Role of helmet in the mechanics of shock wave propagation under blast loading conditions

The effectiveness of helmets in extenuating the primary shock waves generated by the explosions of improvised explosive devices is not clearly understood. In this work, the role of helmet on the overpressurisation and impulse experienced by the head were examined. The shock wave–head interactions were studied under three different cases: (i) unprotected head, (ii) head with helmet but with varying head–helmet gaps and (iii) head covered with helmet and tightly fitting foam pads. The intensification effect was discussed by examining the shock wave flow pattern and verified with experiments. A helmet with a better protection against shock wave is suggested.     

Modeling of weak blast wave propagation in the lung

Blast injuries of the lung are the most life-threatening after an explosion. The choice of physical parameters responsible for trauma is important to understand its mechanism. We developed a one-dimensional linear model of an elastic wave propagation in foam-like pulmonary parenchyma to identify the possible cause of edema due to the impact load. The model demonstrates different injury localizations for free and rigid boundary conditions. The following parameters were considered: strain, velocity, pressure in the medium and stresses in structural elements, energy dissipation, parameter of viscous criterion. Maximum underpressure is the most suitable wave parameter to be the criterion for edema formation in a rabbit lung. We supposed that observed scattering of experimental data on edema severity is induced by the physiological variety of rabbit lungs. The criterion and the model explain this scattering. The model outlines the demands for experimental data to make an unambiguous choice of physical parameters responsible for lung trauma due to impact load.     

Resonance-based oscillations could describe human gait mechanics under various loading conditions

The oscillatory behavior of the center of mass (CoM) and the corresponding ground reaction force (GRF) of human gait for various gait speeds can be accurately described in terms of resonance using a spring–mass bipedal model. Resonance is a mechanical phenomenon that reflects the maximum responsiveness and energetic efficiency of a system. To use resonance to describe human gait, we need to investigate whether resonant mechanics is a common property under multiple walking conditions. Body mass and leg stiffness are determinants of resonance; thus, in this study, we investigated the following questions: (1) whether the estimated leg stiffness increased with inertia, (2) whether a resonance-based CoM oscillation could be sustained during a change in the stiffness, and (3) whether these relationships were consistently observed for different walking speeds. Seven healthy young subjects participated in over-ground walking trials at three different gait speeds with and without a 25-kg backpack. We measured the GRFs and the joint kinematics using three force platforms and a motion capture system. The leg stiffness was incorporated using a stiffness parameter in a compliant bipedal model that best fitted the empirical GRF data. The results showed that the leg stiffness increased with the load such that the resonance-based oscillatory behavior of the CoM was maintained for a given gait speed. The results imply that the resonance-based oscillation of the CoM is a consistent gait property and that resonant mechanics may be useful for modeling human gait.     

Performance of the anaerobic baffled reactor under steady-state and shock loading conditions

The anaerobic baffled reactor (ABR) contains a granulated, mixed anaerobic culture segregated into compartments. Operation of four reactors under a range of hydraulic retention times showed that this novel reactor design offers highly efficient performance in the conversion of carbon in the feed stream to methane and carbon dioxide. The design parameter varied was the number of compartments. COD removal at 20 h retention time was routinely over 95% in all reactors, with low washout of biomass. Very high specific reaction rates were achievable (although with a loss of efficiency) at low biomass concentrations and high loading rates. In order to optimize volumetric reaction rates, a tradeoff has to be made between high biomass concentration, granule size, and the resulting mass transfer limitations. Formate is shown to be an important intermediate in the process under conditions of high loading.     

Modelling human eye under blast loading

Primary blast injury (PBI) is the general term that refers to injuries resulting from the mere interaction of a blast wave with the body. Although few instances of primary ocular blast injury, without a concomitant secondary blast injury from debris, are documented, some experimental studies demonstrate its occurrence. In order to investigate PBI to the eye, a finite element model of the human eye using simple constitutive models was developed. The material parameters were calibrated by a multi-objective optimisation performed on available eye impact test data. The behaviour of the human eye and the dynamics of mechanisms occurring under PBI loading conditions were modelled. For the generation of the blast waves, different combinations of explosive (trinitrotoluene) mass charge and distance from the eye were analysed. An interpretation of the resulting pressure, based on the propagation and reflection of the waves inside the eye bulb and orbit, is proposed. The peculiar geometry of the bony orbit (similar to a frustum cone) can induce a resonance cavity effect and generate a pressure standing wave potentially hurtful for eye tissues.     

Contact mechanics of modular metal-on-polyethylene total hip replacement under adverse edge loading conditions

Edge loading can negatively impact the biomechanics and long-term performance of hip replacements. Although edge loading has been widely investigated for hard-on-hard articulations, limited work has been conducted for hard-on-soft combinations. The aim of the present study was to investigate edge loading and its effect on the contact mechanics of a modular metal-on-polyethylene (MoP) total hip replacement (THR). A three-dimensional finite element model was developed based on a modular MoP bearing. Different cup inclination angles and head lateral microseparation were modelled and their effect on the contact mechanics of the modular MoP hip replacement were examined. The results showed that lateral microseparation caused loading of the head on the rim of the cup, which produced substantial increases in the maximum von Mises stress in the polyethylene liner and the maximum contact pressure on both the articulating surface and backside surface of the liner. Plastic deformation of the liner was observed under both standard conditions and microseparation conditions, however, the maximum equivalent plastic strain in the liner under microseparation conditions of 2000 µm was predicted to be approximately six times that under standard conditions. The study has indicated that correct positioning the components to avoid edge loading is likely to be important clinically even for hard-on-soft bearings for THR.     

