Abstract:In recent military conflicts, the incidence of underbody blasts has led to severe injuries, specifically in the lower extremities. The development of a lower extremity model may lead to a better understanding of injury patterns and mechanisms. A computational finite element model of the lower extremity was developed based on geometry made available in an anatomical repository. The portion of the extremity model below the knee was used in initial comparisons between simulations and experimental data. Impact was applied via a loading plate with a vertical velocity of 5 m/s, 10 m/s, and 12 m/s. Resultant axial force was compared to experimental data. Results of these simulations fall within the range of available experimental data, which gives confidence that this model represents advancement in lower extremity modelling capabilities. Bone fracture has also been modelled and shows consistency with injuries typical of underbody blast scenarios.
This preliminary study aims to computationally model and study the fracture patterns in the human calcaneus during variable impact loading conditions. A finite element model of the foot and ankle is used to understand the effect of loading rates and orientation of the foot on fracture patterns. Simulations are carried out by applying varying impact velocities of steel plate to the foot & ankle model in accordance with data regarding underbody blasts. These impact velocities are applied to reach a peak in 1.5 ms. Fracture of bone is represented using the plastic kinematic constitutive model with element erosion method, where elements are removed from the simulation after an inelastic failure strain is exceeded. The simulations last for 5 ms to observe the extent of fracture in the calcaneus. Following simulations, the resulting fracture patterns are compared to available images from experimental impact tests to qualitatively assess the simufutions. A mesh convergence study is performed to determine the level of refinement of mesh necessary to represent this problem. The mesh appears to converge at the refinement level of the medium coarse mesh. The effect of impact velocities on fracture is studied on unjlexed and flexed foot models. At lower velocities, fracture is observed in the form of a single continuous crack, and a pronounced branched type of network is observed at higher velocities. Finally, variation in fracture networks due to variability in strength of the bone is studied. For lower values of failure strain, significantly larger and branched networks of fracture are observed.
An “underbody blast” (UBB) is the detonation of a mine or improvised explosive device (IED) underneath a vehicle. In recent military conflicts, the incidence of UBBs has led to severe injuries, specifically in the lower extremities The foot and ankle complex, particularly the calcaneus bone, may sustain significant damage. Despite the prevalence of calcaneal injuries, this bone’s unique properties and the progression of fracture and failure have not been adequately studied under high strain rate loading. This research discusses early efforts at creating a high-resolution computational model of the human calcaneus, with primary focus on modeling the fracture network through the complex microstructure of the bone and creating micromechanically-based constitutive models that can be used within full human body models. The ultimate goal of this ongoing research effort is to develop a micromechanics-based simulation of calcaneus fracture and fragmentation due to impact loading. With the goal of determining the basic mechanisms of stress propagation through the internal structure of the calcaneus, a two-dimensional model was employed for preliminary simulations with a plane-strain approximation. In this effort, a cadaveric calcaneus was scanned to a resolution of 55 μm using an industrial micro-computed tomography (microCT) scanner. A mid-sagittal plane slice of the scan was selected and post-processed to generate a 2D finite element mesh of the calcaneus that included marrow, trabecular bone, and cortical bone elements. The calcaneus was modeled using two-dimensional quadratic plane strain elements. A fixed boundary condition was applied to the portion of the calcaneus that, in situ, would be restrained by the talus. A displacement of 1.25 mm was applied to the heel of the calcaneus over 5 ms. In a typical result, following impact, the strain and stress are propagated throughout the cortical shell and then began to radiate into the bone into the bone along the trabeculae. Local stress concentrations can be observed in the trabecular structure in the posterior region of the bone following impact. Upon impact, cortical and trabecular bone show different stresses of 13MPa and 1 MPa, respectively, and exhibit complex high frequency responses. Observed results may offer insight into the wave interactions between the different materials comprising the calcaneus, such as impedance mismatch and refraction. Pore pressure in the marrow may be another important factor to consider in understanding stress propagation in the calcaneus.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
334 Leonard St
Brooklyn, NY 11211
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.