Publications
23 results found
Zhang R, Gardner L, Amraei M, et al., 2023, Testing and analysis of additively manufactured stainless steel corrugated cylindrical shells in compression, Journal of Engineering Mechanics, Vol: 149, ISSN: 0733-9399
Initial geometric imperfections have been identified as the main cause for the large discrepancies between experimental and theoretical buckling loads of thin-walled circular cylindrical shells under axial compression. The extreme sensitivity to imperfections has been previously addressed and mitigated through the introduction of stiffeners; however, sensitivity still remains. Optimized corrugated cylindrical shells are largely insensitive to imperfections and hence exhibit excellent load-bearing capacities, but their complex geometries make their construction difficult and costly using conventional manufacturing techniques. This was overcome in the present study through additive manufacturing (AM). Nine optimized corrugated shells with different diameter-to-thickness ratios, together with one reference circular cylindrical shell, were additively manufactured by means of powder bed fusion (PBF) from austenitic and martensitic precipitation hardening stainless steel. The structural behavior of the AM shells was then investigated experimentally with the testing program comprising tensile coupon tests, measurements of basic geometric properties, and axial compression tests. Numerical analyses were also conducted following completion of the physical experiments. The experimental and numerical results verified the effectiveness of optimized corrugated cylindrical shells in achieving improved local buckling capacity and reduced imperfection sensitivity. Initial recommendations for the structural design of the studied cross-sections are made.
Wynne Z, Buchanan C, Kyvelou P, et al., 2022, Dynamic testing and analysis of the world’s first metal 3D printed bridge, Case Studies in Construction Materials, Vol: 17, ISSN: 2214-5095
The MX3D Bridge is the world’s first additively manufactured metal bridge. It is a 10.5 m-span footbridge, and its dynamic response is a key serviceability consideration. The bridge has a flowing, sculptural form and its response to footfall was initially studied using a 3D finite element (FE) model featuring the designed geometry and material properties obtained from coupon tests. The bridge was tested using experimental modal analysis (EMA) and operational modal analysis (OMA) during commissioning prior to installation. The results have shown that the measured vibration response of the bridge under footfall excitation is 200% greater than predictions based on the FE model and contemporary design guidance. The difference between predicted and measured behaviour is attributed to the complexity of the structure, underestimation of the modal mass in the FE model, and the time-variant modal behaviour of the structure under pedestrian footfall. Both OMA and EMA give a dominant natural frequency for the bridge of between 5.19 Hz and 5.32 Hz, higher than the FE model prediction of 4.31 Hz, and average damping estimates across all modes of vibration below 15 Hz of 0.61% and 0.74% respectively, higher than the 0.5% assumed within the design guidance, slightly reducing the peak response factor predicted for the bridge.
Huang C, Meng X, Buchanan C, et al., 2022, Flexural buckling of wire arc additively manufactured tubular columns, Journal of Structural Engineering, Vol: 148, ISSN: 0733-9445
ire arc additive manufacturing (WAAM) is a metal 3D printing method that enables large-scale structural elements with complex geometry to be built in a relatively efficient and cost-effective manner, offering revolutionary potential to the construction industry. Fundamental experimental data on the structural performance of WAAM elements, especially at the member level, are however lacking. Hence, an experimental study into the flexural buckling response of WAAM tubular columns has been conducted and is presented in this paper. A total of stainless steel square and circular hollow section (SHS and CHS) columns were tested under axial compression with pin-ended boundary conditions. Regular SHS and CHS profiles were chosen to enable direct comparisons against equivalent, conventionally manufactured sections and hence to isolate the influence of the additive manufacturing process, while the cross-section sizes and column lengths were varied to achieve a broad spectrum of member slendernesses. Owing to the geometricundulations inherent to the WAAM process, 3D laser scanning was used to determine the as-built geometry and global geometric imperfections of the specimens; digital image correlation (DIC) was employed to monitor the surface deformations of the specimens during testing. Full details of the column testing program, together with a detailed discussion of the experimental results, are presented. The applicability of the current column design provisions in EN 1993-1-4 and AISC 370 to WAAM stainless steel members was assessed by comparing the test results with the codifiedstrength predictions. The comparisons emphasized the need to allow for the weakening effect of the inherent geometric variability of WAAM elements, in order for safe-sided strength predictions to be achieved
Kyvelou P, Buchanan C, Gardner L, 2022, Numerical simulation and evaluation of the world’s first metal additively manufactured bridge, Structures, Vol: 42, Pages: 405-416, ISSN: 2352-0124
Recent disruptive technological advances, including wire arc additive manufacturing (WAAM) and the concept of digital twins, have the potential to fundamentally transform the way in which we design, build and manage structures. WAAM is a method of metal 3D printing that is well suited to the price-sensitive construction industry and has been used to manufacture the MX3D bridge – the world’s first metal additively manufactured bridge. The intricate geometry, undulating surface finish and particular material properties rendered the bridge outside the scope of any existing structural design standards; hence, physical testing and advanced numerical modelling were carried out for its safety assessment. The key features of the finite element model of the bridge, and its validation against in-situ structural tests, are described herein. Subsequent numerical studies undertaken to verify the structural performance of the bridge under various loading scenarios are presented, while the basis for the development of the smart digital twin of the bridge is also introduced. The presented research provides insight into the use of advanced computational simulations for the verification and ongoing assessment of structures produced using new methods of manufacture.
