Strut Length Research Articles

Metallic Metamaterials with Auxetic Properties: Re-Entrant Structures

The present article is an exploration of metamaterial structures exhibiting auxetic properties. The study shows the effect of three geometric parameters of re-entrant auxetic cells, namely, the internal initial cell angle (θ0), the strut length ratio h/l, and the degree of opening of the unit cells expressed by the change in the Δθ angle, on the value of the Poisson’s ratio. It combines theoretical insights into physical re-entrant auxetic structures with the demonstration of structures that can be subjected to cyclic loading without being damaged. The experimental section features the results of the compression tests of a symmetrical structure made up of four re-entrant cells and tensile tests of a flat mesh structure of size 4 × 4. In the mesh structure, a modification was applied to the re-entrant cells, creating arched strut connections. It was shown that the value of the maximum load for such structures depends on the bending angle and the length of the inclined strut. The mesh structure was created using torsion springs. Its cyclic tension for different amplitudes yielded Poisson’s ratio values in the range of −1.4 to −1.7. These modifications have enabled stable, elastic, and failure-free cyclical changes of the structure’s dimensions under load.

Enhancing Ignition Reliability with Tail-Groove Strut Designs in Cavity-Based Combustors

As the flight envelopes of turbine-based combined cycle (TBCC) engines expand, ensuring reliable ignition and flame stability under varying conditions becomes increasingly critical. Previous work has shown a significantly changed ignition performance and flow pattern in cavity-based combustors when strut structure parameters were altered, indicating a strong correlation between the ignition process, flame structure, and the strut configuration. This suggests that further investigation is required to determine the optimal strut design. Therefore, this study examines the impact of various strut configurations through numerical simulations, validated by high-speed imaging. Findings show that the tail-groove strut designs improve the flame propagation performance compared to the normal struts, with a critical depth beyond which further increases do not enhance performance. Changes in strut length have a lesser impact than depth. Flow analysis indicates that tail-groove struts create additional recirculation zones that enhance fuel atomization and flame stability. These results suggest that optimizing strut configurations is vital for achieving reliable ignition and flame stability, advancing the development of efficient engines across a wide range of operational conditions.

Behaviour and design of prestressed stayed circular concrete-filled double skin steel tubular (PS-CCFDSST) columns under axial compression

An innovative type of steel-concrete composite column, named the prestressed stayed circular concrete-filled double skin steel tubular (PS-CCFDSST) column, is introduced in this study, aiming to achieve both structural efficiency and economic advantages. Numerical simulation and theoretical analysis on the axial compressive behaviour of PS-CCFDSST columns were carried out, to understand and reveal their fundamental working mechanisms. Nonlinear finite element analysis (FEA) utilising ABAQUS was performed and validated against collected test data of CCFDSST columns and PS columns. Properly designed PS-CCFDSST columns could gain cost savings of over 30 % while maintaining identical load-bearing capacity as prestressed stayed hollow steel tube (PS-HST) columns with the same steel usage. The effects of initial pretension, nominal steel ratio, hollow ratio, column’s slenderness ratio, relative length of struts, column diameter, strut diameter and cable area on the buckling mode and buckling capacity of PS-CCFDSST columns were evaluated via parametric studies. The stiffness ratio β could be used as an index to comprehensively assess the structural efficiency of PS-CCFDSST columns, and a critical threshold of β = 2 corresponds to the transition between symmetric and anti-symmetric buckling modes. Linear calculation formulae for the theoretical buckling capacity and optimal initial pretension of PS-CCFDSST columns were derived. Finally, practical design equations for predicting the column’s buckling capacity were developed, and recommended values for the actual optimal initial pretension and other primary parameters were provided for PS-CCFDSST columns under axial compression. This study, for the first time, provides the fundamental mechanical behaviour, identification of the critical stiffness ratio for buckling mode transition, and design framework for buckling capacity of the PS-CCFDSST column, which is useful for advancing theoretical exploration and informing engineering practices for this new column type.

