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Metamorphic mechanisms have attracted considerable attention owing to their capability to switch their topology to adapt to different operational tasks. One feature of topological change is the re-contact of different bodies, which inevitably causes collisions affecting operation accuracy and service life. Consequently, in this study, a collision incidence matrix was introduced to describe the topology of a system involved in collisions, and a method for reducing the closed-loop system to an open-loop system was proposed. The complex movement of the metamorphic mechanism in a changing topology was classified into two different running stages of the source metamorphic mechanism. Based on the relative coordinate method, dynamic modeling of the source metamorphic mechanism considering the impact effects was conducted. Combining the classical collision theory and Newton–Euler equation, the generated impact impulse and the motion after collision were determined. Subsequently, a dynamic analytical method for the full configuration of metamorphic mechanisms was proposed to reflect the changes in the topological structure in the dynamic model. Finally, two typical metamorphic mechanisms used in packaging and spinning were considered as examples to verify the correctness and effectiveness of the proposed method, and their impact characteristics during configuration transformation were analyzed. The proposed analytical method of internal impact for a variable topology process provides effective theoretical guidance for the stability analysis of configuration transformation and structural design aimed at minimizing impacts. [ABSTRACT FROM AUTHOR]

Large-scale high-speed granular avalanches can be catastrophic; however, small-scale model tests cannot reproduce the high-speed impact effect, resulting in barrier designs lacking detailed knowledge considering the prototypical dynamic conditions of granular avalanches (e.g., high moving velocities and varied material volumes). In this paper, a well-designed centrifuge model is adopted to reproduce high-speed granular avalanches with variable flow velocities and material volumes, and a calibrated DEM model is also used to offer further insights. The results indicate that under high-speed impact conditions, the effect of granular volume on the pressure distribution pattern dominates, but its influence on the impact loading rate is less obvious. To estimate the high-speed impact force, a constant pressure coefficient of 1 can provide a reasonable estimation for the dynamic component if boulder impacts are excluded, and the static component can be calculated using the weight of the dead zone based on the assumption of a static state of the dead zone. In addition, considering the transition of the impact pressure distribution model caused by different granular volumes and flow velocities, a rectangular pressure profile is suggested for barrier design against high-speed dry granular avalanches when the peak total impact force is adopted as the design load. [ABSTRACT FROM AUTHOR]

The plastic deformation of the spherical tungsten alloy projectile during penetration results in the change of penetration rule. To accurately calculate the penetration depth of the projectile into the low carbon steel target, the concept of projectile shape coefficient was introduced according to the shape of the experimentally recovered projectile, and the deformation penetration process of the projectile was simplified into the rigid penetration process with different shape coefficients at different impact velocities. The rigid penetration model of the spherical, ellipsoidal, and truncated sphere projectile was constructed. The calculation results show that the accuracy of the three models is close to each other. On this basis, the heat map analysis method is used to correlate the impact velocity with the projectile shape coefficient, and a piecewise calculation model of the penetration depth of the spherical projectile is constructed. The error between calculation results and experiment results is less than 10%. [ABSTRACT FROM AUTHOR]

