Function Of Impact Energy Research Articles

Irreversibly absorbed energy and damage in GFRP laminates impacted at low velocity

The scope of this paper was to establish a correlation between the damage occurring in a composite as a consequence of low-velocity impact and the energy dissipated during the impact phenomenon. To this aim, instrumented impact tests were carried out on glass fabric/epoxy laminates of three different thicknesses, using different energy levels. The irreversibly absorbed energy was obtained from the force–displacement curves provided by the impact machine. To assess damage progression as a function of impact energy, ply-by-ply delamination and fibre breakages revealed by destructive tests were measured. A previous model, based on energy balance considerations, was applied to interpret the experimental results, together with an original method of data reduction, allowing for the isolation of the maximum energy portion due to indentation and vibrational effects. From the results obtained, the contribution of fibre breakage and matrix damage to the irreversibly absorbed energy is comparable at low impact energies; with increasing initial energy levels, delamination becomes predominant in determining energy dissipation. However, the critical energy-release rate required to propagate delamination, as calculated from impact data, is considerably higher than the typical values deriving from Mode II delamination tests performed under laboratory conditions.

Damage and energy absorption in GFRP laminates impacted at low-velocity: Indentation model

Low-velocity impact tests were carried out on glass-fibre-reinforced plastic panels, varying the impact energy, laminate thickness, and tup diameter. A previous model, aimed at the prediction of indentation as a function of impact energy, was slightly modified, to establish a correlation of the dent depth with absorbed energy. Good agreement was found between the theoretical predictions and experimental results. Further, the possibility to resort to the absorbed energy from an indentation measurement, using a single curve valid whichever the laminate thickness and impactor diameter, was demonstrated. Analyzing previous experimental data, concerning carbon-fibre-reinforced plastics, the different behaviour of GFRP and CFRP in absorbing energy and undergoing indentation was revealed. New results about basalt fibre laminates based on a limited number of experimental tests were reported too.

Self-healing of low-velocity impact damage in glass fabric/epoxy composites using anepoxy–mercaptan healing agent

Self-healing woven glass fabric-reinforced epoxy composite laminates were made byembedding epoxy- and mercaptan-loaded microcapsules. After being subjected tolow-velocity impact, the laminates were able to heal the damage in an autonomic way atroom temperature. The healing-induced reduction in the damaged areas was visualizedusing a scanning acoustic microscope. The rate of damage area reduction, whichis closely related to the effect of crack rehabilitation and mechanical recovery,is a function of impact energy, content and size of the healing microcapsules.Minor damage, such as microcracks in the matrix, can be completely repaired bythe healing system without manual intervention, including external pressure.Microcapsules with larger size and/or higher concentration are propitious fordelivering more healing agent to cracked portions, while imposition of lateral pressureon damaged specimens forces the separated faces to approach each other. Bothcan improve the rate of damage area reduction in the case of severe damage.

Geophysical consequences of planetary-scale impacts into a Mars-like planet

All planetary bodies with old surfaces exhibit planetary-scale impact craters: vast scars caused by the large impacts at the end of Solar System accretion or the late heavy bombardment. Here we investigate the geophysical consequences of planetary-scale impacts into a Mars-like planet, by simulating the events using a smoothed particle hydrodynamics (SPH) model. Our simulations probe impact energies over two orders of magnitude (2 × 10 27–6 × 10 29 J), impact velocities from the planet’s escape velocity to twice Mars’ orbital velocity (6–50 km/s), and impact angles from head-on to highly oblique (0–75°). The simulation results confirm that for planetary-scale impacts, surface curvature, radial gravity, the large relative size of the impactor to the planet, and the greater penetration of the impactor, contribute to significant differences in the geophysical expression compared to small craters, which can effectively be treated as acting in a half-space. The results show that the excavated crustal cavity size and the total melt production scale similarly for both small and planetary-scale impacts as a function of impact energy. However, in planetary-scale impacts a significant fraction of the melt is sequestered at depth and thus does not contribute to resetting the planetary surface; complete surface resetting is likely only in the most energetic (6 × 10 29 J), slow, and head-on impacts simulated. A crater rim is not present for planetary-scale impacts with energies >10 29 J and angles ⩽45°, but rather the ejecta is more uniformly distributed over the planetary surface. Antipodal crustal removal and melting is present for energetic (>10 29 J), fast (>6 km/s), and low angle (⩽45°) impacts. The most massive impactors (with both high impact energy and low velocity) contribute sufficient angular momentum to increase the rotation period of the Mars-sized target to about a day. Impact velocities of >20 km/s result in net mass erosion from the target, for all simulated energies and angles. The hypothesized impact origin of planetary structures may be tested by the presence and distribution of the geochemically-distinct impactor material.

