Deflection Mechanism Research Articles

Analytical solution to temperature-induced deformation of suspension bridges

Varying ambient temperature may cause significant deformation of long-span suspension bridges. This study investigates the mechanisms of the temperature-induced mid-span deflection and tower-top horizontal displacement of suspension bridges, and formulates the general analytical solutions to the thermal responses of ground-anchored suspension bridges. The temperature-induced mid-span deflection can be determined from the superposition of deflections caused by each of the separate temperature changes of the main-span cable, side-span cables, and towers, while the tower-top horizontal displacement is a combination of the thermal effects of the side-span cables and towers. It is found that the cable temperature plays the dominant role in the mid-span deflection and tower-top horizontal displacement. Moreover, the temperature effective length is proposed and a unified formula of the temperature-induced bridge responses is obtained. The accuracy of the proposed formulas is verified through the field monitoring data of the 2132-m-long Tsing Ma Bridge at Hong Kong. The present study not only provides a simple, general, and unified analytical solution to the temperature-induced deformation of long-span suspension bridges, but also assists engineers in understanding the mechanisms of thermal behaviours of such bridges.

The tensile properties and interlaminar shear strength of microcapsules-glass fibers/epoxy self-healable composites

In the present study, the self-ability based on the microcapsule healing system on the glass fibers-epoxy smart composites was investigated. The microcapsules’ shell and healing agent comprised urea-formaldehyde and diluted epoxy, respectively. The synthesized microcapsules by one-stage in-situ polymerization method were dispersed with the different percentage of 7, 14 and 21 wt% into the epoxy resin. Then, the epoxy-glass fibers composites with the self-healing ability were fabricated by hand lay-up method. The self-healing composites damaged by various damage forces through a quasi-static penetration method. Therefore, the damage forces of 800, 1050 and 1300 N for tensile samples and 2500, 2900 and 3300 N for interlaminar shear strength (ILSS) samples were selected. The obtained results showed that adding 14 wt% microcapsules into the composite increased the tensile strength, due to the crack pining and deflection mechanisms. Whereas, by increasing the percentage of microcapsules up to 21 wt%, the shear strength of composite was reduced, compared with the pristine composite. The maximum obtained healing efficiency for both tensile and ILSS tests were 97.5 and 144.5%, respectively, which belonged to 21 wt% microcapsules-loaded composite. The microscopically investigations of interactions between microcapsules and micro-cracks at the fracture surface illustrated the crack pinning, deflecting, and bowing mechanisms. Also, rupturing the microcapsules, wetting the damaged area by healing agent and forming the polymeric shell in the damaged area were seen.

Spin-dependent radiative deflection in the quantum radiation-reaction regime

A new spin-dependent deflection mechanism is revealed by considering the spin-correlated radiation-reaction force during laser-electron collision. We found that such deflection originates from the non-zero work done by the radiation-reaction force along the laser polarization direction in each half-period, which is larger/smaller for spin-anti-paralleled/spin-paralleled electrons. The resulted anti-symmetric deflection is further accumulated when the spin-projection onto the laser magnetic field is reversed in adjacent half-periods. The discovered mechanism dominates over the Stern–Gerlach deflection for electrons of several hundreds of MeV and 10 PW-level laser peak power. The results provide a new perspective to study the strong-field QED physics in quantum radiation-reaction regime and an approach to leverage the study of radiation-dominated and strong-field QED physics via particle spins.

Design and Development of a Low-Cost Cantilever-Based Flow Sensor

Measuring fluid flow rate in a precise manner plays a vital role in process engineering with important objectives, including monitoring and controlling of process operations to improve productivity and ensure safety. Flow sensing is a well-studied problem to the extent, even there exist many sophisticated sensors. Despite the vast developments, there are matters of concern, particularly in residential and irrigation sectors. The existing sensors are expensive, unidirectional, and less efficient in measuring low flow rates. Hence, the development of low-cost, robust and accurate flow sensors with the simplicity in operation is highly demanded. This work presents a novel low-cost flow sensor based on the principle of cantilever deflection. The proposed flow sensor uses a stainless steel strip as the sensing element and measures the flow based on the angle of deflection of the cantilever through an image analysis technique. A calibration model that relates the flow rate to the angle of deflection is developed from experimental data. The results are subsequently non-dimensionalized in terms of Reynolds number, thereby extending its applicability to other fluids and accommodate pipes of different dimensions. In addition, a simplified theoretical model based on the cantilever deflection mechanism is presented in support of the working principle. The developed cantilever flow sensor is cost-effective, simple, reliable, and capable of measuring even moderate flow rates in the pipeline. Experimental results are presented to demonstrate the precision and accuracy of the proposed flow sensor.