The effect of connective tissue material uncertainties on knee joint mechanics under isolated loading conditions

Although variability in connective tissue parameters is widely reported and recognized, systematic examination of the effect of such parametric uncertainties on predictions derived from a full anatomical joint model is lacking. As such, a sensitivity analysis was performed to consider the behavior of a three-dimensional, non-linear, finite element knee model with connective tissue material parameters that varied within a given interval. The model included the coupled mechanics of the tibio-femoral and patello-femoral degrees of freedom. Seven primary connective tissues modeled as non-linear continua, articular cartilages described by a linear elastic model, and menisci modeled as transverse isotropic elastic materials were included. In this study, a multi-factorial global sensitivity analysis is proposed, which can detect the contribution of influential material parameters while maintaining the potential effect of parametric interactions. To illustrate the effect of material uncertainties on model predictions, exemplar loading conditions reported in a number of isolated experimental paradigms were used. Our findings illustrated that the inclusion of material uncertainties in a coupled tibio-femoral and patello-femoral model reveals biomechanical interactions that otherwise would remain unknown. For example, our analysis revealed that the effect of anterior cruciate ligament parameter variations on the patello-femoral kinematic and kinetic response sensitivities was significantly larger, over a range of flexion angles, when compared to variations associated with material parameters of tissues intrinsic to the patello-femoral joint. We argue that the systematic sensitivity framework presented herein will help identify key material uncertainties that merit further research and provide insight on those uncertainties that may not be as relative to a given response.     

The internal mechanics of the intervertebral disc under cyclic loading

The mechanics of the intervertebral disc (IVD) under cyclic loading are investigated via a one-dimensional poroelastic model and experiment. The poroelastic model, based on that of Biot (J. Appl. Phys. 12 (1941) 155; J. Appl. Mech. 23 (1956) 91), includes a power-law relation between porosity and permeability, and a linear relation between the osmotic potential and solidity. The model was fitted to experimental data of the unconfined IVD undergoing 5 cyclic loads of 20 min compression by an applied stress of 1MPa, followed by 40 min expansion. To obtain a good agreement between experiment and theory, the initial elastic deformation of the IVD, possibly associated with the bulging of the IVD into the vertebral bodies or laterally, was removed from the experimental data. Many combinations of the permeability-porosity relationship with the initial osmotic potential (pi(i)) were investigated, and the best-fit parameters for the aggregate modulus (H(A)) and initial permeability (k(i)) were determined. The values of H(A) and k(i) were compared to literature values, and agreed well especially in the context of the adopted high-stress testing regime, and the strain related permeability in the model.     

Molecular mechanics of silk nanostructures under varied mechanical loading

Spider dragline silk is a self-assembling tunable protein composite fiber that rivals many engineering fibers in tensile strength, extensibility, and toughness, making it one of the most versatile biocompatible materials and most inviting for synthetic mimicry. While experimental studies have shown that the peptide sequence and molecular structure of silk have a direct influence on the stiffness, toughness, and failure strength of silk, few molecular-level analyses of the nanostructure of silk assemblies, in particular, under variations of genetic sequences have been reported. In this study, atomistic-level structures of wildtype as well as modified MaSp1 protein from the Nephila clavipes spider dragline silk sequences, obtained using an in silico approach based on replica exchange molecular dynamics and explicit water molecular dynamics, are subjected to simulated nanomechanical testing using different force-control loading conditions including stretch, pull-out, and peel. The authors have explored the effects of the poly-alanine length of the N. clavipes MaSp1 peptide sequence and identify differences in nanomechanical loading conditions on the behavior of a unit cell of 15 strands with 840-990 total residues used to represent a cross-linking β-sheet crystal node in the network within a fibril of the dragline silk thread. The specific loading condition used, representing concepts derived from the protein network connectivity at larger scales, have a significant effect on the mechanical behavior. Our analysis incorporates stretching, pull-out, and peel testing to connect biochemical features to mechanical behavior. The method used in this study could find broad applications in de novo design of silk-like tunable materials for an array of applications.     

Examination of the protective roles of helmet/faceshield and directionality for human head under blast waves

A parametric study was conducted to delineate the efficacy of personal protective equipment (PPE), such as ballistic faceshields and advanced combat helmets, in the case of a blast. The propagations of blast waves and their interactions with an unprotected head, a helmeted one, and a fully protected finite element head model (FEHM) were modeled. The biomechanical parameters of the brain were recorded when the FEHM was exposed to shockwaves from the front, back, top, and bottom. The directional dependent tissue response of the brain and the variable efficiency of PPE with respect to the blast orientation were two major results of this study.     

