Low Flexural Rigidity Research Articles

Printed nanofilms mechanically conforming to living bodies.

It is anticipated that flexible wearable/implantable devices for biomedical applications will be established for the development of medical diagnostics and therapeutics. However, these devices need to be compatible with the physical and mechanical properties of the living body. In this minireview, we introduce free-standing polymer ultra-thin films (referred to as "polymer nanosheets"), for which a variety of polymers can be selected as building blocks (e.g., biodegradable polymers, conductive polymers, and elastomers), as a platform for flexible biomedical devices that are mechanically compatible with the living body, and then we demonstrate the use of "printed nanofilms" by combining nanosheets and printing technologies with a variety of inks represented by drugs, conductive nanomaterials, chemical dyes, bio-mimetic polymers, and cells. Owing to the low flexural rigidity (<10-2 nN m) of the polymer nanosheets, which is within the range of living brain slices (per unit width), the flexible printed nanofilms realize bio-integrated structure and display various functions with unique inks that continually monitor or detect biological activities, such as performing surface electromyography, measuring epidermal strain, imaging tissue temperature, organizing cells, and treating lesions in wounds and tumors.

Stability modeling with dynamic run-out in high speed micromilling of Ti6Al4V

The low flexural rigidity of the micro-tool makes it susceptible to failure under high cutting forces and/or unstable process conditions. One way to counter the effect of low flexural rigidity is to use high rotational speed which reduces the chip load and, therefore, the cutting forces acting at the tip of the micro-end mill. However, high rotational speeds can amplify the effects of run-out and misalignment. This speed-dependent tool eccentricity, known as dynamic run-out, can be much larger than the quasi-static (speed independent) run-out. The dynamic run-out is more pronounced at high rotational speeds (∼100,000 RPM) due to the increased centrifugal force. The chip thickness is modified due to the dynamic run-out which affects the cutting forces and the stability. It is necessary to incorporate the dynamic run-out in the chip thickness model for an accurate prediction of the forces and the stability limits in high speed micromilling. Consequently, this paper is focused on characterizing the dynamic run-out and incorporating its effect on the undeformed chip thickness, cutting forces and stability limits. The predicted cutting forces with the modified chip thickness due to dynamic run-out shows a better agreement with the experimentally measured cutting forces as compared to the quasi-static run-out and ideal cycloidal chip thickness based force models. The predicted cutting force with dynamic run-out in the feed-direction gives an error of 11.54% as opposed to a relatively large error of 73.1% with a quasi-static run-out based model at 100,000 rpm. The Nyquist stability criterion has been used to predict the stability for 2-DOF chatter model of micromilling process. At a chip load of 3 µm/flute, the predicted stable depth of cut is higher if the dynamic run-out is included at high rotational speeds (> 51,500 rpm). This increase is attributed to a high dynamic run-out which results in cutting via only one flute. However, if the dynamic run-out is relatively low (between 29,500 rpm and 51,500 rpm), both the flutes are engaged in machining and the predicted limit is lower than that of the quasi-static run-out. The predicted values are in reasonably good agreement with the experimentally determined chatter onset points for most cases.

Characterization of a vortex-induced vibrating thin plate energy harvester with particle image velocimetry

Energy of turbulent wakes can be harnessed using vortex induced vibration harvesters. The unequal pressure distribution due to turbulence on the device generates vibrations which can be converted to electricity through piezoelectric transduction mechanism. The energy harvester concept that is investigated here consists in a polymeric thin flexible plate (that can host piezoelectric elements on each side) placed in the wake of a rigid bluff body. The motion of the plate is similar to that of a swimming eel and can be approximated using a cantilever beam model. Experiments were carried out in a water tunnel, different polyethylene plates were clamped to a square cylinder and a high speed camera was used to simultaneously capture both the plate deflection and the flow pattern. Plates were varied in slenderness; the Reynolds number based on the square cylinder ranged between 1500 and 20,000. From each captured frame, the deflection was computed and used to perform modal decomposition and strain energy calculation. The plate deflection pattern evolves from splitter plate oscillations at low Reynolds number or high flexural rigidity into travelling waves at high Reynolds number or low flexural rigidity. Those travelling waves lead to higher strain energy. The measured velocity vectors show that when the normal flow simultaneously impinges at different locations on both sides of the plate, complex bending shapes result. The frequency delay observed with longer plates show that there is more plate-wake interaction sustaining the turbulence in the wake and thus optimizing the energy transfer.

