Applied Shear Force Research Articles

Occurrence of Potentially Pathogenic Bacteria in Epilithic Biofilm Forming Bacteria isolated from Porter Brook River-stones, Sheffield, UK.

Biofilms in aquatic ecosystems develop on wet benthic surfaces and are primarily comprised of various allochthonous microorganisms, including bacteria embedded within a self-produced matrix of extracellular polymeric substances (EPS). In such environment, where there is a continuous flow of water, attachment of microbes to surfaces prevents cells being washed out of a suitable habitat with the added benefits of the water flow and the surface itself providing nutrients for growth of attached cells. When watercourses are contaminated with pathogenic bacteria, these can become incorporated into biofilms. This study aimed to isolate and identify the bacterial species within biofilms retrieved from river-stones found in the Porter Brook, Sheffield based on morphological, biochemical characteristics and molecular characteristics, such as 16S rDNA sequence phylogeny analysis. Twenty-two bacterial species were identified. Among these were 10 gram-negative pathogenic bacteria, establishing that potential human pathogens were present within the biofilms. Klebsiella pneumoniae MBB9 isolate showed the greatest ability to form a biofilm using a microtiter plate-based crystal violet assay. Biofilm by K. pneumoniae MBB9 formed rapidly (within 6 h) under static conditions at 37 °C and then increased up to 24 h of incubation before decreasing with further incubation (48 h), whereas the applied shear forces (horizontal orbital shaker; diameter of 25 mm at 150 rpm) had no effect on K. pneumoniae MBB9 biofilm formation.

2D DNA Microstructures: Generation of 2D DNA Microstructures via Topographic Control and Shearing (Small 34/2020)

In article number 2002449, Dong Ki Yoon and co-workers fabricate 2D DNA microstructures by applying shear force to the DNA solution on the microchannels. The “U”-like textures of DNA are clearly observed when the mechanical shearing is applied on the aqueous DNA sample under topographic confinement, in which the shearing direction is perpendicular to the grooves.

Closed form solution for the energy release rate and mode partitioning of the single cantilever beam sandwich debond from an elastic foundation analysis

The goal of this paper is to derive closed form expressions for the energy release rate and mode partitioning offace/core debonds for the Single Cantilever Beam Sandwich Composite testing configuration, which is loaded with an applied shear force and/or bending moment. This is achieved by an elastic foundation approach, in which a finite length sandwich beam is treated as having a free “debonded” section and a “joined” section where a series of springs exists between the face and the substrate (core and bottom face). The elastic foundation analysis is done for a general asymmetric sandwich construction. A J-integral approach is subsequently used to derive a closed form expression for the energy release rate. It is also shown that the energy release rate is very close to the differential energy stored in the springs at the beginning of the elastic foundation, i.e. the energy released by the “broken” differential spring element as the debond propagates. In the context of this elastic foundation model, a mode partitioning measure is defined based on the transverse and axial displacements at the beginning of the elastic foundation. Since the normal springs account for the transverse compressibility of the core but not for the shear, a correction for the shear of the substrate is included by deriving the expression for the corresponding shear angle and accounting for the additional horizontal “tip” displacement. The results are compared with finite element results for a range of core materials and show very good agreement.

Towards improved reliability of RF-MEMS: mechanical aspects and experimental testing of a micro-switch design with embedded active self-recovery mechanism to counteract stiction

In this work, the operation of an active self-recovery mechanism embedded within microelectromechanical systems (MEMS) switches for Radio Frequency (RF) passives (i.e. RF-MEMS) is reported and discussed. The mechanism is able to counteract stiction induced by charge accumulation and micro-welding formation. It is based on the thermoelectric effect, allowing restoring the MEMS switch back to normal operation after failure. The goal is achieved by means of two factors, namely, the entrapped charges dispersion speed-up within the insulating layer between the electrodes, and the application of shear forces on the welding joints, both induced by the heat. Preliminary experimental results, collected by a few fabricated RF-MEMS switch samples, confirm the viability of the proposed approach. Moreover, the coupled thermos-electro-mechanical multi-physical behaviour of the discussed RF-MEMS switch is also analysed by means of Finite Element Method simulations. In particular, the results of experiments carried out with a dynamic 3D profiling setup show that when driving a current through a micro-heater embedded under the MEMS intentionally brought to stiction due to charge accumulation, the release of the switching membrane and the restoration of its operability is speeded-up. In addition, the reported characterisation includes also the pull-in/pull-out characteristic and the RF measurement of the S-parameters (scattering parameters).

