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• Low-velocity impact response of the orthogonal corrugated sandwich panel are tested and simulated. • Damage area and failure mechanism of the orthogonal corrugated sandwich panel under different shape impactor are analyzed and discussed by finite element simulation method. • The impactor shape affects not only the damage characteristic in the visual inspections of the orthogonal corrugated sandwich panel, but also the in-plane damage propagation range and the main damage and failure modes of the sandwich panel. This study aims at investigating the low-velocity impact resistance of the composite orthogonal corrugated sandwich panel through experimental and simulation methods, considering different shaped impactors. To that scope, the progressive damage model with the sandwich panel is developed and numerical investigations are carried out in ABAQUS / Explicit. The results show that as the impactor changes from flat to hemispherical and then to conical shape, the first peak load gradually decreases, and the maximum displacement of the impactor and total energy absorption gradually increase. The high impact energy makes the sandwich panel more compliant. Furthermore, the expansion area of fiber damage, matrix damage and delamination in the top face sheet, core and bottom face sheet depends on the impactor shape and impact energy. Under high impact energy, the damage under the conical impactor mainly expands along the thickness direction of the sandwich panel rather than in the in-plane direction, while the flat impactor causes large damage area in the in-plane direction as well. [Display omitted] [ABSTRACT FROM AUTHOR]

• A novel I-shape self-locked thin-walled structure (IST-ST) and system (IST-SY) is proposed based on the mortise & tenon joint principle. • The retrofitted new design with the multi-stair mortise & tenon joint principle could effectively eliminate the peak load and avoid deformation instability. • Self-locking systems can suppress lateral splashing of inner elements. • Self-locked systems have better energy-absorbing performance than other self-locked systems. In this paper, an I-shaped self-locked thin-walled system (IST-SY) composed of I-shaped self-locked thin-walled structures (IST-STs), combining with the mortise & tenon joint (MTJ) principle originated from ancient China and the I-shaped thin-walled structure, was proposed to avoid the splashing of the structures. Then, the IST-ST was retrofitted according to the multi-stair MTJ principle to improve the energy absorption capacity. The loading response curve, deformation mode, and energy absorption of the IST-ST and retrofitted IST-STs (RIST-STs) were investigated systematically by combined experimental and numerical efforts. The results show that the IST-ST was particularly susceptible to unstable catastrophic collapses, characterized by multiple peaks in response curves, whereas the RIST-STs with an appropriate stair panel exhibit exceptionally high damage tolerance compared with the original one. The introduction of the stair panels that link to adjacent panels provides additional support to avoid buckling instability that causes catastrophic collapse, thus generating a more uniform plastic deformation distribution. It effectively curtails the initial high crushing resistance and makes the load more stable on the premise of energy absorption. To demonstrate the validity of the self-locked characteristic, flatwise crushing was also carried out on the proposed self-locked systems, which could successfully resist lateral splashing owing to the unique I-shaped section with the concave-convex feature. The proposed self-locked structures & system exhibit better energy absorption performance than the existing self-locked structures & systems, which was 128.11 %, and 62.97 % higher than the foam-filled bidirectional self-locked structures & system, respectively. This work paves a novel avenue for the design diversity of self-locked energy absorption systems. [ABSTRACT FROM AUTHOR]

• Repair of CFRP with asymmetric damage through double-sided adhesive patch. • Investigation on the mechanical performance of the repaired CFRP with different bondline thicknesses. • A numerical damage model was constructed using FEM, aiding the analysis of damage evolution and failure mode in the repaired CFRP with different bondline thicknesses. As a common CFRP repair method, double-sided adhesive patch has been widely used in the automotive and aeronautic industry. More specific research is thus needed to help better understanding the effect of repairing parameters on the mechanical performance of CFRP structures after patch bonding. In this paper, experimental and Finite Element Modelling (FEM) efforts were made on the adhesive repaired CFRP laminate with different bondline thicknesses. Artificial damage was prefabricated in the centre of the CFRP laminate, which was then repaired through double-sided adhesive patch. Quasi-static tensile tests were conducted on the repaired specimen up to failure, to obtain the load-displacement curves. With a bondline thickness of 0.5 mm, the repaired CFRP structure reached its maximum peak load, increased by 25.3% and 26.4% compared to 0.2 mm and 1.0 mm bondline thicknesses, respectively. SEM observations were used to analyse the influence of adhesive thickness on the fracture modes. Combined with Cohesive Zone Model (CZM) for the adhesive layer and Hashin damage criterion for the CFRP, the FE model of the CFRP laminate repaired with double-sided adhesive patch subjected to tensile loading was established. Finally, the damage evolution as well as the failure modes in the parent laminate and adhesive layer with different bondline thicknesses were compared and analysed. It was revealed that bondline thickness can effectively affect the mechanical performance of CFRP laminate after adhesive patch repair. [ABSTRACT FROM AUTHOR]

• Machine learning-based study to understand significant probing parameters for the cylindrical shell under axial compression. • Probe maps constructed with significant probing parameters. • Identification of buckling initiation location along with competing locations using probe maps. • Numerical and experimental study on peak load prediction of cylindrical shells using probe maps. A Machine Learning (ML) based analysis is conducted to find the most influential probing parameter in determining the buckling initiation location by assessing Probe Force–Probe Displacement characteristic curves. This is followed by the construction of Probe maps, which systematically depict the variation of this parameter with the help of numerical simulations incorporating Measured Geometric Imperfections (MGI). The probe maps hence constructed are found to be effective in identifying the critical locations where a single dimple is likely to initiate the buckling, enabling the complete exploration of the critical single dimple states of the structure. The experiments by probing the structure at the critical locations identified using probe maps show accurate prediction of the peak load-carrying capacity. The approach presented in the study may be extrapolated to characterize imperfection-sensitive structures in general. [ABSTRACT FROM AUTHOR]

• A novel origami multi-cell tube was proposed to decrease F max and improve SEA. • Modified Bayesian optimization to handle mixed categorical-continuous variables. • Optimal W2C facilitates origami progressively folding and enhances SEA by 40 %. Multi-cell structures have been widely utilized in energy-absorbing applications for their lightweight and superior mechanical properties. However, they may produce high peak forces that are harmful to occupant safety during a vehicle collision. In addition, the naturally formed folding and global bending modes under axial loads can significantly restrict their energy-absorbing capability. In this study, a novel origami multi-cell structure is proposed to avoid excessive peak loads and at the same time to guide the deformation mode to improve the energy-absorbing capability. Four cross-sectional types of origami multi-cell structures are investigated experimentally and numerically. The results indicated that the web-to-web (W2W) type origami multi-cell structures are most promising for energy absorption, while web-to-corner (W2C) structures yield low peak forces and excellent deformation modes in our study cases. To further exploit the potential of these structures, multi-objective optimization is required to consider the conflicting objectives of maximizing energy-absorbing capability and minimizing the peak force. However, it is challenging for traditional optimization to deal with continuous, integer, and categorical variables simultaneously. Therefore, the Bayesian optimization method based on the Hamming distance is utilized to handle mixed categorical-continuous variables to optimize origami multi-cell tubes. The optimization results indicated that the optimal origami W2C can decrease the peak force by 30 % while keeping a similar level of specific energy-absorbing capability compared with the conventional W2C structure. Moreover, the optimal origami W2C structure can improve the energy absorption by 40 % compared with the origami W2C baseline design. [ABSTRACT FROM AUTHOR]

