Prediction Of Impact Force Research Articles

The relation between hip impact velocity and hip impact force differs between sideways fall techniques

Fall techniques that reduce fall severity may decrease the risk of hip fractures. A fundamental variable for fall severity is impact force, but impact velocity is also used. The purpose of the study was to determine whether impact velocity is valid to determine differences in fall severity between different techniques. Five young adults with martial arts (MA) experience performed sideways falls from kneeling height using three techniques: Block with arm (Block) and MA techniques with and without use of the arm to break the fall. In addition, one subject also performed MA falls from standing height. Linear regression analysis showed a moderate relation between hip impact velocity and force, which was depended on technique. In falls with comparable impact velocities, forces in MA falls were lower than forces in Block falls. Hence, differences in impact force could not be predicted by velocity. In conclusion, hip impact velocity may be useful to make an approximate prediction of impact force within fall techniques. However, to determine differences between techniques it was not always a valid predictor. When direct impact force measurements are not possible, methods combining impact velocity with energy estimates before and after impact might be more valid.

Determination of Railway Vertical Wheel Impact Magnitudes: Field Trials

The authors utilized both experimental and finite element modeling methods earlier to develop both a classical inverse approach as well as a root mean square (RMS) method to estimate the magnitude of wheel impact forces on railway track-like structures. This study presents some results from the field trials of the techniques developed in (Lee, M.L., Chiu, W.K. and Koss, L.L (2005). A numerical study into the reconstruction of impact forces on railway track-like structures. Structural Health Monitoring: An International Journal, 4(1), 19–45. Lee, M.L. and Chiu, W.K (2005). The reconstruction of dynamic impact forces on a railway track-like structure by using an inverse analysis technique. In: Proceedings of the 4th Australasian Congress of Applied Mechanics, pp. 605–610, Melbourne, Australia. Lee, M.L. and Chiu, W.K. (2005). A comparative study on impact force prediction on a railway track-like structure. Structural Health Monitoring: An International Journal, 4(4), 355–376.). A length of track carrying freight rail traffic and situated along the Melbourne–Geelong line (Victoria, Australia) is instrumented with accelerometers and shear-bridges. The instrumentation consists of five rail cribs instrumented with a shear-bridge and an accelerometer on the rail foot at the midspan of each crib. Using the shear-bridge instrumentation as a check, it is found that the proposed inverse analysis method (IAM) shows potential in not only reconstructing clean impact strikes but also in reconstructing strikes occurring outside of the shear-bridge effective zone within a single crib. Furthermore, based on the principle of superposition governing linear systems, multiple impact strikes within a single crib of rail are also able to be reconstructed. Regarding the RMS method, it is found that while a good correlation (R ≈ 0.8) existed between wheel impact force and track response RMS, a significant spread existed in the data.

A Finite Element Scheme for Impact Force Prediction of Robotic Mechanisms

Stress in robots operating at high speed may be considerable. Robots can also be subjected to unexpected, large reaction forces that may not be detected by sensors during high-speed impact. These present major problems since impact may damage the robotic mechanism. We propose the concept of impact force prediction using numerical models and a low-cost finite element scheme considering inertia and large motion of the whole system. We developed a scheme using gap elements to simulate the contact-impact phenomenon. To check the scheme’s validity, we conducted tests and experiments whose results show that impact analysis considering the stiffness of contact objects is possible. Peak of impact forces in numerical analysis agrees well with those of experiments.

The relation between hip impact velocity and hip impact force differs between sideways fall techniques

Fall techniques that reduce fall severity may decrease the risk of hip fractures. A fundamental variable for fall severity is impact force, but impact velocity is also used. The purpose of the study was to determine whether impact velocity is valid to determine differences in fall severity between different techniques. Five young adults with martial arts (MA) experience performed sideways falls from kneeling height using three techniques: Block with arm (Block) and MA techniques with and without use of the arm to break the fall. In addition, one subject also performed MA falls from standing height. Linear regression analysis showed a moderate relation between hip impact velocity and force, which was depended on technique. In falls with comparable impact velocities, forces in MA falls were lower than forces in Block falls. Hence, differences in impact force could not be predicted by velocity. In conclusion, hip impact velocity may be useful to make an approximate prediction of impact force within fall techniques. However, to determine differences between techniques it was not always a valid predictor. When direct impact force measurements are not possible, methods combining impact velocity with energy estimates before and after impact might be more valid.

