Strut Length Research Articles

Achieving high oligocrystalline degree via strut architecture tailoring to increase the damping and mechanical properties of spherical porous CuAlMn SMAs

Spherical and uniform CuAlMn shape memory foams (SMFs) with quasi-oligocrystalline microstructure and various foam structures were manufactured by the silica-gel beads infiltration method. The strut architecture was quantitatively characterized by strut node size N, strut length L and L/N, and the oligocrystalline degree of foams was characterized by grain size d over N (d/N) for the first time. d/N is found to increase linearly with L/N due to the constricted effect of complex strut architecture on two-dimensional grain growth. The coupling effect of strut sizes and oligocrystalline degree on properties of the SMFs was explored. Too thin struts (smaller N) result in higher quenching rate and consequently more quenched-in vacancies, hindering the thermal-induced martensitic transformation and low-amplitude martensite damping. The peak damping becomes more dependent on d/N and tends to increase with increasing d/N, while the high-amplitude martensite damping improves linearly with d/N. The compression recovery strain also increases linearly with d/N under certain porosity, although higher porosity tends to compromise the favorable effect of higher d/N. The results demonstrate that higher d/N, which corresponds to higher oligocrystalline degree and lower grain constraints, favors the boundary mobility and martensite accommodation and thus improves the damping and compression recovery properties of Cu-based SMFs.

Decolourisation of reactive black-5 at an RVC substrate decorated with PbO2/TiO2 nanosheets prepared by anodic electrodeposition

Reticulated vitreous carbon (RVC) substrates were coated with a composite of PbO2 and titanate nanosheets (TiNS) by anodic electrophoretic depostion. The structure and morphological characteristics of the coating were evaluated by field emission scanning electron microscopy (FESEM) and Raman spectroscopy. The TiNS/PbO2/RVC coating contained the anatase phase and showed a well-defined, microporous morphology with hydrophilic character along the length and thickness of the RVC struts. Electrochemical and photocatalytic activity of the coatings facilitated RB-5 dye degradation as a model organic pollutant in wastewater. The electrochemical decolourisation involves the generation of hydroxyl free radicals over the TiNS/PbO2/RVC anode composite surface, whereas photocatalytic decolourisation was driven by the synergetic photocatalytic effect imparted by the photoinduced holes and free electron acceptors. The photocatalytic properties of the TiNS/PbO2 coating were achieved by calcination at 450 °C for 60 min in air which converted the titanate phase to anatase and modified its surface area. This enabled 98% electrochemical decolourisation of the RB-5 dye solution (measured by visible absorption at 597 nm) in a time of 60 min.Graphical abstractᅟ

Porous Silsesquioxane-Imine Frameworks as Highly Efficient Adsorbents for Cooperative Iodine Capture.

The efficient capture and storage of radioactive iodine (129I or 131I), which can be formed during nuclear energy generation or nuclear waste storage, is of paramount importance. Herein, we present highly efficient aerogels for reversible iodine capture, namely, porous silsesquioxane-imine frameworks (PSIFs), constructed by condensation of octa(3-aminopropyl)silsesquioxane cage compound and selected multitopic aldehydes. The resulting PSIFs are permanently porous (Brunauer-Emmet-Teller surface areas up to 574 m2/g), thermally stable, and present a combination of micro-, meso-, and macropores in their structures. The presence of a large number of imine functional groups in combination with silsesquioxane cores results in extremely high I2 affinity with uptake capacities up to 485 wt %, which is the highest reported to date. Porous properties can be controlled by the strut length and rigidity of linkers. In addition, PSIF-1a could be recycled at least four times while maintaining 94% I2 uptake capacity. Kinetic studies of I2 desorption show two strong binding sites with apparent activation energies of 77.0 and 89.0 kJ/mol. These energies are considerably higher than the enthalpy of sublimation of bulk I2.

Temporal course of vascular healing and neoatherosclerosis after implantation of durable- or biodegradable-polymer drug-eluting stents.