Rheology of Water Flows Confined between Multilayer Graphene Walls.

Water confined by hydrophilic materials shows unique transport properties compared to bulk water, thereby offering new opportunities for the development of nanofluidic devices. Recent experimental and numerical studies showed that nanoconfined water undergoes liquid- to solid-phase-like transitions depending on the degree of confinement. In the case of water confined by graphene layers, the van der Waals forces are known to deform the graphene layers, whose bending leads to further nonuniform confinement effects. Despite the extensive studies of nanoconfined water under equilibrium conditions, the interplay between the confinement and rheological water properties, such as viscosity, slip length, and normal stress differences under shear flow conditions, is poorly understood. The current investigation uses a validated all-atom nonequilibrium molecular dynamics model to simultaneously analyze the continuum transport and atomistic structural properties of water in a slit between two moving graphene walls under Couette flow conditions. A range of different slit widths and velocity strain rates are considered. It is shown that under subnanometer confinement, water loses the rotational symmetry of a Newtonian fluid. Under such conditions, water transforms into ice, where the atomistic structure is completely insensitive to the applied shear force and behaves like a frozen slab sliding between the graphene walls. This leads to the shear viscosity increase, although it is not as dramatic as the normal force increase that contributes to the increased friction force reported in previous experimental studies. On the other end of the spectrum, for flows at large velocity strain rates in moderate to large slits between the graphene walls, water is in the liquid state and reveals shear thinning behavior. In this case, water exhibits a constant slip length on the wall, which is typical of liquids in the vicinity of hydrophobic surfaces.

Extending the Mossakovskii method to contacts supporting a moment

In this article, we extend the Mossakovskii approach to half-plane contacts supporting a moment. Since the method relies on approximating the punch geometry by a series of flat punches, we choose the load path in (P, M)-space that fixes the body tilt, which allows us to reduce the standard Cauchy singular integral formulation to a non-symmetric Abel integral equation. We use the formulation to derive simple expressions for the applied normal force and necessary applied moment as functions of the contact extent and indenter tilt, while also deriving the coefficients of the square-root terms in the contact pressure expansion at the edges of the contact. These results are analysed in detail for two specific examples: the tilted wedge and the tilted flat-and-rounded punch. We conclude by briefly discussing the equivalent tangential problem when an applied shear force and differential bulk tensions are present.

Experimental study of the steel/CFRP interaction in shear-strengthened RC beams incorporating macro-synthetic fibers

This paper presents an investigation of the performance of RC beams incorporating macro-synthetic fibers and rehabilitated using Externally Bonded Fiber Reinforced Polymer (EB-FRP) strips. A series of tests were conducted to investigate the EB-FRP contribution to the shear strength recovery of pre-damaged shear-deficient beams. The investigation included studying the effect of macro-synthetic fiber reinforcement on the contribution of EB-FRP to the shear strength of retrofitted beams, as well as the interaction between EB-FRP and steel stirrups in the presence of macro-synthetic fiber reinforcement in the concrete. The key parameters of the investigation included: (a) beam condition (damaged beams and virgin beams), (b) beam shear reinforcement (stirrups and no stirrups), and (c) macro-synthetic fiber dosage (0.5%, 0.75%, and 1.0%). The test results showed that the retrofitting of severely shear-damaged RC beams using EB-FRP significantly enhanced the original shear capacity of the beams with strength gains varying between 50% and 111% depending on the amount of macro-synthetic fibers and/or conventional shear reinforcement present in the specimens. The test results have also provided evidence for the existence of interaction between the steel stirrups, the macro-synthetic fibers and the EB-FRP strips in carrying part of the applied shear force in the retrofitted beams. Such interaction is such that with use of EB-FRP, the conventional shear reinforcement and/or macro-synthetic fibers have lesser contribution to the total shear force in the retrofitted beams. However, the presence of such additional shear reinforcement leads to enhanced crack control thereby delaying the premature debonding of EB-FRP strips and increasing the deflection capacity of the retrofitted beams.