• The novel honeycomb core sandwich structures were fabricated by combinations of solid-state joining and adhesive bonding processes. • The combined friction stir spot welded, with disc inserts and adhesive bonded, demonstrated exceptional peak load-to-weight ratio and fracture energy. • The peak load of the hybrid bonding specimen with disc insert improved by 705 % and 854 % in the peel and shear test compared to the conventional adhesive bonded specimen. • The stiffness and peak load results of FEA of three-point bending were in good agreement with the experimental results for all types of adhesive-bonded specimens. In the present work, the novel sandwich structures with honeycomb core are fabricated by a solid-state joining process — friction stir spot welding (FSSW), without and with disc inserts (abbreviated as FSSW and FSSW_D) and hybrid joints without and with disc inserts (abbreviated as FSSW_AB and FSSW_D_AB). Their mechanical performance was compared with adhesive-bonded (AB) joints through the lap-shear, peel, bend, and scaled-up forming tests. Further, numerical simulations of a few FSSW strategies and AB joints are performed in Abaqus to predict the load-displacement response and Mises stress during bending. Proposing the fabrication stretegies, implementation and testing, along with numerical prediction of behavior of such joints, are the novel contributions. The peel tests showed substantial improvement in load capacity from 232 % to 705 % for FSSW, FSSW_AB, FSSW_D, and FSSW_D_AB joints, compared to AB joints. In the lap-shear tests, all joint types displayed significantly enhanced peak load over AB joints, ranging from 568 % to 1015 %. The hybrid joints, such as FSSW_AB and FSSW_D_AB, consistently outperformed the corresponding spot-welded joints, FSSW and FSSW_D, due to the sharing of load between the AB and metallurgical bonding. The FSSW_D_AB joints demonstrated exceptional peak load-to-weight ratio and fracture energy. The failure modes were consistent, with disc-inserted structures showing failure at the front-side welds for lap-shear and peel tests. During bending, the numerical modelling results were in good agreement up to the peak load. Bending panels made by FSSW_D_AB demonstrated improvement in specific stiffness and peak load by 46 % and 6.12 %, respectively, compared to the AB panel. Lastly, the scaled-up hybrid sandwich panel (FSSW_D_AB) showed significant improvement in deliverables when compared with the AB panel. [ABSTRACT FROM AUTHOR]

• A novel carbon/aramid weft-knitted reinforced hybrid composite with good impact resistance was proposed. • The effects of knitted stitches and loop configurations on the low-velocity response of carbon/aramid hybrid composites were investigated. • Multiple damage observation methods were adopted, such as three-dimensional optical microscopy, ultrasonic C-scan, and micro-CT for multi-scale and quantitative damage analysis. Carbon and aramid fiber hybridization is an effective method to improve the impact toughness of composites, thus this paper attempts to develop carbon/aramid hybrid weft-knitted reinforced composites to improve the impact resistance of carbon fiber composites. Three hybrid and two non-hybrid weft-knitted reinforced composites employing carbon and aramid bundles were prepared. Low-velocity impact tests at different impact energies were performed, and the impacted samples were analyzed for visual and internal damages utilizing a three-dimensional optical microscope, ultrasonic C-scan, and micro-CT to explore the damage mechanisms. The results demonstrate that the knitted stitches and loop configuration affect the peak load, deflection, and damage crack initiation and expansion of the composites. The alternating configurations of carbon and aramid fiber in the in-plane and thickness directions incorporate the advantages of the high strength of carbon fibers and the toughness of aramid, exhibiting good impact mechanical properties and damage tolerance. The tight loop laminated structure had excellent impact resistance, with prominent peak loads and tiny damage volumes, but it encountered internal delamination and loop breakages. [ABSTRACT FROM AUTHOR]

• Reinforcing the CFRP foam sandwich structure by orthogonal grid. • Testing the impact characteristics of each position at different energies. • Comparing the impact resistance of the sandwich panel at different positions. • Numerical simulation of the impact process for each position. • The proposed structure has the advantage of lightweight and high impact resistance. Orthogonal grid structures, which are widely used in engineering, are incorporated into the foam to form the grid reinforced core. However, the impact resistance of this type of sandwich structure varies with position. In this paper, the low-velocity impact performance of orthogonal grid reinforced CFRP-foam sandwich structure at different positions was investigated. The drop hammer low-velocity impact tests were conducted at 30 J, 50 J and 80 J energy for the intersection, rib, and center positions, respectively, and the impact resistance of the three positions was further compared with the impact data. The test results showed that the intersection and rib exhibited fiber fracture and delamination of CFRP face and grid, as well as foam crushing and cracking. The center position showed face perforation and foam crushing. At the same impact energy, the intersection position had the strongest impact resistance, with an initial stiffness about 18 % higher than that of the rib, and their peak load per unit mass was higher than that of CFRP-foam sandwich panels, and the center was the weakest. In addition, numerical simulations were performed which were in good agreement with the tests, and the damage processes at different stages were discussed. The lightweight, high impact resistant sandwich structure proposed can provide a reference for structural design. [ABSTRACT FROM AUTHOR]

• Experimental study on Non-destructive characterization of cylindrical shell by probing. • Geometric imperfections of cylindrical shells is measured to aid the identification of appropriate probe locations. • Least resistance path and probing forces are used to single out a best probe location. • Peak load carrying capacity of the cylindrical shell under axial compression is predicted using probing procedure. In the present study, the prediction of the critical buckling load of an axially compressed cylindrical shell is investigated based on the novel non-destructive probing method with the aid of Measured Geometric Imperfections (MGI). A laser point scanner is used to obtain the imperfection data. The imperfection data is analyzed to find a sample space of points where the buckling is likely to initiate. The optimum location for probing is determined from the sample set by finding the Least Resistance Path (LRP) to probing using two methods, one based on the Energy barrier and the other from the reaction forces observed corresponding to deep probe advancements. It is found that MGI can aid the procedure by improving the selection of the probing points and hence the prediction accuracy; However, MGI does not eliminate the need for multiple probing. The study has shown the possibility of obtaining multiple probing locations that can predict the peak load within acceptable levels of accuracy. [ABSTRACT FROM AUTHOR]

• The seismic behaviour of large-scale concrete-filled FRP tubes consisting of H-steel with shear studs (HS-CFFTs) was investigated. • Hysteretic curves of HS-CFFTs were full fusiform without pinching phenomenon, indicating their ample energy dissipation ability. • The local buckling of H-steel was prohibited due to the efficient concrete support and the effective FRP confinement. • A numerical model was established to provid a computationally efficient and reasonably accurate approach for simulating HS-CFFTs. Existing studies about concrete-filled FRP tubes (CFFTs) are generally focused on their behaviour under axial load, which have demonstrated their excellent compressive ductility. For their applications in regions with seismic risk, longitudinal reinforcements should be provided for CFFTs in order to ensure their ability to resist bending moments. In published literatures, longitudinal reinforcements for CFFTs were mostly steel rebars or FRP rebars, while only limited studies were about CFFTs reinforced with profiled-steel. Against this background, 6 circular large-scale CFFTs consisting of H-steel with shear studs (HS-CFFTs) were investigated experimentally under combined axial load and lateral cyclic load to study their seismic behaviour. These HS-CFFTs were designed with a total height of 2150 mm and a concrete diameter of 300 mm, and the testing parameters included the FRP thickness (t frp = 4.0 mm ∼ 6.0 mm), the axial load ratio (n = 0.2 ∼ 0.33), as well as the area ratio of H-steel (ρ = 4.54% ∼ 5.67%). Test results indicated that, (1) HS-CFFTs exhibited rounded hysteretic curves with ample energy dissipation capacity; (2) the H-steel experienced no local buckling due to the effective concrete support and the sufficient FRP confinement; (3) the FRP tube thickness was positively correlated with the peak lateral load and the ductility of HS-CFFTs; compared with HS-CFFTs with t frp = 4 mm, HS-CFFTs with t frp = 6 mm had a higher peak load F P (7.3% ∼ 7.4% higher) and a larger ductility index μ δ (3.4% ∼ 11.7% higher); (4) increasing the H-steel ratio could effectively improve the seismic performance of HS-CFFTs; HS-CFFTs with ρ = 5.67% had higher peak load (2.5% ∼ 10.0% higher) compared with those with ρ = 4.54%; (5) the ductility of HS-CFFTs would decrease obviously as the axial load ratio increased; the ductility index μ δ for HS-CFFTs with n = 0.33 was smaller (14.1% ∼ 25.0% lower) than the counterparts with n = 0.2. A numerical model incorporating with "NonlinearBeamColumn" elements as well as specific constitutive models for the FRP tube, the H-steel and the concrete core was established on the OpenSees platform. The proposed numerical model provided a simple, computationally efficient and reasonably accurate approach for simulating the hysteretic behaviour of HS-CFFTs. [ABSTRACT FROM AUTHOR]

