Variation Of Impact Energy Research Articles

An experimental study of multi-core composite aluminium honeycomb sandwich panels under low-velocity impacts

This paper aims to evaluate the impact response of the multi-core composite sandwich panels from low-velocity experiments. Geometrical parameters of sandwich panels like cell size, cell height, and facesheet thickness are varied and their effect on peak load, energy absorption, and efficiency is reported in this article. The effect of impact energy variation ongraded and non-graded types of sandwich panels is also studied. Based on these experiments suitable recommendations are given for impact energy absorber applications. From a crashworthiness point of view, graded multi-core composite sandwich panels are found to be more effective than non-graded ones.

Numerical analysis of dynamic collapse response of beam–column substructures under impact loads

To investigate the collapse resistance performance of steel-frame structures at varying scale ratios, numerical simulations were performed to scrutinize the influence of different scale ratios on the dynamic response of beam–column substructures subjected to impact loads. In this study, two drop-hammer impact tests were modeled and simulated, their results were compared, and the accuracy of the finite element modeling method was verified. Concurrently, a detailed model of a double half-span beam–column substructure was established to examine the effect of impact energy variations (altering the mass and velocity of the drop hammer) on the structural impact force and vertical displacement. This study analyzed variations in the impact force, impact time history, vertical displacement, internal forces, and energy absorption for models with different scale ratios when altering the impact energy. Finite element analysis results indicated that the impact velocity of the drop hammer affected the peak impact force of the substructure, whereas the drop-hammer mass influenced the force plateau and impact duration. Both the impact duration and maximum vertical displacement were positively correlated with the impact of the drop hammer and were approximately linearly positively correlated with the impact kinetic energy, resulting in the establishment of a linear fitting model between the maximum vertical displacement and the impact energy. For scaled-down substructures, variations in the impact energy could be achieved by adjusting the drop-hammer impact velocity (drop height). A proposed scale ratio for the substructure drop-hammer impact anti-collapse test is provided.

Investigation of the Indentation Resistance of Aluminum Foam Sandwich Panels with Metallurgical Bonding Interfaces under Low-Velocity Impact

The impact resistance of aluminum foam sandwich panels (AFS) with metallurgical bonding interfaces prepared by the powder cladding rolling method was investigated. Low-velocity impact tests were conducted by using a drop-weight impact facility to explore the dynamic mechanical behavior, deformation and damage mechanisms, and energy absorption of AFS with metallurgical bonding interfaces. The effects of variation of impact energy, panel thickness, and specimen density on the energy absorption performance of AFS were quantitatively evaluated by energy absorption indicators. The results indicate that the load-displacement curve illustrates prominent three-stage characteristics when the impact energy is 120 J containing the front panel yielding stage, the foam core's compressive and shear failure stage, and the back panel fracture stage. The impact strength of the sandwich structure increases with increasing panel thickness and specimen density. The AFS with metallurgical bonding interfaces presents favorable energy absorption efficiency under low velocity.

Dynamic response and microstructure evolution of titanium alloy plates under low-velocity impact

This paper presents an experimental investigation into the dynamic response and microstructure evolution of titanium alloy plates subjected to low-velocity impact load. The impact experiments with different impact energies were designed and conducted. The effects of impact energy on the impact response curves and the interested impact resistance were analyzed. The macro deformation/failure mechanisms were examined by using digital microscope. The microstructure evolution induced by the variation of impact energy was further elaborated via scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) technique. On the basis of same impact condition, the impact behaviors of titanium alloy specimens were compared with the ones of woven carbon fiber reinforced composite laminates (CFRP) with the same areal density. The results show that the impact response of titanium alloy specimens is mainly characterized with linear loading stage, nonlinear loading stage and unloading stage. Linear relationships of peak impact force, maximum impactor displacement and absorbed energy with impact energy are found. The increase of impact energy will increase the content of α phase due to the difference in plastic deformation resistance of microstructures. Different impact behaviors appeared for titanium alloy specimens and CFRP specimens. CFRP specimens exhibited superior impact resistance with lower peak impact force and higher energy absorption relative to titanium alloy specimens.

Particle Impact Energy Variation with the Size and Number of Particles in a Planetary Ball Mill

To investigate the mechanical energy applying to the particles in a grinding process using a planetary ball mill, the impact energy of particles was estimated by simulating the behavior of the particles and grinding balls using the discrete element method (DEM) under different conditions of the size and number of particles, corresponding to their variations during milling. As the impact energy contributing to the particle breakage, we focused on the particle impact energy generated at particle-to-grinding ball/wall and particle-to-particle collisions. The particle size and the number of particles affected the level of particle impact energy at a single collision and the number of collisions of particles, respectively, resulting in an increase of the total impact energy of particles with decreasing particle size and increasing number of particles. The result suggests that milling conditions such as the size of grinding balls should be adjusted appropriately based on the variation of the size and number of particles so that the particles can receive large amounts of the impact energy during milling.

