Quasi-static Displacement Research Articles

Magnetic field assisted bonding technology for released micro actuator and mirror surface

A magnetic field pulling-force assisted bonding technology is reported, which is used to bond a mirror plate with a released microactuator using adhesive. This bonding technology is not sensitive to the micromachining process, i.e., any process for microactuator fabrication containing the ferromagnetic structure layer can be used and bonded with a high surface quality mirror plate after released. The conventional wafer bonding technology bonds unreleased actuator with a mirror plate but it limits to the process compatible with the wafer bonding with a releasing step suitable for wafer bonding. Consequently not all processes (such as those mature and commercially available, and those being able to generate large displacement) can be used to fabricate micromirrors. The bonding technology proposed in this paper applies non-touching magnetic field pulling-force, instead of conventional compression mechanical force through touching, to bring the microactutor and a mirror plate in contact for bonding such as to avoid: (1) any plastic deformation or damage to the released micro actuator; and (2) the risk of sticking the actuator moving part to the substrate due to the adhesive squeezed out from the bonding surfaces. The bonding method is introduced and the critical parameters of the bonding method, i.e., distance between the magnet to the actuator is determined through simulations. A bonding mechanism is built and two different designs are bonded. Bonding results are measured, which verifies the bonding method. The bonding is characterized to have a strength of withstanding vibration for a few hours in frequency 20–200 Hz with 2–5 g acceleration and surviving in the temperature of −30 to 80 °C. After bonding a mirror plate with 15.6 m of the curvature radius and 2 nm of the roughness, the bonded micromirror is tested to have a quasi-static displacement of 120 μm.

Typhoon- and temperature-induced quasi-static responses of a supertall structure

Wind loads and the associated load effects on supertall structures are key factors in structural design. In practice, typhoon-induced quasi-static responses measured from the field mix with temperature-induced responses because temperature varies significantly during a typhoon event. The mixed responses complicate the assessment of the wind loading effects and the separation of the two load effects is difficult in practice. In this study, the wind- and temperature-induced quasi-static responses of the 600m-tall Canton Tower are investigated using a comprehensive long-term structural monitoring system installed on the structure. The structural responses (stresses and displacement) obtained from the field monitoring system during a strong typhoon are presented. The temperature-induced responses are calculated by applying a temperature loading model to the finite element model of the structure. The purely typhoon-induced quasi-static responses are then separated from the total measured responses by subtracting the temperature-induced ones. It shows that the typhoon-induced quasi-static responses of the supertall structure are slightly smaller than the temperature-induced responses in a typical sunny day. The typhoon-induced quasi-static displacement obtained from the field is also compared with the counterpart from the wind tunnel test on an aeroelastic model of the full tower.

Estimations of the Seismic Pressure Noise on Mars Determined from Large Eddy Simulations and Demonstration of Pressure Decorrelation Techniques for the Insight Mission

The atmospheric pressure fluctuations on Mars induce an elastic response in the ground that creates a ground tilt, detectable as a seismic signal on the InSight seismometer SEIS. The seismic pressure noise is modeled using Large Eddy Simulations (LES) of the wind and surface pressure at the InSight landing site and a Green’s function ground deformation approach that is subsequently validated via a detailed comparison with two other methods: a spectral approach, and an approach based on Sorrells’ theory (Sorrells, Geophys. J. Int. 26:71–82, 1971; Sorrells et al., Nat. Phys. Sci. 229:14–16, 1971). The horizontal accelerations as a result of the ground tilt due to the LES turbulence-induced pressure fluctuations are found to be typically $\sim 2 \mbox{--} 40~\mbox{nm}/\mbox{s}^{2}$ in amplitude, whereas the direct horizontal acceleration is two orders of magnitude smaller and is thus negligible in comparison. The vertical accelerations are found to be $\sim 0.1\mbox{--}6~\mbox{nm}/\mbox{s}^{2}$ in amplitude. These are expected to be worst-case estimates for the seismic noise as we use a half-space approximation; the presence at some (shallow) depth of a harder layer would significantly reduce quasi-static displacement and tilt effects. We show that under calm conditions, a single-pressure measurement is representative of the large-scale pressure field (to a distance of several kilometers), particularly in the prevailing wind direction. However, during windy conditions, small-scale turbulence results in a reduced correlation between the pressure signals, and the single-pressure measurement becomes less representative of the pressure field. The correlation between the seismic signal and the pressure signal is found to be higher for the windiest period because the seismic pressure noise reflects the atmospheric structure close to the seismometer. In the same way that we reduce the atmospheric seismic signal by making use of a pressure sensor that is part of the InSight Auxiliary Payload Sensor Suite, we also the use the synthetic noise data obtained from the LES pressure field to demonstrate a decorrelation strategy. We show that our decorrelation approach is efficient, resulting in a reduction by a factor of $\sim 5$ in the observed horizontal tilt noise (in the wind direction) and the vertical noise. This technique can, therefore, be used to remove the pressure signal from the seismic data obtained on Mars during the InSight mission.

