Increase In Energy Absorption Research Articles

Sandwich structures with repairable cores based on truncated cube cells

With dramatic increase in 3D printing applications in industry, sandwich panels with 3D printed cores have gained a lot of attention recently. In harmony with global movement towards sustainability and low-carbon emission industries, sandwich panels with easy-to-repair and cost-effective cores would be very attractive structures. In this regard, implementing separated cells for constructing lattice structures instead of using back-to-back lattice structures makes repairing local damages in the core easier and more cost-effective. Ideally, a damaged cell can be replaced with an intact new cell without the need to change the whole core structure. In this study, mechanical responses of a single truncated cube unit cell, a well-known geometry for constructing regular lattices has been studied analytically, numerically, and experimentally. Analytical relationships were derived for stiffness, yield stress, and Poisson's ratio of a single unit cell. Samples were 3D printed and tested mechanically in large deformation regime. A good agreement between results from analytical derivations, numerical simulations, and experiments was observed. It was shown that an equilateral truncated cube structure has a yield stress at least twice of that for a simple cube structure. Three types of repairable sandwich panels with different uniform core densities as well as four graded cores were studied as well. The functionally graded sandwich panels presented the best performance while considering both energy absorption capacity and mass. The best functionally graded sandwich panels (Type 4) showed an increase in specific energy absorption (SEA) by almost 21% and a decrease in maximum displacement by 2.5% with respect to the second-ranking best option.

Embedded sensing and actuating in CFRP composite structures—concept and technology demonstration for tailored embeddable sensor-actuator layers (TEmSAL)

Carbon fibre reinforced plastic (CFRP) materials are of interest for the aerospace and aviation industry to master growing economic and ecological challenges. In contrast to conventional metallic materials, they offer both higher specific material properties, such as strengths, stiffnesses, and an increased energy absorption capacity in case of impact loading scenarios. Additionally, the possibility of integrating functional elements, such as actuators and sensors, predestine CFRP for the development of more lightweight structural components. In this study, a generic composite structure is instrumented with embedded piezo ceramic sensor elements. A technology for TEmSAL is presented and applied within an autoclave manufacturing process. Aspects of the designing process, manufacturing and instrumentation as well as experimental impact sensing and self-actuation results are presented and discussed.

Effects of porous materials with different thickness and obstacle layout on methane/hydrogen mixture explosion with low hydrogen ratio

The effects of porous materials with different thickness and obstacle layout on the explosion of 10%H2/90%CH4 at stoichiometric condition were studied. Three kinds of porous materials with different thickness were selected in the experiment, which are 1 cm, 2 cm and 3 cm respectively. Three kinds of obstacle layout were designed, which are symmetrical distribution, ipsilateral distribution and staggered distribution. Results show that porous materials with different thickness can promote or inhibit the explosion flame and overpressure when the obstacles are symmetrically distributed. The quenching failure of 1 cm thick porous material is similar to the action of mesh obstacles, which accelerates the flame to break through the bondage of porous material and continue to propagate, with a maximum speed of 87.74 m/s. When the thickness of porous material is 2 cm and 3 cm, the solid structure increases, the energy absorption increases, the flame impact porous materials quench, and the overpressure peak decreases. The greater the thickness of porous material, the better the attenuation effect, and the maximum overpressure attenuation can reach 59.71%. The change of obstacle layout has an important impact on the flame propagation structure. Compared with the ipsilateral distribution and staggered distribution, when the obstacles are symmetrically distributed, the vortex dynamic induced flame turbulence area is larger, the flame combustion rate is increased, and the explosion hazard is greater.

