Greater Energy Absorption Research Articles

Finite element analysis of AHS steel under dynamic loading using a micromechanical modelling

Currently, advanced high strength (AHS) steel sheets have been increasingly used in the automotive structural parts, where improved crashworthiness and lightweight design are required at the same time. Such steel sheets provide an excellent combination between high strength and great energy absorption. Most AHS steels exhibit microstructures containing several phases and constituents with different morphologies and mechanical properties. In this work, the dual phase (DP) steel grade 780 was investigated under dynamic tensile loading by means of a finite element modelling on the micro-scale. A representative volume element (RVE) model was applied to take into account the effects of microstructure characteristics on the mechanical behaviour of steel sheets at high strain rates. For the RVE modelling, the Johnson-Cook constitutive model was applied to describe the stress-strain response, whereas the Johnson-Cook damage model and damage locus were employed for predicting failure development of each individual phases of examined steel. The RVE simulations were performed under varying strain rates and states of stress and the results were subsequently compared.

Mechanical properties of joints in 5052 aluminum made with adhesive bonding and mechanical fasteners

In this work, the mechanical properties of joints made with a ridged tack only, one-part heat-curing epoxy only, and a combination of the two were evaluated. All samples were constructed using 1.6 mm thick 5052 aluminum. Testing was performed in lap shear, cross tension, and at 45°. A set of tests was also performed to investigate the mechanical strength of joints in lap shear under various surface preparation methods.It was found that the peak failure load was governed solely by the adhesive in hybrid joints. The performance gain from the inclusion of the ridged tack was greater energy absorption. The absorbed energy for a hybrid joint in lap shear configuration is closely approximated by the sum of energy absorbed with adhesive only and ridged tack only. The effect was much less pronounced for samples in cross tension and at 45°. Additionally, the adhesive strength was found to be completely unaffected by the surface preparation of the samples.

Fabrication and characterization of hypoeutectic open-cell Al-Si foams using gravity die casting and squeeze casting

Gravity die casting and squeeze casting are the techniques used for the fabrication of hypoeutectic open-cell Al-Si foams which are characterized and studied for their energy absorbing quality in compression tests. The effect of different amounts of sodium chloride (NaCl) (up to 56 vol.%) as a space holder in the casting of aluminum foam on the morphology, density, porosity, compressive and energy absorption properties of aluminum foam was studied. The hypoeutectic Al-Si alloy with NaCl particles as a space holder was used to fabricate the aluminum foam using gravity die casting and squeeze casting. The hypoeutectic open-cell Al-Si foams produced by squeeze casting showed smaller pore size, better pore distribution, higher porosity, good compressive strength and greater energy absorption energy compared to that of gravity die casting. The hypoeutectic open-cell Al-Si foams with 44 vol.% NaCl using squeeze casting showed the best properties among all foams due to its moderate and well-distributed porosity.

Crashworthiness analysis and multi-objective design optimization of a novel lotus root filled tube (LFT)

The purpose of this paper is to propose a novel lotus root filled tube (LFT) for improving the energy absorption capability of crash box under axial impact loading. The LFT consists of a lotus root like core and a basic tube (BT). Firstly, a finite element (FE) model of the LFT is established. Secondly, the FE model is used to study the energy absorption capability of LFT with variations in the thickness of square tube (t 1), the thickness of lotus root like core (t 2), the height of the cell structure (h), as well as the length of the cell structure (l 1 , l 2). Finally, to determine the optimal geometric parameters, multiobjective design optimization (MDO) is performed by integrating optimal Latin hypercube sampling (OLHD), response surface method (RSM) and non-dominated sorting genetic algorithm-II (NSGA-II). The results have demonstrated that the proposed LFT has great energy absorption efficiency and is able to improve vehicle crash performance under frontal impact loading.

Axial and lateral crushing responses of aluminum honeycombs filled with EPP foam

Abstract This paper aimed to experimentally understand the effects of Expanded Polypropylene (EPP) foam filling on the mechanical properties of aluminum (Al) honeycomb panels. The process of lightweight EPP foam with different densities filling in Al honeycomb composites was first studied, then a series of axial (out-of-plane) and lateral (in-plane) compression tests were carried out on the bare and filled honeycombs. It is showed that the peak strength, mean crushing strength and total energy absorption (EA) in the axial tests increased with foam filler (increased by approximately 2.310–43.069%, 34.791–120.219% and 46.765–179.474% with respect to bare honeycomb, respectively); and the higher foam density, the greater filling effect, whereas the specific energy absorption (SEA) remained unchanged with increase in the foam density. Interestingly, more significant improvement in total energy absorption and SEA were found under lateral crushing. All the foam filled panels were of even greater energy absorption than the sum of bare honeycomb and EPP foam separately under both axial and lateral crushing. The foam filler had no significant effect on its deformation pattern under axial crushing, whereas it helped decrease local densification in honeycomb, leading the filled panels to deform in uniform rhombus shapes under lateral crushing.

