Average Impact Force Research Articles

Dynamic response of reinforced concrete sheds against the impact of rock block with different shapes and angles

This study aimed to quantitatively identify the influence of the block impact angle and block shape on the impact effect of reinforced concrete (RC) sheds. The smooth particle hydrodynamic (SPH) method and finite element method (FEM) were coupled and used to solve the simulation difficulty of large deformation of the sand buffer layer in the RC shed. SPH was used to simulate the sand buffer layer in the impact area that experienced large deformation. Concrete, reinforced, bedrock, block and sand buffer layer in the non-impact area were simulated by FEM. The accuracy of the coupled model was verified by the full-scale test data. Finally, the impact forces and the dynamic responses of the RC shed were analyzed, focusing on the effects of the block impact angle and shape. The numerical results show that the coupled SPH-FEM method is effective for simulating how block impacts the RC shed. The block impact angle and shape can significantly influence the normal and tangential impact forces. The design of the RC shed based on the assumption of blocks as free-falling spherical projectiles can lead to inaccuracy in some impact scenarios, and an appropriate correction was put forward in available empirical calculating formulae to include the effect of the irregular shape and impact angle of the block. The sand buffer layer dissipates a large part of the energy, which accounts for at least 58% of the initial impact energy.

Optimization of a Self-Excited Pulsed Air-Water Jet Nozzle Based on the Response Surface Methodology

A self-excited pulsed air-water jet (SEPAWJ) offers many advantages over other jets and has a large number of practical and industrial applications. In order to take better advantage of the SEPAWJ, response surface methodology (RSM) models were established with the experimental impact force characteristics as the dependent variable and three key nozzle parameters as the independent variable. Single and coupling factor effects of these three parameters (oscillation chamber length, oscillation chamber height, and diameter of the downstream nozzle) on performance of nozzle are analysed, and the structural parameters of optimum performance are calculated using RSM models. The external flow field, impact force and cleaning performance of SEPAWJ before and after optimization are analysed and compared experimentally. It is found that the significance levels of established average impact force and impact force amplitude RSM models are lower than 0.05, and their error ratios between calculation and experiment under the optimum construction are both less than 5 %, which confirms their considerable reliability. Meanwhile, the final large water mass of optimized SEPAWJ is formed much earlier, and is more intensive and more concentrated. Compared with the original SEPAWJ nozzle, the impact force and impact force amplitude of optimized SEPAWJ nozzle are increased by 52.00 % and 38.26 %, respectively. In addition, the cleaned area ratio of nozzle before and after optimization is 76 % and 100 % at 50 seconds, respectively, with an increase of 22.4 %.

Evaluating Martial Arts Punching Kinematics Using a Vision and Inertial Sensing System.

Martial arts has many benefits not only in self-defence, but also in improving physical fitness and mental well-being. In our research we focused on analyzing the velocity, impulse, momentum and impact force of the Taekwondo sine-wave punch and reverse-step punch. We evaluated these techniques in comparison with the martial arts styles of Hapkido and Shaolin Wushu and investigated the kinematic properties. We developed a sensing system which is composed of an ICSensor Model 3140 accelerometer attached to a punching bag for measuring dynamic acceleration, Kinovea motion analysis software and 2 GoPro Hero 3 cameras, one focused on the practitioner’s motion and the other focused on the punching bag’s motion. Our results verified that the motion vectors associated with a Taekwondo practitioner performing a sine-wave punch, uses a unique gravitational potential energy to optimise the impact force of the punch. We demonstrated that the sine-wave punch on average produced an impact force of 6884 N which was higher than the reverse-step punch that produced an average impact force of 5055 N. Our comparison experiment showed that the Taekwondo sine-wave punch produced the highest impact force compared to a Hapkido right cross punch and a Shaolin Wushu right cross, however the Wushu right cross had the highest force to weight ratio at 82:1. The experiments were conducted with high ranking black belt practitioners in Taekwondo, Hapkido and Shaolin Wushu.

