Transient Deflection Research Articles

Remediation of Mud Pumping on a Ballasted Railway Track

Maintenance of ballasted railway tracks is a major cost for railway infrastructure owners. In many developed countries, much of the railway infrastructure is mature and was built for service requirements long since superseded. The increased demands on historic infrastructure can lead to the development or exacerbation of localised trackbed problems that require disproportionate levels of maintenance. Identifying these and applying cost effective remediation has the potential to reduce maintenance spend in the long term. However, it is not always clear what the most cost effective remediation will be. One type of localised maintenance issue is the development of wet beds or wet spots, which can occur where saturated clayey subgrade soils are overloaded and result in the development of mud pumping as trains pass. This leads to the migration of fines into the ballast bed and a deterioration in local track performance. Over time the track overlying the wet bed settles disproportionately more, sleepers become progressively more voided, and train ride quality deteriorates. Maintenance of the wet bed may involve locally digging out and replacing the ballast; however, unless the underlying cause is addressed the problem is likely to recur, requiring repeated localised maintenance interventions. This is costly, reactive and ultimately an ineffective approach to managing the problem. This paper presents a study of a wet bed in the UK, both prior to and after a full track renewal. Transient track deflections during train passage were monitored using sleeper mounted geophones and high speed filming techniques. Loaded track geometry data were obtained from a track recording vehicle. It is shown that local maintenance interventions were generally ineffective, but that a renewal of the top 200mm of the trackbed including placement of a geotextile filter and geogrid appears to have been successful in remediating the problem, at least in the short term.

Small Punch Creep deformation and rupture behavior of 316L(N) stainless steel

The Small Punch Creep (SPC) behavior of 316L(N) stainless steel has been evaluated under various loads in the range 300–1000N over a temperature range 898–973K. The SPC curves clearly showed the transient, secondary and tertiary stages of creep. The transient creep deflection data have been analyzed on the basis of Garofalo’s equation. The trend of variations of rate of exhaustion of transient creep deflection and steady state deflection rate with applied load revealed that the SPC deformation obeyed first-order reaction rate theory throughout the transient region. Using Chakrabarty’s membrane stretch model, the creep strain–time curves were derived from deflection–time data measured in SPC tests. The steady state creep rate values calculated from such derived strain curves were closer to corresponding values obtained from conventional creep tests. From the load exponent of steady state deflection rate and estimated activation energy for creep, the mechanism that governs the SPC deformation of 316L(N) stainless steel under investigated conditions was found to be dislocation creep.

Analysis of transient displacements for a ceramic–metal functionally graded cylindrical shell under dynamic thermal loading

The transient displacements of a ceramic–metal functionally graded material(FGM) cylindrical shell subjected to dynamic thermal loading are investigated using the differential quadrature method (DQM). Firstly, the dynamic governing equations of the thin shell with simply supported edges under thermal loading are derived based on the classical shell theory, in which the material properties of the ceramic–metal FGM shells are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. Secondly, the transient temperature field of the ceramic–metal FGM is obtained by using the Laplace transform and power series method. Then, the transient displacements of the axisymmetric deformed shell are obtained by solving governing equations using the DQM. The effects of the shape geometry and the material constitutions on the transient central deflection are also analyzed. It is found that one could easily control the transient deformations of the FGM cylindrical shell under dynamic thermal loading by changing the volume fractions of the ceramics.

Modulation of motor unit activity in biceps brachii by neuromuscular electrical stimulation applied to the contralateral arm.