Impact Behavior of Glass/Epoxy Laminated Composite Plates at High Temperatures

The objective of this study is to investigate the impact behavior of laminated glass/epoxy composite plates with [0/90/0/90]S and [0/90/45/- 45] S stacking sequences at room (~20°C) and high temperatures (60°C and 100°C). The maximum contact force between the impactor and the composite plate, the maximum deflection at the maximum contact force at the center of the composite, and the contact time history were plotted as a function of impact energy. In order to determine the energy absorbing capability of the plates, energy profiling method was used. The results show that the perforation threshold increases with increasing temperature.

Adsorption kinetics and dynamics of CO on silica supported Au nanoclusters—Utilizing physical vapor deposition and electron beam lithography

The adsorption kinetics and dynamics of CO on silica supported Au clusters have been studied by thermal desorption spectroscopy (TDS) and molecular beam scattering. Physical vapor deposition (PVD) and electron beam lithography (EBL) have been used to fabricate the samples. According to our prior study (Kadossov et al., in press [49]), a maximum in the initial adsorption probability, S 0, occurs for 3 nm Au clusters. Therefore, in the present study, we have focused on this cluster size for PVD samples. In addition, 12 nm EBL Au clusters have been studied. This is presently one of the smallest achievable cluster sizes using EBL for macroscopic samples. Auger electron spectroscopy and scanning electron microscopy have been used to further characterize the samples. TDS revealed well-known features for PVD samples; i.e., two peaks assigned to CO adsorption on different defect sites were present. Interestingly, TDS data of EBL samples were dominated solely by one CO desorption peak. The initial adsorption probability of CO, S 0, decreased as a function of impact energy, E i, and adsorption temperature, T s, for both samples, which is consistent with non-activated molecular adsorption. The coverage dependence of the adsorption probability and S 0 are discussed in the framework of the capture zone model.

Deposition Dynamics of Hydrogenated Silicon Clusters on a Crystalline Silicon Substrate under Typical Plasma Conditions

We have studied the deposition dynamics of hydrogenated silicon clusters on a silicon substrate for various cluster sizes and impact energies. The results show that the interaction processes of silicon nanocrystals with a crystalline silicon substrate strongly depend on the impact energy ranging from elastic scattering over soft-landing to cluster destruction with penetration of some cluster atoms into the substrate. Under certain conditions, epitaxial-like recrystallization of clusters has been observed after the initial cluster structure was completely lost upon surface impact. The reaction mechanisms as a function of impact energy are in good agreement with recent experimental results.

Healing of impact damage in woven glass fabric reinforced epoxy composites

Abstract Woven glass fabric reinforced epoxy composite laminates were provided with crack healing capability by pre-dispersing a novel repair system in the composites’ matrix. The healing agent consisted of epoxy-loaded microcapsules and latent hardener CuBr2(2-MeIm)4 (the complex of CuBr2 and 2-methylimidazole). Compression after impact (CAI) tests were conducted to evaluate mechanical performance of the laminates before and after crack healing. Moreover, healing efficiency was studied as a function of impact energy, repair pressure, content and size of the microencapsulated epoxy. The experimental results indicated that the healing agent worked in repairing matrix cracks generated by impact. The composites should be heated to 140 °C for 0.5 h to achieve healing and moderate pressure was needed to close larger crack damage for good healing.

Characteristics and Behavior of High-Burnup Fuel That May Affect the Source Terms for Cask Accidents