In aluminum alloy reticulated shell structures with gusset joints, the roof panel is effectively connected with the structural members through a clamp connection, enabling the roof panels to participate in the force resisting system. The performance of the connection between the roof panels and the members is the foundation for studying the collaborative action of the roof panels and the members. Relevant studies have shown that when the roof panels participate in the force resisting system, there is mainly a tensile force in the roof panels perpendicular to the axis of the members. Therefore, this paper experimentally studied the mechanical performance of the clamp connection between the roof panels and the members under the tensile force in the roof panels, and employed two-dimensional plane digital image correlation (DIC) to measure the deformation of the specimen section during the entire loading process, thus exploring the force transmission mechanism of the connection. The tensile capacity of the connection can be divided into four stages: roof panel sliding, roof panel tension–shear, lower limb bending of the strip, and roof panel bending stages. The mechanical index of the connection is primarily determined by the tension–shear stage of the roof panel, and the ultimate strength and stiffness can be determined as the peak load and linear segment stiffness of the connection at this stage. The refined finite element model was further established, and it was verified that the model could efficiently simulate the mechanical properties of the connection through comparison with the test. Parametric analysis shows that with an increase in the friction coefficient between materials, roof panel thickness, angle between roof panel and flange, and bolt length adjustment, the restraint on the roof panel increases, and the failure mode of the clamp connection changes. Based on the parametric analysis, the recommended values of the friction coefficient between the materials, minimum panel thickness, minimum bolt screw depth, and maximum bolt spacing are provided. Finally, combined with the theoretical analysis, calculation formulas for the tensile strength and stiffness of the connection were proposed. A comparison with the test results indicates that the prediction accuracy of the formula proposed in this study is good. • The force transfer mechanism of aluminum alloy roof panel-member coupler connection under tensile force is obtained. • A high accuracy refined finite element model of aluminum alloy roof panel-member coupler connection is established. • Suggestions on design of aluminum alloy roof panel-member coupler connection are given. • Calculation formulas for the ultimate bearing capacity and stiffness of the connection were proposed. [ABSTRACT FROM AUTHOR]

In this research, an improved friction self-piercing riveting (F-SPR) process with internally threaded rivet and flat die was proposed to achieve hybrid riveted/solid-state bonded connection for low-ductility aluminium alloys. Instead of relying on rivet shank flaring to form mechanical interlock in the existing F-SPR process, a reliable threaded connection was established between the rivet shank and sheets by rapid filling of sheet material into the rivet thread grooves. A perfectly flat joint bottom was formed without inducing large-scale sheet distortion. A series of experimental tests were performed to clarify the joint quality characteristics, formation mechanism and mechanical performance. The results revealed that the quality of newly formed five aluminium threads demonstrated a decline trend from bottom to top. Two kinds of thread formation mechanisms were identified: The mechanism I is solely composed of Filling step and applied to upper four threads; The mechanism II consists of Filling-Fracturing-Welding steps and is applied to the lowest thread. Discontinuous solid-state bonding was formed at the sheet interface around the rivet shank periphery, whilst a bowknot-liked solid-state bonding zone with a weak welded zone and an unwelded zone was formed at the joint centre. Rivet pull-out failure from the bottom sheet was observed for the studied AA7075-T6 joints under both lap-shear and cross-tension loads. The peak loads reached 9.79 ± 0.23 kN and 5.41 ± 0.15 kN in the lap-shear and cross-tension tests, and the corresponding energy absorption was 13.82 ± 0.59 J and 16.42 ± 0.87 J. [Display omitted] • An improved F-SPR process with threaded rivet and flat die was proposed. • Thread connection and solid-state bonding were simultaneously generated. • Two formation mechanisms of the female threads on sheets were identified. • Quality of solid-state bonding was affected by filling state of rivet cavity. • Lap-shear and cross-tension strength was 296.86±6.97 MPa and 164.04±4.55 MPa. [ABSTRACT FROM AUTHOR]

The compression member strengthened by the sleeve can effectively enhance the bearing capacity. In this paper, the calculation equation for the contact force between the core and the outer sleeve is deduced, and a bolt design suggestion of the folded sleeve is provided. The test results show that the peak load of the folded sleeve member is increased by over 55.3%. When the number of bolted regions of the folded sleeve increases, the peak load only slightly increases. There are two failure modes of folded sleeve members, including the global buckling and the end bending of the unrestrained segment of the specimen. The number of bolted regions of the folded sleeve has minimal influence on the failure mode. The performance of the folded sleeve is better than that of the assembled sleeve and similar to that of the seamless sleeve. The Abaqus numerical model of the specimen is established and can effectively simulate the mechanical properties of folded sleeve member. The comparison between the theoretical and numerical simulation results of the contact force shows that the theoretical calculation equation of contact force has high safety. Based on the experimental and numerical simulation results, the safety factor, λ , of the bolt spacing of the folded sleeve member is defined. • Proposing a folded sleeve to reinforce a compression member in space structures. • Giving design suggestion of the bolt diameter and spacing of the folded sleeve. • Folded sleeve enhance the bearing capacity and ductility of compression members. • Summarizing failure modes of compression members strengthened with folded sleeves. • Establishing the reasonable safety factor of the bolt spacing of the folded sleeve. [ABSTRACT FROM AUTHOR]

Fastener pre-tension is commonly used in the practical cases of aluminium alloy bearing-type connections with friction provided by treated surfaces. However, research on the effect of friction on the ultimate resistance is currently limited. In this paper, a numerical investigation on the structural performance and design of aluminium alloy double shear connections fastened by preloaded stainless steel swage-locking pins is presented. Finite element (FE) models were developed using Abaqus explicit dynamic packages and validated against the tests conducted previously. Prior to the numerical modelling of shear connections, the framework of aluminium alloy material properties has been studied. In order to simulate the full-range stress–strain relations and the failure of the tested aluminium alloys, two damage models were evaluated. The adopted model was then used to simulate the fracture occurred at the peak load or the post-peak stage in the double shear connection tests, and investigate their failure mechanism of bearing, shear-out and end-splitting. Upon validation, an extensive parametric study of 330 shear connections was conducted to investigate the effect of friction and pin configuration on the structural performance of shear connections made of different aluminium alloy grades. The values of the friction and pin hole resistance at the ultimate loads were comprehensively discussed. The numerically derived ultimate resistances were also compared with the current design equations, which were shown to provide conservative and scattered results due to the lack of consideration of the friction effect. A new design method was proposed with the friction effect incorporated, resulting in accurate predictions of ultimate resistance for aluminium alloy shear connections with preloaded stainless steel swage-locking pins. • Finite element models of aluminium alloy double shear connections fastened by preloaded swage-locking pins developed. • Ductile damage models in Abaqus calibrated. • Parametric study of 330 shear connections conducted. • Effects of friction on connection resistance analysed. • Design equations of predictions of ultimate resistance for aluminium alloy shear connections proposed. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to investigate the impact of the geometric imperfection on the interaction of buckling modes for thin-walled cold-formed steel members with a quantitative modal identification approach. Previous studies showed that the interaction of buckling modes varies during the loading process and how buckling interacts depends not only on the section itself but also on the geometric imperfections in the member. This interaction could change the failure modes of the member and its strength accordingly. This paper integrates a modal identification approach based on constrained finite strip method to track this interaction out of the shell finite element model for nonlinear collapse analyses. The geometric imperfections are included in the computational shell finite element model using the traditional modal approach with stochastically simulated magnitudes. The simulations are performed on five specially selected cold-formed steel sections that are deemed to be local-dominant, distortional-dominant, local-distortional interacted, P cr -equal interacted, and P n -equal interacted. The deformations of the analyses are categorized into the fundamental deformation modes commonly available to cold-formed members: local, distortional, and global. Sensitivity of imperfection is studied by tracing the variation of mode interaction, in particular, for the failure mode. Peak load and associated mode participations are investigated. In addition, a statistical study of the impact of imperfections on the potential failure mode at peak is provided. The potential correlation of the member strength with mode participation is explored, which will shed light on the coupled instability of cold-formed steel member, in particular on investigating the impact of mode participations to member strength. [ABSTRACT FROM AUTHOR]

