Significant Increases In Energy Absorption Research Articles

Damage-tolerant behavior of structural epoxies with thin PEI and PVDF interlayers

This work examines the crack-arresting capability of PEI and PVDF thermoplastic interlayers in short-glass fiber modified and core–shell rubber toughened epoxy materials under mode-I fracture loading. Experimental results show that the initial crack can be effectively arrested by the thermoplastic-epoxy interface and reinitiation of this crack at the thermoplastic layer requires up to 2.5 times higher load than the crack initiation load of the pristine epoxies. The interlayered designs also exhibit a significant increase in energy absorption by up to 43 times more than their pristine counterparts. Competing damage mechanisms and failure events are captured by microscopy images, digital image correlation and high-speed photography observations. Additionally, elasto-plastic fracture mechanics models based on configurational material forces theory are developed for a preliminary crack-arresting material selection and to elucidate the material inhomogeneity effects.

Evaluation of Factors Affecting the Performance of Fiber-Reinforced Subgrade Soil Characteristics Under Cyclic Loading

This study is focused on evaluating the factors affecting the performance of fiber-reinforced subgrade under cyclic loading. To achieve the objectives of this study, a series of dynamic triaxial (DT) tests was performed, and the following parameters, such as resilient modulus (MR), number of loading cycles (N), cyclic stress (CS), resilient strain (RS), and stress-strain hysteresis response of both the reinforced and unreinforced subgrades were evaluated. Subsequently, a series of scanning electron microscope (SEM) tests was conducted to track the fiber-soil interfacial bonding after the completion of DT test. The results indicated that N and CS triggered an appreciable decrease in MR with significantly high RS deformation for the unreinforced subgrade. However, reversed responses were noted upon the inclusion of sisal fiber due to fiber-soil adhesion and a high ductility response was portrayed by the reinforced subgrades. A reversed response was significant upon 0.25% and 0.5% fiber inclusion, beyond which the CS resistance slightly decreased. The stress-strain hysteresis loop was observed to increase as the axial strain increased proportionally with an increase in fiber contents, thus causing a significant increase in energy absorption in specimens. The SEM micrograph showed tightly knitted fiber-soil adhesion after the DT test. This study indicated that the reinforced subgrade sustained the CS, N, and improved energy absorption capacity, and MRupon fiber inclusion. Doi: 10.28991/CEJ-2023-09-08-015 Full Text: PDF

Reinforcement effect of shear thickening fluid on impact properties of aramid, basalt, and carbon fiber reinforced polymer using a split Hopkinson pressure bar

This study focuses on investigating the impact properties of fiber-reinforced polymer (FRP) materials impregnated with shear thickening fluid (STF) under high strain rates using a split Hopkinson pressure bar (SHPB) test. The study involves the preparation of three types of FRP materials, namely aramid FRP (AFRP), basalt FRP (BFRP), and carbon FRP (CFRP), which are subsequently impregnated with STF to develop FRP composite materials (referred to as FRP-STF). The STF used in the experiment is synthesized by dispersing 15.0 wt.% and 20.0 wt.% of 12 nm silica in Polyethylene glycol. The results of rheological tests show a significant shear thickening effect on viscosity for both STFs. Furthermore, the SHPB tests demonstrate a noteworthy improvement in the impact performance of AFRP, BFRP, and CFRP under high strain rates when impregnated with STF. However, the extent of this improvement varies among the different types of FRP materials. For instance, BFRP exhibits the highest increase in stress peak, reaching 58.9% under a strain rate of 3800 s⁻1 and an STF mass fraction of 20%. AFRP demonstrates the most significant increase in energy absorption, reaching 226.8%. When subjected to a strain rate of 6100 s⁻1, the AFRP-20% STF composite exhibits a highly favorable stress response, while the CFRP-20% STF composite shows an energy absorption of 710.5 J, approximately 3.3 times higher than that of pure CFRP. These trends are also evident in the energy absorption per unit density curve.

Vibro-impact energy harvester with optimal kinetic and elastic energies absorption

Many vibrating energy harvesters convert elastic or strain energy to electricity, while the energy of the structure is mainly distributed between potential and kinetic energies. The focus of the present work is on maximizing energy harvesting of the structure through the optimal energy absorption of its mechanical energy. The collision mechanism is used for this purpose. Primary piezoelectric harvester on the main structure and secondary piezoelectric harvester utilizing impact force in the form of harvesting beam used for this purpose. The results show that there is a significant increase in energy absorption and bandwidth. The effect of different geometrical and mechanical parameters on the system's efficiency is investigated. Experimental validation is presented to evaluate the theoretically obtained results. The presented mechanism gives up to 80 times improvement in the harvested power.

