Significant Deflection Research Articles

Surface textures suppress viscoelastic braking on soft substrates

A gravity-driven droplet will rapidly flow down an inclined substrate, resisted only by stresses inside the liquid. If the substrate is compliant, with an elastic modulus G < 100 kPa, the droplet will markedly slow as a consequence of viscoelastic braking. This phenomenon arises due to deformations of the solid at the moving contact line, enhancing dissipation in the solid phase. Here, we pattern compliant surfaces with textures and probe their interaction with droplets. We show that the superhydrophobic Cassie state, where a droplet is supported atop air-immersed textures, is preserved on soft textured substrates. Confocal microscopy reveals that every texture in contact with the liquid is deformed by capillary stresses. This deformation is coupled to liquid pinning induced by the orientation of contact lines atop soft textures. Thus, compared to flat substrates, greater forcing is required for the onset of drop motion when the soft solid is textured. Surprisingly, droplet velocities down inclined soft or hard textured substrates are indistinguishable; the textures thus suppress viscoelastic braking despite substantial fluid-solid contact. High-speed microscopy shows that contact line velocities atop the pillars vastly exceed those associated with viscoelastic braking. This velocity regime involves less deformation, thus less dissipation, in the solid phase. Such rapid motions are only possible because the textures introduce a new scale and contact-line geometry. The contact-line orientation atop soft pillars induces significant deflections of the pillars on the receding edge of the droplet; calculations confirm that this does not slow down the droplet.

Experimental new ultra-high-speed all-optical coherent streak-camera

We have experimentally studied for the first time a new operation principle of the all-optical coherent streak-camera (Rabi deflector). In the experiment, we observed an effect of significant dynamical angular deflection of a pulse of semiconductor laser during the resonant pumping of the D2 line (780.24 nm) of 87Rb vapor in the range of diffraction angles ϕ = ± 5.45°. We propose to use the Rabi deflector as an energy efficient shaper of classical and single-photon wave packets. We analyze a possibility of the Rabi deflector operation in quantum systems with feedback.

Continuous texture evolution during staged solid solution of Al‐Cu‐Mg and the influence on fatigue resistance

AbstractContinuous texture evolution of the Al‐Cu‐Mg alloy during the staged solid solution and corresponding influence on fatigue property has been studied by means of X‐ray diffraction, electron back scattered diffraction and scanning electron microscopy. The characteristic texture transition rate XCGB and orientation streamline approach was introduced to further investigate the behind mechanisms. The results show that the two‐step solid solution could significantly enhance the XCGB, thereby contributes to reduce the fatigue crack growth rate of Al‐Cu‐Mg T3 sheet during stage Π. The near Cube texture with high Schmid factor (SF) and low Taylor factor (TF) tends to induce significant crack deflection, crack closure and strengthened planar slip. The potential 60°&lt;1, −1, 1&gt; twin relation and mutual transformation existed between Goss and P texture would further reduce the fine random orientation grain and inter‐granular fatigue crack extension. Such above effects would be responsible for the excellent correspondence between XCGB and fatigue resistance.

Long-Term Deflection of Prestressed Concrete Bridge Considering Nonuniform Shrinkage and Crack Propagation by Equivalent Load Approach

Long-span prestressed concrete (PSC) bridges often suffer excessive deflection during their service lives. The nonuniform shrinkage strains of concrete caused by uneven moisture distributions can induce significant additional deflections, when combined with the creep and cracking of the concrete. Current design practices usually overlook these factors, and the few proposed approaches to consider them are complex and computationally expensive. This study proposes a simplified approach for considering the effect of nonuniform shrinkage by using the equivalent load concept in combination with a nonlinear analysis of the creep and cracking using three-dimensional finite element models. The long-term deflections of short-, medium-, and long-span PSC bridges are calculated under the combined effects of creep, shrinkage, and cracking. The results show that the nonuniform shrinkage effect is significant in medium- to long-span bridges, and that the cracking of the concrete reduces the stiffness, thereby increasing the long-term deflection of the bridges (more severely so in combination with creep and shrinkage). The predicted long-term deflections reasonably agree with the measured data. Thus, the equivalent load approach is effective for calculating long-term deflections considering nonuniform shrinkage strains, without the complicated and expensive coupling of moisture transport and structural analyses.

