Flexible Segments Research Articles

CFD analysis of a round shaped air cushion vehicle with inclined skirt segments

This article presents various two-dimensional CFD analyses specific to the area of the flexible skirt segments for a round-shaped air cushion vehicle. This study aims to analyse the flexible skirt segments and the influence of their inclination angle on the lift force values. The simulations, as well as the geometries of the flow domain, were carried out with ANSYS Fluent software, in which three parameters varied: tilt angle, segment height and air clearance height. The choice of segments height was based on a previous study by the authors and the values for air clearance height imposed in the present study were 10, 20, 30, 40 and 50 mm. Regarding the values of the inclination angles, three values were imposed: 45°, 60° and 75°. Using ANSYS CFD-Post application, the resulting pressure / velocity contours and streamlines are interpreted and with Curve Fitting Toolbox application within the MATLAB program, the curves describing lift forces obtained from the simulation are approximated.

CFD analysis of a round shaped air cushion vehicle with flexible skirt segments at 90° and different air clearance height

At present time, the most used flexible skirt in construction of air cushion vehicles is the segmented one. Therefore, this study focuses on performing CFD analysis specific to the area of the segments of such a skirt. The proposed construction model has the outer diameter of flexible skirt segments of 1 meter, the segment thickness of 2 mm and the feed hole of 50 mm. A particular feature of proposed model is the circular ring shape of feed hole. Considering that segments height and air clearance height directly influence the performance of the air cushion, these two parameters were varied. Values ranged between 50 to 200 mm for flexible skirt segment height and from 10 to 50 mm for air clearance height. CFD analyses were performed in ANSYS Fluent program to determine velocity contours, pressure contours and streamlines. The main purpose of simulation was to determine lift force for all analysed configurations. The lift force variation was subsequently plotted according to air clearance height values through MATLAB program. Using Curve Fitting Toolbox application, it was concluded that the power type function with two terms best characterizes the analysed curves.

Static deflection modeling of combined flexible beams using elliptic integral solution

A beam composed of serially connected flexible segments can definitely diversify the option of components for the design of compliant mechanisms. Although the static deflection of such a beam can be considered as the superposition of the deflections of all segments, there is still a lack of available modeling methods due to the comprehensive interactions. This paper presents a method for modeling the static deflection of combined flexible beams (CFBs) composed of either straight or circular-arc segments. By deriving the deflection model of a flexible segment using the elliptic integral solution, an iterative approach is proposed for the deflection analysis of the CFB under the action of combined loads. Then, taking the CFB composed of two straight and one circular-arc segments as an example, the numerical simulation and experimental study are carried out to verify the effectiveness of the derived model. The results show its capability of accurately predicting the tip deflection of the beam.

Effect of structure of nonisocyanate condensation polyurethanes based on benzoic acid on its susceptibility to biodegradation

The present study investigates the effect of the biodegradation time on the properties of condensation segmented nonisocyanate polyurethanes (NIPUs) using the aerobic strain of Gordonia alkanivorans. Polyurethane samples were prepared from phenolsulfonic acid, benzoic acid, polytetramethylene glycol (PTMG 1000) or oligooxypropylene triol (G 1000) and different amounts of formaldehyde. The emulsifying activity, protein concentration, pH, tensile strength and strain at break were evaluated as function of biodegradation time and formaldehyde content. The existence of a segmented structure was confirmed by the existence of two phase transitions in the glass transition temperatures of flexible segments and melting temperatures of hard segments. The tensile strength (TS) of NIPUs based on PTMG 1000 and 50% excess of formaldehyde decreased by about 20%, 60% and 95% after 10, 21 and 90 days of biodegradation. TS decrease was less pronounced for NIPUs prepared from G1000. The 21 days biodegradation caused the most significant changes in the pH, emulsifying activity and protein concentration. The highest degree of cross-linking induced by an excess of formaldehyde led to the highest resistance of NIPU to Gordonia alkanivorans. The DSC, FTIR, SEM and element concentration analyses demonstrated that biodegradation occurred mainly in hydrolysis sensitive hard segments and, to a lesser extent, in flexible oligomerol segments.

