Vertical Impact Load Research Articles

Simulation of A Hot-rolled H-section Steel Beam Subject to Static Loading Based on Discrete Element Method

Abstract In this paper, a new discrete element method (DEM) containing particle flow code (PFC) is presented as an efficient-to-implement alternative to the existing finite element method (FEM) for simulating internal forces and deformations of a hot-rolled H-section steel beam subject to static loading. Unlike FEM, which is efficient to solve continuous problems, the PFC method can solve discontinuous problems, such as collapse procedure of structures, and the collapse procedure of the structure can be monitored at different times in a more time-saving way. First of all, a linear constitutive model in FEM was built to compare with the linear parallel bond model built in PFC, a hot-rolled H-section steel beam considering geometrically non-linearity subject to static loading was simulated and the simulation results were compared with theoretical solution and FEM results. Both internal forces and deformations before yielding were compared and good agreements were achieved. Secondly, with the object-oriented programming technique and the redeveloped interface of PFC, a user-defined parallel bond model was developed to consider material nonlinearity and compared with the bilinear constitutive model built in FEM. Both internal forces and deformations before and after yielding were compared and good agreements were observed. Thus, the DEM model adopted in this paper can be efficiently used to simulate the behavior of the H-section steel beam. In the future, the developed parallel bond model can be used to simulate the performance of H-section steel beam subject to vertical impact loading and three-dimensional steel framed structure subject to horizontal collision.

Interaction mechanism of crushing of tubes and honeycomb under axial loading

ABSTRACTThis paper presents a simple novel crash energy absorbing system made of plain aluminium thin-walled tubes and honeycomb. The proposed tube/honeycomb system is characterized by slightly shorter tubes inserted into the cells of the honeycomb with close fit. The individual tube and honeycomb structures are numerically modelled under low-speed vertical impact loading and compared with experiments conducted in this study. Next, three representative triangular sections, which involve the symmetric boundary conditions of each cell group, are employed to model the tube/honeycomb system. Load-displacement curves and deformation patterns are compared with the experiments. The proposed honeycomb/tube system is found to produce higher energy absorption capacities for both per unit mass and volume, compared to an ordinary superposition of the constituents. Almost a perfect crushing load plateau is achieved without a peak force. These enhancements are associated with the spontaneous pre-deformation of the tubes pushed by the collapsed honeycomb walls. This interaction also enables synchronised deformation throughout the crash. Finally, a parametric study is performed, based on the height difference between the tubes and honeycomb, which is found to be the determiner of the performance for the proposed system.

Greater vertical impact loading in female runners with medically diagnosed injuries: a prospective investigation

BackgroundRunning has been critical to human survival. Therefore, the high rate of injuries experienced by modern day runners is puzzling. Landing on the heel, as most modern day shod runners...

Vertical accelerator device to apply loads simulating blast environments in the military to human surrogates

The objective of the study was to develop a simple device, Vertical accelerator (Vertac), to apply vertical impact loads to Post Mortem Human Subject (PMHS) or dummy surrogates because injuries sustained in military conflicts are associated with this vector; example, under-body blasts from explosive devices/events. The two-part mechanically controlled device consisted of load-application and load-receiving sections connected by a lever arm. The former section incorporated a falling weight to impact one end of the lever arm inducing a reaction at the other/load-receiving end. The “launch-plate” on this end of the arm applied the vertical impact load/acceleration pulse under different initial conditions to biological/physical surrogates, attached to second section. It is possible to induce different acceleration pulses by using varying energy absorbing materials and controlling drop height and weight. The second section of Vertac had the flexibility to accommodate different body regions for vertical loading experiments. The device is simple and inexpensive. It has the ability to control pulses and flexibility to accommodate different sub-systems/components of human surrogates. It has the capability to incorporate preloads and military personal protective equipment (e.g., combat helmet). It can simulate vehicle roofs. The device allows for intermittent specimen evaluations (x-ray and palpation, without changing specimen alignment). The two free but interconnected sections can be used to advance safety to military personnel. Examples demonstrating feasibilities of the Vertac device to apply vertical impact accelerations using PMHS head–neck preparations with helmet and booted Hybrid III dummy lower leg preparations under in-contact and launch-type impact experiments are presented.

