Impact Energy Distribution Research Articles

Impact energy distribution and wavefront shape in granular material assemblies

In this study, we investigated the dynamic response of granular materials subjected to point impact loading based on the discrete element method. The average velocity of the stress pulse was defined. The effect of elastic modulus on wave velocity was analyzed. The energy diffusion process in granular materials is affected by the contact between the particles, which is mainly reflected in two aspects: contact distribution and force transmission ratio. We first compared the wavefront shape in the specimens with different particle arrangements, and then assigned different material properties to the matrix particles. The wavefront shape is consistent with the previous results which proved the influence of the force transmission ratio. Finally, the variations of particle acceleration, kinetic energy and wave velocity at different impact angles are discussed. Our research reveals the energy propagation process through the contact between particles within granular materials. Our research results can be a reference for material design using granular materials for energy collection, energy absorbing etc.

Failure analysis of composite materials subjected to low-velocity impact

A low-velocity impact commonly is associated with the damage due to possible incidents during composite structure’s lifecycle and may cause barely visible damage on impacted surface. This effect induces a problem of residual strength estimation of structure after impact, which is especially apparent on compression after impact (CAI) test. Simulation assumes an application of damage initiation criterion and damage evolution model susceptible to the different complex failure modes. It requires a comprehensive understanding of numerous failure mechanisms in composite materials and execution of complex mechanical tests for obtaining of advanced mechanical characteristics. Presented work proposes an innovative approach for residual strength estimation of composite plate after impact based on topology optimization algorithm for finding of the “worst-case” damage distribution. As special input data, it requires an estimation of impact energy distribution between different damage modes that can be obtained from experimental statistics or direct numerical simulations. The proposed approach implemented into Abaqus software and compared with experimental results.

Impact Response and Energy Distribution of Low Velocity Impact on Composite Laminates

Impact Response and Energy Distribution of Low Velocity Impact on Composite Laminates

Nondimensional model and parametric studies of impact piezoelectric energy harvesting with dissipation

Impact piezoelectric energy harvesting could overcome the frequency matching problem of resonant energy harvesters and achieve broadband performance. However, the mechanism of impact dissipation in impact piezoelectric energy harvesting has not been investigated. No comprehensive model is available being able to analyze the response of impact piezoelectric energy harvesters under different impact velocities. This paper is aimed at developing a comprehensive model of impact piezoelectric energy harvesting by considering impact dissipation mechanism and conducting experiments to validate the developed model. In this paper, the electromechanical model, Hertzian contact theory and Hunt-Crossley model of impact dissipation are considered as constitutive mechanisms. The developed model is analyzed in terms of impact force and energy distribution. A testing method is proposed to investigate the impact piezoelectric energy harvester with a high-speed camera. The developed model is experimentally validated that it well predicts the response of impact piezoelectric energy harvesters by considering impact dissipation mechanism. The dimensionless model is achieved and the implications of mass ratio and impact dissipation on dynamics of the whole system is newly discovered. The guideline for improving harvested energy is proposed based on the results of parametric studies.

Effect of Milling Parameters on the Concentration of Copper Content of Hammer-Milled Waste PCBs: A Case Study

The current study reports optimization of hammer milling parameters to achieve crushed waste printed circuit boards (WPCBs) of − 16 BSS (British Standard Specification) sieve size. The WPCBs, having 22 wt% copper, have been crushed to − 16 BSS sieve size by means of a hammer mill. The result showed that initial milling takes place rapidly and then decreases gradually. Approximately 94% feed material is ground to − 16 BSS sieve size within 7 min, and further increase in the time does not affect the milling rate. It is also revealed that with the increasing feed rate, lower milling rate is experienced due to the distribution of impact energy among more pieces of WPCBs. Study of the size distribution of milled WPCBs (− 16 BSS sieve size) revealed that it follows the similar trend, and the crushed material is mostly concentrated in − 240 BSS and + 72 to − 52 BSS sieve size range. Further, 50–55% crushed fraction attains + 100 BSS sieve size, while the rest is smaller than this sieve size. Chemical analysis of the crushed material of various size fractions elucidated that a fraction above 100 BSS sieve size is copper rich (43 wt%), while − 100 BSS sieve size fraction has lesser copper because the nonmetals which account for majority concentration in WPCBs are milled to a finer size. Microscopic examinations of crushed fraction showed that copper has metallic luster and ruptured foil-type morphology. The fibrous structure of glass fiber and gray/black-colored polygon morphology of nonmetals were also visible.