Investigation of progressive failure in the composite sandwich panels with elastomeric foam core under concentrated loading

Failure and damage of crushable materials employed as core for the sandwich structures reduces serviceability and energy absorption capacity of the components especially under bending load so that many beneficial properties seem to be achieved by application of noncrushable lightweight materials instead of crushable foams as core for the sandwich structures. In this paper, an elastomeric foam is employed as core for two aspect ratios of the composite sandwich panels and the enhancement of the load-carrying capacity in the elastomeric foam-cored sandwich panels is investigated in comparison to which is measured about the individual composite panels applied as skins. Both experimental and finite element simulation programs are included in the research. The load-carrying performance of the elastomeric foam-cored sandwich panels is considered dependent on two main features of the constituent materials as hyperelastic behavior of the foam core and progressive damage of the composite skins which are simulated in the finite element models in order to describe the failure mechanism in the panels. Collapse of the elastomeric foam-cored sandwich panels is considered due to connection of some failure lines in the composite skins; however, the foam core remains undamaged. The elastomeric foam core can transfer the load from the top composite skin to the bottom one so that a great energy absorption capacity is provided for these panels. The elastomeric foam after failure of the composite skins can mobilize the residual strength of the laminates to endure against large deformations prior to final collapse. By application of the composite laminates in sandwich form with elastomeric foam core, the maximum load carrying and energy absorption capacity of the composite laminates increased about 60 and 110%, respectively. The results show more favorite failure behavior for the elastomeric foam-cored sandwich panels in comparison to which is expected usually for the crushable foam-cored sandwich panels which may be concerned in many industrial applications.

Quasi-static and dynamic compression behavior of glass cenospheres/5A03 syntactic foam and its sandwich structure

5A03 aluminum matrix syntactic foam filled with glass cenospheres was synthesized using pressure infiltration technique. This paper focused on the compression behavior of syntactic foam at quasi-static (10−3s−1) and dynamic (strain rate 1×103s−1–3×103s−1) condition, and the dynamic response of syntactic foam core sandwich structure with two different wave impedance front-panels (A3 steel and AZ31) subjected to split-Hopkinson pressure bar. The syntactic foam at dynamic loading exhibited a maximum 43% increase in peak strength, 38% in plateau strength, and 23% in energy absorption capacity compared to quasi-static results, with 0.03 strain rate sensitivity similar to that of aluminum matrix. The dynamic compression behavior can be concluded as thin near-45° shear bands forming, deformed area propagating to the central and lateral parts, and finally densifying with significant lateral expansion. The sandwich structure exhibited great energy absorption capability due to the syntactic foam core. The higher wave impedance front-panel would be conducive to the energy absorption capability of syntactic foam core into full play.

Plastic analyses of thin-walled steel honeycombs with re-entrant deformation style

To get an ideal energy absorbing structure, which has low initial peak force but high energy absorbing efficiency, non-entrant and re-entrant honeycombs have re-entrant deformation styles were designed and fabricated. In-plane compression experiments and numerical simulations were carried out to reveal the progressive crushing process and the energy absorption level. In the crushing, the re-entrant honeycomb contracts laterally and has the potential to turn to a triangular lattice structure. The initial yield force of these honeycombs is not high but the stress after yield keeps high level and the plateau in stable. It is found to get a stable deformation curve the vertical wall must be thicker. Based on the crushing modes, plastic models were built to predict the mean crushing force (MCF) and they fit the test data very well. It is found that the re-entrant honeycomb has better energy absorption than the non-entrant honeycomb. Adopting re-entrant design, the MCF is even greater than the peak force, which benefits engineering design for energy absorbing structures in devices which requires smaller peak force but greater energy absorption.