Conditions of efficient vibrodischarge of rock materials in modern mining and processing technologies

The paper reviews vibration feeders used to discharge storage reservoirs in mineral mining. In spotlight are vibrofeeders equipped with an active member of low flexural rigidity developed at Chinakal Institute of Mining. The authors present the results of the physical and numerical studies on vibratory discharge of cohesive rocks from a bunker.

Large-Scale Direct-Writing of Aligned Nanofibers for Flexible Electronics.

Nanofibers/nanowires usually exhibit exceptionally low flexural rigidities and remarkable tolerance against mechanical bending, showing superior advantages in flexible electronics applications. Electrospinning is regarded as a powerful process for this 1D nanostructure; however, it can only be able to produce chaotic fibers that are incompatible with the well-patterned microstructures in flexible electronics. Electro-hydrodynamic (EHD) direct-writing technology enables large-scale deposition of highly aligned nanofibers in an additive, noncontact, real-time adjustment, and individual control manner on rigid or flexible, planar or curved substrates, making it rather attractive in the fabrication of flexible electronics. In this Review, the ground-breaking research progress in the field of EHD direct-writing technology is summarized, including a brief chronology of EHD direct-writing techniques, basic principles and alignment strategies, and applications in flexible electronics. Finally, future prospects are suggested to advance flexible electronics based on orderly arranged EHD direct-written fibers. This technology overcomes the limitations of the resolution of fabrication and viscosity of ink of conventional inkjet printing, and represents major advances in manufacturing of flexible electronics.

Three-dimensional Architecture Enabled by Strained Two-dimensional Material Heterojunction.

Engineering the structure of materials endows them with novel physical properties across a wide range of length scales. With high in-plane stiffness and strength, but low flexural rigidity, two-dimensional (2D) materials are excellent building blocks for nanostructure engineering. They can be easily bent and folded to build three-dimensional (3D) architectures. Taking advantage of the large lattice mismatch between the constituents, we demonstrate a 3D heterogeneous architecture combining a basal Bi2Se3 nanoplate and wavelike Bi2Te3 edges buckling up and down forming periodic ripples. Unlike 2D heterostructures directly grown on substrates, the solution-based synthesis allows the heterostructures to be free from substrate influence during the formation process. The balance between bending and in-plane strain energies gives rise to controllable rippling of the material. Our experimental results show clear evidence that the wavelengths and amplitudes of the ripples are dependent on both the widths and thicknesses of the rippled material, matching well with continuum mechanics analysis. The rippled Bi2Se3/Bi2Te3 heterojunction broadens the horizon for the application of 2D materials heterojunction and the design and fabrication of 3D architectures based on them, which could provide a platform to enable nanoscale structure generation and associated photonic/electronic properties manipulation for optoelectronic and electromechanic applications.

Evidence based recommendations for reducing head-neck taper connection fretting corrosion in hip replacement prostheses.

This systematic review seeks to summarise the published studies investigating prosthetic design, manufacture and surgical technique's effect on fretting corrosion at the head-neck taper connection, and provide clinical recommendations to reduce its occurrence. PubMed, MEDLINE and EMBASE electronic databases were searched using the terms taper, trunnion, cone and head-neck junction. Articles investigating prosthetic design, manufacture and surgical technique's effect on fretting corrosion were retrieved, reviewed and graded according to OCEBM levels of evidence and grades of recommendation. The initial search yielded 1,224 unique articles, and 91 were included in the analysis. There is fair evidence to recommend against the use of high offset femoral heads, larger diameter femoral heads, and to pay particular consideration to fretting corrosion's progression with time and risk with heavier or more active patients. Particular to metal-on-metal hip prostheses, there is fair evidence to recommend positioning the acetabular component to minimise edge loading. Particular to metal-on-polyethylene hip prostheses, there is fair evidence to recommend the use of ceramic femoral heads, against use of cast cobalt alloy femoral heads, and against use of low flexural rigidity femoral stems. Evidence related to taper connection design is largely conflicting or inconclusive. Head-neck taper connection fretting corrosion is a multifactorial problem. Strict adherence to the guidelines presented herein does not eliminate the risk. Prosthesis selection is critical, and well-controlled studies to identify each design parameter's relative contribution to head-neck taper connection fretting corrosion are required.