Structural Behavior of Reinforced Concrete Beams Containing Pet Waste Particles as Sand Replacement

Abstract This paper examined the polyethylene terephthalate (PET) polymer waste effect that using as a partial replacement for fine aggregate on the R.C beams structural behavior. Six replacement percentages by weight were used in this study: 5 %, 7.5 %, 10 %, 12.5 %, 15 %, and 20 %. Seven concrete beam specimens with dimensions of 150 × 300 × 2300 mm were tested, in which one specimen for each PET replacement percentage was added to the reference specimen. four-point load setting were used to test all specimens via failure load, maximum deflection, energy absorption, stiffness, ductility index, flexural strain, first crack load, and crack pattern. Results showed that raising of PET percentage in the concrete beams leads to an increase in failure load, maximum deflection, ductility index, strain, and energy absorption compared with the reference beam in the ranges 0 – 4 %, 23.2 – 93.7 %, 12.13 – 93 %, 432 – 1139 %, and 51.8 – 275.4 %, whereas its causes a decrease in initial stiffness and secant stiffness in the ranges 5.8 – 38.44 % and 19.2 – 46.4 %. Moreover, crack investigations revealed that the load at which the first crack forms raise when the PET waste content increases.

Effect of recycled polymer fibre on dynamic compressive behaviour of engineered geopolymer composites

To enhance the cost-effectiveness and sustainability of engineered geopolymer composites (EGC), polyvinyl alcohol (PVA) fibres in EGC can be partially replaced with recycled tyre polymer (RTP) fibres. This paper presents a systematic experimental study on the effects of PVA fibre volume fraction (1.0%, 1.5% and 2.0%) and RTP fibre content (0.25%, 0.5%, 0.75% and 1.0%) on the dynamic compressive behaviour of EGC under various strain rates (54.43–164.13 s−1). Results indicate that the flowability, quasi-static compressive strength and elastic modulus of EGC reduce with the increase of PVA fibre content, where the reductions can be effectively mitigated by adding RTP fibres. The dynamic compressive properties of all investigated mixtures including dynamic compressive strength, dynamic increase factor (DIF) and energy absorption capacity show a pronounced strain rate dependency which can be well described using the proposed equations for DIF against strain rate ranging from 10−5 s−1 to 103 s−1 with R2 values of mostly greater than 0.9. The dynamic compressive properties of EGC are enhanced with the increasing PVA fibre dosage under various strain rates while replacing PVA fibre with a certain amount of RTP fibre (0.25% and 0.5%) can result in better dynamic compressive properties compared to EGC with 2.0% PVA fibre. EGC containing 1.75% PVA fibre and 0.25% RTP fibre can be considered as the optimal mixture given its superior quasi-static and dynamic compressive properties in comparison with EGC with 2.0% PVA fibre.

Dynamical polarization, optical conductivity and plasmon mode of a linear triple component fermionic system

We investigate the density and optical responses of a linear triple component fermionic system in both non-interacting and interacting regimes by computing its dynamical polarization function, random phase approximation dielectric function, plasmon mode and long wavelength optical conductivity and compare the results with those of Weyl fermions and three-dimensional free electron gas. Linear triple component fermions are pseudospin-1 generalization of Weyl fermions, consisting of two linearly dispersive bands and a flat band. The presence of flat band brings about notable modifications in the response properties with respect to Weyl fermions such as induction of a new region in the particle–hole continuum, increased static polarization, reduced plasmon gap, shift in absorption edge, enhanced rate of increase in energy absorption with frequency and highly suppressed intercone transitions in the long wavelength limit. The plasmon dispersion follows the usual ω ∼ ω 0 + ω 1 q 2 nature as observed in other three-dimensional systems.

Analytical and experimental investigation of steel friction dampers and horizontal brake pads in chevron frames under cyclic loads

Recent observations of earthquake-related damage have shown that some structural damage occurs in welded joints. Because of weak connections, the idea of using chevron bracing with a horizontal friction brake pad (FBP) damper, which can easily be replaced after an earthquake, has been proposed. First, in this study, a high-performance friction damper that can be manufactured and installed at a low cost is introduced. First, nine models were analysed numerically with ABAQUS software, and then two optimal models were selected and tested in a structural laboratory. ABAQUS software was also used to model the optimal damper inside a chevron frame and analyse its performance. In addition, three 8-story buildings were considered, one with a moment-resisting frame (MRF), one with a structural bracing system with an added damping and stiffness (ADAS) damper, and one with an FBP damper. Then, eleven far-field earthquake records were used for nonlinear time history analysis. Next, the effect of the friction damper between two adjacent buildings was investigated by modelling a 5-story structure using OpenSees software under seven earthquake records. The results show that a very high stress concentration occurs in the damper area of the brake pad after a load is applied to the bracing frame, while dampers in other elements, such as beams and columns, provide less stress. The ten-screw model has the highest energy absorption, according to parametric studies. Compared to other frames, the chevron frame with a friction damper exhibits a 32% increase in energy absorption. By analysing other seismic parameters of the frame, the damper improves frame performance