To solve the problem of high energy absorption conflicting with small load fluctuation, a multi-tube combined energy absorption structure with induced ring based on the load curve staggered compensation strategy was proposed. The effects of the number, height, and thickness of the induced rings on the load curve trend were investigated by experiment and simulation, and the initial structural parameters suitable for the design of load curve staggered compensation. were determined. Then, the influences of height difference and induced ring distribution on the load curve trend were revealed, and the control method that can make the appropriate difference in each tube load curve was summarized. Moreover, the diagram of the correlation between the key multi-tube combination parameters and the load curve control effect was plotted based on classical theory and the acquired temporal influence. Finally, a multi-tube structure with suitable height difference and variable induction ring distribution was proposed. Compared with the multi-tube structure with the same configuration parameters, the combined structure proposed in this study decreases the initial peak and load fluctuation by 49.45% and 58.93%, respectively, while maintaining a high energy absorption. • The initial structural parameters of the induced ring are determined. • The influence law of height difference on the load curve is analyzed. • The influence law of induced ring distribution on the load curve is revealed. • The load curve control effect of key combination parameters is obtained. • The design idea of load curve staggered compensation is proposed. [ABSTRACT FROM AUTHOR]

Sandwich structures made of composites are designed mainly for higher and efficient load capacity. Mostly, the use of composite materials in lattice core sandwich structures is limited to the face sheet; whereas, the core is usually made of metals due to the difficulty in producing the FRP lattice shape. A sandwich with a core made of FRP is believed to be lighter and better in terms of specific strength and absorbed energy. In order to manufacture the sandwich core, several methods and techniques were developed based on the designed core profile. In this paper, the core was extracted (using laser cutting) from the standard flame retardant carbon fiber hat stiffener. Four values of the strut angle α were considered (α=45, 60, 75, and 90°). Crushing tests were performed using Instron Compression machine and a load cell of 5 kN capacity. Similar post crushing profiles were obtained for all the specimens. However, the peak load is being shifted upward. Improvements of 75% and 54% were recorded for the peak and the average crushing loads respectively. It is worth remarking that the crush load efficiency was kept constant during the tests. The energy and the specific energy absorption showed that the unit cells with 90° are at advantage since it is almost 53% higher than that of the 45°. For the effect of filler, the tests results show how important it is to fill such thin skeletal structures. [ABSTRACT FROM AUTHOR]

A structural steel fire design approach through second-order inelastic analysis with strain limits is proposed and applied to the fire design of steel columns as a first step in the establishment of a novel fire design framework for steel structures in this paper. The proposed method is carried out using beam finite elements, utilising their computational efficiency. In the proposed design approach, the strength and stiffness deterioration of steel in fire, the spread of plasticity, global instability effects, indirect fire actions and thermal expansion are fully taken into account through second-order inelastic analysis, while strain limits are employed to consider the deleterious influence of local buckling on the ultimate resistance. Ultimate capacity of a steel member or system is determined by (i) the load or temperature level at which the predefined strain limit is attained or (ii) the peak load or critical temperature observed during the analysis, whichever occurs first. A systematic numerical parametric study is carried out through nonlinear shell finite element modelling, taking into account a high number of I-section and hollow section steel columns whose response is considered (i) using isothermal and anisothermal analysis techniques and (ii) with and without axial and rotational end-restraints. It is demonstrated that the proposed fire design approach consistently furnishes significantly more accurate capacity and limit temperature predictions for steel columns in fire relative to EN 1993-1-2 [1] design provisions. • A new structural steel fire design approach is proposed. • The proposed method is applied to the fire design of steel columns. • The method fully considers the detrimental factors affecting behaviour in fire. • The failure modes of steel members in fire can be explicitly accounted for. • Accuracy and reliability of the proposed design approach are extensively verified. [ABSTRACT FROM AUTHOR]

A novel multi-cell glass fibre-reinforced polymer (GFRP) pultruded square column reinforced with lattice-webs (MP-LSHc) was proposed. Twelve column specimens with various thicknesses of face sheets and lattice webs were tested to investigate the compressive behaviour and failure modes of MP-LSHcs. The experimental results revealed that all the specimens with lattice-web reinforcements failed due to the rupture of face sheets followed by the compressive damage of pultruded tubes. With the application of lattice-webs, the loading capacity of the specimens increased. The thickness of the lattice-webs strongly affected the pseudo-ductile behaviour of the column specimens. Improvements in interfacial bonding performance were also found in specimens by increasing the thickness of face sheets. By modelling the specimens as individual plates, the compressive failure and buckling behaviour of laminates were analysed to predict the peak loads of the specimens. A good correlation was found between the analysed results and the experimental observations. • Novel multi-cell GFRP pultruded square columns reinforced with lattice-webs were proposed. • Axial compressive behaviour including interface bonding properties and compressive damage was studied. • Applications of multi-cell structures and lattice structures improved the mechanical performance of pultruded tubes. • Static equilibrium equations and analytical expressions were adopted for evaluating the peak load of the specimens. [ABSTRACT FROM AUTHOR]

In this paper, the failure behavior of sandwich beams with aluminum foam core and glass fiber-reinforced epoxy/aluminum laminates (GLARE) face-sheets under three-point bending is studied by experimental and numerical methods. Through the observation of the experiments, the initial failure modes of GLARE sandwich beams are observed, i.e., indentation and core shear. The deformation and failure process of GLARE sandwich beams are explored. Finite element simulations are performed by using ABAQUS software, and the numerical results agree well with experimental results for peak loads of GLARE sandwich beams. The effects of geometrical and material parameters on the peak loads of GLARE sandwich beams are discussed in details. It is shown that the peak loads and energy absorption of GLARE sandwich beams increase with the increase of face-sheet thickness and foam strength and the decrease of span length. The effects of elastic modulus of foam and fiber laying angle of face-sheet are very small. • Bending failure behavior of GLARE sandwich beams is studied experimentally and numerically. • Initial failure modes of GLARE sandwich beams are observed in tests. • Numerical peak loads agree well with experimental ones. • Peak loads of sandwich beams with the increase of face-sheet and foam strength and decrease of span length. [ABSTRACT FROM AUTHOR]

