Rigid Segments Research Articles

Free vibration analysis of cracked beams by using rigid segment method

This paper deals with the analysis of influence of crack parameters to the modal characteristics of beams at various boundary conditions by using rigid segment method. The beam was discretized by a number of rigid segments which were connected by elastic joints with three degrees of freedom, while the crack was described by cracked element based on fracture mechanics. This model allows detection of coupling between the axial and transverse vibrations under the special boundary conditions. The proposed approach covers both the Euler–Bernoulli and Timoshenko beam model. The efficiency of the method was shown through the few numerical examples.

Changes to the Contour Length, Molecular Chain Length, and Solid-State Structures of Nanocellulose Resulting from Sonication in Water.

Sonication in water reduced the average contour lengths of nanocellulose prepared from wood cellulose fiber and microcrystalline cellulose. Most of the kinks in the wood cellulose nanofibrils were formed during the initial 10 min of sonication. Fragmentation occurred at the kinks and rigid segments associated with depolymerization during subsequent sonication for 10-120 min, resulting in the formation of cellulose nanocrystals with low aspect ratios. Solid-state cross-polarization magic angle sample spinning 13C-nuclear magnetic resonance revealed that the original crystalline regions of the cellulose were partly transformed to fibril surfaces or disordered regions by both pretreatment and the subsequent fragmentation of molecular chains during sonication. The nanocellulose prepared from microcrystalline cellulose had different fragmentation behavior with regard to molecular chain length following sonication. The results indicated that on average the hexagonal 36 cellulose chain structure formed the cross-section of each wood cellulose microfibril.

Modeling of Stripe Patterns in Photosensitive Azopolymers.

Placed at interfaces, azobenzene-containing materials show extraordinary phenomena when subjected to external light sources. Here we model the surface changes induced by one-dimensional Gaussian light fields in thin azopolymer films. Such fields can be produced in a quickly moving film irradiated with a strongly focused laser beam or illuminating the sample through a cylindrical lens. To explain the appearance of stripe patterns, we first calculate the unbalanced mechanical stresses induced by one-dimensional Gaussian fields in the interior of the film. In accordance with our orientation approach, the light-induced stress originates from the reorientation of azobenzenes that causes orientation of rigid backbone segments along the light polarization. The resulting volume forces have different signs and amplitude for light polarization directed perpendicular and parallel to the moving direction. Accordingly, the grooves are produced by the stretching forces and elongated protrusions by the compressive forces. Implementation into a viscoplastic model in a finite element software predicts a considerably weaker effect for the light polarized along the moving direction, in accordance with the experimental observations. The maximum value in the distribution of light-induced stresses becomes in this case very close to the yield stress which results in smaller surface deformations of the glassy azopolymer.

Star-Shaped Crosslinker for Multifunctional Shape Memory Polyurethane.

Star-shaped cyclophosphazene (ACP) was employed as covalent crosslinker to form a rigid segment in polyurethanes network, to enhance the mechanical performance and to add extra flame retardant property. The effects of different ACP contents on the shape memory ability and fire resistance performance of polyurethane (PU) were studied. Tensile tests suggested high flexibility of the PUs with the maximum elongation-at-break of 161.59%. Dynamic mechanical analysis (DMA) indicated good shape recovery ratio of 72.58% after more than three repeated cycles. Under thermal treatment, the temporary shape could recover to its original state in 10 s. The peak heat release rate (pHRR), total heat released (THR) and temperature at pHRR (Tp) of flame-retardant shape memory polyurethane (FSPU) by micro-combustion calorimeter (MCC) was as low as 183.2 W/g, 21.4 KJ/g, 330.8 °C respectively, suggesting good inherent fire-resistant performance. As amine-containing crosslinkers are one of the most common building units in thermosetting polymers, we anticipate that our finding will have significant benefits beyond shape memory and fire-resistance.

Synthesis and characterization of metformin-pluronic based polyurethanes for controlled drug delivery

Segmented polyurethanes (SPU) were synthesized with Pluronic F127 (PLU) as soft segment and 4,4′-methylene-bis(cyclohexyl) diisocyanate (HMDI) and Metformin (Met) as rigid segment (HMDI-Met) while antidiabetic content increased by using 20%, 30%, 40%, and 50% of rigid segments. The Met incorporation was provided by FTIR, Raman, NMR, and XPS. By increasing the content of rigid segments, the first decomposition temperature tends to increase from 317 °C to 361 °C while Tg was modified from −80 °C to −50 °C. Mass loss was observed during accelerated degradation and therefore SPU-PLU-Met can deliver up to 40 µg/30 days of Met. Cytotoxicity test showed no deleterious effect.

