Stone Geometry Research Articles

A method for quantifying impact loads from stone impact in mountain biking

High performance mountain bike frames nowadays are commonly built of carbon composites (CFRP), because of their excellent material properties allowing very high stiffness and strength at low weights. But this material has also disadvantages as it is sensitive to transversal impact loads. Impacts damage the material inside and can therefor affect the structural safety. As impact damages are often barely visible from the outside, they are very critical for structural parts like bike frames. A mountain bike frame suffers from different types of impacts like crashes and stone impacts. In order to evaluate the effect on structural integrity, the occurring impact energies have to be known. This paper describes a method for quantifying the impact load levels of stone impacts in order to evaluate the effect on the structural safety. Therefor the down tube of a mountain bike is shot using a high speed camera Casio Exilim EX FC 100 during biking. Impact events are identified in the videos and the impact energy is assessed, analyzing the stone geometry and its speed. Therefor a correlation between the two dimensional images of the stones and its mass was developed in an empiric approach. Using the above mentioned method, relevant impact energy levels and their frequency of occurrence are investigated.

Dynamics of bubbles near a rigid surface subjected to a lithotripter shock wave. Part 1. Consequences of interference between incident and reflected waves

In this paper we consider the dynamics of bubbles near a kidney stone subjected to a lithotripter shock wave. We address the effect of kidney stone geometry and composition on the cavitation potential near the stone in a shock wave lithotripter. The analysis is based on the previously developed work metric in which the work done on a bubble by the lithotripter shock wave (LSW) is used to determine the maximum radius the bubble achieves. Results of the reflection of the LSW from cylindrical kidney stones with proximal surfaces of varying geometry show that the presence of the stone enhances bubble growth near the stone and decreases growth further away, owing to constructive and destructive interference, respectively. These effects hold true regardless of the shape and curvature of the face, and are strongest for stones with concave faces and higher reflection coefficients. A consequence of the analysis is an elucidation of the mechanism for enhanced cavitation activity and creation of deep craters on the proximal side of a kidney stone, as have been observed in recent experiments.

Modeling the Lofting of Runway Debris by Aircraft Tires

Runway debris lofting by aircraft tires can lead to considerable damage to aircraft structures, yet there is limited understanding of the lofting mechanisms. The aim of this study is to develop accurate physically based models to understand and predict the stone lofting processes. The research entailed both experimental work and finite element modeling of a tire partially rolling over a stone. Parametric studies were conducted to characterize the influence of factors such as stone geometry and tire conditions in the lofting processes. To validate the finite element models, experimental studies were conducted using a modified drop weight impactor covered with rubber to simulate a tire vertically approaching aluminum balls and real stones. A high-speed video camera was used to observe the loft mechanisms and calculate the loft velocities, angles, and spin rates. A finite element model of the impactor demonstrated good agreement with the experimentally observed loft mechanisms.In general, lofting occurred either at high speed and low angles or vice versa, depending on the degree of interaction between the stone and the ground.

Numerical Analysis of Kidney Stone Fragmentation by Short Pulse Impingement: Effect of Geometry

To better understand the behavior of stresses generated inside a kidney stone by direct pulse impingement during extracorporeal shock wave lithotripsy (ESWL), numerical analyses are performed in this work. LS-DYNA, an explicit Finite Element code for non-linear dynamic analysis is employed to investigate the effect of stone geometry to the stress field evolution inside the stone when subjected to short pulse wave. Circular disks with parts removed from the front and the back are used to model the stones that assumed have already had initial fracture. The other variation of spherical geometry such as ellipse is also considered in the numerical calculation.

Troubleshooting in Studying the Behavior of Ballast Stones using Molecular Dynamic Simulation

AbstractFor the safety of the railways very important, beside tracks and trains, is the behavior of ballast stones. In the last years many scientists have started to investigate the behavior of the ballast stones and the parameters that influence them. In order to describe this behavior, one can choose a continuum mechanical description of the system or a discrete one. The problem with the first method is that the material parameter set depends on stone geometry, humidity and further factors. The second method (also called Molecular Dynamic Method MDS) makes possible a close‐to‐reality rendition of each ballast stone by means of numeric time step integration. We use MDS in order to built up a model for the system ballast stones ‐ track. Through our model we analyze small ballast stones range like under a magnifying glass. The ballast stones appear as polygons with a number of corners between 5 and 8, written in ellipses, and a size of 2 to maximally 6.3 cm. In the first step the model B70 has been selected for the track and the parameter of the model has been investigated. In the second step the program became more flexible and one can decide if the system consists from one track and ballast stones or from two tracks and ballast stones. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Numerical Analysis of Kidney Stone Fragmentation by Short Pulse Impingement: Effect of Geometry