A multiscale DEM-PBM approach for a continuous comilling process using a mechanistically developed breakage kernel

The population balance approach (PBM) is generally used in the literature to simulate a milling process. The formulation of a breakage kernel to represent particle breakage phenomenon is an important part of the model. This study proposes a methodology to estimate parameters of a breakage kernel that captures material property dependent particle level dynamics through discrete element method (DEM) simulations of a comill process. The DEM model takes into account a threshold impact energy that if exceeded, results in granule breakage. The impact energy distribution data for various size classes and impellor speeds is obtained from DEM. Comill experiments at various impeller speeds result in different observed size distributions and other process variables such as hold up amount, and time required for process to reach steady state. An iterative algorithm is proposed that uses mechanistic information from DEM and process variables from experiments to calibrate the breakage kernel through which material specific kernel parameters are estimated. A multi-scale modeling framework utilizing DEM, PBM as well as experimental data is developed. The framework is implemented to estimate material specific properties using milling experimental data at various impeller speeds. The milled particle size distribution predicted from the model with parameters estimated using this framework, demonstrated excellent agreement with experimental results.

Development of Impact Energy Distribution of Various Abrasives during Cyclic Impact/Abrasion Testing

In heavy industries like mining or steel production vast amounts of loose materials need to be transported, relocated or otherwise processed. During these routines severe stresses are applied on heavy machinery components such as excavator grabs and clamshells, which ultimately lead to excessive wear. The dominant wear mechanisms under such conditions are impact and abrasion. The focus of this paper is to investigate the fracture behaviour of various abrasives as experienced under real application in the steel industry. Breaking events of abrasive particles affect the impact energies on tool equipment. The Cyclic Impact/Abrasion Test rig (CIAT) was applied to investigate the stability and fracture behaviour of the abrasives. Rotating counter bodies made of martensitic quenched and tempered steel were used to generate impact events on loose abrasive particles. After certain time intervals the abrasives were screened and particle size fractions documented. Impact energy is strongly dependent on size and density, as well as fragility and cracking of particles. As fracturing events diminish particle dimensions and shift size distributions to lower size fractions, each abrasive showed a distinctive impact energy distribution over the course of the test duration. Impact energy distributions of abrasives were correlated to wear rates of the steel samples for each abrasive used. The results indicate a distinct behaviour of each abrasive, yielding certain impact energy distributions. Depending on processing specific abrasive goods in actual applications, impact energies and associated wear loss can differ significantly.

Predicting response of reinforced concrete slabs under low-velocity impact

A two-degrees-of-freedom (2-DoF) dynamic model is proposed to predict the response of reinforced concrete (RC) slabs subjected to low-velocity impact. In this model, the slab stiffness is calculated based on its dynamic load–displacement curve, which is built using moment–curvature analysis and critical shear crack theory. The contact between the impactor and the impacted RC slab is modelled with an elastic spring and a viscous damper. The effectiveness of the 2-DoF model was verified by comparisons with experimental data. The results obtained from the 2-DoF model are further processed to show the distribution of impact energy during the impact process, and a simple method is recommended for a quick estimation of the energy capacity of RC slabs.

