Initial Impact Energy Research Articles

Impact Response of Novel Fibre-Reinforced Grouted Aggregate Rubberized Concrete

The consumption of waste tyre rubber in concrete is considered to be a critical factor addressing environmental issues and sustainability. Rubberized concrete is a novel building material that poses high energy absorption capacity compared to normal concrete and finds many applications in civilian infrastructures. The concept of impact strength of fibre-reinforced grouted aggregate rubberized concrete (FRGARC) has been pioneered in this study. In the fabrication of FRGARC, combination of steel fibres and treated rubber aggregates was placed in the formwork, and then, a flowable grout was injected to fill the voids. The rubber used in this experiment was pre-treated by immersing in water with 10% NaOH solution for a time period of 0.5 h. The variables examined in this investigation are crumbed rubber aggregate replacement ratios of 5%, 10%, 15%, 20%, 25% and 30% with three different water/binder ratios (0.45, 0.50 and 0.55). Hooked-end steel fibres were used at a constant dosage of 0.5% volume of concrete. The density reduction factor, compressive strength (CS), number of impact that induced initial crack and failure, initial crack and failure energy increasing factor of FRGARC were studied. Linear and power regression equations were developed to assess the density reduction factor and initial crack and failure energy increasing factor. FRGARC exhibits reduction in CS with increasing rubber content, and it significantly contributes to the enhancement of initial crack and failure impact energy absorption capacity.

Brain Injury and Impact Characteristics

Almost all studies of traumatic brain injuries have only focused on the maximum acceleration associated with the impact. However, it has been noted that other impact characteristics should also be considered. This study has examined the effect on brain deformation [maximum principal strain (MPS)] associated with changing three characteristics of an isosceles trapezoid acceleration profile: initial slope (jerk), maximum acceleration, and impact energy (maximum velocity squared). This involved using a preexisting finite element model of the brain and applying the trapezoidal acceleration impact to the center of the forehead. The results showed the largest values of MPS were found along a line between the coup and contrecoup positions, and that a strong direct relationship existed between maximum acceleration and brain deformation as measured using MPS. In addition, a strong direct relationship was found to exist between impact energy and brain deformation as measured using MPS. However, it was found that there was almost no observable change in MPS with respect to different jerk values, and in fact there was a slight decrease in MPS as jerk values increased. This comported with a shock spectrum analysis of a simple one dimensional multiple degree of freedom system exposed to similar trapezoidal impulses.

Experimental and numerical study of sandwich beams with layered-gradient foam cores under low-velocity impact

The low-velocity impact response of sandwich beams with aluminum alloy face-sheets and three core configurations (i.e., the positive layered-gradient core, negative layered-gradient core and non-gradient monolithic core) was first investigated by using a drop-weight machine. The impact bending tests were performed on specimens at five impact energy levels – 9.80 J, 22.05 J, 39.19 J, 61.24 J and 88.18 J – by varying the drop height of the weight. Based on experimental results, the corresponding numerical simulations and a multi-objective design optimization were performed. The experimental results show that all sandwich beams fail via the global bending deformation without local crack/fracture under lower initial impact energy, while they fail via larger bending deformation accompanied by obvious core tensile crack at mid-span and core shear at clamped ends with the increased initial impact energy. The resistance of both gradient core sandwich beams to impact flexure loading is weaker than that of non-gradient monolithic core sandwich beams. Simulation results indicate that the ratio of energy absorbed by core decreases with the increased impact energy, while the ratio of energy absorbed by face-sheets increases with the increased impact energy. The boundary condition is demonstrated to have great influence on the force-displacement response for all sandwich beams. Finally, the corresponding Pareto fronts representing a group of best trade-off designs were obtained.

