Impact Location Research Articles

Characterization of sensor location variations in admittance-based TPA methods

When determining the critical paths for the transmission of sound and vibration in assembly products, transfer path analysis (TPA) is a reliable and effective tool. TPA represents a source with a set of forces that replicate the operational responses. However, admittance-based TPA methods are prone to experimental errors, as small measurement inaccuracies can lead to large discrepancies in the source characterization. The admittance of the transfer paths is preferably obtained through impact testing. Thus, poor repeatability in the position of the successive impacts affects the consistency of the interface forces. In this study, uncontrolled location variations in a structure’s excitation are characterized by a sensitivity analysis based solely on an experimental model. The functional dependency of a frequency response function on the impact location is deduced from the measured data. This makes it possible to reconstruct numerous responses for variations in the impact location and provides an appropriate sample size for the global sensitivity analysis. The influence of a random error at an individual impact location is quantified on the basis of variations in the response prediction. The approach is useful for cases where the source characterization is affected by location variations of the force input, e.g., lightly damped or complex structures where the impact locations are not easily accessed. An experimental study on an electric motor demonstrates that controlling the impact location’s repeatability in a TPA is important and can lead to a more consistent source characterization.

Dynamic response of the S-shaped composite foldcore sandwich structure under high-velocity impact loads

The dynamic response of the S-shaped foldcore sandwich structure was investigated at high-velocity impact load by combining the experimental and numerical methods. The ballistic tests were performed with a blunt projectile at different velocities, ranging from 49.7 m/s to 154 m/s, and the ballistic limit velocity (BLV) was estimated. The test results show that the impact location exerted great influence on the failure modes and energy absorption of the core. The BLVs of the sandwich structure are 64.2 m/s and 56.2 m/s for node and base impacts, respectively. And the different modes are observed for the top face sheet, the core and the bottom face sheet. The corresponding numerical simulations were performed by using Abaqus finite element software. The simulation results show that the BLVs predicted by the simulation correlated well with the tests. The failure modes of the sandwich structures with fiber fracture, delamination and compression failure are predicted reasonably. For the node impact conditions, the absorbed energy of the core is significantly higher than that of the top and bottom face sheet. For the base impact conditions, there is no significant difference on the energy consumed for three components of the structures.

Predicting the kinematic response of a helmeted headform during oblique impacts

A total of 160 oblique impact tests were performed to study the relationship between the kinematic response of a helmeted headform and the impact severity caused by a change in speed (Group 1) and anvil angle (Group 2). In this study, the kinematic response of a helmeted headform was evaluated by measuring its linear acceleration, rotational acceleration, and rotational velocity. In Group 1, a football helmet was tested at 45° anvil angle at four different impact speeds ranging from 4.5 to 7.4 m/s on five impact locations. The results showed that, for all cases, the relationship between the impact speed and helmeted headform kinematic response was linear, with an average R2 value of 0.98. At each impact location, a prediction line was generated using the data points for the lowest and highest speeds. For the speeds of 5.5 and 6.5 m/s, the prediction of the helmeted headform kinematic response was validated with an average error of 4.7%. In Group 2, the helmeted headform was tested at 5.5 m/s impact speed at six different anvil angles between 15° and 55°, and the response was fitted with a second-degree polynomial (curve) with an average R2 value of 0.96. The kinematic response of the higher and lower impact speeds was obtained experimentally for one angle, and the fitted curve for 5.5 m/s was offset to pass through the obtained kinematic response. The predicted helmeted headform kinematic response was experimentally validated, and the average error was found to be 8.3%. The results showed that it is possible to predict the kinematic response of a helmeted headform by interpolating or extrapolating the data without having to perform an additional impact test. An analysis of other research works also showed similar predictable behaviour for headform equipped with other helmet models. Therefore, the number of tests during the process of evaluating helmet performance can be reduced.