Finite element analysis and experimental investigation of nonlinear features of rail fastening systems

The more demanding requirements for the reduction of vibration in passenger railways and urban railway lines have led to a trend towards lower-stiffness rail fastening systems accompanied by greater deformation of their rubber components. Nonlinearities under large deformation due to the boundary conditions, geometric properties, intrinsic hyperelasticity and viscidity of the rubber material, and dynamic nonlinear features such as the Payne effect have become prominent and cannot be ignored. In this research, a shear-type fastening system and a bonded compression-type rail fastening system have been designed and produced using the same rubber material. A set of mechanical experiments of the used rubber material was first performed to obtain the rubber properties; this information was later used as an input to a three-dimensional finite element model constructed using Abaqus. Laboratory tests of the two fastening specimens were then performed to obtain the quasi-static and dynamic displacement–force curves. Later, the three-dimensional finite element models were presented, and the calculated curves were compared to the measured values. Finally, the two fastening systems were comparatively analyzed, and the influences of their various nonlinear properties were discussed. The combined experimental and numerical analyses of the nonlinear properties of the two typical types of rail fastening systems are believed to enhance the understanding of their mechanical behavior and to improve the product design, structural optimization, and testing in practice.

Effect Study of Aperture Distribution on the Capillary Pressure-Saturation Relation for the Single Fracture

A systematic numerical method was presented to investigate the effect of aperture distribution on the relation of capillary pressure versus fluid saturation (P-S relation) for a single fracture. The fracture was conceptualized as a two-dimensional lattice-grid model and its aperture field was described by a probability distribution. Based on the invasion percolation theory, a program was developed to simulate the quasi-static displacement. The simulation was verified validly by comparisons of the experimental results. The effects of the statistical parameters were further quantified. The results show that the largest local aperture on the fracture boundary determines the AEV. The larger mean decreases the variation coefficient, which causes the more uniform aperture field, smoother air invasion front, and steeper capillary pressure-saturation curve (CPSC). The larger standard deviation increases not only the range but also the contrast degree of the apertures, thus providing a nondeterministic rule in the P-S relation. The larger correlation length causes a more homogeneous aperture field and a dual connectivity of the fracture. The increase of the difference and contrast degree between the small and large apertures results in dual-aperture fields. The dual-aperture field and dual connectivity of the fracture both contribute to the bimodal characteristic of the CPSC.

Nonlinear dynamics of a fluid-conveying pipe under the combined action of cross-flow and top-end excitations

We report a theoretical investigation of an elastic and slender fluid-conveying pipe with a top-end excitation subjected to uniform cross flows. Considering the mean drag force and the time varying vortex-induced lift force which is modeled using a nonlinear van der Pol oscillator, the nonlinear partial differential equations of the motion of coupled fluid-structure system are constructed and simplified to a reduced-order model through the Galerkin-type discretization. By virtue of quasi-static displacement conditions, the characteristics of vortex-induced vibration of the pipe are evaluated for the first two lock-in modes. The results show that the top-end excitation can increase the vibration amplitude of the pipe when the cross-flow speed is out of the lock-in regions. When the cross-flow speed is within the lock-in region, however, the top-end oscillation causes a transition between quasi-periodic and periodic in the responses of the pipe, significantly reducing or increasing the vibration amplitudes depending on the excitation acceleration and frequency. This finding has an important guidance in suppressing vortex-induced vibrations by balancing the internal fluid velocity and the top-end excitation.

