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- Fisk, Martin
(författare)
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Modelling of induction heat treatment in a manufacturing chain
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Due to increased competitiveness in the aerospace industry, deeper knowledge of the manufacturing process is needed. It is, for example, known that the microstructure is important for the performance of the components. In order to make a cost effective prediction of a product's final shape and mechanical properties, modelling of the various processes in a manufacturing chain is of interest. The finite element method is the best and most common tool used for this purpose.The main route for manufacturing of structural components in aero engines are either forging, casting or fabrication. During these steps, manufacturing defects such as cracks or voids can occur. Repair welding is then necessary. However, welding changes the microstructure of the material. In order to restore the microstructure, and reduce welding residual stresses an heat treatment of the component is necessary. The heat treatment is usually performed by placing the component in a furnace, i.e. a global heat treatment, although it is only a local region that needs to be restored. One method to perform a local heat treatment is by induction heating.The possibility to replace global heat treatment with local using induction heating has been evaluated in the project, both numerically using the finite element method as well as with validation experiments. Finite element models has also been used in order to simulate induction heating in the manufacturing process chain of stainless steel tubes.The aim of this work has been to simulate a process chain consisting of repair welding and local heat treatment with induction heating. It is then possible to predict deformations as well the residual stress state and the change in microstructure. For this has a material model been developed. It is a dislocation density based flow stress model in which precipitate hardening for alloy 718 is taken into account.
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| 2. |
- Lundbäck, Andreas
(författare)
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Modelling and simulation of welding and metal deposition
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fusion welding is one of the most used methods for joining metals. This method has largely been developed by experiments, i.e. trial and error. The problem of distortion and residual stresses of a structure due to welding is important to control. This is especially important in the aerospace industry where the components are expensive and safety and quality are very important issues. The safety requirements and the high costs of performing experiments to find different manufacturing routes is the motivation to increase the use of simulations in design of components as well as its manufacturing. Thus, in the case of welding, one can evaluate the effect of different fixtures, welding parameters etc on the deformation of the component. The effects of previous processes are also important to consider, as well as it is important to bring forward the current state to subsequent processes.When creating a numerical model, the aim is to implement the physical behaviour of the process into the model. However, it may be necessary to compromise between accuracy of the model and the required computational time. The aim of the work presented in this thesis was to develop a method and model for simulation of welding and metal deposition of large and complex components using the finite element method. The model must be reliable and efficient to be usable in the designing and planning of the manufacturing of the component. In this thesis, the meaning of efficiency of a model is wider than just the computational efficiency. The time for creation and definition of the model should also be included. The developed methods enable the user to create a model for welding or metal deposition with a minimum of manual work. The method for defining weld paths and heat input together with activation of elements is now implemented in the commercial finite element software MSC.Marc. The implementation is based on the experience in this work and communication with the author. The approach has been validated against test cases. Naturally, this validation is dependent on sufficient accuracy of the heat input model and material model that are used. It is the first time a dislocation density model has been used to describe the flow stress in a welding simulation. The work has also demonstrated the possibility to calibrate heat input models with a physical based heat input model, thus relieving the need to calibrate the heat source versus measurements.Efficiency in terms of computing time has also been investigated in the course of this work. Three different methods has been explored and used, adaptive meshing, substructuring and parallel computation. The method that is found to be the most versatile and reduce the overall simulation time the most is parallel computation. It is straightforward for the user to employ and it introduces no reduction in the accuracy.
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| 3. |
- Wedberg, Dan
(författare)
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Modelling of high strain rate plasticity and metal cutting
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Metal cutting is one of the most frequently used forming processes in the manufacturing industry. Extensive effort is made to improve its process and simulation has become an integrated part, not only in the product development process but also in the customer relations. However, simulation of metal cutting is complex both from numerical as well as physical point of view. Furthermore, modelling the material behaviour has shown to be crucial. Errors in the material model cannot be reduced by the numerical procedures. The magnitudes of strain and strain rate involved in metal cutting may reach values of 1-10 and 103-106 s-1. The dissipative plastic work together with the chip tool friction also leads to locally high temperatures. These extreme ranges of conditions imply that a diversity of physical phenomena is involved and it is a challenge to develop a material model with adequate accuracy over the whole loading range. Furthermore, this intense and severe deformation represents thermo-mechanical behaviour far from what is generated from conventional material compression and tension testing. A highly desirable feature is also a material model that can be extrapolated outside the calibration range. This is not trivial since materials exhibit different strain hardening and softening characteristics at differentstrains, strain rates and temperatures. Models based on modelling some aspects of the underlying physical process, e.g. the generation of dislocations, are expected to have a larger range of validity than engineering models. Though, engineering models are the far most common models used in metal cutting simulations.The scope of this work includes development of validated models for metal cutting simulations of AISI 316L stainless steel. Particular emphasis is placed on the material modeling and high strain rate plasticity phenomena. The focus has been on a physically based material model. The approach has been to review the literature about flow stress models and phenomena and particularly at high strain rates. A previous variant of a dislocation density model has thereafter been extended into high strain rate regimes by applying different mechanisms. Some of the models have been implemented in commercial finite element software for orthogonal cutting simulations. Experimental measurements and evaluations that include SHPB-measurements, cutting force measurements, quick-stop measurements and some microstructural examinations has been conducted for calibration and validation. The compression tests, within a temperature and strain rate range of 20-950 °C and 0.01-9000 s-1 respectively, showed that the flow stress increased much more rapidly within the dynamic loading range and hence depends on the strain rate. The dynamic strain aging (DSA) that has been observed at lower strain rates is non-existent at higher strain rates. The temperature and strain-rate evolution is such that the DSA is not necessary to include when modelling this process. Furthermore the magnetic balance measurements indicate that the martensite transformation-strengthening effect is insignificant within the dynamic loading range.In the present work the concept of motion of dislocations, their resistance to motion and substructure evolution are used as underlying motivation for description of the flow stress. A coupled set of evolution equations for dislocation density and mono vacancy concentration is used rendering a formulation of a rate-dependent yield limit in context of rate-independent plasticity. Dislocation drag due to phonon and electron drag, a strain rate dependent model of the subcell formation, a strain rate and temperature dependent recovery function and a structural dependent thermally activated stress component have among others been considered. Best predictability was obtained with a strain rate dependent subcell formulation. Dislocation drag did not improve the predictability within the measured testing range. Although showed to has a greater influence outside the range of calibration when extrapolated. It has been shown that extrapolation is uncertain. Results from experiments and modelling of material behaviour and metal cutting together with the literature indicate that the predictability of the material behaviour within and outside the measured testing range can be further tuned by implementing models of the phenomenon mechanical twining and recrystallization.
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