To better understand the behavior of stresses generated inside a kidney stone by direct pulse impingement during extracorporeal shock wave lithotripsy (ESWL), numerical analyses are performed in this work. LS-DYNA, an explicit Finite Element code for non-linear dynamic analysis is employed to investigate the effect of stone geometry to the stress field evolution inside the stone when subjected to short pulse wave. Circular disks with parts removed from the front and the back are used to model the stones that assumed have already had initial fracture. The other variation of spherical geometry such as ellipse is also considered in the numerical calculation.

A Simple Catapult System for Studying the Small Projectile Impact Resistance of Various Glass Laminates

Abstract A catapult arrangement capable of propelling small granite chippings at velocities of between 4 and 20 ms-1 at laminated glass structures similar to those used in car windscreens has been designed and manufactured. The results from a series of studies utilizing this equipment are presented, with the overall aim of reducing the weight of these constructions with no loss in impact resistance. The impact resistance of the laminates has been shown to depend strongly on the thickness of the outer glass layer, while the inner glass layer is of secondary, and in most cases, minor relevance. Tests in which the composition and thickness of the interlayer have been varied have revealed that this layer is of no consequence in terms of the impact resistance of the structure as a whole. Chemical strengthening of the outer glass layer has been carried out, and no improvement in performance is observed due to the nature of the stone geometry. Finally, tests on bilayer systems have been carried out, and these results indicate a potential weight saving for no loss in impact performance.

Surface stone cover on desert hillslopes; parameterizing characteristics relevant to infiltration and surface runoff

AbstractSurface stones are a common feature of desert hillslopes. They influence slope processes ranging from the interception and partitioning of rainwater to the dislodgement and transport of regolith particles. The aspects of a stone mantle which relate to these various influences are diverse, and include surface cover fraction, dimensions of the infiltration annulus, and geometric and packing effects.Analyses of the characteristics of stone cover at two study sites were made using photographic methods and are used to evaluate different means of reporting mean stone sizes. It is found that mean diameter based on weight, as conventionally employed in sieve analysis, is insensitive to important stone cover characteristics and may be influenced greatly by uncommon, large stones. Similarly, mean diameters based on count become inappropriate if large numbers of small stones dominate the calculated mean, concealing other site‐to‐site differences in stone cover. As a more appropriate parameterization of stone geometry, the use of mean diameters weighted by stone surface area and perimeter length are proposed. These weighting factors have the advantage that they relate closely to stone characteristics relevant to slope hydrology and erosion processes.

Reflections and emissions from stones during electrohydraulic lithotripsy.

Lithotripsy is a noninvasive procedure to destroy biliary and renal concretions using shock waves generated externally to the patient and focused at the stone site. The effectiveness and safety of lithotripsy procedures are partially determined by the accuracy of stone targeting. The presentation will cover analysis of pressure waves reflected from the stone to determine stone location, degree of pressure wave focusing, and stone geometry (with changes in stone geometry providing a measure of stone destruction). In the experiments, a Wolf model 2137.50 electrohydraulic lithotripter is used in conjunction with an ellipsoidal focusing system. Piezoelectric pressure transducers within the focusing system provide a means to measure pressure waves both before and after reflection from a variety of targets. In addition, a computer simulation for axisymmetric shockwave propagation in an ellipsoid is developed to predict reflections from stones of arbitrary geometry and position relative to the far focus of the ellipsoid. This ray method solution of the high-frequency approximation to the wave equation accounts for the formation of caustics, while other nonlinear effects are neglected. The simulation allows the visualization of time varying pressure fields within the lithotripter focusing system and around the targeted stone. This research could provide a starting point for a method of dose estimation in lithotripsy procedures. [Work supported by NSF, BCS-8957206.]