The purpose of the study was to determine the influence of neuromuscular electrical stimulation (NMES) current intensity and pulse width applied to the right elbow flexors on the discharge characteristics of motor units in the left biceps brachii. Three NMES current intensities were applied for 5 s with either narrow (0.2 ms) or wide (1 ms) stimulus pulses: one at 80% of motor threshold and two that evoked contractions at either ∼10% or ∼20% of maximal voluntary contraction (MVC) force. The discharge times of 28 low-threshold (0.4-21.6% MVC force) and 16 high-threshold (31.7-56.3% MVC force) motor units in the short head of biceps brachii were determined before, during, and after NMES. NMES elicited two main effects: one involved transient deflections in the left-arm force at the onset and offset of NMES and the other consisted of nonuniform modulation of motor unit activity. The force deflections, which were influenced by NMES current intensity and pulse width, were observed only when low-threshold motor units were tracked. NMES did not significantly influence the discharge characteristics of tracked single-threshold motor units. However, a qualitative analysis indicated that there was an increase in the number of unique waveforms detected during and after NMES. The findings indicate that activity of motor units in the left elbow flexors can be modulated by NMES current and pulse width applied to right elbow flexors, but the effects are not distributed uniformly to the involved motor units.

Application of Coupled Train-Track Modelling of Critical Speeds for High-Speed Trains using Three-Dimensional Non-Linear Finite Elements

It is known that as trains traverse soft soils a critical point can be reached whereby the train speed will exceed the Rayleigh ground wave velocity leading to critical velocity issues. If track structures are present, such as stiffened embankments, increases in the train's critical speed can occur. This higher ground wave velocity is termed the critical track velocity. Approaching a critical speed will lead to an increase in the transient track deflection when compared to the quasi-static case. As resonant conditions develop, very high transient track displacements will occur, including the potential for track uplift. In the past, these sites were few in number as the train speeds were relatively low, however as train speeds continue to increase critical speed issues will become more of an issue. This paper first presents simple graphs and equations of the permissible train speed versus Young's modulus and undrained shear strength for typical homogenous clay subgrades. However, for nonhomogenous soils (layered soils), it is necessary to understand the development of the dynamic interaction and hence determine the most cost effective mitigation strategy. For layered soils, this can become difficult to determine without more sophisticated analysis. The development of critical velocities is studied in this paper using a threedimensional time domain finite element program in which the train and track are coupled and the soil is simulated using non-linear soil constitutive models where the stiffness is a function of the isotropic and deviatoric stress, and the damping ratio is a function of the deviatoric strain. This paper benchmarks the analyses using measured data from the Ledsgard site and shows that this approach is able to model the development of track dynamic conditions with train speed through plots of the transient sleeper deflection, and displacement contour plots of the overall ground surface behaviour. The non-linear variation in the different layers' stiffness is highlighted through plots of the time histories of Young's modulus with train speed and depth.

Convenient ultra-broadband femtosecond optical gating utilizing transient beam deflection effect.

A simple but robust ultra-broadband femtosecond optical gating method utilizing transient beam deflection effect is demonstrated with direct CCD imaging of the distorted single-color probe and the measurement of the chirp structure of a white light continuum generated from a CaF₂ plate. The non-collinear configured beam deflection gating technique not only preserves all the advantages of the previous optical Kerr lens based gating methods, such as having no phase matching conditions, little dependence on probe intensity or special nonlinear media, and no requirements on the pump-probe polarization relationship, but it also extends the measurable probe bandwidth. Meanwhile, it is also proved that the current gating technique is easy-aligned, free from the influence of the pump-probe pulse-front mismatch and the probe beam profile, which is much convenient for the characterization of ultra-broadband light pulses in the applications of ultrafast spectroscopy.

The effect of inclination and stand-off on the dynamic response of beams impacted by slugs of a granular material