Disulfide group influence on the surface properties and reversible cross-linking functionalization of natural polymer coating

For the sake of the sustainable development, we prepared a blend by diallyl drisulfide and natural polymer coating-urushiol through radical chain termination reaction under UV irradiation. Based on the successful preparation of target materials which was characterized by FT-IR, the surface energy and reversible cross-linking functionalization of materials are mainly explored. The basic mechanisms active in microstructure and the associated surface energy were elucidated. Various disulfide densities brought about different microstructures on the modified urushiol. It was found that the surface energy of film had been enhanced after UV-curing and its increase was related to the phase inversion (represented by microstructure). The reversibly cross-linking test showed that the introduction of disulfide bonds assists in achieving the reversible cross-linking under extreme alkalinity. What was more, the existence of flexible segments offered the coating composition with excellent flexibility (2 mm) and rheological properties (5 mPa. S), while the hardness of coating dropped to 3H.

The flexible segment adjusted gelation of the aliphatic polycarbonates: Preparation, mechanical properties, and self-healing behavior

Many methods are used to improve the mechanical properties of hydrogels, but it is still challenging to generate comparable to natural hydrogels, let alone synchronously give it excellent self-healing properties. Herein, we synthesize a novel type of the aliphatic polycarbonate hydrogel with the above advantages. In this work, the ring-opening polymerization of 2-methyl-2-benzyloxy carbonyl propylene carbonate (MBC) and 1, 3-trimethylene carbonate (TMC) are initiated by the hydroxyl group of methoxy poly(ethylene glycol) (mPEG113, Mn = 5000). The effect of the TMC as flexible segments on the structure, mechanical properties, and self-healing behavior of the obtained materials is systematically studied. The swelling ratios of the obtained gels in water are enhanced as the content of the monomer TMC increases. The self-healing ability of the materials is drove by the hydrogen bonds and the hydrophobic associations to heal the fracture interfaces. The obtained gels exhibit outstanding mechanical properties and excellent ability of self-healing at room temperature. Both of these abilities can be adjusted by the variation of the TMC flexible segment. Thus, we provide a novel strategy for the fabrication of modified tough hydrogel, which will expand the modification field of hydrogels.

Relationship Between Functionalized Multi-Walled Carbon Nanotubes and Damping Properties of Multi-Walled Carbon Nanotubes/Carbon Fiber-Reinforced Plastic Composites for Shaft.

The mechanical properties and damping behavior of carbon fiber-reinforced plastic composites with functionalized multi-walled carbon nanotubes were examined. The functionalized multi-walled carbon nanotubes were blended with epoxy resins to prepare multi-walled carbon nanotubes/carbon fiber-reinforced plastic composites. The dispersion properties of functionalized multi-walled carbon nanotubes in epoxy resins were examined using surface free energy. The mechanical properties of functionalized multi-walled carbon nanotubes/carbon fiber-reinforced plastic composites were measured by interlaminar shear strength and torsion strength. The functionalized multi-walled carbon nanotubes/carbon fiber-reinforced plastic composites had superior mechanical properties due to the increase in dispersion properties of functionalized multi-walled carbon nanotubes in epoxy resins. However, the tan delta values of damping behavior, analyzed by dynamic mechanical analysis, varied with the type of functional groups of functionalized multi-walled carbon nanotubes. The composites obtained from functionalized multi-walled carbon nanotubes obtained through spermidine amidation reaction and carbon fiber-reinforced plastic showed excellent tan delta values due to the flexible segments in side chains.