Body Anthropometry and Bone Strength Conjointly Determine the Risk of Hip Fracture in a Sideways Fall

We hypothesize that variations of body anthropometry, conjointly with the bone strength, determine the risk of hip fracture. To test the hypothesis, we compared, in a simulated sideways fall, the hip impact energy to the energy needed to fracture the femur. Ten femurs from elderly donors were tested using a novel drop-tower protocol for replicating the hip fracture dynamics during a fall on the side. The impact energy was varied for each femur according to the donor’s body weight, height and soft-tissue thickness, by adjusting the drop height and mass. The fracture pattern, force, energy, strain in the superior femoral neck, bone morphology and microarchitecture were evaluated. Fracture patterns were consistent with clinically relevant hip fractures, and the superior neck strains and timings were comparable with the literature. The hip impact energy (11 – 95 J) and the fracture energy (11 – 39 J) ranges overlapped and showed comparable variance (CV = 69 and 61%, respectively). The aBMD-based definition of osteoporosis correctly classified 7 (70%) fracture/non-fracture cases. The incorrectly classified cases presented large impact energy variations, morphology variations and large subcortical voids as seen in microcomputed tomography. In conclusion, the risk of osteoporotic hip fracture in a sideways fall depends on both body anthropometry and bone strength.

A novel method for impact force estimation in composite plates under simulated environmental and operational conditions

During its lifetime, an aircraft structure is subjected to various impacts from various sources such as tool drops, hail, ground service equipment, etc. In modern composite structures, these impacts have a significant chance of generating barely visible damage (BVID) which may lead to catastrophic failure of a structure if left undetected to grow. However, BVID is difficult to detect during routine visual inspection without specialised non-destructive inspection and thus there is large interest in developing monitoring systems for estimating the location and severity of impact events. Currently, most systems and methods have been developed for controlled lab conditions and do not consider the wide range of impact parameters in real life operation (environmental conditions, vibration, impactor stiffness, angle, etc) which may severely compromise the accuracy of these methods. In this study we have explored two methods for maximum impact force estimation, deconvolution and a novel gradient method, for the purpose of reliable severity assessment in composite aircraft structures under simulated environmental and operational conditions. It is shown that both methods allow accurate and robust estimation of the maximum impact force from various cases of impacts (variation of impact energy, mass, stiffness, angle, temperature, source) using minimum initial data from a single impact case. From further testing it is demonstrated that the gradient method is robust towards the effects of impact localisation errors and noise. The gradient method also has much less computational and storage requirements and is thus more feasible to integrate with current data acquisition systems being developed for structural health monitoring. Thus, we conclude that the proposed gradient method is suitable for impact force monitoring and severity assessment in composite aircraft structures in the simulated environmental and operational conditions.

Tensile post-impact behaviour of thin carbon/epoxy and glass/epoxy hybrid woven laminates – Part I: Experimental study

This article concerns the study of post-impact damage propagation in two thin hybrid woven composite laminates loaded in tension. Low velocity normal drop weight impact tests are first performed. Post-impact quasi-static tensile tests are then carried out and monitored by Digital Image Correlation. The influence of the impact energy variation on the fracture surfaces and the residual strength is studied. In order o have a better understanding of the mechanisms involved into the hybrid laminates, four monomaterial sample configurations are also tested. When the damage after impact is barely visible, the sample behaves as a non-impacted sample. When the damage is visible, it propagates whatever the impact energy. The damage grows in the direction perpendicular to the loading for all the monomaterial laminates while two different damage scenarios are observed for the hybrid laminates. The residual strength evolves in three steps depending on the impact energy: first a very low decrease, then an important drop and finally a plateau.

Effect of inter-lamellar spacing and test temperature on the Charpy impact energy of extremely fine pearlite

Pearlitic steels with three different inter-lamellar spacing ranging from 79 to 120 nm have been developed in bulk by austenitization and subsequent isothermal transformation with varying degree of under-cooling. The colony size was found to decrease with reduction of transformation temperature. However, the pearlitic nodule size had a similar range for all the specimens. Charpy impact energy of the specimens has been determined for all the transformation conditions at different test temperatures. At 25 °C, the variation of impact energy was negligible with the variation of inter-lamellar spacing and the fracture was completely brittle with clear cleavage facets. The facet size had a strong correspondence with the pearlitic nodule size. However, as the test temperature was raised to 125 °C and 250 °C, the impact energy was enhanced and the pearlite with the finest inter-lamellar spacing fractured after absorbing the highest energy. At higher temperatures, a region of ductile fracture was observed in the fracture initiation region which expanded with an increase in test temperature and decreasing lamellar spacing. At lower testing temperatures, the crack seemed to be cutting through the colonies without any noticeable deformation of cementite lamellae. However, the cementite for all the specimens bent significantly before breaking at higher temperatures. The bent in the direction of crack propagation increased with refinement of inter-lamellar spacing. The study shows that although nodule size determines the impact toughness at lower testing temperatures, inter-lamellar spacing influences it at higher temperatures.

