Academic literature on the topic 'Imact dynamics'

The demand for a cost effective site investigation method has resulted in the introduction of various advanced in-situ testing techniques. These techniques utilise modern electronics instrumentation to monitor various soil parameters during site investigation. The data is then processed using high speed, low cost digital computers which allow an accurate and rapid assessment of the conditions of the foundation soil under a proposed construction site. In this thesis, a site investigation tool that drives a coring tube into the ground under a combination of vibration and impact is considered. This machine, called a vibro-impact corer, is fully instrumented to provide penetrometer-type information and a core sample for further inspection in the laboratory. The self-adjusting mechanism inherent in this machine delivers the minimum level of energy required to overcome soil resistance which thereby allows continuous penetration of the coring tube. This mechanism is also results in minimal induced disturbance during the coring process. This thesis investigates use of the vibro-impact corer as a soil classification tool. It involves the design of data analysis software to perform the soil classification procedure. Due to the nature of the system, the resistance monitored through the annular load cell fitted at the tip of the coring tube consists of the dynamic end resistance waveform and the peak magnitude of these waveforms over a sampling period. The vibro-impact soil classification system is based on the distinct self-adjusting mechanism of the machine. The self-adjustment mechanism imparts a different level of impact and vibration as soil conditions change which produces distinct dynamic soil resistance waveforms. In addition, the penetration rate and the magnitude of the soil resistance encountered also varies according to the material being penetrated. These two features are used to form the basis of the soil classification system in this software. The software also includes options for empirical correlation of the results obtained from the vibro-impact penetrometer with the CPT and SPT tests to allow comparison. The vibro-impact soil classification software is designed to be user-friendly. It reads the data files from a Biodata Transient Capture System for the classification process. The output devices such as plotter and printer are used to produce hardcopy records for various data. All the options are menu driven. A two degree freedom simulation of the operational responses of the vibro-impact machine is also included in this thesis. The main objective of this simulation is to study the soil response during vibro-impact mode of driving. This allows a comparison of the simulation soil responses to the model test results to provide an understanding of the soil behaviour under a combination of both vibratory and impact loadings. This thesis presents the results of several laboratory model and full scale vibro-impact penetrometer tests. It concentrates on the main subject of soil classification during the discussions although in some occasions the operational mechanism of the machine is mentioned. The results justify the approaches adopted for the soil classification system using a vibro-impact machine.

The dynamics and wear of non-linear impact oscillators, comprising a single-degree of freedom system as well as continuous beam systems are analysed. The considered beams are of cantilever type with the lateral motion of the free end constrained by elastic supports. They are modelled as Bernoulli beams with Rayleigh damping. A finite-element method is used for discretisation in space and Newmark's method for time integration. Wear is quantified using the work-rate concept. The model calculations are compared with measurements of contact forces and displacements made on a loosely supported nuclear fuel rod span subject to both harmonic and random excitation. Details of the vibro-impact dynamics in the time domain are well reproduced in the digital simulations. Work-rates computed from measured and simulated quantities are also in good agreement. Furthermore, the dynamics of vibro-impacts are characterised through global and local stability and bifurcation analysis. Global analysis is made by extensive time integration for both harmonic and stochastic excitation. The local analysis is made by way of a Poincaré mapping method relating the states at subsequent impacts at the elastic supports for harmonically excited systems. The domains of stability are mapped out and the work-rate at stable periodic orbits is examined.<br>Godkänd; 2001; 20070225 (ysko)

Armor-piercing (AP) ammunition generally carries a hard penetrator within a copper jacket. Upon impact on a hard target, the copper case is destroyed, but the penetrator continues its motion and pierces the target. The most efficient AP ammunition is built with penetrators made from either tungsten alloys or depleted uranium, but alloy steel penetrators are also commonly used, because they are less expensive and less polluting, even if they are much less efficient. The impact deformation and fracture behavior of armor-piercing penetrators fabricated with three tool steels, and their resultant ballistic efficiency, are investigated, both to better understand the optimal mechanical properties of armor piercing materials, and to describe the fracture mechanics of the tested materials. Moreover, the ballistic results of the three tool steels are compared with those of plain medium-carbon steel and cemented tungsten carbide.

Electric charges are often found in naturally or artificially formed droplets, such as raindrops and those generated by Kelvin's water dropper. In contrast to the impact of neutral droplets on a flat solid surface upon which a thin convex lens shape layer of the gas film is typically formed, I show that the delicate gas thin film can be fundamentally altered for even weakly charged droplets both experimentally and numerically. As the charge level is raised above a critical level of about 1% of the Rayleigh limit for representative impact conditions, the Maxwell stress overcomes the gas pressure buildup to deform the droplet bottom surface. A conical liquid tip forms and pierces Through the gas film, leading to a circular contact line moving outwards that does not trap any gas. The critical charge level only depends on the capillary number based on the gas viscosity. The deformation applies to common liquids and molten alloy droplets. Even dielectric surfaces can also induce conical deformation. The charged droplets can also deform upon hydrophobic surfaces, and increase the contact time on hydrophobic surfaces or even avoid bouncing.<br>Doctor of Philosophy<br>Electric charges are often found in naturally or artificially formed droplets, such as raindrops, waterfall, and inkjet printer. Neutral droplets impact on flat surfaces will usually trap a bubble inside because of the viscosity of air. The air bubble entrapped can be ignored if the droplet is water because the air bubble will eventually pinch-off. However, if the droplet is metal or some other viscous liquid, the air bubble will stay inside the liquid. This entrapped air bubble is undesired under some circumstances. For example, the existence of air bubble during metal 3D printing can influence the physical property. I show that the delicate gas thin film can be fundamentally altered for even weakly charged droplets both experimentally and numerically. As the charge level is raised above a critical level of about 1% of the maximum charges a droplet can carry for representative impact conditions, the electric stress will dominate the deformation of droplet. A conical liquid tip forms at the droplet bottom, avoiding the entrapment of air bubble. The critical charge level is experimentally proved to be only dependent on the gas viscosity and impact velocity. The deformation applies to common liquids and molten alloy droplets. Even dielectric surfaces can also induce conical deformation. The charged droplets can also deform upon hydrophobic surfaces, and increase the contact time on hydrophobic surfaces or even avoid bouncing.

In the past, personal body armor was constructed of simple plates of high- strength alloys. However, with the advancement of modern combat and weaponry, particularly armor-piercing ammunition, personal body armor has evolved into more complex and effective metal, ceramic, and composite structures. This paper lays the groundwork for experimental and modeling methods used to understand the effectiveness of new armor designs. Focusing on the first layer of modern body armor, the ”High Impedance” layer. Experiments measuring the change in velocity of bullets passing through aluminum and titanium plates were conducted. These experiments were then replicated through FEA simulation.

In this thesis we ran a series of 2D simulations of femtosecond laser pulses filamenting in air using the FDTD method, a saturable Lorentz oscillator model of air [1], and two separate models of plasma: a Drude model where the plasma density is static in space, and a particle-in-cell model where plasma is free to migrate throughout the simulation space. By comparing matched pairs of simulations, which varied in pulse size, duration, and intensity, we can gauge the impact plasma dynamics has upon the evolution of a filamenting laser pulse. From these tests we determine that, while there are some visible differences between dynamic and static plasmas, plasma dynamics do not significantly alter the evolution of the pulse.