scholarly journals Why Impacted Yarns Break at Lower Speed Than Classical Theory Predicts

2011 ◽  
Vol 78 (5) ◽  
Author(s):  
James D. Walker ◽  
Sidney Chocron
Keyword(s):  
Impact Velocity ◽  
Classical Theory ◽  
Impact Speed ◽  
Projectile Impact ◽  
Theoretical Maximum ◽  
Theory Result ◽  
Single Yarn ◽  
The Impact ◽  
Good Agreement ◽  
Minimum Impact

Fabrics are an extremely important element of body armors and other armors. Understanding fabrics requires understanding how yarns deform. Classical theory has shown very good agreement with the deformation of a single yarn when impacted transversely. However, the impact speed at which a yarn breaks based on this classical theory is not correct; it has been experimentally noted that yarns break when impacted at a lower speed. This paper explores the mechanism of yarn breakage. The problem of the transverse strike of a yarn by a flat-faced projectile is analytically solved for early times. It is rigorously demonstrated that when a flat-faced projectile strikes a yarn, the minimum impact speed that breaks the yarn will always be at least 11% less than the classical-theory result. It is further shown that when the yarn in front of the projectile “bounces” off the projectile face due to the impact, the impact speed that breaks the yarn is further reduced. If the yarn bounces elastically off the projectile face at twice the impact velocity (the theoretical maximum), there is a 40% reduction in the projectile impact speed that breaks the yarn.

scholarly journals A smart passive MR damper with a hybrid powering system for impact mitigation: An experimental study

2021 ◽  
pp. 1045389X2098808
Author(s):  
S. Jin ◽  
L. Deng ◽  
J. Yang ◽  
S. Sun ◽  
D. Ning ◽  
...  
Keyword(s):  
Impact Velocity ◽  
Mr Damper ◽  
Damping Force ◽  
Softening Effect ◽  
Impact Speed ◽  
Impact Mitigation ◽  
Passive Damper ◽  
Comparison Results ◽  
Wide Range ◽  
The Impact

This paper presents a smart passive MR damper with fast-responsive characteristics for impact mitigation. The hybrid powering system of the MR damper, composed of batteries and self-powering component, enables the damping of the MR damper to be negatively proportional to the impact velocity, which is called rate-dependent softening effect. This effect can keep the damping force as the maximum allowable constant force under different impact speed and thus improve the efficiency of the shock energy mitigation. The structure, prototype and working principle of the new MR damper are presented firstly. Then a vibration platform was used to characterize the dynamic property and the self-powering capability of the new MR damper. The impact mitigation performance of the new MR damper was evaluated using a drop hammer and compared with a passive damper. The comparison results demonstrate that the damping force generated by the new MR damper can be constant over a large range of impact velocity while the passive damper cannot. The special characteristics of the new MR damper can improve its energy dissipation efficiency over a wide range of impact speed and keep occupants and mechanical structures safe.

scholarly journals Research on Tunnel Surrounding Rock Failure and Energy Dissipation Based on Cyclic Impact and Shear Loading

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Yu Ding ◽  
Zhuoying Tan ◽  
Shuguang Li ◽  
Runke Huo ◽  
Ziliang Liu ◽  
...  
Keyword(s):  
Shear Stress ◽  
Impact Velocity ◽  
Rotation Speed ◽  
Rock Failure ◽  
Surrounding Rock ◽  
Stress Strain ◽  
Impact Speed ◽  
Upper Limit ◽  
Cyclic Impact ◽  
The Impact

Aiming at the cyclic impact deformation and failure of tunnel surrounding rock under shear stress, a self-developed rotation-impact simulation test platform was used to determine the number of failures, stress-strain curves, and energy in the process of cyclic impact failure. The failure process of rock under different impact velocities and shear stresses has been systematically studied. Results show that, under the same impact speed, the shear stress will increase with the increase in the rotation speed, but an upper limit will exist. When the rotation speed reaches this upper limit, the shear stress will no longer increase. The presence of shear stress will reduce the number of impacts required for rock failure. When the impact speed is 7.2 m/s, the number of impacts at the maximum rotation speed is 60% of the static state. When the impact velocity is 16.8 m/s, this value is only 33.3%. At the same impact velocity, the stress-strain curves under different rotation speeds do not change significantly, but with the increase in the rotation speed, the slope of the elastic stage of the stress-strain curve gradually decreases, and the corresponding stress of the rock sample decreases when the maximum strain is reached. With the increase in shear stress, the crushing specific energy required for rock failure gradually decreases. The greater the impact velocity, the more obvious the impact of shear stress on energy dissipation. In the tunnel process, when the surrounding rock is subjected to impact loads from different directions, only the axial strain analysis will have certain safety hazards, and timely support and reinforcement work are required.

scholarly journals Numerical Simulation of Single-Droplet Dynamics, Vaporization, and Heat Transfer from Impingement onto Static and Vibrating Surfaces