Assessment of Compressive Thoracolumbar Injury Potential and Influence of Seat Cushions on Vertical Impact Loading of a Seated Occupant

Assessment of Compressive Thoracolumbar Injury Potential and Influence of Seat Cushions on Vertical Impact Loading of a Seated Occupant

Finite Element Model of the THOR-NT Dummy under Vertical Impact Loading for Aerospace Injury Prediction: Model Evaluation and Sensitivity Analysis

Finite Element Model of the THOR-NT Dummy under Vertical Impact Loading for Aerospace Injury Prediction: Model Evaluation and Sensitivity Analysis

Establishment of the Dynamics Modal for the Fire-Suction Hydraulic Impactor

The drilling speed to shorten the drilling cycle plays a decisive role in drilling process.Using the fire-suction hydraulic impactor can achieve percussive-rotary drilling.The fire-suction hydraulic impactor can transform drilling fluid’s pressure energy into mechanical energy.Withing bit static pressure,rotational cutting and vertical impact loading,the way of rock breaking will be faster and more efficient.Using Newton's second law to establish the corresponding kinetic equations,motion equations and displacement equations.The comparison between parameters and measured data validated the correctness of the formulas,which provides a theoretical basis for the products to improve and seriation.

Long-Term Gait Deviations in Anterior Cruciate Ligament–Reconstructed Females

Little is known of the potential long-term gait alterations that occur after an anterior cruciate ligament (ACL) reconstruction. In particular, variables, such as impact loading, which have been previously associated with joint deterioration, have not been studied in walking and running after an ACL reconstruction. The purpose of this study was to define the alterations in impact forces, loading rates, and the accompanying sagittal plane kinematic and kinetic mechanics at the time of impact between the ACL-reconstructed group and a healthy control group. Forty females (20 with ACL reconstruction and 20 controls) participated in the study. An instrumented gait analysis was performed on all subjects. Between-group and between-limb comparisons were made for the initial vertical impact force, loading rate, and sagittal plane knee and hip angles as well as moments. During walking and running, the ACL cohort had significantly greater initial vertical impact force (P = 0.002 and P = 0.001, respectively) and loading rates (P = 0.03 and P = 0.01, respectively), as well as a smaller knee extensor moment and hip angle during walking (P = 0.000 and P = 0.01, respectively). There was a trend toward a smaller knee moment and hip angle during running (P = 0.08 and P = 0.06, respectively) as well as a larger hip extensor moment during walking (P = 0.06) in the ACL group. No differences were found for hip extensor moment during running and for knee angles between groups during walking or running. Lastly, no between-limb differences were found for any variable. Gait deviations such as elevated impact loading and loading rates do not resolve long term after an individual has resumed previous activity levels and these may contribute to the greater risk of early joint degeneration in this population.

Numerical Simulation of Helicopter Cockpit Seat subjected to Crash Impact

Sikorsky S-61 or better known as “Nuri” had served the Malaysian aviation sector for the past four decades. It is mainly used for transportation, combat search and rescue purposes. However, there were Nuri helicopter crashes or accident cases reported during its operation period which involved loss of its occupants. The pilot survivability rate can be improved provided that the vertical impact loading on the helicopter is reduced during the crash accident. Utilization of an energy absorbing pilot seat or cockpit structure maybe one of the approaches to minimize the impact shock exerted to the occupants. However, the shock or maximum acceleration of the cockpit/pilot seat has to be first determined before a thorough design scheme can be undertaken. In this study, a vertical crash event of the Nuri pilot seat from 500 feet altitude was simulated and the maximum acceleration rate was determined using MSC PATRAN/LS-DYNA. The pilot survivability was determined by comparing the result with human tolerance criteria data available in other published works. From the result, it was found that the maximum acceleration of the Nuri pilot seat was 584.4g at 19. 63 milliseconds, thus it can be concluded that the survivability aspect of the pilot is fatal when compared to other published works.

