Mechanical surface treatments using an elastic-plastic cold working process can develop residual stresses on the surface of a workpiece. Compressive residual stresses on the surface increase resistance against surface crack propagation, so the overall mechanical performance can be improved by this technique. Compressive residual stresses can be created by different methods such as hammering, rolling, and shot peening. Shot peening is a well-established method to induce compressive residual stresses in the metallic components using cold working, and often ascribed to being beneficial to fatigue life in the aerospace and automobile industries. In this method, the surface is bombarded by high-velocity spherical balls which cause plastic deformation of the substrate, leading to a residual compressive stress after shot peening on the surface of the part. Computational modeling is an appropriate and effective way which can predict the amount of produced residual stresses and plastic deformation to obtain surface roughness after shot peening simulation. Finally, an experimental method to measure the magnitude of the residual stress using a nanoindentation technique was developed. The experimental indentation method was compared to both computational predictions (in aluminum) and with x-ray diffraction measurements of stress (in an alloy steel). The current study validates the relation between the nanoindentation method and numerical simulation for assessing the surface residual stresses resulting from single or multiple shot peening processes.

There is an upsurge of research interest on Alloy 718 additively manufactured (AM) by electron beam powder bed fusion (EB-PBF) technique in aero and land-based gas turbine engines. However, the surface quality of the manufactured components has always been a major challenge. Several factors, including powder particle size, layer thickness, beam parameters, scanning strategies, and inclination angle of the build, govern the surface characteristics. Along with surface roughness resulted from partially melted powder particles, surface defects such as balls, satellites, microcracks as well as up-skin and down-skin surfaces can enhance the vulnerability of the manufactured parts to corrosion. When the surface is unable to withstand the exposed environment adequately, corrosion can be triggered. The surface-induced corrosion failures are increasingly becoming more challenging as the AM components often have complex geometries that render them even more difficult to finish. So, the relatively poor surface finish is the barrier to the full exploitation of the AM industry. In the present study, to achieve the desired surface quality, hence an improved high temperature corrosion performance, shot peening was implemented on Alloy 718 parts manufactured by EB-PBF. The high temperature corrosion behavior of the parts was investigated in an ambient air environment at 650 and 800 °C for up to 336 h. The underlying physical and chemical factors at play of the parts exposed to the corrosive environment were investigated too. The effect of topographical features (e.g., surface roughness) and microstructural characteristics (e.g., grain structure, phases, and defects) on high temperature corrosion behavior were analyzed by 3D surface profilometry, hardness test, optical microscopy (OM), scanning electron microscopy (SEM) equipped with energy disperse spectroscopy (EDS), X-ray diffractometry (XRD) and electron backscatter diffraction (EBSD). The surface roughness and high temperature corrosion rate of the parts was significantly reduced after shot peening.

A proposta deste estudo é fornecer uma visão íntegra e profunda da vida em fadiga de um material aço SAE 5160 para a fabricação de feixes de mola, cujo objetivo principal é otimizar o projeto deste componente na tentativa de reduzir custo e peso, para tanto, o aço SAE 5160 submetido aos processos de tratamento térmico e shot peening, através do levantamento de uma curva de fadiga pelo ensaio de flexão por três pontos. Apresenta também, os resultados obtidos na caracterização do material, como pôr a análise de tensões residuais por difração por raios-X, das microestruturas, da dureza e da composição química, visando o objetivo de identificar possíveis variáveis que possam influenciar nas características técnicas e interferir na vida à fadiga deste aço SAE 5160. Os ensaios realizados mostram o comprometimento da resistência à fadiga deste material, pois é possível verificar uma não homogeneidade nos valores de dureza, a presença de descarbonetação e variação nos valores de tensões residuais, invalidando as amostras na ordem de cinquenta por cento. Com os resultados obtidos no levantamento da curva de fadiga e dados coletados em campo, é demonstrado a validação das curvas de projeto. / The purpose of this study is to provide a full and deep view of fatigue life of a steel material SAE 5160 for the production of leaf springs, whose main objective is to optimize the design of this component in order to reduce cost and weight, therefore the SAE 5160 steel was subjected to the heat treatment processes, and shot peening, via a test fatigue curve by the three-point deflection test. It also presents the results obtained in the characterization of the material, how to put the analysis of residual stresses by X-ray diffraction, the microstructure, hardness and chemical composition, in order to identify potential variables that may influence the technical characteristics and interfere with the fatigue life of the SAE 5160 steel. The tests performed present reduced resistance to fatigue of the material; it is not possible to verify the homogeneity of hardness, the presence of decarburization and variation in the values of residual stresses, invalidating the samples in the order of fifty percent. With the results in the lifting of fatigue and data collected in the field curve, is present the validation of design curves.