Reprint of: Ionization probabilities of Ne, Ar, Kr, and Xe by proton impact for different initial states and impact energies

In this contribution we present ab initio results for ionization total cross sections, probabilities at zero impact parameter, and impact parameter moments of order +1 and −1 of Ne, Ar, Kr, and Xe by proton impact in an extended energy range from 100 keV up to 10 MeV. The calculations were performed by using the continuum distorted wave eikonal initial state approximation (CDW-EIS) for energies up to 1 MeV, and using the first Born approximation for larger energies. The convergence of the CDW-EIS to the first Born above 1 MeV is clear in the present results. Our inner-shell ionization cross sections are compared with the available experimental data and with the ECPSSR results. We also include in this contribution the values of the ionization probabilities at the origin, and the impact parameter dependence. These values have been employed in multiple ionization calculations showing very good description of the experimental data. Tables of the ionization probabilities are presented, disaggregated for the different initial bound states, considering all the shells for Ne and Ar, the M-N shells of Kr and the N-O shells of Xe.

Numerical simulation of GLARE 4A fiber-metal laminates subjected to ballistic impact

This article deals with the evaluation of the ballistic resistance of GLARE 4A fiber-metal laminates subjected to high velocity impact by a cylindrical projectile. Important impact variables such as the ballistic limit, the impact load and the absorbed energy time histories are predicted using the ANSYS LS-DYNA software. The simultaneous existence of various impact damage mechanisms, which is unique in fiber-metal laminates, is demonstrated using the numerical results. Each of the mechanisms absorbs a part of the initial impact energy and contributes to the high ballistic impact resistance the materials. With reference to the considered GLARE 4A panels, the behavior of the transient impact load is analyzed and useful conclusions are drawn. It is found that the maximum impact load is applied at the beginning of ballistic impacts, during the initial local indentation of the panels under the projectile. It is substantially higher than the following peak values of the impact force time history. It is revealed that during the beginning of ballistic impacts, the impulse of the collision increases as the thickness of the panels is increased. The work done by the impact load during the local indentation stage is also an increasing function of the panels’ thickness.

Regimes during single water droplet impacting on hot ethanol surface

In order to deepen the knowledge of the mechanisms of liquid pool fire suppression with water mist/spray, a series of preliminary experiments were carried out for a water droplet impacting upon target liquid surface. Ethanol was chosen as the target liquid and heated to simulate the temperature conditions as it burned. The water droplet used in the experiments was about 2.0mm with impact Weber number altering from 30 to 695. The results show that three typical impact regimes including crater-jet, penetration and surface bubble are observed. The pool temperature and Weber number have important influences on the impact behaviors and characteristic parameters including the crown height, and the energy conversion rate during the crater evolution and jet evolution. The maximum crown height depends on Weber number but is weakly dependent on the pool temperature. The ratio of the sum of crater potential energy and surface energy to initial impact energy is linearly related to the dimensionless pool temperature. Likewise, for the cases of crater-jet, as the Weber number and pool temperature increase, the conversion rate of crater potential energy and surface energy to jet potential energy and surface energy increases linearly.

Energy absorption property of warp-knitted spacer fabrics with negative Possion’s ratio under low velocity impact

Auxetic warp-knitted spacer fabric is known for its excellent mechanical properties, shear-resistance, cushioning property, energy absorbing abilities, therefore draws more and more attention to this kind of fabrics. In order to study the impact resistance and energy absorption ability of auxetic warp-knitted spacer fabrics under low-velocity impact, falling weight impact tests are adopted in this paper and influence relations of energy absorption and impact resistance to auxetic performance and initial impact energy are analyzed. Results show that the larger absolute value of negative Poisson’s ratio is, the better energy absorption ability and impact resistance could be obtained, and the initial impact energy has little influence on the overall energy absorption of fabrics under low-velocity impact.