Numerical study on the cyclic response of AFRP reinforced columns with externally unbonded energy dissipaters

Fiber-reinforced polymer bars are gaining increased use in the construction market as a replacement to steel reinforcement for concrete structures. However their use as compression members is limited due to their mechanical properties, typically low flexural rigidity, so that local buckling may occur relatively at low stress levels. Their premature rupture in reinforced concrete (RC) columns could be eliminated by enhancing the columns’ response elastically and concentrating damage to the externally installed, replaceable post-tensioned structural fuses. This paper is part of a larger numerical and experimental investigation to develop and validate design methods for a rocking aramid fiber reinforced polymer (AFRP) reinforced concrete column. The numerical study, implemented using the Extreme Loading for Structures software, consists of a total of thirteen columns. The columns were subjected to axial load followed by cyclic lateral load up to failure to examine the effectiveness of the rocking connection and overall response. The effect of key variables such as longitudinal bar ratio, structural fuse sizes and tie spacing was investigated. Ductility and energy dissipation gains of the rocking AFRP RC columns were compared to that of the conventionally reinforced steel column, and expected performance of the rocking connection was achieved.

Taper Technology in Total Hip Arthroplasty.

* The taper junction comprises a male trunnion and female bore at specific taper angles, which join together in an interference cold weld fit.* Studies have suggested that an impaction force of 4,000 N provides sufficient interference fit on modern taper designs.* Factors that may correlate with corrosion are mixed-alloy components, insufficient taper assembly force, a wet taper when assembling, lower flexural rigidity, and previous taper damage. Inconclusive factors are head length, head size, trunnion neck length, lateral offset, taper angle and design, contact area, and percent of taper contact.* A ceramic femoral head may reduce taper corrosion.* Researchers are investigating newer technologies and coatings to decrease taper corrosion.

Hot climate inhibits volcanism on Venus: Constraints from rock deformation experiments and argon isotope geochemistry

The disparate evolution of sibling planets Earth and Venus has left them markedly different. Venus’ hot (460°C) surface is dry and has a hypsometry with a very low standard deviation, whereas Earth’s average temperature is 4°C and the surface is wet and has a pronounced bimodal hypsometry. Counterintuitively, despite the hot Venusian climate, the rate of intraplate volcano formation is an order of magnitude lower than that of Earth. Here we compile and analyse rock deformation and atmospheric argon isotope data to offer an explanation for the relative contrast in volcanic flux between Earth and Venus. By collating high-temperature, high-pressure rock deformation data for basalt, we provide a failure mechanism map to assess the depth of the brittle–ductile transition (BDT). These data suggest that the Venusian BDT likely exists between 2 and 12km depth (for a range of thermal gradients), in stark contrast to the BDT for Earth, which we find to be at a depth of ∼25–27km using the same method. The implications for planetary evolution are twofold. First, downflexing and sagging will result in the sinking of high-relief structures, due to the low flexural rigidity of the predominantly ductile Venusian crust, offering an explanation for the curious coronae features on the Venusian surface. Second, magma delivery to the surface—the most efficient mechanism for which is flow along fractures (dykes; i.e., brittle deformation)—will be inhibited on Venus. Instead, we infer that magmas must stall and pond in the ductile Venusian crust. If true, a greater proportion of magmatism on Venus should result in intrusion rather than extrusion, relative to Earth. This predicted lower volcanic flux on Venus, relative to Earth, is supported by atmospheric argon isotope data: we argue here that the anomalously unradiogenic present-day atmospheric 40Ar/36Ar ratio for Venus (compared with Earth) must reflect major differences in 40Ar degassing, primarily driven by volcanism. Indeed, these argon data suggest that the volcanic flux on Venus has been three times lower than that on Earth over its 4.56billion year history. We conclude that Venus’ hot climate inhibits volcanism.