Biomechanical Studies on Patterns of Cranial Bone Fracture Using the Immature Porcine Model

This review was prepared for the American Society of Mechanical Engineers Lissner Medal. It specifically discusses research performed in the Orthopaedic Biomechanics Laboratories on pediatric cranial bone mechanics and patterns of fracture in collaboration with the Forensic Anthropology Laboratory at Michigan State University. Cranial fractures are often an important element seen by forensic anthropologists during the investigation of pediatric trauma cases litigated in courts. While forensic anthropologists and forensic biomechanists are often called on to testify in these cases, there is little basic science developed in support of their testimony. The following is a review of studies conducted in the above laboratories and supported by the National Institute of Justice to begin an understanding of the mechanics and patterns of pediatric cranial bone fracture. With the lack of human pediatric specimens, the studies utilize an immature porcine model. Because much case evidence involves cranial bone fracture, the studies described below focus on determining input loading based on the resultant bone fracture pattern. The studies involve impact to the parietal bone, the most often fractured cranial bone, and begin with experiments on entrapped heads, progressing to those involving free-falling heads. The studies involve head drops onto different types and shapes of interfaces with variations of impact energy. The studies show linear fractures initiating from sutural boundaries, away from the impact site, for flat surface impacts, in contrast to depressed fractures for more focal impacts. The results have been incorporated into a "Fracture Printing Interface (FPI)," using machine learning and pattern recognition algorithms. The interface has been used to help interpret mechanisms of injury in pediatric death cases collected from medical examiner offices. The ultimate aim of this program of study is to develop a "Human Fracture Printing Interface" that can be used by forensic investigators in determining mechanisms of pediatric cranial bone fracture.

Effects of Thermal Aging on Ductile-to-Brittle Transition Temperature Behavior of Welded A516 Steel

Prolonged high temperature exposure of welded C-Mn steels is likely to cause microstructural changes leading to an inrease in the ductile-to-brittle transition temperature (DBTT) of the welded joint. Consequently, such degrading material properties should be quantified in view of establishing accurate component life prediction model. This study examined effects of isothermal aging on DBTT behavior of the heat affected zone (HAZ) in welded Type A516 Gr 70 steels. Microstructures of the as-received weld region revealed the presence of pearlite and ferrite in the base metal while upper and lower bainite are found in the HAZ and weld metal, respectively. Hardness measures for the weld metal region, HAZ and base steel are 172, 209 and 150, respectively. Aging at 420 oC, 500 hours lowers hardness value of the HAZ by 20 %. A series of Charpy impact tests on V-notched specimens are performed for as-received and thermally aged samples at 420 oC for 500, 800 and 1200 hours. Results showed that the absorbed impact energy displays a sigmoidal variation with test temperatures. DBTT ranges from -60 to 5 oC for HAZ while narrow range from -25 to 12 oC for weld metal region. Absorbed impact energy variations in samples aged for durations up to 800 hours display another saturation level over test temperatures between -30 to 10 oC. Fractographic analysis on HAZ fracture surface indicated brittle fracture at -60 oC while ductile failure dominated at 27.7 oC. A mix-mode fracture mechanism is displayed for test conducted at -38 oC.

An elastic–plastic free–free beam under asymmetric normal and oblique impact

The dynamic transient elastic–plastic response of the free–free beam subjected to normal and oblique impact at any cross section along the length of the beam is reported in the study. Total Lagrangian finite element formulation has been adopted together with the Newmark's time integration algorithm to obtain response of the beam. The contact force has been evaluated using the elastic–plastic contact law. The different modes of beam bending behaviour depending on the impact position of the beam have been discussed. The beam shows its stiffest behaviour against bending when the load is applied at 0.3L (L = half-length of the beam) from the free end. However, the beam becomes flexible in bending when the load is applied either at free end or at mid-span. The variation of impact energy, the energy gained by the beam and energy used in elastic–plastic deformation is also discussed.

Instantaneous surface work function dependence of [formula omitted] molecular ion emission under varying Cs environments

Kinetic energy distributions of MCs n + ( n = 0, 1, 2, …) molecular ions (M – target element to be analyzed and Cs + – primary ion) emitted in the SIMS process have been studied for Al under varying Cs environments. Experiments were performed for different impact energies and angles. The peak shifts of the energy distributions are due to the changes in the instantaneous surface work functions. The impact angle variation on the work function change is found to be more sensitive than the impact energy variation on the same. Different work function changes for AlCs + and AlCs 2 + ions at the same impact angle signify that the emitting sites of these two species are different.

