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Stress triaxiality plays a major role in the nucleation and growth of ductile damage in metals and alloys. Although, the mechanisms responsible for ductile failure are the same at low and high strain rate, in impact dynamics, in addition to time resolved stress triaxiality and plastic strain accumulation, pressure also contributes to establish the condition for ductile failure to occur. In this work, ductile damage development in 1100 commercially pure aluminum was investigated by means of rod-on-rod (ROR) impact tests. Based on numerical simulations, using a continuum damage mechanics (CDM) model that accounts for the role of pressure on damage parameters and stochastic variability of such parameters, the impact velocity for no damage, incipient and fully developed damage were estimated. ROR tests at selected velocities were performed and damage distribution and extent were investigated by sectioning of soft recovered samples. Comparison between numerical simulations and experimental results is presented and discussed.

Some seabirds (such as Northern Gannets and Brown Boobies) can dive from heights as high as 30 m reaching speeds of up to 24 m/s as they impact the water surface. It is perceived that physical geometry, particularly of the beak, allows them to endure relatively high impact forces that could otherwise kill non-diving birds. Acceleration data from simplified models of diving birds agree with simulated data for one species (Northern Gannet), however, no reliable experimental data with real bird geometries exist for comparison purposes. This study utilizes eleven 3D printed diving birds (five plunge-diving, five surface-diving and one dipper) with embedded accelerometers to measure water-entry impact accelerations for impact velocities ranging between 4.4 - 23.2 m/s. Impact forces for all bird types are found to be comparable under similar impact conditions and well within the safe zone characterized by neck strength as found in recent studies. However, the time each bird requires to reach maximum impact acceleration and its effect represented here by the derivative of acceleration (i.e., jerk), is different based on its beak and head shape. We show that surface diving birds cannot dive at high speeds as the non-dimensional jerk experienced exceeds a safe limit estimated from human impact analysis, whereas those by plunge divers do not.

Understanding the interaction of supercooled metastable water with superhydrophobic surface textures is of fundamental significance for unraveling the mechanisms of icing as well as of practical importance for the rational development of surface treatment strategies to prevent icing. We investigate the problem of supercooled water drops impacting superhydrophobic textures for drop supercooling down to -17 degrees C and find that increased viscous effects significantly influence all stages of impact dynamics, in particular, the impact and meniscus impalement behavior, with severe implications to water retention by the textures (sticky versus rebounding drop) and possible icing. Viscous effects in water supercooling conditions cause a reduction of drop maximum spreading (similar to 25% at an impact speed of 3 m/s for a millimetric drop) and can significantly decrease the drop recoil speed when the meniscus partially penetrates into the texture, leading to an increase of the contact time up to a factor of 2 in supercooling conditions compared to room temperature. We also show that meniscus penetration upon drop impact occurs with full penetration at the center, instead of ring shape, common to room temperature drop impact. To this end, we describe an unobserved mechanism for superhydrophobicity breakdown: unlike for room temperature drops, where transition from bouncing to sticky (impaled) behavior occurs sharply at the condition of full texture penetration, with a bubble captured at the point of impact, under supercooled conditions, the full penetration velocity threshold is increased markedly (increasing by similar to 25%, from 2.8 to 3.5 m/s) and no bubble is entrapped. However, even though only partial texture penetration takes place, failure to completely dewet because of viscous effects can still prohibit complete supercooled drop rebound.

Considered in this investigation is the dynamic behavior of space flexible probe-cone docking mechanism, in which the soft cone technology is applied. Kane method and Hertz contact theory are used to obtain the governing equations describing the response of the flexible docking mechanism. These equations are then coded into a computer program and solved using fourth-order Runge–Kutta methods. Results of the theoretical mode are found to be in good agreement with the experimental results, and the numerical results obtained from ANSYS/LS-DYNA software. Furthermore, the influence of soft cone parameters on impact process is discussed based on theoretical model systemically.

