Flexible Barrier Research Articles

Load-attenuation mechanisms of flexible barrier subjected to bouldery debris flow impact

The impulse load of boulders at the front of debris flows is critical to the design of structural defense measures, which are commonly constructed on hillsides to mitigate landslide risk. Field evidences have demonstrated the capability of some steel flexible barriers in intercepting debris flows with bouldery inclusions. However, there is still a lack of fundamental understanding of the load-attenuation mechanisms of flexible barriers, especially under bouldery debris flow impact. In this study, systematic tests of mono-disperse and bi-disperse bouldery flows impacting an instrumented flexible barrier were conducted using a geotechnical centrifuge. The impact kinematics and barrier responses, such as mobilized structural forces and elongation of cables, were recorded synchronously. The results reveal that the load-attenuation mechanism of flexible barriers for the frontal impact originates from the barrier deflections and extended interaction duration. Only 30% of the frontal momentum is transferred to the flexible barrier. The performance of the flexible barrier is compared with that of a rigid barrier model under identical testing conditions. It is found that the boulder impulse loads on flexible barrier are significantly attenuated, resulting in a “plateau” pattern of the impact time history. The practical implication is that the design of flexible barriers may not demand separate considerations of the bulk debris and individual boulder impact loads. Detailed examination of the state of debris deposited behind the flexible barrier indicates that the static dry debris is close to the active failure state due to the large barrier deflection.

Stress analysis of ore particle flow behaviour under the influence of a flexible barrier

Additional stresses caused by a flexible barrier, drawpoints and the self-weight of ore particles were investigated based on a physical experiment of the shrinkage stoping method of synchronous filling, and the flow behaviour of ore particles is described by the component forces. This study shows that when ore particles are drawn from multiple drawpoints under the influence of a flexible barrier, the stress distribution of the ore particles is sinusoidal, with an amplitude that gradually decreases with increasing height. The values of σx and σy gradually decrease with increasing height; the maximum σy values occur at x = 0, the maximum σx values occur at x = ± 10 and the maximum shear stresses occur near the lateral walls. The shape of the draw column is determined by the additional vertical stress, and its contour determines the essential morphology of the drawbody. The surface of the ore particles is smoothed by the additional stress caused by the barrier, and the self-weight of the ore particles is the inherent cause of the additional stress.

Circular steel tubes filled with rubberised concrete under combined loading

The research on rubberised concrete (RuC) could promote the recycling of end-of-life tyres and reduce natural resource extraction. To mitigate the greatly reduced compressive strength and fully utilise the desirable characteristics such as improved ductility and energy absorption of RuC, confinement through a steel outer tube could be adopted. This paper investigated the effect of using circular steel tube as confinement of the RuC under axial, flexural and combined loading conditions. A total of 4 circular hollow tube sections with d/t (depth/thickness) ranging from 18 to 36 was used in this study. Three rubber replacement ratios (0%, 15%, 30%) by mass of the total aggregates were examined, along with 4 load eccentricities (0, 0.25d, 0.5d and bending) used to construct the interaction diagrams. As a result of the steel confinement, the difference in load capacity between RuC and normal concrete significantly reduced compared to the plain concretes. Additionally, RuC filled steel tube (RuCFST) members were more ductile than their normal concrete counterparts. The circular cross-section showed superior load carrying capacities compared to the square sections, due to a relatively uniform stress distribution in the cross-section. The interaction diagrams of RuCFST members could be reasonably predicted in terms of accuracy and safety of design. The tested moment capacity of RuCFST also greatly exceed the predicted values. This study has demonstrated the possibility of using RuCFST in applications where high energy absorption and ductility capacities were sought, for example, the structural members in seismic regions and flexible roadside barriers.

New Simple Method for Calculating Impact Force on Flexible Barrier Considering Partial Muddy Debris Flow Passing Through

AbstractFlexible barriers trap large particles and boulders in debris flow but allow slurry and small particles to pass through. Field tests and real cases indicate that a certain amount of slurry ...