Seismic Performance of Compact Beam–Column Connections with Welding Defects in Steel Bridge Piers

AbstractWelding defects and fatigue cracks in full-penetration welded beam–column connections, resulting in partial-penetration welds, are found in existing steel moment-resisting frame bridge piers. The welding defects may have an unfavorable effect on the seismic performance of a large number of existing piers, most of which have been in operation for over 50 years. This study aims to clarify the effects of the weld profile, e.g., weld leg length, penetration depth, and incomplete penetration depth, on seismic performance of the beam–column connections in existing piers with welded box sections. The effect of gusset stiffeners (termed fillets in this paper) at the beam-web-to-column-web joint on the improvement of seismic performance is also studied. In this study, experiments on 10 specimens with different incomplete penetration depths and fillet radii are performed under quasi-static cyclic large displacement loading. Based on the test results, cracks may initiate either at the beam end or at the weld...

Controlled elastic postbuckling of bilaterally constrained non-prismatic columns: application to enhanced quasi-static energy harvesters

Axially compressed bilaterally constrained columns, which can attain multiple snap-through buckling events in their elastic postbuckling response, can be used as energy concentrators and mechanical triggers to transform external quasi-static displacement input to local high-rate motions and excite vibration-based piezoelectric transducers for energy harvesting devices. However, the buckling location with highest kinetic energy release along the element, and where piezoelectric oscillators should be optimally placed, cannot be controlled or isolated due to the changing buckling configurations. This paper proposes the concept of stiffness variations along the column to gain control of the buckling location for optimal placement of piezoelectric transducers. Prototyped non-prismatic columns with piece-wise varying thickness were fabricated through 3D printing for experimental characterization and numerical simulations were conducted using the finite element method. A simple theoretical model was also developed based on the stationary potential energy principle for predicting the critical line contact segment that triggers snap-through events and the buckling morphologies as compression proceeds. Results confirm that non-prismatic column designs allow control of the buckling location in the elastic postbuckling regime. Compared to prismatic columns, non-prismatic designs can attain a concentrated kinetic energy release spot and a higher number of snap-buckling mode transitions under the same global strain. The direct relation between the column’s dynamic response and the output voltage from piezoelectric oscillator transducers allows the tailorable postbuckling response of non-prismatic columns to be used as multi-stable energy concentrators with enhanced performance in micro-energy harvesters.

A translation micromirror with large quasi-static displacement and high surface quality

A large displacement with high surface quality translation micromirror is presented. The micromirror consists of a magnetic actuator and a mirror plate. The actuator and the mirror plate are fabricated separately using two processes and then bonded together. The actuator consists of a moving film which is a 20 µm thick nickel film fabricated by MetalMUMPs and a solenoid located underneath the moving film. The moving film is designed to curve up through the residual stress gradient in the nickel film and a curve-up mechanism which includes four trapezoidal plates and anchoring springs. The mirror plate is simply diced from a polished silicon wafer and coated with a metal thin film. The mirror plate is bonded onto the central ring of the moving film. A solenoid attracts the moving film along with the mirror plate downwards to realize translation. A quasi-static displacement of 123 µm is achieved at a driving current of 400 mA. A high mirror surface quality is realized, e.g. 15.6 m of curvature radius and 2 nm surface roughness.

Cyclic tests of all-steel web-restrained buckling-restrained brace subassemblages

In this study, cyclic tests of a buckling-restrained brace (BRB) subassemblage with an all-steel web-restrained brace (WRB) were conducted to investigate hysteretic behavior under combined axial and rotational demands. Four full-scale WRB frame subassemblages were subjected to the quasi-static displacement protocol used for BRB qualification described in the AISC 341–10 Seismic Provisions for Steel Buildings. Three different sizes of steel core plates were examined. One specimen used a nominal 7.9-mm thick by 152-mm wide plate, two WRB specimens used a nominal 12.7-mm thick by 152-mm wide plate, and one specimen used a nominal 12.7-mm thick by 229-mm wide plate. All specimens successfully completed the cyclic testing up to 2% story drift without experiencing brace instability, brace end connection failure, or rupture. Specimens with a 12.7-mm thick core plate survived additional cycles at 1.5% story drift before rupture. The test results also showed that the maximum compression forces were less than 1.3 times the maximum tension forces for each cycle corresponding to a deformation greater than the yield displacement, demonstrating that compression overstrength of the WRB was comparable with typical BRBs.