Granite, as a typical anisotropic hard and brittle rock, is generally in a uniaxial, biaxial, or triaxial state of stress in deep underground engineering and is frequently influenced by extreme dynamic loads including earthquakes, occasional burst, and excavation disturbance. A series of dynamic compression tests were conducted on granite using a true triaxial split Hopkinson pressure bar (SHPB) system on initially anisotropic granite. Using X-ray three-dimensional (3-d) computed tomography (CT) scanning technology and ultrasonic testing, the mechanical properties and fracture behaviors of anisotropic granite under combined dynamic and static loading conditions were studied. Results show that the failure mode of granite changes from damage, to splitting failure, and finally to crushing failure with the rising strain rate under dynamic uniaxial compression. In addition, the axial prestress increases the proportion of transmitted energy in the rock and significantly influences failure strain of the rock. Under biaxial static prestresses, the granite is split along the direction of its free faces and the failure mode is affected by the value of the anisotropy index in the direction of free faces. Under the triaxial static prestresses, the rock is very unlikely to be damaged and the damage effect occurs only after multiple impacts. In the same prestress state, the strain rate of granite increases with the increasing impact velocity and the prestress constraint reduces the dynamic strain rate in the granite. The initial anisotropy of the longitudinal wave velocity of granite is gradually enhanced as the cyclic impact continues. Increasing the strain rate will induce more significant evolution of initial anisotropy of granite, while the prestress constraint restricts the development of initial anisotropy. The results improve understanding of the evolution of impact damage and the dynamic failure characteristics of anisotropic rocks under high geostress. Highlights: Conducted a series of dynamic fracture tests of granite under unprestressed, uniaxial, biaxial and triaxial prestressed conditions. Revealed the dynamic impact damage evolution mechanism of granite under multi-axial stress constraints from a microscopic perspective. Investigated the confining pressure effect and strain rate effect on dynamic damage anisotropy of granite under multi-axial stress constraint. [ABSTRACT FROM AUTHOR]

The protective performance of a three-layer explosive welded composite plate consisting of steel and aluminum plates is studied in ballistic experiments and numerical simulations. The mechanism of target plate failure under the impact of spherical fragments is investigated. [ABSTRACT FROM AUTHOR]

In this study, a rapid prediction method for the damage range evaluation of steel box structures under internal blast load was proposed. First, we carried out a dimensional analysis of the damage range, determined the main influencing factors, and built a predictive model. Then, a large number of numerical simulations were conducted with consideration of different steel grades, structural dimensions, plate thicknesses, and explosive weights. After that, according to the damage range data for all the working conditions obtained with the simulation, the failure mode diagrams were drawn on a dimensionless coordinate axis and a two-dimensional dimensionless number coordinate system. Based on this, the damage range for different working conditions was observed, and empirical equations were proposed to quickly predict the damage range of the steel box structure during a blast load. Finally, the correctness of the proposed quick prediction method was verified through field blast experiments result. [ABSTRACT FROM AUTHOR]

The "self-sharpening" effect has been observed experimentally in the penetration of tungsten high-entropy alloy (WHEA) into steel targets in previous study. From the microscopic observation of the residual WHEA long-rod projectile (LRP), the multiphase structure at micro-scale of WHEA is the key effects on self-sharpening penetration process. In order to describe the distinctive penetration behavior, the interaction between micro phases is introduced to modify the hydrodynamic penetration model. The yield strengths of WHEA phases are determined based on the solid solution strengthening methods. Combined with the elbow-streamline model, the self-sharpening mechanism is revealed in view of the multi-phase flow dynamics and the flow field in the deformation area of the LRP nose is characterized to depict the shear layer evolution and the shape of the LRP's nose as well as the determination of the penetration channel. The self-sharpening coefficient considering the reduction of nose radius is proposed and introduced into the penetration model to calculate the depth of penetration and the penetration channel. Results show that the multi-phase interaction at the microscopic level contributes to the inhomogeneous distribution of the WHEA phases. The shear layer evolution separates part of the LRP material from the nose and makes the nose radius decrease more quickly. It is also the reason that WHEA LRPs have a pointed nose compared with the mushroom nose of WHA heavy alloy (WHA) LRPs. The calculated results agree well with the corresponding experimental data of WHA and WHEA LRPs penetrating into semi-infinite medium carbon steel targets with elevated impact velocities. The flow field in the projectile nose was established to describe the self-sharpening penetration process of the tungsten high-entropy alloy. Combined with the solid solution strengthening methods, the flow field of the projectile nose was structured based on the multi-phase flow. The nose radius before separation was set as r b and after separation is r a . The shear layer evolution separated part of the material from the nose and made the nose radius decrease more quickly. [ABSTRACT FROM AUTHOR]