Study on pore fabric, dilatancy, dissipation function and yield function for sand

The mechanical behavior of sand is affected by the anisotropic fabric. Integated with the micromechanics theory, and linked with void fabric tensor, the relations among macroscopic volumetric strain, shear strain and void fabric are established, and it is further shown that dilatancy and anisotropy under applied shear force of sand are necessarily induced. By means of thermomechanics theory, the inclined elliptical yield function in dissipation space is built, and considering the effects of anisotropic fabric, there exists three important lines, just as the normal consolidation line, phase transformation line and peak value line, and corresponding with three characteristic lines passing through the origin in true stress space which relatively truly reflect the mechanical characteristics for sand, especially dense sand.

Formulation of Petrolatum/Clay Nanocomposite Coating and Characterization of its Corrosion Resistance Properties

Montmorillonite organoclay, in different amounts (between 1 to 5 wt %), was incorporated into the petrolatum using mechanical stirring and sonication process. Anti-corrosive properties of the compounded nanocomposites were investigated using salt spray and electrochemical impedance spectroscopy (EIS) methods. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy analysis (EDX) showed that the interlayer spacing of clays was increased after addition of petrolatum resin along with applying shear force and ultrasounication. Electrochemical analyses showed improvement in the barrier and anti-corrosive characteristics of formulated nanocomposite coatings. The best performance of formulated coatings was achieved with coating containing 1 wt % clay concentration.

Shear-sensitive adhesion enables size-independent adhesive performance in stick insects.

The ability to climb with adhesive pads conveys significant advantages and is widespread in the animal kingdom. The physics of adhesion predict that attachment is more challenging for large animals, whereas detachment is harder for small animals, due to the difference in surface-to-volume ratios. Here, we use stick insects to show that this problem is solved at both ends of the scale by linking adhesion to the applied shear force. Adhesive forces of individual insect pads, measured with perpendicular pull-offs, increased approximately in proportion to a linear pad dimension across instars. In sharp contrast, whole-body force measurements suggested area scaling of adhesion. This discrepancy is explained by the presence of shear forces during whole-body measurements, as confirmed in experiments with pads sheared prior to detachment. When we applied shear forces proportional to either pad area or body weight, pad adhesion also scaled approximately with area or mass, respectively, providing a mechanism that can compensate for the size-related loss of adhesive performance predicted by isometry. We demonstrate that the adhesion-enhancing effect of shear forces is linked to pad sliding, which increased the maximum adhesive force per area sustainable by the pads. As shear forces in natural conditions are expected to scale with mass, sliding is more frequent and extensive in large animals, thus ensuring that large animals can attach safely, while small animals can still detach their pads effortlessly. Our results therefore help to explain how nature's climbers maintain a dynamic attachment performance across seven orders of magnitude in body weight.

Covalent Bonding and Atomic-Level Plasticity Increase Adhesion in Silicon-Diamond Nanocontacts.