A computationally efficient model for granular material piling in a container

This paper describes the development of a novel computationally efficient model to simulate the granular material piling process inside a container. The model computes both the granular material profile inside the container and spillage amount and location out of the container based on the cart geometry, impact location and orientation of flow of the grain transmitted into the container. The performance and utility of the grain fill model strategy is demonstrated via simulation of the grain piling process inside a grain cart during agricultural combine harvester grain unloading from the combine into a tractor-driven grain cart. The simulation demonstrates that the model can simulate both the grain profile change and spillage in real time. Experimental data collected from a benchmark system with LiDAR was used to quantify the model accuracy during grain unloading. The experimental results show that the model can achieve 0.2-m accuracy during a corn unloading process from an empty to a full grain cart.

Identifying importation points of the SARS-CoV-2 Omicron variant into the USA and potential locations of early domestic spread and impact.

We identified the U.S. airports and metropolitan areas, particularly New York City, Miami, and Los Angeles, that were the most likely locations of importation and domestic spread of Omicron from South Africa. Vaccination coverage suggested that several cities in Georgia, Texas, and Utah were particularly vulnerable to public health impacts.

Sex-specific cognitive effects of mild traumatic brain injury to the frontal and temporal lobes

BackgroundCognitive deficits are the most enduring and debilitating sequelae of mild traumatic brain injury (mTBI). However, relatively little is known about whether the cognitive effects of mTBI vary with respect to time post-injury, biological sex, and injury location. ObjectivesThe aim of this study was to assess the effect of the side and site of mTBI and to determine whether these effects are sexually dimorphic. MethodsMale and female ICR mice were subjected to either a sham procedure or mTBI to the temporal lobes (right-sided or left-sided) or to the frontal lobes (bilateral) using a weight-drop model. After recovery, mice underwent a battery of behavioral tests at two post-injury time points. ResultsDifferent mTBI impact locations produced dissociable patterns of memory deficits; the extent of these deficits varied across sexes, time points, and memory domains. In both sexes, frontal mTBI mice exhibited a delayed onset of spatial memory deficits. Additionally, the performance of the frontal and left temporal injured males and females was more variable than that of controls. Interestingly, only in females does the effect of mTBI on visual recognition memory depend on the time post-injury. Moreover, only in females does spatial recognition memory remain relatively intact after mTBI to the left temporal lobe. ConclusionThis study showed that different mTBI impact sites produce dissociable and sex-specific patterns of cognitive deficits in mice. The results emphasize the importance of considering the injury site/side and biological sex when evaluating the cognitive sequelae of mTBI.

Analysis of impact events at arbitrary locations for isotropic plates and their main driving variables

Plates are widely used for lightweight structures in various disciplines, e.g. aircraft construction. However, these plates are susceptible to lateral forces due to impacts from falling tools, bird strikes, collisions with objects, etc. These impacts can occur anywhere on the plate. Here we report the dependence of the impact location on the impact itself. We use a semi-analytical approach that is verified in a code-to-code analysis using a commercial FE solver. Based on this code, a strong dependence of the impact location as well as the mass ratio of impactor and plate is found for the plate deflection and contact force. In addition, a general explanation for impact events is developed, leading to the distinction between small and large mass impacts. This work supports previous findings on the influence of mass ratio and completes the understanding of impact events at arbitrary locations.

Numerical investigation into impact responses of an offshore wind turbine jacket foundation subjected to ship collision

Offshore wind turbine structures are increasingly implemented but they could be largely exposed to ship collision in heavy maritime traffic area. This study aims to carry out a systematic parametric study on impact responses of the whole ship-offshore wind turbine jacket foundation system, thereby identifying the most dangerous impacting cases and vulnerable components. The three-point bending tests on DH-36 steel tubes designed by scaling jacket tubular members were performed. The effects of impact locations, collision angles and impact velocities on crashing responses, impact energy distributions and interactive deformation mechanisms were studied. Finally, the most dangerous impact cases and deformation were analyzed. It was showed that the bow impact on a leg tube resulted in the maximum local deformation of the leg and the maximum tower top displacement. The centric impact caused more severe local deformation than eccentric impact. And increasing the impact velocity from 0.5 to 3 m/s could increase the peak bending moment at the impact position of jacket leg. In the most dangerous location, the damage area and local indentation of the leg reached to 5.77 m2 and 916 mm (65.4% of diameter). The study can gain important insights into the development of crashworthy offshore wind turbine structures.

