Browse Topic: Biomechanics
Modern combat helmets improve wearer survivability through preventing ballistic penetration via delamination or deformation of the shell material. However, this deformation may impinge upon the skull and present a risk of behind-helmet blunt trauma (BHBT). While legacy aramid helmets from the late 1970s–1980s inform current NIJ testing standards, the advent of lower areal density ultra-high molecular weight polyethylene (UHMWPE) and modern suspensions may incur unknown changes that present an unknown effect on BHBT risk. This study investigates whether current standards relying on a peak acceleration threshold and residual clay deformation may not reflect changes in deformation geometry seen in newer shell materials and suspension designs. Thirty-eight helmets categorized into three groups, older aramid, newer aramid (with new suspension), and prototype UHMWPE (with old suspension), were mounted on Hybrid III ATD head-necks and impacted on the temporal surface with 9 mm NATO projectiles at velocities between 388 and 482 m/s. Flash x-ray imaging captured deformation geometry. Deformations were digitized to measure maximum depth, volume, and surface area recruited. Multiple linear regression identified the influence of shell material and suspension on geometry. Results indicated that shell material significantly affected deformation volume and area (p < 0.05). Notably, UHMWPE exhibited a qualitatively more “pointed” deformation profile compared to aramid, recruiting material differently as depth increased. In contrast, suspension type and helmet design did not significantly influence deformation geometry. These findings suggest that the BHBT geometry in UHMWPE helmets differs fundamentally from aramid helmets. As UHMWPE helmets encounter higher-energy threats, current acceleration threshold or depth-based standards may not fully capture the risk of skull fracture. To future-proof helmet validation, testing standards should evolve beyond current standards to include area recruitment and other geometric measures.
Letter from the Guest Editors
Youth bicycle helmet manufacturers often add shell protrusions to make helmets more attractive or fun for children, yet the safety implications of these features are not well understood. While prior work suggests protrusions may affect head impact kinematics, no study has evaluated their effectiveness in location-matched impacts between helmets with and without protrusions. Twelve youth bicycle helmet models, with protrusions intact and removed, underwent matched oblique impacts at three locations and 4.2 m/s to capture resulting peak linear acceleration (PLA) and peak rotational acceleration (PRA). A linear mixed model was used to quantify the effect of protrusion presence on PLA, PRA, and impact duration. The youth bicycle helmet models produced a wide range of kinematics. Protrusion presence had a strong effect on PLA, PRA, and impact duration. PLA averaged 103.0 ± 22.8 g for helmets with protrusions compared to 143.9 ± 21.4 g for helmets without protrusions, while PRA averaged 4432 ± 1570 rad/s2 for helmets with protrusions and 5177 ± 2110 rad/s2 for helmets without protrusions. These findings suggest that helmet protrusions can reduce peak head accelerations in youth bicycle helmet impacts.
The gathered journalists cover their ears as a loud hydraulic ram begins to load and a warning alarm sounds. Less than a minute later… FOOSH… BAM! A 9.9-pound model of a human head is launched into the front-end structure of a test vehicle, deforming the hood and sending the head bouncing to the ground. The violence of the moment, which is part of pedestrian safety research, is a stark reminder of the seriousness of all the testing that happens at Toyota's North American Research and Development Headquarters in York Township, Michigan. The $187-million (in 2007 dollars) facility includes 180,000 sq.ft. of research and testing space.
Letter from the Editor-in-Chief
Researchers recently helped Skydio, the leading U.S. drone manufacturer, demonstrate compliance to the Federal Aviation Administration's rules for safe flights over people and vehicles. Virginia Polytechnic Institute and State University, Blacksburg, VA Operators using a drone from the leading manufacturer in the U.S. can now conduct missions over people and vehicles much easier and with even greater confidence in their safety. In January, the Federal Aviation Administration (FAA) accepted a declaration of compliance for such flights for the parachute-equipped Skydio X10 drone from Skydio, a San Mateo, California-based company that supplies its drones to customers in public safety, utilities, and national security. The acceptance came as the result of working with Virginia Tech's Mid-Atlantic Aviation Partnership (MAAP) and Center for Injury Biomechanics to complete their FAA-approved means of compliance testing.
It all started when Owen Kent and Todd Roberts became roommates at the University of California Berkeley. Owen has muscular dystrophy and had recently acquired a robotic arm, which he noticed he was using to do range of motion. Todd had come to Berkeley to study mechanical engineering with a focus on biomechanics, and both were enrolled in Designing for the Human Body, a biomechanics course taught by Mechanical Engineering Professor Grace O’Connell.
Letter from the Focus Issue Editors
Thorax injuries are a significant cause of mortality in automotive crashes, with varying susceptibility across sex and age demographics. Finite element (FE) human body models (HBMs) offer the potential for injury outcome analysis by incorporating anthropometric variations. Recent advancements in material constitutive models, cortical bone fracture and continuum damage mechanics model (CFraC) and an orthotropic trabecular bone model (OrthoT), offer the opportunity to further improve rib models. In this study, the CFraC and OrthoT material modes, coupled with age-specific material properties, were progressively implemented to the Global Human Body Model Consortium small female 6th rib. Four distinct 6th rib models were developed and compared against sex and age-specific experimental data. The updated material models notably refined the predictions of force–displacement responses, aligning them more closely with the experimental averages. The CFraC model significantly improved the prediction of displacement at fracture, suggesting that incorporating stress triaxiality criteria can better account for the complex loading conditions ribs face in crashes, such as combined cortical tension and shear due to rib bending and torque. The study highlights the importance of using biofidelic material models and sex and age-specific data to simulate hard tissue fractures. The improved rib model demonstrates the effectiveness of integrating updated material properties and constitutive models to enhance injury prediction accuracy, which can inform better automotive safety designs and reduce mortality rates. Further research is recommended to extend these models across different demographic groups to fully capture population variability in rib fracture risk.