We experimentally investigated the impact dynamics of a water drop on oil-infused nanostructured surfaces using high-speed microscopy and scalable metal oxide nano surfaces. The effects of physical properties of the oil and impact velocity on complex fluid dynamics during drop impact were investigated. We show that the oil viscosity does not have significant effects on the maximal spreading radius of the water drop, while it moderately affects the retraction dynamics. The oil viscosity also determines the stability of the infused lubricant oil during the drop impact; i.e., the low viscosity oil layer is easily displaced by the impacting drop, which is manifested by a residual mark on the impact region and earlier initiation of prompt splashing. Also, because of the liquid (water)-liquid (oil) interaction on oil-infused surfaces, various instabilities are developed at the rim during impact under certain conditions, resulting in the flower-like pattern during retraction or elongated filaments during spreading. We believe that our findings will contribute to the rational design of oil-infused surfaces under drop impact conditions by illuminating the complex fluid phenomena on oil-infused surfaces during drop impact.

The impact dynamics, impact effect, and post-impact unstable motion suppression of free-floating space manipulator capturing a satellite on orbit are analyzed. Firstly, the dynamics equation of free-floating space manipulator is derived using the second Lagrangian equation. Combining the momentum conservation principle, the impact dynamics and effect between the space manipulator end-effector and satellite of the capture process are analyzed with the momentum impulse method. Focusing on the unstable motion of space manipulator due to the above impact effect, a robust adaptive compound control algorithm is designed to suppress the above unstable motion. There is no need to control the free-floating base position to save the jet fuel. Finally, the simulation is proposed to show the impact effect and verify the validity of the control algorithm.

Three Cu films with different three-level hierarchical structures were fabricated using a one-step electric brush-plating technique. Impact dynamics of water droplets on three Cu films was investigated. In the absence of surface chemical modification, the Cu films showed static hydrophobicity and even superhydrophobicity. Under dynamic impact, the two hydrophobic Cu films were wetted partially, whereas the superhydrophobic Cu film exhibited considerably robust water-repellency in a wide range of Weber number. Analysis based on the pressure balance relation revealed that the considerably robust water-repellency of the superhydrophobic Cu film arises from the damping role of the varied height and shape of the micro-protrusions in lowering the water hammer pressure, the delaying role of the submicro-bumps on the side of the micro-protrusions in preventing the penetration process of the depinned water–air interface and the critical surface hydrophobization role of the nano-scale structure in changing the wetting property of the basal surface of the Cu film from hydrophilicity to hydrophobicity.

The impact of a liquid droplet on a solid surface is one of the most common phenomena in nature and frequently encountered in numerous technological processes. Despite the significant progress on understanding the droplet impact phenomenon over the past century, the impact dynamics, especially the coupling effects between the properties of a liquid and surface wettability on the impact process, is still poorly understood. In this work, we experimentally investigated the impact of viscous droplets on superamphiphobic surfaces, with the viscosity of liquids ranging from 0.89 to 150 mPa s. We showed that an increase in liquid viscosity will slow down the impact process and cause bouncing droplets to rebound lower and fewer times. The critical impact velocity, above which droplets can rebound from the superamphiphobic surface, was found to linearly increase with the liquid viscosity. We also showed that the maximum spreading factor increases with Weber number or Reynolds number but decreases with the liquid viscosity. Scaling analyses based on energy conservation were carried out to explain these findings, and they were found to be in good agreement with our experimental results.

In contrast to rigid body autonomous underwater vehicle (AUV) models, elastic AUV models will exhibit hydrodynamic effects due to elastic deformation of the shell during water entry, influencing their load-response characteristics. In this paper, the predictive capability of the selected simulation method is first verified by comparing the simulation results with test data acquired from experiments conducted in a drop-test tank. Then, the effects of the head shape parameters, shell thickness and water-entry state, such as the water-entry velocity and angle, on the acceleration, pressure, stress and structural deformation of an elastic AUV during water-entry impact are investigated. By comparing the characteristics of rigid and elastic bodies, the influence of the hydroelastic effect is revealed. The research results can provide guidance on the design of airborne vehicles and transmedia vehicles.