Delayed healing and endothelial dysfunction may occur with drug-eluting stents (DES), promoting accelerated infiltration of lipids in the neointima and development of neoatherosclerosis (NA). Pathology data suggest durable polymer (DP) of DES to play a major role in this process. Whether biodegradable polymer (BP) may address these issues is uncertain. We compared in vivo vessel healing and NA of current generation BP- or DP-DES using serial optical coherence tomography (OCT) assessments. Ninety patients with multivessel coronary artery disease were randomized 1:1 to BP everolimus-eluting stents (EES, Synergy) or DP zotarolimus-eluting stents (ZES, Resolute Integrity). Co-primary endpoints were the maximum length of uncovered struts at 3 months (powered for non-inferiority) and the percentage of patients presenting with frames of NA at 18 months (powered for superiority) as measured by OCT. The maximum length of uncovered struts at 3 months was 10 ± 8 mm in the BP-EES group and 11 ± 7 mm in the DP-ZES group (mean difference -1 mm; upper 97.5% confidence interval +2 mm; P = 0.05 for non-inferiority; P = 0.45 for superiority). The percentage of patients presenting with frames of NA at 18 months was low and similar between BP-EES and DP-ZES groups (11.6% vs. 15.9%; P = 0.56). There was no stent thrombosis in both groups at 24 months. BP-EES and DP-ZES showed a similar healing response at 3 months and a low incidence of NA at 18 months. Biocompatible polymers, regardless of whether they are durable or biodegradable, may favourably impact the long-term vascular response to current-generation DES.

Compressive property of Al-based auxetic lattice structures fabricated by 3-D printing combined with investment casting

Auxetic lattice structures are a new kind of structures that show unique mechanical performance, particularly negative Poisson's ratio behavior. In the present study, an Al-based auxetic lattice structure has been fabricated by 3-D printing and investment casting, and the compressive mechanical behavior was studied. It is shown that increasing the length of re-entrant struts or re-entrant angle leads to decreased compression strength but increased Poisson's ratio. If the relative density of the structures keeps constant, the elastic modulus and compression strength will be enhanced as the Poisson's ratio increases owing to the auxetic effect.

Additive Manufacturing and size-dependent mechanical properties of three-dimensional microarchitected, high-temperature ceramic metamaterials

Abstract

Effect of strut length on combustion performance of a trapped vortex combustor

Experimental studies with four different strut setups are conducted to investigate the effect of strut length on combustion performance of a trapped vortex combustor (TVC). The experimental results indicate that ignition, lean blowout (LBO) and combustion efficiency depend to a great extent upon the length of the strut. The longer struts show prominent advantages in terms of ignition and LBO, whereas the shorter ones perform rather poorly. Interestingly, the combustion efficiency achieved by the shorter struts is higher than the longer ones. Furthermore, RANS based simulations are also performed to explain the experimental results. From the detailed numerical simulations, it can be inferred that the poor ignition performance and LBO limits of the shorter struts are mainly caused by the great amount of mainstream air entrained into the cavity. And the higher combustion efficiency achieved by the shorter struts is mainly attributed to much more wake regions formed behind the struts.

Controlled synthesis of conjugated polycarbazole polymers via structure tuning for gas storage and separation applications

A series of conjugated microporous polymers (CMPs) based on 1,3,6,8-tetrabromocarbazole (N4CMP-1–5) is synthesized via Suzuki cross-coupling or Sonogashira polycondensation. The porosity properties and surface area of these polymer networks can be finely tuned by using a linker with different geometries or strut length. These polymers show the Brunauer-Emmett-Tellerthe (BET) surface areas ranging from 592 to 1426 m2 g−1. The dominant pore sizes of the polymers on the basis of the different linker are located between 0.36 and 0.61 nm. Gas uptake increases with BET surface area and micropore volume, N4CMP-3 polymer can capture CO2 with a capacity of 3.62 mmol g−1 (1.05 bar and 273 K) among the obtained polymers. All of the polymers show high isosteric heats of CO2 adsorption (25.5–35.1 kJ mol−1), and from single component adsorption isotherms, IAST-derived ideal CO2/N2 (28.7–53.8), CO2/CH4 (4.6–5.2) and CH4/N2 (5.7–10.5) selectivity. Furthermore, N4CMPs exhibit the high CO2 adsorption capacity of 542–800 mg g−1 at 318 K and 50 bar pressure. These data indicate that these materials are a promising potential for clean energy application and environmental field.