On the transition of temperature regime of the White Sea Region to a new phase state

Changes in near surface air temperature (SAT) and vorticity of the wind speed field of the White Sea and the territory of the Murmansk and Arkhangelsk regions and the Republic of Karelia are investigated. We analyzed the monthly average NCEP/ NCAR reanalysis data for the period 1950–2020. The average surface air temperature growth estimated using a linear trend was +0.240C/10 years. Against the background of this linear growth, significant interdecadal changes in surface air temperature are observed. The following periods are highlighted: the strengthening of the continentality of the climate (1950–1976), a more maritime climate (1977–1998), and the rapid growth of surface air temperature (1999–2020). The transition from a period of increasing continentality of the climate to a period of a more maritime climate is associated with an increase in the influence of the North Atlantic on the region under study. A hypothesis has been put forward that the period of rapid growth of surface air temperature is caused by the transition of the climatic system of the western part of the Russian Arctic into a new phase state. The observed warming in the Arctic has caused a reduction in sea ice, which has led to an increase in solar energy absorption by the surface of the Barents and White Seas.

High-velocity impact resistance of doubly curved sandwich panels with re-entrant honeycomb and foam core

This work describes the high-velocity impact behavior of doubly curved sandwich panels. The sandwich panels are manufactured using carbon/fiber epoxy composite face sheets, polyurethane foam core and 3D-printed PLA plastic cellular auxetic (re-entrant) honeycombs. High-velocity impact tests are carried out by using a single-stage air gas gun test machine. A spherical steel projectile with the radius of 5 mm is impacted to the center of the specimens with the speed of 100 m/s. The experimental data are used to validate explicit finite element models of the doubly curved structures. An analytical model is also developed for the ballistic limit of the flat and doubly curved sandwich panels, and the analytical results are compared to those obtained from the numerical ones. Parametric numerical analyses of the high-speed impact of the curved sandwich panels are then carried out considering various radii of curvature of the panels. The results show that the energy absorption is increased as the curvature is decreased for the panels with both foam and re-entrant core. In addition, the core configuration provides a key role in the impact resistance of the sandwich panels. Re-entrant models show an increase in specific energy absorption (SEA) compared to the foam core types.

The compressive response of additively-manufactured hollow truss lattices: an experimental investigation

The mechanical response of additively-manufactured hollow truss lattices is experimentally investigated under quasi-static compression testing. Exploiting the recent developments in the Fusing Deposition Modelling (FDM) technique, two families of lattices have been fabricated, obtained as tessellation in space of octet-truss and diamond unit cells. Four specimens for each family of lattices have been designed with prescribed relative density, selecting different inner-to-outer radius ratios r/R of their hollow struts. Compression experiments prove that mechanical properties and failure mechanisms of hollow truss lattices are significantly dependent on the r/R ratio. In particular, a shift from quasi-brittle to ductile mechanical response at increasing r/R values has been revealed for the octet-truss lattice, leading to a stable collapse mechanism and increased energy absorption capacity. On the other hand, a more compliant behaviour has been observed in the diamond lattice response, with a monotonic improvement of mechanical properties as a function of the r/R ratio. Such results substantiate the potentialities of additively-manufactured hollow lattice structures as an attractive solution when lightweight, resistant and efficient energy absorption materials are required.Graphic

Flexural behavior of beams reinforced by GFRP bars with CFRP sheets immersed in epoxy as shear