Study of combustion flow field in a scramjet engine under inflow oscillation variations based on OpenFOAM

In this study, a compressible supersonic numerical model was established based on the open-source computational fluid dynamics software OpenFOAM. The supersonic air inflow was set in sinusoidal variation and gas hydrogen was employed as fuel for the DLR engine numerical simulation. The SST k-ω model and a 9-species 27-reaction hydrogen/oxygen chemical reaction model was employed as the turbulence and reaction mechanical kinetics models respectively. The effect of continuous variable inflow on the combustion performance for the scramjet engine was analyzed and the results showed that the combustion flame inside the scramjet engine exhibited significant partitioning phenomena around the combustion stabilization zones under periodic continuous variable inflow conditions. It was found that intense combustion zones were formed at both upstream and downstream flow as the induction of intersecting shock waves. When the flame was stabilized in the engine, the initiation position of the intense combustion zone at the upstream was transferred to the distance of twice the strut length, while the initiation position of the intense combustion zone at the downstream was anchored at a distance of about five times the strut length.

Mechanical Analysis of the Connection Structure of a Double-Layered Valve Stent within an Annuloplasty Ring

Background: In this study, to address the failure of mitral valve repair surgery, a novel valve-in-ring model for an artificial mitral valve annuloplasty ring and a new double-layer mitral valve were established. A suitable number and length of ventricular fixation struts within the annuloplasty ring, as well as the implantation depth, result in variations in stress and strain for the inner and outer stent layers. Methods: The compression and self-expansion model of the stent was established via finite element analysis. The changes in stress and strain were analyzed by setting the length and number of the ventricular fixed struts and implantation depth. Results: When only affected by factors such as blood pressure, the maximum stresses of stent structures with three and six ventricular fixed struts are 476 and 222 MPa, respectively, in the right posterior annular region. At implantation depths of 0, 0.5, 1, and 2 mm, the maximum stresses are located in the left posterior annular region of the outer stent and are 740, 697, 709, and 742 MPa, respectively, and the maximum displacements of the inner stent are all in the right posterior ventricular fixed strut region of the posterior annulus and are 3.71, 3.10, 2.48, and 1.87 mm, respectively. In the three and six ventricular fixed strut stents, when the ventricular fixed strut length is 3, 4, and 5 mm, the maximum stresses are 570, 557, and 621 MPa and 674, 666, 644 MPa, respectively. Conclusions: Appropriately increasing the number of ventricular fixed struts can effectively reduce damage to the stent inside the body, and the damage to the stent is relatively consistent across different implantation depths; however, the right side of the stent's posterior annulus is particularly susceptible to damage. However, if the implantation depth is lower, the impact on the inner stent will be more significant. As the number of ventricular fixed struts increases, the strut length variation has a relatively stable impact on stent damage.

Optimization of additive manufactured Ti-based pyramidal lattice structure applied to interface strengthening of Mg/Ti bimetal composites

Mg/Ti bimetal composites were fabricated by ultrasonic-assisted solid−liquid compound casting with an additively manufactured Ti-based pyramidal lattice structure at the interface. The Taguchi method was carried out to optimize the lattice parameters. The optimized geometric parameters include: the strut diameter (d) is 1 mm, the ratio of strut length to diameter (l/d) is 3, and the ratios of the upper and lower node to diameter (d1/d and d2/d) are 2.5 and 2.5, respectively. The ratio of strut length to diameter is the most significant factor affecting failure strength. The failure strength of the Mg/Ti bimetal joint with the optimized lattice structure is 77.3 MPa. Experimental and simulated results show that the failure strength increases first and then decreases with the increase of l/d, and it reaches the peak value when l/d is 3.

VAM-based equivalent-homogenization model for 3D re-entrant auxetic honeycomb structures

