Increase In Energy Absorption Research Articles

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.

Designing carbon nanotube and nanofiber-polypropylene hybrid cementitious composites with improved pre- and post- crack load carrying and energy absorption capacity

This study reports recent developments on carbon nanotube (CNT), nanofiber (CNF), and polypropylene microfiber (PP) hybrid reinforced cementitious composites. Notable characteristics are (i) significantly enhanced load carrying capacity; and (ii) increased energy absorption capability at both elastic and post-first cracking stages. Three point bending tests on notched and unnotched specimens have shown that the addition of 0.3 vol% CNTs and CNFs in PP reinforced mortars increases the modulus of elasticity and first crack strength and toughness by 93%, 64% and 49% respectively. The experimental values perfectly agree with the theoretically determined modulus using a micromechanics-based model. Hybrid mixes showed considerable increase in toughness, exhibited toughness index values I5 of 4 or more, and 4 times higher residual strength. Relative to the PP microfiber reinforced mortar, the developed hybrid material is able to sustain a much higher load and successfully transfer tensile stresses across cracks, without losing its tensile load carrying capacity. Such exceptional mechanical behavior is an important performance factor for serviceability and is interpreted in terms of the mechanism of a synergistic interaction between the nano and micro scale fiber reinforcement.

Study on compression load and energy absorption characteristics of glass fiber honeycomb tube

In terms of the deficiency of the existing research on the compression load and energy absorption characteristics of composite structures, a glass fiber honeycomb tube with different thickness and different cell number was proposed. The static compression test was carried out by universal testing machine. The results show that the failure forms of honeycomb tube are fiber fracture damage, fiber layer delamination and their composite forms. The peak compression load and total energy absorption increase with the increase of cell number and thickness, and the specific energy absorption increase only with the increase of thickness. The compression peak load of single-cell honeycomb tube with wall thickness of 0.4 mm is the smallest, which is 2.21 KN; and the compression peak load of eight-cell honeycomb tube with wall thickness of 1.2 mm is the largest, which is 91.48 KN. The corresponding total energy absorption is 25.16 J and 2257.57 J respectively; the corresponding specific energy absorption is 8.38 J/g and 45.06 J/g respectively.

Experimental study of the performance of hemispherical solar still with optimum value of rocks as heat transfer enhancers

<abstract> <p>Transformation of salty seawater into fresh water by the aid of solar energy is one of the solutions for overcoming the lack of these waters with an eco-friendly procedure. The use of solar stills is one of the solutions that use solar energy with a simple design to produce fresh water in small to moderate amounts. Hemispherical solar stills are one kind of still design that does not require a particle rotational orientation, and they have proved to be more efficient than traditional designs. Solar stills generally possess a low thermal efficiency, with limitations of working hours, i.e., only daytime. To overcome these problems, rocks placed in the saline water basin are used as heat storage materials to increase the working period of the design. In the present work, different amounts of river rocks are utilized to study the effect of this addition experimentally. Steady state tests are conducted to study the influence of these additive rocks on the enhancement of solar energy absorption, since increased working time is assured by published research. Two volumes of rocks (300 mL and 600 mL) were tested, and both increased water productivity, by 52% and 58%, respectively. The increases are explained by the increases in solar energy absorption, since steady state cases were used.</p> </abstract>

Fracture behavior study of self-healing bacterial concrete

Presently, the construction sector expects quicker strength attainment in concrete so that the works can be finished on or before the schedule. This mandate is solved by high early strength cement and the usage of a low water/cement ratio. However, the above process results in a large amount of thermal and drying shrinkage, modulus of elasticity, and lower creep coefficients. Further, with a large amount of cement, concrete shows larger cracking behavior because of amplified thermal shrinkage and drying shrinkage. Therefore, high early strength concrete enhances the risk of cracking compared to moderate strength concrete. To decrease the effect of initial cracks and to repair the generated cracks in the concrete, several methods have been used in the industry. Self-healing bacterial concrete is one such method. Preliminary investigations have shown that using bacterial self-healing concrete helps us in increasing the mechanical properties of concrete along with healing the cracks up to a width of 0.3 mm. In this research, an effort is made to comprehend the effect of bacterial self-healing concrete on the fracture behavior of reinforced concrete beams. To understand this, several parameters such as beam deflection, load-carrying capacity, cracking pattern, energy absorption capacity, ductility factor, and ultimate moment carrying capacity, were checked with M25 grade concrete with fly ash and silica fume. Different parameters confirm that the load-carrying capacity of self-healing concrete increased up to 21% with a change in fracture behavior and deflection with a greater number of cracks and less width. Further ductility of beam increased up to 45%, and with a minimum of increased energy absorption of 100%. This shows that bacterial concrete is a sustainable alternative for the future construction industry as it extends the durability of the structure.

Awareness of the causes, impact and solutions to global warming among undergraduate students from different schools in the University of The Gambia

Climate Change is unequivocal and occurring at an alarming pace. Increasing greenhouse gas emissions, their concentration in the atmosphere and increased energy absorption have resulted in in changes in climate. This study was a cross sectional study conducted from April 12th to May 12th, 2021. The survey was conducted online using Google form that was circulated via "WhatsApp" groups and emails received from the University admissions office. This study comprises of students in their; first year 26.5%, second year 22.8%, third year 17.9% and fourth-year students 32.8%. Students from the school of Medicine and allied health science showed a satisfactory knowledge of 67% towards the causes of global warming. Students from the school of Engineering also demonstrated a satisfactory knowledge towards the impact of global warming 61% and its solution 69%. In conclusion, students at the University of The Gambia demonstrated a satisfactory understanding of the causes of global warming (63%) and a fair awareness of the consequences (52%) and remedies to global warming (54%). We recommend that, climate change awareness course should be incorporated into the curriculum of the University of The Gambia and should be made mandatory for every student.

Mouldability analysis and impact performance of 3D aramid angle-interlock fabric panels for ballistic helmets

Modern ballistic helmets made from textile composites offer enhanced protection with lightweight, but the discontinuity of the reinforcing materials is a potential problem affecting the helmet performance. This work uses 3D angle-interlock fabrics to provide reinforcement continuity, and evaluates 3D through-the-thickness angle-interlock (TTAI) fabrics to study the influence of fabric structural parameters on fabric mouldabilty and ballistic performance for ballistic helmet application. The mouldability was measured through experiments and modelled numerically, and the ballistic impact test was carried out to identify the optimal fabric structures for constructing ballistic helmet shells. The results show that increase in weft density of the TTAI fabrics causes decrease in the mouldability of the TTAI fabrics, and that the addition of wadding yarns into the TTAI fabrics has little influence on fabric mouldability compared to the conventional TTAI fabrics with the same weft density. However, the involvement of wadded TTAI fabrics demonstrates a 34% increase in ballistic energy absorption and 3% higher estimated ballistic limit over the conventional counterpart. Taking both mouldability and ballistic protection into account, the wadded TTAI fabric structure is an effective continuous reinforcement for ballistic helmet shells, offering required mouldability and improved ballistic performance.