Quantization of plasmon in two-dimensional square quantum dot system

Plasmon in quantum dot system is one of the most notable research topics in the field of optoelectronics. With the development of nanotechnology, plasmon in nano-structure has received considerable attention due to its potential applications in future natural science areas. To better understand the quantum effect and the properties of plasmon, in this paper we use the linear response theory and the tight-binding approximation to investigate the collective response of charge in a twodimensional square quantum dot system. The results show that when the frequency of the external field equals the frequency of the plasmon, there are strong charge collective oscillations in the quantum dot system, accompanied by great energy absorption and near-field enhancement. Owing to the quantization of plasmon, the collective charge oscillations in a two-dimensional square quantum dot system are found at different frequencies. The number of quantum modes of plasmon increases with the size and electron number of square quantum dots increasing, this behaviour of quantum mode of plasmon is similar to the one of phonon. The reasons for this behaviour are as follows. First, with the increase of quantum dot size, there are more energy levels around the fermi energy, and the electrons can jump from more energy levels to the outside of fermi circle, so there are more collective excitation frequencies (i.e., more quantum modes of plasmon) in a larger size system. Second, with the increase of electron number in quantum dots, there are more energy levels occupied by electrons, so there are more quantum modes of plasmon too. Furthermore, the size dependence of plasmon shows that with the increase of quantum dot size, the frequency interval between two neighbouring modes of plasmon is smaller, and the discrete modes of plasmon will gradually display quasi-continuous characteristic and transform gradually into the classical continuous modes of plasmon, and the frequency spectrum of plasmon turns into the classical dispersion relation. Such a characteristic is in accord with Bohr's correspondence principle, implying that the quantum plasmon and classical plasmon are gradually unified in a macroscopic size. The dependence of plasmon on the size and electron number of quantum dots also show that with the increase of the quantum dot size, the frequencies of the plasmon is red-shifted and the excitation intensity of the plasmon increases; with the increase of the electron number in quantum dot, the frequency of the plasmon is blue-shifted and the excitation intensity of the plasmon increases.

Inertial effects on the mechanical response of aluminium foam-filled braided stainless steel tubes under transverse loading

ABSTRACTMechanical responses of quasi-static and dynamic transversely loaded empty/foam-filled braided tubes were investigated with a custom load frame and pneumatic gun/projectile at velocities ranging from 21 to 27 m/s. Braided tubing was woven from AISI 304 wire (wire diameter: 0.51 mm, external diameter: 64.5 mm, length: 330 mm). Foam density ranged between 162 and 520 kg/m3. Localised foam collapse at mid-span under impact resulted in greater energy absorption for foam-filled specimens compared to quasi-static tests. Foam density significantly influenced force efficiency for reduced deflections. For low-density quasi-static tests, the average force efficiency was 58.3% decreasing to 41.9% under impact. Force efficiency for high-density foam under quasi-static loading was 42.8% decreasing to 23.4%. High-density foam cores exhibited minimal foam crushing as the increased mechanical properties of the foam resulted in braided tube failure. Low/medium-density foam cores yielded both optimal specific energy absorption over the full deflection range and force efficiency for reduced deflections.

Fracture Mechanics Parameters of Fine Grained Concrete with Polypropylene Fibres

Fracture mechanics is widely used to analyze the material behaviour in a structure. The paper reports the results of an experimental programme focused on the effect of various synthetic fibres on the fracture properties of concrete investigated in Mode I conditions. The changes in concrete properties were analysed on the basis of the critical stress intensity factor KIc, the critical value of crack tip opening displacement (CTODc) and the fracture energy GF. The addition of the synthetic fibres had a slight effect on the strength properties of concrete but, at the same time, it had a significant influence on the fracture mechanics parameters by the modification of pre-cracking and particularly post-cracking behaviour of the concrete. Results of measuring the toughness and energy-absorption characteristics showed that the specimens reinforced with synthetic fibres acquired a great ductile behaviour and energy absorption capacity, compared to ordinary concrete specimens.

Case Study on Retrofit of Steel Plate Shear Walls Using Low Yield Point Steel Infill Plates

Steel plate shear walls (SPSWs) have been frequently used in seismic design and retrofit of buildings over the past three decades or so. Employment of infill plates made of low yield point (LYP) steel with considerably low yield stress and high elongation capacity is believed to provide the possibility in order to improve the structural and seismic characteristics of such lateral force-resisting systems. Among the various benefits is the early yielding of LYP steel infill plates, which can result in greater energy absorption capacity and limitation of the plastic deformation demand to the surrounding frame structure. On this basis, a case study is performed using numerical simulations and reported in this paper on the seismic retrofit of SPSWs using LYP steel infill plates of double thickness. It is shown that the retrofit of a steel shear wall using a LYP steel infill plate of double thickness can result in desirable plate-frame yielding sequence and interaction. Moreover, this retrofit strategy can improve the initial stiffness, buckling stability, and energy dissipation capacity of the existing SPSW system.