Sensitive observations of orbital electron density image by electron momentum spectroscopy with different impact energies

Electron momentum spectroscopy studies of the ethylene highest occupied 1b 3u orbital are reported. The experiments were performed at impact energies of 400, 600, 800, 1000, 1200 and 1600 eV using a high resolution and high sensitivity (e, 2e) spectrometer. The orbital electron momentum distributions of 1b 3u are presented at a wide range of impact energies, which are used to examine the validity of plane wave impulse approximation and provide an experimental analysis of distorted wave effects in the higher momentum region of molecule with the variation of impact energy.

A Study on the 43$0^{\circ}C$ Degradation Behavior of Cast Stainless Steel(CF8M)(I);Evaluation of Degradation mechanism, Static and Fatigue Strength

The five classes of the thermally aged CF8M specimen are prepared using an artificially accelerated aging method. Namely, after the specimens are held for 100, 300, 900, 1800, and 3600hrs at 430 respectively, the specimens are water-cooled to room temperature. The impact energy variations are measures for both the aged and virgin specimens through the Charpy impact tests in addition to the microstructure observation, tensile, hardness and fatigue crack growth tests. From the present investigation the following results are obtained : 1) The difference among the thermally degraded specimens can be distinguished through their microstructures, 2) Hardness and tensile strength are increased to 300hrs, degradation specimen, while elongation and reduction area are decreased to 3600hrs degradation specimen, and impact energy is decreased to 1800hrs degradation specimen, 3) The FCG rates for thermally degraded specimens are larger than that of the virgin specimen.

Determinação de temperatura de transição dúctil-frágil de plásticos através de testes de impacto instrumentado

Nesse trabalho é realizada uma análise descritiva do teste de impacto tipo Izod instrumentado e são mostradas suas vantagens em relação ao impacto convencional na obtenção de diagramas de força e energia de fratura em tempo-real. Estes diagramas além de fornecerem dados do material em termos de sua resistência ao impacto tradicional, contém informações detalhadas sobre os mecanismos de fratura e as principais características apresentadas durante a propagação da trinca no corpo de prova. A medida da variação da resistência ao impacto com a temperatura pode ser utilizada como uma forma de se determinar a existência de transições dúctil-frágeis ou alternativamente a suscetibilidade de materiais poliméricos à concentração de tensões, i.e., profundidade e raio da extremidade do entalhe. As curvas de carga e energia, obtidas à várias temperaturas, são utilizadas na determinação de parâmetros do material e da temperatura de transição dúctil-frágil de um copolímero de acrilonitrila-butadieno-estireno (ABS). A análise da superfície de fratura por microscopia eletrônica de varredura, (MEV) permitiu a correlação da forma das curvas de impacto com o modo de fratura observado e detalhes da microestrutura do material.

Observation of temporary-negative-ion states in condensed methanol via vibrational excitation induced by slow electron scattering.

We report the measurements of electron-impact vibrational excitation of amorphous methanol condensed on a polycrystalline Pt substrate over incident energies of 1--20 eV at a large off-specular angle. The spectra obtained show that vibrations within solid methanol in its ground state are rather sensitive to the variation of impact energy and there is tangible evidence of the formation of at least three compound temporary-negative-ion (TNI) states. The low-energy feature lying between 3 and 6 eV is assigned tentatively to a $^{2}$A\ensuremath{'} valence-shape resonance with a $^{2}\mathit{N}$,(8a\ensuremath{'}\ensuremath{\sigma}*${)}^{1}$] configuration, whose parent state is the ground state $^{1}$A\ensuremath{'} of the molecule. The origin of the second broad structure centered around 7.0 eV in the excitation functions may be threefold: a Feshbach-type resonance $^{2}$A\ensuremath{''} of the electronic configuration $^{2}[$(2a\ensuremath{''}${)}^{1}$,(3sa\ensuremath{'}${)}^{2}$] (about 7 eV); a nearby shape resonance $^{2}$A\ensuremath{'} of $^{2}[$(N,(9a\ensuremath{'}\ensuremath{\sigma}*${)}^{1}$] (about 8 eV); and probably also a minor contribution from another $^{2}[$(7a\ensuremath{'}${)}^{1}$,(3sa\ensuremath{'}${)}^{2}$] Feshbach resonance $^{2}$A\ensuremath{'} (about 9 eV). The third broad bandlike resonant feature, extending from 11 up to 17 eV, may consist of overlapping TNI states, dominated by the $^{2}[$(6a\ensuremath{'}${)}^{1}$,(3sa\ensuremath{'}${)}^{2}$] Feshbach resonance $^{2}$A\ensuremath{'}. Plausible decay channels from their configurations are discussed. \textcopyright{} 1996 The American Physical Society.