Strength evaluation of the relocatable building frame made of the polymer composite material

The article reviews the application of composite materials in the construction of primary bearing rods of relocatable buildings. After loss of stability a rod made of composite materials continues to function with significant deflections, so it is possible to use such a property to increase the calculation value of buckling critical load. The obtained analytical expression allows us to calculate the collapsing force depending on the length of rods, form of section, stiffness characteristics of the material as exemplified by calculation of a multilayer rod made of composite materials.

Identifying changes in the milking rubber of milking machines during testing and under industrial conditions

Milking rubber is the only part of the milking equipment that comes into direct contact with the cow’s teats. The task is to establish the high-quality technical and technological characteristics of the rubber liners for milking machines. It has been established that milking rubber after 600‒650 hours of operation acquires significant deflection in the range of 5.5±0.03–3.7±0.04 mm while a teat cup deformation varies within 1.3±0.02–3.5±0.05 mm. A positive correlation dependence of the milking rubber elasticity on the deformation of its teat cup (r=+0.948) has been found. The method of passing the electric discharge was used to assess the readiness of milking rubber for use, whereby a variation coefficient of υ˂10 % was determined for the milking rubber DD 00.041A AO «Bratslav», which makes it possible to estimate the product quality. It was found that the change in the mass and volume of milking rubber over 72 hours of its treatment with the liquid SZHR-3 at t=150 °C exceeds the indicators obtained in contact with the liquid Skydrol LD-4 by more than 2.5 times. A positive correlation dependence of the milking rubber mass on its volume (r=+0.965) has been established. It was found that at a rubber tension in the range of 0 to 90 N the duration of the deformation loss experienced by the milking rubber shell was not long; it is 0.05‒0.06 s. With an increase in the service life of milking rubber to 4 months, there is a decrease in its tension, from 56‒60 N to 43‒45 N, which adversely affects the maximum speed of milk yield – it decreases by 1.5 times. A positive correlation dependence of the milking rubber service life on the level of its bacterial insemination (r=+0.960) has been established

Steady Motion of a Slack Belt Drive: Dynamics of a Beam in Frictional Contact With Rotating Pulleys

Abstract We seek the steady-state motion of a slack two-pulley belt drive with the belt modeled as an elastic, shear-deformable rod. Dynamic effects and gravity induce significant transverse deflections due to the low pre-tension. In analogy to the belt-creep theory, it is assumed that each contact region between the belt and one of the pulleys consists of a single sticking and a single sliding zone. Based on the governing equations of the rod theory, we for the first time derive the corresponding boundary value problem and integrate it numerically. Furthermore, a novel mixed Eulerian–Lagrangian finite element scheme is developed that iteratively seeks the steady-state solution. Finite element solutions are validated against semi-analytic results obtained by numerical integration of the boundary value problem. Parameter studies are conducted to examine solution dependence on the stiffness coefficients and the belt pre-tension.

Insights into flashback-to-flameholding transition of hydrogen-rich stratified swirl flames

In this study, we investigate the flame stabilization behavior in hydrogen-enriched stratified swirl flames after the flame flashes back into an annular mixing tube with an axial swirler of swirl number 0.9. Two different modes of flame stabilization, namely intermediate stabilization and flameholding, are identified. For 80% or higher hydrogen enrichment of the fuel, the flashback is found to result in flameholding. Acetone-PLIF measurements are used to assess the equivalence ratio distribution in the mixing tube. It is shown that the flow inside the mixing tube has intermittent presence of fuel-rich pockets. Furthermore, high speed laser diagnostic and simultaneous chemiluminescence imaging was carried out to understand the transition of flame propagation from the center-body boundary layer to the outer wall boundary layer. With the help of time-resolved images and simultaneous velocity fields, four different stages of flashback-to-flameholding transition were identified. It was noted that the bright flame kernels formed due to the flame's interaction with fuel-rich pockets, impose significant deflection on the approach flow in the vicinity of the outer wall boundary layer. Acute-tipped narrow flame structures were found to anchor the flame on the outer wall. These flame structures were found to accelerate upstream upon reaching the fuel-rich regions in the outer wall boundary layer.