Hadjipantelis N, Weber B, Buchanan C, et al., 2022, Description of anisotropic material response of wire and arc additively manufactured thin-walled stainless steel elements, Thin Walled Structures, Vol: 171, Pages: 1-17, ISSN: 0263-8231
In contrast to conventionally-produced structural steel and stainless steel elements, wireand arc additively manufactured (WAAM) elements can exhibit a strongly anisotropicmaterial response. To investigate this behaviour, data obtained from tensile tests on machined and as-built coupons extracted from WAAM stainless steel sheets are analysed.The observed mechanical response in the elastic range is described accurately using anorthotropic plane stress material model requiring the definition of two Young’s moduli, thePoisson’s ratio and the shear modulus. In the inelastic range, the anisotropy is capturedthrough the Hill yield criterion, utilising the 0.2% proof stresses in the three different loading directions relative to the deposition direction; plastic Poisson’s ratios are also reported.The presented findings and constitutive description highlight significant variation in theproperties of the studied stainless steel with direction, which opens up opportunities toenhance the mechanical performance of WAAM structures by optimising both the locationand orientation of the printed material.
Kyvelou P, Huang C, Gardner L, et al., 2021, Structural testing and design of wire arc additively manufactured square hollow sections, Journal of Structural Engineering, Vol: 147, Pages: 1-19, ISSN: 0733-9445
Wire arc additive manufacturing (WAAM) is a method of metal 3D printing that has the potential for significant impact on the construction industry due to its ability to produce large parts, with reasonable printing times and costs. There is currently however a lack of fundamental data on the performance of structural elements produced using this method of manufacture. Seeking to bridge this gap, the compressive behavior and resistance of WAAM square hollow sections (SHS) are investigated in this study. Testing reported in a previous study by the authors of sheet material produced in the same manner as the studied SHS is first summarized. The production, measurement and testing of a series of stainless steel SHS stub columns are then described. Regular cross-section profiles were chosen to isolate the influence of 3D printing and enable direct comparisons to be made against equivalent sections produced using traditional methods of manufacture. A range of cross-section sizes and thicknesses were considered to achieve variation in the local cross-sectional slenderness of the tested specimens, allowing the influence of local buckling to be assessed. Repeat tests enabled the variability in response between specimens to be evaluated; a total of 14 SHS stub columns of seven different local slendernesses was tested, covering all cross-section classes of AISC 370 and Eurocode 3. Advanced non-contact measurement techniques were employed to determine the as-built geometric properties, while digital image correlation measurements were used to provide detailed insight into the deformation characteristics of the test specimens. Owing to the higher geometric variability of WAAM relative to 2 conventional forming processes, the tested 3D printed stub columns were found to exhibit more variable capacities between repeat specimens than is generally displayed by stainlesssteel SHS. Comparisons of the stub column test results with existing structural design rules highlight the need to
Dodwell T, Flemming L, Buchanan C, et al., 2021, A data-centric approach to generative modelling for 3D-printed steel, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 477, ISSN: 1364-5021
The emergence of additive manufacture (AM) for metallic material enables components of near arbitrary complexity to be produced. This has potential to disrupt traditional engineering approaches. However, metallic AM components exhibit greater levels of variation in their geometric and mechanical properties compared to standard components, which is not yet well understood. This uncertainty poses a fundamental barrier to potential users of the material, since extensive post-manufacture testing is currently required to ensure safety standards are met. Taking an interdisciplinary approach that combines probabilistic mechanics and uncertainty quantification, we demonstrate that intrinsic variation in AM steel can be well described by a generative statistical model that enables the quality of a design to be predicted before manufacture. Specifically, the geometric variation in the material can be described by an anisotropic spatial random field with oscillatory covariance structure, and the mechanical behaviour by a stochastic anisotropic elasto-plastic material model. The fitted generative model is validated on a held-out experimental dataset and our results underscore the need to combine both statistical and physics-based modelling in the characterization of new AM steel products.