The integration of two vertically crossed re-entrant honeycombs gives rise to a 3D re-entrant honeycomb (3D-RH), which displays intricate three-dimensional auxeticity. To simplify the modeling complexity, this study employs asymptotic analysis of the energy functional stored in the unit cell of the 3D-RH to develop unified constitutive models for 3D structures and panels with multiple length scales. Based on this, an equivalent 3D Cauchy continuum model is established for multi-layer 3D-RH, while a 2D equivalent plate model is developed for sandwich panel with single-layer 3D-RH (SP-3D-RH). The accuracy and effectiveness of these equivalent models are subsequently confirmed through investigations of the X-shaped compressive deformation of multi-layer 3D-RH, as well as the in-plane auxetic deformation and out-of-plane dome-shaped deformation of single-layer 3D-RH. Compared to traditional hexagonal and re-entrant honeycomb sandwich panels, the SP-3D-RH exhibited enhanced equivalent tensile stiffness while effectively mitigating maximum deformation and strain energy under bending and tension conditions. However, due to its relatively low equivalent shear stiffness, the SP-3D-RH exhibited significant deformation and strain energy when subjected to torsional loads, resulting in local stress concentration in the connect region between adjacent facesheets. Parameter analysis shows that the facesheet-to-strut thickness ratio had a substantial impact on the equivalent stiffness and in-plane behavior of the SP-3D-RH, while adjusting the horizontal strut length, strut depth, and re-entrant angle of the 3D-RH can improve the out-of-plane behavior.

Design, analysis and optimization of porous titanium alloys scaffolds by using additive manufacture

In order to have a stronger bond with the surrounding bone, the bone prosthesis needs to have interconnecting pores for bone cells to grow and more importantly to avoid stress shielding. At the same time, human bones have different composition and structure of bone tissue in different parts of the body due to different physical factors of the person, so the elastic modulus of the bones that need to be supported and replaced are not the same. And additive manufacturing has the advantages of rapid, efficient and precise manufacturing of complex shapes and high-quality three-dimensional structures, which can manufacture porous scaffold bone prosthesis, and achieve more accurate mechanical property requirements by controlling the design parameters. To study the effect of design strut length and design strut cross-section diameter size on the elastic modulus of tetrahedral titanium alloy scaffold unit, and with the help of UG NX, several digital models of porous titanium alloy scaffolds were constructed with the strut length and the strut cross-section diameter size as the parameters of variation, and then the elastic modulus of each porous titanium alloy scaffold was measured by ANSYS Workbench 2022, and the elasticity modulus of each porous titanium alloy scaffold was further derived from the relationship between the strut length and strut cross-section diameter size and the porous titanium alloy scaffold. Then the elastic modulus of each porous titanium alloy bracket was measured by ANSYS Workbench 2022, and the mathematical model between the strut length, strut cross-section size and elastic modulus of the porous titanium alloy bracket was further derived. Then, ANSYS Workbench 2022 was used to measure the elastic modulus of each porous titanium alloy bracket and further derive the mathematical model between strut length, strut cross-section diameter size and elastic modulus of the porous titanium alloy bracket, with the help of which the elastic modulus of the porous titanium alloy bracket with specific diameters and strut lengths was finally deduced to validate the correctness of the above predicted mathematical model, and to make reasonable explanations and corrections for the deviations. explanation and correction of deviations. As a result, the rapid prototyping technology can be used to design the required porous titanium alloy bracket in a more detailed way.

Prestress analysis and geometry optimization for conical cable domes with zero Gaussian curvature

The conical cable dome with a rotating cone and zero Gaussian curvature is a new type of cable dome with the generatrix that follows a straight line. The paper studies the prestress design and mechanical properties of such cable domes. First, on the basis of the section and vertical diagrams of the proposed cone, a simplified method is developed to calculate feasible prestresses of cables and struts using the principle of nodal balance. Second, prestress distribution, load-bearing capacity, and prestress of the conical cable domes with 15 different combinations of rise-span ratio and inner triangular slope under both prestress and load states are studied. Additionally, the paper proposes five load conditions to assess the performance of the conical cable domes. Finally, the total strain energy, basic frequency, radial reaction, and gravity are optimized through single-criterion and multi-criterion based on the combination of a genetic algorithm and the Newton iteration method. To keep the outer appearance of the conical cable dome, the work selects the strut length as the optimization variable. An optimized conical cable dome is recommended with a low prestress uniformity index and high uniformity index. The results indicate that the conical cable dome is sensitive to the asymmetrical loads, especially the wind loads. For the single-criterion optimization, the structure with the basic frequency under loads as the objective function has the best load-bearing capacity. After optimization, the maximum nodal displacement is 32% and 43% of the original one under LC4 and LC5. Besides, to get a synthetic optimization result, a multi-criterion optimization is suggested.