On the fatigue crack growth behavior of Ti–10V–2Fe–3Al in gaseous hydrogen

The fatigue crack growth behavior of Ti–10V–2Fe–3Al in gaseous hydrogen (H2) was assessed through comparative experiments conducted in laboratory air and 8.3 MPa H2. The measured fatigue crack growth rate (da/dN) versus applied stress intensity factor range (ΔK) relationships and observed fracture morphologies for laboratory air and H2 were comparable up to ΔK ≈ 6.9 MPa√m, when tested at a load ratio of 0.1 and frequency of 10 Hz. At higher ΔK values, significant crack deflection and subsequent catastrophic failure occurred in the specimen tested in H2. This degradation was not observed in a specimen pre-exposed to 8.3 MPa H2 for 96 h and then immediately tested in laboratory air. X-ray diffraction of the failed H2-tested specimen revealed that the material remnants were predominantly composed of TiH2, suggesting that hydride formation was the catalyst for catastrophic failure in H2. The mechanistic implications of these results and their impact on current material compatibility assessments for Ti alloys in hydrogen service are then discussed.

Enhanced Kinetic Impactor for Deflecting Large Potentially Hazardous Asteroids via Maneuvering Space Rocks

Asteroid impacts pose a major threat to all life on Earth. The age of the dinosaurs was abruptly ended by a 10-km-diameter asteroid. Currently, a nuclear device is the only means of deflecting large Potentially Hazardous Asteroids (PHAs) away from an Earth-impacting trajectory. The Enhanced Kinetic Impactor (EKI) concept is proposed to deflect large PHAs via maneuvering space rocks. First, an unmanned spacecraft is launched to rendezvous with an intermediate Near-Earth Asteroid (NEA). Then, more than one hundred tons of rocks are collected from the NEA as the EKI. The NEA can also be captured as the EKI if the NEA is very small. Finally, the EKI is maneuvered to impact the PHA at a high speed, resulting in a significant deflection of the PHA. For example, to deflect Apophis, as much as 200 t of rocks could be collected from a NEA as the EKI based on existing engineering capabilities. The EKI can produce a velocity increment (∆v) of 39.81 mm/s in Apophis, thereby increasing the minimum geocentric distance during the close encounter in 2029 by 1,866.93 km. This mission can be completed in 3.96 years with a propellant cost of 2.98 t. Compared with a classic kinetic impactor, the deflection distance can be increased one order of magnitude. The EKI concept breaks through the limitation of the ground-based launch capability, which can significantly increase the mass of the impactor. We anticipate that our research will be a starting point for efficient planetary defense against large PHAs.

Fast Nondestructive Technique for Analyzing Deflection of Membranes Located on the Substrate

We describe a nondestructive technique for automated analysis of deflection of substrate-mounted membrane structures, which are a key element of devices based on microelectromechanical systems (MEMS devices). The technique includes analysis of substrates with an optical profiler operating in a specialized mode and mathematical processing of measurement results. The technique allows determining the magnitude and sign of deflection of membrane structures for each measurement area. The procedure results in grading the value of deflection and detecting the following types of the state of membrane structures, which are important for assessing the yield and reliability of MEMS devices based on these structures: separation or rupture of the structure, its significant deflection, its slight deflection, and lack of a deflection. All results are displayed in map format on the surface of a substrate with membrane structures with the ability to access more detailed data. The developed technique makes it possible to localize regions with a maximum, predetermined, and low yield of suitable crystals of MEMS devices, as well as flawed regions over the entire substrate surface. The use of the technique significantly increases the accuracy and reduces the measurement time for estimating the yield of suitable membrane structures, and also makes it possible to adjust the process route so as to increase the yield of suitable crystals of MEMS devices.