Corrosion in steel bars is considered a big problem because corrosion is mainly responsible of decrease virtual age of structures and many risks indicated by deterioration. In addition, corrosion increases the cost of maintenance, particularly structures exposed to harsh environmental condition. FRP bars (Fiber Reinforced Polymer) became an alternative material from traditional steel bars. FRP had properties made it used in civil engineering sectors which are lightweight, non-corrosive, non-conductive made it a preferred alternative from steel bars in aggressive environments. FRP bars don’t have yield made it con not bind outside its linear behavior to make ties, because of the brittle behavior of FRP bars up to failure. So that, the new innovative manner by using CFRP sheets stirrups immerged by sikadur330 for produce beams can resist the harsh condition and purely reinforced with FRP in a new manner can provide stirrups in full different sizes and with lower cost. Twelve beams reinforced with GFRP bars in three different ratios of tension reinforcement (four beams for each ratio). Three control beams with steel stirrups: two beams were designed to fail in shear. Whilst, the residual nine beams with shear reinforcement made from CFRP sheets strips, immerged by sikadur330. The main variable were studied is the change in type and amount of secondary reinforcement and change in amount of primary reinforcement. The test was conduct under four point loading and in simply supported conditions. The result of tested beams illustrated that, beams had a higher percentage of tension reinforcement and shear reinforcement displayed an increasing in ultimate load about 38.1% from related control beam. While, an equivalent amount of shear reinforcement displayed an increasing in carrying load capacity up to 10%. In maximum ratio of CFRP sheets immerged by sikadur330 stirrups convert failure mode from shear to flexural indicated by crushing in cover of concrete. In addition, increased energy absorption, changed cracks orientation, increased energy absorption, decrease principal strain and increased concrete tensile.

Use of pressure sensitive adhesives to create flexible ballistic composite laminates from UHMWPE fabric

Fiber reinforced composites (FRC) have been widely used for ballistic resistance where hot resin melt is infused into the fabric layers and cured to form the composite. Here, we explore the use of pressure-sensitive adhesive (PSA) and its cold lamination as a simple, rapid and inexpensive method to integrate plain-weave UHMWPE and demonstrate that these composites have attractive ballistic performance. Simple compression lamination of 22 layers of fabric with interlay of PSA, for 1 min at 4 or 8 MPa, was able to confer the ability to stop 9 mm bullets shot at ∼357 m/s. Increasing the processing pressure results in an increase of inter-ply bonding strength significantly while only affecting the bending stiffness slightly. It also results in an increase in energy absorption of laminate which leads to smaller backface signature and volume and better ballistic performance. They are also more flexible, thinner and lightweight compared with hot melt FRC.

Prediction of micro impregnation phenomena in additively manufactured composite materials

Additive manufacturing is attractive to manufacture composite materials with advanced architectures and minimal wasted material. Hybrid resin composites (a composite with multiple types of resins) are of particular interest for ballistic applications, where they have been shown to increase energy absorption. The incorporation of additive manufacturing techniques in the manufacturing of composite materials opens up a unique opportunity for designing hybrid resin composites with a controlled resin distribution at the fiber tow scale. This work presents a three dimensional numerical model for predicting the wicking of resin drops into fiber tows, taking into account the interaction with neighboring drops. A parametric study is conducted with this process model to explore the influence of select parameters on resin impregnation and distribution in the tow. This will allow one to design the process to obtain a desired porosity distribution within the tow, which can then be infused with a second type of resin to form a hybrid resin composite. The model should prove useful for tailoring the properties of composites through strategic placement of resin within fiber tows.