A contribution to the definition of a new method to predict the catastrophic disintegration of spacecraft after collision with large orbital debris

The main limitation of the currently adopted method for predicting spacecraft catastrophic fragmentation due to a collision with large debris is the total independence of the critical value of the energy-to-target mass ratio from both the satellite configuration and the impact point; in fact these two issues are not accounted for by the classical 40J/g rule.To go beyond this limitation, the method proposed in this paper evaluates the distribution of impact energy into the system using the mechanical properties of the structural parts and the knowledge of the impact location. In this way, it becomes possible to predict how impact energy is partitioned among some selected macroscopic structural parts, each of them is finally evaluated versus its own minimum value of impact energy for which the part is fragmented (shattering threshold). Energy partition is performed by solving a system of equations written according to Statistical Energy Analysis (SEA). The paper describes in detail the proposed energy-partition method and presents its application to a geometrical representative model of a spacecraft subject to impact at different points. Results are finally compared to those obtained by the application of the classical 40J/g rule. It is shown that the evaluation of spacecraft disintegration is highly influenced by the impact point and the structural properties of the components.

En route to multi-model scheme for clinker comminution with chemical grinding aids

We present a multimodel simulation approach, targeted at understanding the behaviour of comminution and the effect of grinding aids in industrial cement mills. On the atomistic scale, we use molecular dynamics (MD) simulations with validated force field models to quantify elastic and structural properties, cleavage energies as well as the organic interactions with mineral surfaces. Simulations based on the discrete element method (DEM) are used to integrate the information gained from MD simulations into the clinker particle behaviour at larger scales. Computed impact energy distributions from DEM mill simulations can serve as a link between large scale industrial and laboratory sized mills. They also provide the required input for particle impact fragmentation models. Such a multiscale, multimodel methodology paves the way for a structured approach to the design of chemical additives aimed at improving mill performance.

Insight into first-order breakage kinetics using a particle-scale breakage rate constant

This study formulates a particle-scale breakage rate constant of the linear time-variant population balance model (PBM) for batch dry-milling. The breakage rate constant separates material properties from the milling environment which is defined by the impact energy distribution obtained by the discrete element method (DEM). The breakage rate constant determined by experiments and DEM simulations of the ball milling of polydispersed silica glass were in close agreement confirming the validity of the proposed methods. The breakage rate constant formulated in this study also allowed a detailed and rigorous energy-based analysis of the milling environment which provided insight into the origin of first-order breakage kinetics and the time-invariance of the breakage rate constant. Feeds of varying polydispersity and the time-wise evolution of the particle size distribution (PSD) were simulated in DEM to show that the PSD does not affect the specific breakage rate constant as assumed in first-order breakage. The adherence to first-order breakage kinetics was attributed to the low feed loading in the mill and the absence of particle beds where mechanical multi-particle interactions can cause non-first-order breakage. It was found that a threshold impact energy must be accounted for in the analysis of DEM results because the majority of low energy impacts do not contribute to particle breakage. Without rigorous assessment of the impact energy distribution, DEM simulations may lead to an erroneous evaluation of milling performance. The findings of this study contribute to a unified DEM−PBM framework to model and analyze milling process and demonstrate that milling performance can be quantified from particle-scale interactions using DEM.

Formulation of a physically motivated specific breakage rate parameter for ball milling via the discrete element method

A physically based specific breakage rate parameter of the population balance model for batch dry‐milling is formulated, which explicitly accounts for the impact energy distribution calculated by the discrete element method (DEM). Preliminary DEM simulations of particle impact tests were first performed, which concluded that dissipation energy should be used in contrast to collision energy to accurately define the impact energy distribution. Subsequently, DEM simulations of the motion of spheres representing silica glass beads in a ball mill were performed to determine the specific breakage rate parameter, which was in good agreement with those found experimentally. An analysis of the impact energy distribution, which was only possible within context of the physically motivated specific breakage rate parameter, emphasized the importance of accounting for a threshold impact energy. Without proper assessment of the impact energy distribution, DEM simulations may lead to an erroneous evaluation of milling experiments. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2404–2415, 2014

