Thin-walled Structures Research Articles

Effect of Deposit Scale on Mechanical Properties of In-Situ Alloyed CrCoNi Medium Entropy Alloys Formed by Directed Energy Deposition

Directed energy deposition (DED), as an additive manufacturing technology, has shown unique advantages in multi-material additive manufacturing and remanufacturing. In this study, two types in-situ alloyed CrCoNi medium entropy alloys that have thin-walled structures with different thicknesses (T1 and T2) were manufactured by the DED process, and the mechanisms of differences in relative density, microstructure, and mechanical properties at different heights were systematically analyzed. In terms of microstructure, the T1 and T2 samples along the building direction exhibit significant differences in crystallographic orientation, grain size, and dislocation density, which are related to the local temperature gradient differences caused by the scanning path and heat accumulation. In terms of mechanical properties at different heights of the two types of thin-walled structures, the yield strength is higher but the elongation is lower at the bottom position of sample, while the yield strength is lower but the elongation is higher at the middle and top positions. The differences of mechanical properties at different heights of the T1 and T2 samples are related to the microstructure and relative density. This finding provides new insights for the design and performance analysis of complex thin-walled structures formed by additive manufacturing.

Investigation of Fabricating Stainless Steel 304L Thin-Wall Structure Using Laser Marking-Assisted Wire Arc Additive Manufacturing Process

Investigation of Fabricating Stainless Steel 304L Thin-Wall Structure Using Laser Marking-Assisted Wire Arc Additive Manufacturing Process

Elucidating the effects of metal transfer modes and investigating the material properties in wire-arc additive manufacturing (WAAM)

AbstractStudies have shown the influence of WAAM process parameters on mechanical properties, bead formation, dimensional accuracy, and microstructure. However, metal transfer modes and their interactions with input variables have not been investigated thoroughly. Therefore, short/spray, pulse and double pulse modes were investigated in this study at different current levels. Bead-on-plate trials were conducted by depositing ER70S-6 wire to investigate bead morphology, dilution, microstructure, and hardness. The study was supported by a detailed statistical approach, including analysis of variance (ANOVA) and regression analysis. Similarly, the combined effects of hatch distance and current were studied on bead formation in multi-layer deposits. Moreover, a thin wall and a cubic structure were deposited to realize the WAAM capability for larger depositions. The microstructures of thin wall and cubic structure were analyzed using optical microscopy (OM) and scanning electron microscopy (SEM). The study concludes that metal transfer modes at various currents significantly influence bead geometry, microstructure and hardness. The microstructure of bead-on-plate trials show fine lamellar structure at low current in all modes. Higher current results in coarse grains with a polygonal and columnar morphology. The hardness shows a decreasing trend as the current increases. The combined effects of current and hatch distance alter bead morphology; however, an optimized combination yields smoother surfaces. The microstructure of thin wall showed a slight anisotropy along the building direction. The presence of small pores was witnessed from OM and SEM images. Similarly, the cubic structure showed a more homogeneous microstructure with much lower porosity. The hardness profile of the thin wall exhibited small fluctuations along the building direction, while that of the cubic structure was more uniform.

Study of mechanical and metallurgical properties of wire arc additively manufactured inconel 718 alloy

The current research work deals with the investigation of mechanical, wetting transition on grain boundary (GB) and metallurgical properties of Inconel 718 alloy used in aerospace industrial applications. The fabrication of thin-wall structure (multilayer structure) is fabricated using wire arc additive manufacturing (WAAM) technique. The novelty of this method is that gas metal arc welding (GMAW) is used as energy source and cold metal transfer (CMT) is used as mode of droplet transfer. Four tensile samples are extracted asper ASTM E8/E8M standards and three microstructure samples are extracted from thin wall structure. Optical microscopy (OM), SEM, EDAX, and EBSD analysis were carried out. In addition, Hardness and tensile tests, as well as fractography analysis were conducted. The grain boundary wetting transition (GBWT) analysis is also carried out. SEM analysis reveals that Nb-rich MC-type carbide contains grain boundaries of droplets, indicating incomplete wetting. Laves and delta (δ) phases are also identified as liquids of a continuous layer separated by Ni elements, indicating complete wetting. EBSD analysis indicates the average grain size as 251.2 μm. The average value of micro hardness as 417.3 HV and UTS as 609.75 MPa are achieved.