Design optimization of an articulated frame steering system

The articulated frame-steered vehicles (AFSV) exhibit enhanced maneuverability but reduced yaw stability and greater steering power consumption. Apart from kinematics of the steering system, the dynamics of the actuating system strongly influence the performance of the AFSV, which is generally neglected in the reported studies. In this study, a yaw-plane model of the articulated vehicle coupled with the kinematic and dynamics properties of the steering struts is formulated to identify objective measures of the AFSV under steering inputs. The results suggest that the vehicle yaw oscillation/stability, steering power efficiency and maneuverability can be objectively measured in terms of the strut length, yaw oscillation frequency and damping ratio, steering gain, and steering response rate and overshoot. The layout of steering struts and properties of the steering valve and hydraulic fluid are optimized while employing the weighted-sum method and a combination of pattern search and sequential quadratic programming algorithms. The relative weights of individual performance measures were obtained using the analytic hierarchy process (AHP) model. The solutions of the optimization problem revealed more compact articulated frame steering (AFS) system design with over 20% reduction in strut length and 24% gain in the yaw oscillation frequency. Increasing the fluid bulk modulus resulted in more compact AFS layout and further increase in the yaw oscillation frequency with lower response overshoot. The optimal design based on weighted sum of various performance measures, however, revealed negligible changes in terms of the steering power efficiency.

Effects of Replica Ceramic Foam Microstructure on Porous Media Combustion Temperature Distribution

Replica ceramic foam (RCF) is a widely used material in porous media combustion. The macro-structural and thermal properties such as porosity and effective thermal conductivity are governed by RCF’s micro-structure and the properties of the material. The aim of this paper is to study the essential influence of the cell structure and the material on porous media combustion temperature distribution. Kelvin model is adopted to describe the micro-structure of the RCF and to establish the correlations between micro-structure with porosity and effective thermal conductivity. Based on these correlations, the effects of strut length, strut cross sectional size, vertex shape together with different materials (include alumina, zirconia and silicon carbide) on the gas and solid temperature profiles are numerically investigated. Results indicate that the SiC RCF burner has the highest temperature peaks of both gas and solid at the same operating parameters. The temperature profiles of gas and solid are significantly affected by the strut length, the strut cross sectional radius and the length of nodes.

Adapting trabecular structures for 3D printing: an image processing approach based on μCT data

Materials with a trabecular structure notably combine advantages such as lightweight, reasonable strength, and permeability for fluids. This combination of advantages is especially interesting for tissue engineering in trauma surgery and orthopedics. Bone-substituting scaffolds for instance are designed with a trabecular structure in order to allow cell migration for bone ingrowth and vascularization. An emerging and recently very popular technology to produce such complex, porous structures is 3D printing. However, several technological aspects regarding the scaffold architecture, the printable resolution, and the feature size have to be considered when fabricating scaffolds for bone tissue replacement and regeneration. Here, we present a strategy to assess and prepare realistic trabecular structures for 3D printing using image analysis with the aim of preserving the structural elements. We discuss critical conditions of the printing system and present a 3-stage approach to adapt a trabecular structure from μCT data while incorporating knowledge about the printing system. In the first stage, an image-based extraction of solid and void structures is performed, which results in voxel- and graph-based representations of the extracted structures. These representations not only allow us to quantify geometrical properties such as pore size or strut geometry and length. But, since the graph represents the geometry and the topology of the initial structure, it can be used in the second stage to modify and adjust feature size, volume and sample size in an easy and consistent way. In the final reconstruction stage, the graph is then converted into a voxel representation preserving the topology of the initial structure. This stage generates a model with respect to the printing conditions to ensure a stable and controlled voxel placement during the printing process.