Shake-table study of plaster effects on the behavior of masonry-infilled steel frames

The effects of plaster on the behavior of single-story single-bay masonry-infilled steel frames under in-plane base accelerations have been experimentally investigated by a shake-table. Tested structures were made in a 1/3 scale, with realistic material properties and construction methods. Steel frames with high and low flexural rigidity of beams and columns were considered. Each type of frame was tested with three variants of masonry: (i) non-plastered masonry; (ii) masonry infill with conventional plaster on both sides; and (iii) masonry infill with a polyvinyl chloride (PVC) net reinforced plaster on both sides. Masonry bricks were made of lightweight cellular concrete. Each frame was firstly successively exposed to horizontal base accelerations of an artificial accelerogram, and afterwards, to horizontal base accelerations of a real earthquake. Characteristic displacements, strains and cracks in the masonry were established for each applied excitation. It has been concluded that plaster strengthens the infill and prevents damages in it, which results in more favorable behavior and increased bearing capacity of plastered masonry-infilled frames compared to non-plastered masonry-infilled frames. The load-bearing contribution of the adopted PVC net in the plaster was not noticeable for the tested specimens, probably due to relative small cross section area of fibers in the net. Behavior of masonry-infilled steel frames significantly depends on frame stiffness. Strong frames have smaller displacements than weak frames, which reduces deformations and damages of an infill.

Nanomembrane-Based, Thermal-Transport Biosensor for Living Cells.

Knowledge of materials' thermal-transport properties, conductivity and diffusivity, is crucial for several applications within areas of biology, material science and engineering. Specifically, a microsized, flexible, biologically integrated thermal transport sensor is beneficial to a plethora of applications, ranging across plants physiological ecology and thermal imaging and treatment of cancerous cells, to thermal dissipation in flexible semiconductors and thermoelectrics. Living cells pose extra challenges, due to their small volumes and irregular curvilinear shapes. Here a novel approach of simultaneously measuring thermal conductivity and diffusivity of different materials and its applicability to single cells is demonstrated. This technique is based on increasing phonon-boundary-scattering rate in nanomembranes, having extremely low flexural rigidities, to induce a considerable spectral dependence of the bandgap-emission over excitation-laser intensity. It is demonstrated that once in contact with organic or inorganic materials, the nanomembranes' emission spectrally shift based on the material's thermal diffusivity and conductivity. This NM-based technique is further applied to differentiate between different types and subtypes of cancer cells, based on their thermal-transport properties. It is anticipated that this novel technique to enable an efficient single-cell thermal targeting, allow better modeling of cellular thermal distribution and enable novel diagnostic techniques based on variations of single-cell thermal-transport properties.

Modeling of Dynamic Instability Via Segmented Cutting Coefficients and Chatter Onset Detection in High-Speed Micromilling of Ti6Al4V

Miniature components with complex shape can be created by micromilling with excellent form and finish. However, for difficult-to-machine materials, such as Ti-alloys, failure of low-flexural stiffness microtools is a big limitation. High spindle speeds (20,000–100,000 rpm) can be used to reduce the undeformed chip thickness and the cutting forces to reduce the catastrophic failure of the tool. This reduced uncut chip thicknesses, in some cases lower than the cutting edge radius, can result in intermittent chip formation which can lead to dynamic variation in cutting forces. In addition, the run-out and the misalignment effects are amplified at higher rotational speeds which can induce dynamic force variation. These dynamic force variations coupled with low-flexural rigidity of micro end mill can render the process unstable. Consequently, accurate prediction of forces and stability is essential in high-speed micromilling. Most of the previous studies reported in the literature use constant cutting coefficients in the mechanistic cutting force model which does not yield accurate results. Recent work has shown significant improvement in the prediction of cutting forces with velocity–chip load dependent coefficients but a single-function velocity–chip model fails to predict the forces accurately at very high speeds (&gt;80,000 rpm). This inaccurate force prediction affects the predicted stability boundary at those speeds. Hence, this paper presents a segmented approach, wherein a function is fit for a given range of speeds to determine the chip load dependent cutting coefficients. The segmented velocity–chip load dependent cutting coefficient improves the cutting force prediction at high speeds, which yields much accurate stability boundary. This paper employs two degrees-of-freedom (2DOF) model with forcing functions based on segmented velocity–chip load dependent cutting coefficients. Stability lobe diagram based on 2DOF model has been created for different speed ranges using Nyquist stability criterion. Chatter onset has been identified experimentally via accelerometer data and the power spectral density (PSD) analysis of the machined surface topography. Critical spatial chatter frequencies and magnitudes of PSD corresponding to onset of instability have also been determined for different conditions.