Effect of geocomposite reinforcement on the performance of thin asphalt pavements: Accelerated pavement testing and laboratory analysis

The objective of this study is to assess the effect of geocomposite reinforcement on fatigue cracking, reflective cracking and permanent deformation accumulation of thin asphalt pavements. For this purpose, a full-scale trial section was constructed with different interfaces: unreinforced (reference) and reinforced with three types of geocomposites, formed by the combination of a bituminous membrane with a fabric or grid. The experimental program included accelerated pavement testing (APT) carried out by means of Fast Falling Weight Deflectometer (FastFWD) and laboratory tests (three point bending tests) on samples taken from the trial section. After APT, significant permanent deflections were observed, likely due to the plastic yielding of the unbound layers. Nevertheless, all the geocomposites improved the permanent deformation resistance as compared to the unreinforced pavement by reducing the vertical strain at the top of the subgrade. Moreover, the geocomposites increased the energy necessary for the crack propagation by three to eight times with respect to the unreinforced pavement. Overall, these findings indicate that the use of geocomposites can extend the service life of thin asphalt pavements in terms of both cracking and permanent deformation accumulation.

The Effects of Multipropped Deep Excavation‐Induced Ground Movements on Adjacent High‐Rise Building Founded on Piled Raft in Sand

In this paper, a three‐dimensional numerical parametric study was conducted to predict the deformation mechanism of a 20‐storey building sitting on a (4 × 4) piled raft to an adjacent 25 m deep basement excavation. The influences of different excavation depths were investigated. An advanced hypoplastic sand model (which is capable of taking small‐strain stiffness into account) was adopted to capture soil behaviour. The computed results revealed that excavation adjacent to a building resting on the piled raft caused significant settlement, differential settlement, lateral deflection, and interstorey drift in the building. With settlement due to working load (i.e., 4.8dp%), the total settlements of the building (7.8dp%) exceed the maximum allowable foundation settlement (i.e., 50 mm). In addition, substantial bending moment, shear forces, and changes in axial load distribution along pile length were induced. The findings from this study revealed that the building and pile responses are significantly influenced by the excavation depth.

Comparison of Point and Snow Load Deflections in Design and Analysis of Tensile Membrane Structures

Tensile membrane structures are often used as protective structures in order to provide cover from snow, rain, and direct sunlight. They are widely popular because of their advanced structural and architectural properties. Currently, their application is common at sport stadia and public spaces. There are several types of loads acting on tensile membrane structures, most importantly prestress, snow load, and wind load. However, concentrated loads also act on these structures, but they are frequently neglected during the structural analysis. There is yet no European standard on designing tensile membrane structures that would give guidance on structural analysis and incorporation of point load actions in the analysis. In addition, there is little scientific knowledge on how point loads affect tensile membrane structures. This research aims at revealing whether point loads can produce significant membrane deflections and in such way cause damage to the structure or to the objects underneath the membrane. In order to evaluate their importance, point load deflections are compared to deflections induced by snow load. This was done on a large number of numerical models differing in several parameters. Models represent typical geometries of hypar membrane structures on a square base. Obtained results show that, in many cases, point loads can produce larger membrane deflections compared to the snow load. This finding will have an impact on including the point load actions into standardization of design and analysis procedures of tensile membrane structures in Europe.

Engineering crack tortuosity in printed polymer–polymer composites through ordered pores

A recently developed multimaterial printing approach, solution mask liquid lithography, is used to produce porous polymer–polymer composites inspired by hierarchical natural structures that exhibit significant crack deflection.