Efficient PMV computation for public environments with transient populations

Thermal Comfort (TC) is an important environmental parameter strongly affecting human well-being. Nevertheless, it is not being routinely monitored in public environments (e.g., hospitals and shopping malls) characterized by high occupancy and transient populations. Furthermore, the unique computational demands of TC models for such environments are less studied. We establish large datasets representing such settings and corresponding Predicted Mean Vote (PMV) values as calculated by ISO7730 (Fanger’s model). We then demonstrate that PMV values can be reasonably estimated using linear regressions if the full PMV range is piecewise segmented. Support Vector Machine (SVM) regression provides certain accuracy improvement over linear that becomes marginal for sufficiently small segments. However, while SVM computation becomes orders of magnitude slower than ISO7730 algorithm for large datasets, linear computation becomes exponentially faster. Furthermore, the latter does not require unique expertise in mathematics/TC and constitutes an excellent first-step checkpoint to more accurate algorithms adapting the environment to transient populations. Spatial/temporal flexible segment resolution adds compliance with dynamic demands. To conclude, PMV piecewise linear regression can greatly expedite implementing TC and thus conserving energy in public environments, particularly those exposed to extreme climates. To this end, future TC models must consider computation efficiency besides accuracy.

Structure and Physical Properties of Hydrophilic Polyamide Copolymers Fiber Based on Nylon 6 and Nylon 4,6

Recently, hydrophilic synthetic fiber products have been sought to substitute natural fibers. This paper investigates the structure and properties of spined copolymer of nylon 6, nylon 4,6 and polyethylene oxide (PEO) — polypropylene oxide (PPO) diamine according to contents of PEO-PPO diamine (15–40%). The structure of new polyamide (NPA) were analyzed by X-ray diffraction (XRD), differential scanning calorimeter (DSC), dynamic mechanical analysis (DMA), gradient density column and gas pycnometry. Through XRD and DSC analysis, it was confirmed that the structure of NPA was similar to nylon 6 regardless of the content of PEO-PPO diamine. The DMA results show that the mobility of polymer chain in non-crystalline structure increases. It was considered that PEO-PPO diamine provides flexible segments and hydrophilic moieties to NPA. The analysis of moisture regain and tenacity was revealed that NPA exhibited 7.38% moisture regain and 2.85 g/denier tenacity.

Stiffness of out-of-plane-motion stages with large-motion folded fractal flexible hinges.

This paper introduces a new planar flexible hinge of fractal configuration to be incorporated in out-of-plane-motion compliant stages that cover a wide stiffness range. The large-displacement fractal hinge consists of a series of scaled-down, concentric, circular-axis flexible segments that are connected in a folded manner by radial rigid links. In-plane and out-of-plane compliance matrices are derived for fractal hinges with variable planar geometry features. The flexible hinges are assembled in a radial architecture to form compliant stages that can be utilized for piston-type, out-of-plane sensing or actuation. The analytical model calculates the stage active, out-of-plane stiffness, as well as its parasitic, in-plane stiffness. The stage analytical stiffness is confirmed by the experimental testing of a prototype and by finite element simulation. Furthermore, analytical-model simulation is performed to evaluate the variations in the active and parasitic stiffnesses with key geometric parameters, which also enables optimization.

Self-healing ability based on hydrogen bonds in organic coatings for corrosion protection of AA1200

Biobased polyurethane coatings derived from vegetable oils, with 2 different compositions, were prepared and applied on the AA1200 aluminum alloy to confer corrosion protection. The influence of the ratio between the polyester (flexible segment) and the prepolymer (rigid segment) was investigated. Infrared spectroscopy studies evidenced the difference between the areas of the bands (NH) and optical and scanning electron microscopy evidenced the morphological features of the coating surface before and after immersion in aggressive medium. The barrier properties and anti-corrosion performance of the coatings were evaluated by electrochemical impedance spectroscopy and the results revealed an increase of impedance over the immersion time. Localized corrosion studies confirmed the self-healing effect in coatings formulated with the highest content of polyester.