The effect of cold forming residual stresses in local fatigue approaches: A numerical perspective

Thin-walled structures generally rely on cold-formed mild steel profiles. Due to cold forming, a significant formation of residual stresses impacts their overall fatigue behaviour. In this work, a state-of-the-art framework for fatigue life prediction is proposed and applied to both roll-formed and press-braked full-scale profiles. In summary, the profile’s manufacturing process is numerically simulated to obtain a representative residual stress field. These results are then used as the initial state during a subsequent structural and fatigue analysis. A clear detrimental residual stress effect is verified. Importantly, however, is to note that prediction accuracy increases significantly when these effects are considered.

Effect of atomic oxygen and vacuum thermal aging on graphene and glass fibre reinforced cyanate ester-based shape memory polymer composite for deployable thin wall structures

Deployable components and structures are a crucial part of space exploration. Due to fewer parts, low weight and cost, shape memory polymers (SMPs) and their composites (SMPCs) are considered ideal candidates for this. However, lower thermal stability and poor durability in the space environment have limited their applicability. This research work details the development of Graphene Nanoplatelets (GNP) filled Glass Fibre (GF) reinforced cyanate ester-based SMPC with 0/90° and ±45° sandwich fibre lay-up configuration capable of multidirectional shape programming. The SMP matrix was synthesised by mixing Cyanate Ester and Polyethylene Glycol (PEG) with added GNP. SMPC was fabricated by pouring the SMP mixture into a pre-prepared glass mould with the added GF layers. The synthesised SMPC showed shape programming and recovery at 169.01 ± 0.62 °C and stable thermomechanical properties at the temperature of 130 °C. Durability tests at extreme environmental conditions including Atomic Oxygen exposure, thermal vacuum aging, and elevated-temperature behaviour tests were conducted as these tests evaluate the durability and applicability of the SMPC for use in Earth's orbits and lunar environments. The performances of the samples before and after durability tests were measured through mechanical tests, shape memory effect tests and a series of characterisation methods such as microscopic image analysis, FTIR and dynamic mechanical analysis. According to the results, AO exposure affected the SMPCs by eroding their surface. There were no changes in the chemical structure of the SMPC yet the thermomechanical, mechanical and shape memory properties were decreased without compromising their safe operational levels such as storage onset temperatures (128.79 ± 3.08 °C), maximum tensile stress (114.99 ± 21.52 MPa), shape fixity (100 %) and recovery ratios (100 %). The erosion resistance of the GNP-filled SMPCs was improved with ∼54.35 % less erosion than the SMPC without GNP. The vacuum thermal aging slightly slowed shape recovery from 31.17 % to 8.32 % at 160 °C due to PEG crosslink degradation, however, 100 % shape recovery was achieved at the end. Further durability tests under cryogenic temperatures and effects after vacuum thermal cycles are warranted to observe the synergistic effect on the SMPC for future developments. Exploring the scalability and additive manufacturability of the developed SMPC can be advantageous in the future while mitigating challenges such as complex shape programming, long-term materials degradation, resource efficiency and compliance with safety standards.