Inspired by the self-cleaning ability of lotus leaves and stickiness (towards water) of rose petals, we investigate the droplet impact dynamics on such bioinspired substrates. Impact studies are carried out with water droplets for a range of impact velocities on glass, PDMS and soft lithographically fabricated replicas of the lotus leaf and rose petals, which exhibit near identical wetting properties as that of the original biological entities. In this work, we investigate the spreading, dewetting and droplet break-up mechanisms subsequent to impact. Surprisingly, the rose petal and lotus leaf replicas manifest similar impact dynamics. The observation is extremely intriguing and counterintuitive, as rose petal and its replicas are sticky in contrast to lotus leaves. However, these observations are based on experiments performed with sessile water droplets. By contrast, in the current study, we find that rose petal replicas exhibit non-sticky behaviour at the short time scale ∼ ( O ( 10 − 3 ) ) s similar to that exhibited by lotus leaf replicas. Air entrapment in the micrometre features of bioinspired surfaces prevent frictional dissipation of droplet kinetic energy, leading to contact edge recession. We have also unveiled interesting universal physics that govern the spreading, recession of the contact edge and subsequent break-up modes (ligament or bulb-ligament) of the droplet.

A new nonlinear model based on the absolute nodal coordinate formulation (ANCF) and the nonlocal elasticity theory is proposed to investigate the single-layered graphene sheets (SLGSs) impacted by nanoparticles. The geometrical definition of SLGSs is described by using the ANCF thin plate element, and the strain energy is expressed by using the nonlocal theory. The Lennard–Jones pair potential is adopted to model the van der Waals (vdW) force between SLGSs and nanoparticles. The impact dynamics of the system is simulated in multibody framework by using the generalized-alpha numerical integration method. The impact response of the gold atom–SLGSs system is simulated to validate the performance of the proposed model. Three impact dynamic simulations are conducted to investigate the influence of nanoparticles on the impact dynamics of SLGSs. The results show that the coupling of SLGSs vibration and vdW force led to the amplitude inconsistence of [Formula: see text]-position for nanoparticles.

To overcome the computational burden associated to the three-dimensional finite element simulation of fracture phenomena in polysilicon MEMS during dynamic loading, like e.g. impacts, a domain decomposition technique is used. The approach extends a method developed for linear elastic materials, by including cohesive crack propagation and it allows for the simulation of inter and trans-granular fracture initiation and propagation in polycrystals and it is a step forward in the construction of a complete simulation tool for the description of fracture phenomena in microsystems. Applications to critical MEMS details show encouraging results in reproducing local failure mechanisms.

This paper formulated noise sources of synchronous belt in terms of structure-borne noise and airborne noise. The structure-borne noise consists of structural impact noise and friction-induced noise. The airborne noise is due to airflow-induced acoustic wave during belt-sprocket tooth engaging. Based on the analysis of impact dynamics of belt-sprocket tooth interface, the impact response, the friction-vibration interaction, and the airflow-induced acoustic wave are comprehensively modelled. The spectral signatures of the varied noise are quantified, and the case studies are given to illustrate the influences of the tooth parameters and operation conditions on noise. The noise due to belt span vibration under impact ranges from hundreds to several thousand Hz. The impact noise, friction-induced noise and airflow-induced noise of belt tooth ranges from 3 kHz to 10 kHz.

Four aluminum surfaces with wettability varied from superhydrophilic to superhydrophobic were prepared by combining an etching and a coating process. The surface wettability was checked in terms of water contact angle (CA) and sliding angle (SA) under different humidity at -10 C. High-speed photography was applied to study water droplet impact dynamics on these surfaces. It was found that single and successive water droplets could rebound on the superhydrophobic surface and roll off at a tilt angle larger than 30 under an extremely condensing weather condition (-10 C and relative humidity of 85-90%). In addition, the superhydrophobic surface showed a strong icephobic property, the ice adhesion on this surface was only 13% of that on the superhydrophilic surface, though they had a similar nano/microtopological structure. Moreover, this superhydrophobic surface displayed an excellent durability of the icephobic property. The ice adhesion only increased to 20% and 16% of that on the superhydrophobic surface after the surface was undergone 20 icing/ice-breaking cycles and 40 icing/ice-melting cycles, respectively. Surface profile and XPS studies on these surfaces indicated a minor damage of the surface nano/microstructure and the coating layer upon these multiple ice-breaking and ice-melting processes. Therefore, this superhydrophobic surface could be a good candidate for icephobic applications. © 2013 American Chemical Society.