Penetration of Energized Metal Fragments to Porcine Thoracic Tissues.

Energized fragments from explosive devices have been the most common mechanism of injury to both military personnel and civilians in recent conflicts and terrorist attacks. Fragments that penetrate into the thoracic cavity are strongly associated with death due to the inherent vulnerability of the underlying structures. The aim of this study was to investigate the impact of fragment-simulating projectiles (FSPs) to tissues of the thorax in order to identify the thresholds of impact velocity for perforation through these tissues and the resultant residual velocity of the FSPs. A gas-gun system was used to launch 0.78-g cylindrical and 1.13-g spherical FSPs at intact porcine thoracic tissues from different impact locations. The sternum and rib bones were the most resistant to perforation, followed by the scapula and intercostal muscle. For both FSPs, residual velocity following perforation was linearly proportional to impact velocity. These findings can be used in the development of numerical tools for predicting the medical outcome of explosive events, which in turn can inform the design of public infrastructure, of personal protection, and of medical emergency response.

Full-scale ship-structure ice impact laboratory experiments: experimental apparatus and initial results

ABSTRACT This article presents the results of three ice impacts against a stiffened panel cut from the recently decommissioned ex-HMCS IROQUOIS. The upgraded experimental apparatus (the large double-pendulum), its sensors, and experimental conditions are also presented. The apparatus consists of two pendulums, one constrains and supports an ice feature, and the other constrains and supports a ship hull grillage structure. The first ice impact had data integrity and ice cone geometry issues, and so is treated as a commissioning test. During the second impact the impact force peaked at 553.9 kN, the total impact duration was 0.055 s and the hull plating acceleration at the centre of the impacted location was a maximum of 10877 m/s2. The third impact exhibited a peak force of 773.6 kN, 9691 m/s2 of acceleration, and had an impact duration of 0.039 s.

Flocking Bird Strikes on Engine Fan Blades and Their Effect on Rotor System: A Numerical Simulation

Bird strikes are a common, serious, and devastating event in aviation accidents, and multi-bird strikes are also frequently reported. A numerical multi-bird-strike simulation was performed to investigate the effect of flocking birds striking on engine blades. The smooth particle hydrodynamics (SPH) method was adopted in the hemispherical-ended bird substitute model, and the finite element method (FEM) with EOS state equation was adopted for the fan model as well. Impact analyses have been presented using different flocking birds and impact location distributions. A “0-2-1” supported rotor system dynamic model was established to study the effect of the multi-bird-strike impact forces on the rotor system. The results show that bird-strike severity is related to the impact location distribution, with blade-root impacts being the most dangerous. The small flocking bird strikes had little effect on the fan compared to the cases of medium flocking birds and the large single bird. The dynamic response of the fan to the small flocking birds was the same as without a bird strike, while the other cases changed the motion period and excited the rotor first-order vibration.

Adult occupant injury risk in rear impact and frontal impact: Effect of impact conditions and occupant-related factors