Ionization probabilities of Ne, Ar, Kr, and Xe by proton impact for different initial states and impact energies

In this contribution we present ab initio results for ionization total cross sections, probabilities at zero impact parameter, and impact parameter moments of order +1 and −1 of Ne, Ar, Kr, and Xe by proton impact in an extended energy range from 100keV up to 10MeV. The calculations were performed by using the continuum distorted wave eikonal initial state approximation (CDW-EIS) for energies up to 1MeV, and using the first Born approximation for larger energies. The convergence of the CDW-EIS to the first Born above 1MeV is clear in the present results. Our inner-shell ionization cross sections are compared with the available experimental data and with the ECPSSR results. We also include in this contribution the values of the ionization probabilities at the origin, and the impact parameter dependence. These values have been employed in multiple ionization calculations showing very good description of the experimental data. Tables of the ionization probabilities are presented, disaggregated for the different initial bound states, considering all the shells for Ne and Ar, the M-N shells of Kr and the N-O shells of Xe.

Impact protection behavior of NiTi shape memory alloy wires

This work studies the impact protection properties of both martensite NiTi wires and superelastic NiTi wires, with 0.5mm diameter, at different initial impact energies using a new-designed impact test plant. In particular, impact experiments under a specific temperature range of As-Af, were performed for the martensite NiTi wires. The test results show that both the martensite NiTi wires and superelastic NiTi wires have excellent impact protection properties and can dissipate a significant amount impact energy compared to other more metal materials such as Cu, Fe, and Al. Otherwise, the martensite NiTi wires can dissipate more impact energy in a shorter period of time than superelastic NiTi wires while generating a smaller impact force, Fmax, due to their larger plastic deformation energy. Moreover, the dissipated energy, Wd, of martensite wires increases from 23.8 MJ/m3 to 53.6 MJ/m3, and the impact force, Fmax, increases from 42.96N to 95.9N, while the temperature rises from 35°C to 65°C. That means the impact protection properties of martensite NiTi wires are temperature dependent in a specific temperature range As-Af. Those results in this study also reveal that the impact protection properties of both martensite NiTi wires and superelastic NiTi wires represent the basis for new shape memory damping element applications, particularly in automotive safety systems.

Simplified dynamic analysis of reinforced-concrete beams under impact actions

A two-degree-of-freedom mass-spring model considering the local effect of the contact component is developed to investigate the dynamic responses of reinforced concrete beams under low-velocity impact actions. The local modified coefficient is proposed by parameter regression from drop-hammer impact test results, and then the simplified model is validated by other relevant research. As shown, the simplified model is able to capture the dynamic responses of reinforced concrete beams. In addition, the impact process is simulated and further analysed. The effects of initial impact velocity and the yield criterion of reinforced-concrete beams are investigated. The energy dissipation levels for various cases with the same initial impact energy are compared. An analysis proposal is also developed to predict the dynamic responses of reinforced concrete beams if the impact action case is uncertain.

Numerical simulation on rock fragmentation by discontinuous water-jet using coupled SPH/FEA method

To investigate the rock fragmentation mechanism and its influence factors under discontinuous water-jet impact, the fluid-structure coupled smoothed particle hydrodynamics (SPH) and finite element analysis (FEA) was used to simulate the rock fragmentation process. A rate-dependent constitutive model was adopted to describe the mechanical behavior of rock, and the shock equation of state was used to simulate the water-jet. The rock fragmentation statuses under continuous and discontinuous water-jet impact were simulated and compared under the same initial impact energy, and the rock failure mechanisms, such as the crushing zone and crack formation, were investigated through the elements of pressure and stresses as a function of time. The effects of water-liquids distance and length on rock fragmentation by the discontinuous water-jet were also analyzed. With the same energy, the rock fragmentation performance of the discontinuous water-jet was better than that of the continuous water-jet. The failure of the rock crushing zone was mainly caused by plastic behavior; however, the crack propagation presented brittle failure. The “water cushioning effect” would appear when the water-liquids distance was too small, which restricted the impact effect on rock fragmentation. Discontinuous water-jet with a shorter water-liquid length would result in a deeper crushing zone and volume fragmentation of rock.