Buckling of a column with rigid segments on an elastic foundation

A beam-column consisting of linked rigid segments with rotational resistance at the joints rests on an elastic foundation. The buckling problem due to axial compression is formulated for N identical segments. The characteristic equation show the buckling force depends on N and a parameter representing the relative importance of joint rigidity and foundation resistance. Exact solutions are found for columns up to N = 5 segments.

Fine-tuned order-order phase transitions in giant surfactants via interfacial engineering

Thermotropic order-order phase transitions (OOTs) in block copolymers are not commonly observed in the strong segregation region. Phase separation of giant surfactants composed of hydrophilic molecular nanoparticles (MNPs) as heads and hydrophobic flexible polymer chains as tails occurs generally in the strong segregation region. By introducing a rigid molecular segment at the junction point of the giant surfactants, the interface between the MNPs and polymer tails could be delicately manipulated, resulting in the occurrence of thermotropic OOTs that are sensitively dependent on the properties of those junction segments. For samples with hydrophilic junction segments, no thermal-induced OOT has been observed. However, for samples with hydrophobic junction segments, complicated thermotropic OOTs between as many as four different ordered phases in a single giant surfactant system, from lamellae (LAM) to hexagonally perforated layer structure (HPL), double gyroids (DG), and finally to hexagonally packed cylinders (HEX), have been observed with increasing temperature. These results demonstrated that interfacial engineering could be used to regulate the self-assemble behavior of macromolecules at the nanometer scales.

Evaluation of variable pitot inlet concepts for transonic and supersonic civil aviation

Purpose This paper aims to describe the selection of the ideal variable inlet concept group by using results of aerodynamic investigations, system safety analyses and integration studies. Design/methodology/approach Aerodynamic and functional inlet requirements are explained and variable inlet concept groups are introduced. The concept evaluation by means of a weighted point rating is presented. The respective concept groups are analysed and evaluated regarding economic, functional and safety requirements. Findings By means of this evaluation, the concept group that adjusts the inlet geometry by rigid segment repositioning is identified as most suitable concept group. Originality/value The early selection of the most suitable concept group enables more detailed subsequent concept investigations, potentially enabling the technology of variable inlets for future commercial aircraft.

Synthesizing Mechanical Chains for Morphing Between Spatial Curves

Abstract This paper extends the kinematic synthesis methodology for designing a chain of bodies to match a set of arbitrary curves to the spatial case. The methodology initiates with an arbitrary set of spatial curves, and concludes with a set of bodies defined by their spatial features. The bodies synthesized can be one of three types: a rigid segment, a helical segment with constant curvature and torsion but varying length, and a growth segment that maintains its geometry but may be scaled to become larger or smaller. To realize mechanical chains for mechanisms that achieve spatial shape change, only rigid and helical segments are used. After designing the segments, they may be aligned with the original spatial curves with their ends connected via an optimization. For two curves, these connections may be made with revolute joints to obtain high accuracy. For three or more curves, spherical joint connections allow for best accuracy. To compare curves as is useful in morphometry, all three segment types may be employed. In this case, an accurate description of the changes between curves is important, and optimizing to connect the segments is not needed. The procedure for redefining the curves in a way that the techniques in this paper may be applied, as well as the methodologies for synthesizing the three segment types are presented. Examples include a continuum robot problem and the morphometric analyses of cochlear curves and the lambdoidal suture located on a human skull. This work extends the established planar techniques for synthesizing mechanisms and addressing morphometric issues that are motivated with curves in two-dimensions.

Neat 3D C3N4 monolithic aerogels embedded with carbon aerogels via ring-opening polymerization with high photoreactivity

Ring-opening polymerization affords an extremely powerful driver for large-scale delocalization of π-electrons and good charge transport via incorporating aromatic repeat units and rigid molecular skeleton. Herein, we first developed a branched six functional benzoxazine monomer (BZ) through Mannich condensation reaction. The rigid chain segment structure of crosslinked polybenzoxazine (PBZ) penetrated into the π-conjugated planes of C3N4 via the room-temperature HCl-catalyzed polymerization of the monomer, leading to the formation of a range of 3D C3N4 monolithic aerogels embedded with carbon aerogel. High nitrogen self-doped carbon aerogels were flexibly embedded in situ into the C3N4 matrix during the heat curing process, leading to the redshift of the C3N4 absorption edge and the increase of electrical conductivity. The special framework of the NC/C3N4 monolithic aerogels can tremendously enrich the electron-trapping sites through the generation of delocalized big π bonds. This work provides new insights into the understanding of polymer chemistry and photocatalysis mechanism.

