Low-energy Impact Research Articles

Dynamic mechanical, ballistic and tribological behavior of luffa aegyptiaca fiber reinforced coco husk biochar epoxy composite

AbstractIn the current work, light weight epoxy bio‐composites are created for low‐cost technological applications using luffa aegyptiaca fiber and biochar particles derived from coco husk (CHB). This study aims to evaluate the effects of CHB particles added at different concentrations (3 vol% and 5 vol%) on the dynamic mechanical, ballistic and tribology behavior of epoxy composites constructed from luffa aegyptiaca fiber with different fiber loading (20%, 30% and 40 vol%). The composites are prepared using hand layup process provided with post curing operation. The combination of 3 vol% CHB particles and 40 vol% luffa aegyptiaca fiber having the improved viscoelastic properties by means of high storage modulus (5.05 GPa) and low loss factor (0.31). Moreover, this composite shows better ballistic properties in terms of low velocity impact energy (17.1 J). The optical image of impact damage behavior shows minimum damage of impactor on the composite and penetration effect found to be lower. This luffa aegyptiaca fiber reinforced epoxy composite also shows the lowest value of coefficient of friction (COF) with 0.48 and the lowest specific wear rate of 0.011 mm3/Nm. These epoxy composites made from luffa aegyptiaca fiber and CHB particles may be useful in a variety of engineering applications that can use materials for manufacture sporting goods, home furnishings, food packaging, and transportation.

Root cause of embrittlement of in-service exposed high pressure steam pipeline

A segment of tube cut off from the high pressure steam pipeline was subjected to routine basic material tests, which resulted in very low impact energy of the pipe material (low-alloyed Cr steel). A part of the segment (and a comparative non-operated sample) was then subjected to detailed mechanical tests (including creep), metallographic investigations and fractographic analyses with an aim to determine a root cause of the embrittlement. The results showed that grain boundaries of exposed steel are covered by particles of primary and secondary cementite. However, a matrix is weakened more, therefore a fracture of creep, tensile and impact specimens is always transgranular and the cleavage facets are limited to grain size, if present. Thus, the cause of embrittlement was determined not by a rapid ageing, but by an unsuitable initial heat treatment of the pipe material.

Nonlinear Lamb Wave Imaging for Low Energy Impact Damage of CFRP Laminates

Nonlinear Lamb Wave Imaging for Low Energy Impact Damage of CFRP Laminates

Sustainable Materials Based on Geopolymer-Polyvinyl Acetate Composites for Art and Design Applications.

The recent introduction of the Next Generation EU packages on the circular economy and the Italian Ecological Transition Plan has further boosted the research of effective routes to design materials with low energy and low environmental impact, in all areas of research, including art and design and cultural heritage. In this work, we describe for the first time the preparation and characterization of a new sustainable adhesive material to be used in the art and design sector, consisting of a geopolymer-based composite with polyvinyl acetate (PVAc), both considered more environmentally acceptable than the analogous inorganic or polymeric materials currently used in this sector. The key idea has been the development of organic-inorganic composites by reacting low molecular weight polymers with the geopolymer precursor to obtain a material with reduced brittleness and enhanced adhesion with common substrates. Structural, morphological, and mechanical studies pointed out the consistent microstructure of the composite materials if compared to the neat geopolymer, showing lower density (up to 15%), improved flexural strength (up to 30%), similar water absorption and a relevant toughening effect (up to 40%). Moreover, the easy pourability in complex shapes and the excellent adhesion of these materials to common substrates suggest their use as materials for restoration, rehabilitation of monuments, and decorative and architectural intervention. The organic-inorganic nature of these new materials also makes them easily recognizable from the support on which they are used, favoring, in line with the dictates of good restoration practices, their possible complete removal. For all these reasons, these new materials could represent promising candidates to overcome the limits related to the creative industry for what concerns the selection of environmentally friendly materials to meet design requirements with low environmental impacts.