Experimental investigation on the shear performance of hybrid structures comprising textile reinforced concrete stay-in-place formwork and reinforced concrete

Recently, the application of textile-reinforced concrete (TRC) in thin-walled precast structures has gained significant attention. Among these innovations, the combination of TRC and reinforced concrete (RC) has emerged as an effective method for creating hybrid structural systems. This paper presents the experimental results analyzing the shear behavior of a hybrid deck slab structure consisting of TRC stay-in-place (SiP) formwork and RC components. Shear performance was evaluated using 3-point bending tests on four large-scale specimens with aspect ratios (a/d) varying from 1.6 to 2.3. The average load carried by the TRC SiP formwork prior to failure—due to textile reinforcement rupture—was approximately 26.3 kN, with compressive strains at the top edge ranging from 2.8 to 3.4 ‰, just below the concrete's ultimate strain. The findings demonstrate the versatility of TRC SiP-formwork, highlighting its adaptable cross-section and substantial load-bearing capabilities, making it particularly suitable for composite bridge deck applications. The specimens experienced both shear compression and diagonal shear failures. Moreover, the TRC SiP-formwork effectively mitigated transverse cracking at the interface, enhancing bond strength and improving overall structural performance

The crack propagation behaviors, microstructure and mechanical properties of T-welded joints for TIGW with crystal plasticity model and XFEM

In view of the significant impact of welding defects on the fracture behaviors involving the strength, stress concentration and bearing capacity of welded joint, etc., the propagation behaviors and mechanical properties of welded joints with porosity and micro crack are deeply investigated using a multiscale method. In this work, a crack nucleation and propagation model based on crystal plasticity theory, combined with the extended finite element method (XFEM), is established for the T-welded joint. The maximum slip on the predominant slip system method is applied to predict the crack propagation path of pores and micro cracks in the weld zone (WZ), and the effect of crystal orientation on crack growth is explored. Then, a continuous model is used to analyze the micro and macro fracture behaviors near the weld under tensile load, combined with the maximum principal stress method. The WZ and heat affected zone (HAZ) are observed using electron backscatter diffraction (EBSD) to study the microstructure evolution. Considering grain boundaries, the image information of crystal morphology is processed through binary image analysis for FE modeling. The local mechanical properties testing is carried out using micro-specimens of HAZ and WZ to calibrate the crystal plastic parameters. The results show that the resolved shear stress of the predominant slip system of crack initiation and propagation elements is increased by pore and crack defects. The fracture positions of tensile specimens through numerical simulation are in good agreement with the macroscopic experimental results. It will provide an analysis basis for preventing fracture failure and improving the service performance of thin-walled structures in future.

A one-dimensional higher-order dynamic modeling method for thin-walled beams with circular cross-sections

This paper addresses the construction of a dynamical model for a thin-walled beam with circular cross-section in the framework of one-dimensional higher-order beam theory. And a method for pattern recognition of circular thin-walled structures is proposed based on principal component analysis. Initially, a set of equal length linear segments are defined to discretize the mid-line of a circular section. Preliminary deformation modes of thin-walled structures, defined over the cross-section through kinematic concept, are parametrically derived through changing the discretization degree of the section. Next, the generalized eigenvectors are derived from the governing equations, and the characteristic deformation modes of circular sections with different discretization degrees are solved based on principal component analysis. In addition, a reduced higher-order model can be obtained by updating the initial governing equations with a selective set of cross-section deformation modes. The features include further reducing the number of degree of freedoms (DOFs) and significantly improving computational efficiency while ensuring accuracy. For illustrative purposes, the versatility of the procedure is validated through both numerical examples and comparisons with other theories.

Curved-crease origami hybrid structures with tailorable buckling and energy absorption