Dynamic crushing of tailored honeycombs realized via additive manufacturing

Enhancing the energy absorption characteristics of a material/structure without compromising its strength and stiffness has been a longstanding challenge in the pursuit of lightweight engineering. Here, we introduce a novel tailoring strategy where the wall thickness of the honeycombs is bi-linearly graded along the out-of-plane direction to tune their energy absorption and impact resistance by varying two design parameters, the gradation parameter α and the normalized taper length η'. Based on the proposed scheme, hexagonal honeycombs of the same mass and varying parameters [α, η'] were designed and realized via Digital Light Processing (DLP) additive manufacturing. Low-velocity out-of-plane impact tests and dynamic FE calculations were performed to examine the collapse response of geometrically tailored honeycombs and assess their energy absorption characteristics and collapse mechanisms in relation to those observed in conventional (non-tailored) honeycombs of the same mass. The measurements and predictions revealed that the bi-linearly wall-thickness tailored honeycombs consistently outperform their non-tailored counterparts when the impact energy is high, reporting an increase in energy absorption as high as 250%. Such remarkable enhancement in energy absorption is attributed to a transition in the underlying collapse mechanism from global buckling mode to progressive crushing of the cell-walls. We also examined the impact response of honeycombs with periodic variations in cell-wall thickness and found that the latter structures collapse rapidly in an unstable manner, similar to what observed in conventional honeycombs, leading to limited capacity to dissipate the impact energy. With careful selection of the design parameters [α,η′], we experimentally demonstrate that bilinearly wall-thickness tailored honeycombs can exhibit simultaneous improvements in energy absorption and impact resistance, providing new opportunities for expanding the property space of honeycombs and opening the door for a wide range of applications.

Crashworthiness analysis of gradient hierarchical multicellular columns evolved from the spatial folding

Based on the gradient hierarchical distribution of vascular bundles of bamboo, a gradient hierarchical multicellular column (GHMC) evolved from the spatial folding was proposed. Crashworthiness analysis of GHMC was carried via Abaqus/Explicit. Results show that the proposed GHMC has better energy absorption ability compared with the square tube under the same thickness or the same mass. The folding wavelength of GHMC is significantly decreased and it can produce more number of folds compared with the square tube. Under the condition of the same mass, the peak crushing force of GHMC decreases meanwhile its energy absorption increase by 10.1% to 72.44% compared with the square tube. Effect of hierarchical level and cell wall thickness on the energy absorption and their deformation mode under different height-length ratio (H/L) and cell wall thickness have been analyzed. Simplified super folding element theory was used to predict the mean crush force of GHMC, and the results were in good agreement with the simulations.

Test of Dynamic Mechanical Properties of Ambient-Cured Geopolymer Concrete Using Split Hopkinson Pressure Bar

The application of geopolymer concrete (GPC) in construction could reduce a large amount of carbon dioxide (CO2) emission, which is greatly beneficial to environmental sustainability. Structures made of GPC might be subjected to extreme loading such as impact and blast loads. Therefore, a good understanding of the dynamic properties of GPC is essential to provide reliable predictions of performance of GPC structures subjected to dynamic loading. This study presents an experimental investigation on the dynamic compressive and splitting tensile properties of ambient-cured GPC using split Hopkinson pressure bar (SHPB), with the strain rate up to 161.0 s−1 for dynamic compression and 10.3 s−1 for dynamic splitting tension. The failure mode and damage progress of GPC specimens, energy absorption, and dynamic increase factor (DIF) were studied. Test results showed that ambient-cured GPC exhibited strain rate sensitivity. The compressive and splitting tensile DIFs increased with the strain rate and the ambient-cured GPC with lower quasi-static compressive strength exhibited higher DIFs under both dynamic compression and splitting tension. Empirical formulas were proposed to predict the DIF of ambient-cured GPC. Furthermore, the specific energy absorption of ambient-cured GPC under dynamic compression increased approximately linearly with the strain rate.

A novel class of bioinspired composite via ultrasound-assisted directed self-assembly digital light 3D printing

The advent of advanced manufacturing technologies brings about the possibilities of novel materials with potentially unprecedented material properties. Through ultrasound-assisted directed self-assembly digital light processing, we present a novel class of composite – the discontinuous interpenetrating-phase composite (d-IPC) – where the cellular filler phase is based on lines of particle assemblies, as opposed to continuous materials. Through yttria particle doping, we fully illustrate the unique microstructural-specific mechanical properties of the d-IPC. Despite being fully bulk and having a similar density (1.18 g/cm3) and strength (68 MPa) as the matrix polymer, it presents an additional plateau-deformation behaviour under large compressive strains and hence a 218% increase in specific energy absorption up to 37 J/g. The enabling mechanism is derived from the peculiar discontinuous and macroscopically aligned particle-based struts which do not contribute to a notable diminution of strength but can yet modulate high-strain deformation via induction of progressive localized failures. The concept of d-IPC is also extendable to solid fillers of all materials, morphology, and reasonable sizes, allowing the d-IPC to be highly customizable with multifunctional potentials. Through this work, we also aim to demonstrate the potentials of using advanced microstructural-controllable manufacturing techniques to achieve conceptually new and advanced composite materials.

