Academic literature on the topic 'Mechanical and Aerospace Engineering. Blast effect Blast effect'

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.<br>Includes bibliographical references (p. 65).<br>The use of double hull construction is commonplace within the shipping industry though it is largely unexploited within naval vessels. The Impact and Crashworthiness Lab at MIT has proposed the use of adaptive sandwich structures to improve the blast resistance of naval hulls. This project will address two main areas of investigation through the use of simplified analytical models: the integration of hardening and softening plastic core responses in the crushing of a rigidly supported sandwich panel; and the deformation analysis of a sandwich panel supported by non-rigid connections. The analytical solutions were utilized to perform a series of parametric studies to evaluate both the useable range of the models as well as to investigate the general behavior of a sandwich panel under a uniform load when supported by crushable connections. This initial investigation provides the simplified tools to begin and to validate a more detailed, numerical analysis.<br>by Christian R. Brown.<br>S.M.

The inclusion of venting areas in aircraft unit load devices (ULDs) as a potential blast mitigation technique is investigated in this work. Damage to the ULD, such as large deflections or container rupture, from an internal explosion threatens to tear the aircraft skin and cause fuselage decompression. The loading within a luggage container was expected to be reduced when the explosive products were vented into the adjacent ULDs. Although previous work has investigated the effect of venting on ULD blast loading, this has only considered a single venting side and not multiple venting configurations. To determine if a multiple-venting system would be beneficial in ULDs, experimental blast testing was performed by subjecting a 1:6 scaled ULD box to representative blast loads with different venting configurations. The blast response of the side of the ULD which would be positioned closest to the fuselage was measured. Numerical simulations were established to provide insight into the blast loading effects not measured experimentally. The loading within the ULD box, in terms of the number and magnitude of blast wave reflections, and internal pressure build-up, was reduced when introducing venting areas. Final deformations were reduced by 11% and 22% when using a single- and double-venting configuration, respectively. Further deformation reduction was expected if more venting area was made available: unconfined blasts tests (demonstrating complete absence of ULD confinement) reduced deformations by 44%. The fully-confined (no venting) blast test resulted in rupture failure when blasted with a 20 g explosive, whereas the vented tests exhibited no tearing when blasted with higher charge masses. The double-venting configuration demonstrated better blast mitigation than the single-venting configuration. However, since both reduced the deformations and rupture probability of the container, the implementation of a multiple-venting system within aircraft ULDs would improve the survivability of the ULD container during a blast event.

Includes abstract.<br>Includes bibliographical references (leaves 191-197).<br>Landmines are the epitome of the perfect soldier: always ready, never tiring. Landmines also do not choose their victims - it may very well be an armed and protected soldier or an innocent civilian who activates the detonator. As such, land mines have reached epidemic proportions in the Third World, affecting both combatants and civilians, whether they are on foot or in a vehicle. When stepping on an anti-personnel land mine, traumatic amputation of the foot, lower leg or upper leg is generally expected. However, an anti-vehicle landmine detonating underneath a vehicle can have equally as detrimental results, as the occupants of the vehicle are bound to sustain serious injuries to the lower extremities. These injuries can vary from being less life threatening to being fatal in some extreme cases. Anthropomorphic test devices have been developed and refined over the years to represent the occupant exposed to simulated land mine detonation and then to retrieve valuable technical information from the test data. In the present investigation a simplified aluminium surrogate lower leg was designed, manufactured and subjected to axial blast testing. In addition, a rubber layer representing the sole of a standard army combat boot was placed below the foot model in a separate series of blast tests. The main factors investigated in this study were the effect of varying the amount and positioning of the explosives and the attenuation produced by including the rubber sole layer. The blast tests were conducted using a horizontal ballistic pendulum, with the foot model placed axially in the pendulum. The disc shaped explosives of different mass was placed in the centre of the detonation plate and axially in line with the heel respectively to draw a comparison between the respective stresses induced in the lower leg. As expected, the stress recorded by the strain gauges placed on the lower leg was significantly higher when the explosives were positioned in line with the heel than when placed in the centre of the detonation plate. The same series of blast tests were performed with the rubber sole being included in the test setup. Alternating the positioning of the explosives did not yield a significant difference in induced stress. Investigation of the blast attenuation provided by the rubber layer showed that the peak stress is mitigated by approximately 70%, which was much greater than expected. An elementary analytical solution was performed as a preliminary validation of the experimental test results. Furthermore, a finite element model of the aluminium surrogate foot and the rubber layer was created and a numerical simulation of each blast test was executed. Material data for the aluminium and rubber obtained via Split-Hopkinson Pressure Bar testing were employed to construct the material models used in the finite element model. The results from the numerical simulations compare well to the experimental test results for the blast loading conditions where the rubber layer was excluded from the test setup. In the case where the rubber layer was included in the testing, the trend and shape of the stress graphs obtained from the numerical simulation results agrees with the stress curves recorded during the actual blast tests. However, the peak stresses recorded during the experimental blast tests are found to be significantly higher than the peak stresses yielded by the numerical simulations.

Injury from blast is significant in both military and civilian environments. Although injuries from blast are well-documented, the mechanisms of injury are not well understood. Developing better protection requires knowledge of injury mechanisms and material response to blast loading. The importance of understanding how soft materials such as foams and fabrics behave under blast loading is further apparent when one realizes the capacity for some of these materials, frequently used in protective ensembles, to increase the potential for injury under some conditions. The ability for material configurations to amplify blast pressure and injury has been shown experimentally by other researches, and numerically in this study. Initially, 1-D finite element and mathematical models were developed to investigate a variety of soft materials commonly utilized in ballistic and blast protection. Foams, which have excellent characteristics in terms of energy absorption and density, can be used in conjunction with other materials to drastically reduce the amplitude of the transmitted pressure wave and corresponding injury. Additionally, a more fundamental examination of single layers of fabric was undertaken to investigate to the effects of parameters such as fabric porosity and density. Shock tube models were developed and validated against experimental results from the literature. After the models were validated, individual fabric properties were varied independently to isolate the influence of parameters in ways not possible experimentally. Fabric permeability was found to have the greatest influence on pressure amplification. Kevlar, a ballistic fabric, was modelled due to its frequent use for fragmentation protection (either stand-alone or in conjunction with a hard ballistic plate). The developed fabric and foam material models were then utilized in conjunction with a detailed torso model for the estimation of lung injury resulting from air blast. It was found that the torso model predicted both amplification and attenuation of injury, and all materials investigated as a part of the study had the capacity for both blast amplification and attenuation. The benefit of the models developed is that they allow for the evaluation of specific protection concepts.