Objectives The objectives of this study were to compare the adult occupant injury risk on specific body regions in frontal and rear impact and to investigate the effect of those crash conditions and occupant-related factors on the injury risk. Method Data from the NASS-CDS and Crash Investigation Sampling System were studied for crashes during 2000 to 2019 involving model year 2000 to 2020 motor vehicles, including frontal collisions and rear-end collisions. The injury risk by specific body regions were compared by descriptive statistics, and logistic regression models were developed to examine the effects of various factors on injury risk by specific body regions, controlling for crash type (frontal impact and rear impact), vehicle impact speed, vehicle impact location, vehicle model year, and occupant gender, age, belt use, and seating position. Results After controlling for the confounding factors, the occupants in frontal impact had higher overall injury risk than in rear impact (at Maximum Abbreviated Injury Scale [MAIS] 3+; odds ratio [OR] = 6.23; 95% confidence interval [CI] [6.06–6.40]), except for lower neck/spine injury risk at MAIS 1+ (OR = 0.47; 95% CI [0.46–0.47]). The impact speed (at MAIS 3+; OR = 1.10; 95% CI [1.10–1.10]) and aging (at MAIS 3+; OR = 1.05; 95% CI [1.05–1.05]) increase overall injury risk, and the unbelted occupants had higher overall injury risk than belted occupants not only in frontal impact (at MAIS 3+; OR = 4.04; 95% CI [3.98–4.10]), but also in rear impact (at MAIS 3+; OR = 28.4; 95% CI [26.4–30.5]). Females had higher overall injury risk than males in frontal impact (at MAIS 3+; OR = 2.01; 95% CI [1.99–2.04]) but not in rear impact (at MAIS 3+; OR = 0.77; 95% CI [0.73–0.81]). Conclusions Occupants in rear impact had lower injury risk than in frontal impact at MAIS 1+ to MAIS 3+, except for neck/spine at MAIS 1+. The belt restraint was effective not only in frontal impact but also in rear impact. This study provided injury risk references for current vehicles that may provide insight to the potential injury risk of rear-facing occupants in future vehicle configurations.

Multi-FBG sensor array-based impact localization with an energy eigenvector

To locate the impact source on a composite material structure, an energy eigenvector and correlation interpolation (EECI) method is proposed based on a multi-fiber Bragg grating (FBG) sensor array. The fundamental frequency interference is eliminated by the wavelet transformation. The signal energy feature vector is extracted by the wavelet packet transformation. A two-dimensional correlation matrix is obtained by analyzing the correlation between impact response signals and signals in the reference database. The linear interpolation is then applied to accurately predict the impact location. The EECI method is verified on a carbon fiber composite plate with an effective test size of 400 × 400 (mm). The experimental result shows that the mean absolute error is 16.18 mm and the mean relative error (MRE) is 4.04%. The influence of the FBG sensor arrays and the quantity on the localization accuracy is also discussed to optimize the layout of the localization system. It shows that the MRE is [25.32%, 44.50%] for a single FBG sensor array, [17.19%, 42.63%] for two FBG sensor arrays, [15.63%, 22.47%] for three FBG sensor arrays, which shows the advantages of multi-FBG sensor arrays.

Sensitivity-based characterization of the bias errors in frequency based substructuring

A reliable experimental application of frequency based substructuring requires very accurate acquisition of frequency response functions (FRFs). Even a relatively small error introduced during the measurement can result in erroneous substructuring results. The measurement errors can be either random or systematic, with the latter often referred to as bias. Impact excitation is popular in dynamic substructuring due to the rapid FRF calculation for each separate location. However, deviations in the location of the excitation affect the FRFs across the whole frequency range. This paper proposes a novel methodology to characterize the bias errors in frequency based substructuring using the small deviations in impact excitation from typical experimental measurements. The small deviations are utilized to reconstruct a range of FRFs, which are directly used in the global sensitivity analysis. The sensitivity analysis is utilized to characterize how each impact location affects an arbitrary quality indicator, such as reciprocity or passivity. Therefore, the effect of the bias can be evaluated directly from a single series of measurements, without the need for a numerical model. The proposed approach is first shown on a synthetic numerical example, where the advantages and limitations are outlined. Finally, an application involving experimental frequency based substructuring on a beam-like structure is depicted.