Current risk assessments of spent fuel in storage and transportation casks use the properties of light water reactor fuel below 45 GWd/t U. Fuel is being driven to higher burnups that may influence the source term in cask accidents. To achieve these burnups the manufacturers are introducing new assembly designs and cladding alloys. As a result, at the higher burnups (≥50 GWd/t U) some of the characteristics of the fuel pellets, cladding, and assembly design used in the safety analysis have changed. The fuel pellet has developed a fine-grained, Pu-rich rim zone on its exterior surface. The source term may increase by up to three orders of magnitude over that expected from the particulate size distribution based on the fracture of the body of the pellets. The actual increase will depend on the fracture characteristics of the rim and number of fracture sites in the cladding. The cladding may acquire hydrogen contents up to 700 parts per million by weight during the increased exposure. Embrittlement of the cladding with subsequent loss of ductility may occur, especially if there is hydride reorientation. As a result, there may be a greater propensity for fracture of the rods upon impact, with subsequent release of fuel particulate and gas. Significantly improved source terms can be developed if additional data on fuel rim fracture as a function of impact energy, the dependence of cladding ductility for Zircaloy and the newer cladding alloys as a function of hydride reorientation, and release characteristics for fractured rods are obtained. Chalk River unidentified deposit spallation characteristics only make a significant contribution to the source term if the rods do not fracture in the accident or if a fire-only accident occurs.

Design and performance of an (e, e+ion) spectrometer for studies of fragmentation of dipole and non-dipole states of gaseous molecules

An (e, e+ion) spectrometer has been constructed that has the capability to measure time-of-flight (TOF) mass spectra of gases in coincidence with energy selected inelastically scattered electrons, as a function of impact energy, electron energy loss and electron scattering angle. Relative to earlier dipole-regime implementations of the (e, e+ion) technique, this spectrometer can be used to study molecular fragmentation under both dipole and non-dipole electronic excitation and ionization conditions. The spectrometer uses a position-sensitive electron detector and a TOF tube positioned at 90° with respect to the electron impact and scattering plane. The TOF design makes it possible either to extract all ions from the interaction region, or to discriminate preferentially for ions that have kinetic energy along the axis of the TOF tube, thus allowing one to collect spectra with maximum efficiency, or to study the dynamics of the production of the molecular and fragment ions. The design and construction of the spectrometer is described, along with preliminary results for ionization in the S 2p excitation and ionization region of SF 6.

Modified SDOF Models for Improved Representation of the Impact Response of Composite Plates

Previous research has shown that simple single degree of freedom (SDOF) models can be used successfully to reproduce the force-time response of composite plates subjected to low-velocity impacts (LVI). In particular, a simple spring-mass (SM) model yields accurate estimates of the peak contact force as a function of impact energy. The major limitation of this model is that it applies only to elastic impact events, and ceases to be valid after the onset of damage. The effort of this investigation is to modify the SM model, while retaining the simplicity of its formulation, and to extend its range of validity to the super-critical regime. Three models are derived, namely the damaged stiffness, the dissipated energy, and the spring-mass-dashpot models, and their validity is examined through comparisons with experimental data. Impact force-time traces for carbon/epoxy laminates exhibiting various combinations of laminate thickness and support span are collected, and it is found that the additional unknowns introduced for each of the models, although determined empirically, are strongly related to the structural parameters for each configuration investigated.

Energy losses of swift protons to hydrogen atoms

Full and reduced three-body classical trajectory Monte Carlo (CTMC) theory are used to calculate energy losses of the projectile in proton–hydrogen atom collisions as a function of impact energy. The total stopping power is presented along with partial contributions of the energy deposition among the channels of excitation, ionization and capture. Contributions of the projectile–electron and projectile–target nucleus interactions to the total stopping power are also investigated. Our results are compared with other theoretical calculations and experimental data. The present calculations verify that high order effects should be included for a proper description of electronic stopping power.

Adsorption of CO2 on oxidized, defected, hydrogen and oxygen covered rutile (1 ? 1)-TiO2(110)

Presented are initial, S(0) and coverage, Theta, dependent S(Theta), adsorption probability measurements of CO(2) as a function of impact energy, E(i) = 0.12-1.3 eV, adsorption temperature, T(s) = 85-300 K, hydrogen and oxygen pre-exposure, as well as density of defects, Gamma, as varied by annealing (T = 600-900 K) and Ar(+) ion sputtering (dose chi(Ar) at 600 eV at 85 K) of a rutile (1 x 1) TiO(2)(110) surface. The defect densities were qualitatively characterized by thermal desorption spectroscopy (TDS) of CO(2). The CO(2) TDS curves consisted of two structures that can be assigned to adsorption on pristine and oxygen vacancy sites, in agreement with earlier studies. S(0) decreased linearly with E(i) and was independent of T(s). The adsorption dynamics were dominated by the effect of precursor states leading to Kisliuk-like shapes over the E(i) and T(s) range studied. Oxygen vacancy sites reduced S(0) of CO(2). Preadsorbed oxygen blocked preferentially defect sites, which led to an increase in S(0). Hydrogen preadsorption results in physical site blocking with decreased S(0) as H-preexposure increased, while the shape of S(Theta) curves was conserved. In contrast to oxygen, hydrogen does not adsorb preferentially on defect sites. The adsorption probability data were parameterized by analytic functions (Kisliuk model) and by Monte Carlo simulations (MCSs).