Study on cushioning and energy absorption of sports mouthguard

PURPOSE Using impact test to study cushioning and energy absorption of sports mouthguard of different thickness, material and combination. METHODS According to the thickness, material and combination, the mouthguards were divided into 7 groups with 6 testing pieces in each group. A pendulum device was used to apply impact energy to the mouthguard and dentition model, and the magnitude of the impact energy was measured by changing the release height of the pendulum. The force sensor and the laser vibrometer were respectively connected to the data acquisition and signal analyzer to obtain the incident speed, rebound speed, maximum collision force, collision start time and collision end time of the hammer head. Collision time, energy absorption and energy absorption ratio of the mouthguard were calculated, which reflected different mouthguard cushioning and energy absorption characteristics. One-way analysis of variance and t test in SPSS 22.0 software package was used to analyze the difference between different groups. RESULTS No matter what type of mouthguard was worn by the dentition model, the impact force was significantly reduced than without mouthguards. At the same height, there was significant difference between the average maximum collision force and the average collision time among soft mouthguards with thicknesses of 2, 3, 4, and 5 mm(P<0.05); among which the average maximum collision force of the 5 mm was the smallest and the average collision time was the shortest. There was no significant difference in the average energy absorption and the average energy absorption ratio among these 4 groups. There was significant difference in the average maximum collision force, average collision time, average energy absorption and average energy absorption ratio between the two groups of mouthguards with the same thickness of splints and different materials(P<0.05). Among them, the average maximum impact force of the 4 mm soft mouthguard was smaller and the average collision time was longer. CONCLUSIONS Wearing sports mouthguard can reduce the risk of tooth fracture during collision. Soft mouthguard has the best cushioning performance and it is positively related to thickness. Locally strengthening hard materials can enhance energy absorption and provide better protection.

Experimental validation of a new semi-empirical impact force model of the dry granular flow impact against a rigid barrier

The maximum impact force of granular flow and its action point on a rigid barrier are the key indices of the anti-slip and the anti-overturning calculation, respectively. On the basis of the present impact force models and the observation in model experiments, this paper proposes a new semi-empirical impact force model focusing on the normal impact force and its point of action. By comparing the analytical solution and the experimental results, the new semi-empirical analytical model can estimate the normal impact force composed of both dynamic and static components with an error margin within ± 20% compared with the experimental results and so is for the corresponding point of action and tangential force. To calculate the residual force generated only by the static dead zone, the static friction angle between the dead zone and the chute base should be less than what was measured under kinetic conditions. Based on a large number of tests, it was found that assuming that the reaction force generated by the chute base operates at 2/3 of the deposition length makes the estimated normal impact force best suited to the experimental results.

An improved calculation model for predicting the coefficient of restitution and maximum impact force of rockfalls

Rockfalls, which are a common natural hazard, collide and continuously bounce along slope surfaces during their movement; the coefficient of restitution (COR) and impact force are two important characteristic parameters related to the impact process of a rockfall. In this paper, considering the elastoplastic characteristics of the ground material, a theoretical model is proposed to obtain the normal COR and normal impact force at different stages of the impact process. Subsequently, the tangential COR and tangential force are calculated based on the improved friction theory. Finally, an engineering case is studied to illustrate the applicability of the proposed model. The calculation results show that the COR is positively correlated with the incident angle under the same incident velocity and negatively correlated with the incident velocity under the same incident angle; the impact force is linearly and positively correlated with the incident velocity. Under a given slope condition, the theory proposed in this paper can explain the locking phenomenon between the boulder and the slope during impact.

Pengujian Struktur Sepatu Kuda Bahan Komposit Polymeric Foam Berpenguat Fiberglass Menggunakan Uji Impak Jatuh Bebas

This study aims to determine the mechanical structure of polymeric foam reinforced with fiberglass horseshoes. Observations are focused on the average maximum impact force and the average maximum impact stress obtained from the free fall impact test. Testing the free fall impact structure with an impactor weight of 10 kg on five horseshoe test specimens 1, 2, 3, 4 and 5 with an impact distance of 2.5 meters, 2 meters, 1.5 meters, 1 meter and 0.5 meters, the results are horse shoe test specimens does not experience cracks / broken. The results obtained are in the form of the highest stress on the 1A test specimen with a stress value of 0.154 MPa and the maximum force found in the 1A test specimen of 874.95 N. with an impactor weight of 12.5 kg the test specimen cracks / breaks at a height of 3 m and 2.5 m, resulting in the highest impact stress value in sample 6B of 0.21 MPa and a force of 1185.5 N. then the force and stress will be higher but the level of damage will also be greater.