Self-Healing Polyurethane-Based Nanocomposites Modified with Carbon Fibres and Carbon Nanotubes

Self-healing polyurethanes (PUs) were synthesized as a matrix of nanocomposites containing two fibrous carbon components, i.e., functionalized carbon nanotubes (CNF-OH) and short carbon fibers (CF). Two types of PUs differing in the content of flexible chain segments (40% and 50%) were used. Changes in mechanical strength were analyzed to assess the ability to self-healing of PU-based matrix nanocomposites with experimentally introduced damage in the form of an incision. The healing process was activated by heating the damaged samples at 60°C, for 30 minutes. The addition of CNT-OH and CF caused a slight reduction in the self-healing ability of the nanocomposites as compared to the neat PUs. After heating to 60°C, the nanocomposites self-healed up to 72% of the initial strength of the undamaged samples. The introduction of fibrous components to the polymer matrix improved the thermal conductivity of nanocomposites and facilitated heat transfer from the environment to the interior of the samples, necessary to initiate self-healing. Low content of carbon components in the PU matrix, i.e., 3 wt% of CF and 2 wt% of CNF-OH increased the total work up to fracture of samples after healing by about 53%.

Degradation Urushiol Coating Composition Crosslinked by Diallyl Trisulfide

Urushiol (UR) was a kind of natural paint with a long history and excellent performance. Its high price restricts its development. For the sake of the sustainable development of UR, we prepared a new urushiol based coating composition which is of degradation. To be more specific, we develop a blend by diallyl trisulfide (TS) and urushiol, in which a free radical copolymerization process would take place to form a coating composition under UV irradiation. In this work, FT-IR was used to prove the reaction proces; the reversibly cross-linking properties and the rheological properties were also been proved; the basic mechanisms active in microstructure and the associated surface energy was elucidated; mechanical analysis and showed the mechanical property of coating composition. It was found that a copolymer formed by copolymerization of diallyl trisulfide and urushiol. The introduction of trisulfide bonds assists in achieving the reversibly cross-linking under extreme alkalinity (pH > 8). various trisulfide densities brought about different microstructures on the modified urushiol. The surface energy of coating composition had been enhanced after UV-curing and its increase was related to the phase inversion (represented by microstructure). What was more, the existence of flexible segments offered the coating composition with excellent flexibility (2 mm) and rheological properties (15 MPa.S), while the hardness of coating dropped to 2H.

Tumor-Suppressor p53TAD1-60 Forms a Fuzzy Complex with Metastasis-Associated S100A4: Structural Insights and Dynamics by an NMR/MD Approach.

Conformationally flexible protein complexes represent a major challenge for structural and dynamical studies. We present herein a method based on a hybrid NMR/MD approach to characterize the complex formed between the disordered p53TAD1–60 and the metastasis‐associated S100A4. Disorder‐to‐order transitions of both TAD1 and TAD2 subdomains upon interaction is detected. Still, p53TAD1–60 remains highly flexible in the bound form, with residues L26, M40, and W53 being anchored to identical hydrophobic pockets of the S100A4 monomer chains. In the resulting “fuzzy” complex, the clamp‐like binding of p53TAD1–60 relies on specific hydrophobic anchors and on the existence of extended flexible segments. Our results demonstrate that structural and dynamical NMR parameters (cumulative Δδ, SSP, temperature coefficients, relaxation time, hetNOE) combined with MD simulations can be used to build a structural model even if, due to high flexibility, the classical solution structure calculation is not possible.

Preparation and characterization of active rejuvenated SBS modified bitumen for the sustainable development of high-grade asphalt pavement