Behaviour of Deformed Steel Columns Exposed to Impact Load During Earthquakes: Numerical Analysis

It has been observed during earthquakes that the so called soft-storey failure of an upper floor of a building leads to considerable vertical impact load acting on structural members of the lower storeys. The aim of this paper is to investigate numerically the behaviour of horizontally deformed columns (deformation as the result of earthquake loading) that are additionally subjected to vertical impact load. In the first stage of the study, different static pre-deformations of the column as well as various impact load time histories have been considered. Then, the detailed nonlinear analysis has been conducted by exciting dynamically the base of the specimen as well as by applying impact vertical load at different times of the harmonic ground motion excitation. The results of the first stage of the study show that with the increase in the static pre-deformation of the column the peak mean normal stress values induced at the bottom of the specimen as well as the peak horizontal displacement at the middle of the column show a substantial increase trend for all height drop values considered. The results of further study show that vertical impact may substantially influence the response of the column, which is dynamically excited in its horizontal direction. Moreover, the time of impact has been found to play a substantial role in the overall behaviour indicating that the response may be increased significantly if impact takes place when the specimen is in the range of its peak horizontal deformation.

Vertical Impact Loading in Runners with a History of Patellofemoral Pain Syndrome

Vertical Impact Loading in Runners with a History of Patellofemoral Pain Syndrome

Photoelastic analysis of stress waves in building subjected to vertical impact under laboratory earthquake experiments

In an earthquake occurring directly under a city, the vertical impact induced from the source may cause a large amount of damage to a column and beam of the building. Model-based simulations are carried out with photoelastic material in order to examine the effect of a vertical impact on the building in the case of a near-field type earthquake. The dynamic photoelastic method combined with strain gages is utilized to conduct direct full field and real time observations of stress waves in a building due to vertical impact in laboratory earthquake experiments. The conditions under which vertical impact loading is applied to the model building in a controlled laboratory environment are derived from the data recorded for the 1995 Hanshin-Awaji earthquake in Japan. The experimental apparatus with which an impact of a longitudinal stress pulse is able to be applied to a model of a real building is shown. It is estimated from our earthquake simulations that large dynamic stress concentrations are produced in the beam–column joints of the building by the vertical impact arising from a seismic source located directly below a surface.

Failure process and energy transmission for single-layer reticulated domes under impact loads

No failure, moderate failure, severe failure, and slight failure are the four failure modes generalized observed in the dynamic response of the single-layer reticulated dome under vertical impact load on apex. TE (the time that the end of impact force) and TF (the time that members are broken) are two key times in the failure process. Characteristics of dynamic responses at the two key times are shown in order to make the failure mechanism clear. Then three steps of energy transfer are summarized, i.e. energy applying, energy loss and energy transfer, energy consumption. Based on the three steps, energy transfer process for the failure reticulated dome under once impact is introduced. Energy transmissibility and local loss ratio are put forward firstly to obtain ELF (the energy left in the main reticulated dome) from the initial kinetic energy of impactor. Moreover, the distribution of failure modes is decided by ELF which leads to the maximum dynamic response of the reticulated dome, but not by the initial impact kinetic energy of impactor.

The effect of increasing inertia upon vertical ground reaction forces and temporal kinematics during locomotion

The addition of inertia to exercising astronauts could increase ground reaction forces and potentially provide a greater health benefit. However, conflicting results have been reported regarding the adaptations to additional mass (inertia) without additional net weight (gravitational force) during locomotion. We examined the effect of increasing inertia while maintaining net gravitational force on vertical ground reaction forces and temporal kinematics during walking and running. Vertical ground reaction force was measured for 10 healthy adults (five male/five female) during walking (1.34 m s(-1)) and running (3.13 m s(-1)) using a force-measuring treadmill. Subjects completed locomotion at normal weight and mass and at 10, 20, 30 and 40% of added inertial force. The added gravitational force was relieved with overhead suspension, so that the net force between the subject and treadmill at rest remained equal to 100% body weight. Ground reaction forces were affected by the added inertial force, but not to the magnitude predicted by the increase in mass, suggesting that adaptations in motion occurred. Vertical ground reaction force production and adaptations in gait temporal kinematics were different between walking and running. Peak vertical impact forces and loading rates increased with increased inertia during walking, and decreased during running. As inertia increased, peak vertical propulsive forces decreased during walking and did not change during running. Stride time increased during walking and running, and contact time increased during running. The increased inertial forces were utilized independently from gravitational forces by the motor control system when determining coordination strategies.