In this study, the axial compressive performance of steel–concrete–steel​ composite walls (SCSCWs) with novel dumbbell-shaped connectors (DSCs) was investigated. Six specimens were designed and tested, and the study parameters included the physical dimensions and arrangement schemes of DSCs. The failure mode, axial displacement, steel strain, and bearing capacity of the specimens were analyzed. The external steel plates exhibited local buckling, and the internal concrete was crushed. The variation in the physical dimensions of the DSC had little effect on the failure modes, and increasing the number of connectors improved the bearing capacity of the specimens. The axial load–displacement relationships of the SCSCWs were calculated considering the effects of local buckling and post-buckling behavior of steel faceplates in the constitutive relationship. The theoretical curves were in good agreement with the experimental results. A simplified formula for the bearing capacity was proposed, and the average ratio of the experimental to theoretical peak loads was 0.98, indicating that the simplified formula had high accuracy. ABAQUS software was used to simulate the axial behavior of SCSCWs. The simulated results were similar to those of the experiments, and the average ratio of the experimental bearing capacity to the corresponding simulated value was 0.99. Based on the benchmark model, further parameter analyses were conducted to study the effects of material strength and physical dimensions on the axial behavior of SCSCWs. Increasing the material strength and sectional thickness could increase the bearing capacity, and the failure mode was not affected. The theoretical initial stiffness of the SCSCWs was calculated, and the accuracy of the formulas was verified using the simulated results. [Display omitted] • Dumbbell-shaped connector was proposed for steel–concrete–steel composite wall. • Axial compressive behaviors of six specimens were experimentally investigated. • Local buckling and post-buckling behaviors were considered in formulas. • Axial load–displacement relationship was theoretically predicted by formulas. • Finite element models were established for further parameter analysis. [ABSTRACT FROM AUTHOR]

Multi-stage nested multi-cell hollow structures inspired by the macroscopic architecture of wood are characterized for their energy absorption in this study. After investigating numerous variations, the three best-performing nested multi-cell architectures are revealed using the modified MULTIMOORA (Multi-Objective Optimization on the basis of a Ratio Analysis plus the full MULTIplicative form) methodology. To investigate the influence of the foam core on the crashworthiness performance, an analysis of foam-filled structures with foam core's various density was also carried out. Decreasing the peak collapsing load and controlling the deformation mechanism express the perfect crashworthy characteristics, indicating the efficiency of the multi-stage structure. The structure deformation demands a higher collapsing load level at the second and third stages due to the connection between foam core and tubes, which shows a high reinforcing effect of the architecture being tested. Structure, foam core, and impact velocity are three main factors enhancing the crashworthiness performance of a structure and controlling its collapsing behaviour. The newly conceived architecture revealed peak collapsing load (PCL) and specific energy absorption (SEA) of foam-filled structures increases in the range of 21%–57% and 4%–20%, respectively, while second collapsing load efficiency increases up to 29% at the highest foam core's density, compared with their counterparts. In addition to the numerical analysis, theoretical models that are in good agreement to predict average crushing load (ACL) are also developed for structures with and without foam • Bio-inspired multi-stage nested multi-cell architecture informed by macrostructure of wood is presented. • The SEA of structure with foam was 18% higher than that of the counterpart. • The modified MULTIMOORA method was used to rank the performance of the bio-inspired multi-stage nested multi-cell structures with foam. • The theoretical models of average crushing load agreed well with the numerical results. [ABSTRACT FROM AUTHOR]

Axial crushing of tubes with multiple patterns of cut-outs is studied using numerical analysis. Commercially available finite element ABAQUS/Explicit® package is used to simulate the model under impact loading condition. Split-Hopkinson Pressure Bar (SHPB) is modelled to dynamically test the tube specimens with and without cut-outs. Number, size, and shape of cut-outs are kept constant in all specimens to have a constant weight reduction. In order to improve the crashworthiness characteristics of tubes, cut-outs are arranged on a tube surface along the circumferential and longitudinal direction in multiple rows. Crashworthiness parameters i.e., peak and mean collapse load, crushing efficiency, energy absorption characteristics are studied. The results revealed that a moderate weight reduction of tube can significantly affect the crushing characteristics of tube. In terms of load characteristic values, only 1% of weight reduction in modified tube samples has helped in 4.46% peak load reduction as compared to the normal tube, and crushing efficiency of the modified tube (T2) is found to be 2.17% higher than normal tube (T). In terms of energy absorption characteristic values, 1% of weight reduction in modified tube samples has helped in 1.95% reduction in energy absorption capacity as compared to the normal tube, and energy efficiency of modified tube (T2) is found to be 2.56% higher than the normal tube (T). After arranging the cut-outs in a multiple pattern, the location of cut-out is also seen to be influencing on the tube behaviour. It helps the tube to reduce the initial peak collapse load and optimize the mean collapse load. Further, force–deformation characteristics are also discussed to improve the crashworthiness characteristics of tube under impact load. • SHPB helps to understand the real-life impact force condition. • Cut-outs on a tube surface affects the progressive buckling of tube. • Diamond cut-outs in multiple row pattern are found to be more effective. • Longitudinal cut-out arrangement is predominant than circumferential arrangement. • Force–displacement characteristics can be improved by using different cut-out sizes. [ABSTRACT FROM AUTHOR]

Structural members termed frusta (conical shells or tapered prismatic tubes) are used as energy absorbers due to the stable plastic behavior during axial crushing process and to the decrease of peak crushing load in comparison with cylindrical columns or parallelepiped-shaped​ thin-walled columns. The paper presents the parametric study into crashworthiness performance of prismatic steel thin-walled frusta of square base and various apex angles produced from two face to face channel section bars, both hollow and foam filled, subjected to axial impact load. Material used for filled frusta was the polypropylene foam. An influence of geometrical parameters : wall inclination angle (frustum apex angle), wall thickness and frustum height as well as influence of foam filling on energy absorption and crashworthiness performance is investigated. The parametric study is performed using Finite Element simulations. Two step analysis was carried out (the eigenvalue buckling analysis and subsequently the non-linear explicit dynamic analysis). Crushing behavior (buckling and failure modes) and load–shortening characteristics obtained on the basis of FE numerical results are discussed. Energy absorbing effectiveness is analyzed using crashworthiness indicators, namely Peak Crushing Force (PCF), Crash Load Efficiency (CLE) and Total Efficiency (TE). Effect of synergy in case of foam filled frusta is examined. On the basis of the analyses some conclusions are derived concerning the most effective configurations of geometrical parameters of frusta under investigation as well as some of the drawbacks and limitations of the applicability of indicators used in the analysis. Further research topics are presented, including an identification of new or modified crashworthiness indicators and multi-objective optimization of examined frusta. • Thin-walled prismatic frustum, both hollow and foam-filled subject to axial impact load is investigated. • The comprehensive parametric study of influence of several factors (height, thickness and apex angle of frustum) upon the energy absorption effectiveness is analyzed. • Polypropylene foam filling improves the crashworthiness performance, synergy effect is observed. • A necessity to develop new crashworthiness indicators is discussed. [ABSTRACT FROM AUTHOR]

Even though CFS framed shear walls have been the subject of many research, test data on walls sheathed with OSB panels on both sides using relatively small fastener spacing is scarce. The current investigation aims to fill this gap through an integrated experimental and numerical study on lateral load response of double side sheathed CFS-framed wall panels utilizing relatively small fastener spacing. The experimental investigation included cyclic tests on nine 1220x2440 mm wall panels. For the tested walls the predominant failure mode was buckling of boundary studs. The average maximum drift ratios of all tests were 3.2% and 3.0% in two loading directions. The corresponding average drift ratios at peak load capacity were 2.9% and 2.7%. The numerical part of the study included detailed modeling of wall panels using the OpenSees platform following the fastener-based and equivalent brace modeling approaches. In the fastener-based models, the nonlinear behavior of each screw between the CFS framing members and the sheathing panel was simulated by a nonlinear spring element. Material models used for these nonlinear spring elements were calibrated with the data from physical testing of connection screws. In the equivalent brace model, inelastic response of all connection screws was lumped into two nonlinear brace elements. Material models used for these brace elements were calibrated with the measured lateral load-drift data from wall panel testing. Good agreement was obtained between the numerical responses from both modeling approaches and the measured response. • Providing sheathing on both sides in CFS shearwalls increases force demand in wall studs. • Response of double side sheathed walls differ from those sheathed on one side. • Stud buckling is a typical failure mode for walls with sheathing on both sides. • Fastener-based and equivalent brace modeling approaches accurately predict lateral load response of walls. [ABSTRACT FROM AUTHOR]