Validation of a novel large animal intra-articular tibial plafond fracture model

BackgroundLarge animal fracture models that allow for anatomic fracture fixation are currently lacking. It was hypothesized that a compressed air impaction system can generate a reproducible tibial plafond fracture and be adjustable to create fractures consistent with high and low energy fractures seen in humans. MethodsPilot testing of the impaction system was done by impacting polyurethane foam blocks at varying compressed air pressures. A guillotine impaction test was performed on the same foam blocks to create an energy conversion. A total of 12 porcine hindlimb hindlimbs were subjected to low-energy (42.2 J) and high-energy (73.9 J) impact to create tibial plafond fractures. FindingsGuillotine impaction test demonstrated strong correlations between potential energy and foam block impaction depth (R2 = 0.99). Compressed air impaction system test strongly correlated with foam block impaction depth (R2 = 0.99). All six porcine hindlimbs in the low-energy group developed simple coronal split tibial plafond fractures. All six porcine hindlimbs in the high-energy group developed complex, multi-fragmentary tibial plafond fractures. InterpretationThis porcine fracture model created tibial plafond fracture patterns with similar fracture morphology as human patients without violation of the soft tissue structures or adjacent joints. This model would allow for anatomic fixation, the study of post-traumatic osteoarthritis, or the delivery of locally targeted therapeutics to the ankle joint.

Direct carbon dioxide-methane solid oxide fuel cells integrated for high-efficiency power generation with La0.75Sr0.25Cr0.5Fe0.4Ni0.1O3–δ-based dry reforming catalyst

Solid oxide fuel cell (SOFC) can directly convert carbon-based fuels to power with low environmental impact and high energy efficiency, while there is still one of the key challenges that carbon deposition over Ni-based cermet anodes causes serious performance degradation. Herein, a Ni-doped perovskite, La0.75Sr0.25Cr0.5Fe0.4Ni0.1O3–δ (LSCFN), is prepared to design exsolution systems and evaluated as the dry reforming catalyst for direct carbon dioxide-methane SOFCs. It is demonstrated that the reducing atmosphere in anode effectively induce the NiFe alloy nanoparticles exsolution from LSCFN, and provide abundant active sites for dry reforming. Anode supported single cells with LSCFN-Ce0.9Gd0.1O2–δ (LSCFN-GDC) composite reforming catalyst show excellent electrochemical performance in both H2 and CH4-CO2, and the peak power densities of 686.05 and 684.83 mW·cm−2 are obtained at 800 ℃, respectively. The dry reforming of 50 %CH4-50 %CO2 integrated with LSCFN-GDC reforming catalyst is sustained for 100 h stable performance at 700 ℃ without any degradation, which are further confined by the experimental verification and thermodynamic calculation. These results demonstrate that additional dry reforming catalyst is an effective strategy to effectively manipulate CH4-CO2 reforming and electrochemical performance for energy purposes.

On the time of well transition to industrial production mode

The purpose of the article wasanalysis of the reasons for the different velocity of transition of the "well-reservoir" system from one thermodynamic state to another based on experimental data on time and main energy parameters for the conditions of gas and oil and gas fields. The methods. Experimental determination of the transition time of wells to industrial production mode; and analysis of experimental data. Findings. The transition time of the "well-reservoir" system from one thermodynamic state to another is determined by the internal energy of the reservoir and depends on the energy of external influence and the determining parameters: reservoir pressure and temperature. For traditional reservoirs - collectors, including for reservoirs with low reservoir pressures, it is 104 - 107 s. For formations with high formation pressures, the forecast time for the transition of the well to the mode of industrial production or emergency release of formation fluid is 100 - 103 s. Theoriginality. The work shows that in the case of low-energy impact, structural changes in rocks in reservoir conditions occur under sublimit slow loads at the level of approximately 40...70% of the limit value of the dynamic strength of the reservoir rock. It is experimentally shown that the transition of the "well-reservoir" system from one thermodynamic state to another flows for a time that depends on the internal energy of the reservoir and it decreases from t=104 – 107 s to t=100 – 103 and from ln t = 9.3...14.8 to ln t = 0...6.9 in the case of an increase in the energy of external influence, or reservoir parameters - pressure and temperature. Practicalimplementation. The transition time of the "well-reservoir" system from one thermodynamic state to another is determined by the internal energy of the reservoir and depends on the energy of external influence and the determining parameters: reservoir pressure and temperature, as well as the energy of elastic or elastoplastic deformation of the rock. The practical value is the ability to determine the type of oil and gas deposit based on this parameter and choose equipment.