A proposta deste estudo é fornecer uma visão íntegra e profunda da vida em fadiga de um material aço SAE 5160 para a fabricação de feixes de mola, cujo objetivo principal é otimizar o projeto deste componente na tentativa de reduzir custo e peso, para tanto, o aço SAE 5160 submetido aos processos de tratamento térmico e shot peening, através do levantamento de uma curva de fadiga pelo ensaio de flexão por três pontos. Apresenta também, os resultados obtidos na caracterização do material, como pôr a análise de tensões residuais por difração por raios-X, das microestruturas, da dureza e da composição química, visando o objetivo de identificar possíveis variáveis que possam influenciar nas características técnicas e interferir na vida à fadiga deste aço SAE 5160. Os ensaios realizados mostram o comprometimento da resistência à fadiga deste material, pois é possível verificar uma não homogeneidade nos valores de dureza, a presença de descarbonetação e variação nos valores de tensões residuais, invalidando as amostras na ordem de cinquenta por cento. Com os resultados obtidos no levantamento da curva de fadiga e dados coletados em campo, é demonstrado a validação das curvas de projeto. / The purpose of this study is to provide a full and deep view of fatigue life of a steel material SAE 5160 for the production of leaf springs, whose main objective is to optimize the design of this component in order to reduce cost and weight, therefore the SAE 5160 steel was subjected to the heat treatment processes, and shot peening, via a test fatigue curve by the three-point deflection test. It also presents the results obtained in the characterization of the material, how to put the analysis of residual stresses by X-ray diffraction, the microstructure, hardness and chemical composition, in order to identify potential variables that may influence the technical characteristics and interfere with the fatigue life of the SAE 5160 steel. The tests performed present reduced resistance to fatigue of the material; it is not possible to verify the homogeneity of hardness, the presence of decarburization and variation in the values of residual stresses, invalidating the samples in the order of fifty percent. With the results in the lifting of fatigue and data collected in the field curve, is present the validation of design curves.