Grooved tubes benefit from optimized energy absorption characteristics compared to regular tubes. This paper investigated the crashworthiness characteristics of cylindrical tubes with various types of grooves under high-speed impact loads. Furthermore, the dynamic load response of tubes with external grooves having linear thickness distribution was studied experimentally and numerically for the first time. To assess the performance of gradient grooved tubes (GGTs), the crashworthiness of typical cylindrical specimens and tubes having internal or external grooves with uniform thickness distributions was compared. The results showed that the dynamic crush mode of GGTs was axisymmetric, progressive, and sequential. Furthermore, the mean crushing force (MCF) in GGT tubes was considerably less compared to other tubes (e.g., 89% difference between GGT and non-gradient tube). Moreover, the initial peak forces of all types of tubes having the same number of grooved sections were almost in the same range. However, the crushing force efficiency of GGTs was remarkably lower than other tubes due to their non-uniform load response. The numerical results showed that by increasing the number of grooves in GGTs, peak force, energy efficiency, and axial shortening decreased, but mean crushing and overall crushing forces increased. Altogether, the highest energy efficiency belonged to the GGT specimens, in which 17%, 4.2%, and 96% increases were observed compared to external and internal groove tubes and typical cylindrical tubes, respectively. Also, the energy efficiency increased with the number of grooves. • Gradient grooved tubes and regular cylindrical tubes subjected to axial high rate impacts are experimentally and numerically investigated. • A gas gun is used in order to perform high-rate tests, and a load cell is utilized to measure the force at the distal end. • Crashworthiness characteristics such as force time curve, peak load and mean crushing force are experimentally and numerically calculated. • Gradient grooved tubes are good candidates to use as energy absorbers since they can absorb the input energy by transmitting the low amount of force to protected specimens and occupants. [ABSTRACT FROM AUTHOR]

The present study reports the low-velocity impact (LVI) performance of carbon woven reinforced polymer (CWRP) composites with varying temperatures. The fabrication of carbon woven lamina and carbon woven reinforced two-layered laminate (named CWRP-1 and CWRP-2) was done using a vacuum-assisted resin transfer molding (VARTM) process. CWRP-1 samples were tested at varying impact velocities of 1, 2, 3, and 4 m/s at − 25, 25, and 50 °C for each incident velocity. CWRP-2 samples were tested at room temperature at varying incident velocities to determine the effect of multiple woven layers. The impact resistance of the first-crack load, peak impact load, and absorbed energies were recorded and evaluated under different loading conditions. In addition, the Weibull probability method is adapted to forecast failure behavior as a function of load. Visual inspection, optical microscopy, and scanning electron microscope (SEM) images were used to assess the damage pattern and failure morphologies in forecasting the failure phases during LVI. The low-velocity impact behavior of CWRP-1 at − 25 °C with various velocities was shown to be random due to the polymer matrix freezing condition. The softening of the resin matrix at 50 °C is responsible for the difference in damage tolerance. The relevance of multiple layered composites for better impact resistance characteristics was demonstrated during testing of CWRP-2 at room temperature. Overall, the results of this experiment showed that CWRP lamina and laminates are highly sensitive to the impact velocities and external temperatures. • Low velocity impact characteristics of single layer lamina and two layered laminates are investigated in this study. • Experimental results suggested that thickness of the composite, incident velocity and external temperature significantly affect the LVI performance. • Temperature variations had a significant impact on the characteristics of the polymer matrix, which is an essential element of composite. • The mechanisms of failure patterns are observed through the SEM images which is capable to represent different failure modes like fiber debonding and fracture. [ABSTRACT FROM AUTHOR]

Bending collapse of thin-walled steel tubes is a major energy absorption mechanism in lightweight structures, especially for crashworthiness. External composite reinforcements can increase the energy absorption and strength of steel tubes. However, to this date there are still difficulties to determine the maximum load and the collapse behavior of reinforced, multi-material shapes, e.g., steel shapes covered by CFRP. In this work, a theoretical analysis of the collapse of a partially reinforced CFRP–Steel tube is performed, which encompasses the calculation of both the peak bending moment and the bending collapse curve of tubes with either the flanges or webs with reinforcements. The theoretical approach is validated with three-point bending experimental tests and an adequate agreement with experiments is found. The results also show an important increase of up to 57% in the peak load and 45% in the specific energy absorbed for partially reinforced tubes, with a maximum 14% increase in weight, when compared with unreinforced tubes. The developed theoretical model enhances even further the existing bending collapse theories, as it incorporates reinforcements in the model and provides a powerful tool for engineering analyses, and can be implemented in concept models, and optimization algorithms with ease. These findings can be used for enhancing existing and new lightweight structures and improving the crashworthiness of several automotive structures. • Bending collapse behavior of partially reinforced hybrid hollow shapes is studied. • Reinforcing the webs alone can provide the same level of enhancements as reinforcing the flanges. • A theoretical approach is taken to predict the maximum load and bending collapse stage for the hybrid shapes. • Reinforcements can partially hold the load after fracture from bending collapse. • Hybrid shapes suffer a localized collapse; thus, reinforcements can be applied only in these areas. [ABSTRACT FROM AUTHOR]

To examine the tensile properties of T-joints reinforced by traditional lock stitching with stitch spacing not smaller than 5 mm, tensile experiments are conducted and the reinforcing effect of stitching and Z-pinning is compared. Results show that both the location of the innermost column of stitching and stitch spacing have a remarkable influence on the tensile property of stitched T-joints. The maximum average peak load achieved is 44.2% by stitching. Although the diameter of the stitch is 24% thinner than that of a thick Z-pin, the maximum load capacity of stitched T-joints is 14.2% greater than that of Z-pinned T-joints. [Display omitted] • Both the location of the innermost column and column spacing of stitching have a remarkable influence on T-joints. • The maximum average peak load achieved was 44.2%. • Stitching is superior to Z-pinning in terms of improving initial load drop, peak load, and stabilizing crack propagation. [ABSTRACT FROM AUTHOR]

Cold-formed steel (CFS) walls with novel sheathing have been of growing interest in hysteretic behavior. This study investigated the effect of diagonal bracings and sheathing magnesium crystal boards (MCBs) on the hysteretic behavior of CFS walls. Furthermore, a novel refined vertical loading system was proposed to solve the key problems caused by conventional distribution beam loading systems. Monotonic or hysteretic loading was conducted on six full-size CFS walls sheathed with MCB and one pure CFS frame wall to obtain the failure modes, yield loads and corresponding displacements, peak loads and corresponding displacements, and lateral stiffness of the specimens. Finally, the failure mode of the MCB located in the vertical seam was observed and discussed, and the influence of the flexible diagonal brace on the lateral bearing capacity and ductility of the CFS wall was further analyzed. • Six pieces of CFS composite walls was experimented under monotonic or hysteretic loads. • Cold-formed composite wall sheathed with novel MCB exhibited stable and favorable ductility. • High initial stiffness of CFS wall was primarily contributed by the screw connection between sheathing and skeleton. • Extensive parameters, including diagonal braces, stud forms and whether sheathing boards, have been investigated. [ABSTRACT FROM AUTHOR]