Low-velocity impact behavior of SWRH82B steel wires considering different section shapes based on experiments and simulations

SWRH82B steel wires are commonly used in suspended-cable structures, large-span structures, and cable-stayed bridges owing to their light weight, strong bearing capacity, and safe and reliable operation. In this study, the dynamic mechanical performance of SWRH82B steel wires under low-velocity impact was studied experimentally and numerically. A drop-hammer impact test system was adopted for the impact experiments, considering the influence of the specimen diameter, specimen span, indenter shape, and impact position. Two-section steel wires, including circular and Z-shaped wires, were investigated. The experimental results indicated that local denting deformation occurred at the impact position with a lower impact energy, and wire breakage occurred near the position of the clamping device with a larger impact energy. Circular wires were stronger and stiffer than Z-shaped wires of the same diameter because they can provide a higher impact resistance and stronger energy absorption capacity with a regular section shape. The experimental data indicated that the specimen diameter positively affects the impact bearing capacity, providing more flexural rigidity. However, the specimen span negatively influences the dynamic performance of both types of steel wires; a greater increase in peak load was observed when using a cylinder hammer. In addition, a finite element model was established to further analyze the failure modes and discuss a larger range of parameters. Finally, a numerical model of prestressed steel wires was developed using ABAQUS/EXPLICIT, with the results indicating that the prestress force could strengthen the impact resistance of steel wires at a lower level.

New Sensing and Radar Absorbing Laminate Combining Structural Damage Detection and Electromagnetic Wave Absorption Properties

Within the paradigm of smart mobility, the development of innovative materials aimed at improving resilience against structural failure in lightweight vehicles and electromagnetic interferences (EMI) due to wireless communications in guidance systems is of crucial relevance to improve safety, sustainability, and reliability in both aeronautical and automotive applications. In particular, the integration of intelligent structural health monitoring and electromagnetic (EM) shielding systems with radio frequency absorbing properties into a polymer composite laminate is still a challenge. In this paper, we present an innovative system consisting of a multi-layered thin panel which integrates nanostructured coatings to combine EM disturbance suppression and low-energy impact monitoring ability. Specifically, it is composed of a stack of dielectric and conductive layers constituting the sensing and EM-absorbing laminate (SEAL). The conductive layers are made of a polyurethane paint filled with graphene nanoplatelets (GNPs) at different concentrations to tailor the effective electrical conductivity and the functionality of the material. Basically, the panel includes a piezoresistive grid, obtained by selectively spraying onto mylar a low-conductive paint with 4.5 wt.% of GNPs and an EM-absorbing lossy sheet made of the same polyurethane paint but properly modified with a higher weight fraction (8 wt.%) of graphene. The responses of the grid's strain sensors were analyzed through quasi-static mechanical bending tests, whereas the absorbing properties were evaluated through free-space and waveguide-based measurement techniques in the X, Ku, K, and Ka bands. The experimental results were also validated by numerical simulations.

Effect of solidification end impact vibration on the internal quality of a continuous casting billet

ABSTRACT Application of vibration impact at the outer arc side of a billet with a central linear liquid fraction of 25% -35% at 9.5 m from the meniscus. The results show that the impact vibration with low frequency and high impact energy can not only reduce the central porosity degree of the billet from 1.532 to 1.169, but also compact the liquid core, improve the central porosity and promote the heterogeneous nucleation of the molten pool. High frequency and low impact energy can not only increase the proportion of mixed crystal zone by about 8 %, but also reduce the central carbon segregation index from 1.08 to 1.04. Meanwhile, the two kinds of impact vibrations increase the area ratio of the central carbon segregation index in the range of 0.95-1.05 from 56.32% to 70.26% and 80.17%, respectively, and uniform the central carbon distribution of the billet.

L-Shell Ionization Cross Sections for Silver by Low-Energy Electron Impacts

The L-subshell ionization cross sections and total L–X-ray production cross sections for the Ag atom by the electron impact near the ionization threshold were calculated with a classical-trajectory Monte Carlo method. The results were compared with experimental data, quantum mechanical calculations, and the cross sections by positron impact. It was demonstrated that the classical treatments are useful for electron–atom collisions at energies higher than about six times the binding energies of target electrons but overestimate L-shell ionization and L–X-ray production cross sections at low energies near the threshold. Possible reasons for this discrepancy are discussed.