Numerical Parametric Study of Settlement and Load Transfer Mechanism of Pile Group Due to Twin Stacked Tunnelling with Different Construction Sequences

Construction of tunnels in urban cities may induce excessive settlement and tilting of nearby existing pile foundations. In this study, numerical parametric study was conducted to investigate the influences of twin stacked tunnelling with different construction sequences on an existing (2 × 2) pile group. Twin stacked tunnelling was simulated one after the other with the first tunnel excavated near the mid-depth of the pile shaft and the second either next to the toe of the pile (case ST) or below the pile (case SB). In addition, two more analyses were performed with change of construction sequence of twin stacked tunnels (i.e. cases TS and BS). The first tunnel was excavated either near the pile toe (case TS) or below the pile (case BS) and second tunnel near the mid-depth of the pile shaft. The different construction sequence of twin stacked tunnels at different depth had a limited effect on induced pile group settlement, tilting, lateral deflection and load transfer mechanism. The computed cumulative pile group settlement was about 22% larger for tunnelling sequence TS than for tunnelling sequence TS.

Deflection Mechanism and Safety Analysis of Coal Mine Shaft in Deep Soil Strata

The main shaft and auxiliary shaft in the Guotun Coal Mine underwent large deflections, with deflection values of 359 mm and 322 mm, respectively. These two deflections represent the first occurrence of such large vertical shaft deviations in the soil strata in China. The deflection problem has seriously affected the hoisting safety and lining safety and has become a serious impediment to the sustainable production of mines. Therefore, the deflection mechanism must be determined. For this purpose, based on mining subsidence theory, the spatial probability integral method and a more accurate time function were used to establish a model, called 3D dynamic prediction model, for predicting the shaft movement. The formulas for calculating the lining stress caused by coal mining were based on established models. With measured shaft deflection data, the prediction parameters for deep soil strata were calculated on the basis of an inversion analysis. A comparative analysis of measured and calculated deflection values revealed that the reason for shaft deflection in Guotun Coal Mine is the insufficient size of the protection coal pillar (PCP); namely, the design parameters of the PCP in current codes are not applicable to the deep soil strata. As a result, under the asymmetric mining conditions, mining causes the shaft to deflect without damage and under the symmetric mining conditions, mining causes the lining to fracture. The results have an extremely important significance for the prevention and control of shaft deflection, for the rational design of PCP, and for the sustainability of mine production.

The effect of nano-TiO2 additions on the densification and mechanical properties of SiC-matrix composite

This research studied the effect of adding TiO2 nanoparticles along with Al2O3 and Y2O3 additives on the physical and mechanical properties of a SiC-matrix composite. The samples were fabricated through a pressureless process at 1900 °C. The results showed that the addition of TiO2 nanoparticles up to 4.5 wt% inhibited the excessive growth of SiC grains. According to the investigations, the microstructure and final properties of composites were affected by density, synthesized phases as well as their distribution in the matrix, and grain size. The highest density, Young's modulus, hardness, indentation fracture resistance, and flexural strength, alongside with the lowest brittleness index were respectively, 98.7%, 401.2 GPa, 27.1 GPa, 6.1 MPa m1/2, 522.7 MPa and 292.19 × 10−6 m−1, attributed to sample containing 4.5 wt% TiO2. Microstructural observations showed that the stresses caused by the difference in the thermal expansion coefficients of SiC and TiC, the formation of micro-cracks, the occurrence of crack deflection and crack branching mechanisms, as well as grain pull-out were the main reasons for the improvements in indentation fracture resistance.

Phase assemblage and properties of a nonoxide composite fabricated by a two-step gas-pressure sintering

In this work, a composite composed of [Formula: see text]-Sialon (Z[Formula: see text]=[Formula: see text]4) and ZrN has been fabricated by a two-step gas-pressure sintering method, and the effects of ZrN content and applied pressure on the phase behavior, densification and mechanical properties have been investigated. The phase behaviors were mainly dependent on the ZrN content and the applied pressure. The composites composed of [Formula: see text]-Sialon (Z[Formula: see text]=[Formula: see text]4), ZrN, 15R-Sialon (0.4 MPa) and 12H-Sialon (0.7 MPa) as major phases, with different intermediate phases depending on the ZrN content. It is revealed that with the two-step sintering technique, a higher applied gas pressure has a positive effect on mass loss, and significantly improved the mechanical properties. The addition of ZrN particles greatly helped the densification behavior, reduced the mass loss, and increased fracture toughness of the composites, but decreased hardness due to formation of intermediate phases and grain coarsening. The addition of ZrN increased the fracture toughness due to the toughening mechanisms of crack branching, crack deflection and crack bridging.