Nanoindentation and sliding experiments using single-crystal silicon atomic force microscope probes in contact with diamond substrates in vacuum were carried out in situ with a transmission electron microscope (TEM). After sliding, the experimentally measured works of adhesion were significantly larger than values estimated for pure van der Waals (vdW) interactions. Furthermore, the works of adhesion increased with both the normal stress and speed during the sliding, indicating that applied stress played a central role in the reactivity of the interface. Complementary molecular dynamics (MD) simulations were used to lend insight into the atomic-level processes that occur during these experiments. Simulations using crystalline silicon tips with varying degrees of roughness and diamond substrates with different amounts of hydrogen termination demonstrated two relevant phenomena. First, covalent bonds formed across the interface, where the number of bonds formed was affected by the hydrogen termination of the substrate, the tip roughness, the applied stress, and the stochastic nature of bond formation. Second, for initially rough tips, the sliding motion and the associated application of shear stress produced an increase in irreversible atomic-scale plasticity that tended to smoothen the tips' surfaces, which resulted in a concomitant increase in adhesion. In contrast, for initially smooth tips, sliding roughened some of these tips. In the limit of low applied stress, the experimentally determined works of adhesion match the intrinsic (van der Waals) work of adhesion for an atomically smooth silicon-diamond interface obtained from MD simulations. The results provide mechanistic interpretations of sliding-induced changes and interfacial adhesion and may help inform applications involving adhesive interfaces that are subject to applied shear forces and displacements.

Impact of adhesive system generation and light curing units on orthodontic bonding: In vitro study

We aimed to compare adhesive performance of fourth, fifth and seventh generation adhesive systems (GASs) and the effect of two different light curing units on shear bond strength (SBS). One hundred and twenty extracted human upper premolars were divided in four groups. Bonds were assessed as following: group 1 using 4th GAS, group 2 using 5th GAS, group 3 and 4 using 7th GAS with two different light curing units (1500 and 800mw/cm2). Adhesive remnant index (ARI) scores were counted. Group 1 and 2 showed similar SBSs (P=0.7) which were significantly higher than group 3 (P=0.0002). Group 4 exhibited significantly the weakest SBS with mean=2.15±0.25. Applying shear forces less than 15MPa on group 3 bonds led to the release of almost all of the of brackets. Whereas, applying the same forces on group 2 bonds leads to the release of 66.7% of brackets. Notably, only 40% of brackets in group 1 were debonded. Group 4 brackets were totally debonded when applying shear forces less than 10MPa. While ARI=0 was the most frequent in group 1, ARI=3 was the most frequent in group 3. Fourth and fifth GASs showed similar SBS higher than seventh GAS. Fourth GAS bonds were able to resist longer against traction forces than those set up by fifth generation. Seventh GAS bonds offered the least efficient resistance. ARI=0 was the highest in group 1. However, Group 4 showed the highest ARI=1 and ARI=2 revealing cohesive failure. We also found that the adhesive power is proportional to the power of the lamp used. In fact, we concluded that 1500 mw/cm2 units light curing during 30seconds generated an ideal energy to enhance orthodontic bracket adhesion.

The Enhancement of Wear Properties of Compo-Cast A356 Composites Reinforced with SiC nano Particulates

Metal matrix composites producer of a new generation of metal materials in which ceramic reinforcement has been added to the metal field, which has enhanced various properties such as special strength, wear resistance, corrosion resistance and elastic modulus. Aluminum composites reinforced with ceramic particles due to excellent mechanical, physical and tribological properties are among composites with extensive application. Among these, Al–SiC composites have been considered important in certain industries such as aerospace and automotive for their desirable properties such as strength, wear resistance, toughness, and suitable hardness. In this study, the effect of casting methods on the wearing properties of Al–SiC composites has been investigated. Also, the effect of applied shear force on the hardness and porosity of these composites has been thoroughly investigated. According to the results of the wear test, by increasing the applied current rate, wear resistance in the samples improved, the reason of which is the direct dependence of the wear strength of the samples on hardness, and the porosity in the composites.

Transient Bending Vibration of a Piezoelectric Semiconductor Nanofiber Under a Suddenly Applied Shear Force

We study transient bending vibration of a ZnO piezoelectric semiconductor nanofiber fixed at one end with a suddenly applied shear force at the other end. A one-dimensional model based on the phenomenological theory of piezoelectric semiconductors consisting of the equations of piezoelectricity coupled to the continuity equation of electrons is used. An approximate theoretical analysis is performed, accompanied by a finite element analysis using COMSOL. The evolutions of deflection, electric potential and electron distribution are calculated and examined. It is found that when the fiber reaches its largest deflection, the distributions of the electromechanical fields are qualitatively similar to those in the case of static loading under the same shear force, but the amplitudes of the fields are about twice as large roughly.