Zhang R, Buchanan C, Matilainen V-P, et al., 2021, Mechanical properties and microstructure of additively manufactured stainless steel with laser welded joints, Materials and Design, Vol: 208, Pages: 1-20, ISSN: 0264-1275
Powder bed fusion (PBF) is a commonly employed metal additive manufacturing (AM) process in which components are built, layer-by-layer, using metallic powder. The component size is limited by the internal build volume of the employed PBF AM equipment; the fabrication of components larger than this volume therefore requires mechanical joining methods, such as laser welding. There are, however, very limited test data on the mechanical performance of PBF metal with laser welded joints. In this study, the mechanical properties of PBF built 316L stainless steel parts, joined together using laser welding to form larger components, have been investigated; the microstructure of the components has also been examined. 33 PBF 316L stainless steel tensile coupons, with central laser welds, welded using a range of welding parameters, and with coupon half parts built in two different orientations, were tested. The porosity, microhardness and microstructure of the welded coupons, along with the widths of the weld and heat-affected zone (HAZ), were characterised. The PBF base metal exhibited a typical cellular microstructure, while the weld consisted of equiaxed, columnar and cellular dendrite microstructures. Narrow weld regions and HAZs were observed. The PBF base metal was found to have higher proof and ultimate strengths, but a similar fracture strain and a lower Young’s modulus, compared with conventionally manufactured 316L stainless steel. The strengths were dependent on the build direction – the vertically built specimens showed lower proof strengths than the horizontal specimens. The laser welds generally exhibited lower microhardness, proof strengths and fracture strains than the PBF base metal which correlated with the observed structure. This work has demonstrated that PBF built parts can be joined by laser welding to form larger components and provided insight into the resulting strength and ductility.
Kyvelou P, Slack H, Wadee MA, et al., 2021, Material testing and analysis of WAAM stainless steel, Sheffield, UK, Eurosteel 2020
Zhang R, Gardner L, Buchanan C, et al., 2021, Testing and analysis of additively manufactured stainless steel CHS in compression, Thin Walled Structures, Vol: 159, ISSN: 0263-8231
Additive manufacturing, also referred to as 3D printing, has the potential to revolutionise the construction industry, offering opportunities for enhanced design freedom and reduced material use. There is currently, however, very limited data concerning the performance of additively manufactured metallic structural elements. To address this, an experimental and numerical investigation into the cross-sectional behaviour of circular hollow sections (CHS),produced by powder bed fusion (PBF) from Grade 316L stainless steel powder, is presented. The experimental programme comprised tensile coupon tests, initial geometric imperfection measurements and five axially loaded stub column tests on specimens with a range of diameter to-thickness (D/t) ratios. Similar cross-sectional behaviour to that of conventionally produced stainless steel CHS was observed, with the more slender cross-sections displaying increased susceptible to local buckling. In parallel with the experimental study, numerical simulations were carried out initially to replicate the experimental results and then to conduct parametric studies to extend the cross-sectional capacity data over a wider range of D/t ratios. The generated experimental and numerical results, together with other available test data on stainless steel CHS from the literature, were used to evaluate the applicability of existing design approaches for conventionally formed sections to those produced by additive manufacturing. Keywords: Additive manufacturing; Circular hollow sections; Current design approaches; Digital image correlation (DIC); Powder bed fusion (PBF); Stainless steel; Stub column testing; Tensile coupon tests; 3D printing.