The dynamic response of end-clamped sandwich and monolithic beams to impact by high-velocity tungsten carbide (WC) particle columns (slugs) has been measured with the aim of developing an understanding of the interaction of ejecta from a shallow-buried explosion with structures. The monolithic beams were made from stainless steel, while the sandwich beams of equal areal mass comprised stainless steel face sheets and an aluminium honeycomb core. High-speed imaging was used to measure the transient transverse deflection of the beams, to record the dynamic modes of deformation, and to observe the flow of the WC particles upon impact. The experiments show that sandwich beams deflect less than the monolithic beams both in normal and inclined impact situations. Moreover, the deflections of all beams in the inclined orientation were less than their respective deflections in the normal orientation at the same slug velocity. Intriguingly, the ratio of the deflection of the sandwich to monolithic beams remains approximately constant with increasing slug velocity for inclined impact but increases for normal impact; i.e. inclined sandwich beams retain their advantage over monolithic beams with increasing slug velocity. Dynamic force measurements reveal that (i) the momentum transferred from the impacting slug to both monolithic and sandwich beams is the same, and (ii) the interaction between the impacting particles and the dynamic deformation of the inclined monolithic and sandwich beams results in a momentum transfer into these beams that is equal to or greater than the momentum of the slug. These experimental findings demonstrate that contrary to intuition and widespread belief, the performance enhancement obtained from employing beam inclination is not due to a reduction in transferred momentum. Finally, we show that increasing the stand-off distance decreases beam deflections. This is because the slugs lengthen as they traverse towards their target and thus the duration of loading is extended with increasing stand-off. However, combining increased stand-off with sandwich construction does not yield the synergistic benefits of sandwich construction combined with beam inclination.

Nonlinear transient response of functionally graded shallow spherical shells subjected to mechanical load and unsteady temperature field

This paper is concerned with the transient deformation of functionally graded (FG) shallow spherical shells subjected to time-dependent thermomechanical load. Based on Timoshenko-Mindlin hypothesis and von Karman nonlinear theory, a set of nonlinear governing equations of motion for FG shallow spherical shells in regard to transverse shear deformation and all the inertia terms are established using Hamilton's principle. The collocation point method and Newmark-beta scheme in conjunction with the finite difference method are adopted to solve the governing equations of motion and the unsteady heat conduction equation numerically. In the numerical examples, the transient deflection and stresses of FG shallow spherical shells with various material properties under different loading conditions are presented.

Marking the counterfactual: ERP evidence for pragmatic processing of German subjunctives.

Counterfactual conditionals are frequently used in language to express potentially valid reasoning from factually false suppositions. Counterfactuals provide two pieces of information: their literal meaning expresses a suppositional dependency between an antecedent (If the dice had been rigged…) and a consequent (… then the game would have been unfair). Their second, backgrounded meaning refers to the opposite state of affairs and suggests that, in fact, the dice were not rigged and the game was fair. Counterfactual antecedents are particularly intriguing because they set up a counterfactual world which is known to be false, but which is nevertheless kept to when evaluating the conditional's consequent. In the last years several event-related potential (ERP) studies have targeted the processing of counterfactual consequents, yet counterfactual antecedents have remained unstudied. We present an EEG/ERP investigation which employed German conditionals to compare subjunctive mood (which marks counterfactuality) with indicative mood at the critical point of mood disambiguation via auxiliary introduction in the conditional's antecedent. Conditional sentences were presented visually one word at a time. Participants completed an acceptability judgment and probe detection task which was not related to the critical manipulation of linguistic mood. ERPs at the point of mood disambiguation in the antecedent were compared between indicative and subjunctive. Our main finding is a transient negative deflection in frontal regions for subjunctive compared to indicative mood in a time-window of 450–600 ms. We discuss this novel finding in respect to working memory requirements for rule application and increased referential processing demands for the representation of counterfactuals' dual meaning. Our result suggests that the counterfactually implied dual meaning is processed without any delay at the earliest point where counterfactuality is marked by subjunctive mood.

The Transition Effect in Rail Tracks – Assessment of Transient Energy for Low Frequency Vibrations

Abstract The transition effect between different track-foundation systems is examined from the point of view of energy that is produced during the passage of load. Analytical solution is given. A model of beam on elastic foundation with damping is used as the base model. It is developed into a model composed of two parts that represent the track-subgrade system with an abrupt change in mechanical parameters: bending stiffness, foundation stiffness, damping, and mass. Several calculations are carried out including examples of comparative calculations with the Finite Difference Model and the Finite Element Model. Transient rail deflections and energy are determined, which may serve to estimate the rate of track-subgrade deterioration.