The National Aeronautics and Space Administration (NASA) Glenn Research Center (GRC) is well recognized for its contributions toward development of advanced materials and structures for aerospace propulsion and power systems. The Structures and Materials Division conducts research across a broad range of technical areas relevant to the agency’s future aeronautics and space mission requirements. This paper will introduce the technical areas of strategic importance in the Structures and Materials Division today and briefly address some of the specific research activities within these areas. A broad look at how the research areas of emphasis have evolved over time, beginning in the early 1940s when the GRC was first formed, will be discussed. Examples of some of the more notable research accomplishments and their impact on the aerospace industry over this time period will be included. A discussion of the division’s planned technical directions believed to be required to meet the longer-term national ...

In this paper, the noise sources of synchronous belt are decomposed and formulated based on the analysis of the impact dynamics of belt-sprocket tooth interface. The impact/contact of belt-sprocket tooth and the vibration of belt span are modeled. The friction–vibrations interaction of belt tooth and the airflow-induced acoustic wave during belt-sprocket tooth engagement are comprehensively formulated. The structure-borne noise consists of structural impact noise and friction-induced noise. The airborne noise is due to airflow-induced acoustic wave during belt-sprocket tooth engaging. The spectral signatures of the varied noise are quantified, and the case studies are given to illustrate the influences of the tooth parameters and operation conditions on noise. The noise due to belt span vibration under impact ranges from hundreds to several thousand Hz. The impact noise, friction-induced noise and airflow-induced noise of belt tooth ranges from 3 kHz to 10 kHz.

We investigate the impact dynamics of droplets containing silica nanoparticles and/or poly(ethylene oxide) (PEO) additives by using a high speed camera, and relate the impact behavior to the rheological properties of liquids. For a droplet with both particles and polymer additives, the rebound is damped much faster and the instability behavior is suppressed. Interestingly, the rebound can be inhibited even when impact is at high velocity (1.88 m s−1). The transition from “rebound” to “stick” by enhancing the impact velocity is mainly due to the increase of the friction force of the nanoparticles and polymer aggregates with the substrate. This is confirmed by the increase of the sliding angle with impact velocity.

The rear-end crash pulse generator has been considered to be a key device for performing car impact safety research under laboratory conditions. According to the international regulation, ECE R44, the polyurethane (PU) tube was recommended to produce a standard rear-end pulse. However, little literatures on the impact dynamics of PU tube were known. In this study, a was established under ANSYS/LS-DYNA. With this finite element model, the following conditions to generate the standard rear-end impact pulses were determined: the initial impact velocity of sled was 30km/h, the resultant mass of sled was 680kg, number of PU-tubes was three, and outer diameter of olive knob was 46mm. Compared with the standard deceleration-time curve of actual rear-end crash, this finite element model of rear-end crash pulse generator was preliminarily validated.

Biomechanical deviations long (approx. 5years) after anterior cruciate ligament reconstruction have not been quantified in males, despite their distinct risk profile as compared to females. These deviations can indicate altered joint loading during chronic, repetitive motions.Cross-sectional study, comparing kinematic and kinetic variables between 15 male anterior cruciate ligament reconstructed patients and 15 healthy controls. During walking and running gait, measurements were taken of impact dynamics, knee and hip sagittal plane angles and moments, and knee varus angles and adduction moments.Comparing affected limbs to control limbs, significantly lower maximum (P=0.001) and initial (P=0.003) loading rates were found during running, but not in walking. Hip angles were lower for affected limbs of patients compared to the control group (P=0.039) in walking, but not during running. Between-limb comparisons showed important differences in symmetry of the affected patients. Maximum force during running was higher in the unaffected limb (P=0.015), which was linked with a higher loading rate (P=0.008). Knee flexion angle was reduced by 2° on average for the affected limb during running (P=0.010), and both walking and running knee and hip moments showed differences. Knee varus angle showed a 1° difference during walking (P0.001), but not during running. Knee adduction moment was significantly lower (more valgus) during both walking and running.Male anterior cruciate ligament reconstructed patients demonstrate persistent, clinically important gait asymmetries and differences from healthy controls long after surgery in kinematics, kinetics, and impact biomechanics.