DEM-PBM approach to predicting particle size distribution in tumbling mills

Tumbling mills using balls as grinding media are used extensively in the mining and cement industries to produce fine powders; however, it is well known that the process of size reduction is highly energy-intensive. For this reason, much of today’s comminution research is aimed at understanding grinding mechanisms, by estimating power draft and modeling milling circuits using the discrete element method (DEM). DEM predicts individual particle trajectories, the distribution of energy and contact forces at each collision, lifter wear and power draw. This paper presents a prediction of the discharge particle size distribution using three components, mass balance model (sometimes referred to as a population balance model, PBM), impact energy distribution of the mill obtained from the simulation of the charge motion using DEM and breakage characteristics of particles determined from drop-ball tests DEM simulation of the charge of a tumbling mill was done using the code MinProSim 1.0 to obtain impact spectra at different operative conditions. Then, thepopidation balance model (PBM), based on impact energy distribution, was used to predict the final particle size distribution in a batch mill and compared with experimental data. It is demonstrated that the DEM-PBM approach allows a reliable solution to predict particle size distribution for tumbling mills. Ideally, the model has to predict size distribution for any operational condition and feed characteristic; however, it has been shown that predictions include some degree of error.

외연적 유한요소기법을 활용한 리저널급 항공기 동체 내추락 특성 분석

The impact energy absorbing is a very important characteristic of an aircraft to enhance the survivability of occupants when an aircraft is under the survivable accident such as an emergency landing condition. The impact energy is generally transmitted into the occupant and absorbed through a landing gear, a subfloor (lower structure of fuselage), and a seat. The characteristic of crash energy absorbing of a subfloor depends on the type of an aircraft, a shape of structure, and an applied material. Therefore, the study of crashworthiness characteristics of a subfloor structure is very important work to improve the safety of an aircraft. In this study, a finite element model of a narrow body fuselage section for the 80~90 seats regional aircraft was developed and crash simulation was executed using an explicit finite element analysis. Through survey of the impact energy distribution of each structural part of a fuselage and floor-level acceleration response, the crashworthiness characteristics and performance was evaluated.

Ion impact energy distribution and sputtering of Si and Ge

The spatial distribution of ion deposited energy is often assumed to linearly relate to the local ion-induced sputtering of atoms from a solid surface. This—along with the assumption of an ellipsoidal region of energy deposition—is the central mechanism used in the Bradley and Harper [J. Vac. Sci. Technol. A 6, 2390 (1988)] explanation of ion-induced surface instabilities, but it has never been assessed directly. To do this, we use molecular dynamics to compute the actual distribution of deposited energy and relate this to the source of sputtered atoms for a range of ion energies (250 eV and 1500 eV), ion species (Ar, Kr, Xe, and Rn), targets (Si and Ge), and incidence angles (0°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, and 80°). It is found that the energy deposition profile is remarkably ellipsoidal but that the relation between local deposited energy and local sputtering is not simple. It depends significantly upon the incidence angle, and the relation between energy and local sputter yield is nonlinear, though with a nearly uniform power-law relation. These results will affect, in particular, surface instability models based upon simpler approximations.

The Mechanism of Influence of Roof Properties on Impact Energy Distribution

The properties of roof play an important role in the formation and occurrence of rock burst. FLAC 3D is used to simulate the process of excavation and collapse in face advance with difference roof properties based on the elastic theory and field data of “7.16 Accident of rock burst” at Chengshan coal mine. As a result, the energy distribution law on the monitoring plan under different roof properties is given with Fish function. According to the analysis above, hard roof is a crucial reason to cause the accident.

The Pressure Relief Control Technology of the Defects Method on Dynamic Pressure Area in Zhaogezhuang Coal Mine

Because of deep mining and the serious dynamic pressure appearance in Zhaogezhuang coal mine, this paper has statistical and analyzed phenomena of dynamic pressure appearance, and proposed the engineering defects method to relief the pressure for high stress zone of working face and roadway according to the actual situation, which can transfer the stress distribution of coal rock and release impact energy. Based on the numerical simulation analysis of pressure relief on cavity defects, it has analyzed the feasibility of pressure relief using engineering defect, acquired good effect of pressure relief and achieved the safety of coal mining in the 2337E working face.