Debris flow impact on flexible barrier: effects of debris-barrier stiffness and flow aspect ratio

Conventionally, flexible barriers are rated based on their ability to resist a free-falling boulder with a particular input energy. However, there is still no well-accepted approach for evaluating performance of flexible barrier under debris flow impact. In this study, a large-nonlinear finite-element model was used to back-analyze centrifuge tests to discern the effects of impact material type, barrier stiffness, and flow aspect ratio (flow height to flow length) on the reaction force between the impacting medium and flexible barrier. Results show that, in contrast to flexible barriers for resisting rockfall, the normal impact force induced by the highly frictional and viscous debris is insensitive to barrier stiffness. This is because the elongated distributions of kinetic energy are mainly dissipated by the internal and boundary shearing, and only a small portion is forwarded to the barrier. Furthermore, a new stiffness number is proposed to characterize the equivalent stiffness between a debris flow or a boulder, and a flexible barrier. Under the circumstance of an extremely elongated debris flow event, i.e., low aspect ratio, the load on a barrier is dominated by the static component and thus not sensitive to the barrier stiffness.

Generating Enhanced Interfaces between Micro-Patterned Lithium Electrodes and Solid Polymer Electrolytes

Lithium is a very promising anode material for the next generation of rechargeable batteries. The research on such battery systems is motivated especially by the high theoretical specific capacity (3860 mAh/g) and the low density (0.53 g/cm³), which qualifies lithium particularly also for portable devices. Furthermore, this metal features the lowest negative electrode potential (-3.04 V vs. SHE), which enables a high cell voltage and high specific energy, respectively.[1-2] Nevertheless, there are also some challenges, like the inhomogeneous deposition of lithium metal during cycling leading to high surface area lithium (HSAL). Such deposits can be dendritic or needle-like and can easily penetrate the separator inducing short circuits and local heating, which in the end can lead to fires or even explosions.[1-3] To counteract the safety issue of HSAL, many different approaches were studied which should lead to a more homogeneous deposition of lithium.[4-7] One of them are solid polymer electrolytes (SPEs). They have the benefits to be very thermally and electrochemically stable, their exothermal decomposition kinetics are slow and they generate a flexible and dense barrier between the electrodes. Furthermore, the less volatility of the components of SPEs leads to a lower risk of explosion and toxication, which represent disadvantages of liquid organic electrolytes.[3-5] Another approach is the mechanical modification of lithium electrodes with micro patterning to increase the electrode surface, which leads to a lower current density resulting in a reduced formation of HSAL. Moreover, HSAL shows the tendency to deposit first at the walls of the defects before it later on grows on the remaining surface. For this reason, the dendritic growth towards the counter electrode is delayed and thereby the risk of short circuits is decreased.[2, 6-7] In this work, the focus lies on the combination of these two approaches. Herein, we will present a new way to combine SPEs with modified lithium electrodes by an advanced coating method. The wetting of the micro patterned lithium surface by the SPE and the directed lithium deposition in the defects are verified by SEM analysis and the electrochemical properties are investigated on the basis of constant current cycling and impedance experiments. [1] K. Zhang, et al., Adv. Energy Mater. 2016, 6, 1600811. [2] P. Schmitz, et al., Phys. Chem. Chem. Phys. 2017, 19, 19178-19187. [3] M. Joost, et al., Electrochim. Acta, 2013, 113, 181-185. [4] Q. Pan, et al., Adv. Mater. 2015, 27, 5995-6001. [5] J. Paulsdorf, et al., Solid State Ion . 2002, 169, 25-33. [6] M.-H. Ryou, et al., Adv. Funct. Mater. 2015, 25, 834-841. [7] J. Park, et al., Adv. Mater. Interfaces 2016, 3, 1600140.