The effect of mono- versus multi-segment musculoskeletal models of the foot on simulated triceps surae lengths in pathological and healthy gait

BackgroundEstimating muscle-tendon complex (MTC) lengths is important for planning of soft tissue surgery and evaluating outcomes, e.g. in children with cerebral palsy (CP). Conventional musculoskeletal models often represent the foot as one rigid segment, called a mono-segment foot model (mono-SFM). However, a multi-segment foot model (multi-SFM) might provide better estimates of triceps surae MTC lengths, especially in patients with foot deformities. Research questionWhat is the effect of a mono- versus a multi-SFM on simulated ankle angles and triceps surae MTC lengths during gait in typically developing subjects and in children with CP with equinus, cavovarus or planovalgus foot deformities? Methods50 subjects were included, 10 non-affected adults, 10 typically developing children, and 30 children with spastic CP and foot deformities. During walking trials, marker trajectories were collected for two marker models, including a mono- and multi-segment foot; respectively Newington gait model and Oxford foot model. Two musculoskeletal lower body models were constructed in OpenSim with either a mono- or multi-SFM based on the corresponding marker models. Normalized triceps surae MTC lengths (soleus, gastrocnemius medialis and lateralis) and ankle angles were calculated and compared between models using statistical parametric mapping RM-ANOVAs. Root mean square error values between simulated MTC lengths were compared using Wilcoxon signed-rank and rank-sum tests. ResultsMono-SFM simulated significantly more ankle dorsiflexion (7.5 ± 1.2°) and longer triceps surae lengths (difference; soleus:2.6 ± 0.29 %, gastrocnemius medialis:1.7 ± 0.2 %, gastrocnemius lateralis:1.8 ± 0.2%) than a multi-SFM. Differences between models were larger in children with CP compared to typically developing children and larger in the stance compared to the swing phase of gait. Largest differences were found in children with CP presenting with planovalgus (4.8 %) or cavovarus (3.8 %) foot deformities. SignificanceIt is advisable to use a multi-SFM in musculoskeletal models when simulating triceps surae MTC lengths, especially in individuals with planovalgus or cavovarus foot deformities.

Low back pain affects coordination between the trunk segments but not variability during running

This study aimed to analyze the coordination and variability between the thorax, lumbar, and pelvis segments in runners with chronic low back pain group (LBPG) and matched control group (CG). Twenty-six recreational runners were evaluated on a treadmill at 3.3 m/s. The coordination of the pelvis–lumbar and lumbar–thorax in all three planes and between the transverse and frontal plane of the lumbar segment were evaluated using the vector coding technique. Coordination was analyzed via histograms with the percentage of each pattern and the coupling angle during the cycle. The variability coordination was calculated from the angular deviation between the cycles. Differences were observed in the coordination patterns and in the coupling angle during the cycle. Between the pelvis–lumbar in the frontal plane, the LBPG (x¯ = 50.6% (SD = 10.7)) presented more in-phase pattern than the CG (38.6% (8.7; P = 0.05). For the lumbar–thorax, differences occurred in all planes. Between the frontal–transverse plane of the lumbar segment, the LBPG (27.6% (7.9)) presented more in-phase pattern than the CG (38.6% (8.7); P = 0.02). The variability did not demonstrate the differences between the groups; these differences were observed in coordination between the lumbar and adjacent segments in all planes. The model of rigid segments and the coordination analyses were sensitive to detect these differences, and the presence of more in-phase patterns could be related to the protection mechanism in order to avoid painful movements.

Numerical analysis of passenger kinematics and injury risks during a railway vehicle collision: The effect of safety belts

The aim of this paper is to contribute to investigation of passive safety of passengers in railway vehicles using numerical simulations. At first, a typical interior of a railway vehicle is created in the Virtual Performance Solution software. It includes finite element models of seats. Their mechanical properties have been determined experimentally. Particular attention is paid to the table in the backseat as a potentially harmful element. In numerical simulations, both folded and unfolded states of the table are considered. The passenger is represented with the virtual human body model Virthuman. Its structure is composed of rigid bodies and deformable segments to account for deformability of soft tissues. It allows for the prediction of injury risk. The numerical simulations aim to investigate the potential benefit of standard seat belts in a railway vehicle. Therefore, the passenger is seated considering three configurations: seating with no constraints, belted with a two-point belt and a three-point belt. The interior is loaded with a crash-pulse prescribed by the GM/RT2100 regulation. The results are discussed in terms of passenger kinematics and injury risk.