To fully restore the performance of waste SBS modified asphalt mixture, better realize its recycling and application in high-grade pavement, achieve the concept of sustainable green development of asphalt pavement. In this paper, the synergistic effects of bio-rejuvenator and active isocyanate rejuvenators (including hexamethylene diisocyanate (HDI), diphenyl-methane-diisocyanate (MDI) and toluene-2, 6-diisocyanate (TDI)) on the chemical structure, physical and rheological properties of aged SBS modified bitumen were thoroughly investigated. Fourier infrared spectrum and Gel permeation chromatography analysis indicate the isocyanate groups of active rejuvenators react with hydroxyl or carboxyl group from the degraded SBS segments to form new amide groups that can reconnect the broken segments of aged SBS and partly restore its molecular weight distribution. From physical and rheological properties, bio-rejuvenator can restore the low-temperature properties by rebalancing the colloidal structure of aged binder, meanwhile, active rejuvenators can greatly improve the high-temperature performance of rejuvenated SBS modified bitumen with bio-rejuvenator through reconnecting the broken segments of aged modifier SBS. Furthermore, MDI with benzene ring structure is more conducive to enhancing the high temperature rutting resistance of rejuvenated SBS modified bitumen. While HDI can bring some flexible segments into the restored structure of SBS, which is more beneficial to improve its low-temperature cracking resistance of rejuvenated binder. And the fluorescence images further demonstrate isocyanate rejuvenators can partly restore the crosslinking network structure of aged modifier SBS in rejuvenated SBS modified bitumen. This research would be conductive to promoting the application of rejuvenated SBS modified bitumen into the construction of high standard pavement.

Novel biocompatible multiblock Polydimethylsiloxane-PA1212 copolymers

Although polyamide-co-polyether, the most important co-polyamide species, has achieved big success, the inadequate biocompatibility still restricts it further application in biomedical area. In this paper, polydimethylsiloxane (PDMS) segment is introduced into copolymer to replace polyether segment, which is intended to fulfill the copolymer with improved surface performance. Two prepolymer condensation process was used to synthesis the novel PA1212-b-PDMS series, which is constructed by PDMS flexible segment (Mn = 1000 g/mol) and PA1212 rigid segment (Mn = 1000, 3000, 5000, 7000, 10,000 g/mol). FTIR and 1H NMR were carried out to evidence the success of the copolymerization and verify the chemical structure. Melting and crystallization behavior, thermal stability, and crystal structure of the series were characterized by DSC, TG and XRD, respectively. To explore the potential usage of the copolymers, mechanical properties were thoroughly investigated. The series possess tunable toughness and rigidity corresponding to different chain compositions. When Mn of PA1212 segment is above 5000 g/mol, the copolymer presents typical tough and stiff feature with an ultimate elongation rate of around 500% and a fair tensile strength around 35 MPa. More than that, the platelet adhesion and activation test was conducted to estimate the biocompatibility of the polymers. The contact angel goniometry and XPS were further utilized to understand their surface performance. The as-prepared copolymers give distinct-different performance from homo-polyamide and polyamide-co-polyether. Barely cell adhesion on the surface indicates the greatly improved biocompatibility achieved by the series, which promises the mechanical-property-adjustable novel co-polyamide a broad prospect in biomedical area.

Melt fluidity and thermal property of thermosetting siloxane-containing polyimide resins and their organic/inorganic hybrid characteristics

A series of thermosetting siloxane-containing polyimide resins were synthesized by incorporating of bis(p-aminophenoxy)dimethylsilane or bis(p-aminophenoxy)tetramethyldisiloxane with various concentrations into formulated oligoimides. These thermosetting polyimide resins exhibited good combination of processability and thermal resistance. It was found that siloxane-containing oligoimides provided significant advantages over unmodified oligoimides, relative to melt fluidity and processing window, due to the flexibility of D[(CH3)2SiO2/2] siloxy units. The siloxane-containing polyimide resins cured at 380 °C revealed relatively higher glass transition temperatures (Tg) than that of unmodified polyimides, despite the incorporation of flexible siloxane segment in oligoimides. Dynamic mechanical analysis and microstructure investigation suggested that some D[(CH3)2SiO2/2] siloxy units in the surface layer of polyimide transformed into T[CH3SiO3/2] and Q[SiO4/2] siloxy units in the curing procedure besides crosslinking of phenylethynyl groups, due to oxidation crosslinking of siloxane. That led to inorganic silica-like structures formed in situ, and inter-connected by organic polyimide segments. This organic/inorganic hybrid characteristics endowed polyimide resins with enhanced thermal property. After post-curing at 450 °C, D[(CH3)2SiO2/2] siloxy units completely transformed into T[CH3SiO3/2] and Q[SiO4/2] siloxy units, and the polyimide reins gave the Tg even exceeding 550 °C. Meanwhile, the corresponding T700 carbon fiber reinforced composite presented excellent mechanical property and durability at the temperature as high as 500 °C.