Effects of surface pretreatment and deposition conditions on the gas permeation properties and flexibility of Al2O3 films on polymer substrates by atomic layer deposition

The effects of surface pretreatment and deposition conditions on the gas permeation properties—including permeability of He, O2, and H2O; the size; and the density of permeation-enhancing defects—and mechanical flexibility of Al2O3 films on polymer substrates by atomic layer deposition (ALD) were investigated to develop flexible gas barrier films for organic and flexible electronics. Pretreating polyimide (PI) and poly(ethylene terephthalate) (PET) substrates with an aqueous KOH solution greatly lowered the gas permeability of the ALD Al2O3 films as a result of improved affinity between the substrate surface and the ALD precursors. Varying the ALD conditions—including lengthening the precursor exposure, elevating the deposition temperature, and changing the precursor sequence—enhanced physisorption of ALD precursors on the polymer substrate, which improved nucleation of the ALD films to reduce defects in the films and lower their gas permeability. Activation energy for permeation determined from the temperature dependence of the permeability of the ALD films indicated that the ALD films deposited under the optimized condition contained smaller and few permeation-enhancing defects. The optimized ALD films possessed a low water vapor transmission rate of ~ 10−6 g/m2 day that met the stringent requirement of organic and flexible electronics, while also exhibiting excellent mechanical flexibility by withstanding repeated bending with small increases in gas permeability. Our results provide valuable insights into the development of flexible barrier thin films for the encapsulation of organic and flexible electronics.

Toward a Generic Computational Approach for Flexible Rockfall Barrier Modeling

Flexible rockfall barriers are protection structures used to mitigate rockfall hazards in mountainous areas. The complex nonlinear mechanical behavior of these structures under impacts requires powerful modeling tools to perform structural analysis. In this article, a generic computational approach to rockfall barriers analysis is introduced. First, the generic formulation and numerical implementation in the GENEROCK software are detailed. Then, two barrier models are considered and validated against experimental full-scale tests on two different technologies. This numerical investigation permits insightful numerical investigation of the barriers’ behavior. Exploratory numerical simulations are eventually performed to highlight the strengths and generality of the proposed approach. The influence of the curtain effect modeling in simulation results is presented. The effects of repeated impacts on rockfall barriers are investigated and present new insight into barrier behavior and management practices. Stochastic modeling methods are also used to study the propagation of uncertainty and variability of the structure itself in its dynamic response.

Load model for designing flexible steel barriers for debris flow mitigation

Light-weight flexible steel net barriers catch coarse debris, but let some of the fine material and water pass through the net. They are difficult to design so that they can withstand the impact pressures of both boulder-laden granular and water-saturated debris flows. Using results from laboratory and full-scale field tests, a debris flow load model has been developed for flexible barriers in torrent channels. The model accounts for the forces of initial impact as well as the filling process discretized stepwise over time (barriers in the field and laboratory fill continuously). Laboratory tests with fast debris flow front velocities revealed a run-up behaviour that was not observed in the field (“pile-up”). The load model divides the flow forces into a hydrostatic component and a dynamic part depending on a pressure coefficient, the flow velocity, and the density of the flow. This dynamic part, which is more complex to quantify, accounts for the wide-ranging debris flow characteristics from watery and muddy debris floods to granular friction-dominated mass flows.

Quantitative analysis of debris-flow flexible barrier capacity from momentum and energy perspectives

In-depth understanding of debris-structure interaction is hindered by a lack of physical data of debris flow impacting structures. This study reports a set of centrifuge experiments investigating the impact load exerted by debris flow on rigid and flexible barriers. A combination of high-speed imagery and load-displacement sensors enabled a comprehensive grasp of the impact details, including flow depth, velocity, impact pressure, bending moment, and cable force-elongation of flexible barrier. Test results reveal that the debris-structure interaction plays a major role in the energy dissipation and impact load reconstruction. The built-up of static load behind the barrier occurs simultaneously with the grow-up of impact force. As a result, the momentum flux of incoming flow is not merely a surrogate of the impact force. A quantitative analysis from the energy perspective has been conducted. Under the experimental conditions of this study, debris flow impact results in over 90% of debris energy dissipated through the internal and boundary shearing, leaving <10% absorbed by the flexible barrier. Findings from the energy and momentum perspectives could facilitate the optimization of flexible barriers in mitigation of debris flow hazards.