The main aim of this paper is to demonstrate the benefit of the application of high-performance computing techniques in the field of non-linear science through two kinds of dynamical systems as test models. It is shown that high-resolution, multi-dimensional parameter scans (in the order of millions of parameter combinations) via an initial value problem solver are an efficient tool to discover new features of dynamical systems that are hard to find by other means. The employed initial value problem solver is an in-house code written in C++ and CUDA C software environments, which can exploit the high processing power of professional graphics cards (GPUs). The first test model is the Keller–Miksis equation, a non-linear oscillator describing the dynamics of a driven single spherical gas bubble placed in an infinite domain of liquid. This equation is important in the field of cavitation and sonochemistry. Here, the high-resolution parameter scans gave us the opportunity to lay down the basis of a non-feedback technique to control multi-stability in which direct selection of the desired attractor is possible. The second test model is related to a pressure relief valve that can exhibit a special kind of impact dynamics called grazing impact. A fine scan of the initial conditions revealed a second focal point of the grazing lines in the initial-condition space that was hidden in previous studies. [ABSTRACT FROM AUTHOR]

This paper presents a unifying dynamics formulation for nonsmooth multibody systems (MBSs) subject to changing topology and multiple impacts based on a linear projection operator. An oblique projection matrix ubiquitously yields all characteristic variables of such systems as follows: (i) the constrained acceleration before jump discontinuity from the projection of unconstrained acceleration, (ii) post-impact velocity from the projection of pre-impact velocity, (iii) impulse during impact from the projection of pre-impact momentum, (iv) generalized constraint force from the projection of generalized input force, and (v) post-impact kinetic energy from pre-impact kinetic energy based on projected inertia matrix. All solutions are presented in closed-form with elegant geometrical interpretations. The formulation is general enough to be applicable to MBSs subject to simultaneous multiple impacts with nonidentical restitution coefficients, changing topology, i.e., unilateral constraints becoming inactive or vice versa, or even when the overall constraint Jacobian becomes singular. Not only do the solutions always exist regardless of the constraint condition, but also the condition number for a generalized constraint inertia matrix is minimized in order to reduce numerical sensitivity in computation of the projection matrix to roundoff errors. The model is proven to be energetically consistent if a global restitution coefficient is assumed. In the case of nonidentical restitution coefficients, the set of energetically consistent restitution matrices is characterized by using a linear matrix inequality (LMI). [ABSTRACT FROM AUTHOR]

Insect contamination on aircraft leading edge surfaces can result in premature transition of the boundary layer, leading to an increase in skin friction drag and fuel consumption. An evaluation of candidate anti-contamination coatings was undertaken. Coatings were characterized before impact testing. Surface energy was quantified by dynamic contact angle analysis and surface roughness measured using a profilometer. Superhydrophobic coatings showed a reduction in contamination when compared to the higher surface energy specimens tested. The surface topography and chemistry, in particular the sliding angle of a coating, were found to have a significant influence on the effectiveness of a coating. Insect residue areas were theoretically predicted using high-speed liquid droplet theory and compared to experimentally obtained results. Tests with different insect species were conducted to investigate the effect of insect size and type on the effectiveness of the coatings and the evaluation procedure. Good correlations were obtained between the two test facilities used. The effect of substrate temperature on insect impact dynamics and adhesion was also evaluated. [ABSTRACT FROM AUTHOR]

Formulating a consistent theory for rigid-body dynamics with impacts is an intricate problem. Twenty years ago Stewart published the first consistent theory with purely inelastic impacts and an impulsive friction model analogous to Coulomb friction. In this paper we demonstrate that the consistent impact model can exhibit multiple solutions with a varying degree of dissipation even in the single-contact case. Replacing the impulsive friction model based on Coulomb friction by a model based on the maximum dissipation principle resolves the non-uniqueness in the single-contact impact problem. The paper constructs the alternative impact model and presents integral equations describing rigid-body dynamics with a non-impulsive and non-compliant contact model and an associated purely inelastic impact model maximizing dissipation. An analytic solution is derived for the single-contact impact problem. The models are then embedded into a time-stepping scheme. The macroscopic behaviour is compared to Coulomb friction in a large-scale granular flow problem. [ABSTRACT FROM AUTHOR]