Influence of impactor mass on the low energy impact response of thin GLARE plates

Even though the influence of impact energy on the low velocity impact of laminated plate is well reported, the influence of relative mass of the impactor has not been addressed extensively. This work investigates the effect of impactor mass relative to that of target and other associated factors like impactor velocity and the target plate size on the impact response of a GLARE plate. A 3 D finite element analysis incorporating Newmark-β method and Hertzian contact is used considering appropriate contact stiffness to evaluate the contact force. Results show that the impactor mass significantly influences the contact force and interfacial delamination.

Instrumentation and preliminary evaluation of a drop tower tester for low and medium impact energy

Soft, porous structures imbibed with liquids have good impact attenuation properties. Literature survey reveals a continuous need for new impact tests to assess impact response for the newly developed soft, porous materials. This paper presents a versatile drop tower tester which is based on an impactor that slides inside a transparent tube. The test rig is equipped with high-speed transducers (force and acceleration) and a laser system used to measure the deformation of the experimental cell. A high-speed camera records subtle details of the impact that are not are visible with the naked eye. Preliminary experiments made on dry and imbibed soft fibrous tridimensional textile have shown good repeatability during impact. The experiments presented validate the experimental procedure, based on the analysis of the contact force-displacement curve, acceleration, and impact force-transmitted force. The obtained results demonstrate that true impact response is described with high resolution.

Fibre–Wood Laminate Biocomposites: Seawater Immersion Effects on Flexural and Low Energy Impact Properties

The present paper explores a new concept of a hybrid eco-composite by substituting the natural fibre plies with thin wood veneers. The new composite, named Fibre–Wood Laminate (FWL), is inspired by fibre–metal laminate materials. The studied FWL configuration consisted of a single thin pinewood veneer at each of the outer layers of a flax woven fabric reinforced bio-epoxy composite manufactured by infusion. Three-point bending results showed that wood veneer gives a highly anisotropic nature to the FWL. In the best case, with the grain of the wood at 0°, the stiffness and the strength increased by 28 and 41%, respectively, but reduced the strain-at-break by 27% compared to the flax fibre reinforced bio-epoxy (FFRB). The penetration and perforation energy thresholds and the peak force of the FWL obtained by falling weight impact tests were 32, 29, and 31% lower than those of the FFRB, respectively. This weakening was due to using single wood veneers, so the challenge for improving impact properties will be to explore thicker FWLs with different stacking sequences and orientations. The effect of immersing the FWL in seawater also showed considerable differences. The epoxy matrix filled the cellular structure of the wood veneers, creating a barrier effect and reducing the amount of water absorbed by the flax fibres.

Efficacy of various structural forms of disentangled polyethylene laminates against low velocity impact

Filament-based unidirectional laminates of para-aramid and ultra-high molecular weight polyethylene exhibit excellent impact resistance performance. This research explored the possibility of using disentangled polyethylene (DPE) tape, instead of filaments, as an alternative impact resistant material. The effects of laminate structure, binding resin content and processing temperature on the tensile and impact properties of cross-ply laminates prepared from DPE tape was investigated. Three types of cross-ply laminates prepared from tape, woven fabric of untwisted tape and woven fabric of twisted tape were explored. Tensile properties and low velocity impact resistance of laminates were evaluated. Laminate made from woven untwisted tape showed much lower impact energy absorption than cross-ply laminate, while the woven twisted tape based laminate performed the worst. Cross-ply laminates made with low resin content showed better tensile and impact resistance performances. Cross-ply laminates prepared at higher moulding temperature showed significantly enhanced impact energy absorption than its counterpart prepared at a lower temperature. Therefore, cross-ply laminate of DPE tape with low resin content is ideal for impact resistance applications.

Computational Assessment on Impurity Sourcing and Transport Using High-Temperature Graphite and Silicon Carbide Plasma-Facing Walls in a Tokamak Environment