Origami-inspired structures (OIS), renowned for their lightweight design, encounter energy absorption challenges attributed to global buckling. This paper presents a design and hybridization strategy that integrates origami-inspired structures with existing state-of-the-art cellular lattices to create origami-inspired hybrid structures (OIHS), aimed at addressing buckling concerns and customizing the crushing behavior of thin-walled structures. The investigation explores the compressive response of additively-manufactured curved crease OIS and prismatic structures (PS) with diverse cross-sections, including circular origami structure (COS), triangular origami structure (TOS), square origami structure (SOS), and hexagon origami structure (HOS). The experimental results indicate that the COS design offered the highest specific energy absorption (SEA) of 11 kJ/kg, due to controlled deformation associated with the crease lines. The COS hybridized structure, with cellular lattices, exhibited a yielding-dominated behavior, resulting in a lower peak force, a sustained plateau force and a well-controlled deformation response. Furthermore, the COS hybridized with a plate lattice, exceeded the SEA of the auxetic and BCC OIHS structures by 62 % and 71 %, respectively. The circular origami plate hybrid (COPH) design was selected to investigate the effect of varying the top edge angle (α) and the relative density on the mechanical properties and the SEA. It was found that increasing the value of alpha resulted in a higher peak stress and an increased buckling load. Moreover, with its higher relative density, the vertical plate within the OIS contributed to a greater level of structural stability in the plateau region, resulting in an increase in mechanical properties and SEA. These findings advance the understanding of OIS by presenting effective hybridization strategies to mitigate buckling and achieve stable plateau stresses and higher crushing force efficiencies, particularly at lower relative densities, surpassing those reported in the literature. This contributes significantly to the broader field of lightweight structural design.

Crashworthiness and optimization design of additive manufacturing double gradient lattice enhanced thin-walled tubes under dynamic impact loading

It is of paramount importance to ensure the protection of both infrastructure and personnel in scenarios characterized by a high strain rate dynamic impact. In order to develop lighter weight and higher crashworthiness energy-absorbing structures, this paper incorporates the bionic design of lattice reinforced thin-walled tube structures in the form of double gradient, as a means of achieving the aforementioned objectives. Material mechanical properties and the designed structures at high strain rate were researched using Split Hopkinson Pressure Bar (SHPB) experiment. The effects of gradient form and gradient parameters on the deformation pattern and crashworthiness of lattice enhanced thin-walled tubes are researched by means of the validated finite element model and the experimentally fitted Johnson-Cook material model. The results indicate that the specific energy absorption of the double gradient lattice enhanced thin-walled tube (T3L3) is increased by 36.19 % and the peak crush force is reduced by 21.19 % compared to the lattice enhanced thin-walled tube without gradient. Finally, the multi-objective optimization analysis of the T3L3 with the objective of achieving the maximum SEA and minimum PCF is carried out by Response Surface Methodology (RSM) and Non-dominated Sorting Genetic Algorithm-II (NSGA-II) to find the Pareto optimal solution set. Double-gradient bionic structure offers a new idea for designing energy-absorbing structures under high-speed impact conditions.

Practical experience in the implementation of innovative building materials and products

The improvement and creation of new production technologies is largely determined by the level of innovation in the field of materials science. In this paper, the experience of practical implementation of innovative building materials and products made of light steel thin-walled structures in the real sector of the economy is considered. Suggestions are given for possible use in state programs for the restoration and development of new territories of Russia. The problem of economic recovery, creation of new jobs, implementation of development programs for specific subjects of new territories can be solved by consolidating the subjects of the Russian Federation and forming professional construction teams on the basis of specialized enterprises of the subject of the Russian Federation for the implementation of state programs. The authors, if necessary, offer services for training and transfer of scientific and technical knowledge to Customer specialists at the place of construction of prefabricated facilities.

Experimental and Numerical Investigation of Acoustic Emission Source Localization Using an Enhanced Guided Wave Phased Array Method.

To detect damage in mechanical structures, acoustic emission (AE) inspection is considered as a powerful tool. Generally, the classical acoustic emission detection method uses a sparse sensor array to identify damage and its location. It often depends on a pre-defined wave velocity and it is difficult to yield a high localization accuracy for complicated structures using this method. In this paper, the passive guided wave phased array method, a dense sensor array method, is studied, aiming to obtain better AE localization accuracy in aluminum thin plates. Specifically, the proposed method uses a cross-shaped phased array enhanced with four additional far-end sensors for AE source localization. The proposed two-step method first calculates the real-time velocity and the polar angle of the AE source using the phased array algorithm, and then solves the location of the AE source with the additional far-end sensor. Both numerical and physical experiments on an aluminum flat panel are carried out to validate the proposed method. It is found that using the cross-shaped guided wave phased array method with enhanced far-end sensors can localize the coordinates of the AE source accurately without knowing the wave velocity in advance. The proposed method is also extended to a stiffened thin-walled structure with high localization accuracy, which validates its AE source localization ability for complicated structures. Finally, the influences of cross-shaped phased array element number and the time window length on the proposed method are discussed in detail.