Erosion resistance and toughening mechanism of AlBO and BNw whiskers modified thermal barrier coatings

In order to improve the erosion resistance and toughness of thermal barrier coatings, YSZ coatings, 20 vol%-AlBOw whisker modified YSZ coatings and 20 vol%-BNw whisker modified YSZ coatings were prepared by plasma spraying. The cross-section structure, morphology, composition and phase composition of coatings and powders were analyzed by SEM, EDS and XRD. The erosion resistance of three coatings was tested by self-made erosion tester. The crack growth resistance of coatings was tested and calculated by Vickers hardness tester. The results show that the density of the coating is improved by adding AlBOw and BNw. The whisker inhibits the crack propagation through the mechanisms of crack deflection, whisker pull-out and whisker bridging. The addition of whisker improves the erosion resistance of YSZ coating by 8.17% and 13.94%, which can effectively improve the service life of thermal barrier coating.

Handling and protecting your flexible ureteroscope: how to maximise scope usage.

Flexible ureteroscopy is an important therapeutic and diagnostic procedure and has seen rapid rise in its utilisation in recent years. There have been numerous developments in flexible ureteroscope (fURS) technology but scope fragility, and the associated high maintenance costs, remains a concern. A comprehensive Medline search for related publications from the last 20 years was undertaken to identify common causes of fURS damage and ascertain practices to minimise this. Flexible ureteroscopy can be due to intraoperative causes (loss of the deflection mechanism, damage to the working channel due and fibreoptic bundle injury) and non-operative damage which occur during cleaning, sterilisation and handling of the fURS. The review summarises the available literature to help highlight common mechanisms of scope damage, and outlines evidence-based measures to reduce the risk of damage and maximise durability. Scope fragility remains a problem with significant associated cost implications. In a culture of rising fURS use and reducing re-imbursement for endourologists, prolonging the longevity of the fURS is imperative for maintaining profitability. There are simple and inexpensive practices which can be immediately adopted to maximise fURS use and reduce the need for repairs.

Sources of Microtemporal Clustering in Sociolinguistic Sequences.

Persistence is the tendency of speakers to repeat the choice of sociolinguistic variant they have recently made in conversational speech. A longstanding debate is whether this tendency toward repetitiveness reflects the direct influence of one outcome on the next instance of the variable, which I call sequential dependence, or the shared influence of shifting contextual factors on proximal instances of the variable, which I call baseline deflection. I propose that these distinct types of clustering make different predictions for sequences of variable observations that are longer than the typical prime-target pairs of typical corpus persistence studies. In corpus ING data from conversational speech, I show that there are two effects to be accounted for: an effect of how many times the /ing/ variant occurs in the 2, 3, or 4-token sequence prior to the target (regardless of order), and an effect of whether the immediately prior (1-back) token was /ing/. I then build a series of simulations involving Bernoulli trials at sequences of different probabilities that incorporate either a sequential dependence mechanism, a baseline deflection mechanism, or both. I argue that the model incorporating both baseline deflection and sequential dependence is best able to produce simulated data that shares the relevant properties of the corpus data, which is an encouraging outcome because we have independent reasons to expect both baseline deflection and sequential dependence to exist. I conclude that this exploratory analysis of longer sociolinguistic sequences reflects a promising direction for future research on the mechanisms involved in the production of sociolinguistic variation.

Numerical Simulation on Deflecting Hydraulic Fracture with Refracturing Using Extended Finite Element Method

Refracturing is a key technology in enhancing the conductivity of fractures from hydraulically-fractured wells. However, the deflecting mechanism of the diverting fracture is still unclear. In this paper, a fully coupled seepage-stress model based on the extended finite element method (XFEM) was developed to realize the deflection mechanism of the refracturing fractures. The modified construction of refracturing was then verified by laboratory experiments. Furthermore, two new deflection angles considering the influence area along initial fracture length were introduced to evaluate the refracturing. The numerical results demonstrated that: (1) lower stress difference, larger perforation angle and longer perforation depth can lead to a higher deflection angle, thereby a more curving propagation path of the diverting fracture; (2) increasing injection rate or fluid viscosity can significantly enhance the diverting behavior; and (3) an initial location near the root of the initial fracture results in a larger value of the deflection angle, which is preferred for far-field refracturing. The conclusions in this study can be a systematic guide for the parameter optimization in refracturing treatment.

