidade, perfil de microdureza e efetuadas análises da fratura e da superfície do material com e sem jateamento. Os resultados apontaram uma melhoria significativa no desempenho em fadiga com a esfera S110 na condição de 100% de cobertura associado às tensões residuais compressivas obtidas. / This work study the effects of shot peening on mechanical components. This process introduces compressive residual stresses in the surface of the material, and cause delays the nucleation of cracks of fatigue, promoting increase in the life fatigue. The material used was SAE 1060 steel, cold rolled, with section of 15x5mm. For the shot peening two sizes of steel spheres had been selected: S110 and S280. For each size three conditions of superficial covering in the material had been carried through: 80%, 100% and 500%. Had been realized analysis of metallography, tensile test, analysis of residual stresses, fatigue test, analysis of roughness, hardness test, surface analysis in the material with and without shot peening. The results indicated a significant improvement in the fatigue performance with the S110 sphere in the 100% of covering condition associated with the compressive residual stresses.

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Este trabalho foi estruturado visando apresentar os efeitos causados pelo shot peening (jateamento por esferas) em componentes mecânicos. Este processo introduz tensões residuais compressivas na superfície do material, o que retarda a nucleação de trincas de fadiga, promovendo aumento na vida em fadiga. O material utilizado foi o aço SAE 1060, laminado, com um perfil de 15 por 5mm. Para o jateamento foram selecionados dois tamanhos de esferas de aço: S110 e S280. Para cada tamanho foram realizadas três condições de cobertura superficial no material: 80%, 100% e 500%. Foram realizados metalografia, ensaio de tração, análise de tensões residuais, curvas de fadiga, rugosidade, perfil de microdureza e efetuadas análises da fratura e da superfície do material com e sem jateamento. Os resultados apontaram uma melhoria significativa no desempenho em fadiga com a esfera S110 na condição de 100% de cobertura associado às tensões residuais compressivas obtidas. / This work study the effects of shot peening on mechanical components. This process introduces compressive residual stresses in the surface of the material, and cause delays the nucleation of cracks of fatigue, promoting increase in the life fatigue. The material used was SAE 1060 steel, cold rolled, with section of 15x5mm. For the shot peening two sizes of steel spheres had been selected: S110 and S280. For each size three conditions of superficial covering in the material had been carried through: 80%, 100% and 500%. Had been realized analysis of metallography, tensile test, analysis of residual stresses, fatigue test, analysis of roughness, hardness test, surface analysis in the material with and without shot peening. The results indicated a significant improvement in the fatigue performance with the S110 sphere in the 100% of covering condition associated with the compressive residual stresses.

Made available in DSpace on 2014-10-09T12:48:51Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:09Z (GMT). No. of bitstreams: 1 09601.pdf: 14581150 bytes, checksum: 039930ea0467d8cb98d0f2a68ecb3072 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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The main objective of this research is to investigate the effect of wide peening and cleaning (WPC) also known as fine particle peening on the surface properties and cutting performance of cemented carbide inserts. In WPC, the surface of the material is bombarded with millions of high-velocity fine shot generating a uniform layer of plastic deformation near the surface. The plastically deformed layer will have higher compressive residual stress levels, higher surface hardness, experience changes in surface morphology and changes in microstructure. Selecting suitable peening parameters is crucial for achieving proper results. In this study, tools are treated under different pressures varying between 0.2 to 0.4 MPa, and for different peening durations of 2.5 to 10 s. The cutting performance of uncoated tools treated with WPC was examined while turning ductile cast iron and AISI 4140. To have a better understanding, the surface morphology, microstructure, surface roughness, cutting edge radius, residual stresses, and surface hardness were measured and discussed. The results are also compared with untreated tools. The compressive residual stresses were significantly higher after WPC. In addition, uncoated tools treated with WPC resulted in a 12-30% higher tool life over untreated tools. Based on the findings outlined in this thesis, WPC can be recommended as a surface treatment on uncoated cemented carbide inserts for increasing tool life. Also, this study shows significant potential for using WPC as a pre-coating treatment for improving coating adhesion on cemented carbide cutting inserts. / Thesis / Master of Applied Science (MASc)