The present study offers a regularized approach for multi-link flexible manipulator arms with frictional impacts. The complex risks of global dynamics simulation, which involve nonlinear frictional impact, stick-slip, and foreshortening deformation, as well as multi-scale numerical problems, were implemented. The system is described as an assembly of n flexible links connected by n rotary joints. The stretching, bending, and the torsional deformations of the flexible links were considered in addition to the flexibility and mass of the joint. The introduction of a contact force potential energy approach transformed the non-differentiable functions of the normal and tangential frictions into differentiable ones, thereby generating Lagrange equations for the general recursive formulation of the systems. A numerical simulation for the double pendulum and spatial manipulator arms collision with targets was generated, thereby allowing the calculation of the frequent switching between the stick/sliding and forward/backward sliding. Several normal contact and friction models were adopted, and their corresponding results were analyzed. The generated ordinary differential equations of the proposed smoothed algorithm were solved using explicit solvers to verify any improvements in the global computational efficiency of the frictional collision dynamics for the flexible manipulator arms. [ABSTRACT FROM AUTHOR]

The impact problem of a flexible multibody system is a non-smooth, high-transient, and strong-nonlinear dynamic process with variable boundary. How to model the contact/impact process accurately and efficiently is one of the main difficulties in many engineering applications. The numerical approaches being used widely in impact analysis are mainly from two fields: multibody system dynamics (MBS) and computational solid mechanics (CSM). Approaches based on MBS provide a more efficient yet less accurate analysis of the contact/impact problems, while approaches based on CSM are well suited for particularly high accuracy needs, yet require very high computational effort. To bridge the gap between accuracy and efficiency in the dynamic simulation of a flexible multibody system with contacts/impacts, a partition method is presented considering that the contact body is divided into two parts, an impact region and a non-impact region. The impact region is modeled using the finite element method to guarantee the local accuracy, while the non-impact region is modeled using the modal reduction approach to raise the global efficiency. A three-dimensional rod-plate impact experiment is designed and performed to validate the numerical results. The principle for how to partition the contact bodies is proposed: the maximum radius of the impact region can be estimated by an analytical method, and the modal truncation orders of the non-impact region can be estimated by the highest frequency of the signal measured. The simulation results using the presented method are in good agreement with the experimental results. It shows that this method is an effective formulation considering both accuracy and efficiency. Moreover, a more complicated multibody impact problem of a crank slider mechanism is investigated to strengthen this conclusion. [ABSTRACT FROM AUTHOR]

Foot-ground impact is a critical event during the running cycle. In this work, three performance indicators were used to characterize foot-ground impact intensity: the effective pre-impact kinetic energy, representative elements of the effective mass matrix, and the critical coefficient of friction. These performance indicators can be obtained from the inertial properties of the biomechanical system and its pre-impact mechanical state, avoiding the need to carry out force measurements. Ground reaction forces and kinematic data were collected from the running motion of an adult that adopted both rear-foot and fore-foot strike patterns. Different running cycles were analysed and statistical tests performed. Results showed that the three proposed indicators are able to illustrate significant differences between fore-foot and rear-foot strike impacts. They also support the hypothesis that fore-foot strike reduces impact intensity. On the other hand, a higher likelihood of slipping during the contact onset is associated with fore-foot strike pattern. [ABSTRACT FROM AUTHOR]

In the continuum structural mechanics framework, a unilateral contact condition between two flexible bodies does not generate impulsive contact forces. However, finite-dimensional systems, derived from a finite element semi-discretization in space for instance, and undergoing a unilateral contact condition, require an additional impact law: Unilateral contact occurrences then become impacts of zero duration unless (i) the impact law is purely inelastic, or (ii) the pre-impact velocity is zero. This contribution explores autonomous periodic solutions with one contact phase per period and zero pre-impact velocity [case (ii)], for any n-dof mechanical systems involving linear free-flight dynamics together with a linear unilateral contact constraint. A recent work has shown that such solutions seem to be limits of periodic trajectories with k impacts per period as k increases. Minimal analytic equations governing the existence of such solutions are proposed, and it is proven that, generically, they occur only for discrete values of the period. It is also shown that the graphs of such periodic solutions have two axes of symmetry in time. Results are illustrated on a spring-mass system and on a 4-dof two-dimensional system made of 1D finite elements. Animations of SPPs with up to 30 dofs are provided. [ABSTRACT FROM AUTHOR]