Wind Tunnel Test Research on Aerodynamic Characteristics of Iced Conductors

Aiming at that the wind tunnel tests on aerodynamic characteristics of iced conductors were not systematic enough, the wind tunnel test for different icing types was conducted to study the aerodynamic characteristics of iced conductors more systematically. It can accounts for the characteristics of structure and wind field. The aerodynamic characteristics of different icing types such as crescent, fan and corona shapes with different icing thickness were obtained, and the effect of mean wind speed, turbulence and two-dimensional flow on aerodynamic characteristics were also investigated. It is concluded that the icing shapes have much effect on aerodynamic characteristics. The aerodynamic characteristics of rigid segment model with crescent-shaped are regular, while these of corona-shaped and fan-shaped have more peaks and troughs. In addition, the aerodynamic instability of iced conductors is more pronounced in turbulence. Furthermore, the wind speed has significant effects on drag coefficient, but the effects on lift coefficient is little.

Body Wave Generation for Anguilliform Locomotion Using a Fiber-Reinforced Soft Fluidic Elastomer Actuator Array Toward the Development of the Eel-Inspired Underwater Soft Robot.

In the field of marine biology-inspired robotics, anguilliform locomotion, as one of the most common underwater propulsion types, has been widely studied and implemented in many robot prototypes. Most of these robots consisted of rigid parts, and they were able to generate smooth sine waves along the robot body using a great number of rigid segments, electric motors, and complicated control. To simplify the robot structures and improve body compliance, anguilliform robots with a full soft body are highly desirable for better biomimicry. In this article, we propose a serial soft-actuator array consisting of four fiber-reinforced, bidirectionally bending, fluidic elastomer actuators (FEAs) to achieve the generation of anguilliform body waves. The FEA is fabricated using the typical soft lithography method with dual-chamber configuration and fiber reinforcement. The bending performance of the single FEA in free space with static loads was measured and compared with the three-dimensional simulation results using the finite element method. After that, the FEA array was assembled using the through-chamber tube connection and tested in water to investigate the bending performance with dynamic loads. Finally, with coordinated control of each segment, this FEA array achieved the generation of anguilliform body waves with different frequencies and amplitudes, which unveils a novel and promising approach to develop an anguilliform underwater robot. By attaching this FEA array to a miniaturized stand-alone station for control and actuation, an untethered swimming robot was built and successfully propelled by the FEA array, which demonstrates the capabilities and potentials of this soft and slender robot body design.

Undecenoic acid-based polydimethylsiloxanes obtained by hydrosilylation and hydrothiolation reactions

In the present work for the first time polydimethylsiloxanes containing a rigid segment based on N,N-(ethane-1,2-diyl)diundec-10-enamide in the main chain were synthesized by hydrosilylation and hydrothiolation reactions. As a result, oligomers and polymers with various molecular weights from 3000 to 52000 (g mol−1, GPC) were obtained. The thermal properties of the obtained copolymers were investigated by TGA and DSC analysis.All PDMS copolymers containing different amounts of diamide fragments exhibit properties that are distinct from pure polydimethylsiloxane, which indicates a significant influence of a rigid fragment capable of forming hydrogen bonds on the phase behavior of the resulting copolymers.

Role of Aliphatic Chain Characteristics on the Anti-Cracking Properties of Polymer-Modified Asphalt at Low Temperatures.

The anti-cracking properties of polymer-modified asphalt depend largely on the molecular structure of the polymer modifier. However, the mysterious structure-performance relationship is still elusive. In this paper, three kinds of polymers with different chain structures were selected to address this issue. The indices of styrene, trans-butadiene, aliphatic branched-chain, and aliphatic long-chain from the infrared spectrum were used to quantify the functional group compositions of polymer modifiers. Viscoelastic parameters, including relaxation time, dissipation energy ratios, and stiffness were assessed to illustrate the anti-cracking properties of polymer-modified asphalt. Results showed that relaxation time and dissipation energy ratios were mainly determined by the polymer network strength, molecular size, aliphatic chain feature, and the orientations speed of aliphatic chains. The short relaxation time and high dissipation ratio lead to the low stiffness and favorable low-temperature performance of asphalt. The improvement of these performances requires a polymer with high indices of an aliphatic long-chain, styrene, aliphatic branched-chain, and trans-butadiene, respectively. An aliphatic-long chain, aliphatic branched-chain, and trans-butadiene were soft segments in asphalt while styrene was the rigid segment. The soft segments affect the intramolecular friction, orientation, and thermal motion at low temperatures, whereas the rigid segment enhances the strength of polymer networks. Thus, the anti-cracking property of polymer-modified asphalt can be improved by adjusting the ratio of soft and rigid segments in the polymer modifier.