Response of clamped sandwich beams subjected to high-velocity impact by sand slugs

The dynamic response of end-clamped sandwich and monolithic beams of equal areal mass subjected to loading via high-velocity slugs of dry and water-saturated sand is measured using a novel laboratory-based method. The sandwich beams comprise aluminium face sheets and an aluminium honeycomb core: the effect of sandwich core strength and beam thickness on the dynamic beam deflection is investigated by varying the orientation and height of the anisotropic aluminium honeycomb core material. High-speed imaging is used to measure the transient transverse deflection of the beams and to record the dynamic modes of deformation. The measurements show that sandwich beams with thick, strong cores are optimal and that these beams significantly outperform monolithic beams of equal mass. The water-saturated sand slugs cause significantly higher deflections compared to the dry sand slugs having the same mean slug velocity and we demonstrate that this enhanced deflection is due to the larger mass of the water-saturated slugs. Finally, we show that the impact of sand slugs is equivalent to the impact of a crushable foam projectile. The experiments using foam projectiles are significantly simpler to perform and thus represent a more convenient laboratory technique.

A numerical investigation into the effects of slamming impulsive loads on the elastic–plastic response of imperfect stiffened aluminium plates

Nowadays stiffened aluminium panels have been widely used for marine applications such as building high speed vessels. The panels of high speed vessels are subjected to different in plane and out-of-plane loads. One of the most important out-of-plane loads is the impulse caused by bottom slamming. In the present study, the transient large deflection elastic–plastic responses of a number of stiffened aluminium panels subject to slamming impulsive loads are investigated. The impulsive loads are exerted on the finite element models of aluminium panels proposed by Ultimate Strength Committee of ISSC 2003. Several impact conditions are considered to study the influence of several structural factors such as heat affected zone (HAZ) arrangement, boundary conditions, thickness of plating, number of transverse frames and in-plane fixation. Based on these studies, several design-oriented conclusions are issued. Moreover, this paper outlines the various aspects of the influence of the HAZ presence on the strength of the slam-loaded panels with respect to loading time ratio.

Potassium‐induced cortical spreading depression bilaterally suppresses the electroencephalogram but only ipsilaterally affects red blood cell velocity in intraparenchymal capillaries

Cortical spreading depression (CSD) is a repetitive, propagating profile of mass depolarization of neuronal and glial cells, followed by sustained suppression of spontaneous neuronal activity. We have reported a long-lasting suppressive effect on red blood cell (RBC) velocities in intraparenchymal capillaries. Here, to test the hypothesis that the prolonged decrease of RBC velocity in capillaries is due to suppression of neuronal activity, we measured CSD-elicited changes in the electroencephalogram (EEG) as an index of neuronal activity. In isoflurane-anesthetized rats, DC potential, EEG, partial pressure of oxygen (PO₂), and cerebral blood flow (CBF) were simultaneously recorded in the temporo-parietal region. The velocities of fluorescently labeled RBCs were evaluated by high-speed camera laser scanning confocal fluorescence microscopy with our original software, KEIO-IS2. Transient deflection of DC potential and PO₂ and increase of CBF were repeatedly detected only in the ipsilateral hemisphere following topical KCl application. On the other hand, the relative spectral power of EEG was reduced bilaterally, showing the lowest value at 5 min after KCl application, when the other parameters had already returned to the baseline after the passage of CSD. Mean RBC velocity in capillaries was slightly but significantly reduced during and after passage of CSD in the ipsilateral hemisphere but did not change in the contralateral hemisphere in the same rats. We suggest that mass depolarization of neuronal and glial cells might transiently decelerate RBCs in nearby capillaries, but the sustained reduction of ipsilateral RBC velocity might be a result of the prolonged effect of CSD, not of neuronal suppression alone.

