On dynamic behavior of bone: Experimental and numerical study of porcine ribs subjected to impact loads in dynamic three-point bending tests.

This study covers the characterization of the dynamic behavior of isolated porcine ribs based on experimental and numerical approaches. A Split Hopkinson Pressure Bar (SHPB) setup for three-point bending tests was used. Data of 20 tests were considered to be comprehensible for experimental characterization, thereby, showing an influence of strain rate on both time for fracture and amplitudes of force response. A three-dimensional porcine rib model was generated from the DICOM (Digital Imaging and Communication in Medicine) images of High-Resolution peripheral Quantitative Computed Tomography (HR-pQCT) scans. Material properties having been fitted by power law regression equations based on apparent density were assigned to the numerical rib. A modified elastic-plastic constitutive law, capable of considering the effects of strain rate was adopted. An incremental and stress-state dependent damage law, capable of considering effects of strain rate on fracture propagation, non-linear damage accumulation and instabilities was coupled to the constitutive law. The Finite Element (FE) model shows high efficiency in predicting both force-displacement curve and the fracture patterns of tested ribs. Predictions prove the ability of the proposed model to investigate the fracture behavior of human ribs under dynamic loads.

Experimental study of the coupling parameters influencing the terminal effects of thoracic blunt ballistic impacts.

The objective of the study is to better understand how blunt projectile ballistic parameters and material properties influence the events leading to injuries. The present work focuses on lateral thoracic impacts and follows an experimental approach. The projectiles are made with a soft foam nose assembled with a rigid rear plastic part. The dynamic properties of the foams were first determined using the Split Hopkinson Pressure Bar (SHPB) system. The impact forces on a rigid wall were then measured to provide reference load data. Lastly, shots were made on isolated thoraxes of porcine cadavers to investigate the response in the vicinity of the impact (wall displacements, rib accelerations and strains, rib fractures). Results show that the severity of the response appears to be mainly correlated with the impulse and with the pre-impact momentum.

On ballistic parameters of less lethal projectiles influencing the severity of thoracic blunt impacts.

The development and safety certification of less lethal projectiles require an understanding of the influence of projectile parameters on projectile-chest interaction and on the resulting terminal effect. Several energy-based criteria have been developed for chest injury assessment. Many studies consider kinetic energy (KE) or energy density as the only projectile parameter influencing terminal effect. In a common KE range (100-160 J), analysis of the firing tests of two 40 mm projectiles of different masses on animal surrogates has been made in order to investigate the severity of the injuries in the thoracic region. Experimental results have shown that KE and calibre are not sufficient to discriminate between the two projectiles as regards their injury potential. Parameters, such as momentum, shape and impedance, influence the projectile-chest interaction and terminal effect. A simplified finite element model of projectile-structure interaction confirms the experimental tendencies. Within the range of ballistic parameters used, it has been demonstrated that maximum thoracic deflection is a useful parameter to predict the skeletal level of injury, and it largely depends on the projectile pre-impact momentum. However, numerical simulations show that these results are merely valid for the experimental conditions used and cannot be generalised. Nevertheless, the transmitted impulse seems to be a more general factor governing the thorax deflection.