The impact dynamics and bouncing performance of high Weber number drops on hydrophobic surfaces with open and closed micro-cells are investigated. Central wetted rings are observed on both closed-cell and open-cell surfaces under high Weber number collisions, which are proposed to constitute the key element affecting the bouncing behaviour. It is found that the drops rebound on closed-cell surfaces where the central area is in the “hybrid wetting state” at high Weber numbers, while the drops adhere to the open-cell surfaces where the central region is in the Wenzel state. A theoretical model is developed to explain this interesting phenomenon, in which the liquid cannot reach the bottom of the closed-cell hydrophobic surfaces since the air stored in micro-cavities prevents the sliding motion of the liquid film and functions as a “gas spring” lifting the liquid lamella. This indicates that the hydrophobic surface with simple micro cavities can maintain the water-repellent characteristics under drop impacts at high Weber numbers. These findings are expected to be crucial to a fundamental understanding of the rapid collisions between drops and micro-structured surfaces, as well as a valuable strategy to guide the fabrication of novel super water-repellant and anti-icing surfaces.

This paper presents modular dynamics for dual-arms, expressed in terms of the kinematics and dynamics of each of the stand-alone manipulators. The two arms are controlled as a single manipulator in the task space that is relative to the two end-effectors of the dual-arm robot. A modular relative Jacobian, derived from a previous work, is used which is expressed in terms of the stand-alone manipulator Jacobians. The task space inertia is expressed in terms of the Jacobians and dynamics of each of the stand-alone manipulators. When manipulators are combined and controlled as a single manipulator, as in the case of dual-arms, our proposed approach will not require an entirely new dynamics model for the resulting combined manipulator. But one will use the existing Jacobians and dynamics model for each of the stand-alone manipulators to come up with the dynamics model of the combined manipulator. A dual-arm KUKA is used in the experimental implementation.

The effect of pitch of the pillars and impact velocity are studied for the impact dynamics of a microliter water droplet on a micropillared hydrophobic surface. The results are presented qualitatively by the high-speed photography and quantitatively by the temporal variation of wetted diameter and droplet height. A characterization of the transient quantitative results is a novel aspect of our work. Three distinct regimes, namely, non-bouncing, complete bouncing and partial bouncing are presented. A critical pitch as well as impact velocity exists for the transition from one regime to another. This is explained with a demonstration of Cassie to Wenzel wetting transition in which the liquid penetrates in the grooves between the pillars at larger pitch or impact velocity. The regimes are demarcated on a map of pitch and impact velocity. A good agreement is reported between the present measurements and published analytical models., Experimental Thermal and Fluid Science, 2015

We speak of a multiple impact when several collisions occur at the same time in a multibody system. Multiple impacts are complex phenomena which possess particular features, not shared by single impacts. In the first part of this chapter, these specific properties are described. Then, two models of multiple impacts are presented: the first one extends kinematic laws (Newton’s and Moreau’s impact laws), while the second one extends Darboux-Keller’s impact dynamics and uses energetic coefficients of restitution at each contact/impact point. The extension of Poisson’s kinetic law is briefly introduced. Chains of balls and the rocking block systems serve as examples.

Understanding high–velocity microparticle impact is essential for many fields, from space exploration to medicine and biology. Investigations of microscale impact have hitherto been limited to post–mortem analysis of impacted specimens, which does not provide direct information on the impact dynamics. Here we report real–time multi–frame imaging studies of the impact of 7 μm diameter glass spheres traveling at 700–900 m/s on elastomer polymers. With a poly(urethane urea) (PUU) sample, we observe a hyperelastic impact phenomenon not seen on the macroscale: a microsphere undergoes a full conformal penetration into the specimen followed by a rebound which leaves the specimen unscathed. The results challenge the established interpretation of the behaviour of elastomers under high–velocity impact., United States. Office of Naval Research (ONR DURIP Grant No. N00014-13-1-0676), United States. Army Research Office (Grant W911NF-13-D-0001)

As a passive blood drop impacts a hard surface, it is observed to collapse and spread laterally, then retract and settle. During the spreading phase, the edge of the drop may rise forming a crown extending into spines and breaking up into secondary drops. When a similar drop falls onto a textile surface these same processes may occur, but the process of blood wicking into the fabric complicates stain formation. These processes are described within for passive drip stains collected under controlled conditions using anticoagulated porcine blood. Three stages of this impact process were identified and could be separated into distinct time zones: (1) spreading (time t≤2.5ms) and (2) retraction (2.5≤t≤12ms) on the surface with potential splashing at the periphery, and (3) wicking (30ms ≤t≤30min) of the blood into the fabric. Although wetting and wicking may also occur for tplain-woven>cardboard. Conversely, the size of the satellite stains correlates with the amount of wicking in the fabric with the satellite stain size for plain-woven>jersey knit>cardboard.