Suspended graphene variable capacitor

Electromechanical variable capacitors, or varactors, find a wide range of applications including sensing applications and the tuning of electrical circuit resonance. We demonstrate a nano-electromechanical graphene varactor, a variable capacitor wherein the capacitance is tuned by voltage controlled deflection of a dense array of suspended graphene membranes. The low flexural rigidity of graphene monolayers is exploited to achieve low actuation voltage and high tunable capacitance density in an ultra-thin structure. Large arrays comprising thousands of suspensions were fabricated to give a tunable capacitance of over 10 pF mm−2. This capacitance density suggests that graphene offers a potential solution to the challenge of reducing the size of micro-electromechanical systems (MEMS). A capacitance tuning of 55% was achieved with a 10 V actuating voltage, exceeding the 50% tuning limit of Hookean parallel plate pull-in without the use of complex mechanical schemes that occupy substrate area. Capacitor behavior was investigated experimentally, and described by a simple theoretical model. Mechanical properties of the graphene membranes were measured independently using atomic force microscopy. We present a comparison of state-of-the-art MEMS and graphene varactors. The quality factor of graphene varactors is limited by graphene sheet resistance, pull-in voltage can be improved with more aggressive scaling, while the power handling and cycling stability of graphene varactors remains unknown.

Conformal, graphene-based triboelectric nanogenerator for self-powered wearable electronics

Long-term operation is a key requirement for the widespread use of wearable devices and systems. Typical energy-storage and harvesting approaches relying on rigid materials and device structures hinder conformable integration on soft and wrinkled human skin. Here, we report triboelectric nanogenerators (TENGs) that can form directly on human skin and operate wearable devices without recharging process. TENGs with a single-electrode-based structure were fabricated with atomically thin graphene (<1nm), polydimethylsiloxane (<1.5µm) and polyethylene terephthalate (<0.9µm) as the electrode, electrification layer and substrate, respectively, for low flexural rigidity. The conformal TENGs formed on human skin generated electricity by contact with various clothes or the human body. Their triboelectric performance depended on the effective contact area enabled self-powered touch sensors for an assistive communication system by converting analogous information of human motions to digital signals. Thus, TENGs have potential applications in a wide range of future wearable electronics.

Hybrid composite wires for tensile armours in flexible risers: Manufacturing and mechanical characterisation

With the rising global demand for hydrocarbon fuels, there is a growing need for the oil and gas industry to operate in deeper offshore waters. In this context, the traditional metallic tensile armours in flexible risers pose certain limitations (e.g. weight, corrosion, fatigue damage) in demanding service environments. This paper presents a novel and proprietary hybrid composite wire as an alternative to metallic (carbon steel) wires. The hybrid composite wire consists of an over-braided (Dyneema® (Dyneema is a trademark of DSM) fibres) core, with the core consisting of hexagonally packed composite rods (pultruded carbon fibre and vinyl ester). These hybrid composite wires can provide high tensile strength and stiffness accompanied by low flexural and torsional rigidities, which can easily be tailored by varying geometrical and manufacturing parameters. This paper presents the manufacturing methods used, and the mechanical behaviour of the hybrid composite wires with various configurations.