Quasi-static axial crushing of hexagonal origami crash boxes as energy absorption devices

Abstract. Thin-walled tubes are widely used as energy absorption devices for their low cost and high manufacturability. Introduction of the origami technique enables the tube to follow a pre-determined failure mode and to improve its energy absorption efficiency. This paper examines the energy absorption characteristics of the origami crash box under quasi-static axial crushing. Both experimental and numerical results show that the origami pattern develops a diamond-shaped mode, bringing a reduction in initial peak force and a significant increase in energy absorption compared to the conventional hexagonal tube. The sensitivity of its energy absorption performance to various parameters is studied, and it is shown to achieve 68.29 % increase in the specific energy absorption and 13.91 % reduction in the initial peak force in the optimal case. Furthermore, an analytical solution is presented for the energy absorption, which achieves reasonable agreement with the numerical results.

Blast mitigation performance of cladding using square dome-shape kirigami folded structure as core

Structural response of the sacrificial cladding with square dome-shape kirigami (SDK) structure as core under blast loads is investigated in this study. A sample of SDK core folded from a pre-cut aluminium sheet is crushed under quasi-static loading condition. A numerical model is then developed and calibrated using experimental data. The calibrated model of SDK foldcore cladding is then placed on to a rigid block as a sacrificial layer to resist blast loading for structure protection. To evaluate the blast mitigation capacities, the parameters such as peak load transmitted to the protected structure, energy absorption, centre crushed distance and loading duration are compared among the claddings with different cores. Compared to square honeycomb, superior performance of blast mitigation is demonstrated for the proposed SDK foldcore sacrificial cladding by yielding a uniform collapsing similar to aluminium foam. Significant increase in energy absorption of the core is observed for the sacrificial cladding with SDK foldcore. It also yields a higher plateau stress than aluminium foam of the same density and is applicable to a wider range of blast loadings. The peak transmitted load to the protected structure is reduced by more than 70% comparing with the case without cladding. SDOF analysis of the sacrificial cladding systems is carried out and validated using numerical results. Based on the SDOF analysis, complete solution is derived and then used to obtain simplified design charts to show the suitable range of blast load scenarios where the sacrificial claddings are effective.

Cyclic performance of concrete-filled steel batten built-up columns

Steel built-up batten columns are common types of columns in Iran and some other parts of the world. They are economic and have acceptable performance due to gravity loads. Although several researches have been conducted on the behavior of the batten columns under axial loads, there are few available articles about their seismic performance. Experience of the past earthquakes, particularly the 2003 Bam earthquake in Iran, revealed that these structural members are seismically vulnerable. Thus, investigation on seismic performance of steel batten columns due to seismic loads and providing a method for retrofitting them are important task in seismic-prone areas. This study aims to investigate the behavior of concrete-filled batten columns due to combined axial and lateral loads. To this end, nonlinear static analyses were performed using ANSYS software. Herein, the behaviors of the steel batten columns with and without concrete core were compared. The results of this study showed that concrete-filled steel batten columns, particularly those filled with high-strength concrete, may cause significant increases in energy absorption and capacity of the columns. Furthermore, concrete core may improve post-buckling behavior of steel batten columns.

Nylon‐coated ultra high molecular weight polyethylene fabric for enhanced penetration resistance

ABSTRACTA coating of Nylon 6,6 or 6,12 was used to improve the penetration resistance of ultra high molecular weight polyethylene (UHMWPE) fabric that would be potentially useful in the manufacture of flexible body armor against spike/knife threats. Quasi‐static test results for the spike penetrator showed a 77% and 86% improvement in the puncture resistance of Nylon 6,6 and Nylon 6,12 coated UHMWPE (respectively) over a neat fabric target of equivalent areal densities. Dynamic impact testing demonstrated dramatic improvement in the puncture resistance of nylon‐coated fabrics while only a slight improvement in stab resistance was observed comparing samples with equivalent areal densities. Photography of ruptured areas after quasi‐static testing revealed limited fiber motion or fiber stretching with no evidence of fiber pullout for nylon‐coated fabric samples in contrast to neat fabric. This suggests that there was a significant increase in energy absorption by nylon‐coated fabrics at impact. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40350.