Mechanical behavior of three-dimensional pyramidal aluminum lattice materials

Al based pyramidal lattice truss materials have been fabricated through 3-D printing and molten metal infiltration technology. It is shown that the designable structures with thin struts and small cells can be realized by this technology. Similar to usual porous materials, the present Al based lattice materials also exhibited three-stage compressive mechanical behavior, i.e. linear elastic, plateau and densification stages. The mechanical properties of the lattice materials showed obvious dependence on the structure parameters including the inclination angle of strut with the bottom plane, strut length and strut diameter etc, but actually all these dependences can be attributed to varied relative densities of the lattice materials. Moreover, it is found that the deformation mode of the lattice materials was different if the inclination angle was obviously changed. When the inclination angle was relatively small, the deformation uniformly took place in the form of strut buckling, while it occurred in a localized zone followed by the extending of the zone if the inclination angle was large enough.

Cylindrical porous inserts for enhancing the thermal and hydraulic performance of water-cooled cold plates

In the present study, a new class of porous inserts with the Rhombi-Octet unit cell design was proposed for enhancing the thermal and hydraulic performance of water-cooled cold plates with a cylindrical flow channel. Selective laser melting (SLM) was employed to fabricate the cold plates where the inserts were integrated to the flow channel walls in a single built piece. In all, three cold plates (P1, P2 and P3) with their flow channels fully filled with the porous structures of different unit cell sizes and three partially-filled cold plates (AP1, AP2 and AP3) with porous structures of the same unit cell size but with different fill ratios pp+s were investigated. Their results were compared against the cold plates with empty flow channel and flow channel with helical inserts of different twist ratios (Y/D). The geometrical characteristics of the porous structures such as porosity (ε), strut length (l), width (w) and average pore diameter (dave) were determined and their hydraulic performances were characterized using the Forchheimer-extended Darcy equation where the permeability (K) and inertia coefficient (CE) of the respective porous structures were obtained. The cold plates with porous inserts show significant enhancements in the local (hx) and length-averaged (have) heat transfer coefficients as compared to the cold plate with empty channel and helical inserts. In all, P1 exhibits hx values as high as 18322W/m2·K and up to 383% enhancement in have as compared to the empty channel cold plate. On the other hand, the heat transfer coefficients also increase with increasing fill ratio, with AP3 exhibiting the highest h‾ave amongst the cold plates with partially-filled porous inserts and surpassing those of the empty channel, helical insert and a fully-filled porous insert (P3) cold plate. At constant pumping power, P1, P2, P3 and AP3 also show consistently lower average thermal resistances (Rave) than all the other cold plates tested.

Effect of microstructure closed-pore content on the mechanical properties of flexible polyurethane foam

Poroelastic models are constructed based on a set of physical parameters known as the Biot’s parameters (for isotropic materials these are comprised of 5 non-acoustical parameters and 4 mechanical parameters). These macroscopic properties are inter-correlated and dependent on the microstructure of the foam. Therefore, to optimize vibroacoustic behavior, the correlation between foam microstructure and macroscopic properties is needed. In this study, the effect of closed windows content (known as reticulation rate), cell size, and relative density on the mechanical properties of polyurethane (PU) foam are numerically studied using an isotropic, tetrakaidecahedral unit cell. Then, an existing analytical model that correlates unit cell microstructure properties (thickness and length of struts) of fully reticulated foams to their mechanical properties is extended numerically. The membrane thickness is considered to be thinner at the center and larger at the edge of the window. The ratio of membrane thickness to strut thickness is either considered to be fixed or variable. Results show that the Young’s modulus and Poisson’s ratio of unit cells with smaller cells size, when relative density is fixed, are more affected by closed window content.

Analysis of strut-to-bone lengthening ratio for hexapod frames using mathematical modeling

Background: Hexapod external fixators often incorporate bone lengthening as part of a multi-planar deformity correction plan. The hexapod struts, however, do not distract in the direction of bone lengthening. Their oblique orientation to the ring creates a vector that is the summation of multiple individual strut adjustments. We demonstrate that a 1 mm lengthening of each of all six struts always created more than 1 mm of lengthening at the bone. Methods: The amount of lengthening was analyzed with the Taylor Spatial Frame™ (Smith and Nephew, Memphis, TN, USA) software using two different methods. Results: As the strut lengths got longer the ratio got closer to one but it never reached 1.0. Conclusions: This information is critical when using very short struts or very large rings. In these two scenarios, the Δ frame height relative to the Δ strut length becomes much greater than one. Clinical Relevance: A strut length much greater than one will cause the bone to lengthen much faster than the surgeon desires. It may also lead to unhealthy regenerate bone formation and could create delays in bone healing.