Gardner L, Kyvelou P, Herbert G, et al., 2020, Testing and initial verification of the world's first metal 3D printed bridge, Journal of Constructional Steel Research, Vol: 172, Pages: 1-10, ISSN: 0143-974X
Wire and arc additive manufacturing (WAAM) is a method of metal 3D printing that is suited to the requirements of the construction industry in terms of scale, speed and cost. Using this technology, a 10.5 m span footbridge, the first of its kind, has been printed. The testing, analysis and initial verification of the bridge and its components are described herein. The experiments performed included advanced geometric analysis, material testing, compressive testing of cross-sections and full-scale load testing of the bridge at various stages throughout and post construction. Parallel finite element modelling of the full bridge and its constituent elements has also been performed as part of the verification. Confirmation that the bridge was able to sustain its full serviceability design load enabled to the bridge to be unveiled to the public, with controlled access, for Dutch Design Week 2018. Further testing under ultimate limit state design loading is planned before the bridge is placed in its final location and fully opened to the public. The project highlights the potential for metal 3D printing in structural engineering, as well as the necessary considerations for design.
Kyvelou P, Slack H, Daskalaki Mountanou D, et al., 2020, Mechanical and microstructural testing of wire and arc additively manufactured sheet material, Materials and Design, Vol: 192, ISSN: 0264-1275
Wire and arc additive manufacturing (WAAM) is a method of 3D printing that enables large elements to be built, with reasonable printing times and costs. There are, however, uncertainties relating to the structural performance of WAAM material, including the basic mechanical properties, the degree of anisotropy, the influence of the as-built geometry and the variability in response. Towards addressing this knowledge gap, a comprehensive series of tensile tests on WAAM stainless steel was conducted; the results are presented herein. As-built and machined coupons were tested to investigate the influence of the geometrical irregularity on the stress-strain characteristics, while material anisotropy was explored by testing coupons produced at different angles to the printing orientation. Non-contact measurement techniques were employed to determine the geometric properties and deformation fields of the specimens, while sophisticated analysis methods were used for post processing the test data. The material response revealed a significant degree of anisotropy, explained by the existence of a strong crystallographic texture, uncovered by means of electron backscatter diffraction. Finally, the effective mechanical properties of the as-built material were shown to be strongly dependent on the geometric variability; simple geometric measures were therefore developed to characterise the key aspects of the observed behaviour.
Buchanan C, Zhao O, Real E, et al., 2020, Cold-formed stainless steel CHS beam-columns – testing, simulation and design, Engineering Structures, Vol: 213, Pages: 1-23, ISSN: 0141-0296
The present work was prompted by shortcomings identi ed in existing design provisions for stainless steel circular hollow section (CHS) beam-columns. First, addressing a lack of existing experimental data, a series of ferritic stainless steel CHS beam-column tests was undertaken at the cross-section and member levels. In total, 26 beam-column tests, including two section sizes (a non-slender class 3 and slender class 4 cross-section), two member slenderness values for each cross-section type and a wide range of loading eccentricities were carried out to investigate the interaction between local and global buckling. Followingvalidation of nite element (FE) models, a numerical study was then undertaken to explore the buckling response of stainless steel CHS beam-columns, covering austenitic, duplex and ferritic grades with a wide range of local and global slendernesses and applied loading eccentricities. Over 2000 numerical results were generated and used to assess new designproposals for stainless steel beam-columns, featuring improved compression and bending end points and new interaction factors. The new proposals are more consistent and more accuratein their resistance predictions than the current EN 1993-1-4 (2015) design approach. The reliability of the new proposals has been veri ed by means of statistical analyses accordingto EN 1990 (2005).