Morphology and crystallization kinetics of Rubber-modified Nylon 6 Prepared by Anionic In-situ Polymerization

Abstract In this work, we modified nylon 6 with liquid rubber by in-situ polymerization. The infrared analysis suggested that HDI urea diketone is successfully blocked by caprolactam after grafting on hydroxyl of HTPB, and the rubber-modified nylon copolymer is generated by the anionic polymerization. The impact section analysis indicated the rubber-modified nylon 6 resin exhibited an alpha crystal form.With an increase in the rubber content, nylon 6 was more likely to generate stable α crystal. Avrami equation was a good description of the non-isothermal crystallization kinetics of nylon-6 and rubber-modified nylon-6 resin. Moreover, it is found that the initial crystallization temperature of nylon-6 chain segment decreased due to the flexible rubber chain segment. n value of rubber-modified nylon-6 indicated that its growth was the coexistence of two-dimensional discoid and three-dimensional spherulite growth. Finally, the addition of the rubber accelerated the crystallization rate of nylon 6.

Quadruple Hydrogen Bonding Supramolecular Elastomers for Melt Extrusion Additive Manufacturing.

This manuscript describes the versatility of highly directional, noncovalent interactions, i.e., quadruple hydrogen bonding (QHB), to afford novel polyurea segmented supramolecular polymers for melt extrusion three-dimensional (3D) printing processes. The molecular design of the polyurea elastomers features (1) flexible polyether segments and relatively weak urea hydrogen-bonding sites in the soft segments to provide elasticity and toughness, and (2) strong ureido-cytosine (UCyt) QHB in the hard segments to impart enhanced mechanical integrity. The resulting polyureas were readily compression-molded into mechanically-robust, transparent, and creasable films. Optimization of polyurea composition offered a rare combination of high tensile strength (95 MPa), tensile elongation (788% strain), and toughness (94 MJ/m3), which are superior to a commercially available Ninjaflex elastomer. The incorporation of QHB facilitated melt processability, where hydrogen bonding dissociation provided low viscosities at printing temperatures. During cooling, directional self-assembly of UCyt QHB facilitated the solidification process and contributed to part fidelity with the formation of a robust physical network. The printed objects displayed high layer fidelity, smooth surfaces, minimal warpage, and complex geometries. The presence of highly directional QHB effectively diminished mechanical anisotropy, and the printed samples exhibited comparable Young's moduli along (x-y direction, 0°) and perpendicular to (z-direction, 90°) the layer direction. Remarkably, the printed samples exhibited ultimate tensile strains approaching 500% in the z-direction prior to failure, which was indicative of improved interlayer adhesion. Thus, this design paradigm, which is demonstrated for novel polyurea copolymers, suggests the potential of supramolecular polymers with enhanced mechanical performance, melt processability, recyclability, and improved interlayer adhesion for melt extrusion additive manufacturing processes.

Polycarbonate-based polyurethane - attractive materials for adhesives, binders and sealants production

In the last few years, a very wide range of oligocarbonate diols, oligomers of carbonic acid esters terminated on both sides with hydroxyl groups, have appeared on the chemical market. They are mainly used for the production of flexible segments in precious grades of polyurethanes used in biomedical engineering. Poly(carbonate-urethane) due to high resistance to oxidizing and hydrolytic agents is also an attractive material for the production of adhesives and coatings with increased resistance to weather conditions. This paper presents the current state of knowledge on the methods of synthesis and main producers of oligomerols with carbonate groups, methods of poly(carbonate-urethane) synthesis and examples of its commercial applications.