Experimental and Finite Element Method of Castellated Steel Beam with and without Hexagonal web opening

Castellated beams are made from the conventional I section by the process named as Castellation Process. As of late, broad examination on these castellated steel beams has been directed, including various shapes in web openings. The primary objective of these examination works was to assess and dissect its ideal opening sizes and shapes arrangement. For the most part castellated beam are given hexagonal, round and square formed openings. The finite element investigation is most favored technique for comprehension the flexural strength of castellated beams. In this examination, experimental and numerical displaying approach is utilized for deciding spacing between openings on hexagonal castellated beam. ANSYS software was utilized for the investigation. Opening edge 60o with various opening dispersing 0.15d and 0.25d have beam utilized. Investigation was selected steel beam with and without web openings of ISMB 150 and solid ISMB200 section. Results demonstrated that the castellated bar with hexagonal opening indicated more load carrying capacity and less significant deflection contrasted with solid beam.

Functional Linking Between Negative and Positive ERPs for Syntactic Processing in Japanese: Mutual Enhancement, Syntactic Prediction, and Working Memory Constraints.

This study attempts to detect the differences in event-related potentials (ERPs) associated with two syntactic processes: the syntactic integration of discontinuous dependency and the detection of a violation of the syntactic island constraint. We recorded the electroencephalogram elicited by complex sentences in Japanese that included a dependency between a quantifier and its head noun, in which we changed the word order of the two words to manipulate the presence and absence of a syntactic integration and a syntactic island violation while keeping the lexical items and construction unchanged. We found significant negative and positive deflections for the syntactic integration only when a quantifier preceded its head noun. We also observed significant negative and positive deflections for the syntactic island violation, for which the negativity was more salient when a quantifier preceded its head noun. This study is the first to report a late positive ERP for a violation of the syntactic island constraints in Japanese, and the results showed that the ERP elicited by syntactic integration and that by syntactic island violation were different in terms of their latency, topography, and duration. More importantly, the ERPs elicited by the two syntactic processes were biphasic, and the amplitudes of the negative ERP and of the positive ERP were positively correlated. This positive correlation could be a characteristic of syntactic processing because it contrasted with the negative correlation reported for the ERP elicited by semantic anomalies in English. Furthermore, the amplitude of the ERP for syntactic integration was negatively correlated with the individual capacity of working memory (WM). That is, a reader with greater WM capacity showed smaller negativity and positivity for the syntactic integration, whereas the amplitude for the syntactic island violation showed no significant correlation with the individual capacity of WM. Our results suggested that linguistic ERPs functionally interacted with each other and that the ERP involving the retention and the retrieval of a distant word could be constrained by the individual differences in WM capacity. We discuss the possible reasons for the contrast between English and Japanese on the basis of the cross-linguistic differences in the two languages.

Reduces blade shaft deflection with improved mount design to increase vertical hybrid wind turbine performance

In a vertical hybrid turbine with a shaft bearing holder on one side, it has a shaft deflection problem that interferes with turbine performance. This study aims to improve the design of the turbine holder. The methodology used in this study is to analyse the deflection behaviour of the turbine when rotating. Next in the turbine design review, and the result is to increase the distance of the shaft holder bearings and increase the bearing diameter in the triangular frame. Deflection testing with the help of tracker software that’s able to measure deflection distance in one field when the shaft rotates. The results of the deflection comparison before and after the design improvement show a significant deflection reduction.

Psychoneuroendocrinoimmunology-based meditation (PNEIMED) training reduces salivary cortisol under basal and stressful conditions in healthy university students: Results of a randomized controlled study

