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This investigation presents an analytical and computer-aided study on the dynamics of meshing gears with backlash. Based on the rotary gear impact model of Yang and Sun, a modified model with additional considerations of bending deflection, axial compression, and Coulomb friction is developed. Despite the complexity in gear geometry, formulas for modeling these phenomena are all analytically derived. A computer simulation package is developed for this model. Consequently gear impact dynamics and the relative importance among the included considerations are studied. Results show that the energy loss due to the Hertzian damping is usually larger than that from the Coulomb friction, and the axial compressive energy is negligible in comparison to tooth bending energy. It is believed that the model and the finding in this study contribute toward understanding of impact behaviors of high-speed geared systems with frequent stop-and-start or intermittent motions.

The impact fracture created in the elastic-plastic response régime has been characterized in terms of its surface extension and penetration. A numerical dynamic analysis has been performed of a typical impact within this régime to indicate some of the principal characteristics of the contact behaviour and the stress field. The damage has then been analysed, by using simplified postulates based on key features of the impact dynamics and basic fracture mechanics concepts. This has enabled the primary material and target parameters affecting the impact fracture to be identified. Thereafter, some implications for strength degradation and erosion have been discussed.

A reformulation and solution is presented of the equations of impulse and momentum for an arbitrarily shaped rigid body striking a flat massive surface. The model makes use of the classical coefficient of restitution, e , and tangential coefficient, μ. The latter is defined as the ratio of the tangential to normal impulse components. It is shown that a distinction between μ and friction coefficients, f , is necessary for a proper interpretation of impact data. The expression of impact energy loss is placed into a particularly convenient form. Comparisons are made of this impact model to others from the field of solid particle erosion and wear.

The impact dynamics of a high strain rate compression test are analyzed and shown to give strain data in good agreement with those obtained by direct observation using high speed photography. The analysis can be used either as a curve fitting procedure for the photographic data or as an independent technique.

Simulations of two scenarios to illustrate processes of regional interindustrial growth and development suggest the dynamics of manpower issues. Using the core of the Sequential Interindustry Model, SIM, the dynamics by which interindustry production supplies continuing final markets is presented and the resulting industry production chronologies illustrated. The latter are transformed into employment chronologies from which labor requirements are computed as distributions of potential jobs by job duration and job starts. Adjustments in potential jobs to represent the dynamic linkages between manpower demand and supply in fluctuating labor markets are discussed as an extension of adaptive behavior in SIM. An encompassing impact dynamics framework for manpower assessment is suggested, including examination of management options of both demand and supply for timely impact mitigation.

In marine applications, composite structures in contact with water are subjected to impacts by projectiles large and small. While the presence of water is known to affect the dynamics of immersed structures, its effects on the impact dynamics is unclear. This study shows that the contact force history is not affected if the mass of the projectile is large. The opposite is true if the mass of the projectile is small compared to that of the target

Description of an impact dynamics facility that will be used to crash test full-scale light aircraft. The aircraft are crashed into the ground as free bodies, using a pendulum swing method to obtain desired flightpath angles and velocities. The aircraft are unrestrained during impact to obtain realistic reactions. Accelerations and strains of the aircraft structure are measured during impact. The crash sequence and structural deformations are obtained by external and internal camera coverage.

The vehicle-occupant impact dynamics during a crash are studied using a simple mathematical model. The model yields explicit analytical relationships between occupant responses and physical parameters of the vehicle structure and occupant restraint system. These parametric relationships, verified by experimental crash tests of the total system, are useful in describing the physical concepts of the impact event, and predicting occupant dynamic behavior during a vehicle crash. The limitations of the model are discussed and the design procedures using the equations and "carpet" plots are presented to aid the designer in the selection of a restraint system and vehicle structural parameters to meet predetermined design criteria. The application of the "carpet" plot in studying the sensitivity of the occupant response to the vehicle structural parameters is also demonstrated.

A comprehensive test program was conducted to establish emulsified fuel screening test procedures, to obtain safety evaluation criteria, and to evaluate the safety performance of emulsified and gelled aviation fuels in a simulated full-scale crash environment. A series of screening tests was formulated and conducted to obtain fuel characteristics as a function of hot- surface ignition, wind shear, and impact dynamics associated with fuel breakup, atomization/dispersion, and ignition. The data obtained from these screening tests were used to establish emulsified fuel safety evaluation criteria. A simulated full-scale experiment was designed to simulate the full-scale helicopter crash environment adequately and, in addition, to be reproducibly controllable at minimal cost. The screening tests revealed that, for the emulsified fuels tested, safety was directly dependent upon the fuel yield stress and its internal phase base fuel. The data obtained from the simulated full-scale tests provided definition of a nonhazardous limiting value for the ignition susceptibility parameter. Further, tests were performed on gelled fuels to offer a comparison between the safety of emulsified and gelled fuels. Three of the emulsified fuels tested were found to result in a nonhazardous postcrash fire: EF8R-104H emulsion, EF8R-104 emulsion, and Jet-A EXP-4 emulsion. The gelled fuels did not perform as well as the emulsified fuels; however, one gel, Jet-A gel no. 1, indicated a sizeable advantage over liquid fuels. In summary, the results of this program confirmed that aircraft fuel emulsions can be formulated which are nonhazardous within the helicopter survivable crash limit envelope.