In this article, bitubal circular energy absorbers consist of two AL-6063-O tubes with unequal diameters placed coaxially and compressed under quasi-static axial load are studied experimentally. The effects of diameter and wall-thickness of each tube and the interaction between two tubes on the crashworthiness parameters are investigated in detail. In order to reduce the high value of peak load induced in the bitubal absorbers, two worthwhile solutions are proposed. The first one is to use two tubes with different lengths and the other one is to cut groove at the end portion of one of the tubes. [ABSTRACT FROM AUTHOR]

Previous studies have demonstrated that the failure mechanism and energy absorption capacity of expanded metal tubes strongly depends on the orientation of the cells. This paper presents an experimental investigation on the collapse of concentric expanded metal tubes subjected to quasi-static axial compression. Square tubes with two different cell orientations are tested to failure, and the energy absorption characteristics are calculated. The results show that the combination of cell geometries lead to a complex buckling mode interaction, which enhances the energy absorption capacity of expanded metal tubes. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and numerical investigation into the failure characteristics of single hat-shaped thin-walled tubular T-joints made of hybrid materials (i.e. CFRP shell, aluminum plate and polyurethane foam-core) under static and impact loading. Novel design and manufacturing methods for single hat-shaped CFRP–aluminum tubular T-joints with and without in-filled foam are presented. Static and impact tests of the prepared T-joints subjected to an out-of-plane loading are conducted. The test results reveal that the polyurethane foam core plays a notable role in increasing the peak load, its associated displacement, and energy absorption. Different failure mechanisms for all the T-joints are identified. Novel integrated finite element analyzes incorporating viable material models, including failure criteria and damage initiation and evolution models, are presented and validated with the both static and impact test results of the T-joints. • Novel fabrication method for hybrid hat-shaped tubular T-joints using bonding and riveting. • Unveil failure modes, dynamic responses and crashworthiness features of the T-joints. • Identify the mechanism of foam core in enhancing dynamic responses of the T-joints. • Effective simulation method for capturing key static and dynamic responses via validation. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of lattice-web layout on the low-velocity impact performance of foam-filled multi-cavity composite panels (FMCPs). The effect of impact velocity has been explored to demonstrate the impact resistance property and energy absorption capacity. Due to the light weight and great energy absorption capacity, the FMCP with double-layer dislocation webs can be used as a good energy buffer device. An energy balance model, based on the energy absorption during impacts, was developed to predict the peak loads of the FMCPs. Numerical models were established and parametric analysis was conducted on the GFRP thickness and foam density. [Display omitted] • Sandwich structures are appealing to anti-collision devices but existing drawbacks. • A novel foam-filled panel had great impact resistance and energy absorption capacity. • An energy balance model was used to predict the peak loads of the foam-filled panels. • Numerical models were established to conduct parametric analysis. [ABSTRACT FROM AUTHOR]

This paper proposes a novel design of origami-inspired honeycomb metamaterial with a self-locking property. The concept of Miura-ori has been used to create a unique family of Miura-ori honeycombs in which a core layer at the middle is sandwiched by two secondary flange layers. The self-locking feature is realized by a prior densification of the flanges when pressed, which increases the overall energy absorption whilst keeping the initial peak load low. Experimental and numerical methods were used to investigate the compression responses and energy absorption capacities of the Miura-ori honeycombs. It was found from the finite element analyses that properly designed honeycombs could reduce the peak force with better load uniformity while maintaining a good specific energy absorption (SEA) in comparison with conventional square honeycomb. Thus, this work shows a promising way of utilizing the concept of origami to create novel metamaterials with controllable mechanical properties. • The novel design of an origami-inspired honeycomb with a self-locking property is proposed. • Parametric analysis is performed using numerical simulation. • Proposed novel honeycomb has good specific energy absorption with better load uniformity. • Obtained results are validated by comparison with experimental data. [ABSTRACT FROM AUTHOR]

Over the past few decades, the majority of research has focused on the ultimate bearing capacity under static load. These beam plates may experience dynamic impact loads in some extreme conditions, hence ultimate bearing capacity of double-beam plate under quasi-static and impact loads, especially for dynamic static ratio of ultimate bearing capacity is very important to structural safety and lightweight design. A discrete method of the beam-plate coupled system is developed to analyse the dynamic and static ultimate bearing capacities of continuous double-beam plates with generalized constrained differential quadrature method in which the two square tube beams are parallel each other and connected with a rectangular plate continuously considering interaction between plates and beams. The contact forces between beams and plates are represented by a series of translational and rotational springs which can ensure the displacement compatibility between beams and plates. A series of tests of double-beam plates under quasi-static and dynamic loads is conducted to investigate the dynamic response and verify the proposed method. Additionally, the effects of the initial imperfection, width–thickness ratio, aspect ratio, rotational spring stiffness, impact time and peak load on dynamic and static ultimate bearing capacities as well as dynamic static ratio of ultimate bearing capacity are analysed. The study indicates that the ultimate bearing capacity of the double-beam plate under dynamic impact load is quite different from that of the double-beam plate under quasi-static load. The initial imperfection, peak load and impact time have a significant effect on dynamic static ratio of ultimate bearing capacity, while the effect of the edge rotationally-restrained spring stiffness can be ignored. • A generalized constrained differential quadrature method is developed to investigate the ultimate bearing capacity. • A double-beam plate is divided into some plate elements, considering the compatibility between contiguous plate elements. • The effects of the initial imperfection, aspect ratio, rotational spring stiffness, impact time and load amplitude. • A detailed experimental study is conducted to investigate the dynamic strength characteristics of double-beam plates. • The efficiency and accuracy of the proposed method are confirmed by a good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Stability properties of localized states is of great significance in the determination of nonlinear buckling characteristics of an axially loaded cylindrical shell. We have analyzed these localized states with the help of carefully carried out experiments by using an external poker. The focus of this study is on assessing the practical feasibility for obtaining the peak load carrying capacity of an imperfect (near perfect) cylindrical shell, for which no prior knowledge of the location of dominant defect is present. Three different methods are attempted: Method 1- Probing at a single arbitrary location, Method 2 – Probing at multiple locations, Method 3- Probing at multiple locations to find the Least Resistant Path (LRP). The results indicate that the determination of LRP and hence the location which corresponds to the least energy barrier can significantly improve the efficacy of the probing procedure. • Experimental study on Non-destructive prediction of buckling load of compressed cylindrical shell. • Cylindrical shell with unknown defect distribution is used. • Three different methods that make use of lateral probing are studied. • Least Resistance Path to probing is used to predict peak load carrying capacity. [ABSTRACT FROM AUTHOR]

This paper proposed the UHPC-filled high-strength steel tube (UHST) for cold-region buildings/bridges. The cold-region low-temperature environment was simulated in the laboratory using a cooling chamber with LNG. Then, low-temperature compression tests were performed on 23 stub UHSTs to study their low-temperature compression behaviour. The studied parameters included four low temperatures (T = −80, −60, −30, and 30 °C) and three width-to-thickness ratios (C / t ratio = 48.4, 33.5, 22.0). Test results showed that the P (load) − Δ (shortening) curves exhibited a four-stage manner. The UHPC crushing occurred at the ultimate load capacity and UHPC nonlinearities contributed to the nonlinear behaviour of UHSTs. Outward buckling of HSS tube and welding fracture occurred at the recession stage. The decreasing temperature from 30 °C to −80 °C improved the compression behaviour of UHSTs. As T decreases form 30 °C to −80 °C, the ultimate compressive resistance P u (or initial stiffness K 0) value of UHSTs with C / t ratio of 22.0 receives the increments of 20% (24%). With the same decrease of C / t ratio, the increments of peak load capacity decreased as T decreased from 30 °C to −80 °C. This paper also developed finite element models (FEMs) and theoretical models to simulate the axial compression behaviour of UHSTs at low temperatures. Validations of simulations against 23 test results proved that both the FEM and theoretical models provided reasonable simulations on axial low-temperature compression behaviours of UHSTs. • Low temperature improves load capacity of UHPC-filled Q690 high strength steel tube (UHST). • UHST with Q690 UHSS exhibits close compression behaviours at low and room temperature. • FEM predicts well low-temperature compression behaviour of UHST with Q690 HSS. • Developed theoretical models predict well low-temperature P- Δ curves of UHSTs. [ABSTRACT FROM AUTHOR]