Numerical Simulation of Ore Particle Flow Behaviour through a Single Drawpoint under the Influence of a Flexible Barrier

A model of the mass draw and synchronous filling no-top-pillar shrinkage stoping method was created based on the particle element theory and PFC2D software. A numerical simulation of the ore particle flow behaviour through a single drawpoint under the influence of a flexible barrier was performed; following which, a visualization of the change process in the marked layers, draw column, flexible barrier, and cavity was obtained. Finally, the results demonstrated the following. (1) Before the ore particles at the highest horizon were drawn, the morphology of the draw column had an ellipsoidal (whole, closed, and approximate) shape, but after the ore particles were drawn, the morphology of the draw column had a gyroscopic shape (i.e., the shape of a spinning top). (2) The height of the draw column increased rapidly and exponentially in the early period of the draw, presented a linear growth tendency during the medium period with an increase in the accumulated mass drawn, and remained at a certain value in the later period. (3) The morphology of the flexible barrier presented a Gaussian distribution on the whole, but its bottom had an analogous parabola morphology, particularly in the late stage. (4) The cavity began to form with the ore particles at the highest horizon drawn; the cavity development presented an evolutionary process from the microscopic to macroscopic regime, and the morphology of the cavity was crescent in the early stage and triangular in the late stage.

Bio-inspired cellulose nanofiber-reinforced soy protein resin adhesives with dopamine-induced codeposition of “water-resistant” interphases

Poor interface strength and water resistance are significant challenges in taking full advantage of the excellent performances of natural fiber-reinforced biopolymer composites. Herein, a mussel-inspired co-deposition process was developed to synthesize a nanostructured layer on the surface of cellulose nanofiber (CNF) with target water-resistant property and high adhesion strength of soy protein isolate (SPI)/CNF composite adhesives. Renewable resource cardanol was selected as an environmentally sustainable interphase constituent. First, hydrolyzable alkoxy silane cardanol (ASC) was synthesized via an epoxide ring opening reaction of the cardanol-based glycidyl ether with aminopropyltriethoxysilane. When assembled on the CNFs, the ASC/dopamine system conformally coated every fiber, yielding a nanostructured polydopamine (pDA)/ASC hybrid coating that subsequently acted as the resin/fiber interphases during the adhesive preparation. The nanohybrid coatings contained versatile catechol functional groups as “bonding sites” and long aliphatic chains as a “flexible barrier”. The integrated advantages of the CNF network and the “bonding site and flexible barrier” structures on the outside surface contributed to the strong cohesive interaction between the soy protein and nanofibers, and hence the reactive water-resistant barrier was formed between the two substrates. Thanks to the tailored interphase, the resins achieved impressive adhesion properties with a wet shear strength up to 1.27 MPa, which was 189% and 95% higher than that of the neat resin and the adhesive prepared with pristine fibers, respectively. The findings demonstrate that the sustainable cardanol holds potential for the development of water-resistant biobased composites.

Flexible β‐Ga2O3 Nanomembrane Schottky Barrier Diodes

AbstractHere, high power flexible Schottky barrier diodes (SBDs) are demonstrated on a plastic substrate using single crystalline β‐Ga2O3 nanomembranes (NMs). In order to realize flexible high power β‐Ga2O3 SBDs, sub‐micron thick freestanding β‐Ga2O3 NMs are created from a bulk β‐Ga2O3 substrate and transfer‐printed onto the plastic substrate via a microtransfer printing method. It is revealed that the material property of β‐Ga2O3 NMs such as crystal structure, electron affinity, and bandgap remains unchanged compared with its bulk properties. Flexible β‐Ga2O3 SBDs exhibit the record high critical breakdown field strength (Ec) of 1.2 MV cm−1 in the flat condition and 1.07 MV cm−1 of Ec under the bending condition. Overall, flexible β‐Ga2O3 SBDs offer great promise for future flexible energy convergence systems and are expected to provide a much larger and more versatile platform to address a broader range of high‐performance flexible applications.