Operating with hot tokamak plasma-facing components will be essential in fusion reactors to maximize the thermal efficiency of the blanket. The SOLPS-ITER edge plasma code package and the DIVIMP Monte Carlo impurity tracking code were used in tandem to simulate the effect of active wall heating on impurity sourcing and transport in a DIII-D–size tokamak. The SOLPS-ITER plasma background was generated based on a previous DIII-D discharge and includes the effect of particle drifts. DIVIMP simulations found that actively heating the lower divertor (versus the divertor shelf or the entire wall) was the most efficient way to minimize gross erosion and core impurity influx at temperatures above 1000 K. Replacing the graphite wall with a silicon carbide (SiC) wall yielded a 5 to 20× decrease in the estimated gross erosion rate of carbon, with a maximum decrease observed at a lower divertor temperature of 800 K. Gross erosion of Si from SiC was estimated to be almost 100× lower than that of C from SiC, due primarily to the low impact energy of incident D plasma on the divertor targets. The core impurity influx for SiC walls is predicted to be lower than that with graphite walls, but eroded Si ions appear to migrate preferentially (versus C) to the core due to a more peaked erosion profile closer to the strike points where the ion temperature gradient force drives particles upstream. These predictive simulations suggest that active heating of the plasma-facing wall may both lower wall erosion and improve core performance relative to the “warm” walls of current devices that are typically only heated via plasma contact. Relative reductions in gross erosion and upstream accumulation by using SiC instead of graphite as the wall material strengthen the argument for upgrades to current graphite-clad machines and continued development of SiC first-wall and blanket concepts.

Nl-Selective Classical Charge-Exchange Cross Sections in Be4+ and Ground State Hydrogen Atom Collisions

Charge-exchange cross sections in Be4+ + H(1s) collisions are calculated using the three-body classical trajectory Monte Carlo method (CTMC) and the quasi-classical trajectory Monte Carlo method of Kirschbaum and Wilets (QCTMC) for impact energies between 10 keV/amu and 300 keV/amu. We present charge-exchange cross sections in the projectile n = 2 and nl = 2s, 2p states. Our results are compared with the previous quantum-mechanical approaches. We found that the QCTMC model is a powerful classical model to describe the state-selective charge-exchange cross sections at lower impact energies and the QCTMC results are in good agreement with previous observations.

Design, Fabrication, and Characterization of an Impact Dissipative Layer for Fiber-Reinforced Polymer Composites.

This study presents the option of an effective low-impact energy dissipating material applied to GFRP (glass fiber reinforced plastic) composite laminates using auxectic technology in the case of planing hull vessels that use the same high-speed light materials that repeatedly impact the surface of the water when sailing, producing a slamming phenomenon. Research shows that the option to modify the laminate with an auxectic layer protects the laminate from damage. This work proposes the manufacturing of dissipative layers, introduced in laminates made with a polymeric matrix and fiberglass reinforcement, which are evaluated with weight drop tests under different impact energies. The data are collected and processed by a unidirectional gravitometer that gives the acceleration values of the impactor. The tests compare unmodified panels with modified panels, showing that the energy absorbed by the unmodified panel is greater at equal energy levels. The returned energy comparison curve is shown, and the benefits of its use are presented.

Molecular Dynamics Simulations of Nitric Oxide Scattering Off Graphene.

We performed classical molecular dynamics simulations to model the scattering process of nitric oxide, NO, off graphene supported on gold. This is motivated by our desire to probe the energy transfer in collisions with graphene. Since many of these collision systems comprising of graphene and small molecules have been shown to scatter non-reactively, classical molecular dynamics appear to describe such systems sufficiently. We directed thousands of trajectories of NO molecules onto graphene along the surface normal, while varying impact position, but also speed, orientation, and rotational excitation of the nitric oxide, and compare the results with experimental data. While experiment and theory do not match quantitatively, we observe agreement that the relative amount of kinetic energy lost during the collision increases with increasing initial kinetic energy of the NO. Furthermore, while at higher collision energies, all NO molecules lose some energy, and the vast majority of NO is scattered back, in contrast at low impact energies, the fraction of those nitric oxide molecules that are trapped at the surface increases, and some NO molecules even gain some kinetic energy during the collision process. The collision energy seems to preferentially go into the collective motion of the carbon atoms in the graphene sheet.

Incident-angle dependence of deformation characteristics of aluminum surface under low-energy xenon-ion impact

Ion thruster is a revolution technology with potential applications in space mission but the thruster’s operation lifetime is limited by the sputtering from thruster components. In this work, molecular dynamic simulations are performed to explore the dependence of deformation characteristics of an aluminum surface on incident angle and kinetic energy under low-energy xenon-ion impact. The fraction of non-12-coordinated atoms is used to quantitatively characterize the microstructural evolution and defect density levels. It is found that defect density level has a linear relation with incident energy, and there exists a critical incident angle around 20°, at which the aluminum surface has the maximum defect density level. In addition, a collision model is developed to theoretically reveal the physical mechanisms behind the dependence. Our findings may helpful in developing long endurance electric propulsion devices for practical applications.