A composite liquid metal marble made of metal droplet coated with water film was proposed and its impact dynamics phenomenon was disclosed. After encapsulating the liquid metal into water droplets, the fabricated liquid marble successfully avoided being oxygenized by the metal fluid and thus significantly improved its many physical capabilities such as surface tension modification and shape control. The striking behaviors of the composite liquid metal marbles on a substrate at room temperature were experimentally investigated in a high speed imaging way. It was disclosed that such marbles could disintegrate, merge, and even rebound when impacting the substrate, unlike the existing dynamic fluidic behaviors of liquid marble or metal droplet. The mechanisms lying behind these features were preliminarily interpreted. This fundamental finding raised profound multiphase fluid mechanics for understanding the complex liquid composite which was also critical for a variety of practical applications such as liquid metal jet cooling, inkjet printed electronics, 3D printing or metal particle fabrication etc. [ABSTRACT FROM AUTHOR]

Based on the impulsive-dynamics formulation, this article presents the analysis of different strategies to regulate the energy dissipation at the heel-strike event in the context of human locomotion. For this purpose, a seven-link 2D human-like multibody model based on anthropometric data is used. The model captures the most relevant dynamic and energetic aspects of the heel-strike event in the sagittal plane. The pre-impact mechanical state of the system, around which the analysis of the heel impact contribution to energy dissipation is performed, is defined based on published data. In the context of the proposed impulsive-dynamics framework, different realistic strategies that the subject can apply to modify the impact dynamics are proposed and analyzed, namely, the trailing ankle push-off, the torso configuration and the degree of joint blocking in the colliding leg. Detailed numerical analysis and discussions are presented to quantify the effects of the mentioned strategies. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We proposed a multi-propeller multifunction aerial robot (MMAR) that is composed of a quadrotor with two legs. The legs can increase the function of the robot. We found that the legs can increase the safety region of the robot during the landing. To study the safety problem, the dynamics of MMAR interacting with environment should be solved. On the basis of the interaction dynamics, this paper investigates the velocity constraint for safe landing of MMAR. The investigation begins from the kinematics and dynamics of MMAR in flight mode. Then the impact dynamics of MMAR during landing is developed. Furthermore, the landing safety problem is formulated by a series of constraint equations which can give a safety region of the velocity during landing. The safety region can give the safe velocity of the aerial robot before landing. Finally, simulation examples are presented using the proposed methodology. In the examples, a detailed safety region of a simulated MMAR is constructed and shown. [ABSTRACT FROM AUTHOR]

In order to analyze the influence of different thickness distributions on the antipenetration performance of layered plates with a good surface-to-surface combination, five types of two-layer steel/aluminum and three-layer steel/aluminum/steel plates with the same areal density were manufactured by the method of explosive welding. Ballistic experiments and numerical simulation were performed to study the antipenetration performance of the plates impacted by a spherical steel projectile of diameter 8 mm. A 14.5-mm riffled gun was used to launch the projectile, and the numerical simulation were carried out by using the LS-DYNA 3D explicit finite-element code. Effects of the number of layers, their thickness distribution, and total thickness on the antipenetration performance of the layered plates were investigated. Results showed that the antipenetration performance of the multilayer plates was better than that of a monolithic plate with the same areal density - the ballistic limit speed of the two-layer and three-layer plates, on the average, increased by 9.6 and 19.9% compared with that of the monolithic one. In addition, the antipenetration performance of the three-layer plates was better than that of the two-layer ones if the thickness of the steel and aluminum plates was same. The influence of layer thickness distribution on the antipenetration performance was more pronounced for the two-layer plates. [ABSTRACT FROM AUTHOR]