Behavior of concrete-filled steel tubes subjected to axial impact loading

Investigations on concrete-filled steel tubular (CFST) members under static loads have been extensively reported. Still, limited researches have been conducted to investigate the behavior of CFST columns subjected to axial impact loading. This paper presents an experimental study on dynamic behaviors of twelve square and rectangular CFST stub columns subjected to axial impact loading using a drop-weight test apparatus. The instantaneous force and deformation states were recorded during the impact tests. Finite element (FE) models were established and verified using the experimental results and existing research data, in which the strain rate effects of steel and concrete were fully considered. Then the effects of cross-section shape, steel strength, concrete compressive strength, steel ratio and impact energy condition on the dynamic responses of the CFST stub columns were studied using the FE models. The experimental and analytical studies indicate that the circular CFST stub columns perform better than the square and rectangular ones. While, little difference can be found between the square and rectangular CFST stub columns. For all the three shaped CFST stub columns, the average platform impact force increases and the deformation decreases with the increase of steel strength, concrete compressive strength, steel ratio and section area. Based on the parameter studies, a simplified design method was proposed by establishing the relationship between the maximum axial displacement and the impact energy condition to predict the deformation response of CFST stub columns under axial impact.

Crashworthiness design of graded cellular materials: An asymptotic solution considering loading rate sensitivity

Introducing graded cellular materials into energy absorber may improve the crashworthiness of protective structures. In order to meet the crashworthiness requirement that the impact force does not exceed the value that the protected object can afford, a backward strategy guiding the design of relative density distribution of cellular material is improved by considering the loading rate sensitivity in a shock model. Asymptotic solutions of the relative density distribution are obtained for the cases with or without considering the loading rate sensitivity, when a constant impact force is required. It is found that the second-order approximate solutions of the relative density distribution are good enough to approximate the exact solutions calculated by the fourth-order Runge-Kutta scheme. The validity of the design method is further verified by the cell-based finite element method, and the results indicate that the deformation localization at the proximal end is caused by both the density gradient and inertial effect. It is shown that the average impact force from the design without considering loading rate sensitivity exceeds the affordable value of the protected object, but that considering loading rate sensitivity can well meet the crashworthiness requirement. Therefore, the asymptotic solution of the relative density distribution from the design strategy considering loading rate sensitivity is suitable and convenient to guide the crashworthiness design in practical engineering.

Impact Force Identification of the Variable Pressure Flexible Impact End-Effector in Space Debris Active Detumbling

The security of the space environment is under serious threat due to the increase in space debris in orbit. The active removal of space debris could ensure the sustainable use of the space environment; this removal relies on detumbling technology. According to the characteristics of the mechanical impact-type active detumbling method, this paper discusses a method to accurately identify the impact force using a pressure sensor. In this work, the impact force between a flexible impact end-effector and the space debris was analyzed theoretically and experimentally considering the pressure change during impact. Firstly, a nonlinear impact force model was established for the impact between a flexible end-effector and space debris. Secondly, impact experiments were performed and the friction model was modified. Finally, the effect of detumbling was verified through simulation experiments. The results showed that the identification error of normal impact force was less than 6.7% and the identification error of tangential friction force was less than 6.9%. Therefore, this identification method of impact force met the requirements of space debris detumbling, which has important guiding significance for the active removal technology of space debris.