Fluids ◽  
2020 ◽  
Vol 5 (4) ◽  
pp. 188
Author(s):  
J. Thalackottore Jose ◽  
J. F. Dunne
Keyword(s):  
Heat Transfer ◽  
Impact Velocity ◽  
Liquid Droplet ◽  
Droplet Diameter ◽  
Droplet Evaporation ◽  
Time Interval ◽  
Initial Contact ◽  
Droplet Impingement ◽  
The Impact ◽  
Minimum Impact

A numerical study is presented to examine the behavior of a single liquid droplet initially passing through air or steam, followed by impingement onto a static or vibrating surface. The fluid dynamic equations are solved using the Volume of Fluid method, which includes both viscous and surface tension effects, and the possibility of droplet evaporation when the impact surface is hot. Initially, dynamic behavior is examined for isothermal impingement of a droplet moving through air, first without and then with boundary vibration. Isothermal simulations are used to establish how droplet rebound conditions and the time interval between initial contact to detachment vary with droplet diameter for droplet impingement onto a stationary boundary. Heat transfer is then assessed for a liquid droplet initially at saturation temperature passing through steam, followed by contact with a hot vibrating boundary, in which droplet evaporation commences. The paper shows that, for droplet impingement onto a static boundary, the minimum impact velocity for rebound reduces linearly with droplet diameter, whereas the time interval between initial contact and detachment appears to increase linearly with droplet diameter. With the introduction of a vibrating surface, the minimum relative impact velocity for isothermal rebound is found to be higher than the minimum impact velocity for static boundary droplet rebound. For impingement onto a hot surface, in which droplet evaporation commences, it is shown that large-amplitude surface vibration reduces heat transfer, whereas low-amplitude high-frequency vibration appears to increase heat transfer.

Simulation Studies on the Influence of Impact Velocity on the PELE Penetrated and Broken Reinforced Concrete

2013 ◽  
Vol 690-693 ◽  
pp. 3108-3111 ◽  
Author(s):  
Xiao Jun Ye ◽  
Zhong Hua Du ◽  
Chuan Hui Hu ◽  
Cheng Jun Song ◽  
Xiao Sheng
Keyword(s):  
Finite Element Method ◽  
Reinforced Concrete ◽  
Impact Velocity ◽  
Simulation Studies ◽  
Residual Velocity ◽  
Software Simulation ◽  
Definite Effect ◽  
Simulation Results ◽  
The Impact ◽  
Good Agreement

In order to study the effect of the impact velocity for the penetrator with enhanced lateral effect (PELE) penetrating reinforced concrete (RC) targets, penetration of PELE filled nylon against RC target using the different velocity is simulated by LS-DYNA finite element method software. Simulation shows that the impact velocity have definite effect on broken RC. On condition of PELE having penetrated target, with farther increase of impact velocity, the area of PELE broken RC on the direction of decrease firstly and augmentation thereafter, the residual velocity after penetrating target is less at the same time; Take into account validity of lateral effect and general launching condition, selecting the impact velocity at the range of 800 m/s-1300 m/s is suitable for PELE broken RC. The simulation results are in good agreement with those of the experiments.

Response of aluminum corrugated sandwich panels under foam projectile impact – Experiment and numerical simulation

2016 ◽  
Vol 19 (5) ◽  
pp. 595-615 ◽  
Author(s):  
Xin Li ◽  
Shiqiang Li ◽  
Zhihua Wang ◽  
Jinglei Yang ◽  
Guiying Wu
Keyword(s):  
Impact Velocity ◽  
Aluminum Foam ◽  
Sandwich Panels ◽  
Face Sheet ◽  
Front Face ◽  
Comparable Amount ◽  
Projectile Impact ◽  
The Face ◽  
Core Height ◽  
The Impact

The paper studied the dynamic response of square aluminum corrugated sandwich panels under projectile impact. The aluminum foam projectile was utilized to apply the impulse on the sandwich panels. In order to increase the applied impulse under controlled impact velocity ( V < 200 m/s), a cylindrical Nylon mass was adhered to the back of foam projectile. Corrugated sandwich panels with two different configurations were tested and their typical deformation modes were obtained in the experiment. Based on the experiment, corresponding numerical simulations were presented. The energy absorption and deformation mechanism of corrugated sandwich panels were studied through the simulation. The influence of impact velocity, thickness of face sheet and wall thickness of corrugated core were discussed. The results indicated that the corrugated sandwich panels with smaller core height produce larger deformation than the panels with larger core height. The face sheets of corrugated sandwich panel absorbed comparable amount of energy with the corrugated core. The velocity histories show that under the combined action of aluminum foam projectile and nylon back mass, a second peak velocity of front face sheet can be produced during the impact process, which is defined as “accelerating impact stage” in current study. The influence of “accelerating impact stage” to the response of structures is sensitive to the impact velocity.