A proposta deste estudo é fornecer uma visão íntegra e profunda da vida em fadiga de um material aço SAE 5160 para a fabricação de feixes de mola, cujo objetivo principal é otimizar o projeto deste componente na tentativa de reduzir custo e peso, para tanto, o aço SAE 5160 submetido aos processos de tratamento térmico e shot peening, através do levantamento de uma curva de fadiga pelo ensaio de flexão por três pontos. Apresenta também, os resultados obtidos na caracterização do material, como pôr a análise de tensões residuais por difração por raios-X, das microestruturas, da dureza e da composição química, visando o objetivo de identificar possíveis variáveis que possam influenciar nas características técnicas e interferir na vida à fadiga deste aço SAE 5160. Os ensaios realizados mostram o comprometimento da resistência à fadiga deste material, pois é possível verificar uma não homogeneidade nos valores de dureza, a presença de descarbonetação e variação nos valores de tensões residuais, invalidando as amostras na ordem de cinquenta por cento. Com os resultados obtidos no levantamento da curva de fadiga e dados coletados em campo, é demonstrado a validação das curvas de projeto. / The purpose of this study is to provide a full and deep view of fatigue life of a steel material SAE 5160 for the production of leaf springs, whose main objective is to optimize the design of this component in order to reduce cost and weight, therefore the SAE 5160 steel was subjected to the heat treatment processes, and shot peening, via a test fatigue curve by the three-point deflection test. It also presents the results obtained in the characterization of the material, how to put the analysis of residual stresses by X-ray diffraction, the microstructure, hardness and chemical composition, in order to identify potential variables that may influence the technical characteristics and interfere with the fatigue life of the SAE 5160 steel. The tests performed present reduced resistance to fatigue of the material; it is not possible to verify the homogeneity of hardness, the presence of decarburization and variation in the values of residual stresses, invalidating the samples in the order of fifty percent. With the results in the lifting of fatigue and data collected in the field curve, is present the validation of design curves.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-08-03T14:04:39Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação_Rev_final_JARDEL_JACKSON_DE_OLIVEIRA_SILVA.pdf: 3811936 bytes, checksum: 4a7248119dc20e2495a0ab7364a93c3f (MD5) / Made available in DSpace on 2016-08-03T14:04:39Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação_Rev_final_JARDEL_JACKSON_DE_OLIVEIRA_SILVA.pdf: 3811936 bytes, checksum: 4a7248119dc20e2495a0ab7364a93c3f (MD5) Previous issue date: 2016-01-22 / Item withdrawn by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-10-16T11:25:55Z Item was in collections: Dissertações de Mestrado - Engenharia Mecânica (ID: 87) No. of bitstreams: 3 Dissertação_Rev_final_JARDEL_JACKSON_DE_OLIVEIRA_SILVA.pdf.txt: 135457 bytes, checksum: 0ac0f4cb0f018b3b07305afd432fe49e (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação_Rev_final_JARDEL_JACKSON_DE_OLIVEIRA_SILVA.pdf: 3811936 bytes, checksum: 4a7248119dc20e2495a0ab7364a93c3f (MD5) / Item reinstated by Julia Almeida (julia.carneiroalmeida@ufpe.br) on 2018-04-26T22:17:54Z Item was in collections: Dissertações de Mestrado - Engenharia Mecânica (ID: 87) No. of bitstreams: 3 Dissertação_Rev_final_JARDEL_JACKSON_DE_OLIVEIRA_SILVA.pdf: 3811936 bytes, checksum: 4a7248119dc20e2495a0ab7364a93c3f (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação_Rev_final_JARDEL_JACKSON_DE_OLIVEIRA_SILVA.pdf.txt: 135457 bytes, checksum: 0ac0f4cb0f018b3b07305afd432fe49e (MD5) / O processo de shot peening faz parte da família de processos de jateamento usado amplamente para tratamento superficial de peças e estruturas no ramo industrial, é uma das técnicas mais eficazes quando o assunto é aumento de resistência à fadiga. O processo de shot peening é uma das principais etapas no processo de produção de componentes sujeitos a esforços cíclicos, e, consequentemente, falha por fadiga. Desta forma este trabalho tem como objetivo geral estudar os efeitos induzidos pelo processo de shot peening na microdureza, tensão residual e rugosidade no aço JIS SCM 420 HV2, e como objetivos específicos definir os parâmetros adequados para cobertura conforme norma SAE J442, definir pressão de jateamento para obter diferentes alturas de Almen, avaliar perfil de microdureza e tensão residual variando altura de Almen, avaliar a correlação entre a microdureza e tensão residual e avaliar a rugosidade para diferentes alturas de Almen. Foi observado que o shot peening provoca um aumento da microdureza até uma profundidade de 0,06mm, assim como os picos de tensão residual compressiva foram obtidos a uma distancia de 0,03mm, assim como para a rugosidade o que tem maior influencia é a dureza superficial da peça a ser submetida ao shot peening. / The process of shot peening is part of the family of blasting processes widely used for surface treatment of parts and structures in the industrial sector, it is one of the most effective techniques when it comes to increased resistance to fatigue. The process of shot peening is one of the key steps in the production process of components subject to cyclic stresses and thus fatigue failure. Thus this work has as main objective to study the effects induced by shot peening process in hardness, residual stress and surface roughness in the steel JIS SCM 420 HV2, and as specific objectives set appropriate parameters for coverage as SAE J442, set blasting pressure for different heights of Almen evaluate hardness and residual stress profile of varying height Almen to evaluate the correlation between the hardness and residual stress, and evaluate the surface roughness for different heights of Almen. It was observed that the shot peening causes an increase in microhardness to a depth of 0.06 mm, and the compressive residual stress peaks were obtained at a distance of 0.03 mm, as well as the roughness has the greatest influence is the hardness surface of the part to be submitted to shot peening.