Lateral performance of a Pres-Lam frame designed for gravity loads

This paper analyses the lateral load performance of a post-tensioned timber (Pres-Lam) frame which was designed with the primary function of supporting gravity loading. A full scale, two bay frame was used and subjected to quasi-static horizontal displacement. A total of four tests were performed, one with only the post-tensioning cables to resist horizontal loading and three with the addition of sacrificial steel elements externally attached and acting as dissipative reinforcing. This external reinforcing increased the moment capacity of the frame connections and the ability of the frame to release energy through hysteretic damping. Following a description of the test setup the results show that although the primary functions of the post-tensioning is to reduce section height and increase bay length under gravity loading it will also provide a significant contribution to the lateral resistance of the structure. Finally, a simplified design procedure is presented which allows assessing the magnitude of this contribution.

Single-phase and two-phase flow properties of mesaverde tight sandstone formation; random-network modeling approach

3D random networks are constructed in order to represent the tight Mesaverde formation which is located in north Wyoming, USA. The porous-space is represented by pore bodies of different shapes and sizes which are connected to each other by pore throats of varying length and diameter. Pore bodies are randomly distributed in space and their connectivity varies based on the connectivity number distribution which is used in order to generate the network. Network representations are then validated using publicly available mercury porosimetry experiments.The network modeling software solves the fundamental equations of two-phase immiscible flow incorporating wettability and contact angle variability. Quasi-static displacement is assumed. Single phase macroscopic properties (porosity, permeability) are calculated and whenever possible are compared to experimental data. Using this information drainage and imbibition capillary pressure, and relative permeability curves are predicted and (whenever possible) compared to experimental data.The calculated information is grouped and compared to available literature information on typical behavior of tight formations. Capillary pressure curve for primary drainage process is predicted and compared to experimental mercury porosimetry in order to validate the virtual porous media by history matching. Relative permeability curves are also calculated and presented.

Experimental evaluation of the seismic performance of reinforced concrete structural walls with different end configurations

The Canterbury Earthquake Royal Commission report (2013) showed that cantilever reinforced concrete (RC) walls failed at a lower ductility capacity than expected due to a plasticity concentration region within a very limited height near the location of the primary cracks at the base of the walls. The New Zealand Standards (NZS 3101) (2006) [2] and the Canadian design standards (CSA A23.3-14) (2014), adopt the same capacity design approaches for RC walls design, with both standards specifying a minimum vertical reinforcement ratios (ρv%) of 0.25% for RC walls. Subsequently, the current study was conducted to study the seismic performance of RC walls with different vertical reinforcement ratios and cross sectional configurations. In this paper, six half-scaled RC structural walls were constructed and tested under quasi-static displacement controlled cyclic loading. The walls had three different cross sectional configurations; rectangular, flanged and boundary elements and were tested with specific design characteristics selected to evaluate and compare the wall ductility capabilities. In this respect, wall ductility can be defined as the ability of the walls to undergo inelastic deformations with no/low strength degradation, which is essential in Seismic Force Resisting Systems (SFRS) as it is not economically feasible to design SFRS to behave elastically under seismic loadings. So the ductility quantification of the structural walls used were ductility ratio between the intended displacements with the yield displacement. Based on the test results, the ultimate drift at 20% ultimate strength degradation varied between 0.9% and 1.6% and the ultimate level displacement ductility (μΔ0.8u), ranged approximately between 4.0 and 6.0. Although the flanged walls and the walls with boundary elements were designed to develop almost the same capacity as that of the rectangular walls, the seismic performance of the former wall type was found to be superior to that of their rectangular counterparts with respect to both the ultimate displacement capacity and ductility level. Moreover, using the flanges and the boundary elements walls resulted in approximately 30% reduction of the vertical reinforcement compared to that of the rectangular walls when designed to resist the same lateral loads while carrying identical gravity loads. In addition to gaining insights on the response of walls with boundary elements, the results indicated that structural walls with low vertical reinforcement ratio can experience reduced ductility as indicated in the Canterbury Commission Report.

