Study on chest injury and bulletproof vest protection under the combined action of blast wave and fragments

Using a simulation based method, this paper analysis the damage effect of blast wave and fragments on human body and the protective effect of bulletproof vest. The results show that compared with the single blast shock wave, the chest injury is more serious under the combined action of blast shock wave and fragments. The peak stress of sternum, costal cartilage and rib increases by 334.34%, 170.23% and 39.72%, respectively. The peak stress on the side of the lung decreases by 3.95%, with little change. The peak stress on the front and back of the lung increases by 83.58% and 409.09% respectively. Overall, the lung injury is aggravated. With the addition of the bulletproof vest, the damage caused by fragments is reduced, and the peak stress of the sternum and the costal cartilage decreases by 48.77% and 69.78%, respectively. Due to the interaction of the blast wave with the vest and the chest, the damage caused by blast wave is aggravated. The peak stress of rib increases by 13.55%, and the peak stress of lung front, side and back increases by 1.22%, 6.51% and 3.57%, respectively.

Study on the mesh size determination method of blast wave numerical simulation with strong applicability

With the rapid development of computer hardware and software technology, numerical simulations have become one of the most important tools for studying propagation law of blast wave. Results of numerical simulations of explosion events greatly depend on the mesh size. The mesh size determination methods in the literature are relatively weak in generality. In this paper, a mesh size determination method with strong applicability is proposed. According to this method, the mesh size is the product of the scale coefficient and the third root of the equivalent TNT mass. The scale coefficient is related to the model dimension, scaled distance and simulation accuracy, and is independent of the TNT shape and the location of the detonation point. A large number of numerical simulation results confirm the accuracy of this method. The recommended scale coefficient to meet the engineering accuracy requirements is related to the model dimension and scaled distance. In general, when the scaled distance and model dimension are larger, the recommended scale coefficient will be larger. In this paper, the figures and tables of the recommended scale coefficients of 1D, 2D and 3D models varying with the scaled distance are given, and their rationality is verified by the existing numerical simulation events of blast wave. They can be used as a reference to determine the mesh size in numerical simulation of blast wave.

Revealing the Effect of Skull Deformation on Intracranial Pressure Variation During the Direct Interaction Between Blast Wave and Surrogate Head

Intracranial pressure (ICP) during the interaction between blast wave and the head is a crucial evaluation criterion for blast-induced traumatic brain injury (bTBI). ICP variation is mainly induced by the blast wave transmission and skull deformation. However, how the skull deformation influences the ICP remains unclear, which is meaningful for mitigating bTBI. In this study, both experimental and numerical models are developed to elucidate the effect of skull deformation on ICP variation. Firstly, we performed the shock tube experiment of the high-fidelity surrogate head to measure the ICP, the blast overpressure, and the skull surface strain of specific positions. The results show that the ICP profiles of all measured points show oscillations with positive and negative change, and the variation is consistent with the skull surface strain. Further numerical analysis reveals that when the blast wave reaches the measured point, the peak overpressure transmits directly through the skull to the brain, forming the local positive ICP peak, and the impulse induces the local inward deformation of the skull. As the peak overpressure passes through, the blast impulse impacts the nearby skull supported by the soft and incompressible brain tissue and extrudes the skull outward in the initial position. The inward and outward skull deformation leads to the oscillation of ICP. These numerical analyses agree with experimental results, which explain the appearance of negative and positive ICP peaks and the synchronization of negative ICP with surface strain. The study has implications for medical injury diagnosis and protective equipment design.

Blast-induced hearing loss suppresses hippocampal neurogenesis and disrupts long term spatial memory

Acoustic information transduced by cochlear hair cells is continuously relayed from the auditory pathway to other sensory, motor, emotional and cognitive centers in the central nervous system. Human epidemiological studies have suggested that hearing loss is a risk factor for dementia and cognitive decline, but the mechanisms contributing to these memory and cognitive impairments are poorly understood. To explore these issues in a controlled experimental setting, we exposed adult rats to a series of intense blast wave exposures that significantly reduced the neural output of the cochlea. Several weeks later, we used the Morris Water Maze test, a hippocampal-dependent memory task, to assess the ability of Blast Wave and Control rats to learn a spatial navigation task (memory acquisition) and to remember what they had learned (spatial memory retention) several weeks earlier. The elevated plus maze and open field arena were used to test for anxiety-like behaviors. Afterwards, hippocampal cell proliferation and neurogenesis were evaluated using bromodeoxyuridine (BrdU), doublecortin (DCX), and Neuronal Nuclei (NeuN) immunolabeling. The Blast Wave and Control rats learned the spatial navigation task equally well and showed no differences on tests of anxiety. However, the Blast Wave rats performed significantly worse on the spatial memory retention task, i.e., remembering where they had been two weeks earlier. Deficits on the spatial memory retention task were associated with significant decreases in hippocampal cell proliferation and neurogenesis. Our blast wave results are consistent with other experimental manipulations that link spatial memory retention deficits (long term memory) with decreased cell proliferation and neurogenesis in the hippocampus. These results add to the growing body of knowledge linking blast-induced cochlear hearing loss with the cognitive deficits often seen in combat personnel and provide mechanistic insights into these extra auditory disorders that could lead to therapeutic interventions.