Gardner L, Buchanan C, Wan W, 2020, Opportunities for metal 3D printing in structural engineering
3D printing, more formally known as additive manufacturing (AM), has the potential to revolutionise the construction industry, with anticipated benefits including greater structural efficiency, reduced material consumption and wastage, streamlining and expedition of the design-build process, enhanced customisation, greater architectural freedom and improved accuracy and safety on-site. Unlike traditional manufacturing methods for construction products, metal 3D printing offers ready opportunities to create non-prismatic sections, internal stiffening, openings, functionally graded elements, variable microstructures and mechanical properties through controlled heating and cooling and thermally-induced prestressing. It is envisaged that AM will complement, rather than replace, conventional production processes, with clear potential for hybrid solutions and structural strengthening and repairs. These opportunities are explored in this paper, along with early applications of metal additive manufacturing in the construction industry and other engineering disciplines.
Buchanan C, Wan W, Gardner L, 2020, Testing of wire and arc additively manufactured stainless steel material and cross-sections
3D printing, or additive manufacturing (AM), is starting to be explored as a viable manufacturing technique in the construction industry. A 10 m span stainless steel pedestrian bridge is being built using Wire and Arc Additive Manufacturing (WAAM) and, upon completion, will be placed in the centre of Amsterdam, the Netherlands. Material tests and cross-section testing on circular hollow section (CHS) and square hollow section (SHS) columns have been undertaken to support this novel project. The unusual nature of the geometry and material properties has necessitated the use of advanced laser scanning and digital image correlation measurement techniques, along with Archimedes' measurements and silicone casting. The material response has been observed to be anisotropic, with a lower Young's modulus and material strength in certain orientations. The ultimate compressive capacities of the tested cross-sections have been observed to have a larger variation between repeat specimens than typically seen with conventionally produced elements, and the ultimate compressive capacities are generally overpredicted by current design methods.
Buchanan C, Gardner L, 2019, Metal 3D printing in construction: a review of methods, research, applications, opportunities and challenges, Engineering Structures, Vol: 180, Pages: 332-348, ISSN: 0141-0296
3D printing, more formally known as additive manufacturing (AM), has the potential to revolutionise the construction industry, with foreseeable benefits including greater structural efficiency, reduction in material consumption and wastage, streamlining and expedition of the design-build process, enhanced customisation, greater architectural freedom and improved accuracy and safety on-site. Unlike traditional manufacturing methods for construction products, metal 3D printing offers ready opportunities to create non-prismatic sections, internal stiffening, openings, functionally graded elements, variable microstructures and mechanical properties through controlled heating and cooling and thermally-induced prestressing. Additive manufacturing offers many opportunities for the construction sector, but there will also be fresh challenges and demands, such as the need for more digitally savvy engineers, greater use of advanced computational analysis and a new way of thinking for the design and verification of structures, with greater emphasis on inspection and load testing. It is envisaged that AM will complement, rather than replace, conventional production processes, with clear potential for hybrid solutions and structural strengthening and repairs. These opportunities and challenges are explored in this paper as part of a wider review of different methods of metal 3D printing, research and early applications of additive manufacturing in the construction industry. Lessons learnt for metal 3D printing in construction from additive manufacturing using other materials and in other industries are also presented.
Buchanan C, Real E, Gardner L, 2018, Testing, simulation and design of cold-formed stainless steel CHS columns, Thin Walled Structures, Vol: 130, Pages: 297-312, ISSN: 0263-8231
Stainless steel tubular members are employed in a range of load-bearing applications due to their strength, durability and aesthetic appeal. From the limited existing test data on stainless steel circular hollow sections (CHS) columns it has been observed that the current Eurocode 3 provisions can be unconservative in their capacity predictions. A comprehensive experimental programme has therefore been undertaken to provide benchmark data to validate numerical models and underpin the development of revised buckling curves; in total 17 austenitic, 9 duplex and 11 ferritic stainless steel CHS column buckling tests and 10 stub column tests have been carried out. Five different cross-section sizes (covering class 1 to class 4 sections) and a wide range of member slendernesses have been examined. The experiments were initially replicated using finite element (FE) simulations; the validated FE models were then used to generate 450 additional column buckling data points. On the basis of the experimental and numerical results, new design recommendations have been made for cold-formed stainless steel CHS columns and statistically validated according to EN 1990.
