Browsing by Author "Sadeghi, M. M."
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Item Open Access Crashworthiness of composite seats for civil aircraft(Cranfield University, 1992-01) Stephens, V. M.; Sadeghi, M. M.A study has been conducted into the design of civil aircraft seats which are forward-facing and use the lap-belt method of restraint. Within these terms of reference, the response of the seat restraint occupant system (SROS) to impact loading has been analysed using physical (dynamic testing) and analytical (computer simulation) modelling techniques. With the increasing use of fibre-reinforced polymer composites in aircraft for weight efficiency, and the consequent appearance of composite seats, attention must be given to the crash performance of these structures. Composite structures are characterised by brittle failure with low impact energy absorption, in comparison to the collapse of metal structures which may exhibit plastic deformation prior to failure. However, using the developing technology of composite sub-structures with high specific energy absorption capability, seat structures have been modified to incorporate composite load-limiting elements. The redesign process involved the compatibility of energy absorber loads with occupant dynamics to minimise injury potential, together with the alleviation of forces in the structural load path to reduce damage and preclude failure of the seat, floor track, and other components. Shortcomings of existing seat designs were assessed, and the dynamics of lap-belted occupants analysed, including secondary head impact with the forward seat structure. The computer' model created was validated against the results of dynamic tests, and then used in a parametric study of occupant dynamics. Conclusions and recommendations include guidlines relating to the future design of both metal and composite seats.Item Open Access Pedestrian accident simulation and protection technology evaluation(2002-12) Howard, M. S.; Sharp, Robin S.; Sadeghi, M. M.Pedestrian safety is an important societal issue and as one of the stakeholders, vehicle manufacturers are attempting to improve pedestrian protection by enhancing vehicle design. In order to enhance vehicle design, first it is necessary to gain an improved understanding of the interactions between a pedestrian and a vehicle during an accident. Secondly, this knowledge needs to be transformed into vehicle design and technology changes. This thesis focuses on the construction of new models and methodologies to provide an improved understanding and the application of this understanding to design, develop and evaluate a number of pedestrian protection technologies. A review of the pedestrian safety issue and different approaches to pedestrian protection research provide the background to the chosen approach. This is described in terms of an overall methodology for any pedestrian protection technology that also provides a framework for this research. The construction and evaluation of pedestrian accident simulations with a reference C class vehicle are described in detail. The influence of accident conditions and the expected ranges of various quantitative pedestrian injury and motion measures are identified. Vehicle impact velocity, pedestrian size and stance have significant influences on these measures. Therefore it is not possible to state, for instance, that under all accident conditions, one vehicle impact location is likely to cause lower injury measures than another is. There is a clear increase in pedestrian measures (e.g. head velocity, HIC, tibia acceleration, knee bending) with a large increase in impact velocity (i.e. 25 to 40 km/h). However, some measures (e.g. HIC) do not necessarily increase with a small increase in impact velocity (e.g. 25 to 30 km/h) because of the new pedestrian motion (e.g. a new head impact location). Large differences exist between the 6 year old pedestrian and adult pedestrian model measures (e.g. larger post head impact motion but smaller HIC and tibia acceleration) and pedestrian stance has a complex influence on all measures with few overall trends. Pedestrian protection headlamp, bumper system and hood system concepts are developed in biomechanical, analytical and numerical component models. These concepts are used to construct and subsequently benchmark, with pedestrian accident simulations, two modified vehicle models that incorporate different combinations of the technologies. Both the absolute measures and ranges of the measures from the reference vehicle simulations are compared. There are large differences between the pedestrian measures from the reference and modified vehicles but much smaller differences between the modified vehicles. Impacts with the modified vehicles cause the largest differences in pedestrian motion at 40 km/h, for the 6 year old pedestrian, in stance TV, in the early (up to 20 ms) and late (after 140 ms) stages of the accident simulations. Although the modified vehicles reduce pedestrian injury measures for some of the accident conditions, neither of them reduce all measures for all of the conditions. However, significant improvements in experimental sub system measures [EEVC 1998] are achieved with a prototype modified vehicle that incorporates some of the technologies. Benchmarking is hindered by complex injury measure trends and by pedestrian and vehicle model limitations. Recommendations are made with respect to all of these factors. Further recommendations include the need for optimisation of the modified vehicle technologies in accident simulations, a more complete investigation of other technology functional requirements (e.g. low speed damageability) and accident reconstruction as a means to achieve improved model validation.Item Open Access A simplified simulation of the combined bending/torsion collapse of thin walled beams in the explicit DYNA3D code(Cranfield University, 1993-04) Vignjevic, Rade; Sadeghi, M. M.; Kecman, D.Abstract not availableItem Open Access Theoretical analysis and pressure distribution of thin-walled metal inverbuckle energy absorbing tubes(Cranfield University, 1998-05) Chirwa, Efford Clive; Sadeghi, M. M.This dissertation presents an investigation in the energy absorbing capacity of thin-walled metal inverbucktubes loaded in axial compression. It also presents the inversion-buckling(curling-buckling) behaviour achieved in both, quasi-static and dynamic loading conditions. In addition, for the first time, the experimental results of the pressure or normal stress distribution between the inside surface of the inverbucktube and die fillet radius interface are stipulated. These were very successful, using the pressure transducer method. Furthermore, a mathematical model has been developed, based on theory of plasticity and making use of energy method. This predicts the amount of energy absorbed in the assumed seperate collapse processes. Results yielded from the theory, showed good agreement with the experimental results which had geometry factor within feasibility boundaries of inverbuckling collapse (6.5 ( 5/2t,, ( 22.5). The successful prediction of energy absorbed, inverbuckling load and pressure distribution, not only proves the validity of the model, but also confirms the quality of the modelling approach proposed in this dissertation. Using this mathematical model, inverbucktubes could be designed, developed and applied.