221 research outputs found

    Experimental and Numerical Analysis of the Surface Integrity resulting from Outer-Diameter Grind-Hardening

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    AbstractBesides conventional heat treatment operations, an innovative approach for surface hardening is the grind-hardening process. During this process the dissipated heat from grinding is used for a martensitic phase transformation in the subsurface region of machined components. Additionally, compressive residual stresses are induced in the grindhardened surface layer. However, for the implementation of grind-hardening into industrial production extensive experimental tests are required to achieve iterative results of hardening depth. This paper focuses on the identification of parameter sets for a sufficient grind-hardening in outer-diameter grinding. On the one hand, grinding tests were conducted supported by metallographic investigations; on the other hand, a finite-element-based model was used to predict the surface integrity resulting from grind-hardening

    Micromechanical fatigue experiments for validation of microstructure-sensitive fatigue simulation models

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    Crack initiation governs high cycle fatigue life and is sensitive to microstructural details. While corresponding microstructure-sensitive models are available, their validation is difficult. We propose a validation framework where a fatigue test is mimicked in a sub-modeling simulation by embedding the measured microstructure into the specimen geometry and adopting an approximation of the experimental boundary conditions. Exemplary, a phenomenological crystal plasticity model was applied to predict deformation in ferritic steel (EN1.4003). Hotspots in commonly used fatigue indicator parameter maps are compared with damage segmented from micrographs. Along with the data, the framework is published for benchmarking future micromechanical fatigue models

    Micromechanical fatigue experiments for validation of microstructure-sensitive fatigue simulation models

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    Crack initiation governs high cycle fatigue life and is sensitive to microstructural details. While corresponding microstructure-sensitive models are available, their validation is difficult. We propose a validation framework where a fatigue test is mimicked in a sub-modeling simulation by embedding the measured microstructure into the specimen geometry and adopting an approximation of the experimental boundary conditions. Exemplary, a phenomenological crystal plasticity model was applied to predict deformation in ferritic steel (EN1.4003). Hotspots in commonly used fatigue indicator parameter maps are compared with damage segmented from micrographs. Along with the data, the framework is published for benchmarking future micromechanical fatigue models

    Dry grinding technology for automotive gears manufacturing: process modeling and optimization

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    The following thesis focused on the dry grinding process modelling and optimization for automotive gears production. A FEM model was implemented with the aim at predicting process temperatures and preventing grinding thermal defects on the material surface. In particular, the model was conceived to facilitate the choice of the grinding parameters during the design and the execution of the dry-hard finishing process developed and patented by the company Samputensili Machine Tools (EMAG Group) on automotive gears. The proposed model allows to analyse the influence of the technological parameters, comprising the grinding wheel specifications. Automotive gears finished by dry-hard finishing process are supposed to reach the same quality target of the gears finished through the conventional wet grinding process with the advantage of reducing production costs and environmental pollution. But, the grinding process allows very high values of specific pressure and heat absorbed by the material, therefore, removing the lubricant increases the risk of thermal defects occurrence. An incorrect design of the process parameters set could cause grinding burns, which affect the mechanical performance of the ground component inevitably. Therefore, a modelling phase of the process could allow to enhance the mechanical characteristics of the components and avoid waste during production. A hierarchical FEM model was implemented to predict dry grinding temperatures and was represented by the interconnection of a microscopic and a macroscopic approach. A microscopic single grain grinding model was linked to a macroscopic thermal model to predict the dry grinding process temperatures and so to forecast the thermal cycle effect caused by the process parameters and the grinding wheel specification choice. Good agreement between the model and the experiments was achieved making the dry-hard finishing an efficient and reliable technology to implement in the gears automotive industry