Investigation on attitude disturbance control and vibration suppression for fuel-filled flexible spacecraft

This paper is mainly focused on the attitude dynamics and control of a fuel-filled flexible spacecraft subjected to the thermal payload during eclipse transitions. The flexible appendages are considered as Euler–Bernoulli beams, and the sloshing liquid is modeled as in two modes multi-spring-mass models; the governing equations of this coupled system are developed by using Hamilton’s principle. Numerical results show that the spacecraft attitude responses consist of a quasi-static displacement and superimposed vibration. Then, we design an adaptive sliding mode and use the Lyapunov approach control law to control the attitude disturbance and suppress the thermal jitter and liquid sloshing for the fuel filled flexible spacecraft subject to the thermal payload. Numerical results are presented to verify the efficiency of the hybrid control methods. The results show that the adaptive sliding mode method might be effective to handle the steady-state errors and the Lyapunov control algorithm would suppress the residual vibration. The attitude dynamics control and vibration suppression are investigated for a fuel-filled spacecraft with single solar panel subjected to thermal bending moment during eclipse transitions.

Magnetic resonance acoustic radiation force (impulse) imaging (MR-ARFI)

MR-ARFI adds to the rich toolbox of MR imaging methods for guiding focused ultrasound. MRI has exquisite soft tissue contrast for targeting focused ultrasound and a variety of contrast mechanisms for assessing the effect of focused ultrasound. In addition, MR can provide temperature mapping in near-realtime. MR-ARFI is an imaging method that compliments these other capabilities: MR-ARFI can provide a very low temperature rise method to locate the focal spot, calibrate the beam intensity, and potentially evaluate and improve focusing. MR-ARFI typically uses a relatively long ultrasound pulse (1-20 ms) during the application of a magnetic field gradient to encode the displacement of tissue into the phase of the MR image. MR-ARFI is related to elastography, shear-wave imaging, and harmonic motion imaging methods, which evaluate tissue stiffness by evaluation of the ultrasound shear wave that propagates after the ultrasound pulse. However, MR-ARFI is instead visualizing the quasi-static displacement of tissue during the ultrasound pulse, rather than the shear wave after the pulse.

Dynamic Performance of Flush End-Plate Beam-Column Connections and Design Applications in Progressive Collapse

An experimental program was conducted in this study to investigate the dynamic behavior of flush end plate steel beam-column cruciform connections following instantaneous removal of a central supporting column. The dynamic tests were performed by using a quick-release mechanism to simulate sudden column-removal scenarios. In the test program, the geometries of the flush end-plate connections remained unchanged but subjected to five different magnitudes of uniformly distributed load. Another five quasi-static tests were also carried out for comparison with the dynamic response and investigation of the dynamic increase factors (DIF). Test results showed that the release-time durations of the column support force were approximately 30 ms for all five dynamic tests. For the same initial applied dead loads, the maximum dynamic displacement was significantly increased compared to the corresponding quasi-static displacement. In order to observe the full dynamic performance of the tested connection until final failure, a general-purpose finite-element software was used to conduct the three-dimensional numerical simulations. Comparison results showed that the numerical model could accurately simulate the monotonic quasi-static test results and the dynamic test results under sudden column removal. Subsequently, a series of parametric studies was conducted to investigate the connection behavior considering the load-release time, different loading methods, and the magnitude of uniform distributed load. By comparing the full dynamic response of the flush end-plate connection with its corresponding quasi-static response, both the displacement-based DIF and force-based DIF could be respectively determined. The paper also addresses which DIF is more appropriate for the design of structures to resist progressive collapse.