Exotic Rydberg atom formation in low-energy antiproton–helium collisions

Exotic Rydberg atom formation in collisions between low-energy antiprotons and helium atoms is studied. We present state-selective (n, l) capture cross sections for antiproton-capture from 3He and 4He targets as a function of impact energy. The simulation is based on the 3-body classical trajectory Monte Carlo method. We find the resulting (n, l) distributions of captured antiprotons in good agreement with recent measurements.

Electron loss from 0.74- and 1.4-MeV/u low-charge-state argon and xenon ions colliding with neon, nitrogen, and argon

Absolute total-, single-, and multiple-electron-loss cross sections are measured for $({\mathrm{Ar}}^{+}\ensuremath{-},$ ${\mathrm{Ar}}^{2+}\ensuremath{-},$ ${\mathrm{Xe}}^{3+})\ensuremath{-}(\mathrm{Ne},$ ${\mathrm{N}}_{2},$ Ar) collisions at 0.74 and 1.4 MeV/u. In addition, a many-body classical trajectory Monte Carlo model was used to calculate total- and multiple-electron-loss cross sections for ${\mathrm{Ar}}^{+}$ impact. For ${\mathrm{N}}_{2}$ and Ar targets, excellent agreement between the measured and calculated cross sections is found; for the Ne target the experimental data are approximately 40% smaller than the theoretical predictions. The experimental data are also used to examine cross-section scaling characteristics for electron loss from fast, low-charge-state, heavy ions. It is shown that multiple electron loss increased the mean charge states of the outgoing argon and xenon ions by 2 and 3 respectively. The cross sections decreased with increasing number of electrons lost and scaled roughly as the inverse of the sum of the ionization potentials required to sequentially remove the most weakly bound, next most weakly bound, etc., electrons. This scaling was found to be independent of projectile, incoming charge state, and target. In addition, the experimental total loss cross sections are found to be nearly constant as a function of initial projectile charge state. As a function of impact energy, the theoretical predictions yield an ${E}^{\ensuremath{-}1/3}$ behavior between 0.5 and 30 MeV/u for the total loss cross sections. Within error bars, the data are consistent with this energy dependence but are also consistent with an ${E}^{\ensuremath{-}1/2}$ energy dependence.

Partial dissociative ionization ofSF6by electron impact using an ejected electron-ion coincidence technique

The relative differential partial ionization cross sections for the production of ionic fragments of ${\mathrm{SF}}_{6}$ molecule under impact of 10--20 keV electrons have been measured using an ejected electron-produced ion coincidence technique in a crossed beam apparatus with a time-of-flight analysis of the ions. The detection angle of the ejected electrons of nondiscriminated energies was kept at 90\ifmmode^\circ\else\textdegree\fi{} with respect to the incident electron-beam direction. The 14 ionic fragments: ${\mathrm{SF}}_{5}^{+},$ ${\mathrm{SF}}_{4}^{+},$ ${\mathrm{SF}}_{3}^{+},$ ${\mathrm{SF}}_{2}^{+},$ ${\mathrm{SF}}^{+},$ ${\mathrm{S}}^{+},$ ${\mathrm{F}}^{+},$ ${\mathrm{SF}}_{4}^{2+},$ ${\mathrm{SF}}_{3}^{2+},$ ${\mathrm{SF}}_{2}^{2+},$ ${\mathrm{S}}^{2+},$ ${\mathrm{F}}^{2+},$ ${\mathrm{SF}}_{3}^{3+},$ and ${\mathrm{S}}^{3+}$ resulting from the dissociative ionization of the ${\mathrm{SF}}_{6}$ molecule were identified and their relative production cross sections have been measured. The branching ratios of 8 ionic fragments ${\mathrm{SF}}_{m}^{n+}$ $(m=1$ to 5 and $n=1$ to 3) as a function of impact energy have been determined. These ratios are found to have an almost a constant value over the considered impact energy range within the experimental uncertainty of the measurements. For the investigated impact energies, no previous data or theoretical calculations exist for a direct comparison with the present results.