(SiC-Si3N4)w/SiBCN composite ceramics with tunable electromagnetic properties

In this study, composite ceramics with tunable electromagnetic properties were developed based on SiC-Si3N4 hybrids. First, SiC-Si3N4 whisker preforms with various SiC whisker (SiCw) concentrations were prepared by the nitridation of Si in SiCw-Si powder compacts. The in-situ-grown Si3N4 whiskers (Si3N4w) were dispersed uniformly in the voids inside the interconnected network formed by SiCw. The whisker reinforcements effectively toughened the SiBCN matrix through interface debonding, crack deflection and whisker pullout mechanisms. The electromagnetic properties of the composite ceramics can be tuned by adjusting the composition of (SiC-Si3N4)w preforms. The composite ceramic with 31.9 vol% SiCw exhibited the broadest effective absorption bandwidth (EAB) of 2.9 GHz in X band. Furthermore, a multilayer radar absorbing structure (RAS) composed of ceramic composites with gradient electromagnetic parameters was constructed to further improve the absorption properties. By adjusting the structure of the RAS, the resulting EAB of the RAS covered the entire X band.

Fabrication of halloysite nanotubes/reduced graphene oxide hybrids for epoxy composites with improved thermal and mechanical properties

Halloysite nanotubes-reduced graphene oxide hybrids (HRGO), prepared by simultaneous reduction and hybridization of graphene oxide with halloysite nanotubes, were incorporated in epoxy resin to improve the thermal and mechanical properties. The presence of HNTs effectively prevented the aggregation of RGO sheets in epoxy matrix. The thermal stability and thermal conductivity of HRGO/epoxy composites were enhanced. The epoxy composites with the addition of HRGO exhibited significant enhancements of tensile strength, storage modulus and fracture toughness. The improved dispersion of HRGO in epoxy matrix resulted in the better interfacial load transfer efficiency. The improvement in fracture toughness was disclosed of crack deflection and crack pinning mechanisms.

Analysis of strengthening and toughening mechanisms of bioinspired mineral bridges on hot-pressed alumina-based ceramics through finite element method

Bioinspired intergranular mineral bridges were fabricated in alumina-based ceramics through in situ synthesis of Al2TiO5 whiskers. The effects of mineral bridges on the mechanical properties of ceramics were investigated. Results showed that the flexural strength and fracture toughness of the alumina-based ceramics increased by 33.97% and 33.52%, respectively, after introducing the mineral bridges under hot pressing. Moreover, the effects of the mineral bridges on the crack tip stress (CTS) of models were calculated by finite element method for the first time. The mineral bridge buds and mineral bridges reduced the CTS by 15.54% and 22.22%, respectively. This finding revealed the root cause of the crack deflection mechanism of the mineral bridges and directly confirmed their strengthening and toughening effects.

Processing, microstructure and mechanical properties of HfB2-ZrB2-SiC composites: Effect of B4C and carbon nanotube reinforcements

The fully dense HfB2-ZrB2-SiC composites were processed using spark plasma sintering (SPS) at 1850 °C. The effect of reinforcements (B4C and CNT) on the densification as well as mechanical properties were investigated and compared (with monolithic) in the present study. The study showed that the addition of B4C and CNT were not only beneficial for the densification but also towards enhancing the mechanical properties (hardness, elastic modulus, and fracture toughness) of HfB2-ZrB2-SiC composites. The augmentation in the mechanical properties establish the synergy between solid solution formation (with the equimolar composition of HfB2/ZrB2) and the reinforcements (SiC, B4C, and CNT). The highest increase in the indentation fracture toughness with the reinforcements of B4C as well as CNT is >3 times (~13.8 MPam0.5 when it is 3–4 MPam0.5 for monolithic ZrB2/HfB2) on HfB2-ZrB2-SiC composites, which is attributed to the crack deflection and pull-out mechanisms. An increase in the analytically quantified interfacial compressive residual stresses in the composites during SPS processing with the synergistic addition of reinforcements (SiC, B4C, and CNT) and its effect on the indentation fracture toughness has also been addressed.