3D‐Printed Flexible Tactile Sensor Mimicking the Texture and Sensitivity of Human Skin

AbstractThe development of 3D printing technology toward multifunction devices may affect various fields from intelligent systems and wearable electronic devices to energy storage and flexible light‐emitting devices. A new type of piezoresistive sensor is designed by mimicking the texture and sensitivity of human skin. It is fabricated by 3D printing with a new kind of ink that is composed of interconnected polydimethylsiloxane microspheres (MPs) with carbon nanotubes distributed on their surfaces. This structure gives an electronic skin fabricated from these sensors modulus similar to that of human skin; furthermore, it elastically deforms under external forces. The response of the electronic skin to shear forces is evaluated by simulating the touch behavior of human skin, and it is found that the tactile sensors are sensitive to applied shear forces. They demonstrate sensitivity as low as 2.08 kPa−1 at a pressure of just 0.12 kPa, with short response time (50 ms), high durability (over 8000 cycles), and flexibility.

Strength assessment of Al-Humic and Al-Kaolin aggregates by intrusive and non-intrusive methods

Resistance to breakage is a critical property of aggregates generated in water and wastewater treatment processes. After flocculation, aggregates should ideally keep their physical characteristics (i.e. size and morphology), to result in the best performance possible by individual separation processes. The integrity of aggregates after flocculation depends upon their capacity to resist shear forces while transported through canals, passages, apertures, orifices and other hydraulic units. In this study, the strength of Al-Humic and Al-Kaolin aggregates was investigated using two macroscopic measurement techniques, based on both intrusive and non-intrusive methods, using image analysis and light scattering based equipment. Each technique generates different information which was used for obtaining three floc strength indicators, namely, strength factor (SF), local stress from the hydrodynamic disturbance (σ) and the force coefficient (γ) for two different study waters. The results showed an increasing trend for the SF of both Al-Humic and Al-Kaolin aggregates, ranging from 29.7% to 78.6% and from 33.3% to 85.2%, respectively, in response to the increase of applied shear forces during flocculation (from 20 to 120 s−1). This indicates that aggregates formed at higher shear rates are more resistant to breakage than those formed at lower rates. In these conditions, σ values were observed to range from 0.07 to 0.44 N/m2 and from 0.08 to 0.47 N/m2 for Al-Humic and Al-Kaolin, respectively. Additionally, it was found that for all studied conditions, the resistance of aggregates to shear forces was nearly the same for Al-Humic and Al-Kaolin aggregates, formed from destabilized particles using sweep coagulation. These results suggest that aggregate strength may be mainly controlled by the coagulant, emphasizing the importance of the coagulant selection in water treatment. In addition, the use of both intrusive and non-intrusive techniques helped to confirm and expand previous experiments recently reported in literature.

Load-bearing capacity and characteristic forms of destruction of furniture joints made with rastex 15 and P-10 clamex fasteners

Load-bearing capacity and characteristic forms of destruction of furniture joints made with rastex 15 and P-10 clamex fasteners. The study tested the relationship between the load and angular deflection in furniture joints. The tests were carried out for two types of fasteners and five types of materials: chipboard, MDF, hardwood plywood, glued pine boards and glued oak boards. The furniture joint samples contained two fasteners preloaded only with a bending moment (without application of shear forces). The results were converted per single fastener specifying: its maximal load capacity, 50 mrad (2.9°) limit deflection and rigidity coefficient. It was found that rigidity is a better structural property of the tested joint types than their load capacity. As far as rigidity is concerned, the most durable is the combination of oak glued board – rastex 15 fastener (13.2 Nm bending moment per fastener), while the least durable combination is chipboard – clamex P-10 fastener (4.8 Nm bending moment per fastener). Photographic documentation of damaged furniture joint samples was prepared and analysed. In case of chipboard and MDF combinations (where the load is determined by the combined material), the combined boards suffer a disastrous damage, while in combinations of plywood boards and pine or oak glued boards, (where the capacity is determined by the fastener), both clamex P10 and rastex 15 fasteners are damaged.