Polarization of argonKx radiation following electron-impact ionization

The angular and impact-energy dependence of the characteristic K x radiation of argon produced from collisions of electrons with 10.0--24.0 keV energies has been investigated. The radiation is found to show a net linear polarization of up to $(17\ifmmode\pm\else\textpm\fi{}6)%$ in the investigated range of impact energy. This anisotropy is believed to arise from the strong polarization of $K\ensuremath{\alpha}$ satellite lines of argon produced by the simultaneous decay of a single K- and multiple L-shell vacancy states created in the collisions. Also, the behavior of the net polarization of K radiation as a function of impact energy in the range of 10.0 to 24.0 keV has been studied. Over the range of impact energies, the polarization is found to show a nearly constant value within the experimental uncertainty.

Collisions of fullerenes with surfaces at the 5–100 eV impact energy range

In this paper, we will present recent studies on the scattering dynamics of neutral and charged fullerenes from surfaces at the hyperthermal impact energy range. The energy range for the neutral colliders is 5–50 eV (aerodynamic acceleration in seeded beams) while with negatively charged ions we extend it up to 100 eV. The smooth overlap of the two energy regions using neutral and charged C 60 is demonstrated. The translational energy of the scattered particles (both C 60 0 and C 60 − ) was found to scale linearly with impact energy for both near normal and near grazing scattering angles. Kinetic energy losses varied with scattering angle from ∼15% (near normal incidence) to ∼40% (near grazing incidence). Analysis of the results in terms of simple kinematical models demonstrates nearly complete decoupling between normal and tangential energy losses. Furthermore, the accuracy of our energy measurements (±0.1 eV) enables us to extract, for the first time, molecule–surface binding energies from kinetic energy losses measured in molecular beam–surface scattering experiments. We compare this dynamically determined value with the equilibrium one as measured by temperature-programmed desorption experiments. The yield of C 60 − negative ions following scattering of hyperthermal neutral C 60 molecules from a graphite monolayer on nickel surface (Ni/C) was measured as a function of impact energy. An increase of two orders of magnitude was observed going from 4 to 42 eV. Energy and angle distributions of both scattered ions (C 60 − ) and neutrals (C 60 0 ) were measured and compared for this impact energy range. The C 60 − ion yield was found to obey an exponential dependence on the inverse of the outgoing normal velocity component similar to that observed before for atom–surface collisions at much higher energies. The shifts observed between the angular and energy distributions maxima of the neutral and negative ion could be analysed and explained in terms of image charge effects on the outgoing trajectory (deflection) and exit energy (retardation) of the C 60 − . A large critical distance for ion formation was extracted from the results. The charge transfer dynamics is consistent with final charge state exclusively determined along the exit trajectory.

Auger-electron cascades in diamond and amorphous carbon

We have analyzed cascades of secondary electrons in diamond and amorphous carbon generated by the thermalization of a single Auger electron. The elastic electron mean free path was calculated as a function of impact energy in the muffin-tin potential approximation. The inelastic scattering cross section and the energy loss of electrons ~expressed in terms of the differential inverse mean free path! were estimated from two ‘‘optical’’ models that utilize the measured dielectric constants of the materials. Using these data, a Monte Carlo model describing the time evolution of the cascade was constructed. The results show that at most around 20‐ 40 secondary cascade electrons are released by a single Auger electron in a macroscopic sample of diamond or amorphous carbon. Consideration of the real band structure of diamond reduces this number further. The release of the cascade electrons happens within the first 100 fs after the emission of the primary Auger electron. The results have implications to planned experiments with femtosecond x-ray sources.

The computer simulation of the scattering of fullerenes from a graphite surface: Energy partitioning and vibrational spectra

Molecular dynamics computer simulation is used to investigate the scattering behaviour of C 60, C 76 and C 84 fullerene molecules from a graphite surface. In particular the energy partitioning into translational, vibrational and rotational motion is determined and the vibrational frequency spectra are calculated and the principal structure identified. At the glancing angle of incidence, studied here, it was found that the fraction of retained kinetic energy after impact increases to about 90% as the initial impact energy increases. The fraction of energy retained as translational motion remains constant as a function of impact energy. Only a small fraction (∼1%) of the energy goes into rotational motion. The rotational frequency remains constant regardless of impact energy ( ∼5×10 11 Hz ). A number of vibrational modes can be identified easily from the vibrational spectra. In particular the C–C and CC bonds and a “breathing” vibrational mode are seen.