Wake impact on aerodynamic characteristics of horizontal axis wind turbine under yawed flow conditions

Wind turbines spend most of time in complex and unsteady environment, such as yawed flow, atmospheric wind turbulence, wind shear, and gust. Under yawed flow condition, velocity component parallel to the rotating plane causes a development of skewed wake structure, thus leading to an azimuthal variation in the aerodynamic loads on wind turbine blades. Moreover, the trailing and shed wake vortices unequally expand, and a strong wake interaction between the hub and tip vortices, and the asymmetrical velocity deficit around the rotor area occur. In the present study, the impacts of the skewed wake on the unsteady aerodynamic behavior around rotor blade were numerically investigated and a wake deflection mechanism was discussed in detail. For this purpose, the nonlinear vortex lattice method (NVLM) coupling with a time-accurate vortex particle method (VPM) was used. A numerical simulation on the NREL Phase VI wind turbine model, exposed to a low wind speed with different yaw angles, was carried out and predicted results were compared against measurements. Comparison results showed that the aerodynamic loads can be accurately calculated, even for highly yawed flow conditions and complex wake dynamics can be clearly observed.

Deflection Mechanism and Treatment Technology of Permanent Derrick of Freeze Sinking on Deep Alluvium

Aiming at the problems of deflection and operation safety of permanent derrick of freeze sinking shafts, the mechanism analysis of uneven settling of the derrick foundations in frost‐thawed soil was conducted. In addition, research on ground stabilization and derrick deviation rectification technologies was also studied in this paper based on the engineering practice of derrick of auxiliary shaft in the Dingji Coal Mine. Firstly, since the soil texture and artificial freeze temperature field are uneven, the bearing capacity and compression modulus of soil mass decrease after freeze thawing, resulting in uneven settlement of the foundation soil of the derrick footing and causing the deflection of the derrick. The finite element numerical analysis indicates that, in the event of uneven settling, the greatest tensile stress in the derrick structure of Dingji auxiliary shaft increased by 39.83% and the largest pressure stress increased by 33.33%. Secondly, this study used sleeve valve pipe single‐fluid static pressure grouting technology to reinforce the foundation of the derrick footing. The reinforced depth of grouting is 32 m, and every derrick foundation has adopted three circles of grouting holes for grouting reinforcement. Meanwhile, the hydraulic synchronous jacking system was used to rectify the deviation of the derrick, restoring the centre line of derrick ascension to the original design state. Finally, the practice of grouting, foundation consolidation, and derrick deviation rectification projects of the Dingji auxiliary shaft suggest that, after grouting reinforcement, the rate of foundation settlement is gradually decreased and tends to be stable. This has resulted in uniform settlement, and through four basic jacking, the deflection of the derrick has been corrected to its initial design state.

Fracture toughness and R-curve behavior of laminated ZrB2–SiC/SiCw ceramic

Laminated ZrB2–SiC/SiCw (LZSw) was prepared via tap-casting and hot-pressing processes. The R-curve behavior of the ceramic materials was evaluated using indentation-strength method. The flexural strength and fracture toughness values of the materials were found to reach up to 607 MPa and 14.5 MPa·m1/2, respectively, when employing SiC whiskers as a strong interface. The indentation strength was observed to decrease upon an increase in the indentation load, and compared with the steep decreasing trend exhibited by the monolithic ZrB2–SiC (ZS20), LZSw showed a slow decreasing trend. LZSw showed a distinct upward trend in its R-curve, which was found to be dependent on the indentation collapse caused by its laminated structure and the increasing crack propagation path as a result of crack deflection and branching mechanisms.

Experimental investigation of flapping mechanism of the black-headed gull in forward flight

Many developments in aerospace science have originated from nature. One of these developments has been obtained through inspirations from flying locomotion. The aim of this study is to simulate the flapping mechanism of the black-headed gull in forward flight. The wing of the black-headed gull is characterized entirely by complex dihedral, dividing the wing into two distinct parts. Hence, a flapping mechanism with different bending deflection angles is constructed and compared with a primitive flapping mechanism. Firstly, parametric studies are conducted to assess the role of flapping frequency, velocity and bending deflection angle on the lift, thrust and power loading of the membrane flexible wing at 10 ° angle of attack. Secondly, dimensional analysis is used to establish the similarity between the real gull and the constructed mechanism. Superiority of the bending deflection mechanism is concluded in forward flight against simple flapping wing in terms of aerodynamic forces as well as power loading parameter. It is found that although the aerodynamic coefficients decrease with increase in advance ratio, the best power loading of the black-headed gull is obtained between advance ratio of 2 and 3, in the gull's aerodynamically quasi-steady regime.