Droplet impact dynamics onto a deep liquid pool of wavy free surface

The impact of a droplet on a deep pool of water with a flat-free surface results in a deep cavity followed by the emergence of a thick jet with a secondary drop when the Froude number and Weber number of the impacting droplet are 220 and 252, respectively. The disturbances in the free surface of the liquid pool modify the crater and the jet dynamics under identical drop impact conditions. Here, we present the simulations of the water drop impact on a deep liquid pool having various wavy profiles mimicking the free surface ripples. Long slender jets with the formation of multiple secondary droplets are observed when the droplet impacts the trough of an axisymmetric wavy surface. The influence of wave number on the wavy profile becomes more pronounced at large wave amplitudes. While capillary-inertia instability governs the pinch-off of thick Worthington jets, the pinch-off of these slender jets is found to be mainly inertia driven. However, if the drop impacts the crest of an axisymmetric wave, a short thick jet forms with one or two secondary droplets. Axisymmetric waves with radially outward moving interface, as in ripples, showed the occurrence of complete coalescence when droplet impacted on the crest; but the dynamics remain mostly the same as that of a stationary wave for the droplet impact on a trough. Entrainment of air bubbles after cavity collapse and bent jet occurred for an impact on a sinusoidal planar wave when the impact location was in between the two consecutive extremes.

Characterization of Head Impact Exposure in Women's Collegiate Soccer.

Soccer players are regularly exposed to head impacts by intentionally heading the ball. Evidence suggests repetitive subconcussive head impacts may affect the brain, and females may be more vulnerable to brain injury than males. This study aimed to characterize head impact exposure among National Collegiate Athletic Association women's soccer players using a previously validated mouthpiece-based sensor. Sixteen players were instrumented during 72 practices and 24 games. Head impact rate and rate of risk-weighted cumulative exposure were compared across session type and player position. Head kinematics were compared across session type, impact type, player position, impact location, and ball delivery method. Players experienced a mean (95% confidence interval) head impact rate of 0.468 (0.289 to 0.647) head impacts per hour, and exposure rates varied by session type and player position. Headers accounted for 89% of head impacts and were associated with higher linear accelerations and rotational accelerations than nonheader impacts. Headers in which the ball was delivered by a long kick had greater peak kinematics (all P < .001) than headers in which the ball was delivered by any other method. Results provide increased understanding of head impact frequency and magnitude in women's collegiate soccer and may help inform efforts to prevent brain injury.

Examining the changes in the spatial manifestation and the rate of arrival of large tornado outbreaks

This study presents an assessment of the spatial and temporal characteristics of large tornado outbreak (LTOs) days, in which several counties were impacted by tornadoes rated F2(EF2) or greater on the Fujita (Enhanced Fujita) scale in one day. A statistical evaluation of changes in the LTO clusters for two periods, 1950–1980 and 1989–2019, has been performed. There is a geographical shift of the nucleus (central impact location) towards the southeast United States. This spatial shift is also accompanied by reduced spatial variance, suggesting LTOs have become less dispersed (or more localized) in the recent period. The overall inter-arrival rate of LTOs, and how it changed during successive 31-year climatological blocks between 1950–2019 was investigated using an exponential probability model. The arrival rate has changed from 124 days during 1950–1980 to 164 days during 1977–2007 and remained relatively constant during later periods, indicating that LTOs are becoming less frequent.

Hydrodynamic Interaction Between Tear Film and Air Puff From Noncontact Tonometry.

PurposeThe purpose of this study was to investigate the mechanism of potential droplet formation in response to air puff deformation with two noncontact tonometers (NCTs).MethodsTwenty healthy volunteers were examined using two NCTs, Ocular Response Analyzer and Corvis ST, and two contact tonometers, iCare and Tono-Pen. High-speed videos of the tear film response were captured with at spatial resolution of 20 microns/pixel at 2400 fps. Droplet size, droplet velocity, distance between air puff impact location, and the tear meniscus-lid margin were characterized.ResultsOne subject was excluded due to technical issues. Droplets were detected only in tests with instilled eye drop. Videos showed the tear film rolls away from the apex while remaining adherent to the ocular surface due to the tendency of the fluid to remain attached to a solid surface explained by the Coanda effect. Twelve out of 38 videos with an eye drop administration showed droplet formation. Only one resulted in droplets with predominantly forward motion, which had the shortest distance between air puff impact location and lower meniscus. This distance on average was 5.9 ± 1.1 mm. The average droplet size was 500 ± 200 µm.ConclusionsResults indicate no droplet formation under typical clinical setting. Hence, standard clinical use of NCT tests is not expected to cause droplets. NCT testing with eye drop administration showed droplet formation at the inferior eyelid boundary, which acts as a barrier and interrupts tear flow.Translational RelevanceStudy of tear film interaction with NCT air puff shows that these tonometers are not expected to cause droplet formation in standard use and that if external drops are required, both eyelids should be held if patients need assistance to maintain open eyes to avoid droplets with predominantly forward motion.