Coherent modulation of theYBa2Cu3O6+xatomic structure by displacive stimulated ionic Raman scattering

We discuss the mechanism of coherent phonon generation by stimulated ionic Raman scattering, a process different from conventional excitation with near visible optical pulses. Ionic Raman scattering is driven by anharmonic coupling between a directly excited infrared-active phonon mode and other Raman modes. We experimentally study the response of $\mathrm{YB}{\mathrm{a}}_{2}\mathrm{C}{\mathrm{u}}_{3}{\mathrm{O}}_{6+x}$ to the resonant excitation of apical oxygen motions at 20 THz by midinfrared pulses, which has been shown in the past to enhance the interlayer superconducting coupling. We find coherent oscillations of four totally symmetric $({\mathrm{A}}_{\mathrm{g}})$ Raman modes and make a critical assessment of the role of these oscillatory motions in the enhancement of superconductivity.

Negative stiffness honeycombs for recoverable shock isolation

Purpose – The purpose of this paper is to study the behavior of negative stiffness beams when arranged in a honeycomb configuration and to compare the energy absorption capacity of these negative stiffness honeycombs with regular honeycombs of equivalent relative densities. Design/methodology/approach – A negative stiffness honeycomb is fabricated in nylon 11 using selective laser sintering. Its force-displacement behavior is simulated with finite element analysis and experimentally evaluated under quasi-static displacement loading. Similarly, a hexagonal honeycomb of equivalent relative density is also fabricated and tested. The energy absorbed for both specimens is computed from the resulting force-displacement curves. The beam geometry of the negative stiffness honeycomb is optimized for maximum energy absorption per unit mass of material. Findings – Negative stiffness honeycombs exhibit relatively large positive stiffness, followed by a region of plateau stress as the cell walls buckle, similar to regular hexagonal honeycombs, but unlike regular honeycombs, they demonstrate full recovery after compression. Representative specimens are found to absorb about 65 per cent of the energy incident on them. Optimizing the negative stiffness beam geometry can result in energy-absorbing capacities comparable to regular honeycombs of similar relative densities. Research limitations/implications – The honeycombs were subject to quasi-static displacement loading. To study shock isolation under impact loads, force-controlled loading is desirable. However, the energy absorption performance of the negative stiffness honeycombs is expected to improve under force-controlled conditions. Additional experimentation is needed to investigate the rate sensitivity of the force-displacement behavior of the negative stiffness honeycombs, and specimens with various geometries should be investigated. Originality/value – The findings of this study indicate that recoverable energy absorption is possible using negative stiffness honeycombs without sacrificing the high energy-absorbing capacity of regular honeycombs. The honeycombs can find usefulness in a number of unique applications requiring recoverable shock isolation, such as bumpers, helmets and other personal protection devices. A patent application has been filed for the negative stiffness honeycomb design.

Experimental investigation of the cyclic response of reinforced precast concrete framed structures

This paper summarizes the results of an experimen- tal program devoted to assessing the main structural characteristics and criticalities in the seismic response of typical reinforced precast concrete structures in Italy that were severely damaged by major earthquakes in May 2012. Two 3⁄4 scale two-bay, three-story precast concrete frames with and without cladding panels were subjected to a quasi-static cyclic top displacement his- tory consisting of symmetric stepwise increasing drift cycles. Pinned beam-column connections consisted of neoprene pads with vertical steel dowels working in shear. The flexibility of the cantilevered static scheme forced large displacement demand and incompatible transfer of the horizontal forces to occur in joints lack- ing shear and ductility capacity. In addition, displace- ment incompatibility between structural elements and cladding panels caused the premature failure of their connections. The results demonstrate the inadequate performance of this structural solution because of its beam-to-column and panel-to-structure connection systems, the responses of which reaffirm that this frame typology should not be used in areas of high seismic hazard because of its nearly elastic-fragile behavior.

FE Dynamic Analysis Using Moving Support Element on Multi-Span Beams Subjected to Support Motions

In the present study, finite element dynamic analysis or time history analysis of two-span beams subjected to asynchronous multi-support motions is carried out by using the moving support finite element. The elemental equation of the element is based on total displacements and is derived under the concept of the quasi-static displacement decomposition. The use of moving support element shows that the element is very simple and convenient to represent continuous beam moving, deforming and vibrating simultaneously due to support motions. The comparison between the numerical results and analytical solutions indicates that the FE result agrees with the analytical solution.