Factors influencing the ballistic impact resistance of elastomer-coated metal substrates

An experimental study was carried out of various factors affecting the ballistic penetration resistance of elastomer/steel bilayers. For blunt penetrators, the contribution of the coating to performance is optimized using the hardest substrates, front surface placement of the elastomer, and (when normalizing by added weight) thin, ca. 2–3 mm, coatings. These results, none of which are predicted by existing models, evince the marked coupling of coating and substrate in the impact response of the bilayer. We also show that nanoparticle fillers have a modest effect on ballistic performance of polyurea coatings, changing the penetration velocity by a few percent or less. This contrasts with the linear dynamic mechanical behavior, which shows much more significant increases in energy absorption due to nano-reinforcement.

Effects of boundary conditions on the energy absorption of thin-walled polymer composite tubes under axial crushing

Polymer composite tubes can be designed to absorb high levels of impact energy by progressive crushing. When a tube is crushed onto a flat platen, energy is absorbed by bending failure of the plies, delamination and friction mechanisms. In the present work, significant increases in energy absorption are shown when a shear mode of failure is initiated by crushing the tube onto a radiused plug (or initiator). A study of plug radius, R, normalised with respect to the tube wall thickness, t, in the range of 0⩽ R/ t⩽5 for circular tube diameter/thickness ratios of 10< D/ t<33 was undertaken with continuous filament random mat glass/polyester composite. Different radii plugs lead to significantly different deformed shapes and crush zone morphologies. Large radius initiators ( R/ t>2) cause the tubes to split and energy is absorbed primarily through friction and axial splitting. As the initiator radius decreases, the amount of through-thickness shear damage in the fronds increases along with specific energy absorption (SEA). When the plug radius becomes small compared to the wall thickness ( R/ t<0.75) a debris wedge forms between the initiator and the tube and acts like a larger radius initiator. The highest energy absorption was seen to occur at R/ t⩽1 when through-thickness shear damage was induced. In this range, under static loading conditions, SEA was seen to be higher than that for tubes crushed onto a flat platen.

Ballistic Impact Resistance of SMA and Spectra Hybrid Graphite Composites

The effect of adding small amounts of high strain hybrid components on the impact resistance of graphite epoxy composites subjected to projectiles traveling at ballistic velocities (greater than 900 ft/sec) has been studied. The hybrid components tested include superelastic shape memory alloy (SMA) and a high performance extended chain polyethylene (ECPE) known as Spectram. In all cases, the embedded SMA fibers were pulled through the graphite without straining to their full potential. It is believed that this is due to high strain rate effects coupled with a strain mismatch between the tough SMA and the brittle epoxy resin. However, a significant increase in energy absorption was found by adding ECPE and ECPE/SMA layers to the backface of the composite.

Concrete and Fiber Reinforced Concrete Subjected to Impact Loading

ABSTRACTDespite its extensive use, low tensile strength has been recognized as one of the major drawbacks of concrete. Although one has learned to avoid exposing concrete structures to adverse static tensile load, these cannot be shielded from short duration dynamic tensile stresses. Such loads originate from sources such as impact from missiles and projectiles, wind gusts, earthquakes and machine vibrations. The need to accurately predict the structural response and reserve capacity under such loading has led to an interest in the mechanical properties of the component materials at high rates of straining.One method to improve the resistance of concrete when subjected to impact and/or impulsive loading is by the incorporation of randomly distributed short fibers. Concrete (or Mortar) so reinforced is termed fiber reinforced concrete (FRC). Moderate increase in tensile strength and significant increases in energy absorption (toughness or impact-resistance) have been reported by several investigators in static tests on concrete reinforced with randomly distributed short steel fibers. A theoretical model to predict fracture toughness of FRC is proposed. This model is based on the concept of nonlinear elastic fracture mechanics.As yet no standard test methods are available to quantify the impact resistance of such composites, although several investigators have employed a variety of tests including drop weight, swinging pendulums and the detonation of explosives. These tests though useful in ascertaining the relative merits of different composites do not yield basic material characteristics which can be used for design.The author has recently developed an instrumented Charpy type of impact test to obtain basic information such as load-deflection relationship, fracture toughness, crack velocity and load-strain history during an impact event. From this information, a damage based constitutive model was proposed. Relative improvements in performance due to the addition of fibers as observed in the instrumented tests are also compared with other conventional methods.