The limited past research on light-weight cold-formed steel (CFS) composite sections have indicated their success in addressing the buckling instabilities, but have been confined to flexural members. Thus, there is a need to extend this research to columns as well. In the first part of this study, an experimental investigation was carried out on lightweight CFS composite built-up battened columns composed of channel sections, connected in the face-to-face configuration. Two series of tests were performed to evaluate the axial compression capacity and stability response of built-up sections formed using various light-weight materials like GFRP and timber, as composites with CFS channels. The structural performance of these composite built-up battened columns was assessed in terms of their peak loads resisted, load–displacement response, axial stiffness, failure modes and strength-to-weight comparison. The second part deals with the theoretical analysis of the lightweight CFS composite built-up sections using the current codes for checking their adequacy. The third part presents the finite element simulation of the lightweight CFS composite built-up sections for validating the test results. • Light-weight CFS composite built-up columns are developed using GFRP and timber. • Monotonic tests performed to explore the structural behaviour of composite columns. • FE simulation of the behaviour of such composite built-up columns is carried out. • Theoretical strengths were determined and compared with the test strengths. • Large improvement in the strength, stiffness & strength-to-weight ratio is achieved. [ABSTRACT FROM AUTHOR]

Abstract: Axial compression experiments on aluminium cylindrical shells of diameter to thickness ratios (D/t) between 11.5 and 31.49 were conducted on a gravity drop hammer set up and Zwick machine. Typical histories of their deformation, variation of shell thickness along the fold length, inner and outer radii, folding parameter and size of fold, load–compression curves, energy absorbing capacity, initial peak load, and mean collapse loads obtained from the experiments are presented. Influence of the D/t values of the shell on their modes of collapse and energy absorption capacities are discussed. The shells are numerically simulated and analysed in detail by using the finite element code FORGE2. The material was modelled as rigid-viscoplastic. The experimental and computed results are compared. Typical contours of equivalent strain, equivalent strain rate, different stress components and velocity distribution are presented. The impact response of the shells is compared with their static response. [Copyright &y& Elsevier]

Abstract: Tapered thin-walled tubes have been considered desirable energy absorbers under axial loading due to their relatively stable crush load and deformation response compared with straight tubes. This paper compares the energy absorption response of straight and tapered thin-walled rectangular tubes under quasi-static axial loading, for variations in their wall thickness, taper angle and number of tapered sides. Overall the study highlights the advantages of using tapered tubes as energy absorbers. In particular, the peak load required to crush the tubes decreases with the introduction of a taper, and as the taper angle increases. This is desirable for minimising the impact loads transmitted to the protected structure. The practical outcome of the study is design information for the use of tapered thin-walled rectangular tubes as energy absorbers in impact loading applications. Analysis has been undertaken using a finite element model, validated using existing theoretical and numerical models. [Copyright &y& Elsevier]

Hollow thin composite tubular structures are widely used in many industrial applications and there is a growing need to innovate both the manufacturing process which is suitable for mass production as well as the material aspects to improvise the mechanical properties and the weight. The current research presents a detailed study on manufacturing thin hollow woven carbon fibre (WC)/Elium® (EL) rectangular tubular structures. Bladder resin transfer moulding process optimization study is carried out and the moldability zones were defined. A detailed experimental investigation was carried out to understand the impact and flexure properties of woven carbon (WC) tubular configurations with Elium® (EL) and Epoxy (EP) matrix system. Impact tests were performed at 6 different energies to derive the energy profiling diagrams by studying the penetration and preformation thresholds. WC/EL tubular configuration has shown a maximum 12.5% increase in peak load and 55% increase in absorbed energy as compared to WC/EP composite, respectively. The WC/EL composite tubes have shown similar or better results in terms of bending strength (10% higher) and there was a noticeable increase in deformation owing to the extended plasticity behaviour of acrylic thermoplastic resin compared to WC/EP composites. The rationale and underlying reasons for the differences in the mechanical performance and failure mechanisms for both the tubes tested in impact and flexural are studied with the help of high-speed camera examination and microscopic study and are deliberated in this paper. [Display omitted] • Mechanical performance of novel thin thermoplastic composite tubular structures. • LVI with in-situ high-speed camera and 3-point bending investigation. • Comparison of woven carbon/Elium® (WC/EL) vs woven carbon/Epoxy (WC/EP). • 12.5% and 55% higher peak load and absorbed energy for WC/EL composite. • More deformation owing to extended plasticity for WC/EL under 3-point bending. [ABSTRACT FROM AUTHOR]

riveted–adhesive hybrid joining technique is suitable for joining dissimilar material due to excellent performance and tightness of the joint. In this paper, electromagnetic self-piecing riveted–adhesive hybrid joining method was proposed to join Al/steel structure. The mechanical properties and failure behavior of electromagnetic self-piecing riveting, adhesive and its hybrid joints were compared. The shear tests were conducted, and digital image correlation (DIC) technique was employed to analyze the strain of the sheets. The typical failure fracture was observed to reveal the failure mechanism. The results showed that the peak load of the hybrid joint was 177.3% larger than that of the riveted joint, and the energy absorption of the hybrid joint was 360.0% and 47.9% higher than that of the riveted and bonded joint respectively. The failure process of electromagnetic self-piecing riveted–bonded hybrid joint could be divided into two parts: adhesive failure firstly and then rivet failure. The rivet in hybrid joint after adhesive failure could still suffer a certain amount of load, so that suddenly complete failure was not easy to happen. This indicated that the hybrid joint had better reliability and security. In general, the combination of electromagnetic self-piecing riveting and adhesive bonding could produce beneficial coupling effect. • Electromagnetic self-piecing riveted–adhesive hybrid joining technique was proposed to join steel/Al structure. • The mechanical properties of the electromagnetic self-piecing riveting, adhesive and hybrid joints were compared. • The failure mechanism of the electromagnetic self-piecing riveting, adhesive and hybrid joints was analyzed. [ABSTRACT FROM AUTHOR]

In this study the energy absorption of elastomeric foam-filled aluminum honeycomb under quasi-static compression loading and low velocity impact was experimentally investigated. Commercially available Al honeycomb made of Al5052 H38 filled with elastomeric polyurethane foam was used as the specimens. Pure polyurethane had a shore hardness of 30A and to make it foam, different volume fraction of glass microballoon was added to it and a novel material was synthesized that simultaneously had the properties of elastomers and foams Energy absorption of the specimens were evaluated by different parameters such as peak load, crushing load and absorbed energy. Also, the effective failure mechanisms were fully discussed. The results showed that the addition of polyurethane to the honeycomb cells had no significant effect on energy absorption enhancement. However, the addition of glass microballoon particles to the elastomer considerably raised the maximum load, mean crushing load, and total absorbed energy and unlike conventional filled structures, it had been significantly less deformed and could act as an energy absorber against impact many times. • The addition of glass microballoon particles to the elastomer reduced the weight. • The elastomer-foam filled honeycomb experienced much smaller permanent deformation. • The addition of glass microballoon particles to the elastomer considerably decreased the ultimate deformation. • Considering the small ultimate permanent deformation of the filled honeycomb could continue to be used as energy absorbers after the impact. [ABSTRACT FROM AUTHOR]