Verification of Numerical Models of High Thin-Walled Cold-Formed Steel Purlins.

High thin-walled cold-formed steel purlins of the Z cross section are important elements of large-span steel structures in the construction industry. The present numerical study uses the finite element method to analyse the 300 mm and 350 mm high Z cross sections in-depth. The prepared numerical models are verified and validated at several levels with experiments that have been previously published. Significant agreement between the numerical models and the experimental results regarding Mises stress, proportional strain, failure mode, and force-deformation diagram have been obtained. With the verification, the presented procedure and partial findings can be applied to other similar problems. The results can be used to help research and corporate groups optimise the structural design of cold-formed thin-walled steel structures.

Parametric Analysis of Critical Buckling in Composite Laminate Structures under Mechanical and Thermal Loads: A Finite Element and Machine Learning Approach.

This research focuses on investigating the buckling strength of thin-walled composite structures featuring various shapes of holes, laminates, and composite materials. A parametric study is conducted to optimize and identify the most suitable combination of material and structural parameters, ensuring the resilience of structure under both mechanical and thermal loads. Initially, a numerical approach employing the finite element method is used to design the C-section thin-walled composite structure. Later, various structural and material parameters like spacing ratio, opening ratio, hole shape, fiber orientation, and laminate sequence are systematically varied. Subsequently, simulation data from numerous cases are utilized to identify the best parameter combination using machine learning algorithms. Various ML techniques such as linear regression, lasso regression, decision tree, random forest, and gradient boosting are employed to assess their accuracy in comparison with finite element results. As a result, the simulation model showcases the variation in critical buckling load when altering the structural and material properties. Additionally, the machine learning models successfully predict the optimal critical buckling load under mechanical and thermal loading conditions. In summary, this paper delves into the study of the stability of C-section thin-walled composite structures with holes under mechanical and thermal loading conditions using finite element analysis and machine learning studies.

Limit states of thin-walled composite structures with closed sections under axial compression

The subjects of the study were thin-walled composite columns with closed cross sections manufactured using the autoclave technique. The composite profiles were characterized by the fact that they had a constant height and arrangement of laminate layers, however, varied cross-sectional shapes. The study was conducted using several interdisciplinary experimental research methods and advanced numerical simulations. In the course of the research, both forms of structural stability loss were registered, and damage to composite structures was assessed. In the course of the research, the influence of the shape of the cross-section on the stability and load-carrying capacity of the structure was evaluated. A measurable effect of the conducted research was the determination of the structure's post-buckling equilibrium paths, which made it possible to determine the structure's behavior in the full range of loading. In addition, the author's numerical models developed enabled validation of parallel experimental studies. The developed numerical models were based on a failure criterion known as progressive failure analysis - which allowed a thorough assessment of the failure mechanism of the composite material.

Experimental-Numerical Analysis of Thin-Walled Box Structures Stiffened with Corrugated Ribs, Subjected to Torsion

Experimental-Numerical Analysis of Thin-Walled Box Structures Stiffened with Corrugated Ribs, Subjected to Torsion

Prediction of sectional collapse of thin-walled structure under pure bending by nonlinear composite beam theory