BackgroundMeditation represents an effective and safe practice to lower distress and promote well-being. PsychoNeuroEndocrinoImmunology-based Meditation (PNEIMED) is a validated method that can reduce stress-related symptoms and salivary cortisol secretion. To date, few randomised controlled trials (RCTs) have assessed cortisol levels through salivary samples, collected both in the morning phase and during acute mental stress elicitation, in healthy young subjects following brief meditation training. AimThe present study aims to investigate, in healthy young undergraduate students, the effects of a brief PNEIMED training course on HPA axis by measuring salivary cortisol levels. MethodsForty students attending the Faculty of Psychology, without comorbidities and previous experience of meditation, were enrolled in the study. Twenty subjects were randomly assigned to 30 h of PNEIMED training (intervention group, IG), and twenty subjects were randomly assigned to 30 h of academic lessons (control group, CG). Salivary cortisol measures included basal morning (t0 = baseline time, collected 30 min after waking) and under stress-eliciting task values. Cortisol measurement under the stress-eliciting task was provided through the Subtraction Stress Task (SST) at scheduled time intervals (t1 = 5 min pre-SST, t2 = 10 min post-SST, t3 = 30 min = post-SST). Salivary cortisol was measured among all subjects (IG + CG) at the beginning (pre-test) and at the end (post-test, four days later) of the study. ResultsANOVA between-group analysis of basal diurnal salivary cortisol showed a significant hormone deflection in the IG at the end of the PNEIMED course (post-test) when compared to the CG (IG post-test 5.64 ± 4.2 vs CG post-test 9.44 ± 4.9; F1,38 = 6.838; p = 0.013). RM-ANOVA within-group analysis for the IG also showed that time and condition effects were statistically significant, with Ftime = 5.438; p = 0.002 and Fcondition = 10.478; p = 0.004, respectively. The IG group presented a significant reduction in basal morning cortisol at the end of the PNEIMED course (post-test) compared to the salivary concentration at baseline (pre-test) (IG pre-test 9.42 ± 6.0 vs IG post-test 5.64 ± 4.2; F1,38 8,354; p = 0.009). RM-ANOVA for the control group showed only the main effect of time (F1,38 = 40.348; p < 0.001). Regarding cortisol measures under the SST-stress eliciting task, ANOVA between-groups analysis showed higher cortisol levels in the IG than in the CG before the PNEIMED course, with significant differences between groups at time t2 and time t3. After the PNEIMED course, the cortisol levels in the IG had decreased, although the differences between groups were not significant. Interestingly, ANOVA within-groups analysis showed that in the IG, the cortisol levels post-test (after the PNEIMED course) were lower than at pre-test (before the PNEIMED course), showing a significant difference of cortisol salivary concentration between conditions at t3 (F = 5.326; p = 0.032). In the control group, the post-hoc analyses for pairwise comparisons between conditions (pre-test vs post-test) did not show significant differences. ConclusionAlthough the low number of subjects enrolled in the study does not allow for definitive conclusions to be drawn, the present findings confirmed the capability of the PNEIMED method to lower stress hormone secretion both at baseline and under acute mental stimulation in a group of young naïve practitioners and make a contribution to the existing literature by increasing the number of published RCTs about the topic.

Strengthening and toughening mechanisms in refilled friction stir spot welding of AA2014 aluminum alloy reinforced by graphene nanosheets

Refilled friction stir spot welding is proposed to replace friction stir spot welding to solve the problem of keyhole in joining of light metals. However, it is rather challenging to ensure the mechanical property of refilled friction stir spot welding joints because of hook defect. In this study, a novel method was proposed to use graphene nanosheets to strengthen the tip of hook defect and improve overall mechanical properties of joint. The joints of AA2014 aluminum alloy with 0.6%wt graphene nanosheets were fabricated by refilled friction stir spot welding. The results show that the tensile/shear strength of joint increases by 31% and the fracture toughness also is improved by nearly 20% with graphene nanosheets. Extension in fatigue life was achieved on joint with graphene nanosheets. Microstructural observations, fracture characteristics and electron back scattered diffraction analysis were systematically investigated to clarify the mechanism for improvement of strength and toughness. The synergetic effect including grain refinement, load transfer, dislocation strengthening and crack bridging, caused by graphene nanosheets, leads to hardening behavior of graphene nanosheets pinned zone and a significant crack deflection during fracture process, which contributes greatly to improving strength and toughness of joint.