Study on orthopaedic path planning of Taylor spatial frame

AbstractAimTaylor spatial frame (TSF) is a kind of six‐axis external fixator based on Stewart platform, which is widely used in the fields of trauma orthopaedics and orthopaedic reconstruction.PurposeTo reduce the irregular movement of TSF's moving platform during orthopaedic process and decrease the risk of complications caused by collision between bone and surrounding tissue.MethodWe combine the kinematics solutions with the multi‐objective genetic algorithm and ant colony optimization to get the optimal solution for adjustment of strut length and order. We conduct simulation and physical experiment of orthodontic process respectively to prove the effectiveness of our method.ResultAfter optimization, the average offset during a single adjustment is less than 1 mm, and the offset during the whole orthopaedic process is reduced by about 38.8%.ConclusionIt demonstrates that our method can effectively reduce the offset of moving platform while ensuring orthopaedic accuracy.

Design exploration of additively manufactured chiral auxetic structure using explainable machine learning

A design exploration of hexachiral structures using explainable machine learning (ML) is performed in this work. The hexachiral structures are fabricated using resin via vat photopolymerization (VPP). The ML model is used to build the function that explains the association between Poisson’s ratio and the hexachiral design parameters. The data set for ML model construction is first collected by using the Halton sequence and simulated using the finite element method (FEM). To validate the data set, the results obtained from the FEM simulation are compared with those obtained from the compression test. The Gaussian Process Regression (GPR) models for Poisson’s ratio and porosity are constructed to extract important design insight. A Global Sensitivity Analysis (GSA) and Shapley Additive Explanations (SHAP) are used to analyze the sensitivity of the porosity and Poisson’s ratio to the hexachiral design parameters. GSA result shows that the strut’s thickness is the most decisive parameter that affects the Poisson’s ratio. The application of SHAP also reveals that the relationship between the strut thickness and Poisson’s ratio is nonlinear. Finally, the minimum Poisson’s ratio value is achieved by design with minimum strut thickness, minimum node radius, and maximum strut length.

A new configuration of Geiger-type cable domes with sliding ridge cables: Computational framework and structural feasibility investigation

Cable domes have been widely used in the field of structural engineering for their lightweight feature that is fit for large-span structures. Geiger-type cable domes have gained much attention due to their simple configurations. This paper proposes a modified Geiger-type cable dome with sliding ridge cables. Compared to conventional forms, the pre-stresses in the cables are more uniform, and the number of cables is fewer. An energy-based method is adopted to derive the equilibrium equations for the form-finding and load response analysis of the sliding cable system. The Levenberg-Marquardt algorithm is used to solve the non-linear equilibrium equations. A numerical example is employed to demonstrate the feasibility of the proposed structural form in terms of structural strength, stiffness, and stability. The influence of two design parameters, i.e., the force ratio of the hoop and ridge cables and the strut length, on the structural performance is investigated. In general, the new cable dome has better construction features and feasible mechanical properties and is believed to have the potential for practical applications.

In Situ Reconfigurable Continuum Robot with Varying Curvature Enabled by Programmable Tensegrity Building Blocks

Reconfigurable continuum robots exhibit programmable interaction capability, enabling them to cope with challenges poorly addressed by conventional rigid robots. However, the regulation of the module type and/or sequence may result in time‐consuming and labor‐intensive problems. Therefore, in situ reconfiguration schemes are required to develop in a simple yet robust solution for continuum robot design. Herein, inspired by the structure characteristics of the seahorse tail, an original template based on a tensegrity building block (TBB) for creating an in situ reconfigurable continuum robotic paradigm is proposed. As the length of the stretchable struts in the TBB could be programmed, five typical homologous types from the template are derived. Then, ten TBBs into a continuum robot are assembled and the multi‐body dynamic framework is employed to develop a mechanical model for predicting the profile after deformation. Theoretical predictions demonstrate that the robotic shape can be customized in situ by switching the type of TBBs, without disassembling the robot. Furthermore, the tailored continuum robotic configurations are applied to conformally interact with the varying‐curvature objects. The experimental results suggest that the proposed programmable template offers a facile and rapid reconfiguration scheme for the continuum robots, which greatly improves the robotic interaction capability.