    Ferritic nitrocarburizing process development for minimization of distortion

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    Nitrocarburizing is a thermochemical diffusion process that has been proposed as an alternative to carbonitriding to improve the surface characteristics of automotive components without producing unacceptable part distortion. In this study, gas, ion and vacuum ferritic nitrocarburizing using various heat treatment schedules were investigated and compared with a current carbonitriding procedure. Dimensional distortion and residual stresses in Navy C-Rings and torque converter pistons resulting from each treatment process were evaluated. The microstructure and microhardness, as well as the phase composition of the specimens, were also characterized. The results of this study indicated that the nitrocarburizing process utilizing suitable heat treatment procedures gave rise to smaller size and shape variations in specimens than carbonitriding. However, given the tensile surface residual stresses induced by nitrocarburizing, additional wear testing needs to be carried out to confirm the possibility of replacing the current carbonitriding process with an appropriate ferritic nitrocarburizing procedure

    FEM-based study of precision hard turning of stainless steel 316L

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    This study aims to investigate chip formation and surface generation during the precision turning of stainless steel 316L samples. A Finite Element Method (FEM) was used to simulate the chipping process of the stainless steel but with only a restricted number of process parameters. A set of turning tests was carried out using tungsten carbide tools under similar cutting conditions to validate the results obtained from the FEM for the chipping process and at the same time to experimentally examine the generated surface roughness. These results helped in the analysis and understanding the chip formation process and the surface generation phenomena during the cutting process, especially on micro scale. Good agreement between experiments and FEM results was found, which confirmed that the cutting process was accurately simulated by the FEM and allowed the identification of the optimum process parameters to ensure high performance. Results obtained from the simulation revealed that, an applied feed equals to 0.75 of edge radius of new cutting tool is the optimal cutting conditions for stainless steel 316L. Moreover, the experimental results demonstrated that in contrast to conventional turning processes, a nonlinear relationship was found between the feed rate and obtainable surface roughness, with a minimum surface roughness obtained when the feed rate laid between 0.75 and 1.25 times the original cutting edge radius, for new and worn tools, respectively

    Mechanical performance assessment and dynamic crash simulation of composite materials

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    In this PhD thesis, several technological aspects regarding the use of fibre reinforced composite materials are presented. The crashworthiness topic is studied with the aim to build and calibrate a numerical damage model for the prediction of the energies absorbed during axial crush of a sample specimen. A full experimental characterisation campaign is implemented, and several simulations are used to reach the final validation stage. Following, a small-scale test setup was developed and built to measure the permeability of dry reinforcement, necessary to predict and simulate the flow front propagation in resin injection processes. Test results are compared with experimental trials. Finally, an overview on innovative metal-composite bonding techniques using additive manufacturing processes is presented, highlighting the principal design variables that come into play in developing such advanced connections

    Papers on Technical Science = Műszaki Tudományos Közlemények 2022

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    A MULTI-SCALE CRYSTAL PLASTICITY FINITE ELEMENT MODELING FRAMEWORK FOR PREDICTING STRAIN-RATE SENSITIVE DEFORMATION OF HEXAGONAL METALS

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    This work presents improvements to the methods used in crystal plasticity simulations. It shows how these improvements can be used to accurately predict the deformation behavior of two magnesium alloys, WE43, and AZ31. The first improvement to the methodology is guidance on the type of finite elements to use in explicit grain crystal plasticity simulations. This study found that quadratic tetrahedral and linear hexahedral elements are the most accurate element types included in the study. The study also concluded that tetrahedral elements are more desirable due to fast mesh generation and flexibility to describe geometries of grain structures. The second improvement made was the addition of a numerical scheme to enable the use of any rate sensitivity exponent in the fundamental power-law representation of the flow rule in crystal visco-plasticity. While allowing the use of even very large exponents that many materials exhibit, this numerical scheme adds little to no increase in computational time. This crystal plasticity model was used to accurately predict the deformation behavior of both WE43 and AZ31 under quasi-static and high rate deformation, predicting the stress-stain response and the evolution of texture, twinning and the relative activities of the various deformation modes
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