[EN] This work presents a methodology for interfacing with the students in order to study impact problems. The results are derived from the Bachelor Thesis developed at the end of the fourth course in the Security Engineering Degree. The knowledge regarding security topic and the use of new analysis tools (commercial finite element solver) have proved to be extremely useful for future Guardia Civil officers., The authors acknowledge the financial support for the work to the Ministry of Economy and Competitiveness of Spain under the Project DPI2011-25999.

Taking the limit intensity as a starting point, a plasticity design theory is introduced in the design of the transit platform’s panel of double trolley quayside container crane for replacing elasticity design theory as a conventional method. As to the impact dynamics issue, the study gives a theoretical derivation based on the energy law as well as a verification of the experiments of the lockpins’ falling , and uses simulations with Ansys/Ls-dyna condition. Combining the above three aspects, the results prove to be correct. Given the limitations and requirements of the practical situation and the standards, a reasonable design is offered. Through full consideration, it provides the value of the experience for future reference design and should be widely extended to use.

In this article, author studied the application of two models of "single point damping-spring" model and "contact" model in the process of impact dynamic analysis. Research shows that the load and force could be transmitted smoothly in all these methods. But there still have limitations in two methods, we could not study the impact response of bearing itself and the shaft neck contacted with bearing in the "single point damping-spring" model, on the other hand, the penetration of contact parts could not be avoided completely in the "contact" model, sometimes, the numerical calculation even could not be converged if the parameters were not be set properly in this method. Of course, this two methods also have their own advantages, we could select different model according to different circumstances.

Novel compliant flooring systems are a promising approach for reducing fall-related injuries in seniors, as they may provide up to 50% attenuation in peak force during simulated hip impacts while eliciting only minimal influences on balance. This study aimed to determine the protective capacity of novel compliant floors during simulated 'high severity' head impacts compared to common flooring systems. A headform was impacted onto a common Commercial-Carpet at 1.5, 2.5, and 3.5 m/s in front, back, and side orientations using a mechanical drop tower. Peak impact force applied to the headform (F(max)), peak linear acceleration of the headform (g(max)) and Head Injury Criterion (HIC) were determined. For the 3.5 m/s trials, backwards-oriented impacts were associated with the highest F(max) and HIC values (p0.001); accordingly, this head orientation was used to complete additional trials on three common floors (Resilient Rubber, Residential-Loop Carpet, Berber Carpet) and six novel compliant floors at each impact velocity. ANOVAs indicated that flooring type was associated with all parameters at each impact velocity (p0.001). Compared to impacts on the Commercial Carpet, Dunnett's post hoc indicated all variables were smaller (25-80%) for the novel compliant floors (p0.001), but larger for Resilient Rubber (31-159%, p0.01). This study demonstrates that during 'high severity' simulated impacts, novel compliant floors can substantially reduce the forces and accelerations applied to a headform compared to common floors including carpet and resilient rubber. In combination with reports of minimal balance impairments, these findings support the promise of novel compliant floors as a biomechanically effective strategy for reducing fall-related injuries including traumatic brain injuries and skull fractures.

The game of hurling is ranked as one of the fastest and most skilful field games in the world. It is played by a stick, hurley, made of ash wood and a ball, sliotar, made of a cork core or similar viscoelastic materials. Better standardisation of the game equipment requires analysing impacts to quantify precisely the effect of variations in equipment design on the resultant impact force at low and high striking speeds. Therefore, the purpose of the present study was to use a high-speed camera to (1) characterise the impact dynamics in term of impact force magnitude and duration, and (2) investigate whether a relationship exists between the game equipment and the magnitude of the impact force. An air cannon unit (ACU) test rig was set up to cause the sliotar to strike the hurley at predetermined speeds. A high-speed camera operating at 12,500 frames per second (fps) was used to capture 32 experimental impacts covering a range of sliotar and hurley brands, impact locations and impact speeds. The factor “sliotar brand” was identified as the most significant factor for the impact force among other main factors and two-factor interactions at a constant speed and it had a significant effect with up to 27 % difference between sliotar brands. It was demonstrated that, at higher impact speeds, the force–deformation curves of the sliotar brands varied significantly, even though similar force–deformation curves have been reported at quasi-static compression and similar COR values at low impact speeds using the standard free-drop test. This is the first known study to characterise the unique, highly non-linear and anisotropic sliotar–hurley impact using high-speed camera technology. It highlights the need for a tighter standard for sliotar materials and manufacturing to increase uniformity between different brands and strongly suggests that the standard free-drop test is not sufficient to characterise and compare game equipment.