Understanding the superior mechanical properties of hollow-strut metal lattice materials

Intricate hollow-strut metal lattice materials are an emerging class of novel metallic cellular materials enabled by additive manufacturing. This work shows that hollow-strut Ti-6Al-4V lattice materials are consistently stronger and stiffer (up to 60% better) than their solid-strut counterparts of the same relative density, both experimentally and through finite element analysis (FEA). The underlying reasons are investigated using analytical models derived from the Timoshenko-beam theory, which considers deformation by concurrent stretching, bending and shear, rather than the single-mode deformation mechanism assumed by the Gibson-Ashby model. Hollow-strut lattices exhibit higher resistance to bending than solid-strut lattices at the same strut length and relative density, thereby leading to increased strength and stiffness. Hollow-strut metal lattices offer an unusual option for lightweight designs, with better mechanical properties at the same or lower density than solid-strut metal lattices.

The Energy Absorption Behavior of 3D-Printed Polymeric Octet-Truss Lattice Structures of Varying Strut Length and Radius.

We investigate the compressive energy absorption performance of polymeric octet-truss lattice structures that are 3D printed using high-resolution stereolithography. These structures are potential candidates for personal protective equipment, structural, and automotive applications. Two polymeric resins (high-strength/low-ductility and moderate-strength/high-ductility) were used in this work, and a comprehensive uniaxial tensile characterization was conducted to establish an optimal UV curing time. The external octet-truss structure geometry (3″ × 3″ × 3″) was maintained, and four different lattice cell densities (strut length, L) and three different strut radii (R) were printed, UV cured, and compression tested. The compressive stress-strain and energy absorption (EA) behavior were quantified, and the EA at 0.5 strain for the least dense and smallest R structure was 0.02 MJ/m3, while the highest density structure with the largest R was 1.80 MJ/m3 for Resin 2. The structural failure modes varied drastically based on resin type, and it was shown that EA and deformation behavior were related to L, R, and the structures' relative density (ρ¯). For the ductile resin, an empirical model was developed to predict the EA vs. compressive strain curves based on L and R. This model can be used to design an octet-truss lattice structure based on the EA requirements of an application.

Effectiveness of high implantation of SAPIEN 3 in preventing pacemaker implantation: A propensity score analysis

BackgroundIn transcatheter aortic valve implantation, high implantation on the aortic annulus may prevent conduction pathway injury, leading to a decrease in the rate of permanent pacemaker implantation. AimTo assess the impact of high implantation of SAPIEN 3 on the prevention of permanent pacemaker implantation. MethodsSince August 2020, we have performed high implantation by fluoroscopically positioning the lower part of the lucent line at the virtual basal ring line on a coplanar view before valve implantation. Patients treated before the adoption of this method were defined as the conventional group. We compared the high implantation group with the conventional group using propensity score analysis. ResultsOverall, the high implantation group (n=95) showed a significantly shorter ventricular strut length than the conventional group (n=85): median 1.3 (interquartile range 0.2–2.4) mm vs 2.8 (1.8–4.1) mm (P<0.001). The permanent pacemaker implantation rate was significantly lower in the high implantation group than in the conventional group (2.1% vs 11.8%; P=0.009). According to 100 propensity score analyses based on multiple imputation and the selection of appropriate covariates, the median P value for the comparison of permanent pacemaker implantation rates after transcatheter aortic valve implantation between the high implantation group and the conventional group ranged between 0.001 and 0.017, indicating a more significant reduction in the permanent pacemaker implantation rate in the high implantation group than in the conventional group. Neither valve dislodgement nor the need for a second valve was observed in either group. ConclusionsThe high implantation of SAPIEN 3 successfully decreases ventricular strut length, reducing the permanent pacemaker implantation rate after transcatheter aortic valve implantation.