Effect of Cushioned Insoles on Impact Forces During Running

The use of cushioned or shock-absorbing insoles has been suggested as a mechanism to reduce the impact forces associated with running, thereby protecting against overuse injuries. The purpose of this study was to determine whether the use of cushioned insoles reduced impact forces during running in healthy subjects. Sixteen recreational runners (9 females and 7 males) ran at a self-selected pace for five trials with and without the use of cushioned insoles. During each trial, ground reaction forces, tibial accelerations, lower-extremity kinematics, and subject-perceived comfort were recorded. All variables were tested with the level of statistical significance set at alpha = .05. The use of cushioned insoles resulted in significant reductions in mean vertical ground reaction force peak impact (6.8%) and ground reaction force loading rate (8.3%), as well as peak tibial acceleration (15.8%). Spectral analysis of the tibial acceleration data in the frequency range associated with impact accelerations (12-25 Hz) revealed no change in the predominant frequency or the power of the predominant frequency. The knee flexion angle at initial contact and perceived comfort were similar for the two conditions. This study demonstrates the effectiveness of one type of cushioned insole in reducing peak impact force and tibial acceleration at initial foot-ground contact during running. The impact reduction observed was independent of knee kinematic adjustments or changes in perceived comfort. Further study is required to determine whether the reduction in loading that accompanied the use of the cushioned insoles can affect the incidence of running-related injuries.

The influence of deceleration forces on ACL strain during single-leg landing: A simulation study

Anterior cruciate ligament (ACL) injury commonly occurs during single limb landing or stopping from a run, yet the conditions that influence ACL strain are not well understood. The purpose of this study was to develop, test and apply a 3D specimen-specific dynamic simulation model of the knee designed to evaluate the influence of deceleration forces during running to a stop (single-leg landing) on ACL strain. This work tested the conceptual development of the model by simulating a physical experiment that provided direct measurements of ACL strain during vertical impact loading (peak value 1294 N) with the leg near full extension. The properties of the soft tissue structures were estimated by simulating previous experiments described in the literature. A key element of the model was obtaining precise anatomy from segmented MR images of the soft tissue structures and articular geometry for the tibiofemoral and patellofemoral joints of the knee used in the cadaver experiment. The model predictions were correlated (Pearson correlation coefficient 0.889) to the temporal and amplitude characteristic of the experimental strains. The simulation model was then used to test the balance between ACL strain produced by quadriceps contraction and the reductions in ACL strain associated with the posterior braking force. When posterior forces that replicated in vivo conditions were applied, the peak ACL strain was reduced. These results suggest that the typical deceleration force that occurs during running to a single limb landing can substantially reduce the strain in the ACL relative to conditions associated with an isolated single limb landing from a vertical jump.

A multifunctional testing device for rock fragmentation by combining cut with impact