Impact affects the dynamic characteristics of mechanical multi-body systems and damages those rotating parts, such as the joint rolling element bearings, which are high-precision, defect intolerant components. Based on multi-body dynamic theory, Hertzian contact theory, and a continuous contact model, this study proposed a modelling method that can describe the dynamic behaviour of planar mechanical multi-body systems containing a rolling ball bearing joint under impact. In this method, the rigid bodies and bearing joint were connected according to their joint force constraints; the impact constraint between the multi-body system and the target rigid body was constructed using a continuous contact force model. Based on this method, the reflection relationship between the external impacts of the mechanical multi-body system and the variation law governing the dynamic load on the rolling bearing joint were revealed. Subsequently, an impact multi-body system, which was composed of a sliding-crank mechanism containing a rolling ball bearing joint and the target rigid body with an elastic support, was analysed to explore the dynamic response of such a complex discontinuous dynamic system andthe relevant relationship governing the dynamic load on the rolling bearing joint. In addition, a multi-body dynamic simulation software was used to build a virtual prototype of the impact slider-crank system. Compared with the theoretical model, the prototype had an additional deep groove ball bearing. That is to say, the prototype model took account of the specific geometric structural characteristics and the complex contact relationship of the inner and outer races, rolling balls, and bearing cage. Finally, the effectiveness of the theoretical method proposed in this study was verified by comparative analysis of the results. The results suggested that the external impact of a mechanical multi-body system was prone to induce sudden changes in the equivalent reaction force on its bearing joint and the dynamic load carried on its rolling balls. This study provided an effective method for exploring the distribution characteristics of dynamic loads on rolling ball bearing joints under working impact load conditions. Moreover, it offered support for the parameter optimisation of geometric structure, performance evaluation, and dynamic design of the rolling ball bearings. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The impact dynamics of a flexible multibody system is investigated. By using a partition method, the system is divided into two parts, the local impact region and the region away from the impact. The two parts are connected by specific boundary conditions, and the system after partition is equivalent to the original system. According to the rigid-flexible coupling dynamic theory of multibody system, system’s rigid-flexible coupling dynamic equations without impact are derived. A local impulse method for establishing the initial impact conditions is proposed. It satisfies the compatibility conditions for contact constraints and the actual physical situation of the impact process of flexible bodies. Based on the contact constraint method, system’s impact dynamic equations are derived in a differential-algebraic form. The contact/separation criterion and the algorithm are given. An impact dynamic simulation is given. The results show that system’s dynamic behaviors including the energy, the deformations, the displacements, and the impact force during the impact process change dramatically. The impact makes great effects on the global dynamics of the system during and after impact. [ABSTRACT FROM AUTHOR]

Anytime that tornadoes interface with people, the results are often grim. The varied characteristics of tornado windfields and the diverse techniques of home construction complicate the expected outcomes of such interactions. Since it is now known that tornadoes do not produce unfathomable winds, engineers have developed techniques for increasing a home's tornado resistance; thus, increasing the odds of survival of the inhabitants. Even considering these advances, tornadoes still wreak havoc and cause much causality every year. The story of tornado survival is partly chance, partly knowledge, and partly science. This essay utilizes analogies between a popular motion picture and the state of the art of tornado-resistant construction to illustrate the good, the bad, and the ugly facts of tornado survival. First examined are the positive aspects of tornado probability. The odds of experiencing a tornado are so low that massive expenditures are not necessarily cost effective. Next, various techniques of tornado-resistant construction practices are included for new and existing structures. Introduction of equations for predicting debris penetration are compared with various building techniques to describe the viability of tornado protection. The negative aspect of tornado/structure interfaces describes the fact that despite contemporary construction and prevention exercise, the unpredictability of the tornado windfield causes tremendous damage and loss of life. The final section examines the interface between tornadoes and mobile homes. This proves very ugly in every aspect of the word. Statistics and equations confirm the inherent dangers of such an interaction. Also, described is a novel approach to the design of a portable tornado shelter. [ABSTRACT FROM AUTHOR]

