Flexural Buckling Behavior of WAAM-Fabricated Tubular Columns: An Experimental Analysis

Significance 

Additive manufacturing, in its essence, involves layer-by-layer material deposition, a method contrasting starkly with conventional subtractive and formative manufacturing techniques. Wire Arc Additive Manufacturing (WAAM), a subset of Direct Energy Deposition processes, utilizes wire feedstock to deposit molten material, enabling the creation of complex and large structural components. This process not only enhances manufacturing flexibility but also reduces material wastage, aligning with sustainable manufacturing principles. Despite its burgeoning application across various sectors, the structural engineering field is yet to fully understand the material and geometric variabilities introduced by WAAM, especially concerning their impact on the structural integrity and performance of fabricated elements. To address this, a new study published in the Journal of Structural Engineering and conducted by Dr. Cheng Huang, Dr. Xin Meng, Dr. Craig Buchanan, and Professor Leroy Gardner from the Imperial College London, the authors focused on understanding the flexural buckling response of stainless steel tubular columns manufactured using WAAM. Their experimental work aimed to fill the gap in knowledge regarding the structural performance of WAAM-fabricated elements, specifically at the member level, under axial compression loads.

The research study involved the testing of 18 stainless steel columns, comprising both square hollow section (SHS) and circular hollow section (CHS) profiles, under axial compression. These columns were manufactured using WAAM, a process that deposits material layer by layer using an electric arc as the heat source and metal wire as the feedstock. The selection of regular SHS and CHS profiles allowed for direct comparison with conventionally manufactured sections, thereby isolating the influence of the WAAM process on structural performance. The researchers varied the cross-section sizes and column lengths to cover a broad spectrum of member slenderness.

To accurately characterize the as-built geometry and global geometric imperfections inherent to the WAAM process, the team employed advanced techniques including 3D laser scanning to capture the detailed geometry of each column, facilitating the measurement of specimen geometries and the detection of global imperfections, while digital image correlation technology was applied to monitor surface deformations of the columns during the axial compression tests. This non-contact optical method enabled the researchers to measure strains and displacements across the column surfaces, providing a comprehensive understanding of the deformation behavior. The authors’ experimental data revealed that the WAAM columns exhibited flexural buckling behavior similar to those for equivalent, conventionally manufactured tubular sections, although the geometric undulations and variability inherent to WAAM had a noticeable impact on the structural performance of the columns. The presence of these imperfections necessitated adjustments in the analysis and design approaches to ensure accurate prediction of the columns’ buckling strengths. Furthermore, the study highlighted the significance of considering the as-built material properties of WAAM-fabricated elements in structural design. These properties differ from those of conventionally manufactured materials due to the anisotropy and heterogeneity introduced by the layer-wise manufacturing process. Additionally, the researchers assessed the applicability of current structural design provisions (from EN 1993-1-4 and AISC 370) to WAAM-fabricated stainless steel members. They found that, with appropriate consideration of the as-built geometric and material characteristics, these design provisions could be adapted to predict the buckling strength of WAAM columns reasonably well. However, the study highlighted the need for further research and potential revision of design standards to fully account for the nuances of additive manufacturing processes. In conclusion, the experimental investigation of Huang et al. provided detailed insight into the flexural buckling of WAAM-fabricated tubular columns and generated valuable data for the advancement of structural analysis and design of WAAM elements. It also highlighted the critical role of geometric imperfections and material properties specific to WAAM, and contributed to the development of more accurate and reliable design methodologies for additive manufactured structural elements.

Flexural Buckling Behavior of WAAM-Fabricated Tubular Columns: An Experimental Analysis - Advances in Engineering

About the author

Dr. Cheng Huang is a Research Associate in the Department of Civil and Environmental Engineering at Imperial College London. He obtained his Bachelor’s degree in Civil Engineering from Hunan University and his Master’s degree in Structural Engineering from Tongji University, and then his Ph.D. degree in Structural Engineering from Imperial College London. His principal research interests lie in the areas of structural testing, numerical modelling and the development of stability and fatigue design guidance for 3D printed steel structures. He has published about 20 technical papers in the field of structural engineering and peer-reviewed a number of papers for top international journals, such as Engineering Structures and Thin-Walled Structures. He has also launched a special issue on Metal Additive Manufacturing in Construction on the international journal – Structures. Dr. Huang was awarded the SSRC Vinnakota prize in 2023.

About the author

Dr Xin Meng
Faculty of Engineering, Department of Civil and Environmental Engineering
Imperial College London

Dr Xin Meng is a Research Associate in the Steel Structures Research Group at Imperial College London. He is also a member of the Data-Centric Engineering programme at the Alan Turing Institute, which is the national institute for data science and artificial intelligence of the United Kingdom. His research interests lie in high strength steel structures, tubular structures, metal 3D printed structures and advanced structural design methods, with expertise in structural testing, finite element modelling, development of design methods and structural optimisation.

Xin completed his Bachelor degree in Civil Engineering in 2015 at Tsinghua University, and obtained his MSc degree in 2016 and then PhD in 2020 under the supervision of Prof Leroy Gardner at Imperial College London. He won the Patrick J Dowling Prize for his MSc at Imperial College London. He was later awarded the Skempton Scholarship from the Department of Civil and Environmental Engineering at Imperial College London to support his PhD study. He has peer reviewed a number of technical papers for top international journals including Structures and International Journal of Steel Structures.

Xin has co-supervised a number of undergraduate and postgraduate students at Imperial College London. He has delivered lectures for a postgraduate module at Imperial, and also several guest lectures at other universities including Tianjin University and Xi’an Jiaotong-Liverpool University.

About the author

Professor Leroy Gardner
Faculty of Engineering, Department of Civil and Environmental Engineering
Imperial College London

Leroy Gardner is Professor of Structural Engineering at Imperial College London and a Fellow of the Royal Academy of Engineering. Prof. Gardner is engaged in teaching at both undergraduate and postgraduate level, industry training, specialist advisory work and leading an active research group in structural engineering.

Prof. Gardner’s principal research interests, in respect of which he has co-authored 4 textbooks, 7 book chapters and over 400 technical papers, lie in the areas of structural testing, numerical modelling and the development of design methods for steel structures. He is Editor-in-Chief of two international journals and serves on the Editorial boards of five others. He chairs a number of IStructE and BSI committees, is the UK National Representative on the European Working Group for the structural steel design standard EN 1993-1-1, and is a Fellow of both the Institutions of Civil (FICE) and Structural Engineers (FIStructE). Prof. Gardner was awarded the IABSE prize in 2017 and the ASCE Shortridge Hardesty prize in 2020.

Reference

Cheng Huang, Xin Meng, Craig Buchanan, and Leroy Gardner. Flexural Buckling of Wire Arc Additively Manufactured Tubular Columns. Journal of Structural Engineering, 2023, Volume 148, Issue 9. https://doi.org/10.1061/(ASCE)ST.1943-541X.0003427

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