Brazier (1927) found that when one dimension of the beam cross-section was relatively smaller than the others, large in-plane displacements over the cross-section might occur, even though the strains could remain very small. Under this circumstance, the so-called Brazier effect refers to the cross-sectional ovalization, which leads to nonlinear bending buckling and collapses. This paper studies the Brazier effect by the nonlinear Variational Asymptotic Beam Sectional Analysis (VABS) theory which considers finite cross-sectional deformations. Nonlinear VABS reduces three-dimensional (3D) continuum to a one-dimensional (1D) beam analysis and a two-dimensional (2D) cross-sectional analysis featuring both geometric and material nonlinearities without unnecessary kinematic assumptions. The present theory is implemented using the finite element method (FEM) in the VABS code, a general-purpose beam cross-sectional analysis tool. An iterative method is applied to solve the finite warping field for the classical-type model using the Euler–Bernoulli beam theory. The deformation gradient tensor is directly used to deal with finite deformation, various strain definitions, and several types of material laws. Numerical examples demonstrate the capabilities of VABS to predict the sectional collapse of thin-walled structures under pure bending.

Seismic behavior of lightweight steel frame with thin-walled steel skeleton-lightweight concrete wall

In this study, an innovative prefabricated lightweight steel frame with thin-walled steel skeleton-lightweight concrete composite wall structure (LSF-TSLC) is proposed. The proposed LSF-TSLC has the lightweight steel frame (LSF) as the vertical load-bearing system, whereas the thin-walled steel skeleton-lightweight concrete composite wall (TSLC) acts as the main component for horizontal earthquake resistance. A full-scale LSF specimen and three full-scale LSF-TSLC specimens were prepared considering the variables of wall installation method (embedded, external) and thin-walled steel skeleton distribution (frame type, truss type). The corresponding seismic behavior was experimentally investigated by evaluating the hysteretic characteristics, failure mode, ultimate bearing capacity, deformation performance, stiffness degradation, energy dissipation, and strain characteristics. The results showed that the plastic hinges appeared at the beam ends and column bases of LSF. Due to the shear failure, the embedded and external TSLC exhibited grid cracks and diagonal cracks, respectively. The LSF and TSLC had a good coordinating deformation capacity, while the LSF-TSLC structure had two seismic fortification lines. Compared with LSF, the ultimate bearing capacity and stiffness of LSF-TSLC were increased by 2.1 times and 5.1 times, respectively. The deformation capacity and energy dissipation of LSF-TSLC were significantly improved compared to LSF. The self-tapping nail joint of the embedded wall and the high-strength bolt joint of the external wall had reliable connectivity performance. The numerical simulation of LSF were conducted to verify the plastic analysis model for LSF. And the ultimate bearing capacity calculation method for the LSF-TSLC structure was proposed based on the Strut-and-Tie model.

Effect of forming strategies on the microstructure and mechanical properties of thin-walled CuCrZr alloy fabricated by selective laser melting

Thin-walled structures are widely used in industrial fields such as radiators and critical aerospace components due to their advantages in lightweight design. However, traditional manufacturing techniques struggle to meet the high-precision requirements for complex components. Selective Laser Melting (SLM) technology, characterized by high design flexibility and high geometric production freedom, is a promising alternative. This study employs SLM technology to fabricate CuCrZr alloy thin walls and systematically investigates the effects of interlayer rotation angles and placement strategies on the forming quality and mechanical properties of the thin walls produced by SLM. The results indicate that different interlayer rotation angles and placement strategies lead to variations in defect types and shapes. When the interlayer rotation angle is 0° and the specimens are placed perpendicular to the recoater blade, numerous lack-of-fusion (LOF) defects are observed on the specimens. These lack-of-fusion defects are caused by factors such as low scanning line flatness and uneven energy distribution when the interlayer rotation angle is 0°. In contrast to the 0° interlayer rotation angle, the specimens with a 67° rotation angle exhibit significantly more curved columnar grains in the growth direction. The thin-walled specimens with a 67° interlayer rotation angle and placed parallel to the recoater blade show the best mechanical performance, with a maximum tensile strength of 254.19 MPa and an elongation of 48.81 %.