Le grenaillage de précontrainte est un procédé couramment utilisé dans l’industrie (automobile, aréonautique, …) pour augmenter la durée de vie des pièces mécaniques et de structure : des contraintes de compression sont générées par déformation plastique de la surface. Dans le cas des aciers TRIP (TRansformation Induced Plasticity), qui possèdent une microstructure complexe, l’austénite métastable est susceptible de se transformer en martensite lors du grenaillage. L’état de contraintes obtenu est donc complexe : il résulte de l’effet combiné de la déformation plastique induite par le procédé et de la transformation martensitique qui conduit à une redistribution des contraintes entre l’austénite et la martensite. Ce travail a pour objectif de caractériser expérimentalement l’état mécanique, à l’échelle des phases, de différents aciers TRIP (AISI 301LN, TRIP 780 et 23MnCrMo5) ainsi que leurs fractions de phase respectives après grenaillage et d’en proposer une modélisation par éléments finis pouvant être, à terme, utilisée en bureaux d’études. Le modèle élastoplastique à transformation de phase, développé dans cette thèse, permet de prédire l’évolution des différents champs mécaniques, de manière macroscopique mais également à l’échelle des phases, ainsi que l’évolution de la fraction d’austénite résiduelle. / Shot-peening is commonly used in mechanical industries to increase life duration of mechanical and structural parts: residual compressive stresses are developed at the sub-surface of the material by plastic stretching of the surface. In the case of TRIP-effect steels (TRansformation Induced Plasticity), the metastable austenite can transform into martensite during shot-peening. The final distribution of stress is then more complex than for “standard steels” as it results from the mechanical strain imposed by the process and the martensitic transformation leading to a stress redistribution between austenite, martensite and the other phases. This work aims to characterize experimentally the mechanical state, at phase scale, of different TRIP steels (AISI 301LN, TRIP 780 and 23MnCrMo5) as well as the fraction of each phase after shot-peening and to propose a numerical model by finite elements which could be used in the future by engineering offices. An elastoplastic model with phase transformation was developed in this thesis which permits to predict the evolution of mechanical variables, macroscopically and at the phase scale, as well as the evolution of austenite volume fraction

This master thesis is focused on design and construction of laboratory shot peening machine. This machine is determined for modification of the topography of the friction surfaces specimens. Two types of specimens are used. The first specimen is sphere with diameter 20-40 mm. The second specimen is cylinder with 9.6 mm diameter. In this thesis the setting parameters of shot peening for creation of surface with the micro-texture was described. Influence of the micro-texture to the coefficient of friction was investigated under mixed lubrication and slip condition.

No description available.

Additive Manufacturing (AM) has revolutionized manufacturing processes by enabling the realization of custom products with intricate geometric features that were either too complex or even intractable for subtractive manufacturing processes. Yet, functional surfaces generated in AM have to be often finish machined because of their relatively inferior roughness. The first phase of this research worked around this limitation by tailoring the topography of an AM surface in-process to entail textures that further enhance certain functionalities in a process called Additive Texturing (AT). In this context, the Selective Laser Melting (SLM) process ability to realize intricate surface microfeatures was explored experimentally, evaluating its geometrical limitations. Utilizing such limitations, various patterns comprising pillars, channels, and re-entrant structures were printed to control the wetting behaviour of SLM stainless steel. AT's efficacy is demonstrated in its capability to generate hydrophobic AM surfaces with water contact angles exceeding 140°. Similarly, other texturing patterns comprising dimples, linear, V-shaped, and X-shaped grooves were investigated to tailor the tribological response of textured surfaces under dry sliding conditions. Evidently, a specific wear rate and coefficient of friction reduction of 80% and 60%, respectively, demonstrated another potential for AT. The undesirable tensile Residual Stresses (RS) that inevitably accumulate during the SLM process's rapid heating and cooling cycles were investigated in the second phase of this research. Laser Peening (LP) was utilized to post-process the printed samples to eliminate the initial tensile RS and induce near 500 Mpa compressive RS. Moreover, the LP parameters were explored and optimized to enhance RS, surface roughness, hardness, and wear resistance. / Thesis / Doctor of Philosophy (PhD)