Experimental and numerical analysis of a novel 3D re-entrant auxetic structure

The energy absorption performance during collisions and crushing is one of the critical parameters in the design of vehicle structures. Therefore, researchers are continually trying to improve the energy-absorbing properties of the crash box to reduce the force transmitted to the occupant during an accident. In this research, a novel three-dimensional re-entrant auxetic structure has been proposed to improve energy-absorbing performances. Criteria for evaluating energy absorption including the initial peak crushing force, energy absorption, mean crushing force, crushing force efficiency, and specific energy absorption, were obtained through numerical and experimental methods. The structure showed auxetic behavior in two transverse directions during compressive loading and absorbed more energy. The force-displacement curve showed low initial peak crushing force, and the structure collapsed uniformly during compressive loading. The effects of the angle of the diagonal strut with the vertical axis, the thickness of the struts, and the ratio of horizontal strut length to diagonal strut length on the energy absorption properties of the structure were studied, too.

The compression performance of 3D-printed X structures

To enhance the compressive properties of lattice structures, this paper proposes a fused deposition method of three-dimensional (3D) printing to prepare lattice structures and investigate the effect of different printing and structural parameters on structural compression performance. Based on compression tests, vertically printed X structures with a filling angle perpendicular to the strut length and along the strut length are selected. The effect of strut diameter, strut length, and strut inclination angle on the compressive properties was explored. From the results obtained, the slenderness ratio of struts significantly influenced failure modes of structures and a densification stage occurred only when the slenderness ratio was greater than 0.175. The factors that showed the largest influence on strength and specific strength were strut length and strut inclination angle and the highest strength and specific strength were 8.57 MPa and 53.6 MPa/(g/cm3), respectively. In addition, theoretical analysis and finite-element method simulations are performed to investigate the compression performance of the 3D-printed structures and a post-failure model is proposed. It was found that 3D-printed X structures exhibited superior specific strength, specific stiffness, and energy absorption capacity. This study is of guiding significance for improving the compressing and energy absorption performances of 3D-printed lattice structures.

Directed energy deposition-arc of aluminum-alloy curved-generatrix-shell pyramid lattice structure

The curved-generatrix-shell pyramid lattice structure (CPLS) is an important thermal insulation and load-bearing component of hypersonic vehicles (Mach>5). Directed energy deposition-arc (DED-Arc) is an effective method for fabricating CPLSs. In this study, the characteristics of a CPLS and the unit cells of the CPLS were analyzed in detail. The CPLS consisted of row-lattice unit cells along the axis of the curved-generatrix shell and column-lattice unit cells along the circumference. The strut inclination angles and strut lengths of different rows of each unit cell were different, in contrast to the previously reported planar unit cells. Based on the characteristics of the CPLS and unit cell, the curved-generatrix shell surface slicing method was used to obtain high-accuracy curved-generatrix-surface unit-cell deposition path points, and the initial position correction, variable process parameter values, and secondary deposition were used to control the droplet deposition amount to achieve the same layer height compensation. This ensured high-precision forming of the lattice struts. In this study, the fabrication of a CPLS was the ultimate goal. Thus, an eight-axis collaborative DED-Arc system composed of a six-axis robot and a two-axis positioner was adopted. The flip and rotation angles of the positioner were regulated so that the deposition plane of the formed struts was always horizontal, avoiding the flow of liquid metal in the molten pool. Finally, a large-size aluminum-alloy CPLS consisting of 23 rows of unit cells and 33 columns of unit cells was successfully fabricated using DED-Arc on the aluminum-alloy curved-generatrix shell. The maximum error of the lattice strut forming angle was within ±0.4°, and the maximum error of the forming strut length was within ±0.26 mm.

The design of strongly bonded nanoarchitected carbon materials for high specific strength and modulus

Understanding the structure-mechanics relationships in cellular solids is essential for using the same material to achieve better mechanics. We use multiscale modeling and computation to investigate the mechanics of a series of hierarchical carbon nanoarchitectures with structural features quantitatively characterized. We find that the Young's modulus and tensile strength of the graphene network are mainly determined by its density. However, different density scaling laws of compressive strength are observed and they are related to the length, diameter, and surface roughness of the constituent struts, the buckling form of which yields different scaling laws. Therein, the graphene network with struts of a higher length-to-diameter ratio, smoother surface, and failure mode of shell buckling has a higher compressive strength for a given overall density and topology. Besides, the topology, bonding mode, and multiscale defects explain the large variance of scaling laws of different carbon materials. The work reveals the great potential of architected cellular carbons and provides insight into their future design.