더블 I형 감쇠장치로 보강한 비내진 RC 골조의 내진성능 평가

Abstract: In this study, to examine seismic reinforcement effect of a school building constructed prior to application of seismic design, a Double I-type damper supported by wall was installed to perform comparative analysis on existing non-seismic designed RC frame. As a result o f experiment, while non-seismic designed specimen showed rapid reduction in strength and brittle shear destruction as damages were focused on top a nd bottom of left and right columns, reinforced specimen showed hysteretic characteristics of a large ellipse with great energy absorption abilit y, exhibiting perfectly behavior with increased strength and stiffness from damper reinforcement. In addition, as a result of comparing stiffness reduc tion between the two specimens, specimen reinforced by shear wall type damper was effective in preventing stiffness reduction. Energy dissipation ability of specimen reinforced by Double I-type damper was about 3.5 times as high as energy dissipation ability of non-reinforced specimen. Such e nhancement in energy dissipation ability is considered to be the result of improved strength and deformation.Keywords: Double I-type Hysteretic damper, Strength degradation, Stiffness degradation, Energy dissipation, retrofitted

Soldier-relevant loads impact lower limb biomechanics during anticipated and unanticipated single-leg cutting movements

This study quantified how body borne load impacts hip and knee biomechanics during anticipated and unanticipated single-leg cutting maneuvers. Fifteen male military personnel performed a series of single-leg cutting maneuvers with three different load configurations (light, ~6kg, medium, ~20kg, and heavy, ~40kg). Subject-based means of the specific lower limb biomechanical variables were submitted to repeated measures ANOVA to test the main and interaction effects of body borne load and movement type. With body borne load, stance time (P<0.001) increased, while larger hip (P=0.027) and knee flexion (P=0.004), and hip adduction (P<0.001) moments, and decreased hip (P=0.002) and knee flexion (P<0.001), and hip adduction (P=0.003) postures were evident. Further, the hip (P<0.001) and ankle (P=0.024) increased energy absorption, while the knee (P=0.020) increased energy generation with body borne load. During the unanticipated maneuvers, the hip (P=0.009) and knee (P=0.032) increased energy generation, and peak hip flexion moment (P=0.002) increased relative to the anticipated movements. With the body borne load, participants adopted biomechanical patterns that decreased their locomotive ability including larger moments and reduced flexion postures of the lower limb. During the single-leg cut, participants used greater energy absorption from the large, proximal muscles of the hip and greater energy generation from the knee with the addition of load. Participant׳s performance when carrying a range of loads was not compromised by anticipation, as they did not exhibit the hip and knee kinetic and kinematic adaptations previously demonstrated when reacting to an unplanned stimulus.

Cervical total disc replacement exhibits similar stiffness to intact cervical functional spinal units tested on a dynamic pendulum testing system

Background contextThe pendulum testing system is capable of applying physiologic compressive loads without constraining the motion of functional spinal units (FSUs). The number of cycles to equilibrium observed under pendulum testing is a measure of the energy absorbed by the FSU. ObjectiveTo examine the dynamic bending stiffness and energy absorption of the cervical spine, with and without implanted cervical total disc replacement (TDR) under simulated physiologic motion. Study designA biomechanical cadaver investigation. MethodsNine unembalmed, frozen human cervical FSUs from levels C3–C4 and C5–C6 were tested on the pendulum system with axial compressive loads of 25, 50, and 100 N before and after TDR implantation. Testing in flexion, extension, and lateral bending began by rotating the pendulum to 5°, resulting in unconstrained oscillatory motion. The number of rotations to equilibrium was recorded and the bending stiffness (Newton-meter/°) was calculated and compared for each testing mode. ResultsIn flexion/extension, with increasing compressive loading from 25 to 100 N, the average number of cycles to equilibrium for the intact FSUs increased from 6.6 to 19.1, compared with 4.1 to 12.7 after TDR implantation (p<.05 for loads of 50 and 100 N). In flexion, with increasing compressive loading from 25 to 100 N, the bending stiffness of the intact FSUs increased from 0.27 to 0.59 Nm/°, compared with 0.21 to 0.57 Nm/° after TDR implantation. No significant differences were found in stiffness between the intact FSU and the TDR in flexion/extension and lateral bending at any load (p<.05). ConclusionsCervical FSUs with implanted TDR were found to have similar stiffness, but had greater energy absorption than intact FSUs during cyclic loading with an unconstrained pendulum system. These results provide further insight into the biomechanical behavior of cervical TDR under approximated physiologic loading conditions.