A Highly Efficient Nanostructured Sorbent of Sulfuric Acid from Ecofriendly Electrospun Poly(vinyl alcohol) Mats

Concentrated sulfuric acid is widely used in industrial processes all around the world. Its handling can generate spills with an enormous risk for the operator and the environment. Usually, alkalis are used to remedy this type of spillage, releasing a large amount of heat during the reaction. Absorbent pads are a solution to this problem. Here we present a new and light nanostructured material with extraordinary sorption capacity for concentrated sulfuric acid (98 wt %). The total acid uptake achieved is greater than 1200 wt %, sorbing 12.6 times its own weight of 98 wt % H2SO4, in just 5 min. It was obtained by applying a green process to a biodegradable polymer (poly(vinyl alcohol), PVA). First, an aqueous solution of PVA was electrospun to get a nanofibrous mat. Then, the mat was heat-treated by two sequential steps below 200 °C (900 min at 155 °C and 420 min at 195 °C). We show that both thermal steps are necessary to maximize acid sorption and that when one of them is not performed, the obtained sorption capacity is much lower (about 400 wt %, sorbing only 4 times its own weight). This phenomenon is explained in terms of transformations of polymeric structures caused by the proposed heat treatment. The sorption mechanism begins with the chemical addition of sulfuric acid to the polymer’s surface unsaturations, followed by an increase in surface energy and additional absorption of acid into the material. This study opens up new possibilities for the development of sorbents from environmentally friendly materials and processes.

Use of patterned thermoplastic hot film to create flexible ballistic composite laminates from UHMWPE fabric

Thermoplastic resin is infused into fabric layers to form rigid fiber-reinforced composites (FRCs), which are commonly used for ballistic resistance purposes. Here, we explore the use of patterned thermoplastic hot film as a rapid and straightforward method to laminate plain-weave UHMWPE and demonstrate that these composites have attractive ballistic and stiffness properties. Lamination of 25 layers of fabric using hot press compression lamination of each individual layer with hot film was able to confer the ability to stop 0.357 magnum ammunition shot at 435.9 ± 9 m/s. Patterning the hot film resulted in the composite panels retaining most of their flexibility without losing their ballistic performance compared to when they are laminated with plain (not patterned) hot film. Using the hot film for lamination results in an increase in energy absorption of the laminates with a smaller backface signature and backface volume. These laminates are lighter and more flexible than the commonly used hot resin-infused FRC.

Experimental Study on Dynamic Mechanical Characteristics and Energy Evolution of Sandstone under Cyclic Impact Loading

In order to study the dynamic mechanical properties of the surrounding rock of roadway in deep mines with rock burst, cyclic impact compression tests of sandstone under different impact velocities were carried out by using the split Hopkinson pressure bar (SHPB) test system, and the dynamic stress-strain curves of the samples under cyclic impact loads and the relationship between energy dissipation and impact numbers were analyzed. The results show that, as the impact loading times increase, the initial elastic modulus of sandstone samples decreases, the peak stress decreases, and the peak strain increases; the average strain rate increases. The cumulative damage of sandstone samples under impact load is significantly affected by impact velocity and times. During the cyclic impact test, the reflected energy of sandstone increases with the increase of impact numbers, while the transmitted energy decreases and the absorbed energy increases; the cumulative specific energy absorption variable is introduced, and the cumulative specific energy absorption value of the samples increases with the increase of impact numbers, which can better characterize the variation of energy accumulation and dissipation of sandstone samples under cyclic impact.