Design and synthesis of conjugated polymers of tunable pore size distribution

Conjugated microporous polymers of tunable pore size distribution were synthesized by Yamamoto homo-coupling or co-coupling of 1,3,5-tris(4-bromophenyl)benzene with five chaining monomers of different strut length, respectively. Conjugated microporous polymers with apparent BET surface area in the range from 172 to 820 m2 g−1 were prepared. The materials were found to have excellent microporosity, which could be accurately tuned by changing the strut length of chaining monomers. It was revealed that copolymerization of the core monomer and several chaining monomers with different strut length was an effective strategy to fine-tuning properties of the materials. Moreover, the incorporation of “flexible” double bonds into the chaining monomers could further promote this strategy. H2 and CO2 adsorption capacity of conjugated microporous polymers were also systematically investigated.

Numerical simulation of thermal conductivity of graphene filled polymer composites

Abstract In this work, the thermal behavior of graphene foam (GF) filled polymer composite is investigated using the finite element method. Owing to the interconnected structure of GF, which forms effective heat pathways, GF filled polymer composite is endowed with good thermal properties. The effect of contact thermal resistance, interfacial thermal conductance, as well as GF strut length and diameter on thermal conductivity is simulated and compared with experimental results. It is found that the contact thermal resistance is more important than interfacial thermal conductance in terms of thermal conductivity of composite. The contact thermal resistance between GF filled polymer composite and copper block is about 10 −4 to 10 −3 m 2 KW −1 . The shorter length and larger radius of GF struts are beneficial for heat dissipation. The results prove that the GF filled polymer composite is a good candidate material for heat management of electronic devices.

Form-finding of free-form tensegrity structures by genetic algorithm–based total potential energy minimization

Free-form tensegrities are composed of randomly connected cable and strut elements. The complexity of these structures causes determination of their self-equilibrium form to be a formidable task. There can be an infinite number of solutions with different forms, but it is difficult to identify the best form in terms of stability. Based on the fact that stability of structures is inversely proportional to potential energy, a genetic algorithm minimization process is developed to determine the self-equilibrium form of free-form regular tensegrity structures. The capability of the form-finding process on determination of the most stable form with minimum potential energy is investigated using two main parameters of free-form regular tensegrities which are cable–strut length ratio at rest and number of strut elements. The computational performance of the proposed method is also tested using free-form tensegrities with different number of structural elements.

Strength of Concrete Struts in Three-Dimensional Strut-Tie Models

AbstractThe design of structural concrete using strut-tie models requires establishing the effective strength of concrete struts, ensuring sufficient anchorage of reinforcing bars in nodal zones, and the geometric compatibility of the strut-tie model within the member geometry. In this paper, a consistent and general method applicable to three-dimensional (3D) strut-tie models is presented. The proposed method includes the effects of 3D stresses associated with tensile strains in reinforcing bars crossing a strut, strut length, deviation angle between strut orientation and compressive principal stress flow, compressive strength of concrete, and degree of confinement provided by reinforcement. The proposed method is implemented and then verified using data from 115 reinforced concrete pile caps tested to failure.

Slenderness effects in thin-walled I-section struts susceptible to local–global mode interaction

A variational model that describes the nonlinear interaction between the global and local buckling of a thin-walled I-section strut under pure compression is presented and subsequently exploited. A parametric study is conducted for two limiting cases, where the flange–web joint is assumed to be pinned or rigid. For a chosen set of geometries, the most undesirable parametric spaces are identified for both global and local slendernesses, in terms of the strut length and the flange width respectively, where highly unstable behavior is observed in the post-buckling range. Practical implications are discussed in terms of the idealized design strength relationship.