“Dark” Excited States of Diphenylacetylene Studied by Nonresonant Two-Photon Excitation Optical-Probing Photoacoustic Spectroscopy

Optical probing photoacoustic spectroscopy (OPPAS), a photothermal calorimetric technique, was applied to investigate one-photon forbidden “dark” electronically excited singlet states of diphenylacetylene (DPA), belonging to the D2h point group. When 502 nm light from a pulsed OPO laser was focused into a DPA hexane solution, an acoustic wave was detected as a transient angular deflection of the probe beam (He–Ne laser). The laser power dependence of the OPPAS signal was estimated to be 1.9 ± 0.2, suggesting two-photon absorption for acoustic generation. With the OPPAS technique, we successfully obtained a nonresonant two-photon absorption spectrum of DPA in solution for the first time. The two-photon allowed 11B3g and 21Ag states were found to be above the one-photon allowed 11B1u state. These results show that OPPAS is a highly sensitive technique applicable to two-photon absorption spectral measurements of nonfluorescent species.

Sustained Decrease and Remarkable Increase in Red Blood Cell Velocity in Intraparenchymal Capillaries Associated With Potassium‐Induced Cortical Spreading Depression

To examine changes in red blood cell (RBC) velocity in intraparenchymal capillaries of rat cerebral cortex in response to KCl-induced cortical spreading depression (CSD). In isoflurane-anesthetized rats, the velocity of fluorescently labeled RBCs flowing in capillaries in layer I was measured with a high-speed camera laser-scanning confocal fluorescence microscope, with simultaneous monitoring of DC potential, the electroencephalogram (EEG), partial pressure of oxygen (PO(2) ), and cerebral blood flow (CBF). After KCl application, a transient deflection of DC potential (i.e., CSD) repeatedly appeared concomitantly with depression of EEG, and was propagated in the distal direction. PO(2) transiently decreased and CBF was slowly elevated. The frequency distribution of RBC velocity was shifted downward during CSD and was still low after the passage of CSD. When we observed RBC velocity in 38 individual capillaries, 10 capillaries exhibited slowed-down RBC during CSD and RBC velocity remained low in 2 even after the passage of CSD. On the other hand, RBCs with moderately (<3 mm/sec) or remarkably (>3 mm/sec) increased velocities were seen in 10 and 5 capillaries, respectively. CSD-induced excitation of neurons may sustainably decrease or greatly increase RBC velocity in capillaries.

First Principles Estimation of Shock Tube Tests on Nanoreinforced Composite Materials

Extreme loads events can cause enormous human and infrastructure losses. Computer modeling is the key to reducing the high cost of dynamic monitoring and experimentation. Engineers in various fields have undertaken complicated modeling for structures under abnormal loads. However, an efficient and accurate model is necessary to more rapidly address dangerous shock problems. Composite materials have replaced metals in various applications thanks to their superior shock resistance properties. This investigation particularly relates to their usage on naval ships to achieve improved blast survivability with the additional benefit of lower cost. A relatively simple model is detailed for the approximate centerline response prediction of the specific complex case of composite materials tested in a shock tube. A modal analysis simulation of a beam is performed using gross properties as well as physical geometry and arbitrary shock. Closed form equations have been employed to derive the eigenproblem that generates mode shapes and natural frequencies, and the resulting responses are compared to experimental shock tube test results. The best outcome was generated by the simplest model consisting of a shock pressure pulse averaged in two divisions and applied over the entire beam span. For this case, the simulation and experimental responses had reasonable correlation for fractured E-glass/vinyl-ester composite specimens with both nanoclay and graphite platelet reinforcement. This model is also a conservative estimate for the transient test deflection range for all other specimens.

The soft impact of composite sandwich beams with a square-honeycomb core

The dynamic response of end-clamped monolithic beams and sandwich beams of equal areal mass have been measured by loading the beams at mid-span with metal foam projectiles to simulate localised blast loading. The sandwich beams were made from carbon fibre laminate and comprised identical face sheets and a square-honeycomb core. The transient deflection of the beams was determined as a function of projectile momentum, and the measured response was compared with finite element simulations based upon a damage mechanics approach. A range of failure modes were observed in the sandwich beams including core fracture, plug-type shear failure of the core, debonding of the face sheets from the core and tensile tearing of the face sheets at the supports. In contrast, the monolithic beams failed by a combination of delamination of the plies and tensile failure at the supports. The finite element simulations of the beam response were accurate provided the carbon fibre properties were endowed with rate sensitivity of damage growth. The relative performance of monolithic and sandwich beams were quantified by the maximum transverse deflection at mid-span for a given projectile momentum. It was found that the sandwich beams outperformed both monolithic composite beams and steel sandwich beams with a square-honeycomb core. However, the composite beams failed catastrophically at a lower projectile impulse than the steel beams due to the lower ductility of the composite material.