In situ microtensile testing and X-ray microtomography-based finite element modelling of open-cell metal foam struts and sandwich panels

Microtensile testing was used to determine the mechanical properties of individual aluminium alloy foam struts. Finite element modelling of as-tested struts was carried out using X-ray microtomography scans of the undeformed struts to define the geometry. Strut deformation was described by continuum viscoplastic damage constitutive equations calibrated by microtensile test data of the aluminium alloy in its optimally aged condition. The as-tested strut finite element model was used to develop a procedure that compensates for the effect of grip slippage inherent in the microtensile testing of metal foam struts, which results in a considerable reduction in observed elastic stiffness compared to the typical value of 70 GPa for aluminium alloys. The calibrated constitutive equations were then implemented in finite element models of sandwich panels with the aluminium metal foam as its core material. The finite element models were used in simulations of cases of low energy impact to represent tool drop conditions in order to investigate the suitability of new wing skin designs using metal foam core sandwich panels. An optimal strut aspect ratio was identified through simulation that provides the greatest energy absorption per unit mass while ensuring core damage is accurately reflected by facesheet deformation, which is necessary for detection and repair.

In-situ Micro-tensile Testing and X-ray Micro-tomography based FE Modeling of Open-cell Metal Foam Struts and Sandwich Panels

Microtensile testing was used to determine the mechanical properties of individual aluminium alloy open- cell foam struts. Finite element (FE) modelling of as-tested struts was carried out using X-ray microtomography (XMT) scans of the undeformed struts to define the geometry. Strut deformation was described by continuum viscoplastic damage constitutive equations calibrated by the microtensile test data for the aluminium alloy's optimally aged condition. The as-tested strut FE model was used to develop a procedure that compensates for the effect of grip slippage inherent in the microtensile testing of metal foam struts, which results in a considerable underestimation of the elastic stiffness. The calibrated constitutive equations were then implemented into 3D FE models of open-cell metal foam core sandwich panels to study the effect of varying the strut aspect ratio on the mechanical properties of the core under uniform compression, as well as core damage visibility under localised impact scenarios. An optimal strut aspect ratio was identified through simulation that provides the greatest energy absorption per unit mass whilst ensuring core damage is accurately reflected by face sheet deformation, which is necessary for detection and repair. FE models of the panel subject to three and four point bending were created to provide a virtual standardised test to assess the core elastic properties.

Analysis of lower limb internal kinetics and electromyography in elite race walking

The aim of this study was to analyse lower limb joint moments, powers and electromyography patterns in elite race walking. Twenty international male and female race walkers performed at their competitive pace in a laboratory setting. The collection of ground reaction forces (1000 Hz) was synchronised with two-dimensional high-speed videography (100 Hz) and electromyography of seven lower limb muscles (1000 Hz). As well as measuring key performance variables such as speed and stride length, normalised joint moments and powers were calculated. The rule in race walking which requires the knee to be extended from initial contact to midstance effectively made the knee redundant during stance with regard to energy generation. Instead, the leg functioned as a rigid lever which affected the role of the hip and ankle joints. The main contributors to energy generation were the hip extensors during late swing and early stance, and the ankle plantarflexors during late stance. The restricted functioning of the knee during stance meant that the importance of the swing leg in contributing to forward momentum was increased. The knee flexors underwent a phase of great energy absorption during the swing phase and this could increase the risk of injury to the hamstring muscles.

Study on Mechanical Properties of Cement Clinker and Limestone by Hertzian Indentation Method

The recovery resistance, energy dissipation, and other mechanical properties of cement materials are evaluated based on the Hertzian indentation method in this work. It is significant and efficient for engineering application. In results, the calculated energy dissipation of clinker is higher than that of limestone, which can partially be used to explain why the grinding of clinker consumes a lot of energy in cement industry. The recovery resistance for limestone under the peak load of 100N is almost higher than of clinker. However, in contrast to that of 200N, the recovery resistance for limestone is almost identical to that of clinker. It is indicated that the clinker exhibits better plasticity. and greater energy absorption capacity.

Reflectância de banda larga em recém-nascidos com presença de emissões otoacústicas evocadas por transiente

To characterize the normal values of acoustic energy reflectance obtained with pure-tone stimulation in neonates prior to hospital discharge. Seventy-seven infants (37 girls and 40 boys) were evaluated by measuring acoustic reflectance using pure-tone stimuli, transient-evoked otoacoustic emissions, and tympanometric probe frequencies of 226 Hz and 1 kHz. At low frequencies (258-750 Hz), greater energy reflectance was observed, while at medium frequencies (1-3 kHz), greater energy absorption was observed. There was no difference between ears or between genders. Normal energy reflectance values were obtained for the studied population. The data indicate a reflectance curve with a distinct configuration for the studied age.