Low Cycle Fatigue Weld Optimization using Chaboche Material Model

University essay from KTH/Hållfasthetslära (Avd.); KTH/Hållfasthetslära (Avd.)

Author: Louise Rosenblad; Filippa Hallbäck; [2018]

Keywords: ;

Abstract: In this master thesis a method for optimizing welds has been investigated. The method was developed by the use of a finite element (FE)-model of a silencer. The silencer is exposed to both dynamic and thermal loads. Focus has been on using topology optimization for the welds. The main driver for developing a method for weld optimization is to investigate whether the stresses close to the welds could be decreased if some weld material were to be removed. Another motive for conducting the study is to understand the potential for decreased computation time for modeling welds (continuous welds) should the component have more intermittent welds. Given the loads that the component is subjected to, a plastic material model would be preferable. However as of today, a material model in an optimization is limited to being linear elastic and hence it is not possible to use a plastic material model in an optimization, even though that would better to capture the real conditions of the silencer. Thus, as part of this thesis an investigation aiming to find a transfer function between a plastic material model and an elastic material model was conducted. An important part of an optimization is to have a relevant requirement to optimize against. This requirement could be calculated from the transfer function and then be used in an optimization.Summarizing the findings, a transfer function between a plastic and elastic material model was identified, but only for a specific model and position. The identified function can translate and enable the stricter conditions used in a plastic material model to be adapted to an elastic material model. To get a functional transfer function the Super Neuber needs to be calculated for every element in a time efficient way. This might be done by finding a relation of the geometry and the Super Neuber parameter but this will require more investigations. If the Super Neuber parameters for the model are found then the fatigue requirement can be translated to an elastic stress constraint which will give a more accurate optimization.The method for weld optimization has been evaluated but without a requirement calculated from the transfer function. By changing from continuous to intermittent welds the stresses caused by the thermal load can be decreased.

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