Statistical distribution models for monitoring acoustic emission (AE) energy of abrasive particle impacts on carbon steel

The estimation of energy dissipated during multiple particle impact is a key aspect in evaluating the abrasive potential of particle-laden streams. This paper reports the results of systematic acoustic emission measurements in which a particle laden airflow was directed at a target plate. The impingement conditions were chosen to limit the amount of overlap of particle arrival events in order to develop a model of the stream as the cumulation of individual particle arrival events. To this end, some limited experiments were done with individual particles.The probability distribution of particle impact energy was obtained for a range of particle sizes and impact velocities. Two methods of time series processing were investigated to isolate the individual particle arrivals from the background noise and from particle noise associated with contact of the particles with the target after their first arrival. For the conditions where it was possible to resolve individual impacts, the probability distribution of particle arrival AE energy was determined by the best-fit lognormal probability distribution function. The mean and variance of this function was then correlated with the known nominal mass and impact speed to give a semi-quantitative assessment of particle impact energy.A pulse shape function was devised for the target plate by inspection of the records, backed up by pencil lead tests and this, coupled with the energy distribution functions allowed the records to be simulated knowing the arrival rate and the nominal mass and velocity of the particles. A comparison of the AE energy between the recorded and simulated records showed that the principle of accumulating individual particle impact signatures could be applied to records even when the individual impacts could not be resolved.

Analysis of the Relationship between CTOD Toughness and Micromechanism of Marine Steel Weld Joints

Several tests including CTOD and Charpy impact have been performed on the weld joints of high strength low alloy steel S335G10+N to identify the toughness. The fracture surface and microstructure of samples extracted from the weld joints are characterized using scanning electron microscopy. Based on all data obtained some relationships between toughness and microstructure has been detected. (1) The tendency of Charpy impact energy distribution with the position of notch is similar to the CTOD values in WP and FL but different in FL+2.CTOD values of FL+2 are greater than those of FL, but the Charpy impact energy has an opposite tendency. (2) The appearance of Pearlite and upper bainite found in WP sample S3554 is regarded as one of the reasons for the lowest CTOD values. The cavity and quasi-cleavage in S35510 fracture surface indicate an inferior toughness compared with some dimples and ripple morphology of slip separation in S3552. (3)Grains close to the fracture surface in the 35511 (Stable crack growth) of FL +2 were elongated owing to plastic deformation caused by crack growth. (4)Hardness of the HAZ is equal to fusion zone and lower than base metal or weld position in S35511. Hardness of fusion zone increases with the depth. (5)A big difference of Average Grain Size is found in microstructure close to the fracture surface among S3557, S3556 and S3559.The greater the Average Grain Size is, the lower the CTOD value will appear.

Kinetic simulation of an extreme ultraviolet radiation driven plasma near a multilayer mirror

Future generation lithography tools will use extreme ultraviolet radiation to enable the printing of sub-50 nanometer features on silicon wafers. The extreme ultraviolet radiation, coming from a pulsed discharge, photoionizes the low pressure background gas in the tool. A weakly ionized plasma is formed, which will be in contact with the optical components of the lithography device. In the plasma sheath region ions will be accelerated towards the surfaces of multilayer mirrors. A self-consistent kinetic particle-in-cell model has been applied to describe a radiation driven plasma. The simulations predict the plasma parameters and notably the energy at which ions impact on the plasma boundaries. We have studied the influence of photoelectron emission from the mirror on the sheath dynamics and on the ion impact energy. Furthermore, the ion impact energy distribution has been convoluted with the formula of Yamamura and Tawara [At. Data Nucl. Data Tables 62, 149 (1996)] for the sputter yield to obtain the rate of physical sputtering. The model predicts that the sputter rate is dominated by the presence of doubly ionized argon ions.