Material properties of the placenta under dynamic loading conditions

Trauma during pregnancy especially occurring during car crashes leads to many foetal losses. Numerical modelling is widely used in car occupant safety issue and injury mechanisms analysis and is particularly adapted to the pregnant woman. Material modelling of the gravid uterus tissues is crucial for injury risk evaluation especially for the abruption placentae which is widely assumed as the leading cause of foetal loss. Experimental studies on placenta behaviour in tension are reported in the literature, but none in compression to the authors' knowledge. This lack of data is addressed in this study. To complement the already available experimental literature data on the placenta mechanical behaviour and characterise it in a compression loading condition, 80 indentation tests on fresh placentae are presented. Hyperelastic like mean experimental stress versus strain and corridors are exposed. The results of the experimental placenta indentations compared with the tensile literature results tend to show a quasi-symmetrical behaviour of the tissue. An inverse analysis using simple finite element models has permitted to propose parameters for an Ogden material model for the placenta which exhibits a realistic behaviour in both tension and compression.     

Biotrickling filtration of isopropanol under intermittent loading conditions

This paper investigates the removal of isopropanol by gas-phase biotrickling filtration. Two plastic packing materials, one structured and one random, have been evaluated in terms of oxygen mass transfer and isopropanol removal efficiency. Oxygen mass transfer experiments were performed at gas velocities of 104 and 312 m h^?1 and liquid velocities between 3 and 33 m h^?1. Both materials showed similar mass transfer coefficients up to liquid velocities of 15 m h^?1. At greater liquid velocities, the structured packing exhibited greater oxygen mass transfer coefficients. Biotrickling filtration experiments were carried out at inlet loads (IL) from 20 to 65 g C m^?3 h^?1 and empty bed residence times (EBRT) from 14 to 160 s. To simulate typical industrial emissions, intermittent isopropanol loading (16 h/day, 5 day/week) and intermittent spraying frequency (15 min/1.5 h) were applied. Maximum elimination capacity of 51 g C m^?3 h^?1 has been obtained for the random packing (IL of 65 g C m^?3 h^?1, EBRT of 50 s). The decrease in irrigation frequency to 15 min every 3 h caused a decrease in the outlet emissions from 86 to 59 mg C Nm^?3 (inlet of 500 mg C Nm^?3). The expansion of spraying to night and weekend periods promoted the degradation of the isopropanol accumulated in the water tank during the day, reaching effluent concentrations as low as 44 mg C Nm^?3. After a 7-week starvation period, the performance was recovered in less than 10 days, proving the robustness of the process.     

Simultaneous sulfide and nitrate removal in anaerobic reactor under shock loading

The performance of anaerobic reactor for simultaneous sulfide and nitrate removal under substrate shock loading was studied. The response to the shock loading could be divided into three stages i.e. disturbance, inertial and recovery periods. The effect of the shock loading was directly proportional to the intensity of the shock loads. The reactor performance was stable at a relatively lower intensity (1.5 times shock load), while it was considerably affected by higher intensity (higher than 2.0 times shock load). Nevertheless, the reactor performance recovered from disturbances at all the tested shock loads. The effluent sulfide-sulfur concentration was found as sensitive parameter, which increased up to 18 times of that at steady state; it could be used as an indicator of the reactor’s performance.     

On the shock wave front speed under high-voltage electric discharge in water

The pressure wave propagation under high-voltage electric discharge in water was investigated experimentally. The shock wave front speed was determined for the considered range of parameters.     

Experimental study of muscle permeability under various loading conditions

Biomechanics and Modeling in Mechanobiology - The permeability of a few muscle tissues under various loading conditions is characterized. To this end, we develop an experimental apparatus for...     

Anaerobic semi-fixed bed biofilm reactor (An-SFB-BR) for treatment of high concentration p-nitrophenol wastewater under shock loading conditions

Biodegradation - P-nitrophenol (PNP or 4-NP) has been widely used as a biorefractory raw material in chemical industry, whereas been highly concerned for its characteristics of...     

Damage evolution in acetabular replacements under long-term physiological loading conditions

Damage development in cemented acetabular replacements has been studied in bovine pelvic bones under long-term physiological loading conditions, including normal walking, stair climbing and a combined block loading with representative routine activities. The physiological loading conditions were achieved using a specially designed hip simulator for fixation endurance testing. Damage was detected and monitored using micro-CT scanning at regular intervals of the experiments, and verified by microscopic studies post testing. The results show that debonding at the bone–cement interface defined the failure of cement fixation in all cases, and debondings initiated near the dome of the acetabulum in the superior–posterior quadrant, consistent with the high-stress region identified from the finite element analysis of implanted acetabular models Zant, N.P., Heaton-Adegbile, P., Hussell, J.G., Tong, J., 2008b. In-vitro fatigue failure of cemented acetabular replacements—a hip simulator study. Journal of Biomechanical Engineering, Transactions of the ASME, 130, 021019-1–9]; [Tong, J., Zant, N.P., Wang, J-Y., Heaton-Adegbile, P., Hussell, J.G., 2008. Fatigue in cemented acetabulum. International Journal of Fatigue, 30(8), 1366–1375].