The objective of this study was to investigate the factors affecting ball velocity at the final instant of the impact phase (t1) in full instep soccer kicking. Five experienced male university soccer players performed maximal full instep kicks for various foot impact points using a one-step approach. The kicking motions were captured two dimensionally by a high-speed camera at 2,500 fps. The theoretical equation of the ball velocity at t1 given in the article was derived based on the impact dynamics theory. The validity of the theoretical equation was verified by comparing the theoretical relationship between the impact point and the ball velocity with the experimental one. Using this theoretical equation, the relationship between the impact point and the ball velocity was simulated. The simulation results indicated that the ball velocity is more strongly affected by the foot velocity at the initial instant of the impact phase than by other factors. The simulation results also indicated that decreasing the ankle joint reaction force during ball impact shifts the impact point that produces the greatest ball velocity to the toe side and decreasing the ankle joint torque during ball impact shifts the impact point that produces the greatest ball velocity to the ankle side.

Church bells are exposed to severe loading conditions during ringing, which results in different damage modes due to material wear, fatigue loading, material deficiencies, different clapper-to-bell layouts, etc. As part of the activities of an EU-funded project called Maintenance and Protection of Bells (PROBELL), experimental investigations and finite-element simulations of the local contact between the clapper and the bell were carried out to study the wear-related damage to bells. First a simplified model was built to assess under the laboratory-controlled conditions the consequences of the repetitive impacts between a spherical body made from steel and a flat block made from bronze. After the results of the finite-element simulations for a simplified model were in reasonable agreement with the measured data a full-scale finite-element model for simulating the repetitive clapper-to-bell strokes was built. The simulations with the full-scale model were performed for variations of the parameters that influence the structural behaviour of the bell and the clapper: the clapper material, the clapper mass, the relative impact velocity of the clapper, the shape of the clapper, the clapper's pin support, the clapper's impact angle, the clapper's guide accuracy, the bell's sound-burp thickness and the coefficient of friction between the clapper and the bell. The agreement between the simulated and the measured results and the relation between the local stress–strain state and the damage to the bell in the contact area are discussed.

Droplet impingement experiments were performed on grooved hydrophobic surfaces with cavity fractions of 0, 80, and 93 % using droplets of water and a 50 %/50 % water/glycerol mixture. The influence of liquid viscosity, cavity fraction, and spreading direction, relative to the surface grooves, is explored qualitatively and quantitatively. The maximum droplet spread diameter, velocity of the rebounding jet, and the time delay between droplet impact and jet emission were characterized for Weber numbers, We, based on droplet impact speed and diameter, up to 500. The unequal shear stresses and contact angles influence the maximum spread diameters in the two primary spread directions. At We > 100, the ratio of the spread diameter along the direction of the grooves to the spread diameter perpendicular to the grooves increases above unity with increasing We. The maximum droplet spread diameter is compared to recent predictive models, and the data reveal differing behavior for the two fluids considered. The results also reveal the existence of very high relative jet velocities in the range 5 ≤ We ≤ 15 for water droplets, while such jets were not observed for the more viscous mixture. Further, in the range 115 ≤ We ≤ 265, the water/glycerol jet formation dynamics are radically different from the water behavior. Most evident is the existence of two-pronged jets, which arise from the anisotropy of the surface and the unequal shear stresses and contact angles that prevail on the surfaces. It is these influences that give rise to differences in the maximum spread diameters in the two primary spread directions. Similar two-pronged jet emission was observed for water over the very narrow range of We from 91 to 96. The issuing jet velocities were also observed to increase with increasing cavity fraction for both fluids and over the entire range of We explored. Lastly, the elapsed time between droplet impact and jet emission decreased with increasing cavity fraction.

Taking ship-bridge collision as an example, how the wave propagation and the dynamic behavior of materials influence the impact force and energy transformation are studied from the impact dynamics viewpoint. By using a new flexible, energy-dissipating crashworthy device developed by the authors, both the impact force and energy transformed can be markedly reduced, which is much conductive to protect both bridge and ship.