Rear-end vehicle collisions may lead to whiplash-associated disorders (WADs), comprising a variety of neck and head pain responses. Specifically, increased axial head rotation has been associated with the risk of injuries during rear impacts, while specific tissues, including the capsular ligaments, have been implicated in pain response. Given the limited experimental data for out-of-position rear impact scenarios, computational human body models (HBMs) can inform the potential for tissue-level injury. Previous studies have considered external boundary conditions to reposition the head axially but were limited in reproducing a biofidelic movement. The objectives of this study were to implement a novel head repositioning method to achieve targeted axial rotations and evaluate the tissue-level response for a rear impact condition. The repositioning method used reference geometries to rotate the head to three target positions, showing good correspondence to reported interverbal rotations. Under a 7 g rear impact scenario, the head-turned models were compared with the neutral position and demonstrated increases in the maximum capsular ligament distractions. Increased head rotation was associated with increased ligament distractions. The locations with critical ligament distractions shifted to the lower cervical spine (below C3) and lateral portion of the capsular ligaments for the head-turned position cases. The proposed repositioning method introduced in this study enabled the model to achieve steady head rotations with realistic cervical spine movements, increasing the biofidelity of out-of-position rear impact simulations.
Pelvic orientation in vehicles is crucial for preventing injuries and creating safer vehicles and restraint systems. A better understanding of pelvic orientation could provide more accurate anthropomorphic test device (ATD) models of underrepresented populations such as obese individuals, children, and small females. Sonomicrometry is the use of piezoelectric transducers that transmit ultrasound signals to each other to measure the distance between them. These signals may be aggregated using triangulation. In this experiment, ultrasound crystals were secured to the surface of a porcine surrogate to evaluate pelvic movement. This data was then processed using Sonometrics software to generate a 3D model of four static positions and three dynamic tests. The test was validated using a camera and a 3D measurement arm (CMM) to validate XYZ positions. This article discusses how this method could be helpful for developing more accurate ATD models, preventing fatalities in vehicle crashes.
Ongoing research in simulated vehicle crash environments utilizes postmortem human subjects (PMHS) as the closest approximation to live human response. Lumbar spine injuries are common in vehicle crashes, necessitating accurate assessment methods of lumbar loads. This study evaluates the effectiveness of lumbar intervertebral disc (IVD) pressure sensors in detecting various loading conditions on component PMHS lumbar spines, aiming to develop a reliable insertion method and assess sensor performance under different loading scenarios. The pressure sensor insertion method development involved selecting a suitable sensor, using a customized needle-insertion technique, and precisely placing sensors into the center of lumbar IVDs. Computed tomography (CT) scans were utilized to determine insertion depth and location, ensuring minimal tissue disruption during sensor insertion. Tests were conducted on PMHS lumbar spines using a robotic test system for controlled loading in flexion, compression, and a combination, while monitoring pressure changes. The compression force, flexion angle, and sensor-recorded IVD fluid pressure were recorded during tests. CT images were analyzed to assess sensor placement and its impact on sensing ability. Pressure readings during various loading conditions were examined for different specimens, with data reported from the beginning of tests through relevant loading phases. The study successfully established a methodology for inserting pressure sensors into the IVD and assessed their ability to detect changes in flexion angle, compression, and combined loading. Sensors accurately tracked compression force and detected changes in flexion angle, although with some differences in response. Sensors placed optimally showed expected responses, while those placed suboptimally exhibited variability, particularly in detecting changes during flexion. This variability underscores the importance of sensor placement for accurate detection of loading states. Overall, the study provides a foundation for utilizing pressure sensors to monitor loading states in sled tests, with future work focusing on refining differentiation between loading types.
University of Waterloo Chemical Engineering Researcher Dr. Elisabeth Prince teamed up with researchers from the University of Toronto and Duke University to design the synthetic material made using cellulose nanocrystals, which are derived from wood pulp. The material is engineered to replicate the fibrous nanostructures and properties of human tissues, thereby recreating its unique biomechanical properties.
Scientists at Osaka University, in cooperation with Joanneum Research (Weiz, Austria), have introduced wireless health monitoring patches that use embedded piezoelectric nanogenerators to power themselves with harvested biomechanical energy. This work may lead to new autonomous health sensors as well as battery-less wearable electronic devices.
In the context of Rotorcraft Pilot Couplings, the biomechanics of the pilot body play a fundamental role in determining the stability of the pilot-vehicle closed loop system. The response of the pilot body is, in turn, inherently stochastic, being a function of pilot biometrics and muscular activation. Coupling the statistical distribution of pilot biomechanical behavior determined in specialized experimental campaign with linear models of the helicopter heave dynamics, an uncertainty propagation procedure is developed, with the aim of estimating the statistical distribution of the stability margins of the closed loop pilot-vehicle system. Results obtained varying the collective lever characteristics, as well as the helicopter model parameters, align well with results obtained previously in deterministic settings. However, the new scheme allows to define quantitative robustness indices.
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