From an engineering point of view, church bells are structures that, during ringing, are exposed to severe loading conditions. They are damaged due to material wear, fatigue loading, material deficiencies, different clapper-to-bell layouts, ringing conditions, etc. To get an insight into the wear-related damage of bells, experimental investigations and numerical simulations of the local contact between the clapper and the bell were carried out as part of the activities of an EU-funded project called Maintenance and Protection of Bells. In order to make a full-scale comparison between the measured and simulated results a simplified model was set up. In this model the clapper was replaced by a cylinder with a rounded tip that was dropped against a block representing the bell wall. The aim of the simplified model was to study the impact phenomenon in a controlled way and to adapt the numerical model for simulating the local contact. In the article the synthesis of a finite-element model for simulating the cylinder-drop test is presented. The results of the finite-element simulations of repetitive cylinder drops are compared to the data that were measured in the laboratory. The effects of the cylinder material, the cylinder radius and the drop height of the cylinder on the local elastic-plastic behaviour of the cylinder and the block are also presented and discussed. [ABSTRACT FROM AUTHOR]

This paper examines the effectiveness of analyzing impact events in mechanical systems for design purposes using simple or low ordered finite elements. Traditional impact dynamics analyses of mechanical systems namely stereomechanics, energy method, stress-wave propagation and contact mechanics approaches are limited to very simplified geometries and provide basic analyses in making predictions and understanding the dominant features of the impact in a mechanical system. In engineering practice, impacted systems present a complexity of geometry, stiffness, mass distributions, contact areas and impact angles that are impossible to analyze and design with the traditional impact dynamics methods. In real cases, the effective tool is the finite element (FE) method. The high-end FEA codes though may be not available for typical engineer/designer. This paper provides information on whether impact events of mechanical systems can be successfully modeled using simple or low-order finite elements. FEA models using simple elements are benchmarked against theoretical impact problems and published experimental impact results. As a case study, an FE model using simple plastic beam elements is further tested to predict stresses and deflections in an experimental structural impact. [ABSTRACT FROM AUTHOR]

The effects of the initial conditions of impact dynamics equations are investigated numerically and experimentally. The inadequacies of previous studies on initial conditions are pointed out. Then a coefficient of velocity jump at the moment of impact is introduced, and the experiments for the mental rods are implemented to validate the appending constraints modeling methods for impact process. The comparisons between the experimental and simulated results at different coefficients are used to study the effects of the velocity jump conditions to the numerical simulation. The results indicate that the physical velocity response of bodies during impact is smooth; the different values of velocity jump only have small effects on numerical oscillation of velocity response, and they have no effects on the time history of impact force. [ABSTRACT FROM AUTHOR]

During operation, a MEMS switch is activated by an applied voltage. This causes the switch, often a doped silicon microbeam, to be attracted toward (pulled-into) a substrate. The component–substrate contact completes a circuit and permits the flow of current. Calculations for the minimum voltage required to achieve quasi-static pull-in are well documented. But for these quasi-static pull-in voltages to be meaningful, the voltage would have to be increased gradually until the critical value $V_{\mathrm{pull\mbox{-}in}}$ is reached and the switch closes. Of course, practical considerations might require the switch to cycle on and off quickly, i.e., dynamically. This is particularly true in the case of radio frequency (RF) MEMS switches. In this paper, a model is developed and used to consider the dynamic pull-in characteristics of a clamped-clamped microbeam. This model includes inertial effects, structural and air damping (squeeze-film damping), as well as the impact behavior of the microbeam with the substrate. Parameter combinations leading to various types of behavior (no pull-in, air-bounce, wall bounce, etc.) are clearly identified. In an attempt to ensure fast switch closure and limit bouncing, two new applied voltage profiles are considered. [ABSTRACT FROM AUTHOR]

This article introduces benchmark cases for time integrators devoted to non-smooth impact dynamics. It focuses on numerical properties of explicit integrators. Each case tests one necessary numerical property in computational impact dynamics: energy behaviour at impact, angular momentum conservation, non-linear behaviour. The cases are easy to implement and analyse, providing a benchmark well-suited to first numerical studies. We rewrite explicit schemes for non-smooth impact dynamics with unified notations, and analyse them with the benchmark cases. [ABSTRACT FROM AUTHOR]