Low-velocity impact resistance of ATH/epoxy core sandwich composite panels: Experimental and numerical analyses

Abstract In this study, a new composite sandwich was investigated as a solution for the rehabilitation of existing hydraulic turbine. The innovative sandwich construction with an ATH/epoxy core (i.e. epoxy resin filled with alumina tri-hydrate (ATH) particles) and non-crimp glass fabric fiber-reinforced epoxy face sheets was subjected to low-velocity impact at various energy levels. A 3D progressive damage model was developed to predict the damage characteristics in the face sheets in combination with a viscoplastic-damage model to simulate the nonlinear response of the core. The obtained numerical results were compared with the test data to assess the effectiveness of the proposed model. Good correlation with respect to the contact force and energy-time relationships, permanent deformation, and impact-induced damage was achieved. The performance of the sandwich panel with an ATH/epoxy core was evaluated in term of impact damage resistance and energy dissipation capacity. Microscopic observations were performed to determine the damage and failure modes in the impact zone. The important role of the core material for enhancing the face-sheet damage tolerance was also identified. The various energy dissipation components were also quantified during an impact loading, and the energy dissipated in the sandwich core was approximately 50% of the initial impact energy.

Adsorption dynamics of molecular nitrogen at an Fe(111) surface.

We present an extensive theoretical study of N2 adsorption mechanisms on an Fe(111) surface. We combine the static analysis of a six-dimensional potential energy surface (6D-PES), based on ab initio density functional theory (DFT) calculations for the system, with quasi-classical trajectory (QCT) calculations to simulate the adsorption dynamics. There are four molecular adsorption states, usually called γ, δ, α, and ε, arising from our DFT calculations. We find that N2 adsorption in the γ-state is non-activated, while the threshold energy is associated with the entrance channel for the other three adsorption states. Our QCT calculations confirm that there are activated and nonactivated paths for the adsorption of N2 on the Fe(111) surface, which is in agreement with previous experimental investigations. Molecular dynamics at a surface temperature Ts = 300 K and impact energies Ei in the 0-5 eV range show the relative occupancy of the γ, δ, α, and ε states. The δ-state, however, is only marginally populated despite its adsorption energy being very similar to that of the γ-state. Our QCT calculations trace the dependence of molecular trapping on the surface temperature Ts and initial impact energy Ei and quantify the rates of the different competitive channels that eventually lead to molecular adsorption.

Impact fretting wear behavior of 304 stainless steel thin-walled tubes under low-velocity

This study aimed to investigate the impact fretting wear behavior of thin-walled tubes under different support interfaces with a novel impact wear testing rig. A tube/cylindrical contact model was used, and V-shaped fixtures with varied angles were applied. The 304 stainless steel tubes with varied lengths and a GCr15 bearing steel roller were used as the test materials. The interface deformation, impact energy absorption, and damage behavior were investigated in terms of the influence of the support angle, tube length, and the initial impact energy. After the test, the wear mechanism of the tube was investigated. The results showed that under the same lengths, when the support angle increased, the deformation displacement increased, but the contact peak force, energy absorption, and the area of worn scars decreased. The increasing length increased the contact force, energy absorption ratio, and serious damage but reduced the deformation. The increasing kinetic energy of the initial impact will decrease the energy absorption ratio. Contact fatigue spalling and oxidation are the wear mechanisms of the impact fretting wear of 304 stainless steel.

