Penetration of Energised Metal Fragments to Porcine Thoracic Tissues

Experimental model and simulant for studying blast penetrating injury to the skin

Energised fragments from explosions are the most common wounding mechanism in conflicts and terrorist attacks. Skin covers the vast majority of the human body and is therefore the first anatomical component to be penetrated by fragments, however, its resistance to penetration largely has not been taken into account in models of injury. In this study, an experimental model for ballistic testing of skin is established and a suitable skin simulant for studying resistance to penetration is determined. Fragment-simulating projectiles were fired at human cadaveric skin and skin-simulant candidates. Tissue responses were quantified by evaluating the impact velocity at 50% risk of skin penetration and perforation, and the depth of penetration in cadaveric tissue or skin-simulant candidates. The results identified a 1.5-mm-thick butyl rubber as a suitable skin simulant across the range of threats tested. The findings can help refine assessment of protective systems and predictive models of injury in an effort to improve outcomes of fragment-penetrating injuries.

Damage characteristics and dynamic response of the human thorax under combined shock waves and fragment loading

To investigate the mechanism of coupled damage in human body caused by shock waves and fragment, a finite element model of the human thorax was established. The validity of the model was verified by comparing the thorax damage data under blast and fragment. LS-DYNA finite element software was used to numerically simulate the mechanical response of the thorax under combined shock waves and fragment loading, and to analyze the effects of loading modes, mass of TNT charge, and blast distances on damage to human thoracic organs. The results indicate that the coupling damage effect of organs near the impact area is appreciable under the combined shock waves and fragment loading, and the mechanical parameters of human organs exceed the sum caused by shock waves and fragment individually. As the mass of TNT charge increased, both the peak velocity of skeletons and the stress on organs at the non-impact area under combined loading increase, whereas the effect on the peak stress in organs at the impact area of fragment is smaller and much larger than the sum of the stresses under shock waves and fragment loading alone. Meanwhile, the gap between peak stress of the same organ under combined loading and shock waves loading alone widened for different masses of TNT charge. Furthermore, the combined loading sequence of shock waves and fragment affects the mechanical response of human organs. An approach for evaluating the probability of injury under combined loading was proposed. The calculation results show that in the near field, the injury probability is more sensitive to the impulse of the shock waves.

The risk of fragment penetrating injury to the heart

Injury due to the penetration of fragments into parts of the body has been the major cause of morbidity and mortality after an explosion. Penetrating injuries into the heart present very high mortality, yet the risk associated with such injuries has not been quantified. Quantifying this risk is key in the design of personal protection and the design of infrastructure. This study is the first quantitative assessment of cardiac penetrating injuries from energised fragments. Typical fragments (5-mm sphere, 0.78-g right-circular cylinder and 1.1-g chisel-nosed cylinder) were accelerated to a range of target striking velocities using a bespoke gas-gun system and impacted ventricular and atrial walls of lamb hearts. The severity of injury was shown to not depend on location (ventricular or atrial wall). The striking velocity with 50% probability of critical injury (Abbreviated Injury Scale (AIS) 5 score) ranged between 31 and 36 m/s across all 3 fragments used. These findings can help directly in reducing morbidity and mortality from explosive events as they can be implemented readily into models that aim to predict casualties in an explosive event, inform protocols for first responders, and improve design of infrastructure and personal protective equipment.

Characterization and modeling of partial-thickness cutaneous injury from debris-simulating kinetic projectiles

Partial-thickness cutaneous injuries distributed over exposed body locations, such as the face and extremities, pose a significant risk of infection, function loss, and extensive scarring. These injuries commonly result from impact of kinetic debris from industrial accidents or blast weaponry such as improvised explosive devices. However, the quantitative connections between partial-thickness injuries and debris attributes (kinetic energy, shape, orientation, etc.) remain unknown, with little means to predict damage processes or design protection. Here we quantitatively characterize damage in near-live human skin after impact by debris-simulating kinetic projectiles at differing impact angles and energies. Impact events are monitored using high-speed and quantitative imaging to visualize skin injuries. These findings are utilized to develop a highly predictive, dynamic computational skin-injury model. Results provide quantitative insights revealing how the dermal-epidermal junction controls more severe wound processes. Findings can illuminate expected wound severity and morbidity risks to inform clinical treatment, and assess effectiveness of emerging personal protective equipment.

Berkey and colleagues quantitatively characterized partial-thickness cutaneous injuries after impact from projectiles simulating ballistic fragments. A corresponding damage model was developed to simulate and predict the cutaneous damage from impact, which could guide protective equipment design and clinical treatment.

Cortical bone continuum damage mechanics constitutive model with stress triaxiality criterion to predict fracture initiation and pattern

A primary objective of finite element human body models (HBMs) is to predict response and injury risk in impact scenarios, including cortical bone fracture initiation, fracture pattern, and the potential to simulate post-fracture injury to underlying soft tissues. Current HBMs have been challenged to predict the onset of failure and bone fracture patterns owing to the use of simplified failure criteria. In the present study, a continuum damage mechanics (CDM) model, incorporating observed mechanical response (orthotropy, asymmetry, damage), was coupled to a novel phenomenological effective strain fracture criterion based on stress triaxiality and investigated to predict cortical bone response under different modes of loading. Three loading cases were assessed: a coupon level notched shear test, whole bone femur three-point bending, and whole bone femur axial torsion. The proposed material model and fracture criterion were able to predict both the fracture initiation and location, and the fracture pattern for whole bone and specimen level tests, within the variability of the reported experiments. There was a dependence of fracture threshold on finite element mesh size, where higher mesh density produced similar but more refined fracture patterns compared to coarser meshes. Importantly, the model was functional, accurate, and numerically stable even for relatively coarse mesh sizes used in contemporary HBMs. The proposed model and novel fracture criterion enable prediction of fracture initiation and resulting fracture pattern in cortical bone such that post-fracture response can be investigated in HBMs.