A Comparative Study on Impact Force Prediction on a Railway Track-like Structure

The ability to estimate an impact force being imparted onto a structure is highly valuable to its overall health monitoring scheme. This study compares impact force prediction on a railway track-like structure by a number of methods. One proposed technique utilized to estimate dynamic impacts on railway tracks involve correlating a root mean square (RMS) calculation of the track response over a selected frequency bandwidth with different impact force levels. Another technique involves the use of strain gauges configured into a full bridge circuit to reconstruct the time history of the impact force on the track structure. A third method utilizes a classical inverse analysis approach to reconstruct the force time history with a calibrated transfer function in the frequency domain. This article uses both finite element and experimental techniques to evaluate the aforementioned methods with regard to input impacts with constant magnitude and varying durations. It is seen that the RMS method is not effective in predicting impact forces with like magnitudes but varying durations. This is because the RMS relies on measuring energy in the response spectra, which varies according to input impact energy. It was also shown that measuring strain is an effective method of reconstructing an impact force waveform; however its efficacy is reduced when the impact event becomes highly dynamic. This is because strain relies on structural deformation, which is dependent on the loading time history. It is seen that an inverse analysis technique, which relies on the calibration of a frequency response function to facilitate the reconstruction of impact forces is relatively immune to varying impact durations. This is due to the structure’s relative linearity over the lower frequency region, which is a critical consideration when choosing the inverse analysis method.

A new tube/support impact model for heat exchanger tubes

Heat exchanger tubes are often loosely supported at intermediate points by plates or flat bars. Flow-induced vibrations result in fretting wear tube damage due to impacting and rubbing of tubes against their supports. Prediction of tube response relies on modelling the nonlinear tube/support interaction. The evaluated response is used to predict the resultant wear damage using experimentally measured wear coefficients. An accurate prediction of impact forces and work rate is therefore paramount. The analytical models available in the open literature generally assume tube/support contact occurs at a single point. In this paper, a computational algorithm is proposed to describe tube/support impact considering a finite support width. The new model provides a means of representing tube/support contact as a combination of edge and segmental contact. The proposed model utilizes a distributed contact stiffness to describe the segmental contact. The formulation also incorporates a stick/slip friction model. The model developed is utilized to simulate the dynamics of loosely supported tubes.

A modeling of impact dynamics and its application to impact force prediction

In this paper, the contact force between two colliding bodies is modeled by using Hertz’s force-displacement law and nonlinear damping function In order to verify the appropriateness of the proposed contact force model, the drop type impact test is carried out for different impact velocities and different materials of the impacting body, such as rubber, plastic and steel In the drop type impact experiment, six photo interrupters in series close to the collision location are installed to measure the velocity before impact more accurately The characteristics of contact force model are investigated through experiments The parameters of the contact force model are estimated using the optimization technique Finally the estimated parameters are used to predict the impact force between two colliding bodies in opening action of the magnetic contactor, a kind of switch mechanism for switching electric circuits

計算力学的手法によるマニピュレータ内の衝撃力予測(作業をするロボット)

計算力学的手法によるマニピュレータ内の衝撃力予測(作業をするロボット)

2A1-D01 有限要素法を用いたロボット機構内の衝撃力予測

従来のロボティクス分野では, ロボット機構を構成する部材の強度や安全性を加味した機構設計や姿勢決定, 動作計画などはほとんど行われていないと言える。しかし, ロボットの動作が高速化するにつれ, 外界の物体との接触時に機構内に生じる衝撃力が増し, 部材破壊の可能性が高くなると考えられる。本研究では, ロボット機構の目標軌道から, その機構が地面と接触する際に発生する衝撃力をリアルタイムで解析するシステムを開発した。本報告では, 簡単な2足歩行ロボットに対する適用例を示す。

Quantitative Prediction of Impact Forces In Elastomers

We measure the impact forces and deflections resulting from drop tests of a mass with a flat impact surface onto flat pads of various elastomeric materials, and show that the forces can be predicted quantitatively with no adjustable parameters by using a theory whose only inputs are the linear viscoelastic characteristics of the materials, measured in small-amplitude oscillatory deformations. The theory, which models the elastomer as a nonlinear neo-Hookean material, is accurate for several elastomeric solids including polyurethanes, polynorbomene, and poly-vinyl-chlorides (PVCs), over a wide range of impact velocities, masses, temperatures and pad thicknesses. Some steps are taken to extend the model to surfaces which are not flat. The application in mind is the rational design of elastomeric components in impact-tolerant portable electronic equipment.

