Anil Kalra

Finite element modelling of 10-year-old child pelvis and lower extremities with growth plates for pedestrian protection

For improved protection for pedestrians in the 10 years (YO) old age group, it is imperative to investigate the injury mechanisms using paediatric finite element (FE) model. A 10 YO child FE pelvis and lower extremities (PLEX) model was developed in this study. The model was validated by comparing simulated results against available paediatric experimental data and scaled adult test results. Growth plates were then embedded into this baseline model at the lower extremities. The anatomical features were kept and the mechanical properties were properly estimated based on literature findings. Subsequently, the effect of the growth plates at knee joint regions was studied in a car-to-pedestrian impact scenario. Results showed that the presence and early fracture of growth plates at knee region could alter the injury pattern at the lower extremities. Failure criterion of tension or shearing assumed in this model could also greatly influence the fracture progress.

Parametric analysis of the biomechanical response of head subjected to the primary blast loading – a data mining approach

Abstract Traumatic brain injury due to primary blast loading has become a signature injury in recent military conflicts and terrorist activities. Extensive experimental and computational investigations have been conducted to study the interrelationships between intracranial pressure response and intrinsic or ‘input’ parameters such as the head geometry and loading conditions. However, these relationships are very complicated and are usually implicit and ‘hidden’ in a large amount of simulation/test data. In this study, a data mining method is proposed to explore such underlying information from the numerical simulation results. The heads of different species are described as a highly simplified two-part (skull and brain) finite element model with varying geometric parameters. The parameters considered include peak incident pressure, skull thickness, brain radius and snout length. Their interrelationship and coupling effect are discovered by developing a decision tree based on the large simulation data-set. The results show that the proposed data-driven method is superior to the conventional linear regression method and is comparable to the nonlinear regression method. Considering its capability of exploring implicit information and the relatively simple relationships between response and input variables, the data mining method is considered to be a good tool for an in-depth understanding of the mechanisms of blast-induced brain injury. As a general method, this approach can also be applied to other nonlinear complex biomechanical systems.

Pedestrian safety: an overview of physical test surrogates, numerical models and availability of cadaveric data for model validation

Numerous efforts have been made to replicate pedestrian-car crashes experimentally or numerically to study the pedestrian injury biomechanics for developing countermeasures for pedestrian protection. This overview summarises such efforts towards pedestrian safety and available surrogates used in optimisation of pedestrian-friendly vehicle designs. This paper provides not only available physical surrogates (impactors and pedestrian dummies) used by different regulatory agencies, but also a collection of various numerical models used to predict injury responses in car-pedestrian impacts. Additionally, an overview of many reported cadaveric experiments performed as sustained by pedestrians in car crashes is presented. A validation matrix is proposed for correlating existing/future numerical models with available cadaveric test data. This is to ensure development of high predictive quality FE whole body human models to assess injury risk to pedestrians in car crashes, and in turn for continued improvement over design of pedestrian friendly vehicle front-end and effective countermeasures for pedestrian protection.

Evaluation of full pelvic ring stresses using a bilateral static gait-phase finite element modeling method

Trauma to the pelvis is debilitating and often needs fixation intervention. In 58% of patients with this trauma, the injuries can lead to permanent disability, preventing the return to jobs. Of all unsuccessful fixation procedures, 42% are caused by failures of the method, sometimes due to mobilization during healing. Patients would benefit by havibridgetv@comcast.netng fixation hardware in place that enabled ambulation. During walking the bilateral hip joint plus leg and trunk muscle forces, including those from hip motion, can induce torsion into the pelvic ring and across the joint cartilages, and affect the internal stresses of the pelvis. For an accurate understanding, fixation that bridges the bilateral innominate bones needs to be evaluated considering all of these factors, and the affect on the stresses throughout the pelvic ring. Yet there is no bilateral, comprehensive method to do so in the literature. In this study a method was developed that incorporates all of the necessary factors in four bilateral, static, finite element models representing eight gait phases. The resulting stress migration through the full pelvic ring and pubic symphysis displacements were demonstrated under these conditions. In subsequent work, fixation improvements can be applied to these models to evaluate the change in internal stresses, joint displacements and deformations of the hardware, leading to a better quality of design and permitting ambulation during healing for the patient.

An Experimental and Numerical Study of Hybrid III Dummy Response to Simulated Underbody Blast Impacts

Anthropometric test devices (ATDs) such as the Hybrid III dummy have been widely used in automotive crash tests to evaluate the risks of injury at different body regions. In recent years, researchers have started using automotive ATDs to study the high-speed vertical loading response caused by underbody blast impacts. This study analyzed the Hybrid III dummy responses to short-duration, large magnitude vertical accelerations in a laboratory setup. Two unique test conditions were investigated using a horizontal sled system to simulate underbody blast loading conditions. The biomechanical responses in terms of pelvis acceleration, chest acceleration, lumbar spine force, head accelerations, and neck forces were measured. Subsequently, a series of finite element (FE) analyses were performed to simulate the physical tests. The correlation between the Hybrid III test and numerical model was evaluated using the correlation and analysis (cora) version 3.6.1. The score for the Wayne State University (WSU) FE model was 0.878 and 0.790 for loading conditions 1 and 2, respectively, in which 1.0 indicated a perfect correlation between the experiment and the simulated response. With repetitive vertical impacts, the Hybrid III dummy pelvis showed a significant increase in peak acceleration accompanied by a rupture of the pelvis foam and flesh. The revised WSU Hybrid III model indicated high stress concentrations at the same location, providing a possible explanation for the material failure in actual Hybrid III tests.

Effect of vehicle front end profile on pedestrian kinematics and biomechanical responses using a validated numerical model

Traumatic injuries and biomechanical responses of a pedestrian depend on vehicle front end characteristics as well as the pedestrian anthropometric details in vehicle-pedestrian crashes. A number of laboratory experiments were conducted using post mortem human subjects (PMHS) to understand the biomechanics behind the injuries in a pedestrian crash. However, different vehicular front ends were used in these studies making comparisons among studies impossible. The current research work focuses on validating simulated pedestrian kinematics and accelerations responses of MADYMO full body pedestrian model with the experimental results. In general, overall kinematics of the body for pedestrian models were also compared with that recorded in the video snapshots from the cadaveric experimental tests at 50 ms time intervals. Along with the validation of kinematics of pedestrian, the acceleration responses of head, chest, pelvic and lower leg of the pedestrians were also validated against the corresponding experimental data. Other responses like head angle as well as head impact velocity during primary impact with the hood were analyzed at different impact speeds. Once the responses were validated for a particular front end of the vehicle, a series of numerical parametric studies were further conducted using several front end profiles based off a mid-sized sedan. For the parametric study, different pedestrian models representing three pedestrian sizes, a 50th male, a 5th female, and a 6 years-old child, were used in the simulations. Finite element model of a vehicle front end was changed in terms of the heights of bumper, bonnet leading-edge, and bonnet rear reference-line using a mesh-morphing technique. In most simulations, primary head impact location depends on the pedestrian size, and the secondary impact with ground at the head region is affected by type of vehicle and its front end profile. Kinematics of the pedestrians as well as the angle of primary head impact varies a great deal based upon the front-end profile of the striking vehicle (e.g., raised front-end profile or lowered front-end profile). Leg and pelvis accelerations were found to be high in vehicles with raised front end profiles. Chest and head accelerations were also found to be affected by vehicle front end profile and pedestrian size. However, it should be noted that there were some front-end profiles that help in avoiding pedestrian secondary head impact with the ground.Copyright