Comparative Study of Current Methods of Analysis of R.C. Structural Frames Based on Pushover Analysis

There has been a growth in extensive research aimed at examining the effects of seismic events on the performance of a structure. Buildings have a tendency to exhibit inelastic deformation in during seismic activities and post-elastic behavior. Hence, better insights of the performance of structure can be obtained by examining its post-elastic behavior. Non-linear static analysis (also known as Pushover Analysis) is an improved and effective modern way of examining structural performance in the event of potential seismic impact. Such an approach involves horizontally pushing a structure using a predetermined loading pattern which constantly increases over time thereby making it possible to determine the collapse conditions, associated lateral displacement and total applied shear force. It offers a sound Perception of Structural Performance against earthquake as well as damages suffered. Thus, pushover analysis makes it feasible to ascertain the responsive behavior of buildings in non-linear zones which is not catered for by conventional elastic designs.

Tunable Membrane Potential Reconstituted in Giant Vesicles Promotes Permeation of Cationic Peptides at Nanomolar Concentrations.

We investigate the influence of membrane potential on the permeation of cationic peptides. Therefore, we employ a microfluidic chip capable of capturing giant unilamellar vesicles (GUVs) in physical traps and fast exchange of chemical compounds. Control experiments with calcein proved that the vesicle membranes' integrity is not affected by the physical traps and applied shear forces. Combined with fluorescence correlation spectroscopy, permeation of fluorescently labeled peptides across vesicle membranes can be measured down to the nanomolar level. With the addition of a lipophilic ruthenium(II) complex Ru(C17)22+, GUVs consisting of mixed acyl phospholipids are prepared with a negative membrane potential, resembling the membrane asymmetry in cells. The membrane potential serves as a driving force for the permeation of cationic cell-penetrating peptides (CPPs) nonaarginine (Arg9) and the human immunodeficiency virus trans-activator of transcription (TAT) peptide already at nanomolar doses. Hyperpolarization of the membrane by photo-oxidation of Ru(C17)22+ enhances permeation significantly from 55 to 78% for Arg9. This specific enhancement for Arg9 (cf. TAT) is ascribed to the higher affinity of the arginines to the phosphoserine head groups. On the other hand, permeation is decreased by introducing an additional negative charge in close proximity to the N-terminal arginine residue when changing the fluorophore. In short, with the capability to reconstitute membrane potential as well as shear stress, our system is a suitable platform for modeling the membrane permeability of pharmaceutics candidates. The results also highlight the membrane potential as a major cause of discrepancies between vesicular and cellular studies on CPP permeation.

Emerin induces nuclear breakage in Xenopus extract and early embryos.

Emerin is an inner nuclear membrane protein often mutated in Emery–Dreifuss muscular dystrophy. Because emerin has diverse roles in nuclear mechanics, cytoskeletal organization, and gene expression, it has been difficult to elucidate its contribution to nuclear structure and disease pathology. In this study, we investigated emerin’s impact on nuclei assembled in Xenopus laevis egg extract, a simplified biochemical system that lacks potentially confounding cellular factors and activities. Notably, these extracts are transcriptionally inert and lack endogenous emerin and filamentous actin. Strikingly, emerin caused rupture of egg extract nuclei, dependent on the application of shear force. In egg extract, emerin localized to nonnuclear cytoplasmic membranes, and nuclear rupture was rescued by targeting emerin to the nucleus, disrupting its membrane association, or assembling nuclei with lamin A. Furthermore, emerin induced breakage of nuclei in early-stage X. laevis embryo extracts, and embryos microinjected with emerin were inviable, with ruptured nuclei. We propose that cytoplasmic membrane localization of emerin leads to rupture of nuclei that are more sensitive to mechanical perturbation, findings that may be relevant to early development and certain laminopathies.