The application of a reinforced plaster mortar for seismic strengthening of masonry structures

Abstract The effects of plaster mortar on the behaviour of 1/3 scaled, one storey, one bay masonry-infilled steel frames under horizontal in-plane static loading are experimentally investigated in this paper. Two types of steel frames are considered: one with high flexural rigidity of the beams and columns and another with low flexural rigidity of the beams and columns. Each frame was tested with three masonry variants: (i) bare masonry infill, (ii) masonry infill with pre-mixed plaster on both sides and (iii) masonry infill with pre-mixed plaster on both sides and reinforced with a polyvinyl chloride (PVC) net. All of the frames were loaded successively by a horizontal force in the beam direction until structural collapse. Afterward, the experimental results were compared to those from the presented numeric model for the nonlinear static analysis of planar structures made of concrete, steel and masonry. The model was upgraded by including the effect of plaster on the overall stiffness and strength of the masonry and verified using the experimental tests. This experimental investigation shows that plaster significantly contributes to the strength and load-bearing capacity of masonry and therefore to the strength and load-bearing capacity of masonry-infilled frames.

Deformable devices with integrated functional nanomaterials for wearable electronics.

As the market and related industry for wearable electronics dramatically expands, there are continuous and strong demands for flexible and stretchable devices to be seamlessly integrated with soft and curvilinear human skin or clothes. However, the mechanical mismatch between the rigid conventional electronics and the soft human body causes many problems. Therefore, various prospective nanomaterials that possess a much lower flexural rigidity than their bulk counterparts have rapidly established themselves as promising electronic materials replacing rigid silicon and/or compound semiconductors in next-generation wearable devices. Many hybrid structures of multiple nanomaterials have been also developed to pursue both high performance and multifunctionality. Here, we provide an overview of state-of-the-art wearable devices based on one- or two-dimensional nanomaterials (e.g., carbon nanotubes, graphene, single-crystal silicon and oxide nanomembranes, organic nanomaterials and their hybrids) in combination with zero-dimensional functional nanomaterials (e.g., metal/oxide nanoparticles and quantum dots). Starting from an introduction of materials strategies, we describe device designs and the roles of individual ones in integrated systems. Detailed application examples of wearable sensors/actuators, memories, energy devices, and displays are also presented.

A Comparative Analysis of Towels Produced from Twisted and Twistless Cotton Pile Yarns in Terms of Absorptive Capacity and Flexural Rigidity

The study compares cotton towels produced from twisted and twistless cotton pile yarn. The towels were manufactured with different weft density, different weft yarn counts, and different pile heights. The water absorptive capacity, absorbency time and flexural rigidity properties of twisted pile towels were compared with those of twistless pile towels. The test results were evaluated using statistical analysis. Effects of twisted and twistless pile yarn, pile height, weft density, and weft yarn count on absorptive capacity, absorbency time, and flexural rigidity of fabrics were examined using analysis of variance (ANOVA). The results indicate that the towels woven with twistless pile yarns have greater absorptive capacity, longer absorbency time, and lower flexural rigidity than towels woven with twisted pile yarns.

Biomechanical properties of the terrestrial mosses Pleurozium schreberi (Brid.) Mitt. and Pogonatum japonicum Sull. and Lesq. along altitudinal gradients in northern Japan

Altitudinal gradients along mountain slopes provide valuable opportunities to study variation in plant traits in response to changes in environmental conditions along such gradients. This study focused on biomechanical traits of two moss species, the more or less horizontally growing Pleurozium schreberi and the erect-growing Pogonatum japonicum, along altitudinal gradients on two mountains in Hokkaido, northern Japan. We measured stem diameter in two directions to determine the second moment of area I, used three-point bending tests with free stem ends to determine the slope of the force-deflection curve dF/dx, and used these data to calculate Young’s modulus and flexural rigidity of the stems. Both species showed much variation in all traits among replicates in the samples at each altitude. Environmental variation associated with altitude had more effect on the biomechanical traits of P. japonicum than on those of P. schreberi. Stems of P. japonicum were thicker (larger I) than those of P. schreberi and had a larger Young’s modulus and flexural rigidity. Stems tended to become thinner (lower second moment of area) and less rigid (lower flexural rigidity) at increasing altitude in both species.