This thesis investigates the use of laser shock peening (LSP) to improve mechanical properties, electrochemical behavior, and stress corrosion cracking (SCC) resistance in laser powder bed fusion (LPBF) stainless steel. The thesis begins by introducing metal additive manufacturing and reviews the current technological frontiers of LSP before elucidating the fundamentals behind the imaging, experimental, and theoretical frameworks used in the subsequent chapters. The experimental work is roughly divided into two parts; the first half is dedicated to study of the plasticity response augmentation by LSP in anisotropic stainless steel. The prevalence of back stress hardening occurring in anisotropic metal parts causes reduced fatigue life under random loading. LSP is known to improve fatigue life by inducing compressive residual stress and has been applied with promising results to AM metal parts. It is here demonstrated that LSP may also be used as a tool for mitigating tensile back-stress hardening. This discussion is initially applied to rolled and annealed 304L stainless steel which is shown to exhibit material anisotropy. Back stress is extracted from hysteresis tensile testing for treated and untreated samples. Analysis of plasticity response by orientation imaging microscopy (OIM) and finite element analysis (FEA) describes back stress and residual stress development during tensile testing and LSP treatment. The research indicates LSP's potential to address manufacturing design challenges caused by yield asymmetry due to back stress and is thus next applied to additively manufactured 316L. The microstructure and texture in additively manufactured metal lead to anisotropic hardening behavior. Comparison of LSPed and as-built LPBF samples shows LSPed samples processed along the build direction demonstrate significant back-stress reduction. Electron backscatter diffraction (EBSD) illuminates grain morphologies' role, while crystal plasticity finite element (CPFE) modeling reveals mechanisms underlying back-stress reduction across different build orientations and crystal planes.In the second half of the thesis, LSP’s effect upon LPBF 316L material performance in corrosive environments is investigated. This effort begins with analysis of LSP’s improvement to electrochemical and wetting behavior of as-built LPBF surfaces. The corrosion performance of LPBF stainless steel varies between studies and build parameters, thus motivating the search for postprocessing methods that enable wetted surface applications. The study examines electrochemical properties before and after LSP, measuring pitting potential, electrochemical impedance, contact angle, surface free energy, and surface finish. LSP imparts surface improvement which is attributed to morphology and chemistry alterations as well as compressive residual stress. LPBF stainless steel is also particularly susceptible to SCC due to surface-level tensile residual stress. The final study demonstrates LSP's ability to enhance SCC behavior in LPBF stainless steel by increasing time to crack initiation. Analyses of residual stress, texture, dislocation distribution, hardness, microstructure, and fracture surfaces are conducted to understand the mechanisms underlying SCC improvement. Dynamic crack modeling supports observed outcomes, linking residual stress and failure modes to LSP's effects. This work highlights LSP's potential as a versatile tool for enhancing the performance and reliability of LPBF stainless steel components in demanding engineering applications. Further, it identifies the key relevance of the anisotropy of LPBF material structure to mechanical behavior and also to the effectiveness of LSP surface processing.

O tratamento superficial de shot peening tem por objetivo aumentar a resistência à fadiga sendo comparada pelas medidas de tensão residual. O processo peen forming é uma variante do processo shot peening onde se obtém uma curvatura na placa produzida pelo jateamento das esferas através da compressão dos grãos localizados próximos à superfície. Foi estudado neste trabalho a influência dos parâmetros pressão e tamanho de granalha, utilizado no processo de peen forming, no perfil de tensão residual e no raio de curvatura em amostras de alumínio 7050. A avaliação do perfil de tensão de residual foi efetuada por difração de raios-x utilizando o método de sen2 . Os resultados mostram que a formação da altura do arco de curvatura é proporcional a pressão de jateamento e ao tamanho das esferas e inversamente proporcional a espessura da amostra, e que o fator de concentração de tensões é maior para amostras jateadas com menores esferas. Na seção final deste trabalho apresenta um estudo complementar sobre microdeformação e tamanho médio de cristalito, podendo avaliar o perfil das amostras após jateamento. / Shot peening is a superficial cold work process used to increase the fatigue life evaluated by residual stress measurements. The peen forming process is a variant of the shot peening process, where a curvature in the plate is obtained by the compression of the grains near to the surface. In this paper, the influence of the parameters such as: pressure of shot, ball shot size and thickness of aluminum 7050 samples with respect to residual stress profile and resulting arc height was studied. The evaluation of the residual stress profile was obtained by sin2 method. The results show that the formation of the curvature arc height is proportional to the shot peening pressure, of spheres size and inversely proportional to the thickness of the sample, and that stress concentration factor is larger for samples shot peened with small balls. On final of this paper presents an additional study on microstrain and average crystallite size, which can evaluate the profile of the samples after blasting.