Mechanical rock fragmentation is widely used in the fields of mineral resources exploitation, geological prospecting, tunnel excavating, civil engineering construction and national defence building, etc. At home and abroad researches on loading ways of rock fragmentation were mainly concentrated on the single static pressure or impacting loading, and the optimum loadings as well. Recent studies on brittle fracture showed that stress impulse can effectively improve the propagation of the crack, and the combination of impact and static pressure can increase the effect of breakage. In order to further understand the feasibility and efficiency of the cutting-impact rock fragmentation technology, a multi-function testing device was developed and its major parameters were analyzed by the authors. Principally the method of fragmenting rock by cutting-impact is putting a cutter on the surface of rock, applied with horizontal cutting force, vertical static pressure and impact load, and then the rock is broken under the combined loading. The multi-function testing device was designed on the basis of the above mentioned principle of rock fragmentation. It includes three parts: the static loading mechanism, the impact mechanism and the cutting mechanism. To carry out impact with different energy, the hammer's mass were designed to eight classes: 16.0, 18.5, 21.0, 23.5, 26.0, 28.5, 31.0 and 33.5 kg. According to the whole structure of the test setting, the largest stroke was chosen to be 300 mm. The low frequency which is adjusted by buncher and f=30-50 min-1 were selected. The device can conduct single breaking rock tests including cutting under horizontally static load as well, fragmentation under impact load and indentation under static load, and combined cutting impact test under the dynamic and static load. Not only can it be applied for single cutter test, but also for multi-cutters or roller cutter test. Granite and concrete samples with different strength were tested on the testing machine by PDC (Polycrystalline Diamond Compact) flat cutters and carbide alloy cutters under different loadings. The results show that the testing parameters are adjustable and the data are reliable. The testing device is a suitable and easy to operate one, and has reasonable structure in laboratory for simulating rock drilling or breaking under the combination of dynamic and static load, and has much value in designing and manufacturing of tunnel machine and mechanized excavators. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

Wave Propagation Behaviour of Spatial Structures: Impact Response Analysis of Single Layer Lattice Domes

Many researchers have investigated the wave propagation behaviors of continuum spatial structures such as plate and cylindrical shell. But due to the numerical difficulty, there is very little research related to discrete spatial structures. The objective of this paper is to examine wave propagation behavior of single layer lattice domes subject to vertical impact load at the centre node. In the first part, an analytical method based on the Fourier transform and a matrix method is presented. In the second part, an impacted two dimensional lattice beam is analyzed in order to estimate the validity of the analytical program. In the last part, nine types of single layer lattice domes are analyzed to estimate the effect of member distribution density, member arrangement pattern and the jointing system, etc., upon the wave propagation behavior.

RESPONSE OF A LAYERED ELASTIC MEDIUM TO A MOVING STRIP LOAD

Analytical determination of stresses and deformations caused by moving loads is vital to foundation and pavement designs. In current applications, moving loads are often approximated to be vertical impact loads. In this work, however, a live load is modelled as a uniform distribution of normal or shear stresses in actual motion. Then, a layer stiffness approach utilizing linear elasticity is followed in determining the surface and interior deformations due to the live load. By superimposing the two solutions for normal and shear surface stresses, the new approach can be made to provide an approximate solution to the problem of evaluating stresses and deformations caused by a wide wheel load rolling on a layered elastic system. Although elastic solutions in general are inadequate to explain the more significant consequences of pore pressure generation and dissipation in the soil subgrade, these results can certainly be useful to examine the shearing effects of wide rolling wheels on the asphalt layer and immediate settlement of the subgrade. It is found that the dynamic effects of a smoothly rolling wide load are significant at relatively low wheel velocities compared to those of shear waves in the subgrade and base.

Biomechanical considerations of impact forces and foot stability in running

The interaction between "man-shoe and surface" is presented as a model to discuss the complexity of human locomotion. Only if the physiological system "man" interacts positively with the physical requirements of shoe and surface quality running will become effective and economical. Especially during the early ground contact phase the hardness of the shoe construction determines the height of the vertical impact load. These adaptations have consequences in the emg amplitudes during the stretch activation phase of the contact. Comparing various jogging shoes with altered construction properties it can be shown that the "hardness" of the shoe material is well adapted by the variation in the emg amplitude. The influence of the amount of pronation on the impact forces has been confirmed in a separate study. Increased pronation resulted in an increased emg amplitude in the extensor muscles whereas activation in the flexor muscles was decreased. By means of different shoe and insole constructions it is possible to adjust the "man-shoe-surface" interaction to an optimum to carry loads by muscles, joints and ligaments and to avoid overuse and injuries.