Ultrastructural brain abnormalities and associated behavioral changes in mice after low-intensity blast exposure

Explosive blast-induced mild traumatic brain injury (mTBI), a "signature wound" of recent military conflicts, commonly affects service members. While past blast injury studies have provided insights into TBI with moderate- to high-intensity explosions, the impact of primary low-intensity blast (LIB)-mediated pathobiology on neurological deficits requires further investigation. Our prior considerations of blast physics predicted ultrastructural injuries at nanoscale levels. Here, we provide quantitative data using a primary LIB injury murine model exposed to open field detonation of 350 g of high-energy explosive C4. We quantified ultrastructural and behavioral changes up to 30 days post blast injury (DPI). The use of an open-field experimental blast generated a primary blast wave with a peak overpressure of 6.76 PSI (46.6 kPa) at a 3-m distance from the center of the explosion, a positive phase duration of approximate 3.0 milliseconds (ms), a maximal impulse of 8.7 PSI × ms and a sharp rising time of 9 × 10^-3 ms, with no apparent impact/acceleration in exposed animals. Neuropathologically, myelinated axonal damage was observed in blast-exposed groups at 7 DPI. Using transmission electron microscopy, we observed and quantified myelin sheath defects and mitochondrial abnormalities at 7 and 30 DPI. Inverse correlations between blast intensities and neurobehavioral outcomes including motor activities, anxiety levels, nesting behavior, spatial learning and memory occurred. These observations uncover unique ultrastructural brain abnormalities and associated behavioral changes due to primary blast injury and provide key insights into its pathogenesis and potential treatment.

Blast wave dynamics: The influence of the shape of the explosive

A numerical model is developed to analyse the influence of the shape of a high-explosive on the dynamics of the generated pressure wave. A Multi-Material Arbitrary Lagrangian Eulerian (MM-ALE) technique is used as the CONWEP approach is not adequate to model such situations. Validation and verification of the proposed numerical model is achieved based on experimental data obtained from the bibliography. The numerical model provides relevant information that cannot be obtained from the experimental results. The influence of the mass and shape of the high-explosive is studied and correlated to the dynamics of the generated blast wave through the analysis of peak pressures, time of arrival and impulse. Tests are done with constant mass hemispherical, cylindrical and flat-shaped Formex F4HV samples. A detailed analysis of the generated blast wave is done, along with a thorough comparison between incident and reflected waves. It is concluded that the dynamic effects of the reflected pressure pulses should always be considered in structural design, most relevantly when analysing closed structures where the number of reflections can be significant. The model is proved reliable, concluding that the frontal area of the high-explosive is a determinant driving parameter for the impulse generated by the blast.

Primary blast waves induced brain dynamics influenced by head orientations

There is controversy regarding the directional dependence of head responses subjected to blast loading. The goal of this work is to characterize the role of head orientation in the mechanics of blast wave-head interactions as well as the load transmitting to the brain. A three-dimensional human head model with anatomical details was reconstructed from computed tomography images. Three different head orientations with respect to the oncoming blast wave, i.e., front-on with head facing blast, back-on with head facing away from blast, and side-on with right side exposed to blast, were considered. The reflected pressure at the blast wave-head interface positively correlated with the skull curvature. It is evidenced by the maximum reflected pressure occurring at the eye socket with the largest curvature on the skull. The reflected pressure pattern along with the local skull areas could further influence the intracranial pressure distributions within the brain. We did find out that the maximum coup pressure of 1.031 MPa in the side-on case as well as the maximum contrecoup pressure of -0.124 MPa in the back-on case. Moreover, the maximum principal strain (MPS) was also monitored due to its indication to diffuse brain injury. It was observed that the peak MPS located in the frontal cortex region regardless of the head orientation. However, the local peak MPS within each individual function region of the brain depended on the head orientation. The detailed interactions between blast wave and head orientations provided insights for evaluating the brain dynamics, as well as biomechanical factors leading to traumatic brain injury.

Blast Injuries

Blasts injuries are responsible for about two-thirds of the conventional combat injuries during any military operation and account for a sizeable number during terrorist activities. The pathophysiology, clinical presentation and urgency of management vary significantly in primary blast injuries. These can lead to a wide range of overt and covert injuries, making diagnosis and management difficult. The clinical picture varies from acute respiratory distress to deafness with absence of any external injuries. Such patients are best identified and dealt with by a team of health care professionals well acquainted with battle field injuries.