Artificial bird strike on Hopkinson tube device: Experimental and numerical analysis

This work shows a combined experimental-numerical research in bird impact. In order to perform the experimental tests, a artificial bird has been prepared and impacted against a Hopkinson tube in a wide range of impact velocities (70–200 m/s). The Hopkinson tube was designed in order to measure the induced force transmitted in the tube by the impact. This force could be used to compare different experimental tests and also to validate the numerical models proposed. In addition, the whole process of impact was recorded by means of high speed video cameras. The images captured allow to perform the analysis of the bird kinematics during the impact. Numerically, in order to reproduce the high deformations experienced by the artificial bird in the impact process, the Smooth Particle Hydrodynamics (SPH) technique has been used. Concerning the artificial bird material behaviour, four different models were employed, combining the two material models and two equations of state most used in the literature. The four cases have been compared with the experimental measurements and benchmarked. After the analysis of the results, it can be concluded that the combined experimental-numerical methodology proposed successfully can be used to study and validate the numerical models for simulating the behaviour of soft impactor when subjected to high velocity impacts. It can be seen that the normal impact forces induced by the impact are reproduced adequately for all the numerical models. However the radial spreading of the soft impactor is not reproduced as adequately as the other cases, especially in low velocity impacts. This effect can be important to reproduce the radial distribution of pressures and the secondary impacts produced by this radial expansion.

A Comparison of Football and Rugby Tackling During Spring Ball

ObjectiveThe study examined the effects tackling style has on forces translated to the brain in football and rugby.BackgroundTackling is linked to concussion due to high or repetitive impact forces. A small number of NFL teams are incorporating the rugby tackle mechanics due to keeping the head out of the way. Rugby style tackle use is increasing in football.Design/MethodsA convenient sample of 30 male football and rugby participants from two universities participated in this observational study. 20 football participants (20 ± 1.61 YO, 71.63 ± 2.71 in, 210.84 ± 45.52 lbs.) had impact sensors placed in the helmet (CUE™ Sports Sensor, Athlete Intelligence, Kirkland, WA) and 10 rugby participants (20.22 ± 3.31 YO, 70.78 ± 2.11 in, 211.78 ± 40.62 lbs.) were fitted with an instrumented mouthguard (VECTOR™ Sports Sensor, Athlete Intelligence, Kirkland, WA) during their respective spring seasons. Participants practiced without intervention. Devices were returned to researchers after activity, and the data was uploaded. Welch’s ANOVA with a Games-Howell post-hoc analyzed the data with significance set at 0.05.ResultsFootball participants tallied 3921 impacts over the course of 12 practices, compared to 1868 impacts over 9 practices received by rugby participants. Welch’s ANOVA determined that there is a difference in the frequency of impacts between football and rugby participants (Welch’s F (1, 4119.84) = 29.41, p &lt; 0.001). Football participants encountered linear impacts at 62.95 ± 36.57g. Rugby participants sustained impacts 20.59 ± 15.79g. The Welch’s ANOVA determined a difference in impact force between the football and rugby participants exists (Welch’s F (1, 5741.884) = 3780.385, p &lt; 0.001).ConclusionsImpact frequency appears to be lower in rugby athletes than football athletes during spring ball. Also, the average impact force appears to be less in rugby athletes. The use of a rugby-style tackle generated lower impact forces in athletes when contact occurs.

Debris flow impact on flexible barrier: effects of debris-barrier stiffness and flow aspect ratio

Conventionally, flexible barriers are rated based on their ability to resist a free-falling boulder with a particular input energy. However, there is still no well-accepted approach for evaluating performance of flexible barrier under debris flow impact. In this study, a large-nonlinear finite-element model was used to back-analyze centrifuge tests to discern the effects of impact material type, barrier stiffness, and flow aspect ratio (flow height to flow length) on the reaction force between the impacting medium and flexible barrier. Results show that, in contrast to flexible barriers for resisting rockfall, the normal impact force induced by the highly frictional and viscous debris is insensitive to barrier stiffness. This is because the elongated distributions of kinetic energy are mainly dissipated by the internal and boundary shearing, and only a small portion is forwarded to the barrier. Furthermore, a new stiffness number is proposed to characterize the equivalent stiffness between a debris flow or a boulder, and a flexible barrier. Under the circumstance of an extremely elongated debris flow event, i.e., low aspect ratio, the load on a barrier is dominated by the static component and thus not sensitive to the barrier stiffness.