An experimental and numerical study on scaling effects in the low velocity impact response of CFRP laminates

Scaling effects in the low velocity impact response of plain weave carbon-fibre-reinforced plastic (CFRP) panels have been investigated both experimentally and numerically. The experimental tests were undertaken using an instrumented drop-weight impact tower and the numerical simulations were conducted using the commercially-available finite element (FE) solver ABAQUS/Explicit. Here a rate-dependent damage model was implemented through the ABAQUS user-defined material interface, VUMAT, to describe the mechanical behaviour of the composite laminates. The experimental tests and numerical simulations both indicate that at energies above the damage threshold, damage does not obey a simple scaling law, becoming more severe as the scale size is increased. An examination of the damaged samples in the tests and numerical simulations indicated that, for a given scaled impact energy, fibre damage, in the form of large cracks extending in the warp and weft directions, was more severe in the larger samples. It is argued that the energy absorbed in fibre fracture scales with the square of the scale factor, i.e. n2, whereas the initial impact energy scales as n3. This discrepancy results in increased levels of energy needing to be absorbed in larger scale sizes, leading to greater levels of impact damage in the larger scale sizes.

The energy absorption behavior of hybrid composite laminates containing nano-fillers under ballistic impact

Hybrid composite laminates consisting of woven Kevlar fiber fabric, epoxy and AA 5086-H32 aluminum sheets were produced and the effects of addition of micro and nano-fillers to the fiber on ballistic response of the hybrid laminates were investigated. The micro and nano-fillers used in this study are powders of aluminum, gamma alumina, silicon carbide, colloidal silica and potato flour. They were introduced into the Kevlar fabrics by mixing with polyethylene glycol (PEG-400), followed by impregnation of the Kevlar fabric with the mixture and drying to eliminate the solvent. The energy absorption by the hybrid composite laminates containing the various nano-fillers under ballistic impact were determined and compared with laminate containing no nano-filler impregnation. The ballistic impact resistance of the produced hybrid composite laminates was tested according to NATO standards using a caliber 270 Winchester rifle. The projectile penetration and the resulting perforations of the hybrid laminates were studied in order to determine the influence of the deposited nano-fillers on Kevlar fibers on their energy absorption and impact resistance. The relationship between areal density and energy absorbed are discussed to determine which specimens perform better under ballistic impact. Protection levels achieved by targets were analyzed in relation to the initial impact energy from low caliber weapons. The results indicate that the ballistic impact resistance and impact energy absorption of the hybrid composite laminates were enhanced by deposition of micro and nano-fillers into surface of the Kevlar fibers fabrics. The highest impact energy absorption capacity was achieved by deposition of aluminum powder followed be colloidal silica and silicon carbide powder in that order. Addition of gamma alumina powder and potato flour has produced the least effect of enhancing the impact energy absorption capability of the laminates. These findings indicate that introduction of micro- and nano-fillers coating on Kevlar fabrics using PEG-400 is a promising method for strengthening interfacial bonding between the matrix and fibers in hybrid composite laminates.

Response of glass fiber-reinforced hybrid shear thickening fluid (STF) under low-velocity impact

This paper addresses the response of glass fiber-reinforced shear thickening fluid (STF) under low-velocity impact. Experimental tests were performed according to ASTM: D5628 for initial impact energy 6.89 J and for samples with STF+ nanoclay (30% silica and 3% clay nanoparticles), STF+ nanoclay (30% silica and 1% clay nanoparticles), STF (30% silica nanoparticles), and STF (20% silica nanoparticles).The effect of impregnating glass fabrics with STFs on their quasi-static puncture resistance performance has been investigated. A STF was prepared successfully, and rheological behavior was investigated. The results of rheological tests indicate that the increase in the fraction weight of nanosilica and nanoclay leads to the increase in suspension viscosity and reduction in the critical shear rate. One of the disadvantages of STF is high concentration. Glass fabrics were soaked in STF/ethanol solution to prepare STF–glass fabric composite and STF–nanoclay–glass composite. For better immersion of fibers, at first STF is diluted in ethanol, and then, the fibers are left therein for a specified period in order to impregnate all fibers with the fluid. After this stage, to eliminate the ethanol in the sample, it is heated at a temperature range of 60–70 °C. The composite’s sensitivity to the impact will be reduced through ethanol combining with the fluid and its elimination. Quasi-static resistant tests were carried out on both the neat glass fabrics and STF–glass fabric and STF–nanoclay–glass fabrics composites using a hemispherical penetrator based on the areal density. This study clearly displays a significant enhancement in penetration resistance of glass fabric impregnated with different combination of STF and STF–nanoclay. In sample with higher weight fraction of nanosilica and nanoclay, displacement to yield point is higher and resistance to penetration does not have much difference.