Tunable Structure and Properties of Segmented Thermoplastic Polyurethanes as a Function of Flexible Segment.

Segmented thermoplastic polyurethanes (PUs) were synthetized using macrodiols with different functional groups (carbonate, ester, and /or ether) as a segment with a molar mass of 1000 and 2000 g/mol, and 4,4’-diphenylmethane diisocyanate (MDI) and 1,4-butanediol as a rigid segment. The polyurethanes obtained reveal a wide variation of microphase separation degree that is correlated with mechanical properties and retention of tensile properties under degradation by heat, oil, weather, and water. Different techniques such as differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), Fourier transform infrared (FTIR), and synchrotron small-angle X-ray scattering (SAXS) were used to determine rigid-flexible segments’ phase behaviour. Retention of tensile properties determines the stability of the samples under different external factors. This work reveals that pure polycarbonate-based macrodiols induce the highest degree of phase miscibility, better tensile properties, hardness shore A, and retention of tensile properties under external agents.

A model-based motion capture marker location refinement approach using inverse kinematics from dynamic trials.

Marker-based motion capture techniques are commonly used to measure human body kinematics. These techniques require an accurate mapping from physical marker position to model marker position. Traditional methods utilize a manual process to achieve marker positions that result in accurate tracking. In this work, we present an optimization algorithm for model marker placement to minimize marker tracking error during inverse kinematics analysis of dynamic human motion. The algorithm sequentially adjusts model marker locations in 3-D relative to the underlying rigid segment. Inverse kinematics is performed for a dynamic motion capture trial to calculate the tracking error each time a marker position is changed. The increase or decrease of the tracking error determines the search direction and number of increments for each marker coordinate. A final marker placement for the model is reached when the total search interval size for every coordinate falls below a user-defined threshold. Individual marker coordinates can be locked in place to prevent the algorithm from overcorrecting for data artifacts such as soft tissue artifact. This approach was used to refine model marker placements for eight able-bodied subjects performing walking trials at three stride frequencies. Across all subjects and stride frequencies, root mean square (RMS) tracking error decreased by 38.4% and RMS tracking error variance decreased by 53.7% on average. The resulting joint kinematics were in agreement with expected values from the literature. This approach results in realistic kinematics with marker tracking errors well below accepted thresholds while removing variance in the model-building procedure introduced by individual human tendencies.

Short Carbon Fiber Reinforced Polymers: Utilizing Lignin to Engineer Potentially Sustainable Resource-Based Biocomposites.

Carbon fiber reinforced composites have exceptional potential to play a key role in the materials world of our future. However, their success undoubtedly depends on the extent they can contribute to advance a global sustainability objective. Utilizing polymers in these composites that can be potentially derived from biomasses would be certainly vital for next-generation manufacturing practices. Nevertheless, deep understanding and tailoring fiber-matrix interactions are crucial issues in order to design carbon fiber reinforced sustainable resource-based biocomposites. In this study, cellulose derivatives (cellulose propionate and cellulose acetate butyrate) are utilized as model polymer matrices that can be potentially fabricated from biomasses, and the mechanical properties of the prepared short carbon fiber reinforced composites are engineered by means of a functional biobased lignin coating on the fiber surface. Furthermore, polyamide 6 based composites are also prepared, the monomer of this polymer could be obtained using C6 sugars derived from lignocellulosic biomasses in the future (through 5-hydroxymethylfurfural). Lignin was successfully immobilized on the carbon fiber surface via an industrially scalable benign epoxidation reaction. The surface modification had a beneficial impact on the mechanical properties of cellulose propionate and polyamide 6 composites. Furthermore, our results also revealed that cellulose-based matrices are highly sensitive to the presence of rigid fiber segments that restrict polymer chain movements and facilitate stress development. It follows that the physicochemical properties of the cellulosic matrices (molecular weight, crystallinity), associated with polymer chain mobility, might need to be carefully considered when designing these composites. At the same time, polyamide 6 showed excellent ability to accommodate short carbon fibers without leading to a largely brittle material, in this case, a maximum tensile strength of ~136 MPa was obtained at 20 wt% fiber loading. These results were further contrasted with that of a petroleum-based polypropylene matrix exhibiting inferior mechanical properties. Our study clearly indicates that carbon fiber reinforced polymers derived and designed using biomass-derived resources can be promising green materials for a sustainable future.