Impact tribocharging of soft elastic spheres

The transfer of charge between a solid sphere and a metal plate during an oblique collision has been studied, using larger, more compliant elastic spheres than in previous studies. This relatively slow collision with large maximum strain allowed the normal and tangential impact forces to be measured directly, and the cumulative rolling and sliding contact areas to be deduced using a dynamic model. A rich variety of charging behaviour was observed for different collision regimes, and suggests very different charge transfer mechanisms for sliding, non-sliding, heavy and light contact. The charge transfer to initially-negative and initially-positive spheres was also strikingly different. Although the reasons for this could not be definitively determined, several hypotheses are discussed in detail, including mechano-ion transfer, bulk material transfer, and the effect of the spatial distribution of the initial charge on the statistical distribution of charge transfer events.

Frictional responses of concrete-to-concrete bedding planes under complex loading conditions

Concrete-to-concrete bedding planes (CCBP) are observed from time to time due to the multistep hardening process of the concrete materials. In this paper, a series of direct/cyclic shear tests are performed on CCBP under static and dynamic normal load conditions to study the frictional behavior effect by the shear velocities, normal impact frequencies, horizontal shear frequencies, normal impact force amplitudes, horizontal shear displacement amplitudes and normal load levels. According to the experimental results, apparent friction coefficient k (k = FShear/FNormal) shows different patterns under static and dynamic load conditions at the stable shear stage. k is nearly constant in direct shear tests under constant normal load conditions (DCNL), while it is cyclically changing with nearly constant peak value and valley value for the direct shear tests under dynamic normal load conditions (DDNL), where k increases with decreasing normal force and decreases with increasing normal force. Shear velocity has little influence on peak values of k for the DCNL tests, but increasing shear velocity leads to increasing valley values of k for DDNL tests. It is also found that, the valley values of k ascend with decreasing impact normal force amplitude in DDNL tests. The changing pattern of k for the cyclic shear tests under constant and dynamic normal load conditions (CCNL and CDNL tests) are similar, but the peak value of k is smaller in CDNL tests than that in CCNL tests. Normal load levels, shear displacement amplitudes, vertical impact frequencies, horizontal shear frequencies and normal impact force amplitudes have little influence on the changing pattern of k for the cyclic shear tests. The tests of this study provide useful data in understanding the frictional behavior of the CCBP under distinct loadings, and these findings are very important for analyzing the stability of the jointed geotechnical structures under complicated in situ stress conditions.

Experimental Study on Rockfall Impact Force Applied to Frame Shed Tunnels

A model experiment is performed to test the rockfall impact force applied to frame shed tunnels under the protection of different types of cushions embedded on tunnel roof slabs. The changing rule of impact force induced by rockfall is analyzed according to different impact energies and types of cushions embedded on shed tunnels. An enlargement coefficient reflecting the relationship between average impact force and maximum impact force is presented using experimental data and theoretical analysis. The improved method for calculating rockfall impact force can consider the many factors that affect this phenomenon. For a particular rockfall impact energy, the rockfall impact force with different types of cushion properties is affected by the cushion property function f∼(h,E,μ,γ). A large f value equates to the minimal discreteness of the expansion coefficient of rockfall impact force under different types of cushion, and vice versa.

Joint kinematics and ground reaction forces in overground versus treadmill graded running