Prediction of impact forces in a vibratory ball mill using an inverse technique

To understand the dynamic mechanisms of the mechanical milling process in a vibratory mill, it is necessary to determine the characteristics of the impact forces associated with the collision events. However, it is difficult to directly measure the impact force in an operating mill. This paper describes an inverse technique for the prediction of impact forces from acceleration measurements on a vibratory ball mill. The characteristics of the vibratory mill have been investigated by the modal testing technique, and its system modes have been identified. In the modelling of the system vibration response to the impact forces, two modal equations have been used to describe the modal responses. The superposition of the modal responses gives rise to the total response of the system. A method based on an optimisation approach has been developed to predict the impact forces by minimising the difference between the measured acceleration of the vibratory ball mill and the predicted acceleration from the solution of the modal equations. The predicted and measured impact forces are in good agreement.

Prediction of impact force by impulse response method

A method has been established which permits prediction of impact force history from the velocity response of each impacting body to an impulsive force applied to its impact face, and the impact velocity. The bodies may consist of one or several linearly elastic or viscoelastic materials. However, the method is limited to cases of impact without significant effects of friction and slip, with constant contact area and with small deformations. It has been applied to four cases of axial impact of a truncated cone or a compound cylinder on a long cylindrical rod. The truncated cone was made of Nylon-6, the compound cylinder of Nylon-6 and aluminium, and the long cylindrical rod of steel. For the truncated cone and the compound cylinder, measured as well as theoretically predicted impulse responses were used, while for the long cylindrical rod only a theoretically predicted impulse response was employed. In all cases good agreement was obtained between the impact force histories predicted, using the impulse response method, and those measured with the aid of strain gauges on the long cylindrical rod. Because of three-dimensional effects the best agreement was obtained for the predictions based on measured impulse responses for the truncated cone and the compound cylinder.

Prediction of impact forces using Hertzian contact theory and measured modal structural data

A method is presented for predicting the impact force between a mass of known velocity and a structure using measured frequency response functions to characterise the dynamics of the underlying structure and a Hertzian model of the local contact stiffness at the point of impact. The method is applied by obtaining Laplace domain parameters determined by curvefitting the measured frequency response functions and writing linear state equations to characterise the structure. The non-linear contact stiffness is represented by a two parameter Hertzian model, identified by matching a predicted force pulse with a measured force pulse. It is shown that the non-linear dynamic characteristics of an elastomeric pad at the point of contact are modeled very satisfactorily by static Hertz theory during the deformation period and reasonably well during the restitution period of impact.

The evaluation and prediction of impact forces during landings

The investigation of impact force attenuation during landings may help identify performance strategies. The purpose of the study was to evaluate the effects of height (three), distance (three), and technique (three) on impact forces during landings. Three male volunteer subjects were filmed while performing three right foot landings onto a force platform for each combination of height, distance, and technique for a total of 81 trials per subject. Between- and within-subject three-way ANOVAs and three regression models (mechanical, biomechanical, refined biomechanical) were computed on the dependent variables of first (F1) and second (F2) maximum vertical force. Results of the between-subject ANOVAs indicated significant (P less than 0.05) height, distance, and technique main effects for F1 and a height x technique interaction for F2. The within-subject ANOVA results identified unique models for each of the three subjects. The biomechanical regression model exhibited the best predictions of F1 and F2 for S1 (81.0 and 72.0% explained variance, respectively), while the refined biomechanical model accounted for 83.4, 81.3, 80.9, and 88.0% of the F1 and F2 variances for S2 and S3, respectively. In conclusion, the within-subject results identified unique individual landing strategies that were masked by the group analyses suggesting that caution be exercised in using between-subject analysis techniques.