Buchanan C, Gardner L, Zhao O, et al., 2018, Design of stainless steel CHS beam-columns, Pages: 503-511
The EN 1993-1-4 (2015) design approach for stainless steel CHS beam-column members has been observed from prior experimental studies to provide capacity predictions that can be either overly conservative or unconservative depending upon the ratio of axial load to bending moment. Hence, a numerical parametric study has been undertaken to explore the buckling response of stainless steel CHS beam-columns, covering austenitic, duplex and ferritic grades with a wide range of local and global slendernesses and applied loading eccentricities. Over 2000 numerical results have been generated and used to assess new design proposals for stainless steel beam-columns, featuring improved compression and bending end points and new interaction factors. The new proposals are more consistent and, on average, 4% more accurate in their resistance predictions than the current EN 1993-1-4 (2015) design approach. The reliability of the existing and new proposals has been verified by means of statistical analyses according to EN 1990 (2005).
Buchanan C, Matilainen V-P, Salminen A, et al., 2017, Structural performance of additive manufactured metallic material and cross-sections, Journal of Constructional Steel Research, Vol: 136, Pages: 35-48, ISSN: 0143-974X
Additive manufacturing, a common example of which is 3D printing, has become more prevalent in recent years with it now being possible to form metallic structural elements in this way. There are, however, limited available experimental data on the material behaviour of powder bed fusion (PBF) additive manufactured metallic structural elements and no existing data at the cross-section level; this is addressed in the present paper through a series of tests on additive manufactured stainless steel material and cross-sections. Tensile and compressive coupon tests were used to assess anisotropy, symmetry of stress-strain behaviour and the influence of building direction on the material properties. The yield and ultimate tensile strengths were seen to generally decrease in magnitude with increasing build angle, while a reduction in ductility was observed in some building orientations, and the Young's moduli were typically insensitive to the build angle. The structural behaviour of PBF additive manufactured cross-sections was investigated through a series of square hollow section (SHS) stub column tests, and the results compared with conventionally produced stainless steel SHS. The generated test results have been used to evaluate the applicability of existing design guidance for conventionally produced sections to additive manufactured sections.
Buchanan C, Real E, Gardner L, 2016, Beam-column behaviour of ferritic stainless steel CHS members, 7th International Conference on Coupled Instabilities in Metal Structures. CIMS.
Buchanan C, Gardner L, Liew A, 2016, The continuous strength method for the design of circular hollow sections, Journal of Constructional Steel Research, Vol: 118, Pages: 207-216, ISSN: 0143-974X
Circular hollow sections (CHS) are widely used in a range of structural engineering applications. Their design is covered by all major design codes, which currently use elastic, perfectly-plastic material models and cross-section classification to determine cross-secti\on compressive and flexural resistances. Experimental data for stocky sections show that this can result in overly conservative estimates of cross-section capacity. The continuous strength method (CSM) has been developed to reflect better the observed behaviour of structural sections of different metallic materials. The method is deformation based and allows for the rational exploitation of strain hardening. In this paper, the CSM is extended to cover the design of non-slender and slender structural steel, stainless steel and aluminium CHS, underpinned by and validated against 342 stub column and bending test results. Comparisons with the test results show that, overall, the CSM on average offers more accurate and less scattered predictions of axial and flexural capacities than existing design methods.
Buchanan C, Gardner L, Liew A, 2015, The continuous strength method for circular hollow sections, Pages: 621-628
Circular hollow sections (CHS) are widely used in a range of structural engineering applications. Their design is covered by all major design codes, which currently use elastic, perfectly-plastic material models and cross-section classification to predict cross-section compressive and flexural resistances. Experimental data for stocky sections show that this can result in overly conservative estimates of cross-section capacity. The continuous strength method (CSM) has been developed to reflect better the observed behaviour of metallic materials, with a continuous relationship between cross-section slenderness and deformation capacity, and a strain hardening material model. In this paper, the CSM is extended to cover the design of structural steel, stainless steel and aluminium CHS, underpinned by and validated against 519 stub column and bending test results. Comparisons with the test results show that the CSM offers more accurate and less scattered predictions of axial and flexural capacities than existing design methods.
Gardner L, Law A, Buchanan C, 2014, Unified slenderness limits for structural steel circular hollow sections, Romanian Journal of Technical Sciences, Applied Mechanics, Vol: 59, Pages: 153-163
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