An Experimentally Validated Finite Element Model of the Lower Limb to Investigate the Efficacy of Blast Mitigation Systems

Abstract

Improvised explosive devices (IEDs) used in the battlefield cause damage to vehicles and their occupants. The injury burden to the casualties is significant. The biofidelity and practicality of current methods for assessing current protection to reduce the injury severity is limited. In this study, a finite-element (FE) model of the leg was developed and validated in relevant blast-loading conditions, and then used to quantify the level of protection offered by a combat boot. An FE model of the leg of a 35 years old male cadaver was developed. The cadaveric leg was tested physically in a seated posture using a traumatic injury simulator and the results used to calibrate the FE model. The calibrated model predicted hindfoot forces that were in good correlation (using the CORrelation and Analysis or CORA tool) with data from force sensors; the average correlation and analysis rating (according to ISO18571) was 0.842. The boundary conditions of the FE model were then changed to replicate pendulum tests conducted in previous studies which impacted the leg at velocities between 4 and 6.7 m/s. The FE model results of foot compression and peak force at the proximal tibia were within the experimental corridors reported in the studies. A combat boot was then incorporated into the validated computational model. Simulations were run across a range of blast-related loading conditions. The predicted proximal tibia forces and associated risk of injury indicated that the combat boot reduced the injury severity for low severity loading cases with higher times to peak velocity. The reduction in injury risk varied between 6 and 37% for calcaneal minor injuries, and 1 and 54% for calcaneal major injuries. No injury-risk reduction was found for high severity loading cases. The validated FE model of the leg developed here was able to quantify the protection offered by a combat boot to vehicle occupants across a range of blast-related loading conditions. It can now be used as a design and as an assessment tool to quantify the level of blast protection offered by other mitigation technologies.

Stature and mitigation systems affect the risk of leg injury in vehicles attacked under the body by explosive devices

“…The response of the FE model had been shown previously in comparison with that from physical experiments across a range of UBB-loading encompassing anatomical variability (Rebelo et al, 2021). The introduction of the IMPAXX ™ floor mat in the model expectedly changed the resulting response; albeit there are no experimental data against which comparisons can be made, the response did not change to an extent that would render the model invalid.…”

“…Software, Santa Ana, CA, United States), solved in Dytran (v2018, MSC. Software, Santa Ana, CA, United States), and validated for UBB-related loading conditions was used (Rebelo et al, 2021) (Figure 1). Briefly, the FE model is of a cadaveric lower limb with anthropometry close to that of the 50th percentile American male (height = 1.727 m; weight = 72.6 kg).…”

“…UBB-representative vehicle-floor velocity profiles with peak velocities ranging from 5 to 17.5 m/s and time to peak between 1.5 and 9 ms were applied to the loading plate (Rebelo et al, 2021) (Supplementary Table S1). These profiles were triangular in shape, consisting of a section in which the loading velocity increased until the peak velocity reached at the time to peak velocity and a second section in which the velocity decreased to zero with the same slope as it increased to peak velocity.…”

“…FIGURE 1Distal part of the finite-element model developed previously byRebelo et al (2021) and used here to study the effect of the IMPAXX floor mat and stature on injury.…”

Lower Leg Injury Mechanism Investigation During an IED Blast Under a Vehicle Using an Anatomic Leg Model

“…Methodology with a similar approach can be found in Rebelo et al (2021) , which presents FEM model of lower limb used for evaluation of blast mitigation systems and evaluates protection offered by a combat boot.…”