Radial yield variations in semiconductor wafers : Albert V. Ferris-Prabhu, Larry D. Smith, Henry A. Bonges and James K. Paulsen. IEEE Circuits Devices Mag., 42 (March 1987)

Breaking wave loads on coastal structures depend primarily on the type of wave breaking at the instant of impact. When a wave breaks on a vertical wall with an almost vertical front face called the “perfect breaking”, the greatest impact forces are produced. The correct prediction of impact forces from perfect breaking of waves on seawalls and breakwaters is closely dependent on the accurate determination of their configurations at breaking. The present study is concerned with the determination of the geometrical properties of perfect breaking waves on composite-type breakwaters by employing artificial neural networks. Using a set of laboratory data, the breaker crest height, hb, breaker height, Hb, and water depth in front of the wall, dw, from perfect breaking of waves on composite breakwaters are predicted using the artificial neural network technique and the results are compared with those obtained from linear and multi-linear regression models. The comparisons of the predicted results from the present models with measured data show that the hb, Hb and dw values, which represent the geometry of waves breaking directly on composite breakwaters, can be predicted more accurately by artificial neural networks compared to linear and multi-linear regressions.

Optimum multilayer design selection in relation to production errors : H. Zorc. Vacuum37 (1/2), 101 (1987)

Breaking wave loads on coastal structures depend primarily on the type of wave breaking at the instant of impact. When a wave breaks on a vertical wall with an almost vertical front face called the “perfect breaking”, the greatest impact forces are produced. The correct prediction of impact forces from perfect breaking of waves on seawalls and breakwaters is closely dependent on the accurate determination of their configurations at breaking. The present study is concerned with the determination of the geometrical properties of perfect breaking waves on composite-type breakwaters by employing artificial neural networks. Using a set of laboratory data, the breaker crest height, hb, breaker height, Hb, and water depth in front of the wall, dw, from perfect breaking of waves on composite breakwaters are predicted using the artificial neural network technique and the results are compared with those obtained from linear and multi-linear regression models. The comparisons of the predicted results from the present models with measured data show that the hb, Hb and dw values, which represent the geometry of waves breaking directly on composite breakwaters, can be predicted more accurately by artificial neural networks compared to linear and multi-linear regressions.

Prediction of Impact Force and Duration Due to Low-Velocity Impact on Circular Composite Laminates

Two simple and improved models — energy-balance and spring-mass — were developed to calculate impact force and duration during low-velocity impact of circular composite plates. Both models include the contact deformation of the plate and the impactor as well as bending, transverse shear, and membrane deformations of the plate. The plate was a transversely isotropic graphite/epoxy composite laminate and the impactor was a steel sphere. In the energy-balance model, a balance equation was derived by equating the kinetic energy of the impactor to the sum of the strain energies due to contact, bending, transverse shear, and membrane deformations at maximum deflection. The resulting equation was solved using the Newton-Raphson numerical technique. The energy-balance model yields only the maximum force; hence a less simple spring-mass model is presented to calculate the force history. In the spring-mass model, the impactor and the plate were represented by two rigid masses and their deformations were represented by springs. Springs define the elastic contact and plate deformation characteristics. Equations of equilibrium of the resulting two degree-of-freedom system, subjected to an initial velocity, were obtained from Newton’s second law of motion. The two coupled nonlinear differential equations were solved using Adam’s numerical integration technique. Calculated impact forces from the two analyses agreed with each other. The analyses were verified by comparing the results with reported test data.

Impact Force Prediction Using Measured Frequency Response Functions

A method is presented for predicting impact forces using measured frequency response functions when an ideal mass elastically impacts a stationary structure. It is shown that a frequency response function measured at the point of impact on the structure together with the impactor’s mass and velocity can be used to form a function which, after inverse Fourier transformation yields the predicted force. After the basic equation is developed, predicted and measured force pulses are compared for a steel missile impacting an aluminum casting. The limitations of the method due to hardware and experimental technique are also discussed.

Computer simulation study of offshore collisions and analysis of ship-platform impacts

The paper deals with a study of relative probabilities and inherent consequences of impacts on offshore platforms caused by ship collisions. A new approach to the analysis of relative frequency of collision is presented. The method is based on the simulation technique. By introducing a selection of critical failure events affecting the manoeuvrability of ships under various environmental conditions, the ship paths are statistically predicted. The load-deformation characteristics and impact energy absorption in ship structures subject to collisions are of major importance for the proper prediction of impact forces. A simplified theoretical calculation model is outlined based on large plastic deformations of the colliding ships suffering indentations of one of the sides. The impact resistance of concrete as well as steel platforms subject to ship collisions is discussed to some extent. A number of simple tests with pendulum impacts on fendered and unfendered reinforced concrete cylindrical shells are described in this context.