Transient deflection response in microcantilever array integrated with polydimethylsiloxane (PDMS) microfluidics

We report the integration of a nanomechanical sensor consisting of 16 silicon microcantilevers with polydimethylsiloxane (PDMS) microfluidics. For microcantilevers positioned near the bottom of a microfluidic flow channel, a transient differential analyte concentration for the top versus bottom surface of each microcantilever is created when an analyte-bearing fluid is introduced into the flow channel (which is initially filled with a non-analyte containing solution). We use this effect to characterize a bare (nonfunctionalized) microcantilever array in which the microcantilevers are simultaneously read out with our recently developed high sensitivity in-plane photonic transduction method. We first examine the case of non-specific binding of bovine serum albumin (BSA) to silicon. The average maximum transient microcantilever deflection in the array is -1.6 nm, which corresponds to a differential surface stress of only -0.23 mN m(-1). This is in excellent agreement with the maximum differential surface stress calculated based on a modified rate equation in conjunction with finite element simulation. Following BSA adsorption, buffer solutions with different pH are introduced to further study microcantilever array transient response. Deflections of 20-100 nm are observed (2-14 mN m(-1) differential surface stress). At a flow rate of 5 μL min(-1), the average measured temporal width (FWHM) of the transient response is 5.3 s for BSA non-specific binding and 0.74 s for pH changes.

A modified energy-balance model to predict low-velocity impact response for sandwich composites

Abstract An energy-balance model is often used to analyze impact dynamics for composite structures. However this model tends to overestimate the peak impact load after the onset of damage since it does not account for damage initiation and propagation. In this paper, the energy-balance model is coupled with the law of conservation of momentum to extend its validity beyond the elastic response regime for a composite sandwich structure subjected to low-velocity impact. Closed-form solutions were derived for the plate’s elastic structural stiffness and the critical load at the onset of damage. The critical load was theoretically predictable by accounting for the elastic energies absorbed by the plate up to core failure. Impact test results also showed that the relative loss of the plate’s transverse stiffness after damage was directly related to the energy absorbed by the plate, which could be calculated given the damage initiation energy. The stiffnesses and the critical load were then used in the modified energy-balance model to predict transient load and deflection histories. Predicted results were comparable with test data, in terms of critical and peak loads, as well as the overall behaviour. This impact model is an efficient design tool which can complement detailed FE simulations.

Advancing age alters the influence of eye position on sound localization

Vision and audition provide spatial information about the environment to guide natural behavior. Because the eyes move in the head while the ears remain head-fixed, input conveying eye position in the head is required to maintain audiovisual congruence. Human perception of auditory space was previously shown to shift with changes in eye position, regardless of the target's frequency content and spatial cues underlying horizontal and vertical localization. In this study, we examined whether this interaction is altered by advancing age. Head-restrained young (18-44 yo), middle-aged (45-64 yo), and elderly (65-81 yo) human subjects localized noise bursts under conditions of transient and sustained ocular deflection. All three age groups demonstrated a time-dependent shift of auditory space in the direction of eye position. Moreover, this adaptation showed a clear decline with advancing age, but only for peripheral auditory space (beyond ±10° from midline). Alternatively, adaptation in the periphery may occur, but is more sluggish than in the central field and therefore not fully observed in this experiment. The age-dependent effect cannot be readily explained by senescent peripheral hearing loss, suggesting a change in central processing of auditory space in relation to the control of gaze.