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Modified Inherent Strain Method for Predicting Residual Deformation in Metal Additive Manufacturing

Liang, Xuan (2020) Modified Inherent Strain Method for Predicting Residual Deformation in Metal Additive Manufacturing. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Additive manufacturing (AM) of metal components has seen rapid development in the past decade, since arbitrarily complex geometries can be manufactured by this technology. Due to intensive heat input in the laser-assisted AM process, large thermal strain is induced and hence results in significant residual stress and deformation in the metal components. To achieve efficient simulation for metal printing process, the inherent strain method (ISM) is ideal for this purpose, but has not been well developed for metal AM parts yet.
In this dissertation, a modified inherent strain method (MISM) is proposed to estimate the inherent strains from detailed process simulation. The obtained inherent strains are employed in a layer-by-layer static equilibrium analysis to simulate residual distortion of the AM part efficiently. To validate the proposed method, single-walled builds deposited by directed energy deposition (DED) process are studied first. The MISM is demonstrated to be accurate by comparing with full-scale detailed process simulation and experimental results.
Meanwhile, the MISM is adapted to powder bed fusion (PBF) process to enable efficient yet accurate prediction for residual stress and deformation of large components. The proposed method allows for calculation of inherent strains accurately based on a small-scale simulation of a small representative volume. The extracted mean inherent strains are applied to a part-scale model layer-by-layer to simulate accumulation of residual deformation. Accuracy of the proposed method for large components is validated by comparison with experimental results, while excellent computational efficiency is also shown.
As further applications, the MISM is extended to deal with efficient simulation for residual deformation of thin-walled lattice support structures with different volume densities. To achieve this goal, asymptotic homogenization is employed to obtain the homogenized inherent strains and elastic modulus given the specific laser scanning strategy and process parameters for fabricating those thin-walled lattice support structures. Accuracy of the homogenization-based layer-by-layer simulation have been validated by experiments. Moreover, the enhanced layer lumping method (ELLM) is developed to further accelerate the layer-by-layer simulation to the largest extent for metal builds produced by PBF. By using tuned material property models, good accuracy can be ensured while directly lumping the equivalent layers in the layer-wise simulation.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Liang, XuanXUL31@pitt.eduXUL31
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairTo, Albert C.
Committee MemberXiong, Wei
Committee MemberZhao, Xiayun
Committee MemberChen, Kevin P.
Date: 28 September 2020
Date Type: Publication
Defense Date: 18 June 2020
Approval Date: 28 September 2020
Submission Date: 24 July 2020
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 189
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Mechanical Engineering and Materials Science
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: Additive Manufacturing, Inherent strain, Residual Deformation, Metal depositions
Date Deposited: 28 Sep 2020 20:34
Last Modified: 28 Sep 2020 20:34


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