BackgroundTreadmills are often used to assess running biomechanics, however the validity of applying results from treadmill graded running to overground graded running is currently unknown. Research questionThe purpose of this study was to investigate whether treadmill and overground graded running have comparable kinematics and ground reaction force parameters. MethodsEleven healthy male adults ran overground and on an instrumented treadmill as motion capture and force platform data were collected for the following conditions: downhill running at a slope of −8° at 10, 13 and 16 km⋅h−1; level running at 10 and 13 km⋅h−1; uphill running at a slope of +8° at 8, 10 and 13 km⋅h−1. Sagittal joint angles at heel strike, mid-stance, and toe-off were computed for the ankle, knee and hip. Ground reaction force parameters including peak average and instantaneous normal loading rate, peak impact and active normal force, peak tangential (braking and propulsive) forces, and normal and tangential impulses were also calculated. ResultsJoint kinematics and ground reaction forces for level running were generally similar between overground and treadmill conditions. The following variables were significantly higher during overground uphill running (mean difference ± SD): average normal loading rate (14.4 ± 7.1 BW⋅s−1), normal impulse (0.04 ± 0.02 BW⋅s), propulsive impulse (0.04 ± 0.02 BW⋅s), and vertical center of mass excursion (0.092 ± 0.031 m). The following variables were significantly higher during overground downhill running (mean difference ± SD): ankle plantarflexion at toe-off (−5.39 ± 6.19°) and vertical center of mass excursion (0.046 ± 0.039 m). SignificanceThese findings suggest that subtle differences in kinematics and ground reaction forces exist between overground and treadmill graded running. These differences aside, we believe that overground kinematics and ground reaction forces in graded running are reasonably replicated on a treadmill.

Small nanoparticles, surface geometry and contact forces.

In this molecular dynamics study, we examine the local surface geometric effects of the normal impact force between two approximately spherical nanoparticles that collide in a vacuum. Three types of surface geometries-(i) crystal facets, (ii) sharp edges, and (iii) amorphous surfaces of small nanoparticles with radii R<10 nm-are considered. The impact forces are compared with their macroscopic counterparts described by nonlinear contact forces based on Hertz contact mechanics. In our simulations, edge and amorphous surface contacts with weak surface energy reveal that the average impact forces are in excellent agreement with the Hertz contact force. On the other hand, facet collisions show a linearly increasing force with increasing compression. Our results suggest that the nearly spherical nanoparticles are likely to enable some nonlinear dynamic phenomena, such as breathers and solitary waves observed in granular materials, both originating from the nonlinear contact force.

Optimization of Multi-Layer Dome Structures for Enhanced Performance and Comfort of Protector Pads

A multi-material, multi-layer dome structure is proposed for desigining futuristic body protection pads that will address a safety issue prominent among the population of elderly people, patients, industry workers, military personnel, and sport players. Those people are prone to be subjected to blunt impacts due to falls, bullets, and blast waves, which can result in serious injuries, early death, and extremely high medical costs. Protector pads can effectively reduce impact force and prevent injuries in high-risk individuals. However, most currently available protection pads are bulky, heavy, or rigid. Therefore, new body protectors need to be developed to satisfy the requirements of wearing comfort, ease of fitting, ensured protection, and cost-effectiveness. Out of many different design ideas generated, the most promising ones were identified through an evaluation process based on various criteria such as performance, comfort, and manufacturability. One of those designs utilizes a dome-shaped top layer and thin fabric membrane component that is very strong in tension but flexible in bending. Such structure will make the pads excellent in dissipating shock energy by diverting normal impact force to lateral direction and minimizing the force directly transmitted to the weakest body parts. Through finite element analyses, the best combinations of materials and components were identified. The selected pad structure was optimized for light-weight and flexibility while keeping excellent resistance to the compression. The thickness of the shell element and the overall thickness of the whole pad were optimized for the same level of deflection and stress as other simple shell pads. The results showed that the dome-shaped structure could be a useful component of effective body protection pads through optimal combination of various materials and layers.

Optimization design of scraper angle based on orthogonal test

The scraper angle of milling machine has a direct effect on the milling efficiency. This research establishes the finite element model of scraper, and designs the cutting front angle and the cutting back angle as factor, impact force and the average force for orthogonal test of evaluation indexes. Through simulation analysis, the force is obtained at the different level. At the same time, the simulation results are verified by experiments. The results show that the simulation results of contact force in the X direction are close to the measured results, and prove the accuracy of the simulation results. The optimized scraper is that the cutting angle is 5.5°, and the cutting back angle is 9°. The impact force is minimum, and the resultant of average force and impact force is minimum. The optimization of scraper angle can effectively reduce the impact force and the average force, which provides guidance for the improvement of scraper.