Apollo command module land impact capability, discussing impact dynamics, possible landing area, spacecraft structure, crew couch and strut attenuation system, etc

The impact dynamics of micro-scale mechanisms deviates from the classical theories applied to traditional macro-systems, This is because of multiplicity of forces acting in nano-scale contacts, which have negligible effect at the larger scale. A fundamental understanding of these forces and their interplay is required to advise design of such mechanisms based on fundamental physics. The paper highlights the significance of some of these forces and circumstances where their influence becomes significant.Copyright © 2008 by ASME

International audience; Numerical simulations for tires are challenging. They involve large deformations models in highly heterogeneous structures, made of non-linear materials. And impact simulation adds fast transient dynamics. An explicit time-integrator is then well suited. Non-linear stresses are easily estimated with the explicit displacement, making computation cost low. At contact zone, stresses are particularly high. They can even lead to rupture. Therefore their computation must be very accurate. Contact formulation with Lagrange multipliers are then preferred to penalty methods.The Non-Smooth Contact Dynamic (NSCD) framework provides robust algorithms. They deal with velocity discontinuities at impact without adjusting time-step.CD-Lagrange scheme presents these properties. For time-integration, it uses the explicit central difference method. It keeps the symplectic properties of this method: energy and angular momentum conservation. This is required for accuracy in non-linear large rotations \cite{DiStasio}.For contact condition, it uses Lagrange multipliers on velocity. This formulation is more stable than classic formulations on displacement, and present a better energy balance.But an issue remains for the contact problem. It is generally a Linear Complementary Problem (LCP) which links all degrees of freedom at contact zone. This work investigates how to simplify this LCP, or solve it fast. A simpler contact problem is obtained using mass redistribution methods on CD-Lagrange scheme. This new scheme keeps the conservation properties of classic CD-Lagrange. And for classic CD-Lagrange, new LCP solving methods are proposed more suited to explicit time-integration.

Wave propagation in granular solids is found to have at least two regimes: a low-frequency ballistic signal and a high-frequency diffusive tail. The latter is attributed to granules clapping or elastic waves within the granules themselves. The low frequency front is traditionally attributed to the rigid-body motion of particles and their interactions via quasi-static contact forces. We present results obtained with experimental and numerical models indicating that the low-frequency ballistic wavefront is itself the result of surface waves in the granules. We find surface waves to be the principal mechanism of energy transmission.

International audience; This contribution suggests a modification of Moreau-Jean’s scheme to obtain an energy conserving formulation for frictionless vibro-impact problems involving an inelastic impact law. In this approach, the velocities of the non-contacting masses are modified in order to balance the amount of energy dissipated during impact. This correction is shown to be useful to avoid dissipation of energy through the simulation of a two-degree-of-freedom vibro-impact system involving sticking phases. It is found that the modification yields an energy conserving scheme for inelastic impact dynamics. The objective of this modification is to find families of periodic solutions of discrete systems involving sticking phases, which is not possible with the current approach due to the numerical dissipation.

We use aerosol techniques to investigate the cohesive and granular properties of solids composed of colloidal semiconductor nanocrystals (quantum dot solids). We form spherical agglomerates of nanocrystals with a nebulizer and direct them toward a carbon substrate at low (~0.01 m/s) or high (~100 m/s) velocities. We then study the morphology of the deposit (i.e., the "splat") after impact. By varying the size of the agglomerate and the spacing between the nanocrystals within it, we observe influences on the mechanical properties of the quantum dot solid. We observe a liquid-to-solid transition as the nanocrystals become more densely packed. Agglomerates with weakly interacting nanocrystals exhibit liquidlike splashing and coalescence of overlapping splats. More dense agglomerates exhibit arching and thickening effects, which is behavior typical of granular materials.

The interpretation of bloodstain patterns at crime scenes has received increased attention in recent years. Important to an understanding of this is knowledge of the fundamentals of blood droplet formation and impact dynamics. A review of the literature reveals that a considerable amount of work has been done with aqueous drop dynamics. Workers in the forensic science area seem to have been unaware of this. In addition, some of the most important and comprehensive early work with blood droplet dynamics seems to have been forgotten. It is not cited in more recent publications dealing with bloodstain pattern interpretation. This literature is reviewed and discussed as well. The present study presents results of experiments with blood droplet dynamics and high-speed photographs of blood droplet impacts on stationary target surfaces. Some longstanding misconceptions of importance to forensic scientists engaged in crime scene reconstruction are discussed.