Studying the strengthening mechanism and thickness effect of elastomer coating on the ballistic-resistance of the polyurea-coated steel plate

Experiments have shown that the ballistic performance of the steel plate improves significantly after coating polyurea at the impact face. However, the strengthening mechanism of the elastomer coating on the ballistic-resistance is not understood well until now. In this paper, the strengthening mechanism and thickness effect of the coating under fragment simulating projectiles (FSP) impact are studied through numerical and experimental analysis. Firstly, a viscoplastic constitutive model of polyurea is developed based on experimental characterization and thermodynamic equation of state. It can capture strongly nonlinear volumetric behavior and impact-induced shearing stiffening and strengthening considering the coupling of high pressure, high temperature, and high strain rate under ballistic impact. Then, by applying this newly developed viscoplastic model of polyurea, the underlying ballistic-resistant mechanism of the polyurea-coated steel plate is numerically studied. The analysis shows that the dynamic behavior of polyurea under ballistic impact and propagating regulation of impact wave jointly play the key role. One side, the impact-induced stiffening and strengthening of the polyurea change the failure modes of the steel plate and considerably improve the ballistic-resistance of the structure. The other side, increasing coating thickness can only provide the limited benefit for improving the ballistic-resistance of the structure, as obtained in experiments. For the impact-face-coated steel plate, the low-thickness polyurea coating suffering from FSP impact can increase the frequency of the compressive wave reflection-superposition on the high-impedance polyurea/steel interface before the energy transfer from the impacted location. This helps to improve the pressure level and enhance the instantaneous energy storage and dissipation of the polyurea per volume significantly. However, increasing coating thickness can make the pressure level and the specific energy density of polyurea decrease gradually during penetration. It is also found that the energy dissipation of FSP during penetration is reduced after increasing the coating thickness because of the erosion mitigation from the structure. The new insight on the strengthening mechanism of elastomer coating will be helpful for the light armor design.

Potential of Soft-Shell Rugby Headgear to Mitigate Linear and Rotational Peak Accelerations

Rugby union is a popular sport played across the world. The physical contact inherent in the game means that players are at increased risk of concussive injury. In 2019, World Rugby created a new category of permitted headgear under Law 4 as a medical device. This established a pathway for headgear designed to reduce peak accelerations to be worn in matches. Investigations of the potential of soft-shelled protective headgear to reduce head impact accelerations have been mostly limited to the analysis of linear kinematics. However rotational head impact accelerations have long been implicated as far more injurious. The aim of this study, therefore, was to assess the linear and rotational acceleration reduction brought about by soft-shelled rugby headgear. A Hybrid III headform and neck were dropped onto a modular elastomer programmer impact surface, impacting at four different velocities (1.7–3.4 m/s) in five different impact orientations. Impact surface angles were 0°, 30°, and 45°. Peak linear and rotational accelerations, PLA and PRA respectively, were recorded. All headgear significantly reduced PLAs and PRAs when compared to a no headgear scenario. The new generation, headgear reduced all measures significantly more than the older generation of headgear. Impact locations offset from the center of mass of the headform resulted in the highest PRAs measured. As the impact surface angle increased, both PLAs and PRAs decreased. The study demonstrated that headgear tested lowered PLAs by up to 50%, and PRAs by up to 60% compared to the bare headform. Our data suggest that new generation headgear could make a difference on the field in reducing injurious impact accelerations in a collision.