The issue considered in this paper is the dynamic behavior of flexible probe based on space probe-cone docking mechanism in the docking process. The theoretical model of docking impact dynamics based on flexible beam is built according to the Lagrange Analytical Mechanics theory. The contact problem is solved by using Hertz point-surface contact model. Assumed Modes Method is introduced to describe the deformation of flexible beam. Runge–Kutta numerical method is used to solve this theoretical model. Results of the theoretical model show a good agreement with the experimental and MSC.Patran/Dytran simulation results. Moreover, the influence of flexible beam parameter on docking impact process is analyzed based on the theoretical model.

The issue considered in this paper is a flexible beam based on space probe-cone docking mechanism, which aims to buffer impact effects replacing buffering mechanism. The theoretical model of docking impact dynamics based on flexible beam is built according to the Lagrange Analytical Mechanics theory. The shape of docking probe is optimized by using genetic algorithm.

The impact dynamics of water droplets on an artificial dual-scaled superhydrophobic surface was studied and compared with that of a lotus leaf with impact velocity V up to 3 m/s. The lower critical impact velocity for the bouncing of droplets was about 0.08 m/s on both surfaces. At relatively low impact velocities, regular rebound of droplets and air bubble trapping and flow jetting on both surfaces were observed as V was increased. For intermediate V, partial pinning and rebound of droplets were found on the artificial dual-scaled surface due to the penetration of the droplets into the micro- and nano-scale roughness. On the lotus leaf, however, the droplets bounced off with intensive vibrations instead of being partially pinned on the surface because of the irregular distribution of microbumps on the leaf. As the impact velocity was sufficiently high, droplet splashing occurred on both surfaces. The contact time and restitution coefficient of the impinging droplets were also measured and discussed.

In this paper, the dynamic behavior of a cantilever beam impacting two flexible stops as well as rigid stops is studied both experimentally and numerically. The effect of contact stiffness, clearance, and contacting materials is studied in detail. For the numerical study of the system, a finite element model is created and the resulting differential equations are solved using a Time Variational Method (TVM). To achieve higher computational efficiency, the Newton-Krylov method is used along with TVM. Experimental results validate the contact model proposed for predicting the first mode system dynamics. A new nonlinear force estimation function has been proposed based on measured accelerations, which enables the understanding of the impact dynamics. � 2011 Springer Science+Business Media B.V.

When a human needs to generate a large force, they will try to apply an impulsive force with dynamic cooperation of the whole body. In this paper we first discuss impact dynamics of humanoid robots and then propose a way to generate impact motions for a humanoid robot to exert a large force while keeping a balance. In the impact motion generation, Sequential Quadratic Programming (SQP) is used to solve a non-linear programming problem in which an objective function and constraints may be non-linear functions of the motion parameters. Impact motions are generated using SQP so that the impact force is maximized while the angular momentum is minimized. Breaking wooden boards with a Karate chop is taken as a case study because it is a typical example of tasks that utilize impulsive force. A humanoid robot motion for the Karate chop is generated by the proposed method. In order to validate the designed motion, experiments are carried out using a small humanoid robot Fujitsu HOAP-2. The Karate-chop motion generated by the proposed method is compared with the motion designed by a human. The results of breaking the wooden boards experiments clearly show the effectiveness of the proposed method.

An energy-balance model is often used to analyze impact dynamics for composite structures. However this model tends to overestimate the peak impact load after the onset of damage since it does not account for damage initiation and propagation. In this paper, the energy-balance model is coupled with the law of conservation of momentum to extend its validity beyond the elastic response regime for a composite sandwich structure subjected to low-velocity impact. Closed-form solutions were derived for the plate’s elastic structural stiffness and the critical load at the onset of damage. The critical load was theoretically predictable by accounting for the elastic energies absorbed by the plate up to core failure. Impact test results also showed that the relative loss of the plate’s transverse stiffness after damage was directly related to the energy absorbed by the plate, which could be calculated given the damage initiation energy. The stiffnesses and the critical load were then used in the modified energy-balance model to predict transient load and deflection histories. Predicted results were comparable with test data, in terms of critical and peak loads, as well as the overall behaviour. This impact model is an efficient design tool which can complement detailed FE simulations.