Nonlinear Numerical Modeling of the Wire‐Ring Net for Flexible Barriers

To investigate the nonlinear mechanical behavior of the wire‐ring net, this paper presents a new numerical model that can collectively consider equivalence between numerical and actual wire rings. Quasi‐static tests, including tensile tests on steel wires and one‐ring specimens, and puncturing tests on net specimens were conducted. Based on the test results, the axial constitutive curves of steel wires were obtained. The linear correlation equations for the breaking loads of the one‐ring specimens and the puncturing strength of wire‐ring nets were established, both of which were related to the number of windings. The wire rings were modeled via an equivalent structure with a single winding and a circular cross section. Equivalence between the numerical and actual wire rings in terms of bending and tensile strength, total mass, contact with sliding friction, and rupture behavior were also derived and presented. In particular, the emphasis was on simulating the flattening effect, a phenomenon rarely accounted for in conventional numerical models. All dominant factors were reflected in a model with the material law by the input of material parameters. The proposed mechanical model was calibrated and verified by the data from the tests of the wire‐ring net. The calibrated mechanical model is also shown to successfully simulate a full‐scale test of a flexible rockfall protection barrier according to the ETAG027 standard.

Optical calcium test for measurement of multiple permeation pathways in flexible organic optoelectronic encapsulation.

Organic photovoltaic (OPV) devices and other organic electronics have the promise to provide lightweight, flexible alternatives to traditional rigid semiconductor technologies. However, organic electronics often degrade rapidly upon exposure to oxygen, water, light, and combinations thereof, as well as upon exposure to elevated temperatures. This requires the use of high gas barrier packaging in order for devices to have operational lifetimes on the order of years. To meet the challenge of transparent high gas barrier materials which maintain the flexibility of organic optoelectronics, many different materials and encapsulation schemes have been developed including the lamination of devices between flexible multi-layer barrier films. Because of their excellent barrier properties, these materials often require specialized testing for permeation measurements which evaluate materials independently. In this work, we demonstrate the use of an optical calcium test, which uses a sample geometry that closely mimics an OPV device, to evaluate a complete encapsulation scheme and to elucidate the relative importance of different permeation pathways. Using an encapsulation scheme of laminating a device between two multi-layer barrier films using an adhesive, measurements were made for water vapor permeation through the barrier film, the bulk adhesive, and along the adhesive-to-barrier film interface. The results show that the combined lateral permeation, including through the bulk adhesive and along the adhesive-to-barrier film interface, can constitute over 50% of the total permeation for small devices (4.5 cm × 4.5 cm). The adhesive-to-barrier film interface was also found to be a very important pathway as it was deemed responsible for more permeation than the bulk adhesive. The technique was also used to evaluate encapsulation design variables such as the effects of adhesive thickness and surface treatments on the lateral water permeation. We demonstrate that decreasing the adhesive thickness leads to a decrease in the lateral water permeation.

High barrier performance of the multilayer film based on epoxy and montmorillonite

A flexible organic device needs a protective encapsulating layer to resist degradation of the device due to environmental oxygen and moisture. The performance of organic devices degrades with time due to a self-process of delamination and oxide formation of the cathode by environmental oxygen and moisture for electrochemical processes. Here, a flexible multilayer barrier film, which is a sandwiched composite layer with organic layers, has been fabricated in an inexpensive way under atmospheric conditions using an applicator on PET substrate. An organic layer (POL) consists of bisphenol A-type phenoxy resin and epoxy resin. For the middle composite layer (MMT), a composite with montmorillonite has been used as an interactive barrier. The multilayer film with ball-milled montmorillonite 2% composite layer shows lower moisture permeation rate of 2.850 × 10−2 gm−2day-1 than only POL on PET substrate. Fabrication of flexible multilayer barrier film from solution has promising industrial prospects due to facile processing at low temperatures.