Asteroid and Comet Impact Speeds upon Mars: Significance for Panspermia and the Supply of Organics

1997 ◽  
Vol 161 ◽  
pp. 197-201 ◽  
Author(s):  
Duncan Steel
Keyword(s):  
Probability Distributions ◽  
Regions Of Interest ◽  
Significant Fraction ◽  
Organic Chemicals ◽  
Impact Speed ◽  
The Mean ◽  
The Impact

AbstractWhilst lithopanspermia depends upon massive impacts occurring at a speed above some limit, the intact delivery of organic chemicals or other volatiles to a planet requires the impact speed to be below some other limit such that a significant fraction of that material escapes destruction. Thus the two opposite ends of the impact speed distributions are the regions of interest in the bioastronomical context, whereas much modelling work on impacts delivers, or makes use of, only the mean speed. Here the probability distributions of impact speeds upon Mars are calculated for (i) the orbital distribution of known asteroids; and (ii) the expected distribution of near-parabolic cometary orbits. It is found that cometary impacts are far more likely to eject rocks from Mars (over 99 percent of the cometary impacts are at speeds above 20 km/sec, but at most 5 percent of the asteroidal impacts); paradoxically, the objects impacting at speeds low enough to make organic/volatile survival possible (the asteroids) are those which are depleted in such species.

Modeling of Tread Block Contact Mechanics Using Linear Viscoelastic Theory3

2008 ◽  
Vol 36 (3) ◽  
pp. 211-226 ◽  
Author(s):  
F. Liu ◽  
M. P. F. Sutcliffe ◽  
W. R. Graham
Keyword(s):  
High Speed ◽  
Slip Rate ◽  
Material Model ◽  
Contact Forces ◽  
Block Modeling ◽  
Rate Dependent ◽  
Linear Viscoelastic Material ◽  
Linear Viscoelastic ◽  
The Impact ◽  
Good Agreement

Abstract In an effort to understand the dynamic hub forces on road vehicles, an advanced free-rolling tire-model is being developed in which the tread blocks and tire belt are modeled separately. This paper presents the interim results for the tread block modeling. The finite element code ABAQUS/Explicit is used to predict the contact forces on the tread blocks based on a linear viscoelastic material model. Special attention is paid to investigating the forces on the tread blocks during the impact and release motions. A pressure and slip-rate-dependent frictional law is applied in the analysis. A simplified numerical model is also proposed where the tread blocks are discretized into linear viscoelastic spring elements. The results from both models are validated via experiments in a high-speed rolling test rig and found to be in good agreement.

Dynamic model for high-speed rotors based on their experimental characterization

2017 ◽  
Vol 2 (4) ◽  
pp. 25
Author(s):  
L. A. Montoya ◽  
E. E. Rodríguez ◽  
H. J. Zúñiga ◽  
I. Mejía
Keyword(s):  
Dynamic Model ◽  
High Speed ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Experimental Characterization ◽  
Rotating Systems ◽  
Computing Performance ◽  
The Impact ◽  
Stiffness Distribution ◽  
Good Agreement

Rotating systems components such as rotors, have dynamic characteristics that are of great importance to understand because they may cause failure of turbomachinery. Therefore, it is required to study a dynamic model to predict some vibration characteristics, in this case, the natural frequencies and mode shapes (both of free vibration) of a centrifugal compressor shaft. The peculiarity of the dynamic model proposed is that using frequency and displacements values obtained experimentally, it is possible to calculate the mass and stiffness distribution of the shaft, and then use these values to estimate the theoretical modal parameters. The natural frequencies and mode shapes of the shaft were obtained with experimental modal analysis by using the impact test. The results predicted by the model are in good agreement with the experimental test. The model is also flexible with other geometries and has a great time and computing performance, which can be evaluated with respect to other commercial software in the future.

scholarly journals Measuring Hydrometeors Using a Precipitation Microphysical Characteristics Sensor: Sampling Effect of Different Bin Sizes on Drop Size Distribution Parameters

2018 ◽  
Vol 2018 ◽  
pp. 1-15 ◽  
Author(s):  
Xichuan Liu ◽  
Taichang Gao ◽  
Yuntao Hu ◽  
Xiaojian Shu
Keyword(s):  
Drop Size ◽  
Rain Rate ◽  
Monte Carlo Model ◽  
Rain Gauge ◽  
Sampling Schemes ◽  
Distribution Parameters ◽  
Optimum Sampling ◽  
Simulation Results ◽  
The Impact ◽  
Good Agreement

In order to improve the measurement of precipitation microphysical characteristics sensor (PMCS), the sampling process of raindrops by PMCS based on a particle-by-particle Monte-Carlo model was simulated to discuss the effect of different bin sizes on DSD measurement, and the optimum sampling bin sizes for PMCS were proposed based on the simulation results. The simulation results of five sampling schemes of bin sizes in four rain-rate categories show that the raw capture DSD has a significant fluctuation variation influenced by the capture probability, whereas the appropriate sampling bin size and width can reduce the impact of variation of raindrop number on DSD shape. A field measurement of a PMCS, an OTT PARSIVEL disdrometer, and a tipping bucket rain Gauge shows that the rain-rate and rainfall accumulations have good consistencies between PMCS, OTT, and Gauge; the DSD obtained by PMCS and OTT has a good agreement; the probability of N0, μ, and Λ shows that there is a good agreement between the Gamma parameters of PMCS and OTT; the fitted μ-Λ and Z-R relationship measured by PMCS is close to that measured by OTT, which validates the performance of PMCS on rain-rate, rainfall accumulation, and DSD related parameters.

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