New criteria for simulating failure under multiple impacts of the same total energy on glass fiber reinforced aluminum alloy laminates

The low-velocity impact behavior of glass-fiber-reinforced aluminum alloy laminates (GLARE) is analyzed under single and multiple impacts of the same total energy. A new failure-judgment method is proposed by modifying previous failure criteria. This method is combined with a materials performance gradual degradation method and is employed by writing the LS-DYNA user subroutine for the impact simulation and testing of GLARE. The established finite-element model is proved reliable by comparing test results. Analyzing the simulated single and multiple impacts of the same total energy reveals that, GLARE sustains greatest internal damages under single impact. However, repeated impacts induce the largest deformation. If the impact frequency is maintained constant, the GLARE's damaged area widens as the initial impact energy increases.

Ballistic impact response of laminated hybrid materials made of 5086-H32 aluminum alloy, epoxy and Kevlar® fabrics impregnated with shear thickening fluid

The ballistic impact behavior of hybrid composite laminates synthesized for armor protection was investigated. The hybrid materials, which consist of layers of aluminum 5086-H32 alloy, Kevlar® 49 fibers impregnated with shear thickening fluid (STF) and epoxy resin were produced in different configurations using hand lay-up technique. The hybrid materials were impacted by projectiles (ammunitions of 150g power-point) fired from a rifle Remington 7600 caliber 270 Winchester to strike the target at an average impact velocity and impact energy of 871m/s and 3687J, respectively. The roles of the various components of the hybrid materials in resisting projectile penetration were evaluated in order to determine their effects on the overall ballistic performance of the hybrid laminates. The effects of hybrid material configuration on energy dissipation during ballistic impacts were investigated in order to determine a configuration with high performance for application as protective armor. The energy dissipation capability of the hybrid composite targets was compared with the initial impact energy of low caliber weapons (according to NATO standards) in order to determinate the protection level achieved by the developed hybrid laminates. Deformation analysis and penetration behavior of the targets were studied in different stages; the initial (on target front faces), intermediate (cross-section), and final stages (target rear layers). The influence of target thickness on the ballistic impact response of the laminates were analyzed. Differences in ballistic behavior were observed for samples containing Kevlar® impregnated with STF and those containing no STF. Finally, mechanisms of failure were investigated using scanning electron microscopic examination of the perforations.

Numerical analysis of penetrometers free-falling into soil with shear strength increasing linearly with depth

Dynamic penetrometers have been used for offshore oil and gas industry applications such as pipeline feasibility studies and anchoring systems, and military applications including naval mine countermeasures and terminal ballistic studies. The main challenge of using dynamic penetrometers is the interpretation of their test results in order to deduce the mechanical properties of the penetrated soil via empirical or theoretical relations. Recently, a robust numerical method based on the Arbitrary Lagrangian–Eulerian (ALE) technique has been developed for analysing dynamic penetration problems and used to investigate a smooth penetrometer free falling into a uniform layer of clayey soil. Numerical as well as experimental results indicate that the penetration characteristics, including the impact energy, total time, and total depth of penetration, depend on the mechanical properties of the soil including its stiffness and strength parameters as well as the geometry of the penetrometer and its initial impact energy. In this study, the ALE method is employed to study the effect of shear strength increasing with depth (a common condition of seabed deposits) on the penetration characteristics of a free falling penetrometer. Conducting more than two thousand numerical simulations has shown that there is an approximate quadratic relation between the final embedment depth of a FFP penetrating into a non-uniform clay soil and the combined kinetic energy on contact with the soil and subsequent loss in potential energy of the penetrometer.