Studies on flexible rockfall barriers for failure modes, mechanisms and design strategies: a case study of Western China

A field investigation on the actual protective performance of a flexible rockfall barrier along a mountain road in western China is presented in this paper. The total area of the flexible rockfall barrier under investigation was approximately 20,000 m2. Five typical failure modes of the flexible rockfall barrier were revealed, including steel post buckling, connection failure, ring net destruction, steel cable rope breakage and anchorage point failure. In addition, component rusting, which leads to decrease in durability, was noted. Furthermore, failure mechanisms were analysed, and the main factors that were found to induce flexible rockfall barrier failure included the sliding capacity of the cable ropes at the end post support positions, the boundary conditions of the steel posts and the compatibility between the energy dissipating devices and connected cable ropes. From these observations, corresponding design strategies were proposed. In addition, an improved flexible rockfall barrier system was constructed, and its effectiveness was verified by a full-scale impact test using 5000 kJ of impact energy. Finally, the impact deflection, impact force, cable force and energy dissipation of the improved flexible rockfall barrier system were studied in combination with a non-linear numerical simulation which could be a useful tool for design of flexible barrier systems.

Highly Reliable Liquid Metal–Solid Metal Contacts with a Corrugated Single‐Walled Carbon Nanotube Diffusion Barrier for Stretchable Electronics

AbstractLiquid metals (LMs) are a special case of metals that exist in a liquid at room temperature, making them one of the most attractive conductive materials in stretchable electronics. In many cases, however, the LM attacks other metals in contact with the LM through penetration, embrittlement, and alloying. To address these critical issues, there have been efforts to introduce robust barriers, which can preserve the underlying metals without degradation. For example, graphene is employed as a flexible barrier owing to its chemical inertness and impermeability. Nevertheless, this material is difficult to utilize in stretchable electronics because its defects result in inevitable fracture, even at a low strain (&lt; 6%). In addition, it is a challenge to pattern the graphene layer on the point‐of‐interest area in a facile manner. Herein, it is shown that the insertion of single‐walled carbon nanotubes (SWCNTs) at the liquid metal–solid metal interface provides a proper barrier for LM under large deformation conditions. A tangled 1D structure of the SWCNTs formed from a solution process greatly suppresses the crack generation/propagation and maintains conductivity even under large strains, which facilitates the use of SWCNTs as stretchable barriers with long‐term reliability through the introduction of a corrugated structure.

Large-scale physical modelling study of a flexible barrier under the impact of granular flows

Abstract. Flexible barriers are being increasingly applied to mitigate the danger of debris flows. However, how barriers can be better designed to withstand the impact loads of debris flows is still an open question in natural hazard engineering. Here we report an improved large-scale physical modelling device and the results of two consecutive large-scale granular flow tests using this device to study how flexible barriers react under the impact of granular flows. In the study, the impact force directly on the flexible barrier and the impact force transferred to the supporting structures are measured, calculated, and compared. Based on the comparison, the impact loading attenuated by the flexible barrier is quantified. The hydro-dynamic approaches with different dynamic coefficients and the hydro-static approach are validated using the measured impact forces.

Large-scale physical modeling study on the interaction between rockfall and flexible barrier

Flexible barriers have been widely applied in rockfall mitigation in recent years. However, the behavior of flexible barriers under the impact of boulders is still not fully understood. To investigate the interaction between a flexible barrier and a falling boulder, a large-scale physical modeling device has been constructed at a site in Hong Kong. Using this device, large-scale impact tests using boulders with different diameters were conducted. Test results are presented and analyzed in this paper. The motion of the boulder during impact is traced and analyzed. The impact forces on the flexible ring net and the supporting structures are measured and compared. From the comparison, the impact reduction rates (IRR) of boulders with different diameters are calculated. Moreover, a simple approach for estimating the impact loading of a boulder on a flexible barrier is proposed in this study. This approach is calibrated and verified using measured impact forces in the tests.